• Recall the main sources of nutrition

Proteins (70-100g p day)

Carbohydrates (250-800g p day)

Lipids (25-160g p day)

vitamins and minerals are also essential, they must be consumed or gained (eg - sunlight) they cannot be produced by only our bodies or if they are tehay are produced in incorrect amounts.

• Define “digestion” and “absorption” in the context of human nutrition and physiology

Digestion = The breakdown of nutrients into absorbable molecules

Absorption = The movement of nutrients, water and electrolytes from the gut lumen into the internal environment

• Explain how the structure of the small intestine is adapted for efficient absorption

the small intestine contains many vili which themselves contain micro villi which act to increase surface area, the small intestine is also about 7 meters long and has many folds which also increase surface area available for absorption - This increased surface area allows for a larger contact area between the intestinal epithelial cells and the digested nutrients, facilitating efficient absorption.

the inner lining of the small intestine is made up of Enterocyte cells which contain the vili and microvili on their surface along with enzymes that they produce (lactase, maltase and sucrase)

which help to break down disaccharides into absorbable simpler forms

lacteals are present which are small capillary lymphatic vessels, chylomicron cells are made up within the enterocytes from the fat breakdowns and they are packaged in the golgi before being added to the lacteals where they eventually reach the thoracic duct and arrive into the blood stream.

finally the epithelial layer in the lumen of the small intestine is only one cell thick making absorption easy, the vili have a rich vascular capillary supply and so there are many capillary blood vessels that can be absorbed into if the molecules are small enough to do so.

• Explain how and where carbohydrates, lipids and proteins are digested