Chapter 29 - Urine Concentration Flashcards
Osmolarity definition
amount of solute (mainly sodium chloride) divided by the volume of the extracellular fluid
Total body water is controlled by (#2)
(1) total fluid intake - determined by thirst
(2) renal water excretion - determined by kidney function
Body osmolarity when there is an excess in water
osmolarity is reduced
Body osmolarity when there is a deficit in water
osmolarity is high
(True/False)
The kidney is able to excrete a large volume of dilute urine or a small volume of concentrated urine without major changes in rates of excretion of solutes such as sodium and potassium
- ability to regulate water excretion independently of solute excretion
True
Increases water reabsorption and decreases urine volume but does not alter the rate of renal solute excretion
Antidiuretic Hormone (ADH) or vasopressin
ADH is produced in (1) and secreted by (2)
(1) supraoptic nuclei of the hypothalamus
(2) posterior pituitary gland
(1) ADH stimulus
(2) ADH action
(3) ADH target structure
(1) increase in the osmolality in the blood
(2) increase permeability to water by upregulating aquaporins
(3) distal convoluted tubules and collecting ducts
(True/False)
Excess water in the body decreases osmolarity and increases secretion of ADH
False
reduced osmolarity will reduce the secretion of the ADH to reduce the permeability of the distal tubule and collecting ducts to water - less reabsorption, more excretion (diluted urine)
(True/False)
THE RATE OF ADH SECRETION DETERMINES/CONTROLS URINE COCENTRATION
True
- urine volume increased 6-times normal within 45 minutes of fluid intake
- solute excreted remained relatively constant
- urine osmolarity decreased from 600 to 100 mOsm/L
Plasma osmolarity
300 mOsm/L
Tonicity of the renal medulla (hypotonic, isotonic, hypertonic)
Hypertonic
(True/False)
Tubular fluid becomes more concentrated as it flows into the inner medulla (descending loop of Henle)
True
as fluid descends to the loop of Henle, water is reabsorbed by OSMOSIS - filtrate becomes concentrated
The proximal tubule reabsorbs water and solute in equal proportions.
There is no change in osmolarity where it remains () to the plasma
isotonic
REGARDLESS OF WHETHER ADH IS PRESENT OR ABSENT, FLUID LEAVING THE EARLY DISTAL TUBULAR SEGMENT IS ()
Hypo-osmotic
osmolarity of only 1/3 of plasma osmolarity (100 mOsm/L)
The thick ascending loop of Henle is permeable to (1) - avid reabsorption and impermeable to (2).
Filtrate the becomes (3)
(1) sodium, potassium, and chloride
(2) water
(3) diluted
In the absence of ADH, the distal tubule and collecting duct will have additional absorption of solutes which will cause
tubular fluid to become more dilute (50 mOsm/L)
MECHANISM TO FORMING DILUTE URINE
- continue reabsorbing solutes from the distal segments of the tubular system
- reducing water reabsorption
KIDNEYS CONSERVE WATER BY
Excreting concentrated urine
MECHANISM TO FORM CONCENTRATED URINE
- excrete solutes
- increasing water reabsorption - decreasing urine volume
Maximal urine concentration ability
1200 mOsm/L
Obligatory urine volume
0.5 L/day
Specific gravity of a more concentrated urine
High specific gravity
Normal specific gravity
1.002 to 1.028 g/mL
High ADH and high osmolarity of the renal medullary interstitial fluid are the basic requirements that will lead to a
concentrated urine
water that leaves the tubules via osmosis are carried away from the renal interstitium by
vasa recta
Define Countercurrent multiplier mechanism
The process where renal medullary interstitial fluid remains hyperosmotic
Components of the countercurrent multiplier mechanism
(1) loops of Henle
(2) vasa recta - of the juxtamedullary nephrons
(3) peritubular capillaries
(4) collecting ducts
percentage of nephrons that are juxtamedullary nephrons in the kidney
25%
(True/False)
The osmolarity of interstitial fluid in all parts of the body (except for the renal medulla) are about 300 mOsm/L - similar to the osmolarity of the blood
True
Osmolarity of the renal medulla can increase progressively into
1200 to 1400 mOsm/L
Major factors for increased osmolarity in the renal medulla
- Active transport of sodium ions and co-transport of potassium, chloride, and other ions out of the thick portion of the ascending limb of the loop of Henle into the medullary interstitium
- Active transport of ions from the collecting ducts into the medullary interstitium
- Facilitated diffusion of urea from the inner medullary collecting ducts into the medullary interstitium
- Diffusion of only small amounts of water from the medullary tubules into the medullary interstitium— far less than the reabsorption of solutes into the medullary interstitium
TUBULE CHARCTERISTICS
