Lecture 8: Renal function Flashcards
Where are the kidneys located in relation to the peritoneum?
They are located retroperitoneally
Adjacent to the posterior body wall
Water is added to the body by two major sources. What are these sources?
- Ingested
- Synthesized in the body by oxidation of carbohydrates.
The total body fluid is distributed mainly between two compartment. What are these compartments?
- The extracellular fluid
- The intracellular fluid
How does this image replicates our body?
- Continuous cleaning of the original tank
- A tube allows drainage of the waste-filled fluid. The pump, instead of removing waste particles, must focus on identify and reclaim drained water and needed particles (such as food); it allows the waste to continue along the elimination tube
- If the pump breaks down, the tank fluid (water and food) will not be reclaimed, and everything will be excreted
- This pump represents the kidneys and their process of excretion
The kidneys clear our waste products by passing fluid through a filter, which is located in which part of the kidney?
Glomerulus
The kidneys filter fluid through the glomerulus. This filtered fluid is then largely reclaimed by the portion of the nephron known as the?
The renal tubule
Define the term “steady state” ?
We eliminate as much of a substance as we ingest and produce
Elimination = Ingestion + Production
The result is that the concentration of that substance in the body remains constant
What percentage of the body’s cardiac output goes to the kidneys?
20%
What volume of fluid is filtered through the glomeruli daily?
180 L
As filtrate passes across the endothelium of the capillary loops into the lumen of the tubule, called the urinary space. Why is it called this?
As it has actually passed to the “outside” of the body (there is a continuous path from the renal tubule to the collecting system of the kidney, to the ureters, which empty into the bladder, and then to the urethra and the outside world).
The body fluid circulates within the body continuously among three major compartments.
Name these three compartments?
- Intracellular space
- Intravascular space - within arteries, veins, and capillaries
- Interstitial space - outside of the cell and outside of the vasculature
The body compartments (intracellular, intravascular and interstitial space) are defined by barriers.
Name the barriers that seperate each compartment?
- The cell membrane
- Seperates the intracellular and the interstitial space.
- Thin layer of endothelial cells (lines blood vessels)
- Seperates the intravascular and the interstitial space.
Name these major fluid compartments of the body (blue) and the barriers (orange)
What are the functions of the kidneys?
- Removing metabolic waste from the extracellular fluid (urea, acids)
- Controlling the volume of extracellular fluid (close link to blood pressure)
- Maintaining optimal concentrations of vital solutes in the extracellular fluid e.g. sodium
- Production of erythropoietin
Urea is formed from the breakdown of which structures?
Proteins
The extracellular compartment is composed of which fluid compartment(s)
Intravascular + Interstitial compartment
The intracellular compartment is composed of which fluid compartment(s)
Intracellular space
What percentage of the body weight is attributable to water?
60%
60% of the total body weight is attributed to water. Of the body water, approximately 40% lie within the ____ body fluid compartment, and the remaining 20% lies within _____ body fluid compartment?
A) Intracellular
B) Extracellular (interstitium + Intravascular)
i.e. The majority of the fluid in the body is found within cells
Compare oncotic and hydrostatic forces?
Osmotic (aka oncotic) forces:
Osmotic pressure draws fluid back in the capillary.
Hydrostatic forces:
Hydrostatic pressure forces fluid out of the capillary,
Which force (hydrostatic or oncotic) determines the volume of disruption between the intracellular and interstitium compartment (cell barrrier)?
Oncotic force- asserted by the cell proteins that are imperable through the cell membrane
Define osmotic pressure?
It is the pressure created by water moving across a membrane due to osmosis. Osmosis is the movement of water from an area of low concentration of solute to an area of higher concentration of solute. A solute is atoms, ions, or molecules dissolved in a liquid.
Define the term “semipermeable membrane”
Membrane in which water, but not particles, can cross.
The cell membrane is semi-permeable, meaning water can diffuse freely but is impermeable for large proteins.
Describe the two effects the presence of the cellular proteins have on the cell?
- The protein particles themselves create an oncotic gradient favoring the movement of water into the cell.
- The presence of the negative charges on the proteins creates an electrical gradient, favoring the movement of positive charges into the cell
ie. creates osmotic and electrochemical gradients occur the cell membrane
Describe the Na/K ATPase?
- Sodium potassium ATPase
- Energy dependent cellular pump
- Pumping 3Na+ ions out in exchange for each 2K+ ions pumped in
- Continuously pumping
- It balances the oncotic pressure asserted by the cell proteins (to prevent a constant intake of water into the cell)
Which force (hydrostatic or oncotic) determines the volume of disruption between the intravascular and interstitium compartment (the vascular barrier)?
hydrostatic and osmotic (oncotic) forces
Describe the oncotic pressures asserted on the vascular barrier?
Large proteins, cannot cross these endothelial junctions.
The intravascular proteins provide an inward osmotic force favoring movement of water from interstitium to intravascular.
Describe the hydrostatic pressures asserted on the vascular barrier?
Represented by the mechanical pressure exerted by the fluid within the blood vessel, predisposes to the movement of fluid from the intravascular to the interstitial compartment
Describe the oncotic pressures asserted on the cell membrane?
Large proteins, cannot cross the cell membrane barrier.
The intracellular proteins provide an inward osmotic force favoring movement of water from interstitium to intracellular compartment.
This force is known as the oncotic pressure
Balanced by the Na/K ATPases
The summation of the oncotic and hydrostatic forces across the vascular endothelial wall determines fluid balance between the intravascular and interstitium compartments of the body.
But how do these forces change across the length of a capillary
At the beginning of the capillary, outward hydrostatic forces are at their highest. The inward oncotic force of protein within the lumen of the vessel is quantitatively less than the hydrostatic forces. Therefore, fluid flows from the intravascular outwards into the interstitium. As the distance from the contractile arteriole to any given point in the capillary increases and as additional fluid moves out of the lumen into the interstitial compartment, the plasma hydrostatic pressure falls. With these changes, a net inward gradient arises, reclaiming some of the initially filtered fluid.
Why do we not give pure water as an intravenous fluid?
Sterile water is hypotonic (0 mOsm/L) meaning it has a tonicity lower than the body plasma. As a result, the water moves from the intravascular space to the interstitial space, and eventually into the intracellular space. The hypotonic administration creates an environment where the interstitial and intracellular spaces have higher concentrations of electrolytes than the intravascular space. The osmotic change results in the body moving water from the intravascular space to the cells in an attempt to dilute the electrolytes.
Water is driven into the RBCs and cause them to rupture.
Describe what would occur in the fluid compartments if a hypertonic liquid was administrated via IV?
e.g. sodium
Hypertonic solution (tonicity higher than the body plasma >300mOSM/kg). Administration causes causes water to shift from the interstitial and intracellular spaces into the intravascular space, increasing the intravascular volume. This osmotic shift occurs as the body attempts to dilute the higher concentration of electrolytes contained within the IV fluid by moving water into the intravascular space
Describe what would occur in the fluid compartments isotonic fluid was administrated?
e.g. Sodium + Water = Normal saline
Isotonic solution (tonicity is equal than the body plasma =300mOSM/kg)
When administered to a normally hydrated patient, isotonic crystalloids do not cause a significant shift of water between the intravascular compartment and the intracellular compartment. Thus, the fluid is added to intravascular nd interstitial space. No change in the intracellular space.
What is the function of these these cells in the glomerulus (arrowing pointing to them)?
Cells located inside to keep the capillaries open
Describe the parietal and visceral layers of the Bowman’s capsule and what lies between these layers?
Parietal layer is made up of a simple layer of epithelium.
Visceral layer is made up of podocytes
Bowmans’ space is located between these layers, into which the filtrate enters after passing through the filtration slits.
Name these parts of the anatomy of the nephron?
Describe the countercurrent multiplication?
Occurs in the loop of Henle.
Fluid travels down the descending loop (DL). The DL is permeable to water but not electrolytes. Water is reabsorbed, via osmosis, as the interstitial space has a higher osmolality i.e. more sodium chloride. As the fluid travels further down, more water is reabsorbed, which results in an increase in osmolality in the tubule. The maximum osmolality occurs at the loop end. The ascending loop is permeable to solutes but not solvent (electrolytes but not water). Sodium is transported out via the Na/K ATPase, resulting in the reduction in the osmolality.
Because of the shape of the henle, the sodium that is transported out surrounds the descending loop- causing the high osmolality in the interstitial space.
Define the juxtaglomerular apparatus?
This is a specialized structure formed by the distal convoluted tubule and the glomerular afferent (into the glomerular) arteriole.
Main function is to regulate blood pressure and the filtration rate of the glomerulus.
