Lecture #9 Flashcards
Stages of Urine Formation
- Glomerular Filtration - creates a plasma like filtrate of blood
- Tubular Reabsorption- removes useful solutes from filtrate and returns them to the blood
- Tubular Secretion- Removes wastes from blood
- Water Conservation - Removes water from the urine and returns it to the blood
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
Glomerular Filtrate
the fluid in the capsular space
Tubular Fluid
fluid from the proximal convoluted tubule through the distal convoluted tubule
Urine
fluid that enters the collecting ducts
Filration Membrane
- Endothelial cell of glomerular capillary
- Basement Membrane
- Filration Slits
Filtration Pressure a Function of:
- Blood Hydrostatic Pressure
- Colloid Osmotic Pressure
- Capsular Pressure
High BP in glomerulus makes kidneys vulnerable to hypertension
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
GFR is controlled
by adjusting glomerular blood pressure from moment to moment
GFR control is achieved by three homeostatic mechanism
- Renal autoregualtion
- Sympathetic Control
- Hormonal control
- 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
A. Myogenic Mechanism
- tendency of smooth muscle to contract when stretched.
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
Regulation of Glomerular Filtration (2)
- Sympathetic Control
- Sympathetic nerve fibers richly innnervate the renal blood vessels
- constricts the afferent arterioles
Regulation of Glomerular Filtration (3)
- Hormonal Control
- JG (granular) cells secrete renin in response to low BP
Renin - Angiotensin - Aldosterone Mechanism
Is a system of hormones that help control BP and GFR
Stages of Angiostensin
- Potent Vasoconstrictor – raising BP
- Constricts efferent arteriole raising GFR
- Stimulates adrenal cortex to secrete aldosterone, promotes NA and H2O reabsorption
- Stimulates posterior pituitary to secrete ADH which promotes H2O reabsorption
- Stimulates thirst
The proximal convoluted Tubule
- reabsorbs 65% of glomerular filtrate, removes from blood then secretes them into the (tubular fluid) urine
- tubular fluid is hypertonic
Sodium Reabsorption
in tubular reabsorption, Na creates an osmotic and electrical gradient that drives the reabsorption of water and other solutes
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
Transport maximum is reach when
transporters are saturated.
Each solute has its own transport maximum
Tubular Secretion
renal tubule extracts chemicals from capillary blood and secretes them into tubular fluid
Proposes of secretion in PCT and nephron loop:
- Acid Base Balance
- secretion of varying proportion of hydrogen and bicarbonate ions help regulate pH of body fluids - Waste removal
- Clearance of rugs and contaminants
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
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:
- Aldosterone
- Atrial Natriuretic Peptide
- Antidirectic hormone
Aldosterone -
salt retaining hormone
secreted by adrenal cortex
Triggers for aldosterone secretion:
- Low blood Na concentration
- High Blood K concentration
- Drop in BP
Functions of Aldosterone
stimulates reabsorption and NA and a secretion of K
net effects is that the body retains NaCl and water
Atrial Natriuretic Peptide (ANP)
Secretes by atrial myocardium of the heart in response to high blood pressure
Actions of ANP
- Dilates afferent & constricts efferent arteriole
- Inhibits renin and aldosterone secretion
- Inhibits secretion of ADH
- Inhibits NaCl reabsorption by collecting duct
Antidiuretic Hormones
Secreted in posterior pituitary in response to:
- Dehydration
- Loss of blood Volume
- Rising Blood osmolarity
Action of ADH – increases permeability of collecting duct to water
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
Define Renal Clearance
the volume of blood plasma from which a particular waste is completely removed in 1 minute
Represents the net effect of three processes
- Glomerular Filtration of the waste
- Amount added by tubular secretion +
- Amount removed by tubular reabsorption = renal clearance
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
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
Renal Clearance
- Water Balance
- Electrolyte Balance
- Acid- Base Balance
Water balance
Total Body Water (TBW) 45-75% of body weight
Fluid Compartments:
- 65% Intracellular Fluid (ICF)
- 35% Extracellular Fluid (ECF)– tissue, blood plasma, lymph, transcellular fluid.
Regulation of Fluid Intake
Governed mainly by thirst
osmoreceptors respond to Angll and rising osmolarity
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
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
Where would fluid accumulate
tissue fluid
Profuse sweating
negative water balance
Electrolyte Balance
Important for:
- Metabolism
- Electrical potential
- Body fluid osmolarity
Major Cation:
Major Anions:
Cations: Na, K, Ca, Mg, H
Anions: Cl, HCO3, P
Normo
Hyper
Hypo
normal
above normal
below normal
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
