Download ENDOCRINE SYSTEM

ENDOCRINE SYSTEM
Endocrine Glands
• Unlike exocrine glands (which secrete
their products into ducts) endocrine glands
secrete their products (hormones) into the
blood
Heterocrine Glands
• Have both and endocrine and exocrine
function
• Examples are the pancreas, ovaries, and
testes
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Effects of Hormones
(1) Regulates chemical composition of
extracellular fluid
(2) Regulates metabolism and energy
balance
(3) Contraction of heart and visceral muscle
(4) Helps body cope with stress
(5) Helps the immune system
(6) Growth and development
(7) Reproductive process
Target Cells
• Are any cell that responds to a hormone
• Have integral proteins on their cell
membranes that are receptive to certain
hormones
• Different cells with receptors for the same
hormone may respond differently to that
hormone
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Feedback Control of hormones
• There are two types of hormone feedback
(1) Negative feedback
(2) Positive feedback
Negative feedback
• The response is opposite to the stimulus
• Example: an increase in blood sugar (the
stimulus) causes the release of insulin
from the pancreas resulting in the lowering
of blood sugar (the response)
Positive Feedback
• The bodies response intensifies the stimulus
• Example; When a baby nurses it stimulates
nerve endings around the nipple causing the
release of the hormone oxytocin (the stimulus)
which causes the breast to eject milk (the
response) which increases suckling which leads
to more oxytocin which cause more milk ejection
etc.
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What stimulates hormonal
secretion?
(1) The Nervous System. For example the
sympathetic division of the autonomic nervous
system secretes norepinephrine
(2) Chemical changes in the blood. For example
less calcium in the blood will trigger the
release of Parathyroid hormone
(3) Other hormones. For example Thyroid
stimulating hormone from the pituitary causes
the secretion of thyroid hormones from the
thyroid gland
The Pituitary Gland
• Often referred to as the “Master Gland”
because it controls other glands
• Attaches to the brain by a stalk called the
infundibulum
• Is divided into two lobes:
(1) Adenohypophysis (anterior lobe)
(2) Neurohypophysis (posterior lobe)
Adenohypophysis
• Glandular portion of the pituitary
• Releasing hormones and Inhibiting
hormones from the hypothalamus control
the secretion of hormones from the
adenohypophysis
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Neurohypophysis
• Is derived from the same embryonic tissue
layers as the brain
• Contains the axons of secretory neurons
that originate in the hypothalamus
The Hypophysis
Blood supply to the hypophysis
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Hormones of the Adenohypophysis
Human Growth Hormone (hGH)
• Causes body cells to grow (especially
muscle and bone)
• Causes cells to increase:
- their uptake of amino acids
- their rate of protein synthesis
Causes cells to decrease the use of
proteins and sugars for energy (leading to
hyperglycemia (diabetogenic effect)
Pituitary Dwarfism
• Caused by hyposecretion of growth
hormone in growth years
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Pituitary dwarf
Giantism
• Hypersecretion of growth hormone in
growth years
Giantism
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Acromegaly
• Hypersecretion of growth hormone in adult
years
Acromegaly
Thyroid Stimulating Hormone
(TSH)
• Stimulates the thyroid gland to secrete its
hormones T3 and T4
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Adenocorticotropic Hormone
(ACTH)
• Controls the synthesis and secretion of
hormones from the adrenal cortex
Follicle Stimulating Hormone (FSH)
• Stimulates the development of follicles and
ova in the ovaries and the secretion of
estrogen
• Stimulates the development of sperm in
the testes
Luteinizing Hormone (LH)
• In females stimulates the secretion of
estrogen by ovarian cells, stimulates
ovulation and the formation of the corpus
luteum
• In males stimulates the production of
testosterone in the Leydig cells
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Prolactin
• Controls the production of milk in the
mammary glands
• Needs other hormones to work including
estrogen, progesterone, corticosteroids,
hGH, T4, insulin, oxytocin, and human
chorionicsomatomammotropin
Melanocyte Stimulating Hormone
• Stimulates the melanocytes to secrete
melanin to darken the skin
Neurohypophysis
• The posterior lobe of the pituitary
• The hormones released from the
neurohypophysis are produced in the
hypothalamus by neurosecretory cells and
transported to the neurohypophysis by the
axons of the cells in the hypothalamichypophyseal tract
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Hormones of the Neurohypophysis
• Two hormones are produced:
(1) Oxytocin
(2) Antidiuretic hormone (ADH)
Oxytocin
• Stimulates the contraction of smooth
muscle in the uterus and mammary glands
• Positive feedback control of secretion
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Antidiuretic Hormone (ADH)
• Controls the volume of urine by causing
the removal of water from the urine in the
distal convoluted tubule of the kidney
• Raises blood pressure by constricting
arterioles
• Negative feedback
The Thyroid Gland
• Consists of two lobes on either side of the
trachea joined by an isthmus
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Hormones of the Thyroid Gland
• Thyroxine (T4) and Triiodothyroine (T3)
are secreted by the follicular cells
• Calcitonin is secreted by the parafollicular
cells
Hormones T3 and T4
• Effects of these hormones includes:
(1) Metabolism
(2) Growth and development
(3) Nervous system activity
Calcitonin
• Homeostasis of blood calcium (it lowers
blood calcium by activating osteoblasts in
the bone which remove calcium from the
blood to build bone
• Antagonistic to parathyroid hormone
(PTH)
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The Parathyroid Gland
• There are two pairs of glands embedded
in the lateral lobes of the thyroid gland
(see slide 36 above)
• Secretes parathyroid hormone (PTH)
Parathyroid Hormone (PTH)
• Raised blood calcium levels by:
(1) Stimulating osteoclasts to break up bone
(2) Increasing the absorption of calcium from
the G.I. tract
(3) Causing the kidneys to retain calcium
Needs vitamin D to be effective
PTH is antagonistic to Calcitonin
The Adrenal Gland
• Two glands in humans, one on the top of
each kidney (suprarenal)
• Structurally and functionally divided into
two regions:
(1) Adrenal Cortex
(2) Adrenal medulla
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The Adrenal Cortex
• Subdivided into three zones:
(1) Zona Glomerulosa secretes
mineralocorticoids
(2) Zona Fasciculata secretes
glucocorticoids
(3) Zona Reticularis secretes
gonadocorticoids
Mineralocorticoids
• Help control water and electrolytes
homeostasis, especially NaCl
• The main hormone is Aldosterone
• The release of aldosterone is regulated by
the Renin-Angiotensin Pathway
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Renin-angiotensin Pathway
• Renin is released by juxtaglomerular cells
in the kidney in response to low blood
pressure
• Renin converts Angiotensinogen from the
liver into Angiotensin I
• When Angiotensin I reaches the lungs in
the blood it is converted into Angiotensin II
• Angiotensin II stimulates the adrenal
cortex to release Aldosterone
Glucocorticoids
• Control metabolism and resistance to
stress
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The three major Glucocorticoids
• (1) Cortisol (Hydrocortisone) – most
abundant
• (2) Corticosterone
• (3) Cortisone
Effects of Glococorticoids
• Promotes normal metabolism
• Resistance to stress by increasing blood
sugar and raising blood pressure
• Anti-inflammatory responses
Gonadocorticoids
• Same effects as testosterone but at such a
low level as to be too low for effects to be
significant
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The Adrenal Medulla
• Directly innervated by the Autonomic
Nervous System
• Two hormones are produced:
(1) Epinephrine
(2) Norepinephrine
These hormones are sympathomimetic (they
imitate the effects of the sympathetic
nervous system i.e. fight-or-flight)
Pancreas
• Is both and endocrine and exocrine gland
(heterocrine)
• Has specialized areas called Islets of
Langerhans that secrete 4 hormones
• The exocrine function is the secretion of
NaHCO3 (sodium bicarbonate) to
neutralize and acidic chyme coming from
the stomach
Hormones from the Pancreas
• The pancreas secretes four hormones
(1) Glucagon
(2) Insulin
(3) Somatostatin
(4) Pancreatic Polypeptide
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Glucagon
• Release is stimulated by low blood sugar
• Raises blood sugar levels
• Negative feedback
Insulin
• Stimulation for release is high blood sugar
• Insulin lowers blood sugar levels
• Negative feedback
Somatostatin
• Inhibits the secretion of insulin and
glucagon when blood sugar levels are
normal
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Pancreatic Polypeptide
• Regulates the release of pancreatic
digestive enzymes. This prevents the
breakdown and absorption of
carbohydrates from the small intestine if
the blood sugar level is too high, and
increases the digestion and absorption of
carbohydrates if the blood sugar level is
too low.
• The figure on the next slide illustrates the
fact that the pancreas is both an endocrine
and an exocrine gland. The pancreas has
a duct system that empties digestive
enzymes into the duodenum. The
pancreas also has Islets (D) that secrete
hormones into the blood
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Ovaries
• Produce four different hormones:
(1) Estrogen
(2) Progesterone
(3) Relaxin
(4) Inhibin
Estrogen
• Responsible for the development and
maintenance of female sexual
characteristics, regulation of menstruation
and lactation
Progesterone
• Makes the stratum functionalis of the
endometrium of the uterus thick and highly
vascularized to prepare the embryo for
implantation
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Relaxin
• Relaxes the symphysis pubis and cervix
during the birth process
Inhibin
• Inhibits the secretion of follicle stimulating
hormone during pregnancy so that a new
menstrual cycle does not begin while there
is a fetus in the uterus
Testes
• Produces two hormones:
(1) Testosterone
(2) Inhibin
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Testosterone
• Development and maintenance of the
male sexual characteristics
Inhibin
• Inhibits the secretion of FSH to limit the
production of sperm to 200 million a day
Thymus
• Secretes hormones that promote the
proliferation and maturation of T cells for
immunity
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Other Endocrine Tissue
• Other tissue secrete hormones but are not
considered glands because they have
other predominate functions. They include
- Gastrointestinal tract
- Placenta
- Kidneys
- Skin
- Cardiac muscle
Hormones of the G.I. Tract
• Stomach gastrin – causes food to move
along inside the G.I. tract
• Enteric gastrin – causes the stomach to
empty its contents into the duodenum
• Secretin – causes the pancreas to secrete
sodium bicarbonate
• Cholecystokinin stimulates gallbladder
contraction and pancreatic enzyme
secretion
• Enterocrinin secretion of intestinal
enzymes
Hormones of the Placenta
• Human chorionic gonadotropic
hormone causes the corpus luteum in the
ovary to persist
• Human chorionic somatomammotropin
stimulates the breast to produce milk
• Estrogen, progesterone and relaxin –
same functions as these hormones from
the ovaries
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Hormones of the Kidney
• Renal Erythropoietic Factor causes
stem cells in the bone marrow to produce
red blood cells
• Vitamin D activation
Skin
• Vitamin D
Cardiac Muscle
• Atrial Natiuretic Factor lowers blood
pressure by stimulating the kidneys to
secrete water and salt into the urine
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Pineal Gland
• Secretes Melatonin which inhibits
reproductive activities until puberty
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