The lymphatic system maintains fluid balance, serves as part of the immune system, and helps absorb lipids. It consists of lymphatic vessels that collect excess fluid from tissues and return it to the bloodstream. The immune system protects against microbes and abnormal cells using phagocytic cells, natural killer cells, and lymphocytes. B cells produce antibodies to help fight pathogens while T cells help regulate the immune response. Together the lymphatic and immune systems work to maintain health.

1. Lymphatic and Immune Systems
Dragan Nikolic

2. Components of the Lymphatic and
Immune Systems
The lymphatic system has at least three
different functions:
functions
– Serves to maintain the fluid balance of our internal
body environment
– Serves as part of our immune system
– Helps regulate the absorption of lipids from digested
food in the small intestines and its transport to the large
systemic veins

3. Components of the Lymphatic and
Immune Systems (Cont’d)
The immune system serves as an
internal “security force” to deal with abnormal
cells
– Repels and destroys microorganisms
– Defends us from our own abnormal cells that
can cause cancer

4. Lymphatic System
Overview of the Lymphatic System
– The lymphatic system solves the problem of
fluid retention in tissues
• Acts as a drainage system
• Collects excess tissue fluid and return it to the venous
blood just before it reaches the heart
– Lymphatic system is a part of the circulatory
system
• Consists of moving fluid derived from the blood and
tissue fluid, as well as a group of vessels that return
the lymph to the blood

6. Lymphatic System (Cont’d)
Lymphatic vessels do not
form a closed system of
vessels
• They begin blindly in the
intercellular spaces of the soft
tissue of the body

9. Lymphatic System (Cont’d)
Lymph and Interstitial Fluid
– Lymph – clear fluid found in the lymphatic
vessels
– Interstitial fluid – complex fluid that fills the
spaces between the cells
– Both fluids closely resemble blood plasma in
composition
– Difference is that lymph cannot clot like blood

10. Lymphatic System (Cont’d)
Lymphatic Vessels
– Lymphatic vessels – microscopic blind-ended
lymphatic capillaries; wall of each lymphatic capillary
consists of a single layer of flattened endothelial
cells
• Networks of lymphatic capillaries branch and then
rejoin repeatedly to form a network throughout the
interstitial spaces of our bodies
• Lymphatic capillaries merge to form larger and larger
vessels until main lymphatic trunks are formed –
right lymphatic duct and thoracic duct

11. Lymphatic System (Cont’d)
Structure of lymphatic vessels
• Walls of lymphatic capillaries
– Have numerous openings or clefts between
the cells
– As lymph flows from the thin-walled capillaries
into vessels with larger diameters, the walls
become thicker
• Eventually these larger vessels have the
three layers typical of arteries and veins
• One-way valves are abundant in lymphatic
vessels of all sizes

13. Lymphatic System (Cont’d)
Function of lymphatic
vessels
• Permeability of the lymphatic
capillary wall permits very large
molecules and even small particles
to be removed from the interstitial
spaces

14. Lymphatic System (Cont’d)
Circulation of Lymph
– About 50% of the total blood protein
leaks out of the capillaries into the
interstitial fluid; ultimately returns to
the blood by way of the lymphatic
vessels

16. Lymphatic System (Cont’d)
The lymphatic pump
• Lymph moves slowly and steadily along in its
vessels into the general circulation at about 3
liters per day
– Lymph flow is possible because of the large
number of valves that permit fluid flow only in
the general direction toward the heart
– Breathing movements and skeletal muscle
contraction aid in this motion

17. Lymphatic System (Cont’d)
Lymph Nodes
– Structure of lymph nodes
• Oval-shaped or bean-shaped structures; widely
distributed throughout the body
• Lymph nodes are linked together by the lymphatic
vessels
• Fibrous partitions or trabeculae extend from the covering
capsule toward the center of a lymph node, creating
compartments called cortical nodules
• Center, or medulla, of a lymph node is composed of
sinuses; separate medullary cords composed of plasma
cells and B cells

19. Lymphatic System (Cont’d)
Locations of lymph nodes
– Most lymph nodes occur in groups, or clusters
– Approximately 500-600 lymph nodes are located in the
body
Functions of lymph nodes
– Defend our bodies from invading pathogens; sites of both
biological and mechanical filtration
– Provide sites for the maturation of some types of
lymphocytes

20. Lymphatic System (Cont’d)
Structure and Function of the Tonsils
– Tonsils – form a protective ring under the mucous
membranes in the mouth and back of the throat
• Protect against bacteria that may invade tissue in the area
around the openings between the nasal and oral cavities;
first line of defense from the external environment
– Tonsils:
– Palatine – located on each side of the throat
– Pharyngeal tonsils (adenoids) – lie near the
posterior opening of the nasal cavity
– Lingual – lie near the posterior opening of the nasal
cavity

22. Lymphatic System (Cont’d)
Structure and Function of
Aggregated Lymphoid Nodules
– Also called Peyer patches – small, oval patches or
groups of lymph nodes that form protective layer in
mucous membrane of the small intestine
• Provide protection in a spot that is potentially
open to external environment via the mouth
• Macrophages and other cells prevent most
bacteria from penetrating the gut wall

23. Lymphatic System (Cont’d)
Structure and Function of the Thymus
– Thymus – a primary organ of the lymphatic
system
• Consists of two pyramid-shaped lobes
• Located in the mediastinum, extending up into
the neck, close to the thyroid gland
• Thymus plays a critical part in the body’s
defenses against infection
• Soon after birth, thymus begins secreting a
group of hormones that enable lymphocytes to
develop into mature T cells

25. Lymphatic System (Cont’d)
Structure and Function of the Spleen
– Spleen – located directly below the diaphragm, just
above most of the left kidney and behind the fundus of
the stomach
• Roughly oval in shape
• Spleen has variety of functions:
– Defense
– Hematopoiesis
– Erythrocyte and platelet destruction
– Reservoir for blood

27. Immune System
Organization of the Immune System
– Identification of cells and other particles:
• Antigens – cells, viruses, and other particles with unique
molecules on their surfaces
– Self
– Non-self – molecules on the surface of foreign or
abnormal cells or particles that serve as recognition
markers by our immune system
– Self-tolerance – ability of our immune system to attack
abnormal or foreign cells while sparing our own cells
• Two categories of defense mechanisms:
– Innate immunity (Nonspecific)
– Adaptive immunity (Specific)

28. Immune System (Cont’d)
Innate (Non-specific) Immunity
Phagocytosis and phagocytic cells
• Phagocytosis – ingestion and destruction of microorganisms
and other small particles by cells called phagocytes
• Phagocytosis is classified as an innate defense
• The most numerous type of phagocyte is the neutrophil; other
neutrophil
types include macrophages and dendritic cells (DC)
Chemo-tactic factors cause neutrophils and other phagocytes to
adhere to the endothelial lining of capillaries servicing the affected area
– After this, phagocytic cells squeeze through the wall of a blood vessel to
get to the site of the injury or infection; diapedesis

30. Immune System (Cont’d)
Innate (Non-specific) Immunity
– Natural killer cells – provide important innate
defensive functions for our bodies
• Kill many types of tumor cells and cells infected by
different kinds of viruses
• Produced in the red bone marrow and make up about
15% of the total lymphocyte number
• Recognize markers on surface membrane of invading or
defective cells

31. Immune System (Cont’d)
Adaptive immunity – involves mechanisms that program
the body to recognize specific threatening agents; specific
agents
immunity
• Primary types of cells involved in innate immunity:
– Epithelial barrier cells
– Phagocytic cells
– Natural killer (NK) cells
• Primary types of cells involved in adaptive immunity:
– T cells
– B cells

32. Immune System (Cont’d)
Adaptive immunity – body’s third line of
defense; provided by two different types of
lymphocytes
• Two major classes of lymphocytes:
– B lymphocytes (B cells)
– T lymphocytes (T cells)
• B cells produce molecules called antibodies
that attack the pathogens or direct other cells,
such as phagocytes, to attack them; antibodymediated immunity

34. Immune System (Cont’d)
B Cells and Antibody-Mediated Immunity
– Diversity of antibodies – every normal baby is born with an
enormous number of different clones of B cells
– Classes of antibodies – five classes of immuno-globulin antibodies;
identified by letter names as immunoglobulins M, E, G, A, and D
(USE MNEMONIC: MEGA-D)
MEGA-D
• IgM – antibody that immature B cells synthesize and insert into
their plasma membranes
• IgG – most abundant circulating antibody; cross-placental barrier
during pregnancy to give passive immunity to baby
• IgA – major class of antibody in the mucous membranes of the
body; also in saliva and tears
• IgE – produce the major symptoms of allergies and kill parasites
• IgD – small amount in blood; function unknown

37. Immune System (Cont’d)
Types of Adaptive Immunity
– Acquired immunity – classified as either
natural immunity or artificial immunity
• Natural immunity – results from nondeliberate exposure to antigens
• Artificial immunity – results from deliberate
exposure to antigens; immunizations

38. Immune System (Cont’d)
Types of Adaptive Immunity
– Natural and artificial immunity may be “active” or
“passive
• Active immunity – results when an individual’s own
immune system responds to a harmful agent—
regardless of how it was encountered
• Passive immunity – results when immunity to a
disease that has developed in another individual is
transferred to an individual who was not previously
immune

39. References
• Hill, David J., (2012) Essentials of Anatomy and
Physiology, Mosby, St. Louis. ISBN
9780323085113
• Metchnikoff, Elie; Translated by F.G. Binnie.
(1905). Immunity in Infective Diseases (Full Text
Version: Google Books). Cambridge University
Press. ISBN 68025143