Q.11 Explain the physiology of blood circulation in man along with suitable diagrams. (2005)
Related Questions -
Q. Write short note on heart. (2013)
Ans. Heart is the central pumping station of the blood vascular system. The heart regularly and rhythmically contracts and relaxes at short intervals throughout life without pause and fatigue. This inherent activity is called its pulsation or beating. Each pulsation or heart beat obviously has two phases-contraction phase or systole, and relaxation phase or diastole. In systole the heart volume reduces so that the blood is forcefully pumped out into arterial vessels for distribution throughout the body. In diastole the heart relaxes. Hence its volume increases to become normal so that the venous vessels returning from various parts of body pour their blood into it.
Cardiac Cycle: -
Various parts of the heart neither contract nor relax at the same time ,different parts pulsate one after the other in a fixed sequence. That is why, the flow of blood in the heart follows a fixed course and each heart beat is termed a cardiac cycle. The latter is defined as the period from the beginning of one heart beat to the beginning of the next.
Cardiac cycle is in reverse ratio of the rate of heart beat. In man for example the rate of heartbeat is about 75 times per minute. Hence the time of a cardiac cycle is 60/75=0.8 seconds. The time taken respectively in contraction and relaxation of atria is 0.1 and 0.7 seconds and of ventricles is 0.3 and 0.5 seconds. Obviously the pulsations of atria and ventricles overlap.
By beating about 75 times our heart pumps about 5 litres of blood into the arteries every minute and receives the same amount from veins (venous return). Thus in average span of 50 years of life our heart beats about two billion times pumping about 13 crore litres of blood into the arteries. Of the blood pumped out to the brain, 25% to the organs of digestive system, about 10%goes to the heart muscles, 15%to the brain, 20% to the kidneys and 30%to the other organs. During exercise or hard labour, heartbeat rate and cardiac output may be doubled or even tripled.
Each cardiac cycle begins with the contraction of right atrium closely followed by that of left atrium. Thus the blood of both atria is pumped into the respective ventricles. Presumably this atrial systole is responsible only for about 25%filling of the ventricles in man. The ventricles receive their remaining 75%of blood earlier during their diastole. Plenty of blood accumulates in the atria during ventricular systole, because the atrio-ventricular valves are closed. The pressure of blood in the atria, therefore rises. Consequently, just as the ventricles relax and ventricular pressure falls the auricular pressure pushes opens the valves and the blood of the atria rapidly flows into the ventricles during the first third of ventricular diastole. During the middle third of ventricular diastole only a small amount of blood which continuously seeps into the atria from the great veins goes into the ventricles. This period is called diastasis. During the last third of ventricular diastole the atria contract, completing the remaining 25%filling of the ventricles.
The ventricular systole is simultaneous in both ventricles. It is much stronger than atrial systole, because the ventricles have to pump their blood into the aortae. The gradually increasing contraction of ventricular muscles during this systole first causes the closure of bicuspid and tricuspid valves, producing a low pitched lubb sound. Later it causes the opening of the semilunar valves of systemic and pulmonary aortae. At the end of ventricular systole ,semilunar valves shut ,producing the second, louder heart sound the dup. Thus each hear beat is accompanied by a lubb-dup sound. By detecting these sounds by means of stethoscope, doctors determine the rate of heartbeat.
Cardiac Circuit: -
The heart pumps pure, oxygenated blood for circulation throughout body as well as impure blood into the respiratory organs for purification .Similarly it receives impure blood from all parts of body as well as purified blood from the respiratory organs. This means that all blood should ideally pass twice through heart before circulating in the body, once as impure blood and then as purified blood. This is called double hart circuit. It is possible only if there is proper arrangement in the heart for complete separation of pure and impure blood.
The right part receives impure blood from the whole body and sends it to the lungs for oxygenation. The left part receives purified blood from the lungs, and supplies it to the whole body. Thus the right and left parts of the heart respectively serve as completely separated pulmonary and systemic hearts. This is the double heart circuit.
Conducting System of the Heart: -
It involves two nodes of nodal fibres, an internodal pathway ,an A-V bundle and the left and right bundles of purkine fibres. The two nodes are called S-A node and A-V node.
The S-A node (sinu atrial) is a small flattened and ellipsoidal mass of excitatory nodal fibres embedded in the wall of right atrium near the opening of right anterior venecava. Fibres of this node are continuous with the normal cardiac muscle fibres of right atrium. These spontaneously generate the contaraction impulses of cardiac cycles at short intervals. The S-A node is therefore “pacemaker” or “contraction center.” Each wave of contraction beginning in this node spreads immediately into the cardiac muscle fibres of the right atrium and then muscle fibres of left atrium.
The A-V (atrio-ventricular) is embedded in posterior part of interatrial septum towards right atrium near the opening of coronary sinus. It is somewhat smaller and thinner than S-A node. Some fibres of the specialized conducting system run between the two nodes, establishing an internodal pathway. The latter quickly conducts the contraction impulses from S-A node to A-V node. The A-V node now sends out the impulses into the wall of ventricles. The arrangement of nodal fibres in the A-V node is such that onward transmission of impulses is delayed for a fraction of second, so that atria may empty their contents into the ventricles before ventricular contraction begins.
All impulse-conducting fibres which relay the contraction impulses from A-V node into the walls of ventricles are called purkinje fibres. A small dense bundle of these fibres called atrio-ventricular bundle or “bundle of his” originates from the A-V node, extends upto interventricular septum and then splits into right and left bundles which extends back within the septum, one on each side. The right limb is a cylindrical bundle of slender fibres which repeatedly branch and profusely ramify in papillary muscles and beneath the endocardium of right ventricle. The left limb of fibres is somewhat flattened and band like. Its fibres branch and ramify into the papillary muscles and beneath the endocardium of left ventricle.
Q.12 Write note on Amoebiasis. (2010)
Ans. This is caused by the infection of Entaomeba histolytica. Its trophozoite, actively secrete proteolytic enzymes which partially disolve and loosen the mucosa, submucosa and blood capillaries of colon wall. Then the trophozoites innade the colon wall and actively ingest (holozoic nutrition) intestinal tissues and red blood cells. Simultaneously they increase and multiply in number by repeated binary fission. Gradually the colon wall is seriously damaged and many small flask shaped ulcers forms in it. Stools of the host become loose and contain mucus and blood, oozing out from the ulcers. This is “amoebic dysentry”. The host also suffers with a characteristic intermittent colic pain. The disease may be further aggranated by a bacterial infection of the ulcers. This leads to inflammation and pus-formation. In chronic cases the colon wall becomes perforated. Also the trophozoites, may get into the blood stream and migrate to other parts of the host body as liver, lungs, brains, etc. establishing secondary infection.
Q.13 Describe the digestion and absorption of carbohydrates. (2010)
Other Related Questions -
Q. Write short note on digestion of carbohydrates. (2017)
Ans. Carbohydrate digestion begins in the mouth where salivary amylase is secreted in the salina. It digests starch into maltoze. Further carbohydrates reaches to the stomach. In the stomach ‘gastrin or a cells’ of pyloric glands secrete a hormone called gastrin. When gastrin circulating in blood, reaches into gestric wall, it stimulates the gastric glands to secrete and release the gastric juice at a fast rate. This is assisted by histamine secreted by gastric mucoza and by acetylcholine released as a result of autonomic reflexes established through parasympathetic fibres of hajus reunes.
Gastric juice contains carbohydrate splitting gastric amylase enzymes in the minimum quantity.
Later on the complete digestion of carbohydrates occurs in small intestine where pancreatic juice is secreted by the pancreas. It contains pancreatic amylase. Thisenzyme hydrolyzes the remaining starches, glycogen and other carbohydrates of chyme mostly into disaccharides (mostly maltose).
In the secretory cells of crypts of leiberkuhn is secreted intestinal juice which is transparent, yellowish and alkaline (ph 7.5 to 8.0) which includes carbohydrate digesting enzymes.
Maltose, sucrose and lactose, which complete the digestion of carbohydrates by splitting all disaccharides into monosaccharides. Thus maltose hydrolyses maltose into its component glucose molecules, sucrose hydrolyzes sucrose into fructose and glucose and lactose hydrolyze lactose into galactoze and glucoze.
Q.14. Write note on Testes as an endocrine gland. (2010)
Ans. Each testes consists of numerous seminiferous tubules embeded in a connective tissue stroma. In between the tubules, the stroma contains many small dusters of lipid rich endocrine cells called interstitial cells or cells of leydig. These cells secrete various male hormones (androgens) derived from choesterol. The main androgen is testosterone. Testosterone is a masculinizing harmone. From puberty to the age of about twenty years (i.e. adoleschence, or the period of sexual maturation or attainment of adulthood). It is secreted in considerable amount and promotes growth of bones, muscles and all accessory reproductive organs - epididymes vasa deferentia, sevinal vesicles, scrotal sacs, penis accessory genital glands, etc to their normal sizes. Under its effects, protein anabolism increases mucles and bones become strong growth zones in the bones close enythropolisis in bone marrow increases and male secondary sexual characteristics, like beard, moustache, pubic, axillary and chest hairs, retreating hairlines on forehead, thick noice, stronger built of the body and shoulders aggresssive nature and sex urge develop. In brief testosterone determines libido. It is also required together with the follicle stimulating harmone (FSH) of pituitery for initiators and competition of spermatogenesis. All androgens are also secreted in traces from adrenal glands in both boys and girls.
Under the effect of chorionic gonado tropic hormone, secreted by placenta during pregnancy the testis of eight to nine months old fetus start secreting testosterone. The latter regulates differentiation and development of urinogenital system, accessory genital organs and external genitalia in the embryo. During childhood (age of 11 to 13) testes remains quiescent, so that androgens are not secreted. At puberty the gonadotropic hormones of pituitary reactionates the testes which therefore start producing sperms and resume secreting androgens upto the age of about 40 years, androgens are secreted in sufficient amounts. Thereafter their secretion starts gradually declining, but the capability of reproduction still continues for many years.
Q.15 Write note on Reflex action. (2010, 13)
Ans. A reflex reaction is an intermediate involuantry response to a stimules. Suppose we unknowingly happen to touch a hot object, the thermoreception of the skin of concerned finger become exited and pans on the relevant somatic sensory impulse to sensory nerve fibres of the dorsal ramus of adjacent spiral rerne. These fibres carry the impulse to their cell bodies located in the dorsal root gangtion of the nerve. Axons of these neurons, then carry the impulse into the gray matter of the spinal cord. Here the impulse is transmitted across the synaptic knobs of these axons to the dendrites of adjacent motor neurous. Thus the impulse now becomes a motor impulse. It travels along the axons of these neurons to the muscles of our concerned hand. These muscles immediately contract to move the hand away from the hot object. This is a type of ‘flexion reflex’.
Reflex Arc: -
It is a basic functional unit of nervous system.