Think think What is a lymphocyte Where does

Think, think… What is a lymphocyte? Where does it come from? Where does it go?

The Lymphatic System • consists of organs, ducts, and nodes • transports a watery clear fluid called lymph • distributes immune cells and other factors throughout the body • interacts with the blood circulatory system to drain fluid from cells and tissues

The Lymphatic System • contains immune cells called lymphocytes which protect the body against antigens (viruses, bacteria, etc. ) that invade the body.

Main functions • to collect and return interstitial fluid, including plasma protein to the blood, and thus help maintain fluid balance • to defend the body against disease by producing lymphocytes • to absorb lipids from the intestine and transport them to the blood.

Lymph organs • include the bone marrow, lymph nodes, spleen, and thymus. • Precursor cells in the bone marrow produce lymphocytes. • B-lymphocytes (B-cells) mature in the bone marrow. • T-lymphocytes (T-cells) mature in the thymus gland.

Lymph organs • Besides providing a home for lymphocytes (Bcells and T-cells), the ducts of the lymphatic system provide transportation for proteins, fats, and other substances in a medium called lymph.

BONE MARROW • site of maturation of B lymphocytes • Many pre-B cells die in the bone marrow • B cells that survive this selection process leave the bone marrow through efferent blood vessels.

THYMUS • Flat, bilobed organ situated above the heart and below the thyroid gland • Each lobe is surrounded by a capsule and is divided into lobules • Each lobule is organized into two compartments: the cortex (outer compartment) the medulla (inner compartment)

THYMUS • In the cortex, the network is densely packed with thymocytes (developing T cells) • In the cortex, the network is densely packed with thymocytes. Cells are less dense in medulla. • largest relative size at birth • largest actual size is at puberty • Following puberty the thymus begins to shrink. In elderly individuals it is usually less than 3 grams in weight. • The site of T-cell maturation

Spleen • Creates lymphocytes for the destruction and recycling of old red-blood cells. The spleen is also a blood reservoir. • It supplies the body with blood in emergencies such as a bad cut. The spleen is also the location where white blood cells trap organisms.

Spleen • The spleen is shaped like a loose fist and is tucked under the left side of the diaphragm. • The average weight of an adult spleen is 0. 44 lbs. During and after digestion, the size of the spleen increases. Infection of malaria or mono can also cause the spleen to increase in size.

Lymph nodes • Human lymph nodes are bean-shaped and range in size from a few millimeters to about 1 -2 cm in their normal state. • They may become enlarged due to a tumor or infection. White blood cells are located within honeycomb structures of the lymph nodes. • Lymph nodes are enlarged when the body is infected due to enhanced production of some cells and division of activated T and B cells. • In some cases they may feel enlarged due to past infections; although one may be healthy, one may still feel them residually enlarged.

Tonsils • Tonsils are clusters of lymphatic tissue just under the mucous membranes that line the nose, mouth, and throat (pharynx). • Lymphocytes and macrophages in the tonsils provide protection against harmful substances and pathogens that may enter the body through the nose or mouth.

Lymph • means clear water and it is basically the fluid and protein that has been squeezed out of the blood (i. e. blood plasma). • The lymph is drained from the tissue in microscopic blind-ended vessels called lymph capillaries.

Lymph • These lymph capillaries are very permeable, and because they are not pressurized the lymph fluid can drain easily from the tissue into the lymph capillaries. • As with the blood network the lymph vessels form a network throughout the body, unlike the blood the lymph system is a one-way street draining lymph from the tissue and returning it to the blood.

Lymphatic Capillaries • begin in the tissue spaces as blindended 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 Vessels • lymph capillaries merge to form lymphatic vessels. Small lymphatic vessels join to form larger tributaries, called lymphatic trunks, which drain large regions. Lymphatic trunks merge until the lymph enters the two lymphatic ducts. The right lymphatic duct drains lymph from the upper right quadrant of the body. The thoracic duct drains all the rest.

Lymph Vessels • 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.

Your assignment • Chapter 14 sections 1 -6 –Check your recall pp. 369, 370, 371, 373 –Review exercises p 389 • Q. 1, 3, 4, 5, 6, 7 This will be checked for a grade.