Kidneys

Question 1

What are the adaptations of the PTC to carry filtrate away from the Bowmans Capsule?

Answer 1

• Close association with Capillaries (capillaries around the PCT reabsorb all glucose, AA, some urea, most water and Na+/Cl-
• cubodial epithelial cells in its walls. Microvilli facing lumen increase SA.
• PCT is the longest and widest part of the nephron, it has a large SA because it is long and there are millions of nephrons in the kidney
• many mitochondria to provide ATP for active transport
• tight junctions (protein complexes attaching cells to their neighbours) between cells of the PCT and epithelium. They prevent molecules diffusing between adjacent cells or back into the glomerular filtrate.

Question 2

How are all relevant components reabsorbed from the PCT into blood?

Answer 2

• salts- some passive reabsorption but mainly AT
• Water= passively by osmosis. As ions are absorbed the WP of the blood decreases
• 50% of urea and small proteins by diffusion (as water is lost from the filtrate there is a high concentration there)
• glucose and AA are reabsorbed by co-transport by Na+ ions (see page 127 for specifics on this)

Question 3

Where is the PCT?

Answer 3

Bowmans capsule to the loop of henle

Question 4

What does the blood in the capillaries surrounding the PCT reabsorb?

Answer 4

all glucose and amino acids, some urea, most of the water and some of the sodium and chloride ions.

Question 5

What is the problem with relying on co-transport for glucose reabsorption? When may this occur?

Answer 5

Problem: if glucose concentration is high there may be too few transport molecules in the membrane of the PCT to absorb it all so it will be lost in urine.
This may happen if:
- the pancreas secretes too little insulin
- the response of liver cells to insulin is reduced because insulin receptors in surface membranes are damaged

Question 6

What are the components of filtrate in the bowmans capsule?

Answer 6

Water, glucose, salts, urea, amino acids

Question 7

What are the layers of the bowmans space (space separating glomerulus and bowmans capsule)?

Answer 7

1. endothlium cells of the capillary walls
2. basement membrane (extracellular layer of proteins and collagen), it is the selective barrier
3. Wall of bowmans capsule is made of squamos epithelial cells called podocytes, each has pedicels (like arms) that wrap around a capillary pulling the podocyte closer to the basement membrane.

Question 8

What are the vasa recta?

Answer 8

capillaries surrounding the loop of henle

Question 9

Where are the afferent and efferent arterioles?

Answer 9

• Afferent- into the Bowmans capsule
• efferent- out of the bowmans capsule

Question 10

Is the ascending limb of the loop of henle permeable to water?

Answer 10

No

Question 11

Is the descending limb permeable to water?

Answer 11

Yes

Question 12

What happens in the ascending limb?

Answer 12

sodium and chloride ions are actively transported out of the filtrate into tissue fluid in the medulla.
Filtrate becomes progressively more dilute as it looses ions

A longer loops of Henle means more ions are transported into medulla, therefore lower wp

Question 13

What happens in the descending limb?

Answer 13

water diffuses out into the tissue fluid (which has a low wp) then into the vasa recta (capillaries surrounding the loop of Henle)
Sodium and chloride ions diffuse into the descending limb

As filtrate flows down the descending limb it contains less water and more ions so the filtrate is most concentrated at the hairpin

Question 14

Order of travel through the kindney

Answer 14

Glomerulus, Bowmans capsule, PCT, descending limb, ascending limb, distal convoluted tubule, collecting duct

Question 15

What is the counter current multiplier?

Answer 15

two limbs of the loop of henle flow in opposite directions (counter current) and the concentration of salts is increased (multiplied)

Question 16

What is the advantage of the collecting duct running back down into the medulla?

Answer 16

It passes back through the region of low water potential, therefore water diffuses back out of the colllecting duct by osmosis. The longer the loop of Henle, the lower the water potential in the medulla and the more water leaves the collecting duct by osmosis. The water is then reabsorbed into the vasa recta.

Question 17

Where is ADH released from?

Answer 17

Hypothalamus uses osmoreceptors to monitor the solute potential of the blood. This a coordinator as it signals to the PITUITARY GLAND (effector) to release ADH
(hypothalamus is the coordinator and the recptor)

Question 18

How does ADH get into the blood stream?

Answer 18

reduced wp is detected by osmoreceptors in the hypothalamus.
Secretory granules carry ADH along axons from the hypothalamus to the posterior lobe of the pituitary gland where ADH is secreted into the blood stream

Question 19

What are aquaporins and where are they found?

Answer 19

they are intrinsic membrane proteins through which water moves. Particularly found within the walls of the distal convoluted tubule and the collecting duct

Question 20

What is the ADH mechanism?

Answer 20

1. ADH binds to membrane receptors (in the walls of DCT and collecting duct)
2. Adenyl cyclase catalyses the production of cyclic AMP, the second messenger
3. Cytoplasmic vesicles containing aquaporins move to fuse with the cell membrane
4. aquaporins are incoporated into the cell membrane
5. water molecules move down the wp gradient
6. when intracellular AMP levels fall the aquaporins are removed from the cell membrane they accumulate again in vesicles

Question 21

Explain how the loop of Henle maintains the gradient of ions which allows water to be reabsorbed from the filtrate in the collecting duct?

Answer 21

Na+ ions pumped out of the ascending limb
water passes out of descending limb (into high concentration in tissue fluid)
some sodium ions re-enter descending limb (by diffusion)
high concentration at the base of loop (of ions)
some ions diffuse out near the base increasing concentration outside the loop

Question 22

What are the common causes of Kidney failure?

Answer 22

1. Type two diabetes- high glucose conc in plasma results in glomeruli loosing protein into filtrate
2. High blood pressure - damages capillaries of the glomerulus preventing ultrafiltration
3. Autoimmune disease- body makes antibodies against its own tissues
4. infection
5. crushing injuries e.g RTA

Question 23

If both Kidneys are damaged, regulation of solute concentration and volume of bodily fluids is required? How might you do this?

Answer 23

• reduce intake of protein to reduce urea formation
• reduce intake of calcium and potassium ions
• Drugs to reduce blood pressure. e.g. calcium channel blockers dilate blood vessles, Beta blockers reduce effect of adrenaline (adrenaline makes your heart beat faster), Angiotensin-converting enzyme (ACE) inhibitors reduce the effect of angiotensin (the hormone that constricts blood vessles)

Question 24

Why might you need to reduce intake of potassium and calcium ions if your kidneys are damaged?

Concentration of both is usually maintained by absorption in SI and selective reabsorption at nephron.

Answer 24

• High potassium concentration in the blood leads to arrhythmias (treated with a combination of glucose and insulin)
• High calcium in the blood is correlated with increased risk of heart disease, kidney stones and osteoporosis. Treated with Bisphosphonates (causes calcium to accumulate in bone therefore less circulates in blood)

Question 25

What are the relative concentrations of components of the dialysis fluid compared to blood?

Answer 25

• same wp as blood
• lower ion concetration
• no urea
• same concentration of glucose

blood and dialysis fluid are separated by a selectively permeable membrane

Question 26

By what mechanism does blood flow through the dialysis machine?

Blood is taken from an artery, unually in the arm, and returned to a vein. Blood thinners such as Heparin prevent clotting

Answer 26

counter current mechanism

Question 27

What is CAPD

Answer 27

Continuous ambulatory peritoneal dialysis

Question 28

How does CAPD work?

Answer 28

• patient drains a 1-3dm3 bag of dialysis fluid through a catheter in the body cavity.
• The peritoneum is the membrane lining the body cavity (it has a rich supply of capilaries) and acts as a dialysis membrane and materials are removed from the blood in the capillaries into the dialysis fluid
• The fluid is drained from the abdomen under gravity into an empty bag
• Patient can walk around and carry on normal activities however they must drink little and avoid foods rich in potassium (like bananas) as retention of liquid is common and potassium ions accumulate in the blood

Question 29

Whats the advantage of a live donor for a kidney compared with a deceased one?

Donors must be compatible in their ABO blood group

Answer 29

generally works immediately and last longer. One from a deceased donar may take a few weeks to start working again and dialysis is required in the meantime

Question 30

Why do plants not need to excrete nitrogen containing molecules?

Answer 30

They only synthesis the amino acids and the proteins they need. Active transport and faciliated diffusion allow them to take up nitrate and ammonium ions

Question 31

In a plant, what is transamination?

Answer 31

making amino acids from glutamate

Question 32

How do plants make glutamate initially?

glutamate is an AA which can then be converted to any other AA

Answer 32

Plant cells combine ammonium ions with alpha-keto glutarate. Transamination- an enzyme catalysed reaction that transfers an amino group to an alpha-keto acid, making an amino acid

Question 33

What and why is the excretion of aquatic organisms?

Answer 33

They excrete ammonia. Toxic but soluable in water. The large surface are of fish gills and amoeba allows it to rapidly diffuse out and be immediately diluted.

Question 34

What and why is the excretion of birds, reptiles and insects?

Answer 34

They do not carry around excess water. They convert AA into uric acid for excretion this is insoluale in water and non-toxic. There is a high energy cost for its production but little water is needed to excrete it. This allows these animals to either conserve water to suit their environment or be light enough for flight

Question 35

Excretion of some fish and mammals

Answer 35

urea. Less toxic than ammonia so body fluids can dilute it to tolerate it breifly.

Question 36

How might a dessert animals kidney be adapted for its environment in order to conserve water?

Answer 36

Longer loops of henle. A longer ascending limb (therefore more ion pumps) increase the ion concentration in the medulla therefore more water is reabsorbed from the descending limb and collecting duct

Question 37

What are the two types of nephron and where are they found?

Answer 37

1. Cotical nephron in the cortex- short loop of henle which just penetrates the medulla near its boundary with the cortex. Glomerulus is located in outer cortex. In humans most nephrons are cortical. = Dilute urine
2. Juxtamedullary nephron- Bowman’s capsule closer to the cortex boundary with medulla. Long loop of henle. Animals in dry inhabitats have these nephrons to generate a low water potential to conserve water.

Question 38

What is metabolic water?

Answer 38

Water produced from the oxidation of food reserves

Question 39

How else do dessert animals conserve water?

Answer 39

• use of metabolic water in processes
• living in burrows- cool and humid reduces water loss by evaporation
• be nocturnal - night is cooler so less water lost through evapouration

Question 40

What is creatine?

Answer 40

A compound produced by muscle tissue break down, it is filtered out by the kidneys and excreted in urine

Question 41

What process happens in the liver?

Answer 41

Deamination of amino acids. Amino group is converted into urea [O=C(NH2)2)

Question 42

Capillary is a single layer of endothelium cells, what are the pores called?

Answer 42

Fenestrae

Question 43

Where is the efferent arteriole?

Answer 43

arteriole that leaves the glomerulus

Question 44

What are the four D’s of treating kidney failure?

Answer 44

• Drugs
• Dialysis
• Diet change
• Donor kidney

Question 45

Where is the filtrate isotonic with blood plasma?

Answer 45

The base of the PCT

Question 46

Is the efferant of afferant arteriole wider? What is the advantage of this?

Answer 46

Afferent (into the bowmans capsule, think A before E in alphabet) is wider. Because efferent is narrower it means the blood is under pressure, this aids filtration.