BIOL 2228_Lymphatics_2022

Chapter 21: Lymphatics

21.1 Lymph and Lymph Vessels

Learning Objectives


  • Describe lymph and its contents.Lymph is a clear fluid that circulates through the lymphatic system, formed primarily from interstitial fluid. It contains water, solutes, proteins, cell debris, and pathogens, playing a crucial role in immune function by transporting lymphocytes and other immune cells throughout the body.


  • Discuss the location and anatomic structure of lymphatic capillaries.Lymphatic capillaries are small, closed-ended vessels located throughout body tissues. They have a unique structure characterized by overlapping endothelial cells, which allow interstitial fluid to enter easily but prevent it from escaping back out. These caps are absent in avascular tissues such as cartilage.


  • Explain how fluid enters lymphatic capillaries.Fluid enters lymphatic capillaries due to hydrostatic pressure exerted by interstitial fluid. The pressure gradient along with the unique structure of the capillaries facilitates this absorption process, allowing for efficient collection of excess fluid from tissues.


  • Explain the mechanisms that move lymph through lymphatic vessels, trunks, and ducts.Lymph is propelled through the lymphatic system through various mechanisms, including skeletal muscle contractions that compress lymphatic vessels, respiratory pumps that create pressure changes during breathing, and the rhythmic contraction of smooth muscle in larger lymphatic vessels, which collectively facilitate the one-way flow of lymph.


  • Name the five types of lymphatic trunks and the regions they drain.The five types of lymphatic trunks include:

    1. Jugular trunks: Drain lymph from the head and neck.

    2. Subclavian trunks: Drain lymph from the upper limbs and breasts.

    3. Bronchomediastinal trunks: Drain lymph from the thoracic region.

    4. Intestinal trunks: Drain lymph from abdominal organs.

    5. Lumbar trunks: Drain lymph from the lower limbs and pelvic organs.


  • Describe drainage regions of the right lymphatic duct and thoracic duct.The right lymphatic duct drains lymph from the upper right quadrant of the body, including the right arm, right side of the head and neck, and the right thorax. In contrast, the thoracic duct is the largest lymphatic vessel and drains lymph from the majority of the body, including both lower limbs, left side of the body, and organs in the abdomen, ultimately emptying into the left subclavian vein.

Functions of the Lymphatic System

  • Transport and house lymphocytes and immune cells.

  • Return excess fluid from body tissues to blood to maintain blood volume.

Components of the Lymphatic System

  • Lymph vessels: Transport lymph.

  • Lymphatic tissues and organs: Include various structures involved in immunity.

  • Lymph: Fluid transported within lymph vessels, containing water, solutes, proteins, cell debris, and pathogens.

Structure of the Lymphatic System

Types of Lymphatic Structures

  • Primary lymphatic structures: Thymus and red bone marrow.

  • Secondary lymphatic structures: Lymph nodes and spleen.

21.1a Lymph and Lymphatic Capillaries

Characteristics of Lymph

  • Formed mainly from interstitial fluid that enters lymphatic capillaries.

  • Contains water, solutes, proteins, and occasionally cell debris or pathogens.

Lymphatic Capillaries

  • Structure: Small, closed-ended vessels absorbing interstitial fluid, absent in avascular tissues, and characterized by overlapping endothelial cells.

  • Absorption of lipids: Lacteals in the GI tract absorb lipid-soluble substances.

Movement of Lymph

  • Hydrostatic pressure of interstitial fluid pushes lymph into capillaries.

  • Anchoring filaments maintain vessel shape and prevent collapse.

  • Lymph moves through progressively larger vessels: capillaries ➔ vessels ➔ trunks ➔ ducts.

21.1b Lymphatic Vessels, Trunks, and Ducts

Lymphatic Capillaries

  • Contain valves preventing pooling and backflow.

  • Mechanisms of movement include:

    • Skeletal muscle contractions.

    • Respiratory pumps.

    • Pulsatile blood movement in nearby arteries.

    • Rhythmic contraction of smooth muscle in larger lymphatic vessels.

Lymphatic Trunks

  • Jugular trunks: Drain head and neck.

  • Subclavian trunks: Drain upper limbs and breasts.

  • Bronchomediastinal trunks: Drain the thorax.

  • Intestinal trunks: Drain abdominal structures.

  • Lumbar trunks: Drain lower limbs and pelvic organs.

Lymphatic Ducts

  • Right lymphatic duct: Drains the upper right quadrant of the body.

  • Thoracic duct: Largest lymphatic vessel, drains lymph from most of the body.

21.1c Clinical View: Metastasis

  • Cancerous cells can spread through the lymphatic system, establishing secondary tumors. For example, breast cancer may spread to lungs.

21.2 Overview of Lymphatic Tissue and Organs

Learning Objectives


  • Identify the two categories of lymphatic tissue and organs.The lymphatic system is divided into primary and secondary structures. Primary lymphatic structures, such as the red bone marrow and thymus, are involved in the production and maturation of lymphocytes. Secondary lymphatic structures include lymph nodes, spleen, tonsils, and mucosa-associated lymphatic tissue (MALT), which are involved in the immune response.

Primary vs. Secondary Lymphatic Structures

  • Primary: Includes red bone marrow and thymus (involved in formation and maturation of lymphocytes).

  • Secondary: Includes lymph nodes, spleen, tonsils, and MALT (mucosa-associated lymphatic tissue).

21.3 Primary Lymphatic Structures

Red Bone Marrow

  • Location: Found between trabeculae of spongy bone in flat bones and proximal ends of the limb bones.

  • Function: Site of hemopoiesis; produces T-lymphocytes and B-lymphocytes.

The Thymus

  • Located in the mediastinum, larger in children.

  • Involved in T-lymphocyte maturation and gradually replaced by fat tissue after puberty.

21.4 Secondary Lymphatic Structures

Structure of Lymph Nodes

  • Filter lymph and remove unwanted substances.

  • Common locations: cervical, axillary, and inguinal areas.

  • Comprised of outer cortex (with lymphatic nodules) and inner medulla (with medullary cords).

The Spleen

  • Largest lymphatic organ located in the left upper quadrant.

  • Functions include filtering blood, monitoring foreign materials, and removing defective erythrocytes.

Tonsils

  • Involved in immune surveillance of ingested and inhaled substances.

  • Types include pharyngeal, palatine, and lingual tonsils.

21.4 Clinical Views

  • Lymphedema: Accumulation of interstitial fluid due to lymphatic drainage blockage; may cause swelling and infection, severe cases can cause elephantiasis.

  • Lymphoma: Malignant neoplasm affecting lymphatic structures, symptoms may include non-tender enlarged lymph nodes and possible systemic symptoms like fever.