File:Lymphatic capillary.jpg

Lymphatic Vessels

• Lymphatic vessels, unlike blood vessels, only carry fluid away from the tissues.
• The smallest lymphatic vessels are the lymph capillaries, which begin in the tissue spaces as blind-ended sacs.
• Lymph capillaries are found in all regions of the body except the bone marrow, central nervous system, and tissues, such as the epidermis, that lack blood vessels.
• The wall of the lymph capillary is composed of endothelium in which the simple squamous cells overlap to form a simple one-way valve.
• This arrangement permits fluid to enter the capillary but prevents lymph from leaving the vessel.

Lymph Vessel Network

1. The microscopic lymph capillaries merge to form lymphatic vessels.
2. Small lymphatic vessels join to form larger tributaries, called lymphatic trunks, which drain large regions.
3. Lymphatic trunks merge until the lymph enters the two lymphatic ducts.
4. right lymphatic duct drains lymph from the upper right quadrant of the body.
5. thoracic duct drains all the rest.

Lymph Flow

• Like veins, the lymphatic tributaries have thin walls and have valves to prevent backflow of blood.
• There is no pump in the lymphatic system like the heart in the cardiovascular system.
• The pressure gradients to move lymph through the vessels come from the skeletal muscle action, respiratory movement, and contraction of smooth muscle in vessel walls.

Links: Structure Cartoon | Development Cartoon | Lymphangion Cartoon | Vasculature cartoon | Lymphatic Development | Immune Development

Reference

Image and Text Source:National Cancer Institute - SEER Training Modules http://training.seer.cancer.gov/anatomy/lymphatic/components/