Hormones Introduction Hormones are chemical messengers involved in cell signalling (the process of communication between cells). They travel in the blood. Most hormones are globular proteins/peptides. These hormones have receptor protein (things that detect the presence of a hormone) specific to their target tissue/organ. These hormones are produce by the endocrine system. These hormones have a slower onset of action which can last for days or even weeks. The endocrine system The endocrine system is what makes hormones. This comprises of endocrine glands as a separate organ e.g. the adrenal glands and also glands dotted about in some organs e.g. stomach. Hormones are released in response to a stimuli. This is an internal stimuli e.g. the presence of other hormones, presence of some chemicals etc. and the hormone is secreted. These are inside the body. There are three types of hormones classed in terms of their structure. These are also secreted in different ways:1. Peptides/globular proteins- This group of hormones are secreted by exocytosis e.g. insulin secretion by B cells. 2. Amines- This group is secreted by exocytosis as well at synapses e.g. the hormone adrenalin is secreted in this way. 3. Steroids- This group can diffuse out of the plasma membrane because it is a lipid derivative (made from cholesterol) e.g. the glucocorticoid cortisol secreted from the adrenal cortex. There are many endocrine glands in the human body: 1. Pituitary gland-controls all other endocrine glands but itself is under the control of the hypothalamus through its release of releasing hormones. 2. Pancreas-secrete insulin and glucagon. 3. Ovaries-secrete oestrogens. 4. Testes-secrete testosterone 5. Adrenal glands-secrete adrenalin from adrenal medulla 6. Kidney-secretes erythropoietin(EPO) 7. Thyroid gland- secrete thyroid hormones e.g. thyroxine Hormonal control Peptides/globular proteins and amine hormones have similar action at the target tissue/organ but that doesn’t mean that they have the same effects on targets. These hormones are hydrophilic. This means that they are not lipid soluble/ permeable through the phospholipid bilayer. They are also too large to pass through a channel protein. This means peptide/globular proteins have to cell signal from outside through a first/1ry and second/2ndry messenger system. E.g. the action of adrenalin(e)/epinephrine This the action of hydrophilic hormones. The hormone adrenalin is an example of a first messenger-chemicals which act to spread signal around the body. When a hormone binds to a complementary protein receptor, it activates a (trimetric) G-protein. So therefore this is an example of a G-protein coupled receptor. When a G-protein becomes activated by adrenalin, it causes the Alpha subunit of it to dissociate leaving a beta- gamma complex. It is this beta- gamma complex which activates the plasma membrane enzyme called( adenyl/adenylate/adenylyl )cyclase. This catalyses a reaction In the cytoplasm. ATP made from cellular respiration becomes the substrate and is converted to cyclic AMP/cAMP. This acts as a second messenger-chemicals which spread a signal inside a cell. Cyclic AMP acts to activate other enzymes in a metabolic pathway e.g. protein kinase A/ PKA or it acts to activate proteins which initiate transcription. Effects of adrenalin This hormone is an example which is involved in the flight or fight response. This hormone has many effects on the body, getting it prepared for stressful action:1. Makes hairs stand on end- contraction of erector (pili) muscles in the dermis act to raise hairs. This makes a person more aggressive which is the point of the response 2. Activation of glycogen phosphorylase- This enzyme converts glycogen to glucose(glycogenolysis) which then can be incorporated into glycolysis and subsequently into aerobic respiration if oxygen is available to get a lot of ATP. 3. Contraction of smooth muscle in bronchioles- This acts to increase the surface area of bronchioles so that they can allow more air in and allow more rapid gas exchange 4. Vasodilation in some organs including the brain and muscle. 5. Vasoconstriction in some organs including the gut. 6. Pupils dilate- Contraction of radial smooth muscle and relaxation of circular smooth muscle allows in the iris of the eyes to allow for far vision. 7. Increases the cardiac output/CO of the heart= stroke volume/SV x heart rate/HR. 8. Inhibits peristalsis-contractions of smooth muscle in the gastro-intestinal tract (the mouth to anus journey) 9. Increase in ventilation- There is more demand for oxygen now as there is a demand for MORE ATP through oxidative phosphorylation(where most of the ATP is produced). Adrenal medulla and cortex Adrenalin is secreted from the medulla(inner region ) of the adrenal glands. There are steroid hormones secreted from the cortex of the adrenal gland. Cortex:This region uses cholesterol to produce a variety of steroid hormones e.g.: 1. Glucocorticoids- cortisol, which controls metabolism of proteins and carbohydrates in the liver 2. Mineralocorticoids-aldosterone, which controls levels of sodium ions and potassium ions in the blood. Insulin secretion by beta cells Insulin is a globular protein secreted from beta(B) cells from the pancreas when there is an increase in blood glucose levels. The stimulus for the secretion is glucose as it can readily diffuse from the blood into a b cell (as endocrine cells are embedded in blood capillaries). This triggers some events that lead to insulin secretion. 4. 5. 6. 7. 8. 1. Embedded on the plasma membrane of a B cell are ATP-gated/sensitive potassium ions channel proteins and voltage-gated calcium ion channel proteins. 2. In the resting state (when there is a resting potential maintained), the ATP-sensitive channels remain open the voltage gated channels remain closed. 3. When there is a high concentration of glucose in the blood plasma, it readily diffuses into the b cell by facilitated diffusion through a GLUT channel Glucose is quickly metabolised in the glycolytic pathway/glycolysis to produce ATP(2 ATP per glucose molecule). Because there are ATP-sensitive potassium ion channels embedded, this leads to the closure of those channels. Now there is a depolarisation of the plasma membrane from about -70mV to -35mV. The change in voltage causes the opening of the voltage- gated calcium ion channel proteins which were closed before this point. Calcium ions diffuse down their concentration gradient into the cell where there are vesicles containing insulin made by the rough ER and packaged by the Golgi body. Calcium ions entering cause the release of insulin by exocytosis into the blood. When there is a lower concentration of glucose, insulin secretion will stop as there is less ATP made in the glycolytic pathway, therefore the ATP-sensitive channels open again.