Anatomy and Cell Biology 3309 Lecture Notes - Lecture 12: Lymphatic Vessel, Splenic Artery, High Endothelial Venules
22 May 2018
School
Department
Professor
Histology 3309
Spleen & Thymus
Objectives
- List the functions and structural components of the spleen and thymus
- Distinguish bw the red pulp and white pulp of the spleen in terms of cell population, function
and structure
- Describe the role of the open circulation of the spleen
- Describe the role of epithelioreticular cells in T cell education
Spleen Gross Anatomy
- Have a large vein and artery taking blood to and from the spleen
- The spleen is like a big bag of blood – hight vascularized
Overview of Spleen
- DICT capsule with myofibroblasts (fibroblast that can produce ECM but it can also contract)
- In different animals (not humans), the spleen has a blood storage function so the myofibroblasts
can contract the spleen and let extra blood out into the circulation
- Ex: if you had a bad injury and lost a lot of blood, spleen can contract and release more blood
into the circulation to maintain blood pressure
- Hilum = location of splenic artery and vein, nerves, efferent lymphatic vessels that drain out of
the spleen
o Unlike lymph node, it does not have afferent lymphatic vessel
o So we don’t have lymph coming into it, but that interstitial fluid that makes up our
lymph is draining out of our spleen via the efferent lymphatic vessel
- Unlike the lymph node, there is not an outer cortex and inner medulla – there is red and white
pulp mixing with eachother
- Red pulp plays a role in RBC recycling
Overview of Spleen
- Splenic nodule:
o Same as lymphatic nodules
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o With collection of B cells, germinal center etc
- Has a capsule like the lymph node
- Like lymph node, has trabeculae that gives a gross architecture to the spleen – apart of the
reticular fibers that give an overall structure coming into the spleen
- One way that the spleen and thymus are similar to the lymph node is that both are going to have
reticular fibers to give a loose overall structure
o This is a filtering system – there is going to be lymphocytes moving throughout, lots of
cell movement so we cant have highly organized, restricted organ
- Dark staining regions are the white pulp
- Intermixed with that is the red pulp (around the periphery of the white pulp)
White Pulp and Red Pulp
- White pulp
o Looks white in fresh sections
o In H&E looks basophilic bc it contains mostly B lymphocytes
- Red pulp
o Contains large #s of RBCs
o Made primarily of splenic sinuses separated by splenic cords (the splenic
cords are going to have a variety of cell types – including some immune
cells)
Functions of the Spleen
- Immune system functions →white pulp
o Bc the spleen is going to be filtering blood, its is involved in immune responses
o Antigen presentation
o B/T cell activation
o Antibody production
o Removal of antigens from blood (similar function to lymph nodes – but lymph nodes to
removal of antigens from LYMPH)
- Hematopoietic functions →red pulp
o Removal and destruction of old RBCs
▪ RBCs have a finite circulation time in our body
o Retrieval of Fe from Hb
o storage of blood (ONLY IN ANIMALS – NOT IN HUMANS)
Question:
How are the spleen and the lymph nodes similar?
a) Both filter lymph
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b) Both have high endothelial venules
c) Both filter blood
d) Both have trabeculae
A: D
Overview of the Thymus
- Primary lymphoid organ – involved in T cell education
- T cells come from bone marrow (theyre developing thymocytes)
- all the thymocytes that come into the thymus from the bone marrow are going to be subjected to
a number of tests
o )f they don’t pass their tests, they are killed % of the thymocytes are killed
- The test: are they self reactive? – we don’t want it to react to ourselves and do they react to
anything?
o the thymocytes have to react to something and they cant have a huge amount of self
reactivity
Thymus in a Child: Thymus in Adult:
What is the difference bw the thymus in an adult and the thymus in a child?
- The adult has more adipose tissue (not much basophilia)
- Children have more active thymocytes
- Active thymocytes are still producing T cells (still producing T cells in adult too – but not all
much)
- Adults have an involuted thymus (lots of adipose, very small) – not really active in your adult
life
General Architecture of Thymus
- You can see the trabeculae much easier in the thymus
- The trabeculae establish thymic lobules
- DON’T CONFUSE W)T( SPLEN)C OR LYMP(AT)C NODUELS
o The inner part is all connected (no circular setup)
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find more resources at oneclass.com
Document Summary
List the functions and structural components of the spleen and thymus. Distinguish bw the red pulp and white pulp of the spleen in terms of cell population, function and structure. Describe the role of the open circulation of the spleen. Describe the role of epithelioreticular cells in t cell education. Have a large vein and artery taking blood to and from the spleen. The spleen is like a big bag of blood hight vascularized. Dict capsule with myofibroblasts (fibroblast that can produce ecm but it can also contract) In different animals (not humans), the spleen has a blood storage function so the myofibroblasts can contract the spleen and let extra blood out into the circulation. Ex: if you had a bad injury and lost a lot of blood, spleen can contract and release more blood into the circulation to maintain blood pressure.
