Excretory system Flashcards
(31 cards)
whats the role of the kidneys
Kidneys are involved in homeostasis- maintenance of a constant internal environment
- regulates osmotic pressure
The removal of waste products from the body is called urea
what are the three layers of ultrafiltration
- Fenestrated capillary endothelial cells (small gaps- cells cant get through)
- Basal lamina (basement membrane)- has no holes and collagen gives a negative charge so polar molecules like proteins cant get through
- Inner epithelial layer of Bowman’s capsule (podocyte cells) have many slits between neighbouring extensions – so fluid flows more freely
what materials can and cant move into the tubule during ultrafiltration
- Ions, amino acids, glucose, urea and water go through into the tubule
- Proteins and cells stay in the blood
what does Glomerular filtration rate show and how is it measured
- GFR shows how well the kidneys are filtering, and it’s used as a measure of kidney health
- measure in ml/min per 100g body mass so that its comparable.
whats the equation for GFR (3 factors affecting GFR)
GFR= Glomerular blood pressure - osmotic pressure of plasma proteins - intra renal pressure
what is glomerular blood pressure
- blood pressure is high in the glomerulus due to bottleneck effect-
- The efferent arteriole is narrower than the afferent arteriole and exerts a ‘damming up’ effect causing the rise in blood pressure
describe the osmotic pressure of plasma proteins
- plasma proteins cannot leave the blood. So high concentration of protein in blood plasma and none in glomerular filtrate
- so water potential becomes more negative.
- water moves from an area of high water potential to a lower water potential. water moves into the capillary
describe intra renal pressure
- The pressure of fluid already in the capsule and tubules of the nephron,
- It tends to oppose glomerular blood pressure and so opposes ultrafiltration
Describe the PCT
Glucose, Na+ and Water transported
- Epithelial cells lining the tubule have:
- microvilli at luminal surafce
- folds at capillary surface
- many mitochondria
How does reabsorption occur in the proximal convoluted tubule
Glucose, Na+ and Water transported
- Sodium potassium pump, sodium moves out the epithelial cell and potassium moves in- uses energy of ATP. lower concentration of sodium in the epithelial and high conc in the lumen (GF)
- Sodium moves from lumen to epithelial cells by facililitated diffusion, coupled woth glucose through a cotransport protein.
- Sodium and glucose moving into the epithelial causes the water potential to become higher in the GF than the epithelial cell. so water will move from the lumen to the epithelial cell by osmosis
- The build of glucose in the epithelial cell causes there to be higher concentration in the epithelial cell than the blood cappilary so glucose moves into blood by FD.
describe the loop of henle
- This is a long hairpin-shaped loop within the medulla.
- Ascending and descending limb
- Makes urine more concentrated
- Reabosrbtion of water and ions
How does reabsorption occur in the loop of henle
Countercurrent system:
- Ascending limb: (impermeabele to water)
- actively transports sodium pottasium and chlorid einto the tissue in the medulla which causes the water potential in the tissue to become lower.
- Descending limb
- Water moves out via osmosis into the medulla due to the water potential difference
- Tubule fluid concentrated
- As a result, tissue fluid in the medulla has a high ion concentration (low water potential)
describe the DCT
- Heavily convoluted segment of the nephron
- Function- water resorption
what substances are found in the glomerular filtrate
water, glucose, urea, amino acids, small proteins, ions
what would happen to the GFR if there was a large loss of blood from the body
blood pressure decreased so less pressure forms less substrate
what effect would decreased plasma proteins have on GFR
Lower osmotic pressure so less GFR reabsorbed by osmosis
in 24 hours a person excreted 1660 mg of creatine in his urine. The concentration of creatine in the blood enetering his kidney was constant at 0.01mg/cm-3.
Calculate the GFR in cm3/minute
115.2/115.3
how are the cells of the PCT adapted for reabsorption
- Microviolli provide large surface,
- Carrier proteins in membranes, for active transport
- Channel proteins for facilitated diffusion
- specific carriers for specific molecules /sodium pumps
- many mitchondia for active transport
explain the role of the loop of henle in the absorption of water form the filtrate (8 marks)
- In the ascending limb sodium(ions) actively removed;
- Ascending limb impermeable to water;
- In descending limb sodium(ions) diffuse in;
- Descending limb water moves out / permeable to water;
- Low water potential / high concentration of ions in the medulla / tissue fluid;
- The longer the loop / the deeper into medulla, the lower the water potential in medulla / tissue fluid;
- Water leaves collecting duct / DCT;
- By osmosis / down water potential gradient;
defien hypertonic, isotonic, hypotonic RBCs
hypertonic - water moves out of RBCs (shrinkage)
Isotonic- Water moves in and out of RBCs (regulated)
Hypotonic- Water only moves in RBC- can cause lysis
What is the consequences of over or underhydration
- Dehydration - causes metabolism to slow/stops
- Overhydration **–causes haemolysis
- concentrations of nutrients/ions etc. decreases e.g. NaCl –nervous impulses effected.
What is the ideal percentage of blood in terms of body mass and how is water gained or lost.
Water is kept constantly at 60/70% of body mass
Gained; drink, food, metabolism (respiration)
Lost: Urine, sweat, breath, faeces
what are the mechanisms of osmoregulation
- ADH production
- Changes in GFR
- RAAS (Renin Angiotensin-Aldosterone System)
How does changes in teh GFR affect osmoregulation
- GFR rate is maintained carefully
- Vasoconstriction (narrowing) and dilation of afferent arteriole increases fluid flow to glomerulus
