Lymphatic system - Human Anatomy and Physiology B. Pharma 1st Semester

Lymphatic system

Objectives

At the end of this lecture, student will be able to

• List the components of the lymphatic system

• Explain major functions of the lymphatic system

• Describe the organization of lymphatic vessels

• Explain the formation and flow of lymph

• Differentiate the primary and secondary lymphatic organs and tissues

• Explain the anatomy of thymus and lymph node

• Describe the anatomy of spleen

• List the lymphatic nodules

• Discuss the disorders of Lymphatic system

Content

• Components of lymphatic system

• Lymphatic ducts and trunks

• Formation and flow of lymph

• Primary and secondry lymphatic organs

• Spleen

• Lymphatic nodule

• Disorders

Lymphatic System

• Consists of

– A fluid called lymph

– Vessels - lymphatic vessels

• Lymphatic tissue

– Specialized form of reticular connective tissue

– Contains large numbers of lymphocytes

– B cells and T cells (Adaptive immunity)

Blood Plasma to Lymph

Difference between interstitial fluid and lymph is location

Functions of Lymphatic System

• Removal of excess fluids

– Lymphatic vessels drain excess interstitial fluid from tissue spaces

• Transports dietary lipids

– Transport lipids and lipid-soluble vitamins (A, D, E, and K) absorbed by GIT

• Carries out immune responses

– Initiates high specified responses

– Directed against particular microbes or abnormal cells

Lymphatic vessels

• Lymphatic Capillaries

– Located in the spaces between cells

– Closed at one end

– Unite to form larger lymphatic vessels

– Resemble veins in structure

– Thinner walls and more valves

• At intervals, lymph flows through lymph nodes

Tissues that lack lymphatic capillaries

• Include avascular tissues:

– Cartilage

– Epidermis

– Cornea of the eye

• CNS

• Portions of the spleen

• Portions of Red bone marrow

Details of a Lymphatic Capillary

Lacteals

• In small intestine, specialized lymphatic capillaries - lacteals

• Carry dietary lipids into lymphatic vessels and ultimately into the blood

• Presence of lipids causes the lymph draining from the small intestine to appear creamy white – Chyle

• Elsewhere, lymph is a clear, pale-yellow fluid

Details of Lymphatic Capillary

Lymph Trunks and Ducts

Lymph passes from lymphatic capillaries into lymphatic vessels, then through lymph nodes in a particular region of the body  

Unite to form lymph trunks

The Principal Trunks

• Lumbar

• Intestinal

• bronchomediastinal

• Subclavian

• Jugular trunks

Lymph Trunks

• The lumbar trunks

– Drain lymph from the lower limbs, viscera of the pelvis

– Kidneys, adrenal gland abdominal wall

• The intestinal trunk

– drains lymph from the stomach, intestines

– Pancreas, spleen, and part of the liver

• The bronchomediastinal

– Trunks drain lymph from the thoracic wall, Lung, heart

• The subclavian trunks - Drain the upper limbs

• The jugular trunks - Drain the head and neck

Lymph Ducts

• Lymph passes from lymph trunks into two main channels:

– The thoracic duct

– The right lymphatic duct

The Right Lymphatic Duct

• Receives lymph from the upper right side of the body

The Thoracic Duct

• Main duct for the return of lymph to blood

Thoracic Duct

• Begins as a dilation called the cisterna chyli

• Receives lymph from the left side of the head, neck, and chest, the left upper limb, and the entire body inferior to the ribs

• Drains lymph into venous blood at the junction of the left internal jugular and left subclavian veins

The Right Lymphatic Duct

• Receives

– Lymph from the upper right side of the body

• Drains

– Into venous blood at the junction of the right internal jugular and right subclavian veins

Formation and Flow of Lymph

Blood plasma filter freely through the capillary walls

From interstitial fluid- small amount of proteins (reabsorbed)

Excess filtered fluid— about 3 l/day—drains into lymphatic vessels – Lymph

Proteins that do leave blood plasma cannot return to the blood by diffusion

Thus, important function of lymphatic vessels is to return the lost plasma proteins to the bloodstream

The sequence of fluid flow

Blood capillaries

Interstitial spaces

Lymphatic capillaries

Lymphatic vessels

Lymphatic ducts

Junction of the internal jugular and subclavian veins (blood)

Flow of Lymph – Skeletel Muscle Pump

• The milking action compresses lymphatic vessels (as well as veins)

• Forces lymph toward the junction of the internal jugular and subclavian veins

Flow of Lymph- Respiratory Pump

• During inhalation - Lymph flows from the abdominal region to thoracic region

• During exhalation - The valves

Lymphatic Organs and Tissues

Primary lymphatic organs

• Stem cells divide and become immuno competent - capable of mounting an immune response

• Organs

– Red bone marrow

– Thymus

The secondary lymphatic organs and tissues

• The sites where most immune responses occur

• Lymph nodes

• Spleen

• Lymphatic nodules (follicles)

Red Bone Marrow

• Pluripotent stem cells in red bone marrow give rise to mature:

• immuno competent B cells

• Pre-T cells

Thymus

Anatomy

• Bilobed organ located in the mediastinum

An enveloping layer of connective tissue holds the two lobes closely together

• Trabeculae

Extensions of the capsule

– Penetrate inward and divide each lobe into lobules

Each thymic lobule consists of:

• The cortex

– Large numbers of T cells

• The medulla

– Widely scattered, more mature T cells, epithelial cells, dendritic cells, and macrophages

Thymus - Cells

• Dendritic cells

– Assist the maturation process of T cells

• Epithelial cells

– Serve as a frameworks

– Help educate the pre-T cells in positive selection

– Produce thymic hormones - aid in the maturation of T cells.

• Macrophages

– Help clear out the debris of dead and dying cells

The surviving T cells enter the medulla

Thymic Hassall’s Corpuscles

• Some of the epithelial cells become arranged into concentric layers of flat cells

• Serve as sites of T cell death in the medulla

• Degenerate an d become filled with keratohyalin granules and keratin - Clusters - Thymic Hassall’s Corpuscles

Fate of T Cells

• T cells that leave the thymus via the blood

• Migrate to:

– Lymph nodes

– Spleen

– Other lymphatic tissues

• Colonize parts of those organs and tissues

Lymph Nodes

• Located along lymphatic vessels - 600 bean-shaped lymph nodes

• Scattered throughout the body superficial and deep (in groups)

• Large groups of lymph nodes - Near the mammary glands and in the axillae and groin

• Small, round or oval structures located along the pathways of lymph vessels

Lymph Node - Anatomy

• Lymph nodes are 1–25 mm long

• Covered by a capsule of dense connective tissue

• Stroma

 – The capsule, trabeculae, reticular fibers, and fibroblasts

• Supporting network:

– Internal to the capsule

– Reticular fibers, and fibroblasts

• Trabeculae:

– Divide the node into compartments & provide support

– Provide a route for blood vessels into the interior of a node

The Parenchyma (Functioning Part)

 Superficial cortex

 Deep medulla

Lymph Nodes Function

• As a type of filter

• Reticular fibers

– Foreign substances are trapped the reticular fibers within the sinuses of the lymph node

• Macrophages

– Destroy foreign substances by phagocytosis

• Lymphocytes

– Destroy by immune responses

Spleen

• Oval shaped

• Largest single mass of lymphatic tissue in the body

• Located in the left hypochondriacs region

The superior surface

• Smooth and convex

• Conforms to the concave surface of the diaphragm

Visceral surface

• Neighboring organs make indentations

Spleen - Anatomy

• A capsule - dense connective tissue surrounds the spleen

• Covered by a serous membrane - the visceral peritoneum

• Trabeculae extend inward from the capsule.

• Stroma: The capsule, trabeculae, reticular fibers & fibroblasts

Internal Structure of Spleen

Parenchyma:

2 types of tissue white pulp and red pulp

White Pulp

• Lymphatic tissue – consisting mostly of lymphocytes and macrophages

• Arranged around central arteries

• Blood flow – to the splenic artery enters the central arteries

Red Pulp

• Consists of:

– Blood-filled venous sinuses

– Cords of splenic tissue called splenic (Billroth’s) cords

– Veins are closely associated with the red pulp

• Splenic cords Consist of:

– Red blood cells

– Macrophages

– Lymphocytes

– Plasma cells

– Granulocytes

Internal Structure of Spleen

• Within the white pulp

– B cells and T cells carry out immune responses

– Macrophages destroy blood-borne pathogens by phagocytosis

• Within the red pulp

– Macrophages: Removed raptured, worn out, or defective blood cells and platelets

– Storage of platelets

– Production of blood cells (hemopoiesis) during fetal life

Lymphatic Nodules

• Egg-shaped masses of lymphatic tissue

• Not surrounded by a capsule.

• Scattered throughout the lamina propria of mucous membranes lining:

– GIT

– Urinary and reproductive tracts

– Respiratory airways

• MALT - Mucosa-associated lymphatic tissue

• Many lymphatic nodules are small and solitary

• Some lymphatic nodules occur in multiple large aggregations in specific parts of the body

– Tonsils in the pharyngeal region strategically positioned to participate in immune responses

– The aggregated lymphatic follicles (Peyer’s patches) in the ileum

Nonspecific and Specific Defenses

• Immunity involves nonspecific and specific defenses

Nonspecific defenses

• Include barriers to entry, the inflammatory reaction, NK cells & protective proteins

Specific defenses

• Requires B lymphocytes and T lymphocytes

• B cells undergo colonal selection with production of plasma cells

• Memory B cells - Combine with a specific Ag

T cells

• Responsible for cell mediated immunity

• The two main types: Cytotoxic T cells & helper T cells

• Cytotoxic T cells – Kill virus-infected or cancer cells on contact

• Helper T cells – Produce cytokines and stimulate other immune cells

Induced Immunity

• Immunity can be induced in various ways

• Vaccines are available to induce long-lasting, active immunity

• Antibodies - Temporary, passive immunity

Antigen- Presenting Cell

• For a T cell to recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC)

• Thereafter, the activated T cell undergoes colonal expansion

• Then most of the activated T cells undergo apoptosis

•   A few cells remain as memory T cells

Summary

• The lymphatic network begins with microscopic vessels called lymphatic capillaries

• Lymphatic tissue is specialized form of reticular connective tissue, contains large numbers of lymphocytes

• Specialized lymphatic capillaries in small intestine are known as lacteals

• Lymph passes from lymph trunks into two main channels:

– The thoracic duct

– The right lymphatic duct

• Lymphatic organs are divided into primary and secondary organs

• Primary organs include red bone marrow and thymus

• Secondary lymphatic organs and tissues Lymph nodes, Spleen, Lymphatic nodules

• B-lymphocytes mature in the Bone marrow

• T-lymphocytes mature in the Thymus

• Lymph nodes are small, round or oval structures located along the pathways of lymph vessels