Module 11 Flashcards
List the organs involved in the renal system
Kidneys, ureters, bladder, and urethra
List the principal functions of the kidneys
Regulation of water balance, electrolyte levels, pH of the blood, and long-term regulation of arterial pressure
Basic function is to remove nonessential substances from plasma (waste metabolites, excess water, electrolytes), recover any essential substance (like glucose), elimination of waste or foreign substances (drugs, food additives, vitamins), and endocrine hormone production (erythropoietin, renin, vitamin D, stanniocalcin)
Name the different areas within the kidney
Renal cortex and medulla
Nephrons drain into collecting ducts, draining into calyces that connect to the renal pelvis then to the ureter
Renal pyramids with renal papillae at their tips
Describe the flow of blood through the kidney
Enters through renal artery, branches into interlobar arteries (between renal pyramids) then arcuate arteries (top of pyramid in cortex), then interlobular arteries that supply the nephron capillaries. After the nephron, flows into interlobular vein, arcuate vein, interlobar vein, then large renal vein
List the functions of the nephron
Filter blood, reabsorb essential substances, and excrete nonessential molecules and waste
Describe the structure of a nephron, starting at the blood source
Glomerular capsule surrounds glomerulus, collectively called the renal corpuscle, followed by tubes: proximal convoluted tubule, descending and ascending limbs of the loop of Henle, distal convoluted tubule, and collecting duct
Describe the blood supply surrounding the nephron
Blood in afferent arteriole leads to glomerulus, then leaves via the efferent arteriole to peritubular capillaries, a dense network that surrounds tubes of the nephron, which drains into the interlobular vein
Define filtration
The movement of fluid through the glomerular capillary due to hydrostatic pressures
Define filtrate
The solution created by filtration, composed of water plus all dissolved solutes in the blood (except large proteins too big to be filtered)
Define reabsorption
The movement of substance from the lumen of the nephron back into the blood
Define secretion
The movement of a substance from the blood into the lumen of the nephron
Define excretion
The removal of substances from the body
Excretion = Filtration + Secretion - Reabsorption
Define glomerular filtration
The bulk flow of fluid from the blood into the glomerular capsule, where the filtrate contains the same substances as plasma except for large proteins and RBCs
List the factors affecting glomerular filtration
The permeability of capillaries in the glomerulus (many fenestrations in glomerular epithelial cells), larger diameter afferent arteriole and smaller diameter efferent arteriole, podocytes (special epithelial cells surrounding capillaries, have large filtration slits formed between pedicles), and Starling Forces
Explain Starling Forces in the glomerular capsule and name the different forces
They cause bulk movement of fluid across capillaries due to combination of hydrostatic and colloid osmotic forces
Two hydrostatic pressures (blood hydrostatic pressure and capsular hydrostatic pressure) and one colloid osmotic force (colloid osmotic pressure due to plasma proteins, none in glomerular capsule because few proteins are filtered)
Describe the blood hydrostatic pressure in the glomerular capsule
Pressure due to the difference in diameter of the afferent and efferent arterioles
Causes filtration
Approx 60mmHg (almost 2x a regular capillary)
Describe the colloid osmotic pressure in the glomerular capsule
Due to plasma proteins in the glomerulus
Causes reabsorption
Approx -32mmHg (shown as negative to show direction)
Describe the capsular hydrostatic pressure in the glomerular capsule
Pressure due to the confined space of the glomerular capsule as it fills with filtrate
Causing reabsorption
Approx -18mmHg (shown negative to show direction)
Describe the equation for net filtration pressure (NFP) in the glomerular capsule
NFP = BHP - COP - CP
If positive, net filtration, if negative, net reabsorption
Define glomerular filtration rate (GFR)
The volume of fluid filtered by the glomerulus during a certain time period
Roughly 180L/day
Describe the equation for filtered load
Filter load = GFR x plasma concentration of the substance
Define urine concentration
The amount of solute excreted per unit volume of urine (g/L)
Define amount of solute excreted and describe the equation
The actual amount (in grams) of solute excreted in urine
Amount excreted = Urine Concentration x Amount of water excreted per day (1.8 L/day)
Define amount reabsorbed and describe the equation
The amount of filtered substance that is taken back up by the kidneys
Amount Reabsorbed = Filtered Load - Amount Excreted
Describe the equation for fraction excreted
Fraction Excreted = (Amount Reabsorbed/Filtered Load) x 100%
List the substances reabsorbed and secreted in the proximal tubule
Reabsorbed: glucose, amino acids, Na+, K+, Cl-, HCO3-, H2O
Secreted: H+
66% of total filtrate is reabsorbed
List the substances reabsorbed and secreted in the descending limb of the loop of Henle
Reabsorbed: H2O (15% of filtered water)
Secreted: nothing
List the substances reabsorbed and secreted in the ascending limb of the loop of Henle
Reabsorbed: Na+, K+, and Cl- (20% of the filtered Na+, and 25% of all Na+, K+ and Cl- due to co-transporter)
Secreted: H+ and K+
List the substances reabsorbed and secreted in the distal tubule
Reabsorbed: Na+, HCO3-, and H2O (12% of Na+ filtered at glomerulus)
Secreted: H+ and K+
List the substances reabsorbed and secreted in the collecting duct
Reabsorbed: H2O and Na+ (10% of filtered Na+ and water)
Secreted: H+ and K+
List the transport routes taken for reabsorption in the nephron
Paracellular transport and transcellular transport
Also secondary active transport using the Na+/K+ pump
Describe paracellular transport
Tubular cells are joined together by tight junctions that generally don’t allow substances to cross, but along nephrons, they vary and can be leaky, allowing some substances to diffuse between cells
Generally non-regulated (no hormonal control)
Describe transcellular transport
Some substances are transported across the tubular cell membrane from the lumen into the cell, then into the interstitial fluid and into the blood
Can be regulated by hormones, but most of the time are non-regulated
Describe secondary active transport for reabsorption in the nephron
Na+ concentration gradient established by the Na+/K+ pump used to power other transporters. As Na+ moves down its concentration gradient, other substances either move with Na+ or move out in exchange with incoming Na+
List examples of secondary active transporters in the nephron
Na+/Glucose co-transporter and the Na+/H+ exchanger, both on the luminal side of tubule cells
Na+/Amino acid co-transporter
List the areas of the nephron where Na+ is reabsorbed, and whether it is regulated or unregulated
Proximal tubule, ascending limb of the loop of Henle, and the early distal tubule
Mostly non-regulated, can be regulated in proximal tubule by AngII and in distal tubule by aldosterone
List the areas of the nephron where water is reabsorbed and whether it is regulated or non-regulated
Proximal tubule and descending limb of the loop of Henle (non-regulated) and in the late distal tubule and collecting duct (regulated by ADH)
List the areas of the nephron where K+ is reabsorbed
Proximal tubule and the ascending limb of the loop of Henle
List the areas of the nephron where K+ is secreted and whether it is regulated or non-regulated
In small amounts in the ascending limb of the loop of Henle (non-regulated) and in larger amounts in the late distal tubule and collecting duct (regulated with aldosterone)
List the areas of the nephron where H+ is secreted and whether it is regulated or non-regulated
Proximal tubule and ascending limb of the loop of Henle (regulated and non-regulated) and in the late distal tubule and collecting duct (complex mechanisms)
List the areas of the nephron where glucose and amino acids are reabsorbed
All glucose and amino acids filtered at the glomerulus is reabsorbed in the proximal tubule in a healthy individual
Describe how glucose and amino acids are reabsorbed in the proximal tubule
Na+/Glucose co-transporter (can be regulated by AngII) and Na+/amino acid co-transporter
Describe how Na+ is reabsorbed in the proximal tubule
Due to Na+/K+ pump, the Na+ concentration gradient allows Na+ to be reabsorbed by simple diffusion
Describe why glucose in urine is a sign of diabetes mellitus
Diabetes is a disease affecting the production of insulin, which stores glucose after a meal, so without it glucose concentration builds up in the blood. When lots of glucose is filtered at the glomerulus, it saturates the Na+/glucose co-transporter, so not all cal be reabsorbed and some is excreted in urine
Describe how water is reabsorbed in the proximal tubule
After reabsorbing Na+, glucose and amino acids, filtrate has a lower solute concentration and higher water concentration compared to cell and interstitial fluid, so with this osmotic gradient and aquaporins (special water channels), water moves down concentration gradient by osmosis (simple diffusion)
Reabsorbed both by paracellular and transcellular transport, and only takes place after solutes have been reabsorbed
Describe how K+ and Cl- are reabsorbed in the proximal tubule, and whether it’s regulated or non-regulated
Through 2 types of paracellular transport, both non-regulated: solvent drag and simple diffusion
Cl- is also reabsorbed by transcellular transport
65% of all filtered K+ and Cl- are reabsorbed in the proximal tubule
Define solvent drag
The reabsorption of K+ with movement of water being reabsorbed by osmosis; as it moves between cells, the water carries with it some dissolved substances in the filtrate
Describe how reabsorbed substances return to circulation from the proximal tubule
Starling Forces, with pressures different than around regular capillaries
In kidney, capillary hydrostatic force (Pc) is 13mmHg, interstitial hydrostatic force (PIF) is 6mmHg, osmotic force due to proteins in plasma (πp) is 32mmHg, and interstitial osmotic force (πIF) is 15mmHg
Equation: NFP = (Pc - PIF) - (πp - πIF)
Results in -10mmHg back into the capillary
Describe reabsorption of ions and water in the descending limb of the loop of Henle
Descending limb is very permeable to water and not very permeable to any ion, so water will move out by osmosis into interstitial space, and very few ions will diffuse out
End result is water loss from filtrate, increasing concentration of filtrate from 300mOsm/kg water to almost 1200mOsm/kg water
Describe reabsorption of Na+, K+, Cl- and water in the ascending limb of the loop of Henle
Ascending limb is not permeable to water, so no water movement, but very permeable to Na+, K+ and Cl-, and their movement depends on the Na+/K+ pumps in tubule cells, creating a concentration gradient for Na+ to drive a specific cotransporter, the Na+/K+/Cl- co-transporter
Due to both the pump and co-transporter, K+ concentration increases in tubule cells dramatically, so some will be secreted back out into filtrate by simple diffusion
Filtrate concentration decreases from 1200mOsm/kg water to 100mOsm/kg water
Describe reabsorption of Na+ and water in the distal tubule
Reabsorption of water is controlled by ADH, depends on hydration of the individual, amount varies from 0-15% of the original filtrate
Na+ is reabsorbed in early distal tubule by simple diffusion due to concentration gradient, but in late distal tubule, is regulated by aldosterone, which increases the activity of the Na+/K+ pump, decreasing concentration of Na+ in the cell, and causes cell to manufacture more Na+ channels to allow easier diffusion
Describe secretion of K+ in the distal tubule
Aldosterone causes secretion of K+ into the lumen by increasing the number of K+ channels in the luminal membrane
Describe the reabsorption of water and Na+ in the collecting duct
Always regulated by hormones
Na+ reabsorption by aldosterone
Water reabsorption by ADH
Increase in either hormone increases reabsorption
Describe the secretion of K+ in the collecting duct
Takes place due to aldosterone
Increases Na+/K+ pump activity on basal side of collecting duct cells, increasing intracellular K+ concentration, manufactures more K+ channels, allowing K+ to leak out down concentration gradient into lumen of collecting duct
List the mechanisms by which Na+ is handled by the nephron
Proximal tubule: Na+/glucose co-transporter Na+/amino acid co-transporter Na+/H+ exchanger Simple diffusion of Na+
Ascending limb:
Na+/K+/Cl- co-transporter
Distal tubule:
Na+ under influence of aldosterone
All reabsorption
List the mechanisms by which glucose and amino acids are handled by the nephron
Proximal tubule:
Na+/glucose co-transporter
Na+/amino acid co-transporter
All reabsorption, in a healthy individual all of both is completely reabsorbed
List the mechanisms by which water is handled by the nephron
Proximal tubule:
Non-regulated osmosis
Descending limb:
Non-regulated osmosis and aquaporins
Distal tubule and collecting duct:
Regulated by ADH
All reabsorption
List the mechanisms by which K+ is handled by the nephron
Proximal tubule:
Solvent flux/drag and simple diffusion (reabsorption)
Ascending limb:
Na+/K+/Cl- co-transporter (reabsorption)
Simple diffusion (secretion)
Distal tubule and collecting duct:
Regulated by aldosterone, creating more K+ channels (secretion)
List the mechanisms by which H+ is handled by the nephron
Proximal tubule and ascending limb:
Na+/H+ exchanger, activity increased by AngII
Distal tubule and collecting duct:
Complex mechanism
All secretion
Describe the concept of water balance
In order to have water balance, water lost must be balanced by water gained to maintain homeostasis of body fluids
List ways that water is gained
Drinking, eating, and by metabolism of energy stores
List ways that water is lost
Through urine, sweating, lungs, and feces
Describe how kidneys regulate water balance
Kidneys don’t produce water, only reabsorb it, and that is regulated by ADH (produced in hypothalamus, released from posterior pituitary) by negative feedback using osmoreceptors
Describe osmoreceptors and their function
Sensors to detect changes in body fluid concentrations, located in the hypothalamus, and will determine the release of ADH
Osmoreceptors will shrink or swell depending on osmolarity of body fluids, which signals the release or inhibition of ADH
Describe how dehydration will affect release of ADH
Dehydration concentrates body fluids, increasing osmolarity, causing osmoreceptors to lose water by osmosis and shrink, signalling posterior pituitary to release ADH, which causes kidneys to reabsorb more water from distal tubule and collecting ducts, resulting in lower blood volume and pressure
Describe how overhydration will affect release of ADH
Overhydration dilutes body fluids, decreasing osmolarity, causing osmoreceptors to swell, less ADH is released, less water reabsorbed in distal tubule and collecting duct, more water excreted in urine, resulting in increased blood volume and pressure
List the receptors detecting changes in body fluids to influence ADH release
Changes in blood volume are detected by volume receptors in the walls of the left atrium, and lower blood volume causes release of ADH
Osmoreceptors in the hypothalamus detect osmolarity of body fluids, and high osmolarity (causing them to shrink) causes release of ADH
Describe how ADH affects cells
Causes water reabsorption in distal tubule and collecting duct by acting directly on cells in the regions
Stimulates cells to manufacture aquaporins, which insert into the luminal membrane
This leads to more water reabsorbed by osmosis and less excreted in urine, due to the existing concentration gradient across luminal cells (low solutes outside, high solutes inside)
Reabsorbed water enters peritubular capillaries due to Starling Forces
Explain how alcohol affects ADH
Alcohol inhibits the release of ADH from the pituitary gland, causing people to urinate more after drinking alcohol, due to less aquaporins in the distal tubule and collecting duct, less water reabsorbed and more excreted in urine
Name the system that regulates Na+ levels in the body
The renin-angiotenson system (RAS) and aldosterone, which combined are the renin-angiotensin-aldosterone system (RAAS)
Describe aldosterone and its purpose
A steroid hormone produced by the adrenal glands, secreted into circulation when blood Na+ levels are low or blood K+ levels are high to help return ion concentration to normal
It is secreted in response to AngII and in small amounts by ACTH
Describe how aldosterone functions
Returns Na+ and K+ concentrations to normal by causing Na+ reabsorption and K+ secretion in distal tubule and collecting duct, by causing tubule cells to manufacture more Na+ and K+ channels for the luminal membrane, so they move down their concentration gradients
Also increases Na+/K+ pump activity
Describe the RAS’s function
Regulates Na+ balance in the body by increasing reabsorption of Na+ in the proximal tubule, by converting inactive protein angiotensinogen into active hormone AngII
Describe how the RAS functions
Angiotensinogen (produced by liver) reacts with renin (produced by juxtaglomerular cells in walls of afferent and efferent arterioles)
Renin is released when blood pressure or plasma Na+ levels are low, and converts angiotensinogen to AngI, which is converted to AngII by angiotensin converting enzyme (ACE, produced in lungs)
The final product AngII increases reabsorption of Na+ in proximal tubule and ascending limb
Describe the effects of angiotensin II to reabsorb Na+
Acts directly on proximal tubule and ascending limb cells to increase Na+/H+ exchanger activity, reabsorbing more Na+ and secreting H+
AngII also stimulates secretion of aldosterone from the adrenal gland, which will act on distal tubule and collecting duct cells to reabsorb Na+ and secrete K+
Describe the effects of angiotensin II on the rest of the body
Released when blood pressure is low
AngII is a potent vasoconstrictor, constricts vessels, increasing total peripheral resistance, which increases blood pressure
Stimulates sensation of thirst to trigger drinking to increase blood volume and blood pressure
Stimulates release of ADH from posterior pituitary, causing reabsorption of water by kidneys and absorption of water and Na+ from the digestive tract
