5.1.2 Excretion Flashcards
What is excretion?
removal of metabolic waste
What is the importance of excretion?
maintains metabolism and homeostasis
What happens if carbon dioxide is no excreted?
- carbon dioxide is toxic
- hydrogen carbonate ions reduces the ability to transport oxygen
forms - carbominohaemoglobin which has a low affinity for oxygen that normal Hb - respiratory acidosis
Why is it important to remove nitrogenous waste from the body?
- body cant store amino acids
- but they still contain energy
- in the liver toxic amino acids are removed (deamination)
How is excess amino acids removed?
- liver deaminates amino acids
- amino acid + oxygen = keto acid + ammonia
- ammonia cannot be stored
- converted into less soluble and less toxic = urea = excreted from the body
What are the two blood supplied to the liver?
hepatic artery
hepatic portal view
What is the hepatic artery?
brings oxygenated blood from the aorta
liver requires oxygen for processes such as aerobic respiration = generate ATP
What is the hepatic portal vien?
delivers deoxygenated blood from the digestive tract
includes toxins and nutrients e.g glucose
What blood vessel takes blood away from the liver?
hepatic vein
takes it to the vena cava
taken back to the heart
under lower pressure
What are the lobules of liver called?
hepatocytes
What are sinisoids?
vessels that connect the haptic artery and the hepatic vein to allow hepatocytes to remove harmful substances from blood
What is the role of the bile duct?
hepatocytes make bile
transfers to the gall bladder
What are Kupffer cells?
cells attached to the walls of the sinusoid, they remove bacteria and break down RBC’s
What is the function of hepatic cells?
break down harmful products arriving from the hepatic portal vein from digestive tract e.g alcohol
also make bile
What is urea?
main nitrogenous waste product, produced from the breakdown of excess amino acids
What is the ornithine cycle?
reactions converting ammonia to urea
What is detoxification and where does it occur?
Removal of toxic substances
Occurs in the hepatocytes in the liver
What are the 2 processes to make urea?
1) deamination
2) ornithine cycle
What is deamination?
amino acid + oxygen = keto acid + ammonia
- uses excess amino acids
- amine group is removed from each amino acid
- ammonia is formed which is highly toxic and soluble
What is the use of keto acid produced in deamination?
- can enter the krebs cycle and undergo aerobic respiration
- used to make things like lipids and cholesterol
What is the process of the ornithine cycle?
ammonia + carbon dioxide = urea + water
urea is then taken from the liver to the kidneys where it is excreted when dissolved in water as urine
Draw the ornithine cycle:
What are the 3 functions of the liver?
storage of glycogen
formation of urea
detoxification
How does detoxification occur in the liver when one consumes alcohol?
-ethanol is converted to ethanal
- a hydrogen is removed from the ethanol and accepted by NAD forming reduced NAD
- this process is catalysed by the enzyme ethanol dehydrogenase
-ethanal is produced and it converted to acetate by accepting the hydrogen from reduced NAD forming NAD
- using the enzyme ethanal dehydrogenase
- acetate enters the krebs cycle
How does high alcohol consumption cause a fatty liver?
alcohol causes NAD to become reduced
NAD is used in the liver to oxide fatty acids
If NAD is reduced it cannot oxide fatty acids and this accumulates over time and are converted into fat
the fat is deposited in the liver
Draw the structure of a kidney:
label:
cortex
medulla
pelvis
renal artery
renal vein
ureter
capsule
Draw the structure of a nephron:
glomerulus
efferent arteriole
afferent arteriole
proximal convolated tubule
loop of Henle
distal convoluted tubule
collecting duct
What is the process of ultrafiltration? (vague)
Afferent arteriole has a larger diameter than the efferent arteriole;
therefore has higher hydrostatic pressure;
the endothelium wall of the capillary has small fenestrations;
these all allow ultrafiltration;
water, salts, glucose, amino acids
proteins and RBC’s cannot fit!!!!!!!
What is the filtered out substances called?
glomerular filtrate
pressure is higher in the glomerrulus than the bowmans capsule which pushes the liquid in the capsule
What are the 3 layers for ultrafiltration?
1) endothelium; fenestrations and gaps which allow plasma and substances to pass through
2) basement membrane; stops the removal of large substances
3) podocytes; have finger like projections; to ensure passage of substances
If there is proteins found in the urine what does this suggest?
basement membrane is damaged in the glomeralus allowing large substances to pass through
Where does selective reabsorption take place in the kidney?
proximal convoluted tubule
What molecules are selectively reabsorbed back into the blood?
all glucose, amino acids, vitamins, sodium and chloride ions
by facilitated diffusion
Describe the process of selective reabsorption?
- sodium ions are actively transported out of the cells aligining the PCT into the tissue fluid (ATP used)
- this cause water to move out of the cells alighning and into the blood as water potential is lowered by the sodium ions
- sodium ions from the lumen of the PCT move via facilitated diffusion into the cells aligning the PCT whilst co transporting glucose or amino acids
- amino acids and glucose then diffuse into the blood via facilitated diffusion
What occurs in the ascending limb of the loop of Henle?
- Na+ and Cl- are actively transported out of the loop of Henle
- decreasing the water potential of the surrounding tissue in the medulla
- water potential of the surrounding tissues is lower than the collecting duct
- water moves out and reabsorped back into the blood
Which part of the loop of Henle is impermeable to water?
ascending limb
What occurs at the bottom of the loop of Henle?
- as there is a high concentration of Na+ and Cl- ions
- they diffuse out of the loop of Henle
- decreasing the surrounding cells water potential
- bottom of loop of Henle = lowest water potential
What occurs in the in the descending limb in the loop of Henle?
- wall is permeable to water
- water is removed from the descending limb
- by osmosis to the surrounding tissue
What occurs in the collecting duct?
water is removed from urine
What is osmoregulation an example of?
Negative feedback
How is the water potential of the blood detected if too low?
by osmoreceptors in the hypothalamus that detect low concentration of water in the blood
What hormone is released and where is it transported too if blood water potential is low?
ADH;
is released from the posterior pituritary gland;
transported to the kidneys in the blood;
What occurs when ADH arrives at the collecting duct?
- receptors on the walls of the cells lining the collecting ducks will be specific and complementary to the hormone ADH and therefore will bind
- ADH triggers a response inside the cell where vesicles that contain aquaporins will fuse with the cell surface membrane via the cytoskeleton
- aquaporins inserted into the cell plasma membrane
- more water can be reabsorbed back into the blood
What are aquaporins?
intrinsic proteins
form pores in the phospholipid bilayer
prevent the passage of other solutes
What happens if there is low levels of ADH?
cell surface membrane folds inwards creating new vesicles
these remove the aquaporins making the membrane less permeable
the urine is more dilute and of higher volume
What is haemodialysis?
- blood from the patients vein is passed through small tubes made from partially permeable membranes
- on the outside of the membrane the dialysis fluid flows in the opposite direction
- the fluid has the water potential and concentration of ions and glucose that the patients blood should have
- e.g urea moves out of he blood
What is the use of heprin in haemodialysis?
stops blood clotting
What must be removed before allowing blood to renter the patient when using haemodialysis?
air bubbles
What is peritoneal dialysis?
peritoneum is the layer of tissue that lines the abdominal cavity
a catheter is inserted into the cavity
dialysis fluid is passed in and left there
excess fluid is drained off
What are the disadvantages of kidney failure?
new kidney not recognised as itself;
causes rejection;
by the immune system;
immunosuppressants are needed;
invasive procedure;
required from a living donor;
In what ways are excretory products used in medical diagnosis?
pregnancy testing
testing for drugs and anabolic steroids
How does a pregnancy test work?
- dipped in urine
- if HCG is present it is specific and complementary to the monoclonal antibodies and bind to form a HCG antibody complex
- this will move up the stick with the urine
- the excess antibodies carried up with the urine bind to immobilised antibodies in the upper band = control = causes dye to be released and line forms
- the HCG complex binds to immobilised antibodies due to the specific and complementary shape in the lower band if the women is pregnant
- 2 lines = pregnant
- 1 line = she is not pregnant (control )
What is used to identify anabolic steroids?
gas chromotography
