Pbl 17 War & Peace

PBL 17 – WAR & PEACE

1998 Paper 2, Part D: Q1-9

Question 1.

Explain how urine output could fall. Group your responses into three broad categories. (3 marks)

A decrease in renal output could be due to acute renal failure. Here are 3 possible mechanisms:

1. PRE-RENAL – due to decreased renal perfusion without cellular injury. Reasons for this would be:

· A decrease in circulating blood volume

· Pump failure

· Factors interfering with renal haemodynamics (NSAIDs)

2. RENAL – due to intrinsic damage to the kidney parenchyma. Possible with:

· Tubular disease

· Glomerular disease

· Vascular disease

· Interstitial disease

3. POST-RENAL – due to obstruction to the flow of urine anywhere in between the kidney to the urethra. Could be:

· Extrinsic – for example prostatic hypertrophy

· Intrinsic – stones or myeloma

Question 2. (5 marks)

You order a blood test that comes back with the following findings:

Sodium: 135 mmol/L (135-145)

Potassium: 5.8 mmol/L (3.3-4.5)

Chloride: 101 mmol/L (98-108)

Bicarbonate: 18 mmol/L (22-31)

Urea 21 mmol/L (3.0-7.5)

Creatinine 0.20 mmol/L (0.05-0.10)

(a) Explain why urea and creatinine are found in the plasma and the factors affecting their plasma concentrations.

Urea and creatinine are metabolic end products. Creatinine is the end product of phosphocreatine in muscle metabolism and urea is the end product of protein catabolism. Both of these are filtered by the kidneys and excreted to maintain constant levels in the body. Any alterations, such as an increase is an indication that the excretion mechanism is not working efficiently and there is a problem. Increased levels of urea and creatinine indicate that the renal problem is worse than a simple impairment and possibly is renal failure.

(b) Explain the basis for the raised K+.

In the tubules sodium is exchanged for potassium via active transport in the basolateral and luminal regions of the cell with the potassium flowing back out via a potassium pump. If there is a problem with the tubules and sodium is not being reabsorbed adequately then there would be a build-up of potassium hence the raised potassium.

HCO3- is used as a buffer for excess H+. Normally at the luminal surface H+ is exchanged for sodium. If there is a problem with the tubules and not enough sodium is being reabsorbed then not enough H+ is being excreted from the cell. As a result the HCO3- has to compensate and cannot be excreted from the cell into the clood as it normally would do after CO2 gets taken up by the cell.

(d) Explain why the patient will have a lowered pH.

Due to not enough Sodium being reabsorbed the H+ ions would build up decreasing the pH of the patient.

Question 3. (5 marks)

OPTIONS

A Inferior Vena Cava

B Urethra

C Left adrenal gland

D Kidney

E External urethral orifice

F Renal pelvis

G Renal hilum

H Ureteral orifices

I Right renal vein

J Bladder

K Ureter

L Left renal artery

M Abdominal aorta

From the following diagram, select the appropriate option (A-M) for the parts of the urinary tract labelled 1 to 5.

Answers

1. K - Ureter

2. J - Bladder

3. B - Urethra

4. D - Kidney

5. I – Right renal vein

Question 4. (3½ marks)

OPTIONS

A Glomerulus

B Bowman’s capsule

C Proximal tubule

D Distal tubule

E Collecting duct

F Loop of Henle

G Thin segment

H Pelvis

I Afferent arteriole

J Efferent arteriole

From the following diagram, select the appropriate option (A-J) for the parts labelled 1 to 7.

Answers

1. B – Bowman’s Capsule

2. C – Proximal tubule

3. F – Loop of Henle

4. I – afferent arteriole

5. J – efferent arteriole

6. D – Distal Tubule

7. E – Collecting duct

Question 5. (3 marks)

Identify the organ shown in the image above (H&E stain. X400)

KIDNEY

Name the structures in the image above labelled:

A Glomerulus

B Proximal convoluted tubule

C Distal convoluted tubule

D Juxtaglomerular apparatus

What is the function of the cells in the image above labelled D?

Maintain renal blood pressure – if low secrete after constricting efferent arteriole renin, if high constrict afferent arteriole

Question 6. (5 marks)

Respond to the following statements as TRUE (T), FALSE (F), DON'T KNOW (D):

Indicate which of the following are true or false statements with regard to the normally functioning nephron:

CIRCLE YOUR CHOICE

1. The countercurrent mechanism operates within the loop of Henle T

2. The countercurrent mechanism allows osmotically concentrated

urine to be formed independently of antidiuretic hormone T

3. Glucose is mainly reabsorbed in the proximal convoluted tubule T

4. The amount of creatinine excreted exceeds the amount filtered F

5. The amount of urea excreted equals the amount filtered F

6. Amino acids are mainly reabsorbed in the distal convoluted tubule F

7. Most water is reabsorbed in the distal convoluted tubule F

Question 7.

Why don't plasma proteins pass into the capsular space under normal circumstances? (2 marks)

The filtration membrane is a filtration barrier that prevents the entry of blood cells and protein into the lumen of thee bowman’s capsule but allows other blood constituents in. The fenestrae of the Glomerular capillaries, the basement membrane and the podocyte cells prevent molecules greater than 7nm from entering. Albumin and protein hormones can fit through by are actively reabsorbed hence in healthy people little-no urine is found in the urine. There is also a charge filter, in that the negative charge of the filtration membrane repels most plasma proteins which are also negatively charged.

Question 8.

Indicate the mechanism by which an increased amount of aldosterone would effect K+ concentration in the urine. (2 marks)

Aldosterone is secreted by the adrenal glands and binds to receptors in the distal convoluted tubule and the collecting duct. It increases the synthesis of transport protein molecules that increase the transport of sodium form the lumen into the bloodstream. Sodium is exchanged for potassium at the basolateral and luminal surface and so an increase in sodium levels coming in would increase the levels of potassium going out, hence there would be a greater amount of potassium in the urine.

Question 9.

Explain the effect that a decreased Na+ concentration of filtrate would have on the pH of the fluid in the proximal tubule. (2 marks)

At the luminal aspect of the tubular cells sodium is exchanged for H+. Therefore if there is not enough sodium not only will other substance not be taken up, like glucose which needs cotransport, but there will be a lack of H+ ions hence making the filtrate less acidic then normal or the pH would be higher than normal.

1998 Paper 3, Part A: Q3-5

Mr WilliamT admits to going to the toilet often to pass urine during the night, rising 3 to 5 times. He states that his flow is reduced at night and that he dribbles a little at the end of micturition. He states that he is fine during the day.

Question 3.

What is the one question you need to ask to determine whether or not further evaluation of his urinary status is indicated? (1 mark)

Need to know whether his urination has always been like this or whether it is a recent change. A recent change will require further investigation.

Question 4.

What else would you ask him about his increased need to void during the night? (2 marks)

Other things to ask:

Recent changes to medication or habits (e.g. does he now drink a bottle of wine and 3 cups of coffee before bedtime? Does he take diuretics in the evening?). Also any other associated symptoms with urination – painful urination, haematuria, does he feel completely empty after urination, change in colour of urine, quantity of urine produced. Any other symptoms present +/- related to urination.

The voided volumes are 100-150 ml (per void) day and night.

Question 5.

What volumes would you consider to be reasonably ‘normal’ and what total volume would you consider to be reasonable for a 24 hour period? (1 mark)

Normal volume per void – 200-400mL

Normal 24 hour voided volume – 1.5L per day average.

1999 Paper 3, Part D: Q1-2, 4, 5

Alice B, a 7 year old girl presents to the local GP complaining of pain when she passes urine. Her mother tells the GP that she has recently started wetting her pants during the day. You elicit the history that she has had several similar episodes which resolved spontaneously after a few days.

The GP examines her and finds that she is a small, thin girl who is afebrile with mild tenderness in the right loin, damp pants and redness around her external genitalia. He suspects she has a urinary tract infection.

Question 1. (3½ marks)

1. Glomerulus 6. Loop of Henle

2. Bowman's capsule 7. Afferent arteriole

3. Distal convoluted tubule 8. Proximal convoluted tubule

4. Collecting duct 9. Efferent arteriole

5. Thin segment 10. Medulla

From figure 1 (on the next page), select the appropriate option for the parts labelled A - G.

A. Bowman’s capsule

B. Proximal convoluted tubule

C. Loop of Henle (pic is jacked from Marieb and labeled as such)

D. Afferent arteriole

E. Efferent arteriole

F. Distal convoluted tubule

G. Collecting duct

Question 2.

Identify the organ shown in the image above (H&E stain. X400)

KIDNEY

Name the structures in the image above labelled:

A Glomerulus

B Proximal convoluted tubule

C Distal convoluted tubule

D Juxtaglomerular apparatus

What is the function of the cells in the image above labelled D?

Maintain renal blood pressure – if low secrete after constricting efferent arteriole renin, if high constrict afferent arteriole

A clean catch urine specimen is collected for analysis. The results are:

50 white cells/high power field (normal <10), occasional epithelial cells, occasional mucus thread, culture heavy growth of E. coli

Question 4.

Name three (3) other genera which might be associated with urinary tract infection, AND give the likely source from which all these organisms are most likely acquired.

1) Staphylococcus Aureus – Skin Flora

2) Chlamydia – STI

3) Candida – Skin Flora

Alice is prescribed amoxycillin

Question 5.

How is penicillin excreted by the kidney? What is its renal clearance?

2001 Paper 1, Part A

George J, 19, was discharged following an episode of acute renal failure after injury incurred as a result of a motor vehicle accident. There was substantial blood loss with the accident and he was clinically shocked.

You are reviewing his progress two months after discharge from hospital. He still gets up once or twice at night to pass urine. His creatinine is still elevated at 0.25mmmol/L (RR 0.03-0.12mmol/l) corresponding to a creatinine clearance of approximately 40 ml/min.

Question 1. (3 marks)

List the six (6) major anatomical structures through which urine passes on its way from the kidney to the glans penis.

Major calyx / renal pelvis / ureters / bladder / prostatic urethra / penile urethra

After an overnight fast, George’s urinary osmolarity is 455 mOsmol/kg (compared with plasma osmolarity of 290 mOsmol/kg, and a normal maximal urine concentrating ability of about 1200 mOsmol/kg).

Question 2. (3 marks)

How is water excretion controlled?

ADH causes increased reabsorption of water in the collecting duct

Renin makes angiotensin causes Na reabsorption and increased water follows it back into system. Na / H pump

Question 3. (5.5 marks)

(a) From the following diagram, name the structure labelled. (4 marks)

1. Bowman’s capsule

2. Proximal convoluted tubule

3. Descending Loop of Henle

4. Ascending Loop of Henle

5. Afferent arteriole

6. Efferent arteriole

7. Distal convoluted tubule

8. Collecting duct

(b) Name the location within the tubule where all the glucose is normally reabsorbed.

PCT

Loop of Henle (Think Ascending Limb)

(d) Name the location within the tubule where most acid is secreted. (1/2 mark)

DCT

Question 4. (3 marks)

Explain the concept of clearance, and give a formula.

Clearance is the measure of how much plasma is removed from a substance per unit of time… CL = ([urine] x (rate of flow)) / [plasma]

Question 5. (2 marks)

Briefly explain -

(a) how urea is normally produced (1 mark)

Urea is formed from the metabolism of amino acids and the particularily the ammonia product which is turned into urea because urea is less toxic and easier to remove

(b) how urea is normally handled by the body?

Filtered by glomerulus and concentrated in the kidney and excreted.

Question 6. (3 marks)

Briefly explain -

(a) how creatinine is normally produced. (1 mark)

Normal cell metabolism of muscle from creatine

(b) how creatinine is normally handled by the kidney. (1 mark)

(Zero order kinetics) freely filtered by glomerulus and then some is excreted into the distal tubule

GFR

2002 Paper 1, Part D: Q1, 2, 5, 6

Julie is a 46 year old female with a 25 year history of poorly controlled hypertension. Over the past year her BP measurements have varied from 158/106 to 180/125 on antihypertensive medications. She has significant peripheral oedema, and poor peripheral pulses. Her echocardiography demonstrated significant left ventricular hypertrophy. There has been a progressive reduction in renal function over the years. She has had proteinuria for two (2) years, with her latest 24h urinary protein level at 5g per 24 hour and her creatinine clearance rate was very low at 15ml/min. Her serum creatinine level was also elevated. Recent renal arteriography demonstrated bilateral scarred kidneys and bilateral renal artery stenosis with an 80% stenosis on the right and a 30% stenosis on the left. Her plasma renin level was 320 uU/l (13-56uU/l) with a concurrent plasma aldosterone of 1900 pmol/l (NR 110-900pmol/l). Julie has normal blood glucose levels as she always has done, and her haematocrit level is low at 35% (NR 37-46%). Subsequently, after many months on renal dialysis, Julie received a donated cadaveric kidney transplant.