Lymphatic21

Lymphatic System

Overview

• The lymphatic system comprises semi-independent parts that include:

  • Lymphatic vessels: Transport lymph throughout the body.

  • Lymphoid tissues and organs: Involved in immune responses.

  • Lymph: Once interstitial fluid (IF) enters lymphatic vessels, it is referred to as lymph.

• The primary function is to return interstitial fluid and leaked plasma proteins back to the circulatory system.

Objectives

• Describe the major functions of the lymphatic system and its organization.

• Understand the cellular and histological components of the lymphatic system.

• Discuss homeostatic imbalances related to the lymphatic system and immunity.

Lymphatic Anatomy

Key Components

• Lymphatic Vessels: One-way vessels that carry lymph to the heart, including:

  • Microscopic capillaries

  • Collecting vessels

  • Trunks and ducts

• Primary Lymphatic Structures:

  • Thymus

  • Red bone marrow

• Secondary Lymphatic Structures:

  • Tonsils

  • Lymph nodes (cervical, axillary, inguinal)

  • Spleen

  • MALT (mucosa-associated lymphatic tissue) in the small intestine

Lymphatic Flow

• The flow of lymph is controlled by:

  • The pulsations of nearby arteries.

  • Contractions of the smooth muscle in lymphatic vessels.

  • The movement of surrounding tissues that aid in lymph propulsion.

Lymphatic Capillaries

Function and Structure

• Lymphatic capillaries resemble blood capillaries but are highly permeable due to overlapping endothelial cell edges, which allow the intake of interstitial fluid while preventing its escape.

• Mini-Valves: One-way gates that open to allow fluid entry and close to prevent backflow, maintained by collagen filaments.

Lymph Transport

• Lymph vessels operate under a low-pressure environment without a dedicated pumping organ.

• Approximately 3 liters of lymph are collected daily and returned to the bloodstream via the right lymphatic duct and thoracic duct.

Factors Influencing Lymph Flow

• Contractions of smooth muscle in lymphatic walls.

• Pulsations from adjacent arteries.

• External pressure from surrounding structures contributes to the fluid's movement.

Functions of the Lymphatic System

• Returns excess interstitial fluid and leaked proteins to the bloodstream.

• Transports absorbed fats from the intestines via lacteals.

• Serves as an immunity highway, providing checkpoints for foreign invaders within lymph.

Lymphatic Cells

Lymphocytes

• T Cells: Manage immune response and target foreign invaders.

• B Cells: Produce plasma cells that secrete antibodies to neutralize antigens.

• Phagocytes (Macrophages): Large cells that engulf and digest cellular debris and pathogens.

Lymphoid Tissue and Organs

Primary Structures

• Red Bone Marrow: Production of lymphocytes; site of B-cell maturation.

• Thymus: Maturation of T-lymphocytes, variation in size across age groups.

Secondary Structures

• Lymph nodes:

  • Filter lymph, removing pathogens and debris.

  • Activate immune responses by monitoring for antigens.

• Spleen: Largest lymphatic organ, involved in immune surveillance, lymphocyte proliferation, and blood cleansing.

• MALT: Includes tonsils and Peyer's patches, protects mucosal surfaces from pathogens.

Clinical View: Lymphedema

• Accumulation of interstitial fluid due to blockages in lymphatic drainage can lead to swelling, pain, and complications in wound healing.

• Treatments include compression, exercise, and sometimes surgery.

Developmental Aspects

• Lymphatic vessels form from lymph sacs budding from developing veins by the fifth week of embryonic development.

• Immunity procurement is poor at birth, but exposure to antigens helps develop it.

Summary

• Lymphatic system comprises vessels, tissues, organs, and lymph. It functions primarily to return fluid and proteins to blood circulation and plays a vital role in immunological defense.