lecture 5 endocrine 1

8/9/2019 Lecture 5 Endocrine 1

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ENDORINE SYSTEM

The endocrine system is one of the two coordinatingand integrating systems of the body, the other being the

nervous system. It acts through chemical messengers

(hormones) carried in the circulation.

1. Endocrine Control Mechanisms

A.Nervous and Endocrine Systems Function Together

to Promote Homeostasis

nervous system endocrine system

neuroendocrine system


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B. Hormones

Definition

A hormone can be defined as a chemical substance

which is synthesized and secreted by a specific cell

type, is transported in the circulation and at very low

concentrations elicits a specific response in distant

target tissues

Differences of endocrine, paracrine and autocrinemechanisms

Classification

peptide hormones, e.g. growth hormone, insulin

steroid hormones, e.g. aldosterone, testosterone

amino acid derivatives, e.g. thyroxine and

adrenaline


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Hormone synthesis and secretion

synthesis of peptide hormones follow the sameway as protein synthesis

Precursors proteolytic cleavage peptidehormones or proteins stored in vesicles release upon appropriate stimulus into the

blood synthesis of steroid hormones

- Types of steroid hormones:1) Glucocorticoids

2) Mineralocorticoids

3) Androgens

4) estrogens

5) progestins


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A

B

C


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They all come from a common precursor

cholesterol

Once they are synthesized, they diffuse across

the cell membrane into the interstitial fluid then

into the blood so that their rate of release is

determined by their rate of synthesis.

synthesis and secretion of hormones from

tyrosine derivatives

Hormone transport and inactivation

Once released into the blood stream, lipid-solublehormones, e.g. thyroid and steroid hormones, are

carried bound to various plasma proteins.

Free form bound form = a dynamic equilibrium


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half-life of hormones: minutes to days

Inactivation may occur in the blood, in the liver,

or kidney, or in the target tissues.

Hormone actions

membrane permeability

activity of rate-limiting enzymes in reactionpathways

protein synthesis

gene activation leading to the transcription of

new mRNA species

Control of hormone secretion

negative feedback mechanism

positive feedback mechanism


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Mechanisms ofHormone Action

second messenger model

1) cyclic AMP

2) inositol triphosphate (IP3 ) and diacyglycerol

(DG)3) ions

gene expression model

The time of action for hormone using the twomodels


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The two second messengers: diacylglycerol (DAG) and

inositol triphosphate (IP3)


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2. The Important Endocrine Glands and Their Hormones

A. The pituitary hormones

anatomy of the pituitary gland and its relation to thehypothalamus

anterior lobe

intermediate lobe

posterior lobe

pituitary stalk

supraoptic neucleus

paraventricular nucleus

hypothalamus-pituitary portal system

short portal system


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Regulation of pituitary hormone secretion by thehypothalamus

secretion of posterior pituitary hormones: a typicalneuroendocrine regulatory mechanism

secretion of anterior pituitary hormones: a typical

endocrine regulatory mechanism

important releasing/inhibiting hormones producedin hypothalamus:

- Corticotropin-releasing hormone (CRH)

- Thyrotropin-releasing hormone (TRH)

- Gonadotropin-releasing hormone (GnRH)

- Growth-hormone-releasing hormone (GHRH)

- Prolactin-releasing hormone (PRH)

- Prolactin-inhibitory hormone (PIH)


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Posterior pituitary hormones

Antidiuretic hormone (ADH, vasppressin)

- chemistry: 9 amino acid peptide, produced

primarily by supraoptic nucleus and small

amount by paraventricular nucleus

- actions:

1) water retention by the kidney

qurine volume and o ECF

2) vasoconstriction (in large amounts)

- regulation/stimuli:

1) blood (or ECF) osmolality/osmoreceptors

2) blood volume


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3) others: alcohol, nicotine, barbiturates, etc.

- abnormality: diabetes insipidus Oxytocin

- chemistry: 9 amino acid peptide, produced

primarily by paraventricular nucleus and small

amount by supraoptic nucleus

- actions: 1) regulating breast milk release

2) contraction of pregnant uterus


suckling by a nursing infant

crying sounds from a baby

fear and stress inhibit release


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anterior pituitary hormones

Growth hormone

Prolactin

Thyroid-stimulating hormone

Adrenocorticotrophic hormone

Folicle-stimulating hormone

Luteinizing hormone

Growth hormone (GH)

- chemistry:191 peptide

- actions: see Fig.13-7


Growth hormone releasing hormone (GHRH)


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Growth hormone inhibitory hormone

(somatostadin)

other stimuli:

deep sleep

low blood glucose

stress

amino acids (arginine)

- abnormality:dwarfism

gigantism (acromegaly)


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lecture 5 endocrine 1

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