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

Lymphatic system


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


• Components of lymphatic

• Lymphatic ducts and trunks

• Formation and flow of lymph

• Primary and secondry lymphatic organs

• Spleen

• Lymphatic nodule

• Disorders


• 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)

Plasma to Lymph

Difference between interstitial fluid and lymph is location

of Lymphatic System

• Removal of excess

– 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

– 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

that lack lymphatic capillaries

• Include avascular tissues:

– Cartilage

– Epidermis

– Cornea of the eye


• Portions of the spleen

• Portions of Red bone marrow

Details of
a Lymphatic Capillary


• In small intestine, specialized lymphatic capillaries –

• 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

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

Principal Trunks

• Lumbar

• Intestinal

• bronchomediastinal

• Subclavian

• Jugular 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

• Receives lymph from the upper right side of the body

The Thoracic Duct

• Main duct for the return of lymph to blood


• 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

and Flow of Lymph

Blood plasma filter freely through the capillary walls

From interstitial fluid- small amount of proteins

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

sequence of fluid flow

Blood capillaries

Interstitial spaces

Lymphatic capillaries

Lymphatic vessels

Lymphatic ducts

Junction of the internal jugular and subclavian veins

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

Organs and Tissues

Primary lymphatic

• 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

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

• immuno competent B cells

• Pre-T cells



• 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 –

• 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

• Macrophages

– Help clear out the debris of dead and dying cells

The surviving T cells enter the medulla

Hassall’s Corpus

• 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

• 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

• Scattered throughout the body superficial and deep (in

• 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

Parenchyma (Functioning Part)

 Superficial cortex

 Deep medulla

Lymph Nodes

• 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


• 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 –

• 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 &

Structure of Spleen


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

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

• 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


• Egg-shaped masses of lymphatic tissue

• Not surrounded by a capsule.

• Scattered throughout the lamina propria of mucous
membranes lining:


– 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

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

• 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

• Antibodies – Temporary, passive immunity

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

• Then most of the activated T cells undergo apoptosis

   A few cells remain
as memory T cells


• 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

• 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