The gross structure of the human digestive system limited to oesophagus, stomach, small and large intestines, and rectum. The glands associated with this system limited to the salivary glands and the pancreas.

The salivary glands
Secrete saliva into the mouth.
Saliva contains amylase; this breaks starch down into maltose.
Saliva helps make the food into a slippery sphere called a bolus.

The oesophagus
Connects the mouth and the stomach.
Peristalsis (muscular contractions) moves boluses down.

The stomach
Secretes protease to break down proteins into amino acids.
Acidic PH2 environment (optimum for protease.)
Food in the stomach becomes chime (a runny substance which is what we throw up.)
The stomach produces mucus to prevent its lining being digested.

The pancreas
Produces pancreatic juice containing lipase (lipids into fatty acids and glycerol), amylase and protease.
Secretes this into the duodenum connecting the stomach and the small intestine.

The small intestine
PH7 due to bile which is made in the liver and stored in the gall bladder.
Bile also emulsifies fat; increasing its surface area and making it easier to absorb.
Food molecules are digested here by the enzymes from pancreatic juice.
Absorption happens here through the villi which:
--have a large surface area as they are folded with many protrusions called microvilli
--are only one cell thick (also increasing the rate of diffusion)
Glucose and amino acids are absorbed into the blood, they go through the hepatic portal vein into the liver (which filters blood) and then through the hepatic vein to the rest of the body where they will be assimilated (used by cells.)
Fatty acids and glycerol diffuse into the lymph, to be released into the blood at the neck.

The large intestine
water from the undigested food is absorbed into the blood.
Fibre, undigested food and dead red blood cells form faeces.

The rectum
This is the final section of the intestines.
faeces is stored here before being egested.