3.6.4 Homeostasis Flashcards
What is homeostasis
Internal environment is maintained within set limits around an optimum
Why is it important that core temperature remains stable
Maintain stable rate of enzyme controlled reactions and prevent damage to membranes
Too low = insufficient kinetic energy
Too high = enzymes denature
Why is it important that blood pH remains table
Maintains stable rate of enzyme controlled reactions
Acidic = H+ ions interact with H bonds and ionic bonds in tertiary structures of enzymes - shape of active site changes so no ES complexes
Why is it important that blood glucose conc remains stable
Maintain constant blood wp, prevents lysis and crenation
Maintain constant conc of respiratory substrate - constant level of activity regardless of environmental conditions
Define negative and positive feedback
Neg = self regulatory mechanisms return internal environment to optimum when there is a fluctuation
Pos = a fluctuation triggers changes that result in an even greater deviation from the normal level
Outline the general stages involved in neg feedback
Receptors detect deviation – coordinator – corrective mechanism by effector – receptors detect that conditions have returned to normal
Suggest why separate neg feedback mechanisms control fluctuations in different directions
Provides more control, esp in case of overcorrection, which would lead to a deviation in the opposite direction from the original one
Suggest why coordinators analyse inputs from several receptors before sending an impulse to effectors
Receptors may send conflicting information
Optimum response may require multiple types of receptors
Why is there a time lag between hormone production and response by an effector
It takes time to;
produce hormone
transport hormone in the blood
Factors that affect blood glucose
Amount of carb digested from diet
Rate of glycogenolysis
Rate of gluconeogenesis
Define glycogenesis, glycogenolysis, gluconeogenesis
Glycogenesis: liver converts glucose into glycogen
Glycogenolysis; liver hydrolyses glycogen into glucose
Gluconeogenesis; liver converts glycerol and amino acids into glucose
Outline the role of glucagon when blood glucose conc decreases
Alpha cells in pancreas detect decrease and secrete glucagon into blood
Glucagon binds to surface receptors on liver cells and activates enzymes for glycogenolysis and gluconeogenesis
Glucose diffuses from liver into bloodstream
Outline the role of adrenaline when blood glucose conc decreases
Adrenal glands produce adrenaline, binds to surface receptors on liber cells and activates enzymes for glycogenolysis
Glucose diffuses from liver into blood
Outline what happens when blood glucose conc increases
Beta cells in pancreas detect increase and secrete insulin into blood
Insulin binds to surface receptors on target cells to;
a) increase cellular glucose uptake
b) activate enzymes for glycogenesis
c) stimulate adipose tissue to synthesise fat
Describe how insulin leads to a decrease in blood glucose
Increases permeability of cells to glucose
Increases glucose conc gradient
Triggers inhibition of enzymes for glycogenolysis
How does insulin increase permeability of cells to glucose
Increase number of glucose carrier proteins
Triggers conformational change which opens glucose carrier proteins
How does insulin increase glucose conc gradient
Activates enzymes for glycogenesis in liver and muscles
Stimulates fat synthesis in adipose tissue
Use the secondary messenger model to explain how glucagon and adrenaline work
- Hormone receptor complex forms
- Conformational change to receptor activates G protein
- Activates adenylate cyclase which converts ATP to cAMP
- cAMP activates protein kinase A pathway
- Results in glycogenolysis
Explain the cause of t1d and how it can be controlled
Body cannot produce insulin due to autoimmune response which attacks Beta cells
Treat by insulin injections / pump
Explain the cause of t2d and how it can be controlled
Glycoprotein receptors are damaged or become less responsive to insulin
Poor diet / obesity
Treat by controlling diet and exercise
Outline how colorimetry could be used to identify the glucose conc in a sample
- Benedicts test on solutions of known glucose conc. Use colorimeter to record absorbance
- Plot calibration curve - absorbance y and glucose conc x
- Benedicts test on unknown sample. Use calibration curve to read glucose conc at its absorbance value
Define osmoregulation
Control of blood wp via homeostatic mechanisms
What structures does a nephron include
Bowmans capsule
Proximal convoluted tubule
Loop of henle
Distal convoluted tubules
Collecting duct
Describe the blood vessels associated with a nephron
Wide afferent arteriole from renal artery enters renal capsule and forms glomerulus; branched knot of capillaries which combine to form narrow efferent arteriole
Efferent arteriole branches to form capillary network that surrounds tubules
Explain how glomerular filtrate is formed
Ultrafiltration in bowmans capsule
High hydrostatic presssure in glomerulus forces small molecules out of capillary fenestrations against osmotic gradient
Basement membrane acts as a filter. Blood cells and large molecules remain in capillary
How are cells of the bowmans capsule adapted for ultrafiltration
Fenestrations between epithelial cells of capillaries
Fluid can pass between and under folded membrane of podocytes
State what happens during selective reabsorption and where it occurs
Useful molecules from glomerular filtrate eg glucose are reabsorbed into the blood
Occurs in proximal convoluted tubule
Outline the transport processes involved in selective reabsorption
Glucose co transport with Na+
Active transport from cells lining PCT to intercellular spaces
Diffusion from intercellular spaces to blood capillary lining tubules
How are cells in the proximal convoluted tubule adapted for selective reabsorption
Microvilli; large SA for co transporter proteins
Many mitochondria; ATP for active transport of glucose into intercellular spaces
Folded basal membrane; large SA
What happens in the loop of henle
- Active transport of Na+ and Cl- out of ascending limb
- wp of interstitial fluid decreases
- Osmosis of water out of DL
- Wp of filtrate decreases going down DL; lowest in medullary region, highest at top of AL
Explain the role of the distal convoluted tubule
Reabsorption of water via osmosis and of ions by active transport
Explain the role of the collecting duct
Reabsorption of water from filtrate into interstitial fluid via osmosis
Why is it important to maintain an Na+ gradient
Counter current multiplier; filtrate in collecting ducts always beside an area of interstitial fluid that has a lower wp
Maintains wp gradient for maximum reabsorption of water
What might cause blood wp to change
Level of water intake
Level of ion intake in diet
Level of ions use in metabolic processes or excreted
Sweating
Explain the role of the hypothalamus in osmoregulation
- Osmosis of water out of osmoreceptors in hypothalamus causes them to shrink
- This triggers hypothalamus to produce more ADH
Explain the role of the posterior pituitary gland in osmoregulation
Stores and secrets the ADH produced by the hypothalamus
Explain the role of ADH in osmoregulation
- Makes cells lining CD more permeable to water
Binds to receptor – activates phosphorylase –vesicles with aquaporins on membrane fuse with cell surface membrane - Makes cells lining CD more permeable to urea
wp in interstitial fluid decreasesss
more water reabsorbed = more conc urine
