Lymphatic Tissues Organs Flashcards
What is the origin of the spleen?
Mesoderm
What is the largest lymphoid organ?
Spleen
What is the location of the spleen?
Posterior abdominal wall
What is the function of the spleen?
Filtration of blood
- old erythrocyte
- platelets
Describe structure of spleen
One of the sites where immune response to antigens occur
Spleen is covered by dense tissue capsule
Lower animals characterized by the presence of myofibroblasts
Connective tissue septae arise from the capsule to penetrate the parenchyma called> trabeculaae
Covered by simple squamous epithelium (mesothelium, curved arrow). The splenic capsule
What does the parenchyma of the spleen consist of?
White pulp
Red pulp
What is in the red pulp of the parenchyma of the spleen?
- Cords of cells (cords of bill Roth)
- Sinusoids (capillaries)(also called venous sinuses)
What does the white pulp of the spleen parenchyma consist of?
- Thick accumulation of lymphocytes
- Lymphatic nodules-germinal centers that decrease with age
- Also called Malpighian corpuscles/ splenic nodules
Whaat is the function of trabeculae in the spleen?
Facilitate the passage of blood vessels into the parenchyma from the capsule
What is the significance of white pulp in spleen?
- Splenic artery divides into branches, which run along the capsule- as capsular artery
- These branch off and run through trabeculae -as trabeculae-as trabecular arteries
From the trabecular arteries, branches arise and run through the interior of parenchyma-as central arteries
What is the significance of PALS?
During their course, lymphocytes immediately surround the central arteries- refferred to as PALS (peri arterial lymphatic sheath)
Inner layer of T cells followed by a layer rich in B lymphocytes
A cross section at this level reveals a central artery surrounded by lymphocytes
Central arteries give rise to several smaller penicillar arterioles which ultimately end in venous sinuses (also called splenic sinuses)
The terminal capillaries continue into venules—> pulp veins—> a theory referred to as closed
These capillaries may open into the cords, draining the blood cells and eventually the pulp veins are formed - reffered to as open circulation
What is the clinical significance if the marginal zone of the germinal center?
There are B and T lymphocytes around the periphery of this collection
This zone filled with lymphocytes, along with lymphocytes, along with APCs (antigen presenting cells and macrophages)- reffered to as Marginal zone
In this area, the lymphocytes first come in contact with antigens
Marginal zones of the nodule- Trap antigen from the circulation and present the antigen to the lymphocytes in the spleen
What is the functional significance of the red pulp of the spleen?
Dense network of reticular fibers-numerous erythrocytes, lymphocytes, plasma cells, macrophages and other granulocytes
Between the splenic cords are the venous sinuses
Functional significance - filtration of antigens & senile and abnormal erythrocyte and platelets from the blood
What are splenic sinusoids made up of?
They’re lined by elongated endothelial cells (Reffered to as Littoral cells), arranged like the planks of a barrel, with an intracellular distance of 2-4 microns
They are supported by an incomplete basal lamina composed of reticular fibers.
Macrophages function in the removal of damaged or effect erythrocytes from circulation
What do healthy erythrocytes do in red pulp?
Healthy erythrocytes, squeeze between the endothelial cells to enter the cords
Older rigid erythrocytes are trapped in the space to be broken down and degraded by macrophages which are found right outside these sinusoids
