Homeostasis Flashcards
What is negative feedback?
- When there is a deviation from normal values in the body and it is restored to their original values
- This involves the nervous system + hormones
Role of pancreas
- Detects change in blood glucose levels
- Contains endocrine cells in Islet of Langerhans = release hormone insulin/glucagon to return blood glucose level to normal value
Role of adrenal glands
Releases adrenaline when body thinks there is danger = more glucose released from store of glycogen in liver
Describe negative feedback cycle for increase in blood glucose level
- Increase in blood glucose level
- Detected by beta cells in IOL in pancreas = release insulin
- Liver cells more permeable to glucose + enzymes activated to convert glucose into glycogen
- Glucose removed from blood + stored as glycogen in cells = blood glucose returned to normal
Describe negative feedback cycle for decrease in blood glucose level
- Decrease in blood glucose level
- Detected by alpha cells in IOL in pancreas = release glucagon + adrenal glands = adrenaline
- Second messenger model = activate enzymes to hydrolyze glycogen
- Glycogen is hydrolyzed to glucose = glucose released back into blood
What is glycogenesis?
Excess glucose converted to glycogen in the liver when blood glucose is higher than normal
What is glycogenolysis?
Hydrolysis of glycogen into glucose in the liver when blood glucose levels are lower than normal
What is gluconeogenesis?
- Creating glucose from non-carbs stored in the liver
- Occurs when all glycogen has been hydrolyzed into glucose and the body still needs more
Describe role of beta cells
- In the IOL
- Detect when BGL is too high = secrete insulin = decrease blood glucose
Explain how insulin decreases BGL
1) Attach to receptors on surface of target liver cells: Change to 3’ of channel proteins = more glucose absorbed via facilitated diffusion into liver
2) More protein carriers incorporated into cell membrane: Increases SA = more glucose absorbed from blood into cells
3) Activates enzymes involved in converting glucose-glycogen: Causes glycogenesis
Explain how more protein carriers are incorporated into the cell membrane
- Insulin binds to insulin receptor = intracellular chemical released
- Chemical causes vesicles containing channel proteins to fuse with cell membrane = increased SA
Describe role of alpha cells
- In the IOL
- Detects when BGL is too low = secrete glucagon = increase blood glucose
Explain how glucagon increases BGL
1) Attaches to receptors on surface of target liver cells
2) Binding = activates adenylate cyclase protein to convert ATP into cyclic AMP = activates enzyme protein kinase = hydrolyze glycogen into glucose
3) Activates enzymes involved in conversion of glycerol + amino into glucose
Describe the second messenger model
1) Glucagon binds to the glucagon receptors
2) Binding = change in shape of enzyme adenyl cyclase = activated
3) Activated enzyme convert ATP into cAMP which is the 2nd messenger
4) cAMP activates protein kinase enzyme = hydrolyze the glycogen into glucose
Describe the secondary messenger model of adrenaline
When BGL is low adrenaline is secreted:
1) Attaches to receptors on target cells = protein activated = convert ATP to cAMP
2) cAMP activates enzyme = hydrolyze glycogen into glucose
Describe type 1 diabetes
- Body unable to produce insulin
- Starts in childhood as a result of autoimmune disease where beta cells are attacked
- Insulin injections for treatment
Describe type 2 diabetes
- Receptors on the target cells lose responsiveness to insulin
- Develops in adults due to obesity + poor diet
- Treatment is controlling carb intake + exercize + insulin sometimes
Role of kidney
Osmoregulation occurs in the nephrons which are located in the medulla of the kidney
What is a nephron?
- Long tubules surrounded by capillaries in the kidney
- Site of osmoregulation
- Approx. 1 million nephrons per kidney
Describe the structure of a nephron
1) Afferent arteriole that branches into glomerulus
2) Renal capsule surrounding glomerulus
3) Proximal convoluted tubule
4) Loop of Henle
5) Distal convoluted tubule
6) Collecting duct
Function of nephrons
- Filters the blood to remove waste and selectively reabsorb useful substances back into the blood
- Produce urine
What does urine contain?
- Water
- Dissolved salts
- Urea
- Hormones
- Excess small substances e.g. vitamins
What is not passed into healthy urine?
- Proteins + blood cells: Too large to be filtered out of blood
- Glucose: Gets filtered out but is reabsorbed at the selective reabsorption stage in PCT
6 stages of filtering and reabsorption
1) Ultrafiltration in glomerulus + renal capsule
2) Selective reabsorption in PCT
3) Maintaining Na+ ion gradient in descending LOH
4) Maintaining Na+ ion gradient in ascending LOH
5) Water moves out of DCT
6) Water moves of collecting duct to blood + carries remaining liquid to ureter
Describe ultrafiltration
- Blood enters via afferent arteriole into capillaries of glomerulus = high HSP = H2O + glucose + mineral ions forced out of capillaries = glomerulus filtrate
- Proteins + blood cells too big = remain in blood = blood leaves via efferent arteriole
Describe selective reabsorption
- 85% of glomerulus filtrate is reabsorbed back into blood in PCT
- Leaves urea + excess mineral ions in blood
- Concentration of Na+ is decreased in PCT cell as Na+ is AT out into the blood in capillaries
- Concentration gradient = Na+ diffuse down from lumen into PCT epithelial cells via co-transporter protein
- Co-transports glucose with the Na+ ions = increase in glucose concentration = diffuse down CG from PCT epithelial cells to blood
Adaptations of epithelial cells of PCT
- Lots of microvilli: Provide large SA for reabsorption
- Lots of mitochondria: Provide energy for AT
Describe how the Na+ ion gradient is maintained by LOH
- Mitochondria in the wall of cells provide energy for AT = Na+ ions out of ascending limb
- Accumulation of Na+ ions outside nephron = lowered WP = H2O diffuses out via osmosis into interstitial space from descending limb
- Then reabsorbed into blood in capillaries
- At base of ascending limb Na+ ions transported by diffusion as there is low concentration of Na+ and solution is dilute
Describe adaptations of LOH
- Descending limb: Walls are thinner = permeable to water
- Ascending limb: Walls thicker = impermeable to water = Na+ ions AT out
Describe reabsorption of H2O at DCT + collecting duct
- Filtrate at end of PCT = very dilute as Na+ ions AT out
- Filtrate moves into DCT + CD
- Medulla surrounding this part of nephron has a high concentration = more H2O diffuses out
- Remaining liquid = transported to ureter = urine
How will the length of the LOH differ in a desert animal?
- Longer LOH
- Longer = more Na+ ions AT out = more negative WP = more H2O out via osmosis
- Results in more H2O reabsorbed into blood = very concentrated urine
- Important for survival as essential to limit H2O loss in urine due to not having much in their environment
What is osmoregulation?
Negative feedback which controls the WP of the blood to make sure it remains constant
What happens to blood with low WP
- Hypertonic
- Too much H2O = leaves the cells + moves into blood via osmosis
- Cells = shrivel
What happens to blood with high WP
- Hypotonic
- Too less H2O = moves from blood into cells via osmosis
- Cells = burst
Causes of low WP
- Too much sweating
- Not drinking enough H2O
- Lots of ions in diet
Causes of high WP
- Drinking too much H2O
- Not enough salts in diet
Describe corrective mechanism for low WP
More H2O reabsorbed via osmosis into blood from nephrons = urine more concentrated
Describe corrective mechanism for high WP
Less H2O reabsorbed via osmosis into blood from nephrons = urine more dilute
What is the hypothalamus?
Where change is detected by osmoreceptors + ADH is produced
What is the posterior pituitary gland?
Where ADH is secreted from into blood in capillaries
Describe response by osmoreceptors in low WP
H2O leaves osmoreceptors via osmosis = shrivelling = stimulates hypothalamus to produce more ADH = secreted by PP gland into blood
Describe response by osmoreceptors in high WP
H2O enters osmoreceptors via osmosis = stimulates hypothalamus to produce less ADH
Function of ADH
- Travels through blood to target organ kidney
- Increases permeability of walls of CD + DCT = more water leaves nephron= reabsorbed into blood = urine concentrated
Describe how ADH increases permeability of CD + DCT
- ADH bind to receptors on cell membrane = activates phosphorylase enzyme
- Enzyme causes vesicles with aquaporins to fuse to cell membrane
- More aquaporins = more water leaves DCT + CD and reabsorbed
What is an aquaporin?
Protein channels for water to pass through
Describe the negative feedback cycle for increased WP
- Increase detected by osmoreceptors in hypothalamus
- Hypothalamus produces + releases less ADH
- DCT + CD walls become less permeable to H2O
- Less H2O reabsorbed into blood = dilute urine
Describe the negative feedback cycle for decreased WP
- Decrease detected by osmoreceptors in hypothalamus
- Hypothalamus produces more ADH
- PP gland releases more ADH into blood
- DCT + CD walls become more permeable to H2O
- More H2O reabsorbed into blood = concentrated urine
