Chapter 5: Hormonal Responses to Exercise Flashcards
Neuroendocrinology
Nervous System
- immediate, neuron-mediated mechanisms of action
Endocrine System
- slow, blood-borne mechanisms of action
(blood glucose, calcium concentration, potassium concentration, sodium concentration, water concentration, blood pressure and pH)
Signal Transduction (nervous system vs endocrine system)
- the nervous system uses neurotransmitters
- the endocrine system uses hormones as chemical messengers that bind to specific proteins
Ligands
a molecule that binds to another (usually larger) molecule
Ligand-receptor interaction causes a response in the target cell called _____
signal transduction
(response in the target cell)
Hormones can be divided based on chemical make up into…
amino acid derivatives
peptides
proteins
steroids
The structure of a hormone determines what mechanisms?
- transport
- signal transduction
What is the most important characteristic of hormones?
Whether the hormone can dissolve in water or cross the plasma membrane (lipid bilayer)
Lipophilic hormones
lipid-soluble
- cross membrane easily, don’t dissolve in water
- steroids and thyroid hormones
- receptor in the cytoplasm (translocation) or in the nucleus
- slow-acting, longer lasting effects
Lipophobic hormones
water-soluble
- don’t cross membrane, do dissolve in water
The effect a hormone exerts on tissue is influenced by:
- Number of receptors available for binding
- Plasma concentration of the hormone
Plasma concentration of the hormone is influenced by:
Rate of secretion from the endocrine gland
- magnitude of input and whether it is excitatory or inhibitory
Rate of metabolism or excretion of hormone
- hormone inactivation or removal from the blood
Quantity of transport protein for lipid-based hormones
- steroids and thyroid hormones are transported bound to a protein but to exert their effects they need to be “free” to interact with the receptor (aka not bound to a protein)
Changes in plasma volume
How is plasma volume affected during exercise?
During exercise, plasma volume decreases (due to the movement of water out of the cardiovascular system) which causes a slight increase in hormone concentration in plasma
How is insulin secretion controlled?
(red and green chart)
-Elevations in plasma glucose and amino acids increase insulin secretion
-When present, incretins augment the insulin response due to the rising of blood glucose or amino acid levels
-An increase in sympathetic nervous system activity (increase in epinephrine and norepinephrine concentration) decreases insulin secretion
-An increase in parasympathetic activity (excitatory effect) increases insulin secretion
Incretins
Group of hormones secreted by endocrine cells in the GI tract
What happens to hormones upon binding? In liver ? In kidneys?
Liver: metabolizes hormones
Kidneys: metabolize or excrete excess hormones into the urine
when excretion increases, the concentration of hormone decreases
What is the major site of hormone metabolism?
the liver
slide 135 find answers to those questions
Hormones are carried to all tissues, but only affect…
those tissues with specific receptors (proteins) capable of binding those hormones
Magnitude of effect of hormone on tissues depends on:
- concentration of the hormone
- number of receptors on the cell
- affinity of the receptor for the hormone
affinity: the chemical tendency of the transport protein to bind the hormone
Downregulation
decrease in receptor number in response to chronically elevated concentration of hormone
- results in diminished hormonal response for a given concentration
Upregulation
increase in receptor number in response to chronically decreased concentration of hormone
- tissue becomes very responsive to the available hormone
Chemicals with similar “shape” as a hormone
will compete for the limited receptor sites
Where in the cell are receptors located?
Membrane
Cytoplasm
Nucleus
How can hormones modify cellular activities of their target cell?
- Altering activity of DNA in the nucleus to initiate or suppress the synthesis of a protein (lipophilic hormones)
- Altering of membrane transport mechanisms
(lipophobic hormones) - Activation of special proteins in the cells by “second messengers”
Steroids
due to their lipid like nature, steroid hormones diffuse easily through cell membranes, where they become bound to a protein receptor in the cytoplasm of the cell.
Mechanism of Steroid Hormone Action
- Hormone passes through plasma membrane
- Inside the target cell, the hormone binds to a receptor protein in the cytoplasm or nucleus
- Hormone-receptor complex binds to hormone response element on DNA, regulating gene transcription
- Protein synthesis
- Change in protein synthesis is cellular response
Membrane Transport
lipohobic hormones
hormones bind receptors located on the outer surface of the cell membrane and activate carrier molecules in or near the membrane to increase movement of some ion or substrate from outside to inside the cell
Which hormones cannot easily cross cell membranes? How do they cross?
hormones that are too large or highly charged
- they exert their effects by binding to a receptor on the membrane surface and activate a G protein located in the membrane.
G protein
the link between the hormone-receptor interaction and the subsequent events inside the cell.
may activate an enzyme in the membrane or open an ion channel to allow Ca++ to enter the cell
Second Messenger processes
- Hormone binds to receptor on cell membrane and activates G protein located in the membrane of the cell
- G protein activates adenylate cyclase which turns ATP into Cyclic AMP (low levels of turn of cellular response)
- Phosphodiesterase turns Cyclic AMP into 5’ AMP
-Cyclic AMP activates protein kinase which will lead to a cellular response.
-Active protein kinase stimulates gycogenolysis (glycogen breakdown to glucose—phosphorylase)
-Active protein kinase stimulates the breakdown of triglycerides into free fatty acids (hormone sensitive lipase)
Caffeine effect
Inhibits Phosphodiesterase
- prevents the breakdown of cyclic AMP
High levels of Cyclic AMP increases cellular response
Ca2+ Channel Activation
G-protein can activate Ca2+ ion channels
- Ca2+ enters the cell and activates calmodulin