A&p Ii - Lymphatic System

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Lymphatic System

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Consists of a fluid called lymph, flowing in lymphatic vessels that empty into lymph nodes, plus spleen, tonsils, and thymus gland. The function of it is to return protein-containing fluid from the tissue to the blood. Transports chylomicrons, water-soluble lipoprotein droplets, from the intestines into the blood and the immune system. Immune function includes production of lymphocytes, phagocytosis of bacteria, and secretion of antibodies.

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lymph

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Very much like blood plasma except has less protein and many more WBCs especially lymphocytes. Normally clear or slightly straw-colored, may appear milky white when absorbing a high-fat meal.

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Lymphatic vessels

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originate as lymphatic capillaries, which are mixed in among the blood capillaries. Larger diameters, thinner walls, more permeable and originate as blind-ended tubes. Lymph seeps into the tubes and then tubes start to converge into larger tubes or vessels known as lymphatics. They run along side arteries and veins, and resemble veins except have thinner walls than veins and many more valves. All the lymph in the body will eventually empty into 1 of 2 main channels or pathways:
1. the thoracic duct (most important)
2. right lymphatic duct.

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Cisterna chili

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the enlarged proximal portion of the Thoracic Duct.—receives all of lymph from below the diaphragm. It is near the beginning of the thoracic duct. Near the celiac trunk. As go through upper body, thoracic duct receives lymph from all upper body on left side, and empties lymph into the L subclavian vein.

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right lymphatic duct

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gets all lymph from right upper body and empties into the right subclavian vein.
The various lymphatics drain through lymph nodes at regular intervals.

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Lymph nodes

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are all over. They are oval or bean shaped and indented on one side with an outer fibrous capsule with the connective tissue of the fibrous capsule extending into these to form lymph sinuses. Lymph sinuses contain a large number of microphages and a large number of lymphocytes. Especially find B cells, which secrete antibodies and helper T cells, which help the B cell release antibody.

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afferent lymphatics

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emptying into each node. The lymph trickles through the sinuses and drains out of 1 or 2 efferent lymphatics. So if you have a bacterial infection, bacteria drains into the lymph and into a node where macrophages phagocytize the bacteria. the B cells secrete antibodies into lymph to attack the bacteria. viruses will slip right through.

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efferent lymphatics

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Exit from the lymph node.

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locations of lymph nodes

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They are in high concentration in the cervical, axillary, and inguinal region—places where the extremities meet the trunk. May swell as a result of a bacterial infection.

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What causes lymph to flow?

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It is the same 2 things that cause low pressure venous blood to return to the heart—muscular pump and respiratory pump. Circulate 3-4 liters per day. To fight infection, slow down lymph flow—rest.

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Spleen

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Found just under the diaphragm on the left side. Large and spongy. Has its own artery—splenic off celiac trunk. Is built kind of like a big lymph node. Has lots of macrophages and lymphocytes. Blood goes in and it does for blood what lymph node does for lymph. It also phagocytizes old RBCs. A person can survive without one. People without one have higher incidence of infection from encapsulated bacteria (e.g. pneumonia). Can act as an emergency blood reservoir. For ex., if a person suffers a hemorrhage, it can contract and send out blood.

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Tonsils

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3 main sets—pharyngeal, palatine, lingual. These locations are key. They are largest in childhood and adolescence.

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Thymus gland

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Bilobed organ in the mediastinum. Often on top of heart. Largest in childhood and adolescence and then degenerates. By the time a person is in the mid 30’s, hard to find the thymus. Role of thymus—to produce T cells—a type of lymphocyte. But humans cont. to make T cells without the thymus—just don’t know where yet.