Topic 6.1 Digestion

TOPIC 6.1 DIGESTION The structure of the wall of the small intestine allows it to move, digest and absorb food.

Slide taken from Digestion power point by Stephen Taylor

You might try drawing a digestive system that looks something like this. Clearly show how and where accessory organs connect.

Slide taken from Absorption of Digestion power point by Stephen Taylor Skill 2: Plan Diagram of the small intestine

Contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut Circular Muscle Longitudinal Muscle Mucosa Epithelium Smooth muscle layers Serosa Submucosa

Small Intestine: Contains different regions Duodenum Jejunum ileum Chyme enters duodenum The pancreas secretes enzymes into the duodenum. Pancreatic amylase & lipase Endopeptidases like trypsin (break peptide bonds in the center of polypeptide molecules) Pancreas also secretes sodium bicarbonate which neutralizes the stomach acid. Pancreatic juice also contains water

Slide taken from Digestion power point by Stephen Taylor Rat Pancreas Does this look familiar? This is the internal structure of a pancreas cell.

Enzymes of the pancreas tend to act on larger macromolecules to break them into smaller monomers. See your chart

Membrane bound enzymes: The epithelial lining of the small intestine also secretes enzymes Disaccharidases like maltase Dipeptidases The digestive enzymes in the epithelial cells of villi of the duodenum are are attached to the cell membrane. They are peripheral proteins in the membrane They anchored in the membrane so NOT swept along in the digestive process. If the whole cell detached the enzyme will continue to work in the lumen of the GI tract. Advantages: Products are released close to the membrane & easily absorbed by blood Digestion of disaccharides takes place early in the small intestine.

Villi of the Small Intestine: Campbell Reese 9 th edition, p887 small projections that cover the inner lining of the small intestine. INCREASE surface area for the absorption of digested food.

Majority of digestion occurs in the duodenum while much of the absorption occurs in the ileum. Villi of the Small Intestine: Campbell Reese 9 th edition, p887 Each villus contains: blood capillaries lymph capillaries (the LACTEAL). Amino acids & glucose are absorbed into the blood glycerol and fatty acids absorbed into the lacteal.

Specific molecules absorbed by the epithelium cells of the villi Glucose, fructose, galactose, Amino acids Fatty acids, monoglycerides & glycerol Bases from nucleotides Mineral ions (Calcium, potassium, sodium) Vitamins (vitamin c)

Copy the link below into your browser to see a video reviewing passive diffusion PASSIVE DIFFUSION: Water, fats, fat soluble vitamins, Oxygen, CO 2 & alcohol Absorption of Lipids through epithelial cells Campbell Reese 9 th edition p888

Fructose absorption through the epithelium by Faciliated Diffusion Fructose and other water-soluble molecules (such as vitamins) move down the concentration gradient into the epithelial cells. Integral protein channels allow them to pass through the hydrophobic phospholipid bilayer ug=0 Copy link below to your browser to see the video on facilitated diffusion

Absorption of Monosaccharides through the epithelium =3&debug=0 (glucose & galactose) Copy the link below into your browser to see a video

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Most cellulose is egested in the feces and not broken down Cellulose is a structural polysaccharide found in plant foods Cellulose is digested by cellulase (humans can’t produce this)