The Endocrine System

Pituitary Gland The hypophysis (Gr. hypo, under, + physis, growth),

or pituitary gland Weighs about 0.5 gIt lies in a cavity of the sphenoid bone—the sella

turcica—an important radiological landmarkDuring embryogenesis, the hypophysis develops

partly from oral ectoderm and partly from nerve tissue

Because of its dual origin, the hypophysis actually consists of two glands:

Neurohypophysis AdenohypophysisThey are united anatomically but have different

functions. Neurohypohysis (Posterior Pituitary)neural part. Consists of: Pars nervosa Infundibulum(stalk and median eminence)

Adenohypophysis(Anterior Pituitary)glandular part:

It arises from oral ectoderm.It is subdivided into three portions:Pars DistalisPars Tuberalis Pars Intermedia.

Adenohypophysis Pars Distalis(anterior

lobe) : The largest part of

adenohypophysis The main components of

the pars distalis are cords of epithelial cells .

Highly vascular stroma. The hormones produced

by these cells are stored as secretory granules.

Fibroblasts produce reticular fibers that support the cords of hormone-secreting cells.

The pars distalis accounts for 75% of the mass of the hypophysis.

Common stains allow the recognition of three cell types in the pars distalis:

Chromophobes(Gr. chroma, color, + phobos, fear) Chromophils (Gr. chroma + philein, to love)Two types of chromophils:Basophils according to their affinity for basic dyesAcidophils according to their affinity for acid dyesThe subtypes of basophil and acidophil cells are

named for the hormones they produce. With the exception of the gonadotropic cell, which

produces two hormones, the other cells produce only a single hormone.

Chromophobes(degranulated secretory cells) do not stain intensely and, when observed with an electron microscope, show two populations of cells.

Secretory Cells of the Pars Distalis

Hormone Produced Stain Affinity Cell Type

Growth hormone (GH, somatotropin)

Acidophilic Somatotropic cell

Prolactin (PRL) Acidophilic Mammotropic cell

Follicle-stimulating hormone (FSH)

Luteinizing hormone (LH)

Basophilic Gonadotropic cell

Thyrotropin (TSH) Basophilic Thyrotropic cell

Corticotropin (ACTHα-Melanocyte-stimulating hormone? (α-MSH))

Basophilic Corticotropic cell

α-Melanocyte-stimulating hormone? (α-MSH)

Basophilic Melanotropes?

Pars Tuberalis

The pars tuberalis is a funnel-shaped region surrounding the infundibulum of the neurohypophysis .

Most of the cells secrete gonadotropins (follicle-stimulating hormone and luteinizing hormone)

Are arranged in cords alongside the blood vessels.

Pars IntermediaIs a rudimentary region in humansMade up of cords and follicles of weakly basophilic cells that contain small secretory granules. It produces Melanocyte-stimulating hormone (α-MSH).

Neurohypophysis (Posterior pituitary)It consists ofPars nervosa Infundibulum (neural stalk ) stem and median

eminence.that connects it to the hypothalamus.

The pars nervosa Does not contain

secretory cells.Contains

nonmyelinated axons and nerve endings of neurosecretory neuron

The nerve endings have terminal dilations called Herring bodies

Pars Nervosa Neurosecretory neurons have cell bodies that lie in the supraoptic &

paraventricular nuclei in the hypothalamus • The secretory neurons have all the characteristics of typical neurons• The secretory neurons have well-developed Nissl bodies related to the

production of the neurosecretory material Cells present in Pars Nervosa are:• Pituicytes (glial cell)• fibroblasts • mast cells.

Adrenal Glands This gland is found above the kidney. The dense connective tissue capsule covers the adrenal

gland & sends thin septae into the gland. Septae support the blood vessels and nervesThe stroma consists mainly of a rich network of reticular

fibers that supports the secretory cells.The parenchyma consists of cortex and medulla.

The cortex is subdivided into 3 concentric zones, according to the arrangement of the cells these zones are called: i.ZonaGlomerulosa.

ii. Zona Fasiculata.The cells in this zone are called spongiocyes. iii. Zona Reticularis.