Endocrine System - 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.

Calcitonin lowers plasma calcium, while parathyroid hormone (PTH) increases it. Insulin and glucagon are responsible for blood glucose, not calcium.

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.

Adrenocorticotropic hormone (ACTH) is released from the anterior pituitary, and is responsible for stimulating secretion of glucocorticoids from the adrenal cortex. While cortisol is the most common and physiologically relevant glucocorticoid, others may also be synthesized. Adrenocorticotropic hormone release is stimulated by stress.

Somatotropin, or human growth hormone, is responsible for both bone and cartilage growth. It is the main factor in human growth, up until puberty.

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.

Calcitonin lowers plasma calcium, while parathyroid hormone (PTH) increases it. Insulin and glucagon are responsible for blood glucose, not calcium.

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.

Adrenocorticotropic hormone (ACTH) is released from the anterior pituitary, and is responsible for stimulating secretion of glucocorticoids from the adrenal cortex. While cortisol is the most common and physiologically relevant glucocorticoid, others may also be synthesized. Adrenocorticotropic hormone release is stimulated by stress.

The test, as described in the passage, simply assays for the presence of hCG in the urine. The person using the test would either obtain a positive or negative result. Whether or not this result is valid remains in question because there are no experimental controls involved. In other words, there is nothing to test whether the test reagents are faulty or the procedure was done incorrectly. A positive control would involve using a sample liquid containing hCG and testing to see whether the pregnancy test could actually detect it. If it can't, then something is wrong. A negative control might involve using a urine sample with no hCG in it and seeing if the test gives a false positive result. Such controls are not included in the test as described in the passage. The other answer choices can be eliminated. The answer: 'is only effective after at least one month of pregnancy' is wrong because the passage states that hCG levels are high enough to be detected by the time of the first missed period (anywhere from 7-14 days from the time of fertilization.)

The answer: 'is inaccurate because hCG can be produced normally in the non-pregnant mother,' can be eliminated because the mother does not produce hCG. If she did, the test would be entirely useless. Only the embryo produces the hormone. The answer choice, 'is inaccurate because hCG is sometimes not produced by the fertilized zygote,' is also incorrect because the embryo must produce hCG in order to prevent menstruation and maintain the corpus luteum. If it doesn't, menstruation will occur and the embryo will be sloughed off with the uterine lining.

Somatotropin, or human growth hormone, is responsible for both bone and cartilage growth. It is the main factor in human growth, up until puberty.

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.