Chapter 16 The Endocrine System/Adrenal glands

Four mechanisms that regulate aldosterone secretion

Renin angiotensin aldosterone mechanism Plasma concentration of potassium ACTH (adrenocorticotropic hormone) Atrial natriuretic peptide (ANP)

Zona glomerulosa

The cell clusters forming this superficial layer produce mineralocorticoids hormones such as aldosterone that help control the balance of minerals and water in the blood

Zona reticularis

The cell of this innermost layer next to the adrenal medulla have a netlike arrangement. They mainly produce small amounts of adrenal sex hormones or gonadocorticoids.

Zona fasciculata

The cells of this middle layer arranged in more or less linear cords mainly produce the metabolic hormones called glucocorticoids such as cortisol

Actions

The dramatically higher output of glucocorticoids during stress is essential for negotiating the crisis. Cortisol provokes a marked rise in blood levels of glucose, fatty acids, and amino acids. Cortisol's prime metabolic effect is to provoke gluconeogenesis = the formation of glucose from fats and proteins. In order to save glucose for the brain, cortisol mobilizes fatty acids from adipose tissue and encourages their increased use for energy. Continued>>>>>>

Aldosterone

The most potent mineralocorticoid. Accounts for more than 95% of the mineralocorticoids produced and is essential for life; "salt-retaining hormone" which promotes the retention of Na+ by the kidneys. na+ retention promotes water retention, which promotes a higher blood volume and pressure

ACTH

Under normal circumstances ACTH released by the anterior pituitary has little or no effect on aldosterone release. However when a person is severely stressed the hypothalamus secretes more corticotropin releasing hormone (CRH) and the resulting rise in ACTH blood levels steps up the rate of aldosterone secretion to a small extent. The resulting increase in blood volume and blood pressure helps deliver nutrients and respiratory gases during the stressful period.

Regulation of Secretion continued>>>>>

Various stressors (for ex. hemorrhage, infection, or physical or emotional trauma) interrupt the normal cortisol rhythm. Higher CNS centers override the inhibitory effects of elevated cortisol levels and trigger CRH release. The resulting increase in ACTH blood levels causes an outpouring of cortisol from the adrenal cortex.

Addison's disease chaaracteristic

bronzing of the skin; occurs because the lack of negative feedback by corticosteroids increases ACTH release by the anterior pituitary; high levels ACTH triggers melanin production in melanocytes

The adrenal cortex synthesizes well over two dozen steroid hormones, collectively called

corticosteroids

Aldosteronism

hypersecretion of aldosterone typically results from adrenal tumors. Two major sets of problems result: 1. hypertension and edema due to excessive Na+ and water retention 2. accelerated excretion of potassium ions. If K+ loss is extreme, neurons become nonresponsive, leading to muscle weakness and eventually paralysis

Glucocorticoids

influence the energy metabolism of most body cells and help us resist stressors; help the body adapt to intermittent food intake by keeping blood glucose levels fairly constant and help maintain blood pressure

Renin angiotensin aldosterone mechanism

influences both blood volume and blood pressure by regulating the release of aldosterone and therefore Na+ and water reabsorption by the kidneys

Mineralocorticoids

is to regulate the electrolyte (mineral salt) concentrations in extracellular fluids, particularly of Na+ and K+; promote reabsorption of Na+ and excretion of K+ in kidneys; akdisteribe

renal =

kidney

The large lipid laden cortical cells are arranged in ______________ layers or ___________________

layers or zones; from outside to inside they are: Zona glomerulosa Zona fasciculata Zona reticularis

ad =

near

Cushing's syndrome characterized by

persistent elevated blood glucose levels (steroid diabetes) dramatic losses in muscle and bone protein and water and salt retention leading to hypertension and edema.

In some instances aldosterone can alter the acid base balance of the blood by increasing H+ excretion. Aldosterone also enhances Na+ reabsorption from ________________, _________________ and __________________

perspiration, saliva and gastric juice

natriuretic =

producing salty urine

Glucocorticoid drugs can control symptoms of many chronic inflammatory disorders such as ___________________________and __________________. However these potent drugs are a double edged sword because they also cause the undesirable effects of _________________ of these hormones.

rheumatoid arthritis allergic responses excessive levels

Gonadocorticoids

secreted by the adrenal cortex are weak androgens or male sex hormones such as androstenedione and dehydroepiandrosterone (DHEA). Most are converted in tissue cells to more potent male hormones such as testosterone, and some are converted to estrogens. The amount of Gonadocorticoids produced by the adrenal cortex is insignificant compared with the amounts made by the gonads during late puberty and adulthood.

Adrenal Medulla

secretes epinephrine and norepinephrine

Corticosteroids

steroid hormones released by the adrenal cortex

The so called cushingoid signs

swollen "moon" face, redistribution of fat to the abdomen and the posterior neck (causing a buffalo hump), easy bruising and poor wound healing. Eventually muscles weaken and spontaneous fractures force the person to become bedridden. The only treatment is to remove the cause---be it surgically removing the tumor or discontinuing the drug.

Addison's disease

the major hyposecretory disorder of the adrenal cortex, usually involves deficits in both glucocorticoids and mineralocorticoids. Affected individuals tend to lose weight; plasma glucose and sodium levels drop and potassium levels rise. Severe dehydration and hypotension are common. Corticosteroid replacement therapy is the usual treatment.

Cushing's syndrome

the pathology of glucocorticoid excess may be caused by an ACTH releasing pituitary tumor; by ACTH releasing malignancy of the lungs, pancreas, or kidneys; or by a tumor of the adrenal cortex. However it most often results from the clinical administration of glucocorticoid drugs.

Steroid hormones are not stored in cells. their rate of release depends on

their rate of synthesis

Gonadocorticoids

Adrenal Sex Hormones

Also called the suprarenal glands

Adrenal glands

Glucocorticoid hormones include

Cortisol (hydrocortisone) Cortisone Corticosterone But only cortisol is secreted in significant amounts in humans; act on target cells by modifying gene activity

Regulation of Secretion continued>>>>>

Cortisol secretory bursts, driven by patterns of eating and activity occur in a definite pattern throughout the day and night. Cortisol blood levels peak shortly before we rise in the morning. The lowest levels occur in the evening just before and shortly after we fall asleep. Continued>>>>

The spherical Medullary Chromaffin Cells

Crowd around porous blood filled capillaries; are modified postganglionic sympathetic neurons. The cells synthesize the catecholamines epinephrine and norepinephrine (NE) via a molecular sequence from tyrosine to dopamine to NE to epinephrine

Plasma concentration of potassium

Fluctuating blood levels of K+ directly influence the zona glomerulosa cells in the adrenal cortex. Increased K+ stimulates aldosterone release whereas decreased K+ inhibits it.

Adrenal glands

Hormone producing glands located superior to the kidneys; each consists of medulla and cortex areas; pyramid shaped organs perched atop the kidneys where they are enclosed in a fibrous capsule and cushion of fat. Also called the suprarenal glands

Adrenal medulla

Inner-more like a knot of nervous tissue than a gland, is part of the sympathetic nervous system; secretes epinephrine and norepinephrine

Regulation of Secretion

Negative feedback regulates glucocorticoid secretion. Cortisol release is promoted by ACTH. ACTH release is triggered in turn by the hypothalamic releasing hormone CRH. Rising cortisol levels feed back to act on both the hypothalamus and the anterior pituitary preventing CRH release and shutting off ACTH and cortisol secretion. Continued>>>>>

Under cortisol's influence proteins are broken down to provide building blocks for repair or to make enzymes for metabolic processes. Cortisol's second critical function is to enhance the sympathetic nervous system's vasoconstrictive effects, helping to maintain blood pressure. continued>>>>>>>

Note that ideal amounts of glucocorticoids promote normal function but too much cortisol exerts significant anti inflammatory and anti immune effects. Excessive levels of glucocorticoids: 1. depress cartilage and bone formation 2. Inhibit inflammation by decreasing the release of inflammatory chemicals 3. Depress the immune system Disrupt normal cardiovascular, neural and gastrointestinal function continued>>>>>>

Adrenal cortex

Outer-encapsulating the medulla and forming the bulk of the gland is glandular tissue derived from embryonic mesoderm; secretes cortisol, aldosterone, and sex hormones

ACTH

adrenocorticotropic hormone

Hypersecretion of Gonadocorticoids causes

adrenogenital syndrome (masculinization); in adult males elevated levels may not be noticeable but in prepubertal males and in females the results can be dramatic; in boys the reproductive organs mature and secondary sex characteristics appear early and the sex drive emerges with a vengeance; females develop a beard and a masculine distribution of body hair and the clitoris grows to resemble a small penis

Four mechanisms regulate ___________________________ but two of them the ______________________ mechanism and ________________concentrations of ______________ are by far the most important

aldosterone secretion renin angiotensin aldosterone plasma potassium

Adrenal sex hormones exact role still in question but they contribute to

axillary and pubic hair development. In adult women adrenal androgens are thought to contribute to the sex drive and they largely account for the estrogens produced after menopause when ovarian estrogens are no longer produced

Aldosterone reduces excretion of Na+ from the body. Its primary target is the kidney tubules where it:

1. Stimulates Na+ reabsorption (causing increased blood volume and blood pressure because water follows Na+) 2. Causes K+ secretion into the tubules for elimination from the body

Steps of the renin angiotensin aldosterone mechanism

1. when blood pressure (or blood volume falls specialized cells of the juxtaglomerular complex in the kidneys are excited 2. these cells respond by releasing renin into the blood 3. renin splits off part of the plasma protein angiotensinogen triggering an enzymatic cascade that forms angiotensin II. which stimulates the glomerulosa cells to release aldosterone **See pg 624

Each adrenal gland is structurally and functionally ________________________

2 endocrine glands adrenal medulla and adrenal cortex

ANP - Atrial natriuretic peptide

a hormone secreted by the heart when blood pressure rises fine tunes blood pressure and sodium water balance of the body. One of its major effects is to inhibit the renin angiotensin aldosterone mechanism. It blocks renin and aldosterone secretion and inhibits other angiotensin induced mechanisms that enhance water and Na+ reabsorption. Consequently ANP's overall influence is to decrease blood pressure by allowing Na+ (and water) to flow out of the body in urine (natriuretic = producing salty urine)

supra =

above