The Lymphatic System Vessels Nodes and Other Lymphoid

The Lymphatic System: Vessels, Nodes, and Other Lymphoid Organs Pages 398 -403

Components and Functions � Two parts: 1. Lymphatic vessels 2. Lymphoid tissues and organs � Functions: ◦ Transports escaped fluids back to the blood ◦ Body defense and resistance to disease © 2015 Pearson Education, Inc.

Lymph and the Lymphatic Vessels � 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) © 2015 Pearson Education, Inc.

Figure 12. 1 Relationship of lymphatic vessels to blood vessels. Venous system Arterial system Heart Lymph duct Lymph trunk Lymph node Lymphatic system Lymphatic collecting vessels, with valves Lymph capillary Tissue fluid (becomes lymph) Blood capillaries Loose connective tissue around capillaries

Figure 12. 2 a. BLACK ARROWS INDICATE DIRECTION OF FLUID MOVEMENT Tissue fluid Tissue cell Lymphatic capillary Blood capillaries (a) Arteriole Venule

Figure 12. 2 b Special structural features of lymphatic capillaries. Fibroblast in loose connective tissue Endothelial cell (b) Flaplike minivalve Filaments anchored to connective tissue

Lymphatic Collecting Vessels � 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 © 2015 Pearson Education, Inc.

Figure 12. 3 Distribution of lymphatic vessels and lymph nodes. Regional lymph nodes: Entrance of right lymphatic duct into right subclavian vein Cervical nodes Axillary nodes Internal jugular vein Thoracic duct entry into left subclavian vein Thoracic duct Aorta Spleen Inguinal nodes Cisterna chyli (receives lymph drainage from digestive organs) Lymphatics KEY: Drained by the right lymphatic duct Drained by the thoracic duct

Structure of Lymphatic Vessels �similar to veins of the cardiovascular system �Lymph transported is aided by: ◦ ◦ ◦ ◦ (have the same tunics: intima, media, externa) Thin endothelial walls Valves in larger vessels Low-pressure, pumpless system Milking action of skeletal muscles Pulsations of nearby arteries Pressure changes in thorax during breathing Smooth muscle in walls of vessels © 2015 Pearson Education, Inc.

Lymph Nodes � 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 © 2015 Pearson Education, Inc.

Figure 12. 4 Structure of a lymph node. Afferent lymphatic vessels Germinal center in follicle Capsule Subcapsular sinus Trabecula Afferent lymphatic vessels Cortex Follicle Efferent lymphatic vessels Hilum Medullary sinus Medullary cord

Other Lymphoid Organs � Several other organs contribute to lymphatic function: ◦ ◦ Spleen Thymus Tonsils Peyer’s patches © 2015 Pearson Education, Inc.

Figure 12. 5 Lymphoid organs. Tonsils (in pharyngeal region) Thymus (in thorax; most active during youth) Spleen (curves around left side of stomach) Peyer’s patches (in intestine) Appendix

Spleen � 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 © 2015 Pearson Education, Inc.

Thymus Gland � 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 © 2015 Pearson Education, Inc.

Tonsils � 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 © 2015 Pearson Education, Inc.

Peyer’s Patches � 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 © 2015 Pearson Education, Inc.

Mucosa-Associated Lymphoid Tissue (MALT) � Includes: ◦ Peyer’s patches ◦ Tonsils ◦ Other small accumulations of lymphoid tissue � Acts as a sentinel to protect respiratory and digestive tracts © 2015 Pearson Education, Inc.