Topic 6 - Homeostasis

Homeostasis is the maintanence of a constant internal environment inside or outside cells.

• temperature • oxygen levels • water levels • tissue fluid • composition of blood

Homeostasis is essential to maintain warer potential and also give cells a constant supply of glucose for respiration

Stops organisms being reliant on external environments so therefore they have a wider choice of where to live

Enzymes are sensitive to temperature and PH changes. Big changes could lead to denaturation and stops reactants working

Changing the water potential in blood and tissure fluid. It could make cells shrink or even burst. Which could prevent cells from operating normally.

• the set point optimum (normal) • receptor (detects variation) • controller (cooordinates info and sends instructions) • effector (brings about changes) • feedback loop (tells receptor about changes)

Changes can be detected by a number of different receptors. This gives the brain a better picture of what is being altered. So allows a more informed response to be made

Body temperature is optimum for enzymes. Excess heat denatures enzymes so substrate cannot bind. Therefore reactions are ceased/slowed. Too little reduced kinetic energy so therefore fewer collisisons

Thermoregulation of core body temperature. If there is a change in temperature the body responds by reversing the change if returning to a normal level.

Negative feedback is when any deviation from the normal values are restored to their original level. This involves the nervous system and often hormones too. Eg blood glucose increases following ingestion of food or drink containing carbohydrates and will fall following exercise or if you have not eaten.

The pancreas detects changes in the blood glucose levels. It contains endocrine cells in the Islets of Langerhans which release the hormones insulin and glucagon to bring blood glucose levels back to normal. Islets of langerhans are mainly alpha and beta cells.

Adrenaline is released by adrenal glands when your body anticipates danger and this results in more glucose being released from stores of glycogen in the liver.

The process of excess glucose being converted to glycogen when blood glucose is higher than normal. This occurs mainly in the liver.

The hydrolysis of glycogen back into glucose in the liver. This occurs when blood glucose levels are lower than normal.

The process of creating glucose from non-carbohydrate stores in the liver. This occurs if all glycogen has been hydrolysed into glucose and your body still needs more glucose.

Beta cells in the islets of Langerhans detect when blood glucose levels are too high and secrete insulin in response to this. Insulin will decrease blood glucose in the following ways: • Attaching to receptors on the surfaces of target cells. This changes the tertiary structure of the channel protein resulting n more glucose being absorbed by facilitated diffusion. • More protein channels are incorporated into cell membranes so that more glucose is absorbed from the blood into cells. • Activating enzymes involved in the conversion of glucose to glycogen. This results in glycogenesis in the liver.

Alpha cells in the islets of Langerhans detect when blood glucose is too low and will secrete glucagon in response to this. Glucagon increases blood glucose in the following ways: 1. Attaching to receptors on the surfaces of target cells (liver cells). • When glucagon binds it causes a protein to be activated into adenylate cyclase and to convert ATP in a molecule called cyclic AMP (cAMP). CAMP activates an enzyme, protein kinase, that can hydrolyse glycogen into glucose. • Activating enzymes involved in the conversion of glycerol and amino acids into glucose.

(The second messenger model) Adrenaline will increase blood glucose in the following ways: • Adrenaline attaches to receptors on the surfaces of target cells. This causes a protein (G protein) to be activated and to convert ATP into cAMP. • CAMP activates an enzyme that can hydrolyse glycogen into glucose. • This is known as the second messenger model of adrenaline and glucagon action, because the process results in the formation of cAMP, which acts as a second messenger

Insulin stimulates the uptake of gluclose by all respiring cells mainly liver and muscle cells. Activates other enzymes which convert excess glucose to fatty acids. Activates enzymes in the liver to convert glucose to glycogen Stimulates increased use of glucose in respiration

Type I diabetes is due to the body being unable to produce insulin, it starts in childhood and could be the result of an autoimmune disease where the beta cells were attacked. Treatment involves injections of insulin.

Type Il diabetes is due to receptors on the target cells losing their responsiveness to insulin, it usually develops in adults because of obesity and poor diet. It is controlled by regulating intake of carbohydrates, increasing exercise and sometimes insulin injections.

Protein hormones like insulin and glucagon are polar, lipid insoluable molecules that are unable to diffuse lipid bilayuer of plasma membrane. These hormones bind to receptor proteins in plasma membranes of their target cells and trigger a chain of events such as activate or inhibit biochemical reactions.

• Adrenaline binds to the surface receptor. • Binding induces a change in the shape of the receptor which activates a g protein which is located on inner surface at the membrane