Assoc. Prof. Dr. Karim Al-JashamyIMS/MSU 2010

The Endocrine System

Controls many body functions

• exerts control by releasing special chemical

substances into the blood called hormones

• Hormones affect other endocrine glands or

body systems

• Derives its name from the fact that various glands release hormones directly into the blood, which in turn transports the hormones to target tissues, no need to ducts

Uses chemical signals for cell to cell communication.

Coordinates the function of cells

Response to an endocrine signal occurs within minutes to hours

Exocrine glands - transport their hormones to target tissues via ducts.

Located at the base of the skull

Anterior and Posterior lobes

Portal connection from the hypothalamus

Pituitary Gland(hypophysis)

Flow of Blood to Anterior Pituitary

Controlling hormones enter blood

Travel through

portal veins

Enter anterior pituitary at capillaries

Hypophysis

= Pituitary Gland

Compound gland – 2 parts from different embryonic sources

Epithelial part – pouch pinched off from roof of mouth

Neural part – from downgrowth brain floor (diencephalon)

Pars Distalis (anterior Lobe)

Parenchyma: anastomosing

cords of epithelial cells

Chromophobe cells:

smaller than chromophil

cells; may be inactive form

Chromophil cells:

Cytoplasm granular; more

distinct than chromophobe

cells

2 types of chromophil

cells: acidophil (alpha

cells); basophil (beta

cells)

Acidophils: specific,

spherical granules of

uniform size

Basophils: appreciably

larger; fewer granules

Pars Tuberalis

Cell groups & cords

Cells finely granular

Cysts with colloid not uncommon in this part

Pars Intermedia

Narrow, definite region but ill defined in humans

Cysts common; filled with colloid or hyaline material

Neurohypophysis

Distinct cell type:

pituicyte

Resemble neuroglia

cells

4 subtypes: many

contain fatty droplets,

granules, pigment

Unmyelinated nerve

fibers from the

hypothalamus majority

end in pars nervosa

The pars distalis (A) and the pars intermedia (B) of the adenohypophysis (anterior pituitary) and the pars nervosa (C) of the neurohypophysis (posterior pituitary) can be observed.

The pars distalis secretes Growth Hormone (GH), Thyroid-stimulating hormone (TSH), Adrenocorticotrophichormone (ACTH), Follicle-stimulating hormone (FSH),Lutenizing hormone (LH),and Prolactin.

The pars intermedia secretes Melanocyte-stimulating hormone (MSH).

The pars nervosa stores ADH and Oxytocin which were secreted by the hypothalamus.

At higher

magnifications the dark

staining chromophils (

A) and the very light

staining

chromophobes (B) are

easily distinguished

NEUROHYPOTHYSIS -

PARS NERVOSA

This region of the pituitary

is non secretory. Its cells

are neuroglial-like

pituicytes (C).

b = basophils

col = colloid vesicles

A = pars distalis of adenohypophysis

c= colloid vesicle in pars intermedia

I = pars intermedia

N = pars nervosa of neurohypophysis

pars intermedia

a = acidophil

b = basophil

bv = blood vessel

c = chromophobe

1 = cell cluster consisting of

chromophobes

2 = cell cluster consisting

mainly of acidophils

asterisk = connective tissue

between cell clusters

a = acidophils

b = basophils

bv = blood vessel

pars intermedia

Thyroid Gland

Thyroid Gland

• Fibro-elastic capsule – delicate septa

& trabeculae.

• Septa mark off lobules.

• Lobules not completely separated

• Stroma: areolar & reticular C.T. –highly vascular

• Follicle – closed, single-layered epithelial sac (50 – 500 μ dia.)

• Size dependent on amount of stored secretion

•~ 20 million follicles in thyroid gland

•Epithelium: simple cuboidal (cell height uniform)

•Cytoplasm finely granular; basophilic (pale)

•Blood vessels & lymphatics: intimate plexuses around follicles. Arterio-venus anatomoses common•Thyroxin: in veins & lymphatics (most in veins)

Colloid fills follicle

Rich in nucleoproteins

Contains: thryoglobulin & enzymes

Follicle = sac of stored

hormone (colloid) surrounded

by follicle cells that produced it

– T3 & T4

• Inactive cells are short

between cells called

parafollicular cells produce calcitonin

Formation, Storage and Release of Thyroid Hormones

• Thyroid hormones are synthesized from iodine and tyrosine within a large glycoprotein molecule called thyroglobulin (TGB) and are transported in the blood by plasma proteins mostly thyroxine-binding globulin (TBG).

Actions of Hormones from

Thyroid Gland T3 & T4

– thyroid hormones

responsible for our metabolic rate, synthesis of protein, breakdown of fats, use of glucose for ATP production

Calcitonin

responsible for building of bone & stops reabsorption of bone (lowers blood levels of Calcium)

Parathyroid

Humans: 4 brownish glands, 2 attached to back of each thyroid lobe

Glands are ovoid

Size of an apple seed

Framework

• Delicate fibro-elastic capsule

• Septa divide each gland incompletely

(lobules)

• Invasion of septa begins after birth; continues with age

Adrenal Glands

Cortex

zona

glomerulosathin, outermost zone

zona

fasiculatathick, middle zone

zona

reticularisthin, inner zone

Medulla catecholamines (epinephrine and norepinephrine)

The outermost zone is the zonaglomerulosa. Cells within this zonetend to be columnar in shape and arearranged in irregular cords. cellsadjacent to the capsule are arrangedin quite regular “

The zona fasiculata is the middleand largest of the three zones in thecortex. Cells in the fasiculata arepolyhedral and usually have a foamyappearance due to abundant lipiddroplets. They also are arranged indistinctively straight cords thatradiate toward the medulla.

The innermost zone of the cortex isthe zona reticularis. Cells within thiszone are arranged in cords thatproject in many different directionsand anastomose with one another.