Homeostasis Flashcards
What is homeostasis?
Internal environment is maintained
Why is it important that core temperature remains stable?
Maintain a stable rate of enzyme controlled reactions and prevent damage membranes
Low temperature= insufficient kinetic energy
High temperature= enzymes denature
Why is it important that blood pH remains stable?
Maintain stable rate of enzyme controlled reactions
Acidic pH = shape of active sites change
Why is it important that blood glucose remains stable?
Maintain a constant blood water potential- stops osmotic lysis
Maintain a constant concentration of respiratory substrate
What is negative feedback?
Self regulatory mechanisms return internal environment to optimum when there is fluctuations
What is positive feedback?
A fluctuation triggers changes that result in an even greater deviation from the normal level
Outline the stages involved in negative feedback
Receptors detect changes > Coordinator > effector > receptors detect change is back to normal
Why is there a lag time between hormone production and response by an effector?
It takes time to:
Produce the hormone
Transport the hormone in the blood
Cause required change to the target protein
Name the factors that affect blood glucose concentration?
Amount of carbohydrate in diet
Rate of glycogenolysis
Rate of gluconeogenesis
What is glycogenesis?
Liver converts glucose into glycogen
What is glycogenolysis?
Liver hydrolyses glycogen into glucose which can diffuse into blood
What is gluconeogenesis?
Liver converts glycerol and amino acids into glucose
Outline the role of glucagon when blood glucose concentration decreases
- a cells in Islets of Langerhans in pancreas detect decrease and secrete glucagon into bloodstream
- Glucagon binds to surface cell receptors on liver cells and activates enzymes for glycogenolysis and gluconeogenesis
- Glucose diffuses from liver into blood stream
Outline the role of adrenaline when blood glucose concentration decreases
- Adrenal gland produces adrenaline. It binds to surface receptors on liver cells and activates enyzmes for glycogenolysis
- Glucose diffuses from liver into bloodstream
Outline what happens when blood glucose concentration increases
- B cells in islets of langerhans in pancreas detect increase and secrete insulin into bloodstream
- Insulin binds to receptor cells on target cells to increase glucose uptake and activate enzymes for glycogenesis
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 permeability of cells to glucose?
Increases number of glucose carrier proteins
Opens more glucose carrier proteins
How does insulin increase the glucose concentration gradient?
Activates enzymes for glycogenesis in liver and muscles
Stimulates fat synthesis in adipose tissue
Use the secondary messenger system to explain how glucagon and adrenaline work
- Hormone receptor complex forms
- Change to receptor activates G-Protein
- Activates adenylate cyclase which converts ATP to cyclic AMP
- cAMP activates protein kinase A pathway
- Results in glycogenolysis
Explain the causes of type 1 diabetes and how it can be controlled
The body cannot produce insulin e.g due to an autoimmune response which attacks B cells in 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
Correlation with poor diet/obesity
Treat by controlling diet and exercise regime
Name some symptoms of diabetes
High blood glucose concentration
Glucose in urine
Blurred vision
Sudden weight loss
What is osmoregulation?
Control of blood water potential
Describe the structure of the kidney
Fibrous capsule Cortex Medulla Renal pelvis Ureter Renal artery Renal Vein
Describe the structure of a nephron
Bowmans capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct
Describe the blood vessels associated with a nephron
Afferent arteriole- Wide
Efferent arteriole- Narrow
Explain how glomerular filtrate is formed
Ultrafiltration in Bowmans capsule
High hydrostatic pressure in the glomerulus forces small molecules out of capillary fenestrations against osmotic gradient
Basement membrane acts a filter
How are cells of the Bowmans capsule adapted for ultrafiltration?
Fenestrations between epithelial cells or capillaries
Fluid can pass between podocytes
State what happens during selective reabsorption and where it occurs
Useful molecules from glomerular filtrate e.g glucose are reabsorbed into the blood
Occurs in proximal convoluted tubule
Outline the transport processes involved in selective reabsorption
Glucose from glomerular filtrate > co transport with Na+ > cells lining proximal convoluted tubule > active transport > intercellular spaces > diffusion > blood capillary lining tubule
How are cells in the proximal convoluted tubule adapted for selective reabsorption?
Microvilli
Many mitochondrion
Folded basal membrane
What happens in the loop of henle?
- Active transport of Na+ and 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 the descending limb
Explain the role of the distal convoluted tubule
Reabsorption of water via osmosis and of ions via active transport
Permeability 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
Why is it important to maintain an Na+ concentration gradient?
Countercurrent multiplier - filtrate in collecting duct 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 of excreted
Sweating
Explain the role of the hypothalamus in osmoregulation
- Osmosis of water out of osmoreceptors in hypothalamus causes them the shrink
- This triggers the production of antiduretic hormone (ADH)
Explain the role of the posterior pituitary gland
Stores and secretes ADH produced by the hypothalamus
Explain the role of ADH in osmoregulation
- Makes cells lining collecting duct more permeable to water: binds to receptors > activates phosphorylase > vesicles with aquaporins on membrane fuse with cell surface membrane
- Makes cells lining collecting duct more permeable to urea: Water potential in interstitial fluid decreases, more water reabsorbed = more concentrated urine
