(16) homeostasis Flashcards
define homeostasis
control systems that keep your internal environment roughly constant (within certain limits)
why is it important to maintain the core body temperature
if body temp is too high enzymes can denature so metabolic reactions will be less efficient.
if too low, enzyme activity will be reduced
optimum is 37
why is it important to maintain blood pH
enzymes can denature if it is too alkaline or acidic. optimum is pH 7 but can vary eg stomach enzymes work best at slightly acidic
why is it important to maintain the right conc of glucose in the blood
cells need glucose for energy also if blood glucose conc is too high water potential of blood is reduced so water diffuses out of cells into blood and cells shrivel and die.
if blood glucose conc is too low there isn’t enough for respiration
what is the benefit of having multiple negative feedback systems
more control over changes in the internal environment than just having one. actively increase or decrease a level so it returns to normal. only one would mean slower responses and less control
what is a positive feedback mechanism
amplifies a change from normal level (receptors respond to further increase the level away from normal level)
how is positive feedback used to activate a blood clot after an injury
platelets become activates, release chemical which triggers more platelets to be activated so they quickly form a blood clot at the injury site. ends with negative feedback when the body detects a formed clot
how does hypothermia use positive feedback
heats lost from body quicker than it can be produced. as body temp falls, brain doesn’t work properly and shivering stops so body temp falls even more. continues to decrease unless action is taken
why is positive feedback not said to be a part of homeostasis
because it doesn’t contribute to keeping the internal environment stable
what is the normal concentration of glucose in the blood
90 mg per 100cm3 of blood
what causes fluctuation in blood glucose conc
rises after eating food containing carbohydrate and falls after exercise as glucose is used in respiration
how are insulin and glucagon secreted into the blood
by clusters of cells in the pancreas called the islets of langerhans. beta cells secrete insulin and alpha cells secrete glucagon
how does insulin help control blood glucose conc
binds to specific receptors on cell membranes of liver and muscle cells. increases the permeability of muscle cell membranes to glucose so cells take up more glucose (increased number of channel proteins)
activates enzymes in liver / muscle that convert glucose to glycogen so level of blood glucose is lowered (also increases rate of respiration of glucose)
what is glycogenesis
the process of forming glycogen from glucose
how does glucagon help control blood glucose conc
glucagon binds to specific receptors on liver cell membranes. activates liver cell enzymes to break down glycogen into glucose (glycogenolysis). activates enzymes that are involved in formation of glucose from glycerol and aa (also decreases rate of respiration in glucose cells)
what is GLUT4
a channel protein / glucose transporter in skeletal and cardiac muscle cells. when insulin binds to cell surface membrane receptors it triggers GLUT4 to move from vesicles to membrane so then glucose can be transported into cell by facilitated diffusion
what is adrenaline
secreted when theres low conc of glucose in blood, when you’re stressed or exercising. binds to receptors of cell surface membranes of liver cells. activates breakdown of glycogen to glucose and stops glucose forming glycogen. (makes glucose more available for muscles to respire)
how do adrenaline and glucagon act via a second messenger
bind to receptors on outside of cell, activate enzyme (adenylate cyclase) that converts ATP into a second messenger (chemcial signal). this activates an enzyme called protein kinase A which activates a chain of reactions to breakdown glycogen into glucose
