6.4 Homeostasis Flashcards
What is homeostasis?
Internarnal environment is maintained within set limits around an optimum
Why is it important for core temperature to remain stable?
Maintain stable rate of enzyme-controlled reactions & prevent damage to membranes
What consequence does a low core temperature have?
Enzyme & substrate molecules have insufficient kinetic energy
What consequence does a high core temperature have?
Enzymes denature
Why is it important for blood pH to remain stable?
Maintain stable rate of enzyme-controlled reactions & optimum conditions for proteins
What consequence does acidic blood pH have?
H+ ions interact with H bonds & ionic bonds in teritary structure of enzymes
Shape of active site changes so no ES complexes form
Why is it important for blood glucose concentration to remain stable?
Maintain constant blood water potential to prevent osmotic lysis/crenation of cells
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 stages of 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 with overcorrection
What is meant by “overcorrection” with negative feedback?
Correction of a fluctuation leads to deviation in the opposite direction from orginal
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 reponses by an effector?
Time is needed to produce hormone, transport it in the blood and make the required change to target protein
Name the factors that affect blood glucose concentrtion.
Amount of carbohydrate digested
Rate of glycogenolysis
Rate of gluconeogenesis
What is glycogenesis?
Liver converts glucose intro storage polymer glycogen
What is glycogenolysis?
Liver hydrolyses glycogen into glucose which can diffuse into blood
What is gluconeogenesis?
Liver converts glycerol & amino acids into glucose.
Outline the role of glucagon when blood glucose concentration decreases.
a 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
Adrenaline binds to surface receptors on liver cells & activates enzymes for glycogenolysis
Glucose diffues from liver into bloodstream
Outline what happens when blood glucose concentration increases.
β cells in Islets of Langerhans in pancreas detect increase & secrete insulin into bloodstream
Insulin binds to surface receptors on target cells to:
- increase cellular glucose uptake
- activate enzymes for glycogenesis
- stimulate adipose tissue to synthesise fat
Describe how insulin leads to a decrease in blood glucose concentration.
Increases permeability of cells to glucose
Increases glucose concentration gradient
Triggers inhibition of enzymes for glycogenolysis
How does insulin increase the permeability of cells to glucose?
Increases number of glucose carrier proteins
Trigges conformation 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
Explain how glucagon and adrenaline work using the secondary messenger model.
Hormone receptor complex forms
Conformational change to receptor activates G protein
Activates adenylate cyclase which converts ATP to cyclic AMP (cAMP)
cAMP activates protein kinase A pathway
Results in glycogenolysis
What is the cause of Type 1 diabetes?
The body’s inability to produce insulin
What possible reason is there for a lack of insulin production?
Autoimmune response which attacks β cells of Islets of Langegrhans
How is Type 1 diabetes?
Insulin injections
What is the cause of Type 2 diabetes?
Glycoprotein receptors are damaged or become less responsive to insulin
Strong positive correlation with poor diet/obesity
How can Type 2 diabetes be treated?
Diet control and exercise
List symptoms of diabetes.
High blood glucose concentration
Glucose in urine
Frequent urination
Excessive appetite
Excessive thirst
Blurred vission
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.,
Benedicts test on solutions of known glucose concentration & colorimeter to record absorbance
Plot calibration curve of absorbance (y) against glucose concentration (x)
Benedics test on unknown sample & colorimeter to record absorbance
Benedicts test on unknown sample
Use calibration curve to read concentration at absorbance value
Define osmoregulation.
Control of blood water potential via homeostatic mechanisms
List the features of a mammalian kidney.
Fibrous capsule
Cortex
Medulla
Renal pelvis
Ureter
Renal artery
Renal vein
What is the purpose of the fibrous capsule?
Protection for the kidney
What is the cortex?
Outer region consists of Bowman’s capsules, convoluted tubules, blood vessels
What is the medulla?
Inner region consists of collecting ducts, loops of Henle, blood vessels
What is the renal pelvis?
Cavity that collects urine into ureter
What is the ureter?
Tube that carries urine to bladder
What is the renal artery?
Supplies kidney with oxygenated blood
What is the renal vein?
Returns deoxygenated blood from kidney to heart
State the structures within a nephron.
Bowman’s capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
What is the Bowman’s capsule?
Cup-shaped
Surrounding the glomerus at start of nephron
Inner layer of podocytes
What is the Proximal Convoluted Tubule (PCT)?
Series of loops surrounded by capillaries
Walls made of epithelial cells with microvilli
What is the loop of Henle?
Hairpin loop extends from cortex into medulla
What is the Distal Convoluted Tubule (DCT)?
Similar to PCT but fewer capillaries
What is the collecting duct?
DCT from several nephrons empty into collecting duct
State the blood vessels associated with a nephron.
Wide afferent arteriole
Efferent arteriole
What is the wide afferent arteriole?
Branched knot of capillaries which combine to form narrow efferent arteriole
Enters renal capsule from renal artery & forms glomerulus
What is the efferent arteriole?
Branches to form capilalry network that surrounds tubules
What process forms glomerular filtrate?
Ultrafiltration in Bowman’s capsule
Explain how glomerular filtrate is formed by ultrafiltration.
High hydrostatic pressure in glomerulus forces small molecules (urea, water, glucose, mineral ions) out of capillary fenestrations AGAINST osmotic gradient
Basement membrane acts as filter so blood cells & large molecules e.g. proteins remain in capillary
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
Where does selective reabsorption occur?
Occurs in proximal convoluted tubule
What is selective reabsorption?
Useful molecules e.g. glucose from glomerular filtrate are reabsorbed into the blood
Outline the transport process of selective reabsorption.
Glucose from glomerular filtrate
↓ (co-transport with Na+ ions)
Cells lining proximal convoluted tubule
↓ (active transport)
Intercellular spacesz
↓ (diffusion)
Blood capillary lining tubule
How are cells in the proximal convoluted tubule adapted for selective reabsorption?
Microvilli provide a large surface area for co-transporter proteins
Many mitochondria provide ATP for active transport of glucose into intercellular spaces
Folded base membrane provides a large surface area for absorption
What happens in the loop of Henle?
Active transport of Na+/Cl- out of ascending limb into medulla
Water potential of interstitial fluid decreases
Osmosis of water out of descending limb (ascending limb is impermeable to water)
What changes happen to the water potential within the loop of Henle?
Water potential of filtrate decreases going down descending limb
Where is the water potential highest in the loop of Henle?
At top of ascending limb
Where is the water potential lowest in the loop of Henle?
In the medullary region
Explain the role of the distal convoluted tubule.
Reabsorption of water via osmosis
Reabsorption of ions via active transport
What determines the permeability of walls in the DCT?
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 in the loop of Henle.
Maintains water potential gradient between filtrate in collecting ducts and interstitial fluid for maximum reabsorption
What might cause blood water potential to change?
Level of water intake
Level of ion intake in diet
Levels 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 antidiueritc hormone (ADH)
Explain the role of the posterior pituitary gland in osmoregulation.
Stores & secretes the ADH produced by the hypothalamus
Explain the role of ADH in osmoregulation.
Makes cells lining collecting duct more permeable to water
Makes cells lining collecting duct more permeable to urea
How does ADH make cells lining collecting duct more permeable to water?
Binds to receptor
Activates phosphorylase
Vesicles with aquaporins on membrane fuse with cell surface membrane
Why does ADH make cells lining collecting duct more permeable to urea?
Water potential in interstitial fluid decreases
More water reabsorbed = more concentrated urine
