U1T1 - Homeostasis

Question 1

What is all cellular activity controlled by?

Answer 1

Enzymes. If pH/temp deviates, reaction rates drop so cells don’t function properly + death may occur.

Question 2

What are the steps in a negative feedback response?

Answer 2

Conditions cause level of factor to change from norm, change detected by receptors, receptors communicate info by hormone/nerve impulse to effectors, corrective mechanisms operates to restore factor to norm, receptors detect when norm restored + corrective mechanism turned off.

Question 3

What is the effector referred to if a hormone is involved in negative feedback?

Answer 3

Target Organ.

Question 4

What organs is the urinary system composed of?

Answer 4

Kidneys, renal artery + vein, ureters, bladder + urethra.

Question 5

What are some of the responses to hot + cold environments in humans?

Answer 5

Sweating + vasodilation (hot)

Goosebumps, shivering + vasoconstriction (cold)

Question 6

What are the 2 main functions of the urinary system + kidneys specifically?

Answer 6

Excretion of certain toxic metabolites (nitrogenous waste urea) + osmoregulation.

Question 7

What are the tissue layers present in the kidneys?

Answer 7

Tough outer fibrous capsule, darker outer tissue layer known as cortex, lighter inner layer called medulla, central cavity called pelvis + ureter.

Question 8

What are the key functional parts of the nephron?

Answer 8

Bowman’s capsule, proximal convoluted tubule, descending + ascending limbs of loop of Henle, distal convoluted tubule + collecting duct.

Question 9

Describe nephrons.

Answer 9

Each nephron closely associated with blood vessel network which come from renal artery branch + drain into renal vein.

Question 10

What are the 2 main steps in nephrons producing urine?

Answer 10

Ultrafiltration + selective reabsorption.

Question 11

Why is the blood in the glomerulus under high hydrostatic pressure?

Answer 11

Differing diameters of afferent + efferent arterioles. Aff has wider diameter, creating bottleneck effect, increasing BP. Short distance between kidneys + heart so little pressure decrease + coiled nature of glom capils restricts blood flow so higher pressure.

Question 12

What are the 3 key layers when considering ultrafiltration?

Answer 12

Capillary endothelium of glomerulus, basement membrane + inner wall of Bowman’s capsule.

Question 13

What is the issue with ultrafiltration?

Answer 13

Colloidal Osmotic Pressure + Glomerular Filtrate Pressure.

Question 14

What is the net pressure in the kidneys? (out/in)

Answer 14

Hydrostatic is more than Colloidal + Glomerular so net pressure is out of blood into capsular space. Effective Filtrate Pressure.

Question 15

In terms of selective reabsorption, what is reabsorbed from the lumen of the PCT?

Answer 15

Osmotic gradient produced due to high conc of ions in cells around it. Causes water to be reabsorbed. V.small protein molecules in GF by pinocytosis at microvilli base, broken down emzymatically into AAs.

Question 16

What are the 2 parts of the loop of henle?

Answer 16

Thin descending limb which is permeable to water + thicker ascending limb which is impermeable to water.

Question 17

Describe the conc of water molecules, solute potential, water potential + whether hypo/hyper/isotonic:
Solution with greater conc of solute molecules
Solution with lower conc of solute molecules

Answer 17

Lower conc water molecules, lower Ys, lower Y + hypertonic.

Higher conc water molecules, higher Ys, higher Y + hypotonic.

Question 18

What is the water potential of pure water?

Answer 18

0 kPa (at standard temp + pressure)

Question 19

Are Y + Ys negative or positive values?

Answer 19

Negative.

Question 20

How does the nephron control urine conc?

Answer 20

Alters amount of water which is reabsorbed. Most water reabsorbed in PCT + some is descending limb of LoH, collecting duct can change its water permeability depending on hydration state. ADH responsible.

Question 21

Why might more ADH be released into the bloodstream?

Answer 21

If osmoreceptors detect that blood is too concentrated/has v.negative solute potential/is becoming too hypertonic, then more ADH released into blood stream.

Question 22

Describe the action of ADH in the nephron?

Answer 22

ADH travels through blood + reaches kidneys. Within nephron, cells lining collecting ducts + DCTs + collecting ducts are sensitive to ADH so become more water permeable due to insertion of more aquaporins into cell membranes. More water reabsorbed into blood + less goes to urine so less urine made. Solute potential starts to increase back to norm. Detected by osmoreceptors + amount of ADH released is reduced as a result of negative feedback.

Question 23

What is mammalian tissue made up of?

Answer 23

Collection of cells bathed in fluid medium/extracellular fluid/tissue fluid. Its composition must be kept constant irrespective of external conditions.

Question 24

What are the 3 main features of homeostatic responses?

Answer 24

Control system with receptors to monitor factor, corrective mechanism to return levels to normal + negative feedback system to stop corrective measure when levels normal.

Question 25

What organism might have a longer loop of henle + why?

Answer 25

Saltwater organism e.g. Yellow Tang. More conc urine as can’t use salty water so need plenty of time and space to reabsorb water.

Question 26

What organism might have a shorter loop of henle + why?

Answer 26

Freshwater organism e.g. Sturgeon. Less conc urine as can use water around them. Don’t need to reabsorb much water as they aren’t going to have trouble getting any.

Question 27

Why might the osmoreceptors detect that blood is hypertonic/too concentrated?

Answer 27

Dehydration through sweating through heat/exercise.
Salty foods.
Not drinking much water.

Question 28

How would osmoregulation operate if the osmoreceptors detect that blood was too hypotonic?

Answer 28

Less ADH released, DCT + collecting duct less permeable, fewer aquaporins, less water reabsorbed, more, less concentrated urine. Solute potential of blood decreases back to set point. Detected by osmoreceptors so more ADH released thanks to negative feedback.

Question 29

Explain the changes in the composition of protein + glucose between afferent arteriole + end of PCT.

Answer 29

Protein too large to pass through. Some small proteins pass through + reabsorbed by pinocytosis. Basement membrane acts as effective filter. Glucose small but reabsorbed later by active transport.

Question 30

Comment on changes in sodium conc throughout the nephron.

Answer 30

Sodium passes through Bowman’s Capsule into filtrate. Conc increases at Loop of Henle as water moves out by osmosis. Sodium conc adjusted in DCT by active transport. Water + sodium reabsorbed in similar amounts.

Question 31

Explain changes in urea conc as it moves along nephron.

Answer 31

Urea conc higher as water absorbed by osmosis. Increases again at start of collecting duct as more water reabsorbed.

Question 32

Why would flow rate fall throughout nephron?

Answer 32

Lower solution volume, further from heart, more friction, pressure decreases.

Question 33

Why would glucose rate be higher in urine at 30c?

Answer 33

Reduced resp rate, reduced ATP production, reduce active transport rate. Reabsorption rate slower so not all glucose reabsorbed.

Question 34

Give an account of osmoregulation + the kidney.

Answer 34

Water potential monitored by osmoreceptors in hypothalamus. Low wp causes ADH secretion so released into blood from pituitary gland. ADH increases collecting duct permeability, more water reabsorbed, more concentrated urine, drinking water increaes wp of plasma + when wp returns to normal, ADH secretion reduced.

Question 35

Give an account of the kidney + excretion.

Answer 35

Blood enters glomerulus under high hydrostatic pressure as afferent wider than efferent. Ultrafiltration from glomerulus to BC. Comp of filtrate is plasma - plasma proteins as some molecules too lare to pass through basement membrane. Capsule lining leaky due to podocyte structure, wp plasma lower than filtrate due to plasma proteins so osmotic gradient filtrate to blood. Hydrostatic pressure must be higher than osmotic gradient. Toxic substances remain throughout whilst useful reabsorbed. Glucose reabsorbed by active transport in PCT. Microvilli in PCT increase SA for reabsorption + mitochondria provide energy for AT. WP gradient from PCT to capillary network reduced so water leaves by osmosis. Small proteins reabsorbed by pinocytosis. LoH produces high osmotic gradient in medulla so water reabsorbed from collecting duct. Salts reabsorbed from DCT.

Question 36

Why is homeostatic control of mammalian body systems essential?

Answer 36

Provide optimum conditions for enzyme reactions (pH + temp) + avoids osmotic issues in cells + body fluids.

Question 37

Describe how blood travels through the urinary system.

Answer 37

Aorta + renal artery to kidney at high pressure for filtration. Filtered blood leaves kidney via renal vein whilst excretory products + water go to ureter as urine to bladder for storage. Sphincter muscles in bladder base control urine release which exits body through urethra.f

Question 38

What are the 2 main zones of the kidney?

Answer 38

Cortex + medulla.

Question 39

How does the structure of the capillary walls aid ultrafiltration?

Answer 39

Single layer of squamous endothelial cells contain small pores + B’sC lined with podocytes.

Question 40

Blood plasma (Ws = -3.5, Wp = 6.5) Renal Filtrate (Ws = -0.5, Wp = 1.2) Calculate the net filtration force.

Answer 40

Blood Plasma (-3.5 + 6.5 = 3) + Renal Filtrate (-0.5 + 1.2 = 0.7) = 2.3kPa

Question 41

Why might there be protein in the urine of someone with high blood pressure?

Answer 41

Proteins forced through basement membrane + not reabsorbed.

Question 42

Which 2 regions absorb most water?

Answer 42

PCT + Collecting Duct