The structure and function of the ileum in relation to absorption and digestion.

The ileum is made up of 4 layers:

The mucosa, submucosa, circular muscle and longitudinal muscle.

The mucosa consists of the villiand the crypt of lieberkuhn where intestinal juice for digestion is secreted. The hepatic potal vein and the umphatic system run through the sub mucosa. The sub mucosa and mucosa is separated by a layer called muscularis mucosae.

The following two layers are the muscle layers and beneath all the layers is the serosa.

The main function of the small intestine is absorption although some digestion does occur. The final stages of digestion of carbohydrates, lipids and proteins occur here, while absorption occurs.

Carbohydrates in the form of monosaccharides and amino acids are absorbed partly by diffusion and partly my active transport. Soon after a meal there will be a higher concentration of monosaccharides and amino acids in the ileum, and so a concentration gradient will exist and diffusion of these molecules will occur across the mucosal epithelium in the blood capillaries. This process rather slow and will not take up all the digested food, and so is supplemented by active transport involving the sodium potassium pump.

In the membrane of the epithelial cells is the glucose transporter protein, which has binding sites for both glucose molecules and sodium ions The sodium potassium pump actively transports sodium ions out of the cells against the electro chemical gradient. Glucose molecules and sodium ions bind to the transporter proteins and the sodium ions diffuse into the cells along the electrochemical gradient carrying the glucose molecules with them. Inside the cells the sodium ions and glucose molecules dissociate from the transporter protein, the glucose concentration of the cell increases and the glucose moves to the blood by facilitated diffusion. Similar mechanisms exist for the absorption of dipeptides and amino acids.

For digestion that occurs in the ileum intestinal juice is secreted by the small intestine and the digestion occurs in the small intestine itself. The intestinal juice contains maltase, sucrase, lactase, enterokinase, aminopeptidase, lipase, nucleotidase, mucus. Each are an enzyme which have a specific molecule to act on. Maltase acts on maltose and converts it into glucose. Sucrase acts on sucrose and breaks it down into glucose and fructose. Lactase acts on lactose and breaks it down into glucose and galactose. Enterokinase acts on trypsinogen and breaks it down to trypsin. Aminopeptidase acts on peptides and converts it into amino acids. Lipase acts on fats and converts it into fatty acids and monoglycerides. Nucleotidase breaks down nucleotides and mucus is also secretd for the lubrication of the food mass. The product molecules are all easier to absorb than their precursor molecules.

The ileum of the small intestine eventually leads into the large intestine for further absorption.