Download Endocrine System: http://science.nhmccd.edu/biol/ap1int.htm

Endocrine System:
http://science.nhmccd.edu/biol/ap1int.htm
Overview:
1. Works with the nervous system to regulate physiology.
2. Hormones bind target cell receptors that start pathways that trigger
specific cell response.
3. The hypothalamus and pituitary are the key players in integrating the
arms of the endocrine system.
4. Non- pituitary hormones regulate:
a) Metabolism
b) Homeostasis
c) Development
d) Behavior
5. Invertebrate regulatory systems involve endocrine and nervous
interactions.
1. Hormones (Hormon – excite):
-Chemical signal secreted into extracellular fluid, carried by circulatory
system (blood/hemolymph), to target cells. Other cells unaffected.
- Internal communication and regulation controlled by NS and ES.
-NS consists of high speed electrical signals traveling along neurons causing
movement of body in response to environmental stimuli/changes.
-ES consists of slower but longer lasting responses via hormones to stress,
dehydration, long term development etc.
Neurosecretory cells:
Specialized nerve cells that release hormones into the blood. Part of the
brain contains these cells that release neurohormones.
Epinephrine (adrenalin) is BOTH neurotransmitter and hormone secreted by
the adrenal medulla in “fright or flight responses.”
-NS plays a role in controlling secretions from endocrine gland based on day
length and reproductive cycles.
Fig. 45.2 Basic pathway and feedback loops consist of:
-Stimulus triggering a receptor resulting in signal being sent to a control
center and a response signal being sent to an effector.
- Three types of hormonal pathways (about 20 different hormones have
complex interrelationships of regulating each other).
Feedback mechanisms:
-Positive. Reinforce stimulus and leads to an even greater response ex.
Nursing mother and milk production.
- Negative. Effector response reduces initial stimulus and eventually
response stops. Occurs a lot in maintenance of homeostasis ex. Blood calcium
and glucose levels.
Review Qs pg. 944. 1,2,3.
2. Pathways:
-Hormones in vertebrates are water soluble (proteins, peptides or amines) or
lipid soluble (steroids).
- 3 main steps:
a) Reception
- signal molecules bind specific receptor proteins in/on target cell. This
binding triggers events in the target cell leading to b).
b) Signal transduction
- Fig. 11.10 pg. 211 sequence of reactions leads to c). Result in
phosphorylation cascades that amplify signal.
c) Response
- A change in the target cell’s behavior.
Fig. 45.3 shows water soluble and lipid soluble hormones.
Water soluble hormone:
- Binds surface receptor and triggers signal transduction
pathway that causes a change in the cytoplasmic function or
gene transcription in nucleus.
Lipid soluble hormone:
- Penetrates cell’s plasma membrane and binds intracellular
receptor (in cytoplasm or nucleus).
- Signal-receptor complex acts as transcription factor (activating
gene expression).
A hormone can exert a different effect depending on the target cell it binds
(different receptors). If same receptors different signal transduction
pathways triggered.
Ex:
Estrogen in birds triggers synthesis of ovalbumin (egg white).
Thyroxine in frogs also triggers metamorphosis of tadpoles into adults
(reabsorption of tail etc).
Thyroxine in Humans and other vertebrates regulates metabolism.
Fig. 45.4 pg. 947.
http://www.wisc-online.com/objects/index_tj.asp?objID=AP13704
Local regulators
- Convey signals between neighboring cells = paracrine signaling (11.4).
- Elicit responses from target cells in milliseconds ( 1/1000th sec),. Quicker
than hormones.
Exs:
a) Many neurotransmitters (amino acid derivatives).
b) Cytokines (peptide/protein) in immune response.
c) Growth factors (cell proliferation and differentiation).
d) Gas NO (nitric oxide). When blood O2 levels fall, endothelial cells
release NO which activates enzyme that relaxes smooth muscles so
blood vessels dilate and blood flow to tissues improved.
In males increases blood flow to penis-acts in few seconds and then breaks
down. Viagra interferes with the breakdown of NO (erectile dysfunction).
NO also acts as a neurotransmitter when secreted by WBCs to kill bacteria
and cancer cells.
e) Prostaglandins (PGs).
- Modified fatty acids (derived from lipids in plasma membranes).
- First discovered in prostate gland secretions (add to semen).
-In semen stimulates uterine muscles to contract so sperm can reach
egg.
-In childbirth, secreted by placenta and helps induce labor.
- In immune system induce fever and inflammation (ibuprofin and
asprin inhibit synthesis of prostaglandins). Regulate aggregation of platelets
(asprin taken if at risk of heart attack).
- In respiratory system prostaglandin E relaxes muscles and
prostaglandin F contracts muscles in bvs of lungs.
Qs 1,2,3. Pg. 948 – explain to each other without using books.
Friday: http://www.hormone.org/endo101/
3. Hypothalamus and Pituitary.
- Fig. 45.6 pg. 950 and Table 45.1 Pg. 949.
- Gland, location, effect and regulation.
Hypothalamus- Receives signals via NS from body and other parts of the brain and sends
out endocrine signals.
- Senses to NS to Brain to Hormones.
- Contains two sets of neurosecretory cells whose secretions end up in the
pituitary gland.
Pituitary- Two fused glands develop from two separate regions of the embryo and do
different jobs.
-Anterior (Adenohypophysis)
- Develops from folds of tissue at roof of mouth that grow upwards.
- Endocrine cells that secrete at least 6 different hormones.
- Fig. 45.8.
- Regulated by tropic hormones secreted by neurosecretory cells in
hypothalamus (releasing or inhibiting hormones).
- Each one is controlled by releasing hormone and some have both.
- FSH,LH,TSH,ACTH (tropic- hormone has another endocrine gland as target).
- Prolactin, MSH, Endorphins (Nontropic).
- GH (Tropic and NonTropic effects).
FSH and LH (gonadotrophins) and TSH all similar glycoproteins.
ACTH (adrenocorticotropic H) is a peptide and stimulates secretion of
steroid hormones by adrenal cortex.
All take part in neuroendocrine pathways.
Prolactin – different effects in different vertebrate species.
Mammals-mammary gland growth and milk synthesis.
Birds – Fat metabolism and repoduction.
Amphibians – Delays metamorphosis.
Freshwater fish – Regulates salt and water balance.
Prolactin is an ancient hormone that diversified with evolution of vertebrate
groups.
MSH:
- Regulates activity of pigment cells in some fishes, amphibians and reptiles.
- Humans acts on neurons in brain inhibiting hunger.
Endorphins:
- Bind receptors in brain and dull perception of pain.
- “Runner’s High” is when endorphins released.
- Both MSH and beta-endorphins formed by cleavage of precursor protein
that ACTH.
GH:
- Similar to prolactin.
- Tropic action as signals liver to release insulin-like growth factors (IGFs),
which stimulate bone and cartilage growth.
- Absence of GH stops growth.
- Has effects that raise blood glucose (oppose insulin effects).
- Too much leads to gigantuism (8ft).
- Too much as adult leads to acromegaly ( growth in feet, hands and face).
- Too little (hyposes) leads to pituitary dwafism. Can be treated before
puberty with GH.
- Genetic engineering in 1980’s used bacteria to make hormones.
- Little effect on muscle mass and strength in adults.
b) Posterior Pituitary:
- Extension of hypothalam that grows down towards mouth.
- Fig. 45.7.
- Secretes ADH and oxytocin.
- Made by neurosecretory cells in hypothalamus so are neurohormones.
- Function in simple neurohormone pathways.
- ADH acts on kidneys, water retention regulating osmolarity of blood.
- Oxytocin induces uterine target cells to contract during childbirth and
release milk during nursing. Both are positive feedback pathways.
Pg. 952 Qs: 1,2,3. Review.
Pituitary Gland
The pituitary gland is sometimes called the "master gland" because of its
great influence on the other body organs. Its function is complex and
important for overall well-being.
The pituitary gland is divided into two parts, front (anterior) and back
(posterior).
The anterior pituitary produces several hormones:
Prolactin or PRL - PRL stimulates milk production from a woman's breasts
after childbirth and can affect sex hormone levels from the ovaries in
women and the testes in men.
Growth hormone or GH - GH stimulates growth in childhood and is
important for maintaining a healthy body composition. In adults it is also
important for maintaining muscle mass and bone mass. It can affect fat
distribution in the body.
Adrenocorticotropin or ACTH - ACTH stimulates production of cortisol by
the adrenal glands. Cortisol, a so-called "stress hormone," is vital to survival.
It helps maintain blood pressure and blood glucose levels.
Thyroid-stimulating hormone or TSH - TSH stimulates the thyroid gland to
make thyroid hormones, which, in turn, control (regulate) the body's
metabolism, energy, growth and development, and nervous system activity.
Luteinizing hormone or LH - LH regulates testosterone in men and estrogen
in women.
Follicle-stimulating hormone or FSH - FSH promotes sperm production in
men and stimulates the ovaries to release eggs (ovulate) in women. LH and
FSH work together to allow normal function of the ovaries or testes.
The posterior pituitary produces two hormones:
Oxytocin - Oxytocin causes milk letdown in nursing mothers and contractions
during childbirth.
Antidiuretic hormone or ADH - ADH, also called vasopressin, is stored in
the back part of the pituitary gland and regulates water balance. If this
hormone is not secreted properly, this can lead to problems of sodium (salt)
and water balance, and could also affect the kidneys so that they do not
work as well.
In response to over- or underproduction of pituitary hormones, the target
glands affected by these hormones can produce too many or too few
hormones of their own. For example, too much growth hormone can cause
gigantism, or excessive growth, while too little GH may cause dwarfism, or
very short stature.
Hypothalamus
The hypothalamus is part of the brain that lies just above the pituitary
gland. It releases hormones that start and stop the release of pituitary
hormones. The hypothalamus controls hormone production in the pituitary
gland through several "releasing" hormones. Some of these are growth
hormone-releasing hormone, or (controls GH release); thyrotropin-releasing
hormone, or TRH (controls TSH release); and corticoptropin-releasing
hormone, or CRH (controls ACTH release). Gonadotropin-releasing hormone
(GnRH) tells the pituitary gland to make luteinizing hormone (LH) and
follicle-stimulating hormone (FSH), which are important for normal puberty.
Thymus
The thymus is a gland needed early in life for normal immune function. It is
very large just after a child is born and weighs its greatest when a child
reaches puberty. Then its tissue is replaced by fat. The thymus gland
secretes hormones called humoral factors. These hormones help to develop
the lymphoid system, which is a system throughout the body that help it to
reach a mature immune response in cells to protect them from invading
bodies, like bacteria.
Pineal Gland
Scientists are still learning how the pineal gland works. They have found one
hormone so far that is produced by this gland: melatonin. Melatonin may stop
the action of (inhibit) the hormones that produce gonadotropin, which causes
the ovaries and testes to develop and function. It may also help to control
sleep patterns.
Testes
Males have twin reproductive glands, called testes, that produce the
hormone testosterone. Testosterone helps a boy develop and then maintain
his sexual traits. During puberty, testosterone helps to bring about the
physical changes that turn a boy into an adult male, such as growth of the
penis and testes, growth of facial and pubic hair, deepening of the voice,
increase in muscle mass and strength, and increase in height. Throughout
adult life, testosterone helps maintain sex drive, sperm production, male hair
patterns, muscle mass, and bone mass.
Testicular cancer, which is the most common form of cancer for males
between ages 15 and 35, may need to be treated by surgical removal of one
or both testicles. The resulting decrease or absence of testosterone may
cause decreased sexual drive, impotence, altered body image, and other
symptoms.
Ovaries
The two most important hormones of a woman's twin reproductive glands,
the ovaries, are estrogen and progesterone. These hormones are responsible
for developing and maintaining female sexual traits, as well as maintaining a
pregnancy. Along with the pituitary gonadotropins (FH and LSH), they also
control the menstrual cycle. The ovaries also produce inhibin, a protein that
curbs (inhibits) the release of follicle-stimulating hormone from the anterior
pituitary and helps control egg development.
The most common change in the ovarian hormones is caused by the start of
menopause, part of the normal aging process. It also can occur when ovaries
are removed surgically. Loss of ovarian function means loss of estrogen,
which can lead to hot flashes, thinning vaginal tissue, lack of menstrual
periods, mood changes and bone loss, or osteoporosis.
A condition called polycystic ovary syndrome (PCOS) is caused by
overproduction of male hormones in females. PCOS can affect menstrual
cycles, fertility, and hormone levels, as well as cause acne, facial hair
growth, and male pattern balding.
Thyroid
The thyroid is a small gland inside the neck, located in front of your
breathing airway (trachea) and below your Adam's apple. The thyroid
hormones control your metabolism, which is the body's ability to break down
food and store it as energy and the ability to break down food into waste
products with a release of energy in the process. The thyroid produces two
hormones, T3 (called tri-iodothyronine) and T4 (called thyroxine). Thyroid
disorders result from too little or too much thyroid hormone. Symptoms of
hypothyroidism (too little hormone) include decreased energy, slow heart
rate, dry skin, constipation, and feeling cold all the time. In children,
hypothyroidism most commonly leads to slowed growth. Infants born with
hypothyroidism can have delayed development and mental retardation if not
treated. In adults, this disorder often causes weight gain. An enlarged
thyroid, or goiter, may develop.
Hyperthyroidism (too much hormone) may result in exophthalmic goiter, or
Grave's disease. Symptoms include anxiety, fast heart rate, diarrhea, and
weight loss. An enlarged thyroid gland (goiter) and swelling behind the eyes
that causes the eyes to push forward, or bulge out, are common.
Adrenal Glands
Each adrenal gland is actually two endocrine organs. The outer portion is
called the adrenal cortex. The inner portion is called the adrenal medulla.
The hormones of the adrenal cortex are essential for life. The hormones of
the adrenal medulla are not.
The adrenal cortex produces glucocorticoids (such as cortisol) that help the
body control blood sugar, increase the burning of protein and fat, and
respond to stressors like fever, major illness, and injury. The
mineralcorticoids (such as aldosterone) control blood volume and help to
regulate blood pressure by acting on the kidneys to help them hold onto
enough sodium and water. The adrenal cortex also produces some sex
hormones, which are important for some secondary sex characteristics in
both men and women.
Two important disorders caused by problems with the adrenal cortex are
Cushing's syndrome (too much cortisol) and Addison's disease (too little
cortisol).
The adrenal medulla produces epinephrine (adrenaline), which is secreted by
nerve endings and increases the heart rate, opens airways to improve oxygen
intake, and increases blood flow to muscles, usually when a person is scared,
excited, or under stress.
Norepinephrine also is made by the adrenal medulla, but this hormone is
more related to maintaining normal activities as opposed to emergency
reactions. Too much norepinephrine can cause high blood pressure.
Parathyroid
Located behind the thyroid gland are four tiny parathyroid glands. These
make hormones that help control calcium and phosphorous levels in the body.
The parathyroid glands are necessary for proper bone development. In
response to too little calcium in the diet, the parathyroid glands make
parathyroid hormone, or PTH, that takes calcium from bones so that it will
be available in the blood for nerve conduction and muscle contraction.
If the parathyroids are removed during a thyroid operation, low blood
calcium will result in symptoms such as irregular heartbeat, muscle spasms,
tingling in the hands and feet, and possibly difficulty breathing. A tumor or
chronic illness can cause too much secretion of PTH and lead to bone pain,
kidney stones, increased urination, muscle weakness, and fatigue.
Pancreas
The pancreas is a large gland behind your stomach that helps the body to
maintain healthy blood sugar (glucose) levels. The pancreas secretes insulin,
a hormone that helps glucose move from the blood into the cells where it is
used for energy. The pancreas also secretes glucagon when the blood sugar
is low. Glucagon tells the liver to release glucose, stored in the liver as
glycogen, into the bloodstream.
Diabetes, an imbalance of blood sugar levels, is the major disorder of the
pancreas. Diabetes occurs when the pancreas does not produce enough
insulin (Type 1) or the body is resistant to the insulin in the blood (Type 2).
Without enough insulin to keep glucose moving through the metabolic
process, the blood glucose level rises too high.
In Type 1 diabetes, a patient must take insulin shots. In Type 2 diabetes, a
patient may not necessarily need insulin and can sometimes control blood
sugar levels with exercise, diet and other medications.
A condition called hyperinsulinism (HI) is caused by too much insulin and
leads to hypoglycemia (low blood sugar). The inherited form, called
congenital HI, causes severe hypoglycemia in infancy. Sometimes it can be
treated with medication but often requires surgical removal of part or all of
the pancreas. An insulin-secreting tumor of the pancreas, or insulinoma, is a
less common cause of hypoglycemia. Symptoms of low blood sugar include
anxiety, sweating, increased heart rate, weakness, hunger, and lightheadedness. Low blood sugar stimulates release of epinephrine, glucagon and
growth hormone, which help to return the blood sugar to normal.
Monday: H/W 4. Nonpituitary Hormones:
1. Thyroid Fig. 45.9.
a) T3 and T4 ( triiodothyronine and thyroxine).
- Mainly T 4 made in mammals but target cells convert it to T3. Receptors
have greater affinity for T3.
- Maintains BP, heart rate, muscle tone, digestion and reproductive function,
O2 consumption and cellular metabolism.
Hyperthyroidism
Hypothyroidism
High BP, lots of sweating, weight
Weight gain, lethargy. Cretinism.
loss, irritability, high body temp.
Fig. 45.10 Graves disease-fluid build
up behind eyes results in bulging
eyes.
- Too little iodine in diet leads to goiter (enlarged thyroid). Too little T3
and T4 made so more TSH secreted and causes enlargement of thyroid.
b) Calcitonin Fig. 45.11.
- Secreted when Ca levels too high and lowers Ca levels to homeostatic levels
in blood by
i) Ca deposition in the bone.
ii) Ca uptake in kidneys reduced.
2. Parathyroid:
-Located in the back of the thyroid.
-Secretes parathyroid hormone when Ca levels too low and raises the Ca
levels to homeostatic levels in blood by
i) Ca release from bones.
ii) Ca uptake in kidneys increased.
Note: indirectly, Vitamin D is converted to active hormonal form in kidneys
and stored in liver. Acts on intestine to take up Ca from food.
3. Pancreas:
-Exocrine glands that secrete bicarbonate and enzymes through ducts for
digestion of foods.
-Endocrine glands ( α and β cells).
- α cells secrete glucagon, β cells secrete insulin.
- Important in regulation of glucose levels in blood. Glucose is the major
material for cellular respiration and Carbon needed to make organic
compounds!
- Fig. 45.12.
Note:
- Brain cells are the only ones hat are able to take up glucose ALL the time.
NOT stimulated by insulin.
- Liver and muscles store glycogen.
- Adipose tissue converts sugars to fat.
- ONLY liver cells sensitive to glucagons.
- If insufficient glucose, fat broken down but if severe starvation, the acidic
byproducts lower pH of blood.
Diabetes:
a) Type I:
- Autoimmune condition where β cells destroyed so no insulin.
- Currently transplant of β cells from cadavers. HuESCs may
provide new way of getting these cells – experimental right now.
New Scientist article – Geron and Novacell.
- Treatment is insulin shots.
b) Type II: ( non-insulin dependent)
- Deficiency of insulin action as reduced responsiveness of target
cell receptors for insulin.
- Factors such as excess body weight, unhealthy diet, lack of
sufficient exercise contribute to onset of this condition.
4. Adrenal glands:
- Fig. 45.13 a and b.
- Respond to long term stress ( 45.13b).
a) Adrenal cortex: Fig. 45.13b
- LONG-term stress response.
- Mineralocorticoids and glucocorticoids. ( corticosteroids).
- Responds to ENDOCRINE signals. ACTH stimulates secretion.
- Negative feedback via elevated levels of corticosteroids.
Mineralocorticoids (salt)
Salt and water balance,
Ex. Aldosterone that stimulates
kidneys to reabsorb Na+ and H2O
from filtrate so raising blood volume
and BP.
Aldosterone secretion stimulated by
Angiotensin II Fig. 44.16.
Glucocorticoids
Glucose metabolism from
noncarbohydrate sources – proteins.
Act on skeletal muscle causing
breakdown of muscle proteins. C
skeleton taken to liver and kidneys
where converted to glucose.
Also suppress certain parts of IS.
Anti-inflammatory effects used to
treat arthritis but not for chronic
inflammatory conditions.
-If individual stressed, ACTH levels increase and adrenal cortex secretes
aldosterone as well as glucocorticoids. Elevated levels of corticosteroids in
blood suppress secretion of ACTH – negative feedback.
b) Adrenal medulla:
- Fig. 45.13a.
- Short term stress response.
- Responds to NERVOUS input. Neurohormone pathway.
- Secretes epinephrine and norepinephrine ( hormones and
neurotransmitters).
- Synthesized from tyrosine.
- Catecholamines.
- Increase availability of energy sources, affect cardio and respiratory
systems.
- Epinephrine has stronger effects on heart and metabolic rate.
- Norepinephrine sustains BP.
Also: adrenal glands make small amounts of sex hormones:
- Androgens in females (sex drive).
- Estrogens in males (growth spurt).
5. Gonads:
- Testes secrete androgens.
- Ovaries secrete estrogen and progestins.
6. Pineal gland:
- Secretes melatonin (modified amino acid).
- Depending on species contains light-sensitive cells or nerve connections
from eyes that control it’s secretions.
- Dependent on day length (light).
- Mainly for biorhythms associated with reproduction.
- Secreted at night and amount depends on length of night.
- Target of melatonin are pr of brain structures, suprachiasmatic nuclei
(SCN), function as biological clock.
- melatonin reduces function of neurons in SCN.
Review Qs: Pg. 959 #1,2,3,4.
Tuesday H/W 5. Invertebrates:
- Hydra have hormone that stimulates growth and budding.
- Mollusc (Aplysia) stimulation of lying of thousands of eggs while preventing
sex. Reproduction, feeding and locomotion.
- Fig. 45.15. Molting in Insects and Crustaceans.
- Brain hormone stimulates secretion of ecdysone from prothoracic
glands.
- Ecdysone promotes molting and development of adult
characteristics.
- Juvenile hormone controls Brain H and Ecdysone. Secreted by glands
behind brain (analogous to anterior pituitary), and keeps larval (juvenile),
features.
- When levels of JH high Ecdysone promotes molting but results in a larger
larva.
- When level of JH decreases does Ecdysone induce pupa stage. Now
metamorphosis occurs to give adult form.
- Synthetic versions of JH being used as pesticides to keep insects from
maturing.