Hormones

Target cells

amino acid derivatives

peptide hormones

the largest category of hormones, include ADH and oxytocin. includes all of the hormones secreted by the hypothalamus, pituitary gland, kidneys, heart, gi tract, thymus, and pancreas.

 also includes growth hormone and prolactin

lipid derivative hormones

two classes:

steroid hormones - cholesterol, released by the reproductive organs and the adrenal glands. insoluble in water and are bound to specific transport proteins.

Eicosanoids - fatty acid based (20 carbon based), include prostaglandins, coordinate local cellular activity and affect enzymatic processes (blood clotting for example.)

Hormone action at Cell Membrane

- hormone acts as the first messenger and attatched to the membrane.

- with the help of the G protein, the first messenger activates the second messenger inside the cell

- second messenger (cAMP) activated adenylate cyclase and converts ATP.

-results in alterations in enzyme activity (phosphorilation)

- target cell responds with change in cells metabolic activity. 

Hormone action inside Cell

the hormone is able to diffuse through the cell (cells are soluble in fatty acids - steroids)

- hormone attatches to a receptor cell inside cell. 

- increase in ATP production (can result in target cell response)

- or alterations in structural proteins / enzyme activity inside the nucleus.

Hypothalamus

-highest level of endocrine control

- secretes regulatory hormones that control endocrine cells.

2 classes of regulatory hormones:

- releasing hormones: stimulate the production of one or more hormones in the anterior pituitary

- inhibiting hormones: prevent the synthesis and secretion of pituitary hormones.

- synthesizes ADH and oxytocin (released by posterior pituitary)

- contains autonomic n.s.centers that control the endocrine cells in the adrenal medula. 

The Pituitary Gland

- divided into two distinctive regions.

1. anterior pituitary

2. posterior pituitary

- secretes 9 different hormones

-hangs beneath the hypothalamus

Anterior Pituitary Gland

and the Hypophyseal Portal System

Hypophyseal Portal System:

a direct connection of capillaries that go from the hypothalamus into the anterior pit. portal systems ensure that all of the blood entering the portal vessel reaches certain target cells before entering the general blood circulation. 

The Anterior Pituitary:

- the regulatory hormones produces by the hypothalamus are transferred directly into the A.P. via the H.P.S.

- the rate is regulated through negative feedback loops. 

Hormones secreted by the A.P.

-There are 7 hormones secreted by the anterior pituitary.

-The first four regulate the production of hormones by other endocrine glands.

Thyroid Stimulating Hormone (TSH)

- target is the thyroid gland

- or thyrotropin, targets the thyroid gland and triggers the release of thyroid hormones.

1. first TRH (thyrotripin-releasing hormone) is released  from the hypothalamus stimulating...

2. TSH  which triggers the the production of thyroid hormone. 

-As circulating concentrations of thyroid hormone increase, the rate of TRH and TSH production delcine.

(negative feedback loop!!)

Adrenocorticotropic Hormone (ACTH)

- targets the adrenal cortext

- stimulates the release of steroid hormones by the adrenal cortex.

- specifically targets cells producing hormones called glucocorticoid, which effect glucose metabolism. 

- responds to the release of CRH (by the hypothalamus)

 A rise in glucocorticoid levels causes a decline in the production of ACTH and CRH.

(another negative feedback loop!!)

Follicle-stimulating hormone (FSH)

- targets the follicle cells of the ovaries

- promotes follicle development in females

- stimulates the secretion of estrogens

(steroid hormones produced by ovarian cells.)

- in males FSH stimulates sperm production.

- a peptide hormones called inhibin , released by the cells of the testes and ovaries, inhibits the release of FSH and GnRH through a negative feedback loop.

*hypogonadism: an abnomally low production of gonadotropins

- in children: will not undergo sexual maturation

- in adultes: inability to produce sperm or ova

Luteinizing Hormone (LH)

- targets the follicle cells of the ovaries and sustentacular cells of the testes

- induces ovulation

- promotes the secretion by the ovaries of estrogen and progestins which prepare the body for pregnancy.

- in males it produces androgens which produce testosterone

- GnRH is inhibited by estrogen, progestins and androgens.

Prolactin (PRL)

- interstitial cells of the testes, mammary glands

- stimulates mammary gland development

- PRH inhibits the production of prolactin

- created in the hypothalamus and sent out via the A.P.

Growth Hormone (GH)

- targets all cells

- stimulates cell growth and replication by accelerating the rate of protein synthesis

(skeletal cells and cartilage cells are particularly sensitive to GH)

- Indirect mechanism:

 1. liver cells respond to the presense of GH by synthesizing somatomedins which are peptide hormones that bind to receptor sites on a variety of cell membranes. 

2. somatomedin increase the rate at which amino acids are taken up and incorporated into new proteins.

( happens almost immediately after the presence of GH, important for after meal glucose absorption)

Posterior Pituitary Gland

- contains axons from two different groups of neurons located within the hypothalamus.

- one group manufactures ADH

-the other manufactures oxytocin

- the are transported via the infundibulum into the P.P. and sent out into the body.

Antidiuretic Hormone

- targets the kidneys

- respond to stimuli such as the concentration of electrolytes in the blood/ or a fall in blood volume or pressure.

- primary function is to decrease that amount of water lost in the urine.

- effects inclue the retention of water in the GI tract, reducing the concentration of electrolytes.

- also causes vasoconstriction, constriction of the peripheral blood vessels that helps increase blood pressure.

-ADH is inhibited by alcohol.

Oxytocin

- targets the uterus, mammary glands (females

sperm duct and prostate glands (males)

- stimulates smooth muscle contractions in the wall of the urterus during labor and delivery.

Hormones of the Thyroid and Parathyroid Gland

- thyroid hormones can easily pass through the cell membrane, and bind to mitochondria increasing atp activity. increase in cell metabolic activity.

- Thyroid Gland:

1. Follicular Epithelium -

- thyroxin and triidothyronine: targets most cells,

increase energy utilization, oxygen consumption, growth and development.

2. Calcitonin (C Cells) - targets the bone and kidneys,

decreases the calcium concentrations in the body fluids, increase excretion of calcium in kidneys.

3. inhibited by parathyroid hormone:

enhances absorption of calcium in the kidneys,

release of stored calcium from bones, stimulates calcitriol.

Adrenal  Cortex

- high presence of lipids.

- produces more then 2 dozen steroid hormones collectively called adrenocortical steroids or corticosteroids

- over or underproduction have extremely harmful effects on the body. individual cannot not live without it. 

- affect metabolism

Adrenal Cortex Hormones: 

Mineralocorticoids

- targets the kidneys

- increases the absorption of sodium ions and water by the kidneys: accelerates urinary loss of potassium ions. 

- retention of sodium ions is accompanied by the loss of potassium ions. 

Glucocorticoids

- targets most cells

- release of amino acids from skeletal muscles and lipids from adipose tissues

- promotes liver formation of glycogen and glucose

- promotes peripheral use of lipids

- anti-inflammatory effects.

Adrenal Cortex Hormones:

Androgens

- targets most cells

- uncertain significance under normal conditions. 

Adrenal Medulla Hormones

Epinephrine, Norepinepherin (E, NE)

- targets most cells

- increase cardiac activity, blood pressure, glycogen breakdown.

- release of lipids by adipose tissure

Pineal Gland

- contains neurons, glial cells, and secretory cells that synthesize the hormone melatonin.

- Melatonin: 

- establish day-night cycles

- antioxidant activity

Pancreas

- contains both exocrine and endocrine cells.

- most important cells secreted are the Alpha cells and Beta cells.

- regulate blood glucose levels

Alpha Cells and Glucagon

- alpha cells secrete glucagon

- If glucose levels drop:

1. alpha cells secrete glucagon which

a. increases the break down of glycogen to glucose

b. increases the breakdown of fats to fatty acids

c. increases the synthesis and release of glucose from the liver.

2. which in response increases the blood glucose concentration

- back to homeostatis. 

Beta Cells and Insulin

- beta cells secrete insulin

- If blood glucose leves are too high

1. beta cells are going to secrete insulin into the blood which will,

a. increase the rate of glucose transport into target cell.

b. increase the rate of glucose utilization and ATP generation

c. increase conversion of glucose to glycogen

d. increase amino acid absorption and protein synthesis

e. increase fat synthesis

2. which will lower the blood glucose concentration

- bring it back to homeostasis. 

Calcitriol

- the kidneys synthesize calcitriol

- calcitriol responds to parathyroid hormone.

- dependent on vitamin D3

- stimulaltes the absorption of calcium and phosphate ions across the intestinal lining of the GI tract.

Erythropoeitin (EPO)

- synthesized in the kidneys

- respond to decline in oxygen/blood levels in body tissues. 

- stimulate the production of new blood cells.

Renin

- releases by specialized kidney cells in response to a decline in blood volume, blood pressure, or both.

- once in the blood stream renin starts an enzymatic chain reaction called the renin-angiotensin system (creating angiotensin II which stimulates aldosterone and ADH)

- this combination restricts salt and water loss and increases thirst and blood pressure. 

The Heart and Hormones

- in the walls of the right atrium

- if volume increases too much, stimulates the realease of hormone atrial natruiretic peptide (ANP)

- oppoes the effects of angiotensin II: promotes the loss of water and sodium loss in the kidneys.

The Thymus

- produces hormones called thymosins

- plays a key role in the development of the immune system and maintenance of defenses.

Hormones of the Reproductive System

1. Testes:

- interstitial cells: androgens - most cells, support functional maturation of sperm, proten synthesis in skeletal muscles, associated behaviors, and male secondary sex characteristics

- subtentacular cells: inhibin - anterior pit., inhibits the secretion of FSH

2. Ovaries:

- follicular cells: estrogen - most cells, support follicle maturation, associated behaviors, secondary characteristics

- corpus luteum: inhibin - see above

: progestins - uterus, mam glands

Stress Response and Hormones

1. Alarm Phase: immediate response to stress, under the direction of the sympathetic n.s..

- energy reserves are mobilized and body prepares for physical activity, increases energy use by all cells, changes in circulation, heart and respiratory reats increase

* epinepherine is the primary hormone.

2. Resistance Phase: if stress lasts longer than a few hours. long term metabolic adjustments.

- elevation of blood glucose concentration,

conservation of glucose, mobilization of remaing energy reserves

* glucocorticoids are the primary hormone.

3. Exhaustion Phase: homeostatic regulation breaksdown, collapse of vital systems.

- failure of electrolyte balance, exhaustion of lipid reserves, inability to produce glucocorticoids, functional damage to vital organs. 

Endocrine Disorders :Acromegly/Dwarfism/Gigantism

1. Acromegly : reslts from the over production of growth hormone after puberty, when most of the epiphyseal cartilages have fused. Bone shapes change, and cartilaginous ares of the skeleton enlarg.

2. Dwarfism : a growth hormone deficiency is sometimes the cause of dwarfism.

3. Gigantism : excess of prepubertal growth hormone

Mitogens (IGF's)

- Insulin-like growth factor 1  mediates the major growth-promoting effect of GH as a pancreatic agent at growth plates in the skeletal system.

Protein Kinase and Phosphorylation

G Proteins

- stimulates the production of cAMP from ATP. This is accomplished by direct stimulation of the membrane-associated enzyme adenylate cyclase. cAMP acts as a second messenger that goes on to interact with and activate protein kinase A (PKA). PKA can then phosphorylate a myriad of downstream targets.

- activating or deactivating cells and changing the cells metabolism