The Endocrine System Aims: Must be able to outline the main components of the endocrine system and their roles. Should be able to explain how hormones are specific. Could be able to give specific examples of the endocrine system in homeostatic control.

The Endocrine System consists of a number of endocrine glands which produce hormones. Endocrine glands contain no ducts. When stimulated - release hormones into the interstitial fluid. One of the most important glands is the Hypothalamus, a region of the brain

The Hypothalamus The hypothalamus is a region within the brain. It produces some hormones itself, and also produces inhibiting and releasing hormones which control the release of other hormones

Questions Answer the questions on pages 60 and 61 in the Biozone book.

Endocrine Glands – Pituitary Glands Close to the brain are the anterior and posterior lobes of the pituitary gland. The anterior lobe produces a large number of hormones related to growth and regulation. The posterior lobe acts as a reservoir for the hormones produced by the hypothalamus (ADH and oxytocin*) *Oxytocin is the hormone that triggers uterine muscle contractions during childbirth. This system is regulated by Positive Feedback, where the effect of the stimulus is increased (ie: oxytocin causes muscle to contract, causing the cervix to stretch, which signals the release of more oxytocin)

Hormones Hormones are chemicals involved in the regulation of many body processes. Chemically, they can be fatty acids, peptides, or simple chemicals based on 1-2 amino acids. All Hormones: –Are produced in endocrine glands –Travel in the general circulation or extra-cellular fluids –Exert an effect on specific body tissues, often referred to as Target tissues

Hormones Hormones are concerned with: Long term development of an organism (eg: growth hormones and hormones involved in the development of sexual characteristics) Regulating metabolism and cell function Regulating the body’s concentrations of sugars, calcium and other chemicals Some hormones NEVER enter the blood but act on the same cells that produce them or are secreted into extra-cellular fluid to work on adjacent cells.

Target Tissues The cell that has the receptor for a certain hormone is the 'target cell' of the hormone. The organ that has a lot of target cells is a target organ. The hormone effects only the cells that have the receptor to a certain hormone.The hormone effects only the cells that have the receptor to a certain hormone.

Different Hormones – Different Kinds of Chemicals The chemical nature of the hormone influences the way it interacts with the target cells. There are three different kinds of hormones based on their chemical structures: –Amino Acid derivitives –Steroid Hormones –Protein and Peptide Hormones For each of these state their chemical nature and their features, and give examples (p146).

Different Hormones – Differences in Cell Signalling The differences between different types of hormone: These differences in hormone signalling molecules that result in different mechanisms of transmission inside the cell Amino Acid Derivatives and Protein and Peptide Hormones Steroid Hormones Soluble in WaterInsoluble in Water Unable to pass through cell membrane Able to pass through cell membrane

Position of Cell Receptors Steroid Hormones – Receptors below surface of cell membrane in cytosol – steroid hormones call pass through cell membrane. Water Soluble – Receptors on surface of cell membrane – Unable to pass through cell membrane – receptors activate another protein in the cytosol, acting as a second messenger in the signal pathway. Diagram p147.

After Signal Enters the Cell A cascade of events begins triggered by the initial hormone. Events involve proteins and lead to a biological response relevant to the original signal. Cell converts one form of signal to another by relay molecules – SIGNAL TRANSDUCTION. Original signal is amplified to induce a reaction that involves many substrates. Responses to signals include: –Activation of DNA – Production of Protein, Enzymes –Production of another hormone

Questions Answer the questions on pages 64 and 65 in the Biozone book.

Glucose Regulation The concentration of glucose in the blood is under homeostatic control. The brain is highly sensitive to fluctuations in the blood glucose level, needing a constant and regular glucose supply to maintain function. The body derives glucose from several sources: –Taken up from food in the gut, either directly as glucose or after more complex carbohydrates have been digested into glucose and other simple sugars. –Synthesised from other energy sources, mainly in the liver, in a process known as gluconeogenesis. –Glucose is stored in the liver, muscles, and other tissues in the form of glycogen. On demand, glycogen is broken down into glucose and secreted into the bloodstream

Controlled by Hormones –Blood glucose levels are controlled by two hormones, both produced by the Pancreas: –Insulin : which acts to reduce blood glucose levels. Insulin is synthesised and secreted only in the beta or islet cells of the pancreas. It lowers the blood glucose level by: –Facilitating the uptake of glucose from blood by all cell types. –Reducing gluconeogenesis. –Encouraging the storage of glucose in the form of glycogen. –Glucagon: which acts to increase blood glucose levels

The Pancreas The Pancreas of mammals contains specialised endocrine cells, present in clusters known as Islets of Langerhans. These clusters are responsible for the production of insulin and glucagon. Islets of Langerhans contains 2 types of endocrine cells: Alpha cells – Production of Glucagon Beta Cells – Production of Insulin These cells also act as Receptors for blood glucose levels

Controlling Blood Glucose

Stimulus-Response Diagram Blood Glucose levels Rises Receptor Islets of Langerhans Beta cellsAlpha Cells Decreased production Of glucagon Effector Liver and skeletal muscle Increased production Of insulin Effector Liver and skeletal muscle Response Cells take up glucose from the blood and store it as Glycogen, and they stop breaking down glucose Blood Glucose Level Falls Beta cells Receptor Islets of Langerhans Alpha Cells Decreased production Of insulin Effector Liver and skeletal muscle Effector Liver and skeletal muscle Increased production Of glucagon Response Glycogen is broken down and glucose returned to Blood. Uptake of glucose by cells is reduced.