Glands - MCAT Biological and Biochemical Foundations of Living Systems

The thyroid gland is responsible for helping to regulate basal metabolism and calcium levels. The thyroid gland secretes calcitonin, synthesized from C-cells, to reduce free calcium levels in the blood. Calcitonin antagonizes parathyroid hormone (PTH), which serves to increase the free calcium levels in the blood.

Parathyroid hormone is released from the parathyroid gland. Thyroid-stimulating hormone is released from the anterior pituitary. Aldosterone is released from the adrenal cortex.

Luteinizing hormone is produced and secreted by the anterior pituitary gland.

Antidiuretic hormone is produced by the hypothalamus, but secreted by the posterior pituitary gland. Epinephrine is produced by the adrenal medulla; aldosterone is produced by the adrenal cortex. Thyroxine (T4) is produced by the thyroid.

The thyroid gland is responsible for helping to regulate basal metabolism and calcium levels. The thyroid gland secretes calcitonin, synthesized from C-cells, to reduce free calcium levels in the blood. Calcitonin antagonizes parathyroid hormone (PTH), which serves to increase the free calcium levels in the blood.

Parathyroid hormone is released from the parathyroid gland. Thyroid-stimulating hormone is released from the anterior pituitary. Aldosterone is released from the adrenal cortex.

Hormones cortisol and aldosterone are synthesized in the adrenal glands. Adrenal glands are made up of the adrenal cortex and the adrenal medulla. Adrenal medulla is involved in the synthesize of catecholamines (epinephrine and norepinephrine) whereas adrenal cortex synthesizes mineralocorticoids (aldosterone), glucocorticoids (cortisol), and androgens (testosterone, DHT, and DHEA).

Aldosterone is released upon stimulation from the renin-angiotensin system and serves to increase reabsorption of sodium in the collecting ducts of the kidney. Cortisol is released due to stress and serves to increase the metabolic rate.

In a female, the luteal surge occurs during the menstrual cycle. Its main function is to increase the concentration of luteinizing hormone, or LH. LH is released in both males and females and its main function is to increase the concentration of testosterone in males and estrogen in females; therefore, the luteal surge in females increases the concentration of LH, which causes an increase in estrogen.

Progesterone functions to prepare the lining of the uterus for implantation of the egg, and also produces menstrual bleeding if pregnancy does not occur.

Estrogen induces the development of female sex characteristics. Follicle-stimulating hormone stimulates the synthesis and secretion of estrogen. Luteinizing hormone stimulates progesterone production. Gonadotropin-releasing hormone controls the release of follicle-stimulating hormone.

Endocrine organs are capable of secreting hormones into the bloodstream. Each of the given answer options performs some sort of endocrine function.

The testes secrete testosterone, and are responsible for the development of most secondary sex characteristics in males.

The thyroid gland secretes calcitonin and thyroid hormones, responsible for elevating calcium levels and increasing metabolism, respectively.

The pancreas and liver are both endocrine AND exocrine organs. As an endocrine organ, the pancreas secretes the hormones insulin and glucagon. As an exocrine organ, it secretes several enzymes that are essential for digestion in the small intestine. The liver secretes insulin-like growth factors in response to stimulation by growth hormone. As an exocrine organ, it is also responsible for producing bile to aid in digestion.

Glucagon acts in a negative feedback loop with insulin to regulate blood sugar concentration. Both hormones are secreted from the Islets of Langerhans in the pancreas. Alpha cells in the pancreas have high levels of glucagon synthase, allowing them to synthesize the hormone.

Essentially, glucagon synthase is located in alpha cells, which are found in Islets of Langerhans within the pancreas; thus, all of these answers describe the site of glucagon synthesis.

There is a key difference between exocrine and endocrine glands. Exocrine glands release their product to the external environment, while endocrine glands release their product directly into bodily fluids. The answer is the structure that accomplishes both of these actions. The pancreas does both: it releases digestive enzymes into the small intestine (external environment), and releases hormones into the bloodstream (body fluid). Remember that the entire digestive tract is considered part of the outside environment and is lined by epithelium, rather than endothelium.

The adrenal cortex and thyroid perform only endocrine functions, while the gall bladder is only exocrine.

The endocrine system involves secretions by ductless glands into the bloodstream. The pancreas, pituitary gland, thyroid, and hypothalamus are all endocrine organs that secrete hormone signals to the body. The pancreas, however, also functions as an exocrine gland. When the pancreas secretes insulin and glucagon into the blood stream, it serves as an endocrine organ. When it secretes digestive enzymes through the pancreatic duct into the small intestine, it serves an exocrine function.

Insulin is secreted from the beta cells of the pancreas. The alpha cells secrete glucagon, which acts in a negative feedback loop with insulin to regulate blood glucose levels.

The acinar cells of the pancreas secrete digestive enzymes, and serve the exocrine (rather than the endocrine) function of the pancreas. The adrenal medulla secretes epinephrine and norepinephrine, while the adrenal cortex releases aldosterone.

Somatostatin is synthesized in the delta cells in the islets of Langerhans in the pancreas, and serves to inhibit insulin and glucagon secretion from beta and alpha cells, respectively. Somatostatin serves a number of other purposes, including inhibition of growth hormone and inhibition of the release of pancreatic digestive enzyme release.

Amylin, along with insulin, is released from the beta cells of the pancreas and acts as a synergist to insulin. Ghrelin is released from epsilon cells of the pancreas and has an array of different functions, including inducing appetite. Thyroxine refers to the thyroid hormone T4, or tetraiiodothyronine, which plays a role in metabolism.

Seeing as type I diabetes results from the destruction of the -cells in the pancreas, this is the only feasible answer. These cells are responsible for producing insulin.

Insulin is released into the blood from the pancreas and functions to decrease the glucose concentration in the blood. Elevated levels of blood glucose induces insulin release. Once released, insulin transports glucose back into the cells or facilitates the formation of glycogen. Glycogen consists of multiple glucose subunits and is stored in the liver for later use. Calcitonin, on the other hand, functions to decrease the calcium concentration in the blood. Osteoclasts are cells in bones that break down bones and release bone calcium into the blood. Calcitonin inhibits the activity of osteoclasts and decreases the calcium concentration in the blood. Statement I is false.

Antagonistic hormones are a pair of hormones that have the opposite effects. For example, insulin and glucagon are antagonistic hormones because insulin functions to decrease blood glucose levels, whereas glucagon functions to increase blood glucose levels. Similarly, calcitonin and parathyroid hormone (PTH) are antagonistic hormones because calcitonin functions to decrease blood calcium levels whereas PTH functions to increase blood calcium levels. Insulin and calcitonin are not antagonistic hormones because they do not have opposite effects. Statement II is false.

Recall that insulin and calcitonin are part of the endocrine system. Hormones in the endocrine system are characterized by their ability to travel through blood and act on cells that are far away from the glands that released them; therefore, insulin and calcitonin do not act on cells surrounding their respective glands alone. Statement III is false.

Insulin is secreted by the beta cells of the islets of Langerhans in the pancreas in response to high blood glucose levels. Alpha cells in the islets of Langerhans secrete glucagon, the antagonist of insulin, in response to low blood glucose levels.

The thyroid secretes thyroxine (also known as tetraiodothyronine or T4), which controls the body's metabolism. The thyroid also secretes calcitonin, which promotes bone formation. Cortisol is secreted by the adrenal cortex and works to regulate blood glucose levels and has an anti-inflammatory effect. Cortisol is a corticosteroid that is secreted in response to adrenocorticotropic hormone.

The correct answer is glucagon. Glucagon is secreted by the pancreas, not the pituitary gland. All the other answer choices are major hormones secreted by the pituitary that are essential to bodily functions.

Oxytocin is produced by the hypothalamus, but stored and released by the posterior pituitary, making it the correct answer. Antidiuretic hormone (ADH) is also released by the posterior pituitary, so its pairing with the hypothalamus was incorrect. Calcitonin is released by the thyroid, and aldosterone (like other corticosteroids) is released by the adrenal cortex. Thyroid-stimulating hormone (TSH) is released from the anterior pituitary.

The posterior pituitary secretes oxytocin, which is important for milk ejection from breasts and uterine contractions during labor.

Calcitonin, which serves to decrease serum calcium, is secreted by the thyroid gland. The adrenal cortex secretes aldosterone, which increases blood pressure by increasing sodium reabsorption and potassium secretion. The adrenal cortex also secretes cortisol, a steroid hormone that acts to increase serum glucose, aid in fat, protein, and carbohydrate metabolism, and suppress the body's immune system.

The posterior pituitary gland does in fact secrete oxytocin; however, all of the hormones secreted by the posterior pituitary gland are created in the hypothalamus. The hormones are then sent to the posterior pituitary gland in order to be secreted.

The anterior pituitary creates and secretes follicle-stimulating hormone. The pancreas creates and secretes glucagon and insulin. The adrenal cortex creates and secretes aldosterone.