Download Chapter 15-B Endocrine Glands

• 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
• 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
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.
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Antidiuretic hormone (ADH) : Also
called vasopressin
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It is an antiurination hormone
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ADH helps to avoid dehydration or water
overload
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A. Osmoreceptors (specialized
neurons of hypothalamus monitor
changes in intercellular osmolality)
monitor the solute concentration of the
blood
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With high solutes, ADH secretion
increases
ADH stimulates kidney to retain water
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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
• 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
Giganticism
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
and increase TSH secretion
• Rising blood levels of thyroid hormones act on the pituitary and
hypothalamus to block the release of TSH
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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:
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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