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Chapter 18: Endocrine System


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


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


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


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.


local hormones that act on neighbouring cells


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


Pituitary is attached to the hypothalamus by the



anterior pituitary


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



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.


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-


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


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?


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?


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 -


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?


Hypothalamus has receptors which detect for high osmotic pressure. What are these called?


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?


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.


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


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?


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.


Is calcitonin produced by follicular cells in the thyroid?


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.

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