Download Endocrine System

Endocrine
System
Endocrinology
• Study of endocrine
system
• Endocrine and
nervous system
work together to
maintain a stable
internal
environment
General functions of endocrine and
nervous system
• 1. communication
• 2. integration
• 3. control
Description of endocrine gland:
• Does not have
ducts
• Widely
scattered
throughout body
• Secretes
substance called
hormones
How hormones work?
• A hormone is substance
that signals a response
• They are secreted in
blood stream and go to
certain tissues called
target tissue/cell
• Target cell (tissue)—
cell that can only can be
signaled by a certain
hormone
– They get to the tissue by
traveling thru blood
Hormones are classified based
on function:
• 1. tropic hormones— they target other
endocrine glands and stimulate growth
and secretion (only affect other glands)
• 2. sex hormones— target the
reproductive system only
• 3. anabolic hormone— stimulate
anabolism of their target cells
Classification of hormones
based on structure:
• 1.steroid—manufactured by endocrine
cells from cholesterol which is an
important lipid in the body
– Ex. estrogen, testosterone
• 2. nonsteroid—manufactured by cells
from amino acids
– Ex. peptide hormones
Hormone regulation:
• Most glands secrete hormones continuously
• May be 30-40 types of hormones at a given
time in blood
• Most are transported in the blood by plasma
proteins
• Hormone amounts are regulated by negative
feedback in:
• 1. target tissue,
• 2. liver inactivation, and
• 3.excretion by kidney
Negative feedback regulation
• As one increases, the other decreases
• Example: insulin regulates glucose levels
• 1. Increase glucose causes insulin to be
secreted
• 2. Insulin goes to target tissue causing them to
take up glucose
• 3. This decreases glucose level
• 4. Decrease glucose, decreases insulin causes
glucose to increase again
How hormones work?
• Uses Lock-andkey mechanism
• Hormone must fit
exactly on a
receptor on
surface of a
plasma protein
• Cell that the
hormone attaches
to is called a target
cell
How hormone affects target cell?
• Once hormone has landed on target cell, a
hormone-receptor interaction occurs.
• The chemical reaction causes changes to
occur in the target cell.
How does change in target
cell occur?
Step 1: When hormone
attaches to receptor, an
enzyme is released called
adenyl cyclase (called 1st
messenger).
Step 2: Adenyl cyclase moves
to the cytoplasm of the cell and
triggers ATP to change to
AMP (called second
messenger).
At least 12 hormones use
cyclic AMP as their second
messenger.
Effects of cyclic AMP:
• 1. it activates
specific genes
• 2. it synthesizes
specific proteins
• 3. it regulates
release of
endocrine
hormones
Hormones work together or
alone
• Synergism—when 2 or more hormones
work together to influence a cell better
than they can work alone
Hormone disorders:
• Hypersecretion—secretion of too many
hormones due to a diseased gland
– Example: hyperthyrodism—too many thyroid
hormones
• Hyposecretion– secretion of too few
hormones due to diseased gland
– Ex. hypothyroidism—too few thyroid
hormones
Types of endocrine glands:
•
•
•
•
•
•
•
•
1. pituatary gland
2. thyroid gland
3. parathyroid gland
4. adrenal gland
5. pancreas
6. testes and ovaries
7. thymus gland
8. pineal gland
Pituitary gland:
• Secretes hormones
that control:
• 1. growth
• 2. ovaries
• 3. testes
• 4. adrenal
• 5. cortex
• 6. pregnancy
Pituitary gland cont…
• Called master
gland because
controls the
function of other
glands
• It is about the size
of a pea
Types of hormones
secreted by pituitary:
• 1 releasing hormones—
stimulates or inhibits
release of other hormones
• 2. growth hormone—
stimulates growth of bones,
muscles, and other organs
by increasing synthesis of
protein
• 3. anti-diuretics (ADH)–
prevents dehydration 1. by
increasing water absorption
by the kidneys 2.
conserving water by
constricting blood vessels
Thyroid gland:
• Consists of 2 lobes
that surround
trachea
• Secretes thyroid
hormones that
regulate metabolism
• Hyperthyrodism—too
many hormones—
slim, nervous
• Hypothyroidism—too
few hormones—
overweight, sluggish
Parathyroid gland:
• Embedded at the
back of thyroid
• Function: secretes
parathyroid
hormones that
regulate calcium
levels by increasing
absorption by
intestines
• Increase parathyroid,
increase calcium
absorption
Adrenal gland
• Located above
kidneys
• Has 2 parts:
• Adrenal medulla—
inner
• Adrenal cortex—
outer
Adrenal hormones:
• Epinephrine
(adrenalin) and
norepinephrine
– Increases
energy
• Aldosterone
• Cortisol
• Sex hormones
like estrogen
pancreas
• Hormones secreted
are insulin and
glycogen
• Both regulate
glucose levels
• Beta cells secrete
insulin
• Alpha cells secrete
glycogen
Testes and ovaries:
• Secrete sex hormones
• Male sex hormones
are secreted by
testes
• Female sex hormones
are secreted by
ovaries
• Testosterone—males
• Estrogen and
progesterone-female
thymus gland:
• At upper part of
thoracic cavity
• Secretes
thymosin which
causes certain
white blood cells
(t-cells) so they
can fight off
infection
Pineal gland:
• Small, located
deep in cerebral
hemisphere of
brain
• Secretes hormone
melatonin that
responds to
light—regulates
“biological clock”