Exam 2 (Lecture 2) - Intro to Endocrine Physiology 2 Flashcards
Describe general features of events that are triggered by hormones in target cells.
1) Hormone binds to a specific receptor on the target cell (target cells are sub-populations of cells that are programmed to express receptors for the given hormone).
2) This initiates intracellular events leading to the final physiologic effect.
3) Specifically, the receptor activation triggers changes in enzyme activity or concentration, leading to the regulation of multiple metabolic pathways and eventually to changes detectable at the level of cell and whole organism.
** The hormone concentration together with the number and sensitivity of involved receptors determine the magnitude of the hormone effect.
Hormones are distributed “blindly” to all cells in the organism, yet only some of these cells respond to the signal. Which property of a cell determines whether it will be affected by a particular hormone?
Only target cells with receptors specific to that hormone will respond to the signal.
The hormones encounter these target cells by moving randomly through the system and accidentally bumping into the cell that contains their receptor. (They do not seek out the cell, as they have no way to “find” it).
Where are receptors for lipophilic and lipophobic hormones normally found?
1) Lipophobic receptors = found in the target cell membrane.
2) Lipophilic receptors = found in the nucleus.
What are first and second messengers? How are second messengers activated and what are consequences of their actions?
1) First messengers = extracellular factors that often cannot cross the lipid bilayer (Ex: hormones and neurotransmitters).
2) Second messengers = bind to receptors on membranes to activate other enzymes (Ex: cAMP, IP3, and DG).
A ligand (hormone) binds to a cell surface receptor. This binding causes a conformational change in the receptor. This change can affect the activity of the receptor and result in the production of active second messengers.
Which second messenger systems are most commonly activated by protein and catecholamine hormones? How do second messengers affect the physiology of target cells?
1) cAMP, IP3/DG
2) Second messengers activate protein kinases and these phosphorylate (activate/influence the reaction rate) of other proteins leading to the eventual physiologic effect.
Why can relatively few molecules of hormone produce a large physiologic response?
This is due to signal amplification.
Amplification = a single ligand (hormone) activates multiple G proteins and each of these activates an enzyme that produces multiple molecules of the second messenger. In turn, second messengers activate other enzymes (like protein kinases) and each of these enzymes catalyzes reactions on multiple molecules of the substrate.
Describe the main intracellular events involved in the steroid hormone action.
Steroid hormones directly initiate the production of protein within a cell.
Steroid hormones easily diffuse through the cell membrane. The hormone binds to its receptor in the cytosol, forming a receptor-hormone complex. The receptor-hormone complex then enters the nucleus and binds to the target gene on DNA. Transcription of the gene creates an mRNA that is translated into the desired proteins within the cytoplasm.
What is the synergism of hormonal action?
Different types of hormones work together in some instances. Steroids, for example, increase the synthesis of enzymes which are regulated by catecholamines/polypeptides.
Ex: Gluconeogensis
- Cortisol increases synthesis of hepatic gluconeogenic enzymes.
- These enzymes are stimulated by epinephrine and/or glucagon.
