Assoc. Prof. Dr. Karim Al-Jashamy
IMS/MSU 2010
The Endocrine System
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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
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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.
Pituitary Gland(hypophysis)
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Located at the base of the skull
Anterior and Posterior lobes
Portal connection from the hypothalamus
Flow of Blood to Anterior Pituitary
Controlling
hormones enter
blood
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Travel through
portal veins
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Enter anterior
pituitary at
capillaries
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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
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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), Adrenocorticotrophic
hormone (ACTH), Folliclestimulating 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).
pars intermedia
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
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. Arteriovenus 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
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responsible for our
metabolic rate, synthesis
of protein, breakdown of
fats, use of glucose for
ATP production
Calcitonin
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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
zona
thin, outermost zone
glomerulosa
Cortex
zona
thick, middle zone
fasiculata
zona
thin, inner zone
reticularis
Medulla
catecholamines (epinephrine and norepinephrine)
The outermost zone is the zona
glomerulosa. Cells within this zone
tend to be columnar in shape and are
arranged in irregular cords. cells
adjacent to the capsule are arranged
in quite regular “
The zona fasiculata is the middle
and largest of the three zones in the
cortex. Cells in the fasiculata are
polyhedral and usually have a foamy
appearance due to abundant lipid
droplets. They also are arranged in
distinctively straight cords that
radiate toward the medulla.
The innermost zone of the cortex is
the zona reticularis. Cells within this
zone are arranged in cords that
project in many different directions
and anastomose with one another.