Homeostasis Flashcards
(32 cards)
What is homeostasis?
The maintenance of internal environments within restricted limits in organisms for optimum cell function/enzyme activity
Examples of conditions that need to be controlled in the body
- blood pressure
- body temperature
- blood glucose concentration
What is an example of positive feedback within the body?
- propagation of an action potential - more diffusion of sodium ions = more sodium ion channels stimulated to open
What are the examples of negative feedback within the body?
- control of blood pressure
- control of blood water potential
- control of blood glucose concentration
- control of blood calcium ion concentration
Why does blood glucose concentration need to be controlled?
- if blood glucose levels rise, water potential of the blood decreases causing water to move out of cells eg. red blood cells, therefore red blood cells shrivel and oxygen cannot be transported around the body
- if blood glucose levels fall, there will be insufficient respiratory substrates needed for respiration
What is the second messenger model and how does it regulate blood glucose concentration?
- adrenaline/glucagon binds to receptors on the cell-surface membrane
- this causes the protein to change shape which activates adenyl cyclase
- adenyl cyclase converts ATP to cyclic AMP
- cAMP acts as a second messenger which binds to protein kinase and activates it
- protein kinase catalyses the conversion of glycogen to glucose, which moves out of liver cells via facilitated diffusion into the bloodstream through channel proteins
What type of cells is the pancreas partly made up from?
- hormone-producing cells called islets of Langerhans which contain:
- alpha cells - secrete glucagon
- beta cells - secrete insulin
What is glycogenesis?
the conversion of glucose to glycogen
What is glycogenolysis?
the breakdown of glycogen to glucose
What is gluconeogenesis?
the production of glucose from other sources other than carbohydrates such as amino acids and glycerol
How is blood glucose concentration lowered?
- beta cells in the islet of Langerhans have receptors that detect a rise in blood glucose concentration
- this stimulates the secretion of insulin which binds to complementary receptors on liver cell membranes
- this increases the liver cells permeability to glucose, so more glucose is absorbed
- this also activates enzymes which stimulate the conversion of glucose to glycogen
How is blood glucose concentration increased?
- receptors on alpha cells in the islets of Langerhans detect the decrease in blood glucose concentration
- this stimulates alpha cells to release glucagon, and the release of adrenaline from the adrenal gland
- glucagon binds to complementary receptors on liver cells stimulating glycogenolysis and gluconeogenesis
- second messenger model occurs to activate enzymes to hydrolyse glycogen into glucose
How does the release of insulin cause more glucose to be absorbed?
- attaches to receptors on the surface of target cells which changes the tertiary structure, so more glucose is absorbed via facilitated diffusion
- vesicles containing protein channels fuse with the membrane so more glucose is absorbed from the blood
- activates enzymes involved in the conversion of glucose to glycogen
What other method can be used to decrease blood glucose concentration?
increased rate of respiration - more glucose used in glycolysis as a respiratory substrate
What is type 1 diabetes?
the immune system attacks beta cells in the islets of Langerhans, which prevents the release of insulin so glycogenesis is not stimulated - autoimmune disease
What is type 2 diabetes?
receptors on target cells become unresponsive to insulin - insulin is secreted but glycogenesis is not stimulated
Why is glycogen a better storage molecule than glucose?
- large - cannot cross cell membrane
- insoluble - cannot affect water potential
- glucose is small and soluble
What are the blood vessels within the kidney?
- renal artery - supplies the kidney with blood from the heart
- renal vein - returns blood to the heart
What are the structures within the nephron?
- Bowman’s capsule - surrounded by a mass of capillaries called the glomerulus with high hydrostatic pressure - where ultrafiltration occurs
- proximal convoluted tube where selective reabsorption occurs
- loop of henle
- distal convoluted tube
- collecting duct
What are the afferent and efferent arterioles?
- afferent arteriole supplies the nephron with blood and the efferent arteriole moves blood away from the nephron
- the efferent arteriole has a smaller diameter which increases hydrostatic pressure, leading to ultrafiltration
How is glomerular filtrate formed by ultrafiltration?
There is high hydrostatic pressure in the renal artery because the diameter of the efferent arteriole is small leading to higher pressure. This pushes small molecules such as ions, urea and water through pores in the capillary endothelium and the basement membrane. Larger molecules such as cells and proteins remain.
How is the proximal convoluted tubule adapted for selective reabsorption?
- microvilli - provide a large surface area
- carrier and channel proteins - in the membrane for active transport and facilitated diffusion
- many mitochondria - needed to provide ATP for active transport
How does selective reabsorption occur in the proximal convoluted tubule (PCT)?
- sodium ions are actively transported out of the PCT which lowers the concentration inside the cells
- sodium ions diffuse down their concentration gradient from the lumen of the PCT into epithelial cells by facilitated diffusion - glucose is also carried across via a co-transport protein
- concentration in epithelial cells is greater than the bloodstream so glucose diffuses out
What are the 2 regions in the loop of henle?
- descending limb - highly permeable
- ascending limb - impermeable
