HORMONES 2.1

nervous system exerts control by transmission of nerve impulses to and from various tissues

endocrine system influences activity of cells by the release of chemical messengers (hormones)

maintaining a stable internal environment

exocrine glands: secrete into a duct that carries the secretion to the body surface or to one of the body cavities. e.g. sweat glands, mucous glands, salivary glands, glands of alimentary canal

endocrine glands: secrete hormones into extracellular fluid that surrounds the cells that make up the gland. The secretion then usually passes into the capillaries to be transported by the blood. Endocrine glands are sometimes called ductless glands

<p>-chemicals, secreted by endocrine glands, that are transported throughout the body in the blood. -they change the functioning of cells by changing the type, activities or quantities of proteins produced</p> Signup and view all the answers

<p>-activate certain genes in nucleus so that a particular enzyme or structural protein is produced -change the shape or structure of an enzyme so that it is turned on or off -change the rate of production of an enzyme or structural protein by changing the rate of transcription or translation during protein production</p> Signup and view all the answers

<p>-all cells of body -particular groups of cells (target cells) -particular organs (target organs)</p> Signup and view all the answers

<p>-in blood, hormones bind to transport proteins, so can travel in blood stream -when they reach the target cells, the steroid hormones separate from transport proteins and diffuse across cell membrane -inside cell, they work by combining with a receptor in cytoplasm or nucleus -hormone-receptor complex activates genes controlling formation of particular proteins -does this by binding to promotor section of a certain gene, stimulating (or inhibiting) transcription and, therefore, protein synthesis -steroid hormones are slow to have an effect, but the effect is long lasting</p> Signup and view all the answers

<p>-they attach to receptor proteins in the membrane of the target cell -combination of hormone with receptor causes a secondary messenger substance to diffuse through the cell and activate particular enzymes -e.g. hormone insulin binds to receptor protein and this leads to increase in glucose absorption by cell -protein and amine hormones cause quick response but short lasting</p> Signup and view all the answers

<p>-each cell has limited number of receptor proteins -each receptor is specific to one type of molecule -once all receptor sites are occupied, the cell reaches saturation, meaning that no additional increase in the hormone will further enhance the cell's activity -for instance, when all insulin receptors are bound to insulin, the cell's rate of glucose uptake cannot increase further, even if insulin is present</p> Signup and view all the answers

<p>-enzyme amplification enables a single hormone molecule to trigger a cascade of reactions, significantly the number of molecules activated at each step -this cascading effect means that a single hormone can trigger the production of billions of enzyme molecules, allowing a small stimulus to create a large effect in the cell -this amplification is crucial for cells to respond effectively to low concentrations of hormones</p> Signup and view all the answers

<p>-by breaking down the hormone molecules -some hormones are broken down in target cells, but most are broken down in the liver and the kidneys -degraded hormones are then secreted in either the bile or urine</p> Signup and view all the answers

<p>-by negative feedback systems, where response produced by secretion of hormone is opposite of the stimulus that caused the secretion</p> Signup and view all the answers