Control Of Blood Water Potential Flashcards
(49 cards)
1
Q
What are the eight parts of the excretory system?
A
- Vena cava
- Aorta
- renal vein
- Renal artery
- Kidneys
- Ureter
- Bladder
- Urethra
2
Q
What is the main functions of the kidneys?
A
- excretes toxins like urea
- manages water content of the blood
- manages ion (salt) content of the blood
3
Q
Which blood vessels carry oxygenated blood?
A
- aorta and renal artery
4
Q
Which blood vessels carry deoxygenated blood?
A
- vena cava and renal veins
5
Q
Which tubes does the urine pass from the kidney to the bladder through?
A
- ureter
6
Q
What organ is urine stored in before it leaves the body?
A
- bladder
7
Q
What are the eight structures of the kidney?
A
- Medulla (pyramids)
- Capsule
- Minor calyx
- Cortex
- Renal artery
- Renal vein
- Renal pelvis
- Ureter
8
Q
What is the medulla?
A
- inner region made of loops of Henle, collecting ducts and blood vessels
9
Q
What is the capsule and its function?
A
- fibrous outer membrane for protection
10
Q
What is the minor and major calyx? *not exam spec for context
A
- the extensions leading to the ureter
- major is multiple of them
11
Q
What is the cortex?
A
- outer region made of renal (Bowman’s) capsules, convoluted tubules and blood vessels
12
Q
What is the papilla of the medulla? *not exam spec for context
A
- inner regions of medulla connecting to the minor calyx
13
Q
What does the renal pelvis do?
A
- collects urine
14
Q
How is urea formed?
A
- from excess amino acids and process of deamination breaks down to form urea
15
Q
What are nephrons?
A
- Tubular structures in each kidney form the basic structural and functional units of the kidney
16
Q
Describe the structure of the nephron
A
- Bowman’s capsule
- glomerulus
- Renal artery
- Afferent arteriole
- Efferent arteriole
- Proximal convoluted tubule
- Distal convoluted tubule
- Collecting duct
- Loop of henle (descending limb)
- Loop of henle (ascending limb)
17
Q
Walls of glomerular capillaries have pores between their epithelial cells. Certain substances are able to pass through these pores and the capillary walls, into the nephron, forming the glomerular filtrate. Along with urea, give four other substances which are a) small enough to pass through & four that are b) too large to pass through
A
- a) glucose, amino acids, salts and water
- b) cellular components such as red blood cells, white blood cells, platelets and plasma proteins such as fibrinogen and albumin
18
Q
The efferent arteriole carrying blood away from the renal capsule, has a smaller diameter than the afferent arteriole. Why is the significance of this?
A
- it ensures that blood returning in to the venous circulation (and back to the right side of the heart) is
at a high enough pressure. This difference is also the main source of hydrostatic pressure that pushes the glomerular filtrate through the pores in the capillaries
19
Q
Glomerular filtration rate (GFR) is a good way of measuring the stage at which chronic renal disease is at – what might a very high, or very low GFR indicate?
A
- Too high might indicate hypertension (High blood pressure) and signs of kidney disease in its’ later stages (often accompanied by excess urination, fatigue and nausea)
- Too low may be an indication of inadequate flow through the glomerulus, perhaps a blockage in the kidneys or just a significant volume loss through dehydration
20
Q
Resistance to the flow of filtrate through the glomerulus has a number of contributing factors. Suggest what they might be, and how raising the hydrostatic pressure of the blood in the glomerulus might help to overcome them
A
- the low water potential of the blood in the glomerulus
- connective tissue present and epithelial cells of the blood capillary
- epithelial cells of the renal capsule
- hydrostatic pressure of the fluid in the renal capsule space
21
Q
Describe the steps of ultrafiltration
A
- Blood in the glomerular capillaries is under high hydrostatic pressure
- Filtrate (containing small molecules) is forced through small pores in the capillary endothelial lining by ultrafiltration
- passes through pores in the basement membrane (a porous protein mesh that acts as a filter.). These pores are too small so large plasma proteins cannot leave the blood
- Podocytes are specialised cells that line the Bowman’s capsule. In the final step, filtrate passes beneath and between podocyte branches called foot processes
22
Q
Describe how ultrafiltration produces glomerular filtrate
A
- Blood pressure / hydrostatic pressure;
- Small molecules / named example;
- Pass through basement membrane / basement
membrane acts as filter; - Protein too large to go through / large so stays behind;
- Presence of pores in capillaries / of podocytes;
23
Q
What are the steps for selective reabsorption of substances?
A
- All glucose in proximal convoluted tubule, along with some sodium and potassium ions, some water and all amino acids
- As filtrate moves through the loop of Henley, sufficient salts are reabsorbed back into blood by diffusion and water follows by osmosis
- Water is reabsorbed from the collecting duct - depends on what the body needs
24
Q
Approximately how much of the filtrate is reabsorbed back into the blood and kidney?
A
- 85%
25
Why would the cells lining the proximal convoluted tubule (epithelial cells) a) be folded and covered in microvilli, b) have many channel/carrier proteins and c) have many mitochondria?
a) Increases the surface area for reabsorption of substances such as glucose (and amino acids and ions)
b) Increased facilitated diffusion
c) Mitochondria release ATP (energy)
for active transport of glucose (ensures it all returns to the blood)
26
Using the diagram, explain how glucose is removed and reabsorbed from the filtrate, into the blood in the proximal convoluted tubule.
- Sodium ions and glucose absorbed by co-transport;
- (Co-transport) via carrier protein;
- Sodium ions removed (from epithelial cell) by active transport into blood;
- Maintains low concentration of sodium ions (in epithelial cell) / maintains sodium
ion concentration gradient (between tubule lumen and epithelial cell);
- Sodium ions enter epithelial cells by facilitated diffusion taking glucose with them
(from tubule);
- Glucose moved by facilitated diffusion into blood (from epithelial cells);
27
What numbers could you replace Na+ and K+ with?
- 3NA+
- 2K+
28
Why can Na+ and K+ be replaced with 3Na+ and 2K+?
- Na+/K+ pump helps to maintain osmotic potentials
- Water can freely diffuse by osmosis back into the blood down a water potential gradient
29
What happens if glucose levels are too high?
- all the glucose transporters in the PCT become saturated - in this case, their capacity to move glucose is exceeded and the excess cannot be reabsorbed back into the blood
- Some glucose may appear in the urine
- In diabetics, high levels of glucose in the blood can lead to diabetic kidney disease
30
How is the gradient of Na+ ions maintained by the loop of henle?
- Sodium ions are actively transported out of the ascending limb of the loop of Henle, using ATP provided by the many mitochondria in the cells of its wall
- This creates a low water potential (high ion concentration) in the region of the medulla between the two limbs, (known as the interstitial region). The walls of the ascending limbs are very thick and practically impermeable to water, so barely any escapes by osmosis – which would normally be the case.
- Walls of the descending limb are extremely permeable to water, and because of the low water potential in the interstitial region, it passes out of the filtrate by osmosis. Water then moves from the interstitial space into capillaries (the blood) to be carried away
- As the filtrate passes down the descending limb, water is lost by this method. The lowest water potential is reached by the time the filtrate reaches the base/bottom of the loops (the point of the bend)
- Sodium ions diffuse out of the filtrate at the base of the ascending limb, moreover, they are actively pumped out along its length – as a result, the water potential starts to increase
- An interstitial space exists between the ascending limb and the collecting duct. A water potential exists in this region – highest in the cortex and lowest in the medulla
- The collecting duct is permeable to water so as the filtrate moves down it, water passes out by osmosis, and again, passes into capillaries to be carried away
- The loop of Henle acts as a counter-current multiplier; this ensures that there is always a water potential gradient drawing water out of the tubule (even though water is lost from the collecting duct, lowering its water potential, an even greater one exists in the interstitial space)
- By the time the filtrate leaves the collecting duct (now called urine), it has lost most of its water to become more concentrated than the blood
31
What is the final step of maintaining a gradient of Na+ ions by the loop of Henle?
- cells making up the distal convoluted tubule are lined with microvilli and mitochondria, allowing them to reabsorb material from the filtrate by active transport
- Under the influence of various hormones, its permeability is altered to make final adjustment to the water and salt level, to control blood pH
32
Explain the role of the loop of Henle in the absorption of water from the filtrate.
- In the ascending limb sodium(ions) actively removed;
- Ascending limb impermeable to water;
- In descending limb sodium(ions) diffuse in;
- Descending limb water moves out / permeable to water;
- Low water potential / high concentration of ions in the medulla / tissue fluid;
- The longer the loop / the deeper into medulla, the lower the water potential in
medulla / tissue fluid;
- Water leaves collecting duct / DCT; by osmosis / down water potential gradient;
33
A species of crayfish lives in freshwater. This crayfish does not have kidneys but it does have an organ which excretes nitrogenous waste and controls the amount of water in its body. Using the diagram:
a) Describe how excretion in this organ differs from excretion in a human nephron.
b) Suggest how the production of large amounts of dilute urine enables the crayfish to survive in freshwater.
a) Ammonia not urea; Ammonia (into labyrinth) enters by diffusion, not (ultra) filtration; Reabsorption of glucose from labyrinth, not PCT / no reabsorption in PCT; All salt reabsorbed / no salt in urine, comparison to humans; Concentrated urine not produced;
b) Water potential lower in cytoplasm of cells / freshwater higher water potential than cells / idea of water potential gradient; (Removal of excess water) prevents osmotic damage;
34
What is osmoregulation?
- balancing the salt and water levels in the blood/cells
35
In which ways is water taken in?
- diet, produced in aerobic respiration
36
In which ways is water lost?
- sweating
- urination
- exhalation
37
The cytoplasm of all cells is largely composed of water, as is blood plasma. Maintaining water levels is vital to prevent harmful changes to cells as a result of osmosis. Explain what happens if there is a) too much water in the blood, and b) too little water in the blood
- Too much water in blood = higher water potential outside the cells than inside them;
- water moves into cells via osmosis; cells swell, leads to lysis (bursting).
- Too little water in blood = higher water potential inside cells than outside;
- water moves out of cells via osmosis; Has dehydrating effect; can lead to cell death
38
What is the role of hormones in osmoregulation?
- achieved by the hormone ADH (antidiuretic hormone)
- makes distal convoluted tubule and collecting duct more permeable to water so more gets absorbed back into the bloodstream
39
Describe the steps of osmoregulation for high water potential
- Water potential high – water intake increased, and salts used in metabolism/excreted not being replaced in diet
- Increase detected and osmoreceptors of hypothalamus stimulated – efforts made to reduce water level (thirst centre not stimulated)
- Hypothalamus increases frequency of nerve impulses to posterior pituitary gland to reduce / prevent the release of ADH
- With little/no ADH in the blood, permeability of collecting duct to water and urea decreases
- Less water is reabsorbed into blood from collecting duct. A large amount of dilute urine is produced
- Fall in water potential (correction) detected by osmoreceptors in hypothalamus
- Pituitary gland raises its ADH release back to normal levels (by negative feedback)
- Correct water potential
40
Describe the steps of osmoregulation for low water potential
- Water potential is low – reduced water intake, increased sweating, increased salt intake
- Change detected and osmoreceptors (which have shrunk due to water loss) of hypothalamus stimulated
- Hypothalamus secretes ADH which passes to posterior pituitary gland to be secreted into capillaries
- ADH binds to specific protein receptors on cells lining distal convoluted tubule and collecting duct – this activates phosphorylase enzyme within cells, causing vesicles to move to and fuse with the cell-surface membrane
- Vesicles contain aquaporins (water channel proteins) which become added to the cell-surface membrane, and water permeability increases - more water is reabsorbed by osmosis
- ADH causes collecting duct to become more permeable to urea – this moves out into interstitial region, lowering its’ water potential - encourages further water loss from collecting duct
- A small amount of concentrated urine produced
- Rise in water potential (correction) detected by osmoreceptors
- Pituitary gland reduces ADH release – permeability of collecting duct returns to normal
- Correct water potential
41
A. Name the part of the body which releases antidiuretic hormone (ADH) into the blood
B. Alcohol decreases the release of ADH into the blood. Suggest two signs or symptoms which may result from a decrease in ADH
C. Describe the effect of ADH on the collecting ducts in kidneys
a) Posterior pituitary;
b) Dehydration/thirst; Frequent urination or increase in
volume of urine; Less concentrated urine or dilute
urine or urine paler/lighter in colour;
c) (Stimulates) addition of channel proteins /
aquaporins into membrane; Increases permeability to water or more water (re)absorbed; by osmosis;
42
The table shows the concentrations of dissolved substances in different regions of a nephron in the presence and absence of antidiuretic hormone. Describe and explain the effect of ADH on the volume and concentration of urine produced by the kidney. Give evidence from the table to support your answer.
- Lower volume AND higher concentration;
- ADH increases water reabsorption (in 2nd convoluted tubule / collecting
duct) / increases water permeability / adds aquaporins;
- Evidence: observe increasing concentration (of dissolved substances) (in 2nd
convoluted tubule / collecting duct) / concentration increased
43
Describe the practical to identify the concentration of glucose in an unknown urine sample
- production of dilution series of a glucose solution and use of colorimetric techniques to produce calibration curve with which to identify the concentration of glucose in an unknown urine sample
44
Which formula is used for dilution series?
- C1 V1 = C2 V2
45
What is C1 and V1?
- starting concentration and volume (of stock solution)
46
What is C2 and V2?
- ending concentration and volume (of dilute solution)
47
What is the method to identify the concentration of glucose in an unknown urine sample?
Calibration curve
1. Use distilled water and glucose solution to produce dilution series;
2. Addition of Benedict’s reagent (to each solution);
3. Using a known/specified/constant volume of a solution (e.g. Benedict’s reagent OR
diluted glucose solution;
4. Perform Benedict’s test (heat glucose solution with Benedict’s reagent);
5. Record absorbance of solution using a colorimeter;
6. Plot absorbance on y axis against dilution/concentration of glucose solution (on x axis);
7. Draw a line of best fit.
Determining glucose concentration of unknown “urine” sample
1. Add Benedict’s reagent and heat to perform Benedict’s test on urine samples, using same volumes as with making the calibration curve; (do not dilute the urine samples)
2. Read off glucose concentration associated with absorbance value obtained.
48
What is a calibration curve?
- a graph used to convert one value into another
49
How to produce a (sugar) calibration curve?
- Make/use sugar (e.g. glucose) solutions of known/different concentrations, and carry out quantitative Benedict’s test on each
- Use a colorimeter to measure the colour/colorimeter value of each solution and plot a calibration curve
- Use the calibration curve to find the concentration of an unknown sample (need colorimeter value for the unknown sample)
