Podcast
Questions and Answers
What primarily alters plasma hormone concentrations?
What primarily alters plasma hormone concentrations?
Which organ is considered the major site for hormone metabolism?
Which organ is considered the major site for hormone metabolism?
What is likely to happen to hormone metabolism during exercise due to changes in blood flow?
What is likely to happen to hormone metabolism during exercise due to changes in blood flow?
What occurs as a result of chronic high concentrations of a hormone?
What occurs as a result of chronic high concentrations of a hormone?
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What factor does NOT affect the magnitude of a hormone's effect?
What factor does NOT affect the magnitude of a hormone's effect?
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Where can receptors for hormones be located within a cell?
Where can receptors for hormones be located within a cell?
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Which type of hormones primarily alter the activity of DNA to modify protein synthesis?
Which type of hormones primarily alter the activity of DNA to modify protein synthesis?
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What is the role of G proteins in hormone action?
What is the role of G proteins in hormone action?
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What type of hormones bind to receptors located on the outer surface of the cell membrane?
What type of hormones bind to receptors located on the outer surface of the cell membrane?
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Which of the following is a second messenger activated by G proteins?
Which of the following is a second messenger activated by G proteins?
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Which process involves the hydrolysis of Phosphatidylinositol (PIP2)?
Which process involves the hydrolysis of Phosphatidylinositol (PIP2)?
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What is a key characteristic of lipophilic hormones?
What is a key characteristic of lipophilic hormones?
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Which of the following actions is associated with second messengers?
Which of the following actions is associated with second messengers?
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What effect does glucagon have during exercise?
What effect does glucagon have during exercise?
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What happens to plasma insulin levels during exercise?
What happens to plasma insulin levels during exercise?
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Which hormone is known to increase blood glucose levels during exercise?
Which hormone is known to increase blood glucose levels during exercise?
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What physiological change facilitates increased glucose uptake by muscle during exercise?
What physiological change facilitates increased glucose uptake by muscle during exercise?
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How does training affect circulating levels of epinephrine and norepinephrine during fixed submaximal exercise?
How does training affect circulating levels of epinephrine and norepinephrine during fixed submaximal exercise?
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What is the primary function of leptin in the body?
What is the primary function of leptin in the body?
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Which hormone is secreted by the alpha cells of the pancreas?
Which hormone is secreted by the alpha cells of the pancreas?
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What effect does chronic endurance exercise have on the levels of testosterone in males?
What effect does chronic endurance exercise have on the levels of testosterone in males?
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What occurs with increased fat mass in the body, specifically regarding leptin and adiponectin?
What occurs with increased fat mass in the body, specifically regarding leptin and adiponectin?
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Which steroid hormone is primarily involved in muscle building?
Which steroid hormone is primarily involved in muscle building?
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How does chronic endurance training affect estrogen levels in females?
How does chronic endurance training affect estrogen levels in females?
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What role does somatostatin play in the body?
What role does somatostatin play in the body?
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Adipose tissue is known to secrete which of the following hormones?
Adipose tissue is known to secrete which of the following hormones?
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What effect does growth hormone (GH) have on muscle tissue?
What effect does growth hormone (GH) have on muscle tissue?
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Which gland is responsible for the secretion of antidiuretic hormone (ADH)?
Which gland is responsible for the secretion of antidiuretic hormone (ADH)?
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How does growth hormone affect plasma glucose levels?
How does growth hormone affect plasma glucose levels?
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What is a primary function of thyroid hormones T3 and T4?
What is a primary function of thyroid hormones T3 and T4?
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What triggers the release of antidiuretic hormone (ADH)?
What triggers the release of antidiuretic hormone (ADH)?
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Which of the following is a consequence of high doses of growth hormone?
Which of the following is a consequence of high doses of growth hormone?
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Calcitonin, released by the thyroid gland, is primarily involved in which process?
Calcitonin, released by the thyroid gland, is primarily involved in which process?
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What impact do permissive hormones have on other hormones?
What impact do permissive hormones have on other hormones?
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Study Notes
Plasma Hormone Concentration
- Plasma hormone concentration can be influenced by factors like the rate of hormone secretion and metabolism, the quantity, capacity, and affinity of binding proteins, and the plasma volume.
- Hormone secretion can be controlled by multiple factors, with a good example being insulin secretion, which is determined by the balance of inhibitory and stimulatory input.
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Metabolism and Excretion of Hormones
- Excess hormones are often removed from the bloodstream by the liver and kidneys.
- The liver primarily metabolizes hormones, while kidneys both metabolize and excrete excess hormones into the urine.
- During exercise, blood flow to the liver and kidneys can change, potentially impacting the rate of hormone metabolism and excretion.
- The resulting changes in hormone metabolism and excretion can ultimately influence blood hormone concentration levels during exercise.
Hormone-Receptor Interactions
- Hormones circulate throughout the body, but they only affect tissues that possess specific receptors that bind to them.
- The magnitude of a hormone's effect depends on its concentration, the number of receptors on a cell, and the affinity of the receptor for the hormone.
- Downregulation refers to a decrease in receptor numbers in response to chronically high hormone concentrations.
- Upregulation refers to an increase in receptor numbers in response to chronically low hormone concentrations.
- Substances with similar structures to a hormone can compete for limited receptor sites.
- Receptors can be located in various parts of a cell, including the membrane, cytoplasm, and nucleus.
Mechanisms of Hormone Action
- Hormones can exert their effects by altering DNA activity to modify protein synthesis, activating second messengers through G proteins, or altering membrane transport.
Altering Activity of DNA in Nucleus
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Lipophilic Hormones
- Steroids and thyroid hormones are lipophilic.
- They act by binding to receptors in the cytoplasm (translocation) or directly in the nucleus.
- Their effects are typically slow-acting but longer-lasting.
Membrane Transport
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Lipophobic Hormones
- These hormones bind to receptors on the cell membrane's outer surface.
- They activate carrier molecules within or near the membrane to increase the movement of ions or substrates from outside to inside the cell.
Second Messengers
- Some hormones are too large or highly charged to easily cross cell membranes.
- These hormones bind to receptors on the cell membrane surface and activate a G protein located in the membrane.
- The G protein links the hormone-receptor interaction to subsequent events inside the cell.
- G proteins can activate enzymes in the membrane or open ion channels for calcium (Ca++) entry into the cell.
Second Messengers
- G-proteins can activate Ca++ channels, leading to Ca++ entry into the cell and activation of calmodulin.
- G-proteins can activate membrane-bound phospholipase C.
- Phospholipase C hydrolyzes phosphotidylinositol (PIP2) into inositol triphosphate (IP3) and diacylglycerol.
- IP3 releases intracellular Ca++, while diacylglycerol activates protein kinase C.
- These second messengers can influence each other's actions, demonstrating interconnectedness.
Check your understanding
- The hormone-receptor interaction triggers events at the cell.
- Changing the concentration of the hormone, the number of receptors on the cell, or the affinity of the receptor for the hormone will all affect the magnitude of the effect.
- Hormones achieve their effects by:
- Activating or suppressing genes to modify protein synthesis.
- Activating second messengers.
- Modifying membrane transport.
Hormones: Regulation and Action
- Hormones are secreted from endocrine glands.
- Key endocrine glands include the hypothalamus, pituitary, thyroid, parathyroid, adrenal glands, pancreas, testes, and ovaries.
Growth Hormone
- Secreted by the anterior pituitary gland.
- Stimulates the release of insulin-like growth factors (IGFs), with IGF-1 playing a crucial role in muscle hypertrophy.
- Essential for normal growth of all tissues.
- Stimulates amino acid uptake and protein synthesis.
- Plays a significant role in long bone growth.
- Growth hormone spares plasma glucose.
- Opposes insulin action, reducing glucose utilization.
- Increases gluconeogenesis in the liver.
- Mobilizes fatty acids from adipose tissue.
Growth Hormone and Performance
- GH increases protein synthesis in muscle and long bone growth.
- It's used to treat childhood dwarfism.
- Despite use by athletes and the elderly, high doses of GH have more adverse effects than benefits.
- There's no evidence that GH promotes strength gains, with minimal strength gains compared to resistance training alone.
- Its benefits as an anti-aging therapy are questionable.
Antidiuretic Hormone (ADH) or Vasopressin
- Secreted by the hypothalamus and stored/released by the posterior pituitary gland.
- Reduces water loss to maintain plasma volume.
- Promotes water reabsorption from kidney tubules into capillaries.
- Its release is stimulated by high plasma osmolality (low water concentration) and low plasma volume.
- Increases during exercise (>60% VO2 max) to maintain plasma volume.
Thyroid Gland
- Stimulated by Thyroid-Stimulating Hormone (TSH)
- Produces triiodothyronine (T3) and thyroxine (T4).
- Influences resting metabolic rate.
- Acts as a permissive hormone, allowing other hormones to exert their full effects.
- Secretes calcitonin, which plays a role in regulating plasma Ca++ levels.
- Calcitonin blocks Ca++ release from bone and stimulates its excretion by the kidneys.
Adipose Tissue Is an Endocrine Organ
- In addition to storing triglycerides, adipose tissue secretes hormones.
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Leptin:
- Suppresses appetite through the hypothalamus.
- Enhances insulin sensitivity and fatty acid oxidation.
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Adiponectin:
- Increases insulin sensitivity and fatty acid oxidation.
- With increased fat mass (obesity):
- Leptin levels increase, and adiponectin levels decrease.
- This can contribute to type 2 diabetes and low-grade inflammation.
- Exercise doesn't significantly affect adiponectin or leptin concentrations.
- These hormones are more responsive to changes in body weight.
The Pancreas – Insulin and Glucagon
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Insulin ( cells)
- Promotes the storage of glucose, amino acids, and fats.
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Glucagon ( cells)
- Promotes the mobilization of FFAs and glucose.
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Somatostatin (from cells)
- Controls the rate of nutrient entry into the circulation.
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Digestive enzymes and bicarbonate:
- Secreted into the small intestine.
The Gonads – Sex Hormones
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Testosterone:
- Anabolic, androgenic steroid hormone secreted by the testes.
- Promotes tissue (muscle) building.
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Anabolic steroids:
- Originally developed for medical uses.
- Chronic endurance exercise has been shown to decrease plasma testosterone levels.
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Estrogen:
- Steroid hormone secreted by the ovaries.
- Plays a significant role in bone health.
- Chronic endurance training can lead to decreased plasma estrogen levels, potentially contributing to osteoporosis.
Anabolic Steroids and Performance
- Initial studies showed no benefit for developing muscle mass, contradicting real-world reports.
- "Subjects" in these studies used 10 to 100 times the recommended dosage.
- Associated with negative side effects.
- Widespread use has led to testing of competitive athletes.
- Most users are not competitive athletes and take multiple steroids in extreme doses.
Check your understanding
- Insulin is secreted by the cells of the pancreas and promotes the storage of glucose, amino acids, and fats.
- Glucagon is secreted by the cells of the pancreas and promotes the mobilization of glucose and fats.
- Chronic endurance exercise (training) can decrease testosterone levels in males and estrogen levels in females.
Glucagon vs. Insulin
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Glucagon:
- Uptake and storage of glucose and FFAs ↓ during exercise.
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Insulin:
- Mobilization of glucose and FFA fuels ↑ during exercise.
Effects of Insulin and Glucagon
- Epinephrine: ↑ blood glucose.
- Norepinephrine: ↑ blood glucose.
- Growth Hormone: ↑ blood glucose.
- Cortisol: ↑ blood glucose.
- Glucagon: ↑ blood glucose.
- Insulin: ↓ blood glucose.
Check your understanding
- Plasma glucose is maintained during exercise by increasing liver glycogen mobilization, increasing plasma FFA utilization, increasing gluconeogenesis, and decreasing glucose uptake by tissues.
- The decrease in plasma insulin and increase in plasma E, NE, GH, glucagon, and cortisol during exercise control these mechanisms to maintain glucose concentration.
- Glucose is taken up by muscle 7-20 times faster during exercise than at rest, despite decreased plasma insulin levels.
- This is due to increases in the number of glucose transporters due to high intracellular Ca++ and increased insulin sensitivity.
- Increased blood flow also increases the delivery of oxygen and glucose which facilitates glucose uptake.
- An increased glucose uptake also increases facilitated diffusion of glucose.
- Training causes decreased circulating levels of E and NE responses to fixed submaximal exercise and increased levels of E and NE responses to supramaximal exercise.
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Description
This quiz delves into the plasma hormone concentration, factors affecting hormone secretion, metabolism, and excretion. Learn about the role of the liver and kidneys in hormone regulation as well as how exercise impacts these processes. Test your understanding of hormone-receptor interactions and hormonal control mechanisms.
