Homeostasis

• definition of homeostasis?

  the maintanence of a constant internal environment
• what is negative feedback?

  a response to change that reverses that change (brings values back to normal)
• what is positive feedback ?

  a response to change that increases / amplifies the output signal
• glucose is polar so moves by facilitated diffusion via channel proteins
• what is a gland?

  a group of cells that procude & secrete a substance
• what are endocrine glands?

  -ductless glands that secrete hormones directly into the blood.
• what are exocrine glands?

  -secrete substances (not hormones) into a duct that carries the substance to the site of action.
• hormones are chemical messengers that act on specific target tissues or organs
• what are the two types of hormones?

  -polypeptide derived hormones

  -steroid hormones
• where are the receptors located for polypeptide derived hormones?

  plasma membrane
• where are the receptors located for steroid hormones?

  cytoplasm
• steroid hormones are made from steroids which are a type of lipid, this means they can diffuse through the phospholipid bilayer.
• what organ is involved in the control of blood glucose?

  pancrease
• where are the islets of langerhans found?

  in the pancreas
• what do alpha cells produce?

  glucagon
• what do beta cells produce?

  insulin
• how can blood glucose be increased?

  eating & drinking
• how can blood glucose b decreases?

  exercise

  respiration

  excretion

  fasting

  mental exertion
• what is gluconeogenesis?

  fats converted to glucose
• what is it called when fats are converted to glucose?

  gluconeogenesis
• what is glycogenesis ?

  when glucose is converted to glycogen
• what is it called when glucose is converted to glycogen?

  glycogenesis
• what is glycogenolysis?

  glycogen converted to glucose
• what is it called when glycogen is converted to glucose?

  glycogenolysis
• blood glucose control is regulated by negative feedback
• what happens when blood glucose rises?

  -in the islets of langerhans.

  • alpha cells stop secreting glucagon & beta cells secrete insulin.
  • liver & muscle cells increase uptke of glucose from the blood.
  • glycogenesis occurs converting glucose to glycogen.
  • glycogen is stored for later use.
  • increased use of glucose in respiration.
  • blood glucose falls
• what happens when blood glucose falls?

  -in the islets of langerhans.

  • alpha cells secrete glucagon & beta cells stop secreting insulin.
  • liver releases glucose into the blood
  • glycogenolysis occurs converting glycogen to glucose.
  • gluconeogenesis occurs converting fats to glucose.
  • blood glucose rises.
• how is insulin secreted?

  -potassium ion channels are normally open & K+ difuses out.

  • glucose diffuses into cells when levels are high.
  • glucose is converted to ATP.
  • the ATP closes the potassium ion channels so K+ can no longer leave the cell.
  • this causes a change in potential difference inside the cell (less negative).
  • causing calcium ion channels to open & Ca2+ moves in.
  • calcium ions cause vesicles containing insulin to fuse with the cell membrane.
  • insulin is released out of the beta cell.
• describe insulin action?

  -insulin binds to receptors on target cells.

  • target cells increase uptake of glucose by increasing the number of glucose channel proteins in the cell membrane.
  • insulin activates enzymes to carry out glycogenesis, converting glucose to glycogen.
  • insulin increases the rate of respiration in target cells.
• describe glucagon action?

  -glucagon binds to receptors on target cells.

  • it activates enzymes to carry out glycogenolysis, converting glycogen to glucose.
  • it activates gluconeogenesis, converting fats & amino acids to glucose.
  • it decreases the rate of respiration in target cells.
• how does adrenaline increase blood glucose levels?

  -activates glycogenolysis

  • inhibits glygogenesis
  • activated secretion of glucagon from alpha cells
  • inhibits secretion of insulin from beta cells.
• describe the second messanger model of glucagon / adrenaline?

  -the hormone binds to a receptor on the target cell.

  • causing the receptor to change shape.
  • this leads to activation of enzyme adenylate cyclase.
  • this converts ATP to cAMP.
  • cAMP activates protein kinase which activates reactions leading to breakdown of glycogen to glucose.
• what is hyperglycaemia ?

  blood glucose is too high
• what is hypoglycaemia ?

  blood glucose is too low
• diabetes type 1:

  • beta cells in the pancreas are destroyed by an autoimmune reaction so no insulin is secreted.
  • requires regular injections of insulin & a controlled diet.
• type 2 diabetes:

  • associated with obesity
  • insulin is produced but liver & muscle cells fail to respond due to fewer receptors.
  • controlled by diet.
• what are the functions of the kidneys?

  -filter the blood & remove nitrogenous waste

  -osmoregulation
• what is osmoregulation?

  maintaining the balance of water & dissolved solutes in the blood
• what three processes are controlled at the nephron?

  ultrafiltration

  selective reabsorption

  secretion
• what is hypertonic blood ?

  blood with a too low water potential

  • leading to water leaving the cells by osmosis causing them to shrivel