Hormone Mechanisms and Effects - MCAT Biological and Biochemical Foundations of Living Systems

Growth hormone is secreted by the anterior pituitary and is responsible for increased metabolism and cell growth. Growth hormone increases glucose and free fatty acid levels in the blood, increasing substrates for metabolism for other cells in the body.

Significant amount of blood loss results in a sudden and large drop in blood pressure due to the decreased fluid volume in the body. To compensate for this change, the body will attempt to increase fluid retention. This is directly accomplished by increasing the level of ADH (anti-diuretic hormone) that allows reabsorption of water in the kidneys. Therefore, increased ADH level is the best response.

This question requires knowledge of the negative feedback loop between the anterior pituitary hormones (FSH and LH) and the sex hormones (estrogen and progesterone). Prior to menopause, FSH and LH production is inhibited by estrogen production in the ovaries. When ovarian estrogen production decreases, during menopause, FSH and LH levels increase uninhibited.

Calcitonin decreases blood calcium levels, while parathyroid hormone increases blood calcium levels.

Aldosterone functions to make the collecting duct and distal convoluted tubule in the kidneys to make them more permeable to Na+, Cl–, K+, and H+. When Na+ and Cl– are reabsorbed, water follows them into the blood, thus increasing total blood volume and raising blood pressure.

FSH, LH, estrogen, and progesterone all increase around ovulation to make an environment in the uterus that will be healthy if fertilization occurs. Prolactin promotes milk production at the end of pregnancy and while a mother is breast feeding a child.

When an a meal is consumed, the digestive system is stimulated. This causes the release of secretin and cholecystokinin, hormones that are involved in digestion. Once glucose is in the bloodstream, it interacts with beta cells and causes the release of insulin. Insulin enters the bloodstream and stimulates widespread expression of the GLUT-4 receptor. Glucagon, on the other hand, counters the effects of insulin in a negative feedback loop and would not be expected to increase after a meal is consumed.

Release of ADH would not be associated with release of atrial naturitic hormone. ADH increases blood pressure, while atrial naturitic hormone decreases blood pressure.

Growth hormone (GH) causes increased calcium retention and stimulation of the immune system. It reduces liver uptake of glucose and increases lipolysis. Growth hormone also causes increased protein synthesis, muscle mass, bone mineralization, and _gluco_neogenesis.

An increase in aldosterone will cause an increase in sodium reabsoption, an increase in blood osmolarity, an increase in antidiuretic hormone (ADH) release, an increase in water reabsoption, and an increase in blood volume.

If the lack of a certain hormone can cause high calcium levels, that means the hormone acts to lower plasma calcium when it is present. Only one of the choices, calcitonin, decreases blood calcium. Parathyroid hormone (PTH) and calcitriol increase plasma calcium levels. Aldosterone and glucagon are unrelated to calcium regulation—aldosterone regulates kidney activity to increase blood pressure and glucagon increases blood sugar levels.

The LH surge, a spike in levels of luteinizing hormone, immediately precedes the luteal phase of the menstrual cycle, which begins with ovulation and ends with degeneration of the corpus luteum.

Estradiol, an estrogen, is secreted by theca cells and promotes growth of the endometrium to prepare for implantation.

Follicle-stimulating hormone is important for follicle maturation.

Degeneration of the corpus luteum into corpus albicans occurs in the absence of implantation. This degeneration process typically occurs 14 days after ovulation.

Human chorionic gonadotropin is only released during pregnancy and is responsible for maintaining the corpus luteum.

Of all the choices, the only one released by the anterior pituitary is TSH (thyroid-stimulating hormone). Glucagon is released from the pancreas, parathyroid hormone is released from the parathyroid glands, melatonin comes from the pineal gland, and atrial natriuretic hormone is a heart hormone.

Parathyroid hormone (PTH) does not enhance absorption of vitamin D through the skin.

It does, however, act independently on the bones, kidneys, and gut, to increase blood calcium. Interestingly, cancer cells in various types of cancers (breast and lung) can secrete parathyroid hormone-related protein (PTHrP), which acts similarly to PTH and can cause hypercalcemia (high serum calcium) in cancer patients.

The following answer choices are all examples of anterior pituitary hormones, however, follicle-stimulating hormone (FSH) is the hormone that acts on Sertoli cells in the testes to nourish sperm and facilitate spermatogenesis.

Luteinizing hormone (LH) acts on the testes, but works on Leydig cells in producing testosterone. Adrenocorticotropic hormone (ACTH) and thyroid-stimulating hormone (TSH) do not act on the testes.

The polysaccharides from the meal will be digested down into glucose by various enzymes in the digestive track. That glucose will be absorbed in the small intestine and travel into the bloodstream. This increase in blood glucose will cause a release of insulin to allow for tissue to take up the glucose and use it for energy. In this individual's blood, we would expect insulin to be higher than normal.

Conversely, when little blood glucose is present, glucagon is released to break down glycogen and fat into glucose that is needed for energy. Gastrin, while also involved in digestion, is closely linked to the release of hydrochloric acid, which activates pepsin to digest proteins. Gastrin is not linked to the digestion of carbohydrates and polysaccharides.

Oxytocin is not involved in digestion.

Aldosterone is a mineralcorticoid, meaning that it is released by the adrenal cortex, not the anterior pituitary.

Mineralcorticoids are also steroids, and are able to cross the cell membrane due to their lipophilic nature. Both aldosterone and antidiuretic hormone (ADH) increase blood volume by acting on different regions of the nephrons in the kidney. Finally, angiotensin-converting enzyme (ACE) inhibitors do decrease the secretion of aldosterone, since aldosterone is activated by the renin-angiotensin system and the inhibitors block a vital conversion step in this chain.

Cortisol and glucagon are both elevated when a person is experiencing low blood glucose levels. Glucagon is responsible for elevating blood glucose levels by stimulating glycogenolysis in the liver, and cortisol increases blood glucose levels by stimulating gluconeogenesis in the liver.

Addison's disease is a disorder in which the adrenal cortex is unable to be stimulated by adrenocorticotropic hormone (ACTH). The adrenal cortex is responsible for the secretion of aldosterone and cortisol. Aldosterone is responsible for the increased reabsorption of sodium and increased excretion of potassium, leading to water retention. This process helps raise the blood pressure. Since aldosterone is not being adequately produced in a patient with Addison's disease, the patient's blood pressure will be lower than normal.