Mammalian digestion

Teeth Teeth provide mechanical digestion by tearing food up into bits. See teeth powerpoint for differences in herbivore and carnivore dentition. Food is mixed with saliva which helps form it into a bolus. saliva also contains the enzyme salivary amylase which acts on starch ( see next slide)

Salivary Amylase Salivary amylase works on insoluble starch and breaks it down into maltose which is soluble. Salivary amylase works best in slightly alkali conditions so the mouth has a pH of 11

swallowing muscular contractions of the tongue push the food past the pharynx. The epiglottis closes over the wind pipe preventing food from entering

Peristalsis Food moves through the gut by a wave of peristalsis. The wall of the gut in front of the bolus of food relaxes and the muscles behind the food contract pushing it forward.

The stomach Gastric juice is mixed with the food and it is churned up to produce chyme. pepsin (enzyme) acts on protein to break it down into polypeptides. HCl ( hydrochloric acid) helps break down food and kills most bacteria. Pepsin only works in acid conditions. Food is released through the pyloric sphincter a small amount at a time.

The duodenum (upper small intestine) Lots of enzymes breakdown the food The duodenum secretes:- Maltase to breakdown maltose into glucose. Peptidases to breakdown polypeptides into amino acids. the pancreas secretes:- amylase to breakdown starch to maltose Trypsin and chymotrypsin to breakdown protein to polypeptides. Lipase to breakdown fats to fatty acid and glycerol

… still in the duodenum Bile which is made in the liver and stored in the gall bladder is released. Its job is to emulsify any fat into small droplets to make it easier to digest.

In the ileum ( lower small intestine) Digested food is absorbed through the wall of the gut into the blood. The small intestine is covered with villi which are covered in microvilli to increase the surface area for absorption.

The large intestine this consists of the appendix, caecum and colon. In humans the appendix does nothing(- ish) and the large intestines function is the reabsorption of water, electrolytes ( Na+) and some vitamins. Faeces is collected in the rectum and egested through the anus.

Digestion in ruminants cows, goats and sheep are foregut fermenters. The stomach is divided into a series of chambers to slow digestion and give tough plant material time to break down. They rely on microbes in the rumen to break down cellulose. They regurgitate, rechew and reswallow partly digested food.

Food is digested slowly in different parts of the multi chambered rumen by bacteria. Bacteria ferment the plant material to make methane, and VFA ( volatile fatty acids) which are absorbed into the blood stream. Herbivores have long guts to digest and absorb plants Ruminants burp and fart a lot.

Hindgut fermenters Horses and rodents have bacteria in their hind gut or caecum to digest vegetation to make VFA’s which are absorbed into the blood . Rabbits are caecotrophes (see next slide)

Rabbits make 2 types of poo.

Carnivores have much shorter guts. Meat and animal products are easier to digest and have more energy. This allows carnivores to have much shorter guts.

Carnivore vs ruminant

Insectivore vs hind gut fermenter