what are the main components of the urinary system (where are they located)
- right kidney
- left kidney
- ureter
- urinary bladder
- urethra
- between 11th-12th rib
- kidney are retroperitoneal = not in abdominal cavity
- they are behind peritoneal membrane that holds the abdominal organs
what are the general functions of the kidney
- regulation of extracellular fluid volume and blood pressure
- regulation of osmolarity
- maintenance of ion balance -> Na+, K+, Cl-, Ca2+, PO43-
- homeostatic regulation of pH -> variable excretion of H+ and HCO3-
- excretion of wastes -> creatinine, urea, hormones, uribilinogen
- production of hormones -> erythropoietin (stimulates RBC synthesis)
-> renin (important regulator of blood pressure)
what is the anatomy of the kidney
- nephron = functional part of kidney
- cortex (outside)
- medulla (inside)
- renal pelvis
- ureter
- capsule (outer portion)
- approximately 1 million nephrons per kidney
what are nephrons (the 2 types)
- the functional units of the kidney
- the cortex contains all Bowman’s capsules, proximal and distal tubules
- the medulla contains loops of henle and collecting ducts
- in the cortex = cortical nephron
- in the medulla = juxtamedullary nephron
explain the vasculature of the kidney
- renal arteries take blood to the cortex
- afferent arterioles and glomeruli are all found in the cortex
-> bowmans capsule wrapped around each glomeruli - one nephron has two arterioles and two sets of capillaries that form a portal system
what are some of the main differences between the cortical and juxtamedullary nephron
cortical
- juxtaglomerular apparatus (sensing system for ionic concentration, between afferent and efferent arterioles)
juxtamedullary
- vasa recta
- longer and straighter loop of henle
what is the anatomy of the nephron
- bowman’s capsule
- glomerulus
- bowman’s capsule + glomerulus = renal corpuscle
- proximal tubule
- descending limb of loop begins
- descending limb
- loop of henle
- ascending limb
- ascending limb of loop ends
- distal tubule
- collecting duct
- bladder
what is the nephron made up of
- epithelial cells
- epithelial cell structure differs between regions of the nephron
- reflects the different functions of the various parts of the nephron
explain the functional anatomy of the nephron
- filtration are glomerulus/bowman’s capsule
- 180L/day, 100% volume, 300mOSM
- reabsorption and secretion at proximal tubule
- start of loop of henle = 54L/day, 30% volume, 300mOSM
- reabsorption at descending limb of loop of henle
- reabsorption at ascending limb of loop of henle
- end of loop of henle = 18L/day, 10% volume, 100mOSM
- reabsorption and secretion at distal tubule
- reabsorption and secretion at collecting duct
- end of collecting duct = 1.5L/day, 0.8% volume, 50-1200mOSM
- excretion to external environment
what are the 4 processes of the nephron
- filtration = movement from blood to lumen
- reabsorption = from lumen to blood
- secretion = from blood to lumen
- excretion = from lumen to outside the body
explain how urinary excretion depends on filtration, reabsorption, and secretion
(amount filtered) - (amount reabsorbed) + (amount secreted) = amount of solute excreted
explain filtration fraction
- the % of total plasma volume that filters into the tubule
1. plasma volume entering afferent arteriole = 100%
2. 20% of volume filters
3. >99% of filtrate is reabsorbed
4. >99% of plasma entering the kidney returns to systemic circulation
5. <1% of volume is excreted to external environment
explain the renal corpuscle and filtration
- substances filtered cross 3 filtration barriers
1. glomerular capillary endothelium
2. basal lamina
3. epithelium of bowman’s capsule (podocyte)
podocytes = foot processes that help regulate permeabilities and flow of fluid (can change size of gap)
what are the main substances that are filtered out of the blood plasma at the renal corpuscle
- Na+, K+, Cl-, Ca2+
- PO43-, H+, HCO3-, NH4+
- H2O
- urea
- glucose
- creatinine, urobilinogen
- some proteins (trace amounts), amino acids
what is glomerular filtration rate and what is it influenced by
- the volume of fluid that filters into Bowman’s capsule per unit time
(180L/day) - influenced by:
-> hydrostatic pressure (Ph) - blood pressure
-> colloid osmotic pressure gradient
-> fluid pressure within Bowman’s capsule (Pfluid)
what is osmolarity
- number of osmotically active particles per liter of solution (osmoles/liter)
ex. 1 M glucose = 1 OsM glucose
ex. 1mM NaCL = 1 mOsM Na+ + 1 mOsM Cl- = 2mOsM NaCl
what is osmotic pressure
- water moves across a semipermeable membrane towards the compartment with higher osmolarity until the osmolarity is equal on both side (equilibrium)
- the driving force for osmosis which can be measured as the force that must be applied to prevent osmosis
1. two compartments are separated by a membrane that is permeable to water but not glucose (solution b is more concentrated than solution a)
2. water moves by osmosis into the more concentrated solution, osmosis stops when concentrations are equal
3. compartment a is pure water and compartment b is a glucose solution, osmotic pressure is the pressure that must be applied to oppose osmosis
what is colloid osmotic pressure gradient
- osmotic pressure gradient due largely to the presence of proteins in the plasma, but not in the filtrate
someone with cirrhosis has lower than normal levels of plasma proteins and a higher than normal GFR. why?
- colloid osmotic pressure is lower
how is Ph, colloid osmotic pressure, and Pfluid related
(Ph) - (colloid osmotic pressure) - (Pfluid) = net filtration pressure
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