Homeostasis Flashcards
What is homeostasis?
The maintenance of internal environment within set limits around an optimum
Why is it important that core temperature remains stable?
- maintain stable rate of enzyme-controlled reactions & prevent damage to membranes
- temperature too low = enzyme & substrate molecules have insufficient kinetic energy
- temperature too high = enzymes denature
Why is it important that blood pH remains stable?
- maintain stable rate of enzyme-controlled reactions
- acidic pH = H+ ions interact with H-bonds & ionic bonds in tertiary structure of enzymes - shape of active site changes so no ES complexes form
Why is it important that blood glucose concentration remains stable?
- maintain constant blood water potential: prevent osmotic lysis/crenation of cells
- maintain constant concentration of respiratory substrate: organism maintains constant level of activity regardless of environmental conditions
Define negative feedback
Self regulatory mechanisms return internal environment to optimum when there is a fluctuation
Define positive feedback
A fluctuation triggers changes that result in an even greater deviation from the normal level
Outline the general stages involved in negative feedback
Receptors detect deviation -> coordinator -> corrective mechanism by effector -> receptors detect that conditions have returned to normal
Suggest why separate negative feedback mechanisms control fluctuations in different directions
Provides more control especially 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 effector
Why is there a time lag between hormone production and response by an effector
Takes time to:
- produce hormone
- transport hormone in the blood
- cause required change to the target protein
Name the factors that affect blood glucose concentration
- amount of carbohydrate digested from diet
- rate of glycogenolysis
- rate of gluconeogenesis
Define glycogenesis
Liver converts glucose into the storage polymer glycogen
Define glycogenolysis
Liver hydrolyses glycogen into glucose which can diffuse into blood
Define gluconeogenesis
Liver converts glycerol & amino acids into glucose
Define the role of glucagon when blood concentration decreases
- alpha cells in islets of Langerhans in pancreas detect decrease & secrete glucagon into bloodstream
- glucagon binds to surface receptors on liver cells & activates enzymes for glycogenolysis & gluconeogenesis
- glucose diffuses from liver into bloodstream
Outline the role of adrenaline when blood glucose concentration decreases
- Adrenal glands produce adrenaline which binds to surface receptors on liver cells & activates enzymes for glycogenolysis
- Glucose diffuses from liver into bloodstream
Outline what happens when blood glucose concentration increases
- Beta cells in islets of langerhans in pancreas detect increase & secrete insulin into bloodstream
- Insulin binds to surface receptors on target cells to:
a) increase cellular glucose uptake
b) activate enzymes for glycogenesis (liver & muscles)
c) stimulate adipose tissue to synthesise fat
Define how insulin leads to a decrease in blood concentration
- increases permeability of cells to glucose
- increases glucose concentration gradient
- triggers inhibition of enzymes for glycogenolysis
How does insulin increase permeability of cells to glucose?
- increases number of glucose carrier proteins
- triggers conformational change which opens glucose carrier proteins
How does insulin increase the glucose concentration gradient?
- activates enzymes for glycogenesis in liver & 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 causes of type 1 diabetes and how it can be controlled
Body cannot produce insulin e.g due to auto immune responses which attacks beta cells of islets of langerhans
Treat by injecting insulin
Explain the causes of type 2 diabetes and how it can be controlled
- glycoprotein receptors are damaged or become less responsive to insulin
- strong positive correlation with poor diet/obesity
- treat by controlling diet and exercise regime
Name some signs and symptoms of diabetes
- high blood glucose concentration
- glucose in urine
- polyuria
- polyphagia
- polydipsia
- blurred vision
- sudden weight loss
Suggest how a student could produce a desired concentration of glucose solution from a stock solution
Volume of stock solution = required concentration x final volume needed / concentration of stock solution
Volume of distilled water = final volume needed - volume of stock solution
Outline how colorimetry could be used to identify the glucose concentration in a sample
- Benedict’s test on solutions of known glucose concentration. Use colorimeter to record absorbance
- Plot calibration curve: absorbance (x), glucose concentration (y)
- Benedict’s test on unknown sample use calibration curve to read glucose concentration at its absorbance value
Define osmoregulation
Control of blood water potential via homeostatic mechanisms
What is a fibrous capsule for?
Protecting the kidney
What is the cortex?
Outer region of kidney which consists of Bowman’s capsules, convoluted tubules and blood vessels
What is the medulla?
Inner region of kidney which consists of collecting ducts, loops of Henle and blood vessels
What is the renal pelvis?
A cavity which collects urine into ureter
What is the ureter?
Tube which carries urine to bladder
What is the renal artery?
Artery which supplies kidney with oxygenated blood
What is the renal vein?
Vein which returns deoxygenated blood from kidney to heart
Describe the structure of a nephron
Bowman’s capsule at start of nephron
PCT
Loop of Henle which extends from cortex into medulla
Distal convoluted tubule
Collecting duct which leads into pelvis of kidney
What is Bowman’s capsule’s structure?
Cup-shaped, surrounds glomerulus, inner layer of podocytes
What is the PCT’s structure?
Series of loops surrounded by capillaries, walls made of epithelial cells with microvilli
What is the collecting duct for?
DCT from several nephrons empty into CD which leads into pelvis of kidney
Describe the blood vessels associated with a nephron
Wide afferent arteriole from renal artery enters renal capsule & 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 Bowman’s capsule
High hydrostatic pressure in glomerulus forces small molecules out of capillary fenestrations AGAINST osmotic gradient
Basement membrane acts as a filter
How are cells of the Bowman’s capsule adapted for ultrafiltration?
- fenestrations between epithelial cells of capillaries
- fluid can pass between & under folded membrane of podocytes
State what happens during selective reabsorption and where it occurs
Useful molecules from glomerular filtrate are reabsorbed into the blood
Occurs in proximal convoluted tubule
Outline the transport processes involved in selective reabsorption
Glucose from glomerular filtrate —cotransport with Na+—> cells lining PCT —AT—> intercellular spaces —diffusion—> blood capillary lining tubule
What does PCT stand for?
Proximal convoluted tubule
How are cells in the proximal convoluted tubule adapted for selective reabsorption?
- microvilli: large SA for cotransporter proteins
- many mitochondria: ATP for AT of glucose into intercellular spaces
- folded basal membrane: large SA
What happens in the loop of Henle?
- AT of Na+ & Cl- out of ascending limb
- Water potential of interstitial fluid decreases
- Osmosis of water out of descending limb
- Water potential of filtrate decreases going down descending limb: lowest in medullary region, highest at top of impermeable ascending limb
Explain the role of the distal convoluted tubule
Reabsorption of water via osmosis & ions via AT
Permeability of walls is determined by action of hormones
Explain the role of the collecting duct
Reabsorption of water from filtrate into interstitial fluid via osmosis through aquaporins
Explain why it is important to maintain an Na+ gradient
Countercurrent multiplier: filtrate in collecting ducts is always beside an area of interstitial fluid that has a lower water potential
Maintains water potential gradient for maximum reabsorption of water
What might cause blood water potential to change?
- level of water intake
- level of ion intake in diet
- level of ions used 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
- Triggers hypothalamus to produce more ADH
Explain the role of the posterior pituitary gland in osmoregulation
Stores and secretes the ADH produced by the hypothalamus
Explain the role of ADH in osmoregulation
- Makes cells lining collecting duct more permeable to water
- binds to receptor -> activates phosphorylase -> vesicles with aquaporins on membrane fuse with csm
- Makes cells lining collecting duct more permeable to urea:
- water potential in interstitial fluid decreases
- more water reabsorbed = more concentrated urine
