for Grade XII

Physiology of circulation
Human body is fairly complex and performs wide range of activities. Different organs of body are located far away and may have no connection at all. Our body needs a specialized system of circulation which can connect these organs supplying nutrients, gases, hormones and carrying wastes from these organs. This system of circulation also performs the functions like regulation of things and protection. The system of circulation of some extra cellular fluid is flowing in the body. The structures associated with circulation constitute circulatory system.
Circulatory system must have these basic features
3. A pumping mechanism like heart.
4. A system of tubes through which the circulating fluid can move.
5. Presence of transporting or circulating fluid like blood or lymph.

Structure of heart
A human heart is muscular hollow pumping organ which can maintain continuous flow of blood circulation inside the body. It is roughly triangular in shape. It is about the size of a person’s fist and weighs about 300 grams. It is reddish brown in color. It is situated ventrally in the middle of thoracic cavity in between two lungs. The narrow end of the heart is slightly displaced to the left side. It can be heard towards the left side of the chest.

The heart is enclosed in a double walled membranous sac called pericardium. The inner membrane is attached to the heart. In between two membranes, there is presence of a pericardial fluid. The fluid is shock absorbing so protect heart from any shock and minor injuries. It also allows free movement to the heart.

Anterior broad part is called auricular part and posterior narrow part is called ventricular part. Towards right side of auricular part there is superior and inferior venacavae carrying impure blood from different parts of body except lungs. Towards the left side of auricular part, the pulmonary veins carry pure blood from lungs. The auricular part receives blood. The lower ventricular part sends out blood. The arch of Aorta and Pulmonary trunk carries blood out of the heart.

Internal structure

The human heart is four chambered. The upper two are right and left atria or auricles. The lower two are right and left ventricles. Auricles are thin walled chambered separated by inter auricular septum. There are presence of muscular ridges called musculi pectinati. Right auricle is having openings for superior and inferior venacavae to receive impure or venous blood. Left auricle is having openings for pulmonary veins to receive pure blood from lungs. The opening of inferior venacava is guarded by valve of Eustachius while the opening coronary sinus is guarded by valve of Thebesius. Right and left auricle open into respective ventricle through an auriculo ventricular apertures. These AV apertures are guarded by valves.
The sinus venosus is completely merged into right auricle. So caval veins directly open into auricles. Truncus arteriosus has split into systemic (aortic) and pulmonary trunk in mammals.

The two ventricles are separated by inter ventricular septum. The septum comes right side from the apex. Ventricles are thick walled than atria. The left ventricle is thicker than right ventricle.
Valves
Bicuspid valve is also known as mitral valve. It is situated between the left auricle and left auricle and left ventricle. It allows unidirectional flow of oxygenated blood from left atrium to left ventricle. It consists of two flaps or cusps.
Tricuspid valve is the right AV valve. It consists of three flaps or cusps. It allows impure blood to flow from right atrium to right ventricle.

Both valves are provided with tendons or chords made up of tough strands of connective tissue called chordae tendinae. The chordae tendinae arise from papillary muscle present in the wall of ventricles. Their contractions bring the tightening of chordae tendinae which in turn prevent the valves from turning inside out or from being forced upward during contraction of ventricles.
Semi lunar valves
At the base of pulmonary trunk and aortic arch, there are pulmonary semi lunar and aortic semi lunar valves. Such valve is made up of three flaps attached to inside of arterial wall. These valves allow only unidirectional flow of blood from ventricle to artery and prevent back ward flow.

Course of circulation

1. Pulmonary Circulation

It is the circulation between the heart and lungs. The impure blood(deoxygenated blood) is pumped out from the right ventricle. The pulmonary trunk takes the impure blood. The pulmonary trunk divides into two pulmonary arteries. The pulmonary arteries supply impure blood to the two lungs. In side the lungs, the impure blood is purified. After the purification, the pure blood is returned to the heart through the pulmonary veins. The pulmonary veins open into the left atrium.

2. Systemic circulation
It is the circulation of blood from heart to the whole body except the lungs. In this circulation, the pure blood is pumped from the left ventricle. The aortic arch divides into many arteries carrying pure blood to the different organs and regions of body. In the tissues, the capillary net works allow the exchange of gases and nutrients. The deoxygenated blood is then returned back through venules and veins. The impure blood is returned to right atrium through inferior and superior venacavae.
2a. Portal circulation
it is the special arrangement of veins. In this, the certain veins instead of carrying blood directly to the heart, enter into the another organ. In this case the second set of capillaries is formed. This formation of second set of capillaries is called portal system. The veins coming from the alimentary especially from the intestine and stomach contains glucose rich blood. Such blood is carried to the liver first. In the liver, the excess glucose is stored. After this the blood is carried to the heart.
2b. cororary circulation
it is the circulation of pure blood from the heart to the muscles of the heart. The coronary arteries take pure blood to the muscles of the heart and the coronary veins return the impure blood from the muscles of the heart to the heart through the superior venacava. This circulation is of utmost importance because the heart works continuously pumping the blood the different organs. For this the heart needs lot of energy. If the muscles of heart are deprived from the enough supply of pure blood, heart attack may result.

Double circulation
In one complete circulation, blood enters into the heart twice. Blood enters into the heart(left atrium) once in the form of pure blood from the lungs ( pulmonary circulation). The second time, blood enters into the heart(right atrium) in the form of impure blood from the systemic circulation. In this way, the human heart is said to be having double circulation.

Some terms

Heart beat
Heart beat consists of one contraction phase and one relaxation phase. During the contraction phase, there is maximum point(peak period) which is known as systole. During the relaxation phase also, there is minimum point which is known as diastole.
One heart beat is completed in about 0.8 second time.

Cardiac cycle
Cardiac cycle is the sequence of events during one heart beat. It consists of three phases.
• Atrial systole – the two atria contract simultaneously pumping blood into the respective ventricles. It lasts for 0.1 second.
• Ventricular systole - the two ventricles also contract pumping out the blood to the lungs and whole parts of body. It lasts for 0.3 second.
• Joint diastole - all four chambers of heart under go relaxation. At this time, both atria are filled with blood. It lasts for 0.4 second.

Stroke volume
It is the volume of blood pumped out in every heart beat. It comes to be about 70 ml of blood. It is denoted by SV.

Heart rate
It is the number of heart beats per minute time. In the normal adult, it is about 70 to 80 times. In an average, it comes to be 72 times. This is called heart rate. It is denoted by HR.
Cardiac output
It is the volume of blood pumped out in one minute time. It is given by the product of stroke volume and heart rate. It is denoted by CO
CO=SV X HR

Origin and conduction of heart beat

In the wall of right atrium, there is a special node called Sino Atrial node(SA node). It is self excitatory. It is the point of origin of heart beat. It is also called Pace maker. It is natural Pace maker. The heart cant work without it. If it is injured or damaged artificial pace maker is implanted.

Near inter atrial septum, there is Atrioventricular node (AV node). It receives the impulses in the form of wave and passes it to Purkinje’s system. This system consists of Bundle of His, purkinje fibres. With the help of this system impulses are carried to the wall of ventricle. Then both ventricles contract pumping out blood.

In the normal adult man, heart beats 70 to 80 times per minute. The average is 72 beats per minute. It is called heart rate.








Heart sounds

The first heart sound is lubb. It is produced due the sharp closing of atrioventricular valves like the bicuspid and tricuspid valves. At the beginning of ventricular systole, these valves are closed.
The second heart sound is dup. It is produced due the closing of semilunar valves at the end of the aortic arch and pulmonary aorta. It occurs at the end of ventricular systole.


Blood pressure
It is a force exerted by blood against the wall of arteries, veins and capillaries. It is called BP in short. It is of two types. Systolic blood pressure is maximum pressure during contraction. Diastolic blood pressure is minimum pressure during the relaxation. The systolic and diastolic blood pressure of a normal adult is 120/80 mm of Hg. The range of systolic blood pressure is 100 to 140. 100 is lower limit and 140 is upper limit. The range of diastolic blood pressure is 55 to 80.

Problems related to BP

Hypertension or high BP
It is the condition when the systolic and diastolic blood pressure is 150/90 or above persistently.
Causes
o Unbalanced diet, cholesterol rich food
o Smoking
o Alcohol consumption
o Stress, anxieties
o Loss of elasticity of arteries, arterosclerosis
o Vasoconstriction


Hypotension or low BP
It is the condition when the systolic and diastolic blood pressure is below the lower limit persistently.
Causes
o Unbalanced diet, less nutrient food.
o Loss of blood or less volume of blood
o Vasodilation



Arterial system
There are many arteries in the body. They distribute blood to different parts of body. All these arteries together make arterial system. This system supply pure blood to body organs and impure blood to lungs.

Pulmonary aorta arises from right ventricle. It divides to two branches. They are pulmonary arteries. These arteries supply impure blood to two lungs.

Aortic arch arises from the left ventricle. It gives one branch called innominate on the right side. It divides into right common carotid and right subclavian. On the left side, aortic arch gives left common carotid and left subclavian. The right and left common carotids ascend up through neck. In the head region, they divide into internal and external carotids. The internal carotids supply pure blood to brain. The external carotids supply to outer part of head region such jaw, tongue, face etc. The right and left subclavians enter into the fore limbs(hand). Subclavians divide into radial and ulnare arteries. They all supply pure blood to different parts of hand. There are vertebral arteries also to supply blood to neck region.

The aortic arch runs down and forms the dorsal aorta. It gives many branches. In the chest, there are intercostal arteries to supply blood to intercostal muscles. One pair of inferior phrenic arteries supply blood to the lower part of diaphragm. One coliac artery comes out from the dorsal aorta. It divides into the hepatic and leinogastric arteries. Hepatic artery supplies blood to liver. The leinogastric supplies blood to stomach and spleen. The superior mesenteric arteries divides into many branches and supply blood to duodenum, jejunum and ileum. The right and left renal arteries supply blood to the kidneys. The genital arteries supply blood to testes in male and ovaries in female.
The lumbar arteries supply blood to the wall of abdomen. The inferior mesenteric artery supplies blood to the large intestine like ascending, transverse, descending colon, pelvic colon and rectum.

Then the dorsal aorta divides into two branches called common iliacs. They enter into two legs. The right and left iliacs give small internal iliacs to supply blood to urinary bladder. The external iliacs give deep femoral which supply blood to thigh. The external iliacs run down as popliteal. These divide into anterior and posterior tibials. They supply blood to lower part of leg.


Venous system

All veins in the body together make venous system. This system is for collection of pure blood from lungs and impure blood from rest of the parts of body.

Four pulmonary veins collect pure blood form lungs and open into left atrium. Superior venacava collect blood from anterior part of body. It is made by different veins. Right and left innominate veins join to form superior venacava. Each innominate is made by right and left external and internal jugular veins collecting blood from head and brain. The right and left subclavians collect from hand. The subclavian is again made by axillary and cephalic veings. Azygous vein collects from chest region in the right side. Hemiazygous collect from left side . both open into superior venacava. Inferior venacava is made by different veins. Two short and thick hepatic veins collect blood from liver.

Two common iliac veins join to make the inferior venacava. Each iliac vein is made by internal iliac from urinary bladder, large saphenous from thigh, anterior and posterior tibial from lower part of leg.

The blood collection form stomach and intestine has different arrangement. It is called Portal system. The blood is not directly carried to the heart. It is taken to liver first. Gastric vein, duodenal vein, intestinal veins etc join to form hepatic portal vein. It enters into liver to form hepatic portal system.

Importance of hepatic portal system
o Stores excess glucose in the form of glycogen
o Converts highly poisonous ammonia into less poisonous urea
o Kills Bacteria, germs etc and protect from diseases
o Removes impurities
o Regulate body temperature etc.


Physiology of Excretion

Excretion is the removal of metabolic waste from body particularly nitrogenous waste.

Skin, lungs, liver are considered as accessory excretory organs while kidney is the most important one which forms as important part of the4 urinary system also.

Urinary system of man consists of
1. Kidneys 2. Ureters
3. Urinary bladder 4. Urethra

kidneys paired structures, chief excretory organs in man which can act as efficient
filters. Kidneys excrete nitrogenous and other metabolic wastes in the form of urine.
Ureters two ureters, one arising form each kidney. Carry urine formed in side
Kidney to urinary bladder. Each ureter is a thin muscular tube about 25
cm in length arising from hilum of each kidney. Urine moves by
peristaltic waves of its walls.
Urinary bladder present in the form of storage sac. Collects urine from both the kidneys
via ureters. Urine stored temporarily until it is released via urethra. The
volume of bladder increases as it stores much urine. It has lining of
transitional epithelium which stretches as the volume of urine increases.
Urethra small membranous tube that carries urine at intervals urinary bladder to
the exterior. There is a urethral muscular sphincter at the base of urethra
which consists of a circular band of muscle. By the contraction and
Relaxation of this muscle the flow of urine into urethra is controlled.
Sphincter keeps urethra closed except during voiding of urine.
Micturition it is act of voiding of urine. The urine is carried by peristaltic waves
down the ureter. Accumulation of urine in the bladder raises its pressure
And a continuous reflex is initiated. As the smooth muscle of bladder wall
Contract, the urethral sphincter muscle relaxes evacuating the urine. Urine
does not flow back as the ureters pass obliquely. Their terminal parts get
closed during contractions. Micturition may be initiated or delayed
Voluntarily.

Structure of kidney

A pair of kidneys located on either side of back bone in the abdominal cavity. The left kidney is positioned higher than the right one. At anterior end of kidney adrenal gland is present. Each kidney is bean shaped, about 10 cm long and 6 cm wide and weighs about 150 gm. At the concave side, there is a depression called hilum from where renal artery enters and renal vein and ureters pass out.

Internal structure

Renal cortex outer region is towards convex surface. It contains Bowman’s capsule,
glomerulus, proximal convoluted tubule, distal convoluted tubule and
collecting tubules of nephron.
Renal medulla It is region just inner to renal cortex. It contains loop of Henle and
Collecting ducts inside the renal pyramid. The conical pyramid mass
projects into renal pelvis. Urine is drained into renal pelvis through
minute openings at the apices or papillae of pyramids.
Renal pelvis large funnel shaped space behind medulla. Urine is collected and is
passed down to the ureters.


Each kidney consists of large number of filtering units called nephrons. A kidney has about 1.2 million nephrons. Each nephron is about 3 cm long, tiny, delicate and coiled
tubule which originates in the cortex region and extends into medulla region.

Structure of nephron

Nephron or uriniferous tubule is the functional unit of kidney. Each works as as independent unit and produce miniscule amount of urine. The urine collected by various ducts from all nephrons is finally poured into renal pelvis.

Nephron consists of

1. Renal corpuscle or malpighian body
a) Bowman’s capsule
b) Glomerulus
2. Proximal convoluted tubule or PCT
3. Loop of Henle
a) Descending limb of loop of Henle
b) U shaped part
c) Ascending limb of loop of Henle
4. Distal convoluted tubule or DCT
5. Collecting tubule

Renal corpuscle or malpighian body is formed by Bowman’s capsule and Glomerulus together.
Bowman’s capsule it is cup shaped hollow structure. In the hollow cup there is a network of capillaries called Glomerulus. Bowman’s capsule has inner and outer epithelial layers. Between these layers there is a cavity of Bowman’s capsule. The inner layer is closely applied to walls of Glomerulur capillaries.

Glomerulus It is network of capillaries in the hollow of Bowman’s capsule. It receives the blood through afferent arteriole which breaks up into capillary network. The blood leaves the glomerulus through efferent arteriole. The efferent arteriole is narrower and longer vessel than the afferent. The efferent arteriole breaks up into network of capillaries surrounding whole of PCT, loop of Henle and DCT. At loop of Henle, there is parallel arrangement of capillaries called vasa recta. These capillaries join and return blood to renal vein.

PCT First coiled tubule just behind renal corpuscle. It is lined by cuboidal
ciliated epithelium. It transports glomerular filtrate (GF) from Bowman’s capsule into loop of Henle.

Loop of Henle form U shaped loop. Descends down into medulla and again returns back. Descending limb is thin and long freely permeable to water. It is lined by flat epithelial Cells. Ascending limb is thicker and impermeable to water. It is lined by cuboidal epithelial cells.

DCT second coiled tubule is relatively shorter. It is permeable to water and under the control of Anti diuretic hormone (ADH)

Collecting tubule short and straight opens into collecting duct. It passes down to medulla from cortex.

Duct of Bellini many collecting ducts join to form larger duct of Bellini . it ultimately opens into renal pelvis draining all urine collected from various nephrons.


Urine formation
3 basic steps 1. Glomerular filtration or ultra filtration
2. Selective reabsorption
3. Tubular secretion

Glomerular filtration smaller diameter of efferent arteriole than that of afferent arteriole increases the blood pressure in Glomerulus. Hydrostatic pressure of about 55 mm of Hg is developed which can force out the different substances of blood into the lumen of Bowman’s capsule. This is assisted by the thin and closely applied walls of Bowman’s capsule and walls of capillaries. The hydrostatic pressure is opposed by osmotic pressure of about 30 mm of Hg and filtrate pressure of about 15 mm of Hg. The net filtration pressure is of about 10 mm of Hg.

About 125 ml of Glomerular filtrate is formed from 1200 ml of blood by both kidneys every minute. In one day 180 liters of glomerular filtrate is formed. The glomerular filtrate is composed of water, glucose, amino acids, urea, uric acid, hormones vitamins mineral salts etc. The composition of filtrate is similar to blood except in having larger molecules of protein.

Selective reabsorption of 180 liters of glomerular filtrate per day, only 1.5 liter is put out as urine. 99 % of filtrate is reabsorbed. Out of 125 ml produced every minute 124 ml is returned and 1 ml is put as urine.

Active absorption usually glucose, amino acids are returned by active absorption. It takes place against the gradient at the expense of energy.
Passive absorption normally Sodium chloride, water, urea, ammonia, ketone bodies reabsorbed by osmosis.

At the PCT, the filtrate is isotonic. From the descending limb water is returned so as the filtrate comes down it becomes hypertonic. At the ascending limb, as it impermeable to water and as salts are removed actively, the filtrate becomes hypotonic again. Much water is removed from the DCT and collecting tubule, the urine becomes hypertonic finally.

Tubular secretion If the blood in the capillaries at the DCT contains any urea, uric acid, creatinine, hippuric acid K+ , H+ , ammonia etc these can be directly put into the tubule. K+ is exchanged for Na+.

Composition of urine normally urine does not contain glucose and amino acids. It contains 95 % of water; rest of the 5 % is solute. The largest component by weight other than water is urea which account for 2 %, salts 2 % approx, 0.3 % of uric acid and traces of creatinine, creatine, ammonia etc. Urine is slightly acidic about pH 6. urochrome gives the yellowish color to the urine. The characteristic odor is due to urinod. If the urine is allowed to stand for short time also, it gives the strong smell of ammonia due to action of bacteria to change urea into ammonia.