Biology Test 354

Red blood cells of adult humans do not have cell organelles including nucleus, Golgi bodies, mitochondria, ribosomes, etc. It increases the surface area of RBCs and enables them to contain more haemoglobin (the oxygen carrying pigment).

Thrombocytes are called blood platelets. They are minute disc-shaped cell fragments in mammalian blood. They are formed as fragments of larger cells found in red bone marrow; they have no nucleus. They play an important role in blood clotting and release thromboxane A2, serotonin and other chemicals, which cause a chain of events leading to the formation of a plug at the site of the damage, thus preventing further blood loss. A reduction in their number can lead to clotting factors which will lead to excessive loss of blood from the body.

Arteries have higher blood pressure than vein because blood is forced inside them from heart and also their lumen is narrow.

Whale is a mammal and in mammals, two separate circulatory pathways are found - systemic circulation and pulmonary circulation. Oxygenated and deoxygenated bloods received by the left and right atria respectively pass on to the left and right ventricles. Thus, oxygenated and deoxygenated bloods are not mixed. This is referred to as double circulation.

Erythropoiesis is the formation of red blood cells (erythrocytes) which occurs in the red bone marrow. Proerythroblast is the earliest precursor which gives rise successively to the early erythroblast, intermediate erythroblast and late erythroblast. Then, the nucleus is forced out and a biconcave, enucleated cell called reticulocyte is formed, which is released into blood. In blood, it develops into mature erythrocytes.

The temporary rise in blood pressure during the contraction of the heart is called systolic pressure and the temporary fall in blood pressure during relaxation of the heart is called diastolic pressure. Blood pressure is expressed as the ratio of the systolic pressure over the diastolic pressure. For a healthy resting adult person, the average systolic/diastolic pressures are 120/80mmHg. Aorta is directly supplied by left ventricle thus, the blood pressure in aorta is highest during systole of left ventricle. During it, left ventricle contracts and pushes blood into aorta.

A special neural centre in medulla oblongata can moderate the cardiac function through autonomic nervous system (ANS). Neural signals through the sympathetic nerves (part of ANS) can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output. Parasympathetic neural signals (component of ANS) decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output.

In the given diagram the P-wave represents the electrical excitation (or depolarisation) of the atria, which leads to the contraction of both the atria. The QRS complex represents the depolarisation of the ventricles, which initiates the ventricular contraction. The contraction starts shortly after Q and marks the beginning of the systole. The T-wave represents the return of the ventricles from excited to normal state (repolarisation). The end of the T-wave marks the end of systole.

Spleen is a vertebrate organ, lying behind the stomach, that is basically a collection of lymphoid tissue. Its functions include producing lymphocytes and destroying foreign particles. It acts as a reservoir for RBCs and can regulate the number in circulation. It is also the site for the breakdown of worn out RBCs and thus is known as graveyard of RBCs.

Blood plasma is a faint yellow, slightly alkaline and somewhat viscous fluid. The plasma contains a number of proteins: serum albumin, serum globulins, properdin, prothrombin and fibrinogen. Prothrombin and fibrinogen play a role in blood clotting.