Structural Organisation in Animals Test 22

HCl is hydrochloric acid, strong acid. Bone is made of minerals, and the most prominent mineral is calcium. When a bone is dropped in the HCl medium, the calcium of bone slowly starts dissolve due to the action of the strong acid. HCl + Ca --> CaCl₂ + H₂. Afterward, the bone is depleted of calcium but it does not "melt" because there are other minerals that make up the bone such as potassium, vitamins, and collagen. Since calcium is the main mineral in the bone, the bone becomes brittle and more susceptible to breakage. Therefore, the correct answer is option B.

Volkmann’s canals are any of the small channels in the bone that transmit blood vessels from the periosteum (a dense layer of vascular connective tissue) into the bone and that communicate with the Haversian canals (minute tubes which form a network in bone and contains blood vessels). The perforating canals provide energy and nourishing elements for osteons (cylindrical structures that contain mineral matrix and osteocytes which transport blood).

Spongy (cancellous) bone is lighter and less dense than compact bone. Spongy bone consists of plates (trabeculae) and bars of bone adjacent to small, irregular cavities that contain red bone marrow. The canaliculi connect to the adjacent cavities, instead of a central haversian canal, to receive their blood supply.

The anticoagulants K3EDTA, potassium oxalate or sodium heparin to prevent the blood from clotting. The citrate or citric acid buffer reduces the pH value in the sample immediately after blood collection leading to an instant stabilization of glucose.

Erythropoiesis is the process of formation of erythrocytes. It occurs within the red bone marrow. In the early fetus, erythropoiesis takes place in the mesodermal cells of the yolk sac. By the third or fourth month, erythropoiesis moves to the liver. After seven months, erythropoiesis occurs in the bone marrow. 

Anaemia is defined as a decrease in the amount of red blood cells or the amount of haemoglobin in the blood. There are three main types of anaemia - due to blood loss, decreased red blood cell production, and due to increased red blood cell breakdown. Causes of blood loss include trauma and gastrointestinal bleeding among others. Causes of decreased production include iron deficiency, a lack of vitamin B12, thalassemia and a number of neoplasms of the bone marrow among others. Causes of increased breakdown include a number of genetic conditions such as sickle cell anemia, infections like malaria and some autoimmune diseases among others. Folate-deficiency anaemia is a decrease in red blood cells due to a lack of folate. Folate is a type of B vitamin.

Citrate is essentially a regional extracorporeal anticoagulant, with a short systemic half-life of around 5 min, metabolized predominantly by mitochondria in the liver, skeletal muscle and the kidney. Hirudin is the anticoagulant component of the saliva of medicinal leech and inhibits thrombin by formation of irreversible complexes through binding of its active site.
Basophils contain anticoagulant heparin, which prevents blood from clotting too quickly. They also contain the vasodilator histamine, which promotes blood flow to tissues.

Bilirubin consists of an open chain tetrapyrrole. It is formed by oxidative cleavage of a porphyrin in heme, which affords biliverdin. Biliverdin is reduced to bilirubin. After conjugation with glucuronic acid, bilirubin is excreted.

Monocytes are agranulocytes. They have a kidney-shaped nucleus. These cells are actively motile and phagocytic cells.

Monocytes are a type of white blood cell. Like other white blood cells, monocytes are important in the immune system's ability to destroy invaders, but also in facilitating healing and repair. Monocytes are formed in the bone marrow and are released into peripheral blood, where they circulate for several days.

The inability of the heart to generate tetanic contractions is the result of the long absolute refractory period of cardiac muscle, defined as the period during and following an action potential when an excitable membrane cannot be re-excited. The refractory period lasts almost as long as the contraction.

Erector pili muscles are involuntary.
The arrector pili muscles are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end. Each arrector pili is composed of a bundle of smooth muscle fibres, which attach to several follicles (a follicular unit) and is innervated by the sympathetic branch of the autonomic nervous system. The contraction of the muscle is, therefore, involuntary stresses such as cold, fear etc., may stimulate the sympathetic nervous system and thus, cause contraction, but the muscle is not under conscious control.

Myelin is formed by Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS). Each Schwann cell forms a single myelin sheath around an axon. Myelin itself forms by the spiral wrapping around an axon of an enormously expanded glial plasma membrane that then compacts.

Astrocytes have star-shape morphology and are the most abundant CNS glial cell type. They play essential functions in blood brain barrier maintenance, neuronal survival, and in synapse formation, strength, and turnover.