HUMB1000 Lecture Notes - Lecture 10: Lymphatic Vessel, Loose Connective Tissue, Thoracic Duct
12 Jun 2018
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The Lymphatic System
Functions of the Lymphatic System
❖ Fluid balance
Excess interstitial fluid enters lymphatic capillaries and becomes lymph (30L from capillaries
into interstitial fluid, 27L return leaving 3L, called lymph).
❖ Fat absorption
Absorption of fat and other substances from digestive tract via lacteals.
❖ Defence
Lymphatic system – fights infection. Microorganisms and other foreign substances are
filtered from lymph by lymph nodes and from blood by spleen.
Anatomy of the Lymphatic System
❖ Lymph
❖ Lymphatic vessels
❖ Lymphatic tissue
❖ Lymphatic nodules
❖ Lymph nodes
❖ Tonsils
❖ Spleen
❖ Thymus
Lymph
❖ Water plus solutes from two sources
o Plasma: ions, nutrients, gases, some proteins
o Cells: hormones, enzymes, waste products
❖ Returns to circulatory system via veins; essential for fluid
❖ balance
Lymphatic Vessels
❖ Carry lymph away from tissues
❖ Lymphatic capillaries
o More permeable than blood capillaries
o Epithelium functions as series of one-way valves
o Found in all parts of the body except nervous system, bone and avascular
tissues (without blood vessels - cornea, epidermis).
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Lymphatic Vessels
❖ Lymphatic capillaries join to form lymphatic vessels
❖ Lymphatic vessels: have valves that ensure one-way flow (beaded appearance)
❖ Lymph nodes: distributed along vessels and filter lymph
❖ Lymphatic trunks: jugular, subclavian, bronchomediastinal, intestinal, lumbar
❖ Lymphatic ducts: drain tissues of body and move lymph into major veins
o Right lymphatic duct: drains right side of head, right-upper limb, right thorax
o Thoracic duct: drains remainder of the body
Lymphatic Tissue and Organs
❖ Lymphatic organs contain lymphatic tissue (lymphocytes, macrophages, dendritic
cells)
❖ Lymphocytes: B & T cells - white blood cells derived from bone marrow.
❖ Fine network of reticular fibers. Produced by reticular cells. Act as filter to trap
microorganisms and other particles
❖ May be encapsulated (in a CT capsule)
- Encapsulated- lymph nodes, spleen, thymus
- Non-encapsulated- mucosa-associated lymphoid tissue (MALT).
Found beneath epithelium as first line of attack against invaders.
Diffuse Lymphatic Tissue & Lymphatic Nodules
❖ Diffuse lymphatic tissue: dispersed lymphocytes, macrophages; blends with other
tissues.
❖ Lymphatic nodules: denser aggregations. Numerous in loose connective tissue of
digestie Peer’s pathes, respirator, uriar, reprodutie sstes.
Lymph Nodes
❖ Only structures to filter lymph
❖ Substances removed by phagocytosis or stimulate
lymphocytes to proliferate.
o Cancer cells often migrate to lymph nodes, are
trapped there, and proliferate. Can move from
lymphatic system to circulatory system
spreading cancer through the body.
❖ Afferent and efferent vessels
❖ Organized into cortex and medulla with dense
connective tissue capsule surrounding.
Tonsils
❖ Large groups of lymphoid tissue in nasopharynx and oral cavity
❖ Provide protection against bacteria and other harmful material.
❖ Palatine (tonsils)
❖ Pharyngeal (adenoids)
❖ Lingual
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Spleen
❖ Red pulp associated with veins (75%) – Fibrous network of macrophages and RBCs.
❖ White pulp associated with arteries (25%) – lymphatic tissue.
❖ Functions:
o Monitors blood, detects and responds to foreign antigens.
o Destroys defective red blood cells
o Regulates blood volume
o Limited reserve of RBC
❖ Can be ruptured in traumatic abdominal injuries.
❖ Splenectomy.
Thymus
❖ Located in superior mediastinum.
❖ Cortex (numerous lymphocytes) and medulla (fewer lymphocytes)
❖ Site of maturation of T cells: many T cells produced here, but most degenerate.
❖ Those that remain can react to foreign substances.
❖ Endocrine functions.
Comparative Histology
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Document Summary
Excess interstitial fluid enters lymphatic capillaries and becomes lymph (30l from capillaries into interstitial fluid, 27l return leaving 3l, called lymph). Absorption of fat and other substances from digestive tract via lacteals. Microorganisms and other foreign substances are filtered from lymph by lymph nodes and from blood by spleen. Water plus solutes from two sources: plasma: ions, nutrients, gases, some proteins, cells: hormones, enzymes, waste products. Returns to circulatory system via veins; essential for fluid. Lymphatic capillaries: more permeable than blood capillaries, epithelium functions as series of one-way valves, found in all parts of the body except nervous system, bone and avascular tissues (without blood vessels - cornea, epidermis). Lymphatic capillaries join to form lymphatic vessels. Lymphatic vessels: have valves that ensure one-way flow (beaded appearance) Lymph nodes: distributed along vessels and filter lymph. Lymphatic trunks: jugular, subclavian, bronchomediastinal, intestinal, lumbar.
