Lecture 24 Flashcards Preview

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Flashcards in Lecture 24 Deck (50):
1

Nephrons and collecting ducts perform 3 basic processes:

1. glomerular filtration
2. tubular reabsorption
3. tubular secretion
2 and 3 = both filtration happens once

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glomerular filtration:

a portion of the blood plasma is filtered into the kidney

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tubular reabsorption:

water & useful substances are reabsorbed into the blood

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tubular secretion:

wastes are removed from the blood & secreted into urine

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Rate of excretion of any substance =

rate of filtration + secretion - reabsorption

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Blood pressure produces

glomerular filtrate

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Filtration fraction is

20% of plasma
why? -circulating rate

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Filtering capacity enhanced by:

-thinness of membrane & large surface area of glomerular capillaries
-glomerular capillary BP is high due to small size of efferent arteriole

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Filtration Membrane: 3 Steps

#1 Stops all cells and platelets - Endothial fenestration stops
#2 Stops large plasma proteins - basal lamina stops
#3 Stops medium-sized proteins, not small ones - slit membrane stops

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NFP is

total pressure that promotes filtration

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NFP equation =

GBHP - (CHP + BCOP) = 10mm Hg

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Net Filtration Pressure Steps:

1. GBHP Glomerular Blood Hydrostatic Pressure = 55mmHg major force
2. CHP Capsular Hydrostatic Pressure
3. BCOP Blood Colloid Osmotic Pressure

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What if the concentration is lower than 55 mmHg?

no filtration

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What if the concentration is more than 55 mmHg?

It increased/ more filtration

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GFR:

Glomerular Filtration Rate

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Amount of filtrate formed in

all renal corpuscles of both kidneys / minute

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Homeostasis requires GFR that is

constant

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Too high of GFR =

useful substances are lost due to the speed of fluid passage through nephron

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Too low of GFR:

sufficient waste products may not be removed from the body

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Changes in net filtration pressure does what?

affects GFR by:
-filtration stops if GBHP drops to 45mm Hg
-functions normally with mean arterial pressures 80-180

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Renal Autoregulation of GFR:

Mechanisms that maintain a constant GFR despite changes in arterial BP:
1. myogenic mechanism
2. tubuloglomerular feedback

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myogenic mechanism:

-systemic increases in BP, stretch the afferent arteriole
-smooth muscle contraction reduces the diameter of the arteriole returning the GFR to its previous level in seconds

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tubuloglomerular feedback: 1st step =

1. elevated systemic BP raises the GFR so that fluid flows too rapidly through the renal tubule & Na+, Cl- and water are not reabsorbed

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tubuloglomerular feedback: 2nd step =

2. macula densa detects that difference & releases a vasoconstrictor from the juxtaglomerular apparatus

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tubuloglomerular feedback: 3rd step =

3. afferent arterioles constrict & reduce GFR

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Neural Regulation of GFR: Blood vessels of the kidney are supplied by

sympathetic fibers that cause vasoconstriction of afferent arterioles

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Neural Regulation of GFR: At rest, renal BV

are maximally dilated because sympathetic activity is minimal
-renal autoregulation occurs

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Neural Regulation of GFR: With moderate sympathetic stimulation =

Both afferent & efferent arterioles constrict equally
-decreasing GFR equally

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Neural Regulation of GFR: With extreme sympathetic stimulation =

Vasoconstriction of afferent arterioles reduces GFR
-lowers urine output & permits blood flow to other tissues

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Hormonal Regulation of GFR: Atrial natriuretic peptide (ANP)

increases GFR

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Atrial natriuretic peptide (ANP) does what?

stretch heart = increase BP = hormonal release = normal BP

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Hormonal Regulation of GFR: Angiotensin II

reduces GFR

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Angiotensin II has and does what?

potent vasoconstrictor that narrows both afferent & efferent arterioles reducing GFR

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Normal GFR is so high that volume of filtrate in capsular space in half an hour is

greater than the total plasma volume

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Nephron must reabsorb

99% of the filtrate

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PCT with their microvilli do

most of work with rest of nephron doing just the fine-tuning

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Important function of nephron is tubular secretion:

-transfer of materials from blood into tubular fluid

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2 Types of Reabsorption Routes:

Paracellular
Transcellular

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Paracellular reabsorption:

-50% of reabsorbed materialmoves between cells by diffusion in some parts oftubule

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Transcellular reabsorption

material moves throughboth the apical and basalmembranes of the tubulecell by active transport

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Transport Mechanisms: 2 different membranes of tubule cells have different types of transport proteins?

Apical and basolateral membranes

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What is the most important ion of reabsorption?

Na+
-several transport systems exist to reabsorb Na+
-Na+/K+ ATPase pumps sodium from tubule cell cytosol through the basolateral membrane ONLY

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Water is only reabsorbed by

osmosis

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Water follows

salt

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Glucosuria: Renal symporters can not reabsorb glucose fast enough if blood glucose level is above

200 mg/mL

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Unless urine has UTI, urine is

sterile
-some glucose remain in urine

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***Common cause of Glucosuria =

is diabetes mellitis because insulin activity is deficient and blood sugar is too high

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Reabsorption in the Prox. Con. Tubule: 1st step

Na+ symporters help reabsorb materials from the tubular filtrate

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Reabsorption in the Prox. Con. Tubule: 2nd step

Glucose, amino acids, lactic acid, water-soluble vitamins and other nutrients are completely reabsorbed in the first half of the proximal convoluted tubule

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Reabsorption in the Prox. Con. Tubule: 3rd step

Intracellular sodium levels are kept low due to Na+/K+ pump