Lecture 4 Histology DrWidadJH The Immune Response T cells cellular immunity function to amplify the inflammatory response B cells ID: 661563
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Slide1
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 Slide5Slide6Slide7
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 Slide12Slide13
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 Slide16Slide17Slide18
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
Slide23
. 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
.Slide24Slide25
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
.Slide26
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
Slide30
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