Week 8 - Kidney physiology

Question 1

What are the functions of the kidney?

Answer 1

Kidneys;

• 1) Maintain salt and water balance
• 2) Converting Vitamin D to its active form, by adding an OH group to carbon 25 (see vit. d metabolism)
• 3) Exertion of drugs and non-nutritive materials
• 4) Blood manufacture as produced erythropoietin hormone Among others!

Question 2

What are the steps involved in the formation of urine?

Answer 2

Remember Going To Toilets Saddens! Glomerular Filtration Tubular Reabsorption Tubular secretion Selective Movement

Question 3

What is filtered during glomerular filtration?

Answer 3

Of the 100% of plasma that enters the glomerulus, 20 % is filtered. Things that are filtered: EVERYTHING IN PLASM MINUS PLASMA PROTEINS i.e. Water Sodium Urea Phenols from food Creatinine

Question 4

Outline the process of tubular reabsorption

Answer 4

See week 8 PcS notes

Question 5

What substances are secreted and why?

Answer 5

1. H+ ions - regulating acid base balance (If blood too acidic, more H+ is secreted)
2. K+ ions
3. Organic anions and cations

Question 6

How does the reabsoprtion of Na+ at proximal tubule lead to PASSIVE reabsorption of urea, water and Cl-as well as glucose and amino acids?

Answer 6

• Chloride - Relative to Na+ reabsorption.. as it is an anion it follows Na+
• Water - Follows Na+ down water potential gradient. Passes through aquaporins (water channels)
• Urea - Active Na+ reabsorption and passive water reabsorption produces a concentration gradient
• Glucose and amino acids - Na+ dependent secondary active transport

Question 7

What are the different pressures affecting gloerular filtration at the glomerulus and bowmann’s capsule?

Answer 7

• Hyrdostatic pressure
  1) Glomerular capillary hydrostatic pressure (water/solutes to filtrate)
  2) Capsular hydrostatic pressure (water/solutes out of filtrate to plasma)

Colloid Osmotic pressure

(water/solutes out of filtrate to plasma)

Question 8

How would you calculate Net filtration pressure?

Answer 8

NFP = Glomerular hydrostatic pressure - Capsular hydrostatic pressure - Colloid Osmotic pressure

Question 9

What does the glomerular filtrate depend on?

Answer 9

1. Hydrostatic pressures
2. Colloid osmotic pressures
3. Physical properties of the barrier

Question 10

Although the glomerular filtration rate depend on age, gender and body size, what is the average value?

Answer 10

–Men 130ml/min/1.73m2
–Women 120ml/min/1.73m2

Question 11

What is Kf?

Answer 11

Filtration coefficient, and it depends on

1. Surface area of glomerulus
2. Hydraulic properties (liquid movement under pressure)

Question 12

How is GFR calculated?

Answer 12

= Kf X Net filtration pressure

Question 13

Approximately what is the filtration pressure?

Answer 13

Question 14

What is the clinical relevance of GFR? What can it NOT be used for?

Answer 14

Clinical relevance -

• assess the degree of kidney impairment
• (as it shows sum of all filtration rates in nephrons)
• Effectiveness of renal excretion

Not used for a diagnosis! Thats done by

• Radiological studies
• Renal biopsy
• Urine analysis

Question 15

What does a declining GFR indicate?

Answer 15

• Progression of a diesease process
• Posiible reduced renal perfusion
• No exact correlation to loss of kidney nephrons as kidneys can compensate

Question 16

When measuring GFR, what kind of substance would be an ideal marker, given you cannot measure directly?

Answer 16

A substance that is

1. freely filtered at the glomerulus
2. not secreted or reabsorbed
3. Therefore plasma clearance rate volume of plasma cleared of that substance per min = GFR

Question 17

Inulin is a good marker of GFR, would would you calculate GFR using inulin?

Answer 17

GFR = Urine concentration of inulin X Urine flow rate

_________________________________

PLasma concentration of inulin

= 125 mg/mL X 1

_____________

1

= 125 ml/min

Question 18

Why would using an endogenous substance like creatinine be better than using Inulin?

Answer 18

• Less time consuming
• Don’t have to infuse continuously to determine a constant plasma concentration

Question 19

What is creatinine and what are its characteristics in terms of filtration, reabsorption and secretion?

Answer 19

• Derived from skeletal muscle
• It is freely filtered
• NOT reabsorbed
• Some secretion
• If diet (meat intake), muscle mass etc is constant, creatinine is constant

Question 20

How can yoy improve on creatinine dervived GFR rate?

Answer 20

Incorporate demographic changes i.e. using MDRD eGFR;

1. age
2. gender
3. creatinine
4. ethinicity

Question 21

What is the relationship between MDRD e GFR and measured GFR?

Answer 21

Directly proportional relationship

Graph in notes comes from USA patients with renal impairment showing

• MDRD formula works well at mid GFR levels
• MDRD formula doesn’t work well at higher levels

Question 22

What things affect creatinine clearance?

Answer 22

different muscle mass, (due to age, ethinicity, gender)

Question 23

What does this CT scan show?

Answer 23

Acutely swollen and odematous kidney

Question 24

A patient comes in with loin pain and a CT scan is done.. What does this CT scan show?

Answer 24

An emphesamatous kidney

Question 25

What are the sites of infection in the Urinary tract?

Answer 25

Question 26

What are the symptoms of * **acute pylonephritis** * **Lower UTI** * **Pyonephrosis, cortical abcess, staghorn calculus**

Answer 26

Question 27

What is the prevelance of UTIs in women in comparison to men?

Answer 27

**Women: Occurs more often as shorter urethra** * infancy * preschool * middle age **Men: Less often as longer urethra** * Infancy * Old age

Question 28

What host factors increases a person's suseptibility to getting a UTI?

Answer 28

•Congenital abnormalities of the tract –Vesicoureteric reflux –Anatomical abnormalities –Dilatation +/- obstruction •Acquired abnormalities –Prostatic enlargement •Calculi •Haematuria – ­ increased Fe

Question 29

Angie has come in to the clinic again after being treated for her UTI with IV antibiotics. She says she is getting the same symptoms she has before.. * what is the most likely bacteria that has caused re-infection? * What drugs might you ask her about that may have been involved in this recurrence?

Answer 29

* Most common is **E. Coli**, although you cannot be sure until you analyse the patient's urine * **27% of women** get recurrent infection! * Oral contraceptive pill

Question 30

* What would you suggest to Angie to prevent a recurrent UTI?

Answer 30

* Voiding frequently (2-3 hours) * Voiding before bedtime and after having sex * Cranberry juice, for prevention not treatment! Reduced risk of symptoms

Question 31

What investigations may you do on Angie?

Answer 31

1. Cystoscopy 2. Pre and post mic ultrasound

Question 32

What kind of cells are found at each part of a nephron?

Answer 32

Proximal tubule * cuboidal cells with microvilli for increased surface area (lots of mitochondria for active transport) * Reabsorption occurs here mostly Distal tubule - Cuboidal cells