Mammalian Physiology and Behaviour

Digestion

• Mechanical Breakdown - Mastication, Peristalsis
• Chemical Breakdown - Enzymes

MOUTH - mastication (mechanically breaks down food) creates a larger surface area for enzymes to work on. Saliva containes Amylase. Amylase hydrolyses starch into Maltose.

STOMACH - the entrance and exit controlled by sphincter muscles. Gastric juice is secreted. Gastric Juice contains:

• Hydrochloric acid (HCL)
• Pepsin - endopeptidase
• Mucus

The gastric juice converts the food into acidic CHYME. pepsin is called an endopeptidase because it hydrolyses peptide bonds in the middle of polypeptides creating smaller polypeptide chains.

The rhymic action of the muscles is called peristalsis.

DUODENUM - Chyme is moved along the duodenum via peristalsis. Bile and pancreatic juice neutralises the chyme in the duodenum.

ILEUM - small soluble molecules are absorbed through microvilli. Absorption occurs through:

• Diffusion
• Facilitated Diffusion
• Active Transport

both the duodenum and the Ileum make up the small intestine.

PANCREAS - releases pancreatic juice into the duodenum via the pancreatic duct. Pancreatic juice contains:

• Amylase
• Trypsin
• Chymotrypsin
• Carboxypeptidase
• Lipase
• Alkali that neutralises stomach acid (Sodium Bicarbonate)

COLON - absorbs water, salts and minerals. It has a folded wall to allow a maximum surface area for absorption. Bacteria decompose left over nutrients.

RUMINANTS

Ruminants have 4 stomachs. They use their incisors to crop vegetation. The sections of the stomach:

• RETICULUM
• RUMEN
• OMASUM
• ABOMASUM

the 1st section of the stomach is the RETICULUM. This section forms CUD which is regurgitated so it can be further mechanically broken down by chewing. When swallowed again the CUD by-passes the reticulum and travels through the rumen omasun and abomasum. The rumen is the largest part of the ruminant stomach and contains mutualistic micro-organisms that ferment vegetation in anaerobic conditions. These Bacteria break down cellulose.

Dentition

Carnivore:

• carnivores have canines - used for slicing meat and catching prey.
• Pre-Molars and Molars have sharp edges, also called CARNASSIAL TEETH.

No chemical digestion takes place in the mouth as thier diet does not include starch so no amylase is needed. The Stomach of carnivores conain more concentrated acid than humans.

Herbivore:

• No canines
• Have a diastema - a gap that enables their long tongue to move grass around bringing it to different angles to the teeth so it can be thoroughly chewed.
• Pre-molars and molars do the chewing. They have broad surfaces providing larger surface area.
• Incisors bite agianst the horny pad (where there are no teeth) to grab grass.

A cow's teeth continue to grow, a dog's teeth do not. Roots of cow's teeth remain open allowing a supply of oxygen, and therefore a supply of oxygen and nutrients. Roots of dog's teeth are closed.

LIVER:

• Hepatic Artery - from aorta, delivers oxygenated blood
• Hepatic portal vein - from small intestine, delivers blood rich in glucose and amino acids.
• Hepatic vein - carries blood away from the liver to the vena cava

Blood in hepatic portal vein passes through capillaries in the wall of the small instestine. It is therefore deoxygenated and at a lower pressure than the blood in the hepatic artery.

Liver tissue

• made up of LOBULES. The centre of the lobule is a branch of the hepatic vein.
• Between lobules are branches of the hepatic artery and hepatic portal vein
• The blood flows from here, through lobules into hepatic vein.
• The lobules are made up of cells called HEPATOCYTES.
• The channels carrying blood between these cells are called SINOSOIDS.