7 - Renal Physiology III Flashcards
REVIEW: Which segment of the renal tubules secrets water?
a. The thin descending limb of the loop of Henle
b. The cortical collecting tubule
c. The medullary collecting duct (when ADH is absent)
d. No segment secretes water
No segment secretes water
This is because water is ONLY reabsorbed in the renal tubules
REVIEW: If the thick ascending limb of the loop of Henle would stop to re-absorb sodium, then the final urine would be:
a. Iso-osmotic with plasma in all conditions
b. Dilute
c. Concentrated
d. Dilute or concentrated, depending on ADH
a. Iso-osmotic with plasma in all conditions
The ability of the kidney to form urine that is more concentrated than the plasma is essential for survival of mammals that live on land
The basic requirements for forming a concentrated urine are:
- A high osmolarity of the renal medullary interstitial fluid
- A high level of antidiuretic hormone (ADH) also called vasopressin
What are the two fluid compartments of the body?
- Intracellular fluid
- Extracellular fluid
Describe the intracellular fluid
- Compared with ECF, it has high concentrations of protein, potassium and phosphate and low levels of sodium and chloride
- Most important intracellular cation is K+ (~135 mEq/L)
- Main intracellular anions are phosphates and protein with lesser amounts of SO4-2 and HCO3
Describe the extracellular fluid
- Plasma (intravascular fluid which contains serum electrolytes)
- Interstitial fluid (cations and anions)
Describe homeostasis
Homeostasis: The tendency of a system to maintain its internal stability, owing to the coordinated response of its parts to any situation or stimulus that would tend to disturb its normal condition or function
Describe homeostasis in body fluids
The maintenance of a relative
constant volume and a stable
composition of the body fluid
is essential for homeostasis
Which ions reside primarily in the extracellular compartment?
Na+ and Cl- ions reside
primarily in the extracellular
compartment
What is the most abundant ion in the extracellular compartment?
Na+ is the most abundant ion
in the extracellular compartment
Describe the normal state of the body in terms of intra- and extracellular fluid compartment size and osmolality
Under normal conditions, ICF is 2/3 and ECF is 1/3 of TBW (total body water)
The osmolality of both compartments is 300 mosm/L
What happens when we add H20?
If water is added to the plasma (ECF), ECF osmolality would be diluted initially (become hypotonic) compared to ICF
Water would then enter the ICF space (cells would swell) to equilibriate the osmolality between compartments
The overall effect would be to reduce the osmolality of ICF and ECF and expand the compartment size
What happens when we add isotonic saline?
If isotonis saline solution (solution with NaCl concentration of 300 mosm/L) was added to the plasma (ECF), the fluid will stay in the ECF because it is isotonic, expanding that compartment
This only happens when there is NOT compensatory mechanisms in place
What happens when we add hypertonic saline?
If hypertonic saline was added to the plasma, ECF osmolality would increase greatly initially and fluid would be drawn out of the cells and into the ECF to lower the tonicity of the ECF
This would contract the volume of the ICF compartment (cells would shrink) and increase the volume of the ECF compartment, as well as increase the overall osmolality
This only happens when there is NOT compensatory mechanisms in place
What is the effect of ingesting NaCl on ADH and thirst?
example: eat a salty meal
- Brain osmoreceptors shrink and person feels thirsty and drinks water
- Brain increases release of ADH so more water is re-absorbed (concentrated urine)
- Increased water ingestion and concentrated urine result in expansion of ECF and rise in blood pressure
- Increased blood pressure causes decrease in ADH secretion
- Result pressure diuresis (and natriuresis) which causes return to normal ECF volume
What is the effect of ingesting NaCl on atrial natriuretic peptide?
(example: eat a salty meal)
- Ingesting NaCl expands plasma volume
- Plasma volume expansion stretches the atria which
increases secretion of the natriuretic peptides
What is the renal response to chages in plasma volume and osmolality?
- Control of extracellular fluid (ECF) volume is a continual process, with changes in plasma osmolality and volume signaling
- Multiple neural and hormonal systems regulate plasma volume and osmolality
What is the renal response to volume contraction?
- Renin-angiotensin-aldosterone system is activated
- ADH from the posterior pituitary gland is stimulated
- Sympathetic nerves are stimulated
What is the renal response to volume expansion?
- Sodium- and fluid-retaining mechanisms are decreased (RAAS, ADH both decreased )
- The increased stretch on the cardiac right atrium releases atrial natriuretic peptide
Describe the distribution of the extracellular fluid between the interstitial space and vascular system
- Ingested fluid initially goes into the blood, but it rapidly becomes distributed between the interstitial spaces and the plasma
- Blood volume and extracellular fluid volume usually are controlled simultaneously
- There are circumstances, however, in which the distribution of extracellular fluid between the interstitial spaces and blood can vary greatly
What are the principle factors that can cause accumulation of fluid in the interstitial space?
- Increased capillary hydrostatic pressure
- Decreased plasma colloid osmotic pressure
- Increased permeability of the capillaries
Describe increased hydrostatic pressure
- High BP
- Leads to fluid being pushed out of the vasculature
- Causes edema
Describe decreased osmotic pressure
- Low protein in blood
- Due to nephrotic syndrome (protein leaking out)
- Also causes edema
Give a summary of the key concepts we covered in this lecture
- The maintenance of a relative constant volume and composition of the body fluid is essential for homeostasis
- Total body fluid is distributed mainly between two compartments:
- -> Extracellular fluid
- -> Intracellular fluid
- Extracellular fluid is divided into the interstitial fluid and blood plasma
- Volume and osmolality of extracellular and intracellular fluid are controlled by a combination of neural and hormonal systems
- Edema refers to the presence of fluid in the body tissue. It occurs mainly in the extracellular fluid
