Overview of Renal Physiology Flashcards
Describe in a single sentence the role of the kidney in total body homeostasis.
The main physiological function of the kidneys is the
maintenance of the composition and volume of the
extracellular fluid.
We typically assume an average body mass of _____ kg when estimating fluid levels.
70 kg
State the volume of each of the major body compartments in a standard-sized,
healthy, adult individual.
Intracellular = 28 L ECF= 15 L
Intracellular
- Interstitial Fluid= 12 L
- Plasma= ~3 L
Extracellular
- Noncirculating Cell Volume = 24 L
- Blood Cells= ~ 3 L
total= 42L
Describe the major components and volumes of daily water intake and loss for the ECF.
INPUT
- Ingestion in fluids and food= 2.0 L
- Metabolic processes=0.5 L (e.g. glucose => H2O +CO2)
Total = 2.5 L
OUTPUT
- Sweat and feces 0.1 L
- Respiration, fever, skin leaks etc 0.9 L (these are termed “insensible losses”)
- Urine 1.5 L
Total= 2.5 L
so they are balanced
How, in a general sense, is the ECF optimally maintained to support the life
of the cells?
The body attempts to balance the flows of
each regulated substance into and out of the ECF so that the losses of each substance
equal its gains in the ECF compartment.
Usually ingestion of fluid is in excess of incidental losses (i.e. sweat and respiration). How do we maintain ECF constancy?
As a follow up question, our input and output is balanced at around 2.5 L/day. ingestion of fluid accounts for 2 L of input and urine accounts for 1.5 L of output. what happens if we drink 3 L of fluid in a day?
ECF constancy is achieved by regulating urinary output (TEST)
we just pee more. increased water intake is asssociated with and increased urine output.
Basic Functional Structures:
Nephron has a blood supply and a nephron.
- ) Blood supply of the nephron consists of 2 capillary beds in series. What are they? Where are they located?
- ) There are pretty much 4 main things that happen at the tubules: Filtration, reabsorption, secretion, excretion. briefly describe each.
- glomerular cap. (glomerulus), peritubular (surround the tubules)
2.
-Filtration- filters plasma. free passage of water/solutes. retention of larger colloids
- Tubular reabsorption- kidney can recapture filtered components that it wished to regulate. things are reabsobed across the epithelial cell layer into the peritubular cap. This is regulated by the kidney to maintain ECF constant
- Secretion- substances move from peritubular cap into tubule. molecular transporters involved. A regulated process.
- Excretion- substances leave the body. regulated substances in excess of amt. required to maintain homeostasis. Also waste and urine is excreted.
For a normal sized healthy individual, state the magnitude of renal blood flow,
renal plasma flow, glomerular filtration rate, filtration fraction, and urine flow
rate.
In order to fully explain this you will need to know what % of CO the kidneys receive.
RBF= about 1.3 L/min. the kidneys receive 25% of CO. CO is about 5.2 L/min. So 25% of 5.2 is 1.3
RPF= about 0.65 L/min or 650 mL/min. This depends on the hematocrit. Average hematocrit is around 50%. So just take 50% of RBF (1.3) and that will give you the plasma flow.
FF= 0.2. This is just a percentage of how much plasma flow is filtered at the glomerulus into the tubules and is a number to memorize.
GFR= 130 mL/min. filtration fraction x RPF. so 650 x 0.2= 130 mL/min. It does about 190 L/day
Urine Flow rate= about 1.5 L/day. Thus about 99.9% of filtered H20 is reabsorbed each day.
what is higher reabsorption or excretion?
reabsorption.
The kidney filters and reabsorbs much more than it excretes. This allows it to fine tune and control body fluid volumes easier.
In the baroreceptormediated
renin/angiotensin axis, what is the rate limiting step? What is the primary event?
dec. BP is the primary event. It is sensed at baroreceptors which signals kidney to produce Renin.
angiotensinogen–> Ang I via Renin is the rate limiting step.
