The Lymphatic System

LAB # 5

1- List the functions of Lymphatic System.2- Describe the exchange of blood plasma, extracellular

fluid, and lymph.3- Describe the structure of a lymph node.4- Explain how the lymphatic system drains into the

vascular system5- Describe the gross anatomy and basic histology of

the spleen.

Functions of the Lymphatic System

1- Lymphocyte Production, Maintenance, and Distribution

2- Collection and Returning of Interstitial Fluid from Tissues to the Circulatory System

3- Distribution of Nutrients, Waste, and Hormones from Tissues to the Circulatory System

1- Lymphocyte Production, Maintenance, and Distribution.

After maturation, most of the lymphocytes move into lymph nodes, the spleen and other lymphoid tissues.

Immature lymphocytes are produced in the bone marrow.

B lymphocytes mature in the bone marrow and T lymphocytes mature in the thymus.

Lymphoid organs and tissues

One function of the lymphatic system is to reabsorb this excess and to return it to the blood.

Fluid continually filters from the blood capillaries into the tissue spaces. But the blood capillaries reabsorb only 85%.

15% (2 – 4 L/day) of the water and about half of the plasma proteins are not absorbed by capillaries.

13 mm Hg

7 mm Hg

2- Collection and Returning of Interstitial Fluid from Tissues to the Circulatory System.

85%

15%

85%

The Lymphatic System

- Lymphatic capillaries

- Lymphatic collecting vessels

- Lymphatic trunks

Aggregates of lymphocytes in the connective tissue of mucous membrane and various organs.

Mucosa-associated lymphatic tissue (MALT)

1- Peyer patches in the distal portion of the small intestine.

They have well –defined anatomical sites and at least partial connective tissue capsules.

2- Thymus

1- Lymph nodes

3- Spleen

It is the recovered fluid. Lymph is usually a clear colorless fluid, similar to blood plasma but low in protein.

Lymphatic Vessels

Diffuse Lymphoid

Tissues

Encapsulated Lymphoid

OrgansLymph

- Collecting duct

3- Tonsils (palatine tonsils and pharyngeal tonsils or adenoids).

2- Vermiform appendix

Lymphoid Organs

Lymphatic Vessels

Lymphoid Tissues

1- Lymphatic Vessels

Pulmonarycircuit

Superior vena cava

Bloodflow

Systemiccircuit

Lymphatic system

Cardiovascular system

The lymphatic capillaries converge to form collecting vessels.

Lymphatic capillaries

Collecting vessels

Lymphatic trunks

Collecting ducts (2)

The collecting vessels converge to form lymphatic trunks.

The lymphatic trunks converge to form collecting ducts.

The collecting vessels travel alongside veins and arteries, and at irregular intervals they empty into lymph nodes. In the lymph nodes, bacteria are phagocytized and immune cells monitor the fluid for foreign antigens.

The names indicates their locations and part of the body they drain1- Jugular trunks, 2- Subclavian trunks, 3- Bronchomediastinal trunks, 4- Intestinal trunk, and 5- Lumbar trunks

1- Right lymphatic duct

2- Thoracic duct

Subclavian veins

Inferior Trunks

Inferior vena cava

3- Lymphatic Trunks and Lymphatic Ducts

Lymph Capillaries

Collecting Vessels

Lymphatic Trunks

Lymphatic Ducts

Right Lumbar Trunk

Left Lumbar Trunk

Intestinal Lumbar Trunk Cisterna Chyli

Thoracic Duct

Right lumbar trunk

Left lumbar trunk

Intestinal trunk

Cisterna Chyli

Thoracic duct

Superior vena cava

Superior Trunks

Right Jugular Trunk

Right Bronchomediastinal Trunk

Right Subclavian Trunk Right Lymphatic Duct

Right Jugular Trunk

Right Subclavian Trunk

Right Bronchome-

diastinal Trunk

Thoracic DuctRight Lymphatic

Duct

RIGHT LEFT Left Jugular Trunk

Left Subclavian

Trunk

Left Bronchome-

diastinal Trunk

Right subclavian vein

Left Subclavian veint

Inferior Trunks

Right Lymphatic Duct Thoracic Duct

Right side of the tissues superior to the diaphragm

Right Lymphatic Duct Thoracic Duct

Tissues inferior to the diaphragm and from left side of the upper body

2- Lymphoid Tissues and Lymph Nodes

Lymphoid Tissues Lymphoid tissues are areolar connective tissues with concentrations of lymphocytes.

The lymphatic nodules or follicles have no fibrous capsule surrounding them.

When lymphocytes are densely packed they form lymphoid or lymphatic nodules or follicles.

Germinal centerIt contains dividing lymphocytes.

Lymphatic nodule or

follicle

It is the collection of lymphoid tissues that protect the epithelia of the respiratory, digestive, urinary, and reproductive systems.

Clusters of lymphoid nodules deep to the epithelial lining of the intestine are known as Peyer’s patches.

MALT (Mucosa-Associated Lymphatic Tissue)

The appendix vermiform is other example of MALT. It walls contain a mass of fused lymphoid nodules.

Tonsils

Functions

They are large concentration of lymphoid nodules in the walls of the pharynx.

Pharyngeal tonsil or adenoid (single)

Palatine tonsils (two)

Lingual tonsils (two)

They guard against ingested or inhaled pathogens.

Lymphatic organs have well-defined anatomical sites and have connective tissue capsule that separates the lymphatic tissue from neighboring tissues.

Lymphoid Organs

- Thymus

- Lymph nodes

- Spleen

Lymph nodes

They are the smallest and most numerous lymphatic organs (about 450 in typical young adult).

Thymus

Spleen

Lymph nodes

They range in diameter from 1 mm to 25 mm (about 1 inch)

Cervical lymph nodes

Axillary lymph nodes

Lumbar lymph nodes

Pelvic lymph nodes

Inguinal lymph nodes

Lymph nodes are wide-spread but specially concentrated in some locations.

Lymph nodes

Lymphvessel

Lymphnodes

Hilum

Medullary sinus

Outer cortex (B cells)

Afferentvessel

Medullary cord(B cells and

plasma cells)Capsule

Dense connective tissue

Deep cortex(T cells)

Subcapsularspace

Medulla

Trabeculae

Efferentvessel

Lymph nodeartery and vein

Lymph nodes are shaped like kidney beans.

Cortex

Lymph Node Functions:

1- They filter and purify the lymph before return to venous circulation (they remove 99% of cell debris, bacteria, viruses, fungi).

2- They provide an early warning system against infection in peripheral tissue, responding before infections reach vital organs of trunk.

3- The first step in immune response takes place in the lymph nodes (extracted antigens are “presented” to lymphocytes).

The Thymus

The thymus is located in the mediastinum.

It atrophies after puberty.

The thymus is divided into two thymic lobes.

Rightlobe

Leftlobe

Septa

Lobule

Septa divide lobes into smaller lobules.Thymus

Lobule

Lobule

The thymus gland LM 50

Cortex

Septa

Medulla

Dividing lymphocyte

s

Maturelymphocyte

s

Lymphocytes

CortexSeptaMedulla

Lobule

Lobule

The thymus gland LM 50A thymic corpuscle LM 550

Reticularcells

Thymiccorpuscle

Mature T cells leave thymus by medullary blood vessels.

T lymphocytes divide in the cortex and mature while they migrate to the medulla.

The thymus secretes thymic hormones that stimulate T cell differentiation.

Spleen

Rib

Pancreas

Aorta

Parietal peritoneum

Visceral peritoneum

Stomach

Diaphragm

Gastric area

Diaphragmatic surface

Renal area

Kidneys

Liver Gastrosplenic ligament

SPLEEN

Hilum

The SpleenIt is the body’s largest lymphatic organ.

The spleen LM 50

White pulp ofsplenic nodule

Capsule

Red pulp

Trabecularartery

Central artery insplenic nodule

White pulp isdominated by lymphocytes.

Red pulp contains a large number of red blood cells.

Functions:1- Removal of abnormal and worn out blood cells.

2- Storage of iron recycled from red blood cells.

3- Initiation of immune responses by B cells and T cells.

Histology of the Spleen