Download Follicular cells

Endocrine System
Department of Histology
and Embryology
Introduction
I Composition
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Endocrine glands(thyroid,parathyroid,adrenal gland,
hypophysis ,and pineal body)
Endocrine cell mass(pancreas islets,etc)
Endocrine cells(distributed in the digestive tract)
Introduction
II Function

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Regulate the activities of various cells,tissues,and
organs in the body.
Maintain homeostasis and coordinate body growth and
development.
The endocrine system interacts closely with the nervous
system and the lymphatic system.
Characteristics of endocrine glands
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Cells are arranged in cord, follicle, aggregation
or net-like structure,
Ductless.
containing rich blood
What is Hormone?
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Hormone is molecule that function as chemical signals.
Most hormones act at a distance from the site of their
secretion. Therefore,the endocrine cells are always close to
the capillaries,which receive the secrete hormones and
distribute them throughout the organism.
paracrine secretion

However, many cells produce hormones act at a short
distance by diffusing through the extracellular matrix.This
is called paracrine secretion.
Classification of the Hormones

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Steroids(cholesterol-derived compounds)
Small peptides,proteins,and glycoproteins
Amino acid(catecholamines)
Steroids
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Are synthesized and secrete by cells of
ovaries,testes,and adrenal cortex.
These hormones are released into the bloodstream
and transported to the target cells with the help of
specialized carrier proteins such as androgen –
binding protein(ABP)
Small peptides,proteins,and glycoproteins
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Are synthesized and secrete by cells of
hypothalamus,thyroid gland,parathyroid
gland,pancreas.
Hormones in this group ,when release into
circulation,dissolve readily in the blood and do not
require special carrier proteins.
Amino acid
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Including the catecholamines(norepinephrine and
epinephrine), Are synthesized and secrete by many
neurons and the adrenal medulla.
Hormones in this group ,when release into
circulation,dissolve readily in the blood.
How do the Hormones act on the target cell?
The target cell have receptors that specifically recognize and
response to the hormones.

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Cell surface receptors(peptide hormones)
Intracellular receptors(steroid hormones)
Thyroid gland
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Locate in the cervical region
anterior to the
larynx,consists of two lobes
united by an isthmus.
It originates the endoderm.
Its function is to synthesize
the hormones thyroxine
(T4)and triiadothyroxine(T3).
Thyroid gland

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It is composed of thyroid follicle.The follicles are lined
by a simple epithelium.
The central cavity contains a gelatinous substance
called colloid, which is composed of a glycoprotein of
high molecular mass called thyroglobulin.
Follicular epithelium
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Follicular cells
Parafollicular cells
Follicular cells
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These cells vary in shape and size according to the
functional state of the gland.
In routine HE staining, follicular cells exhibit a slight
basophilic.
They are responsible for production of thyroxine
(T4)and triidothyroxine(T3).
Ultrastructure of follicular cells
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Short microvilli on the apical surface.
Golgi complex,mitochodria,lysosome,rough
endothelial reticulum(rER) are present in the
cytoplasm.
Synthesis of T3 and T4
Take place in the thyroid follicle
 1 Synthesis of thyroglobulin
AA→ RER→ thyroglobulin → Golgi
complex(secreting granules) → colloid.
 2 Resorption,diffusion, and oxidation of
iodide
Iodide → (iodide pump) → iodide oxidation in
cytoplasm → colloid
Formation of T3 and T4
3 Iodination of thyroglobulin.
bound to thyroglobulin → iodated
thyroglobulin(MIT,DIT).
4 Formation of T3 and T4 by oxidative coupling
reactions
The coupling of these molecules (MIT,DIT)
Produce T3 and T4.
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Formation of T3 and T4
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5 Resorption of colloid
Stimulated by TSH, Follicular cells
take up thyroglobulin by endocytosis.
6 Release of T4 and T3 into circulation
T4 and T3 cross the basal membrane and are
discharged into the capillaries.
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Major function of T4 and T3
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regulate growth and development :most cells
require T3/T4 for growth. The nervous system is
especially sensitive.
calorigenic effect: T3/T4 increase basal metabolic
rate (BMR) and affect temperature regulation.
cardiovascular effects: increase heart rate.

T3 and T4 control almost every
metabolic activity in your body so big
variations in their levels can cause
serious problems.
hypothyroidism
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hypothyroidism means circulating levels of T3/T4
are below normal. In children this leads to cretinism
and in adults myxedema.
Adults suffering from hypothyroidism show a very
low rate of metabolism and are extremely lethargic.
Body temperature and heart rate are all low.
cretinism
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Congenital absence of T3 and T4, or
chronic iodine deficiency in infancy.
Cretinism is associated with retarded
growth, sluggish movements,and
severe mental deficiencies. The growth
deficiencies can be corrected by
providing thyroid extract or iodine
supplementation soon after birth, but
mental impairment tends to be
irreversible.
Hyperthyroidism

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In
the
adult,
hyperthyroidism
means
circulating levels of T3/T4 are above
normal. It is associated with a high rate of metabolism,
high body temperature, and high heart rates.
There
are
several
types
of
hyperthyroidism
including
is
termed
Grave's Disease which is an autoimmune
disorder.
Graves' disease


is a autoimmune disorder in which the body makes
antibodies to the thyroid-stimulating hormone receptor
(TSHR), The autoantibodies produced in Graves' disease
are not subject to negative feedback, so they continue to be
produced and bind to TSHR even when thyroid hormone
levels rise too high.
A sign often associated with hyperthyroidism is protrusion
of the eyeballs.
Parafollicular cells
(C cells)
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Locate in the follicular epithelium or as isolated among
thyroid follicles.
Larger than follicular cells and less stained.
Secrete calcitonin, which can decrease the blood Ca2+
level by inhibiting the activity of osteoclasts.
Parafollicular cells
Parathyroid
Four small glands
Locate behind the
thyroid gland
Structure
Cells are arranged in cords.
 Chief cells(principal cells)
 Oxyphil cells
Chief cells
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More numerous cells of the parathyroid gland.
Electron microscope shows granules in the
cytoplasm.They are the secretory granules
containing parathyroid hormones(PTH),which can
increase the blood Ca2+ level.
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PTH is essential for life.Therefore,care must be
taken during thyroidectomy.If the glands are totally
removed,death will ensue because
muscles,including the laryngeal and other
respiratory muscles,go into tetanic contraction as
the blood calcium level falls.
PTH and caltitonin have reciprocal effects in the
regulation of blood calcium level .
Oxyphil cells
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They are larger than chief cells and their cytoplasm
contains many acidophilic granules. The TEM
reveals these granules are mitochondria.
The function and importance of such a large
concentration of mitochondria in these cells are
unknown.
Adrenal gland
They are paired organs
lie near the superior
poles of the kidneys.
They are flattened
structures with a
halfmoon shape.
Adrenal gland
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Cortex: locate In the periphery, derived from
mesoderm. It is the steroid-secreting portion.
Medulla: locate in the center, derived from
ectoderm. It is the catecholamine-secreting portion.
Adrenal gland
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Cortex: The cells of the adrenal cortex,which
have the typical ultrastructure of steroid
secreting cells.It is divided into 3 zones on
the basis of the arragement of its cells.
Zona glomerulosa(15%)
Zona fasciculata(80%)
Zona reticularis(5%)
Zona glomerulosa
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It is the narrow outer zone,the layer immediately
beneath the CT capsule.
The cells are arranged in closely packed,rounded,
or arched cords surrounded by capillaries.
The cells secrete mineralocorticoids
(aldosterone).
aldosterone
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Acts on the distal tubules of the kidney,and the
gastric mucosa to stimulate the resorption of
sodium by the epithelial cells.
Its secretion activity is regulated by reninangiotensin- aldosterone system.
renin-angioten - aldosterone system
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The juxtaglomerular cells release renin in response to a
decrease in blood pressure or a low blood sodium level.
renin catalyse the conversion of angiotensinogen to
angiotensin I, which in turn is converted by angiotensinconverting enzyme(ACE) to angiotensin II. Angiotensin II
stimulate the cells of Zona glomerulosa to secrete
aldosterone.
Zona fasciculata
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The arrangement of the cells in one-or two- cell
thick straight cords run at right angles to the
surface of the organ.
There are a great number of lipid droplets in the
cytoplasm.During tissue preparation,the cells
appear vacuolated.
It secrete glucocorticoids(cortisol)
glucocorticoids
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Promote normal
metabolism,particularly carbohydrate
metabolism.
Supress the immune response by
destroying circulating lymphocytes.
Zona glomerulosa
Zona fasciculata
Zona reticularis
Zona reticularis
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It lies between the zona fasciculata and the medulla.
It contains cells disposed in irregular cords that form
network.
It secrete
gonadocorticoids(dehydroepiandrosterone,
DHEA), influences the sexual development.
Adrenal medulla
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Chromaffin
cells(medullary cells) are
modified neurons that
have lost their axons and
dendrites during
embryonic development
and have become
secretory cells.
Chromaffin cells
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They have abundant granules in the
cytoplasm.
Epinephrine-secreting cells and
norepinephrine-secreting cells
secrete adrenaline/epinephrine and
noradrenaline/norepinephrine,
respectively.
The hormones, the adrenaline and noradrenaline,
which are stored in granules and whose
secretion is stimulated by innervating
sympathetic nerve, can immediately elevate the
heart beating rate and blood pressure,
respectively.
Pituitary gland(Hypophysis )
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Weight 0.5g. Most important endocrine gland
Lies in a cavity of the sphenoid bone—the sella turcica
Component of Hypophysis
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Anterior lobe(Adenohypophysis):the glandular
epithelial tissue
Posterior lobe(Neurohypophysis):the neural
secretory tissue
Hypophysis
Adenohypophysis
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pars distalis
pars tuberalis
pars intermedia
Adenohypophysis
Acidphils
Somatotropes(GH cells)
Lactotropes(PRL cells)
Chromophils
Basophils
Chromophobe
Thyrotropes(TSH)
Gonadotropes(LH,FSH)
Corticotropes(ACTH)
Cells of Adenohypophysis
Somatotropes(GH cells)
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Most commonly cells,constitute 50% of
the anterior lobe.
They produce GH which can stimulates
growth and replication by accelerating the
rate of protein synthesis, which can
stimulates growth of long bone acting on
differentiation of chondrocytes.
Growth Hormone Abnormalities
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Growth hormone stimulates muscular
and skeletal development. If it is
administered before the epiphyseal
cartilages have closed, it will cause
an increase in height, weight, and
muscle mass. In extreme cases,
gigantism can result.
Cells of Adenohypophysis
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Lactotropes(PRL cells)
Constitute 15% to 20% of the anterior lobe.
They produce PRL which promotes mammary gland
development, initiates milk formation.
Cells of Adenohypophysis
Thyrotropes
 Constitute 5% of the anterior lobe.
 They produce thyroid-Stimulating
(TSH). It stimulates thyroid hormone
synthesis,storage and liberation.
Cells of Adenohypophysis
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Gonadotropes
Constitute 10% of the anterior lobe.
They secrete Follicle-stimulating hormone and
luteinizing hormone
Major function of FSH
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In females , FSH Promotes follicle development and
secretion of estrogens by ovarian cells.
In males, FSH stimulates sustentacular cells, In
response, the sustentacular cells promote the
physical maturation of developing sperm.
Major function of LH
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In females, It promotes ovarian follicle maturation
and progesterone secretion which prepare the body
for possible pregnancy.
In males, It is essential for maintenance of
androgen secretion by interstitial cells of the testes.
Cells of Adenohypophysis
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Corticotropes(ACTH)
Constitute 15% to 20% of the anterior lobe.
They produce Adrenocorticotropic Hormone (ACTH)
which stimulates the release of the adrenal cortex.
Pars tuberalis
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It is a funnel-shaped region surrounding the
infundibulum of the Neurohypophysis.
Most of the cells the Pars tuberalis secrete
ACTH.
They are arranged in cords alongside the blood
vessels.
Pars intermedia
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Contains follicles.
Functions unknown.
In frogs,the cells produce MSH, which stimulates
pigment production in melanocytes.
Neurohypophysis
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pars nervosa (neurosecretory axons and their
endings)
Infundibulum(Composed of median eminence
and neural stalk)
Pars nervosa
Unlike the adenohypophysis,does not contain
secretory cells.
 It is composed of unmyelinated axons of
neurosecretory neurons whose cell bodies locate
in paraventricular and supraoptic nuclei in
hypothalamus.
What are Herring Bodies?
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The axon dilations, are light acidophilic and contain
many secretory granules(ADH and OCT)
Major function of ADH
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The antidiuretic hormone (ADH, vasopressin), which
is produced by supraoptic nuclei, promote water
reabsorption in kidney.
In large dose, ADH also stimulates the
contractions of smooth muscle of small arteries
and arterioles.
Major function of Oxytocin
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Oxytocin is actually synthesized by paraventricular nuclei in
the hypothalamus and is stored in the neurohypophysis.
In the uterus, At the end of gestation, the uterus must
contract vigorously in order to deliver the fetus. During the
later stages of gestation, Oxytocin enhances contraction of
uterine smooth muscle to facilitate parturition or birth.
Major function of Oxytocin

In the mammary glands, Oxytocin also stimulates
the ejection of milk when infants suckle.
Blood supply
Hypophyseal portal system
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Blood vessels that link two capillary networks are
called portal vessels, and the entire complex is termed
a portal system
Include primary capillary plexus, hypophyseal portal
vein,and second capillary plexus.
Hypothalamus Control of the Anterior
Pituitary
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Releasing hormones (RH) :RH stimulates the synthesis
and secretion of one or more hormones at the anterior
pituitary,
Inhibiting hormones(IH): IH inhibite the synthesis and
secretion of hormones from the anterior pituitary.
The regulatory hormones released at the hypothalamus
are transported directly to the anterior pituitary by the
hypophyseal portal system.
Relationship among the
hypothalamus,hypophysis,and thyroid gland
Homework

Describe the structure and function
of the thyroid gland and parathyroid
gland.