Transcript The Endocrine System

The Endocrine System
Hypothalamic-Pituitary-Adrenal Axis
• also known as the limbic-hypothalamic-pituitaryadrenal axis
Represents the physiological link between
nervous and endocrine system functions
• a complex set of direct influences and feedback
interactions among three endocrine glands: the
hypothalamus, the pituitary gland and the adrenal
glands
• a major part of the neuro-endocrine system that
controls reactions to stress and regulates many body
processes, including digestion, the immune system,
mood and emotions, sexuality and energy use
• The pituitary, or hypophysis, is a small gland
about the size of a cherry. It is located in a
saddlelike depression of the sphenoid bone
just posterior to the point where the optic
nerves cross. It is surrounded by bone except
where it connects with the hypothalamus of
the brain by a stalk called the infundibulum
• Hormones produced in the anterior pituitary are not
released until releasing hormones arrive from the
hypothalamus.
• Releasing hormones travel to the anterior pituitary by
way of a special type of circulatory pathway called a
portal system.
• By this route, some of the blood that leaves the
hypothalamus travels to capillaries in the anterior
pituitary before returning to the heart.
• As the blood circulates through the capillaries, it
delivers the hormones that stimulate the release of
anterior pituitary secretions.
The “Master Gland”
• Regulates and controls activities of all other
endocrine glands!
• Located at the midpoint of the skull, roughly
behind the eyes and very close to the major
arteries & veins carrying blood to and from
the vein (WHY??)
• Made up of 3 sections: Anterior, Intermediate
and Posterior Lobes
Anterior Lobe
• The front part of the pituitary gland
• Hormones produced regulate metabolic activities of
cells and stimulate other endocrine glands
Produces 6 different hormones:
1. Growth hormone (HGH)
2. Thyroid-Stimulating Hormone (TSH)
3. Adrenocorticotropic Hormone (ACTH)
4. Follicle-Stimulating Hormone (FSH)
5. Luteinizing Hormone (LH)
6. Prolactin (PRL)
• Human Growth Hormone (HGH): also known
as somatotropin, stimulates growth, cell
reproduction and regeneration
• Thyroid-Stimulating Hormone: (TSH)
stimulates the thyroid gland to produce
thyroxine (T4), and then triiodothyronine
(T3)which stimulates the metabolism of almost
every tissue in the body
• Adrenocorticotropic Hormone (ACTH): also
known as corticotropin, is often produced in
response to biological stress. Its principal
effects are increased production and release
of corticosteroids
• ACTH is also related to the circadian rhythm in
many organisms
• Follicle-Stimulating Hormone: FSH regulates
the development, growth, pubertal
maturation, and reproductive processes of the
body. FSH and luteinizing hormone (LH) act
synergistically in reproduction. Specifically, an
increase in FSH secretion by the anterior
pituitary causes ovulation.
• Luteinizing Hormone (LH): also known as
lutropin. In females, an acute rise of LH ("LH
surge") triggers ovulation and development of
the corpus luteum. In males, it stimulates Leydig
cell production of testosterone. It acts
synergistically with FSH.
• Prolactin(PRL): stimulates the mammary glands
to produce milk (lactation), counteracts the
effects of dopamine, linked to production of
testosterone and estrogen
Posterior Lobe
• The back part of the pituitary gland
• Stores hormones produced by the hypothalamus
Produces 2 different hormones:
1. Anti-Diuretic Hormone(ADH), also called
vasopressin – stimulates water retention which
increases BP
2. Oxytocin (OXT) – stimulates uterine contractions
and lactation during childbirth. Modulates HPA
Axis activity, inhibiting the release of ACTH and
cortisol
The Thyroid Gland
• Produces hormones that
regulate metabolism, body
heat and growth
• Located on the front of the
neck, just below the larynx
• Consists of 2 lobes, 1 on
either side of the trachea
• Produces Thyroxine which
regulates the way cells
release energy to create
other substances such as
protein
Thyroid Hormone - Thyroxine
• Overproduction: hyperthyroidism causes
tiredness, anxiety, weight loss, diarrhea and
intolerance to heat
• Underproduction: hypothyroidism causes
tiredness, dry skin, hair loss, weight gain,
constipation and hypersensitivity to cold
Parathyroid Glands
• Found on the lobes of the
thyroid gland
• Produces Parathyroid Hormone
which regulates the body’s
calcium and phosphorus
balance
Adrenal Glands
Consist of 2 parts:
1. Adrenal cortex (outer)
2. Adrenal medulla
(inner)
Adrenal Cortex
• Absolutely essential for life
• Produces Aldosterone which inhibits the
amount of sodium excreted in urine (a key
part of regulating blood pressure and blood
volume)
• Also produces Hydrocortisone, Corticosterone
and Androgen which play a role in
metabolizing fats, proteins and carbohydrates,
as well as inhibiting inflammation of tissues
Adrenal Medulla
• Secretes the hormone Epinephrine (adrenalin
– the ‘fight or flight’ hormone) and
Norepinephrine
• Epinephrine increases heart rate, BP and
respiration and suppresses digestion (WHY??)
• Norepinephrine (noradrenalin) increases
heart rate, blood flow to the brain and skeletal
muscle, triggers the release of glucose from
energy stores
The Pancreas
• Part of both the
endocrine and digestive
systems
• Located behind the
stomach, attached to the
small intestine by a duct
that transports its
digestive juices to the
intestine
• The Pancreas is the site of the Islets of
Langerhans; endocrine cells within the
pancreas that secrete 2 hormones essential
for maintaining blood sugar levels:
• Insulin –stimulates the liver to remove glucose
from the blood and convert it into glycogen
for storage, thus lowering blood sugar levels
• Glucagon – stimulates the liver to convert
glycogen into glucose and release it into the
blood for use in the body’s cells, thus
increasing blood sugar levels
The Gonads
• Ovaries in females and Testes in males
• Hormones released by these glands are
responsible for spermatogenesis and
ovulation and the development and
maintenance of secondary sex characteristics
such as muscle & bone mass, body and facial
hair
• Controlled by the Pituitary Gland