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52 Cards in this Set
- Front
- Back
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Kidneys |
– Paired organs at the back of the abdominal cavity – Processes blood • Produces a filtrate • Removes wastes from blood • Recovers needed materials – Salts,water,etc – Outer portion: cortex – Inner portion: medulla |
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Urinary System |
-Kidneys -Ureter • Bladder – Hollow, distensible sac for storage of urine • Urethra |
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Kidney Functions (1-5) |
1. Maintain proper water balance in the body. 3. Maintain the proper plasma volume and therefore helping to regulating blood pressure (Chapter14). 4. Help maintain the proper acid-base balance of the body. 5. Maintain the proper osmolality of body fluids. |
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Kidney Functions (6-10) |
6. Excrete waste products of metabolism. 7. Excrete many foreign compounds such as drugs, food additives etc. 8. Secrete erythropoietin, the hormone that controls red blood cell production. 9. Secrete renin, an enzyme which participates in regulation of Na+ levels and blood pressure (Chapter14). 10. Convert vitamin D into its active form which helps u |
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Kidney Structure |
• Paired kidneys are on either side of vertebral column below diaphragm – About size of fist • Urine made in the kidneys pools into the renal pelvis, then down the ureter to the urinary bladder. • It passes from the bladder through the urethra to exit the body. • Urine is transported using peristalsis. |
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Kidney Structure cont, |
• The kidney has two distinct regions: – Renal cortex – Renal medulla, made up of renal pyramids and columns • Each pyramid drains into a minor calyxà---->major calyxà---> renal pelvis. |
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Microscopic Kidney Structure: Nephron |
Nephron: functional unit of the kidney – Each kidney has more than a million nephrons. – Nephron consists of small tubules and associated blood vessels. |
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Renal Blood Vessels |
Renal artery ---> Interlobar arteries ---> Arcuate arteries ---> Interlobular arteries ---> Afferent arterioles Glomerulus* ---> Efferent arterioles ---> Peritubular capillaries ---> Interlobular veins ---> Arcuate veins ---> Interlobar veins ---> Renal vein |
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Nephron Tubules |
• Glomerular (Bowman's) capsule surrounds the glomerulus. Together, they make up the renal corpuscle. • Filtrate produced in renal corpuscle passes into the proximal convoluted tubule. • Next, fluid passes into the descending and ascending loop of Henle.
• After the loop of Henle, fluid passes into the distal convoluted tubule. • Finally, fluid passes into the collecting duct. – The fluid is now urine and will drain into a minor calyx. |
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The four processes of the nephron |
• Filtration blood flows through glomerular capillaries • Reabsorption – Occurs when filtrate passes through the tubules – Materials to be kept are reabsorbed across epithelial cells lining tubules and transported to peritubular capillaries • Secretion – Opportunity for body to get rid of non-filtered materials – Selective transfer of non-filtered materials from peritubular blood into tubular lumen for removal • Excretion |
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Two Types of Nephrons |
• Juxtamedullary: better at making concentrated urine • Cortical Why is it important to have concentrated?: -actively transport water |
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Glomerular Corpuscle |
• Capillaries of the glomerulus are fenestrated. – Large pores allow water and solutes to leave arterioles but not blood cells and plasma proteins. • Fluid entering the glomerular capsule is called Ultrafiltrate |
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Ultrafiltrate |
Fluid in glomerular capsule gets there via hydrostatic pressure of the blood, colloid osmotic pressure, and very permeable capillaries.
Contains everything except formed elements and plasma proteins |
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Filtration Rates (GFR) |
Glomerular filtration rate (GFR): volume of filtrate produced by both kidneys each minute = 115−125 ml. – 180 l/ day (45 gallons!) |
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How is GFR controlled? |
– Sympathetic nervous system • Vasoconstriction/dilation
– Autoregulation |
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What happens when you are about to be acacked... |
-SNS shuts the fact that you need to go the bathroom down! |
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Tubular reabsorption |
• Most of what enters the kidneys and nephrons will leave and enter the blood • Reabsorption is highly selecAve • Recycling efficiency – 99% of water – 100% of sugars |
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Reabsorption |
180 l of water is filtered per day, but only 1−2 l is excreted as urine. – This will increase when well hydrated and decrease when dehydrated. – A minimum 400 ml must be excreted to rid the body of wastes = obligatory water loss. – 85% of reabsorption occurs in the proximal tubules and descending loop of Henle. This portion is unregulated. |
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Reabsorption in the Proximal Tubule |
• The osmolality of filtrate in the glomerular capsule is equal to that of blood plasma. • Na+ is actively transported out of the filtrate into the peritubular blood to set up a concentration gradient to drive osmosis. |
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Proximal tubule: Active Transport |
Cells of the proximal tubules are joined by tight junctions on the apical side (facing inside the tubule). – The apical side also contains microvilli. |
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Proximal Tubule: Passive Transport |
The pumping of sodium into the interstitial space attracts negative Cl− out of the filtrate. • Water then follows Na+ and Cl− into the tubular cells and the interstitial space. • The increased concentration of salts and water diffuses into the peritubular capillaries. |
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Proximal Tubular Fluid |
Reduced by 1/3 but still isosmotic – Plasma membrane is freely permeable to water and salts – Because both H2O and electrolytes are reabasorbed here in the same ratio, the tubular fluid stays isotonoic to blood |
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Significance of PCT Reabsorption |
• ≈65% Na+, Cl-, & H20 is reabsorbed in PCT & returned to bloodstream • An additional 20% is reabsorbed in descending loop of Henle • Thus 85% of filtered H20 & salt are reabsorbed early in nephron transport – This is constant & independent of hydration levels – Energy cost is 6% of calories consumed at rest – The remaining 15% is reabsorbed variably, depending on level of hydration |
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Secondary active transport in the Proximal Tubule |
Glucose, amino acids, Ca++, etc. are reabsorbed in the proximal tubule by secondary active transport. • This system is typically 100% efficient – But can be satuarated |
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Loop of Henle: |
the reason why humans can excrete a urine that is hypertonic to their blood |
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Concentration Gradient in Kidney |
• In order for H20 to be reabsorbed, interstitial fluid must be hypertonic • Osmolality of medulla interstitial fluid (1200-1400 mOsm) is 4X that of cortex & plasma (300 mOsm) – This concentration gradient results largely from loop of Henle which allows interaction between descending & ascending limbs |
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The Loop of Henle – the “rules” |
• Descending tube – Only permeable to water • Ascending tubule – Impermeable to water – Only permeable to salts • Active transport (AT) |
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Loop of Henle rules cont. |
• Countercurrent Multiplier System – Descending and Ascending limbs of Loop of Henle represents flow in the opposite direcAons. • The fact that the descending and ascending limbs are in close proximity means they are allowed to interact with each other • This is a positive feedback loop! |
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Ascending Loop of Henle |
• Salt (NaCl) is actively pumped into the interstitial fluid. – Na+ is moved into interstitial space via Na+/K+ pump. Cl− follows Na+ passively due to electrical acraction, and K+ passively diffuses back into filtrate. |
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Why it’s a counter current multiplier |
Active transport of Na+ in ascending limb sets up the osmotic gradient in renal medulla |
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Descending Loop of Henle |
• An additional 20% of water is reabsorbed here. – Happens continuously and is unregulated – The final 15% of water (~27 L) is absorbed later in the nephron under hormonal control. • Fluid entering loop of Henle is isotonic to extracellular fluids... |
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Descending Loop of Henle |
• Is not permeable to salt but is permeable to water • Water is drawn out of the filtrate and into the interstitial space where it is quickly picked up by capillaries. • As it descends, the fluid becomes more solute concentrated. – This is perfect for salt transport out of the fluid in the ascending portion. |
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Ascending Loop of Henle |
• Walls are not permeable to water, so osmosis cannot occur from the ascending part of the loop. • Surrounding interstitial fluid becomes increasingly solute concentrated at the bocom of the tube. • The maximum hyper tonicity of the loop is determined by the maximum ability of the ascending loop to actively transport salt from the tubule – This will then determine the hypertonicity of the interstitial fluid surrounding the Loop of Henle |
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Countercurrent Multiplier System |
• Water cannot be actively pumped out of the tubes, and it will not cross if isotonic to extracellular fluid. • The structure of the loop of Henle allows for a concentration gradient to be set up for the osmosis of water. |
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• But what does Countercurrent multiplier system actually accomplish? |
– The ability to recover water! – If there was no hypertonic interstitial fluid then there would be no way to “persuade” water to leave the nephron and enter back into the circulatory system – This means that our urine would isotonic to our blood.... – We would need A LOT of water to balance the water lost in our urine! • Remember, the kidneys process 180 liters of water a day |
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Vasa recta – countercurrent exchange |
• Counter current exchange – Salt and other solutes (urea) diffuse into descending limb of vasa recta – Same solutes will then diffuse out and back into interstitial fluid in the ascending limb • Vasa recta is blood, has plasma proteins that can’t diffuse out. – Therefore there is always an osmotic pressure drawing water in to vasa recta in ascending portion |
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The Distal Tubule, Collecting Duct, and Urea |
• Distal tubule: water permeable and active sodium transport • Collecting Duct: major regulatory component – Some sodium transport – Lots of urea transport – Variable water permeability • Based on hormonal influence |
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Effects of Urea |
• Urea: waste product of amino acid metabolism • Urea is also used to increase hypertonicity of renal medulla • Urea contributes to high osmolality in medulla – Deep region of collecting duct is permeable to urea & transports it |
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Collecting Duct and ADH |
• Last stop in urine formation • Also influenced by hypertonicity of interstitial space – water will leave via osmosis if able to • Permeability to water depends on the number of aquaporin channels in the cells of the collecting duct – Availability of aquaporins determined by ADH |
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Collecting Duct and ADH process |
• ADH binds to receptors on collecAng duct cells---> cAMP ---> Protein kinase---> Vesicles with aquaporin channels fuse to plasma membrane.
• Water channels are removed without ADH. |
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Collecting Duct and ADH |
Insertion of AQP water channels in collecting duct allows for the final removal of water from urine.
This is the concentrating step that allows hypertonic urine to be produced. Could not be done without the counter current systems in the Loop of Henle causing a hypertonic interstitial condition in renal medulla. |
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FIGURES |
Role of ADH in Plasma & Summary : 17.3 |
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Electrolyte Balance |
• Kidneys regulate levels of Na+, K+, H+, HC03-, Cl-, & PO4-3 by matching excretion to ingestion • Control of plasma Na+ is important in regulation of blood volume & pressure • Control of plasma of K+ important in proper function of cardiac & skeletal muscles |
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Nephron Specific Duties |
pH regulation Na+ and K+ regulation Aldosterone |
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Reabsorption of HCO3- in PCT |
• When urine is acidic, HCO3- combines with H+ to form H2C03 (catalyzed by CA on apical membrane of PCT cells) • H2C03 dissociates into C02 + H2O • C02 diffuses into PCT cell & forms H2C03 (catalyzed by CA) • H2C03 splits into HCO3- & H+ ; HCO3- diffuses into blood |
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Role of Aldosterone in Na+/K+ Balance |
90% filtered Na+ & K+ reabsorbed before DCT – Remaining is variably reabsorbed in DCT & cortical CD according to bodily needs • Regulated by aldosterone (controls K+ secretion & Na+ reabsorption) • In the absence of aldosterone, 80% of remaining Na+ is reabsorbed in DCT & cortical CD • When aldosterone is high all remaining Na+ is reabsorbed |
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Na+ and K+ regulation |
Aldosterone – Produced in Adrenal Cortex – Important for 2. Absorbing Na+ (person has low Na+) – K+ response: depolarizaAon |
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Aldosterone - K+ Secretion |
• Is only way K+ ends up in urine • Is directed by aldosterone & occurs in DCT & cortical CD |
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Aldosterone: Na+ absorption and the Juxtaglomerular Apparatus (JGA) |
• Indirect mechanism for Na+ absorption in nephron
• Not enough NaCl causes drop in blood volume – 2 systems become activated and target the JGA • Sympathetic nervous system – JGA responds by releasing renin into blood vessels that initiates a reaction resulting in the production of aldosterone – Granular cells release Renin |
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Renin-Angiotensin-Aldosterone System |
Is activated by release of renin from granular cells within afferent arteriole • Which is converted to Angio II by angiotensin- converting enzyme (ACE) in lungs • Angio II stimulates release of aldosterone
– Na+ is reabsorbed in DCT of nephron |
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Macula Densa – inhibits renin secretion if Na+ is too high |
• Is region of ascending limb in contact with afferent arteriole
• Cells respond to levels of Na+ in filtrate – Inhibit renin secretion when Na+ levels are high – Causing less aldosterone secretion, more Na+ excretion |
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Atrial Natriuretic Peptide (ANP) |
• Is produced by atria due to stretching of walls – This occurs if blood volume is too high
• Acts opposite to aldosterone – Promotes the removal of Na+ so that water will leave as well
• Stimulates salt & H20 excretion
• Acts as an endogenous diuretic |
