Hormones (Grp.2)

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HORMONES

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For Biochemistry ..

Transcript of Hormones (Grp.2)

Page 1: Hormones (Grp.2)

HORMONES

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Hormones

• Substance secreted by endocrine glands directly into the blood in trace amounts

• Has regulatory effect on the metabolism of specific organs or tissues.

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characteristics

• CHEMICAL NATURE OF HORMONES VARY WIDELY. – AMINO ACID-epinephrine and thyroxine– STEROID- testosterone, progesterone, cortisol– POLYPEPTIDE- ACTH, insulin, prolactin

• ALL CELLS IN THE BODY ARE EXPOSED TO THE HORMONE

• THE RESPONSE OF THE TARGET TISSUES IS INITIATED BY HORMONE RECEPTOR

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characteristics

• HOMEOSTATIC MECHANISM:– NEGATIVE FEEDBACK CONTROL• Commonly employed by the hypothalamic-

pituitary target gland system• Also accomplished through various metabolites

or substrate

– POSITIVE FEEDBACK CONTROL• Exemplified by estrogen and progesterone

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Classification of Hormones• Group I hormones:

-hormones that bind to intracellular receptors-lipolytic-with transport protein, thus have long plasma half-life

• Group II hormones:-hormones that bind to cell surface receptors-usually involves a second messenger-without a transport protein, thus have a short plasma half-life

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Mechanism of action of Hormones

Group I hormonesLipolytic molecule diffuse through

cell membrane and binds with intracellular receptor.

Hormone receptor complex, then binds to specific regions of DNA

and activates or inactivates specific genes and affects

transcription and production of specific proteins (enzymes) which

influence metabolic process.

Group II hormones• Hydrophilic molecules binds to a

receptor site on cell membrane and is regulated with the second messengers, the adenylate cyclase systems which generate a series of regions activating different enzymes.

• Another mechanism involves calcium; where the hormone enhances membrane permeability to calcium thereby increasing calflux and calcium can be deposited into mitochondrial and endoplasmic reticulums pools.

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Hypothalamic Hormones• All hormones of the hypothalamus are

regulatory hormones controlling the release of the tropic hormones from the adenohypophysis.

• This regulation is mediated by means of hypothalamic releasing hormones (RAH) and hypothalamic release-inhibiting hormones(RICH),all of which are small peptides

• Adenohypophyseal hormone regulated• Releasing hormones

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Hypothalamic Regulatory hormones

• Adenohypophyseal hormone regulated• Releasing hormonesCorticotropin-releasing hormone(CRH)Thyrotropin-releasing hormone(TRH)Luteinizing hormone(LH)Follicle Stimulating hormone(FSH)Somatotropin-releasing hormone(SRH)Prolactin-releasing hormone(PRH)Melanotropin-releasing hormone(MRH)

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Inhibitory hormones

• Somatostatin(SRIH)• Prolactin release-inhibiting hormone(PRIH)• Melanotropin release-inhibiting hormone

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Adenohypophyseal hormones

• Most hormones secreted by their adenohypophysis are tropic hormones,that is,their target organs are other endocrine glands.Because of this,the adenohypophysis is considered as the master endocrine gland.

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Somatotropin(SH)/Growth hormone(GH)

• Polypeptide with 191 amino acid residues secreted by acidophilic cells

• Functions:• Stimulates amino acids uptake by muscles and

increases protein • Raises plasma glucose• Promotes release of free fatty acids and

glycerol

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Thyrotropin (TSH)

• Glycoprotein that carries an alpha and a beta chain

• Secreted by basophilic cells• Functions: • Controlls iodine uptake of the thyroid gland

and the synthesis and release of thyroxin • Acts on adipocytes to stimulate lipolysis

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Adrenocorticotropin(ACTH)

• Polypeptide containing 39 amino acids of which only the first 24 constitute the active core.

• Secreted by the basophilic cells• Functions• Stimulate the hydrolysis of cholesteryl esters

stored in the glucocorticoid producing cells of the adrenal cortex

• Stimulates lipolysis in adipocytes

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Gonadotropins (LH and FSH)

• Glycoproteins composed of two subunits,alpha and beta,causes the metabolic action of the hormone,beta imparts target cell specificity by causing it to bind only to its specific receptor.

• Secreted by basophilic cells

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functions:• FSH causes the maturation of the ovarian

follicles in the female; stimulates spermatogenesis in the male.

• LH for stimulation of ovulation, corpus luteum formation and progesterone production in female; stimulates testosterone production in males.

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Prolactin (PRL)

• Also known as luleotrophic hormone (LTH).• Lactogenetic hormone is a simple protein• secreted by a acidophilic cellsFunctions• Stimulates milk production in mammary gland

by inducing the synthesis of two proteins that makes up synthetase, the enzyme responsible for the synthesis of lactose or milk sugar

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Melanotropin (MSH)

• Occurs as beta-MSH in humans.

Small polypeptide• Secreted by basophilic cells

Functions• In human Unknown• It may act on the brain and somehow involve in learning and

memory.• Administration large amount of this hormone causes a

deposition of pigment in the skin

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Calcium Regulation• Calcium– Required for muscle contraction, blood coagulation,

secretory processes, membrane integrity and plasma membrane transport, enzyme reactions, the release of hormones and neurotransmitters, and the intracellular action of a number of hormones.

– This involves three hormonesthat is acting on bones, kidney, and intestine.:

1. parathyroid hormone (PTH), 2. calcitriol 3. calcitonin (CT);

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Parathyroid Hormone (PTH)

• synthesized by the parathyroid gland.• single chain polypeptide with 84 amino acid

residues.• functions:– Increasing the rate of dissolution of bone which moves

calcium into the extracellular fluid (ECF)– Reducing the renal excretion of calcium thus increasing

calcium concentration In the ECF.– Increasing the efficiency of calcium absorption from the

synthesis of calcitriol.

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Calcitriol (Vitamin D)• Stimulated by PTH• Function– Stimulation of Osteoblasts– Increases GI absorption of dietary Ca++

– Stimulates kidney to reabsorb Ca2+ and P043

• Inadequate Vitamin D in diet & body causes osteomalacia and rickets

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Calcitonin

• secreted by the thyroid gland• stimulates Ca2+ deposition in the bones and

secretion by the kidneys, thus lowering blood Ca2+ levels.

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Pancreatic Hormones

• The endocrine portion of the pancreas consists of the islets of langerhans, which secrete at least four hormones: – insulin– glucagons– somatostatin– pancreatic polypeptide

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Insulin• polypeptide consisting of two chains, A and B linked by

two interchain disulfide bridges.• produced by beta cells• functions:– Inhibits gluconeogenes– Decreases the blood glucose level.– Inhibits lipolysis in the liver and adipose tissue.– Stimulates protein synthesis and retards protein degradation.– Supports the growth and replication of many cells of

epithelial origin.

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InsulinHypoglycemia

• oversecretion of insulin due to an exaggerated response of cells to a rise in glucose

Diabetes Mellitus (DM)• Characterized by chronic high

blood glucose levels (hyperglycemia)

• The three cardinal signs of DM are:– Polyuria– Polydipsia– Polyphagia

• Type I (insulin dependent or IDDM) is due to insufficient insulin secretion

• Type II (insulin independent or NIDDM) is due to lack of effect of insulin

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Glucagon

• single chained polypeptide consisting of 29 amino acids

• produced by alpha cells• function:– causes rapid mobilization of potential energy

sources into glucose by stimulating glycogenolysis and into acids by stimulating lipolysis.

– most potent gluconeogenic hormone

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Somatostatin

• Polypeptide with 14 amino acids• Function:– Inhibits the release of the other islet cell

hormones

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Pancreatic Polypeptide

• 36 amino acid peptide • Recently discovered pancreatic hormone• Function still unknown, but effects on hepatic

glycogen levels and gastrointestinal secretion have been suggested.

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Sex Hormones

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1. Testosterone- synthesize in the interstitial cells or cells of Leydig in the testis.

Functions: Produces the male sexual characteristic

2. Estrogen( estradiol, estrone, estriole) –synthesize in the ovarian follicles.Function: Induces the development of secondary sex characteristic of the female Prepares the uterus reception of fertilized ovum Stimulates enlargement of mammary glands

3. Progesterone- synthesized by the corpus luteum in the ovary - continues work of estrogens on uterus, stimulates further growth of mammary glands, inhibits the maturation of additional follicles and ovulation

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Placental Hormone

Human Chorionic Gonadotropin (HCG)-glycoprotein secreted by the placenta as early as 14 days after fertilization-maintains and enlarges the corpus luteum and stimulates its secretion of estrogens and progesterone