<< Chapter < Page Chapter >> Page >

Why is emulsification important for digestion of lipids? Pancreatic juices contain enzymes called lipases (enzymes that break down lipids). If the lipid in the chyme aggregates into large globules, very little surface area of the lipids is available for the lipases to act on, leaving lipid digestion incomplete. By forming an emulsion, bile salts increase the available surface area of the lipids many fold. The pancreatic lipases can then act on the lipids more efficiently and digest them, as detailed in [link] . Lipases break down the lipids into fatty acids and glycerides. These molecules can pass through the plasma membrane of the cell and enter the epithelial cells of the intestinal lining. The bile salts surround long-chain fatty acids and monoglycerides forming tiny spheres called micelles. The micelles move into the brush border of the small intestine absorptive cells where the long-chain fatty acids and monoglycerides diffuse out of the micelles into the absorptive cells leaving the micelles behind in the chyme. The long-chain fatty acids and monoglycerides recombine in the absorptive cells to form triglycerides, which aggregate into globules and become coated with proteins. These large spheres are called chylomicrons . Chylomicrons contain triglycerides, cholesterol, and other lipids and have proteins on their surface. The surface is also composed of the hydrophilic phosphate "heads" of phospholipids. Together, they enable the chylomicron to move in an aqueous environment without exposing the lipids to water. Chylomicrons leave the absorptive cells via exocytosis. Chylomicrons enter the lymphatic vessels, and then enter the blood in the subclavian vein.

Illustration shows a row of absorptive epithelial cells that line the intestinal lumen. Hair-like microvilli project into the lumen. On the other side of the epithelial cells are capillaries and lymphatic vessels. In the intestinal lumen, lipids are emulsified by the bile. Lipases break down fats, also known as triglycerides, into fatty acids and monoglycerides. Fats are made up of three fatty acids attached to a 3-carbon glycerol backbone. In monoglycerides, two of the fatty acids are removed. The emulsified lipids form small, spherical particles called micelles that are absorbed by the epithelial cells. Inside the epithelial cells the fatty acids and monoglyerides are reassembled into triglycerides. The triglycerides aggregate with cholesterol, proteins, and phospholipids to form spherical chylomicrons. The chylomicrons are moved into a lymph capillary, which transports them to the rest of the body.
Lipids are digested and absorbed in the small intestine.

Vitamins

Vitamins can be either water-soluble or lipid-soluble. Fat soluble vitamins are absorbed in the same manner as lipids. It is important to consume some amount of dietary lipid to aid the absorption of lipid-soluble vitamins. Water-soluble vitamins can be directly absorbed into the bloodstream from the intestine.

This website has an overview of the digestion of protein, fat, and carbohydrates.

Art connection

Steps in mechanical and chemical digestion are shown. Digestion begins in the mouth, where chewing and swallowing mechanically breaks down food into smaller particles, and enzymes chemically digest carbohydrates. In the stomach, mechanical digestion includes peristaltic mixing and propulsion. Chemical digestion of proteins occurs, and lipid-soluble substances such as aspirin are absorbed. In the small intestine, mechanical digestion occurs through mixing and propulsion, primarily by segmentation. Chemical digestion of carbohydrates, lipids, proteins and nucleic acid occurs. Peptides, amino acids, glucose, fructose, lipids, water, vitamins, and minerals are absorbed into the bloodstream. In the large intestine, mechanical digestion occurs through segmental mixing and mass movement. No chemical digestion occurs except for digestion by bacteria. Water, ions, vitamins, minerals, and small organic molecules produced by bacteria are absorbed into the bloodstream.
Mechanical and chemical digestion of food takes place in many steps, beginning in the mouth and ending in the rectum.

Which of the following statements about digestive processes is true?

  1. Amylase, maltase, and lactase in the mouth digest carbohydrates.
  2. Trypsin and lipase in the stomach digest protein.
  3. Bile emulsifies lipids in the small intestine.
  4. No food is absorbed until the small intestine.

Elimination

The final step in digestion is the elimination of undigested food content and waste products. The undigested food material enters the colon, where most of the water is reabsorbed. Recall that the colon is also home to the microflora called “intestinal flora” that aid in the digestion process. The semi-solid waste is moved through the colon by peristaltic movements of the muscle and is stored in the rectum. As the rectum expands in response to storage of fecal matter, it triggers the neural signals required to set up the urge to eliminate. The solid waste is eliminated through the anus using peristaltic movements of the rectum.

Common problems with elimination

Diarrhea and constipation are some of the most common health concerns that affect digestion. Constipation is a condition where the feces are hardened because of excess water removal in the colon. In contrast, if enough water is not removed from the feces, it results in diarrhea. Many bacteria, including the ones that cause cholera, affect the proteins involved in water reabsorption in the colon and result in excessive diarrhea.

Emesis

Emesis, or vomiting, is elimination of food by forceful expulsion through the mouth. It is often in response to an irritant that affects the digestive tract, including but not limited to viruses, bacteria, emotions, sights, and food poisoning. This forceful expulsion of the food is due to the strong contractions produced by the stomach muscles. The process of emesis is regulated by the medulla.

Section summary

Digestion begins with ingestion, where the food is taken in the mouth. Digestion and absorption take place in a series of steps with special enzymes playing important roles in digesting carbohydrates, proteins, and lipids. Elimination describes removal of undigested food contents and waste products from the body. While most absorption occurs in the small intestines, the large intestine is responsible for the final removal of water that remains after the absorptive process of the small intestines. The cells that line the large intestine absorb some vitamins as well as any leftover salts and water. The large intestine (colon) is also where feces is formed.

Art connections

[link] Which of the following statements about digestive processes is true?

  1. Amylase, maltase and lactase in the mouth digest carbohydrates.
  2. Trypsin and lipase in the stomach digest protein.
  3. Bile emulsifies lipids in the small intestine.
  4. No food is absorbed until the small intestine.

[link] C

Got questions? Get instant answers now!

Questions & Answers

viruses are composed of what
Daniel Reply
what are some disease caused by virus
Daniel
what are some disease caused by virus
Daniel
what are some disease caused by virus
Daniel
what is the use of biology
Tarkaa Reply
To widen our reasoning abilities about the past and the present events in biology and life at large
Musoke
To understand our biography
Musoke
Among all these which one is the major difference between platyhelminthes and coelenterates? 1. are multicellular 2. have developed a mesoderm 3. reproduce sexually 4. reproduce asexually
Habeeb Reply
what is evolution?
Emmanuelfray Reply
how can you define biology in terms of a burning fire in the bush?
Emmanuelfray
what is a cell
Kagelelo Reply
cell is a functional and unit of life
Sarita
describe the process of testing the presence of starch in a leaf
Estel Reply
give me somes of examples.
Manu Reply
give example of what.
Ante
example of what
Elizabeth
what are chromosomes?
Ante
what is Biology
Darkoa
Biology is the study of animals and plants on their characters and death
Okol
No biology is the study of life (living thing's)
Achibiri
Chromosomes refers to one of the small parts like threads in the NUCLEI (central part )of plants and animals cell that carry the GENES
Estel
Yeah okol....Bio-means life and -logy means study/knowledge
Estel
Ecology is the study of
Abdul Reply
Ecology is the study of the interaction of organism in each other and their environment.
Ante
Ecology is the study of the interaction of organism in each other and their environment
Everlove
oh yes!!! exactly
Great
thank much
Ante
what is biome?
Ante
a geographical area with dinstic species
Francis
thanks much it very helpful
Ante
my pleasure
Francis
characteristics of living things
Jane Reply
excretion, movement, sensitivity, reproduction,growth, respiration,nutrition
Estel
what are there function
Ante
what are their function
Ante
what is the two type of reproduction?
Ante
sexual reproduction and asexual reproduction
Abdul
what are their function
Manu
Hi
Olufunmilokun
What is light independent reaction
Benjamin Reply
correct word or phrase. ______A____ uses carbon dioxide and _____B______ to make sugar during______C______. _____D______ traps light energy during this process. *
Andrea Reply
A_plant ,B_water,C_photosynthesis,D_chlorophyll
Abdul
Plant,sunlight,photosynthesis
Olufunmilokun
by which of the following feature c3 and c4 plant similar A .enzyme used to fix carbon dioxide B.cell where calvin cycle takes place C.cell where carbon dioxide fixation takes place
Kaleab Reply
correct word or phrase. ______A____ uses carbon dioxide and _____B______ to make sugar during______C______. _____D______ traps light energy during this process. *
Andrea
what is biology ?
Bizone Reply
study of organisms
Aurelia
is the study of living organisms
Emmanuelfray
what is link
Lamina Reply
is carbon an organism that matter?
DKP Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask