ENDOCRINOLOGY II (PHS 423) - PowerPoint Presentation

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ENDOCRINOLOGY II (PHS 423)

LECTURER:

BAMIDELE OLUBAYODE

COURSE OUTLINE

The nature of

hypothalamohypophyseal

relationship

Neurohypophyseal

hormones

Hypothalamic functions

Further consideration of synthesis, storage and release of hormones

Mechanism of hormonal actions

Extraction and purification of hormones

Methods of studying endocrine glands

Hormonal assay

Comparative study of hormones as exemplified by vasopressin, thyroxin and

gastrin

THE

NATURE OF HYPOTHALAMOHYPOPHYSEAL RELATIONSHIP

INTRODUCTION

:

This refers to the kind of association between hypothalamus and pituitary gland.

Pituitary gland is otherwise called

hypohysis

Hypothalamus and pituitary gland are primary endocrine glands of the human body.

Hypothalamus is a small area of the brain, which is located below the thalamus.

The pituitary gland is located just below the hypothalamus.

The pituitary gland is made up of two lobes; anterior lobe (

adenohypophysis

) and posterior lobe (

neurohypophysis

).

The nature of the relationship

The hypothalamus is connected to the anterior lobe of the pituitary gland by means of a special portal blood system called

hypothalamohypophyseal

portal system. Hence there is vascular connection between hypothalamus and anterior pituitary gland.

Moreover, the hypothalamus is directly connected to the posterior lobe of the pituitary gland by means of neurons. Therefore neural connection exists between hypothalamus and posterior pituitary gland.

H

ypothalamus regulates the function of the pituitary gland.

The pituitary gland: Hypophysis

It is a small gland (about 1

centimeter

in diameter and 0.5 to 1g in weight) that lies in the

sella

turcica

,

a bony cavity at the base of the brain, and is connected to the hypothalamus by the

pituitary

stalk

.

The gland consists of two parts, the anterior portion (

adenohypophysis

) and the posterior portion (

neurohypohysis

).

The two portions are connected by a small intermediate portion

portion

called pars

intermedia

.

Anterior pituitary gland is developed in embryonic life from the roof of embryonic mouth cavity and it is composed of epithelial tissue similar to the

pharygeal

epithelium. Its three subdivisions are: pars

distalis

, pars

intermedial

and pars

tuberalis

.

The pitutary

gland cont’d

The posterior pituitary gland is formed by a

downgrowth

of the floor of the hypothalamus. It is made up of two parts namely:

pars nervosa and the

infundibulum

.

The blood supply to the pituitary gland is via the superior and inferior

hypophysial

arteries. The superior vessels give rise to a number of capillaries plexuses which extend into the median eminence of the hypothalamus. On returning to the surface, they drain into several long and short portal veins. They supply the sinusoids of the anterior pituitary gland.

The

venules

connecting the capillaries in the median eminence of the hypothalamus with the sinusoidal capillaries of the anterior lobe form the

hypothalamohypophyseal

portal system.

The inferior vessels supply the posterior pituitary gland.

HISTOLOGY

OF ADENOHYPOPHYSIS

There is one cell type for each major hormone formed in the anterior pituitary gland.

With special stains attached to high-affinity antibodies that bind with the distinctive hormones, five cell types can be identified and they are:

Somatotropes

-human growth hormone (

hGH

)

Corticotropes

-

adrenocorticotropin

(ACTH)

Thyrotropes

-thyroid-stimulating hormone (TSH)

Gonadotropes

-gonadotropic

hormones, which include both

luteinizing

hormone (LH) and follicle-stimulating hormone (FSH)

Lactotropes

-prolactin

(PRL)

HISTOLOGY OF ADENOHYPOPHYSIS CONT’D

Approximately 30 to 40 per cent of the anterior pituitary cells are

somatotropes

that secrete growth hormone while 20 per cent are

corticotropes

that secrete ACTH.

Each of the other cell types accounts for only 3 to 5 per cent of the total; nevertheless, they secrete powerful hormones for regulating thyroid function, sexual functions, and milk secretion by the breasts.

Somatotropes

and

lactotropes

stain strongly with acid dyes and are therefore called

acidophils

.

Thus, pituitary

tumors

that secrete large quantities of human growth hormone are called

acidophilic

tumors

.

Thyrotropes

,

gonadotropes

and

corticotropes

are stained with basic dyes and are called

basophils

.

HYPOTHALAMIC REGULATIONS OF HORMONES OF ADENOHYPOPHYSIS

Special neurons in the hypothalamus form and secrete the

hypothalamic releasing

and

inhibitory hormones

that regulate secretion of the anterior pituitary hormones.

These neurons originate in several parts of the hypothalamus and send their nerve

fibers

to the median eminence and

tuber

cinereum

,

an extension of hypothalamic tissue into the pituitary stalk.

The endings of these

fibers

secrete the hypothalamic releasing and inhibitory hormones into the tissue fluids.

These hormones are immediately absorbed into the

hypothalamohypophysial

portal system and carried directly to the sinuses of the anterior pituitary gland.

HYPOTHALAMIC REGULATIONS OF HORMONES OF ADENOHYPOPHYSIS

The function of the releasing and inhibitory hormones is to control secretion of the anterior pituitary hormones.

For most of the anterior pituitary hormones, it is the releasing hormones that are essential except for

prolactin

inhibitory hormone which exerts more control. The major hypothalamic releasing and inhibitory hormones are the

follwing

:

Thyrotropin

-releasing hormone

(TRH): causes release of thyroid-stimulating hormone

Corticotropin

-releasing hormone

(CRH): causes release of

adrenocorticotropin

Growth hormone-releasing hormone

(GHRH), which causes release of growth hormone, and

growth hormone inhibitory hormone

(GHIH), also called

somatostatin

,

which inhibits release of growth hormone

Gonadotropin

-releasing hormone

(

GnRH

):causes release of the two

gonadotropic

hormones,

luteinizing

hormone and follicle-stimulating hormone

Prolactin

inhibitory hormone

(PIH), which causes inhibition of

prolactin

secretion

HYPOTHALAMIC REGULATIONS OF HORMONES OF NEUROHYPOPHYSIS

It is made up of a large bundle of

unmyelinated

nerve fibres.

The cell bodies of these fibres lie in the hypothalamus in the

supraoptic

and

paraventricular

nuclei.

The fibres pass to the pituitary via the

hypothalamo-hypophyseal

tract.

In the posterior pituitary gland, the nerve ending lie close to the network of vascular sinusoids.

The

neurohypophysis

Stores and releases two hormones which are:

oxytocin

and vasopressin otherwise called

antidiuretic

hormone (ADH).

REFERENCES

Guyton and Hall. Textbook of Medical Physiology. 9

th

Edition, W.B Saunders company, London,

TorontoPhiladelphia

.

Lakna

Panawala

. (2017). Relationship Between Hypothalamus and Pituitary Gland. Definition of Anatomy and Physiology.

Oyebola

D.O. (2002)Essential Physiology for students of

Medicin

e, dentistry, Pharmacy and Related disciplines. Volume 1.