Renal System Flashcards
What are the functions of the kidney?
Filter metabolic products and toxins from the blood and excrete them as urine
Regulate the body fluid status, electrolytes, and acid-base balance
Humoral regulation of blood pressure and flow
What does the cortex of the kidney have?
Glomeruli and highly convoluted epithelial structures in the form of tubules
What does the medulla of the kidney have?
Parallel arranged tubules and small blood vessels
What is the nephron?
The basic structural and functional unit of the kidney
What makes up the renal corpuscle?
The glomerulus, Bowman’s space, and Bowman’s capsule
What are filtration slits?
Interdigitations connected by the slit diaphragm
Where is the largest portion of the glomerular filtrate retreived?
The proximal tubule
What are the main functions of the loop of henle?
Assisting in the formation of concentrated or dilute urine, increasing osmolarity of the interstitial space
What is the main function of the distal tubule and collecting duct?
Performing fine control of electrolyte and water excretion
What is the juxtaglomerular apparatus?
The region where the glomerulus makes contact with the thick ascending limb of the loop of henle
What does sympathetic stimulation of the kidney do?
Causes vasoconstriction, sodium reabsorption in the proximal tubules, and renin secretion
What are the three processes of the kidney?
Glomerular filtration, tubule reabsorption, and secretion
What is renal clearance?
The virtual volume of plasma that would be totally cleared of a solute in a given time
Why isn’t inulin used to determine GFR?
It has to be given intravenously and is difficult to measure
What endogenous metabolite is often used to measure GFR?
Creatine phosphate
Why is a high glomerular filtration rate essential?
To maintain stable and optimal extracellular levels of solutes and water
What are the four elements of a glomerular filtration barrier?
Endothelial cells, glycocalyx on the endothelial cells, glomerular basement membrane, and epithelial podocytes
What are the three determinants of the filterability of solutes across the glomerular filtration barrier?
Molecular size, electrical charge, and molecule shape
What determines fluid movement across the capillary wall?
Capillary hydrostatic pressure difference and colloid osmotic pressure difference
Why does the glomerulus filtration rate exceed other regions of the body?
Greater starling forces and higher capillary permeability
Which two forces favour ultrafiltration?
Hydrostatic pressure in the glomerular capillary and oncotic pressure in the Bowman’s space
Which two forces oppose ultrafiltration?
Hydrostatic pressure in the Bowman’s space and oncotic pressure in the glomeruli
What are the two unique features of the renal microvasculature?
Two major sites of resistance (afferent and efferent arterioles) and the two capillary beds in series
Which capillary bed favours filtration and which favours reasorption?
The glomeruli favours filtration and the peritubular capillaries favours reabsoption
What is the myogenic response?
Afferent arterioles have the ability to respond to changes in vessel circumference by contracting or relaxing
What is tubuloglomerular feedback?
Macula densa cells sense increase in GFR which translates into contraction of afferent arterioles and decreases GFR
What kind of transport drives the movement of solutes and water across different sections of the nephron?
Transepithelial transport
What is one of the main jobs of epithelial cells?
To work against the laws of thermodynamics to impact the movement of substances
What is an important feature of epithelial cells that helps mediate movement of ions?
Two membranes with asymmetrical distribution of transporters
What do membrane bound carriers rely on to move solutes?
The cumulative thermodynamic gradient of the substances being moved
Where are the three membrane potentials in an epithelial cell?
The entire endothelial cell, the basolateral membrane, and the apical membrane
What causes paracellular electrical coupling to occur?
Large shunts which allow a lot of current movement through the paracellular space
How does water move through a cell?
It moves from regions of low solute to high solute. It can not be actively transported
What is osmolarity?
A measure of the solute concentration
This is the number of osmoles per liter
Where does reabsorption in the kidney occur and in what quantities?
The proximal tubule (67%)
Loop of Henle (25%)
Convoluted tubule, connecting tubule, initial collecting duct, and cortical collecting tubule (5%)
Medullary collecting ducts (3%)
How is sodium transported across the apical membrane of the proximal tubule?
Cotransporters (glucose, amino acids, etc.) and Na-H exchanger
How is sodium transported across the basolateral membrane of the proximal tubule?
Na-K pump and Na-HCO3 co-transporter
Backleak through the paracellular pathway
How is sodium transported in the thin limb of the loop of henle?
Passively and paracellularly
How is sodium transported across the apical membrane of the loop of henle?
NaKCl co transporter
How is sodium transported across the basolateral membrane of the loop of henle?
Na-H antiporter
How is sodium transported across the apical membrane of the distal convoluted tubule?
Na-Cl co-transporter
How is sodium transported across the basolateral membrane of the distal convoluted tubule?
Na-K pump
How is sodium transported across the apical membrane of the connecting tubule, cortical collecting tubule, and medullary collecting duct?
EnaC
How is sodium transported across the basolateral membrane of the connecting tubule, cortical collecting tubule, and medullary collecting duct?
Na-K pump
How does oxygen consumption relate to Na reabsorption?
There is a linear relationship because Na transport is dependent on the Na-K pump, which is ATP dependent
Where in the proximal tubule is paracellular transport dominant and where is transcellular transport dominant for chloride?
Paracellular is dominant in the early proximal tubules and transcellular is dominant in the later proximal tubules
How is chloride transported across the apical membrane of the proximal tubule?
Cl anion exchangers
How is chloride transported across the basolateral membrane of the proximal tubules?
Cl channels and K-Cl cotransporter
How is chloride transported across the apical membrane of the loop of henle?
NaKCl cotransporter
How is chloride transported across the basolateral membrane of the loop of henle?
Cl channels
How is chloride transported across the apical membrane of the distal convoluted tubule?
Na-Cl cotransporter
How is chloride transported across the basolateral membrane of the distal convoluted tubule?
Cl channel
How is chloride transported across the apical membrane in B intercalated cells of the cortical collecting duct?
Cl-HCO3 exchanger
How is chloride transported across the basolateral membrane of B intercalated cells in the cortical collecting duct?
Cl channels
How is chloride transported across principal cells?
Paracellular transport
What drives water reabsorption?
Small osmotic gradients and high permeability of water to aquaporins
How is water reabsorbed in the proximal tubules?
High levels of aquaporin allow for transcellular and paracellular water flow
What is glomerulotubular balance?
The proximal tubules response to alterations in GFR. It reabsorbs a constant fraction of Na
How does increased filtration fraction impact the driving force for reabsoprtion?
It increases it
What is renin?
An enzyme produced by JGA that leads to the production of ANG II
What does ANG II do?
Binds to AT1 receptors and stimulates Na reaborption
What does aldosterone do?
Stimulates Na reabsorption in later regions of the nephron
How does sympathetic innervation of the kidney impact the circulating volume?
It decreases it
What does arginine vasopressin do?
Produces urine with high osmolarity, which means there is more water retention
What does atrial natriuretic peptide do?
Causes renal vasodilation which increases blood flow and sodium load
Where is most of the filtered glucose reabsorbed?
The proximal convoluted tubule
How is glucose transported across the apical and basolateral membranes?
Apical via secondary active transport through the Na-glucose cotransporter
Basolateral via facilitated diffusion
What is the difference between SGLT1 and SGLT2?
SGLT1 has a high affinity and less activity
SGLT2 has a low affinity and high activity
What is the transport maximum of glucose?
Around 400mg/min
Where is 98% of the amino acids which are filtered reabsorbed?
The glomerulus
How are amino acids moved across the membranes?
Apical via Na or H linked transport
Basolateral via exchangers and facilitated diffusion
Where are the majority of oligopeptides reabsorbed?
The proximal tubule
What prevents the filtration of large amounts of proteins?
Glomerular barrier
What is considered chronic kidney disease?
Decreased kidney function shown by GFR of less than 60ml/min per 1.73m^2 or markers of kidney damage for at least three months duration
What is mesoamerican nephropathy?
Kidney disease with little evidence of diabetes or hypertension with lack of proteinuria. This suggests that kidney disease is primarily tubulointerstitial
What is suggested to be the cause of mesoamerican nephropathy?
High amounts of work being done in extreme temperatures with few breaks and little water
What is causing the increase in mesoamerican nephropathy?
Climate change
What is wet bulb globe temperature?
A composite index that includes air temperature, solar radiation, wind speed, and humidity
How does working in hot conditions decrease blood pressure?
Blood volume is lost through sweat and there is redistribution of blood to muscles and skin
What impacts the function of macromolecules?
Aqueous environments which impact the catalytic rate and affinity
What do solutes do to proteins?
Interact with them which impacts their stability and function
How does fructose impact mesoamerican nephropathy?
Fructose is a precursor to uric acid, which is causing major damage to the kidneys.
What is high intracellular potassium important for?
Maintaining cell volume, regulation of pH, and enzyme function
What happens when potassium is first ingested?
There is transient movement into cells for storage before it can be excreted by the kidneys. This is important for buffering K
How does the distal nephron respond to low dietary potassium?
It reabsorbs K
How does the distal nephron respond to high or normal dietary potassium?
It secretes potassium
How does the proximal tubule reabsorb potassium?
Paracellularly
How does the thick ascending limb move potassium?
NKCC mediated transport
How do the different cells of the cortical collecting tubule differ in their response to potassium?
Principal cells secrete potassium via Na-KATPase and ENaC
a-Intercalated cells reabsorb potassium
How does the concentration of urine change in the loop of henle?
The descending limb is permeable to water so filtrate concentrates
The ascending limb is impermeable to water so the filtrate dilutes
How does the countercurrent multiplier system show positive feedback?
The more transport by the ascending limb, the more concentrated the descending limb fluid gets. This facilitates transport by the ascending limb
What draws excess water and solutes from the medulla?
The vasa recta blood vessels
Where do loop diuretics work?
On NKCC in the apical membrane of the thick ascending loop of henle, which prevents the generation of the hypertonic medulla
How does AVP work?
Interacts with receptors to activate the adenylate cyclase pathway, which results in insertion of aquaporin channels into the apical membrane
