4. fundamentals of renal bio SDL

Question 1

what is osmosis

Answer 1

net movement of water through a semi-permeable membrane from a region of higher water potential to a region of lower water potential.

Question 2

what is water potential

Answer 2

tendency of water molecules to move out of a solution
In pure water, the water potential is 0.

Question 3

what is solute potential

Answer 3

the component of water potential due to solute molecules, it always has a negative value and is also termed osmotic potential

Question 4

what is pressure potential

Answer 4

the component of water potential due to hydrostatic pressure, it usually has a positive value

Question 5

what is hydrostatic pressure

Answer 5

the pressure exerted by a fluid in a closed system

Question 6

what is osmotic pressure

Answer 6

the pressure, exerted by the solute particles in the solution, which prevents the movement of water across a membrane

Question 7

Answer 7

Question 8

outline the gross anatomy of the kidney

Answer 8

• renal capsule
• outer cortex
• inner medulla
• renal pelvis
• renal artery and vein enter through renal hilus
• ureter exits at hilus

Question 9

what is the nephron

Answer 9

• 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

Question 10

discuss the structure of the nephron: where in the kidney are the following structures found

Answer 10

Question 11

what is excretion

Answer 11

the removal from the body of waste products of metabolism

Question 12

what are the functions of the kidneys

Answer 12

• 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)

Question 13

what 2 processes occur in the production of urine

Answer 13

• ultrafiltration
• selective reabsorption

Question 14

what is ultrafiltration

Answer 14

occurs between the capillaries of the lomerulus and bowmans capsule - under pressure, pressure increase caused by having narrower efferent artiriole

Question 15

how does filtration occur

Answer 15

• 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

Question 16

what is glomerular filtration rate

Answer 16

• the volume of fluid passing from the glomerular capillaries into bowmans capsule per minute
• good indication of kidney function

Question 17

what is selective reabsorption

Answer 17

• 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

Question 18

how is sodium reabsorbed by the kidney

Answer 18

active transport

Question 19

how is glucose reabsorbed by the kidney

Answer 19

mostly in first part of PCT

Question 20

how is water reabsorbed by the kidney

Answer 20

sodium moves out of the lumen, therefore water will pass out via osmosis

Question 21

in the case of dehydration, do you still urinate

Answer 21

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

Question 22

what is the loop of henle

Answer 22

• 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

Question 23

explain the counter current system of the loop of henle

Answer 23

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

Question 24

what is the collecting duct

Answer 24

• 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