The Lymphatic System – returns fluids that have leaked from the circulatory system - PowerPoint Presentation

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The Lymphatic System – returns fluids that have leaked from the circulatory system back to the blood; protects the body by removing foreign material; provides a site for immune surveillance

Lecture 4 Histology Dr.Widad.J.H.Slide2

The Immune Response

T cells = cellular immunity; function toamplify the inflammatory responseB cells = humoral

immunity

T Cells and Cell Mediated Immunity

- targets virus or parasite infected cells, cancer

cells, and cells of foreign grafts

3 main types of cells:

1.

Cytotoxic

T (TC) cells: carry out cell

mediated immunity, physically attack

foreign cells

2. Helper T (TH) cells: activate B and TC

cells

3. Suppressor T (TS) cells: moderate the

immune response by inhibiting TC and

B cellsSlide3

Lymphoid cells

Lymphocytes Arise in the red bone marrow Protect the body against antigens

Two types

T lymphocytes (T cells)

Mature in the thymus

Directly attack and destroy foreign cells

B lymphocytes (B cells)

Mature in the bone marrow

Produce plasma cells that manufacture antibodies Slide4

Macrophages – phagocytize foreign substances and activate the T cell response

Dendritic cells – initiate the immune response

Reticular cells – produce the reticular fibers that form the soft skeletal structure of lymphoid organs Slide5
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Components of the Lymphatic System

Lymphatic vessels – return to the blood any fluids that have escaped from the circulation Distribution of lymphatic vessels Lymphatic vessels travel alongside blood vessels

Lymphatic vessels are absent from bones, teeth, bone marrow, and the central nervous system

Lymphatic capillaries – microscopic blind-ended tubes that are interwoven between the tissue cells and the blood capillaries

Lacteals – specialized lymphatic capillaries of the intestinal mucosa

Fatty lymph (

chyme

) containing fats and fat-soluble substances is absorbed in the lacteals Slide8

Lymph transport

The lymphatic circulation is a low-pressure system The lymphatic system lacks a pumping organ; must utilize the valves, respiratory pumps and muscular pumps to promote lymph flow toward the heart

The movement of surrounding tissues is also important in propelling lymph through the

lymphatics

The lymphatic capillaries converge into larger vessels

Lymph flows from the lymphatic capillaries to lymphatic collecting vessels to lymphatic trunks to the right lymphatic duct/thoracic duct Slide9

The right lymphatic duct drains lymph from the right upper arm and the right side of the head and thorax

The thoracic duct receives lymph from the rest of the body Slide10

Lymph nodes

Only the lymph nodes filter lymph Cluster along the lymphatic vessels of the body Lymph is filtered through the lymph nodes before it is returned to the bloodstream

Lymph nodes are embedded in connective tissue

Large clusters of lymph nodes appear near the body surface in the inguinal,

axillary

, and cervical regions.

Functions of lymph nodes

Filters lymph

Assist in activating the immune system Slide11

Anatomy of a lymph node

Most are kidney-shaped Surrounded by a fibrous capsule Strands of connective tissue (

trabeculae

) divide the node into compartments

Two

histologically

distinct regions

Cortex

Contains densely packed follicles with many germinal centers

Deeper portion of the cortex primarily houses T cells

Medulla

Contain both types of lymphocytes Slide12
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Circulation in the lymph nodes

Afferent lymphatic vessels – lymph enters here Once inside the nodes, the lymph moves through a series of sinuses and then exits at the hilus

Efferent lymphatic vessels – lymph exits out

the nodesSlide14

Spleen

The largest lymphoid organ Site of lymphocyte proliferation and immune surveillance and response

Functions of the spleen

Cleanses the blood by removing old RBCs and platelets, as well as debris from the blood.

Stores the breakdown products of RBCs

Site of erythrocyte production in the fetus Slide15

Anatomy of the spleen

Surrounded by a fibrous capsule Contains both T cells, B cells, RBCs and macrophages

Divided

histologically

into two regions

Red pulp – rich in lymphocytes and reticular fibers

RBC disposal and recycling

White pulp – rich in macrophages and reticular fibers

Immune functions Slide16
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Thymus – the site of T cell maturation

Most active in younger children; atrophies with age Does not contain reticular fiberLack B cells, therefore no germinal cells centers are present in the thymus Slide19

. Thymus1. Location - situated above the heart where the great vessels connect.

2. Importance - during early life when the cellular mediated component of the immune system develops. Undergoes atrophy in later life, at which time it loses its functional significance.3. The thymus consists of multiple lobes each containing characteristic cortical and

medullary

structure; however, these are not lymphatic nodules (i.e., not a spherical structure that is distinct from surrounding cells). A connective tissue capsule surrounds the thymus.Slide20

a. Epithelial tissues of embryo’s pharynx are internalized during development and move to site of thymus dorsal to

b. These epithelial tissues are invaded by lymphoblasts (immature T-lymphocytes) that originate from stem cells in the bone marrow.

c. The invading cells organize themselves into the cortical and

medullary

portions of lobules

.Slide21

* Cortical area consists of dense population of so-called thymocytes, that are T-lymphocytes, and scattered epithelial reticular cells that have multiple processes and partially compartmentalize the

thymocytes.* These cells surround a central zone of loose lymphatic tissue called the medullary zone that consists of fewer

thymocytes

and more epithelial reticular cells.

* The cortical and

medullary

zones of lobules are all continuous with each other.Slide22

d. Other cell types found in the thymus are:

* macrophages * plasma cells * mast cells

5. Cortical layer of thymus

a. Site of lymphocyte production - divisions of lymphoblast cells.

b. Thus, there is considerable mitotic activity of

lymphoblasts

c. Epithelial reticular cells are less numerous in this area and have thin and long processes that

evelope

groups of developing

thymocytes

. No reticular fibers are present

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. Medullary zone

a. Contains mostly epithelial-reticular cells and fewer T-lymphoblasts and lymphocytes than the cortex.

b. Also contains specialized structures known as

Hassall's corpuscles

- function unknown

* consist of a central,

eosinophilic

, hyaline core surrounded by concentric layers of epithelial reticular cells containing lots of keratin.

*sometimes they are calcified.

*these structures are characteristic of thymus

.Slide24
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1. Palatine tonsils

a. On left and right in rear area of oral cavity.b. Dense lymphoid tissue that forms a band of lymphatic nodules that lie just below a non-keratinized, stratified,

squamous

epithelium lining the oral cavity in this region.

c. Overlying epithelium forms invaginations called multiple

crypts

that penetrate into the band of nodules.

d. These crypts act as collecting places for cellular debris and bacteria as well as some living lymphocytes that have migrated into the crypts.

e. The band of lymph nodules is separated from underlying tissues by a partial capsule of dense connective tissue

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Tonsils – the simplest lymphoid organs; named according to their location

Palatine tonsils Lingual tonsils

Pharyngeal tonsil

Tubal tonsils Slide27

2. Pharyngeal tonsils

a. Diffuse lymphoid tissue containing nodules, but no crypts.b. Mostly lie beneath a typical

pseudostratified

ciliated columnar respiratory epithelium

in rear roof of pharynx. Some areas of the covering epithelium may be stratified

squamous

.

c. A thin partial capsule of dense connective tissue separates the lymphoid tissue from underlying tissue.Slide28

2. Pharyngeal tonsils

a. Diffuse lymphoid tissue containing nodules, but no crypts.

b. Mostly lie beneath a typical

pseudostratified

ciliated columnar respiratory epithelium

in rear roof of pharynx. Some areas of the covering epithelium may be stratified

squamous

.

c. A thin partial capsule of dense connective tissue separates the lymphoid tissue from underlying tissue.Slide29

3. Lingual tonsils

a. Situated in the root of tongue.b. Each lingual tonsil consists of numerous. lymphoid nodules surrounding a single crypt

c. The crypt is lined by a

non-keratinized

,

stratified,

squamous

epithelium.

d. A thin partial capsule of dense connective tissue separates the lymphoid tissue from underlying tissue

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Aggregates of lymphoid follicles Location of these follicles make them ideal because they are able to:

Destroy bacteria and prevent pathogens from slipping through the intestinal wall Generate many “memory” lymphocytes for long-term immunity

Examples

Peyer’s

patches – found in the distal portion of the small intestine

Appendix –of the

cecum

(the first part of the large intestine) Slide31

Thank you