Functional Overview of the Kidneys Flashcards
What is the primary function of the kidneys?
regulate the composition of the extracellular fluid
In regulating the composition of extracellular fluid, the kidneys also regulate what 6 things?
- blood volume
- extracellular fluid volume
- systemic arterial blood pressure
- hematocrit
- acid-base balance
- plasma concentration of electrolytes, minerals, metabolic waste, and water
7 year old beagle question 1:
Plasma sodium is normal (144 meq/L)
Body fluid volume is normal
Dietary sodium intake is 500 mg/day
How much sodium do you expect to appear in the urine every 24 hours?
A. >500 mg
B. 500 mg
C.
B. 500 mg
7 year old beagle question 2:
Plasma sodium is normal (144 meq/L)
Body fluid volume is normal
Dietary sodium intake is 1500 mg/day
How much sodium do you expect to appear in the urine every 24 hours?
A. >1500 mg
B. 1500 mg
C.
B. 1500 mg
How do you regulate volume?
add or subtract sodium and water will follow
How do you regulate tonicity?
add or subtract water
7 year old beagle question 3:
Plasma sodium is normal (144 meq/L)
Body fluid volume is low
Dietary sodium intake is 500 mg/day
How much sodium do you expect to appear in the urine every 24 hours?
A. >500 mg
B. 500 mg
C.
C.
7 year old beagle question 4:
Plasma sodium is low (137 meq/L)
Body fluid volume is high
Dietary sodium intake is 500 mg/day
How much sodium do you expect to appear in the urine every 24 hours?
A. >500 mg
B. 500 mg
C.
A. >500 mg
What happens if protein intake exceeds use and excretion?
increased nitrogenous waste in the blood (azotemia)
What happens if salt and water intake exceeds use and excretion?
ECF volume expansion, increased blood pressure, and/or edema
What happens if salt intake is greater than water intake?
hypernatremia and decreased ICF volume
What happens if water intake is greater than salt intake?
hyponatremia and increased ICF volume
What are the 3 basic mechanisms of kidney function?
filtration reabsorption secretion
Energy needs of the kidneys are primarily for which one of the following?
A. Reabsorbing water
B. Excreting waste products
C. Reabsorbing sodium
D. Secreting potassium
E. Secreting hydrogen ions
C. Reabsorbing sodium
Definition of excretion
exit of substances from the body
From what point does the urine no longer change in composition?
from the renal pelvis to the tip of the urethra
Where does filtration occur in the kidneys?
glomeruli
Where does reabsorption and secretion occur in the kidneys?
tubules
Definition of glomerular filtration
the process by which water and solutes in blood leave the vascular system through the filtration barrier and enter Bowman’s space
Definition of reabsorption
the process of moving substances from the lumen across the epithelial layer into the surrounding renal interstitium and then on to the bloodstream
What are the two steps of reabsorption?
- removal from the tubular lumen to interstitium 2. movement from interstitium into the blood
Definition of secretion
the process of moving substances into the tubular lumen from the cytosol of epithelial cells that line the walls of the nephron
Determine which picture(s) represent filtration, secretion, and reabsorption
Picture 1: secretion
Picture 2: filtration and reabsorption
Picture 3: reabsorption
Why are there 2 capillary beds in the kidney?
1 capillary bed is for filtration (i.e. goes to the glomerulus)
1 capilary bed is to provide nutrients to the kidney and to reabsorb filtrate from the tubules
What type of large substances cannot pass the glomerular filtration barrier?
albumin
globulins
cells
What happens to protein concentration from one end of the glomerular capillary to the other end?
the protein concentration increases, which results in more fluid flow into the capillary
(this is the effect known as “Starlings Forces” and it occurs in the proximal tubules)
What is filtration fraction and its equation?
Definition: fraction of plasma flowing through the glomerulus that is diverted into Bowman’s space by filtration
FF = GFR/RPF (glomerular filtration rate / renal plasma flow)
Which one of the following is correct?
A. As the filtration fraction increases, the Starling forces promoting reabsorption of fluid into the peritubular capillaries increase
B. As the filtration fraction decreases, the Starling forces promoting reabsorption of fluid into the peritubular capillaries increase
A. As the filtration fraction increases, the Starling forces promoting reabsorption of fluid into the peritubular capillaries increase
What is urine specific gravity?
the density of a urine sample versus the density of water
What do the following urine specific gravity values mean?
- 001
- 050
- 001 = more water than solute
- 050 = more solute than water
Explain the separation of salt and water in the cortex and medulla
cortex - isosmotic with plasma
medulla - progressive hypertonicity
What determines if urine is concentrated or diluted?
insertion (or not) of aquaporins in the collecting duct
What endocrine proteins are made in the kidney?
erythropoietin
calcitriol
renin
prostaglandins
Characteristics of erythropoietin
- a circulating glycoprotein produced in renal peritubular fibroblast-like type-a interstitial cells
- released when tissue hypoxia detected
- causes increased RBC production in bone marrow
Characteristics of calcitriol
- most active form of vitamin D
- produced in the proximal tubules
- it is a hormone, not a vitamin
- regulates calcium and phosphate handling as well as cell growth
Characteristics of renin
- enzyme secreted by the kidney
- participates in the renin-angiotensin-aldosterone axis
- regulates ECF volume and arterial blood pressure
What is the final output of the renin-angiotensin-aldosterone axis and what is the purpose?
final output is aldosterone release
- aldosterone causes increased Na+ absorption and increased K+ excretion
Where is the kidney innervated (predominantly by alpha-adrenergic sympathetic fibers)?
renal arterioles
renal tubular epitehlium
juxtaglomerular apparatus
