Medical Science Test 2 Nddc Scholarship

Thyroid hormones (T3 and T4) are essential for normal growth, brain development, and the regulation of metabolism, including increasing the body's sensitivity to catecholamines (beta-adrenergic response). Decreasing calcium reabsorption is primarily a function of Calcitonin (produced by the C-cells of the thyroid) or related to Parathyroid Hormone (PTH) activity. T3 does not play a direct role in decreasing calcium reabsorption; its focus is on cellular metabolic rate and development.

Hypercalcaemia is frequently caused by malignancy (where cancer cells break down bone) and sarcoidosis (where granulomas produce extra Vitamin D). Paget's disease can also lead to high calcium levels during periods of immobilization. Aldosterone, however, is a hormone primarily concerned with the regulation of sodium and potassium levels in the blood and the management of blood pressure. It has no direct physiological mechanism for raising blood calcium levels.

Cortisol, Testosterone, and Aldosterone are all steroid hormones derived from cholesterol, with progesterone serving as a vital intermediate in their synthesis pathways. Adrenocorticotropic Hormone (ACTH), however, is a polypeptide tropic hormone produced and secreted by the anterior pituitary gland. Its primary role is to stimulate the adrenal cortex to produce cortisol. Because it is a protein-based hormone rather than a steroid, its production is entirely independent of the progesterone precursor.

Chief cells (also known as peptic cells) are located in the base of the gastric glands. They secrete pepsinogen, an inactive zymogen. When pepsinogen comes into contact with the hydrochloric acid (HCl) secreted by parietal cells, it is converted into its active form, pepsin, which begins the digestion of proteins. G cells secrete the hormone gastrin, and plasma cells are part of the immune system and are not involved in gastric enzyme production.

The secretion of gastric enzymes is heavily regulated by the parasympathetic nervous system via the vagus nerve. The vagus nerve releases the neurotransmitter acetylcholine, which directly stimulates chief cells to release pepsinogen and parietal cells to release HCl. Somatostatin and secretin generally act as inhibitors of gastric activity, while gastrin primarily stimulates acid secretion and mucosal growth rather than being the direct 'primary activator' of the zymogen release compared to neural stimulation.

Angiotensin II is one of the most potent vasoconstrictors in the body; it causes systemic 'vasoconstriction' (narrowing of blood vessels) to increase blood pressure, making 'vasodilation' (widening of vessels) the incorrect function. It also stimulates the adrenal cortex to release aldosterone (for sodium retention) and prompts the posterior pituitary to release vasopressin (ADH), both of which work to increase blood volume and overall systemic pressure.

Progesterone is often called the 'hormone of pregnancy.' It causes a slight rise in basal body temperature after ovulation, relaxes smooth muscles (to prevent premature uterine contractions), and promotes the growth of spiral arteries in the uterine lining to support a potential embryo. However, it exerts 'negative feedback' on the pituitary gland, meaning it inhibits—rather than activates—the secretion of Follicle-Stimulating Hormone (FSH) to prevent the development of new follicles while a potential pregnancy is being established.

Estrogen is responsible for breast development, stimulates the growth of ovarian follicles, and inhibits FSH through negative feedback. Crucially, estrogen actually 'increases' the liver's production of various transport proteins, such as Sex Hormone-Binding Globulin (SHBG) and Thyroxine-Binding Globulin (TBG). Therefore, the claim that it decreases overall transport proteins is physiologically incorrect; it enhances their levels in the circulation.

In ABG analysis, a pH above 7.45 indicates alkalosis. When this is accompanied by a high bicarbonate (\(HCO_3\)) level and a high Base Excess, the cause is 'Metabolic'. Because the \(pCO_2\) (the respiratory component) is neutral, it indicates that the alkalosis is primarily driven by metabolic factors (such as loss of stomach acid through vomiting or excessive intake of antacids) and has not yet been compensated for by the respiratory system.

A high pH indicates alkalosis. Because the bicarbonate (\(HCO_3\)) and Base Excess are neutral, the cause is not metabolic. Instead, the low \(pCO_2\) (carbon dioxide is an acid) indicates that the alkalosis is 'Respiratory' in nature. This typically occurs during hyperventilation, where the body 'blows off' too much \(CO_2\), leading to an increase in blood pH. Since the metabolic markers are neutral, it suggests an acute respiratory event that the kidneys have not yet had time to compensate for.