Human Biology Bio 115
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This 12 page Class Notes was uploaded by Jasmine Ngo on Monday March 28, 2016. The Class Notes belongs to Bio 115 at Illinois Institute of Technology taught by Dr. Navaratnam in Winter 2016. Since its upload, it has received 102 views. For similar materials see Principles of Biology in Biology at Illinois Institute of Technology.
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Date Created: 03/28/16
Lecture: Endocrine System The nervous system and the endocrine system work together to regulate the activities of the other systems. Similarities of the two systems: Both systems use chemical signals when they respond to changes that might threaten homeostasis. Differences: The nervous system is organized to respond rapidly to stimuli. This is particularly useful if the stimulus is an external event that endangers our safety—we can move quickly to avoid being hurt. The endocrine system is largely composed of glands. These glands secrete hormones, carried by the bloodstream to target cells throughout the body. It takes time to deliver hormones, and it takes time for cells to respond. The effect initiated by the endocrine system is longer lasting. The endocrine system is organized for a slow but prolonged response. Endocrine glands can be contrasted with exocrine glands: Exocrine glands have ducts and secrete their products into these ducts. The glands’ products are carried to the lumens of other organs or outside the body. Endocrine glands, as stated, secrete their products into the bloodstream, which delivers them throughout the body. Only certain cells, called target cells, can respond to certain hormones. A target cell for a particular hormone will have a receptor protein for that hormone. Both the nervous system and the endocrine system make use of negative feedback mechanisms. If the blood pressure falls, sensory receptors signal a control center in the brain. This center sends out nerve signals to the arterial walls so that they constrict, and blood pressure rises. Now the sensory receptors are no longer stimulated, and the feedback mechanism is inactivated. Similarly, a rise in blood glucose level causes the pancreas to release insulin. This in turn, promotes glucose uptake by the liver, muscles, and other cells of the body. When the blood glucose level falls, the pancreas no longer secretes insulin. Functions of Hormones • Homeostasis • Growth and development • Reproduction • Energy production, storage and use • Behavior • Tropic hormones stimulate production of hormones by other endocrine gland • e.g thyroid stimulating hormone • Nontropic hormones stimulate target cells to regulate growth, metabolism, etc. most hormones act at a distance between body parts. They travel in the bloodstream fromthe gland that produced them to their target cells. However some called local hormones do not. They are not carried elsewhere in the bloodstream. Instead, they affect neighboring cells. Chemical signals that infl uence the behavior of other individuals are called pheromones. Other animals relyheavily on pheromones for communication. The term peptide hormone is used to include hormones that are peptides, proteins, glycoproteins, and modifi ed amino acids. Growth hormone is a protein produced and secreted by the anterior pituitary. Steroid hormones have the same complex of four carbon rings because they are all derived from cheolesterol Peptide Hormones Steriod Hormones Steroids act more slowly than peptides because it takes more time to synthesize new proteins than to activate enzymes already present in cells. Their action lasts longer, however. Hypothalamus and Pituitary Glands The hypothalamus regulates the internal environment through the autonomic system. The hypothalamus also controls the glandular secretions of the pituitary gland. The pituitary has two portions: the posterior and the anterior pituitary. Neurons in the hypothalamus called neurosecretory cells produce the hormones antidiuretic hormone (ADH) and oxytocin. Both of these hormones are transferred to and released by the posterior pituitary. antidiuretic hormone (ADH): regulates water content of blood via the kidney. When cells determine that the blood is too concentrated, ADH is released from the posterior pituitary. Upon reaching the kidneys, ADH causes more water to be reabsorbed into kidney capillaries. As the blood becomes dilute, ADH is no longer released. Inability to produce ADH causes diabetes insipidus. A person with this type of diabetes produces copious amounts of urine. Excessive urination results in severe dehydration and loss of important ions from the blood. The condition can be corrected by the administration of ADH. oxytocin: causes uterine contractions, stimulates milk release during nursing. As a result, oxytocin is produced by the hypothalamus and released from the posterior pituitary. It is a positive feedback Hypothalamus communicates with the AP via a “Portal System”. Portal systems consist of capillary beds that drain to a vein and then to another capillary bed. Portal system also found in liver. Hypothalamus produces releasing or inhibitory hormones which target the anterior pituitary Anterior pituitary is the "master gland": hormones from hypothalamus stimulates or inhibits corresponding systemic hormones Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to produce cortisol. Gonadotropic hormones stimulate the gonads (the testes in males and the ovaries in females) to produce gametes and sex hormones. Acromegaly: Excess Growth Hormone as an adult causes enlargement of bones in face and extremities Too little thyroxin: Conditions such as goiter, cretinism , myxedema (mental retardation) In simple goiter, thyroid enlarges to try to make more thyroxin Too much thyroxin: "Graves's disease"--Hyperactivity insomnia, irritability 2+ Thyroid also produces calcitonin --inhibits osteoclasts, increases Ca deposition in bone by osteoblasts. Not under control of anterior pituitary. Parathyroid Gland: 4 glands embedded in posterior surface of thyroid Produces parathyroid hormone (PTH) 2+ As more PTH released blood [Ca ] rises 2+ PTH targets the digestive tract to absorb more Ca ; Kidneys retain more Ca 2+ Demineralization of bone (stimulus of osteoclasts) Untreated hyperparathyroidism (oversecretion of PTH) can result in osteoporosis because of continuous calcium release from the bones. Hyperparathyroidism may also cause formation of calcium kidney stones. Located at the top of kidneys; consist of cortex and medulla Medulla produces epinephrine & norepinephrine (adrenalin, noradrenalin) => "fight or flight" response Not under control of Anterior pituitary Increased levels of epinephrine and norepinephrine result in: rise in [blood glucose], metabolic heart rate increased respiration, increased blood supply to muscles => increased muscle stamina Two Hormones produced by adrenal cortex: The glucocorticoids, or cortisol whose secretion is controlled by ACTH, regulate carbohydrate, protein, and fat metabolism. The result of the actions of the glucocorticoids is an increase in blood glucose level. Glucocorticoids also suppress the body’s infl ammatory response. Glucocorticoids raise the blood glucose level in at least two ways: (1) They promote the breakdown of muscle proteins to amino acids, taken up by the liver from the bloodstream. The liver then converts these excess amino acids to glucose, which enters the blood. (2) They promote the metabolism of fatty acids rather than carbohydrates, and this spares glucose. The mineralocorticoids regulate water and salt balance, leading to increases in blood volume and blood pressure. Aldosterone is the most important of the mineralocorticoids. Aldosterone primarily targets the kidney, where it promotes renal absorption of sodium (Na+) and renal excretion of potassium (K+). The secretion of mineralocorticoids is not controlled by the anterior pituitary. When the blood Na+ level and, therefore, the blood pressure are low, the kidneys secrete renin. Renin is an enzyme that converts the plasma protein angiotensinogen to angiotensin I. Angiotensin I is changed to angiotensin II by a converting enzyme found in lung capillaries. Angiotensin II stimulates the adrenal cortex to release aldosterone. The effect of this system, called the renin-angiotensin- aldosterone system, is to raise blood pressure in two ways. Angiotensin II constricts the arterioles, and aldosterone causes the kidneys to reabsorb Na+. When the blood Na+ level rises, water is reabsorbed, in part, because the hypothalamus secretes ADH. Reabsorption means that water enters kidney capillaries and thus the blood. Then blood pressure increases to normal. Addison Disease: Low levels cortisol ---> low [blood glucose] Low levels of aldosterone --> low blood pressure low blood pH, susceptible to stress, bronze skin color Cushing Disease: High levels of cortisol can lead to diabetes mellitus less muscle protein, increased subcutaneous fat High levels aldosterone ---> high blood pressure trunk obese, edema of face (moon face); arms, legs normal Pancreas: Insulin is secreted after eating – Stimulates uptake and metabolism of glucose by liver, muscle and fat tissue – Stimulates liver and muscle to store glucose as glycogen – Promotes buildup of fats and proteins and inhibits their use for catabolism. – Blood [glucose] drops Glucagon is secreted between meals • Opposes action of insulin • Promotes breakdown of stored nutrients; blood [glucose] rises Diabetes: • Low blood volume and acidosis --> Blindness, kidney disorders, coma and death • Type I - Insulin dependent diabetes: -no insulin produced: This condition is believed to be brought on by exposure to an environmental agent, most likely a virus, whose presence causes cytotoxic T cells to destroy the pancreatic islets. The body turns to the metabolism of fat, which leads to the buildup of ketones in the blood and, in turn, to acidosis (acid blood), which can lead to coma and death. -Insulin must be provided by injection Type II -Insulin Independent diabetes : -Pancreas produces insulin but cells unresponsive -Found in obese and inactive people. -Prevention by low fat diet, exercise best Other Endocrine Glands: Thymus : Located in the chest Thymosins are hormones that promote T-cell maturation and other immune cells T-cells mature in thymus Pineal Gland (in brain): Produces hormone called melatonin Responsible for circadian rhythms Melatonin high --> sleepiness Prostaglandins: A large class of hormones that are produced and act locally in response to other hormones or to trauma; various effects on many tissues Some menstrual disorders - prostaglandins - treated anti- prostaglandin drugs