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Questions and Answers
What is the primary energy source for the central nervous system during periods of fasting?
Which metabolic process is primarily enhanced in the liver during prolonged fasting?
What hormonal changes occur during starvation that affect metabolism?
What is the primary precursor for gluconeogenesis during fasting?
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Which of the following processes is primarily responsible for producing ketone bodies?
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During the switch from fasting to starvation, what shift in energy sources occurs after several days?
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Which tissue primarily contributes to gluconeogenesis during fasting?
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What role does increased glucagon play in energy metabolism during fasting?
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Which statement about growth hormone (GH) during fasting is correct?
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What is the primary energy source mobilized by GH during moderate exercise?
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Which hormone does NOT increase in response to starvation along with growth hormone?
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How does exercise impact protein metabolism based on the information provided?
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Which process primarily provides glucose rapidly during short-duration intense exercise?
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Which factor does NOT contribute to the release of growth hormone during exercise?
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What is the primary source of ATP during immediate high-intensity physical activities?
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Which statement correctly describes the role of the Cori cycle?
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What process describes the conversion of lactate back to glucose in the liver during prolonged exercise?
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Which hormone primarily regulates blood glucose levels during prolonged exercise by increasing gluconeogenesis?
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During intense prolonged exercise, which fuel source is primarily mobilized for energy due to increased hormone activity?
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Which metabolic process is primarily inhibited by insulin to prevent excessive breakdown of fat during the fed state?
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What substrates are primarily generated from the catabolic processes during fasting and starvation?
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What effect does increased cortisol have on muscle activity during exercise?
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What role does GLU4 play during muscle activity?
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In the context of energy storage post meal, which of the following is directly stimulated by insulin?
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Which process primarily enables the conversion of lactate generated from type IIb muscle fibers back to pyruvate during exercise?
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Which zone of the adrenal cortex is primarily responsible for producing glucocorticoids such as cortisol?
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What is the primary function of aldosterone, a mineralocorticoid secreted by the adrenal cortex?
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Which enzyme is considered essential for the glucocorticoid (GC) activity in the adrenal cortex?
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What directly stimulates the adrenal cortex to increase the production of pregnenolone?
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Which class of steroid hormones includes testosterone and progesterone?
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Which component is the precursor for all steroid hormone synthesis?
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Which condition can lead to the release of cortisol from the adrenal cortex?
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Which adrenal component secretes adrenaline and noradrenaline?
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What is the primary role of growth hormone (GH) during fasting?
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Which statement about energy metabolism during moderate exercise is correct?
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Which of the following hormones primarily increases during fasting conditions?
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What is the primary contribution of catabolic hormones during fasting?
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In the context of energy sources for muscle during exercise, which pathway is most efficient for sustained activity lasting longer than 2 minutes?
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Which metabolic state is characterized by a decrease in insulin and IGF-I levels?
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Which factor does NOT lead to the release of growth hormone (GH)?
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What is the primary substance utilized during immediate high-intensity physical activity?
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What is the primary focus of metabolism during an overnight fast?
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Which hormonal change contributes to increased gluconeogenesis during fasting?
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In the transition from fasting to starvation, what metabolic shift occurs?
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Which of the following substances primarily serves as precursors for ketogenesis?
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As fasting progresses, what primary mechanism maintains blood glucose homeostasis?
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What is the effect of decreased insulin during starvation?
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Which of the following correctly describes the role of gluconeogenesis in the liver during fasting?
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What is the primary source of energy mobilized during moderate to intense exercise?
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Which statement accurately describes the metabolic actions of Growth Hormone (GH)?
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What is the main effect of glucocorticoids during starvation?
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Which physiological response is primarily due to the actions of Growth Hormone in adults?
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How does Growth Hormone exert its metabolic effects in adipose tissues?
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Which of the following scenarios describes a primary action of glucocorticoids?
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What role does lipolysis play in the metabolic effects induced by Growth Hormone?
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In the context of resistance adaptation to stress, what is the primary function of glucocorticoids?
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Which of the following describes the connection between Growth Hormone and insulin during metabolic processes?
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What happens to protein metabolism under the influence of glucocorticoids during periods of starvation?
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How do GH and glucocorticoids interact to affect overall metabolism in the body?
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What process is primarily responsible for converting lactate to glucose during prolonged exercise?
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Which metabolic change occurs in response to decreased insulin during prolonged exercise?
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In which situation does the Cori cycle play a significant role?
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What primarily drives the increased mobilization of fatty acids during extended exercise?
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Which condition is NOT directly influenced by hormonal changes during exercise?
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Which statement best describes the role of GLUT4 during muscle activity?
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During fasting, which source of energy is primarily utilized once glycogen stores are depleted?
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Which of the following substrates is NOT primarily produced from catabolism during fasting?
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Which factor does NOT contribute to maintaining blood glucose levels during prolonged exercise?
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What is a significant effect of the increase in catecholamines (adrenaline) during exercise?
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What is the primary role of aldosterone in the body?
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Which enzyme is crucial for the glucocorticoid synthesis process in the adrenal cortex?
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What stimulates the adrenal cortex to increase production of ACTH?
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Which class of steroid hormones includes cortisol?
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In which zone of the adrenal cortex is cortisol primarily synthesized?
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Which physiological process is primarily regulated by glucocorticoids?
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What is the main precursor for steroid hormone synthesis in the adrenal cortex?
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Which hormone directly influences the uptake and trafficking of cholesterol in adrenal cortical cells?
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Which hormone is primarily responsible for preserving muscle mass during fasting?
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During moderate exercise, which metabolic pathway is most efficient for energy production lasting over 2 minutes?
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What key role does Growth Hormone fulfill during exercise?
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Which metabolic effect occurs as a result of fasting when insulin and IGF-I levels decrease?
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Which factor contributes to the integrated response of the hypothalamus during metabolic activation?
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Which of the following hormones decreases during fasting, impacting glucose homeostasis?
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What is the primary source of energy during immediate high-intensity physical activities?
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What role does glucagon primarily play during periods of fasting?
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What is the primary function of glucagon during fasting?
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What metabolic adaptation occurs in the body after several days of fasting?
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Which statement best describes the role of ketone bodies during prolonged fasting?
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What is the primary metabolic effect of growth hormone on adipose tissue?
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What is the primary precursor for ketogenesis from fatty acids?
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Which of the following describes a direct effect of glucocorticoids on muscle metabolism?
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How does insulin affect muscle and adipose tissue during fasting?
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During a state of stress, which action is primarily associated with glucocorticoids?
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What is one of the consequences of decreased insulin during starvation?
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What is an impact of growth hormone on liver metabolism?
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Which statement correctly describes the effect of growth hormone on glucose metabolism?
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During starvation, which hormone would be expected to increase significantly?
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What ultimately determines the shift from gluconeogenesis to ketogenesis as fasting prolongs?
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What effect does hypoglycemia have on fuel metabolism?
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In an adult with closed epiphyses, what is a primary effect of growth hormone?
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During starvation, which process is essential for maintaining blood glucose homeostasis?
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What is the primary role of growth hormone during periods of fasting?
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What is a consequence of decreased insulin levels during starvation?
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What mechanism contributes to the movement of GLUT4 to the cell membrane during muscle activity?
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During prolonged exercise, which of the following hormones plays a significant role in regulating blood glucose levels?
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Which statement accurately describes the function of lactate produced in muscle during intense exercise?
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What is the primary metabolic process that occurs in the liver during prolonged fasting?
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In what way does insulin inhibit hormone-sensitive lipase (HSL)?
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Which metabolic pathway becomes significant for ATP production during a fast exceeding one hour?
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Which of the following accurately describes the Cori cycle's function?
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What role does plasma glucose play during extenuating muscle activity?
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Which statement best describes the effects of glucagon during fasting?
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What aspect of fat metabolism is directly stimulated by insulin in the postprandial state?
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Study Notes
Endocrine Control During Exercise
- Increased adrenaline and glucagon levels stimulate glycogenolysis and lipolysis, increasing glucose and fatty acid availability for energy.
- Decreased insulin levels reduce glucose uptake by cells, sparing glucose for muscle use.
- Increased cortisol and growth hormone (GH) levels contribute to glucose sparing and promote protein breakdown for energy production.
Muscle Activity During Exercise
- Muscle contraction itself moves GLUT4 transporters to the cell membrane, increasing glucose uptake.
- Plasma glucose becomes important as an energy source after muscle glycogen stores are depleted.
Lactate Metabolism During Exercise
- Lactate produced by Type IIb muscle fibers is converted to pyruvate by other muscle fibers and oxidized for energy.
- Lactate can also be taken up by the liver and converted to glucose (Cori cycle).
Hepatocytes During Exercise
- Gluconeogenesis occurs in the liver, converting lactate back to glucose.
- The Cori cycle plays a major role in prolonged exercise (over 1 hour), providing a continuous supply of glucose.
Fat Metabolism During Exercise
- Lipolysis (breakdown of fat) and fatty acid mobilization increase during prolonged exercise, providing a significant energy source.
- Beta oxidation of fatty acids yields energy for prolonged exercise.
Glucose Homeostasis During Prolonged Exercise
- Blood glucose levels decrease during prolonged exercise.
- This hypoglycemia is regulated by hormones like glucagon, adrenaline, and GH, to maintain glucose availability for the brain and other tissues.
Eating and Anabolism: Energy Storage After a Meal
- Carbohydrates: Insulin stimulates glucose uptake and storage as glycogen in the liver and muscles.
- Protein: Insulin promotes protein synthesis and amino acid uptake into muscle.
- Fat: Insulin stimulates fatty acid uptake and storage as triglycerides in adipose tissue. Insulin also inhibits hormone-sensitive lipase (HSL), preventing fat breakdown.
Fasting and Starvation: Catabolism and Energy Production
- During fasting, the body enters a catabolic state to conserve energy.
- Glycogen stores are depleted through glycogenolysis.
- Proteins are broken down through proteolysis to provide amino acids for gluconeogenesis.
- Triacylglycerides are broken down through lipolysis, releasing fatty acids and glycerol for energy.
- The products of catabolism (glucose, lactate, amino acids, fatty acids, and ketone bodies) are used for energy production.
Fasting: Priorities for Energy Production
- Maintaining blood glucose levels for brain function. The CNS primarily relies on glucose for energy, but can utilize ketone bodies over time. Other tissues can utilize fatty acids for energy.
- Preserving protein reserves. Proteins are essential for muscle function, enzyme activity, and cell signaling.
Overnight Fast: Endocrine and Metabolic Changes
- Increased glucagon levels stimulate glycogenolysis and gluconeogenesis.
- Decreased insulin levels reduce glucose uptake by muscle and adipose tissue.
- Increased lipolysis releases fatty acids for energy.
- Overall, these adaptations contribute to maintaining blood glucose homeostasis.
Transition from Fasting to Starvation
- After several days of fasting, metabolism shifts from gluconeogenesis to ketogenesis.
- Fatty acids become the primary energy source as ketone bodies are produced from fat stores. Ketone bodies provide energy for the brain, muscles, and other tissues.
Endocrine Control During Starvation
- Further decreased insulin and thyroxine levels.
- Increased glucagon, sympathetic nervous system (SNS) activation (adrenaline), cortisol, and GH levels.
Energy Sources During Starvation
- Gluconeogenesis occurs in the liver and kidneys, converting amino acids and glycerol to glucose.
- Ketogenesis occurs mainly in the liver, converting fatty acids to ketone bodies.
Gluconeogenesis and Ketogenesis: Precursors and Energy Production
- Gluconeogenesis: Glycerol and certain amino acids are used as precursors for glucose production.
- Ketogenesis: Fatty acids are broken down through beta oxidation to produce acetyl-CoA, which can enter the citric acid cycle or be used for ketone body production.
Beta Oxidation of Fatty Acids and Energy Yield
- Beta oxidation of fatty acids produces acetyl-CoA and energy, contributing to overall energy production during fasting and starvation.
Metabolic Effects of Growth Hormone (GH) During Fasting
- GH is the only anabolic hormone that increases during fasting, while insulin and Insulin-like growth factor 1 (IGF-I) levels decrease.
- GH acts in concert with the increased levels of catabolic hormones (glucagon, adrenaline, and cortisol) to preserve muscle mass.
Metabolic Effects of GH During Exercise
- GH stimulates lipolysis during moderate exercise, providing alternative energy source through fatty acids.
Hypothalamus and GH Regulation
- Hypothalamus integrates metabolic and neural signals to regulate GH release.
- Signals include: High amino acid levels, low fatty acid levels, hypoglycemia, stress, exercise, deep sleep, malnutrition, and sex steroids.
- GHRH (Growth Hormone Releasing Hormone) and somatostatin (Growth Hormone Inhibiting Hormone) are involved in controlling GH secretion from the pituitary gland.
Energy Sources for Muscle Activity
- Immediate sources: ATP and phosphocreatine (PCr) provide immediate energy for short, powerful bursts of exercise (e.g. power events).
- Non-oxidative sources: Anaerobic glycolysis, using glycogen as fuel, supplies energy for short, intense exercise (e.g. sprints).
- Oxidative sources: Oxidation of glucose and fatty acids provides energy for longer duration exercise (>2 minutes).
Energy Mobilization and Use During Exercise
- Nutrients stored in muscle (e.g. glycogen) provide energy.
- Liver and adipose tissue stores also contribute to energy production during exercise.
- Carbohydrate and fat reserves are mobilized and used for energy, supporting muscle activity.
Introduction
- Adrenal cortex is responsible for producing steroid hormones
- 80% of the adrenal cortex is involved in steroid hormone production, 20% is the adrenal medulla
- Steroid hormone categories include:
- Gonadal or sex steroids: progesterone, testosterone, oestradiol
- Glucocorticoids: cortisol, corticosterone
- Mineralocorticoids: aldosterone
- The adrenal medulla secretes adrenaline and noradrenaline
- Cholesterol is a precursor for the synthesis of steroid hormones, with a pathway producing progesterone, glucocorticoids, mineralocorticoids, androgens, and oestrogens.
- Zona glomerulosa is responsible for the production of aldosterone
- Zona fasciculata and zona reticularis are responsible for the production of cortisol and corticosterone
Glucocorticoid Regulation
- Hypothalamic-pituitary-adrenal (HPA) axis plays a key role
- Hypothalamus releases corticotrophin-releasing hormone (CRH)
- CRH stimulates the anterior pituitary gland to release adrenocorticotrophic hormone (ACTH)
- ACTH acts on the adrenal cortex, specifically impacting zona fasciulata and zona reticularis, and increases cortisol secretion
- Cortisol acts on target cells
- The HPA axis undergoes negative feedback regulation, preventing excessive cortisol production
ACTH Regulation
- ACTH's primary role is to stimulate cortisol production in the adrenal cortex
- ACTH acts on the zona fasciculata and zona reticularis
- ACTH receptors are known as melanocortin type 2 receptors (MC2-R)
- ACTH increases cholesterol uptake and trafficking
- ACTH increases pregnenolone production
- ACTH regulates the expression of key enzymes involved in cortisol synthesis, including:
- P-450scc (side chain cleavage enzyme)
- P-450c11 (11-beta hydroxylase)
- ACTH influences the adrenal gland's response to psychological or physical stress
- ACTH levels are elevated in response to physiological changes, including hypoglycemia and starvation
Cortisol's Effects
- Cortisol's actions are regulated through the HPA axis
- Cortisol plays a vital role in maintaining blood glucose levels by:
- Increasing hepatic glucose output
- Promoting peripheral catabolism
- Cortisol is crucial for metabolic reactions and vascular reactivity, known as permissive effects
- Cortisol facilitates normal water excretion.
- Cortisol plays a role in resistance adaptation to stress by preserving blood glucose
- Cortisol suppresses inflammatory responses and possesses immunosuppressive properties.
Growth Hormone (GH)
- GH is a major determinant of growth
- GH promotes anabolic processes, increasing cell size and number in soft tissues
- GH increases the thickness and length of long bones by increasing bone growth
- GH exerts metabolic effects, independent of its growth-promoting actions
- GH's metabolic actions:
- Stimulate amino acid uptake
- Decrease glucose uptake
- Inhibit protein breakdown
- Promotes muscle mass growth in muscle tissue
- Decreases glucose uptake and increases fat breakdown (lipolysis) in adipose tissue
- Increases protein synthesis and gluconeogenesis in the liver
GH Actions
- GH redistributes nutrients towards processes such as growth
- GH's effects in growing individuals include promoting growth and metabolic actions, such as:
- Stimulates protein synthesis and decreases protein catabolism
- Stimulates lipolysis (anti-insulin effect)
- Increases blood glucose (anti-insulin effect)
- In adults, GH doesn't promote significant growth but plays crucial roles in maintaining muscle mass and regulating metabolism
GH & Lipolysis
- Lipolysis is a key metabolic effect of GH
- GH concentrations in the plasma inversely correlate with abdominal fat
GH's Metabolic Effects
- GH counteracts the effects of insulin, leading to insulin insensitivity and hyperglycemia
- GH's role is to defend against hypoglycemia by maintaining blood glucose levels, even in the presence of insulin
- GH contributes to the development of "stress" diabetes during fasting or inflammatory illness
GH's Role During Fasting
- GH is the only anabolic hormone that increases during fasting; insulin and IGF-I levels decrease.
- GH acts during fasting in synergy with other catabolic hormones, such as glucagon, adrenaline and cortisol
- GH's primary role during fasting is to preserve muscle mass
GH's Role During Exercise
- GH stimulates lipolysis during moderate exercise, providing fatty acids as an alternative energy source
- GH's metabolic effects during moderate exercise:
- Protein and glucose metabolism remain unaffected
- GH stimulates lipolysis, releasing fatty acids for energy
Hypothalamic Regulation of GH
- Hypothalamus integrates metabolic, neural, and hormonal signals that influence GH release.
- Factors triggering GH release:
- High amino acid levels, low fatty acid levels, hypoglycemia
- Stress, exercise, deep sleep
- Malnutrition
- Sex steroids
- Hypothalamus releases two hormones:
- Growth hormone releasing hormone (GHRH)
- Somatostatin (GH inhibiting hormone)
Energy Sources for Muscle
- Muscle uses immediate energy sources, such as ATP or phosphocreatine (PCr) for high-intensity events
- Non-oxidative energy production comes from anaerobic glycolysis (glycogenolysis) during sprint events
- Oxidative energy production relies on glucose and fat oxidation and is the most efficient pathway for long-duration exercise
Energy Sources: Exercise
- Muscle glycogen provides immediate energy during exercise
- The liver and adipose tissue stores supply additional carbohydrate and fat
- Exercise activates the endocrine system:
- Increased adrenaline and glucagon
- Decreased insulin
- Increased cortisol and GH
- Muscle activity itself promotes GLUT4 translocation to the cell membrane, increasing glucose uptake
- Lactate produced by type IIb muscle fibers is utilized by other fibers or converted to glucose by the liver
Energy Sources: Exercise (Metabolic Pathway)
- The Cori cycle, where lactate from the muscle is converted to glucose in the liver, is important for prolonged exercise
- Lipolysis and beta-oxidation of fatty acids to generate energy become crucial during prolonged exercise
Energy Sources: Prolonged Exercise
- During intense exercise, including 180 minutes of cycling, blood glucose levels decrease
- Hormones such as glucagon help regulate blood glucose levels during prolonged exercise
- Energy sources during prolonged exercise include glucose, lactate, glycerol, and free fatty acids (FFA)
Exercise & Energy: Endocrine & Metabolic Changes
- Exercise triggers changes in the endocrine system:
- Decreased insulin
- Increased cortisol and GH
- Increased sympathetic nervous system (SNS) activity: adrenaline
- Metabolic adaptations during exercise:
- Increased glucose uptake and oxidation
- Increased free fatty acid levels due to lipolysis
- Increased glycerol for gluconeogenesis
- Lactate levels remain unchanged, utilized by muscles and gluconeogenesis
Energy Storage: Anabolism After Meal
- After a meal, excess carbohydrates are stored as glycogen in the liver and muscle
- Insulin stimulates glycogen synthesis
- Protein is stored in muscle tissue, with some protein breakdown and amino acids used for energy production
- Insulin stimulates protein synthesis
- Excess dietary fats are stored in adipose tissue
- Insulin stimulates fat storage
- Insulin inhibits hormone-sensitive lipase (HSL), preventing lipolysis
Fasting & Starvation
- During fasting or starvation, the body shifts to catabolic processes to obtain energy
- Energy stores used:
- Glycogen (glycogenolysis)
- Proteins (proteolysis)
- Triacylglycerides (lipolysis)
- Energy sources during fasting: glucose, lactate, amino acids, fatty acids, and ketone bodies
- Primary priorities during fasting include maintaining blood glucose levels for brain function and preserving protein reserves
Energy Sources: Overnight Fast
- Hormonal changes during an overnight fast include:
- Increased glucagon
- Decreased insulin
- Metabolic adaptations during an overnight fast:
- Reduced glucose uptake by muscle and adipose tissue
- Increased glycogenolysis
- Increased gluconeogenesis
- Increased lipolysis
Transition from Fasting to Starvation
- After several days of fasting, metabolism shifts from relying on gluconeogenesis from amino acids to ketogenesis from fat stores
- Ketone bodies provide fuel for the brain, muscles, and other tissues
- Hormonal changes during starvation:
- Decreased insulin and thyroxine
- Increased glucagon, SNS (adrenaline), cortisol, and GH
Gluconeogenesis & Ketogenesis
- Gluconeogenesis occurs primarily in the liver and kidney, using glycerol and amino acids as precursors
- Ketogenesis occurs in the liver, using fatty acids as precursors
- Beta-oxidation of fatty acids produces acetyl CoA, which can enter the Krebs cycle or be used to produce ketone bodies
Beta-Oxidation
- Beta-oxidation is a key process for generating energy from fatty acids
- Beta-oxidation breaks down fatty acids into acetyl CoA, which can enter the Krebs cycle for ATP production
Adrenal Cortex & Hormones
- The adrenal cortex is responsible for producing steroid hormones, including aldosterone, cortisol, and androgens.
- Aldosterone is a mineralocorticoid, primarily secreted by the zona glomerulosa, which regulates mineral/electrolyte balance.
- Cortisol and corticosterone are glucocorticoids, mainly secreted by the zona fasciculata and reticularis, known for their role in increasing blood glucose levels.
- DHEA and androstenedione are androgens produced by the adrenal cortex.
Steroid Hormone Synthesis
- Steroid hormones are synthesized from cholesterol, a common precursor.
- Cholesterol is transformed into various classes of steroid hormones, including progestagens, glucocorticoids, mineralocorticoids, androgens, and estrogens.
- The specific pathway for steroid hormone synthesis depends on the site of production and the enzymes present.
Regulation of Glucocorticoids - The HPA Axis
- The HPA axis is a complex system involving the hypothalamus, pituitary gland, and adrenal cortex, regulating the production of cortisol.
- Corticotrophin-releasing hormone (CRH) is released from the hypothalamus, acting on the anterior pituitary gland.
- Adrenocorticotropic hormone (ACTH) is secreted from the anterior pituitary, stimulating cortisol release from the adrenal cortex.
- ACTH specifically targets the zona fasciculata and reticularis, having minimal effect on aldosterone production in the zona glomerulosa.
- The HPA axis is regulated through negative feedback: high levels of cortisol inhibit CRH and ACTH release.
ACTH Mechanism of Action
- ACTH binds to melanocortin type 2 receptor (MC2-R) on cortical cells.
- This binding increases cholesterol uptake and trafficking, leading to increased pregnenolone production.
-
ACTH also upregulates key enzymes involved in cortisol synthesis:
- P-450scc (side chain cleavage enzyme)
- P-450c11 (11-beta hydroxylase)
Effects of Cortisol
- Cortisol plays a vital role in stress adaptation and energy regulation.
- It contributes to maintaining blood glucose levels by:
- Increasing hepatic glucose output
- Promoting peripheral catabolism (breakdown of muscle and fat)
-
Cortisol also has permissive effects:
- Facilitates metabolic reactions
- Regulates vascular reactivity
- Cortisol is essential for normal water excretion.
- It can suppress inflammatory responses and the immune system, a pharmacological effect.
Growth Hormone (GH) and Metabolism
-
GH is a major determinant of growth, primarily acting anabolically:
- Increasing cell size and number in soft tissues
- Enhancing bone growth
-
GH also has crucial metabolic actions:
- In muscle: stimulates amino acid uptake, decreases glucose uptake, inhibits protein breakdown, increases muscle mass
- In adipose tissue: decreases glucose uptake, increases fat breakdown (lipolysis), reduces fat deposits
- In liver: increases protein synthesis, enhances gluconeogenesis
Summary of GH Actions
- GH promotes the redistribution of nutrients towards growth and production processes.
- In growing individuals, GH supports both growth and metabolic functions, increasing protein synthesis, stimulating lipolysis, and elevating blood glucose.
- In adults, GH is primarily involved in maintaining muscle mass and metabolic processes.
Relationship Between GH & Lipolysis
- Plasma GH concentrations are inversely correlated with abdominal fat mass, suggesting a role in fat metabolism.
GH and Insulin Insensitivity
- GH counteracts insulin's actions, leading to insulin insensitivity and hyperglycemia.
- This "diabetogenic" effect is a defense mechanism against hypoglycemia, ensuring blood glucose maintenance.
GH Role in Fasting & Exercise
-
GH is vital in the starvation response:
- It remains anabolic during fasting while insulin and IGF-1 levels decrease.
- Its role is to preserve muscle mass, working alongside catabolic hormones (glucagon, adrenaline, and cortisol).
- During moderate exercise:
- GH stimulates lipolysis, providing alternative energy source from fatty acids.
Exercise & Energy Sources
- Muscle relies on immediate sources like ATP and phosphocreatine for power activities, non-oxidative anaerobic glycolysis for sprinting, and oxidative pathways for prolonged exercise.
- Muscle glycogen is a primary energy source during exercise, supplemented by mobilized stores from liver and adipose tissue (carbohydrates and fats).
- Hormonal regulation during exercise: increased adrenaline and glucagon, decreased insulin, increased cortisol and GH.
- GLUT4 is moved to cell membrane during muscle activity, supporting glucose uptake.
- Lactate produced by muscle fibers can be converted to pyruvate and oxidized, or utilized by the liver to generate glucose (Cori cycle).
- Prolonged exercise (>1 hour) heavily relies on lipolysis and gluconeogenesis as energy sources.
Eating - Anabolism & Energy Storage
- After a meal, insulin stimulates the storage of nutrients:
- Carbohydrates (G) are stored mainly as glycogen in the liver and muscle.
- Proteins are primarily converted into amino acids, utilized for protein synthesis.
- Fats are stored as triacylglycerols in adipose tissue.
- Insulin inhibits hormone-sensitive lipase (HSL), preventing fat breakdown (lipolysis).
Fasting & Starvation
- During fasting, the body enters a catabolic state, mobilizing energy stores:
- Glycogenolysis (breakdown of glycogen)
- Proteolysis (breakdown of proteins)
- Lipolysis (breakdown of fats)
- The primary goal is to maintain blood glucose levels for brain function.
- Over time, ketone bodies can be utilized as an alternative fuel source for the brain.
- Other tissues are capable of oxidizing fatty acids for energy.
Metabolic Adaptations During Fasting
- Endocrine control shifts during fasting: increased glucagon, decreased insulin.
-
Metabolic changes:
- Decreased glucose uptake in muscle and adipose tissue.
- Increased glycogenolysis and gluconeogenesis.
- Increased lipolysis.
- These adaptations aim to maintain glucose homeostasis by decreasing glucose uptake while increasing glucose production.
Transition from Fasting to Starvation
- After a few days of fasting, metabolic pathways shift:
- Gluconeogenesis (production of glucose from non-carbohydrate sources) is initially enhanced but gradually diminishes.
- Ketogenesis (production of ketone bodies from fatty acids) becomes the dominant metabolic pathway.
- Ketone bodies provide an alternative fuel source for the brain, muscles, and other tissues.
Endocrine Changes During Starvation
- During starvation, there are significant hormonal changes:
- Decreased insulin and thyroxine.
- Increased glucagon, adrenaline, cortisol, and GH.
Ketogenesis
- Ketogenesis occurs mainly in the liver, providing an alternative source of energy for the brain, muscles, and other tissues.
- Precursors for ketogenesis are fatty acids that are beta-oxidized to acetyl CoA.
- Acetyl CoA can either enter the citric acid cycle or form ketone bodies.
Gluconeogenesis in Starvation
- Gluconeogenesis plays a crucial role in maintaining blood glucose levels during starvation.
- Precursors for gluconeogenesis include glycerol and amino acids (like alanine).
- The liver and kidney contribute to gluconeogenesis.
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Description
This quiz explores the body's endocrine control mechanisms and muscle activity during exercise. It covers the roles of hormones like adrenaline, glucagon, and cortisol, as well as lactate metabolism and gluconeogenesis in energy production. Test your understanding of how these processes work together to fuel exercise.
