15.3 excretion, homeostasis + liver

what is excretion?

liver plays crucial role in metabolism (involves lots chem reactions). these reactions generate waste product (CO₂, nitrogenous substances) - can harm cells if accumulate

excretion: removal of metabolic waste from cells. essential for maintaining normal metabolism + homeostasis. ex. CO₂ excreted by cells after respiration + then removed from body by lungs

• many metabolic waste products ex. urea - metabolised in + excreted from liver cells

function of the liver in detoxification

breaks down toxic substances ex. alcohol, medications, hormones + excess amino acids. detoxification process: substances → less harmful compounds that cells can excrete

how liver breaks down amino acids

1. deamination: amine groups removed from amino acids, produces toxic ammonia + organic acids

2. organic acids either used for ATP production/stored as glycogen

3. ammonia + CO₂ form urea via ornithine cycle, occurring partially in mitochondria of liver cells

4. urea excreted from liver cells → bloodstream + filtered out body via kidneys as urine

other substances detoxified by liver:

• alcohol - enzyme alcohol dehydrogenase breaks down ethanol → ethanal, then converted to ethanoate to prevent cell damage

• hydrogen peroxide - enzyme catalase splits hydrogen peroxide → oxygen + water to prevent cell damage

• paracetamol - broken down, prevent toxicity to liver + kidneys

• insulin - metabolised to help regulate blood glucose conc

function of liver in regulating blood glucose

• convert excess glucose → glycogen (storage molecule)

• store glycogen granules in its cells

• release glucose → bloodstream by breaking down glycogen when blood glucose levels fall

function of liver in breaking down red blood cells

haemoglobin from old RBC’s, broken down in hepatocytes (liver cells) → bile pigments. then excreted from liver cells + moved by bile duct → gallbladder (stored before removed from body

structure of liver

key large parts of structure:

1. hepatic artery supplies oxygenated blood

2. hepatic vein carries away deoxygenated blood → heart.

3. hepatic portal vein brings nutrient-rich blood from intestines

4. bile duct transports bile → gallbladder.

structure of liver lobules

liver made of many lobules - mostly consist of hepatocytes (liver cells). hepatocytes - large nuclei, prominent Golgi apparatus + several mitochondria (help carry out many functions)

key cells + tissues of liver in each liver lobule:

1. hepatocytes arranged along channels (sinusoids)

2. sinusoids mix oxygen-rich blood from hepatic artery w blood rich in products of digestion from hepatic portal vein

3. branch of hepatic vein located in centre of each lobule to remove deoxy blood

4. kupffer cells ingest pathogens/foreign particles, help protect against disease

5. channel separate from sinusoids (bile canaliculus) links to branch of bile duct