Homeostasis Flashcards
example of positive feedback
blood clot after injury
- platelets activated - release chemical
- triggers more platelets = activated
- platelets quickly form blood clot at injury site
- process ends with neg feedback - body detects blood clot formed
why isnt pos feedback involved in homeostasis?
doesnt keep internal enviro stable
Beta cells secrete…
insulin into blood
alpha cells secrete…
glucagon into blood
homeostatic mechanisms maintain a constant environment in the body.
the graph shows changes in plasma glucose concentration that occurred in a person who went without food for some time.
explain the role of negative feedback in the control of plasma glucose concentration?
- deviation of value form norm initiates negative feedback
- fluctuations in plasma glucose conc detected by hypothalamus
- initial decrease - no food given - stimulates secretion of glucagon
- increase stimulates secretion of insulin from beta cells as secretors
- dec uptake of glucose by cells
the graph shows on some occasions, the conc of glucose in the girls blood was very high.
suggest why?
- eaten
- meal with carbs/sugars
use the graph to evaluate the use of the urine test as a measure of blood glucose concentration?
- postitive correlation
- range of results for particular value
- urine test only arbitrary scale
diabetic people who do not control their blood glucose conc may become unconscious and go into coma.
a doctor may inject a diabetic person who is in a coma with glucagon.
explain how glucagon would affect the persons blood glucose concentration?
- glycogenolysis
- gluceoneogenesis
give one example, explain why homeostasis is important in mammals?
- temp
- maintaining enzyme action
cross-channel swimmers may suffer from muscle fatigue during which contraction mechanisms is disrupted.
once factor thought to contribute to muscle fatigue is decrease in availability of Ca2+ within muscle fibres.
explain how a decrease in the availability of Ca2+ could disrupt the contraction of mechanism in muscles?
- Ca2+ ions needed to remove tropomyosin
- calcium ions allow formation of actin-myosin crossbridge
- activates ATPase
scientists investigated the control of blood glucose conc in mice.
they kept a group of normal mice without food for 48 hours.
after 48 hours, the blood glucose conc of mice were same as at the start of experiment.
explain how the normal mice prevented their blood glucose conc falling when they had not eaten for 48 hours?
- release glucagon
- activates enzymes that catalyse glycogenolysis
- this activates enzymes that catalyse gluconeogenesis
describe how urea is removed from the blood?
- hydrostatic pressure generated
- causes ultrafiltration at bowmans capsule
- through basement membrane
- enabled by small size urea molecule
explain how urea is conc in filtrate?
- reabsorption of water by OSMOSIS
- at PCT
- at DCT
- active transport of ions
describe how ultrafiltration produces glomerular filtrate?
- hydrostatic pressure
- small molecules
- pass through basement membrane
- proteins too large to go through
- due to presence of podocytes
give components of the blood which are not normally present in filtrate?
- blood cells
- platelets
- proteins
- treated / controlled by diet / exercise
- usually type 2 produce insulin cells / receptors less responsive to insulin
the secretion of osteocalcin (in inactive form) by osteoblasts is controlled by positive feedback.
use the figure to explain why this is positive feedback?
- osteocalcin causes more release of insulin
- more insulin causes more osteocalcin
- changes tertiary structure
- change in ionic/hydrogen bonds
- insulin leads to more transport proteins for glucose
- more glucose for resp/glycolysis enters cell
