Intro to the Kidneys and Body Fluid Flashcards
Provide an overview of the fluid compartments in the body (ie. the percentages in each).
TOTAL BODY WATER: 60% body weight
INTRACELLULAR WATER: 40% body weight
EXTRACELLULAR WATER: 20% body weight
[Osmosis determines the movement of water between the ICF and the ECF.]
What are the two sub-compartments of the ECFV (extracellular fluid volume)?
- plasma (3L)
- interstitial fluid (11L)
Starling’s forces determine fluid and solute movement between the plasma and the interstitial fluid.
What is osmolarity, and how does it relate to the ICF and ECF?
Osmolarity is the total concentration of osmotically active solutes.
Solute composition of the ECF and ICF differs, but osmolarity must be kept the same to avoid excessive shifts of water between the ECF and ICF.
Sodium is the principle electrolyte of the ECF, and therefore sodium (with the associated anions) is the major determinant of ECF osmolarity.
Why is the control of bodily fluids important?
- it’s important for cell structure and function
Large shifts between the ECFV and ICFV will disrupt tissue structure and function. - it’s important for tissue perfusion
This depends on the balance between circulating volume (plasma) and interstitial volume.
What two key processes does salt and water balance depend on?
- OSMOREGULATION: maintains the osmotic equilibrium between the ICFV and ECFV
- VOLUME REGULATION: maintains adequate ECFV to support plasma volume
Describe osmoregulation.
It is the control of ECFV osmolarity in order to maintain osmotic equilibrium between the ICFV and ECFV.
Sodium (with its associated anions) is the principal electrolyte contributing to ECFV osmolarity.
How is plasma osmolarity estimated?
It can be estimated by:
2[Na] + 2[K] + [glucose] + [urea]
(all units in mmol/L)
Describe the mechanism of osmoregulation.
There are two ways to change the osmolarity of a solution:
1) add/ remove solute
2) add/ remove water
The body accomplishes osmoregulation by adding or removing water, NOT sodium.
- if plasma osmolarity rises, more water is needed (the kidneys will respond by producing a small volume of concentrated urine)
- if plasma osmolarity falls, there is too much water (the kidneys will respond by producing a large volume of diluted urine)
Describe volume regulation.
It refers specifically to the control of the circulating (plasma) volume. The changes are detected by stretch and pressure receptors in the cardiovascular system.
A fall in blood volume is opposed by sodium retention (as the water will follow osmotically, restoring volume).
NOTE: although the total AMOUNT of body sodium may be increased, CONCENTRATION (and hence osmolarity) is little changed because the retained sodium brings water with it.
Describe the kidneys and the urinary tract.
The function of the kidney is homeostasis.
The production of urine is a by-product of kidney function. The urinary tract is important for temporary storage and then to remove urine from the body.
List some functions of the kidney.
- osmoregulation
- volume regulation
- acid-base balance
- regulation of electrolyte’s balance (eg. K+, Ca2+, PO4 3-)
- removal of metabolic waste products from the blood
- removal of foreign chemicals in the blood (eg. drugs)
- regulation of RBC production (erythropoietin)
Describe the nephron in the kidney.
The nephron consists of special blood vessels and elaborate tubules (tiny tubes). They are microscopic structures, so there are 1.25 million per kidney. It is here when urine production begins.
Each nephron consists of several major structures:
- blood vessels
- the glomerulus
- Bowman’s capsule
- the renal tubule
List the arrangement of blood vessels and blood flow through the kidney and connection wit nephrons.
1) Renal artery
2) Segmental arteries
3) Interlobar arteries
4) Arcuate arteries
5) Interlobar arteries
6) Afferent arterioles
7) NEPHRONS
8) Venules
9) Interlobar veins
10) Arcuate veins
11) Interlobar veins
12) Renal vein
List the four basic processes of urine formation.
1) Glomerular Filtration
2) Tubular Reabsorption
3) Tubular Secretion
4) Excretion of water and solutes in the urine
Describe the first step of urine formation.
GLOMERULAR FILTRATION
The glomerular filtration rate:
- is the first step in the production of urine
- is the amount of filtrate kidneys produce each minute
- it averages 125 ml/min (approximately 20% of renal plasma flow)
- is reduced in renal failure
- plasma creatine can be used as an index of GFR
Hydrostatic pressure forces fluids and solutes through the glomerular capillary membrane. Small molecules pass readily - large ones (proteins) and cells cannot pass.
This leads to a plasma ultrafiltrate in the Bowman’s Capsule.
