Endocrine Pnciples Flashcards
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
In the anterior pituitary, what do thyrotropes secrete?
-TSH
In the anterior pituitary, what do gonadotropes secrete?
LH ad FSH
In the anterior pituitary, what do lactotropes secrete?
Prolactin
The posterior pituitary consists of magnocellular neurons. Where are these located?
-supraoptic and paraventricular nuclei
Where is ADH formed?
-formed primarily in the supraoptic nuclei
Where is oxytocin formed? What does it do?
-formed primarily in the paraventricular nuclei
+causes contraction of the pregnant uterus
+aids in milk ejection by acting on myoepithelial cells of mammary alveoli
What controls the anterior pituitary?
-hypothalamus via hormones called hypothalamic releasing and inhibitory hormones
+conducted to anterior pituitary via hypothalamic-hypophyseal portal system
+secreted into median eminence
+diffuse into portal system
-collecting center for information concerning internal well being of body
What functions do growth hormones have for growth functions?
- increases deposition of protein by chondrocytic and osteogenic cells
- increases rate of reproduction of chondrocytic and osteogenic cells
- converts chondrocytes into osteogenic cells
- strongly stimulates osteoblasts
What are the functions of growth hormones in terms of protein synthesis?
- directly enhances transport of aas through cell membranes into cytoplasm
- increases RNA translation
- increases transcription rate
- decreases protein catabolism
What are the functions of growth hormones in terms of FA mobilization?
- causes release of FAs from adipose tissue
- enhances conversion of FAs to acetyl CoA
What are the functions of growth hormones in terms glucose utilization?
- decreases glucose uptake in tissues such as skeletal muscle and fat
- increases glucose production by liver
- increases insulin secretion
- GHs effects are diabetogenic
Growth hormones causes liver to form somatomedins (proteins). What does this actually do?
- powerful effect on all aspects of bone growth
- similar to effects of insulin on growth
- also called insulin like growth factors (IGFs)
- most important is somatomedin c (IGF-C)
- injection into epiphyseal plates causes specific growth of these regions
What factors stimulate growth hormone secretion?
- starvation (more important under chronic conditions)
- hypoglycemia (more important under acute conditions)
- exercise
- excitement
- trauma
- ghrelin
- first two hours of deep sleep
