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1st Lec on Endo Physiology by Dr Roomi

Apr 06, 2018

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Mudassar Roomi
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    ENDOCRINE PHYSIOLOGY

    BY

    DR. MUDASSAR ALI ROOMI (MBBS, M. Phil.)

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    INTERCELLULAR COMMUNICATION

    Cell Target Cell

    Cell

    CellTarget Cell

    Target CellNeuron

    Hormone

    Hormone

    Hormone Hormone

    Hormone

    Hormone

    Hormone

    Endocrine

    Paracrine

    Autocrine

    Blood

    Neuroendocrine

    Blood

    Interstitial Fluid

    Interstitial Fluid

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    Endocrine hormones are released by glands or

    specialized cells into the circulating blood and

    influence the function of cells at another

    location in the body.

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    Chemical Structure of hormones

    There are three general classes of hormones:

    1. Proteins and polypeptides2. Steroids

    3. Derivatives of the amino acid tyrosine

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    Steroid hormones

    secreted by the adrenal

    cortex (cortisoland

    aldosterone), the

    ovaries (estrogen andprogesterone), the

    testes (testosterone),

    and the placenta

    (estrogen andprogesterone).

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    Adrenal Cortex

    Testes

    Ovaries

    Corpus Luteum

    Placenta

    Kidney

    Cortisol, Aldosterone,

    Androgens

    Testosterone

    Estrogens, Progesterone

    Estrogens, Progesterone

    Estrogens, Progesterone

    1,25-Dihydroxycholecalciferol

    GLAND/TISSUE HORMONES

    STEROID HORMONES

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    Proteins and polypeptides: including

    hormones secreted by the anterior and

    posterior pituitary gland, the pancreas (insulin

    and glucagon), the parathyroid gland

    (parathyroid hormone), and many others.

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    Hypothalamus

    Anterior pituitary

    Posterior pituitary

    Thyroid

    Pancreas

    Liver

    Parathyroid

    TRH, GnRH, CRH

    GHRH, Somatostatin,

    ACTH, TSH, FSH, LH,

    PRL, GH

    Oxytocin, ADH

    Calcitonin

    Insulin,Glucagon,

    Somatostatin

    Somatomedin C (IGF-1)

    PTH

    Placenta

    Kidney

    Heart

    G.I. tract

    Adipocyte

    Adrenal medulla

    HCG, HCS or HPL

    Renin

    ANP

    Gastrin, CCK,

    Secretin, GIP,

    Somatostatin

    Leptin

    Norepinephrine,epinephrine

    Gland/Tissue Hormones Gland/Tissue Hormones

    PEPTIDE & PROTEIN HORMONES

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    Derivatives of the amino acid tyrosine:

    secretedby the thyroid (thyroxine and

    triiodothyronine) and the adrenal medulla

    (epinephrine and norepinephrine).

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    Tyrosine

    L-Dopa

    Dopamine

    tyrosinehydroxylase

    Norepinephrine

    dopa decarboxylase

    dopamine-

    hydroxylase

    Dopaminergic

    Neurons

    Thyroid Hormones

    Adrenergic

    Neurons

    Epinephrine

    phenylethanolamine-

    N-methyltransferase

    Thyroid GlandAdrenal Glands

    Synthesis of Amine Hormones

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    SYNTHESIS & SECRETION OF PEPTIDE HORMONES

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    Types of Receptors

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    Hormone receptors

    The locations for the different types of hormonereceptors are generally the following:

    1. In or on the surface of the cell membrane. Themembrane receptors are specific mostly for the

    protein, peptide, and catecholamine hormones.2. In the cell cytoplasm. The primary receptors forthe

    different steroid hormones are found mainly in thecytoplasm.

    3. In the cell nucleus. The receptors for the thyroidhormones are found in the nucleus and are believed tobe located in direct association with one or more of thechromosomes.

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    down-regulation of the receptors

    can occur as a result of:

    (1)inactivation of some of the receptor molecules,

    (2) inactivation of some of the intracellular protein signaling

    molecules,(3) temporary sequestration of the receptor to the inside of

    the cell, away from the site of action of hormones thatinteract with cell membrane receptors,

    (4) destruction of the receptors by lysosomes after they are

    internalized, or(5) decreased production of the receptors. In each case,

    receptor down-regulation decreases the target tissuesresponsiveness to the hormone.

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    up-regulation of receptors

    Some hormones cause up-regulation of receptors andintracellular signaling proteins by:

    1. stimulating greater than normal formation of receptor

    2. or intracellular signaling molecules by the protein-manufacturing machinery of the target cell,

    3. or greater availability of the receptor for interactionwith the hormone.

    When up-regulation occurs, the target tissue becomesprogressively more sensitive to the stimulating effectsof the hormone.

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    Cell surface receptors

    Most are embedded inplasma membrane

    Detect signals fromextracellularenvironment

    Three major types are :1. Ion channel linked

    receptors (ligandgated and voltagegated)

    2. G protein linkedreceptors

    3. Enzyme linkedreceptors

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    Ligand-gated ion channels:

    protein pores that open or close in

    response to a chemical signal. Binding changes proteins

    shape to allow or block ionflow, such as Na+ or Ca2+.

    Ion flow changes theconcentration inside thecell.

    e.g Ach gated channels in

    the sk. Muscles.

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    G-Protein coupled receptors

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    Cyclic Adenosine Monophosphate (cAMP) Second

    Messenger Mechanism

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    Cell Membrane Phospholipid Second Messenger

    System

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    JAK-STAT PATHWAY

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    1. The steroid hormone diffuses across

    the cell membrane and enters the

    cytoplasm of the cell, where it binds

    with a specific receptor protein.

    2. The combined receptor proteinhormone then diffuses into or is

    transported into the nucleus.

    3. The combination binds at specific

    points on the DNA strands in the

    chromosomes, which activates the

    transcription process of specific

    genes to form mRNA.

    4. The mRNA diffuses into the cytoplasm,

    where it promotes the translation

    process at the ribosomes to form

    new proteins.

    Steroid & Thyroid Hormones - Mechanism of Action

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    SUMMARY

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    SUMMARY