HomeostasisDone by: Olicia-ann Sylvester

Objective

• With the aid of a diagram, name the endocrine glands in the body and briefly outline the hormones they secrete and their function.

• With the aid of diagrams show the internal structure of the pancreas, showing the A (alpha) cells, B (beta) cells, Islets of Langerhans and acinar cells.

• Give careful treatment to the pancreas and how its hormones (glucagon and insulin) control blood glucose levels.

• State the set point or normal levels of glucose in the human blood, and use the terms Hypoglycemia and Hyperglycemia in explaining how the glucose levels are controlled.

Definition

• Homeostasis generally refers to stability, balance or equilibrium. It is the body's attempt in maintaining a constant internal environment.

• Maintaining a stable internal environment requires constant monitoring and adjustments as conditions change. This adjusting of physiological systems within the body is called homeostatic regulation.

Endocrine System

• The endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body.

• The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts.

• It derives from the Greek words "endo" meaning inside, within, and "crinis" for secrete.

• The endocrine system is an information signal system with effects that are slow to initiate, and prolonged in their response, lasting for hours to weeks.

• The endocrine system is made of a series of glands that produce chemicals called hormones.

Organs and Glands of the Endocrine System

• Glands are small but powerful organs that are located throughout the body. They control very important body functions by releasing hormones.

The following list of glands make up the endocrine system:• Pituitary Gland• Hypothalmus• Thymus• Pineal Gland• Testes• Ovaries• Thyroid• Adrenal Glands• Parathyroid• Pancreas

Diagram Of The Endocrine System

Diagram of organs involve in the endocrine system

Name them:

Endocrine System cont’d

• Hormones are substances (chemical mediators) released from endocrine tissue into the bloodstream where they travel to target tissue and generate a response.

Pituitary Gland

• The pituitary gland is sometimes called the "master gland" because of its great influence on the other body organs. It consist of an anterior and posterior section.

• The anterior pituitary produces several types of hormones:

• Prolactin or PRL - PRL stimulates milk production from a woman's breasts after childbirth and can affect sex hormone levels from the ovaries in women and the testes in men.

• Growth hormone or GH - GH stimulates growth in childhood and is important for maintaining a healthy body composition.

Pituitary Gland

• Adrenocorticotropin or ACTH - ACTH stimulates production of cortisol by the adrenal glands. Cortisol, a so-called "stress hormone," is vital to survival. It helps maintain blood pressure and blood glucose levels.

• Thyroid-stimulating hormone or TSH - TSH stimulates the thyroid gland to make thyroid hormones, which, in turn, control (regulate) the body's metabolism, energy, growth and development, and nervous system activity.

• Luteinizing hormone or LH - LH regulates testosterone in men and estrogen in women.

• Follicle-stimulating hormone or FSH - FSH promotes sperm production in men and stimulates the ovaries to release eggs (ovulate) in women. LH and FSH work together to allow normal function of the ovaries or testes.

Pituitary Gland cont’d

• The posterior pituitary produces two hormones:

• Oxytocin - Oxytocin causes milk letdown in nursing mothers and contractions during childbirth.

• Antidiuretic hormone or ADH - ADH, also called vasopressin, is stored in the back part of the pituitary gland and regulates water balance. If this hormone is not secreted properly, this can lead to problems of sodium (salt) and water balance, and could also affect the kidneys so that they do not work as well.

Pituitary Gland

• Diagram of pituitary

Hypothalamus

• The hypothalamus is part of the brain that lies just above the pituitary gland.

• It releases hormones that start and stop the release of pituitary hormones.

• The hypothalamus controls hormone production in the pituitary gland through several "releasing" hormones.

• Some of these are:• Growth -releasing hormone, or (controls GH release)• Thyrotropin-releasing hormone, or TRH (controls TSH release).• Corticoptropin-releasing hormone, or CRH (controls ACTH release). • Gonadotropin-releasing hormone (GnRH) tells the pituitary gland to make

luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are important for normal puberty.

Diagram of the Hypothalamus

• Located at the front of brain

Thymus

• The thymus is a gland needed early in life for normal immune function.

• It is very large just after a child is born and weighs its greatest when a child reaches puberty. Then its tissue is replaced by fat.

• The thymus gland secretes hormones called humoral factors.

• These hormones help to develop the lymphoid system, which is a system throughout the body that help it to reach a mature immune response in cells to protect them from invading bodies, like bacteria.

Diagram of Thymus

The Thymus

Pineal Gland

• Scientists are still learning how the pineal gland works.

• They have found one hormone so far that is produced by this gland: melatonin.

• Melatonin may stop the action of (inhibit) the hormones that produce gonadotropin, which causes the ovaries and testes to develop and function.

• It may also help to control sleep patterns.

Diagram of Pineal Gland

• Pineal Gland

Testes

• Males have twin reproductive glands, called testes, that produce the hormone testosterone.

• Testosterone helps a boy develop and then maintain his sexual traits.

• During puberty, testosterone helps to bring about the physical changes that turn a boy into an adult male, such as growth of the penis and testes, growth of facial and pubic hair, deepening of the voice, increase in muscle mass and strength, and increase in height.

• Throughout adult life, testosterone helps maintain sex drive, sperm production, male hair patterns, muscle mass, and bone mass.

Diagram of Testes

• Scrotum

Ovaries

• The two most important hormones of a woman's twin reproductive glands, the ovaries, are estrogen and progesterone.

• These hormones are responsible for developing and maintaining female sexual traits, as well as maintaining a pregnancy.

• Along with the pituitary gonadotropins (luteinizing hormone or LH and follicle-stimulating hormone or FSH), they also control the menstrual cycle.

• The ovaries also produce inhibin, a protein that curbs (inhibits) the release of follicle-stimulating hormone from the anterior pituitary and helps control egg development

Diagram of the Ovaries

• Ovum

Thyroid

• The thyroid is a small gland inside the neck, located in front of your breathing airway (trachea) and below your Adam's apple.

• The thyroid hormones control your metabolism, which is the body's ability to break down food and store it as energy and the ability to break down food into waste products with a release of energy in the process.

• The thyroid produces two hormones, T3 (called tri-iodothyronine) and T4 (called thyroxine).

Diagram of the Thyroid

• The Thyroid Gland

Adrenal Glands

• Each adrenal gland is actually two endocrine organs. The outer portion is called the adrenal cortex. The inner portion is called the adrenal medulla.

• The hormones of the adrenal cortex are essential for life. The types of  hormones secreted by the adrenal medulla are not.

• The adrenal cortex produces glucocorticoids (such as cortisol) that help the body control blood sugar, increase the burning of protein and fat, and respond to stressors like fever, major illness, and injury.

• The mineralcorticoids (such as aldosterone) control blood volume and help to regulate blood pressure by acting on the kidneys to help them hold onto enough sodium and water.

• The adrenal cortex also produces some sex hormones, which are important for some secondary sex characteristics in both men and women.

Adrenal Glands cont’d

• The adrenal medulla produces epinephrine (adrenaline), which is secreted by nerve endings and increases the heart rate, opens airways to improve oxygen intake, and increases blood flow to muscles, usually when a person is scared, excited, or under stress.

Diagram of the Adrenal Glands

• Adrenal Gland

Parathyroid Gland

• Located behind the thyroid gland are four tiny parathyroid glands. These make hormones that help control calcium and phosphorous levels in the body.

• The parathyroid glands are necessary for proper bone development.

• In response to too little calcium in the diet, the parathyroid glands make parathyroid hormone, or PTH, that takes calcium from bones so that it will be available in the blood for nerve conduction and muscle contraction.

• If the parathyroids are removed during a thyroid operation, low blood calcium will result in symptoms such as irregular heartbeat, muscle spasms, tingling in the hands and feet, and possibly difficulty breathing.

• A tumor or chronic illness can cause too much secretion of PTH and lead to bone pain, kidney stones, increased urination, muscle weakness, and fatigue.

Diagram of the Parathyroid Gland

• Parathyroid

Pancreas

• The pancreas is a large gland behind your stomach that helps the body to maintain healthy blood sugar (glucose) levels.

• The pancreas secretes insulin, a hormone that helps glucose move from the blood into the cells where it is used for energy.

• The pancreas also secretes glucagon when the blood sugar is low. Glucagon tells the liver to release glucose, stored in the liver as glycogen, into the bloodstream.

•  Diabetes, an imbalance of blood sugar levels, is the major disorder of the pancreas.

• There are two types of diabetes. Type I, and Type II diabetes.

Pancreas cont’d

• Type I diabetes occurs when the pancreas does not produce enough insulin.

• Type II diabetes occurs when the body is resistant to the insulin in the blood).

• Without enough insulin to keep glucose moving through the metabolic process, the blood glucose level rises too high.

• In Type I diabetes, a patient must take insulin shots. In Type II diabetes, a patient may not necessarily need insulin and can sometimes control blood sugar levels with exercise, diet and other medications.

• A condition called hyperinsulinism (HI) is caused by too much insulin and leads to hypoglycemia (low blood sugar).

Diagram of the Pancreas

• Pancreas

Pancreas Cont’d

• Pancreatic endocrine tissue consists of cell clusters known as islets of Langerhans. 

•  These cells produce and secrete hormones into the bloodstream.

• Two of the main pancreatic hormones are insulin and glucagon.

• These hormones work together to maintain the proper level of sugar in the blood.

•  Insulin works to lower blood sugar and glucagon works to increase blood sugar.

• When the insulin-secreting cells fail to function properly diabetes occurs

Islets of Langerhans

• The endocrine tissue of the pancreas includes the islets of Langerhans.  This area is responsible for the production and release of certain hormones into the bloodstream.  The main three types of cells that produce hormones in the islets of Langerhans are:

• Alpha cells - release the hormone glucagon, which triggers the release of glycogen form liver stores and helps to raise the level of glucose (sugar) in the bloodstream 

• Beta cells - release the hormone insulin, which help regulate carbohydrate metabolism into the bloodstream, and 

• Delta cells - release the hormone somatostatin into the bloodstream that acts as an inhibitor to the pituitary hormone called somatotropin and helps tell the body when to make other hormones like insulin, glucagon, gastrin, renin, and secretin

Islets of Langerhans

• Internal View

Pancreas

• Cross section

Diagram of Pancreas

• Showing the different sections through the pancreas

Pancreas cont’d

• Pancreatic acinar cells are functional units of the exocrine pancreas.

• They synthesize, store, and secrete inactive proforms of digestive enzymes into the lumen of the acinus.

• Pancreatic alpha-amylase breaks down starch to dextrins.

Hyperglycemia

• Hperglycemia refers to chronically high blood glucose levels. Persistent hyperglycemia can cause a wide range of chronic complications that affect almost every system in your body. When large blood vessels are affected, it can lead to:

• Stroke (cerebral vascular disease)• Heart attack or Congestive Heart Failure (coronary heart disease)• Circulation disorders and possible amputation (peripheral

vascular disease)• When smaller blood veshsels are affected, it can lead to:• Kidney disease (nephropathy)• Nerve damage (neuropathy)• Eye disease (retinopathy)

Hypoglycemia

• Hypoglycemia refers to dangerously low blood glucose levels that drop below 70 mg/dL ( this is the set point or normal levels of glucose in the human blood). 

• It is an acute complication of diabetes and occurs in individuals who use insulin or specific kinds of oral diabetes medication. Symptoms of hypoglycemia include the following:

• Sweating• Rapid pulse• Shakiness, dizziness, weakness• Decreased coordination• Difficulty concentrating• Blurred vision• Headache• Trouble performing routine tasks

Regulation of Blood Glucose

• Blood sugar levels are regulated by negative feedback in order to keep the body in homeostasis.

• The levels of glucose in the blood are monitored by the cells in the pancreas's Islets of Langerhans.

• If the blood glucose level falls to dangerous levels the Alpha cells of the pancreas release glucagon, a hormone whose effects on liver cells act to increase blood glucose levels.

• They convert glycogen into glucose (this process is called glycogenolysis).

• The glucose is released into the bloodstream, increasing blood sugar levels.

Negative Feedback

Regulation of Blood Glucose cont’d

• When levels of blood sugar rise, whether as a result of glycogen conversion, or from digestion of a meal, a different hormone is released from beta cells found in the Islets of Langerhans in the pancreas.

• This hormone, insulin, causes the liver to convert more glucose into glycogen (this process is called glycogenesis), and to force about 2/3 of body cells to take up glucose from the blood through the GLUT4 transporter, thus decreasing blood sugar.

• When insulin binds to the receptors on the cell surface, vesicles containing the GLUT4 transporters come to the plasma membrane and fuse together by the process of exocytosis and thus enabling a facilitated diffusion of glucose into the cell.

• As soon as the glucose enters the cell, it is phosphorylated into Glucose-6-Phosphate in order to preserve the concentration gradient so glucose will continue to enter the cell.

Regulation of Blood Glucose

Diagram showing how blood glucose is maintained

• Action of hormones and cells

Blood Glucose control

Blood Glucose control

Videos of Blood Glucose Regulation

Videos of Blood Glucose Regulation

Videos of Blood Glucose Regulation

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