CRYDERS-Endocrine System
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Transcript 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
–
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