Physiology - 10 Easy Questions

Piloerection, also known as "goosebumps," is the least useful physiological response to hypothermia in humans. This response occurs when the muscles attached to hair follicles contract, causing the hair to stand on end. While piloerection may help in other animals by trapping a layer of air for insulation, it is not effective in humans due to our lack of dense body hair. Therefore, piloerection is not a significant mechanism for maintaining body temperature in humans during hypothermia.

The first physiological response to hyperthermia is vasodilation. This means that the blood vessels near the surface of the skin widen, allowing more blood flow to the skin. This helps in dissipating heat from the body to the environment. Vasodilation also causes the skin to appear red or flushed. Sweating and increased blood flow to the skin are additional responses that aid in cooling the body down. Thyroxin release and decreased heat production are not the initial responses to hyperthermia.

Aromatase is the enzyme that converts androgen to estrogen in the growing ovarian follicle. Androgens are male sex hormones, while estrogens are female sex hormones. Aromatase plays a crucial role in the synthesis of estrogen from androgens, which is necessary for the development and maturation of the ovarian follicle. This conversion is important for the regulation of the menstrual cycle and the production of female sex hormones.

Neuronal degeneration is the process of damage or death of neurons. Neuropraxia, on the other hand, is a type of nerve injury where the nerve is stretched or compressed, resulting in temporary loss of function. Unlike other conditions mentioned, neuropraxia does not involve degeneration or permanent damage to neurons. Therefore, it is the only option where neuronal degeneration is not seen.

Inhibin is a hormone that plays a crucial role in regulating the reproductive system. Its primary action is to inhibit the secretion of FSH (follicle-stimulating hormone). FSH is responsible for the development of follicles in females and the production of sperm in males. By inhibiting FSH secretion, inhibin helps to regulate the balance of hormones involved in the reproductive cycle, ensuring proper functioning of the ovaries and testes. This inhibition of FSH secretion is essential for maintaining reproductive health and preventing excessive follicle development or sperm production.

Calcitonin inhibits osteoclasts. Osteoclasts are cells responsible for the breakdown and resorption of bone tissue. Calcitonin is a hormone produced by the thyroid gland that helps regulate calcium levels in the body. It works by decreasing the activity of osteoclasts, thereby reducing bone resorption. This ultimately helps to maintain bone density and prevent excessive bone loss.

The magnocellular pathway is a visual pathway in the brain that is primarily responsible for processing motion information. It receives input from the retina and transmits signals related to the detection and perception of movement. Therefore, the involvement of the magnocellular pathway in the detection of movement makes it the correct answer.

The main site for HCO3 reabsorption in the kidney is the proximal convoluted tubule (PCT). The PCT is responsible for the reabsorption of the majority of filtered bicarbonate ions (HCO3-) from the glomerular filtrate back into the bloodstream. This reabsorption occurs through the action of carbonic anhydrase, which converts HCO3- into carbon dioxide (CO2) and water (H2O). The CO2 then diffuses into the PCT cells, where it is converted back into HCO3- and transported across the basolateral membrane into the bloodstream. Therefore, the PCT plays a crucial role in maintaining acid-base balance in the body by reabsorbing HCO3-.

Smooth muscle is the least specialized type of muscle and contains no troponin. The contractile process is similar to the actin-myosin interactions that occur in motility of nonmuscle cells. In the smooth muscle cell, actin and myosin are attached to intermediate filaments at dense bodies in the sarcolemma and cytoplasm. Dense bodies contain alpha-actinin and, therefore, resemble the Z lines of skeletal muscle. Contraction causes cell shortening and a change in shape from elongate to globular. Contraction occurs by a sliding filament action analogous to the mechanism used by thick and thin filaments in striated muscle. The connections to the plasma membrane allow all the smooth muscle cells in the same region to act as a functional unit. Sarcoplasmic reticulum is not as well developed as that in the striated muscles. There are no T tubules present; however, endocytic vesicles called caveolae are believed to function in a fashion similar to the T tubule system of skeletal muscle.

When intracellular calcium levels increase, the calcium is bound to the calcium-binding protein calmodulin. Ca2+-calmodulin is required and is bound to myosin light chain kinase to form a Ca2+-calmodulin-kinase complex. This complex catalyzes the phosphorylation of one of the two myosin light chains on the myosin heads. This phosphorylation allows the binding of actin to myosin. A specific phosphatase dephosphorylates the myosin light chain, which returns the actin and myosin to the inactive, resting state. The actin-tropomyosin interactions are similar in smooth and skeletal muscle.

Smooth muscle cells (e.g., vascular smooth muscle cells) also differ from skeletal muscle cells in that they are capable of collagen, elastin, and proteoglycan synthesis, which is usually associated with fibroblasts.