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BGS Bio A21 > U1T1 - Homeostasis > Flashcards

U1T1 - Homeostasis Flashcards

The principles of homeostasis

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1
Q

What is all cellular activity controlled by?

A

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

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2
Q

What are the steps in a negative feedback response?

A

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.

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3
Q

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

A

Target Organ.

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4
Q

What organs is the urinary system composed of?

A

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

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5
Q

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

A

Sweating + vasodilation (hot)

Goosebumps, shivering + vasoconstriction (cold)

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6
Q

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

A

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

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7
Q

What are the tissue layers present in the kidneys?

A

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

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8
Q

What are the key functional parts of the nephron?

A

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

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9
Q

Describe nephrons.

A

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

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10
Q

What are the 2 main steps in nephrons producing urine?

A

Ultrafiltration + selective reabsorption.

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11
Q

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

A

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.

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12
Q

What are the 3 key layers when considering ultrafiltration?

A

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

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13
Q

What is the issue with ultrafiltration?

A

Colloidal Osmotic Pressure + Glomerular Filtrate Pressure.

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14
Q

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

A

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

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15
Q

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

A

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.

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16
Q

What are the 2 parts of the loop of henle?

A

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

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17
Q

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

A

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

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

18
Q

What is the water potential of pure water?

A

0 kPa (at standard temp + pressure)

19
Q

Are Y + Ys negative or positive values?

A

Negative.

20
Q

How does the nephron control urine conc?

A

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.

21
Q

Why might more ADH be released into the bloodstream?

A

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

22
Q

Describe the action of ADH in the nephron?

A

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.

23
Q

What is mammalian tissue made up of?

A

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

24
Q

What are the 3 main features of homeostatic responses?

A

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

25
Q

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

A

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.

26
Q

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

A

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.

27
Q

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

A

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

28
Q

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

A

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.

29
Q

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

A

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.

30
Q

Comment on changes in sodium conc throughout the nephron.

A

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.

31
Q

Explain changes in urea conc as it moves along nephron.

A

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

32
Q

Why would flow rate fall throughout nephron?

A

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

33
Q

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

A

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

34
Q

Give an account of osmoregulation + the kidney.

A

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.

35
Q

Give an account of the kidney + excretion.

A

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.

36
Q

Why is homeostatic control of mammalian body systems essential?

A

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

37
Q

Describe how blood travels through the urinary system.

A

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

38
Q

What are the 2 main zones of the kidney?

A

Cortex + medulla.

39
Q

How does the structure of the capillary walls aid ultrafiltration?

A

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

40
Q

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

A

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

41
Q

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

A

Proteins forced through basement membrane + not reabsorbed.

42
Q

Which 2 regions absorb most water?

A

PCT + Collecting Duct

BGS Bio A21 (15 decks)

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