Homeostasis Flashcards
what is homeostasis?
the maintenance of an internal environment within restricted limits in organisms, to respond to the external environment
the ability to return to the optimum point
why is homeostasis essential for proper functioning of organisms?
- to maintain a fairly constant internal environment (of pH and temperature) to let enzymes work at their optimum
- changes to the water potential of blood and tissue fluid may cause cells to shrink and expand
- allow for organisms to have a greater geographical range
what are the series of stages for the control of any self-regulating system?
OPTIMUM POINT, monitored by RECEPTOR, informs the COORDINATOR, send instructions to EFFECTOR, which creates a FEEDBACK MECHANISM
what is negative feedback?
when the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off
what is positive feedback?
when a deviation from an optimum causes changes that result in an even greater deviation from the normal
what are hormones and how do they work?
- produced in glands, secrete hormone directly into blood
- carried in blood plasma to target cells
- are effective in very low concentrations, but have widespread and long-lasting effects
what do the islets of Langerhan include?
alpha cells - larger and produce glucagon
beta cells - smaller and produce insulin
what is glycogenesis?
glucose into glycogen
what is glycogenolysis?
breakdown of glycogen to glucose
what is gluconeogenesis?
production of glucose from sources other than carbohydrates
what happens if the concentration of blood glucose increases too high?
lowers the water potential of the blood and creates osmotic problems that can cause dehydration
what are three factors that influence blood glucose concentration?
- directly from diet
- from hydrolysis in the small intestine of glycogen (glycogenolysis)
- from gluconeogenesis
How does insulin reduce the concentration of glucose in blood?
- increases rate of glucose absorption
- increases respiratory rate of cells
- increases rate of glycogenesis
- increases rate of conversion of glucose to fat
what happens to beta cells when the blood glucose concentration reduces?
they reduce their secretion of insulin (=negative feedback)
how does glucagon increase the concentration of glucose in the blood?
- attach to specific protein receptors on liver cell surface membrane
- activate enzymes that convert glycogen to glucose
- activate enzymes involved in gluconeogenesis (from amino acids and glycerol)
what happens to alpha cells when the blood glucose concentration increases?
they reduce their secretion of glucagon (=negative feedback)