Test: Endocrine System and Hormonal Regulation - 1 - MCAT MCQ

When we consume a meal, especially one high in carbohydrates like a banana split, our blood sugar levels rise. In response to elevated blood sugar, the pancreas releases insulin. Insulin plays a crucial role in regulating blood sugar levels by facilitating the uptake of glucose from the bloodstream into cells, particularly muscle and fat cells. It promotes the storage of glucose as glycogen in the liver and muscles, reducing blood sugar levels.

Prolactin, glucagon, and parathyroid hormone are not directly involved in the regulation of blood sugar levels in response to a meal. Prolactin is primarily involved in milk production in lactating women, glucagon acts to raise blood sugar levels when they are too low, and parathyroid hormone regulates calcium and phosphate levels in the body.

Therefore, the correct answer is C. Insulin.

When eating food, our digestive system breaks down the food into macromolecules such as proteins, lipids, and carbohydrates. Hormones that help our body take up these biological molecules would be released after a meal. Glucagon has the opposite effects of insulin and raises blood glucose levels as opposed to taking up the glucose. Therefore glucagon would NOT increase after eating a large meal.

Testosterone is a steroid hormone and belongs to the class of hormones known as steroid hormones or steroid receptors. Steroid hormones are lipid-soluble and can pass through the cell membrane easily. Once inside the cell, they bind to specific receptors located in the cytoplasm or nucleus. The hormone-receptor complex then translocates into the nucleus and binds to specific DNA sequences, regulating gene expression and protein synthesis.

In contrast, hormones such as follicle-stimulating hormone (FSH), prolactin, and growth hormone are peptide hormones. Peptide hormones are water-soluble and cannot pass through the cell membrane directly. Instead, they bind to specific receptors located on the cell surface. These receptors transmit signals through intracellular pathways, ultimately leading to various cellular responses.

Thyroid hormone acts by binding to specific receptors located on the inside of the cell, in the nucleus (option D is correct). These receptors are called thyroid hormone receptors (THR). Once the hormone-receptor complex forms, it binds to specific DNA sequences, influencing gene expression and regulating various metabolic processes within the cell.

The posterior pituitary gland releases two hormones: oxytocin and antidiuretic hormone (ADH), also known as vasopressin. Among these, ADH is primarily responsible for regulating water balance in the body. ADH acts on the kidneys to increase water reabsorption, which reduces urine production and helps retain water in the body. This process is essential for maintaining proper hydration and preventing excessive water loss.
Options A, B, and D are not functions mediated by hormones released by the posterior pituitary. Maturation of the egg and sperm is regulated by follicle-stimulating hormone (FSH) and luteinizing hormone (LH) released by the anterior pituitary, not the posterior pituitary (option A is incorrect). Calcium levels are regulated by parathyroid hormone (PTH) and calcitonin, not hormones from the posterior pituitary (option B is incorrect). The release of thyroid hormone is regulated by the hypothalamus and anterior pituitary, specifically through thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH), respectively (option D is incorrect).

Therefore, the physiological function mediated by a hormone released by the posterior pituitary is water retention (option C).

Peptide hormones, with the exception of tyrosine, are generally hydrophilic.
Hydrophilic molecules do not have favorable interactions with the hydrophobic fatty acid tails within the phospholipid bilayer and therefore do not readily diffuse across the membrane.
Estrogen is a hydrophobic steroid hormone and readily diffuses across the cell membrane and binds to receptors located inside the cell. It does not bind to transmembrane proteins located on the surface of the cell and is the correct answer.

Glucagon is released by the pancreas when blood glucose levels are low. It acts to increase blood glucose levels by stimulating the liver to break down stored glycogen into glucose through a process called glycogenolysis. In this situation, when you skip meals and do not provide a source of glucose, your body will need to rely on stored glycogen to maintain blood glucose levels. Glucagon helps facilitate this process by promoting the release of stored glucose from the liver.

On the other hand, growth hormone (option B) is typically released during sleep and exercise, and its levels are less likely to be influenced by studying or meal skipping. Insulin (option C) is released in response to high blood glucose levels to facilitate the uptake of glucose into cells, so its levels would be expected to decrease in the scenario described. Calcitonin (option D) is a hormone involved in calcium regulation and would not be directly affected by studying or meal skipping.

Therefore, the hormone that would be expected to increase in this situation is glucagon (option A).

hyroid gland and plays a crucial role in regulating metabolism throughout the body. It increases the basal metabolic rate (BMR), which is the amount of energy expended by the body at rest to maintain essential physiological functions.

Thyroid hormone affects almost every organ system in the body, influencing the rate of metabolism of carbohydrates, fats, and proteins. It increases oxygen consumption, heat production, and energy expenditure in cells. Higher levels of thyroid hormone lead to an increased metabolic rate, resulting in more efficient energy utilization and often an increase in body temperature.

Parathyroid hormone (option B) is involved in regulating calcium and phosphate levels in the body. Secretin (option C) is a hormone that stimulates the release of bicarbonate from the pancreas to help neutralize stomach acid. Glucagon (option D) primarily acts to increase blood glucose levels by stimulating glycogenolysis and gluconeogenesis and does not directly influence basal metabolic rate.

Paracrine signaling involves the release of chemical agents, such as growth factors and histamine, by a cell, which then act locally on neighboring cells in the immediate vicinity. These chemical agents are released in small amounts and influence the behavior and function of nearby cells without being transported through the bloodstream to distant target cells.

In contrast, endocrine function (option A) refers to the secretion of hormones into the bloodstream by endocrine glands, which then travel to distant target cells throughout the body. Autocrine function (option B) occurs when a cell releases signaling molecules that bind to receptors on its own surface, affecting its own behavior or function. Growth factors and histamine do not act on the same cells that release them, so they do not exhibit autocrine function.

Therefore, the most appropriate description of the function of growth factors and histamine is paracrine function (option C), where they act locally on neighboring cells in the vicinity of their release.

The liver is an organ that serves as both an endocrine and exocrine gland. As an endocrine gland, the liver produces and releases several important hormones into the bloodstream. For example, it produces insulin-like growth factor 1 (IGF-1), which is involved in growth and development.

Additionally, the liver functions as an exocrine gland by producing and secreting bile into the digestive system. Bile is important for the digestion and absorption of fats. It is stored in the gallbladder and released into the small intestine when needed.

On the other hand, the thyroid gland (option A) is primarily an endocrine gland that produces and releases thyroid hormones, while the adrenal glands (option B) are also primarily endocrine glands that produce and secrete hormones such as cortisol and adrenaline. The parathyroid glands (option C) are small endocrine glands located near the thyroid gland, and they produce and release parathyroid hormone (PTH), which regulates calcium levels in the body. However, these glands do not have an exocrine function like the liver does.