Homeostasis Flashcards
1
Q
What is homeostasis?
A
- maintenance of internal conditions in the body
2
Q
What is negative feedback?
A
- reversing a change in the body to being conditions back to normal limits
- e.g. blood glucose levels
3
Q
What is positive feedback?
A
- the original stimulus produces a response that causes the effect to deviate even more from the normal range
- e.g. dilation of the cervix during labour
4
Q
What effect does insulin have on blood glucose?
A
- blood glucose decreases
- β cells in islets of Langerhans in pancreas secrete insulin
- increases absorption of glucose by liver and muscle cells
- glycogenisis occurs
- increased absorption of glucose by adipose cells
- conversion of glucose to lipids
- blood glucose levels decrease and return to normal
5
Q
What are the effects of glucagon?
A
- α cells in islets of Langerhans in pancreas secrete glucagon
- hydrolysis of glycogen into glucose by muscle and liver cells
- causes gluconeogenesis - formation of glucose from other molecules
- activates enzymes involved in the conversion of glycerol into glucose
- blood glucose levels increase and return to normal
6
Q
How does insulin affect cells?
A
- rate of uptake in liver cells is limited by the number of carrier molecules
- in muscle and adipose tissue, insulin causes more carrier proteins to join to the membrane and therefore increase the rate of glucose uptake
7
Q
Describe the second messenger model
A
- hormone binds the receptor on the cell-surface membrane of the liver cell
- hormone binds to the receptor causes it to change shape on the inside of the membrane this activates the adenyl cyclase enzyme
- the activated adenyl cyclase converts ATP to cyclic AMP which acts as the second messenger
- the cAMP changes shape and activates the protein kinase enzyme
- the active protein kinase enzyme catalyses the conversion of glycogen to glucose
8
Q
A
9
Q
What are the characteristics of type 1 diabetes?
A
- rarer
- developed in childhood
- body is unable to produce insulin
- result of autoimmune response
- B cells attacked (pancreas)
- can be controlled by daily insulin injections, managing carb intake and exercising carefully
10
Q
What are the characteristics of type 2 diabetes?
A
- most common
- developed over the age of 40
- glycoprotein receptors on body cells lost or losing responsiveness to insulin
- controlled by regulating carb intake and matching this to exercise
- may be supplemented by insulin injections
11
Q
What is glycogenesis?
A
- conversion of glucose into glycogen
- when blood glucose is higher than normal the liver removes glucose from the blood and converts it to glycogen
12
Q
What is gluconeogenesis?
A
- the production of glucose from sources other than carbohydrate
- when then supply of glycogen is exhausted, the liver can produce glucose from non-carbohydrate sources such as glycerol and amino acids
13
Q
What is glycogenolysis?
A
- the breakdown of glycogen to glucose
- when blood glucose conc is lower than normal, the liver can convert stored glycogen back into glucose which diffuses into the blood to restore the normal blood glucose concentration
14
Q
What is the structure of the kidneys?
A
- outer fibrous capsule
- cortex, made up of Bowman’s capsules, convoluted tubules and blood vessels
- medulla, made up of loops of Henle, collecting ducts and blood vessels
- renal pelvis collects urine into the ureter
15
Q
How is pressure generated for ultrafiltration?
A
- the incoming (afferent) arteriole is wider than the outgoing (efferent) arteriole
- high blood pressure forces small molecules through the capillary walls into the Bowman’s capsule
16
Q
What layers do cells have to pass through in ultrafiltration?
A
- the endothelium of the capillary walls
- the basement membrane
- podocyte cells
- the capillary walls are specialised with many pores or fenestrations
17
Q
What is ultrafiltration?
A
- small molecules are forced out of the blood through fenestrations in the capillary to form the glomerular filtrate
18
Q
A
19
Q
Why does selective reabsorption occur?
A
- there is a high concentration of protein left in the blood, resulting in a low water potential
20
Q
How are the cells lining the proximal convoluted tubule adapted for reabsorption?
A
- the epithelial cells have microvilli for a large surface area
- infoldings at the bases that give a large surface area to transfer reabsorbed substances into the blood capillaries
- high density of mitochondria to produce ATP for active transport in the endothelial cells have
21
Q
How are useful substances reabsorbed?
A
- sodium ions are actively transported via sodium-potassium pump into blood capillaries
- sodium ions are conc is now lowered and a conc gradient forms
- Na+ ions down the conc gradient by facilitated diffusion through carrier proteins
- carrier proteins also transport another molecule (glucose or amino acid) via co-transport into the proximal convoluted tubule and diffuse into the blood
22
Q
Why might a diabetic person have glucose in their urine?
A
- they don’t produce enough insulin to remove glucose from the blood and so this can be in the urine
23
Q
What is the function of the loop of Henle?
A
- reabsorb water
- create a high concentration of sodium ions and chloride ions in the tissue fluid of the medulla
- allows water to be reabsorbed from the contents of the nephrons as they pass through the collecting duct
24
Q
What are the 2 parts of the loop of Henle?
A
- the descending limb: permeable to water but not permeable to mineral ions such as sodium and chloride
- the ascending limb: is wider, with thicker walls that are permeable to mineral ions
25
Q
Describe how water is reabsorbed in the loop of Henle
A
- descending limb’s walls are permeable to water, so water leaves the filtrate via osmosis into the interstitial space.
- filtrate loses water as it moves down the descending limb, reaching its lowest water potential at the tip in the medulla.
- water that is lost is reabsorbed into blood in the surrounding capillaries by osmosis and is carried away.
- the ascending limb is impermeable to water, but is permeable to sodium (Na+) and chloride (Cl-) ions.
- Na+ and Cl- diffuse out of the filtrate into the interstitial space at the bottom of the ascending limb, due to the low water potential of the filtrate.
- the ions in the interstitial space in the medulla are concentrated, making its water potential very low.
- Na+ and Cl- need to be actively transported out of the top of the ascending limb, because their concentration in filtrate decreases as it ascends (the water potential increases).
- there is a water potential gradient in the interstitial space, with the highest water potential in the cortex and an increasingly lower water potential deeper into the medulla.
- counter-current of ions, ensure water always leaves the loop of Henle and is reabsorbed
26
Q
How can more water be conserved in dry conditions?
A
- increase the length of the loop of Henle
- the water potential can be lowered/higher salt concentration
- greater water potential gradient
- more water is reabsorbed
- small volume of urine produced
27
Q
How is change in blood water potential detected?
A
- osmoreceptors in the hypothalamus in the brain
28
Q
What hormone controls urine concentration?
A
- anti-diuretic hormone
- ADH
29
Q
How is ADH released?
A
- cell bodies in the neurosecretory centre produce ADH
- ADH passes along the axon which terminates in the posterior pituitary gland
- ADH is released into the blood
30
Q
What is the effect of ADH on the cells of the distal convoluted tubule?
A
- ADH detected by cell receptors
- enzyme controlled reactions occur
- vesicles containing water permeable channels (aquaporins) fuse to the membrane
- more water can be absorbed
- permeability of the collecting duct is increased
- less water in urine/more concentrated
