Tissues Test - 32

The fibrous components in connective tissue are of three types - collagenous, elastic and reticular.
Collagen is secreted in the form of tropocollagen molecules by the fibroblasts and then they assemble extracellularly to form striated collagen fibrils. 

Correct option: C

• White blood cells or WBCs are the cells of the immune system, that are involved in defending the body against infections. There are different types of WBCs such as eosinophils, neutrophils, lymphocytes, monocytes etc. 

Monocytes are a type of WBCs. Monocytes mature in different types of macrophages.
Lymphocytes are B- cells or T- cells and they have receptors on their surface and are able to bind antigens and thus help the foreign substance to get removed from the body.
Neutrophils are the most abundant type of WBCs. They are phagocytic in nature and are able to engulf foreign substances.
Erythrocytes are red blood cells, that are involved in delivering the oxygen to various tissues.
So, the first three are WBCs that are involved in the immune system, as they help in eliminating various antigens, while the latter is not involved in the immune response.
Thus, the correct answer is option D.

The longest cell in the human body is the neuron with a length of 90cm-100cm, linking the central nervous system (brain and spinal cord) to other parts of the body.

So, the correct answer is option A.

There is bicarbonate buffering system, which is an important buffer system in the acid-base homeostasis.
In this system, carbon dioxide, CO$$_{2}$$, combines with water (H$$_{2}$$O) to form carbonic acid (H$$_{2}$$CO$$_{3}$$), which in turn rapidly dissociates to form hydrogen ion, H$$^+$$ and bicarbonate ion, HCO$$_{3}$$ as:
CO$$_{2}$$ + H$$_{2}$$O --> H$$_{2}$$CO$$_{3}$$ --> HCO$$_{3}$$$$^-$$ + H$$^{+}$$
This reaction is reversible and is catalyzed by the enzyme carbonic anhydrase.
The most important constituents of blood that keep the pH value within the limits of 6.8 - 7.8 are formed by the sodium bicarbonate (NaHCO$$_{3}$$) and carbonic acid (H$$_{2}$$CO$$_{3}$$). When the proportion of carbonic acid increases, the blood will become acidic. If that happens, one automatically starts to breathe more deeply to get rid of more carbon dioxide through the lungs and to become less acidic. When acidification continues the alkaline buffer, formed by sodium bicarbonate, ensures that the acid in the blood is neutralized.
Thus, the correct answer is option B.

The shape of the nucleus of WBCs is irregular. Different types of WBC have different shapes. Nuclei may be bilobed, trilobed, pentalobed, kidney-shaped, or round it depends on the WBC. 

WBC	Shape (nucleus)
Neutrophils	Multinucleated
Eosinophils	Bi-lobed
Monocytes	Kidney shaped
Thrombocytes	Eccentric
Basophils	Bi-lobed or tri-loped

• Haemolysis is the destruction of red blood cells so that the haemoglobin is freed into the surrounding medium.
• Diapedesis is the migration of blood cells, especially WBCs (leucocytes), through the intact walls of blood vessels into the surrounding tissue to fight foreign agents.
• Phagocytosis is the process by which phagocytes ingest or engulf other cells or particles.
• Rouleaux are stacks or aggregations of RBCs, which form because of the unique discoid shape of the cells.

Thus, the correct answer is option B.

Heparin is a mucopolysaccharide or glycosaminoglycan which is an anticoagulant. It is usually stored in the secretory granules of the mast cells and released into the vasculature at the sites of tissue injury.
So, the correct answer is option B.