Lecture #9 Flashcards Preview

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Flashcards in Lecture #9 Deck (45):
1

Stages of Urine Formation

1. Glomerular Filtration - creates a plasma like filtrate of blood

2. Tubular Reabsorption- removes useful solutes from filtrate and returns them to the blood

3. Tubular Secretion- Removes wastes from blood

4. Water Conservation - Removes water from the urine and returns it to the blood

2

Glomerular Filtration

is capillary fluid exchange in which water and some solutes of the capillaries of the glomerulus into the capsular space of the nephron

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Glomerular Filtrate

the fluid in the capsular space

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Tubular Fluid

fluid from the proximal convoluted tubule through the distal convoluted tubule

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Urine

fluid that enters the collecting ducts

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Filration Membrane

1. Endothelial cell of glomerular capillary
2. Basement Membrane
3. Filration Slits

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Filtration Pressure a Function of:

1. Blood Hydrostatic Pressure
2. Colloid Osmotic Pressure
3. Capsular Pressure

High BP in glomerulus makes kidneys vulnerable to hypertension

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Regulation of glomerular Filration

GFR too high
- flow amount is too fast for renal tubes to absorb
- urine output rises, dehydration

GRF too low
- wastes are reabsorbed
- high levels of nitrogen containing compounds

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GFR is controlled

by adjusting glomerular blood pressure from moment to moment

GFR control is achieved by three homeostatic mechanism
1. Renal autoregualtion
2. Sympathetic Control
3. Hormonal control

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1. Renal Autoregulation

the ability of the nephron to adjust their own blood flow and GFR without external control

Two methods of renal autoregulation: Myogenic Mechanism and Tubuloglomerular feedback

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A. Myogenic Mechanism

- tendency of smooth muscle to contract when stretched.

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B. Tubuloglomerular Feedback

If GFR high
- filtrate contains more NaC;
snesed by Macula densa
Stimulates Juxtaglomerular cell (JG) cells to contact reducing GFR to normal

If GFR is low
macula relaxed afferent arterioles
blood flow increased and GFR rises

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Regulation of Glomerular Filtration (2)

2. Sympathetic Control
- Sympathetic nerve fibers richly innnervate the renal blood vessels
- constricts the afferent arterioles

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Regulation of Glomerular Filtration (3)

3. Hormonal Control
- JG (granular) cells secrete renin in response to low BP

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Renin - Angiotensin - Aldosterone Mechanism

Is a system of hormones that help control BP and GFR

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Stages of Angiostensin

1. Potent Vasoconstrictor -- raising BP

2. Constricts efferent arteriole raising GFR

3. Stimulates adrenal cortex to secrete aldosterone, promotes NA and H2O reabsorption

4. Stimulates posterior pituitary to secrete ADH which promotes H2O reabsorption

5. Stimulates thirst

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The proximal convoluted Tubule

- reabsorbs 65% of glomerular filtrate, removes from blood then secretes them into the (tubular fluid) urine

- tubular fluid is hypertonic

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Sodium Reabsorption

in tubular reabsorption, Na creates an osmotic and electrical gradient that drives the reabsorption of water and other solutes

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The Transport Maxium

is the amount of solute that renal tubules can reabsorb is limited by the number of transport proteins in tubule cell's membrane

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Transport maximum is reach when

transporters are saturated.

Each solute has its own transport maximum

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Tubular Secretion

renal tubule extracts chemicals from capillary blood and secretes them into tubular fluid

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Proposes of secretion in PCT and nephron loop:

1. Acid Base Balance
- secretion of varying proportion of hydrogen and bicarbonate ions help regulate pH of body fluids

2. Waste removal

3. Clearance of rugs and contaminants

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The Nephron Lopp

Generates a salinity gradient that enables collecting duct to concentrate the urine and conserve water

- electrolyte reabsorption from filtrate

-Tubular fluid is very diluted as it enters distal convoluted tubule

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The distal convoluted Tubule and Collecting duct

Fluid arriving in the DCT still contains 20% of H2O from glomerular (AKA still need to reabsorb water)

collecting duct is highly permeable to water

Regulated by hormones:
1. Aldosterone
2. Atrial Natriuretic Peptide
3. Antidirectic hormone

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Aldosterone -

salt retaining hormone
secreted by adrenal cortex

Triggers for aldosterone secretion:
1. Low blood Na concentration
2. High Blood K concentration
3. Drop in BP

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Functions of Aldosterone

stimulates reabsorption and NA and a secretion of K
net effects is that the body retains NaCl and water

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Atrial Natriuretic Peptide (ANP)

Secretes by atrial myocardium of the heart in response to high blood pressure

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Actions of ANP

1. Dilates afferent & constricts efferent arteriole

2. Inhibits renin and aldosterone secretion

3. Inhibits secretion of ADH

4. Inhibits NaCl reabsorption by collecting duct

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Antidiuretic Hormones

Secreted in posterior pituitary in response to:
1. Dehydration
2. Loss of blood Volume
3. Rising Blood osmolarity

Action of ADH -- increases permeability of collecting duct to water

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Water Conservation: The Collecting Duct (CD)

Begins in the cortex where it receives tubular fluid from several nephrons

Runs through medulla,and reabsorbs water, making urine up to 4 X more concentrated

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Define Renal Clearance

the volume of blood plasma from which a particular waste is completely removed in 1 minute

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Represents the net effect of three processes

1. Glomerular Filtration of the waste
2. Amount added by tubular secretion +
3.Amount removed by tubular reabsorption = renal clearance

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Renal Clearance is determined by

collecting blood and urine samples, measuring the waste concentration in each, and measuring the rate of urine output

compare C to normal GFR of 126mL/min 48% is normal clearance for urea

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Glomerular Filtration Rate

- measure GFR to asses kidney disease
- use inulin, a plant polysaccharide to determine GFR, neither reabsorbed or secreted
-Clinically GFR is estimated from creatinine excretion

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Renal Clearance

1. Water Balance
2. Electrolyte Balance
3. Acid- Base Balance

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Water balance

Total Body Water (TBW) 45-75% of body weight

Fluid Compartments:
1. 65% Intracellular Fluid (ICF)
2. 35% Extracellular Fluid (ECF)-- tissue, blood plasma, lymph, transcellular fluid.

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Regulation of Fluid Intake

Governed mainly by thirst
osmoreceptors respond to Angll and rising osmolarity

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Regulation of Fluid Outpu

- Variation in Urine volume
- Usually linked to adjustments in Na reabsorption

Dehydration decreases BV
Increase Na = increase osmolarity = ADH
Increase Blood Volume/increase NA = Inhibit ADH

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Fluid Deficiency

A. Volume Depletion (hypocolemia)
- loss of water and sodium without replacement
- osmolarity remains normal

Dehydration (negative water balance)
- body eliminates more water than sodium
-Osmolarity of ECF rises

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Where would fluid accumulate

tissue fluid

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Profuse sweating

negative water balance

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Electrolyte Balance

Important for:
1. Metabolism
2. Electrical potential
3. Body fluid osmolarity

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Major Cation:
Major Anions:

Cations: Na, K, Ca, Mg, H
Anions: Cl, HCO3, P

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Normo
Hyper
Hypo

normal
above normal
below normal

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Sodium Balance

one of principal ions responsible for resting membrane potentials
- principal cation of ECF (90%-95%)

Adult requires 0.5g/day
typical america 3-7g/day