Flashcards in Physiology - Exam 2, Deck #2 - Endocrine Deck (126)
What two systems are responsible for controlling bodily functions?
1. Nervous System- controls rapid activities of the body = muscular contractions, rapidly changing visceral events, rates of secretion of some endocrine glands;
2. Endocrine System – Principally regulates the metabolic functions of the body
What is controlled by the ENDOCRINE system?
-Metabolic functions of the body;
-Rates of chemical reactions in cells;
-Transport of substances across cell membranes;
-Other parts of cell metabolism — growth and secretion
What is a Hormone?
-A chemical substance that is secreted into body fluids by one cell or a group of cells that exert a physiological control effect on other cells of the body
What are Target Cells/Tissues/Organs?
Those cells, tissues, or organs which are controlled by a specific hormone
What are the types of Hormones?
2. Polypeptides and proteins
What are Amine Steroids?
-Derived from the amino acids tyrosine and tryptophan: epinephrine, thyroxine;
-Hormones secreted by the arena medulla, thyroid, and pineal gland;
What are Polypeptides and Protein Hormones?
1. Polypeptides = generally contain < 100 amino acids
-EX: antidiuretic hormone;
2. Protein = > 100 amino acids:
EX: growth hormone
What are Glycoprotein Hormones?
-Consist of a protein bound to one or more carbohydrate groups:
EX: FSH, LH — Gonadotrophic hormones
What are Steroid Hormones?
-Derived from cholesterol:
EX: testosterone, estradiol, progesterone, and cortisol.
What are the 2 mechanisms by which hormones function?
1. Hydrophilic hormones – use a second messenger system that activates existing
- Adenylate cyclase- cAMP system
- Phospholipase C-Ca++ system
- Tyrosine Kinase system
2. Hydrophobic hormones – use nuclear receptor proteins that activate genes
- Steroid Hormones
- Thyroxine and triiodothyronine
What hormones use the Second Messenger System?
-Glycoprotein and polypeptide;
What are the 3 systems of Second Messengers?
1. Adenylate cyclase- cAMP system
2. Phospholipase C-Ca++ system
3. Tyrosine Kinase system
What is cAMP?
-Intracellular hormonal mediator for POLYPEPTIDE & GLYCOPROTEIN HORMONES;
-Second messenger for hormone action;
-Must be rapidly INACTIVATED to function as a second messenger effectiely
What is the mechanism of cAMP?
1. Hormone binds to receptor causing dissociation of a G-protein subunit;
2. G-protein subunit binds to & activates ADENYLATE CYCLASE;
3. Which converts ATP into cAMP;
4. cAMP attaches to inhibitory subunit of protein kinase
5. Inhibitory subunit dissociates, ACTIVATING protein kinase;
6. Which PHOSPHORYLATES enzymes that produce hormone’s effects
What is Phosphodiesterase?
-An enzyme within the target cell that hydrolyzes cAMO into inactive fragments;
-This inactivation means that the stimulatory effect of cAMP as a second messenger depends upon the CONTINUOUS generation of new cAMP and thus dependent upon the level hormone secretion
What is cGMP?
-Cyclic Guanosine Monophosphate (cGMP);
-Functions as a second messenger in some cases;
-EX: regulatory molecule of nitric oxide effects smooth muscles by stimulating production of cGMP in target cells
When do cAMP and cGMP interact?
-Effects may be either antagonistic or complementary;
-EX: control of cell division and cell cycle is related to the ratio of cAMP to cGMP
How is the concentration of Ca2+ maintained?
-Due to active transport pumps in the plasma and ER membranes of some cells
What is Ca2+ used for in cells?
1. Entry of Ca2+ through voltage-gated Ca2+ channels in terminal boutons of axons = Release of neurotransmitters;
2. Excitation-contraction coupling for electrical stimulation of muscles by release of Ca2+ from the sarcoplasmic reticulum;
3. Second-messenger system for hormones — Phospholipase-C-Ca2+
What is the Phospholipase-C-Ca2+ system?
-Serves as 2nd messenger system for some hormones (hydrophilic);
-Hormone binds to surface receptor, activates G-protein, which activates phospholipase C
What is the mechanism of the P-C-Ca2+ second messenger?
1. Phospholipase C splits a membrane phospholipid into 2nd messengers IP3 (inositol triphosphate) & DAG (diacylglycerol);
3. IP3 diffuses through cytoplasm to ER where it binds to receptor proteins — causing Ca2+ channels to open;
4. ER accumulates Ca2+ ay active transport, there is a steep gradient favoring DIFFUSION of Ca2+ into the cytoplasm;
5. Ca2+ diffuses into cytoplasm & binds to & activates CALMODULIN;;
6. Ca2+-Calmodulin activates PROTEIN KINASES which phosphorylate enzymes that produce hormone's effects
What 2 second messengers can Epinephrine use to act?
1. Beta-adrenergic effect with cAMP;
2. Alpa-adrenergic effect with Ca2+
What does Insulin promote?
ANABOLIC Hormone — acts like other regulatory molecules called Growth Factors;
-Promotes glucose and amino acid transport;
-Synthesis of glycogen, fat and protein;
Targets = Liver, muscle, adipose
What is Tyrosine Kinase?
The receptor protein located in the plasma membrane for insulin and growth factors
What is the Tyrosine Kinase Second Messenger System?
-Used by insulin & many growth factors to cause cellular effects;
-Surface receptor is tyrosine kinase;
-Consists of 2 units that form active dimer when insulin binds
What are the actions of Tyrosine Kinase?
1. Adds PO4- to tyrosine (AA) within proteins;
2. Has 2 units that dimerize when they bind Insulin (ligand) to form active Tyrosine Kinase enzyme;
3. Activated tyrosine kinase phosphorylates SIGNALING MOLECULES that induce hormone/growth factor effects
What are Signaling Molecules?
Some inase enzymes that phosphorylate and activate other second-messenger systems
How does Insulin indirectly stimulate diffusion of glucose into the muscle, liver and adipose?
-Indirectly stimulates the insertion of GLUT-4 carrier proteins = facilitated diffusion of glucose;
- Binding insulin to the receptor causes the activation of GLYCOGEN SYNTHETASE = enzymes in liver and muscle that catalyzes the production of glycogen in these target organs
What types of hormones bind to nuclear receptors and cause the activation of genes cells AFTER being transported to the gene with a carrier protein?
-LIPOPHILIC Hormones — activate genes;
1. Steroid Hormones of the adrenal cortex, ovaries, and testes;
2. Thyroxine (tetraiodothyronine)