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 fr
Neurotransmitters
Released by neurons, diffuse across a narrow synaptic cleft and bind to receptors on the surface of the next cell
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
Hormones
Chemical messengers that are transported by the bloodstream and stimulate physiological responses in cells of another tissue or organ
Endocrine System
The glands, tissues, and cells that secrete hormones constitute this system
Endocrinology
The study of this system and the diagnosis and treatments of its disorders
Endocrine Glands
Most familiar hormone sources are the organs traditionally recognized as endocrine glands, like the pituitary, thyroid, and adrenal glands.
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
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.
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 s
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
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.
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
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
Releasing Hormones
Stimulate the pituitary to release hormones of its own
Inhibiting Hormones
Suppress pituitary secretion
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 stimu
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.
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 fu
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 regul
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 secret
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.
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.
Neuroendocrine reflexes
controls posterior pituitary, releases hormones in response to nerve signals.
Methods of GH-IGF
1. Protein Synthesis
2. Lipid Metabolism
3. Carbohydrate Metabolism
4. Electrolyte Balance
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 synt
Involution
shrinkage of an organ, particularly after a certain age. Ex) Pineal Secretion peaks between the ages of 1-5 and declines after puberty.
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
Thyroid Gland
Largest adult gland to have a purely endocrine function. Lies adjacent to the trachea and immediately below the larynx.
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
.
Thyroxine (T)
(T cells are critically important for immune defense)
Calorigenic effect
increases heat production
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.
Parathyroid glands
Ovoid glands (usually 4 in #) partially embedded in the posterior surface of the thyroid. Secrete parathyroid hormone in response to hypocalcemia.
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.
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.
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 kno
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 d
Zona Glomerulosa
Outermost layer of the adrenal cortex, thin, less developed in humans than any other mammal. Source of mineralcorticoids
Zona Fasciculata
Thick middle layer of the adrenal cortex constituting about 3/4 of cortex. Secretes Glucorticoids and androgens.
Zona Reticularis
Innermost layer of the adrenal cortex, also secretes Glucorticoids and androgens.
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.
Cortisol
known clinically as hydrocortisone
most potent glucocorticoid. Have anti-inflammatory effect. Help body adapt to stress and repair damaged tissues
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.
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 estr
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)
Gonads
Ovaries and Testes, are both endocrine and exocrine. The exocrine products being whole cells-egg and sperm-
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 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 a
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.
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
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.
Adipose Tissue
Fat cells secrete the hormone Leptin, which has long term effects on appetite-regulating centers of the hypothalamus.
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.
The Placenta
Secretes estrogen, progesterone, and other hormones that regulates pregnancy and stimulate development of the fetus and the mother's mammary glands.
Stress
Any situation that upsets homeostasis and threatens one's physical or emotional well being.
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
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.
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 provi
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 pr
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.
Diabetes Insipidus
Condition of chronic polyuria without glucose in the urine.
Hypersecretion
Excessive hormone release. Sometimes caused by tumors resulting in the overgrowth of functional endocrine tissue.
Pheocromocytoma
Tumor of the adrenal medulla that secretes excessive amounts of epinephrine and norepinephrine
Toxic Goiter
Graves Disease. Antibodies mimic effect of TSH on the thyroid, activating TSH receptors, and causing thyroid hypersecretion.
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 dep
Gigantism
Pituitary Dwarfism
Congenital Hypothyroidism
Thyroid Hyposecretion present from birth. Severe or prolonged adult hypothyroidism can cause Myxedema. (both can be treated with oral thyroid hormone)
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 thyroi
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)
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 t
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.
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 p