Digestion & Absorption

This illustration is designed to show you the “tunnels” that nutrients must pass through to get to the blood. The empty space labeled “extracellular fluid” is where the food passes through in the small intestine. The pink area is the inside of a cell. You only see a small portion of the cell. On the other side of the cell (out of our view, towards the bottom) is the blood capillary, ready to pick up nutrients from the cell. Note that fatty acids and cholesterol do not need to travel through tunnels!

Amylose is a form of starch Amylose is a form of starch. Note that it is composed of many glucoses linked together in a chain. The chain is too big to be absorbed into the blood, so it needs to be cleaved into individual glucoses. AmylASE is a digestive enzyme that will hydrolyze starch into disaccharides of 2 glucose (we’ll talk about how those get split up later!)

Example of enzymatic carbohydrate digestion: The enzyme sucrASE splits the disaccharide sucrOSE into its component monosaccharides Glucose and fructose are both small enough to be absorbed We’ll talk about sucrase in ch. 4. I used it as an example here because it is difficult to find good pictures of amylase!

This is how the enzyme lipase works: it splits up triglycerides, which are chains of fatty acids. The fatty acids are now small enough to be absorbed.

Proteases cleave proteins into smaller pieces, including amino acids Proteases cleave proteins into smaller pieces, including amino acids. Now they are small enough to be absorbed. We’ll talk about peptidases in later chapters!

Here is a view of the small intestine. Note how furry it looks Here is a view of the small intestine. Note how furry it looks. The tiny folds are villi. You cannot see microvilli in this picture.

Here is another view of the small intestine Here is another view of the small intestine. Now, when you look at a close-up of each villus (b), you can barely make out microvilli of each cell. An even closer up view (c), shows a little more detail of the microvilli. Note that they are part of each individual cell, while a villus includes many cells.

Here is a close-up of a single villus Here is a close-up of a single villus. Here, the illustrator has included the microvilli, you can see them as tiny hairs on each cell. Note the blood vessels and lymphatic vessels right under the cells. This is where nutrients will go, after they pass through the cells.

One last picture of villi and microvilli!

I lied! This is a real picture, a Scanning Electron Micrograph of villi. You cannot make out the microvilli.

I like this picture, it’s the juncture between the esophagus and stomach. Notice how completely different the linings are!

Denaturation (unraveling) of proteins by hydrochloric acid (HCl) increases the surface area available to proteases

This is an overview of the effects of CCK

This one looks at CCK and secretin

An illustration of emulsification by bile

This illustrates the relationship of the pancreas and small intestine This illustrates the relationship of the pancreas and small intestine. Cells of the pancreas make bicarbonate and enzymes. They put those products into the pancreatic duct, which empties into the duodenum, right after the pyloric sphincter. See next 3 slides!

Picture (a) shows where the pancreatic duct empties into the duodenum Picture (a) shows where the pancreatic duct empties into the duodenum. Picture (b) shows how the pancreatic duct is formed, and how the cells are arranged. Picture (c) is an actual photomicrograph of pancreatic cells.

This shows how the liver sends bile to the gall bladder, and how the gall bladder then sends it to the small intestine; through the same duct (b) the pancreas uses!

Another illustration of pancreatic cells sending products into the duct