Endocrine Principle (lecture 20) Flashcards
1
Q
Give examples of both negative and positive feedback mechanisms as they apply to hormones
A
- Example of positive feedback mechanism:
- LH surge prior ot ovulation
- Prior to ovulation, estrogen stimulates the surge of LH
- LH acts on ovaries to secrete more estrogen
- Secreted estrogen stimulates the release of more LH
- Additional LH results in typical negative feedback
*
- LH surge prior ot ovulation
2
Q
What is often the controlled variable in feedback regulation of hormones
A
- The controlled variable is sometimes not the secretory rate of the hormone but the degree of activity of the target tissue.
3
Q
Give examples of influences that superimpose periodic variations in hormone release on the negative and positive feedback loops
A
- Seasonal changes, various stages of development and aging, the diuranal (daily) cycle, and sleep.
- For eample, the secretion of growth hormone is markedly increased during the early period of sleep but is reduced during the later stages of sleep.
4
Q
Define “down-regulation” state under what conditions it might occur and describe its effect(s)
A
- Number of active receptors may decrease because of increased hormone concentration and increased binding to receptors
- May occur as a result of:
- Inactivation of some of the intracellular protein signaling molecules
- Temporary sequestration of the receptor inside the cell
- inactivation of some of the receptor molecules
- destruction of the receptors by lysosomes after they are interanlized
- decreased production of receptors
- (note of these decrease the target tissue’s responsiveness to the hormones)
5
Q
Define “up-regulation” state under what conditions it might occur, and describe its effect(s)
A
- Number of active receptors or intracellular signaling molecules may increase
- May occur as a result of:
- The stimulating hormone may induce greater than normal formation of receptor or intracellular signaling molecules
- The stimulating hormone may induce greater availability of the receptor for interaction with the hormone
- (note: up regulation increases the target tissue’s responsiveness to the hormones)
6
Q
Characterize ion-channel-linked receptors and G protein-linked receptors and give examples
A
- Ion-channel linked receptors:
- Used primarily by neurotransmitters
- 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)
7
Q
- List the three classes of hormones
- List characteristics of each
- give examples of each
A
- Three Classes of Hormones
- Polypeptide and Protein Hormones
- Steroids
- Amine Hormones
- Polypeptide and Protein hormones
- polypeptide < 100 amino acids
- Proteins > 100 amino acids
- stored in secretory vesicles until needed
- Usually synthesized as preprohormones
- Released via exocytosis
- Usually mediated via calcium ions
- Release for some may involve cAMP
- 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 hromones themselves
- 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 (epinephrine and norepinephrine) are formed in adrenal medulla and stored in vesicles until needed.
8
Q
What are the four examples of signal transduciton mechanisms
A
- Adenyl cyclase
- cAMP second messenger system
- Cell membrane phospholipid second messenger system
- Calcium
- Calmodulin phospholipid second messenger system
- Hormones acting directly on DNA
9
Q
Mechanism of Adenyl cyclase signal transduction
A
- binding of hormones with receptor allows coupling of the receptor to a G protein
- A G protein that stimulates the adenyl cyclase—cAMP system is called a Gs protein
- Adenyl cyclase catalyzes ATP →cAMP
- cAMP activates cAMP-dependent protein kinase
- Protein kinase phosphorylates specific proteins
- This system typically activates a cascade of enzymes
10
Q
Mechanism ofcell membrane phospholipid second messenger system
A
- In this system, hormones activate transmembrane receptors that activate enzyme phospholipase C
- Phospholipase C catalyzes break-down of phospholipids in the cell membrane
- Phosphatidylinositol biphosphate PIP2 →
- inositol triphosphate (IP3)
- mobilizes calcium ions from mitochondria and ER
- Diacylglycerol (DAG)
- with calcium activates protein kinase C
- Note that a component of DAG is arachidonic acid
- inositol triphosphate (IP3)
- Phosphatidylinositol biphosphate PIP2 →
11
Q
Mechanism of calcium-calmodulin phospholipid second messenger system
A
- Calcium entry may be initiated by:
- Changes in membrane potential that open clacium channels
- A hormone interacting with membrane receptors that open calcium channels
- Calcium ions bind with calmodulin
- When 3-4 bidning sites are filled calmodulin initiates multiple effects:
- Activation of protein kinases
- Inhibition of protein kinases
- When 3-4 bidning sites are filled calmodulin initiates multiple effects:
12
Q
Mechanism of hormones acting directly on DNA
A
- Steroid hormones
- diffuse across cell membrane
- bind with receptor proteins in cytoplasm
- Receptor protein-steroid complex diffuses into nucleus
- Complex binds to DNA
- Note that this system takes longer than membrane-receptor mediated signaling
- Thyroid hormones
- bind directlywith receptors in nucleus
- activate genetic mechanisms for many (up to 100+) kinds of proteins, many of which enhance metabolic activity
- Note that thyroid hormones, once bound to DNA, remain bound for days to weeks and continue to function.
13
Q
List sequentially the components of the hypothalamic-pituitary axis
A
- The posterior pituitary is an outgrowth of the hypothalamus and the anterior pituitary is regulated by hromones form the hypothalamus
14
Q
List the five types of secretory cells and their products and function in the anterior pituitary
A
- Somatotropes (acidophils)
- HGF
- promotes growth of the entire body by affecting protein formation, cell multiplication, and cell differentiation
- HGF
- Corticotropes
- ACTH
- controls secretion of some of the adrenocortical homrones, which affect metabolism of glucose, proteins, and fats
- ACTH
- Thyrotropes
- TSH
- controls the secretion rate of thyroxine and triiodothyronine by the thyroid gland, and these hormones control the rates of most intracellular chemical reactions in the body
- TSH
- Gonadotropes
- LH
- FSH
- Lactotropes
- Prolactin
- promotes mammary gland development and milk production
- Prolactin
15
Q
- Identify the nuclei involved in the formation of ADH and oxytocin.
- State the effects of oxytocin
A
- ADH is primarily formed in the supraoptic nuclei and secreted by the poterior pituitary
- Oxytoxin is primarily formed in the paraventricular nuclei and secreted by the posterior pituitary
- Oxytocin function:
- causes contraction of the pregnant uterus
- Aids in milk ejection (milk letdown) by acting on myoepithelial cells of mammary alveoli
