Endocrine System Part I Flashcards
Endocrine Glands
____ glands - glands of ____ secretion.
•
•Secretory product - hormone (a ___messenger), secreted into ___r system or adjacent __ ___
•
•Chemical messengers act on the cells that secrete them (___), adjacent cells (___) or remote target organs (___e).
No ductal system like exocrine glands
They secrete the hormone into the blood stream instead of going into a duct of some sort
Endocrine: Go into blood stream and affect remote organ
Endocrine Glands
•Ductless glands - glands of internal secretion.
•
•Secretory product - hormone (a chemical messenger), secreted into vascular system or adjacent connective tissue.
•
•Chemical messengers act on the cells that secrete them (autocrine), adjacent cells (paracrine) or remote target organs (endocrine).
No ductal system like exocrine glands
They secrete the hormone into the blood stream instead of going into a duct of some sort
Endocrine: Go into blood stream and affect remote organ
Endocrine Glands
- Functions to ___ and___ the actions of various organs and tissues.
- •Acts in concert with nervous system -____ system - but has a longer ___ period and a ___ effect.
- Endocrine cells arrange ____, in ___s, c___s or f___
•
NS is fast on, fast off
Slower to act
Longer time of action though
Ex) your metabolic rate
Longer sustained ability
It will act in concert with NS.
NS may signal the endocrine organ to fcn or they may act together to cause an effect.
Endocrine system supports what is happening with the NS.
Follicles: hollow bal shaped structures.
Endocrine Glands
•Functions to integrate and coordinate the actions of various organs and tissues.
•
•Acts in concert with nervous system -neuroendocrine system - but has a longer latent period and a sustained effect.
•
•Endocrine cells arranged individually, in cords, clumps or follicles.
•
NS is fast on, fast off
Slower to act
Longer time of action though
Ex) your metabolic rate
Longer sustained ability
It will act in concert with NS.
NS may signal the endocrine organ to fcn or they may act together to cause an effect.
Endocrine system supports what is happening with the NS.
Follicles: hollow bal shaped structures.
Endocrine and exocrine start off the same way
Epithelium will ___ and___ downward.
Exocrine: invagination will form a ___t with___ portion at base
Endocrine: lose ___connection to the tissue surface
__ ___ invaginate all around those cells
Secrete into blood vessels around them instead of into a duct.
Endocrine and exocrine start off the same way
Epithelium will proliferate and invaginate downward.
Exocrine: invagination will form a duct with secretory portion at base
Endocrine: lose epitielial connection to the tissue surface
Blood vessels invaginate all around those cells
Secrete into blood vessels around them instead of into a duct.
Different ___ t of cells depending on where you are.
Different arrangement of cells depending on where you are.
Endocrine Glands
•Principal glands.
–___gland.
–___d gland.
–___glands.
–___ glands.
–__ of ___
–__l gland.
–___.
•
•Additional endocrine tissue located in:
__ ___
__
__
___
___
Two types: Prinicple and Secondary
1: Primary fcn is to endocrine system
2: have fcns of endocrine system but primary fcn is something else.
Endocrine Glands
•Principal glands.
–Pituitary gland.
–Thyroid gland.
–Parathyroid glands.
–Adrenal glands.
–Islets of Langerhans.
–Pineal gland.
–Gonads.
•
•Additional endocrine tissue located in:
–G.I. Tract.
–Kidneys.
–Lungs.
–Integument.
–Placenta.
Two types: Prinicple and Secondary
1: Primary fcn is to endocrine system
2: have fcns of endocrine system but primary fcn is something else.
May be situated in more complex tissues
which serve both ___e AND___ functions
__
__
__
__
May be situated in more complex tissues
which serve both exocrine AND endocrine functions
Pancreas
Testes
Liver
Kidney
Pituitary Gland
___ ___
Master endocrine gland
So many different fcns
Regulates many other glands too.
Hypophysis: Pit Gland
Pituitary Gland
Hypophysis cerebri
Master endocrine gland
So many different fcns
Regulates many other glands too.
Hypophysis: Pit Gland
Several glands are of dual development.
They are derived from two different things.
This will help you to understand why it has 2 completely separate fcns
Derived from 2 separate entities
Pit Gland derives from:
__ ___ of oral cavity
__ ___e of the brain
Developing oral cavity in red
Oral ectoderm will invaginate ___ and form +__ ___
As it forms this pouch the developing brain invaginates ___
The developing oral ectoderm loses this connection to the ___ of the mouth
Portion of brain keeps invaginating down.
Eventually, part the developed from oral ectoderm comes up and gives it a___ ___g
Yellow: From brain tissue ___
Red: from ora ______
There are certain structures/parts of each one
Different hormones and different fcns are carried out based on neuro or adeno.
Nuerohypophysis has ___ to ___n…adeno does not
Several glands are of dual development.
They are derived from two different things.
This will help you to understand why it has 2 completely separate fcns
Derived from 2 separate entities
Pit Gland derives from:
Oral Ectoderm of oral cavity
Nervous tissue of the brain
Developing oral cavity (diencephelon) in red
Oral ectoderm will invaginate up and form Rathke’s Pouch
As it forms this pouch the developing brain invaginates downward.
The developing oral ectoderm loses this connection to the roof of the mouth
Portion of brain keeps invaginating down.
Eventually, part the developed from oral ectoderm comes up and gives it a big hug
Yellow: From brain tissueàneurohypophysis
Red: from oralàadenohypophysis
There are certain structures/parts of each one
Different hormones and different fcns are carried out based on neuro or adeno.
Nuerohypophysis has connection to brain…adeno does not
Adenohypophysis: dervided from oral ectroderm
- The big lobe is the ___ ____
- Portion that comes up and hugs neuro is ___ ___
- At midline: see little circular structures insideà ___ ___ All these little circles are called __ ___ These are remnants of rathkes pouch from development
Neurohypophysis: 3 components
Bulk: Pars ___
This forms the Y.
- The whole Y is the ___
- The two arms are ___ ___
- Bottom of Y: ___/___of NH
Note: Posterior/anterior lobe
Anterior: ___ ___
Posterior: ___ ___ and ___ ___
Adenohypophysis: dervided from oral ectroderm
- The big lobe is the pars distalis
- Portion that comes up and hugs neuro is pars tuberalis
- At midline: see little circular structures insideà Pars intermedia. All these little circles are called Rathke’s cysts. These are remnants of rathkes pouch from development
Neurohypophysis: 3 components
Bulk: Pars nervosa.
This forms the Y.
- The whole Y is the infundibulum
- The two arms are median eminence
- Bottom of Y: Stock/ Stem of NH
Note: Posterior/anterior lobe
Anterior: Pars distalis
Posterior: pars intermedia and Pars nervosa
You see its two distinctly different tissues
__ of ___ move down infidibulum and go down to the pars nervosa
You see its two distinctly different tissues
Tracts of axons move down infidibulum and go down to the pars nervosa
Pars Distalis
- ____
- _____– two types.
–____ – two types.
•____ cells.
–____ (___hormone).
–Target: __ ___
•___cells (AKA ____).
–___ (____ hormone, ___).
–Target: __ ___
Two types of cells inside adenohypophysis: Chromophobes and Chromophils
We don’t care about chromophobes. Wont react with ___. Look white.
Chromophilic cells.
2 Types ___ and ___
Acidophils: Loves acidic stains (typical acidic stain we use is___)
They will stain ___
Somatotropic secrete growth hormone
FCN: growth, and many other fcns
Don’t stop secreting this after puberty
If you secrete too much before pubertyà gigantism
If we secrete larger amts of this after puberty…what happens? ___. Affects ___ bones as opposed to long bones. Big ___, ___ and ___
If you don’t secrete enough before pubertyà dwarf
Mammotropic
When women get pregnant
Involved with development of the __ ___ and the ___ ___ itself, (not the milk let down)
Pars Distalis
- Chromophobes.
- Chromophils – two types.
–Acidophils – two types.
•Somatotropic cells.
–Somatotropin (growth hormone).
–Target: general body.
•Mammotropic cells (lactotrophs).
–Prolactin (lactogenic hormone, LTH).
–Target: mammary gland.
Two types of cells inside adenohypophysis: Chromophobes and Chromophils
We don’t care about chromophobes. Wont react with dye. Look white.
Chromophilic cells.
2 Types: acidophils and basophils
Acidophils: Loves acidic stains (typical acidic stain we use is eosin)
They will stain red.
Somatotropic secrete growth hormone
FCN: growth, and many other fcns
Don’t stop secreting this after puberty
If you secrete too much before pubertyà gigantism
If we secrete larger amts of this after puberty…what happens? Acromegaly. Affects flat bones as opposed to long bones. Big forehead, hands, feet.
If you don’t secrete enough before pubertyà dwarf
Mammotropic
When women get pregnant
Involved with development of the mammary glands and the milk production itself, (not the milk let down)
Pars Distalis
–Basophils – three types.
____cells.
–___ __ ___ (TSH, ____).
–Target: ___ ___
____ cells.
–____ hormone (ACTH, ____).
–Target: __ ____
____ cells.
–__ ___ ___ (FSH) & __ ___ (LH).
–Target: ___
TSH: targets thyroid gland. Targets one of the hormones of the thyroid. If you have no TSH secretion, thryoid wont secrete one of its hormones
Corticotropic cells act on the Cortex of Adrenal Glands
ACTH: Acts upon adrenal cortex (not medulla, just cortex) for stimulation and release of their hormones
FSH and LH are not just female
Pars Distalis
–Basophils – three types.
•Thyrotropic cells.
–Thyroid stimulating hormone (TSH, thyrotropin).
–Target: thyroid gland.
•Corticotropic cells.
–Adrenocorticotropic hormone (ACTH, corticotropin).
–Target: adrenal cortex.
•Gonadotropic cells.
–Follicle stimulating hormone (FSH) & Luteinizing hormone (LH).
–Target: gonads
TSH: targets thyroid gland. Targets one of the hormones of the thyroid. If you have no TSH secretion, thryoid wont secrete one of its hormones
Corticotropic cells act on the Cortex of Adrenal Glands
ACTH: Acts upon adrenal cortex (not medulla, just cortex) for stimulation and release of their hormones
FSH and LH are not just female
Pars Distalis
•Releasing hormones (RH) & Inhibiting hormones (IH).
–Tuberal nuclei in ____
–Axons end in primary ___ ____
–Hormone transported to pars distalis via ___ ___ ___
–Stimulate or inhibit release of hormones in __ ____
Why do we secrete these hormones
Part of pit gland secretes from one method.
Other part secretes from another method
Adenohypophysis
1) releasing/inhibiting hormones
1) These ___ in the hypothalamus
2) Usually NS signal will stimulate their release
3) Secreted to release or inhibit hormone secretion somewhere else
4) Adenohypophysis use RH and IH to control release of___ the hormones!
There is a portal system that carries these hormones from the___ to the__ ___
Ex) Releasing and inhibiting hormone for TSH
Pars Distalis
•Releasing hormones (RH) & Inhibiting hormones (IH).
–Tuberal nuclei in hypothalamus.
–Axons end in primary capillary plexus.
–Hormone transported to pars distalis via hypophyseal portal system.
–Stimulate or inhibit release of hormones in pars distalis.
Why do we secrete these hormones
Part of pit gland secretes from one method.
Other part secretes from another method
Adenohypophysis
1) releasing/inhibiting hormones
1) These stored in the hypothalamus
2) Usually NS signal will stimulate their release
3) Secreted to release or inhibit hormone secretion somewhere else
4) Adenohypophysis use RH and IH to control release of all the hormones!
There is a portal system that carries these hormones from the hypothalamus to the pit gland
Ex) Releasing and inhibiting hormone for TSH
Pars Tuberalis
- ____and ___
- ___type cells most common.
____
___
Distalis is the big guy
Tuberalis and intermedia don’t do to much
This is all for humans
Pars Tuberalis
- Chromophobes and chromophils.
- Gonadotropic type cells most common.
–FSH.
–LH.
Distalis is the big guy
Tuberalis and intermedia don’t do to much
This is all for humans
Pars Intermedia
- ___ in humans.
- Secretes ___ ___ ___.
- Target: ___ in ___
Melanocytes will darken the skin
Amphibians can change their skin colors by regulating pigment in the skin.
This is not important for us as humans
Pars Intermedia
- Rudimentary in humans.
- Secretes melanocyte-stimulating hormone (MSH).
- Target: Melanocytes in amphibians.
Melanocytes will darken the skin
Amphibians can change their skin colors by regulating pigment in the skin.
This is not important for us as humans
Pars Nervosa
- ____ – ____ cells.
- ____ ____ tract.
–Hypothalamic neuronal axons terminate in___ ___– ___ ___
–____nuclei.
- ___
- Targets: ___ and __ ___
–__ nuclei.
- ___ ___
- Target: ___
•
Nuero vs Adeno
Hypothalamo-hypophyseal tract
From hypothalamus to Pit Gland
There are tracts of axons that connect hypothalamus to the pituitary
Adenohypohysis___ and ___their hormones
Neurohypophysis __ ___ the hormones. They are made in the ___
Make two classes of hormones depending on which nuclei you are in
These axons come down and they make swellings that the base and those are called herring bodies
Hormone is made in neural cell body which is inside a nucleus in the hypothalamus (inside the CNS)
2 distinct nuclei in the hypothalamus. (Paraventricular and Supraoptic)
These have cell bodies.
Axons leave nuclei, go down tracts of axons and then go into neurohypophysis
End by making the herring body. This is where hormone is ___
It sits there and waits for stimulation
Need an electrical signal to be released
(Store hormone in pars nervosa)
They each predominately make one hormone.
Paraventricular: stimulates oxytocin
Female body knows that men are lazy.
Stimulation of __ ___ causes uterine ___
Why? To help propell sperm up the pathway.
If sperm didn’t get help they wouldn’t get where they are supposed to go.
During childbirth. It causes uterine contractions. Help get the baby out.
Why mammary glands? Prolactin only made the milk. Oxytocin causes __ ___
Not that important in men. But we will learn that each of these hormones can fcn to help stimulate the other.
Supraoptic nuclei
Releases ADH AKA vasopressin
This will help you___water
If you get into a bleeding situation, there are diff hormone that can help retain fluid and prevent bleed out
Pars Nervosa
- Pituicytes – neuroglial cells.
- Hypothalamo-hypophyseal tract.
–Hypothalamic neuronal axons terminate in pars nervosa – Herring bodies.
–Paraventricular nuclei.
- Oxytocin.
- Targets: Uterus & mammary gland.
–Supraoptic nuclei.
- Antidiuretic hormone (ADH, vasopressin).
- Target: Kidneys.
•
Nuero vs Adeno
Hypothalamo-hypophyseal tract
From hypothalamus to Pit Gland
There are tracts of axons that connect hypothalamus to the pituitary
Adenohypohysis both makes and stores their hormones
Neurohypophysis only stores the hormones. They are made in the hypothalamus
Make two classes of hormones depending on which nuclei you are in
These axons come down and they make swellings that the base and those are called herring bodies
Hormone is made in neural cell body which is inside a nucleus in the hypothalamus (inside the CNS)
2 distinct nuclei in the hypothalamus. (Paraventricular and Supraoptic)
These have cell bodies.
Axons leave nuclei, go down tracts of axons and then go into neurohypotphysis
End by making the herring body. This is where hormone is stored.
It sits there and waits for stimulation
Need an electrical signal to be released
(Store hormone in pars nervosa)
They each predominately make one hormone.
Paraventricular: stimulates oxytocin
Female body knows that men are lazy.
Stimulation of uterine wall causes uterine contraction.
Why? To help propell sperm up the pathway.
If sperm didn’t get help they wouldn’t get where they are supposed to go.
During childbirth. It causes uterine contractions. Help get the baby out.
Why mammary glands? Prolactin only made the milk. Oxytocin causes milk release.
Not that important in men. But we will learn that each of these hormones can fcn to help stimulate the other.
Supraoptic nuclei
Releases ADH AKA vasopressin
This will help you retain water
If you get into a bleeding situation, there are diff hormone that can help retain fluid and prevent bleed out
Pituitary Blood Supply
•superior hypophyseal arteries.
–____
–___ ___ ___
•Hypophyseal portal system.
–Via i____ to ___capillary plexus in ___ ___
•Inferior hypophyseal arteries.
–Primarily pars ____
Two sets of arteries and portal system
For neuro…not using RH and IH
Doesn’t need a portal system, just needs a set of arteries to release to.
Pituitary Blood Supply
•Superior hypophyseal arteries.
–Infundibulum.
–Primary capillary plexus.
•Hypophyseal portal system.
–Via infundibulum to secondary capillary plexus in pars distalis.
•Inferior hypophyseal arteries.
–Primarily pars nervosa.
Two sets of arteries and portal system
For neuro…not using RH and IH
Doesn’t need a portal system, just needs a set of arteries to release to.
Adeno:
This is where releasing and inhibiting hormones get released
They get carried down to adeno, get released. They stimulate or inhibit release of hormone. If released, goes to these capillaries
Neuro:
Its all about coming in, getting the hormone, and taking it out.
Adeno:
This is where releasing and inhibiting hormones get released
They get carried down to adeno, get released. They stimulate or inhibit release of hormone. If released, goes to these capillaries
Neuro:
Its all about coming in, getting the hormone, and taking it out.
Thyroid Gland
•Development – dual origin gland.
–Follicles: floor of pharynx – __ ___ on tongue.
–Parafollicular cells: __ ___ ___ (ultimobranchial body).
Gland of dual development
Comes from two separate things so it has Two separate fcns.
Within thyroid, it develops structures called follicles
Easiest to identify histologically.
Follicles that develop are really the bulk of the gland
Follicular cells: form the follice
Secrete hormone that’s stored in the follicle
Parafollicular cells: outside the follicle
They cant secrete into the follicle, they have to secrete into the blood stream
Thyroid gland is the only endocrine gland that can ___ its hormone in large amounts.
Everyone else will make and secrete it as they need, but don’t store very much.
You typically don’t need very much hormone…a little hormone goes a long way
Thyroid Gland
•Development – dual origin gland.
–Follicles: floor of pharynx – foramen caecum on tongue.
–Parafollicular cells: 5th pharyngeal pouch (ultimobranchial body).
Gland of dual development
Comes from two separate things so it has Two separate fcns.
Within thyroid, it develops structures called follicles
Easiest to identify histologically.
Follicles that develop are really the bulk of the gland
Follicular cells: form the follice
Secrete hormone that’s stored in the follicle
Parafollicular cells: outside the follicle
They cant secrete into the follicle, they have to secrete into the blood stream
Thyroid gland is the only endocrine gland that can store its hormone in large amounts.
Everyone else will make and secrete it as they need, but don’t store very much.
You typically don’t need very much hormone…a little hormone goes a long way
Foramen secum on the tongue
Out of the 5th brachial pouch there is the ___ ___ body. This is where PF cells develop from
Foramen secum on the tongue
Out of the 5th brachial pouch there is the ultimo brachial body. This is where PF cells develop from
Thyroid Gland
•Follicles.
–Only gland to store hormone in large quantities.
–__ ___ to low___r epithelium.
–Lumen contains ___-___ ___
•Parafollicular cells.
–Located between follicular cells and __ __ or in clusters in the ___
Made up of a simple epithelium
Epithelium can have different shapes depending on how active thyroid gland is.
Can be anywhere from squamous to columnar
Usually it’s a simple cuboidal epithelium.
Its like a hollow sphere
outside: simple cuboidal
Inside lumen is the follicle. Here we have something called colloid
Follicular cells produce colloid which is iodinated thyroglobulin
We are going to iodinate tyrosine residues on the thryogobulin
Inside follice is all inactive hormone.
Release of colloid into the blood stream wont do anything
Outside follicles we have parafollicular cells.
They don’t make colloid. They don’t have anything to do with the follicle
They make separate hormone that they release into the blood themself
Follicle Makes T3/T4à Metabolism
Parafollicular cells make calcitoninà Ca Regulation
Thyroid Gland
•Follicles.
–Only gland to store hormone in large quantities.
–Simple cuboidal to low columnar epithelium.
–Lumen contains colloid – iodinated thyroglobulin.
•Parafollicular cells.
–Located between follicular cells and basal lamina or in clusters in the interstitium.
Made up of a simple epithelium
Epithelium can have different shapes depending on how active thyroid gland is.
Can be anywhere from squamous to columnar
Usually it’s a simple cuboidal epithelium.
Its like a hollow sphere
outside: simple cuboidal
Inside lumen is the follicle. Here we have something called colloid
Follicular cells produce colloid which is iodinated thyroglobulin
We are going to iodinate tyrosine residues on the thryogobulin
Inside follice is all inactive hormone.
Release of colloid into the blood stream wont do anything
Outside follicles we have parafollicular cells.
They don’t make colloid. They don’t have anything to do with the follicle
They make separate hormone that they release into the blood themself
Follicle Makes T3/T4à Metabolism
Parafollicular cells make calcitoninà Ca Regulation
Thyroid Gland Function
•Follicular cells.
–Hormones:
•____(tetraiodotyrosine, T4).
_____, T3.
–Target: __ ___
- O2 ___ & ___
- CHO ____ in intestine.
- Regulate___ metabolism.
- Fetal influence: body ___ & development of ___ system.
T4: 4 Y residues are iodinated.
T3: 3 Y residues
Out in the colloid we have T1 and T2
Add T1 and T2 make a T3
Metabolic fcns
Thyroid Gland Function
•Follicular cells.
–Hormones:
- Thyroxine (tetraiodotyrosine, T4).
- Triiodotyrosine, T3.
–Target: general body.
- O2 consumption & BMR.
- CHO absorption in intestine.
- Regulate lipid metabolism.
- Fetal influence: body growth & development of nervous system.
T4: 4 Y residues are iodinated.
T3: 3 Y residues
Out in the colloid we have T1 and T2
Add T1 and T2 make a T3
Metabolic fcns
Thyroid Gland Function
•Synthesis of T3 and T4.
–___ synthesis.
–Uptake of __ ___
–Oxidation of___–>___
–Iodination of tyrosine residues of ____
We make thyroglobulin in follicular cells
Thyroid Gland Function
•Synthesis of T3 and T4.
–Thyroglobulin synthesis.
–Uptake of circulating iodide.
–Oxidation of iodide ® iodine.
–Iodination of tyrosine residues of thyroglobulin.
We make thyroglobulin in follicular cells
Thyroid Gland Function
•Release of T3 and T4.
–___ stimulated ____s of thyroglobulin.
–Lysosomal ____ of thyroglobulin.
–Monoiodotyrosine (T1), diiodotyrosine (T2), T3 and T4 liberated into____
–Fre___ and ___–> capillaries.
Thyroid Gland Function
•Release of T3 and T4.
–TSH-stimulated endocytosis of thyroglobulin.
–Lysosomal digestion of thyroglobulin.
–Monoiodotyrosine (T1), diiodotyrosine (T2), T3 and T4 liberated into cytoplasm.
–Free T3 and T4 ® capillaries.
These are the follicular cells
Pink: Lumen
In lumen you have colloid at rest
Follicular cell is typical secreting cell
Makes ____and dumps it into the lumen, store in the c____
At the same time you have iodine in the circulatory sys. Iodine gets taken up by these cells and pumped into the lumen and it iodinates Y residue, 1 or 2 to make __ and ___
When you go from rest to wanting to secrete some active hormone
Release of hormone from thyroid gland is controlled by TSH (secreted by pit gland)
TSH stimulates this cell to take back up the colloid.
Bring colloid back into cytoplasm of follicular cell.
Once inside it will break up colloid
Inside of colloid is T1 and T2
Now we can put them together to make T3 and T4
Release those into the blood stream
Get carried around body to have their action.
Iodinated thyroglobulin in lumen in colloid is inactive
Sits at rest until stimulation by TSH by pit gland
I
These are the follicular cells
Pink: Lumen
In lumen you have colloid at rest
Follicular cell is typical secreting cell
Makes thyroglobulin and dumps it into the lumen, store in the colloid
At the same time you have iodine in the circulatory sys. Iodine gets taken up by these cells and pumped into the lumen and it iodinates Y residue, 1 or 2 to make T1 and T2
When you go from rest to wanting to secrete some active hormone
Release of hormone from thyroid gland is controlled by TSH (secreted by pit gland)
TSH stimulates this cell to take back up the colloid.
Bring colloid back into cytoplasm of follicular cell.
Once inside it will break up colloid
Inside of colloid is T1 and T2
Now we can put them together to make T3 and T4
Release those into the blood stream
Get carried around body to have their action.
Iodinated thyroglobulin in lumen in colloid is inactive
Sits at rest until stimulation by TSH by pit gland
In the thyroid glad there are folllicular cells and parafollicular cells
Follicular cells
Parafollicular cells secretes Calcitonin and its not stored in the lumen
Cells are stimulated to take up iodide.
That is dumped into the lumen.When it gets into colloid if we iodinate the thyroglobulin
Uptake colloid back into the cell
Cell has enzymes to break apart iodinated T and make T3 and T4
Gets released into blood stream
