PSL301H1 Study Guide - Midterm Guide: Sodium Chloride, Bicarbonate, Central Chemoreceptors
KIDNEYS
Functions
-regulate extracellular fluid volume, blood pressure, and osmolarity; maintain ion balance;
regulate pH; excrete wastes and foreign substances; and participate in endocrine pathways
Anatomy
-urinary system is composed of two kidneys, two ureters, and a bladder, and a urethra
-each kidney has about 1 milllion nephrons.
-A kidney is arranged into an outer cortex and inner medulla
-Renal blood flow goes from afferent arteriole to glomerulus to efferent arteriole
to peritubular capillaries.
o The vasa recta capillaries dip into the medulla
-Fluid filters from the glomerulus into Bowman’s capsule
o Flows through the proximal tubule, loop of Henle, distal tubule, and collecting duct,
and then drains into the renal pelvis.
o Urine flows through the ureter to the urinary bladder
Notes
-Filtration = movement of fluid from plasma into Bowman’s capsule
-Reabsorption = movement of filtered materials from tubule to blood
-Secretion = movement of selected molecules from blood to tubule
-Average urine volume: 1.5L/da with osmolarity 50~1200mOsM
-The amount of solute excreted = amount filtered – amount reabsorbed + amount secreted
Filtration
-1/5 of renal plasma flow filters into the tubule lumen
-filtration fraction: the percentage of total plasma volume that filters
-bowman’s capsule epithelium has specialized cells called Podocytes that wrap around
the glomerular capillaries and create filtration slits.
o Mesangial cells are associated with the glomerular capillaries
o Filtered solutes must pass first through glomerular capillary endothelium, then
through a basal lamina, and finally through Bowman’s capsule epithelium
before reaching the lumen of Bowman’s capsule
-Filtration allows most components of plasma excluding blood cells and most
plasma proteins
-Pressures
o Hydrostatic pressure in glomerular capillaries: 55mmHg, favoring filtration +
o Colloid osmotic pressure: 30mmHg (-)
o Hydrostatic capsule fluid pressure: 15mmHg (-)
o Net driving force: 10mmHg, favoring filtration (+)
-GFR (Glomerular Filtration Rate) = amount of fluid that filters into Bowman’s capsule
per unit time
o Avg: 125mL/min or 180L/day
-Hydrostatic pressure in glomerular capillaries can be altered by changing resistance in
the afferent and efferent arterioles
find more resources at oneclass.com
find more resources at oneclass.com
-Autoregulation of glomerular filtration is accomplished by a myogenic response of vascular
smooth muscle in response to pressure changes and by tubuloglomerular feedback
o When fluid flow through the distal tubule increases, the macular densa cells send a
paracrine signal to the afferent arteriole, which constricts
decrease
-Reflex control of GFR is mediated through systemic signals, such as hormones, and
through the autonomic nervous system
Reabsorption
-most reabsorption takes place in the proximal tubule. Finely regulated reabsorption
takes place in the more distal segments of the nephron
-the active transport of Na+ and other solutes creates concentration gradients for
passive reabsorption of urea and other solutes
-most reabsorption involves transepithelial transport, but some solutes and water
are reabsorbed by the paracellular pathway
-glucose, amino acids, ions, and various organic metabolites are reabsorbed by Na+
linked secondary active transport
-most renal transport is mediated by membrane proteins and exhibits saturation,
specificity, and competition
o transport maximum Tm = transport rate at saturation
-the renal threshold is the plasma concentration at which a substance first appears in
the urine
-peritubular capillaries reabsorb fluid along their entire length
Secretion
-secretion enhances excretion by removing solutes froTHe hom the peritubular capillaries
(running closely to proximal tubule)
o K+, H+, and variety of organic compounds secreted
-Molecules that compete for renal carriers slow the secretion of a molecule
Excretion
-Excretion rate of a solute depends
on o its filtered load
o whether it is reabsorbed or secreted as it passes through the nephron
-Clearance = how many milliliters of plasma passing through the kidneys have been
totally cleared of a solute in a given period of time
o Inulin clearance = GFR
o In clinical settings, Creatinine = GFR
-Clearance used to determine how the nephron handles a solute filtered into it
Micturition
-The external sphincter of the bladder is skeletal muscle that is tonically contracted
except during urination
-Micturition is a simple spinal reflex subject to conscious and unconscious control
-Parasympathetic neurons cause contraction of the smooth muscle in the bladder wall.
Somatic motor neurons leading to the external sphincter are simultaneously inhibited
find more resources at oneclass.com
find more resources at oneclass.com
41
PSL301H1 Full Course Notes
Verified Note
41 documents
Document Summary
Functions regulate extracellular fluid volume, blood pressure, and osmolarity; maintain ion balance; regulate ph; excrete wastes and foreign substances; and participate in endocrine pathways. Anatomy urinary system is composed of two kidneys, two ureters, and a bladder, and a urethra each kidney has about 1 milllion nephrons. A kidney is arranged into an outer cortex and inner medulla. Renal blood flow goes from afferent arteriole to glomerulus to efferent arteriole to peritubular capillaries: the vasa recta capillaries dip into the medulla. Fluid filters from the glomerulus into bowman"s capsule: flows through the proximal tubule, loop of henle, distal tubule, and collecting duct, and then drains into the renal pelvis, urine flows through the ureter to the urinary bladder. Filtration = movement of fluid from plasma into bowman"s capsule. Reabsorption = movement of filtered materials from tubule to blood. Secretion = movement of selected molecules from blood to tubule. Average urine volume: 1. 5l/da with osmolarity 50~1200mosm.
