Introduction To Endocrinology

Dr Hameed Batainah

Department of Physiology

Faculty of Medicine

Jordan university of Science and Technology

Outlines : Coordination of body functions by chemical

messengers . chemical structure and synthesis of Hormones. Endocrine Glands, Hormones , and their functions

and structure . Hormone secretion ,transport and clearance from

the blood . Feedback control of hormone secretion . Transport of Hormones in the blood . Clearance of hormones from the blood . Measurement of Hormone concentrations in the

blood.

Types of glands.

Exocrine glands have channels or ducts, which secrete chemicals such as saliva or sweat.

Endocrine glands don’t have ducts. They secrete hormones directly into your bloodstream

Coordination of body functions by chemical messengers .

The multiple activities of the cells, tissues ,and organs of the body are coordinated by the interplay of several types of chemical messenger systems:

Neurotransmitters are released by axon terminals of neurons into the synaptic junctions and act locally to control nerve cell functions .

Endocrine hormones are released by glands or specialized cells into the circulating blood and influence the function of cells at another location .

Neuroendocrine hormones are secreted by neurons into the circulating blood and influence the function of cells at another location in the body .

Paracrines are secreted by cells into the extracellular fluid and effect neighboring cells of different type .

Autocrines are secreted by cells into the extracellular fluid and affect the function of the same cells that produced them .

Cytokines are peptides secreted by cells into the extracellular fluid and can function as autocrines ,paracrine ,or endocrine hormones (interleukins,and lymphokines) .

Chemical structure of hormones

There are three general classes of hormones :

1- protein and polypeptide hormones ,including hormones secreted by anterior and posterior pituitary gland ,the pancreas (insulin and glucagons), parathyroid gland (parathyroid hormone ) .

2-Steroid hormones secreted by the adrenal cortex (cortisol and aldosterone), the ovaries (estrogen and progesterone ), the tests (testosterone ), and the placenta (estrogen and progesterone ).

3- Derivative of the amino acid tyrosine hormones ,secreted by thyroid (thyroxin and triiodothyronine ) and the adrenal medullae epinephrine and norepinephrine ).

Endocrine Glands, Hormones , and their functions and : structure

Gland Gland tissue tissue

Hormones Hormones Major factorsMajor factors Chemical Chemical structure structure

HypothalamuHypothalamus s

Posterior Posterior

pituitarypituitary

-- Thyrotropin Thyrotropin ––releasing hormone TRHreleasing hormone TRH

- - Corticotrophin-Corticotrophin-releasing hormone CRHreleasing hormone CRH

- Growth hormone -- Growth hormone -releasing hormone releasing hormone (GHRH).(GHRH).

- Growth hormone - Growth hormone inhibitory hormone inhibitory hormone (GHIH).(GHIH).

- Gonadotropin-- Gonadotropin-releasing hormone releasing hormone (GnRH).(GnRH).

- Dopamine or - Dopamine or Prolactin-inhibiting Prolactin-inhibiting factor (PIF).factor (PIF).

-Antidiuretic hormone Antidiuretic hormone (ADH)(ADH)

- Oxytocin - Oxytocin

- Stimulates secretion of TSH - Stimulates secretion of TSH and Prolactin and Prolactin

- Causes release of ACTH.- Causes release of ACTH.- Causes release of growth Causes release of growth hormone .hormone .

- Inhibits release of growth Inhibits release of growth hormone .hormone .

- Causes release of LH and Causes release of LH and FSHFSH

- Inhabits release of Prolactin - Inhabits release of Prolactin

- Increase water - Increase water reabsorption by the kidneys reabsorption by the kidneys and causes vasoconstriction and causes vasoconstriction and increased blood and increased blood pressure .pressure .

- Stimulates milk ejection - Stimulates milk ejection from breasts & uterine from breasts & uterine contractions contractions

- Peptide- Peptide

- Peptide- Peptide

Peptide Peptide

- Peptide- Peptide

- Peptide- Peptide

- Amine- Amine

- Peptide- Peptide

- Peptide - Peptide

Anterior pituitaryAnterior pituitary- - Growth hormoneGrowth hormone

- - ThyroidThyroid--stimulating stimulating hormone (TSH).hormone (TSH).

- Adenocorticotropic - Adenocorticotropic hormone (ACTH).hormone (ACTH).

-- Prolactin Prolactin

- Follicle-stimulating - Follicle-stimulating (FSH)(FSH)

- Luteinizing - Luteinizing hormone (LH)hormone (LH)..

- Stimulates protein - Stimulates protein synthesis and synthesis and overall growth of overall growth of most cells and most cells and tissuestissues

- Stimulates protein - Stimulates protein synthesis and synthesis and secretion of thyroid secretion of thyroid hormones (T3,T4)hormones (T3,T4)

- Stimulates protein - Stimulates protein synthesis and synthesis and secretion of secretion of adrenocortical adrenocortical hormones.hormones.

- Promotes - Promotes development of the development of the female breasts and female breasts and secretion of milk secretion of milk

- Causes growth of - Causes growth of follicles in the follicles in the ovaries and sperm ovaries and sperm maturation in sertoli maturation in sertoli cells of testescells of testes- Stimulates - Stimulates testosterone synthesis testosterone synthesis in leydig cells of testes in leydig cells of testes , stimulates ovulation , , stimulates ovulation , formation of corpus formation of corpus luteum , estrogen and luteum , estrogen and progesterone synthesisprogesterone synthesis in ovariesin ovaries

- Peptide- Peptide

- Peptide - Peptide

- Peptide- Peptide

- Peptide- Peptide

- Peptide- Peptide

- Peptide- Peptide

ThyroidThyroid

Adrenal Adrenal cortex cortex

Adrenal Adrenal medullamedulla

pancreaspancreas

ParathyroiParathyroidd

- Thyroxin T4 - Thyroxin T4 and and triiodothyronintriiodothyronine T3.e T3.

- Calcitonin - Calcitonin

- cortisol- cortisol

- Aldosterone - Aldosterone

NorepinephrinNorepinephrine ,epinephrine e ,epinephrine

- Insulin - Insulin

- Glucagon- Glucagon

- Parathyroid - Parathyroid hormones hormones (PTH)(PTH)

- Increases the rates of chemical reactions - Increases the rates of chemical reactions in most cells ,thus increasing the body in most cells ,thus increasing the body metabolic ratemetabolic rate

Promotes deposition of calcium in the Promotes deposition of calcium in the bones and decreases extracellular fluid bones and decreases extracellular fluid calcium in the bones and decrease calcium in the bones and decrease extracellular fluid calcium ion extracellular fluid calcium ion concentration concentration

- Has multiple metabolic functions for - Has multiple metabolic functions for controlling metabolism of controlling metabolism of proteins ,carbohydrates, and fats, also has proteins ,carbohydrates, and fats, also has anti inflammatory effects .anti inflammatory effects .

- Increase renal sodium - Increase renal sodium reabsorption ,potassium secretion ,and reabsorption ,potassium secretion ,and hydrogen ion secretion hydrogen ion secretion

Same effect as sympathetic stimulation Same effect as sympathetic stimulation

- Promoted glucose entry in many cells and - Promoted glucose entry in many cells and in this way controls carbohydrate in this way controls carbohydrate metabolism metabolism

- Increases synthesis and release of - Increases synthesis and release of glucose from the liver into the body fluids glucose from the liver into the body fluids

- Controls serum calcium ion concentration - Controls serum calcium ion concentration by increasing calcium absorption by gut by increasing calcium absorption by gut and kidneys and releasing calcium from and kidneys and releasing calcium from bones .bones .

- Amine - Amine

- - PeptidePeptide

- - SteroidSteroid

- - Steroid Steroid

- Amine - Amine

--Peptide Peptide

--Peptide Peptide

--Peptide Peptide

TestesTestes

OvariesOvaries

PlacentaPlacenta

KidneyKidney

-- Testosterone Testosterone

-Progesterone -Progesterone

- Estrogens - Estrogens

- Human chorionic - Human chorionic Gonadotropin (HCG)Gonadotropin (HCG)

- human - human somatomammotropin somatomammotropin

- Estrogen - Estrogen

- Progesterone - Progesterone -Renin Renin

- 1,25- - 1,25- dihydroxycholecalcifedihydroxycholecalciferolrol

- Erythropoietin - Erythropoietin

- Promotes development of male - Promotes development of male reproductive system and male secondary reproductive system and male secondary sexual characteristics.sexual characteristics.

- Stimulates secretion uterine milk by the - Stimulates secretion uterine milk by the uterine endometrial glands and promotes uterine endometrial glands and promotes development of secretory apparatus of development of secretory apparatus of breasts .breasts .

- Promote growth and development of - Promote growth and development of female reproductive system ,female female reproductive system ,female breasts ,and female secondary sexual breasts ,and female secondary sexual characteristic s characteristic s

- Promotes growth of corpus luteum and - Promotes growth of corpus luteum and secretion of estrogens and progesterone secretion of estrogens and progesterone by corpus luteum .by corpus luteum .

- Probably helps promote development of - Probably helps promote development of some fetal tissues as the mothersome fetal tissues as the mother’’s breasts s breasts

- Catalyzes conversion of angiotensinogen - Catalyzes conversion of angiotensinogen to angiotensin-1(acts as an enzymeto angiotensin-1(acts as an enzyme((

- Increases intestinal absorption of - Increases intestinal absorption of calcium and bone mineralization.calcium and bone mineralization.

- Increase erythrocyte production - Increase erythrocyte production

-Steroid-Steroid

- Steroid- Steroid

- Steroid- Steroid

PeptidePeptide

- - Peptide Peptide

- Steroid- Steroid

- Steroid- Steroid

- - PeptidePeptide

- - steroid steroid

Hormone secretion, transport, and clearance from the blood

-onset of hormone secretion after a stimulus , and duration of action of different hormones:

Some hormones such as norepinephrine and epinephrine ,are secreted within seconds after the gland is stimulated ,and they may develop full action within another few seconds to minutes.

Some hormones such as thyroxin or growth hormone ,may require month for full effect.

-concentrations of hormones in the circulating blood , and hormonal secretion rates .

The concentrations of hormones required to control most metabolic and endocrine functions are incredibly small.

Their concentrations in the blood range from as little as 1 picogram in each milliliter of blood up to at most a few micrograms per milliliter of blood .

Feedback control of hormones secretion

1- Negative feedback prevents overactivity of hormones systems:

the plasma concentrations of many hormones fluctuate in response to various stimuli that occur through out the day, and appeared to be closely controlled .

this control is exerted through negative feedback mechanisms that ensure a proper level of hormone activity at the target tissue .

After stimulus causes release of the hormone ,conditions or products resulting from the hormone tend to suppress its further release .

In other words , the hormone (or one of its products ) has a negative feedback effect to prevent over secretion of hormone or overactivity at the target tissue .

2-surges of hormones can occur with positive feedback :

The positive feedback occurs when the biological action of hormone causes additional secretion of the hormone .

One example of this is the surge of luteinizing hormone(LH) that occurs as a result of the stimulatory effect of estrogen on the anterior pituitary before ovulation .

3- Cyclical variations occur in hormone release :

Superimposed on the negative and positive feedback control of hormone secretion are periodic variation in hormone release that are influenced by seasonal changes , various stages of development and aging , the diurnal (daily) cycle ,and sleep .

for example , the secretion of growth hormone is markedly increased during the early period of sleep but is reduced during the later stage of sleep.

In many cases ,these cyclical variations in hormone secretion are due to changes in activity of neural pathways involved in controlling hormone release .

Transport of hormones in the

blood

Water –soluble hormones (peptide and catecholamine) are dissolved in the plasma and transported from their sites of synthesis to target tissue ,where they diffuse out of the capillaries ,into the interstitial fluid , and ultimately to target cells.

Steroid and thyroid hormones ,in contrast ,circulate in the blood mainly bound to plasma proteins .

For example : more than 99 per cent of the thyroxin in the blood is bound to plasma proteins .

however, protein bound hormones can not easily diffuse across the capillaries and gain access to their target cells and are therefore biologically inactive until they dissociate from plasma proteins .

Clearance of hormones from the blood

Two factors can increase or decrease the concentration of a hormone in the blood .

The first one is the rate of hormone secretion into the blood .

The second one is the rate of removal of the hormone from the blood , which is called the metabolic clearance rate .

Hormones are cleared from the plasma in several ways including :

1- metabolic destruction by the tissues .

2- binding with the tissues .

3- excretion by the liver into the bile

4- excretion by the kidney into the urine

For certain hormones ,a decreased metabolic clearance rate may cause an excessively high concentration of the hormone in the circulating body fluids . For instance ,this occur for several of the steroid hormones when the liver is diseased , because these hormones are conjugated mainly in the liver and then (cleared ) into the bile .

Hormones are sometimes degraded at their target cells by enzymatic process that cause endocytosis of the cell membrane hormone –receptor complex: the hormone is then metabolized in the cell, and the receptors are usually recycled back to the cell membrane .

The first step of a hormone’s action is to bind to specific receptors at the target cell.

Hormonal receptors: are large proteins, and each cell that is to be stimulated usually has some 2000 to 100,000 receptors. also., each receptor is usually highly specific for a single hormone.

Target tissue: the target tissues that are affected by a hormone are those that contain its specific receptors.

Location of hormone receptors1- In or on the surface of the cell membrane: the membrane receptors are specific for

protein, peptide, and catecholamine hormones.

2- In the cell cytoplasm: the cytoplasmic receptors are specific

For steroid hormones.3- In the cell nucleus: the receptors for the

thyroid hormones are found in the nucleus .

Measurement of Hormone Concentration in the Blood RadioimmunoassayMost hormones are present in the blood in

very low concentration 1 picogram per milliliter. Therefore, it is very difficult to measure these concentrations by the usual chemical means.

An antibody that is highly specific for the hormone to be measured is produced.

a small quantity of this antibody is mixed with a quantity of fluid from the animal containing the hormone to be measured.

Mixed simultaneously with an appropriate amount of purified standard hormone that has been tagged with a radioactive isotope. There must be too little antibody to bind completely both the radioactively tagged hormone and the hormone in the fluid to be assayed. So, the natural hormone in the assay fluid and the radioactive standard hormone compete for the binding sites of the antibody.

After binding has reached equilibrium, the antibody-hormone complex is separated from the remainder of the solution, and the quantity of radioactive hormone bound in this complex is measured by radioactive counting techniques. If large amount of radioactive hormone has bound with antibody, it clear that there was only a small amount of natural hormone to compete with radioactive hormone & visa versa.

To make the assay highly quantitative, the radioimmunoassay procedure performed for "standard" solution of untagged hormone at several concentration levels. Then a "standard curve" is plotted.

Pituitary Hormones and Pituitary Hormones and Their Control by the Their Control by the HypothalamusHypothalamus

Out linesOut lines Introduction Introduction Define the pituitary gland Define the pituitary gland Describe the pituitary gland Describe the pituitary gland Pituitary hormones Pituitary hormones Hypothalamus controls pituitary secretion Hypothalamus controls pituitary secretion Hypothalamic-hypophysial portal blood vessels of the anterior Hypothalamic-hypophysial portal blood vessels of the anterior

pituitary gland pituitary gland Physiological functions of growth hormone Physiological functions of growth hormone Regulation of growth hormone secretion Regulation of growth hormone secretion Role of the hypothalamus ,growth hormone Role of the hypothalamus ,growth hormone ––releasing hormone releasing hormone

,and Somatostatin in the control of growth hormone secretion ,and Somatostatin in the control of growth hormone secretion Abnormalities of growth hormone secretion Abnormalities of growth hormone secretion Posterior pituitary gland and its relation to the hypothalamusPosterior pituitary gland and its relation to the hypothalamus Chemical structure of ADH and OxytocinChemical structure of ADH and Oxytocin Physiological function of ADHPhysiological function of ADH Oxytocin Hormone Oxytocin Hormone

Introduction to endocrine glandsIntroduction to endocrine glands

Endocrine gland:Endocrine gland: A gland that secretes a chemical substance (a A gland that secretes a chemical substance (a hormone) into the bloodstream. The endocrine glands are hormone) into the bloodstream. The endocrine glands are "glands of internal secretion." They include the hypothalamus, "glands of internal secretion." They include the hypothalamus, pituitary glandpituitary gland, pineal gland, thyroid, parathyroid glands, islets , pineal gland, thyroid, parathyroid glands, islets of Langerhans in the pancreas, the adrenal glands, the kidney of Langerhans in the pancreas, the adrenal glands, the kidney (which makes renin, and (which makes renin, and erythropoietin), the testes, and the ), the testes, and the ovaries.ovaries.

Endocrine glandsEndocrine glands are organs in the body that produce hormones are organs in the body that produce hormones which are released directly into the bloodstream. Endocrine which are released directly into the bloodstream. Endocrine glands include: include:

Thyroid Thyroid Parathyroid Parathyroid Pituitary Pituitary Thymus Thymus Adrenals Adrenals Pancreas Pancreas Gonads - testes (male) and ovaries (female) Gonads - testes (male) and ovaries (female) Together these glands make up the endocrine system, which Together these glands make up the endocrine system, which

performs essential functions like regulating metabolism, growth performs essential functions like regulating metabolism, growth and reproductionand reproduction

Define the Pituitary glandDefine the Pituitary gland Pituitary glandPituitary gland:: The main endocrine gland. It is a The main endocrine gland. It is a

small structure in the head. It is called the master small structure in the head. It is called the master gland because it produces hormones that control gland because it produces hormones that control other glands and many body functions including other glands and many body functions including growth.growth.

The pituitary gland consists of the anterior and The pituitary gland consists of the anterior and posterior pituitaryposterior pituitary

The The anterior pituitaryanterior pituitary is the front portion of the is the front portion of the pituitary. Hormones secreted by it influence growth, pituitary. Hormones secreted by it influence growth, sexual development, skin pigmentation, thyroid sexual development, skin pigmentation, thyroid function, and adrenocortical function. function, and adrenocortical function.

The The posterior pituitaryposterior pituitary is the back portion of the is the back portion of the pituitary. It secretes the hormone oxytocin which pituitary. It secretes the hormone oxytocin which increases uterine contractions and antidiuretic increases uterine contractions and antidiuretic hormone (ADH) which increases reabsorption of hormone (ADH) which increases reabsorption of water by the tubules of the kidney. Underproduction water by the tubules of the kidney. Underproduction of ADH results in a disorder called of ADH results in a disorder called diabetes insipidus characterized by inability to concentrate characterized by inability to concentrate the urine and, consequently, excess urination the urine and, consequently, excess urination leading potentially to leading potentially to dehydration. .

Describe the parts of pituitary Describe the parts of pituitary glandgland

Pituitary gland is one centimeter in diameter Pituitary gland is one centimeter in diameter and weighs from 0,5-1 gram , and it lies in and weighs from 0,5-1 gram , and it lies in a bony cavity at the base of the brain a bony cavity at the base of the brain (sella turcica) , and is connected to the (sella turcica) , and is connected to the hypothalamus by pituitary stalk hypothalamus by pituitary stalk

Physiologically pituitary divided into :Physiologically pituitary divided into :

1-anterior lobe1-anterior lobe :adenohypophysis :adenohypophysis

2-posterior lobe2-posterior lobe :neurohypophysis :neurohypophysis

Between these two parts lies the pars Between these two parts lies the pars intermedia and most absent in human. intermedia and most absent in human.

Pituitary hormonesPituitary hormones Growth hormone Growth hormone (hGH(hGH): promote growth of the entire body by ): promote growth of the entire body by

affecting protein formation, cell multiplication, and cell affecting protein formation, cell multiplication, and cell differentiation differentiation

Adrenocortecotropin Adrenocortecotropin (corticotrophin,ACTH(corticotrophin,ACTH) : controls secretion of ) : controls secretion of some adrenocortical hormone ,which affecting the metabolism of some adrenocortical hormone ,which affecting the metabolism of glucose , proteins , and fats.glucose , proteins , and fats.

Thyroid stimulating hormoneThyroid stimulating hormone(TSH(TSH) : controls the rate of secretion of ) : controls the rate of secretion of thyroxin and triidothyronine by the thyroid gland , these hormones thyroxin and triidothyronine by the thyroid gland , these hormones control the rates of most intracellular chemical reactions in the control the rates of most intracellular chemical reactions in the body body

ProlactinProlactin(PRL(PRL) : promotes mammary gland development and milk ) : promotes mammary gland development and milk production production

Gonadotropic hormones : include, follicle stimulating hormone Gonadotropic hormones : include, follicle stimulating hormone (FSH)(FSH)

And luteinizing hormone And luteinizing hormone (LH),(LH),These hormones control growth of the These hormones control growth of the ovaries and testes ,as well as their hormonal and reproductive ovaries and testes ,as well as their hormonal and reproductive activities .activities .

Anti diuretic hormone Anti diuretic hormone (vasopressin)(vasopressin): controls the rate of water : controls the rate of water excretion into the urine , helping to control the concentration of excretion into the urine , helping to control the concentration of water in the body fluids water in the body fluids

Oxytocin: helps express milk from the glands of the breast to the Oxytocin: helps express milk from the glands of the breast to the nipples during suckling and helps in the delivery of the baby at the nipples during suckling and helps in the delivery of the baby at the end of gestation end of gestation

Hypothalamus controls pituitary Hypothalamus controls pituitary

secretionsecretion Almost all secretion by pituitary is controlled by Almost all secretion by pituitary is controlled by

either hormonal or nervous signals from the either hormonal or nervous signals from the hypothalamus, indeed when the pituitary gland hypothalamus, indeed when the pituitary gland is removed from its normal position beneath the is removed from its normal position beneath the hypothalamus and transplanted to some other hypothalamus and transplanted to some other part of the body ,its rates of secretion of the part of the body ,its rates of secretion of the different hormones (different hormones (except for Prolactinexcept for Prolactin) fall to ) fall to very low levels. very low levels.

Secretion from the posterior pituitary is Secretion from the posterior pituitary is controlled by nerve signals that originate in the controlled by nerve signals that originate in the hypothalamus and terminate in the posterior hypothalamus and terminate in the posterior pituitary .pituitary .

in contrast secretion by the anterior pituitary is in contrast secretion by the anterior pituitary is controlled by hormones called hypothalamic controlled by hormones called hypothalamic releasing and hypothalamic inhibitory hormones releasing and hypothalamic inhibitory hormones secreted within the hypothalamus itselfsecreted within the hypothalamus itself

Hypothalamic-hypophysial portal blood Hypothalamic-hypophysial portal blood

vessels of the anterior pituitary glandvessels of the anterior pituitary gland The anterior pituitary is the The anterior pituitary is the highly vascular gland with highly vascular gland with

extesive capillary sinusesextesive capillary sinuses among the glandular cells . among the glandular cells . Almost all the blood that enters these sinus passes Almost all the blood that enters these sinus passes

first through another capillary bed in the lower first through another capillary bed in the lower hypothalamus hypothalamus

The blood then flows through small hypothalamic-The blood then flows through small hypothalamic-hypophysial portal blood vessels into the anterior hypophysial portal blood vessels into the anterior pituitary sinuses. pituitary sinuses.

Hypothalamic releasing and inhibitory hormones are Hypothalamic releasing and inhibitory hormones are secreted into the median eminence .special neurons secreted into the median eminence .special neurons in the hypothalamus synthesize and secret the in the hypothalamus synthesize and secret the hypothalamic releasing and inhibitory hormones that hypothalamic releasing and inhibitory hormones that control secretion of the anterior pituitary hormones. control secretion of the anterior pituitary hormones.

The releasing and inhibitory hormones are The releasing and inhibitory hormones are immediately absorbed into the hypothalamic-immediately absorbed into the hypothalamic-hypophysial portal system and carried directly to the hypophysial portal system and carried directly to the sinuses of the anterior pituitary gland sinuses of the anterior pituitary gland

Hypothalamic releasing and inhibitory hormones Hypothalamic releasing and inhibitory hormones control anterior pituitary secretion :control anterior pituitary secretion :the major the major hypothalamic and inhibitory hormones are:hypothalamic and inhibitory hormones are:

thyrotropin releasing hormone thyrotropin releasing hormone (TRH(TRH) :which ) :which causes release of thyroid-stimulating hormone.causes release of thyroid-stimulating hormone.

corticotropin-releasing hormone corticotropin-releasing hormone (CRH)(CRH) :which :which causes release of Adrenocortecotropin hormone.causes release of Adrenocortecotropin hormone.

growth hormone growth hormone ––releasing hormone releasing hormone (GHRH(GHRH): ): which cause release of growth hormone and which cause release of growth hormone and growth hormone inhibitory hormone GHIH also growth hormone inhibitory hormone GHIH also called somatostatin, which inhibits release of called somatostatin, which inhibits release of growth hormonegrowth hormone

Gonadotropin Gonadotropin ––releasing hormone releasing hormone (GnRH(GnRH) : which ) : which causes release of the two gonadotropic causes release of the two gonadotropic hormones (luteinizing hormone and follicle-hormones (luteinizing hormone and follicle-stimulating hormone) stimulating hormone)

Prolactin inhibitory hormone Prolactin inhibitory hormone (PIH):(PIH): which causes which causes inhibition of Prolactin secretion. inhibition of Prolactin secretion.

Specific areas in the hypothalamus control Specific areas in the hypothalamus control secretion of specific hypothalamic secretion of specific hypothalamic releasing and inhibitory hormones releasing and inhibitory hormones all or all or most of hypothalamic hormones are most of hypothalamic hormones are secreted at the nerve endings in the secreted at the nerve endings in the median eminencemedian eminence before being before being transported to the anterior pituitary transported to the anterior pituitary gland .gland .

Electrical stimulation of this region excites Electrical stimulation of this region excites these nerves endings , and therefore these nerves endings , and therefore causes release of essentially all the causes release of essentially all the hypothalamic hormones. hypothalamic hormones.

Glandullar cells of the anterior pituitary Glandullar cells of the anterior pituitary glandgland