Human Endocrine System

Human Endocrine System The endocrine system consists of ductless glands that produce hormones Hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, ovary, testes Hormones are chemical messengers that travel through the blood stream and affect activities throughout the body. Steroid hormones Nonsteroid hormones Human Endocrine System Glands produce and release secretions. Endocrine glands (ductless) produce chemical substances called hormones and release them into the bloodstream. These glands include the hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, ovary and testes. Exocrine glands deliver secretions through a duct or tube to specific locations (salivary glands, sweat glands, mucous glands). Hormones are chemical messengers that bind to target cells and affect cell activities. In general, the response of the body to hormones is slower and more long lasting than the response to nerve impulses. The release of hormones is controlled through a negative feedback system. Negative feedback systems are control mechanisms that operate by inhibiting a process or activity that originally led to starting the process or activity. For example, as glucose levels in the body increase, sensors in the pancreas signal the release of the hormone insulin. Insulin promotes the entry of glucose into cells, lowering glucose levels. As the glucose levels in the blood decrease, the pancreas stops secreting insulin. Steroid hormones are produced from the lipid, cholesterol and are able to pass through cell membranes and bind to receptor proteins. Nonsteroid hormones are made from amino acids and generally cannot pass through the cell membrane. These hormones bind to a receptor site on the outside of a cell in order to initiate chemical reactions inside the cell. References: Campbell, N.E. & Reece, J.B. (2002). Biology,(6th ed.). San Francisco: Benjamin Cummings. Raven, P.H. & Johnson, G.B. (2002). Biology, (6th ed.). McGraw-Hill.

Hormones Hormones are chemical messengers that bind to target cells and affect cell activities Nonsteroid hormones are made from amino acids and generally cannot pass through the cell membrane. These hormones bind to a receptor site on the outside of a cell in order to initiate chemical reactions inside the cell. Steroid hormones are produced from the lipid, cholesterol and are able to pass through cell membranes and bind to receptor proteins.

Nonsteroid hormones – cannot go through cell membrane, must activate proteins in the cell membrane Steroid hormones – can go through cell membrane to reach receptors inside the cell

Hormones have specific shapes that fit receptors or the surface of the target organ or structure they are going to influence Bind with cell receptors If incorrect receptor the particular hormone has no effect

The Brain Pituitary gland biology Animation Endocrine Glands biology Animation Section 35-3 Pons Pituitary gland Hypothalamus Cerebrum Medulla oblongata Spinal cord Cerebellum Pineal gland Thalamus

The Endocrine Glands Section 39-1 Hypothalamus The hypothalamus makes hormones that control the pituitary gland. In addition, it makes hormones that are stored in the pituitary gland. Pineal gland The pineal gland releases melatonin, which is involved in rhythmic activities, such as daily sleep-wake cycles. Thyroid The thyroid produces thyroxine, which regulates metabolism. Pituitary gland The pituitary gland produces hormones that regulate many of the other endocrine glands. Pancreas The pancreas produces insulin and glucagon, which regulate the level of glucose in the blood. Parathyroid glands These four glands release parathyroid hormone, which regulate the level of calcium in the blood. Ovary The ovaries produce estrogen and progesterone. Estrogen is required for the development of secondary sex characteristics and for the development of eggs. Progesterone prepares the uterus for a fertilized egg. Thymus During childhood, the thymus releases thymosin, which stimulates Tcell development. Testis The testes produce testosterone, which is responsible for sperm production and the development of male secondary sex characteristics Adrenal glands The adrenal glands release epinephrine and nonepinephrine, which help the body deal with stress.

Glands I Hypothalamus – coordinates activities of the nervous and endocrine systems and produces hormones to regulate the pituitary gland Pituitary – produces hormones that direct the activities of other endocrine glands Pineal – releases melatonin which is involved in rhythmic or cyclic activities Thyroid – produces hormones that regulate metabolism and development Parathyroid – helps maintain appropriate calcium levels

Glands II Thymus – involved with immune development during childhood Adrenal – regulates the body’s stress response (epinephrine, norepinephrine, cortisol, aldosterone) Pancreas – controls glucose levels in the blood (insulin, glucagon) Ovary – secretes estrogen and progesterone to regulate reproduction Testes – produces testosterone to control formation of sperm and sexual behavior

Negative Feedback The level of one hormone in the blood inhibits or stimulates the production of another hormone or substance Homeostasis biology Animation

CONTROL OF THE ENDOCRINE SYSTEM REGULATED BY FEEDBACK MECHANISMS EX: HEATING SYSTEMS

Negative Feedback The release of hormones is controlled through a negative feedback system Negative feedback systems are control mechanisms that operate by inhibiting a process or activity that originally led to starting the process or activity For example, as glucose levels in the body increase, sensors in the pancreas signal the release of the hormone insulin Insulin promotes the entry of glucose into cells, lowering glucose levels As the glucose levels in the blood decrease, the pancreas stops secreting insulin.

Actions of Insulin and Glucagon Section 39-2 Beta cells release insulin into the blood Body cells absorb glucose Blood glucose level increases Liver converts glycogen to glucose Blood glucose level decreases Homeostasis: Normal blood glucose level Blood glucose level increases Blood glucose level decreases Liver converts glycogen to glucose Alpha cells release glucagon into blood

Disorders Goiter Grave’s Disease Diabetes Enlargement of the thyroid gland due to the inability to manufacture thyroxin (hypothyroidism) Grave’s Disease Hyperthyroidism- over secretion of thyroxin Diabetes Insulin deficiency which results in elevated blood sugar level

Symptoms of Diabetes Excessive thirst Frequent urination Extreme hunger Unexplained weight loss Glucose in urine Fatigue Vision problems Numbness tingling in extremities High infection rate

Calcium and glucose levels Concept Map Section 39-2 The Endocrine System regulates Growth Water balance Reproduction Metabolism Calcium and glucose levels Response to stress by means of the by means of the by means of the by means of the by means of the by means of the Pituitary Ovaries Testes Thyroid Pancreas Adrenals Parathyroids