Transcript Hormonal Responses to Exercise

Hormonal Response to Exercise
1
The Endocrine System
• A communication system
– Nervous system = electrical communication
– Endocrine system = chemical communication
• Slower responding, longer lasting than nervous
system
• Maintains homeostasis via hormones
– Chemicals that control and regulate cell/organ
activity
– Act on target cells
2
The Endocrine System
• Coordinates integration of physiological
systems during rest and exercise
• Maintains homeostasis during exercise
– Controls substrate metabolism
– Regulates fluid, electrolyte balance
3
4
1. Steroid Hormones
• Derived from cholesterol
• Lipid soluble, diffuse through membranes
• Secreted by four major glands
– Adrenal cortex (cortisol, aldosterone)
– Ovaries (estrogen, progesterone)
– Testes (testosterone)
– Placenta (estrogen, progesterone)
5
2. Non-steroid Hormones
• Not lipid soluble, cannot cross membranes
• Divided into two groups
– Protein/peptide hormones
• Most nonsteroid hormones
• From pancreas, hypothalamus, pituitary gland
– Amino acid-derived hormones
• Thyroid hormones (T3, T4)
• Adrenal medulla hormones (epinephrine,
norepinephrine)
6
Hormone Secretion
• Secreted in bursts
– Plasma concentrations fluctuate over
minutes/hours
– Concentrations also fluctuate over days/weeks
*What triggers or regulates hormone bursts?
Secretion regulated by negative
feedback
7
Neuroendocrinology
Blood Hormone Concentration
Determined by:
1. Rate of secretion of hormone from endocrine
gland
• Magnitude of input
• Stimulatory versus inhibitory input
2. Rate of metabolism or excretion of hormone
• At the receptor and by the liver and kidneys
3. Quantity of transport protein
• Steroid hormones
4. Changes in plasma volume
8
Hormone Activity
• Plasma concentration:
– Cells change sensitivity to hormones
– Number of receptors on cell surface can change
• Downregulation:  number of receptors
during high plasma concentration =
desensitization
• Upregulation:  number of receptors during
high plasma concentration = sensitization
9
Hormone Receptors
• Hormone effects are limited by hormonespecific receptors
• No receptor on cell surface = no hormone effect
– Hormone only affects tissues with specific receptor
– Hormone exerts effects after binding with receptor
– Typical cell has 2,000 to 10,000 receptors
• Hormone binds to receptor: hormone–receptor
complex
10
3. Prostaglandins
• Third class of (pseudo)hormones
• Derived from arachidonic acid
• Act as local hormones/ immediate area
– Inflammatory response (swelling, vasodilation)
– Sensitize nociceptor free nerve endings (pain)
11
Hormonal Regulation
of Metabolism During Exercise
• Major endocrine glands responsible for
metabolic regulation:
–
–
–
–
Anterior pituitary gland
Thyroid gland
Adrenal gland
Pancreas
• Hormones released by these glands affect
metabolism of carbohydrate and fat during
exercise
12
Endocrine Regulation of Metabolism:
Anterior Pituitary Gland
• Pituitary gland attached to inferior
hypothalamus
• Three lobes: anterior, intermediate, posterior
• Secretes hormones in response to
hypothalamic hormone factors
– Releasing factors & inhibiting factors
– Exercise  secretion of all anterior pituitary
hormones
13
Hormones: Regulation and Action
Posterior Pituitary Gland
• Antidiuretic hormone (ADH)
– Reduces water loss from the body to maintain
plasma volume
• Reabsorption of water from kidney tubules to
capillaries
– Release stimulated by low plasma volume
• Due to sweat loss without water replacement = less
water in urine
– Increases during exercise >60% VO2 max
• To maintain plasma volume
14
Endocrine Regulation of Metabolism:
Anterior Pituitary Gland
• Releases growth hormone (GH)
– Potent anabolic hormone
– Builds tissues, organs
– Promotes muscle growth
(hypertrophy)
– Stimulates fat metabolism
15
Hormones: Regulation and Action
Growth Hormone
• Essential growth of all tissues
– Amino acid uptake and protein synthesis
– Long bone growth
• Spares plasma glucose
– Reduces the use of plasma glucose
– Increases gluconeogenesis
– Mobilizes fatty acids from adipose tissue
16
Hormonal Control of Substrate Mobilization During Exercise
Growth Hormone
• Slow-acting hormone
• Exercise effect:
– Increase in plasma GH with increased intensity
– Greater response in trained runners
*GH release proportional to exercise intensity
17
Hormones: Regulation and Action
Growth Hormone and Performance
• GH increases protein synthesis in muscle and
long bone growth
– Used to treat childhood dwarfism
– Also used by athletes and elderly
• More adverse effects than benefits
• No evidence that GH promotes strength gains
• Difficult to detect usage by athletes
18
Endocrine Regulation of Metabolism:
Thyroid Gland
• Secretes triiodothyronine (T3), thyroxine (T4)
• T3 and T4 lead to increases in
– Metabolic rate of all tissues
– Protein synthesis
– Number and size of mitochondria
– Glucose uptake by cells
– Rate of glycolysis, gluconeogenesis
– FFA mobilization
19
Hormonal Control of Substrate Mobilization During Exercise
Thyroid Hormones
• Act in a permissive manner to allow other
hormones to exert their full effect & maintain
metabolic rate
– T3 enhances effect of epinephrine to mobilize free
fatty acids from adipose tissue
• No significant change in T3 and T4 during
exercise
20
Hormones: Regulation and Action
Thyroid Gland
• Calcitonin
– Regulation of plasma Ca+2  bone building
– When Ca+2 levels are high = stimulates Ca+2
excretion by kidneys  expelled in urine
– Protects against calcium loss from skeleton
during periods of calcium mobilization 
pregnancy & lactation
21
Hormones: Regulation and Action
Parathyroid Gland
• Parathyroid hormone
(opposes effects of calcitonin)
– Primary hormone in plasma Ca+2 regulation
– When Ca+2 levels are low = stimulates
reabsorption of Ca+2 by kidneys
22
Endocrine Regulation of Metabolism:
Adrenal Medulla
• Releases catecholamines (fight or flight)
–  Exercise   sympathetic nervous system 
 epinephrine and norepinephrine
• Catecholamine release increases:
– Heart rate, contractile force, blood pressure
– Glycogenolysis, FFA
– Blood flow to skeletal muscle
– Fast acting hormone
23
Hormones: Regulation and Action
Adrenal Cortex
• Secretes steroid hormones
– Derived from cholesterol
• Mineralcorticoids
– Aldosterone
– Maintenance of plasma Na+ and K+
• Glucocorticoids
– Cortisol
– Regulation of plasma glucose
• Sex steroids
– Androgens and estrogens
– Support prepubescent growth
24
Hormones: Regulation and Action
Cortisol
• Maintenance of plasma glucose
– Promotes protein breakdown for gluconeogenesis
– Stimulates FFA mobilization from adipose tissue
– Stimulates glucose synthesis
– Blocks uptake of glucose into cells:
Promotes use of free fatty acids as fuel
• Stimulated by:
– Stress
– Exercise
25
Hormonal Control of Substrate Mobilization During Exercise
Cortisol
• Slow-acting hormone
• Effect of exercise:
– Decrease during low-intensity exercise
– Increase during high-intensity exercise
• Above ~60% VO2 max
26
Hormones: Regulation and Action
Adipose Tissue Is an Endocrine Organ
• In addition to storing triglycerides, adipose
tissue also secretes hormones
– Leptin
• Influences appetite
• Enhances insulin sensitivity and fatty acid oxidation
– Adiponectin
• Increases insulin sensitivity and fatty acid oxidation
• With increased fat mass (obesity)
– Higher leptin levels and lower adiponectin
– Leads to type 2 diabetes and low-grade
inflammation
27
Hormones: Regulation and Action
Testes and Ovaries
• Testosterone
– Released from testes
– Anabolic steroid
• Promotes tissue (muscle) building
• Performance enhancement
– Androgenic steroid
• Promotes masculine characteristics
• Estrogen and Progesterone
– Released from ovaries
– Establish and maintain reproductive function
– Levels vary throughout the menstrual cycle
28
Hormones: Regulation and Action
Anabolic Steroids and Performance
• Taken: 10 to 100 times the recommended dosage
• Also associated with negative side effects
– Revert to normal after discontinuation
• Widespread use has led to testing of
competitive athletes
• Most users are not competitive athletes
– Take more than one steroid in megadoses
29
Hormones: Regulation and Action
Pancreas
• Both exocrine and endocrine functions
• Secretes:
– Insulin (from  cells)
• Promotes the storage of glucose, amino acids, and
fats
• Lack of insulin is called diabetes mellitus
– Glucagon (from  cells)
• Promotes the mobilization of fatty acids and glucose
– Somatostatin
• Controls rate of entry of nutrients into the circulation
– Digestive enzymes and bicarbonate
• Into the small intestine
30
Endocrine Regulation of Metabolism:
Pancreas
• Insulin: lowers blood glucose
– Counters hyperglycemia, opposes glucagon
–  Glucose transport into cells
–  Synthesis of glycogen, protein, fat
– Inhibits gluconeogenesis
• Glucagon: raises blood glucose
– Counters hypoglycemia, opposes insulin
–  Glycogenolysis, gluconeogenesis
31
Regulation of Carbohydrate
Metabolism During Exercise
• Glucose must be available to tissues
• Glycogenolysis (glycogen  glucose)
• Gluconeogenesis (FFAs, protein  glucose)
32
Regulation of Carbohydrate
Metabolism During Exercise
• Adequate glucose during exercise requires
– Glucose release by liver
– Glucose uptake by muscles
• Hormones that  circulating glucose:
– Glucagon
– Epinephrine
– Norepinephrine
– Cortisol
33
Regulation of Carbohydrate
Metabolism During Exercise
• Circulating glucose during exercise also
affected by
– GH:  FFA mobilization,  cellular glucose
uptake
– T3, T4:  glucose catabolism and fat metabolism
• Amount of glucose released from liver
depends on exercise intensity & duration
34
Regulation of Carbohydrate
Metabolism During Exercise
• As exercise intensity increases:
– Catecholamine release 
– Glycogenolysis rate  (liver, muscles)
– Muscle glycogen used before liver glycogen
• As exercise duration increases
– More liver glycogen used
–  Muscle glucose uptake   liver glucose release
– As glycogen stores , glucagon hormone levels 
35
Hormonal Control of Substrate Mobilization During Exercise
Blood Glucose Homeostasis
During Exercise
• Plasma glucose maintained through four
processes:
1. Mobilization of glucose from liver glycogen
stores
2. Mobilization of FFA from adipose tissue
• Spares blood glucose
3. Gluconeogenesis from amino acids, lactic acid,
and glycerol
4. Blocking the entry of glucose into cells
• Forces use of FFA as a fuel
36
Regulation of Carbohydrate
Metabolism During Exercise
• Glucose mobilization = only half the story
• Insulin: enables glucose uptake in muscle
• During exercise
– Insulin concentrations 
– Cellular insulin sensitivity 
– More glucose uptake into cells, use less insulin
37
38
Hormonal Control of Substrate Mobilization During Exercise
Role of insulin & Glucagon: Fast-Acting
Hormones
• Insulin
– Uptake and storage of glucose and FFA
– Plasma concentration decreases during exercise
– Decreased insulin response following training
• Glucagon
– Mobilization of glucose and FFA fuels
– Plasma concentration increases during exercise
– Decreased response following training
• Insulin & glucagon secretion influenced by
catecholamines
39
Hormonal Control of Substrate Mobilization During Exercise
Epinephrine and Norepinephrine
• Also Fast-acting hormones
• Maintain blood glucose during exercise
–
–
–
–
Muscle glycogen mobilization
Increasing liver glucose mobilization
Increasing FFA mobilization
Alter glucose uptake
• Plasma E and NE increase during exercise
– Also related to increased heart rate and blood
pressure during exercise
• Decreased plasma E and NE after training
40
Regulation of Fat Metabolism During
Exercise
• FFA mobilization and fat metabolism critical to
endurance exercise performance
– Glycogen depleted  need fat for energy
= release hormones accelerate fat breakdown
(lipolysis)
• Triglycerides  FFAs + glycerol
– Fat stored as triglycerides in adipose tissue
– Broken down into FFAs  transported to muscle
– Rate of triglyceride breakdown into FFAs =
determine rate of cellular fat metabolism
41
Regulation of Fat Metabolism During
Exercise
• Lipolysis stimulated by:
– (Decreased) insulin
– Epinephrine
– Norepinephrine
– Cortisol
– GH
• Stimulate lipolysis via lipase
42