Samacheer Class 11 Bio Zoology - Excretion

The three filtration barriers that solutes must come across as they move from plasma to the lumen of Bowman’s capsule are
* Glomerular capillary endothelium
* Basal lamina or basement membrane
* Epithelium of Bowman’s capsule. Blood corpuscles and plasma protein are excluded by these layers.

• Glomerulus hydrostatic pressure
• Glomerulus pressure
• Opposing pressure: Colloidal osmotic pressure, Capsular hydrostatic pressure
• Net filtration pressure = Glomerular hydrostatic pressure – (Colloidal osmotic pressure + capsular hydrostatic pressure.

1. Juxtaglomerular apparatus:
Juxtaglomerular apparatus is a specialized tissue in the afferent arteriole of the nephron that consists of macula densa and granular cells. The macula densa cells sense distal tubular flow and affect afferent arteriole diameter. The granular cells secrete an enzyme called renin. It plays an important role in reabsorption of water, Na + and excretion of K +.
2. Podocytes:
The visceral layer of the Bowman’s capsule is made up of epithelial cells called podocytes. The podocytes end in foot processes which cling to the basement membrane of the glomerulus. The openings between the foot processes are called filtration slits. It is important for glomerular filtration.
3. Sphincters in the bladders:
Sphincter muscles in the bladder controls the flow of urine from the bladder. When urinary bladder is filled with urine, it stretches and stimulates the central nervous system through the sensory neurons of the parasympathetic nervous system and brings about contraction of the bladder.
Simultaneously, somatic motor neurons induce the sphincters to close. Smooth muscles contracts resulting in the opening of the internal sphincters passively and relaxing the external sphincter. When the stimulatory and inhibitory controls exceed the threshold, the sphincter opens and the urine is expelled out.
4. Renal cortex:
The outer portion of the kidney is the renal cortex. It contains renal corpuscles and the proximal and distal tubules. It is thin and fibrous.

When a molecule or ion is reabsorbed from the lumen of the nephron, it goes to the bloodstream through an efferent arteriole which carries blood away from the glomerulus. If a solute is filtered and not reabsorbed from the tubule, it goes along with urine.

* 1. Distal tubule; 2. Collecting duct
* In the renal tubules H + and NH 4 are secreted and liberated into the tubules and excreted through
urine thus maintaining acid base balance.
* For each H + ions from the liberated filtrate one Na + is reabsorbed in the tubules.
* The secreted HCO 3, PO 3 and NH 3 combines to form carbonic acid and phosphoric acids.
* Thus the H + are maintained and their reabsorption is prevented.

• Blood enters the glomerulus faster with greater force through the afferent arteriole and leaves the glomerulus through the efferent arterioles much slower.
• Because afferent arteriole is wider than efferent arteriole.
• The constriction of this does not affect the rate of filtration.

• A liquid which gathers in the bladder – Urine
• Produced when blood is filtered in a Bowman’s capsule – Glomerular filtrate
• The temporary storage of urine – Urinary bladder
• A ball of intertwined capillaries – Glomerulus
• Removal of unwanted substances from the body – Excretion
• Each contains a glomerulus – Bowman’s Capsule
• Carry urine from the kidneys to the bladder – Ureter
• The scientific term for urination – Micturition
• Regulation of water and dissolved substances in the blood and tissue fluid – Osmoregulation
• Consists of the kidneys ureters and bladder Excretory system
• Removal of useful substances from glomerular filtrate reabsorption
• What solute does blood contain that is not present in the glomerular filtrate? – Plasma Protein

* The type of nitrogenous end product (Urea or Uric acid or ammonia) of an animal excretion depends upon the habitat of the animal.
* For the Excretion of Ammonia, more water is needed.
* Animals that excrete most of their nitrogen in the form of ammonia are called ammonites.
* Fishes Amphibians. Uric acid can be eliminated with a minimum loss of water and is called Uricoteles.
* Reptiles, birds insects, landrails. Mammals and terrestrial amphibians excrete urea and are called ureoteles.
Nitrogenous

Protonephridia
Metanephridia
1. Proto – first it is a network of dead-end tubules lacking internal opening. (E.g) Platyhelminthes
Meta – after They have a tubular internal opening called nephrostome. (E.g) Earthworm
2. Flame cells are excretory structures.
The excretory products are filters and selectively reabsorbed.
3. Excretory product excretes through nephridiopore
The excretory product excretes through the nephridiopore.
4. Excretory structure are usually osmo regulators
Excretory structures are osmo regulators and helps in excretion.

Urine formation involves three main processes namely Glomerular Alteration, tubular reabsorption and tubular secretion.
I. Glomerular filtration:
* Blood enters the kidney from the renal artery into the glomerulus.
* Blood is composed of water colloidal proteins, sugars and nitrogenous end product.
* The filteration is started in the glomerulus. The fluid that leaves the glomerular capillaries and enters the Bowman’s capsule is called the glomerular filtrate. It formed 170-180 litre within 24 hours.
* Glomerular membrane has large surface area. Blood enters the glomerulus faster with greater force through the afferent arteriole and leaves the glomerulus through the efferent arterioles much slower.
* This is because afferent arteriole is wider than efferent arteriole and the glomerular hydrostatic pressure is around 55 mm Hg.
* Molecules larger than 5mm are barred from entering the tubule.
The two opposing forces are contributed by the plasma proteins in the capillaries.
* Colloidal osmotic pressure – 30 mm Hg
* Hydrostatic pressure -15 mm Hg
Both pressures combine. 30 mm Hg + 15mm Hg = 45mm Hg
* The net filtration pressure of 10mm Hg is responsible for the renal filtration.
* Net filtration pressure – Glomerular
* Hydrostatic Pressure – Colloidal Osmotic pressure + Capsular hydrostatic pressure.
Net filteration pressure = 55 mm Hg – (30mm Hg +15mm Hg) = 10mm Hg
Substance
Concentration in blood Plasm / g dm -3
Concentration in glomerular filtrate / g dm -3
Water
900
900
Proteins
80.
0.05
Aminoacids
0.5
0.5
Glucose
1.0
1.0
Substance
Concentration in blood PIasm /gdm -3
Concentration glomerular filtrate/gdm -3
Urea
0.3
0.3
Uric Acid
0.04
0.04
Creatinine
0.01
0.01
Inorganic ions (mainly (Na +, K + and Cl – )
7.2
7.2
II. Tubular reabsorption:
* The volume of filtrate formed per day is around 170 – 180l.
* Urine released is around 1.51 per day. 99% of the glomerular filtrate is reabsorbed by the renal tubules.
Reabsorption in proximal convoluted tubule:
* Glucose lactate amino acids Na in the filtrate are reabsorbed in the PCT.
* Sodium is reabsorbed by active transport through a sodium-potassium pump in the PCT.
* Small amounts of urea and uric acid are reabsorbed.
Reabsorption in Henle Loop:
* Descending limb of Henle’s loop is permeable to water due to the presence of aqua porlns but not permeable to salts.
* Water is lost in the descending limb. Hence Na and Cl get concentrated in the filtrate.
* Ascending limb of Henle’s loop is impermeable to water but permeable to Na +, Cl – andK +.
Distal Convoluted Tubule:
* It recovers water and secretes potassium into tubule.
* Na +, Cl -, and water remain in the DCT.
* Reabsorption of HCO 3 takes place to regulate the blood pH.
* Collecting the tubule is permeable to water potassium ions are actively transported into the tubule and Na + to produce concentrated urine.
Tubular Secretion:
* Once it enters the collecting duct water is absorbed and concentrated hypertonic urine is formed.
* For every H secreted into the tubular filtrate, a Na + is absorbed by the tubular cell.
* The H + secreted combines with HCO + 3, HPO – 3, and NH + and gets fixed as H 2 CO 3, H 2 PO 3, and NH 4 +.
* Since H + gets fixed in the fluid reabsorption of H + is prevented.

In the renal tubules, proximal convoluted tubule and distal convoluted tubule are situated in the cortical region of the kidney and the loop of Henle is in the medullary region.
Cortical Nephron
Medullary Nephron
1. The loop of Henle is too short and extends only very little into the medulla.
Nephrons have a long loop of Henle that run deep in to the medulla.
2. There is no vasa recta.
Vasa recta is present.

The movement of substances such as H +, K +, NH 4 +, creatinine and organic acids from the peritubular capillaries into the tubular fluid, the filtrate is called Tubular secretion.

• When the volume of blood decreases the flow pressure, decreases.
• This can be sensed by the hypothalamus and osmoreceptors are stimulated and the antidiuretic hormone is secreted from the neurohypophysis.
• The aquaporins in the proximal convoluted tubules and collecting tubule reabsorb water. Hence the blood volume increases and the blood pressure increases.

• ADH which is also called vasopressin or Antidiuretic hormone is secreted from the neurohypophysis.
• Fluid loss or if blood pressure increases the osmoreceptors of the hypothalamus is stimulated and hence neurohypophysis is stimulated and secretes ADH.
• When the fluid level and pressure are maintained due to the negative feedback mechanism ADH secretion stops.

• Due to the stimulation of Angiotensin II the adrenal cortex secretes aldosterone. That causes reabsorption of Na +, K + excretion, and absorption of water from distal convoluted tubule and collecting tubule.
• This mechanism is known as Renin – Angiotensin Aldosterone System.

* Excessive stretch of cardiac atrial cells cause an increase in blood flow to the atria of the heart and release Atrial Natriuretic Peptide or factor (ANF) travels to the kidney where H increases Na+ excretion and increases the blood flow to the glomerulus.
* Acting on the afferent glomerular arterioles as a vasodilator or an efferent arterioles as a vasoconstrictor.
* The first identical natri uretic hormone is atrial natriuretic horome of heart.
Part – II.
11th Bio Zoology Guide Excretion Additional Important Questions and Answers
I. Choose The Correct Answer.

Some of the nitrogenous wastes produced by various animals other than ammonia, urea and uric acid are:
Jrimethyl amine oxide (TMO) in marine teleosts, guanine in spiders, hippuric acid in mammals, reptiles and other nitrogenous wastes include allantonin, allantoic acid, omithuric acid, creatinine, creatine, purines, pyramidines and pterines.

The two opposing forces against the glomerular blood pressure
* Collodial osmotic pressure is 30 mm Hg
* Capsular hydrostatic pressure is 15mm Hg
Net filtration pressure- Glomerular
Hydrostatic pressure – Colloidal
Osmotic pressure + Capsular hydrostatic pressure = 55 mm Hg – 30 mm Hg + 15 mm Hg = 10 mm Hg

When two solutions A and B are separated by a semi permeable membrane when water move from solution A to B across the membrane then the B solution is hypertonic and the solution A where the water loses is known as hypotonic solution.

• When we drink or eat salty products the Na+ enters into the body fluids.
• The sodium ions helps in the reabsorption of water
• But when we drink only water as there is no sodium ions the tubules cannot reabsorb water.
• Hence there is an increase in the urine output.

Malfunction of the kidneys can lead to accumulation of urea and other toxic substances, leading to kidney failure. In such patients, toxic urea can be removed from the blood by a process called hemodialysis. A dialyzing machine or an artificial kidney is connected to the patient’s body. A dialyzing machine consists of a long cellulose tube surrounded by the dialyzing fluid in a water bath.
The patient’s blood is drawn from a convenient artery and pumped into the dialyzing unit after adding an anticoagulant like heparin. The tiny pores in the dialysis tube allow small molecules such as glucose, salts, and urea to enter the water bath, whereas blood cells and protein molecules do not enter these pores.
This stage is similar to the filtration process in the glomerulus. The dialyzing liquid in the water bath consists of a solution of salt and sugar in the correct proportion in order to prevent loss of glucose and essential salts from the blood. The cleared blood is then pumped back to the body through a vein.

• The blood vessels supplies to skin constricts and thus there is a decrease in the secretion of sweat prevents loss of water.
• There is a reduction in the glomerular blood pressure and the rate of filtration decreases.
• The reaborption of water in the proximal distal convoluted tubules increase.
• There is absorption of water from the small intestine and large intestine and thus increases the water content in the blood.

Aquaporins are water permeable channels.
Functions
It helps in allowing water to move across the epithelial cells in relation to the osmotic difference from the lumen to the interstitial fluid.

• The main function of Henle’s loop is to reabsorb water from filtrate.
• If the length of the loop is longer then there is more reabsorption of water and if the lengh of Henle’s loop is shorter then the reabsorption of water is less.

Bloodcells and most blood proteins are too big to cross the capsular membrane into the capsule space. But the membrane’s slits and pores allow through water mineral salts polypeptides and other small molecules including waste such as urea ammonia and creatinine.

Blood flows from renal arteriole into the knot of capillaries. It enters at pressure which will force water and other out of the capillaries into the capsular space.

Proximal tubule is nearer to the Bowman’s capsule. This region allows much water to be reabsorbed into the capillaries and surronding fluids as well as glucose mineral salts and other useful substances.

It is also called the vasarecta this network reabsorbs upto 99 percent of the water in the tubule as well as various other substance using active pumps it also moves sodium from the blood to the tubule.

• As the loop of the Henle dipsin to the renal medcula more water moves from the tubule into the blood as well as small amounts of salts and some urea and creatinine.
• Some acids and amines may move into the tubule in which ammonia cango in both the direction.

• Distal tubule is far from capsule. This region may see water go in or out of the tubule depending on the concentration of water already in the tubule/ while hydrogen and potassium ions move to regulate both blood and urine pH.
• Acids amines and ammonia compounds may also transported into the tubule.

• Fine adjustment of urine composition continues into the collecting duct system.
• About 5 percent of all the water and sodium being reabsorbed into the blood is recovered here.

* The renal clearance is equal to the glomerular filtrate then there is efficient filtration with little reabsorption and secretion.
* Thus we can estimate the clearance is equal.
Three Marks
Short Answer –

1. Invertebrate – Protonephridia / Meta nephridia
2. Platvhelminthes – Flamecells
3. Amphioxues – Solenocytes
4 Nematodes – Rennette cells
5. Annelida – Metanephridia
6. Insects – Malpighian tubules
7. Prawn / Crustaceans – Green glands / Antenna! glands

• In the reptiles the glomerulus is reduced or there may be no glomerulus and 1-lenle’s loop and hence produces dilute urine (chypotonic).
• In the mammals the long Henle’s loop produces concentrated urine (hypertonic)
• A glomerular kidneys of marine fishes produce little urine that is isoosmotic to the body fluid.
• Amphibians and freshwater fish lack Henle’s loop hence produce dilute urine.

a. Each kidney weighs an average of 120 – 170 gms.
The outer layer of the kidney is covered by three layers of supportive tissue namely renal fascia perirenal fat capsule fibrous capsule.
b. Draw the LS of kidney and name the parts.
c. Internal Structure of kidney
* The longitudinal section of kidney shows an outer cortex inner medulla and pelvis.
* The inner concave surface of the kidney is renal hilum through which ureter blood vessels and nerves enter.
* Inner to the hium is a funnel shaped renal pelvis with projection called calyces.
* The calyces collect the urine and empties in to the ureter.
* The medulla consists of conical tissues called medullary pyramids or renal pyramids.

a) Hie structural and functional unit of kidney is nephron. It is composed of Malpighian body or renal corpuscle and Urine ferous tubule.
b) Structure of nephron
c. Malpighian body/Renal Corpuscle.
* The Bowman’s capsule and the glomerulus together constitutes Malpighian corpuscle.
* Bowman’s capsule is made up of two layers. It contains blood vessels called glomerules.
* The endothelial of glomerulus has many pores. The viscral layers of glomerulus is made of epithelial cells called podocytes.
* Tire podocytes end in foot processes which cling to the basement membrance of the glomerulus.
* The openings between the foot processes are called filtration slits.

a)
1. proximal convoluted tubule.
2. Henle’s loop
a. Thindescending limb of Henle’s loop.
b. Thick ascending limb.
2. Distal convoluted tubules
The distal convoluced tubules opens in to acollecting duct.
Several collecting ducts fuse to form papillary duct that delivers urine in to the calvces which opens into the renal pelvis.
b) The PCT and DCT are situated in the cortical region of the kidney.
The loop of Henle is in the medulla region.
c) The loop of Henle is too short and extends only very little into the medulla and are called cortical nephron.
Some nephrons have very long loops of Henle that run deep into the medulla and are called Juxta medullary nephrons.

Capillaries of nephron
1. Glomerulus capillary bed
2. Peritubular capillaries
1. Glomerular capillarybed
* It consists of afferent and efferent arteriole.
* The afferent arteriole is broader than efferent arteriole.
* The efferent arteriole that comes out of the glomerulus forms a fine capillary network around the renal tubule called the peritubular capillaries.
Vasa recta
The efferent arteriole serving the juxta medullary nephrons form bundles of long straight vessel called vasa recta and runs parallel to the loop of Henle.

As the glomerular filtrate forms it contain all the substances except plasma protein of blood. Hence it resembles blood.
Substance
Concentration in blood Plasma / g dm -3
Concentration in glomerular filtrate / g dm -3
Water
900
900
Proteins
80.0
0.05
Aminoacids
0.5
0.5
Glucose
1.0
1.0
Urea
0.3
0.3
Uric Acid
0.04
0.04
Creatinine
0.01
0.01
Inorganic ions (mainly (Na +, K + and Cl – )
7.2
7.2

Tubular Secretion:
* The collecting tubule of nephron secrete H + NH 4, Creatinine and Organic acid and liberated into the tubules and excreted through urine.
* Most of the water is absorbed in the proximal convoluted tubule.
* Na – is exchanged for water in the loop of Henle.
* The hypotonic fluid enters the distal convoluted tubule.
* Substances such as urea and salts pass from peritubular blood into the cells as distal convoluted tubule and then to collecting duct.
* Water is absorbed and concentrated hypertonic urine is form ed.
* For every H + secreted into the tubular filtrate a Na + is absorbed by the tubular cell.
* The H secreted combines with HCO 3, HPO 3 and NH 3 and gets fixed as carbonic acid CH 2 CO 3 and Phosphoric acid CH 2 PO 4
* Since H + gets fixed in the fluid reabsorption of H + is prevented.

a) The major function of Henle’s loop is to concentrate Na + and Cl –.
* There is low osmolarity near the cortex and high osmolarity towards the medulla.
* This osmolarity in the medulla is due to the presence of the solutes transporters and is maintained by
the arrangement of the loop of Henle collecting duct and vasa recta.
* The osmolarity of interstitial fluid is 300 m Osm.
* The Henle’s loop create a countercurrent multiplier.
* As the fluid enters the descending limb water moves from the lumen into the inter stitial fluid the osmolarity reduces.
* To counteract this dilution the region of the ascending limb actively pumps solutes from the lumen into the interstitial fluid and the osmolarity increases to about 1200 m OSM in medula.
b) The vasa recta maintains the medullary osmotic gradient via counter current exchanger.
* The counter current exchanger of vasa recta preserves the medullary gradient while removing reabsorbed water and solutes.
* The vasa recta leaves the kidney at the junction between the cortex and medulla.
* When the blood leaves the efferent arteriole and enters vasa recta the osmolarity in the medulla increases (1200 rnOsm) and result in passive up take of solutes and loss of water.
* As the blood enters the cortex the osmolarity in the blood decreases and the blood loses solutes and gain water to form concentrated urine.

Vasa recta maintains the medullary osmotic gradient via counter current exchanger.
* Vasa recta preserves the medullary gradient while removing reabsorbed water and solutes through counter current exchanges.
* The vasa recta leave the kidney at the junction between the cortex and medulla.
* The interstitial fluid at this point is iso – osmotic to blood.
* When the blood leaves the efferent arteriole and enters the vasa recta the osmalarity in the medulla increases (1200 mOsm) and results in passive up take of solutes and loss of water.
* As the blood enters the cortex the osmolarity in the blood decreases (300mOsm) and the blood loses solutes and gains water to form concentrated urine.
* Human kidneys can produce urine nearly four times concentrated than the initial filtrate formed.

a) The structures that regulate kidney functioning
* Hypothalamus
* Juxtaglomerular apparatus
* Heart
b) The functions of ADH
* When there is excessive loss of fluid from the body or when there is an increase in the blood pressure the osmoreceptors of the hypothalamus is stimulated.
* The osmoreceptors stimulate the neurohypophysis to secrete an antidiuretic hormone (AOH) or vasopressin.
* ADH facilitates reabsorption of water by increasing the number of aquaporins on the cell surface of the distal convoluted tubule and collecting duct and prevents excessloss of water.

a) Renin is secreted by granular cells.
b) Granular cells are present in the afferent arteriole.
c) The role of renin
* A fall in glomerular blood flow blood pressure and filtration rate can activate granular cells of juxtaglomerular cells to release renin.
* Renin converts the plasma protein angiotensinogen into angiotensis I and angiotensin II.
* Angiotensis II stimulates Na + reabsorption in the proximal convoluted tubule by vasoconstriction of the blood vessels and increases the glomerular blood pressure.
* Angiotensis II stimulates adrenal cortex to secrete aldosterone that causes reabsorption of Na +,K + excretion and absorption of water.
* This increases the glomerular blood pressure and glomerular filtration rate.
* Hence renin regulates osmoregulation.

a) This is liberated from atrium of heart.
b) Use of Atrial natriuretic peptide
* It increases Na excretion and increases the blood flow to the glomerulus.
* It acts on the afferent glomerular arteriole as a vaso dilator or an efferent arteriole as a vaso constrictor.
* It reduces aldosterone from adrenal cortex and renin secretion.
* Thus decreases the angiotensin II.
* The atrial natri uretic factor acts antagonistically to renin angiotensin system aldosterone and vasopressin.

a) The process of release of Urine from the bladder is called micturition or urination.
b) Urine formed by the nephrons is ultimately carried to the urinary bladder where it is stored till it receives a signal from the central nervous system.
* The stretch receptors present inthe urinary bladder are stimulated when it gets filled with urine.
* At the same time the internal sphincters opens and relaxing the external sphincter.
* The sphincter opens and the urine is expelled out.

a) in the patients of kidney failure toxic urea can be removed from the blood by a process called haemodialysis.
b) The dialyzing machine is a artificial kidney.
c) Hemodialysis
* A dialyzing machine consists of a long cellulose tube surrounded by the dialysing fluid in a water bath.
* A patient’s blood is drawn from a convenient artery and pumped into the dialysing unit after adding an anticoagulant like heparin.
* The tiny pores in the dialysis tube allow small molecules such as glucose salts and urea to enter into the water bath.
* Whereas blood cells and protein molecules do not enter these pores the cleared blood is then pumped back to the body through a vein.

• This involves transfer of healthy kidney from one person (donor) to another person who is with kidney failure.
• The donated kidney may be taken from a healthy person who is declared brain dead or from sibling or close relatives to minimize the chances of rejection by the immune system of the host.
• Immuno suppressive drugs are usually administered to the patient to avoid tissue rejection.

a) 1. Major nitrogenous wastes.
* ammonia
* Urea
* Uricacid
b) Other Wastes:
* Trimethy lamine oxide TMO
* Quanine
* Allantonin
* Creatinine
* Creatine
* Purines

Ammonoteles:
* Animals that excrete most of its nitrogen in the form of ammonia are called ammonoteles.
(e.g) fishes Amphibians aquatic insects.
* In bony fishes ammonia diffuses out acrossthe body surface.
Uricoteles:
* Animals which excrete uricacid crystals with a minimum loss of water is called.
* Uricoteles (e.g) Reptiles Birds land snails and insects.
Ureoteles:
* Animals which excrete urea as a nitrogenous wastes are called ureoteles
* (e.g) Mammals, terrestrial amphibians.

• Reptiles have reduced glomerulus or lack glomerulus and Henle’s loop and produce hypotonic urine (dilute)
• Mammalian kidneys produce concentrated urine due to the presence of long Henle’s loop.
• Aglomerular kidneys of marine fishes produce little urine that is iso osmotic to the body fluid.
• Amphibians and fresh water fishlack Henle’s loop hence produce dilute urine.

The first capillary bed of the nephron is the glomerulus.
The other is peritubular capillaries.
1. Glomerulus:
Blood enters into the glomerulus through afferent arteriole and drained by the efferent arteriole.
2. Peritubular capillaries:
* The efferent arteriole forms a fine cappillary network around the renal tubule called the peritubular capillaries.
* The efferent arteriole serving the juxta medullary nephrons forms bundles of long straight vessel called vasa recta.
* Vasa recta is absent in cortical nephrons.

• In the proximal convoluted tubule glucose lacticacid aminoacid sodium ions are reabsorbed.
• Sodium is reabsorbed – potassium pump in the proximal convoluted tubule.
• Small amounts of urea and uric acid are also reabsorbed.

Descending Loop:
The aquaporin present in the descending limb of Henle permeable to water but not permeable to salts.
Hence Na + and cl – gets concentrated in the filtrate.
Ascending Limb:
It is impermeable to water but permeable to solutes like Na + cl – and K +.

The volume of filterate formed perday is 170-180 is and the urine released in a day is 1.5l
* Nearly 99 % of the glomerular filtrate is reabsorbed by the renal tubules. It is called selective reabsorption.
* Reabsorption is taken place by the tubular epithelial cells in different segments of the nephron by active transport or passive transport diffusion and osmosis.

• Depending on the body’s need the reabsorption taking place here and is regulated by hormones.
• Reabsorption of bicarbonate HCO 3 – takes place to regulate the blood pH.
• Homestasis of K + and Na + in the blood is also regulated in this region.

If there is deficiency or absence of ADH that leads to dilute urine called diabetes incipidus.
Symptoms.
* Excessive thirst
* Excretion of large quantities of dilute urine.
* FaIl in blood pressure.

• Specialized tissue in the afferent arteriole of ncphron is the juxta glomerular apparatus.
• It consists of macula densa and granular cells.
• The macula densa cells sense distal tubular flow and affect afferent alteriole diameter.
• The granular cells secrete renin.

• Female’s urethra is very short and its external opening is close to the analopening.
• Hence improper toilet habits can easily carry faecal bacteria into the urethra.
• The urethral mucusa is continuous with the urianary tract and the inflammation of the urethra is called urethriti’s.

The urinary tract infection leads to inflammation of bladder called cystiti’s.
Symptoms:
* Painful urination
* Urinary Urgency
* Cloudy or bloodtingedurine
* Back pain head ache offen occurs

When the kidney fails to excrete wastes may lead to accumulation of urea with marked reduction in the out put called renal failure.
Types
Acute renal failure
Chronic renal failure

• Though the kidney stops its function abruptly there are chances for recovery of kidney function in acute renal failure.
• But in chronic failure there is a progressive loss of function of the nephron which gradually decreases the function of kidney.

Inflammation of the glomerulus of both the kidneys due to the strepto coccal infection in children is called as Bright’s disease Symptoms
* Haematuria
* Proteinuria
* Salt and water retention – Oligouria (Low urine out put)
* Hypertension and Pulmonaryoedema

• Transfer of healthy kidney from one person (donor) to another person with kidney failure is called kidney transplantation.
• The donated kidney may be taken from a healthy person who is declared brain death or from sibling or close relatives.
• Immuno supressive drugs are administered to the patient to avoid tissue rejection.

• The visceral layer of glomerulus is made of epithelial cells called podocytes and ends in foot processes which cling to the basement membrane of the glomerulus.
• The openings between the foot processes are called filtration slits.

• Blood enters the glomerulus faster with greater force through afferent arteriole.
• Because the afferent arteriole is broader than efferent arteriole that is why the pressure reduces when it goes through the efferent arteriole.

• The osmo receptors in the hypothalamus is stimulated.
• The neurohypophysis is stimulated and anti diuretic hormone is liberated.
• The aquaporins in the tubuler are increased and water is reabsorbed and enters into the interstitial cell and the water loss is rectified.

* Acute renal failure
* Chronic renal failure
1. Acute renal failure
* In acute renal failure the kidney stops its function abruptly.
* There are chances for recovery of kidney function.
2. Chronic renal failure
In chronic renal failure there is a progressive loss of function of the nephron which gradually decreases the function of kidneys.

• When we drink much fruit juice the osmo receptors in hypothalamus is not stimulated and hence the secretion of vaso pressin from neuro hypophysis is reduced.
• The aquaporin escapes from collecting duct to cytoplasm and hence water reabsorption is prevented and formed dilute urine.

* The level of urea in the blood is 17 -30 mg /100ml.
* In chronic kidney failure there is 10 times increase in urea level.
Five marks
IV. Detailed Answers –