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Endocrine system

By

Dr. Sara Mohammed Naguib Assistant professor of Histology

Minia university

Characters of endocrine gland:

=Sites of synthesis and secretion of hormones.

= Composed of secretory cells of epithelial origin

supported by CT.

= Cells are polyhedral and arranged in irregular cords

or clumps.

= Thin highly vascular CT rich in fenestrated blood

capillaries.

=Ductless.

Pituitary gland

Main endocrine organ.

Affects every organ directly or indirectly.

Site: sella turcica and connected with brain by

infundibular stalk.

Have neural and non neural components.

Parts:

1- Anterior lobe "adenohypophysis".

2-Posterior lobe "neurohypophysis".

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Pars Nervosa

-No secretory cells. It consists of:

1. Unmyelinated axons of secretory neurons from

supraoptic and paraventricular nuclei of hypothalamus. Some

axons end blindly in median emenince of hypoyhalamus,

other extend to lower region of posterior lobe.

2. Herring bodies: fusiform swellings of terminal ends of

unmyelinated axons filled with neurosecretory granules.

3. Pituicytes "glial cells": supportive.

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Thyroid gland

Formed of 2 lobes connected by isthmus.

Thyroid parenchyma: Formed of thyroid follicles which are spherical with

lumen filled with gelatinous "colloid". They are lined with simple cuboidal

epithelium and are of "2 types":

Follicular or principal cells: Cuboidal cells with central rounded nucleus

and junctional complexes between cells.

Function: synthesis thyroid hormones (T3 and T4).

Parafollicular or C cells: present in the interfollicular spaces. Paler

than follicular cells so termed "clear or C".

Function: Synthesis of calcitonin hormone "lowers serum Ca level by

inhibiting bone resorption".

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Parathyroid gland

4 small bodies embedded in posteromedial aspect of thyroid

gland.

Parynchema:

3 types of cells separated by fenestrated blood capillaries.

I. Chief or principal cells

II. Oxyphil cells

III. Adipose cells:

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Suprarenal (adrenal) gland

Small paired glands lie on superior pole of kidney and

embeded in adipose tissue.

Parynchema:2 zones different embryologically and

functionally:

outer cortex.

Inner small medulla.

Adrenal cortex: formed of three zones: Zona

glomerulosa , Zona fasciculata &Zona reticularis

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