endocrine glands - doctor 2016 - ju medicine · 2018-08-11 · cell type present. their cytoplasm...
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endocrine glands
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Secretory cells of endocrine glands release their products,
signaling molecules called hormones, into the
neighboring vascularized compartment for uptake by
capillaries and distribution throughout the body.
▪ There is no
secretory duct as in exocrine glands
endocrine glands
Junqueira's
Basic Histology
Text and Atlas,
2014th Edition
Distribution by the circulation allows hormones to act on target cells with receptors for
those hormones at a distance from the site of their secretion.
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endocrine cells produce hormones
that act
on target cells only a short
distance awayThrough
1- local in interstitial fluid
2-short loops of blood vessels
For example :gastrin
made by pyloric G cells reaches
target cells in the fundic
glands
in which a signaling molecule
remains on the secreting cell’s surface
or adjacent extracellular
matrix and affects target cells when
the cells make contact.
Juxtacrine signaling is particularly
important in embryonic
and regenerative tissue interactions
contact-dependent signalling
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Why the CNS is not enough?
Why do we need Endocrine system?
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At puberty the female begins to
undergo regular monthly cycles called
THE OVARIAN CYCLE
Sexual cycles are under the control of the
(GnRH)
Controls the release of the Gonadotropin
FSH and LH
sexual cycles
The hypothalamus acts as a pulse generator which generates the pulsatile release of
Hypothalamus
Gonadotropin releasing hormone (GnRH)
from the anterior part of the pituitary gland
The follicle-stimulating hormone (FSH) luteinizing hormone (LH)
Control
The endometrial cycle ( menstrual cycle )
Controls
Brain
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Histology
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The HEMATOXYLIN stains nucleic acids
(plus calcium deposits and bacteria) blue.
Clear areas represent
water,
carbohydrate
lipid,
gas
The EOSIN stains most proteins
(actually, arginine and lysine) pink.
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Nuclei
Blue with the
will always stain
Hematoxylin.
will stain according to its composition.
The cytoplasm of cells
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Cells of the adenohypophysisDr.shatarat
Pars distalis. This specimen of the pars distalis is
stained with brilliant crystal scarlet, aniline blue,
and Martius yellow to distinguish the various
cell types and connective tissue stroma. The
cords of cells are surrounded by a delicate
connective tissue stroma stained blue. The
sinusoidal capillaries are seen in close
association with the parenchyma and contain
erythrocytes stained yellow. In the region shown
here, the acidophils (Ac) are the most numerous
cell type present. Their cytoplasm stains cherry
red. The basophils (Bas) stain blue. The
chromophobes (Ch), although few in number in
this particular region, are virtually unstained.
640
Histology: A Text and Atlas: With Correlated Cell and Molecular Biology
The adenohypophysis is made of
epithelia cells !!!!!!!! and vascular
Sinusiods supported by a mesh of connective tissue
Most of the anterior lobe of the pituitary gland has
the typical organization of endocrine tissue
The cells are organized in clumps and cords separated
by
fenestrated sinusoidal capillaries of relatively large
diameter
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How many colors can be identified in this H&E section?????
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Adenohypophysis – high power
The adenohypophysis contains 3 cell types:-acidophils (stain red)-basophils (stain blue)-chromophobes (pale stain)
The adenohyphysis stains red-blue on low power because of the acidophils and basophils
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chromophils
(cells which take up
stain)
called acidophils and
basophils.
The anterior pituitary also contains one type of
chromophobe
(cells which stain only weakly)
Histologists identified three types of cells
according to their staining reaction, namely
Basophils (10%)
Acidophils (40%)
2- Chromophobes (50%)
1-Chromophils
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Parenchymal cells of the pars distalis to be
subdivided into acidophil cells (A), basophils
(B), and chromophobes (C) in which the
cytoplasm is poorly stained. Also shown are
capillaries and sinusoids (S)
stained with Gomori trichrome.
(X400
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Cells of the adenohypophysis
Chromophils
Acidophils Basophils
Chromophobes
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Importance of different colors?
• Acidophils secrete growth hormone and
prolactin
• Basophils secrete TSH, LH , FSH and ACTH
• Chromophobes are undifferentiated cells
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Cells of the Adenohypophysis
1- Chromophobes
• small weakly stained cells
• represent stem cells or (most likely)
• partially degranulatedchromophils
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The micrograph shows somatotrophs stained using an antibody
against somatotropin. (X400; Hematoxylin counterstain)
Subtypes of basophilic and
acidophilic cells are identified
by immunohistochemistry
Specific cells are usually named
according to their hormone’s
target cells
Acidophils secrete either growth
hormone (somatotropin) or
prolactin and are called
somatotrophs and lactotrophs
(or somatotropic cells and
lactotropic cells), respectively.
The basophilic cells are the
corticotrophs, gonadotrophs,
and thyrotrophs
Chromophils
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Chromophils
Acidophils
Somatotops Mammotrops
Basophils
Gonadotrops Thyrotrops Corticotrops
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1- Somatotrops:
• LM
• Form ~ 50% of the total number of chromophils.
• Occur in clumps and clusters
• Central nucleus
• EM
• Rod shaped mitochondria
• Many rER
• Many secretory granules (secrete GH)
• Moderate Golgi
• Action of GH: acts on growth of long bones via insulin-like growth factors synthesized in the liver.
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2- Mammotrops
• Form 15-20% of chromophils
• Occur singly
• Small polygonal cells
• Organelles are ill-defined
• During lactation organelles increase in size and number
• Secrete prolactin
• Action of prolactin: promotes milk secretion.
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3- Gonadotrophs
• Form ~ 10% of chromophils.
• Rounded cells.
• Prominent nucleus.
• Many granules with variable size.
• Cytoplasm contains well developed Golgi, many rER.
• Secrete FSH and LH.
• Action of FSH: promotes ovarian follicle development and estrogen secretion in women, and spermatogenesis in men.
• Action of LH: promotes follicular maturation and progesterone secretion in women and Leydig secretion in men.
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4- Thyrotrops
• Form ~ 5% of chromophils.
• Located away from sinusoids.
• Cytoplasm contains many small organelles.
• Secrete TSH.
• Action of TSH: stimulates thyroid hormone synthesis, storage, and liberation.
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5- Corticotrops
• Form 15-20% of chromophils.
• Round-ovoid cells scattered through pars distalis.
• Eccentric nucleus with few organelles.
• Secrete ACTH.
• Action of ACTH: stimulates secretion of adrenal cortex hormones and regulated lipid metabolism.
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• are characterized by a star like appearance with their cytoplasmic
processes encircling hormone-producing cells.
• They have the ability to make cell clusters or small follicles
• they do not produce hormones.
• Folliculostellate cells are interconnected by gap junctions.
• Based on immunocytochemical and electrophysiological studies, it
is hypothesized that the network of folliculo-stellate cells
interconnected by gap junctions transmits signals from the
pars tuberalis to pars distalis.
• These signals may regulate hormone release throughout the
anterior lobe of the pituitary gland. Thus, the folliculo-stellate
network may appear to function in addition to the hypophyseal portal
vein system
* Folliculostellate cells
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It is composed of neural tissue, containing
some 100,000 unmyelinated axons of large
secretory neurons with cell bodies in the
supraoptic and paraventricular nuclei of the
hypothalamus
Also present are highly branched glial
cells called pituicytes that resemble
astrocytes and are the most abundant
cell type in the posterior pituitary
Neurohypophysis (Posterior Pituitary)
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Neurohypophysis – high power
The neurohypophysis resembles neural tissue, with glial cells, nerve fibers, nerve endings, and intra-axonal neurosecretory
granules
Precursors of ADH (vasopressin) and oxytocin are synthesized in
the hypothalamus and transported to the pars nervosa where processing is completed
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Does not contain secretory cells.
Contains axons of secretory nerves; their mother cells are present in the paraventricular and supraoptichypothalamic nuclei.
Pituicytes are the most numerus cells.
Pituicytes resemble astrocytes.
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Neurohypophysis – high power
Hering bodies are large dilated axon terminal endings that are filled with accumulated neurosecretory granules
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Secretory neurons have larger diameter but are histologically and functionally similar to other neurons.
Axons of neurons transport ADH and oxytocin into the pars nervosa.
• Secretory products accumulate in the distal part of the axon in Hering bodies.
• Hering bodies appear slightly acidophilic.
• Secretory products are surrounded by a membrane and bound to neurophysin.
• Nerve impulses trigger the release release of peptides from neurosecretory bodies.
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Most Oxytocin is released from paraventricular nuclei.
Most ADH is released from supraoptic nuclei.
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ADH facilitates resorption of water from the distal tubules and collecting ducts of the kidney by altering the permeability of the cells to water.
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Oxytocin promotes contraction of smooth
muscles of the uterus and myoepithelial cells of the
breast.
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Tumours of the pituitary
may have two special features;
their endocrine disturbances and their relationship to the optic chiasma.
Chromophobe adenoma
is the commonest pituitary tumour.
As it enlarges it expands the
pituitary fossa (sella turcica) and
this may be demonstrated
radiologically. Compression of the
optic chiasma produces the very
rapid typical bitemporal
hemianopia.
The tumour itself is non-secretory
and gradually destroys the normally
functioning gland.
The patient develops
hypopituitarism with loss of sex
characteristics, hypothyroidism and
hypoadrenalism
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The eosinophil adenoma secretes the pituitary
growth hormones. If it occurs before puberty,
which is unusual, it produces gigantism; after
puberty it results in acromegaly.
The basophil adenoma is small, produces no
pressure effects and may be associated with
Cushing’s syndrome, although this more often
results from hyperplasia or tumour of the
suprarenal cortex.
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Gross anatomy
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Glands drain ipsillaterally by superior, middle, and inferior thyroid veins.
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In the fifth week, epithelium
of the dorsal wing
of the third pouch differentiates
into
INFERIOR PARATHYROID
GLANDwhile
the ventral wingforms
THE THYMUS
Both gland primordia lose
their connection with the
pharyngeal wall, and the thymus
then migrates in a caudal and a
medial
direction, pulling the inferior parathyroid
with it
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Epithelium of the dorsal wing of the fourth pharyngeal pouch forms
When the
parathyroid gland
loses contact with the
wall of the pharynx,
it attaches itself to
the dorsal surface of
the caudally
migrating
thyroid as the
superior parathyroid
gland
Epithelium of the dorsal wing of
the fourth pharyngeal pouch
forms
THE SUPERIOR
PARATHYROID GLAND
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Parathyroid Gland – low power
Low power of
parathyroid, showing
random cords of cells.
The parathyroid is
somewhat lobulated in
appearance and
considerable adipose
tissue is intermingled
with secretory portions.
Adipose tissue Cords of cells
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Parathyroid Gland – high power
2 cells types of the Parathyroid:
Chief cells secrete parathormone (PTH). They have large round nuclei with a small amount of clear cytoplasm.
Oxyphil cells have smaller, darker nuclei and
relatively larger amount of cytoplasm. The
significance of the oxyphil cells is not clear.
Some
oxyphil cells show low levels of PTH
synthesis, suggesting that
these cells are transitional derivatives of
principal cells.
Chief
cells
Oxyphil cells
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• Photomicrograph of human
parathyroid gland. This H&E–stained
specimen shows the gland with part
of its connective tissue capsule
(Cap). The blood vessels (BV) are
located in the connective tissue
septum between lobes of the gland.
The principal cells are arranged in
two masses (top and bottom) and are
separated by a large cluster of
oxyphil cells (center).
The oxyphil cells are the larger cell
type with prominent eosinophilic
cytoplasm. They may occur in small
groups or in larger masses, as seen
here. The principal cells are more
numerous. They are smaller, having
less cytoplasm, and consequently
exhibit closer proximity of their
nuclei. Adipose cells (AC) are
present in variable, although limited,
numbers
Rea
d o
nly
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Also called pineal body, epiphysis
cerebri
is an endocrine or neuroendocrine
gland that regulates daily body
rhythm.
PINEAL GLAND
The pineal gland is a flattened, pine
cone–shaped structure
It measures 5 to 8 mm high and 3 to5
mm in diameter and weighs between
100 and 200 mg.
In humans, it is located at the
posterior wall of the third ventricle
near the center of the brain.
It develops from neuroectoderm of
the posterior portion of the roof of
the diencephalon and remains
attached to the brain by a short
stalk.
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The pineal gland contains two types of parenchymal cells:
Pinealocytes
Interstitial (glial) cells.
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The interstitial (glial) cells constitute
about 5% of the cells in the gland.
In addition to the two cell types,
the human pineal gland is characterized
by the presence of calcified concretions called
brain sandIt appears to be derived from precipitation of
calcium phosphates and carbonates on carrier
proteins that are released into the cytoplasm
when the pineal secretions are exocytosed
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Melatonin▪ is released in the dark and regulates reproductive function in mammals by inhibiting
the steroidogenic activity of the gonads
▪ Production of gonadal steroids is decreased by the inhibitory action of melatonin on
neurosecretory neurons located in the hypothalamus (arcuate nucleus) that produce
GnRH.
▪ Inhibition of GnRH causes a decrease in the release of FSH and LH from the anterior
lobe of the pituitary gland. In addition to melatonin, extracts of pineal glands from
many animals contain numerous neurotransmitters, such as serotonin, norepinephrine,
dopamine, and histamine, and hypothalamic-regulating hormones, such as
somatostatin and TRH.
▪ Clinically, tumors that destroy the pineal gland are associated with precocious (early-
onset) puberty.
▪ Animal studies demonstrate that information relating to the length of daylight reaches
the pineal gland from photoreceptors in the retina.
▪ The pineal gland thus influences seasonal sexual activity. Recent studies in humans
suggest that the pineal gland has a role in adjusting to sudden changes in day length,
such as those experienced by travelers who suffer from jet lag.
▪ In addition, the pineal gland may play a role in altering emotional responses to the
reduced length of day during winter in temperate and subarctic zones known as
seasonal affective disorder (SAD)
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Endocrine Pancreas
(Islets of Langerhans)
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Endocrine Pancreas
Islets of Langerhans
Low power High power
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Endocrine Pancreas
• Cells in the islets of Langerhans
– Alpha – secrete glucagon
– Beta – secrete insulin
– Delta – secrete somatostatin and gastrin
– PP – secrete pancreatic polypeptide
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First described by Langerhans in 1869 (as an observation on the urine of pancreactictomized dogs).
In 1893 Gustave-Edouard Laguesse (1861-1927) attached the name Langerhans to the structures. Langerhans did not suggest any function for them. The book has been reprinted with an English translation by H. Morrison.
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Spherical-oval cellular masses between the acini of the pancreas.
Variable in size and number of cells in them.
They form ~ 1 million secretroy units.
Not homogeneously distributed and increase in number towards the tail.
Surrounded by a very thin capsule.
They have the same embryological origin as the rest of the pancreas (endoderm).
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Section of an adult human pancreas stained for glucagon (green) and insulin (red)
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In H & E cells show variation in staining reaction between acidophilia and basophilia.
E.M. shows typical poly peptide secreting cells with variable amount of granules.
Immunohistochemistry is the only accurate method to differentiate between cells.
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Major pancreatic cells cell
Cell Location % Secretion Function
α Peripheral ~ 20 Glucagon ↑ Blood glucose level; ↑ glycogenolysis and lipolysis
β Central ~ 70 Insulin ↓ Blood glucose level
δ Scattered 5-10 Somatostatin Inhibits release of other cells
F (PP) Scattered <1 Pancreatic polypeptide
↑ activity of chief cells, ↓ bile secretion.↓ pancreatic enzyme and HCO3 secretion.↓ intestinal motility
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Suprarenal (adrenal) Glands
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Adrenal Histology
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The gland is divided into an outer cortex and an inner medulla.
The adrenal cortex is composed of three zones histologically:
• Outer zona glomerulosa, site for aldosterone synthesis.
• Central zona fasciculata produce cortisol, and
• Inner zona reticularis produce androgens.
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Zona glomerulosa
Is the exclusive site of production of aldosterone.
Consists ~ 15% of the cortex.
Cells are arranged in closely packed clusters continuous with the next layer.
Cells are small pyramidal-columnar with spherical nuclei.
Clusters of cells are surrounded by fenestrated sinusoidal capillaries.
Cells have abundant sER, large mitochondria with shelf-like cristae, Golgi complex, few rER, and few lipid droplets.
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Zona glomerulosa secretes mineralocorticoids, that function in the regulation of sodium and potassium homeostasis and water balance.
The main mineralocorticoid is aldosterone.
Aldosterone stimulates resorption of sodium from:
• Distal renal tubules.
• Gastric mucosa.
• Salivary glands.
• Sweat glands.
The zona glomerulosa is under the feed back control of the renin-angiotensin-aldosterone system.
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Zona Glomerulosa
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Zona Fasciculata
The thickest middle zone that form ~80% of the cortex.
Cells are large polyhedral, arranged in long straight cords 1-2 cells thick.
Cords are separated by sinusoidal capillaries.
Cells are lightly stained, commonly binucleated.
Cells are typical steroid synthesizing cells.
Cytoplasm contains lipid droplets.
Cells secrete glucocorticoids, mainly cortisol.
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Glucocorticoids may have different, even opposite effects in different tissues:
• In the liver:
• ↑ conversion of aminoacids to glucose.
• ↑ polymerization of glucose to glycogen.
• ↑ uptake of aminoacids and fatty acids.
• In adipose tissue: ↑ breakdown of lipids to glycerol and free fatty acids.
• In other tissues: ↓ rate of glucose use and ↑ oxidation of fatty acids.
• In cells: ↓ protein synthesis and ↑ protein catabolism.
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Zona reticularis
The inner zone, forms 5-7% of the cortex. Contains light and dark cells.
Cells are smaller than the reticularis, their nuclei are more deeply stained.
Cells are arranged in anastomosing cords separated by fenestrated capillaries.
Cells have few lipid droplets.
Cells are typical steroid-secreting cells.
Their principal secretion is weak androgen (minimal glucocorticoids).
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Adrenal medulla
Composed of large, pale staining epithelioid cells; chromaffin cells, connective tissue, sinusoidal capillaries and nerves.
The chromaffin cells are modified neurons.
Myelinated, presynaptic nerves pass directly to chromaffin cells.
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E.M shows that there are two types of chromaffin cells:
• Cells containing large dense core vesicles → secrete norepinephrine.
• Cells containing small homogeneous less dense vesicles → secrete epinephrine.
Chromaffin cells
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Glucocorticoids secreted in the cortex induce the conversion of norepinephrineto epinephrine in chromaffin cells.
Most of chromaffin cells at the cortico-medullary junction secrete epinephrine.
Norepinephrine-secreting cells are also found in paraganglia (collections of catecholamine-secreting cells adjacent to the autonomic ganglia) and in various
viscera. The conversion of norepinephrine to epinephrine (adrenalin) occurs only in chromaffin cells of the adrenal medulla
About 80% of the catecholamine secreted from the adrenal
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The catecholamines, in concert with the glucocorticoids, prepare the body for the “fight-or-flight” response.
Sudden release of catecholaminesestablishes conditions for maximum use of energy.
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are innervated by preganglionic sympathetic neurons,
They trigger epinephrine and norepinephrine release
during stress and intense emotional reactions.
Epinephrine increases:
▪ heart rate
▪ dilates bronchioles,
▪ dilates arteries of cardiac and skeletal muscle.
Norepinephrine constricts:
▪ vessels of the digestive system and skin, increasing
blood flow to the heart, muscles, and brain.
Both hormones stimulate glycogen breakdown, elevating blood glucose levels.
Together these effects augment the capability for defensive reactions or escape of
stressors, the fight-or-flight response.
During normal activity the adrenal medulla
continuously secretes small quantities of these
hormones.
Medullary chromaffin cells
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Thyroid gland
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Thyroid follicle:
• The structural and functional unit of the thyroid gland.
• Consists of a group of cells resting on the same basal lamina surrounding a lumen filled with colloid.
• The follicles are variable in size.
• Hormones are stored in the follicles.
• Each follicle is surrounded by variable amount of connective tissue.
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Follicular cells (principal cells):
• Squamous-columnar cells according to activity.
• Basophilic cytoplasm.
• Nucleus: round-ovoid with 2 nucleoli.
• Many rER.
• Numerous apical lysosomes and mitochondria.
• Supranuclear Golgi complex.
• Apical microvilli.
• Numerous vesicles in the cytoplasm.
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Parafollicular cells (Clear cells, C cells):
• Pale staining, larger than follicular cells.
• Occur singly or in clusters among follicular cells.
• Overlapped by follicular cells.
• E.M:
• Moderate rER.
• Well-developed Golgi.
• small, dense, basal secretory granules.
• Secrete calcitonin:
• Inhibits bone resorption by osteoclasts.
• Stimulated when Ca2 is high.
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C
C
C
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Thyroid gland
1. Recognize and understand the coverings of the thyroid gland and their clinical
importance.
2. Recognize and understand the main parts of the thyroid gland and their locations,
relations and connections.
3. Comprehend the blood supply of the thyroid gland, their relations with recurrent and
external laryngeal nerves.
4. Understand the embryological origins of the pituitary gland and its associated
malformations.
5. Grasp the clinical correlations of the midline structures of neck related to the thyroid
gland and differentiate between them and the those on the lateral side of the neck.
6. Recognize and understand imaging of the thyroid gland.
7. Grasp the histological structure of the thyroid gland and its cells under light.
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Gross anatomy
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Transverse sections through the neck at the
level of the second sixth cervical vertebrae
➢ It is placed anteriorly
in the lower neck
at the level with
the 5th cervical to the
1st thoracic vertebrae
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It consists of
Right and left lobes connected
by
a narrow isthmus 7/14/2018 Dr.Shatarat
its apex being directed upward as far as
the oblique line on the lamina of the
thyroid cartilage
3- Lobs
its base
lies below at the level of the fourth or
5th tracheal ring.
Each lobe is pear shaped
Apex
base
The posteromedial aspects of the lobes are
attached to the side of the cricoid cartilage by a
lateral thyroid ligament
Note
It should be noted that the normal thyroid gland is nearly
always asymmetric. The right lobe may be even twice as
large as the left lobe.
The right upper pole extends higher up in the
neck, and the lower pole extends lower.
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4- THE ISTHMUS
is often present, and it projects
upward from the isthmus
5- Pyramidal lobe
The isthmus extends
across the midline in
front of
the 2ed, 3ed , and 4th
tracheal rings
A fibrous or fibromuscular band, the levator of the thyroid gland, musculus levator glandulae
thyroideae, sometimes descends from the body of the hyoid to the isthmus or pyramidal lobe
Note
persists in at least 15% of
the population
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True capsule
False capsule
6- Coverings and fascia of the thyroid gland
The thyroid gland is surrounded by
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A-True capsule, a thin fibrous
capsule,
which is formed by condensation of
the stroma of the gland.
➢ It is attached by means of dense
connective tissue to the cricoid
cartilage (part of the larynx) and
superior tracheal rings (part of the
trachea).
The True capsule of thyroid capsule is
much denser in front than behind and the
enlarging gland therefore tends
to push backwards, burying itself round the
sides and even the back of the
trachea and oesophagus.
Clinical note
cause dangerous DyspneaDysphagia7/14/2018 Dr.Shatarat
B- False capsuleit is a loose sheath formed by the visceral
portion of the pretracheal layer of deep
cervical fascia external to the true capsule
➢ The false capsule thickens between the
cricoid cartilage and thyroid gland to
form the
ligament of Berry(The suspensory ligament of the thyroid)
gland
(attaches the thyroid gland to trachea)
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The false capsule of the thyroid
gland also
attaches the gland to
the larynx and even to the hyoid
bone
This explains why the thyroid gland
follows the movements of the
larynx in swallowing.
This information is important because any pathologic neck
swelling that is part of the
thyroid gland will move upward when the patient is asked
to swallow
It is clear that the false
capsule is attached to
Both the larynx and
trachea
Clinical note
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a large goitre will extend downwards into the
superior
mediastinum
(‘Plunging Goitre’)
The pretracheal layer of deep cervical fascia is attached to hyoid bone
Retrosternal Goiter
The attachment of the sternothyroid muscles to the thyroid
cartilage effectively binds down the thyroid gland to the larynx
This limits upward expansion of the gland
However, downward expansion has no limitation
And
Or
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7- Relations of the Lobes
C-The
sternothyroi
d
B-The
sternohyoid
D-The anterior
border of the
sternocleidomastoid
A-The
superior belly
of the
omohyoid
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The anastomosis between
the superior and inferior thyroid arteries.
Posterior view
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Posterolaterally:
The carotid sheath with the
common carotid artery, the
internal jugular vein, and the
vagus nerve
The larynx, the trachea, the pharynx,
and the esophagus. Associated with
these structures are the cricothyroid
muscle and its nerve supply, the
external laryngeal nerve. In the
groove between the esophagus and
the trachea is
the recurrent
laryngeal nerve
Medially:
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A-The superior thyroid artery
B-The inferior thyroid artery
C- Sometimes the thyroidea ima.
A-The superior thyroid artery, a branch of
the external carotid artery, descends to the
upper pole of each lobe, accompanied by
The External Laryngeal
Nerve
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The superior thyroid artery on each side is related
to the external laryngeal nerve, which supplies the
cricothyroid muscle.
Damage to the
external
laryngeal
nerve
results in an
inability to
tense the
vocal folds
and in
hoarseness
Thus, The Superior Thyroid Artery during surgery on the thyroid ,
is ligated near the gland to avoid injury to
the external laryngeal nerve 7/14/2018 Dr.Shatarat
➢ a branch of the thyrocervical trunk,
ascends behind the gland to the level of
the cricoid cartilage.
➢ It then turns medially and downward to
reach the posterior border of the gland.
The recurrent laryngeal
nerve crosses either in front of or behind the artery,
or it may pass between its branches.
B-The inferior thyroid artery
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The terminal branches of the
inferior
thyroid artery
on each side are related to the
RECURRENT LARYNGEAL
NERVE.
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Thus, THE INFERIOR THYROID ARTERY during
surgery on the thyroid ,
is ligated away from the gland to avoid injury to
the recurrent laryngeal nerve
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C-The thyroidea ima, In
approximately 10% of people, a
thyroid ima artery
ascends on the anterior surface of
the trachea, which it supplies,
and continues to the isthmus of
the thyroid gland.
The possible presence of this artery
must be considered when performing
procedures in the midline of the neck
inferior to the isthmus because it is a
potential source of bleeding
arises from the brachiocephalic trunk,
or the arch of the aorta,
from the right common carotid
subclavian, or internal thoracic arteriesVari
ab
le
Clinical note
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Lesions of the Laryngeal Nerves
The muscles of the larynx are innervated by
the recurrent laryngeal nerves, with the
exception of the cricothyroid muscle, which is
supplied by the external laryngeal nerve. Both
these nerves are vulnerable during operations
on the thyroid gland because of the close
relationship between them and the arteries
of the gland.
To be discussed next year
7/14/2018 Dr.Shatarat
9-The veins from the thyroid gland
C-The inferior thyroid vein
The inferior thyroid veins of the two
sides anastomose with one another as
they descend in front of the trachea.
They drain into the left brachiocephalic
vein in the thorax
A-Superior thyroid vein
which drains into the internal jugular vein;
B-The middle thyroid vein
which drains into the internal jugular vein;
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10-The lymphatic vessels of the thyroid gland
communicate with a capsular network of
lymphatic vessels
From this network, the vessels pass
initially to prelaryngeal, pretracheal,
and paratracheal lymph nodes, which
drain in turn to the superior and
inferior deep cervical nodes
Inferior to the thyroid gland, the
lymphatic vessels pass directly to the
inferior deep cervical lymph nodes
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The uppermost, just above the
thyroid
isthmus, in front of the cricoid
cartilage, and medial to
a pyramidal lobe, if present, is a
constant node group
of one to five nodes, which has
been termed
The Delphian node
enlargement of which is
indicative of metastasis
from thyroid or
laryngeal carcinoma.
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7/14/2018 Dr.Shatarat
with development of the arches and clefts,
a number of outpocketings,
The pharyngeal
pouches appear
THE PHARYNGEAL ARCHES
are separated
by deep clefts known as
PHARYNGEAL
CLEFTS
In a cross section of the embryo in the area of the head and neck
The following can be noticed
THE PHARYNGEAL ARCHES
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Pharynx (ventral view) 4th week
Thyroid Gland
1-begins to develop during the
third week as an endodermal
thickening in the floor of the
pharynx
between the tuberculum
impar and the copula at a
point later indicated
by the foramen cecum
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2- It descends in front of the pharyngeal gut as a bilobed diverticulum
3- During this migration, the thyroid
remains connected to the tongue by a
narrow
canal, the thyroglossal duct.
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4-As development continues, the duct elongates, and its distal end becomes bilobed. Soon,
the duct becomes a solid cord of cells, and as a result of epithelial proliferation, the bilobed
terminal swellings expand to form the thyroid gland
5-The thyroid gland now migrates inferiorly in the neck and passes either anterior to, posterior to,
or through the developing body of the hyoid bone.
6-By the seventh week, it reaches its final position in relation to the larynx and trachea.
Meanwhile, the solid cord connecting the thyroid gland to the tongue fragments and
disappears. 7/14/2018 Dr.Shatarat
7-The site of origin of the thyroglossal duct on
the tongue remains as a pit called
the foramen cecum.
8-The thyroid gland may now be
divided into a small median isthmus
and two large lateral lobes
Pharynx and derivatives (between 6th and 7th weeks)7/14/2018 Dr.Shatarat
9-The ultimobranchial bodies (from the fifth pharyngeal pouch) and
neural crest cells are believed to be incorporated into the thyroid gland,
where they form the parafollicular cells, which produce
calcitonin.
Second origin of the thyroid gland
as we mentioned before, most glands have two different origins
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Congenital Anomalies of the
Thyroid Gland
1-Agenesis of the Thyroid
Failure of development of the thyroid gland may occur and
is the commonest cause of cretinism
2-Incomplete Descent of the Thyroid
The descent of the thyroid may be arrested at
any point
between the base of the tongue and the trachea
Lingual thyroid is the most common form of
incomplete
descent The mass of tissue
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Aberrant thyroid tissue may be found anywhere along the path of
descent
of the thyroid gland. It is commonly found in the base of the tongue,
just behind the foramen cecum, and is subject to the same diseases
as the
thyroid gland itself.
caution!!!
A mass in the
posterior midline
might be the only
thyroid in the
patient’s body
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Th
yro
glo
ss
al
Du
ct
an
d T
hyro
id A
bn
orm
ali
ties
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3-Persistent Thyroglossal Duct
Conditions related to a persistence of
the thyroglossal duct
usually appear in childhood, in
adolescence, or in young
adulthood
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Thyroglossal Duct and Thyroid
Abnormalities
A thyroglossal cyst may lie at any
point along the migratory pathway
of the
thyroid gland but is always near or in
the midline of the neckby its name, it is a cystic remnant of
the thyroglossal duct, Although
approximately
50% of these cysts are close to or
just inferior to the body of the hyoid
bone they may also be found at the
base of the tongue
or close to the thyroid cartilage.
Sometimes a thyroglossal cyst is
connected to
the outside by a fistulous canal, a
thyroglossal fistula. Such a fistula
usually
arises secondarily after rupture of a
cyst but may be present at birth.7/14/2018 Dr.Shatarat
Thyroglossal cyst.
These cysts, which
are remnants of the
thyroglossal
duct, may be
anywhere along the
migration pathway of
the thyroid gland.
They are commonly
found behind the
arch of the hyoid
bone. An important
diagnostic
characteristic
is their
midline
location.7/14/2018 Dr.Shatarat
Branchial fistulas occur when the
second pharyngeal arch fails to grow
caudally
over the third and fourth arches, leaving
remnants of the second, third,
and fourth clefts in contact with the
surface by a narrow canal.
Such a fistula, found on the lateral
aspect of the neck directly anterior to
the sternocleidomastoid muscle,
usually provides drainage for a
lateral cervical
cyst These cysts, remnants of the
cervical sinus, are most often
just below the angle of the jaw
Branchial Fistulas
Frequently a lateral cervical cyst is not
visible at birth but becomes evident as it
enlarges during childhood.
Patient with a lateral cervical cyst. These cysts are always on the lateralside of the neck in front of the sternocleidomastoid muscle. They commonly lie under
the angle of the mandible and do not enlarge until later in life.7/14/2018 Dr.Shatarat
4-Thyroglossal Sinus (Fistula)
Occasionally, a thyroglossal cyst ruptures
spontaneously,
producing a sinus). Usually, this is a result of
an infection of a cyst. All remnants of the
thyroglossal
duct should be removed surgically
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7/14/2018 Dr.Shatarat
1-As the lateral lingual swellings increase in size, they overgrow the
tuberculum
impar and merge, forming the anterior two-thirds, or body, of the tongue
Since the mucosa covering the body of the tongue originates
from the first pharyngeal arch, sensory innervation to this area is by
the mandibular branch of the trigeminal nerve.
The body of the tongue is
separated from the posterior third by a V-shaped groove,
the terminal sulcus
2-The posterior part, or root, of the tongue originates from the second,
third,
and part of the fourth pharyngeal archThe fact that sensory innervation to
this part of the tongue is supplied by the glossopharyngeal nerve
indicates that
tissue of the third arch overgrows that of the second.
Some of the tongue muscles probably differentiate in situ, but most are
derived from myoblasts originating in occipital somites.
Thus, tongue musculature
is innervated by the hypoglossal nerve.7/14/2018 Dr.Shatarat
Tuberculum impar
Copula
(hypobranchial
eminence
Epiglottal
swelling
Palatine
tonsil
Root of
tongue
Foramen
cecum
in t
he f
loo
r o
f th
e p
hary
nx
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Metastatic disease to the thyroid is common; it
likely
relates to its rich blood supply of approximately
560 mL/100 g tissue/min (a flow rate per gram
of tissue
that is second only to the adrenal glands)
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7/14/2018 Dr.Shatarat