Endocrine Pnciples Flashcards
(37 cards)
What levels can feedback occur?
- gene transcription
- gene translation
- processing of hormones
- releasing of stored hormones
What is an example of positive feedback loops?
-LH surge prior to ovulation
What are two examples of changes in feedback loops?
- seasonal changes
- various stages in development and aging
Where can receptors be found?
- in or on the surface of cell membrane
- in the cell cytoplasm
- in the cell nucleus
What cause down regulation of receptors?
- increased hormone concentration
- increased binding to receptors
What can down regulation of receptors result in? How does this occur?
- decreases the tissue’s responsiveness to the hormones
- inactivation so some of the intracellular protein signaling molecules
- temporary sequestration of the receptor inside the cell
- inactivation of the some the receptor molecules
- destruction of the receptors by lysosomes after they are internalized
- decreased production of receptors
What does up regulation of receptors result in? How does this happen?
- increases the target tissue’s responsiveness to the hormones
- stimulating hormone may induce greater than normal formation of receptor or intracellular signaling molecule
- the stimulating hormone may induce greater availability of the receptor for interaction with the hormone
What are the different types of receptors?
- ion channel linked receptors -> neurotransmitters
- G protein linked hormone receptors
- enzyme linked hormone receptor
Intracellular hormone receptor and Gene activation
What are some characteristics of G protein linked hormone receptors?
- couple with groups of cell membrane proteins called heterotrimeric GTP binding proteins
- all of these receptors have 7 transmembrane segments
- some G proteins are inhibitory (Gi) and some are stimulatory (Gs)
What are some characteristics of enzyme linked hormone receptors?
- single pass transmembrane receptors
- receptor part is extracellular
-intracellular enzyme
+may be part of the receptor (intrinsic)
+may be separate from the receptor
-example is JAK-STAT transduction pathway
What are some characteristics of intracellular hormone receptor and Gene activation?
-intracellular receptors for lipid soluble hormones: \+adrenal and steroidal hormones \+thyroid hormones \+retinoic hormones \+vitamin D
-activated hormone-receptor complex binds to promoter sequence of DNA:
+hormone response element
What are the three classes of hormones?
- polypeptide and protein hormones
- steroids
- amine hormones
Characteristics of polypeptide and protein hormones.
- polypeptide : less than 100 aa
- proteins: more than 100 aa
- stored in secretory vesicles until needed
- usually synthesized as preprohormones
- released via exocytosis (usually mediated via Ca+2)
- release for some may involve cAMP
Characteristics of steroids.
- usually synthesized from cholesterol
- lipid soluble and diffuse readily across cell membranes
- consist of three cyclohexyl rings and one cyclopentyl ring
- large quantities of cholesterol esters stored rather than hormones themselves
Characteristics of amine hormones.
- derived from tyrosine
- include thyroid and adrenal medullary hormones
- formed by actions of enzymes in cytoplasmic compartments of glandular cells
- thyroid hormones are incorporated into macromolecules of thyroglobulin and stored in thyroid gland follicles
- catecholamines (epi and NE) are formed in adrenal medulla and stored in vesicles until needed
What are the signal transduction mechanisms?
- adenyl cyclase- cAMP second messenger system
- cell membrane phospholipid second messenger system
- calcium-calmodulin phospholipid second messenger system
- hormones acting directly on DNA
What do negative feedback systems prevent?
- over activity of hormone systems
- controlled variable is sometimes not the secretory rate of the hormone itself but the degree of activity of the target tissue
Outline the events of the adenyl cyclase-cAMP second messenger system.
- binding of hormones with a receptor allows coupling of the receptor to a G protein
- a G protein that stimulates adenyl cyclase-cAMP system is called a Gs protein
- adenyl cyclase ATP -> cAMP
- cAMP activates cAMP dependent protein kinase
- protein kinase phosphorylates specific proteins
- Gs proteins reduce the formation of ATP
How do cell membrane phospholipid second messenger systems work?
-hormones activate transmembrane receptors that activate enzyme phospholipase C
-phospholipase C catalyzes breakdown of phospholipids in the cell membrane
+phosphatidylinositol biphosphate PIP2 -> IP3 (mobilizes Ca+2 from mitochondria and ER)
+DAG -> activates protein kinase C, component is arachidonic acid
How does the calcium-calmodulin phosphate second messenger system function?
-calcium entry may be initiated by:
+changes in membrane potential that open Ca channels
+a hormone interacting with membrane receptors that open Ca channels
-calcium ions bind with calmodulin
+when 3-4 binding sites are filled, calmodulin initiates multiple effects: Activation or inhibition of protein kinases
How do steroid hormones function?
- diffuse across cell membrane
- bind with receptor proteins in cytoplasm
- receptor protein-steroid complex diffuses into nucleus
- complex binds to DNA
- this system takes longer than membrane receptor mediated signaling
How do thyroid hormones function?
- bind directly with receptors in the nucleus
- activate genetic mechanisms for many kinds of proteins, many of which enhance metabolic activity
- once bound to DNA, remain bound for days to weeks and continue to function
In the anterior pituitary, what do somatotropes/acidophils secrete?
-HGF
In the anterior pituitary, what do corticotropes secrete?
-ACTH
