Nakamura Human Anatomy Lecture 11

Question 1

Kidney function

Answer 1

-Regulation of ECF (formation of urine)
–Salt and Water Regulation
–pH and Electrolyte Regulation
–Blood Volume Regulation

Question 2

Urinary system

Answer 2

Kidneys are not in abdominal cavity 
Renal Arteries and Veins
•Kidneys
•Ureters
•Urinary Bladder
•Urethra

Question 3

Renal blood vessels

Answer 3

.Afferent arteriole
–Delivers blood into the glomeruli.
•Glomeruli
–Capillary network produces filtrate that enters the urinary tubules.
•Efferent arteriole
–Delivers blood from glomeruli to peritubular capillaries (vasa recta)

Question 4

Glomerular capsule

Answer 4

-Glomerular capillary bed is encased in a structure called Bowman’s capsule.
•Filtration of blood in Bowman’s capsule by blood pressure

Question 5

Nephron

Answer 5

.Functional unit of the kidney
-1 kidney, 1 million nephron 
•Glomerular capsule
•Proximal convoluted tubule
•Loop of Henle (descending and ascending limb)
•Distal convoluted tubule
•Collecting duct

Question 6

Type of nephrons

Answer 6

.Cortical nephron:
     –Osmolarity of 300 mOsm/l.
     –Involved in solute reabsorption.
     -85%
     -renal cortex
•Juxtamedullary nephron:
     –Important for producing a concentrated urine
    -15%
    -renal medulla

Question 7

Glomerular filtration membrane

Answer 7

-glomerular capsule has 2 layers with cavity in the middle
-Filtration under pressure forms an ultrafiltrate
•Filtrate must pass through fenestrated capillary, basal lamina, and then through filtration slits of podocytes (visceral layer of glomerular capsule)
•Pores are small enough to prevent RBCs and WBCs from passing through

Question 8

Glomerular filtration

Answer 8

-Ultrafiltrate (the fluid that enters the glomerular capsule) is formed under hydrostatic pressure of the blood
•GFR (glomerular filtration rate)
–Volume of filtrate produced by both kidneys each minute (~120 ml/min)
–The total blood volume is filtered by the kidneys every 40 min, so the average amount of blood filtered per day is 180 liters

Question 9

Reabsorption

Answer 9

Transport (active and passive) from the renal tubules back into the peritubular capillaries
-from tubules to vessel (returned to blood)

Question 10

Secretion

Answer 10

Transport (active and passive) from the peritubular capillaries back into the renal tubules
-from vessels to tubules

Question 11

Excretion

Answer 11

Out of body as waste

Question 12

Proximal convoluted tubular

Answer 12

-The ultrafiltrate that enters the PCT is isosmotic with the blood plasma (300 mOsm)
•65% of the Na+, Cl- and H20 is reabsorbed and returned to the blood.
-The filtrate is still 300 mOsm but has a lower volume
-osmolarity stays the same cuz solvents and solutes move at the same time
-soldium is active and moves first, chloride is passive and follows, H2O follows solutes by osmosis
•Reabsorption in PCT is constant and not subject to hormonal regulation (NO ADH)

Question 13

How reabsorption occurs in the proximal convoluted tubule

Answer 13

•Na+ and glucose are cotransported into the PCT cells across the apical membrane
-goes through cell
-at the basolateral membrane the Na+/K+ ATPase pump creates a diffusion gradient for Na+ across the apical membrane (why sodium able to be into the cell in the first place)
-3 sodium out, 2 potassium in
-primary active transport
•Cl- follows the electrical gradient (secondary active, cotransport)
•H20 follows by osmosis.
-glucose reabsorbed via facilitated diffusion (no glucose in urine)

Question 14

Loop of Henle

Answer 14

.Ascending limb
–Thin and Thick Segments
•Descending limb

Question 15

Descending limb reabsorption

Answer 15

.About 20% of the filtrate (mostly water) is returned to the vascular system (vasa recta)
•Permeable to H20
•Practically impermeable to NaCl
•Fluid volume decreases in tubule, causing [Na+] in the ascending limb to increase
•Gradient of osmolarity with deeper regions of medulla reaching 1400 mOsm/L. (Osmolarity increase because solvent decrease)

Question 16

Ascending limb reabsorption

Answer 16

.Thick Segment of Ascending Limb
–Na+ actively transported across the basolateral membrane by Na+/ K+ ATPase
–Cl- passively follows Na+ down electrical gradient
–Impermeable to H20
•Thin Segment of Ascending Limb
-solutes out, osmolarity decrease
–No active transport and impermeable to water

Question 17

Countercurrent multiplication

Answer 17

• Flow in opposite directions in the ascending and descending limbs sets up a positive feedback loop
• causes higher osmolarity in interstitial space (space between tubules and vessel)

Question 18

Urea recycling

Answer 18

• urea: metabolic waste from nitrogen, made in liver, holds water well
• contributes to total osmolarity of interstitial fluid
• ascending limb and terminal collecting duct are permeable to urea

Question 19

Vasa recta

Answer 19

.•Vasa recta maintains hypertonicity (hypertonic, high osmolarity) of interstitial fluid by countercurrent exchange
•NaCl and urea diffuse into the descending limb from the interstitial fluid and diffuse into the interstitial fluid from the ascending limb
•Ascending limb:
–Fenestrated capillaries allow water in but keep urea and salts out

Question 20

Distal convoluted tubule reabsorption

Answer 20

Distal tubule and cortical region of the collecting ducts
–Active transport of Na+ and Cl- follows passively
–Impermeable to water

Question 21

Collecting duct reabsorption

Answer 21

.•14% of the filtrate is reabsorbed here (depending on the level of ADH)
•Impermeable to NaCl but very permeable to H20
•H20 permeability is regulated by aquaporins which are water channels
•Regulation of aquaporins by ADH

Question 22

Reabsorption overall

Answer 22

99% of filtrate from glomerular capsule is reclaimed

65% at proximal convoluted tubule
20% at loop of Henle
14% at collecting duct

Question 23

Electrolyte balance

Answer 23

-Kidneys regulate plasma Na+, K+, H+, Cl-, HC03-, PO4-2.
•Control of plasma of K+ is important for proper function of cardiac and skeletal muscles
-intracellular 150, extracellular 5
-critical for membrane potential
•Control of Na+ is important in regulation of blood volume and pressure
-extracellular 145, intracellular 12
-H2O osmosis/osmolarity (kidneys)
•Two important roles for aldosterone secretion from the adrenal cortex
–K+ secretion (and then excretion)
–Na+ reabsorption

Question 24

Aldosterone and K+ secretion

Answer 24

.90% K+ reabsorbed primarily from PCT (proximal convoluted tubule)
•When aldosterone is absent, final 10% is reabsorbed in cortical collecting duct so no K+ is excreted in the urine.
•Aldosterone stimulates secretion of K+ from the peritubular capillaries into the cortical collecting duct
•Maximal secretion of aldosterone causes 50X more K+ excretion than what was originally filtered
•Hyperkalemia(more than 5 K+ in blood) directly stimulates aldosterone secretion

Question 25

Aldosterone and Na+ reabsorption

Answer 25

-90% of filtered Na+ is reabsorbed prior to the distal convoluted tubule •Without aldosterone secretion, 8% of Na+ is reabsorbed in the peritubular capillary network, 2% is excreted (30 g/day) •Under conditions of maximal aldosterone secretion, 0% of filtered Na+ is excreted (since aldosterone is for sodium retention)

Question 26

Juxtaglomerular apparatus

Answer 26

- JGA is a structure on the nephron where the afferent arteriole comes in contact with the thick ascending limb of the loop of Henle - contains macula densa (surrounds thick ascending limb) and granular cells - macula densa senses how much sodium in tubule

Question 27

Renin angiotensin aldosterone pathway

Answer 27

Granular (Juxtaglomerular) cells secrete renin which activates the renin-angiotensin-aldosterone pathway •When Na+ levels in the ultrafiltrate are normal (or high), macula densa cells secrete a chemical that inhibits granular cell secretion of renin •Decrease in plasma Na+ indirectly causes secretion of aldosterone via the juxtaglomerular apparatus

Question 28

Renin angiotensin aldosterone pathway diagram

Answer 28

-made by liver -activated in lungs -activates aldosterone in kidneys -causes vasoconstriction as well Edit

Question 29

Aldosterone secretion summary

Answer 29

- high K+: no effect on renin, increased aldosterone (direct stimulation) - low blood volume(low sodium): increased renin, increased aldosterone (stimulation of granular cells) - high blood volume: decreased renin, decreased aldosterone (macula densa inhibit renin release)

Question 30

Renal acid base regulation

Answer 30

.Kidneys help regulate blood pH by excreting H+ (acid) and reabsorbing HC03- (base) •Most of the H+ secretion occurs across the walls of the PCT in exchange for Na+. –Antiport mechanism. •Some H+ secretion occurs in the DCT and cortical collecting duct

Question 31

Reabsorption of HCO3- in the proximal tubule

Answer 31

-Apical membranes of PCT are impermeable to HCO3- •Antiport transfer of Na+ (into PCT cell) and H+ (out of PCT cell) •HCO3- combines with H+ to form H2C03, which is catalyzed by carbonic anhydrase (CA) located in the apical cell membrane of PCT. •HCO3- generated within tubule cell diffuses into peritubular capillary

Question 32

sodium, potassium, and hydrogen relationship

Answer 32

.Na+ reabsorption in the cortical collecting duct (in response to aldosterone) creates an electrical gradient for K+ secretion •Plasma [K+] indirectly affects plasma [H+] -potassium and hydrogen are in competition, whichever has a higher concentration will be secreted •If someone suffers from acidosis (high H+, lower pH), they may have a rise in plasma [K+] •If someone is hyperkalemic, they may have a rise in plasma [H+] (K+ out of vessel more easily, leaves more H+ in vessel)

Question 33

Regulation of GFR

Answer 33

.GFR is the volume of blood filtered each minute by both kidneys (Average is 120 ml/min) •Vasoconstriction or dilation of afferent arterioles affects the rate of blood flow to the glomerulus. •Mechanisms to regulate GFR: –Sympathetic Nervous System(vasoconstriction) – Autoregulation (inhibitory feedback systems) –Hormonal •Renin-angiotension

Question 34

Renal auto regulation

Answer 34

-regulated by smooth muscle of tunica media. Without nerve stimulation Kidney maintains a constant GFR even if the sympathetic innervation is removed •Filtrate flow is detected by the macula densa in the JGA •An increased flow indicates an increase in blood pressure (the afferent arterioles are stretched) and the macula densa signals the afferent arteriole to constrict (via myogenic receptors not via renin) •A decreased flow indicates a decrease in blood pressure and/or blood volume and the granular cells will release renin to activated the renin-angiotensin-aldosterone pathway

Question 35

Renal plasma clearance

Answer 35

.order to measure GFR, one must use a compound that is filtered in the glomeruli but that is neither secreted nor reabsorbed. •Inulin is a sugar produced by a variety of plants. •When injected into a vein the inulin will be filtered by the kidneys. •The amount of inulin filtered by the glomeruli per minute equals the amount excreted per minute.

Question 36

Measurement of GFR

Answer 36

.To determine the clearance rate of inulin, one only needs to measure the the concentration of inulin in the urine and determine the rate of urine formation. Amount excreted (mg/min) = V x U •V = rate of urine formation (ml/min) •U = inulin concentration in urine (mg/ml) The rate of inulin filtration: Amount filtered (mg/min) = GFR x P •GFR (ml/min) •P = inulin concentration in plasma (mg/ml) •Because inulin is neither secreted nor reabsorbed: Amount filtered = Amount excreted GFR X P = V X U One can determine the GFR based on the rate of inulin excretion (V X U) divided by the concentration of inulin in the plasma (P) GFR =V (ml/min) X U (mg/ml)/ P (mg/ml)

Question 37

Renal plasma clearance definition

Answer 37

- Clearance: the volume of plasma from which a substance is completely removed by the kidney in a given amount of time (usually a minute). - Because the kidneys excrete all of the filtered inulin, then the renal plasma clearance of inulin provides the GFR (ml/min).

Question 38

Specific renal plasma clearance

Answer 38

.-Each substance has a specific clearance that depends on its filtration characteristics. - If a substance is filtered and is reabsorbed, then the clearance rate will be less than the GFR - If a substance is filtered and is also secreted, then the clearance rate will be greater than the GFR - For example, the clearance for urea is 65 ml/min. This means that the kidney removes all of the urea in 65 ml of plasma in one minute. Glucose 0 ml/min (completely rebsorbed) Inulin125 ml/min (not reabsorbed and not secreted) PAH 625 ml/min (completely secreted) ***Para-aminohippuric acid (PAH). PAH is partially filtered from plasma at the glomerulus and not reabsorbed by the tubules, is thus useful in calculation of renal plasma flow (RPF).