how do lipids move through the body so they can be digested and absorbed? How are lipids stored in the body? Explain:

http://en.wikipedia.org/wiki/Lipid

http://www.cem.msu.edu/~reusch/VirtualText/lipids.htm

Lipids are essential molecules that are involved in various biological functions. They can be classified into different categories, including triglycerides, phospholipids, and cholesterol. The digestion, absorption, and storage of lipids in the body involve several steps.

1. Digestion:
- Lipid digestion primarily occurs in the small intestine. The process starts in the stomach, where fat globules are broken down into smaller droplets by the mechanical action of stomach contractions.
- When the partially digested food, known as chyme, enters the small intestine, it triggers the release of a hormone called cholecystokinin (CCK).
- CCK signals the gallbladder to release bile into the small intestine. Bile plays a crucial role in lipid digestion by emulsifying the fat droplets, breaking them down into even smaller droplets. This process increases the surface area available for enzymes to act upon.
- Pancreatic lipase, an enzyme produced by the pancreas, is then secreted into the small intestine. It hydrolyzes triglycerides into free fatty acids and monoglycerides, which are the primary products of lipid digestion.

2. Absorption:
- The products of lipid digestion, along with other fat-soluble vitamins, are absorbed in the small intestine.
- The free fatty acids, along with monoglycerides and cholesterol, combine with bile salts to form micelles, which aid in their absorption.
- These micelles move towards the surface of the intestinal cells (enterocytes), where the lipids are taken up by the cells.
- Inside the enterocytes, the free fatty acids and monoglycerides are reassembled and packaged into structures called chylomicrons.
- Chylomicrons, containing various lipids, are released into the lymphatic system through lacteals, specialized lymphatic capillaries found in the walls of the small intestine. From there, they enter the bloodstream.

3. Storage:
- Lipids, particularly triglycerides, are primarily stored in adipose tissue as a long-term energy reserve.
- Once in the bloodstream, chylomicrons are broken down by the enzyme lipoprotein lipase (LPL) present on the surface of capillaries in adipose tissue.
- LPL hydrolyzes the triglycerides in chylomicrons into free fatty acids and glycerol.
- The free fatty acids are taken up by adipocytes (fat cells) where they are reassembled into triglycerides and stored as lipid droplets.
- Triglycerides can also be stored in other tissues, such as muscle cells, for energy use.

In summary, lipids undergo digestion by enzymes in the small intestine, are absorbed into the enterocytes, and are then transported through the lymphatic system as chylomicrons. Once in the bloodstream, they are taken up by adipose tissue or other tissues for storage as triglycerides, serving as an energy reserve in the body.

To understand how lipids move through the body for digestion and absorption, it is helpful to know a bit about their structure. Lipids are a group of molecules that include fats, oils, and certain components of membranes. They are hydrophobic, meaning they do not mix well with water.

When you consume lipids in your diet, the process of digestion begins in the stomach. Gastric lipase, an enzyme secreted by the stomach, begins breaking down some of the lipids into smaller molecules called fatty acids. However, the majority of lipid digestion takes place in the small intestine.

In the small intestine, lipids are emulsified and further broken down by bile salts produced by the liver and stored in the gallbladder. Bile salts act as emulsifiers, breaking up larger lipids into smaller droplets called micelles. This increases the surface area of lipids, making it easier for digestive enzymes to come into contact with them.

Pancreatic lipase, an enzyme released by the pancreas, then acts on the lipids within the micelles. It breaks down triglycerides, the common form of dietary lipids, into individual fatty acids and monoglycerides. These smaller molecules can be easily absorbed by the small intestine.

The absorption of lipids occurs primarily in the small intestine as well. The small intestine is lined with villi, tiny finger-like projections that increase the surface area available for absorption. Within the villi, there are specialized cells called enterocytes that carry out the absorption process.

As the products of lipid digestion (fatty acids and monoglycerides) are absorbed by enterocytes, they reform triglycerides. These triglycerides are then packaged into structures called chylomicrons, which are a type of lipoprotein. Chylomicrons are released from the enterocytes and enter the lymphatic system.

Once in the lymphatic system, chylomicrons travel through the lymphatic vessels and eventually enter the bloodstream. From the bloodstream, they can be transported to various tissues and organs throughout the body.

Regarding the storage of lipids in the body, excess triglycerides that are not needed for immediate energy are stored in adipocytes, which are specialized fat cells found primarily in adipose tissue. Adipose tissue serves as the primary site for lipid storage.

To summarize, lipids move through the body by first being broken down and emulsified in the stomach and small intestine. They are then digested by enzymes, absorbed by enterocytes, and transported through the lymphatic system for eventual distribution to tissues. Excess lipids are stored as triglycerides in adipose tissue.