Homeostasis

• Homeostasis is the maintained constant internal environment despite external environmental changes
• The internal environment of an organism includes temperature, pH and blood glucose
• Maintaining a constant temperature and pH prevents essential enzymes from denaturing, maintaining an optimum
• Homeostasis examples involve glucoregulation of glucose, thermoregulation of temperature and osmoregulation of water
• Positive feedback is rare as it often causes harm
• An example of positive feedback is a decrease in temperature, slowing enzymes and metabolic rate so less heat is released
• Blood glucose levels can be altered by eating a carbohydrate rich meal, glucagon, insulin, adrenalin and exercise
• The pancreas detects changes in blood glucose levels, secretes digestive enzymes and secretes glucagon and insulin
• Hyerglycemia is high blood glucose
• Hypoglycemia is low blood glucose
• Insulin increases the permeability of the cell membrane by increasing the number of glucose channels, number of glucose transporter vesicles and activates enzymes for conversion of glucose to glycogen
• Alpha cells in the islets of langerhans secrete glucagon when the pancreas detects a low glucose concentration
• Beta cells in the islets of langerhans secrete insulin when the pancreas detects high blood glucose
• Gluconeogenesis is the production of glucose from amino acids, fatty acids and glycerol
• Glycogenolysis occurs in cases of low blood glucose where glycogen is hydrolysed
• Gluconeogenesis makes glucose from amino acids and fatty acids in times of low blood glucose
• Glycogenolysis is the hydrolysis of glycogen into glucose, increasing blood sugar
• Glycogenesis occurs when blood glucose levels are high
• Glycogenesis is where glucose enters liver cells and is converted to glycogen, decreasing blood sugar
• When blood sugar levels are high, insulin will bind to specific receptors on liver cells, causing more glucose channels to form and causing enzymes to convert glucose to glycogen
• The second messenger amplifies the signal from the hormone inside the cell
• When a hormone such as adrenaline or glucagon binds to specific receptors on the liver cell, adenyl cyclase undergoes a conformational change of shape and causes ATP to be converted to cAMP, this activates a series of protein kinases and enzymes causing the hydrolysis of glycogen to glucose which is secreted from the plasma membrane
• Too high blood glucose levels can lead to blindness, glucose in urine and damage to brain cells
• Too low glucose levels can lead to fainting and dizziness
• Type 1 diabetes is where an immune response destroys beta cells in the pancreas so insulin is no longer secreted leading to an inability to absorb glucose from the blood
• Type 2 diabetes is an accumulated resistance to insulin, fat can block insulin receptors and insulin receptors can change shape to become no longer complimentary to insulin, not enough insulin may bind to receptors too, leading to high blood glucose
• Drugs can stimulate other pancreatic cells to behave like beta cells, secreting insulin, this is a potential cure to type 1 diabetes
• Type 1 diabetics need to inject insulin after a meal as they cannot secrete their own
• Type 2 diabetics need to control their diet and exercise to keep their blood glucose normal
• Type 2 diabetics cant inject insulin as it will not treat their high blood glucose
• Osmoreceptors in the hypothalamus send a higher frequency of action potentials to the posterior pituitary gland to secrete more ADH for more water reabsorption
• Baroreceptors and chemoreceptors in the aorta will send a higher frequency of action potentials to the medulla oblongata to increase or decrease heart rate