The kidney

Question 1

What is the purpose of the renal artery?

Answer 1

Provide kidneys with oxygenated blood

Question 2

What happens in the kidney’s to blood received from the renal artery?

Answer 2

• blood is filtered in the kidneys
• resulting urine passes into ureters transporting it to bladder
• urine is stored in bladder and eventually removed from body via urethra

Question 3

What is the purpose of the renal vein?

Answer 3

Returns filtered blood to the heart via the vena cava

Question 4

What are the internal structures of the kidney?

Answer 4

Fibrous capsule = outer membrane surrounding and protecting kidney

Renal cortex = outer region containing Bowman’s capsules, DCT, PCT and blood vessels

Renal medulla = inner region containing pyramids, loops of Henle, collecting ducts and blood vessels

Renal pelvis = funnel shaped cavity collecting urine into ureters

Question 5

What is a nephron?

Answer 5

basic structural and functional kidney unit

Question 6

What are nephrons responsible for?

Answer 6

• filtering blood
• reabsorbing useful substances back into blood
• removing waste from blood

Question 7

What is the pathway of the filtrate through a nephron?

Answer 7

1) bowman’s capsule
2) proximal convoluted tubule
3) loop of henle
4) distal convoluted tubule
5) collecting duct

Question 8

What is the function of the bowman’s capsule and glomerulus?

Answer 8

Bowman’s capsule = surrounds and protects a capillary ball (glomerulus)

Glomerulus = forms filtrate and contains podocyte cells in it’s inner layer

Question 9

What is the structure and function of the proximal convoluted tubule?

Answer 9

• epithelial cells in it’s wall have microvilli to increase SA
• reabsorbs useful substances (e.g water, glucose, and salt) into surrounding capillaries

Question 10

What is the structure and function of the loop of henle?

Answer 10

• long hairpin loop extends from cortex into the medulla back into cortex
• creates a high solute gradient in the medulla helping with selective reabsorption

Question 11

What is the structure and function of the distal convoluted tubule?

Answer 11

• surrounded by fewer capillaries than PCT
• fine-tunes water balance by reabsorbing water into surrounding capillaries (due to ADH)

Question 12

What is the structure and function of the collecting duct?

Answer 12

• attaches to nephrons
• collects filtrate from nephrons and further fine-tunes water balance before urine formed is passed to bladder

Question 13

What are the 4 blood vessels associated with nephrons?

Answer 13

Afferent arteriole = supplies glomerulus with blood

Glomerulus = fluid forced out of blood within capillary mass into Bowman’s capsule through ultrafiltration

Efferent arteriole = carries blood away from glomerulus

Capillaries around PCT, DCT loop of Henle = absorb salts glucose, and water

Question 14

What is ultrafiltration?

Answer 14

• small molecules (e.g water, glucose, mineral ions and urea) filter out blood into Bowman’s capsule forming glomerular filtrate
• larger molecules remain in bloodstream

Question 15

Why is ultrafiltration important?

Answer 15

selective movement is essential for filtering blood and maintaining a balance of substances in the body

Question 16

What is the process of ultrafiltration?

Answer 16

1) blood enters glomerulus through afferent arteriole

2) blood leaves glomerulus via smaller efferent arteriole maintaining a high hydrostatic pressure

3) this high pressure forces molecules out of the blood through pores in the capillary endothelium.

4) molecules move through basement membrane with collagen fibres acting as selective filter preventing large molecules and blood cells passing into the Bowman’s capsule

5) molecules move through Bowman’s capsule epithelium (specialised podocyte cells with extensions wrap around capillaries helping to filter blood

6) filtered fluid collects in Bowman’s capsule

Question 17

What substances filter into the glomerular filtrate?

Answer 17

• water
• salt
• glucose
• urea

Question 18

What substances remain in the blood during ultrafiltration?

Answer 18

• blood cells
• platelets
• proteins

Question 19

What is GFR?

Answer 19

glomerular filtrate rate

volume of glomerular filtrate formed per minute, the volume of blood that is filtered through the kidneys in a given time

Question 20

What are the adaptations of the PCT for selective reabsorption?

Answer 20

Microvilli = increase SA for reabsorption

Basal infoldings = further increase SA for moving substances into surrounding capillaries

Numerous mitochondria = organelle provide ATP for active transport involved in reabsorption

Co-transporter proteins in plasma membrane = allow co-transport of substances from filtrate into epithelial cells

Question 21

What is the reabsorption process in the PCT?

Answer 21

• NA+ ions are actively transported to capillaries reducing the Na+ concentration in epithelial cells lining PCT
• Na+ moves from PCT lumen into epithelial cells down its conc gradient
• Na+ is co-transported with substances like glucose and amino acids into the epithelial cells
• these reabsorbed molecules can then diffuse into capillaries

Question 22

What is the role of the DCT?

Answer 22

makes final adjustments to the filtrate’s content by reabsorbing water and salts

Question 23

What does the reabsorption process in the DCT involve?

Answer 23

• reabsorption of any remaining useful substances mainly through active transport
• alteration of DCT membrane permeability to regulate further reabsorption of water and solutes
• regulation of blood pH by selectively reabsorbing certain ions

Question 24

Describe the structure of the loop of henle?

Answer 24

U-shaped tubule within the kidney nephron, starting in the cortex, descending into the medulla

Question 25

Describe the descending limb of the loop of henle?

Answer 25

- 1st section - narrow - impermeable to ions - highly permeable to water

Question 26

Describe the ascending limb of the loop of henle?

Answer 26

- 2nd section - wider - permeable to ions - impermeable to water

Question 27

How does the loop of henle concentrate urine?

Answer 27

- decreases Ψ in medulla via active transport of ions out of filtrate - these ions transport into the tissues of the medulla that surround the loop of Henle (interstitial space) - establishes a Ψ gradient allowing water to be reabsorbed into blood from filtrate in collecting duct

Question 28

How is water reabsorbed in the loop of henle?

Answer 28

1) descending limb walls are permeable to water so water leaves the filtrate via osmosis into interstitial space 2) filtrate loses water as it moves down descending limb reaching its lowest Ψ medulla tip 3) water lost is reabsorbed into blood in surrounding capillaries by osmosis 4) ascending limb is impermeable to H2O but permeable to NA+ and CL- ions 5) Na+ and Cl- diffuse out filtrate into interstitial space at bottom of ascending limb due to low Ψ of the filtrate 6) This concentrates ions in interstitial space in medulla making its Ψ very low 7) Na+ and Cl- are actively transported out of top of ascending limb because their concentration in filtrate decreases as it ascends (the Ψ increases) 8) creates a Ψ gradient in interstitial space with highest Ψ in the cortex and an increasingly lower Ψ deeper into the medulla

Question 29

What happens when filtrate enters the collecting duct?

Answer 29

1) water moves from filtrate in the collecting duct into the interstitial space 2) water moves into surrounding capillaries by osmosis to be carried away 3) water continues to exit filtrate as it moves through collecting duct, even in the medulla when most water has already been lost because of the low Ψ established by the loop of Henle in surrounding interstitial space 4) urine leaving collecting duct has a very low Ψ as most water has been reabsorbed into blood

Question 30

What is the countercurrent multiplyer?

Answer 30

concentrates urine and ensures there is always a Ψ gradient drawing water out of the collecting duct

Question 31

How does the countercurrent multiplier work?

Answer 31

- as filtrate moves down the collecting duct it loses water decreasing its Ψ - due to the pumping of ions out of the ascending limb of the loop of Henle the Ψ of surrounding tissues in medulla is lower than in the collecting duct - allows water to move out of filtrate down whole length of collecting duct

Question 32

What is osmoregulation?

Answer 32

control of Ψ of the blood keeping the Ψ of bodily fluids within a narrow range

Question 33

What are the key features of ADH?

Answer 33

- produced in hypothalamus - stored in posterior pituitary gland after production - target cells are those lining DCTs and collecting ducts in kidneys

Question 34

What are the mechanisms of ADH action?

Answer 34

1) ADH attaches to receptors on cell surface in DCT and collecting duct 2) triggers activation of cAMP a 2nd messenger initiating a series of reactions leading to phosphorylation of water channel (aquaporins) 3) aquaporin vesicles merge with cell-surface membrane 4) water moves through aquaporins by osmosis from DCT and collecting duct into surrounding interstitial space 5) water is then reabsorbed into surrounding blood vessels

Question 35

How is the release of ADH controlled?

Answer 35

negative feedback system involves osmoreceptors in hypothalamus responding to changes in blood water and ion levels

Question 36

What can trigger the release of ADH?

Answer 36

- lack of water - excessive salt intake - sweating

Question 37

What happens in the body when there is a lack of water?

Answer 37

1) Water moves from osmoreceptors into blood by osmosis 2) osmoreceptors shrink detecting decrease Ψ of blood and produce ADH 3) Nerve signals prompt release of ADH from the posterior pituitary gland and ADH is transported via blood to kidneys 4) increase in aquaporins in DCT and collecting duct cell membranes makes them more permeable to water 5) more water is reabsorbed back into blood 6) urine becomes more concentrated and is produced in smaller volumes

Question 38

What happens in the body when there is an excess of water?

Answer 38

1) water moves into osmoreceptors from the blood by osmosis 2) osmoreceptors detect an increase in Ψ of blood 3) nerve signals to posterior pituitary gland decrease reducing ADH release 4) DCT and collecting duct cell membranes become less permeable to water 5) less water is reabsorbed back into the blood 6) urine becomes more dilute and is produced in larger volumes

Question 39

Why is urine often used to sample for medical conditions?

Answer 39

contains water, urea, mineral salts, hormones, toxins, and various breakdown products composition of these substances can give us crucial evidence

Question 40

What are some key indicators for medical conditions found in the urine?

Answer 40

- presence of glucose often indicates diabetes - elevated creatine levels suggest muscle or kidney damage - presence of blood or proteins in urine may signal kidney disorders

Question 41

What are the 2 main causes of kidney failure?

Answer 41

Kidney infections = lead to inflammation and swelling of kidneys damaging cells responsible for filtering and reabsorption High BP = can damage the glomeruli capillaries so proteins and blood leak into the urine

Question 42

What are indicators of kidney failure?

Answer 42

- low GFR indicates less effective blood filtration - blood test can measure level of creatinine in blood which estimates GFR - high creatinine level indicates that kidneys aren't working properly

Question 43

What are the effects of kidney failure?

Answer 43

- mineral ion build up in blood causing loss of osmotic balance - buildup of toxic urea in blood damaging cells - high BP may cause heart problems and strokes - loss of calcium weakening bones - buildup of proteins in blood causing joint pain and stiffness - anemia causing tiredness and lethargy

Question 44

How does renal dialysis filter the blood?

Answer 44

1) patient's blood passes along one side of a semi-permeable membrane while dialysis fluid flows on other 2) dialysis fluid contains normal plasma levels of mineral ions so ions diffuse through the semi-permeable dialysis tubing membrane into blood 3) dialysis fluid contains normal plasma levels of glucose so glucose also diffuses from dialysis fluid into blood 4) dialysis fluid contains no urea so urea is removed from blood into dialysis fluid by diffusion 5) larger molecules like blood cells and proteins remain in the blood as are too large to pass through membrane

Question 45

What is haemodialysis?

Answer 45

Blood leaves patients body and flows into a dialysis machine where it's filtered and returned to the body

Question 46

What is peritoneal dialysis?

Answer 46

- peritoneum is a membrane lining the abdominal cavity - it acts as a surface which substances are exchanged between blood and dialysis fluid - dialysis fluid is injected into then drained from abdominal cavity so blood can be filtered within body

Question 47

What are the pros and cons of peritoneal dialysis?

Answer 47

pros: - no need for specialist equipment - can be done at home - patient can be mobile during treatment cons: - risk of infection - required more frequently

Question 48

What are the pros and cons of haemodialysis dialysis?

Answer 48

pros: - lower infection risk - required less frequently cons: - requires specialist equipment - must be done in hospital - patient must be immobile during treatment

Question 49

What are advantages of kidney transplants?

Answer 49

- no need for regular dialysis - no need for diet monitoring - prevents build up of waste products between dialysis - improves life quality - one of cost

Question 50

What are disadvantages of kidney transplants?

Answer 50

- risk of rejection if immune system recognises antigens on donor organ as foreign and attacks it - shortage of donor kidneys - need of medication to suppress immune system - involves major surgery