4. fundamentals of renal bio SDL Flashcards
what is osmosis
net movement of water through a semi-permeable membrane from a region of higher water potential to a region of lower water potential.
what is water potential
tendency of water molecules to move out of a solution
In pure water, the water potential is 0.
what is solute potential
the component of water potential due to solute molecules, it always has a negative value and is also termed osmotic potential
what is pressure potential
the component of water potential due to hydrostatic pressure, it usually has a positive value
what is hydrostatic pressure
the pressure exerted by a fluid in a closed system
what is osmotic pressure
the pressure, exerted by the solute particles in the solution, which prevents the movement of water across a membrane
outline the gross anatomy of the kidney
- renal capsule
- outer cortex
- inner medulla
- renal pelvis
- renal artery and vein enter through renal hilus
- ureter exits at hilus
what is the nephron
- the kidney contains hundreds of thousands of small functional units called nephrons
- they have a similar structure across vertebrate species
- it is basically a tubule with a vascular component
discuss the structure of the nephron: where in the kidney are the following structures found
what is excretion
the removal from the body of waste products of metabolism
what are the functions of the kidneys
- to excrete waste products from metabolism (urea in mammals)
- osmoregulation: the control of water content in the blood
- hormone secretion (erthyropoieti, calcitriol)
- acid/base homeostasis (excretion of H, reabsorption of HCO3)
- blood pressure regulation via water control
- reabsorption of vital nutrients (glucose)
what 2 processes occur in the production of urine
- ultrafiltration
- selective reabsorption
what is ultrafiltration
occurs between the capillaries of the lomerulus and bowmans capsule - under pressure, pressure increase caused by having narrower efferent artiriole
how does filtration occur
- hydrostatic pressure of blood in glomerulus drives filtration
- it is greater than the tendancy for water to flow from capsule into capillaries (has greater osmotic pressure; generated by proteins)
- primarily caused by efferent arteriole being narrower than afferent
what is glomerular filtration rate
- the volume of fluid passing from the glomerular capillaries into bowmans capsule per minute
- good indication of kidney function
what is selective reabsorption
- most reabsorption occurs in the proximal convoluted tubule (all glucose and amino acids)
- epithelial cells lining tubule have microvilli at the luminal surface, folds at the capillary surface and many mitochondria
how is sodium reabsorbed by the kidney
active transport
how is glucose reabsorbed by the kidney
mostly in first part of PCT
how is water reabsorbed by the kidney
sodium moves out of the lumen, therefore water will pass out via osmosis
in the case of dehydration, do you still urinate
yes - regardless of hydration state of the body, metabolic waste must be eliminated. so even whe dehydrated urine is produced in smaller, more concentrated amounts
what is the loop of henle
- long loops of henle dipping down into the renal medulla are important for water conservation
- desert animals have long loops of henle
- functionn is to increase concentration of ions in the tissue of the medulla
- a counter current system: hairpin structure ensures filtrate flows in opposite directions. this allows descending limb and ascending limb to have different functions
explain the counter current system of the loop of henle
ascending limb
- active transport of Na
- impermeable to water
- leading to
descending limb (no active pumps)
- water leaving via osmosis
- tubule fluid becomes concentrated
as a result, tissue fluid in the medulla has a high ion concentrations and low water potential
what is the collecting duct
- as fluid flows through the collecting duct in the medulla region, water can be reabsorbed from the collecting duct due to the highly concentrated medulla
- this concentrates the urine before it exits the body
- this is regulated by the hormone ADH that increases water retention
- from the collecting ducts, urine passes into the pelvis of the kidney and down the ureter
