CASE 6 Flashcards
Nephrons
- water and solutes move from plasma in nephrons that make up most of the kidney
- modify the composition of fluid
ureter
modified fluid leaves kidney and passes into the ureter
- there are two ureters, one from each kidney leading to the urinary bladder
retroperitoneal
- below the diaphragm and outside the abdominal cavity sandwiched between the membranous peritoneum, which lines the abdomen
renal arteries
branch off the abdominal aorta, supply blood to kidneys
renal veins
carry blood from kidneys to vena cava inferior
- kidneys receive 20-25% of cardiac output, a lot
layers of kidney
- cortex: outer layer
2. medulla: inner layer
renal hilum
central ‘gap’ where its vessels, nerves and urether pass
blood flow kidney
- enters the kidney through renal artery to cortex
- from afferent arteriole (smaller diameter than efferent –> higher pressure –> more filtration) to glomerulus
- blood leaves glomerulus through efferent arteriole
- flows into a second set of capillaries, peritubular capillaries.
- vasa recta
- out of kidney through renal vein
vasa recta
in juxtamedullary nephrons, the long peritubular capillaries that dip into the medulla (vein going upward from the loop of Henle)
renal fascia
- layer of connective tissue encapsulating the kidneys
- separates the renal capsule from overlying pararenal fat
- deeper layers below are called renal capsule and parenchyma (functional tissue of kidney)
Bownman’s capsule
- surround the glomerulus
- combination of glomerulus and bowman = renal corpuscule
flow nephron
- bownman’s capsule
- proximal tubule
- loop of Henle
- thin descending limb (impermeable to salt, but permeable to water)
- ascending limb (impermeable to water, permeable to salts) - distal tubule (final control of pH and salts)
- collecting duct from cortex through medulla and drain into renal pelvis (fluid is now called urine flows into urether)
juxtaglomerular apparatus
part where the nephron twists and folds back on itself so that the final part of the loop of Henle passes between the afferent and efferent arterioles.
- regulates the function of each nephron
3 cell types:
1. macula dens (sensitive to concentration of NaCl)
2. granular cells (secrete renin)
3. extraglomerular mesangial cells
2 types of nephrons
- cortical nephrons
2. juxtamedullary nephrons
cortical nephrons
-located in cortex and are 85% of all nephrons
juxtamedullary nephrons
- located deep in cortex, near medulla.
- long loops of Henle
- produces very concentrated urine, when body needs to save water it uses juxtamedullary nephrons
sphincter
- circular muscle that normally maintain constriction of a natural body passage or hole and which relaxes by normal conditions
histology of urinary tract
zie pagina 78
histology of nephron
zie pagina 79
vascularization of the kidney
zie pagina 79
filtration
movement of fluid from blood into lumen of the nephron. Only takes place in renal corpuscule
reabsorption
process of moving substances in the filtrate back into the blood flowing through peritubular capillaries
secretion
removes selected molecules from the blood and adds them to the filtrate in the tubule lumen. Secretion is more selective than filtration, it uses membranes and transport proteins
primary function of proximal tubule
reabsorption of isosmotic fluid. filtrate leaving the proximal tubule has the same osmolarity as filtrate that entered
primary function loop of henle
primary site creating dilute urine. more solute is reabsorbed than water, filtrate becomes hypoosomotic relative to the plasma.
primary function distal tubule and collecting duct
fine regulation of salt and water balance takes place under control of several hormones.
Secretion
plasma to tubule lumen
excretion
out of the body
filtration fraction
the percentage of total plasma volume that filters into the tubule
substances leaving plasma have 3 filtration barriers
- glomerular capillary endothelium
- a basal lamina
- the epithelium of Bowman’s capsule
the glomerular capillary endothelium
- fenestrated capillaries with large pores that allow most components of the plasma to filter through the endothelium.
- pores are small enough to prevent blood from leaving capillary
a basal lamina
- acellular layer of extracellular matrix
- consists of negatively charged glycoproteins, collagen and other proteins
- acts as a ruwe zeef
the epithelium of Bowman’s capsule
- consists of specialized cells: podocytes (located on top of capillaries)
- have long cytoplasmic extensions called foot processes that extend from the main cell body
- foot processes wrap around the glomerular capillaries and croos with one another, leaving filtration slits
glycosaminoglycans
long unbranched polysaccharides consisting of a repeating disaccharide unit.
- highly polar and attract water
starling forces
- govern the passive exchange of water between the capillary and interstitial fluid
3 starling forces:
- capillary hydrostatic pressure (Ph)
- glomerular colloid osmotic pressure (pi)
- bowman’s capsule pressure (Pfluid)
capillary hydrostatic pressure
- caused by blood flowing through the glomerular capillaries.
- forces fluid through the leaky endothelium
- higher at arterial end than venous end
glomerular colloid osmotic pressure
- favors fluid movement back into capillaries
- constant throughout the whole capillary
- arterial end: capillary hydrostatic pressure is higher than colloid osmotic pressure –> filtration takes place
- other way around in venous end
Bowman’s capsule pressure
- opposes fluid movement into capsule
- presence of fluid creates hydrostatic fluid pressure. Fluid movement back into capillaries
glomerular filtration rate (GFR)
volume of fluid that filters into the Bowman’s capsule per unit time
- determined by the net filtration pressure and filtration coefficient
GFR as subject to autoregulation
- control process in which the kidney maintains a constant GFR.
1. myogenic response
2. tubuglomerular feedback
myogenic response
- ability of vascular smooth muscle to respond to pressure changes
- affects afferent arterioles
- smooth muscle in arteriole wall stretch –> ion channels and muscle cells depolarize ->
opens voltage gated Ca2+ channels –> vascular smooth muscle contracts –> increases resistance –> blood flow diminishes –> decreases filtration pressure in glomerulus
tubuglomerular feedback
- paracrine signaling mechanism through which changes in fluid flow through the loop of Henle influence GFR.
- modified portion of tubule epithelium is macula densa –> nacl delivery across macula densa increases (as a result of increased GFR) –> send a paracrine signal to neighboring afferent arteriole –> constricts (increasing resistance and decreasing GFR)
- the wall of afferent arteriole has juxtaglomerular cells which secrete renin.
macula densa sends 2 signals
- can result in dilation in afferent and constriction of efferent –> higher hydrostatic pressure –> increase GFR
- can also regulate production of renin which leads to vasoconstriction of efferent arteriole
