The Endocrine System CHEMICAL COMMUNICATION The Endocrine System

The Endocrine System CHEMICAL COMMUNICATION

The Endocrine System Endocrine system: secretes hormones in the human body to maintain homeostasis Major glands: pituitary, thyroid, parathyroid, adrenal, pancreas, pineal, thymus, testes, ovaries

Hormones Hormone: a chemical messenger that carries a signal from an endocrine gland to regulate the function of a target cell 2 Types: ◦ Steroid hormones: made from cholesterol (are lipids), water insoluble, diffuse easily into cell ◦ Non-steroid hormones: made from amino acids (are proteins), bind to receptors on cell membrane Hormone secretion is controlled by negative feedback mechanisms

Pituitary Gland Hormone release is controlled by the hypothalamus 2 Parts: anterior and posterior pituitary Anterior Pituitary Hormones: ◦ Growth Hormone (GH): regulates cell division ◦ Prolactin (PRL): regulates milk production in females after childbirth ◦ Follicle-stimulating hormone (FSH) and luteinizing hormone (LH): act on testes and ovaries

Pituitary Gland, Cont’d Posterior Pituitary hormones: ◦ Antidiuretic hormone (ADH): decreases urine production; too little water in the bloodstream triggers release and less urine, too much water stops release and more urine is produced ◦ Oxytocin (OT): contracts smooth muscle in walls of uterus; stimulates uterine contractions in childbirth (Positive Feedback Loop!)

Thyroid Gland Action is controlled by hormones in pituitary gland Important Hormones: ◦ Thyroxine: regulates metabolism of carbohydrates, lipids, and proteins; Determines basal metabolic rate (BMR)- how many calories you burn at rest ◦ Calcitonin: regulates concentration of blood calcium

Parathyroid Glands 4 located on thyroid gland Secretes parathyroid hormone (PTH) PTH regulates blood calcium and blood phosphate concentration

Adrenal Glands Action controlled by hormones in pituitary gland Hormones: ◦ Epinephrine (adrenalin) and norepinephrine: increase breathing rate, heart rate, blood pressure, blood glucose level ◦ Aldosterone: regulates Na+ and K+ levels in body ◦ Cortisol: affects glucose metabolism

Pancreas Insulin: lowers blood glucose levels, stimulates products of glycogen (sugar storage) Glucagon: stimulates breakdown of glycogen, elevates blood glucose levels Diabetes: body loses ability to regulate blood glucose levels ◦ Type 1: immune system destroys cells in pancreas, no more insulin produced ◦ Type 2: pancreas produces insulin, body cells don’t recognize it.

Other Glands Pineal Gland ◦ Melatonin: sleep hormone, released in response to darkness, enables body to distinguish day and night Thymus Gland ◦ Thymosins: affect production of white blood cells

Feedback Systems CONNECTING ELECTRICAL AND CHEMICAL COMMUNICATION IN YOUR BODY

What is Feedback? Feedback is the process in which part of the output of a system is returned to its input in order to regulate its further output. Your body has POSITIVE and NEGATIVE feedback systems to maintain homeostasis.

Negative Feedback Negative feedback occurs when the output of a system acts to oppose changes to the input of the system. A thermostat is an example of a negative feedback system.

Room temp increases Room temp is below the setpoint Set point is reached Goal: Maintain Stable Temperature! Set point is reached Room temp decreases Room temp is above the setpoint

Negative Feedback in Biology Negative feedback also regulates many systems in organisms. The endocrine system has many examples! This diagram shows a negative feedback loop for stress hormones. Areas of negative feedback are indicated with a minus sign, (-).

Endocrine System <3 Nervous System! The brain continuously sends signals to the endocrine glands to secrete and release hormones and the glands, in turn, send feedback to the nervous system. The hypothalamus in the brain is the master switch that sends signals to the pituitary gland which can release up to eight hormones into the bloodstream. The hormone travels to its target organ and usually results in the release of another hormone into the bloodstream.

Endocrine System The hypothalamus then detects the rising hormone levels from the target organ and decreases the release of hormones from the pituitary which results in a decrease in hormone release from the target organ. The process of maintaining normal body function through negative feedback mechanisms is called homeostasis.

Negative Feedback Example: Glucose and Insulin Pancreas Glucose intake occurs during digestion of food that is needed for energy expenditure to perform routine physical activities. The pancreas is the key organ that regulates the glucose levels in body by secreting two hormones, insulin and glucagon. The liver also helps to store the excess glucose in form of glycogen to be utilized later. Liver

Glucose and Insulin Negative Feedback Loop Eating cake Increases Glucose Levels (-) Lowers Blood Glucose levels CYCLE 1 Insulin stimulates the cells to take up glucose from the blood. Stimulates β cells of pancreas to secrete insulin

CYCLE 2 Low Blood Glucose Levels (-) High blood glucose levels and Cycle 1 continues Stimulated Alpha Cells in Pancreas Glucagon is released Glucagon stimulates liver cells to release glucose into the blood

Glucose and Insulin Negative Feedback Loop Two primary Hormones Insulin Lowers Blood Glucose Levels Glucagon Raises Blood Glucose Levels The opposite actions of these two hormones, insulin and glucagon, helps to maintain normal blood sugar levels in the body hence maintain homeostasis of the body.

Feedback Check-up. . ◦ What is a feedback and an example of a negative AND positive system? ◦ What is the endocrine system and why is it important? ◦ Define homeostasis and how normal body function is maintained with feedback mechanisms.

Kidneys and Water Regulation The kidneys play a key role in maintaining water regulation. Renal Cortex Renal Medulla

Kidney and Water Regulation The nephron is the most important functional part of the kidney. It filters nutrients like salts and amino acids in the Bowman’s capsule into ascending loop and filters the urine.

Kidney and Water Regulation Anti-Diuretic Hormone, ADH (also called vasopressin), is secreted by the pituitary gland acts on the nephron to conserve water and regulate the tonicity of body fluids. Anti. Diuretic Hormone ADH acts on Nephron to reabsorb water and decrease blood osmolality (saltiness)

Your Turn! Draw a Negative Feedback loop that demonstrates how your kidneys, blood, and brain work together to regulate the amount of water in your body. Include these terms: ADH Nephron Distal Collecting Tubules Osmoreceptors Hypothalamus Pituitary Gland Concentrated Urine Dilute Urine Permeability

ADH regulated water conservation in kidneys Excess water Less water in the blood Stimulates osmoreceptors in hypothalamus to send signals to the pituitary gland Pituitary glands secretes high levels of ADH Pituitary glands secretes low levels of ADH makes the tubules more permeable and more water is reabsorbed back into the bloodstream (urine is concentrated). Less ADH makes the tubules less permeable and less water is reabsorbed back into the bloodstream (urine is dilute).

ADH regulated water conservation in kidneys Osmoregulators send negative feedback to the hypothalamus about the concentration of water in the bloodstream. The hypothalamus then stimulates the pituitary glands to secrete high or low concentrations of antidiuretic hormone. ADH then makes the tubules more or less permeable and hence, maintains water and electrolyte homeostasis.

Positive Feedback Loops A positive feedback loop occurs when the output of a system acts to enhance the changes to the input of the system. One example of a biological positive feedback loop is the onset of contractions in childbirth. ◦ When a contraction occurs, the hormone oxytocin is released into the body, which stimulates further contractions. ◦ This results in contractions increasing in amplitude and frequency.

Positive Feedback Another example is blood clotting. ◦ The loop is initiated when injured tissue releases signal chemicals that activate platelets in the blood. ◦ An activated platelet releases chemicals to activate more platelets, causing a rapid cascade and the formation of a blood clot. Lactation involves positive feedback so that the more the baby suckles, the more milk is produced.

Positive Feedback In most cases, once the purpose of the feedback loop is completed, counter-signals are released that suppress or break the loop. ◦ Childbirth contractions stop when the baby is out of the mother's body. ◦ Chemicals break down the blood clot. ◦ Lactation stops when the baby no longer nurses.