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Chapter 18: Endocrine System

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Chapter 18: Endocrine System
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Endocrine system
all endocrine glands and hormone-secreting cells. Hormone-mediator molecule released in one part of the body but regulates activity of cells in other parts
Hormone
a mediator molecule that is released in one part of the body but regulates the activity of cells in other parts of the body
(Recall) Exocrine glands
secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ or to the outer surface of the body: sudoriferous (sweat) sebaceous (oil), mucous & digestive glands
Endocrine glands
secrete their products (hormones) into the interstitial fluid surrounding the secretory cells rather than into ducts. From interstitial fluid, hormones diffuse into blood capillaries and blood carries them to target cells throughout the body.
Endocrine glands:
pituitary, thyroid, parathyroid, adrenal, pineal
Other tissues & organs that secrete hormones:
hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue and placenta
Down-regulation
an effect where, if a hormone is present in excess, the number of target-cell receptors may decrease, making a target cell less sensitive to a hormone
Up-regulation
an effect where, if a hormone is deficient, the number of receptors may increase, making a target cell more sensitive to a hormone
Hormone types
circulating + local
Circulating hormones
most endocrine glands are circulating hormones; pass from the secretory cells that make them into interstitial fluid and then into the blood
Local hormones
act locally on neighbouring cells or on the same cell that secreted them without first entering the bloodstream.
Paracrines
local hormones that act on neighbouring cells
Autocrines
local hormones that act on themselves
Chemical classes of hormones
lipid-soluble + water-soluble
Lipid-soluble hormones
soluble in lipids and use transport proteins; steroid, thyroid, nitric-oxide (NO)
Lipid-soluble hormones bind to?
Receptors inside target cells
Steroid hormones
Lipid soluble. Derived from cholesterol
Thyroid hormones
T3 and T4; very lipid soluble; are synthesized by attaching iodine to the amino acid tyrosine
Nitric Oxide (NO)
lipid soluble; a hormone and a neurotransmitter; synthesis is catalized by the enzyme nitric oxide synthaze; On demand, not stored.
Water-soluble hormones
soluble in water and circulate in "free" form; amine peptide/protein, elcosanoid
Water-soluble hormones bind to?
Receptors on the plasma membrane, activating a second messenger system & amplifying original small signal
Amine hormones
synthesized by decarboxylating (-1CO2) and otherwise modifying certain amino acids; called amines b/c they retain an amino group
Some amine hormones
epinephrine, norepinephrine, dopamine; histamine; serotonin, melatonin
Peptide hormones & protein hormones
amino acid polymers
Some peptide hormones
antidiuretic, oxytocin
Some protein hormones
human growth hormone, insulin, thyroid-stimulating hormone
Eicosanoid hormones
derived from arachidonic acid (a 20-carbon fatty acid
2 types of eicosanoid hormones:
prostaglandins, leukotriends
Response to a hormone depends on?
Both hormones & target cell
Responsiveness of target cell depends on ...
1. concentration of hormone; 2. # of target cell receptors; 3. Influence exerted by other hormones
Permissive effects
the 2nd hormone where the action of a hormone on target cells require a simultaneous or recent exposure to a 2nd hormone
Synergistic effects
when the effect of two hormones acting together is greater or more extensive than the effect of each hormone acting alone
Antagonistic effects
when one hormone opposes the action of another hormone
Hormone secretion is controlled by?
1. Signals from nervous system 2. Chemical changes in the blood 3. Other hormones
Most hormonal regulation is a...
negative feedback
_____ is a major link between the nervous & endocrine systems
hypothalamus
Pituitary is attached to the hypothalamus by the
infundibulum
Adenohypophyis
anterior pituitary
Neurohypophysis
posterior pituitary
Releasing hormones
from the hypothalamus, stimulate release of anterior pituitary hormones
Inhibiting hormones
from the hypothalamus, suppress release of anterior pituitary hormones
Hypophyseal Portal System
blood flows from capillaries in the hypothalamus into portal veins that carry blood to capillaries of the anterior pituitary
Recap:
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Autocrine, paracrine or endocrine are assembled from -
epithelially derived organs that share the common characteristic of secreting signal molecules into tissue fluid.
Those signal molecules diffuse away at a short, medium or long distance and if they find a suitable receptor - they will bind to it and change the function of the target cell (that has to have a receptor). Where the receptor is will depend on whether the hormone is water soluble or fat soluble.
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Fat soluble hormones-
are able to leave the bloodstream or leave the fluid having got there by using a transport protein association. Dissociate from the transport protein, diffuse through cell membranes and bind to receptors in the nucleus of the target cell, changing the protein profile of that target cell. Which means, changing what the cell does.
Water soluble molecules -
will be carried through tissue fluid either back on to their own surface, on to their neighbour's surface or on to the surface of a distant cell through diffusion or though carriage through the bloodstream. If there is a receptor out there, that receptor will be on the surface of the cell. So if the surface of the cell is where the receptor is, you know the signal molecule is extremely likely to be water soluble. Because it can't get into the cell. It's too big to go through a channel. The signal molecule is a big molecule relative to channels or things like that.
So, the signal molecule binds to a receptor on the outside of the cell and changes something in the cell.
The something that changes in the cell is usually a second messenger. Often, cAMP but not always (think cGMP -- dark current inside rod photoreceptors).
So, you've got a second messenger that interacts with the protein functions of the cell, essentially changing what the cell does. What controls this?
Mostly negative feedback controlling the cell that produced the original signal. Mostly. Rarely, positive (remember this requires an outside agency .. something outside the loop to intrude on the loop in order to break the loop.)
What does oxytocin do and when is it encountered-
during uterine contractions
The master gland was once thought of as? Why?
The pituitary gland. Because it tells most of the other glands what to do
What feature of the skull houses the pituitary
- sella turcica & it protects
What happens to the pituitary if the head is violently scrambled -
the pituitary c/be torn off
Why is the hypothalamus the real master gland?-
tells the pituitary and the ANS what to do
The hypothalamus is part of the brain T or F-
true
What does the hypothalamus have to do with the blood brain barrier?
The blood brain is incomplete in regions of the hypothalamus.
Why do we say the body's metabolism can be directly sensed by cells (with the appropriate receptors) of the hypothalamus
the BBB Allows cells of the hypothalamus to be directly influenced by blood pressure, blood chemistry, oxygenation of blood
What does the pituitary control?
Most of the other glands
what is the limbic system
Most primitive (reptile brain - asks, "can I eat it or mate with it?"
is the pituitary wired in with the limbic system
yes
How are the 2 parts of the pituitary gland divided and what are they derived from?
anterior and posterior; epithelial tissue
which is larger & what is it derived from
Anterior; derived from cells that used to be at the roof of the pharynx (roof of the mouth). Detach from the epithelia lining the mouth, and migrate up toward the brain and then stop, and meet the cells of the posterior pituitary
What does the posterior pituitary consist of?
axons growing down from the hypothalamus
What 2 kind of signal molecules does the posterior pituitary produce? Oxytocin & Antidiuretic Hormone
...
Does the posterior pituitary synthesize these hormones?
No. It stores and releases hormones made by the hypothalamus
How are the hormones of the P. Pituitary transported?
Transported along the hypothalamohypophyseal tract
Name some important hormones released by the anterior pituitary?
Growth Hormone; insulin-like Growth Factor; follicle stimulating hormones; luteinizing hormones (last 2 mostly covered in reproduction); prolactin; adrenocorticotropic (ACTH); melanocyte stimulating hormone
What is another name for pituitary gland?
Hypophesis
What is the median eminence
a bump on the bottom of the brain (from which comes the pituitary stalk, and then the pituitary
How does the hypothalamus cause a change in the anterior pituitary cells?
Through a portal system
** What is a Portal system
2 capillary beds are connected by veins (found in the intestines ...)
What is important about a portal system?
The hypothalamus produces hormones which are signal molecules which are secreted into tissue fluid, picked up in the hypothalamic capillaries and then transported by veins to 2nd capillaries, where the hormones leak out and bind to receptors on cells in the anterior pituitary causing the cells of the anterior pituitary to change their function - i.e. secrete hormones
Recap portal system in portal circulation
so, hormones of the hypothalamus cause hormone release from the anterior pituitary through a portal system, consisting of a capillary bed connected by veins to another capillary bed (before the blood goes back to the heart)
Give an example of when only one set of capillary beds are used?
Systemic circulation - If blood flows to a muscle: from the heart, through arteries to the muscle, through veins, back to the heart - 1 set of capillary bed
Does the portal system cause a change in the posterior pituitary cells?
No
What are inhibitory hormones?
The hormone from the hypothalamus inhibits the release of hormones from the anterior pituitary.
In the case of releasing and inhibitory hormones, the hypothalamus is - is regulatory
...
Where is growth hormone (GH) released
released by cells of the anterior pituitary
Growth hormone releasing hormone (GHRH) is released by cells of the -
hypothalamus
How does GHRH get to the anterior pituitary?
Travels through the hypophyseal portal system, causing the release of GH, picked up in the second capillary bed and distributed to the rest of the body through systemic circulation (and has an effect on every cell that has a receptor for GH)
What is GHIH
growth hormone inhibiting hormone
How is GHIH released
released by the hypothalamus, through portal system to anterior pituitary, inhibits the cells of the anterior pituitary that release GH
If there's a releasing hormone, there's almost alAways a -
inhibiting hormone
Does the posterior pituitary have a portal system?
No. it has one capillary bed (arteries in , capillaried, veins out)
Posterior pituitary is made up of mostly?
Axons that secrete hormone
What do the axons of the posterior pituitary do that is unusual?
They secrete hormones
How are the hormones that the axons of the posterior pituitary also transmitters?
The hormones that are secreted are molecules that produce action at a distance. In this way, they are hormones, but, b/c they are secreted by axons, they are also neurotransmitters (axons secrete signal molecules)
What 2 hormones are released by the axons in the posterior pituitary?
Oxytocin and Antidiuretic Hormone
Oxytocin does what
stimulates contractions (especially labour contractions); generally operates on smooth muscle to produce rhythmic contraction;
Oxytocin is also referred to as the ____ hormone because ____-
cuddle hormone; it is associated with digestion, orgasm, rhythmic breathing
Oxytocin is associated with release of ___-
dopamine (think chocolate)
**What is Antidiuretic hormone (ADH)-
also called vasopressin ("vessel pressure"); increases blood pressure
What does ADH do
keeps blood pressure up; 1. Shuts down kidney functions to decreases urine production; 2. Sweat decreases (dry skin); 3. Constricts blood vessels
Why does ADH decrease urine production
it is designed to preserve body water
When is release of ADH triggered?
Sudden blood loss
What starts release of ADH
high osmotic pressure (little water in blood, too much salt)
Which cells respond to high osmotic pressure?
Osmoreceptors
Hypothalamus has receptors which detect for high osmotic pressure. What are these called?
Osmoreceptors
What do osmoreceptors trigger?
Release of ADH
How is this a negative feedback system?
High osmotic pressure noted in hypothalamustriggers Release of ADHchanges osmotic pressure in blood altered amounts of ADH released
Pituitary secretes both
glandular secretion and axonal
The posterior pituitary secretes from axons, the cell bodies of those axons are in the walls of-
the third ventricle
What is paraventricular nuclei
("para"=beside; ventricular=the space of the 3rd ventricle) send axons down the pituitary stalk, ending in the posterior pituitary
What is unusual about the axons of the posterior pituitary?
These axons do not have target cells. They don't make synapses.
What is Insulin-like Grown Factor?
Part of the family of hormones that have similar effects on the body; ties in with thyroid hormones, GH. Involved in moving energy molecules into cells as a primary step in the growth and repair of cells
All hormones are produced by?
Secretion by epithelial cells
If hormones are fat soluble, they are
made and released, not through vesicles
Longer acting (ex. Growth) hormones are usually?
Fat soluble; ex steroids,
If hormones are protein/peptide based, they will be____ and packaged in _____?
Water-soluble; vesicles
Water soluble molecules are produced, stored and released when needed because?
Large amounts are needed immediately when needed (ex. Adrenalin); therefore must be water-soluble.
What is adrenocorticotropic hormone (ACTH)?
Adreno=adrenal gland Cortico=cortex tropic=toward; a hormone directed at the adrenal cortex, produced in the anterior pituitary.
What is another word for ACTH?
Coricotropin
What does ACTH produce
stress hormone
Melanocyte stimulating hormone
no good info on; just know that it is produced by the anterior pituitary
Let's talk about adrenocorticotropic hormone.
In the hypothalamus, corticotrophin releasing hormone travels through the portal system to the anterior pituitary where it triggers the release of ACTH, in the second capillary bed, and then released into the blood stream where it goes to the rest of the body, including the adrenal cortex, where the cells have the receptors for it - these cells produce cortisol.
**Define cortisol
circulates through the body. It is a stress-related, danger-related hormone.
What are some things cortisol does?
Suppresses the immune system Reduces inflammation,; allows the body to sustain damage in the preservation of life. Delays healing in order to allow the body to escape danger.
The rising of cortisol in the blood will shut off ___?
Corticotrophin and corticotrophin-releasing hormone
This is an example of a -
negative feedback system
Posterior pituitary-
easier to ask clear questions on the exam - just a tip
What causes the hormones to be secreted in the anterior pituitary
action potentials from the axons.
THYROID GLAND
located inferior to the larynx
T3 and T4 are produced where
thyroid gland
Why are they called T3 and T4?
Because of the number of iodine molecules in the molecule; thyroid hormones require iodine to work
What are T3 and T4 associated with?
GH, Insulin-like growth hormones
What happens when you are hypothyroid?
Put on weight, metabolism slows down
PARATHYROID
Embedded in the lobes of the thyroid gland; usually 4; "para"=beside
Is the parathyroid part of the thyroid gland?
No. it is beside
What hormone comes from the parathyroid?
Parathyroid hormone
What hormone is the parathyroid hormone associated with?
Calcitonin
Recall: where does calcitonin come from?
Thyroid gland
What are the parathyroid and calcitonin effects on blood calcium?
Opposite effects.
How does Parathyroid affect blood calcium levels?
Elevates bone resorption by stimulating osteoclasts
How does calcitonin affect blood calcium levels? Decreases bone resorption by inhibiting osteoclasts.
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Is calcitonin produced by follicular cells in the thyroid?
No.
What do follicular cells in the thyroid produce?
Produce and store T3 and T4
Then where is calcitonin produced?
In the cells between the follicles
So, is calcitonin a thyroid hormone?
No. It is a parathyroid hormone. The thyroid hormones are considered T3 & T4
Calcitonin is produced where?
Cells in the thyroid; it is not produced by follicular cells. The cells between the follicles produce calcitonin
What do follicular cells in the thyroid produce?
Follicular cells in the thyroid produce and store T3 and T4.
Thyroid hormones are
T3 and T4
Calcitonin is produced in the thyroid. Is it considered a thyroid hormone?
No. Calcitonin and Thyroid hormones are both produced in the thyroid, but they are independent
High levels of calcium in the blood stimulates what
parafollicular cells to secrete more calcitonin
What is calcitonin's job
and to participate with parathyroid hormone in the dynamic/homeostatic control of calcium levels in the blood "regulate the storage and liberation of calcium"
What does the calcitonin do
respond to high calcium in the blood and stimulates calcitonin
* Where does calcium come from and why are bones so important
1. Absorbing calcium from the gut (minor); 2. The osteoclast in the bones, secreting acid onto bone surfaces, mobilizes calcium carbonates and calcium phosphates from the bone matrix, and liberating that so that it will diffuse and be taken up into blood vessels in the bone marrow, and out into the general circulation
What else does parathyroid stimulate?
The kidneys to release calcitrol
Calcitrol stimulates
increased absorption of calcium from food.
Results in
higher calcium in blood,
ADRENAL GLAND
One of PJs favourite. "Ad"=on "renal"=kidneys
What hormones does the adrenal medulla synthesize?
Adrenaline and noradrenalin
Adrenal cortex
outer region of the adrenal gland
Adrenal medulla
come in the same source as ganglion cells in the sympathetic cells. The neurons that have cell bodies in the sympathetic ganglia are neurons that make norepinephrine or noradrenalin, and deliver to their target cells. That's what sympathetic ganglion do. The same population of cells in the embryo can become the adrenal medulla if they're next to the kidney.
The adrenal medulla makes?
Adrenalin (also called norepinephrine)
How is noradrenalin (also called norepinephrine) delivered?
By axons rapidly to targets and produces things like flight or flight response
The same signal as the fight or flight signal is, at the same time, signalling the ____ to dump ______? Where?______
Adrenal medulla; adrenalin; throughout the body.
Adrenal cortex
surrounds the adrenal medulla ("cortex"=bark)
What does the adrenal cortex synthesize?
Steroids!
What are the 3 layers in the adrenal cortex and what do they act on?
1. mineralocorticoids (minerals -salt); 2. Glucocorticoids (increase protein breakdown, stimulate gluconeogenesis); 3. Androgens (pubic hair, estrogen in women)
What is the mnemonic to remember the layers of the adrenal cortex?
"salt, sugar, sex, the deeper you go, the sweeter it gets"
Why are the layers important?
Glands are often homes to ¬¬¬Tumours; the location gives info about what kind of cell has gone haywire ex. If there was a cell in the 1st layer, you might see an overproduction of salts.
Does the blood from the adrenal gland go directly to the kidney?
No. They are two separate organs with separate arteries and veins.
Why do you need to know this?
The adrenal gland secretes hormones that affect the kidney. Those hormones have to enter the blood system and be pumped by the heart back to the kidney. This keeps the kidney from getting too high a concentration of the hormone.
PANCREAS
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Pancreatic islands are-
tiny clusters of endocrine tissue, which include 4 types of hormone-secreting cells (definition on test would require listing)
Pancreatic islets are also called
islets of langerhans; they are called this simply b/c they look different from the rest of the "lake"
List the 4 types of hormone-secreting cells in the pancreatic islets, and the hormone each secretes?
1. Alpha (A) cells - glucagon; 2. Beta (B) cells - insulin; 3. Delta (D) cells - somatostatin; 4. F cells - pancreatic polypeptide
How can you remember these?
GISP glue in some pans police
Somatostatin does what
interacts with A & B cells - like a reset
Pancreatic polypeptides do what
inhibits a lot of other things
**What is the effect of low glucose in the blood?
Hypoglycaemia. Stimulates secretion of glucagon from A cells of the pancreatic islets
What is the effect of high glucose in the blood?
Hyperglycemias; stimulates secretion of insulin by beta cells of the pancreatic islets.
Glucagon does what?
Acts on hepatocytes (liver cells) to accelerate the conversion of glycogen into glucose (glycogenolysis) and to promote formation of glucose from lactic acid and certain amino acids (gluconeogenesis). as a result, epatocytes release glucose into the blood more rapidly, and blood glucose level rises. Glucagon promotes dumping sugar into the blood.
Insulin does what?
Accelerate facilitated diffusion of glucose into cells; speed conversion of glucose into glycogen (glycogenesis); increase uptake of amino acids by cells and increase protein synthesis; speed synthesis of fatty acids (lipogenesis); slow conversion f glycogen to glucose (glycogenesis) ; and slow the formation of glucose from lactic acid and amino acids (gluconeogenesis) - blood glucose level falls. Insulin promotes taking sugar out of the blood.
Most of the cells in the pancreas do what?
Make enzymes that break down food
The pancreas is a dual gland. What does this mean?
It exhibits endocrine and exocrine function
Recall: what does exocrine mean?
Glands secrete their products into ducts which lead directly into the external environment
GONADS
more for reproduction
What are gonads-
ovaries and testes, produce gametes and hormones
PINEAL GLAND means
pinecone; PJ likes
Where is the pineal gland
midline gland,
Associated with the secretion of ___.
melatonin (which interacts with serotonin)
Pineal gland also has cells that are:
photoreceptive
What does the pineal gland contribute to?
setting biological clock (a diurnal clock)
More melatonin is liberated during ___ than ____
darkness than light
The pineal gland has
Daily cycles, seasonal cycles and even annual cycles in some animals
What happens in jet lag
"screwing around with the pineal gland"
The pineal secretes
melatonin
The pineal gets neural info from
sun (nb also gets information from artificial light)
Pineal gland is a major influence in what condition?
Seasonal Affective Disorder
STRESS RESPONSE
not a big interest to PJ
Eustress
helpful (eu=normal/best)
Distress
harmful
Your body is designed to handle stress
nb. Almost everything that happens to a body is a stressor.
We have _____ to deal with stress
homeostatic mechanisms
Stress Response diagram
Review for "do I understand what's going on with signal molecules"
Fight-or-fight responses are ___; resistance reactions are ____.
Immediate; long-term
Some stress responses are:
increased heart rate, constriction of blood vessels, dilation of blood vessels in heart, lungs, brain, skeletal muscles, contraction of spleen; conversion of glycogen glucose in liver, sweating, dilation of airways, decrease in digestion activities; water retention & elevated blood pressure.