kidney and fluid balance Flashcards
Describe the main functions of the kidney.
Fluid & Electrolytes
- Extracellular volume (ECV)
- Blood pressure
* Endocrine function (hormones) – like Renin, erythropoietin –
* Excretion of waste products
* Acid-Base
Describe the structure of the functional unit in the kidney (i.e. the nephron) and the different urine formation components along the nephron (filtration, reabsorption and secretion) leading to excretion.
afferent arteriole , efferent arteriole, peritubulr capilaries,glomerulus, bowmans capsule, proximal tubule , loop of henley, thick ascending limp, distal tubule, collecting duct.
Explain the autoregulation of renal blood flow (RBF) and glomerulus filtration rate (GFR).
Mechanisms: Myogenic response
Tubuloglomerular feedback (TGF).
Describe the structure/layers of the glomerular filtration barrier, different Starling forces, net filtration pressure & glomerular filtration rate (GFR).
a)
1) Fenestrated endothelium
2) Glomerular basement membrane (GBM)
3) Podocyte foot process
-slit diaphragm (SD) & filtration slit
push =PGC PBS
pull=πGC πBS
net Filtration Pressure = ΔP - Δπ the area between the two lines
starling forces
filtration and hydrostatic pressure decrease
absorption and oncotic pressure increase in the capilary
Glomerular Filtration Rate
(GFR)
GFR = Kf x (ΔP – Δπ)
Kf = Filtration coefficient
P = Hydrostatic pressure
π = Colloid osmotic pressure
Explain the concept of renal clearance and how this is used:
Calculate GFR based on knowledge of creatinine or inulin levels in urine and plasma as well as urine flow.
Definition: ”the volume of plasma from which a substance is completely
removed by the kidney in a given amount of time (usually one minute)”
Clearance
C = U x V / PA
or
GFR(based on inulin knowledge) =
ClX (ml/min)=[Urine]X* Urine flow /[Plasma]X
� U = [solute] in urine (mg/ml)
� V = volume of urine/min (ml/min)
� PA = [solute] in arterial plasma (mg/100 ml plasma
To Calculate Clearance
PA = 1.0 mg/100 ml plasma
U = 0.1 mg/ml
V = 1.0 ml/min
C = 0.1mg/ml x 1.0 ml/min
mg / 100 ml
C = 10 ml/min
Describe what is normal GFR and how this parameter normally changes with age.
we lose 1ml/min/year
Describe different water, salt and glucose transporters/channels along the nephron.
aquaporine, salt symport, antiport, pump,glucose symport with Na+
Explain normal renal handling of water, salt and glucose along the nephron.
H2O % of filtered amount:
*Proximal tubule: 70%
*Loop of Henle: 10%
*Distal tubule: 10%
*Collecting duct: 9%
In the final urine: 1%
Tubular reabsorption of H2O
Daily filtration: 180 L/day = 125 ml/min
Daily excretion: 1% x 180 L/day = 1.8 L
NaCl % of filtered amount:
*Proximal tubule: 70%
*Loop of Henle: 20%
*Distal tubule: 6%
*Collecting duct: 3%
In the final urine: 1%
Daily filtration: 1500 g/day
Daily excretion: 1% x 1500 g/day = 15 g
Glucose
Daily filtration: 180 g/day
Daily excretion: 0.03 – 0.3 g /day
% of filtered amount:
*Proximal tubule: 99.8-100%
*Loop of Henle: 0%
*Distal tubule: 0%
*Collecting duct: 0%
In the final urine: less than 0.2%
Reabsorption of other
substances:
- Amino Acids (100%)
- Bicarbonate (90%)
- Urea (50%)
Describe known pharmacological targets focused on the RAAS, and the functional cardiorenal effects of this type of treatment strategy.
RAAS
= Renin - Angiotensin - Aldosterone - System
* Important for fluid balance and blood pressure regulation
* Renin secretion from juxtaglomerular apparatus (JGA)
RAAS Activation
* Pharmacological Targets – Reduce RAAS activity:
Enzyme: ACE Inhibitors, (e.g. Captopril)
Receptor: ARBs = AT1 Receptor Antagonist (e.g. Candesartan & Losartan)
Indications: Hypertension, Heart Failure, Diabetes
H2O absorbtion , vasoconstriction, sympathetic activation , Na+ reabsorbtion
Explain the renin-angiotensin-aldosterone system (RAAS) by discussing stimuli of activation, cellular targets and mechanisms of action and the physiological effects (e., body fluid volume, electrolytes & blood pressure).
see diagram
Describe common effects (symptoms) of reduced kidney function (GFR), with a focus on ECV homeostasis, blood pressure, blood formation, excretion of metabolic waste products and acid-base balance.
blood pressure up, blood formation down , excrition down , waste up, acid up
Explain how total body water (TKV) is normally distributed between the intracellular (ICV) and extracellular (ECV) spaces, and describe osmolarity in the ECV and ICV, under normal conditions.
intracelular spaces have more water.
osmolarity same
Describe how body fluid balance and osmolarity change in conditions with altered sodium or water intake
water up = volume up everywhere and osmolarity down everywhere
opposite with little water
excessive Na+= When we consume Na+ we have an increase in osmolarity everywhere and more water going to the ECV ( because that is where NaCl for example goes when we consume it )
opposite when we have little Na+
Why use inulin ?
- Free filtration
- No secretion
- No reabsorption
- Measurable in both urine & plasma
- No biological activity
*Not toxic
Other marker used: - Creatinine
Factors determining GFR?
RBF
Kf->Permeability ,Area
Filtration Pressure->ΔP – Δπ
