Absorption in the Small Intestine

2 INGESTION DIGESTION ABSORPTION EGESTION ASSIMILATION Food is taken into body Carbohydrates, proteins and fats are broken down into soluble glucose, amino acids, fatty acids and glycerol. Glucose, amino acids, fatty acids and glycerol are absorbed into body cells Removal of undigested food e.g. dietary fibre Absorbed nutrients are transported and utilized by the body

ABSORPTION Monosaccharides (glucose, fructose and galactose), amino acids, fatty acids, glycerol and water are absorbed in the small intestine. The absorbed nutrients passes from the lumen of the small intestine into the bloodstream. 3 lumen

How to ensure that nutrients are quickly absorbed?

Adaptations of the Small Intestine 1.Large surface area: volume ratio 1.1The inner walls of the small intestine have numerous folds 5

Adaptations of the Small Intestine 1.Large surface area: volume ratio Folded inner walls are lined with numerous minute finger-like projections called villi 6 Intestinal%20villi%20Jejunum-A.jpg

Adaptations of the Small Intestine 7 1. Continued...Large surface area: volume ratio The epithelial cells of the villi have numerous microvilli.

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Adaptations of the Small Intestine 2.The villi wall (epithelial cell layer) is only one cell thick

Adaptations of the Small Intestine 3.Presence of numerous capillaries to carry away the absorbed nutrients. 10 blood capillaries Lacteal/lymphatic capillary Digested food enters villus lumen epithelial cell layer

Adaptations of the Small Intestine 11 Blood capillaries: transport monosaccharides and amino acids. Lymphatic capillaries (lacteals): transport fats The continual removal of nutrients maintains a concentration gradient for diffusion. liver

Adaptations of the Small Intestine 4.Small intestine is long to provide sufficient time for absorption The small intestine is about 6m long!

How are the nutrients absorbed? Recall what you have learnt in the topic Movement of Substances! (Diffusion, osmosis, active transport….) glucose amino acids Fatty Acids glycerol

How does absorption take place in the villi? Soluble substanceType of movement into the epithelium Note: Monosaccharides (e.g: glucose) Facilitated Diffusion Active Transport High conc. in lumen low conc. in lumen Amino AcidsFacilitated Diffusion Active transport High conc. In lumen low conc. In lumen Fatty acids and glycerolDiffusionGlycerol and fatty combine to form small fat droplets that enter the lacteals. WaterOsmosisEnter the blood capillaries Mineral SaltsFacilitated DiffusionEnter the blood capillaries Water soluble vitamins (B and C) Facilitated DiffusionEnter the blood capillaries Fat –Soluble Vitamins (A, D, E and K) DiffusionEnter the lacteals 14

SUMMARY 15 Adaptations of the small intestine: 1.Large SA: Vol.  folds, villi and microvilli. 2.Villi epithelial wall is one cell thick  rapid diffusion. 3.Blood capillaries and lacteals  maintain concentration gradient. 4.Long  allows sufficient time for absorption Movement into villi: Glucose and amino acids absorbed by facilitated diffusion or active transport into blood capillaries of the villi. Glycerol and fatty acids diffuse into the epithelium  combine to form minute fat globules which enter lacteals. Water and mineral salts are also absorbed by the small intestine.

Egestion In the colon, water and mineral salts are absorbed from the undigested food material. Bacterial Activity Presence of dietary fibre/roughage helps in peristalsis. Unabsorbed matter is stored temporarily in the rectum. Faeces is discharged through the anus. 16 rectum anus