Term
| What is the physiological basis for exercise-associated muscle cramps? |
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Definition
| Two theories attempt to explain the physiological basis for EAMCs. The first suggests that these cramps happen when neuromuscular control becomes altered. Excitation in the muscle spindle and inhibiting the Golgi tendon occur in fatigued muscles, resulting in abnormal a-motor neuron activity and reduced inhibitory feedback. The second is called heat cramps, which involve electrolyte defects after an athlete has been sweating excessively. This leads to large muscle groups locking up when fluids shift from the interstitial compartment to the intravascular compartment, causing neuromuscular junctions to become hyperexcitable. This results in spontaneous discharge and initiation of action potentials. |
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Term
| What is an endocrine gland, and what are the functions of hormones? |
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Definition
| An endocrine gland is a gland that secretes hormones responsible for slow, longer lasting effects when maintaining homeostasis in the body. They secrete their hormones directly into the blood where they act as chemical signals throughout the body until they arrive at specific target cells. |
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Term
| Explain the difference between steroid hormones and non-steroid hormones in terms of their actions at target cells. |
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Definition
| Steroid hormones can pass through cell membranes easily since they are fat soluble while non-steroid hormones cannot easily do so. Steroid hormones include testosterone from the testes, estrogen and progesterone from the ovaries and placenta, and cortisol and aldosterone secreted by the adrenal cortex. Non-steroid hormones are divided into protein or peptide hormones, and amino acid-derived hormones. The latter is produced by the thyroid and adrenal medulla glands while the former makes up all other non-steroid hormones. Their chemical structures determine its mechanism of action on target cells and tissues. |
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Term
| How can hormones have very specific functions when they reach nearly all parts of the body through the blood? |
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Definition
| They have specific functions because each endocrine cell is specialized and transported by the blood to their specific target cells, which have specialized hormone receptors. Once there, hormones can control the target tissue. Essentially, they can only bind to the cells with the specific receptors needed for it. |
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Term
| What determines plasma concentrations of specific hormones? What determines their effectiveness on target cells and tissues? |
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Definition
| Hormones are secreted in irregularly timed short bursts, leading the plasma concentration to fluctuate over periods of an hour or less. However, some hormones affect the plasma concentration for longer, going through daily or even monthly cycles. This is due to a negative feedback mechanism where the body will secrete a certain hormone until the desired change in the body takes place, which in turn will inhibit the body from secreting more of that hormone into the blood. |
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Term
| Define the terms upregulation and downregulation. How do target cells become more or less sensitive to hormones? |
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Definition
| Upregulation is when a cell becomes more sensitive to a hormone because more than one can be bound at one time after it increases its number of receptors. Downregulation is when a cell has fewer hormone receptors which results in fewer hormone molecules that can bind. Thus, the cell becomes less sensitive to a given hormone, needing more of it to gain the same intended effect. They become less sensitive when the pancreas increases its insulin secretion, but in a few instances, a prolonged presence can lead to accepting more of the hormone. |
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Term
| What are second messengers and what role do they play in hormonal control of cell function? |
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Definition
| Second messengers are intracellular messengers that are formed when nonsteroid hormones bind to its membrane receptors, leading to a series of reactions that create it. Nonsteroid hormones relay signals and help intensify the strength of signals. One particularly important second messenger, cyclic adenosine monophosphate, (cyclic AMP or cAMP), mediates multiple hormone-receptor responses. The physiological responses it controls include activation of cellular enzymes, change in membrane permeability, promotion of protein synthesis, change in cellular metabolism or stimulation of cellular secretions. |
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Term
| Anterior pituitary gland, its hormones and specific actions. |
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Definition
| Hormones include growth hormone, thyrotropin, adrenocorticotropin, prolactin, follicle-stimulating hormone and lutenizing hormone. GH promotes development and enlargement of all body tissues until maturation. Increases rate of protein synthesis. Increases mobilization of fats and use of fat as an energy source. Decreases rate of carbohydrate use. TSH controls the amount of thyroxin and triiodothyronine produced and released by the thyroid gland. ACTH controls the secretion of hormones from the adrenal cortex. Prolactin stimulates milk production in breasts. FSH initiates growth in follicles in the ovaries and promotes secretion of estrogen from the ovaries. Promotes sperm development in the testes. LH promotes secretion of estrogen and progesterone and causes the follicle to rupture, releasing the ovum. Causes testes to secrete testosterone. |
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Term
| Posterior pituitary gland, its hormones and specific actions. |
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Definition
| Includes the antidiuretic hormone (ADH or vasopressin) and oxytocin. ADH assists in controlling water excretion by the kidneys. Elevates blood pressure by constricting blood vessels. Oxytocin controls contractions in the uterus and milk secretion. |
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Term
| Thyroid, its hormones and specific actions. |
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Definition
| Includes the thyroxine (T4), triiodothyronine (T3) and calcitonin hormones. T4 and T3 increases the rate of cellular metabolism and contractility of the heart. Calcitonin controls calcium ion concentration in the blood. |
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Term
| Parathyroid gland, its hormones and specific actions. |
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Definition
| Includes the parathyroid hormone (PTH or parathormone). PTH controls calcium ion concentration in the extracellular fluid through its influence on bones, intestines and kidneys. |
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Term
| Adrenal medulla, hormones and specific actions. |
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Definition
| Includes the epinephrine and norepinephrine glands (collectively known as catecholamines). Epinephrine stimulates the breakdown of glycogen in the liver and muscles in adipose tissue in muscle. It also increases skeletal muscle blood flow, increases heart rate and contractility. Increases oxygen consumption. Norepinephrine stimulates lipolysis in adipose tissue and in muscle to a lesser extent. Constricts arterioles and venules, thereby elevating blood pressure. |
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Term
| Adrenal cortex, its hormones and specific actions. |
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Definition
| Includes the mineralocorticoid (aldosterone), glucocorticoid (cortisol), androgen and estrogen hormones. Aldosterone increases sodium retention and potassium excretion through the kidneys. Cortisol controls metabolism of carbohydrates, fats and proteins. Exerts an anti-inflammatory action. Androgens and estrogens assist in the development of female and male sex characteristics. |
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Term
| Pancreas, its hormones and specific actions. |
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Definition
| Includes the insulin, glucagon and somatostatin hormones. Insulin controls blood glucose levels by lowering glucose levels. It increases the use of glucose and synthesis of fat. Glucagon increases blood glucose, stimulates the breakdown of protein and fat. Somatostatin depresses the secretion of both insulin and glucagon. |
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Term
| Kidney, its hormones and specific actions. |
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Definition
| Includes the renin and erythropoietin (EPO) hormones. Renin assists in blood pressure control. EPO stimulates erythrocyte production. |
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Term
| Testes, its hormones and specific actions. |
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Definition
| Includes the testosterone hormone. Testosterone promotes development of male sex characteristics, including the growth of the testes, scrotum, penis, facial hair and change in voice. Also promotes muscle growth. |
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Term
| Ovaries, its hormones and specific actions. |
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Definition
| Includes the estrogen and progesterone hormones. Estrogen and progesterone promote development of the female sex organs and characteristics, increases the storage of fat, and assists in regulating the menstrual cycle. |
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Term
| Which of the hormones outlined in question 7 are of major significance during exercise? |
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Definition
| During exercise, growth hormone, thyrotropin, triiodothyronine, thyroxine, epinephrine, norepinephrine, cortisol, insulin, and glucagon are of major significance. |
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Term
| What hormones are involved in the regulation of metabolism during exercise? How do they influence the availability of carbohydrates and fats for energy during exercise lasting several hours? |
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Definition
The hormones involved in the regulation of metabolism during exercise include glucagon, epinephrine, norepinephrine, cortisol for carbohydrate metabolism and decreased insulin, epinephrine, norepinephrine, cortisol and growth hormone for fat metabolism.
Glucagon promotes glycogen breakdown and glucose formation from amino acids at rest. During exercise, its secretion increases alongside epinephrine and norepinephrine, working together to further increase glycogenolysis. Cortisol then increases during the first 30 to 45 minutes of exercise, which increases protein catabolism, collectively working with the other three hormones to enhance the processes of glycogenolysis and gluconeogenesis. Glucagon and cortisol together are the major hormones during exercise lasting several hours.
In fat metabolism, a decrease in insulin is the major factor responsible for adipose tissue lipolysis during exercise. Cortisol peaks after 30-45 minutes, but during prolonged exercise, growth hormone and catecholamines, (epinephrine and norepinephrine) become the major hormones during prolonged exercise during fat metabolism. |
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