Download Hormonal Responses to Exercise

Powers, Chapter 5
Hormonal Responses to Exercise
Neuroendocrinology 神經內分泌學
• Sense information, organize appropriate responses,
deliver messages to proper organs or tissues
• Endocrine glands 腺體 release hormones directly into
the blood
• Hormones alter the activity of tissues that possess
receptors to which the hormone can bind
• The plasma hormone concentration determines the
magnitude of the effect at the tissue level
Blood Hormone Concentration
Determined by:
• Rate of secretion of hormone from endocrine
gland
• Rate of metabolism or excretion of hormone
• Quantity of transport protein
• Changes in plasma volume
Control of Hormone Secretion
• Rate of insulin secretion from the pancreas is
dependent on:
– Magnitude of input
– Stimulatory vs. inhibitory
Factors That Influence the Secretion of
Hormones
Hormone-Receptor Interactions
• Trigger events at the cell
• Magnitude of effect dependent on:
– Concentration of the hormone
– Number of receptors on the cell
– Affinity of the receptor for the hormone
• Down-regulation of receptor number
– decreased when exposed to chronically elevated
hormone concentrations
• Up-regulation of receptor number
– Chronic exposure to low hormone concentrations
Hormone-Receptor Interactions
• Hormones bring about effects by:
– Altering membrane transport
– Stimulating DNA to increase protein synthesis
– Activating second messengers
•
•
•
•
Cyclic AMP (cAMP)
Ca++
Inositol triphosphate
Diacylglycerol
Mechanism by Which Steroid
Hormones Act on Target Cells
The Cyclic AMP “Second Messenger”
Mechanism
Ca
++
and Phospholipase C Second
Messenger Systems
Hormones: Regulation and Action
• Hormones are secreted from endocrine
glands
– Hypothalamus 下視丘 and pituitary glands 腦
下垂體
– Thyroid 甲狀腺 and parathyroid glands 副甲狀
腺
– Adrenal glands (adrenal medulla and adrenal
cortex) 腎上腺
– Pancreas 胰臟
– Testes 睪丸 and Ovaries 卵巢
Hypothalamus
• Controls activity of the anterior and posterior
pituitary glands
• Influenced by positive and negative input
Positive and Negative Input to the
Hypothalamus
Anterior Pituitary Gland 腦下垂體前葉
Growth Hormone 生長激素
• Secreted from the anterior pituitary gland
• Essential for normal growth
– Stimulates protein synthesis and long bone growth
• Increases during exercise
– Mobilizes fatty acids from adipose tissue
– Aids in the maintenance of blood glucose
Posterior Pituitary Gland
腦下垂體後葉
• Secretes antidiuretic hormone (ADH) 抗利尿
激素
• Reduces water loss from the body to maintain
plasma volume
• Stimulated by:
– High plasma osmolality and low plasma volume
due to sweating
– Exercise
Change in the Plasma ADH
Concentration During Exercise
Thyroid Gland
• Triiodothyronine (T3) & thyroxine (T4) 甲狀腺
素
– Important in maintaining metabolic rate and
allowing full effect of other hormones
• Calcitonin 抑鈣素, 降血鈣素
– Regulation of plasma Ca++
• Parathyroid Hormone 副甲狀腺素
– Also involved in plasma Ca++ regulation
Adrenal Gland
• Adrenal medulla 腎上腺髓質
– Secretes catecholamines: Epinephrine 腎上腺素
and norepinephrine 正腎上腺素
• Adrenal cortex 腎上腺皮質
– Secretes steroid hormones: Mineralcorticoids 礦物
性皮質素, glucocorticoids 糖皮質素
Adrenal Medulla
• Part of the sympathetic nervous system
– Secrete catecholamines
• Epinephrine (E) and norepinephrine (NE)
– Bind to receptors on effector organs
• Alpha () and beta () receptors
– Bring about changes in cellular activity via
second messengers
Response to Catecholamines: Role
of Receptor Type
Receptor
Type
Effect of
E/NE
Membrane-bound
enzyme
Intracellular
mediator
Effects on Various
Tissues
1
E=NE
Adenylate cyclase
 cAMP
 Heart rate
 Glycogenolysis
 Lipolysis
2
E>>>NE
Adenylate cyclase
 cAMP
 Bronchodilation
 Vasodilation
1
ENE
Phospholipase C
 Ca++
 Phosphodiesterase
 Vasoconstriction
2
ENE
Adenylate cyclase
cAMP
Opposes action of 1 & 2
receptors
Adrenal Cortex
• Mineralcorticoids (aldosterone 醛固酮)
– Promote reabsorption of Na+ and K+ in kidney,
Involved in maintaining plasma Na+ and K+
– Part of the renin-angiotensin-aldosterone system of
blood pressure regulation
Adrenal Cortex
• Glucocorticoids (Cortisol)
可體松
– Stimulated by exercise and
long-term fasting
– Promotes the use of free fatty
acids as fuel
– Stimulates glucose synthesis
– Promotes protein breakdown
for gluconeogenesis and tissue
repair
Pancreas
Insulin 胰島素
• Secreted by the  cells of the islets of Langerhans
• Promotes the storage of glucose, amino acids, and fats
• Diabetes mellitus is characterized as a lack of insulin
(Type 1) or a lack of insulin receptors (Type 2)
– Results in high blood glucose levels
– Considered a significant health risk
Glucagon 升糖激素
• Released from the  cells of the islets of Langerhans
• Promotes the mobilization of fatty acids and glucose
Testes
• Release testosterone
睪固酮
– Anabolic steroid
• Promotes tissue
(muscle) building
• Performance
enhancement
– Androgenic steroid
• Promotes masculine
characteristics
Estrogen 女性荷爾蒙
• Establish and maintain reproductive function
• Levels vary throughout the menstrual cycle
Muscle Glycogen Utilization
• Breakdown of muscle glycogen is under
dual control
– Epinephrine-cyclic AMP
– Fig 5.13, 5.14
– Ca++-calmodulin
• Delivery of glucose parallels activation of muscle
contraction
• Glycogenolysis can still occur in presence
of -blocking agent
– Propranolol, fig 5.15
Control of Glycogenolysis
Muscle Glycogen Utilization
• Glycogen breakdown is related to exercise
intensity
– High-intensity exercise results in greater and more
rapid glycogen depletion
Plasma Epinephrine Concentration
During Exercise
Maintenance of Plasma Glucose
During Exercise
• Mobilization of glucose from liver glycogen
stores
• Mobilization of FFA (free fatty acid 游離脂
肪酸) from adipose tissue
– Spares blood glucose
• Gluconeogenesis from amino acids, lactic
acid, and glycerol
• Blocking the entry of glucose into cells
– Forces use of FFA as a fuel
Blood Glucose Homeostasis During
Exercise
• Permissive and slow-acting hormones
– Thyroxine 甲狀腺素
– Cortisol
– Growth hormone
• Act in a permissive manner to support actions
of other hormones
Cortisol
• Stimulates FFA
mobilization from
adipose tissue
• Mobilizes amino
acids for
gluconeogenesis
• Blocks entry of
glucose into cells
Plasma Cortisol During Exercise
• At low intensity: ↓plasma cortisol
• At high intensity: ↑plasma cortisol
Growth Hormone
• Important in the maintenance of plasma glucose
– ↓ glucose uptake, ↑FFA mobilization,
↑gluconeogenesis
Growth Hormone During Exercise:
Trained vs. Untrained
Growth Hormone During Exercise:
Effect of Intensity
Blood Glucose Homeostasis During
Exercise
• Fast-acting hormones
– Norepinephrine and epinephrine
– Insulin and glucagon
• Maintain plasma glucose
– Increasing liver glucose mobilization
– Increased levels of plasma FFA
– Decreasing glucose uptake
– Increasing gluconeogenesis
Role of Catecholamines in Substrate
Mobilization
Epinephrine & Norepinephrine During Ex
• Increase linearly during exercise
• Favor the mobilization of FFA and maintenance of
plasma glucose
Epinephrine & Norepinephrine
Following Training
• Decreased plasma levels in response to
exercise bout
• Parallels reduction in glucose mobilization
• Physical training, stimulates the
sympathetic nervous system, increases the
capacity to respond to extreme challenges
Plasma Catecholamines During
Exercise Following Training
Effect of Insulin and Glucagon on
FFA Uptake and Oxidation
Insulin During Exercise
• Plasma insulin decreases during exercise
– Prevents rapid uptake of plasma glucose
– Favors mobilization of glucose and FFA
Effect of Training on Plasma Insulin
During Exercise
Effect of Training on Plasma Glucagon
升糖激素 During Exercise
Control of Insulin and Glucagon
Secretion During Exercise
Effect of SNS 交感神經系統 on
Substrate Mobilization
Hormonal Responses to Exercise
Free Fatty Acid Mobilization During
Exercise
• FFA mobilization decreases during heavy
exercise
– This occurs in spite of persisting hormonal
stimulation for FFA mobilization
• Could be due to high levels of lactic acid
– Promotes resynthesis of triglycerides
Effect of Lactic Acid on FFA
Mobilization