Pages 398-403

Two parts:1. Lymphatic vessels2. Lymphoid tissues and organs

Functions:◦ Transports escaped fluids back to the blood◦ Body defense and resistance to disease

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Lymph—excess tissue fluid and plasma proteins carried by lymphatic vessels◦ Also includes cell debris, bacteria, viruses

Lymphatic vessels◦ pick up lymph and return it to the blood

Lymph capillaries (smallest) absorb leaked fluid Contain minivalves to ensure one-way flow to heart

Stay closed when vessel pressure > interstitial fluid Remain open when vessel pressure < interstitial fluid

If fluids are not picked up, edema occurs (fluid accumulates in tissues and the area swells)

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Venoussystem

Arterialsystem

Lymphaticsystem

Heart

Lymph duct

Lymph trunk

Lymph node

Lymphaticcollectingvessels,with valves

Lymphcapillary

Tissue fluid(becomes

lymph)

Bloodcapillaries

Loose connectivetissue aroundcapillaries

(a)

Tissue fluid

Tissue cell

Lymphaticcapillary

Bloodcapillaries

Arteriole Venule

(b)

Endothelialcell

Fibroblast in looseconnective tissue Flaplike

minivalve

Filamentsanchored toconnectivetissue

Lymph is collected through a system of vessels that gets progressively larger

Two large ducts return fluid to circulatory veins near the heart◦ Right lymphatic duct

drains the lymph from the right arm and the right side of the head and thorax

◦ Thoracic duct drains lymph from rest of body

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Regionallymph nodes:

Cervicalnodes

Axillarynodes

Inguinalnodes

KEY:

Drained by the right lymphatic ductDrained by the thoracic duct

Entrance of rightlymphatic duct into rightsubclavian vein

Internal jugular vein

Thoracic ductentry into leftsubclavian vein

Thoracic duct

Aorta

Spleen

Cisterna chyli (receiveslymph drainage fromdigestive organs)

Lymphatics

similar to veins of the cardiovascular system◦ (have the same tunics: intima, media, externa)◦ Thin endothelial walls◦ Valves in larger vessels◦ Low-pressure, pumpless system

Lymph transported is aided by:◦ Milking action of skeletal muscles◦ Pulsations of nearby arteries◦ Pressure changes in thorax during breathing◦ Smooth muscle in walls of vessels

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About 500 nodes in the body◦ Large clusters in specific regions:

inguinal, axillary, cervical

Structure:◦ Surrounded by a dense connective tissue capsule◦ Compartmentalized: sinuses lined with endothelial cells◦ Outer cortex contains lymphocytes (B cells & T cells)◦ Inner medulla contains phagocytic macrophages

filter harmful materials before it is returned to the blood◦ Bacteria◦ Viruses◦ Cancer cells◦ Cell debris

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Afferentlymphaticvessels

Afferentlymphaticvessels

Germinalcenter infollicle

Efferentlymphaticvessels

Cortex

Follicle

Medullary cord

Medullary sinus

Hilum

Trabecula

Subcapsularsinus

Capsule

Several other organs contribute to lymphatic function:◦ Spleen◦ Thymus◦ Tonsils◦ Peyer’s patches

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Tonsils (inpharyngeal region)

Thymus (in thorax;most active duringyouth)

Spleen (curvesaround left side ofstomach)

Peyer’s patches(in intestine)

Appendix

left side of the abdomen, beneath diaphragm, around the stomach

Functions:◦ Filters pathogenic debris from blood◦ Destroys worn-out red blood cells

Iron is reused for hemoglobin mfr. Remainder is secreted in bile

Acts as a platelet reservoir Site of hematopoesis in the fetus

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Located low in the throat, just under the sternum

Function:◦ (at peak levels only during childhood)◦ Produces hormones (such as thymosin)

hormones cause T lymphocytes to gain immunocompetency

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masses of lymphoid tissue around the pharynx◦ Palatine tonsils are most often infected

Trap and remove bacteria/foreign materials Tonsillitis -caused by congestion with

bacteria

The ability of the tonsils to trap bacteria generates a wide variety of memory lymphocytes that protect throughout life

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Found in the wall of the small intestine and appendix

Resemble tonsils in structure Capture and destroy bacteria in the

intestine◦ Prevent bacteria from getting into blood here◦ Generate memory lymphocytes for long-term

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Includes:◦ Peyer’s patches◦ Tonsils◦ Other small accumulations of lymphoid tissue

Acts as a sentinel to protect respiratory and digestive tracts

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