Endocrinology

• Endocrine system and the nervous system play a vital role in

maintaining homeostasis

• Both system instruct different cells of the body to adjust and

integrate their responses to changes in the internal and

external environment of the body

Endocrine gland and their location

Hormone

Chemical substance produced by

One cell (endocrine) secreted into

and carried by the blood

To act on a distant target cell

Types of Hormones

• Amines or Amino acid derivatives

• Thyroid hormones and catecholamines

• Protein and Peptides

• FSH, LH, Prolactin, Growth hormone, Insulin,……etc

• Steroid

• Estrogen, Testosterone, Aldosterone, Cortisol

Mechanisms of hormone actions

Mechanism of hormone action: G protein coupled receptor

• Gs: stimulate Adenylyl cyclase and increase cAMP

• Gi: inhibit Adenylyl cyclase and decrease cAMP

G-protein couple Receptor

• phospholipase C

• Steroid Hormone

• Aldosterone

• Estrogen

• Progesterone

• Testosterone

• Vit D

• Thyroid Hormones

Regulation of hormone Secretion:

• Negative feedback system:

the product of the target

cell suppress hormone

production by the

endocrine gland

• Direct stimulation of the nervous system: sympathetic

system stimulation of the adrenal gland in the cases

of stress and fear

• The Hypothalamus:

• part of the diencephalon of the brain

• located in the ventral part of the brain

• Interphase (bridge) between the

nervous system and the Endocrine

system

• Posterior Pituitary Gland

(Neurohypophysis)

• Extension of the hypothalamus into

the pituitary

• Cell bodies of the hypothalamus

produce antidiuretic hormone (ADH)

and oxytocin, which are transported

down nerve to the posterior pituitary

gland, where they are stored.

• Stored hormones then released into

the bloodstream by nerve impulses

from the hypothalamus

• Anterior Pituitary Gland

(Adenohypophysis)

• The hypothalamic

produced releasing or

inhibiting factors

• Releasing factors

transported to the

anterior pituitary

through portal blood

vessels

• The hormones travel the

short distance down to

the anterior pituitary

and regulate its

hormones synthesis

and secretion

Hormones of the hypothalamus and anterior pituitary gland

Releasing Hormone

Hypothalamus

Abb

Tropic Hormone

Anterior Pituitary

Abb

Thyrotropin R.H

TRH

Thyroid Stimulating H

TSH

Gonadotropin R.H

GnRH

Follicle Stimulating H

Lutenizing Hormone

FSH

LH

Growth H.R.H

H.I.H

GHRH

GHIH

Growth Hormone

GH

Corticotropin R.H

CRH

Corticotropin

ACTH

PRL

Adren cortic tropic H

Prolactin I.H

PIH

Prolatin

Relation of hypothalamus and anterior pituitary

Hypothalamus

Releasing Factor

Target Organ Hormone

Target Organ

Anterior Pituitary

Tropic Hormone

The Hormones of Posterior Pituitary

• Antidiuretic hormone (vasopressin)

• Oxytocin

• Antidiuretic Hormone (ADH):

Volume Receptor

• Function to conserve water in

times of short supply or loss

Osmoreceptor

• Act on the kidneys to reabsorb

more water (makes the Urine

concentrated)

Vasopressin ADH

Osmolarity

Volume

• Stimulated by Dehydration and

decrease of blood volume

Normal

• ADH travels to the kidney to

stimulate water reabsorption by

renal tubules

• Causes vasoconstriction and

act to increase blood pressure

Water retention

• ADH deficiency causes diabetes insipidus

• Affected animals:

• produce large quantities of very dilute urine (polyuria)

• and drink large quantities of water (polydipsia).

• Oxytocin:

• Uterus:

• Causes contraction of the myometrium and that aid in the

delivery of the fetus and the placenta (parturition).

• Mammary glands: causes milk letdown

• Regulation of Oxytocin release:

• Stimulation of the teat or nipple by nursing or milking

causes oxytocin to be released into the bloodstream.

• causes contraction of the myoepithelial around the

alveoli and ducts of the mammary gland

• This squeezes milk down to be released

THE THYROID GLAND

• The thyroid gland

consists of two lobes

that are located on

either side of the larynx.

• composed of follicles,

where thyroid hormone

is produced

• Each follicle consists of

cuboidal cells

surrounding the colloid.

Chemistry of thyroid hormone formation

Thyroid Hormone:

. T3 (triiodothyronine) (main hormone)

. T4 (tetraiodothyronine, or thyroxine).

. They are named according to the

number of iodine hormone

Thyroid hormones synthesis and release.

• Iodide is taken up by a sodium-

iodide-symporter (NIS) in the

basal membrane and crosses

to the colloid through the

apical membrane

• T , and T synthesis catalyzed

3

4

by thyroid peroxidase (TPO)

within the thyroglobulin (TG) at

the apical membrane

• Endocytosis of TG by megalin

(TG receptor)

• T and T retrieved by

3

4

intracytoplasmic proteolysis

by lysosomes.

• Iodide of DIT and MIT

recovered by the action of the

enzyme deiodinase.

Regulation of thyroid hormones

. Pituitary TSH

. Cold

. Stress

Goiter (enlargement of the thyroid gland)

• Iodine deficiency

• Inhibition of iodine trapping

function of thyroid

hormone:

Regulate metabolism

• Calorigenic Effect:

Increase the metabolic

rate and causes

nutrients to be burned at

a faster rate which

allows an animal to

generate heat and

maintain a constant

internal body

• For Young and Growing

Animals it is necessary

for the development and

maturation of the central

nervous system,

muscles and bone

Calcium Regulation

• muscle contraction

• Neurotransmitter and hormone release

• blood clotting

• milk secretion

• formation and maintenance of the skeleton.

• Parathyroid Hormone

• Protein hormone produced by the parathyroid gland

• Function:

• prevent hypocalcemia (low blood calcium level) by

• Encourage the kidneys to retain calcium

• Enhance intestine absorption of calcium

• Withdraws calcium from the bones

• Calcitonin:

• Protein hormone produced by parafollicular cells of the thyroid

• Function: prevent hypercalcemia (high blood calcium level) by

facilitating calcium deposition in the bones.

• Vit D:

• Steroid hormone: stimulate calcium absorption from intestine

Vit D Synthesis

Vit D

Adrenal Gland

Zona Glomerulosa

Mineralocorticoid

Aldosterone

Zona Fasciculata

17a-hydroylase

Glucocorticoid

Cortisol

Cortisol

Androgen

Zona Reticularis

Catecohlamines

Functions of Aldosterone

• Affect the kidney functions to

Excrete

K and H

• Reabsorb Na+

• Secret K+ and H+

Retain Na

• Reabsorb water and

regulate body fluid

volume

• Regulate blood pressure

• Regulate acid-base balance

. Hypersecretion causes

• Hypertension

• Metabolic Alkalosis

• Anti-inflammatory effect of cortisol

• Help the body resist the effects of stress

Anti-inflammatory effect

Cortisol

Stabilize

Phospholipase A2

Leukotrienes

Prostaglandin

Thromboxanes

Inhibits allergic

reaction

. Arachdonic Acid

. Inhibits Histamine release from mast cells and allergic reaction

. Suppress immune response

T-Lymphocyte

Metabolic action of Cortisol

Steroid Diabetes

Regulation of cortisol

Adrenal Medulla

• hormones: epinephrine and

norepinephrine in the cases of

fear and stress

• Function

• increased heart rate and

cardiac output

• increased blood pressure

• dilated air passageways in

the lungs

• decreased gastrointestinal

function.

• Dilation of the pupil

• Increase blood and fatty acid

levels

Metabolic actions of catecholamine

• Stimulate glucose production

• Stimulate lipolysis and ketogenesis

• Inhibits insulin secretion

The Pancreas

• Exocrine Portion:

• secret digestive enzymes

• Endocrine Portion (islets of Langerhans): organized into clumps of

cells scattered throughout the pancreas

• Main endocrine cells

• Alpha cells: produce glucagon

• Beta cells: produce insulin

• Delta cells: produce somatostatin.

Regulation of insulin secretion

Insulin function:

• has hypoglycemic effect

• It acts to convert glucose,

amino acids, and fatty acids to

their storage forms.

• Overall effect decrease:

• glucose

• fatty acids

• ketoacids

• amino acids

Glucagon Function:

• Has a hyperglycemic

effect: (opposite to insulin).

• Overall effect:

• Increase glucose

• Increase fatty acids

• Increase ketoacids

• Increase glycerol

• Decrease amino acid

THE GONADS

• Testes:

• Testosterone: Produced by the interstitial cells of the seminiferous tubules

• Function:

• support male secondary sex characteristics, such as libido

• Stimulates male accessory sex glands

• Activate spermatogenesis

• stimulates muscle and bone growth

• The Ovaries

• Estrogens: produced by granulosa cells of and stimulated by FSH

• Function:

• stimulates follicular growth

• responsible for the physical and behavioral changes that prepare the

female for breeding and pregnancy

• Progesterone: Produced by the corpus luteum and stimulated by LH

• Functions:

• prepare the uterus to receive the fertilized ovum

• Support pregnancy

THE KIDNEYS

• Erythropoietin

• stimulates bone marrow to increase production of red blood cells.

• stimulated by a decrease of blood oxygen (hypoxia).

• Anemia might occur with serious kidney disease or kidney failure

THE STOMACH:

• Gastrin produced by G cells of the stomach

• act to stimulate HCL production.

• The Small intestine:

• Secretin:

• Stimulates pancreas to produce sodium bicarbonate neutralize the

acidic chyme from the stomach.

• Cholecystokinin (CCK):

• Stimulates the release of digestive enzymes from the pancreas

• act on the stomach to inhibit gastric motility and gland secretions

• stimulate the gallbladder contraction and release of bile

THE Pineal gland

• Produce melatonin

• play a role in the timing of seasonal estrous cycles in some species.