Transcript File
UNIT 4 Chapter 9: The Endocrine System Section 9.2 9.2 Hormonal Regulation of Growth, Development, and Metabolism Hormones secreted from the pituitary gland are mainly involved in growth and development. Hormones secreted from the thyroid gland are mainly involved in regulating metabolic rate. UNIT 4 Chapter 9: The Endocrine System Section 9.2 The Pituitary Gland The pituitary gland has two lobes (posterior pituitary and anterior pituitary) and is about the size of a pea (1 cm). It is located below the hypothalamus at the base of the brain. The pituitary gland secretes hormones involved in the body’s growth, development, metabolism, reproduction, and other essential life functions. Continued… UNIT 4 Chapter 9: The Endocrine System Section 9.2 The Pituitary Gland The posterior pituitary gland is part of the nervous system. It stores and secretes the hormones antidiuretic hormone (ADH) and oxytocin, which are produced in the hypothalamus. Continued… UNIT 4 Chapter 9: The Endocrine System The Pituitary Gland The anterior pituitary gland produces and secretes six major hormones. Section 9.2 UNIT 4 Chapter 9: The Endocrine System Section 9.2 Human Growth Hormone The anterior pituitary gland regulates growth, development, and metabolism through the production and secretion of human growth hormone (hGH). This hormone affects almost every body tissue. Growth factors from the liver and hGH increase the following processes: • • • protein synthesis cell division and growth breakdown and release of fats in adipose tissue The targets of hGH include the liver, muscle cells, and bone cells. Continued… UNIT 4 Chapter 9: The Endocrine System Section 9.2 Human Growth Hormone Human growth hormone stimulates the growth of muscles, connective tissue, and bones. If the pituitary gland secretes excess amounts of hGH during childhood, it can result in gigantism. Insufficient hGH production results in pituitary dwarfism. (A) The world’s tallest man stands 2.36 m in height. His wife is 1.68 m tall. (B) People with pituitary dwarfism have typical body proportions. Continued… UNIT 4 Chapter 9: The Endocrine System Section 9.2 Human Growth Hormone Overproduction of hGH in adulthood can lead to acromegaly. Since skeletal growth has been completed in adulthood, hGH can no longer cause an increase in height. Instead, there is widening of the bones and soft tissues of the body. Acromegaly results from excessive production of hGH during adulthood. It may be difficult to diagnose the condition in the early stages before a person’s appearance noticeably changes. UNIT 4 Chapter 9: The Endocrine System Section 9.2 The Thyroid Gland The thyroid gland is known as a “metabolic thermostat” because the hormones it secretes regulate metabolic rate. The thyroid gland lies below the larynx and has two lobes. It produces and secretes thyroxine (T4), a hormone that increases the rate at which the body metabolizes fats, proteins, and carbohydrates for energy. Thyroxine stimulates cells in the heart, skeletal muscles, liver, and kidneys to increase cellular respiration. Continued… UNIT 4 Chapter 9: The Endocrine System Section 9.2 The Thyroid Gland Low production of thyroxine is called hypothyroidism and can result in cretinism. Individuals with cretinism are stocky and shorter than average. Hormonal injections are required in childhood so that mental development delays do not occur. Adults with hypothyroidism experience fatigue and weight gain due to a slow metabolism. Overproduction of thyroxine is called hyperthyroidism. Symptoms include anxiety, insomnia, and weight loss. It can result in Graves’ disease, where the immune system attacks the thyroid gland. Hyperthyroidism can be treated with medication or removal of part of the thyroid gland. Continued… UNIT 4 Chapter 9: The Endocrine System Section 9.2 The Thyroid Gland Thyroxine secretion is controlled by negative feedback. (1) The hypothalamus secretes a releasing hormone that stimulates the anterior pituitary gland. (2) The anterior pituitary releases TSH into the bloodstream. (3) TSH targets the thyroid gland. (4) TSH causes the thyroid to secrete thyroxine into the bloodstream. Thyroxine stimulates increased cellular respiration in target cells throughout the body. (5) High levels of thyroxine cause negative feedback on the pituitary and hypothalamus, shutting down production of TSH. Continued… UNIT 4 Chapter 9: The Endocrine System Section 9.2 The Thyroid Gland The thyroid gland requires iodine to make thyroid hormones. If there is insufficient iodine in the diet, thyroxine cannot be made, and there will be no signal to stop TSH secretion. Constant stimulation of the thyroid gland by TSH causes a goitre, which is an enlargement of the thyroid gland. In Canada, it is uncommon for people to have goitres because iodine is added to table salt. Other dietary sources of iodine include seafood and dairy products. UNIT 4 Chapter 9: The Endocrine System The Parathyroid Gland and Calcium Homeostasis Calcium is an essential mineral for nerve conduction, muscle contraction, skeletal development, and healthy teeth. Calcium levels in the blood are regulated in a negative feedback system by two hormones: calcitonin and parathyroid hormone (PTH). When blood calcium levels are too high, the thyroid gland secretes calcitonin to promote uptake of calcium by the bones. Section 9.2 UNIT 4 Chapter 9: The Endocrine System Calcium Homeostasis When blood calcium levels are low, the parathyroid glands release PTH. PTH stimulates bones to break down bone material and secrete calcium into the blood. PTH also stimulates the kidneys to reabsorb calcium from the urine. This activates vitamin D, which stimulates the absorption of calcium from the digestive tract. Section 9.2 UNIT 4 Chapter 9: The Endocrine System Section 9.3 9.3 Hormonal Regulation of the Stress Response and Blood Sugar What happens to your body when you experience stress? The endocrine system helps you cope with stressful situations. The stress response involves many interacting hormone pathways, including those that regulate metabolism, heart rate, and breathing. UNIT 4 Chapter 9: The Endocrine System Section 9.3 The Adrenal Glands The adrenal glands are a pair of organs involved in regulating the stress response and blood sugar levels. Each adrenal gland is composed of two layers: • the adrenal medulla (inner layer) • the adrenal cortex (outer layer) Each layer produces different hormones and functions as an independent organ. UNIT 4 Chapter 9: The Endocrine System Section 9.3 The Adrenal Medulla: Regulating the Short-Term Stress Response The adrenal medulla secretes two hormones: epinephrine and norepinephrine. These hormones regulate a short-term stress response that is also known as the fight-or-flight response. In response to a stressor, the following events occur in the short-term stress response: • Neurons in the sympathetic nervous system carry a signal from the hypothalamus to the adrenal medulla. Continued… UNIT 4 Chapter 9: The Endocrine System Section 9.3 The Hormones of the Pancreas The pancreas functions in both the digestive and endocrine systems. There are over 2000 clusters of endocrine cells, called the islets of Langerhans, scattered throughout the pancreas. These cells secrete the following hormones: • • insulin (secreted by beta cells) lowers blood glucose by making target cells more permeable to glucose glucagon (secreted by alpha cells) increases blood glucose by stimulating the liver to convert glycogen to glucose Both hormones are regulated by negative feedback loops. Continued… UNIT 4 Chapter 9: The Endocrine System Section 9.3 The Hormones of the Pancreas (A) The silhouette shows the location of the pancreas in the human body. (B) A close-up view of the pancreas shows one of the many islets of Langerhans on the surface of the pancreas. Continued… UNIT 4 Chapter 9: The Endocrine System The Hormones of the Pancreas Negative feedback regulates blood glucose levels within a very narrow range. Section 9.3 UNIT 4 Chapter 9: The Endocrine System Section 9.3 The Effects of Glucose Imbalance Diabetes mellitus is a condition that results when the body does not produce enough insulin or does not respond properly to insulin. Glucose stays in the blood after meals instead of entering the cells; as blood glucose levels rise after meals and stay high, the result is high blood sugar (hyperglycemia). Without glucose inside the cells, an individual becomes fatigued and begins using fat and protein for metabolic energy. The kidneys cannot reabsorb the excess glucose, so glucose is excreted in the urine. Over the long term, permanent damage occurs to the eyes, nerves, and kidneys. Severe infection (gangrene) can occur in the limbs. UNIT 4 Chapter 9: The Endocrine System Section 9.3 Causes of Diabetes There are two major types of diabetes: • Type 1: The immune system attacks and destroys the insulin-producing beta cells in the pancreas. People with type 1 diabetes are diagnosed in childhood and need daily insulin injections. • Type 2: Insulin receptors on the body’s cells stop responding to insulin. People who are overweight have a greater chance of developing this condition. It is usually diagnosed in adulthood and can be controlled with diet, exercise, and oral medications. A light micrograph of pancreatic beta cells from someone with type 1 diabetes. Many of the beta cells have been destroyed, leaving behind only non-beta cells (stained purple), and so the islet is malformed. UNIT 4 Chapter 9: The Endocrine System Section 9.3 Toward a Cure for Diabetes In 1921, Canadian scientists Frederick Banting and Charles Best were the first to isolate insulin and use it successfully to treat a person with diabetes. Today, transgenic bacteria are used to produce synthetic insulin in large quantities for diabetes treatment. Successful islet cells transplants have also been performed to restore beta cell function. A continuous blood glucose monitor and insulin pump. The pump releases small amounts of insulin throughout the day, which minimizes the need for insulin injections.