Johny's A&P endocrine system

The
Endocrine
System
By:
Mr. Johny Kutty Joseph.
Asstt. Professor, SMVDCoN

Control of Body Systems
 The nervous
system controls
the body by action
potentials and
neurotransmitters
across the
synapse.
 The nervous
system has faster
transportation
system.
 The endocrine system
controls the body by
hormones.
 The hormones are
released at one gland
which act on nay part
or organ of the body.
 The hormones act in
slower reaction time.
 The endocrine system
regulates all the
activities of the body.
2

3
Endocrine Glands
 Endocrine glands secrete the hormones into
interstitial fluid which further diffuse into blood
capillaries and it circulates it across the body.
 The endocrine glands include pituitary, thyroid,
parathyroid, adrenal and pineal gland.
 The other organs that support the endocrine
function are hypothalamus, thymus, pancreas,
ovaries, testes etc. They secrete
hormones/enzymes but are not exclusive
endocrine organs.
 Endocrinology is the science of structure and
function of endocrine glands and the diagnosis
and treatment of their disorders.

4
Endocrine Organs
 Purely endocrine
organs
 Pituitary gland
 Pineal gland
 Thyroid gland
 Parathyroid glands
 Adrenal: 2 glands
 Endocrine cells in
other organs
 Pancreas
 Thymus
 Gonads
 Hypothalamus

Control of Hormone Release
 Negative feedback mechanism- hormone
release is triggered by stimulus, rising levels of
hormone inhibit further release
 Endocrine stimuli or hormone production is
controlled by;
 Hormonal- hormones stimulate the release
of other hormones.
 Humoral- level of chemicals and ions in
blood stimulates endocrine glands for the
release of hormones.
 Neural- nerve impulses stimulate hormone
release.

Chemical Composition of Hormones
 Chemically the hormones are divided into two
broad classes such as lipid soluble and water
soluble.
 The lipid soluble hormones are divided into steroid
hormones (testosterone=testis, progesterone=
ovaries ), thyroid hormones (T3 and T4 ) and nitric
oxide (it is gas and enzyme. It helps in
vasodilatation and is secreted by endothelium etc.)
 The water soluble hormones are divided into
Amine hormones (catecholamine, epinephrine,
dopamine etc), Peptide hormones (ADH, oxytocin,
GH, insulin) and eicosanoid hormones.
(prostaglandins secreted by all cells)

Mechanism of Action of Hormones
 The water soluble hormones are transported as
free molecules in blood.
 The lipid soluble molecules are bound to carrier
proteins in blood such as albumin and globulin.
 The lipid soluble molecule get attached to the
target cell/receptor cell through lipid layer/plasma
membrane as thy are lipid soluble. This alter the
gene expression of the target cell. As the DNA is
transcribed/modified new mRNA is formed in the
nucleus which enters cystosol and directs the
formation of new protein/enzyme on the ribosome.
The newly formed proteins alter the activity of cells
as a response to hormonal action.

Mechanism of Action of Hormones
 The water soluble hormones (primary messenger) diffuse
from blood to interstitial fluid and attach to the receptor
cell protein called G-protein (guanine binding protein:
located near to plasma membrane and act as route of
signaling under the influence of a
protein/hormone/enzyme).
 The activated G-protein activates adenylate cyclase
which is an enzyme that catalyses/convert ATP into
cyclic AMP(second messenger)
 Cyclic AMP(adenosine mono phosphate) activates one or
more Protein Kinases A (PKA) which is enzyme that have
the capacity to phosphorylate other proteins to
transcribe/modify the gene/DNA of the cells and it causes
physiological responses in the cell.

Hypothalamus & Pituitary Gland
 The Hypothalamus is the
master of endocrine
system establishing a
connection between
nervous system and
endocrine system. It
synthesize nine hormones.
 The Pituitary Gland or
Hypophysis secrete seven
hormones.
 Together it play important
role in the regulation and
function body.

Structure of Pituitary Gland
 It is a pea shaped structure that
measures 1 to 1.5 cm in diameter
and lies in the hypophyseal fossa
of the sphenoid bone (base of the
skull).
 It is attached to hypothalamus
through a stalk called
infundibulum.
 Anatomically and physiologically it
has two lobes.
 Anterior lobe / anterior pituitary /
adenohypophysis
 Posterior lobe / posterior pituitary /
neurohypophysis.

Structure of Anterior Pituitary
 It is the largest portion which covers
75% of the total weight. It is
composed of epithelial tissues.
 It has two portions called as pars
distalis and pars tuberalis near to
infundibulum. The hypothalamic
hormones regulate the secretions of
anterior pituitary.
 The hypophyseal portal system
helps the transportation of blood
from hypothalamus to anterior
pituitary so that the hormones of
hypothalamus reach anterior
pituitary directly. It is similar to the
hepatic portal system.

 The blood supply is from superior
hypophyseal artery branch of
internal carotid arteries.
 The synthesis of hormones in
hypothalamus is under the control of
nervous system and these
hormones are transported to
hypophyseal portal system by
neurosecretory cells (exocytosis)
and this stimulate anterior pituitary to
secrete the hormones into general
circulation.
 The anterior pituitary hormones that
act on other endocrine glands are
called as tropic hormones.

There are five types of cells in anterior pituitary which
secrete seven types of hormones. They are;
Somatotrophs: Secrete human growth hormone (hGH /
GH).
Thyrotrophs: Secrete TSH (thyroid stimulating hormone)
also called as thyrotropin.
Gonadotrophs: Secrete two gonadotrophins: FSH
(follicle stimulating hormone) and LH (luteinizing
hormone).
Lactotrophs: Secrete Prolactin (PRL)
Corticotrophs: Secrete (ACTH) adeno cortico trophic
hormone and (MSH) melanocyte stimulating hormone.

Function of Anterior Pituitary: GH
 GH: secreted by Somatotrophs in abundance.
 The main function of GH is to promote synthesis
and secretion of small protein hormones called
IGFs (Insulinlike growth factors).
 This is secreted by liver, skeletal muscles, bones,
and other tissues under the influence of GH
 IGFs cause growth and multiplication of cells by
increasing protein synthesis.
 During childhood/teenage it increases the growth
rate of skeleton and muscles.
 During adulthood it maintain the mass of muscles
and promotes healing and repair.

Function of Anterior Pituitary: GH
 It enhance lipolysis in adipose tissue to produce
ATP.
 It influence the metabolism of carbohydrates.
 The production of GH is increased by growth
hormone releasing hormone (GHRH) by
hypothalamus. Hypoglycemia stimulates
hypothalamus for it.
 The production of GH is decreased by growth
hormone inhibiting hormone (GHIH) by
hypothalamus. Hyperglycemia stimulates
hypothalamus for it.
 The production of GH is also controlled by
exercise, other hormones such as insulin.

Function of Anterior Pituitary
 TSH: stimulate synthesis and secretion of two thyroid
hormones Triiodothyronine (T3) and Thyroxin (T4)
from thyroid gland. The blood level of T3 and T4
stimulates hypothalamus to secrete thyrotropin
releasing hormone (TRH) which will influence
secretion TSH.
 FSH: It stimulate the development of ovarian follicle
to release oocyte. In male it stimulate the production
of sperm in testis. It also stimulates the secretion of
estrogen in female (sex hormone) and testosterone
in males (sex hormone). GnRH (Gonadotrophin
releasing hormone) from the hypothalamus controls
it. GnRH is controlled by level of estrogen and
testosterone in blood.

 LH: Luteinizing hormone triggers ovulation. It also
stimulate the formation of corpus luteum. It controles
the secretion progesterone (female sex hormone).
FSH and LH have combines roles in the body. It is
also under the regulation of GnRH.
 Prolactin (PRL): Along with other hormones it
initiates and maintains milk production by the
mammary glands. Ejection of milk is under the
control of oxytocin. The hypothalamus secrete
PIH(Prolactin inhibiting hormone) and PRH (Prolactin
releasing hormone) which control the production of
PRL. The level of PRL in blood and the sucking
action controls the production of PIH and PRH.

 ACTH: It controls the production and secretion of
cortisol and glucocorticoids by the cortex of the
adrenal glands. This has many role in body such as
Immunity, Metabolic, Development, Cognition,
Homeostasis etc. The release of ACTH is regulated
by CRH (Corticotrophin releasing hormone) from the
hypothalamus.
 MSH: Melanocyte Stimulating Hormone increases
the skin pigmentations. It does not have any special
roles in body. The increased production can darken
the skin. The secretion is increased by CRH
(Corticotrophin releasing hormone) and decreased
by dopamine from the hypothalamus.

Structure of Posterior Pituitary
 It is composed of neural tissue. It has
two parts such as pars nervosa and
pars intermedia.
 The posterior pituitary does not
synthesize any hormones.
 They secrete two hormones
synthesized in hypothalamus such as
oxytocin and Antidiuretic hormone.
(ADH)
 The ADH is also called as
vasopressin.
 Blood supply is from inferior
hypophyseal arteries branch of
internal carotid.

Functions of Posterior Pituitary
 Oxytocin: It’s major role is during labour and after labour.
It acts on mothers uterus and breasts. During delivery
stretching of cervix influence the release of oxytocin
which enhances contraction of smooth muscles of uterus.
It also stimulates milk ejection from mammary gland in
response to sucking by baby.
 ADH: It decreases the urine production. It helps in
retaining the fluid content of the body. It is also called as
vasopressin as it prevent water loss through sweating
and increases the pressure by vasoconstriction. Alcohol
impairs the functioning of ADH hence chronic alcoholism
destroy kidneys. When the blood volume is lowered due
to hemorrhage, diarrhea and dehydration the osmotic
pressure rises which activates Osmoreceptors in
hypothalamus thus the release of ADH take place.

Thyroid Gland
 It is a butterfly shaped gland.
 Located inferior to the larynx.
 It has right and left lobes interconnected by a an
isthmus which is a narrow passage.
 It also has a third lobe in the superior part which
is called as pyramidal lobe.
 It weighs about 30g
 It contains thyroid follicles which has follicular
cells and it secretes hormones under the
influence of TSH.
 It secrets two hormones called as thyroid
hormones.

Thyroid Gland
 Thyroxine/tetra-iodo-thyronine /
T4 contains four atoms of
iodine.
 Tri-iodo-thyronine / T3 contains
three atoms of iodine.
 a few cells called parafollicular
/ C-cells cells are located in
between the follicular cells
which secrete a hormones
called calcitonine and it helps
in regulation of calcium
homeostasis.

Formation of Thyroid Hormones
 Iodine trapping: Thyroid
follicular cells trap the iodine
ions from blood into the
cystosol of follicular cells.
Maximum amount of iodine
ions in body is stored in thyroid
gland.
 Synthesis of thyroglobulin: The
follicular cells synthesize large
glycoprotein called TGB/
thyroglobulin in the RER. This
gets modified in Golgi
apparatus and secreted by
packaged vesicles.

 Oxidation of iodine: Some amino
acids in TGB are called
Thyrosine. Further the negatively
charged iodide/ 2 I- undergo
oxidation and become I2.
 Iodination of tyrosine: The
Thyrosine act with iodine
molecules (I2). Binding to one
iodine atom forms mono-iodo-
thyrosine (T1) and binding to two
iodine atoms forms di-iodo-
thyrosine (T2). The TGB along
with attached iodine atoms forms
a sticky material is called as
colloid.

 Pinocytosis: Droplets of colloid re-enter the
follicular cells by Pinocytosis and merge with
lysosomes where the break down of TGB takes
place and T3 & T4 molecules are made free.
 Secretion of thyroid hormones: T3 and T4 are
lipid soluble hence it diffuse through the plasma
membrane into ICF and then into blood. T4 is
secreted in large quantity.
 Transport: The Thyroid hormones are secreted in
blood with transport protein called globulin. This
combination is called as TBG(thyroxine-binding
globulin)

Function of Thyroid Hormones
 They increase BMR. It also increases the
metabolism of carbohydrates lipid and protein.
This increases the increased production of ATP.
 They stimulate the production of additional
sodium-potassium pumps. Na+ ions are secreted
from cystosol to ECF and K+ ions vice versa. This
is called calorigenic effect. This play an important
role maintenance of body temperature but this is
not possible for those mammals who have
removed thyroid gland due to any disorder.
 They increase lipolysis and increase the secretion
of cholesterol. This reduce blood cholesterol level.

Function of Thyroid Hormones
 The thyroid hormones regulate beta receptors and
enhance the function of catecholamine
(epinephrine/ nor-epinephrine). Hence the
symptoms of hyperthyroidism include increased
heart beat and increased blood pressure.
 Together with hGH and insulin thyroid hormones
accelerate body growth especially the nervous
system and skeletal system.
 Deficiency of these hormones can result in stunted
skeletal growth and MR.
 The secretion of thyroid hormones are controlled by
TSH (ant.pit.) and TRH( Hypothalamus). Ultimately
it is controlled by level of T3 and T4 in blood.

Calcitonine (CT)
 The hormone produced by par follicular cells
of thyroid gland.
 It decrease the level of calcium in blood by
inhibiting Osteoclast (Break down of bone
tissue) and accelerating the calcium and
phosphate uptake into bone extra cellular
matrix for Osteoblast.
 It is controlled by negative feedback
mechanism.
 Miacalcin, a calcitonin extract from salmone is
prescribed to treat osteoporosis.

Parathyroid Gland
 They are present posterior
to lateral lobes of thyroid
glands.
 It weighs around 40mg.
 They are attached to
thyroid gland.
 It contains two groups of
cell called chief cells and
oxyphil cells. The chief
cell secrete the
parathyroid hormone
called parathormone.

Parathormone
 The main role of PTH is to
regulate Calcium,
Magnesium and
phosphate ions in blood.
 It increases osteoclasts.
 It also act on kidneys and
regulate the excretion of
these ions through urine.
 It helps the formation of
D3 (calcitriol) a vitamin
that helps in absorption of
these ions through GI
Tract.

Adrenal Gland
 They are paired supra
renal glands.
 It is pyramidal in shape
and weighs about
4gms.
 They are structurally
and functionally
separated into two
types of tissues such
as adrenal medulla and
adrenal cortex.
 These glands are
highly vascularized.

Adrenal Cortex: Function
 The adrenal cortex produce steroid hormones.
 The cortex is subdivided into three zones such as
a.Zona glomerulosa: secrete minerelocorticoids.
b.Zona fasciculata: secrete glucocorticoids
c. Zona reticularis: secrete androgens.
 Minerelocorticoids: Aldosterone is the major
minerelocorticoid. It regulate the two minerals
namely sodium ions and potassium ions. It helps
to adjust blood pressure in the body. It promotes
excretions of H+ ions from the body through urine
to decrease the acidity.

RAA pathway
The secretion of Aldosterone is controlled by RAA
pathway. Renin-angiotensin-aldosterone.
1.Dehydration/ Na deficiency/hemorrhage
2.Decreased blood volume and pressure.
3.Stimulate kidneys to secrete renin an enzyme.
4.Renin converts Angiotensin to Angiotensin I.
Angiotensin is a plasma protein secreted liver.
5.Angiotensin I is converted to Angiotensin II in lungs with
help of ACE (angiotensin converting enzyme)
6.Angiotensin II stimulates the secretion of aldosterone.
7.Aldosterone increase re-absorption of Na ions and
increase blood volume by osmosis. This blood pressure is
managed.

Glucocorticoids
 They are also called as hydrocortisone/
corticosterone/cortisone.
 Their secretion is controlled by corticotrophin-
releasing-hormone(CRH) by hypothalamus and
ACTH. Their major functions are
Protein breakdown: in muscle fibers and release
amino acids into blood stream. Thus ATP is
produced.
Glucose formation: liver cells convert some
amino acids/lactic acids to glucose. Such
conversion where of a substance other than
glycogen into glucose is called gluconeogenesis.

Glucocorticoids
 Lipolysis: breakdown of triglycerides to release
fatty acids from adipose tissue.
 Resistance to stress: supply of additional
glucose to combat stress which includes
fight,flight, and other physiological changes like
temperature extreme, high altitude, bleeding by
vasoconstriction. They raise blood pressure.
 Anti-inflammatory effects: it motivates WBCs to
produce anti-inflammatory response.
 Depression of immune responses: high dose of
glucocorticoids can decrease immune response
hence it is used in organ transplantation.

Androgens
 Androgens are sex hormones. But the
androgens secreted by adrenal gland in male is
weak and have negligent function. The major
androgen secreted by testes (testosterone) is
the major one in male.
 In female the adrenal androgens have
significant role to promote libido in addition to
estrogens.
 It also promote the hair growth in axila and pubic
area.
 ACTH controls the release of Androgens.

Adrenal Medulla
 The group of cells present in adrenal medulla is
called chromaffin cells.
 The hormones are epinephrine and norepinephrine.
 Also called as adrenaline and nor adrenaline.
 They are responsible for fight or flight response.
 It enhance the effects of sympathetic division of
autonomic nervous system(ANS) during stress.
 Epinephrine/adrenaline increase heart rate and
force of contraction.
 Norepinephrine/nor adrenaline increase cardiac
output and blood pressure.
 It increase the blood supply to skeletal muscles,
increase metabolism.

Pancreas
 It is both an endocrine and exocrine glands.
 A flattened organ that measures 15cm long,
located in the curve of the duodenum.
 It consists of a head, body and tail.
 The exocrine cells are called acini and it produce
digestive enzymes.

Pancreas
 The digestive juices flow into GI tract through the
ducts.
 There are tiny endocrine cells located among the
exocrine acini. They are called as pancreatic
islets/ islets of Langerhans.
 Pancreas is abundant in blood supply.

Pancreas
 Each pancreatic islets include four types of cells
secreting four hormones.
a. Alpha / A cells: it secrete glucagon. It raises the
blood glucose level.
b. Beta / B cells: it secrete insulin. It decreases the
blood glucose level.
c. Delta / D cells: it secrete somatostatin. It controls
the secretion of glucagon and insulin. It slows the
absorption of nutrients from GI. It inhibits the
secretion of GH.
d. F cells: pancreatic polypeptide. It inhibits the
secretion of somatostatin and controls the secretion
of digestive enzymes by exocrine pancreas.

Regulation of Glucagon & Insulin
 Hypoglycemia stimulates secretion of glucagon from
alpha cells.
 Glucagon act on hepatocytes to accelerate conversion of
glycogen into glucose and formation of glucose from lactic
acid/amino acids. (glycogenolysis & gluconeogenesis)
 Blood glucose level increase.
 Hyperglycemia inhibit release of glucagone (negative
feedback)
 Hyperglycemia stimulates secretion of insulin from beta
cells.
 Blood glucose level falls.
 If it drops below normal the insulin secretion is
stopped(negative feedback) and secretion of glucagon
starts.

Regulation of Glucagon & Insulin
 In addition to blood glucose level the secretion of
insulin and glucagon is also controlled by certain
other factors such as
1.Heavy meal which is protein or carbohydrate rich
can stimulate the release.
2.Increased physical activity; this happens under the
influence sympathetic division.
3.Influence of acetylcholine; a neurotransmitter
liberated from vagus nerve that innervates the
pancreatic islets.

Ovaries & Testes
 They are organs to produce gametes.
 They produce sperm and oocytes.
 The ovaries are located in the female pelvis cavity.
 The testes are oval glands that lie in the scrotum.

Ovaries
1. They secrete estrogen and progesterone.
2. There are two estrogen such as estradiol and estrone.
3. These hormones along with FSH and LH from Anterior
pituitary regulate menstrual cycle.
4. It maintain the pregnancy and it prepare the mammary
glands for lactation.
5. They promote enlargement of breasts and widening of
hips at puberty.
6. They maintain female secondary sexual characteristics.
7. Ovaries produce inhibin to inhibit FSH during pregnancy.
8. The ovaries and placenta produce a peptide hormone
called relaxin which increases the flexibility of pubic
symphysis during labor. This also help the relaxation of
cervix.

Testes
1.It secrete testosterone.
2.It control descent of testes and production of sperm.
3.Develop and maintain male secondary sexual
characteristics such as beard growth and voice
deepening.

Pineal Gland
 A small endocrine gland
attached to the roof of the third
ventricle.
 It weighs around 0.1`-0.2 g.
 It is covered by a capsule
made of pia matter.
 It contains secretory cells
called pinealocytes which
secretes melatonin.
 The melatonin helps in in
setting body’s biological clock.
 This hormone induce sleep in
darkness in response to
message from retina.

Thymus Gland
 The thymus is
located behind
sternum and has an
important role in
immunity.
 It produce a
hormone called
thymosine and
thymopoietin which
promote the
maturation of T
cells.
 Retardation of aging
process.

Other endocrine hormones
 The endocrine hormones secreted by other cells in
addition to endocrine gland are,
1.GI tract: Gastrin (promotion of gastric juice secretion,
increase peristaltic movement).
2.Placenta: hCG: (human chorionic gonadotrophin)
indiaction and maintenance of pregnancy and hCS
(human chorionic somatomammotropin) development
of mammary glands.
3. Kidneys: Renin & Erythropoietin: increases RBC
production.
4.The heart: atrial natriuretic peptide (ANP: It Stimulates
kidney to secrete more salt and decreases excess
blood volume, high BP and high blood sodium
concentration.

Johny's A&P endocrine system

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