Week 8 - Kidney physiology Flashcards
What are the functions of the kidney?
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!
What are the steps involved in the formation of urine?
Remember Going To Toilets Saddens! Glomerular Filtration Tubular Reabsorption Tubular secretion Selective Movement
What is filtered during glomerular filtration?
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
Outline the process of tubular reabsorption
See week 8 PcS notes
What substances are secreted and why?
- H+ ions - regulating acid base balance (If blood too acidic, more H+ is secreted)
- K+ ions
- Organic anions and cations
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?
- 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
What are the different pressures affecting gloerular filtration at the glomerulus and bowmann’s capsule?
-
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)
How would you calculate Net filtration pressure?
NFP = Glomerular hydrostatic pressure - Capsular hydrostatic pressure - Colloid Osmotic pressure
What does the glomerular filtrate depend on?
- Hydrostatic pressures
- Colloid osmotic pressures
- Physical properties of the barrier
Although the glomerular filtration rate depend on age, gender and body size, what is the average value?
–Men 130ml/min/1.73m2
–Women 120ml/min/1.73m2
What is Kf?
Filtration coefficient, and it depends on
- Surface area of glomerulus
- Hydraulic properties (liquid movement under pressure)
How is GFR calculated?
= Kf X Net filtration pressure
Approximately what is the filtration pressure?
What is the clinical relevance of GFR? What can it NOT be used for?
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
What does a declining GFR indicate?
- Progression of a diesease process
- Posiible reduced renal perfusion
- No exact correlation to loss of kidney nephrons as kidneys can compensate
When measuring GFR, what kind of substance would be an ideal marker, given you cannot measure directly?
A substance that is
- freely filtered at the glomerulus
- not secreted or reabsorbed
- Therefore plasma clearance rate volume of plasma cleared of that substance per min = GFR
Inulin is a good marker of GFR, would would you calculate GFR using inulin?
GFR = Urine concentration of inulin X Urine flow rate
_________________________________
PLasma concentration of inulin
= 125 mg/mL X 1
_____________
1
= 125 ml/min
Why would using an endogenous substance like creatinine be better than using Inulin?
- Less time consuming
- Don’t have to infuse continuously to determine a constant plasma concentration
What is creatinine and what are its characteristics in terms of filtration, reabsorption and secretion?
- Derived from skeletal muscle
- It is freely filtered
- NOT reabsorbed
- Some secretion
- If diet (meat intake), muscle mass etc is constant, creatinine is constant
How can yoy improve on creatinine dervived GFR rate?
Incorporate demographic changes i.e. using MDRD eGFR;
- age
- gender
- creatinine
- ethinicity
What is the relationship between MDRD e GFR and measured GFR?
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
What things affect creatinine clearance?
different muscle mass, (due to age, ethinicity, gender)
What does this CT scan show?
Acutely swollen and odematous kidney
A patient comes in with loin pain and a CT scan is done.. What does this CT scan show?
An emphesamatous kidney
What are the sites of infection in the Urinary tract?
What are the symptoms of
- acute pylonephritis
- Lower UTI
- Pyonephrosis, cortical abcess, staghorn calculus
What is the prevelance of UTIs in women in comparison to men?
Women: Occurs more often as shorter urethra
- infancy
- preschool
- middle age
Men: Less often as longer urethra
- Infancy
- Old age
What host factors increases a person’s suseptibility to getting a UTI?
•Congenital abnormalities of the tract
–Vesicoureteric reflux
–Anatomical abnormalities
–Dilatation +/- obstruction
•Acquired abnormalities
–Prostatic enlargement
•Calculi
•Haematuria
– increased Fe
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?
- 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
- What would you suggest to Angie to prevent a recurrent UTI?
- Voiding frequently (2-3 hours)
- Voiding before bedtime and after having sex
- Cranberry juice, for prevention not treatment! Reduced risk of symptoms
What investigations may you do on Angie?
- Cystoscopy
- Pre and post mic ultrasound
What kind of cells are found at each part of a nephron?
Proximal tubule
- cuboidal cells with microvilli for increased surface area (lots of mitochondria for active transport)
- Reabsorption occurs here mostly
Distal tubule -
Cuboidal cells
