13) Immune System Flashcards
What are the Lymphoid Organs?
◦ Lymph nodes
◦ Spleen
◦ Thymus
◦ Tonsils
◦ Small intestine & appendix
aggregated lymphoid nodules
What is the Immune System
◦ Comprises cells, tissues and organs that protects the body’s internal environment from the onslaught of foreign substances (e.g. bacteria, viruses, parasites, etc.) and malignant growths.
The immune system is able to:
◦ Differentiate between self (own) and non-self (foreign & modified self) structures – specificity
◦ Respond: immune response fights against pathogens – tries to eliminate harmful pathogens
◦ Remembers antigens over long periods of time 3
Which lymphoid structures are encapsulated in the immune system?
◦ Lymph nodes (including lymphatic
circulation)
◦ Thymus
◦ Spleen
Which lymphoid structures are NOT and/or partially encapsulated in the immune system?
Partially encapsulated
◦ Tonsils
◦ Adenoids
Non-encapsulated lymphatic tissue
◦ Peyer’s Patches (MALTs, Appendix,
lymphatic nodules in GI tract (GALT),
respiratory tract (BALT), reproductive system
What is the point of the immune system?
Comprises cells, tissues and organs that protects the body’s internal
environment from the onslaught of foreign substances (e.g. bacteria,
viruses, parasites, etc.) and malignant growths.
What is Peyer’s Patch?
- Peyer’s patches are clusters of lymphoid nodules deep to the epithelial lining of the small intestine
- contain lymphocytes and macrophages which remove microorganisms, debris, and antigens
from the digestive tract
List the lymph structures from smallest to biggest
Options:
Spleen
Lymph nodes
Thymus
Lymph nodes, Thymus, Spleen.
What are Lymph Nodes and what do they do?
- They are small, bean like structures distributed throughout the body, along
the paths of lymph vessels.
Function:
◦ Circulating and filtering the lymph
◦ Lymph from any part of the body passes through one or more lymph nodes before entering the blood stream
◦ They act as filter removing bacteria and particulate matter from lymph
◦ Defend against microbial invasion
and provide a place for lymphocytes to meet antigens
◦ for recognition by T and B cells
◦ for destruction by macrophages to prevent systemic spread
◦ production, storage and recirculation of T and B cell
Reminder:
**B cells
Produce antibodies to fight off bacteria, viruses, and toxins. B cells mature in the bone marrow.
T cells
Destroy infected or cancerous cells, and help control the immune response. T cells are produced in the bone marrow and mature in the thymus. **
Lymph Node structure
Capsules are generally dense irregular tissue
Covered by a dense fibrous
connective tissue capsule with
trabeculae that extend into the
node and divide it into lobules
++ Trabeculae is the dividers (looks like fingers) that extend from the capsule into the cortex that contain many of the blood vessels from the lymph node ++
◦ Stroma – the internal connective tissue network of reticular fibers
◦ Each lymph node contains an
outer cortex and inner medulla
◦ The paracortex separates the
cortex and medulla
Lymph Node Structure: Outer cortex and Inner medulla
Outer cortex
◦ Darkly stained -just under the capsule ◦ Consists of a network of reticular fibers and spherical, non-encapsulated aggregations of lymphocytes (called lymphatic follicles or lymphatic nodules)
◦ Outer edge of follicle contains more T cells
◦ Inner paler staining germinal center is the site of B- cell proliferation
Germinal Centers are not always present. They are thought to develop in response to a prolonged demand for antibody production and represent active sites of lymphocyte proliferation.
Inner medulla
◦ Pale staining
◦ medullary cords of lymphocytes, macrophages & plasma cells (activated B cells)
◦ The medullary sinuses drain the lymph from the cortex and course between the medullary cords toward the hilum of the organ
Spleen Functions
The spleen does not have a cortex or medulla, so majority or the area is red pulp
- Largest lymphoid organ
- Present in the upper part of the abdominal cavity behind the stomach.
- Covered by peritoneum
- Initiation of the immune responses by B and T cells in response to antigens circulating in the blood
- Disposal of old blood cells, particularly erythrocytes
- Hematopoiesis in fetus ( and in adults with particular diseases.
- Red pulp is a diffuse cellular meshwork that makes up the bulk of the organ. Red Pulp filters aging blood cells. Within the red pulp small, oval or rounded greyish white areas, the
- white pulp, is formed by lymphoid tissue (mostly lymphocytes and some
macrophages). The lymphocytes are T and B cells.
Thymus characteristic
- The thymus is flat, bi-lobed found in the anterior mediastinum of
the thorax, behind the upper part of the sternum - Small at birth then double in size until puberty. Once puberty is hit, it starts the shrink and undergoes atrophy. As you age it gets smaller and smaller and just gets filled with adipose tissue
Prominent in newborns, almost
disappears by old age
- The thymus is very important for B cells maturation
Thymus layers
- Cortex is deeply stained because its densely packed with lymphocytes
- In the medulla, smaller areas thats lightly stained because theres less lymphocytes. These are where the mature lymphocytes (T Cells) go.
- Hassal’s corpuses: characteristic feature of the thymus. cyst-like, epithelial structures are large and acidophilic. They are thought to have an endocrine function.
Lymphocytes mature in the CORTEX > then go to the MEDULLA > Then they go for general circulation
Secondary lymphoid tissue
- Tonsils
- Peyer’s patch
- Appendix
- Mucosal associated lymphoid tissues (MALT), sites of the immune response toward pathogens that enter via the mucosal surfaces.
+Examples of MALT: tonsils in the oropharynx, Peyer’s patches in the small intestine, and lymphoid aggregates in the large intestine. - MALT also includes various sites of lymphocyte accumulation throughout the respiratory, gastrointestinal, and genitourinary tracts.
- MALT –> Muscosa
- GALT –> Gut
- BALT –> Bronchus
Tonsils sections
- Incompletely encapsulated lymphoid nodules
◦ Palatine: covered by stratified squamous nonkeratinized epithelium; crypts; underlying connective tissue barrier
◦ Pharyngeal: covered by ciliated pseudostratified epithelium, no crypts
◦ Lingual: smaller, at base of tongue; covered by stratified squamous nonkeratinized epithelium; one crypt in each nodule
Crypts in the tonsils are deep invaginations of the epithelial lining that increase the surface area for trapping pathogens and debris, aiding in immune surveillance. These structures help expose antigens to immune cells, playing a role in activating the body’s defense mechanisms.
