Chapter 17: The Endocrine System

Methods of GH-IGF

1. Protein Synthesis 2. Lipid Metabolism 3. Carbohydrate Metabolism 4. Electrolyte Balance

Stage of Resistance

After a few hours, the body's glucose reserves are exhausted, but the nervous system still demands glucose. If a stressful situation is not resolved before the glycogen is gone, the body enters the stage of resistance, where the first priority is to provide alternative fuels for metabolism.

Stress

Any situation that upsets homeostasis and threatens one's physical or emotional well being.

Posterior Pituitary

Arises as a bud growing downward from the brain. *Constitutes the posterior 1/4 of the pituitary. It is actually nervous tissue (nerve fibers and neuroglia) not a true gland.

Anterior Pituitary

Arises from a pouch that grows upward from the embryonic pharynx. *constitutes about 3/4 of the pituitary as a whole. It has no nervous connection to the Hypothalamus but is linked to it by a complex of blood vessels called the hypophyseal portal system

Pineal Gland

Attached to the third ventricle of the brain, beneath the posterior end of the corpus callosum. Pineal gland may play a role n establishing circadian rhythms of physiological function synchronized with the cycle of daylight and darkness. At night, it synthesizes melatonin from serotonin.

Hypoparathyroidism

Causes a rapid decline in blood calcium level; as in little of 2-3 days this can lead to a fatal suffocating spasm in the muscles of the larynx (hypocalcemic tetany)

Hormones

Chemical messengers that are transported by the bloodstream and stimulate physiological responses in cells of another tissue or organ

Adipose Tissue

Fat cells secrete the hormone Leptin, which has long term effects on appetite-regulating centers of the hypothalamus.

Toxic Goiter

Graves Disease. Antibodies mimic effect of TSH on the thyroid, activating TSH receptors, and causing thyroid hypersecretion.

Thyroid Gland

Largest adult gland to have a purely endocrine function. Lies adjacent to the trachea and immediately below the larynx.

Adrenocorticotropic Hormone (ACTH) or Corticotropin

One of the six anterior pituitary hormones. Secreted by cells called *corticotropes*. Its target organ and the basis for its name is the adrenal cortex. ACTH stimulates the cortex to secrete hormones called *glucocorticoids* (especially cortisol) which regulate glucose, protein, and fat metabolism and are important in body's response to stress.

Prolactin (PRL)

One of the six anterior pituitary hormones. Secreted by pituitary cells called *Lactotropes* (mammatropes). The hormone and these cells are named for the role of PRL in lactation. Lactotropes increase in both size and number during pregnancy, and PRL secretion rises proportionately.

Thyroid Stimulating Hormone (TSH)

One of the six anterior pituitary hormones. TSH is secreted by pituitary cells called *thyrotropes*. Stimulates growth of the thyroid gland and the secretion of thyroid hormone, which has widespread effects on metabolic rate, body temperature, and other functions detailed later.

Antidiuretic Hormone (ADH)

One of two posterior pituitary hormones. ADH increases water retention by the kidneys, reduces urine volume, and helps prevent dehydration. Also functions as a brain neurotransmitter.

Oxytocin (OT)

One of two posterior pituitary hormones. OT has a variety of reproductive functions in situations ranging from sex to breast feeding. Surges in both sexes during sexual arousal and orgasm.

Osseous Tissue

Osteoblasts secrete the hormone *osteocalcin* which increases the number of pancreatic beta cells, pancreatic output of insulin, and insulin sensitivity of other body tissues. Osteocalcin also seems to inhibit weight gain.

Zona Glomerulosa

Outermost layer of the adrenal cortex, thin, less developed in humans than any other mammal. Source of mineralcorticoids

Gonads

Ovaries and Testes, are both endocrine and exocrine. The exocrine products being whole cells-egg and sperm-

Corticosteroids

The 5 most important corticosteroids fall into three categories: mineralcorticoids, which regulate the body's electrolyte balance; Glucocorticoids, which regulate the metabolism of glucose and other organic fuels. And finally, sex steroids, with various developmental and reproductive functions.

Zona Fasciculata

Thick middle layer of the adrenal cortex constituting about 3/4 of cortex. Secretes Glucorticoids and androgens.

Hypophyseal Portal System

This system consists of a network of primary capillaries in the Hypothalamus, a group of small veins called portal venules that travel down the stalk, and a complex of secondary capillaries in the anterior pituitary. The Hypothalamus controls the anterior pituitary by secreting hormones that enter the primary capillaries, travel down the venules, and diffuse out of the second capillaries into the pituitary tissue.

Neuroendocrine reflexes

controls posterior pituitary, releases hormones in response to nerve signals.

Calorigenic effect

increases heat production

Thyroxine (T)

(T cells are critically important for immune defense)

Paracrines

* para = next to *crin = to secrete Secreted by one cell, diffuse to nearby cells in the same tissue and stimulate their physiology Also called Local Hormones

Cortisol

*known clinically as hydrocortisone* most potent glucocorticoid. Have anti-inflammatory effect. Help body adapt to stress and repair damaged tissues

Neuroendocrine cells

*some cells defy all attempts to classify them as neuron or gland cells because they act like neurons in many respects, but like endocrine cells, they release secretions. Therefore, they get a hybrid name

Hypersecretion

Excessive hormone release. Sometimes caused by tumors resulting in the overgrowth of functional endocrine tissue.

Diabetes Insipidus

Condition of chronic polyuria without glucose in the urine.

Diabetes Mellitus

Disruption of carbohydrate, fat, and protein metabolism resulting from the hyposecretion or inaction of insulin. symptoms include the 3 "polys" 1. Polyuria (excessive urine output) 2. Polydipsia (intense thirst) 3. Polyphagia ( ravenous hunger) Also can present with three further signs; hyperglycemia (elevated blood glucose), glycosuria (glucose in the urine), and ketonuria (ketones in the urine)

Pancreas

Elongated, spongy gland located below and behind the stomach. Most of it is retroperitoneal. Primarily an exocrine digestive gland. Scattered throughout the pancreas are 1-2 million endocrine cell clusters known as *pancreatic islets (Islets of Langerhans)* Makw up less than 2% of the pancreatic tissue but the islets secrete hormones of vital importance.

Hyperparathyroidism

Excess PTH secretion usually caused by a parathyroidal tumor. Causes the bones to become soft, deformed, and fragile. Raises the blood levels of calcium and phosphate ions and promotes the formation of kidney stones.

Cushing Syndrome

Excess cortisol secretion owing to any of several causes. 1. ACTH hypersecretion by the pituitary, ACTH secreting tumors 2. hyperactivity of the adrenal cortex independently of ACTH. Cushing Syndrome disrupts carbohydrate and protein metabolism, leading to hyperglycemia, hypertension, muscular weakness and edema.

Hyposecretion

Inadequate hormone secretion. Can result from tumors or lesions that destroy an endocrine gland or interfere with its ability to receive signals from another cell.

Zona Reticularis

Innermost layer of the adrenal cortex, also secretes Glucorticoids and androgens.

Acromegaly

Hypersecretion of growth hormone in adults that causes thickening of bones and soft tissues with especially noticeable effects on the hands, feet, and face. When it begins in childhood or adolescence, before the epiphyseal plates of the long bones are depleted, GH Hypersecretion causes *Gigantism* and Hyposecretion causes *Pituitary Dwarfism*

The Liver

Involved in the production of at least five hormones. 1.Converts the cholecaliferol from the skin into *calcidiol* (next step in calcitriol synthesis) 2. Secretes a protein called *angiotensinogen*, which the kidneys and lungs and other organs convert into angiotensin II, a regulator of blood pressure 3. Secretes about 15% of the body's *erythropoietin (EPO)* a hormone that stimulates the red bone marrow to produce red blood cells (erythrocytes) 4. Secretes *Hepcidin* the principal hormone mechanism of iron homeostasis. Promotes intestinal absorption of dietary iron. 5. Secretes *insulin-like growth factor* a hormone that mediates the the action of growth hormone

The Skin

Keratinocytes of the epidermis convert a cholesterol-like steroid into cholecaliferol using UV radiation from the sun. (liver and kidneys further convert the cholecaliferol into a calcium regulating hormone calcitriol)

The Kidneys

Kidneys play endocrine roles in the production of three hormones; calcitriol, angiotensin II, and erythroprotein. Convert calcidiol into Calcitriol and completes the third step in calcium synthesis started by the skin and liver.

Estradiol

Main adrenal estrogen. Normally of minor importance to women of reproductive age because its quantity is small compared to estrogen of the ovaries. Adrenals come into play after menopause, when the ovaries cease function and only the adrenals secrete estrogen.

Endocrine Glands

Most familiar hormone sources are the organs traditionally recognized as endocrine glands, like the pituitary, thyroid, and adrenal glands.

Aldosterone

Most significant mineralcorticoid and is produced by only the zona glomerulosa. Is a part of the rital RAA hormone system that signals the kidneys to retain sodium in the body fluids and excrete potassium in the urine.

Luteinizing Hormone (LH) (gonadotropin)

One of the six anterior pituitary hormones. Also secreted by the gonadotropes. In females, it stimulates ovulation (release of an egg). In males, LH stimulates the testes to secrete testosterone.

Growth Hormone (GH) or Somatotropin

One of the six anterior pituitary hormones. GH is secreted by *somatropes*, the most numerous cells of the anterior pituitary. The general affect of GH is to stimulate mitosis and cellular differentiation, thus to promote tissue growth throughout the body.

Hypothalamo-Hypophyseal Tract

Nerve fibers that arise from certain cell bodies in the hypothalamus, pass down the stalk as a bundle known as the hypothalamo-hypophyseal tract, and end in the posterior lobe

Gap Junctions

One of the body's four principle avenues of communication from cell to cell. Gap junctions join single-unit smooth muscle, cardiac, epithelial and other cells to each other. Enable cells to pass nutrients, electrolytes, and signaling molecules directly from the cytoplasm of one cell to the cytoplasm of the next through pores in their plasma membrane

Follicle-Stimulating Hormone (FSH) (gonadotropin)

One of the six anterior pituitary hormones. Secreted by pituitary cells called gonadotropes. In the ovaries, it stimulates the secretion of ovarian sex hormones and the development of the bubblelike follicles that contain the eggs. In the Testes, it stimulate sperm production.

Parathyroid glands

Ovoid glands (usually 4 in #) partially embedded in the posterior surface of the thyroid. Secrete parathyroid hormone in response to hypocalcemia.

Thymus

Plays a role in three systems: Endocrine, Lymphatic, and immune. It is a bilobed gland in the mediastinum superior to the heart, behind the sternal manubrium. The thymus secretes several hormones like thymopoitetin, thymosin, and thymulin. The thymus is a maturation site for certain white blood cells called T cells.

Androgens

Primary adrenal sex steroids, adrenals also produce small amounts of estrogen. The major androgen is dehydropiandrosterone. It has little biological activity, but many tissues convert it into more potent forms of testosterone and dihydrotestosterone.

Neurotransmitters

Released by neurons, diffuse across a narrow synaptic cleft and bind to receptors on the surface of the next cell

The Alarm reaction

Response to stress mediated mainly by norepinephrine from the sympathetic nervous system and epinephrine from the adrenal medulla. These prepare the body to take action like fighting or escaping danger.

Endemic Goiter

Results from a deficiency in dietary iodine. Without iodine, the gland can't synthesize TH. Without TH, the pituitary gland receives no feedback and acts as if the thyroid were understimulated. Produces extra TSH which stimulates hypertrophy of the thyroid.

The Heart

Rising blood pressure stretches the heart wall and stimulates cardiac muscle in the atria to secrete two similar *natriuretic peptides*. These hormones increase sodium excretion and urine output and oppose the action of angiotensin II. Effects lower blood pressure

The Placenta

Secretes estrogen, progesterone, and other hormones that regulates pregnancy and stimulate development of the fetus and the mother's mammary glands.

Releasing Hormones

Stimulate the pituitary to release hormones of its own

Inhibiting Hormones

Suppress pituitary secretion

Adrenal cortex

Surrounds the adrenal medulla. Much thicker, and constitutes 80% to 90% of the gland. Has a yellowish color due to the high concentration of cholesterol and other lipids. Surrounds the medulla on all sides. Produces more that 25 hormones, collectively known as corticosteroids or corticoids.

Pituitary Gland [Hypophysis]

Suspended from the floor of the Hypothalamus by a stalk (Infundibulum) and housed in a depression of the sphenoid bone, the sella tursica. *composed of two structures, the anterior and posterior pituitary* these two structures have independent origins and separate functions

Stage of Exhaustion

The body's fat reserves can carry it through months of stress, but when fat is depleted, stress overwhelms homeostasis. The stage of exhaustion sets in, often marked by rapid decline and death. With its fat stores gone, the body now relies primarily on protein breakdown to meet its energy needs. This consists of a progressive wasting away of the muscles and weakening of the body. Death would frequently result from heart failure, kidney failure, or overwhelming infection.

Endocrine System

The glands, tissues, and cells that secrete hormones constitute this system

Adrenogenital Syndrome (AGS)

The hypersecretion of adrenal androgens, commonly accompanies Cushing Syndrome. In children, AGS causes the enlargement of the genitals (penis or clitoris) and the premature onset of puberty.

Adrenal Medulla

The inner core of the Adrenal gland, makes up 10% to 20% of the gland. Depending on blood flow, can either be gray to dark red. has a dual nature, acting as both an endocrine gland and a ganglion of the sympathetic nervous system.

Endocrinology

The study of this system and the diagnosis and treatments of its disorders

Congenital Hypothyroidism

Thyroid Hyposecretion present from birth. Severe or prolonged adult hypothyroidism can cause Myxedema. (both can be treated with oral thyroid hormone)

C (clear cells) *Parafollicular cells*

Thyroid gland contains nests of these cells at the periphery of the follicles. Respond to rising levels of blood calcium by secreting the hormone calcitonin.

Pheocromocytoma

Tumor of the adrenal medulla that secretes excessive amounts of epinephrine and norepinephrine

The stomach & small intestine

Various enteroendocrine cells which secrete at least 10 enteric hormones. One role of these hormones is to coordinate different regions and glands of the digestive system with each other.

Target organs / Target cells

When a hormone enters the bloodstream, it goes wherever the blood goes and there is no way to selectively send it to a specific organ . But, sometimes only target organs or target cells respond to it.

Stress Response

With whatever cause, the body reacts to stress in a fairly consistent way, called the stress response or general adaptation syndrome (GAS). The response typically involves elevated levels of epinephrine and cortisol

Isthmus

narrow bridge of tissue that joins the two wing like lobes of the thyroid gland

Thyroid follicles

sacs that make up the thyroid. Each sac is filled with a protein-rich colloid and lined by a simple cuboidal epithelium of *follicular cells*.

Involution

shrinkage of an organ, particularly after a certain age. Ex) Pineal Secretion peaks between the ages of 1-5 and declines after puberty.

Adrenal (suprarenal) glands

sit like a cap on the superior pole of each kidney. Forms by the merges of two fetal glands with different origins and functions.