Understanding Hormones - AP Biology

Melatonin is produced in the pineal gland which is a gland in the brain responsible for the body’s circadian rhythms and sleep/wake cycle. The concentration of melatonin peaks at night and causes us to fall asleep. Melatonin is degraded while we sleep so that when we wake up in the morning we start to produce it again throughout the day.

Hormones are generally slow acting, spread throughout the body by the blood, and can affect a variety of tissues at once. Neurotransmitters on the other hand, are quick acting, localized, and affect only a specific cell. We would not expect hormones to affect only one cell or tissue at a time, as their wide distribution allows them to have multiple target areas.

Steroids are nonpolar, which means that they are able to pass easily through cell membranes, but require a transport protein through the hydrophilic blood in order to do so. The steroid hormone then enters the nucleus and attaches to the DNA in order to increase the desired product at the level of transcription.

A critical concept to understand about hormones in the body is negative feedback. Remember that hormones are not causing the body's condition, but rather, are responding to the body's condition. As a result, parathyroid hormone would be higher than normal in order to increase the concentration of calcium currently in the blood, correcting the existing deficiency.

Luteinizing hormone is responsible for the secretion of testosterone from leydig cells in the testes.

FSH is responsible for the proliferation of sertoli cells, which nurture sperm cell precursors. hGH is responsible for body growth, and is not responsible for testosterone formation. Oxytocin is responsible for increasing uterine contractions during pregnancy.

Insulin is responsible for lowering blood sugar levels, and is therefore released when the body's blood sugar levels are too high. Glucagon is released in response to low blood sugar levels, and acts to increase sugar concentrations.

Thyroid hormones (T3 and T4) are released to increase the body's metabolic rate, but are not directly influenced by blood sugar levels.

The question tells us that slowed output of thyroid hormones can lead to obesity. One can safely assume that receptor insensitivity will have a similar effect. In either scenario, the T3 and T4 hormones are unable to elicit the proper response form the body. Similar to individuals with hypothyroidism, individuals with insensitive receptors would show slowed metabolism and increased weight gain.

Epinephrine, released from the adrenal gland, is important for the fight-or-flight response. During moments of stress, heart rate increases, pupils dilate, and blood vessels constrict in order to prepare for danger. All of this is controlled by epinephrine and norepinephrine, and is part of the sympathetic nervous system.

Oxytocin is responsible for lactation in nursing women. When the nipple is stimulated, oxytocin is released from the posterior pituitary to cause lactation. During labor, release of oxytocin causes positive feedback on the hypothalamus, which causes further oxytocin release.

Luteinizing hormone and follicle-stimulating hormone are released from the anterior pituitary and function to regulate the menstrual cycle. Vasopressin is released from the posterior pituitary and helps to regulate blood pressure and water balance.

Testosterone is well known to be responsible for male secondary sexual characteristics. It also plays a key role in behavior, such as aggression. For example, during mating season in gorillas the testosterone levels in males raise significantly and lead to confrontations between males.

Progesterone and estrogen are responsible for female secondary sexual characteristics, while cortisol plays a role in the body's response to long-term stress.

In order for menstruation to occur, progesterone levels must decrease. When fertilization does not occur, the corpus luteum ceases progesterone production, initiating menstruation. The corpus luteum then transitions into the corpus albicans and removed from the ovary in preparation for the new menstrual cycle.

Prolactin is responsible for the production of milk, while oxytocin is responsible for the ejection of milk. The question asks for the hormone that causes production, so the answer is prolactin. Prolactin is released from the anterior pituitary.

Oxytocin is released from the posterior pituitary and the mammary glands are responsible for releasing milk.

The hormone described in the question is luteinizing hormone (LH). If fertilization occurs, the LH levels will decrease and human chorionic gonadotropin (hCG) is released from the placenta to simulate LH function.

To answer this question, you must have an understanding of the differences between endocrine, paracrine, and autocrine functioning. This example, in which a molecule exhibits autocrine behavior, means that a cell releases a hormone that acts on itself. In paracrine signaling, the molecule does not act on the same cell, but does diffuse through tissue to reach nearby target cells. Finally, endocrine signaling refers to hormone molecules that are released and transported through the bloodstream to act on more faraway target cells in distant regions.

The two hormones known for their effect on plasma calcium levels are calcitonin and parathyroid hormone (PTH). When calcium levels are high, calcitonin is released by the thyroid gland to stimulate the uptake of serum calcium into bone. This effectively decreases calcium levels in the blood. PTH has the opposite effect and is released by the parathyroid gland.

The three remaining answer choices are not known for their effect on calcium levels in the blood.

Growth hormone is released from the anterior pituitary, and has numerous effects on the body. One of its primary effects is to stimulate release of insulin-like growth factors (IGFs) from the liver. These compounds circulate in the blood and directly stimulate bone and cartilage growth.

The release of thyroid-stimulating hormone (TSH) causes the release of T3 and T4, which help speed up metabolism. Glucagon serves to increase blood glucose level. Epinephrine is released in response to short term stress, and stimulates the sympathetic nervous system.

After a large meal the body must quickly remove glucose from the blood. Insulin facilitates the entry of glucose into a variety of body cells, particularly hepatocytes in the liver. Once inside the cell, glucose is either stored as a polymer (glycogen) or reduced into carbon dioxide and water to produce a usable form of energy (ATP) for the cell. Glycogen is stored in the liver until blood glucose levels become low, at which point it can be converted back to glucose and released to maintain homeostasis. This process, known as glycogenolysis, is stimulated by the release of glucagon. Together, insulin and glucagon create a negative feedback loop to regulate glucose in the blood.

Thyroxine (T4) regulates metabolic rate, and is released from the thyroid. Adrenocorticotropic hormone (ACTH) is released from the anterior pituitary and stimulates the release of glucocorticoids (like cortisol) from the adrenal glands. The release of epinephrine is tightly linked to the sympathetic nervous system, and is involved in the immediate stress response.

Insulin works by stimulating adipocytes (fat cells), hepatocytes (liver cells), and skeletal muscle to translocate glucose transporter-rich vesicles to the cell membrane. This allows the diffusion of glucose from the blood into these tissue types after a carbohydrate-rich meal. Without insulin, even if an individual has high blood glucose levels, these three cell types would essentially be deprived of the circulating glucose.

Glucagon works against insulin by increasing blood glucose levels as they decrease via gluconeogenesis and glycogenolysis.

Vitamin D is the only vitamin that can be produced endogenously via UV activation of 7-dehydrocholesterol in the skin. All other vitamins must be obtained from outside sources, namely the digestion of other organic matter.