Biology Chapter 13: Lymphatic System Flashcards

Formation of Lymph

• Lymph is formed when blood plasma filters out of capillaries into tissue spaces due to heart-generated pressure, creating interstitial fluid.
• Most interstitial fluid returns to the bloodstream via capillary membranes, while excess fluid enters the lymphatic system.

Components of the Lymphatic System

• Main parts include Lymph, Lymphatic Vessels, Lymph Nodes, Thymus, and Spleen.

Functions of Lymphatic System Organs

• Filters body fluids to remove harmful particles, preventing damage to other body parts.

Lymphatic Capillaries

• Facilitate the exit of excess tissue fluid and larger substances, including dissolved proteins, from tissue spaces.

Comparison of Lymphatic and Blood Capillaries

• Both are microscopic and consist of a single layer of simple squamous epithelium.
• Blood capillaries have tightly fitting endothelium cells preventing large molecules from entering/exiting, whereas lymphatic capillaries are loose and porous, allowing larger molecules to pass.

Movement of Lymph

• Lymph moves slowly through vessels, following a one-way flow from lymphatic capillaries to venules, then veins.
• Ultimately, lymph empty into the right lymphatic duct or thoracic duct, and then into subclavian veins.

Thoracic Duct

• The largest lymphatic vessel in the body, draining lymph from three-quarters of the body.

Right Lymphatic Duct

• Drains lymph from the right upper extremity, right head, neck, and upper torso.

Cisterna Chyli

• Acts as a temporary holding area for lymph.

Lacteals

• Lymphatic capillaries located in the small intestine that transport fats obtained from food to the bloodstream.

Lymph Nodes

• Act as filters for lymph with varying sizes; they are clustered, serving crucial roles in defense and white blood cell formation.

Lymphoid Organs

• Include lymph nodes, tonsils, thymus, and spleen, all containing lymphoid tissue rich in lymphocytes and related cells.

Biological Filtration

• Lymph nodes filter bacteria and prevent local infections; clustered nodes enhance filtration efficiency.

Afferent and Efferent Lymphatic Vessels

• Afferent vessels (4 per node) deliver lymph to nodes, while a single efferent vessel carries lymph away from the node.

Lymphatic Response to Cancer

• Axillary lymph nodes may be removed if they contain cancer cells filtered from lymph drained from the breast, facilitating spread through the lymphatic system.

Thymus Overview

• A small lymphoid organ located in the mediastinum, largest at puberty (35-40 grams).
• Source of T lymphocytes before birth; T cells mature here before circulation to other lymphoid organs.
• Functions are mostly completed by early childhood to puberty.

Involution of Thymus

• The thymus replaces lymphocytes with fat and connective tissue, becoming half its maximum size by age 60 and virtually disappearing by age 80.

Tonsils

• Located in a protective ring under mucous membranes of the mouth and throat, acting as a first line of defense against bacteria that may invade surrounding tissues.

Palatine Tonsils

• Positioned at each side of the throat, serving a protective role against pathogens.