Unit XIV (75-84) - Endocrinology and Reproduction Flashcards
What hormones are secreted by the posterior pituitary gland?
ADH
Oxytocin
Where are ADH and Oxytocin synthesized respectively?
Supraoptic nuclei - ADH
Paraventricular nuclei - Oxytocin
Where are these cell types found? Somatotropes Corticotropes Thyrotropes Gonadotropes Lactotropes
Anterior pituitary
Somatotropes produce _____
Growth hormone
Growth hormone physiologic roles include: stimulation of: 1.\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 2. \_\_\_\_\_\_\_\_\_\_\_\_\_ and inhibition of: 1.\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 2. \_\_\_\_\_\_\_\_\_\_\_\_\_
Stimulates: 1. secretion of insulin like growth factor 1 2. lipolysis Inhibits: 1. action of insulin on carbohydrates 2. lipid metabolism
Corticotropes produce ______
ACTH
ACTH stimulates: ___________
Adrenal cortex to produce glucocorticoids and androgens
Thyrotropes produce ______
TSH
Where is MSH is produced?
Pars intermedia
A cells in the pars intermedia produce _____
alpha MSH
B cells in the pars intermedia produce ______
ACTH
Lactotropes produce __________
Prolactin
Gonadotropes produce _________
FSH and LH
GHRH
Source:
Effects:
Growth hormone releasing hormone
hypothalamus
stimulates release of GH from anterior pituitary
Somatostatin
AKA:
Source:
Effects:
growth hormone inhibitory hormone
hypothalamus
inhibit release of GH from anterior pituitary
CRH
Source:
Effects:
corticotropin releasing hormone
hypothalamus
stimulate release of ACTH
GnRH
Source:
Effects:
Gonadotropin releasing hormone
hypothalamus
stimulates release of LH and FSH
Examples of protein/polypeptide hormones
secreted by pituitary, parathyroids and pancreas
How are protein and polypeptide hormones synthesized and secreted
Preprohormone is synthesized in RER and then cleaved to a prohormone
Prohormone goes into the golgi - may be modified
Hormone is packaged into vesicles
The vesicles are stored in the cytoplasm and released via exocytosis when needed.
Method of transport of peptide hormones
free in plasma because they are water soluble
Examples of steroid hormones
glucocorticoids, androgens
How are steroid hormones synthesized and secreted
Made in mitrochondria and ER from cholesterol
Not stored
Since they are lipid soluble they are freely permeable (they are released as they are synthesized)
The receptors for protein hormones are located ________________
ON the cell (rely on 2nd messengers)
The receptors for steroid hormones are located _____________
IN cytoplasm (do not need 2nd messengers)
Examples of amino acid derivatives
Tyrosine derivatives
- Thyroid hormones
- Catecholamines
Compare and contrast the tyrosine derivative hormones (MOA, secretion, transport in blood)
- Thyroid hormones - stored in large follicles and released into the blood after amine is split from thyrogloblumin, once secreted they act like steroid hormones (protein bound and has a receptor in the nucleus)
- Catecholamines - taken up into preformed vesicles and stored, once secreted they act like protein hormones (water soluble, rely on second messengers)
What hormones are usually involved with ion channel linked receptors? What is the MOA?
Catecholamines, ACh - cause a change in the receptor = open or close one or more ion channels
What hormones use G-protein linked receptors?
Most hormones (FSH, GnRH, Oxytocin, Glucagon)
Describe the MOA of G-protein linked receptors
Inactive G - protein = Alpha, beta and gamma subunits + GDP
Hormone binds on the extracellular part of the receptor and activates G-protein causing:
1. open or close of ion channels
2. change in activity of a cytoplasmic enzyme or
3. activates gene transcription
Active G-protein (after hormone binds) GDP is displaced by GTP and the alpha subunit dissociates from beta and gamma
Alpha subunit associates with other intracellular signaling proteins that can change cell function
When hormone is removed alpha subunit converts the bound GTP to GDP and combines with beta and gamma subunits
What hormones use enzyme linked receptors?
Tyrosine kinase Leptin Insulin Prolactin ANP Growth factors (insulin like growth factor 1, VEGF)
Structurally, how are enzyme linked receptors different than G-protein linked receptors
G - protein linked receptors go through the membrane 7 times
Enzyme linked receptors go through the membrane once
Describe the MOA of enzyme linked receptors
once the hormone binds on the outside of the cell an intracellular enzyme is activated (or inactivated)
What hormones use intracellular receptors?
Steroids
Thyroid
Retinol
Vit D
Describe the MOA of intracellular receptors
Hormone just goes into cell (since its lipid soluble) The activated hormone-receptor complex binds to a specific promoter sequence of DNA - called hormone response element
What are second messengers involved in intracellular signaling?
cAMP
Ca+Calmodulin
Products of membrane phospholipid breakdown
Describe the role/MOA of cAMP as a second messenger
If a hormone binds to a stimulatory G protein receptor = cytoplasmic ATP catalyzed to cAMP
cAMP can phosphorylate specific proteins and trigger cell response to hormone
If a hormone binds to an inhibitory G protein receptor = adenylyl cyclase is inhibited and cAMP formation is reduced
Describe the role/MOA of Ca+calmodulin as a second messenger
Ca influx into cell and when 3-4/4 calmodulin sites are bound to Ca calmodulin undergoes a change in shape
change shape can lead to phosphorylation of calmodulin dependent kinases
______________ catalyzes breakdown of phospholipids in the cell membrane (ie. phosphatidylinositol biphosphate) into ____________________ and ______________
Phospholipase C
Inositol triphosphate - IP3
diacylglycerol - DAG
What is the MOA of IP3 as a second messenger?
mobilizes Ca ions from mitochondria and ER
Ca then acts as a 2nd messenger itself
What is the MOA of DAG?
Activates protein kinase C which then phosphorylates other proteins leading to cell responses
The cells from the ________ pituitary are epithelial in origin vs the cells from the ___________ are glial in origin.
Anterior
Posterior
Inhibition of ACTH production in the pars distalis is mediated by _______ and by __________ in the pars intermedius
Cortisol
Dopamine
Inhibition of ACTH production in the pars distalis is mediated by _______ and by __________ in the pars intermedius
CRH
Serotonin
The pars ___________ produces the majority of ACTH in dogs
Distalis
What are the physiologic effects of growth hormone?
Increased rate of protein deposition
Increased mobilization of fats
Decrease rate of glucose utilization in the body
Promote cartilage and bone growth
What is the role of insulin like growth factor-1?
where is it produced?
mediates most of GH actions
produced in the liver
What are the physiologic effects of oxytocin?
contraction of pregnant uterus
milk let down
Secretion of ADH is stimulated by
Decreased blood pressure
Decreased blood volume
Increased osmolarity**
what is the site of action of ADH?
collecting tubules and collecting ducts
What is the MOA of ADH
binds to V2 receptor –> forms cAMP –> stimulates movement of aquaporin-2 which forms water channels on the luminal side = increased water permeability
also causes vasoconstriction in response to low blood volume
List the 4 major steps of thyroid hormone synthesis
- Iodide trapping
- Thyroglobulin synthesis
- Oxidation
- Organification
The the thyroid hormone secreted ____% is T4 and ____% is T3
93%
7%
Thyroid hormone is found in plasma bound to __________________ , _______________ and ________________
Thyroxine binding globulin**
Thyroxine-binding prealbumin
Albumin
