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
Activation of membrane-bound phospholipase C
Phosphotidylinositol is hydrolyzed to:
- Inositol triphosphate, which increases intracellular calcium release, which will activate calmodulin
- Diaclyglycerol which activates protein kinase C (PKC)
changes in each of these second messengers can affect action of the other
Increase in calcium activates
calmodulin
Hormones are secreted from endocrine glands including:
- hypothalamus and pituitary glands
- thyroid and parathyroid glands
- adrenal glands
- pancreas
- testes and ovaries
Growth hormone
Slow-acting hormone
- essential for normal growth of all tissues
- stimulates amino acid uptake & protein synthesis
- long bone growth
Growth hormone is secreted by
anterior pituitary gland
Growth hormone stimulates
release of insulin-like growth factors (IGFs) responsible for muscle hypertrophy (muscle growth)
How does growth hormone maintain plasma glucose?
- reduces use of plasma glucose
- increases gluconeogenesis in liver
- increases mobilization of fatty acids from adipose tissue
Effects of Growth Hormone
and exercise effects
Effects:
Supports the action of cortisol
- decreases glucose uptake by tissues
- increases fatty acid mobilization
- enhances gluconeogenesis in the liver
Exercise effect:
- increase in plasma growth hormone with increased intensity
- greater response in trained runners
Antidiuretic Hormone (ADH)
aka Vasopressin
- reduces water loss from the body to maintain plasma volume
- release stimulated by low water concentration and low plasma volume in response to sweat loss without water replacement
Antidiuretic hormone is secreted by
hypothalamus
Antidiuretic hormone is stored/released by
posterior pituitary gland
Antidiuretic effect during exercise
increases during exercise > 60% VO2 max to maintain plasma volume
Thyroid gland hormones
-thyroid gland is stimulated by thyroid stimulating hormone (TSH) to secrete T3 and T4
- T3 and T4 are important for establishing overall metabolic rate
-act in a permissive manner to allow other hormones to exert their full effect
- T3 enhances effect of epinephrine to mobilize free fatty acids from adipose tissue
- no real change in T3 and T4 during exercise
hypothyroid
low plasma T3, lethargic, hypokinetic
hyperthyroid
high plasma T3
Adrenal Gland
two glands: cortex and medulla
Adrenal medulla
secretes the catecholamines, epinephrine and norepinephrine, which are fast acting hormones part of “fight or flight” response
epinephrine- 80%
norepinephrine- 20%
Catecholamines
epinephrine and norepinephrine
-bind adrenergic receptors and change cellular activity (increased HR, mobilization of fatty acids from adipose tissue) via second messengers
(alpha and beta receptors)
magnitude and direction (inhibitory vs excitatory) of the response depends on
which ligand binds with which receptor
Aldosterone
- control Na+/H2O balance
- regulation of blood volume and blood pressure
- part of the renin-angiotensin-aldosterone system (all 3 hormones increase during heavy exercise)
Aldosterone is stimulated by
- adrenal cortex
- increased K+ concentration
- decreased plasma volume
Cortisol
Slow-acting hormone
- makes amino acids available for repair
- Maintenance of plasma glucose during long-term fasting exercise
Effects of Cortisol
and effect of exercise
Effects:
- stimulates FFA mobilization
- enhances gluconeogenesis in liver (promotes tissue protein breakdown)
- decreases rate of glucose utilization by cells (blocks uptake of glucose into cells, thus forcing cells to use more free fatty acids as fuel
Effect of exercise:
- increases proportionally with exercise intensity
- changes in cortisol may be related to repair of exercise-induced tissue damage
What hormones does adipose tissue secrete?
Leptin
Adiponectin
Leptin
secreted by adipose tissue
- influences appetite through the hypothalamus
- enhances insulin sensitivity and fatty acid oxidation
Adiponectin
secreted by adipose tissue
- increases insulin sensitivity and fatty acid oxidation
Increased fat mass (obesity) effect on leptin and adiponectin
- higher leptin levels and lower adiponectin
- higher leptin levels leads to type 2 diabetes and low-grade inflammation
- exercise does not affect adiponectin or leptin concentration
- these hormones are more responsive to changes in body weight
Pancreas makes and releases
insulin and glucagon
Insulin (beta cells)
promotes the storage of glucose, amino acids, and fats
-high blood sugar promotes insulin release
-stimulates formation of glycogen
-stimulates glucose uptake from blood
decreases during exercise
Glucagon (alpha cells)
promotes the mobilization of FFAs and glucose
-low blood sugar produces glucagon release
- stimulates breakdown of glycogen into glucose in the liver
increases during exercise
Somatostatin (from delta cells)
controls rate of entry of nutrients into the circulation
Digestive enzymes and bicarbonate
into the small intestine
The Gonads
sex hormones
-testosterone
-estrogen
Testosterone
anabolic, androgenic steroid hormone secreted by the testes
- promotes tissue (muscle) building
- chronic endurance exercise has been shown to decrease plasma testosterone
Estrogen
steroid hormone secreted by the ovaries
- plays a significant role in bone health
- chronic endurance training can lead to decreased plasma estrogen, which can lead to osteoporosis (less density in bones)
Skeletal muscle produces _____ when it contracts
myokines
Myokines
- stimulate glucose uptake and fatty acid oxidation
- promote blood vessel growth in muscle
- promote liver glucose production and triglyceride breakdown
Interleukin 6 (IL-6)
both proinflammatory and anti-inflammatory effects
- IL-6 produced during exercise promotes anti-inflammatory effect
- regular exercise promotes anti-inflammatory environment (reduction in chronic inflammation and reduced risk of heart disease, type 2 diabetes, and certain cancers)
Carbohydrate control during prolonged vs intense exercise
also review ch 4 figures
during prolonged exercise:
- CHO are necessary for fat oxidation
- greater reliance on blood-borne substrates (glucose and FFA)
during intense exercise:
- CHO are the preferred substrate
- greater reliance on stored substrate (muscle glycogen)
Plasma epinephrine is a powerful stimulator of
glycogenolysis
Glycogenolysis related to exercise intensity
high intensity exercise results in greater and more rapid glycogen depletion
because muscle glycogen is the highest energy source during high intensity exercise
Blood glucose control during exercise
the goal of hormones during exercise is to maintain plasma glucose during times of increased rate of glucose removal from the circulation
Processes used to maintain plasma glucose during exercise:
1. Liver glycogenolysis
2. Liver gluconeogenesis from lactic acid, amino acids, glycerol
3. Mobilization of FFAs from adipose tissue to spare glucose
4. Block glucose entry into cells to force FFA usage
Epinephrine and Norepinephrine
Fast-acting hormones
- increase during exercise (high intensity exercise results in greater increases in plasma epinephrine)
- also related to increased heart rate and blood pressure during exercise
- Maintain blood glucose during exercise by:
– increasing muscle and liver glycogen breakdwn
– increasing FFA mobilization and oxidation
– blocking glucose uptake by the tissues
E and NE in Submaximal intensity exercise
decreased plasma norepinephrine/epinephrine in trained individuals
E and NE in Supramaximal intensity exercise
increased plasma epinephrine and norepinephrine in trained individuals
Effects during absorption of a meal
- increased insulin
- decreased glucagon
- increased storage of glycogen, fat and protein
- decreased plasma glucose, amino acids, and fatty acids
Effects during fasting and exercise
- decreased insulin
- increased glucagon
- increased hydrolysis of glycogen, fat and protein
- increased gluconeogenesis
- increased plasma glucose, amino acids, and fatty acids
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