Download CRYDERS-Endocrine System

• Regulates rate of metabolism
• Ion regulation: Regulates blood pH, Na+, K+, Ca+
conc. in blood
• Water balance : Regulates water balance by
controlling solute conc. of blood
• Immune system regulation
• Heart rate and blood pressure regulation
• Control of blood glucose and other nutrients
• Control of reproductive functions
• Uterine contractions and milk release
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Hypothalamus
Pituitary gland
Thyroid Gland
Parathyroid gland
Adrenal glands
Pancreas
Pineal gland
thymus gland
Reproductive glands
• Part neuronal and part
endocrine in function
• Located in the
diencephalon below the
thalamus
• Control the activities of
pituitary gland
• It is also known as hypophysis
• Size of a pea
• It is attached to the
hypothalamus of the brain by
a stalk called infundibulum
• It is called the master gland
because it releases hormones
that affect the working of
other glands such as thyroid,
gonads etc.
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It is divided into two lobes:
– anterior pituitary
– posterior pituitary
• Posterior pituitary
(neurohypophysis):
• extension of the hypothalamus via the
infundibulum
– Secretes neurohormones
 Anterior pituitary (adenohypophysis)
– Derive from embryonic oral
cavity – Pituitary diverticulum or
Rathke pouch
– Synthesizes and secretes a
number of hormones
– Consists of three areas with
indistinct boundaries:
– pars distalis
– pars intermedia
– pars tuberalis
• The posterior lobe is a
downgrowth of hypothalamic
neural tissue
• Has a neural connection with
the hypothalamus
(hypothalamic-hypophyseal
tract)
• Nuclei of the hypothalamus
synthesize oxytocin and
antidiuretic hormone (ADH)
• These hormones are
transported to the posterior
pituitary
• The anterior lobe of the pituitary
is derived from epithelial tissue
of the embryonic oral cavity
• There is no direct neural contact
with the hypothalamus
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There is a vascular connection,
the hypophyseal portal system,
consisting of:
– Primary capillary plexus
– Hypophyseal portal veins
– Secondary capillary plexus
• The hypothalamus sends a chemical stimulus to the anterior
pituitary via Hypophyseal portal system
– Releasing hormones stimulate the synthesis and release of
hormones of ant. pituitary
– Inhibiting hormones shut off the synthesis and release of
hormones
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Thus, by using neurohormones as chemical messenger
Hypothalamus regulates the secretory activity of the Ant.
Pituitary
• Releasing hormones:
– GHRH. Growth hormone-releasing hormone : Causes the ant.
pituitary to release growth hormone
– TRH. Thyrotropin-releasing hormone : Causes ant. pituitary to
release thyroid-stimulating hormone (TSH)
– CRH. Corticotropin-releasing hormone : Causes ant. pituitary to
produce adrenocorticotropic hormone
– GnRH. Gonadotropin-releasing hormone: Causes anterior
pituitary to produce FSH (follicle stimulating hormone) and LH
(luteinizing hormone)
– PRH. Prolactin-releasing hormone : Causes the anterior
pituitary to release prolactin
• Inhibiting hormones:
– GHIH. Growth hormone-inhibiting hormone,
somatostatin : Causes the anterior pituitary to
decrease release of growth hormone
– PIH. Prolactin-inhibiting hormone : Causes the
anterior pituitary to decrease release of
prolactin.
• Antidiuretic hormone (ADH) : Also called
vasopressin
• It is an antiurination hormone
• ADH helps to avoid dehydration or water overload
• A. Osmoreceptors (specialized neurons of
hypothalamus monitor changes in intercellular
osmolality) monitor the solute concentration of the
blood
• With high solutes, ADH secretion increases
• ADH stimulates kidney to retain water
• With low solutes, ADH is not released, thus causing
water loss
– Because ADH regulates
blood volume its secretion is
also controlled by BP
changes
– B. Baroreceptors
(specialized neurons found
in walls of atria of heart,
large veins, carotid arteries,
aortic arch) sense changes in
blood pressure (BP)
–
If BP decreases, then
ADH secretion is stimulated
• Oxytocin is a strong stimulant of
uterine contraction
• Regulated by a positive feedback
mechanism to oxytocin in the blood
• This leads to increased intensity of
uterine contractions
• Play imp. Role in the expulsion of the
fetus during delivery by stimulating
uterine smooth muscle contraction
• Oxytocin triggers milk ejection in
lactating women
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Growth hormone (GH) or somatotropin
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Melanocyte-stimulating hormone (MSH)
Beta endorphins
Lipotropins
Luteinizing hormone (LH)
Follicle-stimulating hormone (FSH)
Prolactin
• Regulates metabolism
• Regulates blood levels of nutrients
after a meal and during periods of
fasting
• Stimulates uptake of amino acids;
protein synthesis
• Stimulates breakdown of fats to be
used as an energy source
• Stimulates glucose synthesis by liver ;
which releases glucose into the blood
• Functions in regulating growth, tissue maintenance, metabolism
• Direct effect: GH binds to membrane-bound receptors on cells and
causes changes within the cells
• Eg. Adipose cells, Increased breakdown of lipids and decreased use of
glucose as an energy source
• Indirect effect: causes liver and skeletal muscle to produce
somatomedins (polypeptide)
– Somatomedins bind to receptors on membranes of target cells
– Stimulate growth in cartilage, bone; increased synthesis of proteins
in skeletal muscle
• Two neurohormones released from hypothalamus regulate the
secretion of GH
– Growth hormone–releasing hormone (GHRH) stimulates GH
release
– Growth hormone–inhibiting hormone (GHIH) inhibits GH release
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• GHRH secretion in response to low blood glucose, stress, increase in
certain amino acids in blood
• GHIH secretions in response to high blood glucose
• Peak GH levels during deep sleep; levels lower at other times of day
• Growth hormone (GH) disorders
– Pituitary dwarfism results from
hyposecretion of GH during childhood
– Gigantism results from hypersecretion of GH
during childhood
– Acromegaly results from hypersecretion of
GH during adulthood
Gigantism
Hypersecretion causes
excessive growth as
shown in these identical
twins.
Acromegaly Face
• TRH (thyrotropin-releasing hormone) from hypothalamus causes the
release of TSH from anterior pituitary which causes secretion of thyroid
hormones from thyroid gland
• TSH secretion is controlled by TRH from hypothalamus and by thyroid
hormones from thyroid gland
• TRH binds to the membrane-bound receptors
• Receptors respond through a G protein mechanism
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and increase TSH secretion
• Rising blood levels of thyroid hormones act on the pituitary and
hypothalamus to block the release of TSH
• CRH (Corticotropin-releasing hormone) from
hypothalamus causes release of ACTH from
anterior pituitary which
• Causes cortisol secretion from the adrenal cortex
• Causes aldosterone secretion from the adrenal cortex
• ACTH, MSH, endorphins and lipotropins all derived from the same
large precursor molecule when stimulated by CRH
• MSH (Melanocyte-stimulating hormone) causes melanocytes to
produce more melanin
• Endorphins act as an analgesic; produced during times of stress
• Lipotropins cause adipose cells to catabolize fat and release fatty acids
into the blood
• Gonadotropins: glycoprotein hormones that promote growth and function
of the gonads; ovaries and testes
• Two gonadotrophins secrete from ant. Pituitary are:
• LH (Luteinizing hormone) & FSH (Follicle stimulating hormone) :
– Both hormones regulate production of gametes
–
sperm cells in testes and oocytes in ovaries
– And reproductive hormones
• Testosterone in males
• Estrogen and progesterone in females
• GnRH from hypothalamus stimulates LH and FSH secretion
• Prolactin: role in milk production
– Regulation of secretion: prolactin-releasing hormone (PRH) and
prolactin-inhibiting hormones (PIH)
• The largest endocrine gland,
located in the anterior neck,
consists of two lateral lobes
connected by a median tissue
mass called the isthmus
• Thyroid glands contains
numerous follicles , filled with
protein called thyroglobulin
• Thyroid hormones are stored in
the thyroglobulin molecules
• Between the follicles other
endocrine cells, the parafollicular
cells are present which produces
the hormone calcitonin (play imp.
Role in reducing the conc. of
calcium)
• Thyroid hormone – major metabolic hormone
• Consists of two related iodine-containing
compounds
– T4 – thyroxine (tetraiodothyronine); has two
tyrosine molecules plus four bound iodine atoms
– T3 – triiodothyronine; has two tyrosines with
three bound iodine atoms
• TH plays a role in:
– Maintaining blood
pressure
– Regulating tissue
growth
– Developing skeletal and
nervous systems
– Maturation and
reproductive
capabilities
• Thyroglobulin is synthesized
& discharged into follicle
lumen
• Iodides (I–) are actively
taken into the cell, oxidized
to iodine (I2), and released
into the lumen
 Iodine attaches to tyrosine
(part of thyroglobulin),
mediated by peroxidase
enzymes, forming T1
(monoiodotyrosine, or MIT),
and T2 (diiodotyrosine, or
DIT)
• Iodinated tyrosines
link together to form
T3 and T4
• Colloid is then
endocytosed and
combined with a
lysosome, where T3
and T4 are cleaved and
diffuse into the
bloodstream
• Both T4 and T3 bind to target receptors,
but T3 is ten times more active than T4
• Peripheral tissues convert T4 to T3
• Regulation is by negative feedback
Thyroid Hormone
Thyroid hormone disorders
Hyperthyroidism or Graves
disease:
• Enlargement of thyroid gland
• Excess of thyroid secretion
production caused by tumor
• Eyes bulge
• Patient is hyperactive, irritable,
nervous etc
• BMR increases
• Treatable by surgery and
radioactive Iodine
Simple Goiter: ( Iodine deficiency and hormone deficiency)
• Thyroid over stimulated because of lack of usable thyroid hormone
– due to lack of iodine
• Results in hypothyroidism
• Enlarged thyroid gland
• Hypothyroidism (Lack
of stimulation by TSH):
• Crinitism: in child hood.
Slow growth, mental
retardation low body
metabolism
• In adult: called as
myxedema
• Results in physical and
mental sluggishness
• puffiness of face, fatigue,
obesity, dry skin
• Produced by parafollicular cells
• Secretion triggered by high Ca2+ concentration in
blood; acts to decrease Ca2+ concentration
• Primary target tissue: bone. Decreases osteoclast
activity, lengthens life span of osteoblasts.
• Embedded in thyroid
• Two glands on each side
• Secrete PTH: target tissues are bone,
kidneys and intestines.
– Increases blood calcium and
phosphate levels
– Stimulates osteoclasts
– Promotes calcium reabsorption by
kidneys, so that less calcium leaves
the body in urine
– Increases synthesis of vitamin D in
kidney, which, in turn, increases
absorption of Ca and PO4 by
intestines
• Regulation depends on calcium levels.
• Adrenal glands – paired, pyramidshaped organs atop the kidneys
• Inner medulla; outer cortex
• Medulla: formed from neural crest;
sympathetic. Secretes epinephrine and
norepinephrine
• Cortex: glandular tissue derived from
embryonic mesoderm
• three zones from superficial to deep
– Zona glomerulosa
– Zona fasciculata
– Zona reticularis
• Secretory products are
neurohormones: epinephrine
and norepinephrine
• Combine with adrenergic
membrane-bound receptors
• All function through G protein
mechanisms
• Secretion of hormones
prepares body for physical
activity
• Effects are short-lived;
hormones rapidly metabolized
• Epinephrine
– Increases blood levels of
glucose
– Increases fat breakdown
in adipose tissue
– Causes dilation of blood
vessels in skeletal muscles
and cardiac muscles.
• Epinephrine and
norepinephrine increase heart
rate and force of contraction;
cause blood vessels to
constrict in skin, kidneys,
gastrointestinal tract, and
other viscera
• Mineralocorticoids: Zona glomerulosa
– Aldosterone produced in greatest
amounts
– Secreted under low BP condition
– Increases rate of sodium reabsorption by
kidneys thereby increasing sodium blood
levels
• Glucocorticoids: Zona fasciculata
– Cortisol is major hormone. Increases fat
and protein breakdown, increases
glucose synthesis, decreases
inflammatory response
• Androgens: Zona reticularis
• Most gonadocorticoids secreted are androgens (male sex hormones),
and the most important one is testosterone
• Androgens contribute to:
– The onset of puberty
– The appearance of secondary sex characteristics
– Sex drive in females
• Androgens can be converted into estrogens after menopause
• Located along small intestine
and stomach; retroperitoneal
• Exocrine gland
– Produces pancreatic
digestive juices
• Endocrine gland
– Consists of pancreatic islets
– Composed of
• Alpha cells; secrete
glucagon
• Beta cells; secrete insulin
• Insulin
• Target tissues: liver,
adipose tissue, muscle,
and satiety center of
hypothalamus
• Increases uptake of
glucose and amino
acids by cells
• Glucagon
• Target tissue is liver
• Causes breakdown of
glycogen and fats for
energy
• Results from hyposecretion or hypoactivity of
insulin
• The three cardinal signs of DM are:
– Polyuria – huge urine output
– Polydipsia – excessive thirst
– Polyphagia – excessive hunger and food
consumption
• Hyperinsulinism – excessive insulin secretion,
resulting in hypoglycemia
• Male: Testes
• Testosterone
– Regulates production of
sperm cells and
development and
maintenance of male
reproductive organs and
secondary sex
characteristics
• Inhibin
– Inhibits FSH secretion
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from ant. Pituitary gland
• Female: Ovaries
• Estrogen and Progesterone
– Uterine and mammary
gland development and
function, external genitalia
structure, secondary sex
characteristics, menstrual
cycle
• Inhibin
– Inhibits FSH secretion
• Relaxin
– Increases flexibility of
symphysis pubis during
pregnancy
• Small gland hanging from the roof of the third
ventricle of the brain
• Secretory product is melatonin
• Melatonin is involved with:
– Day/night cycles
– Physiological processes that show rhythmic
variations (body temperature, sleep, appetite)
• Lobulated gland located deep to the sternum
• Secretes a hormone called thymosin
• Essential for the development of the T
lymphocytes (T cells) of the immune system
• Heart – produces atrial natriuretic peptide
(ANP), which reduces blood pressure, blood
volume, and blood sodium concentration
• Placenta – releases hormones that influence the
course of pregnancy
• GI tract: several hormones regulate digestion
and enzyme secretion
• Kidneys – secrete erythropoietin, which
signals the production of red blood cells
• Skin – produces cholecalciferol, the precursor
of vitamin D
• Adipose tissue – releases leptin, stimulates
increased energy expenditure
• Gradual decrease in secretory activity of some
glands
– GH as people age except in people who exercise
regularly
– Melatonin
– Thyroid hormones
– Kidneys secrete less renin
• Familial tendency to develop type II diabetes