Chapter 14: Homeostasis Flashcards
List and explain features of the epithelial cells of the PCT that helps the process of selective reabsorption.
Microvilli at luminal membrane
- Allows larger surface area for absorption of Na+, glucose and amino acids
Many mitochondria
- Provides energy for Na+ and K+ pumps
Tight junctions between cells
- Holds adjacent cells together to prevent fluid passing through
Has many co-transport proteins at luminal membrane
Explain what is meant by the term homeostasis.
The maintaining of the body’s internal environment within a set range
Describe the roles of hypothalamus and posterior pituitary in osmoregulation.
Hypothalamus detects change in water potential of blood
If water is low, osmoreceptors shrink = ADH produced in hypothalamus = secreted by posterior PG
Transported to kidney resulting in increase of aquaporins in luminal membranes of collecting duct cells to become more permeable to water = more water reabsorption
Explain how dip sticks function to test for glucose in a sample of urine.
Dip sticks has immobilised enzymes, glucose oxidase, and peroxidase
Dip sticks dipped in urine
- Glucose oxidase oxidises glucose producing gluconic acid and hydrogen peroxide
Hydrogen peroxide reacts with colourless substance to produce colour
Compare colour produced to colour chart = darker means higher concentration
Outline how a high blood glucose concentration returns to normal in a healthy person.
Detected by B cells in pancreas = more insulin secreted into bloodstream = negative feedback mechanism
Insulin mode of action:
- Activates glucokinase so glucose is phosphorylated, trapping glucose inside cells such as liver
- Activates glycogen synthase so allows for glucose converted into glycogen
- Increases glucose uptake by muscle/fat cells by increasing permeability of glucose towards these cells by adding GLUT4 proteins into membrane of vesicles fusing with CSM
- Inhibits secretion of glucagon
- Increase respiration rate
Outline how negative feedback mechanism works.
Receptor detects a change in factor away from normal range
Nerve impulse sent/hormone released, and reaches target effector
Effector performs corrective actions so factor returns to normal range
Name the main filtration barrier in nephron that allows creatinine to pass into the capsule but stop RBC from passing through.
Basement membrane
Describe the process of selective reabsorption
Sodium-potassium pumps Na+ out of PCT cells into blood
Na+ ion concentration decreases in epithelial cells
Na+ enter PCT cells from filtrate by facilitate diffusion through co-transporter protein, carrying another substrate i.e glucose
Then the substances will move down concentration gradient into blood
Water enters PCT cells because lower blood water potential due to filtrate
Describe how the structure of the nephron and its associated blood vessels are adapted to the process of ultrafiltration.
Capillary
- Has many pores
Afferent arteriole wider than efferent arteriole
- High BP = fluid forced into Bowman’s capsule
Podocytes
- Extensions that form slit pores
Basement membrane
- Mesh of collagen, act as main barrier against larger molecules such as RBC, only small solutes and water can pass through
Outline how a biosensor works
Recognition layer contains glucose oxidase reacting with glucose in blood to form gluconic acid and hydrogen peroxide
Hydrogen peroxide oxidised at electrode = electron transfer detected
Biosensor then
i) Amplifies current
ii) Read by processor
iii) Produce digital reading for blood glucose concentration
Give advantages of using biosensor
Reusable
Gives accurate, quantitative reading of blood glucose concentration
Outline the enzyme cascade if glucose concentration decreases
Glucagon binds to receptors in CSM of liver cells = causes conformational change in receptor that activates G protein
G protein activates adenylyl cyclase = adenylyl cyclase catalyses conversion of ATP to cyclic AMP, secondary messenger triggering enzyme cascade:
cAMP binds to and activates protein kinase A enzymes = protein kinase A enzymes activate glycogen phosphorylase enzymes = breaksdown glycogen to glucose
Cascade becasue amplifies original signal from glucagon = results in releasing of extra glucose by liver
Outline what happens in guard cells they want to become flaccid
ABA is a stress hormone = produced during drought
ABA binds to receptor and causes 2 things
i) Inhibits proton pumps = stops protons from leaving guard cells
ii) Causes calcium ions to move into cytoplasm of guard cells through CSM
Calcium ions as secondary messenger
i) Causes channel proteins to open to allow negatively charged ions leave guard cells
ii) So guard cells positively charged, more channel proteins open allowing K+ leave guard cells, and closes channel proteins so stop K+ from entering
Therefore, loss of WP = water leaves guard cells by osmosis = guard cells flaccid
Explain how a tumour develops
Uncontrolled mitosis = abnormal mass of cells formed = no apoptosis
Explain mechanism of ADH
ADH binds to receptors on collecting duct cells
Aquaporins phosphorylated = vesicles with membranes containing aquaporins move towards luminal membranes of collecting duct cells
Vesicles fuse with luminal membranes
Water moves through aquaporins down WP gradient into concentrated tissue fluid
