BIOS 1108 - Chemical and Electrical Signals - Animal Hormones (2)

Hypothalamus

located within the brain, integrates the endocrine and nervous systems; receives input from the body and other brain areas and initiates endocrine responses to environmental changes, synthesizes hormones which are stored in the posterior pituitary gland, and also synthesizes and secretes regulatory hormones that control the endocrine cells in the anterior pituitary gland.

Pituitary Gland

The body’s “master gland” located at the base of the brain and attached to (and regulated by) the hypothalamus.

Anterior Portion of the Pituitary Gland

Regulated by releasing or release-inhibiting hormones produced by the hypothalamus.

Posterior Pituitary

Receives signals via neurosecretory cells to release hormones produced by the hypothalamus.

Thyroid Gland

Butterfly-shaped gland located in the neck; regulated by the hypothalamus-pituitary axis; produces hormones involved in regulating metabolism and growth including T4 and T3

Thyroxine (T4) and Triiodothyronine (T3)

Increase the basal metabolic rate, affect protein synthesis and other metabolic processes, and help regulate long bone growth.

Adrenal Glands

Two glands, each located on one kidney; consist of adrenal cortex (outer layer) and adrenal medulla (inner layer), which each produce different sets of hormones.

Adrenal Cortex

Produces mineralocorticoids, such as aldosterone, which increases reabsorption of sodium by kidneys to regulate water balance; and glucocorticoids, such as cortisol, which is a long-term stress response hormone that increases blood glucose levels by stimulating synthesis of glucose and glucogenesis (converting a non-carbohydrate to glucose) by liver cells; promote the release of fatty acids from adipose tissue.

Adrenal Medulla

Produces epinephrine (adrenaline) a short term stress response hormone that increases heart rate, breathing rate, cardiac muscle contractions, blood pressure, and blood glucose levels; accelerates the breakdown of glucose in skeletal muscles and stored fats in adipose tissue; the release of epinephrine is stimulated directly by neural impulses from the sympathetic nervous system.

Pancreas

Located between the stomach and the proximal portion of the small intestine; regulates blood glucose levels via two opposing hormones: insulin, which decreases blood glucose levels by promoting uptake of glucose by liver and muscle cells and conversion to glycogen (a sugar storage molecule) and glucagon, which increases blood glucose levels by promoting breakdown on glycogen and release of glucose from the liver and muscle.

Gonads (ovaries and testes)

Produce sex steroid hormones that promote development of secondary sex characteristics and regulation of gonad function.

Insulin

Produced by the beta cells of the pancreas, which release insulin when blood glucose levels rise above normal levels (like after eating a meal).

• enhances the rate of glucose uptake and utilization by target cells, which use glucose for ATP production

• stimulates the liver to convert glucose to glycogen, which is then stored by cells for later use

• increases glucose transport into certain cells, such as muscle cells and the liver

• stimulates the conversion of glucose to fat in adipocytes and the synthesis of proteins.

Hypoglycemic Effect

“Low sugar” effect, which inhibits further insulin release from beta cells through a negative feedback loop.

Glucagon

Released from the alpha cells of the pancreas when blood glucose levels decline below normal levels (between meals, glucose utilized rapidly during exercise).

• stimulates the breakdown and release of glucose from glycogen in liver cells

• stimulates absorption of amino acids from the blood by the liver, which then converts them to glucose

• stimulates adipose cells to release fatty acids into the blood

Hyperglycemic Effect

“High sugar” effect

Metamorphosis

is controlled by a set of hormones that determine whether the animal grows into the next larval stage or changes into an adult as it gets larger

Hormones Epinephrine and Norepinephrine

are released by the adrenal medulla and provide a burst of energy cause glycogen to be broken down into glucose and released from liver and muscle cells

• increase blood pressure

• increase breathing rate

• increase metabolic rate

• change blood flow patterns, leading to increased blood flow to skeletal muscles, heart, and brain; and decreased blood flow to digestive system, skin, and kidneys

Long Term Stress Response

the hypothalamus triggers the release of ACTH from the anterior pituitary gland. The adrenal cortex is stimulated by ACTH to release steroid hormones called corticosteroids (the main two being glucocorticoids like cortisol, and mineralocorticoids like aldosterone)

Glucocorticoids

Promote breakdown of fat into fatty acids in the adipose tissue and release into bloodstream for ATP production, stimulate glucose synthesis from fats and proteins to increase blood glucose levels, inhibit immune function to conserve energy

Mineralocorticoids

Promote retention of sodium ions and water by kidneys, increase blood pressure and volume (via sodium/water retention)