Renal physiology Flashcards
How does the kidney help to maintain homeostasis?
it regulates the composition and volume of blood and extracellular fluid by controlling water and solute excretion
What are the parts of the kidney?
- corpuscles (glomeruli/bowman’s capsule)
- proximal and distal convoluted tubules
- loop of henle, collecting duct
What are the parts of the nephron? Give a brief overview of the processes that occur in each of these parts
- Nephron: functional unit of the kidney
- a series of tubes that are connected to each other and eventually provide urine a way to exit into the environment
- glomeruli; bowman’s capsule, proximal convoluted tubule, loop of hence, distal convoluted tubule, collecting duct
What are the key “layers” in the kidney and what parts of the nephron are in each layer?
- Cortex (outer region)
- Medulla (inner portion)
- Renal pelvis
Describe the order of flow of the filtrate through the kidney tubules.
Glomeruli > bowman’s capsule > PCT > Loop of hence > DCT > Collecting duct > calyx > renal pelvis > ureter
What factors determine the rate of glomerular filtration? How does each factor determine the
rate?
- Blood hydrostatic pressure
- Colloid osmotic pressure
- Capsule fluid hydrostatic pressure
What solutes are reabsorbed and/or secreted in the proximal convoluted tubule? In the distal
convoluted tubule? Describe briefly how the transport process works for each solute.
Proximal: absorption- glucose, amino acids, NaCl, HCO3-, K+, H2O; secreion: H+, ammonia, organic compounds (drugs)
Distal: absorption- H2O, Na+
secretion: H+, HCO3-
Where does the majority of glucose and amino acid reabsorption occur? What about sodium and water?
proximal CT, distal CT
What is the main driving factor for solute reabsorption in the proximal convoluted tubule?
Na+, K+, ATPase on the basolateral membrane
How do hormones modify the composition of the urine in the distal convoluted tubules?
Discuss specific examples of hormones and how they alter solute reabsorption.
ADH: increase water reabsorption via aquaporins
Aldosterone: increases Na+ reabsorption and K+ secretion
Parathyroid hormone and vitamin D: increase calcium reabsorption by increasing Ca2+ channels on apical membrane
What is meant by the U/P ratio? What do U/P ratios of = 1, 1 mean?
- Urine solute output to plasma solute input
- U/P = 1: urine and plasma are isosmotic
- U/P > 1: urine is more concentrated in solutes than plasma
- U/P
What is meant by “concentrated urine”? What species are able to concentrate their urine and
why?
- Concentrated urine: reduces total water loss; occurs in the collecting duct and requires the processes of the loop of henle
- mammals, birds, insects have the ability to produce hyper osmotic urine (U/P > 1)
How does membrane permeability to water and solutes vary along the length of the Loop of Henle? How does this contribute to the osmolarity gradient in the medulla?
Descending: permeable to water; water enters the interstitial fluid (and blood) from the urine; urine and medulla become more concentrated
Ascending: active transport of Na+ into the interstitial fluid (and blood) from the urine; impermeable to water; urine and medulla become less concentrated
Why does the blood flow to/from the nephrons not dissipate the osmolarity gradient?
- hairpin loop arrangement; solutes move easily between interstitial fluid and the blood
- maintains the interstitial fluid gradient
- sodium enters blood flowing towards the medulla
- water enters blood flowing away from the medulla
Why is ADH secretion by the endocrine system critical for ensuring the production of
concentrated urine? What parts of the kidney are affected by ADH and what is the specific effect?
- ADH increases the expression of aquaporins on the urine side of the DCT and collecting duct
- osmosis is from low osmotic pressure (high water) to high osmotic pressure (low water)
- ADH allows water to be reabsorbed throughout the collecting ducts, as the osmotic pressure increases as you move deeper into the medulla