The kidneys filter the body's entire plasma volume 60 times each day
The filtrate:
Contains all plasma components except protein
Loses water, nutrients, and essential ions to become urine
The urine contains metabolic wastes and unneeded substances
Urine formation and adjustment of blood composition involves three major processes
Glomerular filtration
Tubular reabsorption
Secretion
Glomerular Filtration
Filtration Membrane
Glomerular endothelium - fenestrated epithelium that allows solute-rich, protein-free filtrate to pass from blood into the glomerular capsule
Glomerular Capsule
The external parietal layer is a structural layer
The visceral layer consists of modified, branching epithelial podocytes
Extensions of the octopus-like podocytes terminate in foot processes
Filtration slits - openings between the foot processes that allow filtrate to pass into the capsular space
Glomerular Filtration Rate (GFR)
The total amount of filtrate formed per minute by the kidneys
Factors governing filtration rate at the capillary bed are:
Total surface area available for filtration
Filtration membrane permeability
Net Filtration Pressure
NFP equals the glomerular hydrostatic pressure (HPg) minus the osmotic pressure of glomerular blood (OPg) combined with the capsular hydrostatic pressure (HPc)
NFP = HPg - (OPg + HPc)
___ = ____ - (____ + ____)
Regulation of Glomerular Filtration
If the GFR is too high - Needed substances cannot be reabsorbed quickly enough and are lost in the urine
If the GFR is too low: - Everything is reabsorbed, including wastes that are normally disposed of
Renal autoregulation (intrinsic system)
Exercise ___BP__________ afferent arteriole to avoid _________ to nephron.
What will happen if BP goes down
Myogenic Mechanism - high BP stretches afferent arteriole smooth muscle causing a reflexive ____________ thus ___ GFR ----Opposite for low BP
When the macula densa cells sense a high osmolarity (high cons. of Na+ & Cl-) in the DCT they release vasoconstrictor chemicals which causes ____________of afferent arteriole thus lower ________.
Extrinsic - Sympathetic Nervous System raises blood pressure during stressful times.
High systemic BP --> Epinephrine ___ -->Afferent and Efferent arterioles __________ and ___ GFR.
Essentially reabsorption in reverse, where substances move from peritubular capillaries or tubule cells into filtrate
Tubular secretion is important for:
Disposing of substances not already in the filtrate
Eliminating undesirable substances such as urea and uric acid
Ridding the body of excess potassium ions
Controlling blood pH
Regulation of Urine Concentration and Volume
Osmolality
The number of solute particles dissolved in 1L of water
Reflects the solution's ability to cause osmosis
Body fluids are measured in milliosmols (mOsm)
The kidneys keep the solute load of body fluids constant at about 300 mOsm
This is accomplished by the countercurrent mechanism
Interaction between the flow of filtrate through the loop of Henle (countercurrent multiplier) and the flow of blood through the vasa recta blood vessels (countercurrent exchanger)
The solute concentration in the loop of Henle ranges from 300 mOsm to 1200 mOsm
Dissipation of the medullary osmotic gradient is prevented because the blood in the vasa recta equilibrates with the interstitial fluid