Chapter 20 Anatomy and 21 Physiology II
Objective 1 Describe the lymphatic system. A meandering network of lymphatic vessels and various lymphoid organs scattered throughout the body The lymphatic system consists of 2 parts – Lymphatic vessels that transport fluids that have escaped the blood system back to the blood – Lymphatic organs house phagocytic cells and lymphocytes which function in body defense and resistance.
The lymphatic system is twice the size of the circulatory system. – this means there is twice the amount of lymph fluid and blood. Acts as a collecting duct for excess fluids and as a filtering system to screen out foreign bodies. Objective 1
Lymph – complicated network of tubes spaced throughout the body which drain fluid from surrounding tissue and back to bloodstream. Lymph fluid is filtered through the – Spleen – Thymus – Lymph Nodes Objective 1
Objective 2 Describe lymphatic vessels and note the differences between lymphatic vessels and arteries and veins. Define circulation pattern of lymphatic fluid. Lymphatic vessels form a one-way network capillaries collecting vessels trunks ducts fluid flows toward the heart. The right lymphatic duct and the thoracic duct empty lymph fluid into the blood vascular system in the neck.
Objective 2 The lymphatic capillaries are blind-ended. – The edges of their endothelial cells overlap, forming flap-like minivalves. – Collagen filaments anchor the endothelial cells to surrounding structures so that an increase in interstitial fluid volume opens the minivalves. – When the pressure is greater inside the capillary, the minivalve closes, preventing fluid from leaking back out.
Objective 2 Highly specialized lymphatic capillaries called lacteals are present in the villi of the intestine where they play a role in absorbing digested fats. Lymphatic vessels are low-pressure vessels that use the same mechanisms as veins to return the lymph to the circulatory system.
Objective 3 Describe the structure of lymph nodes with respect to cells located in the cortex and medulla. At intervals along the lymphatic vessels, lymph flows through the lymph nodes. – Each lymph node has a fibrous capsule, a cortex • containing lymphocytes for the immune response – plus a medulla • containing mostly macrophages which engulf bacteria, viruses, and foreign material and may initiate an immune response
Dendritic cells capture antigens and being them back to the lymph nodes. Reticular cells are similar to fibroblasts and produce the reticular fiber network of the lymph node Objective 3
Afferent = flow into Efferent = flow out
Objective 4 Identify other lymphoid organs and their functions. Spleen – site for – lymphocyte proliferation – destroys aged red blood cells – stores and releases the breakdown products of hemoglobin – site of rbc production in the fetus – stores and releases blood in times of demand – acts as a lymph node for the blood
Objective 4 Thymus – During youth it functions in T cell development.
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