knowledge-20 Homeostasis

• Nephrons are tiny tubules that make up the majority of the kidney. Nephrons remove waste products from the blood and produce urine in a series of steps.
• Nephrons remove waste products by:

  • formation of glomerular filtrate
  • reabsorption of glucose and water by proximal convoluted tubule
  • maintaining a concentration gradient of sodium ions across the medulla by the loop of Henle
  • reabsorption of water by the distal convoluted tubule and collecting ducts
  • urine is stored in the bladder until it is released from the body.
• Osmoregulation- maintaining the water potential of blood by removing excess water or retaining water.
• Excretion- removing nitrogenous waste (excess protein) in the form of urea from the blood.
• There are two kidneys (only one is needed for survival) , each receives blood from the renal artery.
• kidneys act like filters, removing urea from the blood and diluting it with water to form urine.
• The hypothalamus is a part of the brain that contains osmoregulatory receptors and produces ADH.
• The kidney reabsorbs important amino acids, salts and glucose that it filters out of the blood initially so that they are not lost in urine.
• The amount of water in the urine is adjusted to maintain the water potential of the blood.
• The cortex- is the outer layer jammed pack full of the filtration parts of the nephrons. Filters the blood.
• Renal pelvis - where all the collecting ducts come together and connect to the ureter.
• Medulla (kidney)- the inner layer which contains the tubes carrying filtered wastes to the centre of the kidney. Contains the loop of Henle and collecting ducts parts of the nephrons.
• Type 1 diabetes:

  • caused by the pancreas not producing insulin , typically occurs in childhood.
  • treated with ; 2-4 injections a day of insulin and blood glucose concentration is monitored using biosensors.
• Ureter- transports urine to the bladder to be excreted.
• Type 2:

  • caused by glycoproteins receptors on the cell surface membranes are lost or lose sensitivity : sometimes leading to reduction in insulin production.
  • treatment ; regulate dietary carbohydrates , especially refined sugars ;may require insulin or drugs to stimulate insulin production.
• Antidiuretic hormone (ADH)- a hormone made by the hypothalamus and secreted by the pituitary gland; acts on target cells in collecting ducts in the kidneys to increase water absorption into the blood.
• ultrafiltration happens in the bowman's capsule at one end of the nephron.
• A knot of capillaries called the glomerulus sits in the bowman's capsule.
• glomerulus- fluid is forced out of the blood using blood pressure.
• At the entrance of the glomerulus the afferent arteriole is thick whereas at the end of the glomerulus the efferent arteriole is thin.
• efferent arteriole has a narrower lumen compared to the afferent.
• The difference in lumen size in the glomerulus creates high hydrostatic pressure which forces plasma from the blood through the walls of the capillaries into a filter called the bowman's caspule.
• Small molecules leaving the glomerulus pass through gaps in the capillary endothelium called fenestrations.
• if there is kidney damage then proteins ; red blood cells ; white blood cells will be inside the urine.
• Homeostasis in mammals is the maintenance of a stable internal environment within restricted limits by physiological control systems.
• Core temperature needs to be controlled for enzyme activity.
• blood ph needs to be controlled for enzyme activity.
• blood glucose concentration needs to be controlled for water potential and availability of glucose as a respiratory substrate.
• negative feedback is where a change from the set level will cause the body to correct change to bring it back to the normal value.
• glycogenesis: the conversion of glucose to glycogen
• glycogenolysis: the conversion of glycogen to glucose.
• gluconeogenesis: the conversion of non-carbohydrates to glucose.
• liver cells are the target cells for the hormones insulin and glucagon.
• The second messenger model:

  1. Adrenaline (or glucagon) the first messenger binds to specific receptors on target cell surface membrane to form a hormone-receptor complex.
  2. the hormone-receptor complex activates an enzyme , adenylate cyclase , inside the membrane.
  3. the activated adenylate cyclase converts ATP into cAMP.
  4. cAMP acts as a second messenger and activates another enzyme in the cytoplasm - a protein kinase this causes the conversion of glycogen to glucose.
• Adrenaline is a hormone gland released by the adrenal glands in response to stress , excitement and fear. Adrenaline raise blood conc by:

  1. attaching to receptors on the surface of target cells.
  2. Activating enzymes involved in the conversion of glycogen to glucose - glycogenesis.
• Blood-glucose concentration:

  factors that influenced blood glucose concentration:

  1. the breakdown of carbohydrates in the diet.
  2. the breakdown of glycogen stored in the liver - glycogenolysis
  3. new glucose molecules synthesized from substances other than carbohydrates - gluconeogenesis.
  4. level of physical and mental activity.
• Insulin is one of two hormones that control blood glucose concentration (reduce) by:

  1. causing more glucose channels to be inserted into the cell membrane, so increasing the uptake of glucose , especially by muscle cells.
  2. increasing the rate of respiration , so more glucose is used.
  3. activating enzymes involved in the conversion of glucose to glycogen - glycogenesis - in muscle and liver cells
  4. causing excess glucose to be converted into fat
• Glucagon works in opposition to insulin , raising blood glucose concentration by:

  1. attaching to receptors on the surface of target cells.
  2. activating enzymes involved in the conversion of glycogen to glucose - glycogenolysis.
  3. activating enzymes involved in the conversion of glycerol and amino acids into glucose - gluconeogenesis.
  4. causing the body to use body fats in respiration.