Renal Lectures 1-2 Flashcards
Functions of the kidney
CENTRAL PHYSIOLOGIC ROLE: control volume and composition of body fluids
- Excretion of metabolic waste products and foreign chemicals
- Regulation of water and electrolyte balance
- Regulation of body fluid osmolality and electrolyte concentrations
- Regulation of arterial pressure
- Regulation of acid-base balance
- Secretion, metabolism, and excretion of hormones
- Gluconeogenesis
by weight, how much of the body is composed of water
50-70% (we will use 60%)
-this value is greater in leaner people (and lower in people with more fat)
what average values will we use for our calculation
70kg man
42L of total body water
(1L of water = 1kg mass)
-intracellular fluid (2/3 body water –40% body weight— 28L)
- extracellular fluid (1/3 body water –20% body weight— 14L)
1. interstitial fluid (11L)
2. plasma volume (3L)
barrier b/w interstitial fluid and plasma volume
capillary wall
barrier between intracellular fluid and extracellular fluid is
cell membrane
normal blood volume of average individual and how to calculate it
~5L
Plasma volume / (1- hematocrit)
which compartment is first acted upon by intake or output mechanisms
plasma
order of blood fluid/cells
- Capillary has blood plasma in it
- then it crosses the capillary membrane to go into the interstitial fluid
- then it crosses the cell membrane to get into the intracellular fluid
capillary wall permeability
highly permeable to
- water
- electrolytes
- small molecules
-NOT proteins
So the plasma volume (in the capillary) has more proteins in it than the interstitial fluid
what two forces oppose each other
oncotic pressure due to protein in the plasma (draws fluid into the capillary)
and
hydrostatic force int he blood vessels (pushes fluid out of the capillaries)
cell membrane permeability
highly permeable to
-water
-NOT electrolytes or proteins
ECF has high Na+, Cl-, and HCO3-
ICF has high K+, PO43-, and organic anions and proteins
Na+/K- pump
3Na+ out
2K+ in
*this is why you have more Na in ECF and more K in the ICF
measurement of body fluid volumes
Volume = Quantity remaining in body (amount) / Concentration (amount/volume)
how to measure intracellular volume
total body water - extracellular volume
how to measure interstitial volume
extracellular volume - plasma volume
osmolarity
function of total number of particles in solution
- so if something doesnt dissociate it counts as 1 but if it does then it counts as however many parts it dissociates into
- independent of mass, charge, or chemical composition
osmotic pressure
The dissolved particles (osmolytes) exert a force which tends to pull water across semi- permeable membranes (osmotic pressure)
-permeable to water only (no solutes)
osmosis
movement of water across a semi-permeable membrane due to differences in osmolarity (osmotic pressure gradient)
flux equation:
Where:
Kf = ultrafiltration coefficient (function of surface area for exchange)
Pc = capillary hydrostatic pressure
πif = interstitial oncotic pressure
πp=plasma oncotic pressure
Pif=interstitial hydrostatic pressure
Flux=(Kf)[Pc +πif -πp -Pif]
what happens when you add isotonic NaCl solution to extracellular fluid
TBW- increases
ECFV- increases
ICFV- same
Steady state osmolarity– same
what happens when you add hypertonic NaCl solution to extracellular fluid
TBW- increases
ECFV- increases
ICFV- decreases
steady state osmolarity- increases
what happens when you add hypotonic NaCl solution to extracellular fluid
TBW- increases
ECFV- increases
ICFV- increases
steady state osmolarity- decreases
Hypernatremia vs Hyponatremia
- elevated plasma Na+ concentration > 150 mEq/l
- reduced plasma Na+ concentration <135mEq/l
Hyperkalemia
Hypokalemia
-elevated plasma K+ concentration > 5.0 mEq/l
- reduced plasma K+ concentration
< 3.5 mEq/l
Hypercalcemia vs. Hypocalcemia
- elevated plasma Ca++ concentration > 10 mg/dl
- reduced plasma Ca++ concentration < 8 mg/dl
Acidosis vs. Alkalosis
- reduced plasma pH < 7.3
- elevated plasma pH > 7.5
Edema
-condition in which there is excess fluid in the tissues
Common causes:
- elevation in capillary hydrostatic pressure/elevated venous pressure (heart failure)
- a drop in capillary oncotic pressure/loss of plasma protein (cirrhosis of liver, nephrotic syndrome)
- lymphatic blockade
first couple step in urine formation
bulk filtration in glomerulus
-filters ~100-125ml/min of plasma in a normal human
tubule is where reabsorption occurs
-returns 99% of filtered fluid to extracellular fluid space
secretion
when some substances are transported from ECF into tubular lumen
excretion =
filtration - reabsorption + secretion
parts of the nephron
- Bowman’s Capsule (which combines with the glomerular capillaries to form the glomerulus),
- Proximal Tubule
- Loop of Henle (thin descending limb, thin ascending limb, and thick ascending limb)
- distal tubule (early distal tubule)
- connecting tubule (late distal tubule)
- collecting duct system (cortical, outer medullary, and inner medullary segments).
kidney divided into…
8-18 pyramids consisting of cortex, outer medulla, and inner medulla
-kidney is approximately 0.5% body weight, yet receives 20-25% of cardiac output
Common renal parameters
Blood Flow
renal arterial blood flow (how much cardiac output do the kidneys receive)
renal arterial plasma flow
20-25% of cardiac output ~1200ml/min
~700ml/min
Common renal parameters
Filtration
glomerular filtration rate
filtration fraction
filtered load
Glomerular Filtration Rate (GFR) ~ 125 ml/min
Filtration Fraction (GFR/RPF=125/700=18%) Range- 15-25%
Filtered Load (GFR X Plasma Concentration= mass/time)
Common renal parameters
Reabsorption
99% of filtered solute and water ~ 124 ml/min
Common renal parameters
Secretion
Transport of solutes from blood into tubular lumen
Common renal parameters
Excretion
Urine Flow ~1 ml/min
Common renal parameters
Venous blood flow
~ 1199 ml/min
two types of nephrons
- Cortical nephrons (90% of nephrons)- peritubular capillaries
- Juxtamedullary nephrons (10% of nephrons) - vasa recta capillaries
glomerular capillaries
have high hydrostatic pressure which favors ultrafiltration (net filtration out of these capillaries)
2 renal capillaries
- glomerular capillaries
- high hydrostatic pressure
- favors net filtration out - postglomerular capillaries
- peritubular and vasa recta
- low hydrostatic pressure
- favors reabsorption
Resistance vessels are located before and after the high pressure glomerular capillaries
initial step in the formation of urine
glomerular filtration which is a bulk process (approximately 100-125 ml/min is filtered every minute–Step 1)
steps in urine composition
- filtration
- reabsorption
- secretion
- excretion
concentration of salts/organic substances in plasma vs. filtered fluid
they are around the same concentrations
glomerular filtrate
bulk filtration process
- ~3L every .5hour
- excluded: large proteins, substances bound to protein, cellular elements
3 kidney forces that are analogous to other capillaries around the body?
- glomerular hydrostatic pressure (like capillary pressure)
- glomerular COP
- bowman’s capsule pressure (like interstitial fluid pressure)
in a healthy 700kg man how much plasma flows in the glomeruli every minute?
700ml flows into glomeruli
- 125 is filtered every minute
- 575 leaves via efferent arteriole every minute
size of glomerulus
really small
approximately 100microns in diameter
filtration barrier of glomeruli
3 layers
- capillary wall
- fenestrated, freely permeable to small molecules
- negatively charged glycoproteins in surface - basement membrane
- porous matrix of extracellular proteins including type IV collagen, laminin, fibronectin and other negatively charged proteins - podocytes (with processes and slit pores-40x140 Å)
- long finger like processes with negatively charged proteins
SO the filtration barrier is…
-size-selective: more permeable to small molecules
-charge-selective: more permeable to positively charged molecules (proteins
generally are negatively charged)
two need to know proteins of the glomerular molecular lattice
main reason for size selectivity (albumin cant get through cause the slit is too small for it)
- nephrin (N)
- P-cadherin (P-C)
- some genetic diseases dont have these which can cause proteinuria
Filtration Fraction (ff)
FF = Flomerular filtration rate / Renal blood flow
where do you have a higher concentration of hematocrit?
at the efferent end of the capillary
how does postglomerular resistance influence changes in RR, GFR, and RBF
increase in postglomerular resistance causes:
RBF- decreases
GFR and FF- increase
decrease in postglomerular resistance causes:
RBF- increases
GFR and FF- decrease
Pathophysio. causes of decreased glomerular filtration rate
- renal disease
- diabetes
- hypertension
- urinary tract obstruction (kidney stones)
- increased plasma protein
what happens when things are filtered out of the blood and into bowmens capsule?
increases GFR
