The Lymphatic System

Prepared by:
Mr. Bairagi S M
Asst. Prof.
Department of Pharmacology
MES’s College of Pharmacy, Sonai,

The Lymphatic System

• Functions Of The Lymphatic System

• Transport Excess Interstitial Fluid Back To
Bloodstream

• Transport Dietary Lipids

• House Lymphocytes

• Generate An Immune Response

Orders Of Lymphatic Vessels

• Lymph capillaries – smallest
lymph vessels, first to receive
lymph

• Lymphatic collecting vessels –
collect from lymph capillaries

• Lymph nodes – scattered along
collecting vessels

• Lymph trunks – collect lymph
from collecting vessels

• Lymph ducts – empty into
veins of the neck

Lymphatic Capillaries
• Located near blood capillaries

• Receive tissue fluid from CT

• Minivalve flaps open and allow fluid to enter

• Highly permeability allows entrance of tissue fluid, bacteria, viruses,
and cancer cells

• Lacteals – specialized lymphatic capillaries

• Located in the villi of the small intestines

• Receive digested fats, Fatty lymph – chyle

Lymphatic Collecting Vessels

• Accompany blood vessels
• Composed of the same three tunics as blood

vessels
• Contain more valves than veins do

• helps direct the flow of blood

• Lymph propelled by:
• contraction of skeletal muscles
• pulse pressure of nearby arteries
• Tunica media of the lymph vessels

Lymph Nodes
• Cleanse the lymph of pathogens

• Human body contains around 500

• Lymph nodes are organized in clusters

Microscopic Anatomy of a Lymph Node

• Fibrous capsule – surrounds
lymph nodes

• Trabeculae – connective tissue
strands

• Lymph vessels
• Afferent lymphatic vessels

• Efferent lymphatic vessels

Lymph Trunks
• Lymphatic collecting vessels

converge
• Five major lymph trunks

• Lumbar trunks
• Receives lymph from lower

limbs

• Intestinal trunk
• Receives chyle from

digestive organs

• Bronchomediastinal trunks
• Collects lymph from thoracic

viscera

• Subclavian trunks
• Receive lymph from upper

limbs and thoracic wall

• Jugular trunks
• Drain lymph from the head

and neck

Lymph Ducts

• Cisterna chyli – located at the union
of lumbar and intestinal trunks

• Thoracic duct – ascends along
vertebral bodies

• Empties into venous circulation

• Junction of left internal jugular
and left subclavian veins

• Drains three quarters of the body

• Right lymphatic duct – empties into
right internal jugular and subclavian
veins

The Immune System

• Recognizes specific foreign molecules

• Destroys pathogens effectively

• Key cells – lymphocytes

• Also includes lymphoid tissue and lymphoid
organs

Lymphocytes

• Infectious organisms attacked by inflammatory response,
macrophages, then lymphocytes

• T Lymphocytes
• Helper T-lymphocytes have receptors (CD4+) that can recognize

an antigen
• Secrete cytokines (chemical signals that bind to receptors on other

lymphatic cells and activate them) and
• Present the antigen to a B-lymphocyte.

• Cytotoxic T lymphocytes attack foreign cells directly
• Receptors (CD8) bind to antigen-bearing cells
• Perforates cell membrane
• Signals cell to undergo apoptosis (self destruction)

• B lymphocytes
• Become plasma cells
• Secrete antibodies – bind and mark cells for destruction by

macrophages

Lymphocyte Function

Figure 20.7

Lymphocyte Activation

• Lymphocytes originate in bone marrow

• Some travel to the thymus gland – T lymphocytes

• Some stay in bone marrow – B lymphocytes

• Able to recognize a unique antigen
• Gain immunocompetence

• Travels through blood stream

• Meets and binds to a specific antigen

Lymphocyte Activation

• Activating T or B cells produce
• Effector lymphocytes – short-lived, attack

immediately

• Memory lymphocytes – wait until body encounters
their antigen again

• Basis of acquired immunity

• Guard against subsequent infections

Lymphocyte Activation

Figure 20.8

Lymphoid Tissue

• Lymphoid tissue – areolar connective tissue and
lymphocytes

• Most important tissue of the immune system
• Mucous membranes of digestive, urinary,

respiratory, and reproductive tracts

• Mucosa-associated lymphoid tissue
(MALT)

• Makes up lymphoid organs (except thymus)

Lymphoid Organs

• Primary lymphoid organs

• Bone marrow

• Thymus

• Secondary lymphoid organs

• Designed to gather and
destroy infectious
microorganisms

• Lymph nodes, spleen, tonsils

• Aggregated lymphoid
nodules – masses of lymphoid
tissue NOT surrounded by a
fibrous capsule.

• Appendix

Thymus
• Immature lymphocytes develop into T lymphocytes
• Secretes thymic hormones
• Most active in childhood
• Functional tissue atrophies with age
• Composed of cortex and medulla

• Medulla contains Hassall’s corpuscles (thymic corpuscles)
• Differs from other lymphoid organs

• Functions strictly in lymphocyte maturation
• Arises from epithelial tissue

Lymphoid Organs

• Lymph nodes
• Lymph percolates through lymph sinuses

• Most antigenic challenges occur in lymph nodes

• Antigens destroyed – and activate B and T lymphocytes

• Spleen
• Largest lymphoid organ

• Two main blood-cleansing functions
• Removal of blood-borne antigens

• Removal and destruction of old or defective blood cells

• Site of hematopoiesis in the fetus

Spleen
• Destruction of antigens
• Site of B cell maturation into plasma cells
• Phagocytosis of bacteria and worn-out blood cells
• Storage of platelets
• White pulp

• Thick sleeves of lymphoid tissue
• Provides the immune function of the spleen

• Red pulp – surrounds white pulp, composed of
• Venous sinuses – filled with whole blood
• Splenic cords – reticular CT rich in macrophages

Tonsils
• Simplest lymphoid organs

• Four groups of tonsils
• Palatine, lingual, pharyngeal and tubal tonsils

• Arranged in a ring to gather and remove pathogens

• Underlying lamina propria consists of MALT

Aggregated Lymphoid Nodules And Appendix

• MALT – abundant in walls of
intestines

• Fight invading bacteria

• Generate a wide variety of
memory lymphocytes
• Aggregated lymphoid

nodules (Peyer’s patches)
• Located in the distal part of

the small intestine

• Appendix – tubular offshoot
of the cecum