Why are gonads exocrine and endocrine

Receptors bind a specific hormone, resulting in a specific physiologic normal response of the body. PTH opposes the effect of thyrocalcitonin or calcitonin , a hormone produced by the thyroid gland that regulates calcium levels.

It does this by removing calcium from its storage sites in bones and releasing it into the bloodstream. It also signals the kidneys to reabsorb more of this mineral, transporting it into the blood. PTH can also signal the small intestine to absorb calcium by transporting it from the diet into the blood. Calcium is important for metabolization to occur.

Blood cannot clot without sufficient calcium. Skeletal muscles require this mineral in order to contract. A deficiency of PTH can lead to tetany, a condition characterized by muscle weakness due to lack of available calcium in the blood. More specifically, PTH increases blood calcium concentrations when calcium ion levels fall below normal. First, PTH enhances reabsorption of calcium by the kidneys; it then stimulates osteoclast activity and inhibits osteoblast activity.

PTH and calcitonin work in opposition to one another to maintain homeostatic calcium levels in body fluids. Adrenal glands are composed of the adrenal cortex and medulla; both produce hormones that control essential body functions and responses.

Distinguish between the hormones produced by the adrenal cortex and adrenal medulla and the functions they regulate. Adrenal glands are a pair of ductless glands located above the kidneys. Through hormonal secretions, the adrenal glands regulate many essential functions in the body, including biochemical balances that influence athletic training and general stress response.

The adrenal glands consist of an outer adrenal cortex and an inner adrenal medulla, which secrete different hormones. Adrenal glands : Adrenal glands are located on top of the kidneys. These glands are composed of the adrenal cortex and the adrenal medulla. The adrenal cortex is made up of layers of epithelial cells and associated capillary networks. These layers form three distinct regions: an outer zona glomerulosa that produces mineralocorticoids; a middle zona fasciculata that produces glucocorticoids; and an inner zona reticularis that produces androgens, which are sex hormones that promote masculinity.

Androgens are produced in small amounts by the adrenal cortex in both males and females. They do not affect sexual characteristics and may supplement sex hormones released from the gonads. The hormones made by the adrenal cortex supply long-term responses to stress. The two major hormones produced are the mineralocorticoids and the glucocorticoids.

The mineralocorticoids regulate the salt and water balance, leading to the increase of blood volume and blood pressure. The main mineralocorticoid is aldosterone, which regulates the concentration of sodium ions in urine, sweat, pancreas, and saliva. Aldosterone release from the adrenal cortex is stimulated by a decrease in blood concentrations of sodium ions, blood volume, or blood pressure, or by an increase in blood potassium levels.

The three main glucocorticoid hormones are cortisol, corticosterone, and cortisone. The glucocorticoids stimulate the synthesis of glucose and gluconeogenesis converting a non-carbohydrate to glucose by liver cells. They also promote the release of fatty acids from adipose tissue. These hormones increase blood glucose levels to maintain levels within a normal range between meals.

Cortisol is one of the most active glucocorticoids. It usually reduces the effects of inflammation or swelling throughout the body. It also stimulates the production of glucose from fats and proteins, which is a process referred to as gluconeogenesis.

Aldosterone is one example of a mineralcorticoid. It signals the tubules in the kidney nephrons to reabsorb sodium while secreting or eliminating potassium. If sodium levels are low in the blood, the kidney secretes more renin, an enzyme that stimulates the formation of angiotensin from a molecule made from the liver. Angiotensin stimulates aldosterone secretion.

As a result, more sodium is reabsorbed as it enters the blood. Aldosterone, the major mineralcorticoid, stimulates the cells of the distal convoluted tubules of the kidneys to decrease re-absorption of potassium and increase re-absorption of sodium.

This in turn leads to an increased re-absorption of chloride and water. These hormones, together with such hormones as insulin and glucagon, are important regulators of the ionic environment of the internal fluid. The adrenal medulla contains large, irregularly-shaped cells that are closely associated with blood vessels.

These cells are innervated by pre-ganglionic autonomic nerve fibers from the central nervous system. The adrenal medulla contains two types of secretory cells: one that produces epinephrine adrenaline and another that produces norepinephrine noradrenaline. Epinephrine is the primary adrenal medulla hormone, accounting for 75 to 80 percent of its secretions.

Epinephrine and norepinephrine increase heart rate, breathing rate, cardiac muscle contractions, blood pressure, and blood glucose levels. They also accelerate the breakdown of glucose in skeletal muscles and stored fats in adipose tissue.

The release of epinephrine and norepinephrine is stimulated by neural impulses from the sympathetic nervous system. Secretion of these hormones is stimulated by acetylcholine release from pre-ganglionic sympathetic fibers innervating the adrenal medulla.

These neural impulses originate from the hypothalamus in response to stress to prepare the body for the fight-or-flight response. The pancreas produces digestive enzymes and hormones, which are important in blood sugar regulation and other body functions. The pancreas is an elongated organ that is located between the stomach and the proximal portion of the small intestine.

It contains both exocrine cells that excrete digestive enzymes and endocrine cells that release hormones. It is sometimes referred to as a heterocrine gland because it has both endocrine and exocrine functions. Pancreas : The pancreas is found underneath the stomach and points toward the spleen.

It is both an endocrine and exocrine gland. As an endocrine gland, the pancreas produces several important hormones,such as insulin and glucagon, which are secreted into the bloodstream to regulate blood sugar levels, along with other activities throughout the body.

As a digestive organ, the pancreas secretes pancreatic juice containing digestive enzymes that assist the absorption of nutrients and the digestion in the small intestine. Food particles are reduced to basic elements that can be absorbed by the intestine and used by the body. Epinephrine and norepinephrine cause immediate, short-term changes in response to stressors, inducing the so-called fight-or-flight response.

The responses include increased heart rate, breathing rate, cardiac muscle contractions, and blood-glucose levels. They also accelerate the breakdown of glucose in skeletal muscles and stored fats in adipose tissue, and redirect blood flow toward skeletal muscles and away from skin and viscera.

The release of epinephrine and norepinephrine is stimulated by neural impulses from the sympathetic nervous system that originate from the hypothalamus. The pancreas is an elongate organ located between the stomach and the proximal portion of the small intestine Figure It contains both exocrine cells that excrete digestive enzymes and endocrine cells that release hormones.

The endocrine cells of the pancreas form clusters called pancreatic islets or the islets of Langerhans. Among the cell types in each pancreatic islet are the alpha cells, which produce the hormone glucagon, and the beta cells, which produce the hormone insulin. These hormones regulate blood-glucose levels. Alpha cells release glucagon as blood-glucose levels decline. When blood-glucose levels rise, beta cells release insulin. The gonads—the male testes and female ovaries—produce steroid hormones.

The testes produce androgens, testosterone being the most prominent, which allow for the development of secondary sex characteristics and the production of sperm cells. The ovaries produce estrogen and progesterone, which cause secondary sex characteristics, regulate production of eggs, control pregnancy, and prepare the body for childbirth.

There are several organs whose primary functions are non-endocrine but that also possess endocrine functions. These include the heart, kidneys, intestines, thymus, and adipose tissue. The heart has endocrine cells in the walls of the atria that release a hormone in response to increased blood volume. The gastrointestinal tract produces several hormones that aid in digestion. The endocrine cells are located in the mucosa of the GI tract throughout the stomach and small intestine.

They trigger the release of gastric juices, which help to break down and digest food in the GI tract. The kidneys also possess endocrine function. Two of these hormones regulate ion concentrations and blood volume or pressure. Erythropoietin EPO is released by kidneys in response to low oxygen levels.

EPO triggers the formation of red blood cells in the bone marrow. EPO has been used by athletes to improve performance. But EPO doping has its risks, since it thickens the blood and increases strain on the heart; it also increases the risk of blood clots and therefore heart attacks and stroke. The thymus is found behind the sternum. The thymus produces hormones referred to as thymosins, which contribute to the development of the immune response in infants.

Adipose tissue, or fat tissue, produces the hormone leptin in response to food intake. Leptin produces a feeling of satiety after eating, reducing the urge for further eating.

Hormone production and release are primarily controlled by negative feedback, as described in the discussion on homeostasis. In this way, the concentration of hormones in blood is maintained within a narrow range. For example, the anterior pituitary signals the thyroid to release thyroid hormones.

Increasing levels of these hormones in the blood then give feedback to the hypothalamus and anterior pituitary to inhibit further signaling to the thyroid gland Figure These hormones regulate blood glucose levels.

As blood glucose levels decline, alpha cells release glucagon to raise the blood glucose levels by increasing rates of glycogen breakdown and glucose release by the liver.

When blood glucose levels rise, such as after a meal, beta cells release insulin to lower blood glucose levels by increasing the rate of glucose uptake in most body cells, and by increasing glycogen synthesis in skeletal muscles and the liver. Together, glucagon and insulin regulate blood glucose levels.

Figure 2. The islets of Langerhans are clusters of endocrine cells found in the pancreas; they stain lighter than surrounding cells. Tabiin, Christopher P.

White, Grant Morahan, and Bernard E. The principal androgen is testosterone , which is secreted by the testes. A small amount is also produced by the adrenal cortex. Production of testosterone begins during fetal development, continues for a short time after birth, nearly ceases during childhood, and then resumes at puberty.