Test: Body Fluids and Circulation - Assertion and Reasoning - NEET MCQ

During wound, germs are removed by the process of phagocytosis by WBC. WBCs accumulate at the site of wound by diapedesis. It is the squeezing of leucocytes out from the endothelium of capillaries to fight against foreign agent.

Matured mammalian RBCs lacks cell organelles including nucleus, mitochondria, ribosomes, centrioles and endoplasmic reticulum. It increases the surface area of RBCs and enables them to contain more haemoglobin. Thus, almost entire cytoplasm is filled with haemoglobin.

Lymphatic system comprises of lymph, lymphatic capillaries, lymphatic vessels, lymphatic nodes and lymphatic ducts. Lymph is a transparent fluid derived from blood and other tissues, that accumulates in the interstitial spaces as the interstitial fluid. It also contains leucocytes, mainly the lymphocytes. This fluid has a composition similar to that of plasma, except that it is low in proteins.

If a blood transfusion is made between an incompatible donor and recipient, reaction of antigens on the cells and antibodies in the plasma will produce clots that will clog the capillaries. Type O blood group individuals are without A and B antigens on their RBCs, but consists antibodies for both these antigens in their plasma. Hence, these persons can donate blood to anyone. O blood group is the most important blood group for transfusion.

When an injury is caused to a blood vessel, bleeding starts which is stopped by blood clotting. At the site of injury blood platelets release platelet factor - 3 and injured tissues release thromboplastin. The two combine to form prothrombinase enzyme which converts prothrombin to thrombin. The latter stimulates formation of fibrin thread or clot. Blood contains an anticoagutant heparin which prevents blood clotting in uninjured vessels.

A coagulam is mainly formed of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped. Fibrins are produced by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin. Thrombins, in turn are formed from another inactive substance present in the plasma called prothrombin. An enzyme complex, prothrombinase, is required for the above reaction.

The clot seals the wound and stops bleeding. After its formation, clot starts contracting and a pale yellow fluid, the serum, oozes out. This serum is blood plasma minus fibrinogen and blood corpuscles.

Activated platelets are essential for blood clotting because several of the cascade reactions occurs on the surface of platelets. When an injury is caused, the blood platelets release certain chemicals that are called platelet factors (e.g., thromboplastin). These factors combine in presence of calcium ions (Ca²⁺) and form prothrombinase which in turn catalyze the formation of thrombin from prothrombin. Thrombin acts as an enzyme, which helps in the formation of fibrin molecules. Fibrin is an essential component of blood clotting. Vitamin K is essential for production of prothrombin. Prothrombin and many plasma clotting factors are produced in the liver. The liver requires vitamin K to produce prothrombin and several other clotting factors.

Prothrombinase enzyme is necessary for blood clotting. It acts as antiheparin. Coagulation of blood in vessels is prevented by heparin, a quick acting anticoagulant. It inhibits conversion of prothrombin to thrombin and is used in open-heart surgery.

Insect blood is colourless and does not play any role in transport of oxygen. Insects have tracheal respiration.

When the blood pressure of an individual decreases due to loss of blood volume, then vasoconstriction of veins occurs. This shifts the little amount of blood from veins to arteries.

Through the sympathetic nerves (part of ANS) neural signals can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output. On the other hand, parasympathetic neural signals (another component of ANS) decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output.

The closed circulatory system is more efficient than the open circulatory system because in open circulatory system, open spaces and channels the blood flows through whereas in closed circulatory system, the blood flows through proper blood vessels. Also, in closed circulatory system arterial musculature and precapillary sphincters regulate the flow of blood, due to the volume of blood flowing through a tissue or an organ may be regulated according to needs. Moreover in closed circulatory system, the blood flows far more rapidly in closed blood vesssels than in wide open channels and body cavities. Thus, blood takes much shorter time to circulate through the closed system than in open circulatory system.

Amphibians and the reptiles (except crocodiles) consists a 3-chambered heart with two atria and a single ventricle, whereas crocodiles, birds and mammals possess a 4-chambered heart with two atria and two ventricles. In amphibians and reptiles, the left atrium receives oxygenated blood from the gills/lungs/skin and the right atrium gets the deoxygenated blood from other body parts. However, they get mixed up in the single ventricle that pumps out mixed blood (incomplete double circulation). In birds and mammals, oxygenated and deoxygenated blood received by the left and right atria respectively passes on the ventricles of the same sides. The ventricles pump it out without any mixing up, i.e., two separate circulatory pathways are present in these organisms, hence, these animals have double circulation.

Left ventricle has thickest muscles because it pumps the blood to the whole body.

In the human heart, there is no mixing of deoxygenated and oxygenated blood due to the presence of inter - atrial and inter - ventricular septum. These septa completely divide the atria and ventricles into right and left and thus avoid mixing of blood. The presence of valves that prevents the backflow of the blood. The two atria are separated from the ventricles by membranous valves. The valve separating the right atrium from the right ventricle is known as the right atrioventricular valve or tricuspid valve (as it is made of three flaps or cusps). The valve separating the left atria and the left ventricle is called left atrioventricular valve or the bicuspid valve or the mitral valve (since it is made of two flaps). They allow the flow of blood from atria to ventricles and not in the backward direction. At the base of the aorta are present three membranous, pocket-shaped semilunar valves. These valves check the return of the blood to the ventricle.

From the great veins into the atria; blood normally flows continuously about 80 per cent of the blood flows directly through the atria into the ventricles, even before the atria contract. Then, atrial contraction usually leads to an additional 20 per cent filling of the ventricles. Therefore, the atria simply functions as primer pumps that increase the ventricular pumping effectiveness as much as 20 per cent.

The heart is a pumping organ for blood circulation which consists of chambers communicating with each other. In fishes the heart is two-chambered, consisting of an auricle and a ventricle. An accessory chamber called sinus venosus is also present which serves as a reservoir and opens anteriorly into auricle through the sino - atrial aperture. Fish heart contains and pumps only deoxygenated blood because after getting oxygenated from gills, the blood doesn't return back to the heart. Instead, it is supplied directly to the various parts of the body.

There are some reasons behind the effectiveness of closed circulatory system over the open type. These are -
(i) The blood flows more rapidly in closed blood cavities
(ii) It takes much shorter time to circulate through the closed system and return to the heart.
(iii) This quickens the supply and removal of materials to and from the tissues by the blood.
(iv) In the closed system, the arteriolar diameter can be regulated to alter the blood flow, so the volume of blood flowing through a tissue or organ may be regulated according to its needs. No such regulation is possible in open type.

The valve present in heart when pushed by blood in the right direction causes the flaps of the valve to swing apart and allow the blood to flow through, but when pushed in the opposite direction, the flaps close sharply to block the passage through the valve. Thus these valves resemble swing doors in action. Hence, the valves of the heart maintain unidirectional flow of blood and prevent it's regurgitation in the opposite direction.

Blood pressure is the arterial blood pressure taken in left brachial artery and the instrument used to measure blood pressure is sphygmomanometer