Erythrocytes or RBCs transport respiratory gases mainly through haemoglobin. Leucocytes or WBCs protect the body through immune responses and phagocytosis. Platelets release substances involved in blood coagulation.
Formed elements are erythrocytes, leucocytes and platelets.
Fibrinogen is needed for coagulation of blood. Globulins are mainly involved in defence mechanisms. Albumins help maintain osmotic balance of blood plasma.
Plasma proteins help in clotting, defence and osmotic balance.
Eosinophils resist infections/allergic reactions. RBCs transport respiratory gases. AB blood group is the universal recipient. Platelets are involved in coagulation. Systole is contraction of the heart chambers.
(a)-(iii), (b)-(v), (c)-(ii), (d)-(i), (e)-(iv).
Blood has plasma as matrix and formed elements as cells. It links tissues by carrying gases, nutrients, hormones, wastes and defence components throughout the body.
Blood is considered a connective tissue because it has cells suspended in a fluid matrix and connects body parts by transporting materials.
Lymph is derived from interstitial fluid and drains back to veins through lymphatic vessels. It has similar mineral distribution to plasma but lower protein content and lacks most formed elements. Blood circulates in closed blood vessels and transports gases, nutrients and wastes.
Blood contains plasma, RBCs, WBCs and platelets; lymph is colourless tissue fluid with fewer proteins and mainly lymphocytes, lacking RBCs and platelets.
The right ventricle sends deoxygenated blood to the lungs and oxygenated blood returns to the left atrium. The left ventricle sends oxygenated blood to the body and deoxygenated blood returns to the right atrium. This separation prevents mixing of oxygenated and deoxygenated blood and supports efficient oxygen delivery.
Double circulation means blood passes through the heart twice in one complete circuit: pulmonary circulation and systemic circulation.
(a) Blood has plasma, RBCs, WBCs and platelets; lymph is colourless, lacks RBCs/platelets and has fewer proteins with lymphocytes. (b) In open circulation, blood flows into sinuses/body cavities; in closed circulation, blood remains in vessels. (c) Systole is contraction of heart chambers; diastole is relaxation. (d) P-wave represents atrial depolarisation; T-wave represents ventricular repolarisation.
The pairs differ in composition, circulatory pathway, heart muscle state and ECG meaning respectively.
Fishes have a two-chambered heart with one atrium and one ventricle and show single circulation. Amphibians and most reptiles have three chambers with two atria and one ventricle, resulting in incomplete double circulation. Crocodiles, birds and mammals have four chambers with two atria and two ventricles, allowing complete separation of oxygenated and deoxygenated blood and complete double circulation.
Vertebrate hearts show progression from two chambers in fishes to three chambers in amphibians/reptiles and four chambers in crocodiles, birds and mammals.
Nodal tissue, especially the sino-atrial node, is autoexcitable and generates action potentials that start each heartbeat. Nerves can modify the rate and force, but initiation is intrinsic to the heart muscle.
The heart is called myogenic because its rhythmic contractions are initiated by specialised cardiac muscle tissue, not by external nerves.
The SAN can generate about 70-75 action potentials per minute, higher than other nodal tissues. It sets the pace for atrial and then ventricular contraction, producing the normal heartbeat.
The SA node is called the pacemaker because it generates the maximum number of action potentials and initiates the rhythmic activity of the heart.
The impulse generated by SAN reaches AVN, then passes through AV bundle, bundle branches and Purkinje fibres to ventricular musculature. This ensures ventricles contract after atria and pump blood into pulmonary artery and aorta.
The AV node and AV bundle conduct impulses from atria to ventricles and coordinate ventricular contraction.
At 72 beats per minute, one cardiac cycle lasts about 0.8 s. Cardiac output = stroke volume x heart rate. With stroke volume about 70 mL and heart rate about 72/min, cardiac output is about 5 L/min in a healthy person.
A cardiac cycle is one complete sequence of systole and diastole of atria and ventricles. Cardiac output is the volume of blood pumped by each ventricle per minute.
The first heart sound, lub, is caused by closure of the tricuspid and bicuspid/mitral valves at the beginning of ventricular systole. The second heart sound, dub, is caused by closure of semilunar valves at the beginning of ventricular diastole. They have clinical diagnostic significance.
Heart sounds are the 'lub' and 'dub' sounds produced during each cardiac cycle by valve closure.