Samacheer Class 11 Bio Zoology - Body Fluids and Circulation

a. The main artery’ of the blood.
Dorsal aorta
b. Valves between the left atrium and ventricle.
Bicuspid valve
c. Technical name for relaxation of the heart.
Diastole
d. Another name for atria.
Auricle
e. The main vein.
Vena cava
f. Vessels which carry blood away from the heart.
Aorta
g.Two names for the upper chambers of the heart.
Auricle
h. Thick-walled chambers of the heart.
Ventricle
I. Carries blood from the heart to the lungs.
Pulmonary artery
j. Takes about 0.8 sec to complete.
Cardiac cycle
k. Valves situated at the point where blood flows out of the heart.
Semilunar valve
l. Vessels which carry blood towards the heart.
Vein
m. Carries blood from the lungs to the heart.
Pulmonary vein
n. The two lower chambers of the heart.
Ventricle
o. Prevent blood from re-entering the ventricles after entering the aorta.
Semilunar valve
P. Technical name for one heartbeat.
Cardiac cycle
q. Valves between right atrium and ventricles.
Tricuspid valve
r. The technical name for the contraction of the heart.
Systole
s. Very narrow blood vessels.
Capillaries

Arteries
Veins
1. They carry blood away from the heart
They carry blood from the parts of the body towards the heart.
2. They lie deep inside the body.
They lie on the surface beneath the skin.
3. The walls are thick and non-collapsible
They have thinner walls.
4. There are no valves.
They have valves.
5. Except for the pulmonary artery all the arteries carry oxygenated blood.
Except for the pulmonary vein, all the veins carry deoxygenated blood.
6. Blood pressure is high in the arteries
Blood pressure is low in the veins.
7. A small sphincter lies at the junction between the arterioles and capillaries to regulate the blood supply.
There is no sphincter muscles

Open circulation and closed circulation are two distinct types of circulatory systems found in different organisms. In open circulation, blood pumped from the heart flows through blood vessels but then empties into body cavities called hemocoel, where it directly bathes the organs and tissues before returning to the heart. This system is found in arthropods and mollusks. In closed circulation, blood remains confined within blood vessels throughout its journey from the heart to tissues and back, never directly contacting the body cavity. Closed circulation is found in annelids and vertebrates. The key distinction is that open circulation allows blood to leave vessels and permeate body spaces, while closed circulation maintains blood within a continuous network of vessels. Closed circulation generally allows for more efficient oxygen delivery and faster blood flow rates compared to open circulation.

Mitral valve
Semilunar valve
1. It guards the opening between the left atrium and left ventricle
It guards the opening of the pulmonary artery and aorta.
2. It allows the blood to flow from auricle to ventricle
It allows the blood to flow from the ventricle to the pulmonary artery and aorta.
3. It prevents the backflow of blood
It prevents the backflow of blood.
4. The mitral valve closes during contraction of heart and produces a sound lub.
The dub sound is produced due to the closure of lunar valves on dialation of heart
5. The chordae tendinae is not connected to this valve.
The chordae tendinae is connected to this valve.

The right ventricular wall is thinner than the left ventricular wall because of the different pressures required to pump blood to different destinations. The right ventricle pumps deoxygenated blood through the pulmonary artery to the lungs, which are located close to the heart and offer relatively low resistance to blood flow. Therefore, the right ventricle requires less muscular force to accomplish this task. In contrast, the left ventricle pumps oxygenated blood through the aorta to all parts of the body, including distant tissues that offer greater resistance to blood flow. The left ventricle must generate much higher pressure to overcome systemic vascular resistance and deliver blood throughout the entire body. Consequently, the left ventricular wall is significantly thicker with more muscular tissue to generate the necessary force. This structural difference reflects the functional demands placed on each ventricle.

• The number of red blood cells decreases.
• Due to the depletion of haemoglobin he finds it difficult to breath.
• Due to the deficiency of iron anaemia may develop.
• Due to the deficiency of iron, the oxygen-carrying capacity of haemoglobin reduces.

The human heart is myogenic in nature.
* The heartbeat is originated from a pacemaker. The total rate of heartbeat is decided by this node.
* This pacemaker is situated in the right sinuatrial node.
* On the left side of the right atrium is a node called auricula ventricular node.
* Two special cardiac muscle fibres originate from the auriculo ventricular node and are called the bundle of His which runs down into the interventricular septum and the fibres spread into the ventricle called Purkinje fibres.
Origin of heartbeat:
* Pacemaker cells produce excitation through depolarisation of their cell membrane. The j excitation is spread in to the auricle. Then this is passed on to bundle of His through auriculo ventricular node.
* The purkinje fibres cause ventricular contraction.
Regulation:
* The pacemaker cells produce excitation through depolarisation of their cell membrane. Each polarisation is slow taken place by sodium influx and reduction in potassium efflux.
* Minimal potential is required to activate voltage gated calcium (Ca+) channels that causes rapid depolarisation which results in action potential.
* The pacemaker cells repolarise slowly via K+ efflux.

About 90% of fluid that leaks from capillaries eventually seeps back into the capillaries and the remaining 10% is collected and returned to blood system by me of a series of tubules known as lymph vessels or lymphatics.
The fluid inside the lymphatics is called lymph. The lymphatic system consists of a complex network of thin walled ducts (lymphatic vessels), filtering bodies (lymph nodes) and a large number of lymphocytic cell concentrations in various lymphoid organism.
The lymphatic vessels have smooth walls that run parallel to the blood vessels, in the skin, along the respiratory and digestive tracts. These vessels serve as return ducts for the fluids that are continually diffusing out of the blood capillaries into the body tissues.
Lymph fluid must pass through the lymph nodes before it is returned to the blood. The lymph nodes that filter the fluid from the lymphatic vessels of the skin are highly concentrated in the neck, inguinal, axillaries, respiratory and digestive tracts.
The lymph fluid flowing out of the lymph nodes flow into large collecting duct which finally drains into larger veins that runs beneath the collar bone, the subclavian vein and is emptied into the bloodstream. The narrow passages in the lymph nodes are the sinusoids that are lined with macrophages.
The lymph nodes successfully prevent the invading microorganisms from reaching the bloodstream. Cells found in the lymphatics are lymphocytes. Lymphocytes collected in the lymphatic fluid are carried via the arterial blood and are recycled back to the lymph. Fats are absorbed through lymph in the lacteals present in the villi of the intestinal wall.

Rhythmic contraction and expansion of the heart are called heartbeat. The contraction of the heart is called systole and the relaxation of the heart is called diastole. The heart normally beats 70-72 times per minute in a human adult. During each cardiac cycle, two sounds are produced that can be heard through a stethoscope.
The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves whereas the Second heart sound (dub) is associated with the closure of the semilunar valves. These sounds are of clinical diagnostic significance. An increased heart rate is called tachycardia and decreased heart rate is called bradycardia.

a. Disc-shaped cells which are concave on both sides.
Red cells
b. Most of these have a large bilobed nucleus
Leucocytes
c. Enable red cells to transport blood.
Haemoglobin
d. The liquid part of the blood
Plasma
e. Most of them move and change shape like an amoeba
Leucocytes
f. Consists of water and important dissolved substances.
Plasma
g. Destroyed in the liver and spleen after circulating in the blood for four months.
Red cells
h. The substances which give red cells their colour
Haemoglobin
i. Another name for red cells
Erythrocytes
j. Blood that has been changing to jelly
Blood clot
k. A word that means cell eater
Phagocytes
l. Cells without nucleus
Red cells
m. White cells made in the lymphatic tissue
Lymphocytes
n. Blocks wound and prevent excessive bleeding.
Blood clot
o. Fragment of cells which are made in the bone marrows
Platelets
p. Another name for white blood cells.
Leucocytes
q. Slowly releases oxygen to blood cells.
Haemoglobin
r. Their function is to help blood clots in wounds.
Platelets

• Blood is the most common body fluid that transports substances from one part of the body to the other. It is known as fluid connective; tissue.
• The plasma constitutes 55% of total blood volume.
• The average blood volume is about 5000 mZ (51) is an adult weighing 70 kg.

• The average life span of red cells is 120 days.
• After 120 days the red cells are destroyed in the spleen. Hence the spleen said to be a graveyard of RBCs.

• There is no tunica media in the capillaries
• It is the site for the exchange of materials between blood and tissues.
• The blood volume is high but the flow of blood is low.
• The walls of the capillaries are guarded by semilunar valves.
• The oxygenated and deoxygenated blood is present in the capillaries.

• Single circulation is seen in fishes. There is only one auricle and ventricle in the heart of fishes.
• The blood flows from heart to gills there it gets oxygenated and supplies to the organ and then returns to the heart.

• There are well divided 2 auricle and 2 ventricles in the heart of birds, crocodiles and mammals.
• The oxygenated and deoxygenated blood is completely separated.
• The pulmonary and systemic circulation is well defined.

Orthostatic hypotension is a temporary decrease in blood pressure that occurs upon standing up from a lying or sitting position. When a person is lying flat, the gravitational force is evenly distributed throughout the body, and blood pressure is relatively uniform. When you stand up, gravity causes blood to pool in the lower extremities, particularly in the veins of the legs, reducing the amount of blood returning to the heart. This decreased venous return leads to a temporary reduction in cardiac output and a consequent drop in blood pressure. The body normally compensates for this through baroreceptor reflexes that increase heart rate and cause vasoconstriction, restoring blood pressure within seconds. However, if these compensatory mechanisms are inadequate or delayed, orthostatic hypotension occurs, which may cause dizziness, lightheadedness, or fainting. This condition is more common in elderly individuals, those with prolonged bed rest, or people taking certain medications.

Diseases
Defects
1. Coronary heart disease
When the coronary arteries are blocked the amount of blood goes to heart muscles decreases leads to oxygen and nutrient deficiency.
2. Vascular diseases
Infection in the arteries veins and lymphatic glands
3. Aorta disease
The wall of the aorta weakened and bulges to form a balloon-like sac aneurysm.
4. Pericarditis
Inflammation in the layers of the pericardium
5. Cardio myopathy
An abnormally thick heart muscle causing the heart to pump weaker than normal and leads to heart failure.
6. Heart valve disease
One or more of the heart valves does not work.
7. Heart failure
The heart cannot pump as powerfully as it need to in order to supply like body with 0, and nutrients carrying heart muscles to overwork and weaker.
8. Arrhythmia
The heart beats irregularly

• When the heart contracts the blood is pushed into the artery hence the pressure in the arteries increases.
• To withstand the pressure the artery walls nearer to the heart are more elastic and hence they relax and reduce the pressure.

• It states that the tension in the walls of the blood vessel is proportional to the blood pressure and vessel radius.
• This law is used to understand the structure and function of blood vessels and the heart.

When blood volume drops down abruptly, several physiological changes occur. The amount of blood returning to the heart decreases significantly, which reduces the venous return. According to the Frank-Starling mechanism, the volume of blood filling the ventricles during diastole directly affects the force of contraction. When there is a drop in blood volume, the blood flowing to the heart decreases, and consequently, the ventricles are filled with less blood. This results in a decrease in the stroke volume, which is the volume of blood pumped out by the heart during each contraction. The stroke volume is directly proportional to the end-diastolic volume of the ventricles. Therefore, when blood volume drops abruptly, the stroke volume decreases because there is less blood available to be ejected from the heart with each beat. This can lead to reduced cardiac output and potentially affect oxygen delivery to tissues if the condition persists.

• Oxygen and carbon dioxide are exchanged in the luiìgs and tissues.
• Nutrients are taken from the digestive system and are carried to the liver and through blood taken to all parts of the body.
• Wastes from the tissues are carried by the blood and finally removed by the kidneys.
• The hormones are transported to their target organs.
• Circulatory system helps to maintain the homeostasis of the body fluids and body temperature.

Rh factor is a protein (D antigen) present on the surface of the red blood cells in the majority (80%) of hum. This protein is similar to the protein present in Rhesus monkey, hence the term Rh. Individuals who carry the antigen D on the surface of the red blood cells are Rh + (Rh-positive) and the individuals who do not carry antigen D, are Rh – (Rh-negative). Rh factor compatibility is also checked before blood transfusion.
When a pregnant woman is Rh + and the foetus is Rh + incompatibility (mismatch) is observed. During the first pregnancy, the Rh antigens of the foetus do not get exposed to the mother’s blood as both their blood are separated by the placenta. However, small amount of the foetal antigen becomes exposed to the mother’s blood during the birth of the first child.
The mother’s blood starts to synthesize D antibodies. But during subsequent pregnancies, the Rh antibodies from the mother (Rh – ) enters the foetal circulation and destroys the foetal RBCs. This becomes fatal to the foetus because the child suffers from anaemia and jaundice. This condition is called erythroblastosis foetalis. This condition can be avoided by administration of anti D antibodies (Rhocum) to the mother immediately after the first childbirth.

• Red blood cells are abundant than other blood cells. There are about 5 – 5.5 million RBC mm of blood in a healthy man and 4.5 – 5 million RBC mm” in healthy women.
• The red colour of the RBC is due to the respiratory pigment haemoglobin and it involves in the transport of respiratory gases.
• The biconcave-shaped RBC s increase the surface area.
• The RBCs are devoid of nucleus mitochondria ribosomes and endoplasmic reticulum.
• The average life span of RBC is about 120 days after which they are destroyed in the spleen.
• RBCs are synthesized in the bone marrow.

• Platelets are known as thrombocytes.
• They are synthesized by the megakaryocytes of bone marrow.
• They are devoid of a nucleus.
• Blood normally contains 150000 – 350000 platelets mm3 of blood.
• They are involved in blood coagulation.
• The reduction in platelet number can lead to clotting disorders leads to excessive loss of blood from the body.

Blood groups are classified based on the presence or absence of specific antigens on the surface of red blood cells and corresponding antibodies in the plasma. The ABO blood group system consists of four main blood groups. Blood group A has agglutinogen A on the red blood cells and agglutinin anti-B antibodies in the plasma. Blood group B has agglutinogen B on the red blood cells and agglutinin anti-A antibodies in the plasma. Blood group AB has both agglutinogen A and agglutinogen B on the red blood cells but no agglutinin antibodies in the plasma, making it the universal recipient. Blood group O has no agglutinogens on the red blood cells but has both anti-A and anti-B agglutinin antibodies in the plasma, making it the universal donor. This arrangement of antigens and antibodies is crucial for blood transfusions, as incompatible blood types can cause agglutination and hemolysis, leading to serious complications.

• These are connections of one blood vessel with another blood vessel.
• They provide an alternate route of blood flow if the original blood vessel is blocked.
• Arteries in the joints contain numerous anastomoses. This allows blood to flow freely even if one of the arteries closes during bending of the joints.

• Blood vessels that supply blood to the cardiac muscles with all nutrients and remove wastes are the coronary artries and veins.
• Heart muscle is supplied by two arteries namely the right and left coronary arteries.
• These arteries are the first branch of the aorta.
• These arteries usually surround the heart in the manner of a crown hence called the coronary artery.
• Right ventricle and posterior portion of the left ventricle are supplied by the right coronary artery.
• Anterior and lateral part of the left ventricle is supplied by the left coronary arteries.

• Rhythmic contraction and expansion of heart is called heartbeat. The contraction of the heart is called systole and the relaxation of the heart is called diastole.
• The heart normally beats 70 – 72 times per min in a normal adult. Lub and dub sound is produced. These are heart sounds.
• The sound lub is associated with the closure of the tricuspid and bicuspid and the dub sound is associated with the closure of the semilunar valves.
• The heart sounds can be heard through a stethoscope.
• These sounds are of clinical diagnostic significance.
• An increased heart rate is called tachycardia and decreased heart rate is called bradycardia.

• Blood pressure is the pressure exerted on the surface of blood vessels by the blood.
• This pressure circulates the blood through arteries veins and capillaries.
• There are 2 types of pressure the systolic pressure and diastolic pressure.
• Systolic pressure is the pressure in the arteries as the chambers of the heart contract.
• Diastolic pressure is the pressure in the arteries when the heart chambers relax
• Blood pressure is measured using a sphygmomanometer.
• Normal blood pressure in man is about 120 / 80 mm Hg.

Single circulation:
* The blood circulates once through heart and supplies blood to all the parts of the body. This is single circulation.
* There is systemic and pulmonary circulation. (Eg.) The two-chambered heart of fishes.
Double circulation:
There are two types of circulation.
Systemic circulation:
* The oxygenated blood entering the aorta from the left ventricle is carried by a network of arteries to the tissues.
* The deoxygenated blood from the tissue is collected and emptied into the right atrium.
Pulmonary circulation:
The blood from right ventricle is taken to the lungs by the pulmonary artery and the oxygenated blood from the lungs is emptied into the left auricle by the pulmonary vein.

• The alveoli are very thin. Hence exchange of gases are taking place easily.
• If the pressure of the blood vessels of alveoli increases the blood vessels will damage and there is collection of tissue fluid

• This heart failure is due to a decrease in cardiac muscle contractility.
• When the blood supply to the heart muscle is remarkably reduced it leads to the death of the muscle fibres.
• The blood clot or thrombosis blocks the blood supply to the heart and weakens the muscle fibres.
• It is also called Ischemic heart disease due to a lack of oxygen supply to the heart muscles.
• If this persists it leads to chest pain or angina.
• Prolonged angina leads to death of the heart muscle resulting in heart failure.

Cardiopulmonary resuscitation (CPR) is a life-saving emergency procedure performed when a person's breathing or heartbeat has stopped abruptly due to conditions such as drowning, electric shock, heart attack, or severe trauma. CPR is essential in maintaining blood circulation and oxygen supply to vital organs, particularly the brain and heart, during cardiac arrest. The procedure involves two main components: rescue breathing, which is achieved through mouth-to-mouth breathing to deliver oxygen directly to the victim's lungs, and external chest compression, which involves rhythmic pressing on the chest to mechanically circulate blood to vital organs. CPR must be initiated as quickly as possible and should be performed within 4 to 6 minutes of cardiac arrest, as brain damage can occur after this period due to lack of oxygen. In addition to CPR, a brief electric shock called defibrillation may be administered to the heart using an automated external defibrillator (AED) to restore the normal rhythm of the heart. The combination of these techniques significantly increases the chances of survival and recovery in cardiac emergency situations.

• The veins are so dilated that the valves prevent the backflow of blood.
• The veins lose their elasticity and become congested.
• Common sites are legs rectal anal regions, and spermatic cords.

• It is the obstruction of the blood vessel.
• It is due to the abnormal mass of materials such as fragments of the blood clot.
• If embolus occurs in the lungs coronary artery or liver that leads to death.

• Rheumatic fever is an auto immense disease.
• It is due to the streptococcal infection in the throat.
• The fever occurs 2-4 weeks after the infection.
• The antibodies developed to combat the infection cause damage to the heart.
• The symptoms include fibrous nodules on the mitral valve.
• Fibrosis of the connective tissue and accumulation of fluid in the pericardial cavity.

Stroke is a serious cardiovascular condition that occurs when blood vessels in the brain burst or when there is a blockage in the artery that supplies blood to the brain. When a cerebral artery is damaged or blocked, the brain tissue supplied by that artery is deprived of oxygen and nutrients, leading to the death of brain cells, a condition known as cerebral infarction. This can result in loss of consciousness, paralysis, speech difficulties, or other neurological deficits depending on which part of the brain is affected. Angina pectoris is a condition characterized by chest pain or discomfort that occurs when the coronary arteries supplying the heart muscle are partially blocked, usually due to atheroma formation. Atheroma is the accumulation of fatty deposits in the arterial walls that narrows the lumen and reduces blood flow to the heart muscle. This reduced blood supply causes insufficient oxygen delivery to the heart tissue, resulting in tightness, choking sensation, and difficulty in breathing. Angina pectoris typically lasts for a short duration and may be relieved by rest or medication. Both stroke and angina pectoris are serious conditions that require immediate medical attention and lifestyle modifications to prevent further complications.

• The first heart transplantation surgery was performed by South African professor – Christian Bernard in the year 1959.
• He has done heart transplantation operation on December 3rd, 1967 Inkrute shour hospital at Capetown.
• In India, in 1994 at AIMS hospital on August 3rd Dr. Anangipalli Venu Gopal has performed heart transplantation surgery.

An aneurysm is a serious cardiovascular condition characterized by the weakening and bulging of the wall of an artery or vein. Due to weakened regions in the vessel wall, the affected area bulges outward to form a balloon-like sac that protrudes from the normal vessel diameter. This weakening can result from various causes including high blood pressure, atherosclerosis, trauma, or genetic connective tissue disorders. An unruptured aneurysm may exert pressure on adjacent tissues and organs, potentially causing pain or dysfunction depending on its location and size. More critically, an aneurysm carries the risk of rupture, which can cause massive hemorrhage and internal bleeding that may be life-threatening. Ruptured aneurysms require immediate medical intervention as they can lead to shock, organ damage, or death if not treated promptly. Common sites for aneurysms include the abdominal aorta, cerebral arteries in the brain, and thoracic aorta.

White blood cells are colourless amoeboid nucleated cells devoid of hemoglobin and hence colourless.
* 6000 – 8000 per cubic mm of WBC s are seen in the blood. WBCs are synthesized in the bone marrow these are of two types.
* Granulocytes and agranolocytes.
I Granulocytes:
a) Neutrophils:
* They are also called heterophils. Hence the nucleus has 3-4 lobes they are called polymorphonuclear.
* This constitutes about 60 – 65 % of the total WBC.
b) Eosinophils:
* They have a bilobed nucleus.
Eosinophils Basophils Neutrophils
* It constitutes about 2 – 3 % of total WBCs.
* Their number increases during allergic reactions.
c) Basophils:
* They are less numerous than any other type of WBCs constituting 0.5 % -1 % of total WBCs.
* The nucleus is large and has granules in the cytoplasm.
* They secrete heparin serotonin and histamines.
II A granulocytes:
a) Lymphocytes:
* They are secreted in the lymph gland and spleen.
* Lymphocytes constitute 28% of WBCs. They have large nucleus and small amount of cytoplasm.
* The two types of lymphocytes are B and T cells.
* B cells produce antibodies to neutralize the harmful effects of foreign substances. T cells are involved in cell-mediated immunity.
b) Monocytes:
* They are phagocytic cells. They have kidney-shaped nucleus. They constitute 1 – 3 % of the total WBCs.
* The macrophages of the central nervous system are the microglia and in the liver they are called “Kupffer cells” and in the pulmonary region they are the alveolar macrophages.

The amount of blood pumped out by each ventricle per minute is called cardiac output (CO). It is a product of heart rate (HR) and stroke volume (SV). Heart rate or pulse is the number of beats per minute. Pulse pressure = systolic pressure – diastolic pressure. Stroke volume (SV) is the volume of blood pumped out by one ventricle with each beat. SV depends on ventricular contraction.
CO = HR x SV. SV represents the difference between EDV (amount of blood that collects in a ventricle during diastole) and ESV (volume of blood remaining in the ventricle after contraction). SV = EDV – ESV. According to Frank-Starling law of the heart, the critical factor controlling SV is the degree to which the cardiac muscle cells are stretched just before they contract.
The most important factor stretching cardiac muscle is the amount of blood returning to the heart and distending its ventricles, venous return.
During vigorous exercise, SV may double as a result of venous return.
Heart’s pumping action normally maintains a balance between cardiac output and venous return. Because the heart is a double pump, each side can fail independently of the other. If the left side of the heart fails, it results in pulmonary congestion and if the right side fails, it results in peripheral congestion. Frank – Starling effect protects the heart from abnormal increase in blood volume.

The mechanism by which excessive blood loss is prevented by the formation of clot is called blood coagulation.
* The clotting process begins when the endothelium of the blood vessel is damaged and the connective tissue in its wall is exposed to the blood.
* Platelets adhere to collagen fibres in the connective tissue and release blood clotting factors.
* The blood clotting factors with platelets form the platelet plug which provides emergency protection against blood loss.
* Clotting factors released from the clumbed platelet mix with clotting factors in the plasma.
* The inactivated prothrombin is converted into active thrombin in the presence of calcium and vitamin K.
Thrombin converts soluble fibrinogen into insoluble fibrin in plasma Fibrinogen Thrombin Fibrin
The threads of fibers become interlinked into a patch that traps blood cell and seals the injured vessel and prevents blood loss.

About 90% of fluid that leaks from capillaries seeps back into the capillaries and the remaining 10% is collected and returned to the blood system by means of lymph vessel.
* The fluid inside the lymphatics is called lymph.
Lymphatic system:
* The lymphatic system consists of a complex network of thin-walled ducts having group of immune response cells.
* The lymphatic vessels have smooth walls that run parallel to the blood vessels in the skin along the respiratory and digestive tracts.
* These vessels serve as return ducts for the fluids that are continually diffusing out of the blood capillaries into the body tissues.
* The lymphatic nodes arc concentrated in the neck ingunial axillaries respiratory and digestive tracts.
* The lymph fluid flowing out of the lymph nodes flows into large collecting ducts which finally drains into larger veins that run beneath the collar bone the subclavian vein and is emptied into the bloodstream.
* The lymph nodes contain macrophage cells and they prevent the invading microorganisms from reaching the bloodstream. Cells found in the lymphatics are lymphocytes.
* Fats are absorbed through lymph in the lacteals present in the villi of the intestinal wall

• The structure of the human heart was described by Raymond devises in 1706.
• It is situated in the thoracic cavity and its apex portion is slightly tilted towards left. It weighs about 300 g in a adult. The size of our heart is roughly equal to a closed fist.
• Heart is divided into four chambers upper two auricles and lower two ventricles.
• The walls of the ventricles are thicker than the auricle.
• The heart is covered with pericardium. The pericardial space is filled with pericardial fluid.
• The heart wall is made up of three layers. The outer epicardium middle myocardium the inner endocardium.
• The two auricles are separated by inter auricular septum and the two ventricles are separated by interventricular septum.
• Tricuspid valve is present in between the opening of right auricle and right ventricle and the bicuspid valve is present in between the opening of left auricle and left ventricle.
• From the right ventricle arises pulmonary artery and from the left ventricle arises the dorsal aorta.
• The semilunar valve is present at the beginning of these arteries.
• The deoxygenated blood from all the parts of body reaches left auricle through superior and inferior venacava.
• The oxygenated blood reaches the left auricle through four pulmonary vein.

The events that occur at the beginning of heart beat and lasts until the beginning of next beat is called cardiac cycle. It lasts for 0.8 seconds.
Phase I:
Ventricular diastole – During this phase the blood pressure increases AV valves are opened and the semilunar valves are closed. Blood flows from the auricles into the ventricles passively.
Phase II:
During atrial systole the ventricle is in relaxed position. The contraction of the auricles pushes maximum volume of blood to the ventricles.
The end-diastolic volume is related to the length of the cardiac muscle fibre. More the muscle is stretched greater the EDV and the stroke volume.
Phase III:
Ventricular systole – During this phase the ventricular pressure increases and the AV value closes.
The blood is pumped from the ventricles into the aorta.
Phase IV:
Ventricular systole – During this phase the ventricular pressure increases that forces semi lunar valve to open.
Blood is ejected out of the ventricles without back flow of blood.
This point is the end of systolic volume.
Phase V:
Ventricular diastole – The ventricles begins to relax pressure in the arteries exceeds ventricular pressure resulting in the closure of semilunar valves.
The heart returns to phase I of the cardiac cycle.

In 1956, James Elam and Peter Safar were the first to use mouth-to-mouth resuscitation. CPR is a life-saving procedure that is done at the time of emergency conditions such as when a person’s breath or heart beat has stopped abruptly in case of drowning, electric shock or heart attack.
CPR includes rescue of breath, which is achieved by mouth to mouth breathing, to deliver oxygen to the victim’s lungs by external chest compressions which helps to circulate blood to the vital organiser.
CPR must be performed within 4 to 6 minutes after cessation of breath to prevent brain damage or death. Along with CPR, defibrillation is also done. Defibrillation me a brief electric shock is given to the heart to recover the function of the heart.