L11 - Renal Physiology I Flashcards
describe the anatomy of the renal system
The kidney
- highly vascular organ
The nephron and collecting duct
- proximal convoluted tubule
- loop of henle (descending limb and ascending limb)
- distal convoluted tubule
- collecting duct
The renal corpuscle
-> filtration apparatus
- afferent and efferent arterioles
- bowman’s capsule (parietal layer and visceral layer)
- glomerulus (capillary network - covered by visceral layer)
- peritiubular capillaries
- vasa recta on juxdamedullary nephron
what are the three key principles for renal function
Amount excreted = amount FILTERED + amount SECRETED - amount REABSORBED
- glomerular filtration
- tubular secretion
- tubular reabsorption
- toxins are 100% excreted (20 filtered, 80 secreted)
- Na+/K+ are 10% excreted. (20 filtered, 10 reabsorbed)
- glucose 0% excreted (20 filtered, 20 reabsorbed)
describe renal function - glomerular filtration and how it is determined/happens
Filtration across capillaries is determined by Starling forces (hydrostatic pressures and osmotic forces)
- osmotic force in Bowmans space would favour filtration but is 0
Favouring filtration:
- glomerular capillary blood pressure (Pgc) - 60mmHg
Opposing filtration:
- fluid pressure in Bowmans space (Pbs) - 15mmHg
- osmotic force due to protein in plasma (pie gc) - 29mmHg
Net glomerular filtration pressure = 16mmHg
- water and most small molecules are filtered
- large molecules or large complexes of bound molecules are not filtered
what is the glomerular filtration rate and what depermines the GFR
Glomerular filtration rate (GFR) = volume of fluid filtered from glomeruli into Bowmans space per unit of time
GFR determinants:
1. glomerular filtration pressure - relative high Pgc
2. permeability of corpuscular membranes (high)
3. surface area (large)
Average GFR (70kg person): 125mL/min
- kidneys filter entire plasma volume almost 45 times per day
how can renal function be determined using GFR
GFR is not fixed but physiologically related
Afferent arteriole and efferent arteriole are crucial for regulating GFR, both support and oppose GFR by regulating the pressure gradient for filtration
- they are regulated by local, metabolic , neuronal, hormonal control
Decreased GFR results from: constricting AA or dilating EA
Increased GFR results from: constricting EA or dilating AA
describe tubular secretion and its role in renal function
move substances from the peritubular capillaries into the tubular lumen
- H+, K+, choline, creatinine, penicilin
Active secretion from:
1. blood via interstitial fluid into tubular cell - across basolateral membrane then across apical membrane (transcellular)
2. interstitial fluid into tubular lumen (paracellular)
active/passive transport - active commonly coupled with Na+ exchange
combination of active and passive transport bc in order to have a gradient for diffusion (passive) need an active process to make it
describe tubular reabsorption and its role in renal function
Na+, glucose, vitamin C
Active reabsorption from:
1. tubular lumen into tubular cell - across apical membrane - then across the basolateral membrane (transcellular)
2. tubular lumen into interstitial space - into capillaries (paracellular)
active/passive transport - active commonly coupled with Na+ exchange
describe how you can use GFR to assess kidney function, and what are certain GFRs that indicate certain things?
Plasma volume from which a substance is completely cleared (removed) by the kidneys per unit time
Substance properties required for GFR determination:
- freely filtered
- not secreted
- not reabsorbed
- not metabolised, not toxic
Exogenous Inulin - polysaccharide
Exogenous creatine - muscle waste product
Increase creatine levels the blood - less clearance - low levels of creatinine in the urine = low GFR and impaired kidney function
GFR
- Male: 88-128 mL/min
- Female: 97-137 mL/min
Low plasma creating - GFR ~125 mL/min both kidneys are working
Fairly normal plasma creatinine - GFR ~60mL/min - only one kidney working
High plasma creating - critical kidney dysfunction - medication required
Exponential shape of GFR-creatining curve indicates relative insensitive at mild dysfunction
describe kidney dysfunction - chronic kidney disease
Gradual loss of kidney function dangerous build-up of fluid, electrolytes and waste products
Fluid retention - swelling in your arms and legs, high blood pressure (hypertension and venous return increases), fluid in your lungs (pulmonary oedema)
Hypertension and diabetes (cause or consequence), genetics
Associates with kidney fibrosis (scarring)
Irreversible damage to kidneys (end-stage kidney disease) -> dialysis or a kidney transplant required for survival
how to deal with chronic kidney disease in dental practice?
- composmised immune system - tendency to infection - candidiasis and ulcers in oral cavity (antibiotics prior to dental procedure help against infection/procedures on non-dialysis days)
- anemia - reduced EPO production -> pale soft tissues in oral cavity
- bleeding - platelets dysfunction or heparin during dialysis
- loose teeth or fall out - loss of calcium (Vitamin D)
- risk for lethal cardiac arrhythmia - a rise of K+ in blood can lead to hyperkalaemia
describe the sodium and water balance (how it is regulated and why, and what each segment of the nephron is responsible for + physiological principles of this)
the regulation of body water (and Na+) balance is critical for physiology - essential for (ion) homeostasis.
Disturbances of Water-Na+ homeostasis leads to pathophysiology
Water and Na+:
- freely filtered
- not secreted
- almost fully (99%) reabsorbed
- limited excreted
The movement of water between body compartment and cellular membranes is closely linked to Na+
Segments:
- PCT: responsible for the bulk reabsorption of solute and water
- Loops of Henle: generate the medullary osmotic gradient; allow for the passive reabsorption of water in the CD
- DCT and CD: most regulation (fine-tuning) of the excretion of solutes and water)
Physiological principles:
- active Na+ reaborption
- passive water reabsorption (driven by osmosis due to Na+)
describe Na+ reabsorption in more detail
PCT:
- Na+/K+ ATPase pumps Na+ out of the tubule cell across the basolarteral membrane in the interstitial fluid, keeping the intracellular Na+ in the tubule cell low
- Na+ gradient allows Na+ to move from the tubular lumen across the apical membrane into the tubule cell - allow H+ counter-transport out of, and co-transport of other substances into the tubule cell
CD:
- Na+/K+ ATPase pumps Na+ out f the CD cell across the basolateral membrane in the intersistial fluid, keeping the intracellular Na+ in the duct cell low
- Na+ gardent allows Na+ to move from the tubular lumen across the apical membrane into the duct cell via Na+ channels (NCC or ENaC)
Na+ movement -> basolateral via Na+/K+ ATPase
Na+ movement -> apical depends on tubule segment: Co-/counter- transporter -> proximal epithelium (leaky) or Channel -> distal epithelium (tight)
describe the water reabsorption in more detail
Na+ reabsorption (and solutes) allows water reabsorption by osmosis
Movement of Na+ and solutes (Cl-, HCO3-, glucose, AAs, other ions) drops local tubular lumen osmolarity and increases interstitial fluid osmolarity (interstitial H2O drops)
The difference in water concentration between lumen (H2O increases) and interstitial (H2O drops) drives diffusion of water across the tubular cells
Water can only diffuse when the membrane are water permeable - depended on number and type of aquaporins
Water, Na+ and solutes via bulk flow move into peritubular capillaries
describe the regulation of sodium and water balance
- cortical and collecting tubes are segment under physiological control
- Vasopressin (VP) and anti-diuretic hormone (ADH) - posterior pituitary secreted hormone VP recruits more aquapirins - increases water reabsorption (VP high, urine volume low) -> cardiac output!
- VP is low - CD water reabsorption minimal - large volume of water remains in tubular lien -> more water is excreted as urine - water diuresis (VP low, urine volume high)
