how would you describe the structure of the small intestine in relation to its function?

the small intestines function is for the reabsorption of nutrients into the blood. The small intestine has multiple structural adaptations in relation to its function, primarily the mucosa which is a layer composed of intestinal villi which makes up the exchange surface for nutrients to enter the blood stream. Villi are small extensions/folds of tissue, which increase the surface area to volume ratio in order to get maximum absorption of nutrients into the blood. These villi are one cell thick, minimising the number of diffusion surfaces that the nutrients has to pass before entering the blood stream. The villus epithelial cells have tight junctions preventing loss of nutrients. They also have many mitochondria, producing ATP for active transport across the phospholipid bilayer from the lumen of the intestine. The epithelial cells also have microvilli on the cell surface facing the lumen, further increasing the surface area to volume ratio. Another structural adaptation is the layer of circular and longitudinal muscles around the intestine. These muscles contract and relax, helping to mix and churn the digestive juices and aid with chemical digestion, they also initiate peristalsis which pushes the food along the small intestine to get to the large intestine. The small intestine also has ducts releasing digestive juices (eg: enzymes such as lipase) into the lumen from the pancreas. The length of the small intestine helps to ensure maximum absorption of the nutrients.