2. Human endocrine system, group of ductless
glands that regulate body processes by
secreting chemical substances called
hormones. Hormones act on nearby tissues or
are carried in the bloodstream to act on
specific target organs and distant tissues.
3.
4. Diseases of the endocrine system can result
from the oversecretion or undersecretion of
hormones or from the inability of target organs
or tissues to respond to hormones effectively.
5. The endocrine system is the collection of
glands that produce hormones that regulate
metabolism, growth and development, tissue
function, sexual function, reproduction, sleep,
and mood, among other things.
6. Pituitary gland, also called hypophysis,
ductless gland of the endocrine system that
secretes hormones directly into the
bloodstream. The term hypophysis (from the
Greek for “lying under”) refers to the gland’s
position on the underside of the brain.
7. The pituitary gland is sometimes called the
“master gland,” because its hormones regulate
other important endocrine glands—including
the adrenal, thyroid, and reproductive glands
(e.g., ovaries and testes)—and in some cases
have direct regulatory effects in major tissues,
such as those of the musculoskeletal system.
8. The pituitary gland (hypophysis) is an
endocrine gland that lies in a bony cavity in
the skull. This cavity lies in the sphenoid bone
and is called the sella turcica, which is behind
the nose and immediately beneath the
hypothalamus.
9. The pituitary gland is attached to the
hypothalamus by a stalk composed of neuronal
axons (infundibular stalk) and is contained in a
capsule that is continuous with the dura mater
(a tough membrane surrounding the brain).
10. The normal adult pituitary gland is a reddish-
grey bean shaped gland. The average gland
weighs between 500-900mg (with the female
gland usually being slightly heavier than the
male). The dimensions of the pituitary are 10-
17mm from side to side, 5-15mm from front to
back and 5-10mm from top to bottom.
11. pituitary gland is divided into three lobes: the
anterior lobe (the adenohypophysis), the
intermediate lobe(pars intermedia), and the
posterior lobe (also called the
neurohypophysis or pars nervosa). In humans
the intermediate lobe does not exist as a
distinct anatomic structure but rather remains
only as cells dispersed within the anterior lobe,
although it may increase in size during
pregnancy.
12. Nonetheless, the anterior and posterior lobes
of the pituitary are functionally, anatomically,
and embryologically distinct. Whereas the
anterior pituitary contains abundant hormone-
secreting epithelial cells, the posterior pituitary
is composed largely of unmyelinated (lacking
a sheath of fatty insulation) secretory neurons.
13.
14. An important anatomical relation to the
pituitary gland is the optic chiasm, which lies
just above the pituitary fossa. Therefore, any
expanding lesion of the pituitary or
hypothalamus can present with visual field
defects
15.
16. The cells of the anterior pituitary are
embryologically derived from an outpouching
of the roof of the pharynx, known as Rathke’s
pouch. Although the cells appear to be
relatively homogeneous under a light
microscope, there are in fact at least five
different types of cells, each of which secretes
a different hormone or hormones.
17. The thyrotrophs synthesize and secrete
thyrotropin (thyroid-stimulating hormone;
TSH); the gonadotrophs, both luteinizing
hormone (LH) and follicle-stimulating
hormone (FSH); the corticotrophs,
adrenocorticotropic hormone (ACTH;
corticotropin); the somatotrophs, growth
hormone (GH; somatotropin); and the
lactotrophs, prolactin.
18. Somatotrophs are plentiful in the anterior
pituitary gland, constituting about 40 percent
of the tissue. They are located predominantly
in the anterior and the lateral regions of the
gland and secrete between one and two
milligrams of GH each day.
19. Posterior pituitary hormones
The posterior lobe of the pituitary gland
consists largely of extensions of processes
(axons) from two pairs of large clusters of
nerve cell bodies (nuclei) in the hypothalamus.
One of those nuclei, known as the supraoptic
nuclei, lies immediately above the optic tract,
while the other nuclei, known as the
paraventricular nuclei, lies on each side of the
third ventricle of the brain
20. . Those nuclei, the axons of the cell bodies of
nerves that form the nuclei, and the nerve
endings in the posterior pituitary gland form
the neurohypophyseal system. There are neural
connections that run from those nuclei to other
regions of the brain, including to regions that
sense osmolality (solute concentrations) and
regulate thirst.
21. The major neurohypophyseal hormones are
vasopressin (antidiuretic hormone) and
oxytocin, which are synthesized and
incorporated into neurosecretory granules in
the cell bodies of the nuclei. Those hormones
are synthesized as part of a precursor protein
that includes one of the hormones and a
protein called neurophysin. After synthesis and
incorporation into neurosecretory granules, the
precursor protein is cleaved, forming separate
hormone and neurophysin molecules, which
remain loosely attached to one another
22. Those granules are carried through the axons
and are stored in the posterior lobe of the
pituitary gland. Upon stimulation of the nerve
cells by internal or external events (e.g., breast
suckling in the case of oxytocin-secreting
neurons), the granules fuse with the cell wall
of the nerve endings, the hormone and
neurophysin dissociate from one another, and
both the hormone and the neurophysin are
released into the bloodstream. The hormones
are released into the circulation in response to
nerve signals that originate in the
hypothalamus and are transmitted to the
23. Oxytocin stimulates contraction of the uterus,
an important aspect of labour and parturition
and of milk ejection during breast-feeding.
Vasopressin raises blood pressure and
increases reabsorption of water from the
kidneys, thus conserving body water and
defending against dehydration. Vasopressin
secretion is stimulated by decreased serum
osmolality, which is an indication of
dehydration.
24. Blood Supply
The blood supply to the hypothalamus and
pituitary is derived from the circle of Willis at
the base of the brain. The most important
blood supply is from the superior hypophysial
arteries which arise from the internal carotids.
The blood from this artery enters a primary
capillary plexus at the median eminence.
25. Blood from this plexus flows down long portal
vessels to a secondary capillary plexus in the
adenohypophysis. The portal vessels run down
the pituitary stalk (infundibulum) to arrive at
the pituitary gland. This system is known as
the hypothalamo-hypophysial portal system.
26.
27. The thyroid gland is a butterfly shaped
structure that lies on the windpipe below the
Adam's Apple.The thyroid can be likened to a
butterfly. The thyroid lobes can be imagined as
wings that wrap themselves around the
windpipe while the body lies in front of the
windpipe and is called the thyroid isthmus.
28.
29. Embryologically, the thyroid gland develops as
a thickening in the pharyngeal floor that
elongates inferiorly as the thyroglossal duct,
dividing into two lobes as it descends through
the neck
30.
31. The isthmus usually lies over the second and
third tracheal rings opposite the fifth, sixth and
seventh cervical vertebrae. The lobes of the
thyroid are almost always asymmetrical with
the right lobe larger than the left. The thyroid
is usually larger in women than men. The total
weight of the thyroid is approximately 20-25
grams but is smaller in parts of the world
where supplies of iodine are abundant.
32. Beneath the visceral layer of the pretracheal,
deep cervical fascia, the thyroid gland is
surrounded by a true inner capsule, which is
thin and adheres closely to the gland. The
capsule sends projections into the thyroid
forming septae and dividing it into lobes and
lobules. Dense connective tissue attachments
secure the capsule of the thyroid to both the
cricoid cartilage and the superior tracheal
rings.
33. The lobules of the gland are composed of
follicles, the structural unit of the
thyroid. Each follicle is lined by a simple
layer of epithelium surrounding a colloid-filled
core. This colloid contains iodothyroglobulin,
the precursor to thyroid hormones.
34. The thyroid is a very vascular organ and is
surrounded by a sheath. This sheath attaches
the thyroid to the larynx and the trachea.
Anteriorly, the sternohyoid and sternothyroid
muscles overlie each of the lobes. A pyramidal
lobe is also often present and it projects
upwards from the isthmus as seen in the
diagram. A fibrous or muscular band
frequently connects the pyramidal lobe to the
hyoid bone.
35.
36. The Blood Supply
The blood flow to the thyroid has been
estimated to be approximately 5ml/gram of
tissue. This makes the blood supply almost
twice as rich as that of the kidney. When the
thyroid is very large, the massive blood flow
to the gland is audible as a noise (bruit). There
are three main arteries supplying the thyroid
gland:
1) Superior thyroid artery
37. The hypothalamus is a part of the brain
located superior and anterior to the brain stem
and inferior to the thalamus. It serves many
different functions in the nervous system, and
is also responsible for the direct control of the
endocrine system through the pituitary gland.
The hypothalamus contains special cells called
neurosecretory cells
40. All of the releasing and inhibiting hormones
affect the function of the anterior pituitary
gland. TRH stimulates the anterior pituitary
gland to release thyroid-stimulating hormone.
GHRH and GHIH work to regulate the release
of growth hormone—GHRH stimulates
growth hormone release, GHIH inhibits its
release.
41. GnRH stimulates the release of follicle
stimulating hormone and luteinizing hormone
while CRH stimulates the release of
adrenocorticotropic hormone. The last two
hormones—oxytocin and antidiuretic
hormone—are produced by the hypothalamus
and transported to the posterior pituitary,
where they are stored and later released.
42. The pineal gland is a small pinecone-shaped
mass of glandular tissue found just posterior to
the thalamus of the brain,located below the
corpus callosum.The pineal gland produces the
hormone melatonin that helps to regulate the
human sleep-wake cycle known as the
circadian rhythm.
43.
44. The activity of the pineal gland is inhibited by
stimulation from the photoreceptors of the
retina. This light sensitivity causes melatonin
to be produced only in low light or darkness.
Increased melatonin production causes
humans to feel drowsy at nighttime when the
pineal gland is active.
45. The adrenal glands are a pair of roughly
triangular glands found immediately superior
to the kidneys. The adrenal glands are each
made of 2 distinct layers, each with their own
unique functions: the outer adrenal cortex and
inner adrenal medulla.
46.
47. Adrenal cortex: The adrenal cortex produces
many cortical hormones in 3 classes:
glucocorticoids, mineralocorticoids, and
androgens.
◦ Glucocorticoids have many diverse
functions, including the breakdown of
proteins and lipids to produce glucose.
Glucocorticoids also function to reduce
48.
49. Androgens, such as testosterone, are produced
at low levels in the adrenal cortex to regulate
the growth and activity of cells that are
receptive to male hormones. In adult males,
the amount of androgens produced by the
testes is many times greater than the amount
produced by the adrenal cortex, leading to the
appearance of male secondary sex
characteristics.
50.
51. Adrenal medulla: The adrenal medulla
produces the hormones epinephrine and
norepinephrine under stimulation by the
sympathetic division of the autonomic nervous
system. Both of these hormones help to
increase the flow of blood to the brain and
muscles to improve the “fight-or-flight”
response to stress. These hormones also work
to increase heart rate, breathing rate, and blood
pressure while decreasing the flow of blood to
and function of organs that are not involved in
52. The pancreas is a large gland located in the
abdominal cavity just inferior and posterior to
the stomach. The pancreas is considered to be
a heterocrine gland as it contains both
endocrine and exocrine tissue.
53. It is attached to the second and third portion of
the duodenum on the right. The parts of the
pancreas are the head, neck, and body of tail.
Pancreas is supplied by splenic,
gastroduodenal, and superior mesenteric
arteries and drains into superior & inferior
mesenteric veins. The major components of
pancreatic exocrine function are acinar cells
and ductal system. Pancreatic ductal system is
the network of conduits that carry the exocrine
secretion into the duodenum.
54.
55. The endocrine cells of the pancreas make up
just about 1% of the total mass of the pancreas
and are found in small groups throughout the
pancreas called islets of Langerhans. Within
these islets are 2 types of cells—alpha and
beta cells.
56. The alpha cells produce the hormone glucagon,
which is responsible for raising blood glucose
levels. Glucagon triggers muscle and liver cells to
break down the polysaccharide glycogen to
release glucose into the bloodstream. The beta
cells produce the hormone insulin, which is
responsible for lowering blood glucose levels
after a meal. Insulin triggers the absorption of
glucose from the blood into cells, where it is
added to glycogen molecules for storage.
57.
58. Each the size of a grain of rice, parathyroid
glands are located in front of the neck, below
the larynx (voice box). The body’s four
parathyroid glands have a very rich blood
supply, which comes in handy since they
monitor the calcium level in the blood. As
blood filters through the parathyroids, they
detect the amount of calcium and make more
parathyroid hormone (PTH) when calcium
levels are too low.
59.
60. Once PTH is released, it circulates to the cells
of the bones and causes them to release
calcium into the bloodstream. When calcium
levels are too high, the parathyroids make less
PTH or cease producing it until normal levels
are restored.
61. Calcium is the element that allows the normal
conduction of electrical currents along
nerves—it’s how our nervous system works,
how one nerve “talks” to the next, and is the
primary element which causes muscles to
contract. The parathyroids also help the lining
of the intestines become more efficient at
absorbing calcium in the diet.
62. The thymus is a soft, triangular-shaped organ
found in the chest posterior to the sternum.
The thymus produces hormones called
thymosins that help to train and develop T-
lymphocytes during fetal development and
childhood.
63.
64. The T-lymphocytes produced in the thymus go
on to protect the body from pathogens
throughout a person’s entire life. The thymus
becomes inactive during puberty and is slowly
replaced by adipose tissue throughout a
person’s life.
65. The ovaries, the female gonads,are a pair of
almond-shaped glands located in the pelvic
body cavity lateral and superior to the uterus,
below the opening of the fallopian tubes (tubes
that extend from the uterus to the ovaries),have
two main reproductive functions in the body:
they produce oocytes (eggs) for fertilization
and the reproductive hormones estrogen and
progesterone.
66.
67. Estrogen is involved in the development of
female sexual features such as breast growth,
the accumulation of body fat around the hips
and thighs, and the growth spurt that occurs
during puberty. Both estrogen and
progesterone are also involved in the
regulation of the menstrual cycle and prepare
the lining of the uterus for pregnancy in the
event of the released egg being fertilized.
68. The testes, also known as testicles or male
gonads,are a pair of ellipsoid organs found in
the scrotum of males,have two functions: to
produce sperm and to produce hormones,
particularly testosterone, which regulate body
changes associated with sexual development.
69.
70. Also including enlargement of the penis, the
growth spurt that occurs during puberty, and
the appearance of other male secondary sex
characteristics such as deepening of the voice,
growth of facial and pubic hair, and the
increase in muscle growth and strength.
![JOHNY WILBERT, M.SC[N]
LECTURER,
APOLLO INSTITUTE OF HOSPITAL MANAGEMENT AND
ALLIED SCIENCE](https://image.slidesharecdn.com/endocrinesystem-180619142937/85/Endocrine-system-1-320.jpg)
