Endocrine system : easy and brief handout

Name of endocrine glands (ductless gland)

1. Hypophysis or pituitary glands
2. Adrenal glands
3. Pancreas
4. Thyroid glands
5. Parathyroid glands
6. Pineal glands

Endocrine system : It produce various secretions called hormones that serve as effectors to regulate the activities of various cells, tissues and organs in the body

Hormone: it is a  biological substance acting on specific target cells 

Pituitary glands

Gross structure & development:  

Anterior lobe (adenohypophysis), the glandular epithelial tissue. It is derived from the evagination of ectoderm of oropharynx 

Posterior lobe (neurohypophysis) the neural secretory tissue. It is derived from the neuroectoderm of the floor of the third ventricle

 •         Location: It lies in the sella turcica ( a depressed area in the body of sphenoid )

•         It has two functional components

Anterior lobe

•         Pars distalis

•         Pars intermedia

•         Pars tuberalis

Posterior lobe

•         Pars nervosa

•         Infundibulum

Blood supply of pituitary glands

•      The blood supply of hypophysis is derived from the internal carotid artery

•      The superior hypophyseal arteries supply the median eminence and neural stalk. This artery divide into fenestrates capillaries which irrigates the median eminence and stalk. These capillaries rejoin to form veins that developed the second capillaries plexus in the adenohypophysis. This hypophyseal portal system carries neurohormones from the median eminence to the adenohypophysis where they control the function of the cells of this part of the hypophysis 

•      The inferior hypophyseal arteries supply the neurohypophysis

Histological features of anterior lobe of pituitary gland (also known as Adenohypophysis ) : contain cells and capillaries

•         There are two cells types:

1. Chromophobes (do not stain intensely)
2. Chromophils i) Basophils ii) Acidophils 

(Five functional cell types are identified in the anterior lobe on the basis of immunocytochemical reactions

•         Somatotrope (GH cell)

•         Lactotrope (PRL cell)

•         Corticotrope (ACTH cell)

•         Gonadotrope (FSH and LH cell)

•         Thyrotrope (TSH cell))

Pars intermedia surrounds a series of  small cystic cavities that represent the residual lumen of Rathke’s pouch

Histological features of Posterior lobe ( Pars nervosa and infundibular stalk ) :

•         These have the appearance of nervous tissue.

•         pituicytes are present : they are the  cells of the pars nervosa , resembling neuroglial cells. They probably support the unmyelinated nerve fibres,

•          Herring bodies are present : terminal regions of unmyelinated nerve fibres are expanded by neurosecretion is  known as Herring bodies

Suprarenal gland

Histological features

1. outer cortex has  three concentric zones, zona glomerulosa, zona fasciculata and zona reticularis
2. inner medulla containing  large veins and contain chromaffin cells and large autonomic ganglion cells
3. capsule is present

 Short description of Cortex

•         Zona glomerularis is immediately deep to the capsule. It consists of columnar cells arranged in arches and spherical clusters.

•         Zona fasciculata : the thickest zone of the cortex. The more or less cuboidal cells (spongiocytes) are arranged in long, parallel cords.spongiocytes appear highly vacuolated except those of the deepest region which are smaller and much less vacuolated

•         Zona reticularis : the innermost zone of the cortex . It is composed of small, dark cells arranged in irregularly anastomosing cords. The intervening capillaries are enlarged 

Thyroid glands

Parts : two lobes and isthmus

Location: in front of trachea and thyroid cartilage

Histological features of thyroid glands

1. thyroid follicle is lined by simple cuboidal epithelium
2. thyroid follicle is filled by colloid
3. parafollicular cells are present periphery of the thyroid follicle but within the basement membrane of follicular cells
4. capsule is present

follicular cells secrete: T3 and T4

parafollicular cells secrete: calcitonin

development : parts of gland

stoma : develops from mesoderm

parenchyma are the glandular part : cells of parenchyma : follicular cells develops from endoderm and parafollicular cells develops from neural crest (part of neuroectoderm )

Parathyroid gland

•         Capsule is present

•         Parenchymal cell

1. Chief cells are numerous, small cells with large nuclei that form cords
2. Oxyphils cells are larger, acidophilic and much fewer in number than chief cells

Pineal body

•         Capsule derived from pia mater

•         Parenchymal cells

1. Pinealocytes are recognized by the large size of their nuclei
2. Neuroglial cells posses smaller, denser nuclei than the pineatocytes

•         Brain sand: characteristic of the pineal are the calcified accretions in the intercellular spaces known as brain sand or corpora arenacea.