Download Osmoregulation: Urinary System

Osmoregulation:
Urinary System
Maintaining H2O & ion homeostasis
Excreting wastes
Problems
Anatomy of kidney
Physiology of nephrons
Osmoregulation
• Excreting excess
– Water and Nitrogenous wastes (N waste = toxic!)
– Creatinine
– Toxic products (poisons, etc.)
– Sugars, salts, organic acids, phosphates, sulfate
ions
– CO2
• Moves across Transport Epithelium
– With or against concentration gradients (ATP
dependent)
Nitrogenous Waste
• By product of metabolic activity
– Typically starts as - NH2 (amino)
– Combines with H+ to form Ammonia – NH3
• This forms an ammonium ion (NH4+) which is toxic
because it interferes with oxidative phosphorylation &
therefore, ATP production.
– Excreted in a variety of forms
– Depends of water availability
Urea
• Cost: Energetically costly
• Benefit: Relatively nontoxic
• Can transport in high
concentration
• Produced in liver
• H2O soluble…but we
need to conserve water
Avenues of H2O loss
• Urine: lots of water reclamation occurs in kidneys
– Response to increased salt concentrations of extracellular
(interstitial fluid)
• Sweat: Radiant heat & convective currents evaporate
H20 from skin
• Exhalation: Lose some moisture, but we do
dehumidify air as is passes over mucous membranes
of nasal turbinates
• Feces: Little lost here
Basic Excretion
• Blood driven through cell
membrane via hydrostatic
pressure = filtration
• Small stuff crosses, large stuff
stays
• Selective reabsorptions
• Selective additions = secretions
• Excretion = “urine”
Osmoregulatory organ
• Kidney (Cortex, medulla, renal pelvis) ureter,
bladder, urethra
• Pyramids & nephrons
Juxtamedullary & Cortical nephrons
• Glomerulus, Bowman’s capsule, proximal tubule, loops
of Henle, distal tubule, collecting duct
Renal corpuscle structure
• Bowman’s capsule:
filtration unit
– Fenestrated
capillaries - pores
– Podocytes create
filtration slits
– Contractile mesangial
cells
Hydrostatic & Osmotic pressures
•
•
•
•
Glomerular hydrostatic pressure = 50
Capsular hydrostatic pressure = 15
Osmotic pressure = 25
Net Filtration Pressure NFP = GHP-CsHPOP = 10mm Hg
Bridge question
• What would happen to filtration rate if GSP
increased? If capsular OP increased?
• Under what natural conditions do you think
GHP might drop?
Controlling GFR
• Autoregulation
– Local contraction
or dilation
• Hormonal
– Renin,
Angiotensin,
Aldosterone
• Autonomic
– Angiotensin
increases thirst,
ADH secretion,
systemic BP
Increase CO, reduce venous blood
reservoir, increase vasoconstriction
RAA pathway
• Renin, Angiotensin,
Aldosterone
• Increases blood volume &
blood pressure
• Stimulus: low BP, measured
at glomerulus
• Response: JGA releases Renin
– Arteriole & precapillary
constriction
Methods of Reabsorption
• Countercurrent multiplier
• Carrier-mediated transport
–
–
–
–
Passive
Active
Cotransport
countertransport
Bridge Question
• As most reabsorption occurs in the PCT, do
you expect those epithelial cells to have any
special structure (think of your digestive
system)? Why or why not?
Secretion & absorption
• Countercurrent multiplier
– Salt concentration
gradient
– Huge ATP hog
• Active & passive transport of
solutes into interstitial fluid
• H2O follows
• Reabsorb useful ions
• Secrete waste, toxins &
acidifying ions
• Loop some nitrogenous
wastes
PCT
• Reabsorption of useful
stuff
– H20
– Organic nutrients
– Valuable ions
• Secretion of excess
Loop of Henle
• Descending – Passive
Reabsorption
– H2O: Many aquaporins =
passive transport
• Ascending - Reabsorption
– NaCl, both passive & active
– Impermeable to H2O
DCT
Secretion: K+ , H+, Cl- and NH4+
Reabsorption: HCO3- & Na+
Solute & Urea concentration increase
• Urea concentration
increases due to
impermeability of tubules
& ducts
Collecting duct
• Reabsorption…or not
– Transport epithelia
adjusts its aquaporin
density
• Increasing
concentration of filtrate
ADH
• Stimulus:
Hypothalamus
measures high blood
osmolality OR
Angiotensin II is
present.
• Pituitary releases
ADH
• Binds to PM receptor
– Intracellular 2nd
messenger cascade
• Response: More
aquaporin channels
produced