3.6.4.3 Control of blood water potential Flashcards
Describe and explain ultrafiltration
- afferent arteriole narrows
- increases hydrostatic pressure
- high hydrostatic pressure causes ultrafiltration of smaller molecules
- e.g. water, glucose, mineral ions forced out
- through basement membrane into filtrate
- filtrate passes through spaces between podocytes
- Large proteins can’t- too big
Where does ultrafiltration occur?
Bowman’s capsule / glomerulus / basement membrane
Name substances which will be present in glomerular filtrate
- water
- glucose
- amino acids
- mineral ions
- glycerol
- urea
Explain the effect on the glomerular filtration rate of a large loss of blood from the body
- blood pressure decreased
- forms less filtrate
Where does reabsorption of glucose and water occur?
Proximal convoluted tubule
Describe the steps of reabsorption of glucose and water
PCT = proximal convoluted tubule
- sodium ions actively transported out of cells lining PCT into blood capillaries
- this decreases sodium ions concentration in PCT cells
- sodium ions from lumen of PCT enter down their concentration gradient by co-transport
- through different co-transporter proteins, each bringing other molecules through (e.g. glucose, amino acids, chloride ions)
- Water follows down it’s water potential gradient by osmosis
- these molecules then diffuse into the blood via facilitated diffusion
Give 3 components of blood not usually present in filtrate
- Large proteins
- blood cells
- platelets
How does a lack of insulin (diabetes) affect reabsorption of glucose?
- High concentration of glucose in blood
- High concentration in filtrate
- reabsorbed by facilitated diffusion /active transport
- which requires carrier proteins
- these are saturated
- not all glucose is reabsorbed at proximal convoluted tubule - some lost in urine
How are the cells of the proximal convoluted tubule adapted for reabsorption?
- microvilli provide large surface area
- carrier proteins for active transport
- channel proteins for facilitated diffusion
- specific carriers for specific molecules
- many mitochondria for active transport
How is urea concentrated in the filtrate?
DCT = distal convoluted tubule
- reabsorption of water by osmosis
- at PCT / descending loope of Henle
- at DCT / collecting duct
- active transport of ions/glucose creates gradient
Describe and explain the role of the loope of Henle in the absorption of water from the filtrate
- sodium ions and chloride ions are actively transported out of ascending limb
- this decreases water potential in tissue fluid (interstitial region)
- Water can’t leave ascending limb (impermeable to water)
- Water can leave filtrate in the descending limb by osmosis
- Water absorbed into blood capillaries by osmosis
Compare the ascending and descending limb
Descending: very permeable to water (narrow, thin walls)
Ascending: not permeable to water (wide, thick walls)
How can water be conserved in the loope of Henle?
- by increasing loope of Henle
- an even lower water potential can be created with a higher salt concentration
- to create a greater water potential gradient
( maintain water potential gradient for longer) - so more water reabsorbed
- smaller volume of filtrate so more concentrated urine produced
Where are osmoreceptors located in mammals?
Hypothalamus
What happens to osmoreceptors when a person is dehydrated?
- Water potential of blood will decrease
- Water moves from osmoreceptors into blood by osmosis
How does ADH secretion affect urine produced by kidneys?
- permeability of membrane increased
- more water reabsorbed from DCT/ collecting duct by osmosis
- smaller volume of urine
- urine becomes more concentrated
How is more ADH released?
- if dehydrated, the water potential of the blood decreases and gets too low
- detected by osmoreceptors in the hypothalamus
- Water moves from osmoreceptor into blood
- by osmosis
- causes posterior pituitary gland to secrete more ADH
How does ADH increase movement of water from lumen of collecting duct into the blood?
- ADH causes vesicles containing aquaporins to be inserted into cell membrane
- Water enters through aquaporins
- by osmosis down water potential gradient to capillary
- via interstitial fluid
How does the structure of protein molecules allow them to form channels that only specific molecules can pass through?
- each protein has a tertiary structure
- which gives specific shape to inside of channel
Describe the effect of ADH on the collecting duct?
(Increases permeability)
* ADH causes vesicles containing aquaporins to fuse with membrane of collecting duct cells so aquaporins are inserted into membrane
* Water enters collecting duct cells through aquaporins
* by osmosis down a water potential gradient
* (from cell) to capillary
* via interstitial fluid
* smaller volume of urine
* urine becomes more concentrated
