Chapter 21: Endocrine System : Regulation Of Energy Metabolism And Growth

Glucocorticoids are a type of hormone that plays a role in regulating blood sugar levels. When present in the body, glucocorticoids promote an increase in plasma glucose levels. This is because they stimulate the liver to produce and release glucose into the bloodstream. Additionally, glucocorticoids also decrease the uptake and utilization of glucose by various tissues in the body. As a result, the overall effect of glucocorticoids is an increase in plasma glucose levels.

During the absorptive period, the body is in a fed state and glucose levels in the blood are high. Insulin is responsible for regulating glucose metabolism and promoting the uptake of glucose into cells, where it can be used for energy or stored as glycogen. Therefore, an increase in insulin secretion is necessary to facilitate the absorption and utilization of glucose from the bloodstream, helping to maintain blood sugar levels within a normal range.

Beta cells are the cells of the pancreas that secrete insulin. Insulin is a hormone that helps regulate blood sugar levels by allowing cells to take in glucose from the bloodstream. Alpha cells in the pancreas secrete glucagon, which has the opposite effect of insulin, raising blood sugar levels. Delta cells secrete somatostatin, which helps regulate the release of insulin and glucagon. Exocrine cells in the pancreas secrete digestive enzymes, while duct cells help transport these enzymes to the small intestine.

Plasma glucocorticoids have an inhibitory effect on the secretion of ACTH. This means that when the levels of glucocorticoids in the blood are high, they suppress the release of ACTH. ACTH is a hormone that stimulates the production and release of glucocorticoids from the adrenal glands. Therefore, when there is already an excess of glucocorticoids in the blood, there is no need for further stimulation of ACTH secretion.

During the absorptive state, which occurs after a meal, the body has an abundant supply of glucose from the digestion and absorption of carbohydrates. This excess glucose can be converted into other molecules, including amino acids, through various metabolic processes. Therefore, the conversion of amino acids to glucose is more likely to occur in the absorptive state when there is a surplus of glucose available for these metabolic reactions.

Glucagon actually stimulates gluconeogenesis, which is the production of glucose from non-carbohydrate sources such as amino acids and glycerol. This process is not a glucose sparing effect, as it involves the creation of new glucose molecules rather than conserving existing glucose. Therefore, the correct answer is false.

An increase in plasma thyroid hormone levels tends to make the body's energy balance more negative. This is because thyroid hormones play a crucial role in regulating metabolism. When thyroid hormone levels increase, it leads to an increase in metabolic rate, which means the body is burning more calories and utilizing energy at a faster rate. This results in a negative energy balance, as the body is expending more energy than it is taking in through food.

Triglycerides are a type of fat molecule that can be broken down into their components, which are fatty acids and glycerol. Glycerol is a sugar alcohol that can be converted into glucose, which is then used by cells as an energy source. Therefore, when triglycerides are broken down, the resulting glycerol can be utilized by cells for energy production.

Stress tends to inhibit GHRH secretion. When the body is under stress, the release of growth hormone-releasing hormone (GHRH) is suppressed. This is because stress activates the hypothalamic-pituitary-adrenal (HPA) axis, leading to the release of cortisol, which in turn inhibits the secretion of GHRH. This inhibition of GHRH secretion ultimately affects the release of growth hormone (GH) from the pituitary gland, which plays a crucial role in growth, metabolism, and other physiological processes.

Cortisol is a steroid hormone produced by the adrenal glands. It plays a crucial role in regulating various metabolic processes in the body, including the immune response, stress response, and inflammation. Steroid hormones are derived from cholesterol and are characterized by their ability to easily pass through cell membranes. Cortisol fits this description as it is lipid-soluble and can directly enter cells to bind to its specific receptors and exert its effects. In contrast, the other hormones listed (thyroid hormones, insulin, glucagon, and growth hormone) are not steroids.

During the postabsorptive state, the body is not receiving any nutrients from the diet and relies on stored energy reserves to maintain blood glucose levels. In this state, amino acids can be converted into glucose through a process called gluconeogenesis. This conversion helps to provide a steady supply of glucose to the body's cells, especially the brain, which requires a constant source of glucose for energy. Therefore, the conversion of amino acids to glucose is more likely to occur in the postabsorptive state when the body needs to maintain blood glucose levels.

Glucagon is a hormone that promotes energy mobilization in the body. When blood glucose levels are low, such as during fasting or intense exercise, the pancreas releases glucagon. Glucagon acts on the liver to stimulate the breakdown of glycogen into glucose, which is then released into the bloodstream to be used as fuel by the body's cells. This process helps to increase blood glucose levels and provide energy to the body. In contrast, insulin promotes energy storage by facilitating the uptake of glucose from the bloodstream into cells and promoting glycogen synthesis.

When energy is taken into the body, it can either be stored or used to perform work. In the context of this question, the missing word that completes the sentence is "heat". This means that the energy that is not stored or used for work appears as heat. Heat is a form of energy that is produced as a result of metabolic processes in the body. It is generated when the body converts food into energy, and it helps to maintain the body's temperature.

In the postabsorptive state, the body relies on stored energy to meet its energy needs. Glucose is the primary source of energy for the central nervous system during this state because it can be readily broken down and used by the brain. Fatty acids and ketones can also be used as an energy source, but they are not the primary source for the central nervous system. Amino acids are primarily used for protein synthesis and are not the main source of energy for the brain. Glycerol is a component of triglycerides and can be converted to glucose, but it is not the primary source of energy for the central nervous system.

Hypoglycemia, which is a condition characterized by low blood sugar levels, inhibits the secretion of insulin. Insulin is a hormone produced by the pancreas that helps regulate blood sugar levels by allowing cells to take in glucose from the bloodstream. In cases of hypoglycemia, the body's blood sugar levels drop too low, causing a decrease in insulin secretion as a natural response to prevent further lowering of blood sugar. Therefore, insulin secretion is inhibited during hypoglycemia.

T3, or triiodothyronine, has greater activity at target cells compared to T4, or thyroxine. T3 is the more biologically active form of thyroid hormone and is responsible for regulating metabolism, growth, and development in the body. T4, on the other hand, is a prohormone that is converted into T3 in peripheral tissues. While both T3 and T4 play important roles in thyroid function, T3 is considered to have a stronger and more direct impact on target cells.

Insulin and glucagon are both hormones that play a crucial role in regulating blood glucose levels. Insulin is released by the pancreas when blood glucose levels are high, and it helps to lower them by promoting the uptake of glucose into cells. On the other hand, glucagon is released when blood glucose levels are low, and it helps to raise them by stimulating the liver to release stored glucose into the bloodstream. Therefore, both insulin and glucagon work together to maintain a stable plasma glucose concentration.

Stress stimulates the secretion of various hormones including growth hormone, epinephrine, thyroid hormone, and ACTH. When the body is under stress, these hormones are released to help the body respond to the stressful situation. Growth hormone promotes growth and repair of tissues, epinephrine (also known as adrenaline) prepares the body for a fight-or-flight response, thyroid hormone regulates metabolism, and ACTH stimulates the release of cortisol, which helps the body cope with stress. Therefore, all of the above hormones are secreted in response to stress.

The effect of thyroid hormone on growth is an example of a permissive effect of a hormone. This is because thyroid hormone does not directly stimulate growth, but rather it enhances the responsiveness of target cells to other growth-promoting hormones. Therefore, the presence of thyroid hormone is necessary for the full expression of the growth-promoting effects of other hormones.

Cortisol stimulates lipolysis, which is the breakdown of stored fat into fatty acids. This is considered a glucose-sparing effect because when fatty acids are used as an energy source, it reduces the need for glucose to be broken down for energy. This allows glucose to be conserved and used for other important functions in the body.