Endocrine System
Overview
• Endocrine
system
includes all
cells and
tissues that
produce
hormones or
paracrine
factors with
effects
beyond their
tissues of
origin.
Intercellular
• Direct communication: When
cellular activities are coordinated Communication
through gap junctions of
adjacent cells
• Paracrine communication:
chemical messengers from cell to
cell within a tissue
▫ Hormones are chemical
messengers that are released
from one tissue & transported
in the bloodstream to alter
activities in other tissues
 Cells within those tissues are
called target cells.
Intercellular Communication
• Endocrine communication:
When hormones coordinate
cellular activities in distant
portions of the body.
▫ Stimulate synthesis of an
enzyme/protein
 An enzyme is a protein that
synthesizes a specific reaction
▫ Increase/decrease rate of
synthesis of an enzyme
▫ Turn existing enzyme channel
“on” or “off”
Chemical Messengers
• Amino Acid Derivatives
▫ Small molecules related to amino acids (building blocks of
proteins) (by thyroid and pineal gland).
• Peptide Hormones
▫ Chains of amino acids (diverse visceral organ/brain release)
• Lipid Derivatives
▫ Eicosanoids; small molecules with 5-carbon ring (involved in
blood clotting)
▫ Leukotrienes; eicosanoids released by activated white blood
cells (leukocytes). (coordinate tissue response to injury)
• Steroid Hormones
▫ Lipid (similar to cholesterol) released by the reproductive
organs
Secretion and Distribution
• Typically at occurs where the capillaries are abundant
& hormones quickly enter the bloodstream (2 min-hr)
▫ Inactivation
 1. diffuses out of the bloodstream and binds to
receptors on target cells
 2. its absorbed and broken down by cells in the
liver or kidneys
 3. its broken down by enzymes in the plasma or
interstitial fluid
Mechanisms of Hormone Action
• Hormones and cell membrane receptors; in order to
affect a target cell, the hormone must first interact
the the appropriate receptor
▫ Each cell has receptors for several different
hormones
▫ Lipid based hormones can diffuse across cell
membranes
▫ Non-lipid based hormones must bind to receptor
proteins to enter the cell
First and Second Messengers
• First messenger: (hormone) does something to the
appearance of a second messenger in the cytoplasm.
• Second messenger: may act as an enzyme activator,
inhibitor, or cofactor.
▫ Net result is changes in the rates of various
metabolic reactions.
 Down regulation: process in which the presence of
a hormone triggers a decrease in the number of
hormone receptors.
 Up regulation: process in which abundance of a
hormone triggers an increase in the number of
hormone receptors
Overview of Endocrine System
• http://www.youtube.com/watch?v=8fh2HmdxQ
jQ&feature=related
Control of Endocrine Activity
• Direct response to:
▫ Changes in the extracellular fluid composition
▫ Arrival or removal of a specific hormone
▫ Arrival of specific neurotransmitters
Simple reflexes only involve one hormone
Complex reflexes involves one or more
hormones
Patterns of Hormonal Interaction
• Extracellular fluid
contains a mixture of
hormones and more
than one hormone can
affect a cell at a time.
• 1. Antagonistic effect: (the two
hormones have opposing
effects)
• 2. Synergistic effect: (the two
hormones produce the same
effect)
• When a cell receives
• 3. Permissive effect: 1 hormone
instructions from 2
is needed in order for the other
hormones at the same
hormone to produce an effect
time 1 of 4 outcomes is
possible:
• 4. Integrative effects: hormones
produce different but
complementary results
Pituitary Gland
• Anterior lobe:
contains a variety of
endocrine cells
▫ Extensive capillary
network radiates
through these
regions-gives cells
immediate access to
the circulatory
system
http://www.youtube.com/watch?v=V08d
Wz5XNBA&feature=related
Hormones of the Anterior Lobe
Thyroid-Stimulating
Hormone
▫ Triggers the release of
thyroid hormones
• Andrenocorticotropic
Hormone
▫ Stimulates the release
of steroid hormones by
the adrenal-targets
cells that affect glucose
metabolism
Hormones of the Anterior Lobe
• Growth hormone
▫ Stimulates cell growth and
replication by accelerating
the rate of protein synthesis
(especially skeletal muscle
and cartilage)
• Melanocyte-Stimulating
Hormone
▫ Stimulates the melanocyte
of the skin
Hormones of the Anterior Lobe
• Gonadotropins
▫ Regulate the activities of the gonads (testes and
ovaries)
 Low levels causes hypogonadism-leads to inability
to produce sperm/eggs
 Follicle-stimulating hormones: promotes follicle
development in females and helps stimulate
secretion of estrogens
 Luteinizing hormone: induces ovulation
(production of reproductive cells in females)
• Prolactin
▫ Works with other hormones to stimulate mammary
gland development
Hormones of the posterior lobe
• Antidiuretic hormone
• Oxytocin
▫ Released in response
▫ Stimulates smooth
to fall in blood
muscle contraction
volume or blood
of the uterus in
pressure
labor.
 Decreases water
loss, retains
electrolytes, causes
vasoconstriction
(closes) to help raise
blood pressure
Thyroid Gland
• Curves in front of the trachea
▫ Contains fluid 3ox higher in iodide (I-) than the
blood
 Iodide is the building blocks of thyroidstimulating hormones
▫ Extensive blood supply
 Delivers nutrients and gets rid of wastes
Thyroid Gland
Thyroid hormones effect almost every cell
▫ In the cytoplasm they are held in storage
▫ In mitochondria the increase rate of ATP production
▫ In the nucleus they synthesize enzymes that control
energy transformation
 Increases metabolic rate of the cell
• C cells release calcitonin which helps regulate
Ca+ in body fluids
▫ Responds directly to Ca+ concentrations in the
blood
 Stimulates bone growth and density
Parathyroid Glands
• 2 pairs are embedded in
the posterior side of the
thyroid gland
▫ Chief cells
 Produce parathyroid
hormones
 Increases Ca+ in body
fluids
▫Allows Ca+ to be
taken from the bone
Adrenal Glands:
One triangle shaped gland sits on top
(superior) of each kidney
• Adrenal cortex
▫ Yellow because of stored lipids
(steroids)
▫ Collectively called the corticosteroids
 vital for life (gene transcription)
Outer region
 Produces hormones that affect the
composition of fluids
Inner border towards the medulla
 Hormones affect glucose
metabolism
 Anti-inflammatory effects
Narrow band borders the medulla
 Produces androgens
Adrenal Glands Cont.
Adrenal medulla: Secretory activities are controlled
by the sympathetic nervous system
Epinephrine: 75-80%
Norepinephrine: 20—25%
In skeletal muscle:
Mobilize glycogen reserves
Accelerate glucose breakdown into ATP
In adipose tissue:
Stored fat is broken down, released into the blood stream for
production of ATP
In the liver:
Glycogen is broken down, released into the blood for use by neural
tissue
In the heart:
Triggers increase in rate and force of cardiac muscle contraction
Adrenaline
• http://www.youtube.com/wat
ch?v=4g25d7_Afmc&feature=
related
The Pineal Gland
• Inside the epithalamus
• Synthesizes the hormone
melatonin
▫ Made from molecules of
serotonin
 Inhibits reproductive
function
 may play a role in
determining
maturation
 Protects against free
radicals
 Sets circadian rhythm
The Pancreas
• Lumpy organ the abdomen between the inferior
border of the stomach (bottom) and the proximal
(closest) portion of the small intestine.
• Primarily a exocrine organ (99%) but it makes
digestive enzymes
• The endocrine pancreas (1%) consists of clusters
known as pancreatic islets.
▫ Surrounded by capillaries that carry hormones
to the blood stream
Glucagon
• Released by Alpha
cells:
▫ raises blood
glucose levels
▫ Target primarily
the liver
▫ Stimulates release
of glucose into the
blood
 Typically in
times of energy
need after a
period of not
eating
Insulin
• Peptide hormone released by beta
cells when glucose concentrations
exceed normal levels
▫ Typically after eating, especially
after eating carbohydrates
• Insulin receptors are present in most
cells membranes making them
insulin dependent
▫ Cells that do not need insulin to
utilize glucose are called insulin
independent
Insulin
• Effects of Insulin on target cells:
▫ Acceleration of glucose utilization (all target cells)
and enhanced ATP production
▫ Stimulation of glycogen formation (skeletal muscle
and liver)
▫ Stimulation of amino acid absorption and protein
synthesis
▫ Stimulation of triglyceride formation in adipose
tissue
Endocrine Tissues and Other Systems
• Intestines
▫ Pace of digestion typically controlled by hormones released
locally
• Kidneys
▫ Calcitrol (part of the group of steroids we call Vitamin D)
 Steroid
 Stimulates absorption of Calcium and Phosphate in the
digestive tract
▫ Erythropoietin
 Stimulates production of red blood cell in the marrow when
o2 levels in the kidneys are low
▫ Renin
 Restricts salt and water loss in the kidneys when renal
blood flow declines
Endocrine Tissues and Other Systems
• Heart
▫ When stretched they reduce blood volume and
pressure by reducing thirst and promoting salt and
water loss in the kidneys
• Thymus
▫ Under the sternum
▫ Important in the immune defense
Thymosin
promotes development of lymphocytes (white
blood cells)
Endocrine Tissues and Other Systems
• Gonads
▫ Androgens
 Testosterone
 In embryos effects development of the CNS
 Effect development of sperm
 Protein synthesis in muscles
 Secondary sex traits: hair, voice, build…
▫ Estrogens
 Follicle maturation (for ovulation)
 Secondary sex traits: hair, voice, build…
▫ Progestins
 Prepare uterus for implantation
 Prepare mammary glands
Endocrine Tissues and Other Systems
• Adipose tissue
▫ Leptin
 Feedback control of appetite, released when glucose is
absorbed by adipose tissue; gives satiation and suppress
appetite
▫ Found obese people already have increased levels but
have defective receptors for the hormone
 Must also be present for normal gonadotropin synthesis
 Explains why decreased fat % can cause amenorrhea
 Increased fat % can improve fertility
 Female maturation is later
▫ Resistin
 Reduces insulin sensitivity
 Explains why body fat % can influence type 2 diabetes
Role of Hormones in growth:
Normal growth requires many hormones to cooperate
▫ Growth Hormone (GH)
▫ Parathyroid Hormone
 More important in children, (PTH) & Calcitrol
its role is to produce skeletal  Without them bone
muscle and skeletal bones
density and strength are
diminished
▫ Thyroid hormones
 If not present in fetal or 1st ▫ Reproductive hormones
year development can cause
 Absence would prevent
nervous system to fail
gender-related differences
including skeletal
▫ Insulin
proportions and
 Without it energy is
secondary sex traits
diminished
Hormonal Responses to Stress
• Anything that disrupts homeostasis is a form
of stress.
• General Adaptation Syndrome (GAS) or Stress
Response
▫ Exposure to a wide variety of stress causing factors
will produce the same general pattern of hormonal
and physiological adjustments
▫ Divided into three stages:
• 1. Alarm Phase: Immediate response to stress
▫ Directed by the SNS
▫ Energy reserves are mobilized (glucose)
▫ “fight or flight” occurs
 Epinephrine
• 2. Resistance Phase: (weeks to months if necessary,
depending on general health and fat stores)
▫ When efforts of alarm phase do not overcome imbalance
 Glucose demands are high
 Use glucorticiods: mobilize lipid and protein reserves,
conserve glucose for neural tissue, keep blood glucose
elevated, conserve water and electrolytes
• 3. Exhaustion Phase: when resistance breaks and
homeostasis is lost
▫ Failure of one or more systems-- can be fatal