Structure and Function of the Kidney Flashcards
describe the responsibilities of the kidney
the responsibilities of the kidneys are:
A WET BED
Acid-base balance
Water balance
Electrolyte Balance
Toxin Removal
Blood pressure control
Epo production
D (vitamin D) metabolism
explain how the glomerulus assists filtration and the peritubular capillaries assist reabsorption and how hydrostatic pressure is different for both.
As blood flows through the glomerulus, blood pressure pushes water and solutes from the capillaries into the capsule through a filtration membrane. This glomerular filtration begins the urine formation process. The hydrostatic pressure is about 55 mmHg in the glomerulus and it is high because the efferent arteriole is narrower than the afferent arteriole.
the peritubular capillaries assist reabsorption by reabsorbing Sodium, potassium, chloride, calcium and phosphate ions as well as urate, glucose, amino acids–reabsorbed across the epithelium. Hydrostatic pressure is approximately 15 mmHg.
The hydrostatic pressure of the peritubular capillaries is relatively low because much of the intravascular pressure is lost after blood passes through the afferent and efferent arterioles.
describe the factors that regulate the glomerular filtration rate (GFR).
What is a normal GFR?
glomerular filtration rate is regulated by: capillary hydrostatic pressure (filtration pressure), capillary colloidal osmotic pressure (reabsorptive pressure), capillary permeability.
a normal GFR is 125 ml/minute or 180L/day
review figure 32.8 and identify the reabsorption and secreting components of the tubules.
PROXIMAL CONVOLUTED TUBULE:
Reabsorbs: Na+, Cl-, HCO3-, K+, H2O, glucose, amino acids
Secretes: H+, organic acids and bases
DISTAL CONVOLUTED TUBULE
Early distal tubule: reabsorbs: Na+, Cl-, Ca2+, Mg2+
Late distal tubule/collecting duct:
principal cells:
reabsorption: Na+, Cl-
secretion: K+
* *ADH mediated H2O reabsorption
Intercalated cells
reabsorption: HCO3-, K+
secretion: H+
state where in the nephron filtered glucose is reabsorbed and define renal threshold as it relates to glucose found in the urine (abnormal)
filtered glucose is reabsorbed at the proximal convoluted tubule
renal threshold for glucose found in urine is 320mg/minute. any excess of that would have glucose spilling into urine.
explain the role of the countercurrent mechanism in regulation of urine formation
the countercurrent mechanism is found some of the loops of Henle and the vasa recta.
In this case, there is an exchange of solutes between the adjacent descending and ascending loops of Henle and between the ascending and descending sections of the vasa recta. Because of these exchange processes, there is a high concentration of osmotically active particles. These presence of these osmotically active particles in the interstitium surrounding the medullary collecting tubular facilitates the ADH-mediated reabsorption of water.
all together, this helps the kidney extract the minerals and nutrients that are reabsorbed in the water.
define autoregulation and it’s role in maintaining renal blood flow
what type of response?? what does it induce?
where does the response happen?
what kind of feedback??
WHY is the second type of feedback effective?
what diameter gets adjusted?
Two mechanisms contribute to autoregulation of RBF. The first is the myogenic response of preglomerular arterioles. Elevations in transmural pressure (the difference in pressure between two sides of a wall or equivalent separator) induce contraction of preglomerular arterioles, predominantly at the level of afferent arterioles.
The other mechanism is tubuloglomerular feedback which acts in concert with the myogenic response. It senses changes in the concentration of sodium chloride in the tubular fluid reaching the macula densa cells in the distal tubule and adjusts the diameter of the afferent arteriole accordingly.
Tubuloglomerular feedback serves as an effective autoregulatory mechanism because the sodium chloride concentration of the fluid reaching the macula densa is dependent on flow rate, which in turn, is related to the GFR and glomerular capillary pressure.
describe the role of the hormones ADH and aldosterone in the regulation of the filtrate.
ADH: Antidiuretic hormone stimulates water reabsorbtion by stimulating insertion of “water channels” or aquaporins into the membranes of kidney tubules. Also produces vasoconstriction of renal vessels so less can get out.
ADH=LESS URINE
Aldosterone: aldosterone increase the amount of urine and also increases the amount of sodium reabsorbed back into the bloodstream, while further increasing the amount of potassium excreted in the urine.
ALDOSTERONE=MORE URINE
list and describe the contents and ranges to be expected in a normal urinalysis
(Table 32.1)
general characteristics and measurements
color: yellow, like straw
appearance: clear to slightly hazy
specific gravity: 1.005 to 1.025 with a normal fluid intake
pH=4.5 to 8.0, average person has a pH of 5-6
volume: 600-2500 ml/24 hours; average volume is 1200 ml/24 hour
list and describe the contents & ranges to be expected in a normal urinalysis.
table 32.1
chemical determinations
glucose: negative
ketones: negative
blood: negative
protein: negative
bilirubin: negative
urobilinogen: 0.5-4.0 mg/day
nitrate for bacteria: negative
leukocyte esterase: negative
list and describe the contents and ranges to be expected in a normal urinalysis
table 32.1
microscopic examinations of sediment
casts negative: occasional hyaline casts red blood cells: negative or rare crystals: negative (none) white blood cells: negative or rare epithelial cells: few, hyaline casts 0-1 (low power feild)
what do serum creatinine and blood urea nitrogen show regarding kidney function?
how would the values change with dehydration?
serum creatinine reflects the glomerular filtration rate (GFR).
thin woman=0.7 mg/dL
normal adult man=1.0 mg/dL
muscular man=1.5 mg/dL
BUN:
A blood urea nitrogen (BUN) test measures the amount of urea nitrogen in your blood. Levels of urea nitrogen is one marker on how well your kidneys are working. High levels=bad
normal levels are 5.0-8.0-20.00 (how much would you spend on a hamburger? about 5, up to 20.00 for a speciality hamburger)
with dehydration:
creatinine would be elevated, but BUN will be more elevated. You’ll want to pay attention to the BUN-creatinine ratio.
