Ion and Water Balance 4: Mammalian Kidneys Flashcards
what are vertebrate kidneys’ roles in homeostasis (6)
- ion balance
- osmotic balance
- blood pressure
- pH balance
- excretion of metabolic wastes and toxins
- hormone production
kidney structure: layers (2)
- outer cortex: renal cortex
- inner medulla: renal medulla
how would liquids move through the kidney (5)
- renal cortex and renal medulla through the renal pyramid
- renal papilla
- minor calyx
- major calyx
- renal pelvis
how does urine leave the kidneys (3)
- exits via the ureter
- empties into the urinary bladder
- urine leaves urinary bladder through the urethra
nephron (2)
- functional unit of the kidney
- millions contained in a mammalian kidney
nephron general composition (2)
- renal tubule
- vasculature
nephron: renal tubule (2)
- lined with transport epithelium
- various segments with specific transport functions
nephron: vasculature (2)
- glomerulus
- capillary beds surrounding renal tubule for blood supply
glomerulus
- ball of capillaries where filtrate/urine is produced
what is the glomerulus surrounded by
- Bowman’s capsule
how do fluids travel through the nephron (6)
- glomerulus
- Bowman’s capsule
- proximal tubule
- loop of Henle
- distal tubule
- collecting duct
what four processes are involved in urine production (4)
- filtration
- reabsorption
- secretion
- excretion
urine production: filtration
- filtrate of blood formed at glomerulus
urine production: reabsorption
- specific molecules in filtrate removed (water, ions, etc)
urine production: secretion
- specific molecules added to the filtrate (toxins, etc)
urine production: excretion
- urine is excreted from the body
urine production: where does filtration occur
- from the glomerulus to the Bowman’s capsule
urine production: where does reabsorption occur (5)
- proximal tubule
- descending loop of Henle
- ascending loop of Henle
- distal tubule
- collecting duct
urine production: where does secretion occur (3)
- proximal tubule
- distal tubule
- collecting duct
urine production: where does secretion occur
- from the end of the collecting duct into the external environment
what components of the blood are filtered into the Bowman’s capsule (2)
- water
- small solutes
what components of the blood are not filtered into the Bowman’s capsule (2)
- blood cells
- large macromolecules
glomerular capillary structures/features (3)
- capillaries are leaky
- podocytes with foot processes form filtration structure
- mesangial cells pack between the capillaries
podocytes with foot processes
- provide framework to support the capillaries during filtration
mesangial cells
- control blood pressure and filtration within glomerulus
mesangial cell constriction
- decrease filtrate production
mesangial cell dilation
- increase filtrate production
what is the glomerular filtration rate affected by
- blood pressure
what affects the blood pressure in the glomerulus (3)
- glomerular capillary hydrostatic pressure
- Bowman’s capsule hydrostatic pressure
- oncotic pressure
oncotic pressure
- osmotic pressure due to protein concentration
direction of pressure in glomerulus: glomerular hydrostatic pressure
- toward the Bowman’s capsule lumen
direction of pressure in glomerulus: Bowman’s hydrostatic pressure
- toward the glomerulus
direction of pressure in glomerulus: oncotic pressure
- toward the glomerulus
primary urine
- initial filtrate filtered in Bowman’s capsule that is isoosmotic to the blood
reabsorption: primary urine
- most water and salt in primary urine reabsorbed using transport proteins and energy
rate of reabsorption limit
- limited by number of transporters
renal threshold
- concentration of specific solute that will overwhelm reabsorptive capacity
how are transporters distributed in the nephron
- each zone of the nephron has transporters for specific solutes
reabsorption: how does kidney filtrate modified through the nephron (3)
- 20% of the plasma volume entering the glomerulus is deposited into the Bowman’s capsule
- over 19% is reabsorbed
- less then 1% is excreted
reabsorption: glucose (2)
- reabsorbed by secondary transport and taken up by the blood
- Na+/K+ ATPase creates negative potential to drive Na+/glucose co-transporter
reabsorption: Na+ and Cl-
- primary and secondary active transport
passive reabsorption: osmosis (2)
- as Na+, Cl-, and other solutes are reabsorbed actively, the extracellular fluid (EF) is more concentrated than fluid in lumen
- causes water to move out of the lumen to higher osmolarity
passive reabsorption: passive diffusion (2)
- as water leaves by osmosis, other substances (urea) becomes more concentrated in lumen
- substances by out of lumen by passive diffusion down its concentration gradient
what kind of molecules are moved during secretion (5)
- K+
- NH4+
- H+
- pharmaceuticals
- water-soluble vitamins
what is required for secretion (2)
- transport proteins
- energy
proximal tubule specialization
- most solute and water reabsorption
distal tubule specialization
- reabsorption completed for most solutes here
collecting duct specialization (2)
- drains multiple nephrons
- carries urine to renal pelvis
what accounts for the differences in transport and permeability in tubule regions of the nephron
- differences in epithelium along the tubule
proximal tubule epithelium (2)
- long microvilli extend into lumen
- tight junctions between cells
loop of Henle descending limb epithelium (2)
- lack tight junctions between cells
- lack microvilli
loop of Henle ascending limb epithelium (2)
- microvilli extend toward the basolamina
- tight junctions between cells
collecting duct epithelium (2)
- contains principal and intercalated cells
- tight junctions between cells
how is reabsorption conducted in the proximal tubule (2)
- many solute reabsorbed by Na+ cotransport
- water follows by osmosis
what is reabsorbed in the proximal tubule (11)
- Na+
- Cl-
- K+
- Ca2+
- HCO3-
- water
- glucose
- amino acids
- vitamins
- urea
- choline
what is secreted in the proximal tubule (4)
- H+
- NH4+
- toxins
- drugs
what is reabsorbed in the descending limb
- water
what is reabsorbed in the ascending limb (6)
- Na+
- Cl-
- K+
- Mg2+
- Ca2+
- NH4+
what is reabsorbed in the distal tubule (4)
- Ca2+
- Na+
- Cl-
- water
what is secreted in the distal tubule (2)
- H+
- K+
what is reabsorbed in the collecting duct (8)
- Na+
- Cl-
- K+
- Ca2+
- HCO3-
- H+
- urea
- water
what is secreted in the collecting duct (3)
- K+
- H+
- NH4+
what occurs in the descending limb of the loop of Henle (3)
- water is reabsorbed
- volume of primary urine decreases
- primary urine becomes more concentrated
what occurs in the ascending limb of the loop of Henle (3)
- no water movement, impermeable to water
- ions are reabsorbed
- primary urine becomes dilute
how does the osmotic gradient change after the loop of Henle (2)
- reabsorbed ions accumulate in interstitial fluid
- osmotic gradient created in the medulla
nephron countercurrent multipliers: structures (2)
- loop of Henle
- collecting duct
countercurrent multiplier function
- create osmotic gradients that facilitate transport processes
how is the gradient of the renal medulla maintained
- vena cava capillaries
what does the osmotic concentration of the final urine depend on
- permeability (aquaporins) of the distal tubule and collecting duct, which can be regulated
what urine will result from impermeable distal tubule and collecting duct
- dilute urine due to low water reabsorption
what urine will results from permeable distal tubule and collecting duct
- concentrated urine due to high water reabsorption
mechanism for concentrating urine (4)
- ascending limb of loop of Henle actively pumps Na+ out of tubule lumen
- Cl- and K+ follow
- causes increased ion concentration in interstitial fluid of medulla
- water moves passively out of the descending limb by osmosis
how does the vasa recta function with the loop of Henle (6)
- ions pumped out of ascending loop (↑osmotic pressure outside, ↓OP inside)
- water flows out of descending tubule by osmosis (↑OP in descending tubule, becoming more [ ])
- blood entering vasa recta is isoosmotic with the cortex
- as blood moves deeper into medulla, it loses water and picks up ions from interstitial fluid (↑osmolarity)
- when blood of vasa recta flows back toward cortex, high plasma osmolarity attracts water being lost from descending limb, ↓osmolarity of the blood
what occurs in longer loop of Henle (2)
- medulla gradient is larger
- more water reabsorption is achieved, helping with water conservation
excretion process (3)
- urine leaves kidneys and enters urinary bladder via ureters
- urine temporarily stored in the bladder
- urine leaves bladder via urethra
what controls urine flow from the bladder
- sphincters of smooth muscle
what controls the sphincters opening/closing at the urethra (2)
- spinal cord reflex arc
- can be influences by voluntary controls
