5.2 Excretion Flashcards
Define excretion
removal of metabolic waste from the body
What are the 4 main excretory organs?
- lungs: CO2 diffuses into and out of alveoli to be excreted as you breathe out
- liver: some substances produced passed into bile for excretion with faeces. also involved in converting amino acids to urea.
- kidneys: urea removed to form part of urine
- skin: loss of water and salts as sweat
How is the pH of blood kept fairly constant?
- proteins in blood act as buffers
- if theres a small change. the extra H+ is detected by medulla oblongata and breathing rate will increase to remove CO2 formed.
- if it drops too much = acidosis. Rapid heart rate.
CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
Why do amino acids have to be removed? How?
body cannot store excess
deamination -> keto acid formed and used in respiration. ammonia formed also.
Then ornithine cycle
What is a key adaptation for all liver cells?
good blood supply to ensure as much blood as possible flows past as many cells as possible
What is the role of the hepatic artery, hepatic portal vein, and hepatic vein?
artery: supplies oxygen needed for aerobic respiration
portal vein: deoxygenated blood straight from digestive system, carrying digestion products. concs must be adjusted
vein: blood leaving liver, rejoins vena cava
What is the role of the bile duct and bile canaliculus?
canaliculus: join together to form bile duct
bile duct carries bile from liver to gallbladder
How are liver cells organised?
Into cylindrical lobules in lobes
What are the inter-lobular and intra-lobular vessels?
inter run between and parallel to lobules - branches from hepatic portal vein and hepatic artery at intervals.
intra = central hepatic vein
What is the sinusoid?
- lined with hepatocytes
- where blood from vessels are mixed
- hepatocytes able to remove substances from the blood
- empty into intra-lobular vessel
What is the role of Kupffer cells?
- special macrophages break down and recycle old RBC - bilirubin
- also engulf pathogens
Adaptations of hepatocytes?
- many mitochondria
- dense cytoplasm
- thin cells for short diffusion distance
- fennestrations for increased permeability
What are the functions of the liver?
- storage of glycogen and vitamins, iron
- detoxification of alcohol
- control of amino acid, glucose and lipid levels
- synthesis of bile, plasma proteins and cholesterol
- breakdown of RBC and hormones
What does detoxification involve? What enzymes help?
- methylation, combination with another molecule, oxidation, reduction
- catalase which catalyses formation of water and oxygen from hydrogen peroxide
- cytochrome p450 catalyses breakdown of drugs. can interfere with other metabolic roles and cause unwanted side effects
What is the process of alcohol detoxification?
- ethanol -> ethanal (dehydrogenation, ethanol dehydrogenase)
- ethanal -> ethanoic acid (dehydrogenation, ethanal dehydrogenase)
- ethanoic acid/acetate joins with coenzyme A to form acetyl coenzyme A which enters Krebs cycle.
Whats the problem if too much alcohol has been consumed?
- too much detoxified
- it uses up NAD and has insufficient for fatty acid breakdown
- lipids in hepatocytes -> liver enlargement -> fatty liver -> cirrhosis/hepatitis
Describe deamination
- amino acid + oxygen -> keto acid + ammonia (highly soluble and highly toxic)
Describe the ornithine cycle
ammonia and carbon dioxide in
water out
CITRULINE
ammonia in and water out
ARGININE
water in and urea out (less soluble and less toxic)
ORNITHINE
Starting from inside to outside, what is the structure of a kidney?
ureter, pelvis, medulla, cortex, capsule