Anatomy and biology of immune system

Prof M.I.N. Matee

Chapter 20 The Lymphatic and Immune systems

• Structures:

• Lymphatic vessels and lymph

• Lymphocytes

• Lymphoid tissue

• Lymphoid organs

Introduction• Immune system is important in the defense

against infection– Accounts for 5% of body weight– Consist of 5x1013

Immune organs• Generative/Primary = origin

–Bone marrow, thymus• Peripheral/secondary = mature cells

respond to foreign antigens

–Lymph-nodes, spleen, Mucosal associated lymphoid tissue (MALT), cutaneous immune system

Lymphoid organs

• Peripheral – remove and destroy antigens in the blood and lymph– Tonsils– Lymph nodes– Spleen– Intestinal lymphoid tissues

• Central – site of maturation of cells– Thymus– Bone marrow

Lymphocyte Activation

ANATOMY OF THE IMMUNE SYSTEM

• The immune system is localized in several parts of the body– immune cells

develop in the primary organs - bone marrow and thymus (yellow)

– immune responses occur in the secondary organs (blue)

ORGANS OF THE IMMUNE SYSTEM• Thymus – glandular organ near the heart – where T cells

learn their jobs

• Bone marrow – blood-producing tissue located inside certain bones– blood stem cells give rise to all of the different types of blood cells

• Spleen – serves as a filter for the blood– removes old and damaged red blood cells – removes infectious agents and uses them to activate cells called

lymphocytes

• Lymph nodes – small organs that filter out dead cells, antigens, and other “stuff” to present to lymphocytes

• Lymphatic vessels – collect fluid (lymph) that has “leaked” out from the blood into the tissues and returns it to circulation

Shared properties of peripheral lymphoid organs

1. a means to collect antigen

2. a means to recruit lymphocytes

3. distinct B and T cell zones

Lymphatic System

• Consists of 2 semi-independent parts:– Network of lymphatic

vessels• Function primarily to

return fluid to the vascular system

– Various lymphoid organs and tissues scattered throughout the body

• Functions in immune defense

Lymph capillaries

• Closed-ended vessels

• Lined by endothelium

• 1-way flaps into capillary– Allows passage of tissue fluid,

large proteins, bacteria, viruses, cancer cells, cell debris

20.2ab

Lymph capillaries

• Found in all areas of blood capillaries except:– Bone, teeth, bone marrow, CNS

• Lacteals – lymph capillaries in villi of small intestine transports fat (chyle) [compare with blood capillaries]

20.2a 22.17b

Lymphatic Vessels

• Lymphatic Collecting Vessels– Receive lymph from lymphatic capillaries– Have the same 3 tunics as veins, but:

• Are thinner, have more internal valves, and anastomose more

• Lymphatic Trunks– Formed from the union of the largest of the

lymphatic collecting vessels– Drain large areas of the body

Lymphatic Vessels

• Lymphatic Ducts– 2 vessels that receive lymph from lymphatic trunks

• Right Lymphatic Duct– Drains lymph from the right upper arm and the right side of the

head and the thorax– Empties into the vascular system at the junction of the right

internal jugular vein and right subclavian vein– How would obstruction of this duct affect the circumference of

the right arm?• Thoracic Duct

– Drains lymph from the left upper arm, left side of the head and thorax, and digestive organs, pelvis, and legs

– Much larger– Empties into the vascular system at the junction of the left

internal jugular vein and left subclavian vein

Lymphoid Tissue

• 2 main functions:– Houses and provides a proliferation site for

lymphocytes– Provides an ideal site for surveillance.

• Composed largely of reticular connective tissue and lymphoid cells

• Can be found as:– Diffuse lymphatic tissue

• Scattered reticular tissue and lymphoid cells found in most organs and especially prominent beneath mucous membranes

– Lymphoid Follicles• Spherical, tightly packed bodies of reticular and lymphoid

cells– Lymphoid Organs

Lymph nodes

• Scattered in trunk

• Located along lymphatic vessels– Cleanses lymph

20.3

20.1

Lymph Node Function

• Produce new B and T cells

• Filter lymph

Lymph node structure

• Functional tissue– Cortex

• Lymph nodules• Lymph sinuses

– Macrophages– Lymphocytes

– Medulla• Lymph sinuses• Lymph cords

– Lymph filter• Afferent lymphatic• Lymph sinuses• Removal of unwanted

material• Efferent lymphatic

20.4a

Lymph Node Function• Multiple afferent lymphatic vessels enter a lymph at its hilus - the indented region on the concave side

• Lymph percolates thru the node and it is scrutinized by macrophages and lymphocytes ready to mount an immune response

• Lymph leaves via a few efferent lymphatic vessels

• Lymph usually has to pass thru several nodes before it is “clean”

Why is it significant that there are more afferent than efferent lymphatic vessels?

Lymph trunks

• Lumbar trunks

• Intestinal trunks

• Bronchomediastinal trunks

• Subclavian trunks

• Jugular trunks

20.3

Lymph ducts

• Thoracic (L) lymphatic duct– Drains ¾ of lymph– L head, neck, thorax, upper

extremity– R&L abdomen, lower

extremities

• Right lymph duct– R head, neck, thorax, upper

extremity

• Ducts drain into subclavian veins 20.6a

Lymphoid Cells

• Lymphocytes– What are the 2 types?

• What are plasma cells?– What do they secrete?

• Lymphoid macrophages– What is their function?

• Reticular cells– Fibroblastlike cells that produce the reticular

fiber stroma – the network that supports other cell types in lymphoid organs

Spleen

• Supporting tissue– Capsule

• Hilus• Splenic artery

– Trabeculae• Trabecular arteries

20.11ab

Spleen• Functional tissue:

• White pulp– Lymphocytes around

central arteries– Branches of trabecular

arteries– Immune response to

antigens– Produces both B & T

lymphocytes20.11b

Spleen• Red pulp

– Venous sinuses (splenic sinusoids)

– Splenic cords• Lymphocytes • Reticular fibers• Macrophages• Cleanse blood• Remove old rbcs

20.11b

Thymus • Located in thorax

– Posterior to sternum

• Supporting structures– Capsule– Trabeculae

20.9,20.10b

Thymus

• Functional tissue - lobules

• Site of T lymphocyte development

• Most active during childhood

• Decreases from adolescence to adult

20.10

Tonsils

20.12

• Aggregations of lymphocytes and lymph nodules

• MALT – mucosa associated lympoid tissue

Tonsils

• Palatine tonsils – in pharynx, near palate

• Lingual tonsils – in tongue

• Pharyngeal tonsils – in pharyngeal roof

21.3a

Spleen• Largest

lymphoid organ. About the size of a fist.

• Location:– Left side of the

abdominal cavity, just beneath the diaphragm and curling around the anterior stomach

• Served by the splenic artery and vein which enter at its hilus

• Surrounded by a fibrous CT capsule with inward extending trabeculae

• Functions include:– Extracting old & defective RBCs and removal of debris and foreign matter

from blood– Storage of blood platelets and iron

• Internal structure consists of:– White Pulp

• Smaller portion• Islands of lymphocytes and reticular fibers

– Red Pulp• Venous sinuses and splenic cords (regions of reticular fibers and

macrophages)

Thymus• Found in inferior neck and anterior thorax• Secretes hormones that allow T lymphocyte maturation• Prominent in newborns, it increases in size throughout childhood.

In adolescence, it begins to atrophy and is fatty/ fibrotic in adults.• Only lymphoid organ that does not fight antigens

Tonsils

• Form a ring of lymphoid tissue around the entrance to the pharynx

• 3 main sets:– Palatine

• Located on either side of the posterior oral cavity

• Largest and infected most often

– Lingual• Lie at the base of the

tongue

– Pharyngeal • Found in the posterior

wall of the nasopharynx• Called adenoids when

infected

Lymphocyte Activation