Chapter 19: The Kidneys Part 2単語カード | Quizlet

What is the juxtaglomerular apparatus?

Contains the Macula Densa: junction of ascending loop of Henle and renal corpuscles

contains juxtaglomerular or granular cells

- afferent arteriole

- produce renin

What are mesangial cells?

smooth muscle cells (modified)

- between and around loops of glomerular capillary

- regulate blood flow by contractile activity

- they contract and alter blood flow through the capillaries

- also secrete cytokines associated w/immune and inflammatory processes

What are the 3 basic process that take place in the nephron?

filtration, reabsorption, secretion

Urine formation

What is the standard glomerular filtration rate or GFR?

for a 70 kg person

180L/24 hours

7.5L/hour

125mL/min

3L of plasma filtered sixty times per day

300 mOsm

Is all of the plasma filtered?

filtration fraction = 20%

is the percentage of total plasma volume that filters into the tubule

After filtrate leaves Bowman's capsule, what happens?

it is modified by reabsorption and secretion.

What is reabsorption and where does it occur?

process of moving substances in the filtrate from the lumen of the tubule back into the blood flowing through the peritubular capillaries

filtrate to blood

- only reabsorbs good material

occurs in the Proximal tubule, loop of henle, and distal convoluted tubule

What is secretion and where does it occur?

selectively moves molecules from the blood and adds them to the filtrate in the tubule lumen

Blood to filtrate

occurs ONLY in the distal convoluted tubule

Amount excreted equation

Amt excreted = amt filtered - amt reabsorbed + amt secreted

E = F-R+S

amounts vary w/physiological control

What does it mean when excretion>filtration?

glomerular filtration and tubular secretion

NO reabsorption

What does it mean when excretion

glomerular filtration and some tubular reabsorption

- no secretion

What does it mean when excretion = 0?

glomerular filtration and total tubular reabsorption

NO secretion

How do you calculate filtration of a solute?

filtration of solute = [solute] in plasma x GFR

What is the glomerular filtration rate?

amount of plasma filtered per time

70 kg person -

180 L/24 hrs or 7.5 L/hr or 125 mL/min

3 L of plasma filtered 60 times per day

Where does most reabsorption occur?

in the proximal tubule

What are mechanisms by which reabsorption occurs?

1. Paracellular pathway

2. Epithelial transport

- Na active transport

- 1 and 2 prime active transport symport w/Na

3. Urea passive reabsorption

4. Plasma protein endocytosis

How does reabsorption occur via paracellular pathway?

by using electrochemical gradients

Na and K flow opposite

water follows Na

How does reabsorption occur via epithelial transport?

1⁰ & 2⁰ active transport

Lumen to cell: apical cell surface

- SGLT: Na+-glucose transporter

Cell to interstitial fluid: basolateral cell surface

- GLUT: glucose transporter

- Na+/K+ ATPase

How does reabsorption occur via urea passive reabsorption?

diffusion following [urea] conc. gradient

How does reabsorption occur via plasma protein endocytosis?

only small proteins should enter filtrate and are reabsorbed by endocytosis

Glucose transport maximum

The proximal tubule can only reabsorb a limited amount of glucose (~375 mg/min)

Renal threshold for glucose

When the blood glucose level exceeds about 160-180 mg/dL, the proximal tubule becomes overwhelmed and begins to excrete glucose in the urine

Reabsorption: What are 2 key factors of transport maximum for Glucose?

1. renal threshold

2. saturation of transporters

What is saturation of transporters?

refers the max rate of transport that occurs when all available carriers are occupied by substrate

# solutes vs # of transporters and speed of transport

What is the renal threshold?

↑ [solute] → no further ↑ in transport & reabsorption

solute excreted

300

What is the relationship between filtration and GFR?

Glucose

direct relationship

↑ [glucose] → ↑ GFR of glucose

the more there is, the more you filter

What is the relationship of reabsorption to Tmax (transport maximum)?

Glucose

Tmax is at 375 mg/min

Below Transport maximum:

↑ [glucose] → ↑ reabsorption rate

- if you have high [glucose] but you are below transport max, then you will have reabsorption

Above Transport max:

↑ [glucose] → constant reabsorption rate

- if you have high [glucose] but you have reached transport max, then you have constant reabsorption rate (you are saturated on transporters)

How is excretion related to Tmax (transport maximum)?

Glucose

renal threshold: 300 plasma glucose

Below renal threshold: glucose is reabsorbed!

↑ [glucose] → no excretion of glucose

Above renal threshold: glucose is NO LONGER reabsorbed! It reached threshold. It stays in filtrate.

↑ [glucose] → ↑ excretion of glucose

- Glucosuria

↑↑ [glucose] in blood → diabetes mellitus

Faulty glucose transporters → genetic

Summary of filtration, reabsorption and excretion of glucose

filter glucose at all plasma conc.

reabsorb glucose up to renal threshold

excrete glucose above renal threshold

What is passive reabsorption into capillaries?

follow [solute] gradients

net filtration favors reabsorption!

PC - peritubular capillary hydrostatic pressure (filtration), 10 mm Hg

πC - capillary colloid osmotic pressure (absorption), 30 mm Hg

NFP = PC - πC

10 - 30

NFP: 20

What is secretion?

addition of solute to filtrate

moves against its conc. gradient

Interstitial fluid to cell: basolateral cell surface

- Active transport: Primary, secondary and tertiary active transport

Cell to lumen: apical cell surface

- Facilitated diffusion

Where does most secretion occur?

proximal tubules

What is renal clearance?

clearance of a substance = mass of substance excreted per time/plasma [substance] conc.

volume of plasma from which substance is removed per unit time

- proportion of substance removed from the plasma

So how well someone filters out a substance

What is the renal clearance equation?

Cs = Us x V/Ps

Cs = clearance of S

Us = urine conc. of S

V = urine vol. per unit time

Ps = plasma conc. of S

UsV = amt in the urine

ex: Cs = 5 L/hr

The substance is removed from 5L of plasma in 1 hour

What is inulin?

a polysaccharide not normally found in the body

What does inulin clearance = ?

inulin clearance = GFR

- inulin is filtered, but not reabsorbed or secreted

What can inulin be used to do?

be used to monitor glomerular filtration rate

- give inulin intravenously to maintain Pin (Plasma concentration of Inulin)

PIN = 4 mg/L

UIN= 300 mg/L

V = 0.1 L/hr

CIN = ?

CIN = (300 mg/L * 0.1 L/hr) / 4 mg/L

CIN = 30 mg/hr / 4 mg/L

CIN = 7.5 L/hr

7.5 L of plasma is cleared of inulin in 1 hour (CIN = GFR)

Can creatinine be used as a viable alternative to inulin?

yes. constant production: constant plasma conc.

but a small amount is secreted.

meaning that clearance would be higher because it is secreted (added to the filrate)

With inulin, clearance = GFR...what does that mean?

no reabsorption, no secretion

With glucose, clearance = 0, what does that mean?

total reabsorption

With urea, clearance < GFR, what does that mean?

about 50% is reabsorbed

reabsorption

clearance is lower than GFR

With penicillin, clearance > GFR, what does that mean?

secretion

clearance is higher than GFR

What is micturition?

urination

Detrusor muscle (bladder): normal state is relaxed in order to fill

Sympathetic system inhibits contraction - keeps it relaxed

smooth muscle

Internal urethral sphincter: normal state is passively contracted

Sympathetic system

smooth muscle

External urethral sphincter: normal state is tonically contracted

Somatic motor system

skeletal muscle

What is the micturition state?

Urinary bladder and urethra

Stretch reflex: Detrusor stretch receptors

- Integration in the spinal cord (spinal reflex)

1. Parasympathetic stimulation of detrusor muscle

2. Increased pressure will open internal urethral sphincter

3. Inhibition of somatic control of external urethral sphincter

4. Micturition

What is the voluntary control of micturition?

Prevent micturition: learned reflex, conscious control

1. Micturition center in the brainstem and cerebral cortex:

- inhibit parasymp. system and promote sphincter contraction.

2. Continued stimulation of stretch receptors

- can only delay mict. temporarily

- max bladder content = 500-600 ml

- at full capacity or at will, promote micturition

Additional promotion of micturition is done by what?

valsava maneuver

- voluntary contraction of abdominal walls and expiratory muscles

- compression of detrusor muscle stimulates micturition reflex