Hormones and Homeostasis

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Maud Malone
5 years ago
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1 Hormones and Homeostasis The endocrine system is a system of organs that releases chemical message molecules, called hormones, into the blood. Unlike the nervous system whose action helps the body react immediately to change, such as quickly jumping out of the way of an oncoming cyclist, the endocrine system controls changes that happen to the body over a long period of time; from minutes, hours, to years of change. The endocrine system is made up of many glands that are located in different areas of the body. Hormones are chemical messenger molecules that are made by cells in one part of the body and cause changes in cells in another part of the body. Hormones regulate the many and varied functions that keep you alive. Hormones are made and secreted by cells in endocrine glands. Endocrine glands are ductless organs that secrete hormones directly into the blood or the fluid surrounding a cell rather than through a duct. The primary function of an endocrine gland is to make and secrete hormones. The endocrine glands collectively make up the endocrine system. The body produces many different hormones, but each hormone is very specific for its target cells. A target cell is the cell on which a hormone has an effect. Target cells are affected by hormones because they have receptor proteins that are specific to the hormone. Hormones will travel through the bloodstream until they find a target cell with the specific receptors to which they can bind. When a hormone binds to a receptor, it causes a change within the cell. There are two main types of hormones, and a group of hormone-like substances: Amino Acid-Based Hormones Amino acid-based hormones are made of amino acids. Some amino acid-based hormones are made of a few amino acids and are simple in structure while others are made of hundreds of amino acids and are very large. These hormones are not fat-soluble and therefore cannot diffuse through the plasma membrane of their target cell. They usually bind to receptors that are found on the cell membrane. Cholesterol-Based Hormones Cholesterol-based hormones are made of lipids such as phospholipids and cholesterol. Hormones from this group are also called steroid hormones. Steroid hormones are fat soluble and are able to diffuse through the plasma membrane. Steroid hormone receptors are found within the cell cytosol and nucleus. The effects of hormones vary widely. Many of the responses to hormones regulate the metabolic activity of an organ or tissue. Other effects of hormones can include: Stimulation or inhibition of growth and maturation Induction or suppression of programmed cell death (apoptosis) Regulation of metabolism Control of the reproductive cycle

Hemoglobin and Oxygen Hemoglobin is the protein molecule in red blood cells that carries oxygen from the lungs to the body's tissues and

Hemoglobin is made up of four protein molecules (globulin chains) that are connected together. Hemoglobin levels in your blood can vary.

A lower than normal number of red blood cells is referred to as anemia and hemoglobin levels reflect this number.

Some of the more common causes of anemia are: nutritional deficiency (iron, vitamin B12, folate), abnormal hemoglobin structure (sickle

2 Hemoglobin and Oxygen Hemoglobin is the protein molecule in red blood cells that carries oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues back to the lungs. Hemoglobin is made up of four protein molecules (globulin chains) that are connected together. Hemoglobin levels in your blood can vary. A low hemoglobin level is referred to as anemia or low red blood count. A lower than normal number of red blood cells is referred to as anemia and hemoglobin levels reflect this number. There are many reasons (causes) for anemia. Some of the more common causes of anemia are: nutritional deficiency (iron, vitamin B12, folate), abnormal hemoglobin structure (sickle cell anemia) What is sickle cell disease? Sickle cell disease is a genetic condition in which the quality of hemoglobin is defective. This condition can cause abnormal hemoglobin that can result in abnormally-shaped (sickled) red blood cells (see illustration). These abnormal red blood cells cannot easily pass through small blood vessels leading to inadequate oxygen for the tissues of the body.

Insulin, Blood Glucose Levels, and Homeostasis Glucose Regulation in the Human Body: Glucose is a simple sugar that fuels all the cells of the body.

3 Insulin, Blood Glucose Levels, and Homeostasis Glucose Regulation in the Human Body: Glucose is a simple sugar that fuels all the cells of the body. Glucose is absorbed by the intestines from the food that we eat and is distributed all over the body through the bloodstream. It is important for the body to have a steady level of glucose even between mealtimes. The brain is a major consumer of glucose and it needs a steady supply of it. Our bodies rely on insulin and glucagon, two hormones produced by the pancreas, to achieve a constant level of glucose. When we eat food, glucose is absorbed by the intestines and the level of glucose in the bloodstream rises. When there is a high level of glucose in the blood, insulin is secreted by the pancreas. Insulin helps move glucose from the bloodstream into cells by functioning as a key that unlocks receptors on the cell. Once the receptors are unlocked by insulin, glucose can enter the cell and is used by the cell to make energy. Insulin also stimulates the formation of glycogen. Glycogen molecules are long chains of glucose molecules that can be stored in the liver and released when the level of glucose in the blood is low. When blood glucose is low, for example when a person hasn t eaten for a long time or is sleeping, glycogen can be converted back to glucose by the hormone glucagon. However, the storage of glucose as glycogen is limited; therefore, most excess glucose is stored as fat, of which we can store a lot! As an example of glucose homeostasis, an average person usually secretes about 1 unit of insulin per hour; however, approximately one hour after eating, the pancreas secretes up to 5 units of insulin per hour to help transport the additional glucose that is available in the bloodstream. As time goes by and more glucose is being taken in by the body cells, the amount of glucose in the bloodstream is decreased. This stimulates the glucagon to convert stored glycogen in the liver into glucose, which is released into the bloodstream. In turn, the newly released blood glucose causes the pancreas to secrete more insulin to transport the glucose into the cells for use. As the amount of glucose in the bloodstream drops, the pancreas secretes less insulin. The relationship of insulin and glucagon creates a stable blood glucose level. However, if a person does not produce enough insulin (insulin deficiency), or the insulin is not capable of transporting the glucose into the cells (insulin resistance), the cells will not get the energy needed to function. This condition is known as diabetes. In type 1 diabetes, the pancreas does not make insulin. Without insulin present to unlock the receptors on the cells, glucose cannot enter the cells and builds up in the bloodstream. In type 2 diabetes, the body still produces insulin but it may make a lower amount than average, or there may be a decrease in the number and/or responsiveness of the receptors on the cell. Even though insulin is present, it cannot be used as effectively as it should be, so it is more difficult for glucose to enter the cells. Eventually the beta cells will become exhausted trying to overcome the insulin resistance.

4 Enzymes

Control of Blood Sugar Levels

Control of Blood Sugar Levels Why? Control of Sugar Levels What hormones are involved in the homeostasis of blood sugar? All living things use as a source of energy. In vertebrates it is critical that the levels of in the blood are