In the arms of a city,

• 2:09 PM, 3.10.07

okaaay. been mugging at macs for the past two days! :D
quite okay, lol. yesterday we saw two lesbians at macs. :S they sat beside us lol.
today we sawwww lingrongchan and mrchia! they marking papers. :S
anddd i forgot to bring my file home lmfao, luckily lingrongchan came running up to us with my file. :D
errrrm, geog i dai. physics i sleep for one hour. i think i no hope. :D okaybyebye.

i'm supposed to do human digestive system anddd respiration notes!
sally's supposed to excretion and cells.
klinsen's gonna do transport in humans and osmosis andddd diffusion. :O
chiong finish now then can dota later yay. >D

so, starto!

Human Digestive System.

Mechanical/Physical Digestion;
-physically breaking down the food.
-takes place in mouth(chewing), and stomach (churning of food by stomach walls)

Chemical Digestion;
-use enzymes to break down food substances into their simplest form.
~starch --amylase-> maltose.

Why must food be digested?
-large molecules too fat. can't pass through cell membrane.
-must go on diet, become small molecule. then can diffuse through.

Mouth;
-food is ingested here.
-mechanical digestion occurs (chewing)
-chemical digestion also occurs in mouth.
~salivary amylase turns starch into maltose.
-saliva (pH7) contains water, mucus and salivary amylase.
~softens and moistens the food.
-tongue mixes the food with the saliva and rolls the food into a bolus before swallowing.
-teeth masticates (chews) food into small pieces to increase SA for digestion

Oesophagus;
-minimal digestion.
-carries food by peristalsis.
-has circular and longitudinal muscles which are antagonistic.
~when circular muscles contract, longitudinal muscles relax and vice-versa.

Peristalsis;
-enables food to be mixed with the digestive juices.
-moves the food along the gut.
-gravity and slippery mucous lining helps push food down too.

picture!

Stomach;
-stores food temporarily.
-stomach muscles churns and mixes food with gastric juice to form CHYME. (also by peristalsis)
-gastric juice contains HCl and enzymes like rennin and pepsin. (protease)
~HCl is super acidic, thus it kills all the bacteria inside as well as stopping the action of salivary amylase.
~provides acidic medium for gastric enzymes to work.
-only protein digestion here.
-"guarded" by sphincter muscles which control the amount of food entering and leaving the stomach.

Small Intestine;
-divided into duodenum, jejunum and ileum.
~duodenum does most of the digestion. ileum more of absorption.
~ileum is long and coiled to provide neough chyme for absorption.
-in the SI, chyme stimulates;
1. pancreas to secrete pancreatic juice which has pancreatic amylase and digests starch.
2. gall bladder to secrete bile which emulsifies fats.
3. intestinal glands to secrete intestinal juice.
-all three juics secreted are alkaline, pH 8.5.
-pancreatic and intestinal juice contain many digestive enzymes.
-bile does not contain enzymes. it emulsifies fats, increasing SA for lipase action.

Large Intestine (Colon);
-large inverted U shaped tube.
-bo digestion.
-absorption of water and mineral salts nia.
-stores faeces.

Rectum;
temporarily stores faeces.

Anus;
egests faeces.

Gall Bladder;
-temporarily stores bile which is secreted by liver.
-it starts secreting bile in the presence of CHYME.
-bile breaks up the fat fat (LOL) droplets into small fat droplets.
~increases SA for lipase action.
~not enzyme, so not affected by temp.

Pancreas;
-connects to small intestine by pancreatic duct.
-produces pancreatic juice.
-secretes hormones like insulin and glucagon. (glucose -> glycogen thing)

Liver;
-produces bile.
-regulates the blood glucose concentration.
-iron storage.
~red blood cells destroyed in spleen, haemoglobin sent to liver, broken down. iron released and stored in liver.
-protein synthesis.
~synthesizes proteins found in blood plasma. (fibrinogen)
-deanimation of amino acids.
~excess amino acids are transported to liver where their amino groups are removed and converted to urea.
-detoxification.
~liver cells contain alocohol dehydrogenase to break down alcohol.
~alcohol bad. stimulates acid secretion in the stomach, then increases risk of gastric ulcer.
~might lead to liver cirrhosis. (destruction of liver cells)
-heat production.
~how we maintain body temperature.

Adaptation of the SI for absorption;
-veryvery long.
-has many folds.
-on these folds, have finger-like projections called villi.
-all these increase SA for absorption.

Villus;
-one cell thick epithelium for efficient absorption of food particles.
-lacteal, where fatty acids and glycerol recombine in the epithelium to form fat which then enters the lacteal as fine fat droplets.
-blood capillaries, transport sugar and amino acids away from the SI.
-this continual transport maintains the concentration gradient for the absorption of digested food substances.
~concentration of simple nutrients is higher in the SI than in the capillaries that pass through the villi.
~thus nutrients diffuse across a region of high concentration to lower concentration.
~absorption by active transport also possible.
~blood capillaries in SI unite! form larger blood vessels that unite! and become hepatic portal vein.
~hepatic portal vein transport the nutrients to the liver.

Glucose;
-used as a source of enegy.
-excess glucose returned to liver and stored as glycogen.
-insulin converts glucose to glycogen.
-glycogen converted back into glucose by glucagon.

Amino Acids;
-converted into new protoplasm that is used for growth and repair.
-form enzymes and hormones.
-excess deanimated by liver.