Topic 8 - Excretion: Kidneys

Question 1

Learning Outcomes

Answer 1

1. Describe the anatomy of the kidney and structure of the nephron
2. Name and describe the structure and fuction of regions of the nephron
3. Describe the glomerular filter
4. Distinguish the proterties of the blood components the glomerular filter allow to pass & appreciate meathods used to measure it.
5. Describe the mechanism of reabsorption of glucose
6. Explain the concept of a renal threshold
7. Describe the tole of the Proximal Convoluted tubule, Loop of Henle, Distal Convoluted tubule and Collecting duct in the reabsorption and excretion of Na+, K+, and water.
8. Explain the role of the kidney in the homeostatic regulation of Na+ and K+ in the blood, and water balance.

Question 2

The Kidney Role

Answer 2

• Removes waste and maintainers of balance
• Maintains extracellular fluid composition and volume (blood)
• Maintains mass balance/ clearance (Inputs & Outputs)
• Filtration followed by reabsorption
• Secretion of some waste products
• Produce some hormones

Filters Approx. 180L fluid per day

Question 3

External anatomy of the Kidneys

Answer 3

• Renal Veins (into Vena Cava)
• Vena Cava (Kidneys to heart - Blue)
• Aorta (Heart to kidneys - Red)
• Renal Arteries (Aorta to Kidneys)
• Ureters (Kidneys to Urinary bladder)

Question 4

Internal anatomy

Answer 4

• Cortex
• Medulla
• Renal Pyramids
• Renal Pelvis
• Renal Vein
• Renal Artery
• Nephrons

Question 5

Cortex

Answer 5

Outer-most layer

Question 6

Medulla

Answer 6

Inner-most layer

Question 7

Renal Pyramids

Answer 7

Bundles of vessels making urine, conducting towards renal pelvis

Question 8

Renal Pelvis

Answer 8

Acts like a drain to remove urine into ureter for excretion

Question 9

Renal Vein

Answer 9

Takes deoxygenated blood from the kidneys to the heart

Question 10

Renal artery

Answer 10

Breaks off into smaller vessels to transmit oxygenated blood throughout the kidney
- Receives blood from the Aorta

Question 11

Nephrons

Answer 11

• Surrounded by capillaries
• Functional subunit of the kindey
• Together provide the function of producing urine
• Sit in the Cortex, while its loop of Henle sits in the Mudulla
• Blood does not flow through it, but is filtered in the glomerulous

Question 12

Renal Corpuscle

Answer 12

• Made up of the bowmans capsule and glomerulous
• It is the filtration site where blood is filtered, the filtrate is then carried through the nephron.

Question 13

Proximal convoluted tubule

Answer 13

• Approx. 70% of filtrate is reabsobed back into the blood here
• Is the main site of reabsorption of most solutes (Na+, glucose, amino acids etc.)
• PCT cells contain microvilli to maximise the SA:V ratio for reabsorption

1. Takes almost everything out of the blood
2. Checks the composition
3. Puts 70% of it back into the blood, whilst the rest is removed in urine.

Question 14

Loop of Henle

Answer 14

• The only part of the nephron that goes into the medulla of the kidney
• Descending (thin) & Ascending (thick) limbs
• Assists in reducing water content of urine

Question 15

Descending Limb of Loop of Henle

Answer 15

• Osmolarity of extracellular fluid increases as you go down the descending limb as the concentration of solute outside is higher
• With osmosis, water moves from inside the loop of henle into the extracellular fluid to the low H2O concentration.

Question 16

Ascending Limb of the Loop of Henle

Answer 16

• Has a thicker wall than the descending limb for which water cannot pass through back into the loop of henle. This allows for a hypertonic solution inside the loop.
• The Ascending limb contains active pumps, to pump ions such as Na+ & Cl- back into the extracellular fluid to balance osmolarity.

Question 17

Hormonal control of the Kidney

Answer 17

Aldosterone
Anti-Diuretic Hormone

Question 18

Role of Aldosterone in the kidney

Answer 18

• Helps maintain water balance in the kidney
• Produced by the adrenal gland (Meaning it is ontop of the kidney)
• Increases the reabsorption of Na+ back intot he blood stream from the distal convoluted tubule and collecting duct.

- Because more solute is then in the bloodstream, water then follows it passively. Allowing water to be reclaimed from urine and is not lost in urine.

Question 19

The Role of Anti-Diuretic Hormone (ADH) in the Kidney

Answer 19

• Produced by the hypothalamus in response to a high solute concentration in the blood
• Increases the reabsorption of water in the collecting duct by inserting aquaporins in the collecting duct walls
• More water passes out of the urine/ tubules into the blood stream
• Effects are inhibited by alcohol
• Release is inhibited by caffein (hence caffein is a diuretic)

Question 20

Distal Convoluted tubule

Answer 20

• Has less microvilli than the Proximal convoluted tubule (not reabsorbing as much)
• Excess K+ ions are actively secreted into the Distal convoluted tubule under the control of aldosterone
• Excess H+ ions are also secreted to maintain the blood pH levels

Question 21

Collecting Duct

Answer 21

Collects the urine produced from many nephrons by joining together into the renal pelvis, ready to be taken away from the kidney

Involved with water balance:
- Permiable to water
- Reabsorbs water under influence of ADH
- ADH increases the permiability of the collecting duct through aquaporins

Question 22

Movement of solutes in the nephron

Answer 22

• Nephron is surrounded by capillaries
• Substances leaving the nephron are reabsorbed back into the blood stream

Question 23

Renal threshold

Answer 23

The concentration of blood component above which the kidney removes it in urine
- If the concentration in the blood stream gets higher than the renal threshold, then the substance will appear in urine.
- Can be used to measure blood components

Question 24

Composition of urine

Answer 24

• 95% water
• 2.5% urea - By product of protein metabolism (nitrogenous waste)
• Next largest component is Na+ ions
• Then Urochrome - By product of breakdown of haemoglobin (makes urine yellow)

Question 25

Polyuria

Answer 25

• Copious urine production
• Caused by a decrease in aldosterone secretion, due to damage to the adrenal glands
• Can also be a concequence of diabates
• If High concentration of glucose is present in the urine, then water will follow it passively via osmosis due to concentration gradients

Question 26

Glomerulus

Answer 26

Apart of the renal corpuscle
- Tangle of porous capillaries
- Site of ultrafiltration into the bowmans capsule

Blood flows into the Glomerulus in a larger vessel than when it leaves, creating high pressure

Question 27

Bowmans Capsule

Answer 27

Apart of the Renal Corpuscle
* Surrounds the Glomerulus
* Takes up filtrate from the Glomerulus

Question 28

Glomerular Filter anatomy and function

Answer 28

3 Layers
1. Wall of capillary (Endothelium)
2. Glomerular basement membrane
3. Podocytes (Cells that surround glomerular capillaries)

• large proteins and blood cells cannot pass through, and stay in the capillary
• Small molecules and ions (<3nm) can entre the bowmans capsule

Question 29

Measuring glomerular filtration

Answer 29

2 Tests
Inulin test (NOT INSULIN):
- Plant carbohydrate cannot be absorbed by the body, passes straight into nephron

Creatinine (NOT CREATINE):
- Muscle breakdown byproduct that isn’t reabsorbed by the body (harder to track as body produces regularly)

Question 29

Golerular Filtration Rate (GFR)

Answer 29

Concentration of Inulin X Urine flow rate (mL/min)
––––––––––––––––––––––––––––––––––
Concentration of inulin in blood

Question 30

Reabsorption of Glucose

Answer 30

Glucose diffuses in , but would eventually stop at equilibrium.
Na+ is actively pumpedout of the tubule, glucose is Co-transported with Na+ via transmembrane proteins