2/21/2019 1 ENDOCRINOLOGY - PowerPoint Presentation

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ENDOCRINOLOGY

Lec. 2

Dr. Ali al-bayati

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Introduction

Endocrinology is the study of hormonally regulated conditionsEndocrinology involves hormones from:

Hypothalamus

Pituitary

Thyroid

Pancreas

Adrenals

Kidneys

Gonads

Smaller glands (Thymus, Pineal etc)

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The Players

Other endocrine organs

endothelial vascular cells

adipocytes

heart

bone

liver

kidney

????

Hypothalamus

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Definitions

Endocrinology-

study of the biosynthesis, storage, chemistry, and physiological function

and abnormalities of hormones.

The term hormone

(hormao G = to excite)

was first used by

William M. Bayliss

and

Ernest

H. Starling, who showed that a chemical substance (secretin) from the intestine could stimulate the action of a pancreatic secretion. These substances were then called as “chemical messengers”Went and Thiemann (1937) defined a hormone as “a substance which, produced in any one part of an organism, is transferred to another part and there influences a specific physiological process.”

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The endocrine

system: is a series of glands that produce and secrete hormones that the body uses for a wide range of functions. These control many different

functions

, including: Respiration, Metabolism, Reproduction, Sensory perception, Movement, Sexual development and Growth.

Characteristics of the Endocrine System;

Composed

of glands that secrete hormones into the circulatory system.

Hormones

are secreted in minute amounts into the interstitial space.

Hormones enter

the circulatory system and arrive at specific target tissues.

Functions are similar to the nervous system. Differences;Amplitude-modulated vs. Frequency-modulatedResponse of target tissue to hormones is usually slower and of longer duration than that to neurons.

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Based on their site on action, the hormones are of two types: local and general.

The

local hormones

,

have

specific local effects,

example;

acetylcholine, secretin, cholecystokinin etc.

The general hormones,

secreted

by specific endocrine glands and are transported in the blood to cause physiologic actions at points remote from their place of origin. A few of the general hormones affect almost all cells of the body,

e.g., growth hormones (GH) and thyroid hormones ; whereas other general hormones, however, affect specific tissues far more than other tissues, e.g., adrenocorticotropic (a hormone secreted from adenohyprophysis and stimulating the adrenal cortex) and ovarian hormones (affecting the uterine endometrium).

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Functions of hormones

Regulatory or homeostatic function.

Permissive function

Integrative

function.

Morphogenetic

function.

Classes of Hormones

Hormones are classified by various criteria:

By Proximity of their site of synthesis to their site of action,

By their chemical structure,

By their degree of solubility in aqueous medium

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3 classes of hormones based on proximity of site of Synthesis to Site of Action:

Autocrine Hormones

: those that act on the same cells that synthesize them;

Paracrine Hormones

: those that are synthesized very close to their site of action;

Endocrine Hormones

:

those that are synthesized by endocrine glands and transported in the blood to target cells that contain the appropriate receptors;

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Four classes of hormones based on chemical structure:

Peptides or Protein hormones:

Amino acid derivatives:•

Adrenaline

, Catecholamines,

Thyroid

Hormones

Fatty

acid derivatives:

Eicosanoids, {

prostaglandins, prostacyclins, leukotrienes and

thromboxane}, In contrast to hormones, prostaglandins usually act locally, affecting only adjacent cells or the very cell that secreted it.rapidly inactivated by being metabolized, and are typically active for only a few seconds Steroid hormones:; Example: Estradiol, Testosterone, Cortisol.

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Two classes of hormones based on solubility in aqueous medium;

Hydrophilic Hormones (Lipophobic Hormones);

Lipophilic Hormones (Hydrophobic Hormones);

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Hormones’ Receptors and Target Cells

Target tissue:-

For a given hormone is a tissue contains specific receptor proteins that bind the hormone and initiate a cellular response

Receptors :-

Are specific molecules within the cell membrane , cytoplasm or nucleus of the target cell that are necessary for recognition and binding of extra cellular messenger (hormone)

Target tissue must have two characters in

responce

to the hormone

1-

The tissue should recognize the hormone by a receptor.

2-

The tissue should have intracellular capacity of translating the massage of the hormone to biochemical event or reaction.

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Regulation of target tissue activity

.

The hormones regulate the activities of their target tissues in two ways:-

1-

By regulating the activities of

already present proteins (enzymes)

in the cells, this takes place rapidly within minutes.

2-

By regulating the

synthesis or degradation of proteins,

taking place more slowly requiring hours or days

.

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Hormones as a signal

Hormonal signaling involves the following:

1-

Biosynthesis

of a particular hormone in a particular tissue.

2-

Storage and

secretion

of the hormone.

3-

Transport of the hormone to the target cell(s).

4-

Recognition of the hormone by an associated cell membrane

or

intracellular

receptor

protein.

5-

Relay and amplification of the received hormonal signal via a

signal transduction

process: This then leads to a cellular response.

6-

Degradation of the hormone.

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Interactions with receptors

Hormone-receptor complex concentrations

are effectively determined by three factors:

1-

The number of

hormone

molecules available for complex formation.

2-

The number of

receptor

molecules available for complex formation.

3-

The

binding affinity

between hormone and receptor

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Characteristics of Receptors

Hormone specificity

Receptors can bind one hormone only. Agonists and antagonists can also bind the receptors. Many neurohormonal ligands and hormones can bind several different receptors usually within the same molecular family of receptors (i.e. epinephrine binds α1, α2, β1, and β2 adrenergic receptors).

Affinity:

refers

to the concentration of hormones required to activate sufficient receptors to trigger a biological effect

.

Receptors number

:

Tissue

Specificity: The presence of the appropriate type of receptors in the respective tissue is essential for proper hormone function.

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Two main type of hormone receptor

pathways

Pathways Involving Intracellular Hormone Receptors (Group I)

Involving

Cell Membrane Hormone Receptors (Group II)

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Intracellular Hormone

Receptors

Group I

Hormones that bind to this type of receptor must be able to cross the cell membrane

.

Steroid hormones are derived from cholesterol and therefore can readily diffuse through the lipid bilayer

Thyroid hormones, which contain benzene rings studded with iodine, are also lipid-soluble and can enter the cell

.

binding generates a hormone-receptor

complex

that moves toward the chromatin in the cell nucleus and binds to a particular segment of the cell’s DNA.

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Intracellular Hormone

Receptors Group I

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Structure of Intracellular Receptors

When hormone binds to receptor, a characteristic series of events occurs

:

Receptor

activation is the term used to describe conformational changes in the receptor induced by binding hormone. The major consequence of activation is that the receptor becomes competent to bind DNA.

Activated

receptors bind to hormone response elements, which are short specific sequences of DNA which are located in promoters of hormone-responsive genes.

Transcription

from those genes to which the receptor is bound is affected. Most commonly, receptor binding stimulates transcription.

The hormone-receptor complex thus functions as a transcription factor.

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Thank you