Samacheer Class 11 Bio Zoology - Chemical Coordination and Integration

The correct answer is d) hypothalamic hypophyseal axis. The posterior pituitary, also known as the neurohypophysis, is controlled by the hypothalamic-hypophyseal axis through a neuroendocrine mechanism. Unlike the anterior pituitary, which is controlled by releasing hormones transported through the hypothalamic-hypophyseal portal blood vessels, the posterior pituitary is directly connected to the hypothalamus by nerve fibers called the hypothalamic-hypophyseal tract. The hypothalamus produces two main hormones, antidiuretic hormone (ADH) and oxytocin, which are synthesized in the supraoptic and paraventricular nuclei respectively. These hormones are transported down the axons of neurons to the posterior pituitary, where they are stored in nerve terminals and released directly into the bloodstream in response to appropriate stimuli. This direct neural control through the hypothalamic-hypophyseal axis allows for rapid and precise regulation of posterior pituitary hormone secretion.

The pituitary gland has a dual embryonic origin reflecting its two distinct lobes. The anterior lobe, also called the adenohypophysis, originates from the embryonic invagination of pharyngeal epithelium known as Rathke's pouch. This pouch arises from the roof of the oral cavity and grows upward during embryonic development. The posterior lobe, also called the neurohypophysis or pars nervosa, originates from the base of the brain as a downward outgrowth of the hypothalamus. This neural origin explains why the posterior lobe maintains direct neural connections with the hypothalamus. The two lobes eventually fuse together to form the complete pituitary gland, which becomes situated in the sella turcica, a bony cavity beneath the brain. This dual origin accounts for the different functions and control mechanisms of the anterior and posterior lobes.

Growth hormone (GH):
It is also known as somatotropic hormone (STH) or Somatotropin. It is a peptide hormone Growth hormone promotes the growth of all the tissues and metabolic processes of the body. It influences the metabolism of carbohydrates, proteins, and lipids and increases the rate of protein biosynthesis in the cells.
It stimulates chondrogenesis (cartilage formation), osteogenesis (bone formation) and helps in the retention of minerals like nitrogen, potassium, phosphorus, sodium, etc., in the body. GH increases the release of fatty acid from adipose tissue and decreases the rate of glucose utilization for energy by the cells. Thus it conserves glucose for glucose-dependent tissues, such as the brain.

Follicle-stimulating hormone (FSH) is a glycoprotein hormone secreted by the anterior pituitary gland that regulates the functions of the gonads. In males, FSH acts on the germinal epithelium of the seminiferous tubules of the testes. It works synergistically with androgens to stimulate spermatogenesis, which is the production and development of sperm cells. FSH promotes the proliferation and differentiation of spermatogenic cells, ensuring continuous production of mature spermatozoa. The hormone maintains the structural and functional integrity of the seminiferous tubules and supports the Sertoli cells, which provide nutritional and developmental support to developing sperm cells. Without adequate FSH levels, spermatogenesis is impaired and male fertility is compromised. In females, FSH acts on the ovaries to stimulate the development and maturation of ovarian follicles, preparing them for ovulation.

• The hormones are released into the blood and circulated as chemical signals
• The target organs contain receptor molecules either on the surface or within the cell.
• The cells that contain the receptor molecules specific to the hormone are physiologically activated.
• Whereas other hormones that come in contact can not be activated.

Amine hormones and steroid hormones differ in several fundamental ways. Amine hormones are small, water-soluble molecules derived from amino acids such as tyrosine or tryptophan. Examples of amine hormones include adrenaline, noradrenaline, melatonin, and thyroid hormones. These hormones are hydrophilic and can dissolve in blood plasma, allowing them to circulate freely in the bloodstream. In contrast, steroid hormones are mostly lipid-soluble molecules derived from cholesterol. Examples include cortisol, aldosterone, testosterone, oestrogen, and progesterone. Because steroid hormones are lipophilic, they require carrier proteins to transport them through the bloodstream. Additionally, amine hormones typically bind to receptors on the cell surface, while steroid hormones can penetrate the cell membrane and bind to intracellular receptors. The structural differences between these two classes of hormones result in different mechanisms of action and different rates of metabolism and excretion from the body.

Exocrine glands and endocrine glands are two distinct types of glands that differ in structure and function. Exocrine glands possess ducts that carry their secretions to epithelial surfaces such as the skin or mucous membranes. These glands secrete substances like enzymes, saliva, sweat, and digestive juices. Examples of exocrine glands include salivary glands, sweat glands, and gastric glands. In contrast, endocrine glands lack ducts and instead release their secretions directly into the surrounding tissue fluid and bloodstream. The secretions of endocrine glands are called hormones, which are chemical messengers that regulate various physiological processes throughout the body. Examples of endocrine glands include the pituitary gland, thyroid gland, pineal gland, adrenal glands, and parathyroid glands. While exocrine glands have localized effects at the site of secretion, endocrine glands produce systemic effects as their hormones circulate through the bloodstream to reach distant target organs and tissues.

• Exclusive endocrine glands, e.g. Pituitary thyroid, Parathyroid, Pineal, Adrenal
• Neuroendocrine gland – Hypothalamus
• Partial endocrine glands, e.g. Pancreas, gastrointestinal tract epithelium, kidney, heart gonads, and placenta – have endocrine tissues.

• The pituitary gland is known as the master endocrine gland, but it is in turn controlled by the hypothalamus and so the statement may not be totally applicable.
• The hypothalamus with its neurosecretory cells produces neurotransmitters which regulate the secretions of the pituitary.

• The pituitary gland is located in the bony cavity of the sphenoid bone the sella tunica at the base of the brain so is also called the hypothalamus cerebri.
• it is about one centimeter in diameter and 0.5gm in weight.

The pineal gland, also known as the epiphysis cerebri or conarium, is a small endocrine gland located behind the third ventricle of the brain. It is composed of parenchymal cells and interstitial cells that work together to produce and secrete melatonin. Melatonin plays a central role in regulating the circadian rhythm of the body, which is the 24-hour cycle of biological activities associated with natural periods of light and darkness. This hormone is crucial for maintaining the normal sleep-wake cycle, as its secretion increases during darkness and decreases during light exposure. Beyond circadian rhythm regulation, melatonin also regulates the timing of sexual maturation and the functioning of the gonads. Additionally, melatonin influences several other physiological processes including metabolism, skin pigmentation, the menstrual cycle in females, and the defence mechanisms of the body. The pineal gland thus serves as an important link between the nervous system and the endocrine system in maintaining overall homeostasis and coordinating various biological functions with environmental light-dark cycles.

• Alcohol consumption has widespread effect on endocrine system.
• It impairs the regulation of blood glucose level.
• More over it reduces the testosterone level
• Increases the risk of osteoporosis.

• Humiline-N is administered to diabetic patients.
• Human insulin is administered as injection and not by oral consumption.
• The reason is if it is administered by oral consumption it may be digested by digestive enzymes.

Circadian rhythm is a 24-hour cycle of biological activities that is associated with the natural periods of light and darkness in the environment. These rhythms are endogenous, meaning they are generated internally by the body, but they are synchronized or entrained by external environmental cues, particularly the light-dark cycle. Various physiological processes follow circadian rhythms, including the sleep-wake cycle, body temperature fluctuations, appetite and feeding behaviour, hormone secretion patterns, and metabolic activities. The pineal gland, through the secretion of melatonin, plays a central role in regulating circadian rhythms. Disruption of circadian rhythms due to factors such as shift work, jet lag, or irregular sleep schedules can lead to various health problems including sleep disorders, metabolic dysfunction, and mood disturbances. Understanding circadian rhythms is important for maintaining optimal health and well-being.

• Simple goitre is otherwise known as endemic goitre.
• It is due to the hypo secretion of thyroxine.
• The symptoms are Enlargement of thyroid gland, Fall in serum thyroxine level, Increased TSH secretion.

• The hyposecretion of parathyroid hormones leads to a decrease in calcium level and increase in phosphate level, it causes.
• convulsion in muscle, locking of jaws, increased heart beat rate increased body temperature muscular spasm lead to tetany.

Cushing's syndrome is a hormonal disorder caused by prolonged exposure of the body's tissues to high levels of the hormone cortisol. This can be due to the body producing too much cortisol (endogenous Cushing's syndrome) or taking too much of corticosteroid medication (exogenous Cushing's syndrome). Symptoms of Cushing's syndrome are varied and can include obesity, particularly around the trunk and face (moon face), leading to a rounded, puffy appearance. Other characteristic symptoms include thinning of the skin, which may appear reddish or purplish, and the development of stretch marks (striae) on the abdomen, thighs, breasts, and arms. Excessive hair growth (hirsutism) can occur in women, and bones may lose minerals, leading to osteoporosis and an increased risk of fractures. Additionally, individuals may experience high blood pressure (systolic hypertension) and mood changes such as irritability or depression.

Dwarfism is a condition caused by the hypo-secretion or insufficient production of growth hormone in children. Growth hormone, secreted by the anterior pituitary gland, is essential for normal skeletal growth and development. When growth hormone levels are abnormally low during childhood and adolescence, skeletal growth is severely arrested and sexual maturity is delayed or prevented. Children with growth hormone deficiency typically attain a maximum height of approximately 4 feet, resulting in short stature relative to their peers. The condition may result from various causes including pituitary dysfunction, hypothalamic disorders, genetic mutations affecting growth hormone production, or damage to the pituitary gland from tumours or injury. Early diagnosis and treatment with synthetic growth hormone can help improve growth outcomes in affected children.

• Due to the hyper-secretion of growth hormone in children there is a over growth of skeletal
• structure may occur up to 8 feet height. The visceral growth is not appropriate with that of limbs.

In this frightening situation, my body would undergo a series of physiological responses triggered by the sympathetic nervous system and the release of the hormone adrenaline. Upon perceiving the threat, my hypothalamus would stimulate the adrenal medulla to release adrenaline into the bloodstream. This surge of adrenaline would cause several immediate responses: my heart rate would increase to pump blood more rapidly, my blood pressure would rise, and my muscles would receive increased blood flow and glucose supply, providing the energy needed for a fight or flight response. The adrenaline would also cause piloerection, resulting in goose bumps as the arrector pili muscles contract due to vasoconstriction. My pupils would dilate to improve vision, and my breathing rate would increase to supply more oxygen to my muscles. Despite being frightened, the energy and heightened alertness provided by adrenaline would enable me to either fight the attacker or flee from the dangerous situation. This is an example of how the endocrine system, particularly the adrenal glands, prepares the body to respond to acute stress and threats to survival.

Glucocorticoids are considered life-saving hormones because they play a critical role during emergency or stress situations. When the body faces an emergency, glucocorticoids stimulate the synthesis of glucose from non-carbohydrate sources through the processes of lipolysis and proteolysis, which break down lipids and proteins respectively. This mobilization of energy substrates increases blood glucose levels, providing the body with readily available energy to meet the demands of the emergency situation. Additionally, glucocorticoids enhance cardiovascular function, increase blood pressure, and suppress non-essential functions like digestion and immunity, allowing the body to redirect resources toward survival. By rapidly increasing energy availability and preparing the body for immediate action, glucocorticoids enable survival during critical physiological stress, making them essential for maintaining homeostasis and life during emergencies.

• Cortisone involved in maintaining cardio vascular and kidney functions. It produces anti inflammatory reactions and suppresses the immune response, it stimulates the RBC production.
• Hence it is known as stress combat hormone.

• The hormones are released into the blood and circulated as chemical signals and act on specific target organs.
• Hormones may speed up or slow down or alter the activity of the target organs.
• The hormones secreted do not remain permanently in the blood.
• They are converted by the liver into inactive compound and excreted by kidneys.

• It is a collection of special structures located in the middle of the brain.
• It is also known as paleo mammalian brain.
• It controls emotions, behavior, motivation of long term memory and olfaction.

• Hypothalamic hormones control anterior pituitary secretion through hypothalamic hypophyseal portal blood vessel.
• The nerve signal produced by the hypothalamic hypophyseal axis control the posterior pituitary secretion.
• Hypothalamus maintains homeostasis.
• Blood pressure
• Body temperature.
• Cardio and fluid electrolyte balance of the
• As the part of limbic system it influences various emotional responses.

• It is a glycoprotein hormone
• It is also known as Interstitial cell stimulating hormone (ICSH) in males.
• The ICSH hormones acts on the interstitial cells of testis to produce the male sex hormone testosterone.
• In females along with FSH matures the ovarian follicles.
• LH independently induces ovulation, maintains the corpus luteum and promotes synthesis and release of ovarian.
• FSH and LH secretion starts only during pre pubertal period.
• FSH and LH are collectively referred as gonadotropins.

Vasopressin and oxytocin are both nonapeptide hormones composed of nine amino acids, but they differ in their amino acid sequences at specific positions. Vasopressin has the amino acid sequence: cysteine–tyrosine–phenylalanine–glutamine–asparagine–cysteine–proline–arginine–glycine. Oxytocin has a similar structure with the amino acid sequence: cysteine–tyrosine–isoleucine–glutamine–asparagine–cysteine–proline–leucine–glycine. The key structural differences are that vasopressin contains phenylalanine at position three and arginine at position eight, whereas oxytocin contains isoleucine at position three and leucine at position eight. These subtle differences in amino acid composition result in significant functional differences between the two hormones. Despite their structural similarity, vasopressin functions primarily in water reabsorption and blood pressure regulation, while oxytocin is involved in uterine contractions during childbirth and milk ejection during lactation. These structural variations demonstrate how minor changes in peptide hormone sequences can lead to distinct physiological roles.

• ADH is a peptide hormone
• It promotes absorption of water and electrolytes by distal tubules of nephron and there by reduces loss of water through urine.
• Hence it is called as anti diuretic hormone.
• ADH deficiency causes Diabetes insipidus which induces the production of large amount of urine.
• This is how it helps in osmoregulation.
• ADH when released in large amount causes constriction of blood vessels and increases blood pressure.

• It is secreted by pineal gland.
• It plays a central role in the regulation of circadium rhythm of our body
• Maintains the normal sleep wake cycle.
• It also regulates the timing of sexual maturation of gonads.
• In addition it also influences metabolism, pigmentation, menstrual cycle and defence mechanism of our body.

• It regulates the Basal Metabolic Rate (BMR) and body heat production.
• It stimulates protein synthesis and promotes growth
• It is essential for the development of skeletal and nervous system.
• It plays an important role in maintaining blood pressure
• It reduces serum cholesterol levels.
• Optimum levels of thyroxine in the blood are necessary for gonadial functions.

• The parathyroid hormone (PTH) is the hypercalcemic hormone.
• It is a peptide hormone.
• It involves in controlling the calcium and phosphate homeostasis.
• The secretes or PTH is controlled by calcium level in the blood.
• It increases the blood calcium level by stimulating osteoclasts to dissolve the bone matrix.
• As a result calcium and phosphate are released into the blood.
• PTH enhances the re-absorption of calcium and exertion of phosphates by the renal tubules.
• It promotes activation of vitamin D to increase calcium absorption by intestinal mucosal cells.

The heart functions as a partial endocrine gland through the secretory activity of specialized cardiac cells. Cardiocytes located in the walls of the atria, particularly in response to increased blood volume and pressure, secrete an important peptide hormone called Atrial Natriuretic Factor or ANF. When blood pressure rises above normal levels, ANF is released into the bloodstream where it acts on various target tissues. ANF causes vasodilation of blood vessels, reducing peripheral vascular resistance and thereby lowering blood pressure back to normal levels. Additionally, ANF promotes sodium and water excretion by the kidneys, which decreases blood volume and further contributes to blood pressure reduction. ANF also inhibits the secretion of renin and aldosterone, hormones that would otherwise increase blood pressure. Through these mechanisms, the heart's endocrine function helps maintain cardiovascular homeostasis and regulates blood pressure, demonstrating that the heart is not merely a mechanical pump but also an important endocrine organ that participates in hormonal regulation of the body.

It is generally not advisable to consume synthetic soft drinks regularly. These beverages often contain high amounts of sugar, artificial sweeteners, and various chemicals that can negatively impact the endocrine system. When sugary soft drinks are consumed, there is a rapid increase in blood glucose levels. This prompts the pancreas to secrete more insulin to bring the blood sugar back to normal. Chronic high insulin levels can lead to insulin resistance, diminished immune function, and contribute to weight gain and obesity. Furthermore, regular consumption is linked to an increased risk of cardiovascular disorders, type 2 diabetes, and dental problems due to the acidic nature and sugar content.

Doctors often avoid prescribing steroid tablets routinely due to the significant and potentially severe health risks associated with their abuse or prolonged use. Steroids can disrupt numerous bodily functions, leading to serious conditions such as high blood pressure, heart diseases, liver damage, and an increased risk of stroke and certain cancers. They can also cause blood clots. Additionally, steroid abuse can result in a range of unpleasant side effects including nausea, vomiting, headaches, joint pain, muscle cramps, diarrhea, and sleep disturbances. In some cases, they can lead to ligament and tendon injuries. Therefore, their use is typically reserved for specific medical conditions under strict supervision.

• Glycogenolysis is breakdown of glycogen to glucose
• This process is carried out in the liver by the Glucagon hormone.
• Glucagon thus releases glucose from the liver cells increasing Gluconeogenesis.
• it is the synthesis of glucose from lactic acid and from non-carbohvdrate molecules is called Gluconeogenesis. this increases the blood glucose levels.

• Poly urea – Excessive urination
• Polyphagia – Excessive intake of food
• Polydipsia – Excessive consumption of liquids due to thirst.
• Ketosis – Breakdown of fat into glucose results in accumulation of ketone bodies.

• Hypothalamus is a small cone shaped structure that projects downward from the brain ending into the pituitary stalk.
• It interlinks both the nervous system and endocrine system.
• Pituitary gland is controlled by the hypothalamus.
• It produces neuro transmitters which act either as a releasing hormone or as an inhibitory hormone.
• Hypothalamus contains groups of neuro secretory cells which produces neuro transmitters which regulate the secretions of the pituitary gland.

• It is located behind the third ventricle of brain.
• In human it is called epiphysis cerebri conarium.
• It is formed of parenchymal cells and interstitial cells.
• It secretes the hormone melatonin.
• It plays a central role in the regulation of circadian rhythm of our body and maintains the normal sleep wake cycle.

• In man, four tiny parathyroid glands are found in the posterior wall of the thyroid glands.
• It composed of two types of cells. The chief cells and oxyphil cells.
• The chief cells secrete parathyroid hormone.
• The functions of oxyphil cells are not known.

• Thymus gland is partially an endocrine and partially a lymphoid gland.
• It is a bi-lobed structure located just above the heart and aorta behind the sternum.
• It is covered by a fibrous capsule.
• Anatomically it is divisible into an outer cortex and an inner medulla.
• It secretes four hormones such as thymulin, thymosin, thymopoietin and thymic humoral factor (THF).
• The primary function is the production of immuno competent T lymphocytes which provides cell mediated immunity.

Acromegaly is a hormonal disorder characterized by excessive secretion of growth hormone (GH) in adults, typically occurring after the epiphyseal plates have closed. This excess GH leads to the abnormal growth of bones, particularly in the hands, feet, and facial structure, resulting in enlarged hands, feet, and a prominent jaw. The condition also affects internal organs, causing enlargement of the viscera, tongue, lungs, heart, liver, and spleen. Furthermore, acromegaly can lead to malfunctioning of the gonads and impact other endocrine glands, such as the thyroid, potentially causing secondary hormonal imbalances. It is a progressive condition that can lead to significant disfigurement and health complications if left untreated.

Hyperparathyroidism is a condition resulting from the overproduction of parathyroid hormone (PTH) by the parathyroid glands. This excess PTH leads to elevated levels of calcium in the blood (hypercalcemia). A primary symptom is the demineralization of bones, as the excess PTH draws calcium from the skeletal system, leading to softening of the bones and the formation of cysts within them. This bone loss can cause pain and increase the risk of fractures. Other symptoms include a loss of muscle tone, general weakness, and fatigue. The condition can also affect the kidneys, leading to renal disorders such as kidney stones due to the increased calcium excretion.

Addison’s disease, also known as primary adrenal insufficiency, occurs when the adrenal cortex fails to produce adequate amounts of glucocorticoids and mineralocorticoids. This deficiency leads to a range of symptoms reflecting the vital roles of these hormones. Patients often experience significant muscular weakness and fatigue, along with low blood pressure (hypotension). Appetite loss, nausea, and vomiting are common gastrointestinal symptoms. A characteristic sign is hyperpigmentation of the skin, particularly in sun-exposed areas and skin creases, due to increased ACTH levels stimulating melanocytes. The metabolic rate is lowered, leading to subnormal body temperature and weight loss. Reduced aldosterone levels impair the body's ability to retain sodium and water, leading to dehydration and electrolyte imbalances, with increased urinary excretion of sodium chloride and water, and decreased potassium excretion.

Adrenaline, also called epinephrine, is a hormone secreted by the adrenal medulla with several important general functions. It mobilizes the brain and body for immediate action by increasing heart rate, blood pressure, and blood glucose levels, thereby preparing the body to respond to stressful situations. Adrenaline also increases alertness, dilates the pupils, and redirects blood flow to muscles. The nature of adrenaline secretion varies according to physiological states and emotional conditions. During sleep, adrenaline secretion is minimal, but it increases during wakefulness and normal daily activities. During stress situations such as fear, anger, or physical danger, adrenaline secretion reaches much higher levels, triggering the characteristic fight or flight response. This response prepares the organism either to confront the threat or to escape from it by mobilizing energy reserves and enhancing physical performance. The fight or flight response is an adaptive mechanism that has evolved to help organisms survive threatening situations by rapidly activating the sympathetic nervous system and increasing metabolic activity.

In mammals the role of pass intermedia is insignificant.
* In other vertebrates it secretes melanocyte stimulating hormone (MSH)
* It induces pigmentation in skin.
(5 Marks)
IV. Brief Answers

• Peptide hormones cannot cross the phospholipid cell membrane and bind to the receptors on the exterior cell surface.
• They are transported to the golgi which is the site of modification.
• It acts as a first messenger in the cell.
• Hormones generate a second messenger like cyclic AMP (cAMP) that regulates cellular metabolism. This cAMP is catalyzed by the adenylate cyclase ezyme.
• The interaction between the hormone surface and the effect of cAMP within the cell is known as a signaling cascade. There may be amplication at each step.
• One hormone molecule may bind to multiple receptor molecules before it is degraded.
• Each receptor activates to form more cAMP and produces more signals.

• Steroid hormones can easily cross the cell membrane and bind their receptors which may be intracellular or intercellular.
• Then they pair up with another receptor and form a receptor-hormone complex. This can bind to DNA and alter its transcription.
• As it changes the mRNA and protein the effect will be with stand for a long time. Eg. Estrogen

• There is a hyper pigmentation of the skin. It is caused due to hypo secretion of glucocorticoids from the adrenal cortex.
• Muscular weakness low BP, loss of appetite vomiting, low metabolic rate subnormal temperature reduced blood volume and weight are the other symptoms of Addison’s disease.

• Hypothyroidism is the cause of cretinism in infants. There is a retarded skeletal growth absence of sexual maturity, retarded mental ability, thick wrinkled skin protruded enlarged tongue bloated face thick and short limbs.
• There is low BMR, slow pulse rate subnormal body temperature and elevated blood cholesterol levels.

Insulin and glucagon are the hormones secreted by Islets of Langerhans of the pancreas:-
Insulin:
Insulin is a peptide hormone and plays an important role in glucose homeostasis. Its main effect is to lower blood glucose levels by increasing the uptake of glucose into the body cells, especially muscle and fat cells. Insulin also inhibits the breakdown of glycogen to glucose, the conversion of amino acids or fats to glucose, so insulin is rightly called a hypoglycemic hormone.
Glucagon:
Glucagon is a polypeptide hormone. It is a potent hyperglycaemic hormone that acts on the liver and promotes the breakdown of glycogen to glucose (Glycogenolysis), synthesis of glucose from lactic acid and from non-carbohydrate molecules (gluconeogenesis).
Releases glucose from the liver cells, increasing the blood glucose levels. Since glucagon reduces the cellular uptake and utilisation of glucose it is called a hyperglycemic hormone. Prolonged hyperglycemia leads to the disorder called diabetes mellitus.

Exophthalmic goiter, also known as Graves' disease, is a condition caused by hypersecretion of thyroid hormones (thyroxine and triiodothyronine) by the thyroid gland, leading to hyperthyroidism. The symptoms are a direct result of the body's metabolic rate being excessively increased. These include significant enlargement of the thyroid gland (goiter), a markedly increased basal metabolic rate (BMR), elevated respiratory and excretory rates, and a rapid, often irregular, heart beat (tachycardia). Blood pressure is typically high, and body temperature is elevated, leading to increased heat production and intolerance to heat. A characteristic feature is the protrusion of the eyeballs (exophthalmos) due to swelling of tissues behind the eyes and weakness of the eye muscles, which can impair eye movement. Patients also experience significant weight loss despite increased appetite, along with nervousness, tremors, and fatigue.

Negative feedback mechanism is a regulatory process in which an increase in the level of a product inhibits further production of that product, thereby maintaining homeostasis. A classic example is the regulation of thyroxine levels by the hypothalamic-pituitary-thyroid axis. When thyroxine levels in the blood decrease below the set point, the hypothalamus senses this change and releases thyrotropin-releasing hormone or TRH. TRH stimulates the anterior pituitary gland to secrete thyroid-stimulating hormone or TSH. TSH then acts on the thyroid gland to stimulate the synthesis and release of thyroxine. As thyroxine levels in the blood increase and reach normal or elevated levels, thyroxine itself acts as a negative feedback signal on both the hypothalamus and the anterior pituitary gland. Thyroxine inhibits the release of TRH from the hypothalamus and suppresses the secretion of TSH from the pituitary gland. This inhibition reduces the stimulus for further thyroxine production, bringing thyroxine levels back to the set point. This self-regulating cycle ensures that thyroxine levels remain relatively constant, demonstrating how negative feedback mechanisms maintain physiological stability and prevent excessive hormone production.

• It increases the blood calcium level by stimulating osteo clasts to dissolve the bone matrix.
• It enhances the reabsorption of calcium and also increases calcium adsorption by intestinal mucosal cells.
• By all these action it increases the blood calcium level. Hence it is known as hypercalcemic hormone.

In infants, hypothyroidism causes cretinism. A cretin shows retarded skeletal growth, absence of sexual maturity, retarded mental ability, thick wrinkled skin, protruded enlarged tongue, bloated face, thick and short limbs occurs. The other symptoms are low BMR, slow pulse rate, subnormal body temperature and elevated blood cholesterol level.
Hyposecretion of the thyroid in adults causes myxoedema. It is otherwise called Gull’s disease. This disease is characterised by decreased mental activity, memory loss, slowness of movement, speech, and general weakness of body, dry coarse skin, scarce hair, puffy appearance, disturbed sexual function, low BMR, poor appetite, and subnormal body temperature.
Grave’s disease also called thyrotoxicosis or exophthalmic goiter. This disease is caused due to hypersecretion of the thyroid. It is characterised by enlargement of the thyroid gland, increases BMR (50% -100%), elevated respiratory and excretory rates, increased heartbeat, high BP, increases body temperature, protrusion of eyeball, and weakness of eye muscles and weight loss.
Simple goitre is also known as Endemic goitre. It is caused due to hyposecretion of thyroxine. The symptoms include enlargement of thyroid gland, fall in serum thyroxine level, increases TSH secretion.

• Insulin lowers the blood glucose level by increasing the uptake of glucose into the body cells.
• It inhibits the conversion of amino acids or fat to glucose.
• Insulin is called a hypoglycemic hormone.

The parathyroid gland can develop various disorders related to abnormal secretion of parathyroid hormone or PTH. Tetany is a serious disorder caused by hyposecretion or insufficient production of PTH by the parathyroid glands. Due to decreased PTH secretion, serum calcium levels drop significantly, a condition called hypocalcemia, while serum phosphate levels increase correspondingly. The decreased calcium and phosphate excretion by the kidneys further contributes to these imbalances. Tetany is characterized by generalized convulsions, locking of the jaws, increased heart rate, elevated body temperature, and severe muscular spasms that can be life-threatening. Hyperparathyroidism is the opposite disorder, caused by excessive secretion of PTH leading to abnormally high levels of PTH in the blood. This results in hypercalcemia and causes demineralization of bones as calcium is mobilized from bone tissue into the bloodstream. Patients with hyperparathyroidism experience loss of muscle tone, general weakness, fatigue, kidney stones, and various renal disorders due to excessive calcium excretion. Both disorders represent extremes of PTH dysfunction and require medical intervention to restore normal parathyroid function and calcium-phosphate homeostasis.

a) The systems that regulate and co-ordinate the physiological functions of our body are
* Nervous or neural system
* Endocrine system
b) The meaning of the word “Hormone”is “to excite”
c) General characters of hormones:
* The endocrine system influences the metabolic activities through the hormones
* These are chemical messengers released in to the blood and acts specifically on certain target organs or target tissues.
* Hormones may speed up or slow down or alter the activity of the target organs.
* Hormones secreted do not remain permanently in the blood.
* After their function they are converted by the liver into inactive compounds and excreted by the kidneys.

Hyperglycaemia is otherwise known as Diabetes mellitus. Is caused due to reduced secretion of insulin. As the result, the blood glucose level is elevated. Diabetes mellitus is of two types, Type! Diabetes and Type II Diabetes. Type I diabetes is also known as Insulin-dependent diabetes, caused by the lack of insulin secretion due to illness or viral infections. Type II diabetes is also known as Non-Insulin dependent diabetes, caused due to reduced sensitivity to insulin, often called insulin resistance.
Symptoms of diabetes include polyuria (excessive urination), polyphagia (excessive intake of food), polydipsia (excessive consumption of liquids due to thirst), ketosis (the breakdown of fat into glucose results in accumulation of ketone bodies) in blood. Gluconeogenesis (Conversion of non-carbohydrate) also occurs in diabetes.

The hypothalamus produces several releasing and inhibiting hormones that regulate the secretion of anterior pituitary hormones. Thyrotropin-releasing hormone or TRH stimulates the secretion of thyroid-stimulating hormone or TSH from the pituitary. Gonadotropin-releasing hormone or GnRH stimulates the secretion of follicle-stimulating hormone or FSH. Corticotropin-releasing hormone or CRH stimulates the secretion of adrenocorticotropic hormone or ACTH. Growth hormone-releasing hormone or GHRH stimulates the secretion of growth hormone or GH. Prolactin-releasing hormone or PRH stimulates the secretion of prolactin. Luteinizing hormone-releasing hormone or LHRH stimulates the secretion of luteinizing hormone or LH. Melanocyte-stimulating hormone-releasing hormone stimulates the secretion of MSH. Growth hormone-inhibiting hormone or GHIH, also known as somatostatin, inhibits the secretion of growth hormone. Prolactin-inhibiting hormone or PIH inhibits the secretion of prolactin. Melanocyte-stimulating hormone-inhibiting hormone inhibits the secretion of MSH. These hypothalamic hormones work through the hypothalamic-hypophyseal portal blood system to regulate anterior pituitary function and maintain endocrine homeostasis.

• Hypothalamus is a small cone-shaped structure that projects downward from the brain ending into the pituitary stalk.
• It interlinks both the nervous system and endocrine system.
• Hypothalamus contains a group of neuro secretary cells and it produces neuro transmitters which regulate the secretions of the pituitary.
• The hormones produced by the hypothalamus act either as a releasing hormone or as an inhibitory hormone.
• Though the pituitary gland is known as the master endocrine glands really it is in turn controlled by the hypothalamus.
• The hypothalamus and pituitary gland are anatomically different they are interlinked and functioning as a co-ordinated unit in maintaining the physiological process. They can not functions as a separated unit.
• The hypothalamic hypophyseal portal blood vessel allows hypothalamic hormones to control the anterior pituitary.
• The nerve signal produced by the hypothalamic hypophyseal axis (nerve bundle) controls the posterior pituitary secretion.
• Hypothalamus maintains homeostasis.
• Maintains blood pressure, body temperature cardio, and fluid-electrolyte balance of the body it influences emotional responses.
• The pituitary gland through its hormones performs various functions.

Hormones can be classified into three major classes based on their chemical nature and properties. The first class comprises amines, which are small, water-soluble molecules derived from the amino acids tyrosine or tryptophan. Examples of amine hormones include adrenaline and noradrenaline derived from tyrosine, melatonin derived from tryptophan, and thyroid hormones. The second class consists of protein and peptide hormones, which are water-soluble macromolecules composed of amino acid chains. Examples include insulin and glucagon secreted by the pancreas, and various pituitary hormones such as growth hormone, prolactin, and gonadotropins. The third class comprises steroid hormones, which are lipid-soluble molecules derived from cholesterol. Steroid hormones include cortisol and aldosterone produced by the adrenal cortex, testosterone produced by the testes, and estrogen and progesterone produced by the ovaries. The chemical nature of hormones determines their solubility, transport mechanisms in the bloodstream, and the types of receptors they bind to on target cells. Water-soluble hormones like amines and peptides bind to cell surface receptors, while lipid-soluble steroid hormones can cross cell membranes and bind to intracellular receptors.

A pair of the testis is present in the scrotal sac of males.
* The testis functions as a sex organ and also as an endocrine gland.
* Testis composed of seminiferous tubules and Ley dig cells.
* Lay dig cells secrete several male sex hormones collectively called Androgens.
* The main male sex hormone is Testosterone.
Functions of Testosterone:
* Under the influence of FSH and LH, testosterone initiates the maturation of the male reproductive organ.
* The appearance of secondary sexual characters. Eg. Muscular growth, growth of facial and axillary hair, masculine voice, and male sexual behaviour.
* It enhances the total bone matrix and stimulating the process of spermatogenesis.

Females have a pair of ovaries located in the pelvic region of the abdomen.
* It is composed of ovarian follicles and stromal tissue.
* It produces the egg or ova.
* It secretes the steroid hormones oestrogen and progesterone.
Functions:
* Oestrogen is responsible for the maturation of reproductive organs and the development of secondary sexual characters at puberty.
* Along with progesterone, oestrogen promotes breast development and initiates the menstrual cycle.
* Progesterone prepares the uterus for implantation of the fertilized ovum.
* It decreases the uterine contraction during pregnancy and stimulates the development of mammary glands and milk secretion.
* It is responsible for premenstrual changes in the uterus and for the formation of the placenta.

Heart: The cardiocytes on the atrial walls secrete an important peptide hormone called atrial natriuretic factor (ANF)
Function: When blood pressure is increased ANF is secreted and causes dilation of the blood vessels to reduce the blood pressure.
Kidney: Three hormones are secreted by the kidneys. They are Renin, erythropoietin, and calcitriol.
Renin:
* It is secreted by Juxta glomerular Cells (JGA).
* It increases blood pressure when angiotensin is formed in the blood.
Erythropoietin:
* It is also secreted by JGA.
* Stimulates erythropoiesis ie formation of RBC in bone mawow.
Calcitriol:
* It is secreted by proximal tubules of the nephron.
* It is an active form of vitamin D3.
* It promotes calcium and phosphorus absorption from the intestine and accelerates bone formation.

The person may be suffering from either cretinism or Dwarfism.
The following symptoms may be observed in cretinism. It is due to the hypo-secretion of Thyroxine.
* A cretin shows retarded skeletal growth.
* Absence of sexual maturity.
* Retarded mental ability.
* Thick wrinkled skin.
* Protruded enlarged tongue.
* Bloated face.
* Thick and short limb occur
* Low BMR
* Slow pulse rate.
* Subnormal body temperature
* Elevated blood cholesterol levels.
If the person shows the following symptom, he may have Dwarfism, it is due to hyposecretion of growth hormone.
* Skeletal growth and sexual maturity is arrested.
* They attain a maximum height of 4 feet only.

i) Structure of pancreas:
* Pancreas is a composite gland which performs both endocrine and exocrine functions.
* It is located just below the stomach as a leaf-like structure.
* It is composed of two major tissues such as acme and islets of Langerhans
* Acme secretes digestive enzymes and the islets of Langerhans secretes hormones like insulin and glucagon.
* Human pancreas has 1 -2 million islets of Langerhans.
* In each islet about 60% cells are beta cells 25% cells are alpha cells and 10% are delta cells.
* The alpha cells secrete glucagon the beta cells secrete insulin and delta cells secrete somatostatin.
ii) Structure of Islets of Langerhans (pancreas)
iii) Insulin control-blood sugar:-
* Insulin is a peptide hormone and plays an important role in glucose homeostasis.
* Its main effect is to lower blood glucose levels by increasing the uptake of glucose into the body cells
* especially muscle and fat cells.
* Insulin also inhibits the breakdown of glycogen to glucose, the conversion of amino acids or fats to glucose.
* So insulin is rightly called a hypoglycemic hormone.
* Reduced secretion of insulin leads to diabetes mellitus. As a result glucose level is elevated.
* It is of two types. Type I. Diabetes and Type II Diabetes. Type I Diabetes is caused by lack of secretion of insulin due to illness or viral infection. Type II or Non-insulin-dependent diabetes caused due to reduced sensitivity to insulin.
iv) Role of Glucagon:
* Glucagon is a polypeptide hormone.
* It is a potent hyper glycemic hormone.
* It acts on the liver and promotes the break down of glycogen to glucose (glycogenolysis)
* It also promotes synthesis of glucose from lactic acid and from non-carbohydrate molecules is called Gluconeogenesis.
* Glucogon releases glucose from the liver cell increasing the blood glucose levels.
* Since glucagon reduces the cellular uptake and utilisation of glucose it is called a hyperglycemic hormone. Prolonged hyperglycemia leads to the disorder called diabetes mellitus.

• Polyurea – excessive urination
• Polyphagia – excessive intake of food
• Poly dispsia – excessive consumption of liquids due to thirst.
• Ketosis – breakdown of fat into glucose results in accumulation of ketone bodies in blood.
• Gluconeogenesis also occur ie conversion of the non-carbohydrate form like amino acids and fat into glucose.

a. Location of pituitary gland:-
* It is located in a depression called sella tursica a bony cavity of the sphenoid bone below the brain.
* The pituitary gland means “to grow under”.
* It is connected to the brain by a stalk called the infundibulum
* Dimension:- It is about 1cm in diameter and 0. 5gm in weight.
b. Internal structure:-
* The pituitary consists of two lobes, anterior glandular adenohypophysis and posterior neural neuro hypophysis.
* Anatomically the anterior lobe or adenohypophysis has three lebesor zones namely pass intermedia, pass distalis and pass tuberalis.
* The neurohypophysis is otherwise known as pars nervosa.
* Embryonic origin:- The anterior lobe originates from the Embryonic invagination of pharyngeal epithelia called Rathke’s pouch.
* The posterior lobe originates from the base of the brain as an outgrowth of the hypothalamus.
c. Hypothalamus and pituitary gland

It secretes six hormones.
1. Growth Hormone:-
* It is also known as somatotropic hormone (STH) or somatotropin
* It is a peptide hormone.
* It promotes the growth of all the tissues and metabolic processes of the body.
* It influences the metabolism of carbohydrates, proteins, and lipids and increases the rate of biosynthesis in the cells.
* It stimulates chondrogenesis (cartilage formation), osteogenesis (bone formation).
* It helps in the retention of minerals like nitrogen and potassium, phosphorous, sodium, etc. in the body.
2. Thyroid Stimulating Hormone TSH or Thyrotropin:-
* It is a glycoprotein.
* It stimulates the thyroid gland to secrete Tri-iodothyronine (T3) and Thyroxine (T4).
* TSH secretion is regulated by a negative feedback mechanism.
* Its release from the anterior pituitary is induced by the thyrotropin-releasing hormone (TRH).
* When thyroxine level in the blood increases TRH acts on both the pituitary and hypothalamus to inhibit TSH secretion.
3. Adreno Corticotropic Hormone (ACTH):-
* It is a peptide hormone.
* It stimulates the adrenal cortex to secrete glucocorticoids and mineral corticoids.
* It stimulates melanin synthesis in melanocytes induces the release of fatty acids from adipose tissues and stimulates insulin secretion.
* its secretion is regulated by a negative feedback mechanism.
4. Follicle Stimulating Hormone (FSH):-
* It is a glycoprotein hormone.
* It regulates the functions of the gonads.
* In males, FSH along with androgens act on the germinal epithelium of seminiferous tubules and stimulates the production and release of sperms (Spermatogenesis).
* In females, it acts on the ovaries and brings about the development and maturation of graffian follicles.
5. Luteinizing hormone (LH):-
* It is a glycoprotein hormone.
* It is also known as interstitial cell-stimulating hormone.
* In females LH, along with FSH matures the ovarian follicles.
* LH independently induces ovulation, maintains the corpus luteum and promotes synthesis and release of ovarian hormones.
* In males, ICSH acts on interstitial cells of testes to produce the male sex hormone testosterone.
6. Luteo Tropic Hormone (LTH):-
* It is a protein hormone.
* It is also called luteotropin or lactogenic hormone or prolactin or mammotropin.
* It stimulates milk secretion after childbirth.
* Since it induces the corpus luteum hence named as a luteotropic hormone.

a. Neuro hypophysis secretes two hormones.
* Vasopressin or anti-diuretic hormone
* Oxytocin.
Vasopressin or Anti diuretic Hormone (ADH):-
* It is a peptide hormone.
* it promotes reabsorption of water and electrolytes by distal tubules of the nephron and thereby reduces the loss of water through urine.
* Hence it is called an anti-diuretic hormone.
* When released in large amounts it causes constriction of blood vessels and increases blood pressure.
* ADH deficiency causes Diabetes insipidus which induces the production of a large amount of urine.
Oxytocin:-
* It means quick birth.
* It is a peptide hormone.
3. It stimulates vigorous contraction of the smooth muscles of the uterus during childbirth.
4. And it also stimulates the ejection of milk from the mammary glands.
b. Chemical nature:
* The insulin hormone is a peptide hormone with 51 amino acids.
* The molecular weight of insulin hormone is 5734 Dalton.
* It consists of two chains A and B which are linked together by disulphide bridges formed between cystine residues.
Role of Insulin:
* It increases uptake of glucose into body cells especially muscle and fat cells.
* It inhibits the breakdown of glycogen to glucose, the conversion of amino acids or fats to glucose.
Thus it decreases the blood glucose level and so insulin is rightly called as a hypoglycemic hormone.
c. How can this condition be reversed?
* maintenance of normal body weight through adoption of nutritional habits ie. balanced diet and physical exercise.
* Correction of over nutrition and obesity may reduce the risk of diabetes and its complications.
* Alcohol and smoking should be avoided.
* Control of high blood pressure elevated cholesterol and high triglyceride levels.

a) Hormones are chemical messengers because they act as organic catalysts and co-enzymes to perform specific functions in the target organs.
b) Special features of target organs:
* The target organs contain receptor molecules either on the surface or within the cell.
* Although different hormones come in contact, only the cells that contain receptor molecules specific to the hormone are physiologically activated.
* A single hormone may have multiple effects on a single target tissue or on different target tissues.
* Many hormones exhibit long-term changes like growth, puberty, and pregnancy.
* Serious deficiency or excess secretion of hormones leads to disorders.
* Hormones coordinate different physiological mental activities and maintain homeostasis.

Four tiny parathyroid glands are found in the posterior wall of the thyroid gland.
* It is composed of Chief cells and oxyphil cell.
* The chief cells secrete parathyroid hormone and the function of oxyphill cell are not known
Functions
* It involves in calcium and phosphate.
* It promotes the activation of vitamin D to increase calcium absorption by intestine.
Hyper secretion
* Hyper parathyroidism causes demineral isation of calcium in bones.
* Thus increasing the calcium and phosphate level in the blood.
* PTH enhances the reabsorption of calcium and excretion of phosphate by the renal tubules.
Hypo secretion
* Due to the hyposecretion of PTH serum calcium level decreases and the serum phosphate level increases.
* Generalised convulsion occurs.

a) Position
A pair of adrenal glands are located at the anterior end of the kidney. Hence called supra renal glands.
b) Structure
The adrenal gland is composed of the outer cortex and an inner medulla.
The cortex consists of
* zona glomerulosa
* zona fasciculata
* zona reticularis.
1. zona glomerulosa
– secretes minerals corticoids
2. zona fasciculata
– secretes gluco corticoids
3. zona reticularis.
– secretes androgen and oestrogen.
b) Functions
* Gluco corticoids stimulate gluco neogenesis.
* Cortisolies involved in maintaining cardio vascular and kidney functions.
* Cortisol stimulates RBC production.
* Mineralocorticoids regulated the water and electrolyte balance of our body.
* Androgen plays a role in hair growth in the axial region pubis and face during Puberty.

Maintenance of constant internal environment of the body by the different co-ordinating system.
* The maintenance of the constant internal environment of the body is due to the functioning of the endocrine system and nervous system.
Endocrine gland.
1. a) If the calcium level in the blood decreases the parathyroid gland secretes parathyroid hormones and increases the calcium level in the blood.
b) If there is more calcium in the blood the other hormone secreted by the parathyroid gland called calcitonin acts against the parathormone and reduces calcium level.
2. a) The adrenalin secreted by the adrenal gland in emergency increases heartbeat rate and blood pressure.
b) The other hormone secreted by the adrenal is nor-adrenalin which reduces heartbeat rate and blood pressure.
Nervous system:
1. a) The sympathetic nervous system at the time of shock induces tear glands to secrete tears,
b) The parasympathetic nerve at the time of shock and emotion reduces the tear secretion.

Hormones are justifiably known as chemical messengers because they function as signaling molecules that carry specific chemical information throughout the body. When hormones are secreted by endocrine glands, they are released into the bloodstream and circulated to all parts of the body. However, they act specifically only on certain organs or tissues called target organs or target tissues, which possess specific receptors for those particular hormones. Upon reaching their target tissues, hormones bind to these receptors and trigger specific physiological responses. They can speed up or slow down the metabolic activities of target tissues, or alter their functions in precise ways. This selective action on specific target tissues, combined with their role in transmitting chemical signals from one part of the body to another, justifies their designation as chemical messengers. Unlike the nervous system which uses electrical impulses and neurotransmitters for rapid point-to-point communication, hormones provide slower but longer-lasting systemic communication that coordinates various bodily functions such as growth, metabolism, reproduction, and homeostasis.

• Oestrogen hormones promote the growth of the ovarian follicle
• While the follicles are growing it secretes the hormone oestrogen which in turn promotes the ovum to develop.
• The shedding up of ovum at the Luteal phase takes place by the influence of the Luteinizing hormone.

The acini of the thyroid gland are the functional units of the gland and have a distinctive microscopic structure. The thyroid gland is a bilobed endocrine gland, and each lobe is subdivided into many lobules. These lobules are composed of follicles called acini, which are the basic secretory units. Each acinus is lined with a single layer of glandular epithelial cells that may appear cuboidal or squamous in shape depending on their functional state. The epithelial cells of the acini are responsible for synthesizing and secreting thyroid hormones. The central cavity or lumen of each acinus is filled with colloid, which is a thick, viscous, glycoprotein mixture. This colloid primarily consists of thyroglobulin molecules, which serve as the storage form of thyroid hormones. Thyroglobulin is synthesized by the epithelial cells and accumulates in the colloid, where thyroid hormones (T3 and T4) are bound to it. When thyroid hormones are needed, the epithelial cells reabsorb the colloid through endocytosis, break down the thyroglobulin, and release the free hormones into the bloodstream. This structural arrangement allows for both synthesis and storage of thyroid hormones within the same functional unit.

• Diabetes emeritus: If the insulin is not secreted sufficiently the liver and muscles are unable to convert the glucose into glycogen. As a result, more glucose enters into the bloodstream raising the blood sugar level leads to diabetes mellitus.
• Diabetes Insipidus: The hormone antidiuretic hormone is secreted by the neurohypophysis, which promotes reabsorption of water and thus reduces the loss of water through urine ADH deficiency induces the production of large amounts of urine leads to diabetes insipidus.

Acromegaly is a pathological condition caused by excessive secretion of growth hormone (somatotropin) in adults, after the epiphyseal plates of long bones have already closed. Since linear growth is no longer possible, the excess growth hormone causes abnormal enlargement of bones and soft tissues in the extremities and face. The characteristic symptoms of acromegaly include pronounced overgrowth of the bones of the hands and feet, leading to enlarged and coarse features, enlargement of the jawbones (mandible and maxilla) resulting in a protruding jaw and malocclusion of teeth, and thickening of the tongue. Additionally, there is malfunctioning of the gonads, which may lead to reduced fertility and sexual dysfunction. The condition also causes enlargement of various viscera and internal organs, including the lungs, heart, liver, and spleen, which can lead to cardiovascular and respiratory complications. Endocrine glands such as the thyroid and adrenal glands may also become enlarged. Other symptoms include excessive sweating, weakness, headaches, and visual disturbances if the pituitary tumor causing the hormone excess compresses the optic nerves. The metabolic rate increases, and patients may experience joint pain and arthritis due to abnormal bone growth.

Cretinism is a condition resulting from severe hypothyroidism during infancy or early childhood, meaning there is insufficient production of thyroid hormones from birth or shortly after. This deficiency profoundly impacts growth and development. A cretin child typically exhibits retarded skeletal growth, leading to dwarfism. There is a significant impairment of mental development, resulting in intellectual disability. Physical characteristics include thick, short limbs, a bloated face with puffy skin, and a tongue that is enlarged and protrudes from the mouth. Sexual maturity is often absent or severely delayed. Physiologically, cretins have a low basal metabolic rate (BMR), a slow pulse rate, subnormal body temperature, and elevated levels of blood cholesterol, all indicative of a severely slowed metabolism.

The thyroid gland is a butterfly-shaped, bilobed endocrine gland situated below the larynx on each side of the upper trachea. The two lobes are connected by a median tissue mass called the isthmus, which lies across the ventral surface of the trachea. Each lobe is composed of numerous lobules, which are the structural subdivisions of the gland. The lobules consist of follicles called acini, which are the basic functional units of the thyroid. Each acinus is lined with a single layer of glandular epithelial cells that are typically cuboidal in shape when active, though they may appear squamous when inactive. The epithelial cells are responsible for synthesizing thyroid hormones. The central cavity or lumen of each acinus is filled with colloid, a thick, viscous glycoprotein mixture that serves as a storage depot for thyroid hormones. The colloid primarily consists of thyroglobulin molecules, which are large protein molecules to which thyroid hormones are bound and stored. The thyroid gland secretes two main hormones: Tri-iodothyronine (T3) and tetra-iodothyronine (T4), also called thyroxine. These hormones are concerned with regulating the basal metabolic rate of the body, promoting growth and development, and maintaining body temperature. They increase oxygen consumption and heat production in tissues, and are essential for normal physical and mental development, particularly during childhood and adolescence.

A pair of adrenal glands are located at the anterior end of the kidneys. Elence, they are called suprarenal glands. The outer region is called cortex and the inner region is medulla. The adrenal cortex has three distinct zones,
* Zona Glomerulosa
* Zona fasciculata
* Zona reticularis
1. Zona Glomerulosa:
* It is the outer thin layer. It constitutes about 15% of the cortex.
* It secretes mineralocorticoids.
2. Zona fasciculata:
* It is the middle wide layer constituting about 15% of the adrenal cortex.
* It secretes glucocorticoids such as cortisol, corticosterone and trace amounts of adrenal androgen and oestrogen.
3. Zona reticularis:
* It is the inner zone of adrenal cortex.
* It constitutes about 10% of adrenal cortex.
* It constitutes about 10% of adrenal cortex.
* It secretes the adrenal androgen, trace amount of oestrogen and glucocorticoids.

Hyperglycemia and hypoglycemia are two opposite metabolic conditions related to blood glucose levels. Hyperglycemia is a pathological condition characterized by an abnormally increased blood glucose level, where the concentration of glucose in the blood rises above the normal range of 70-100 mg/dL in the fasting state. This condition may result from reduced secretion of insulin by the pancreatic beta cells, reduced sensitivity of tissues to insulin, or excessive intake of carbohydrates. Prolonged hyperglycemia is a hallmark of diabetes mellitus. Symptoms of hyperglycemia include excessive thirst (polydipsia), frequent urination (polyuria), fatigue, and blurred vision. In contrast, hypoglycemia is a condition in which the blood glucose level decreases below the normal range, typically below 70 mg/dL. This condition may result from increased secretion of insulin, excessive physical activity without adequate carbohydrate intake, prolonged fasting, or certain medications. Hypoglycemia causes acute symptoms such as trembling, sweating, anxiety, rapid heartbeat, weakness, and in severe cases, loss of consciousness or seizures. While hyperglycemia develops gradually and causes long-term complications, hypoglycemia is an acute emergency requiring immediate treatment with glucose or carbohydrates to prevent serious neurological damage.

Cholecystokinin (CCK) is a hormone secreted by the duodenal and jejunal mucosa in response to the presence of fats and partially digested proteins (peptides and amino acids) in the small intestine. This hormone has multiple important functions in the digestive process. CCK acts on the gallbladder to stimulate its contraction, causing the release of stored bile into the duodenum. Bile is essential for the emulsification and absorption of dietary fats. Additionally, CCK stimulates the pancreas to increase the secretion of pancreatic enzymes, including lipases, proteases, and amylases, which are necessary for the digestion of fats, proteins, and carbohydrates respectively. CCK also promotes the discharge of these pancreatic enzymes into the duodenum through contraction of the pancreatic ducts. Furthermore, CCK slows down gastric emptying, allowing more time for the stomach contents to be properly mixed and for the small intestine to process the food at an optimal rate. This hormone also promotes the secretion of bicarbonate from the pancreas, which neutralizes the acidic chyme coming from the stomach, creating an optimal pH for pancreatic enzyme activity in the small intestine.

Growth hormone promotes growth of all the tissues and metabolic process of the cell. The growth hormone stimulates the growth in the following ways
* It influences the metabolism of carbohydrate proteins and lipids.
* It increases the rate of protein biosynthesis.
* It stimulates cartilage formation of chondrogenesis.
* It stimulates bone formation osteogenesis.
* It helps in the retention of minerals like nitrogen, potassium, phosphorous sodium in the body.
* It increases the release of fatty acid from adipose tissue.
* It decreases the rate of glucose utilization for energy by the cell, by which it conserves glucose for glucose-dependent tissues such as the brain.

The pineal gland, also known as the epiphysis cerebri or conarium, is a small endocrine gland located deep within the brain, positioned behind the third ventricle. It is composed of two main types of cells: parenchymal cells (pinealocytes) which are the functional secretory cells, and interstitial cells which provide structural support. The pineal gland secretes the hormone melatonin, which is synthesized from the amino acid tryptophan. Melatonin plays a central role in the regulation of the circadian rhythm, which is the body's internal biological clock that follows a 24-hour cycle. It maintains a normal sleep-wake cycle by increasing in concentration during darkness to promote sleep and decreasing during daylight to promote wakefulness. The pineal gland also regulates the timing of sexual maturation of the gonads, with melatonin having an inhibitory effect on gonadal development during childhood. Beyond these primary functions, melatonin influences various other physiological processes including metabolism and energy expenditure, skin pigmentation through effects on melanocytes, the menstrual cycle in females, and the defence mechanism of the body by enhancing immune function. The pineal gland is sensitive to light, with darkness stimulating melatonin production and light suppressing it, making it a crucial link between the external environment and internal physiological processes.

• Adrenalin increases liver glycogen breakdown into glucose and increases the release of fatty acids from fat cells.
• During emergency, it increases heartbeat rate and blood pressure.
• It stimulates the smooth muscles of cutaneous and visceral arteries to decrease blood flow.
• It increases blood flow to the skeletal muscles thereby increases the metabolic rate of skeletal muscles cardiac muscles and nervous tissues.

The pancreas is a unique organ that functions as both an exocrine and endocrine gland. It is located just below the stomach as a leaf-like structure, extending across the abdominal cavity. As an exocrine gland, the pancreas secretes digestive enzymes into the small intestine through the pancreatic duct. These enzymes include amylases for carbohydrate digestion, proteases for protein digestion, and lipases for fat digestion. As an endocrine gland, the pancreas secretes hormones from the islets of Langerhans, primarily insulin and glucagon, which regulate blood sugar levels. If the pancreas is removed from the body, multiple serious consequences would occur. The loss of pancreatic digestive enzymes would severely impair digestion, leading to malabsorption of nutrients and malnutrition. The loss of insulin secretion would result in persistent hyperglycemia and the development of diabetes mellitus, requiring lifelong insulin replacement therapy. The loss of glucagon secretion would impair the body's ability to raise blood glucose during fasting periods. Additionally, the removal of other pancreatic hormones such as somatostatin would disrupt various metabolic processes. Overall, pancreatic removal would be incompatible with normal life without extensive medical intervention and hormone replacement therapy, making the pancreas an organ essential for both digestion and metabolic homeostasis.

Kidney has endocrine tissues which act as a partial endocrine gland. It secretes renin, erythropoietin, and calcitriol. Renin is secreted by juxtaglomerular cells. It increases blood pressure when angiotensin is formed in the blood.
Erythropoietin is also secreted by the juxtaglomerular cells of the kidney and stimulates erythropoiesis in the bone marrow. Calcitriol is secreted by proximal tubes of nephrons. It is an active form of vitamin D3 which promotes calcium and phosphorus absorption from the intestine and accelerates bone formation.
Part – II.
11th Bio Zoology Guide Chemical Coordination and Integration Additional Important Questions and Answers
I. Choose The Correct Answer