Download Animation: Lipid Absorption Lipids are digested and absorbed

Animation: Lipid Absorption
Lipids are digested and absorbed differently from carbohydrates and proteins because they are not
soluble in water and so cannot enter our bloodstream easily. Digestion of triglycerides in our foods
begins in the mouth. The lingual glands in the tongue produce an enzyme known as lipase that
chemically digests some of the triglycerides. This role is limited, however, and most of the triglycerides
reach the stomach intact. The majority of the digestion of triglycerides occurs in the small intestine,
where the compounds are prepared for absorption by the action of bile and lipase enzymes from the
pancreas and small intestine. The bile acts as an emulsifier, breaking the fats into smaller droplets.
Pancreatic lipase breaks the fatty acids away from the glycerol backbone, forming two free fatty acids
and one monoglyceride, ready for absorption. The water-insoluble free fatty acids and monoglycerides
form micelles in the small intestine. These fat-bile salt clusters enter the brush border of the villi
through diffusion. Once inside the cell, the micelle splits. The bile salts return to the liver, and the
triglyceride molecule reforms and combines with other lipids for absorption in the form of a
chylomicron. Some short-chain and medium-chain fatty acids can be absorbed through the capillaries
and transported to the liver via the portal vein. However, most fatty acids, including the long-chain fatty
acids, are absorbed into the lymph fluid as part of the chylomicron. The lipids in the sandwich have now
been absorbed, ready to be used by the body.
file:///D:/Chapter_05/A_PowerPoint/a_PPT_Lecture/lipid_absorption.html
Animation: Fat Digestion
Fats, including tryiglycerides, phospholipids, and cholesterol, are not soluble in water, so they cannot
enter our bloodstream easily and thus are digested and absorbed differently from carbohydrates and
proteins. The mechanical digestion of the sandwich begins in the mouth, where chewing mixes the fats
with saliva to moisten and prepare the food to be swallowed. The saliva contains an enzyme called
lingual lipase that chemically digests some of the fats, also known as triglycerides. This role is limited,
however, and most of the triglycerides reach the stomach intact. The primary role of the stomach in fat
digestion is to separate the fat from the other macronutrients. Because they are not soluble in water,
these droplets float on top of the watery digestive juices in the stomach until they pass into the small
intestine. As the fat reaches the duodenum, the gallbladder releases bile, which acts as an emulsifier
and breaks the fat into smaller droplets. At the same time, the pancreas releases a lipid-digesting
enzyme called pancreatic lipase, which breaks the fatty acids away from the glycerol backbone, forming
two free fatty acids and one monoglyceride. Once formed, the long chain fatty acids are transported as
a micelle into the intestinal cells and then transported through the lymph fluid.
file:///D:/Chapter_05/A_PowerPoint/a_PPT_Lecture/fat_digestion.html
from top left: Protein, Phospholipid, Cholesterol, Fat droplet (triglyceride)
Label the Chylomicron above, see p. 147
1. In notebook define, micelles, lymph, lipoproteins & chylomicron.
Micelles-small transport carriers in the intestine that enable fatty acids and other compounds to
be absorbed
Lymph-Watery fluid that circulates through the body in lymph vessels and eventually enters the
blood
Liproproteins- Capsule-shaped transport carriers that enable fat and cholesterol to travel
through the lymph and blood
Chylomicron-a type of liproprotien that carries digested fat and other lipids through the lymph
system into the blood
2. Name the fat “digesting” enzyme found in the mouth, released by the stomach, and released
into the SI by the pancreas.
Lingual lipase, gastric lipase and pancreatic lipase
3. How do the actions of gastric lipase compare to those of pancreatic lipase when acting on
triglyceride?
Gastric lipase breaks down some of the fat (triglycerides) into a fatty acid and a diglyceride, whereas
the pancreatic lipase breaks the triglyceride down into two fatty acids and a monoglyceride.
4. Why is bile needed in the small intestine during the digestion of fat? What is its particular role?
Bile mixes with the fats and water fluids in the intestine. The bile contains bile acids that help
emulsify the fat into smaller globules in the water digestive solution this helps increase surface
area of fats so that the pancreatic lipase can have an easier task or breaking down the fats
5. What is the role of the phospholipid lecithin during fat digestion?
After the pancreatic lipase has done its job, the monoglycerides and fatty acids are packed
with the lecithin, a phospholipid, the bile, and other substances to create a micelles (small
transport carrier). This structure is able to travel through intestinal cells.
6.
What happens to short-chain fatty acids during fat digestion/absorption?
Short-chain fatty acids will enter your blood stream and go directly to your liver.
7. What happens to long-chain fatty acids during fat digestion/absorption?
Long-chain fatty acids cannot enter your bloodstream directly, the enter your lymph system and need
transport carriers (micelles)
8.
What is packaged inside protein-containing carries called lipoproteins? What is the structure of
this lipoprotein? What is an example of such a liproprotein? p. 147
Lipoproteins are protein-containing carrier. They are capsule-shaped fat “carriers” have an outer shell
high in protein and phospholipids and an inner compartment that carries the insoluble fat, as well as
cholesterol, through your lymph system and bloodstream. Carries “reformulated” fats. An example is
a chylomicron