SPLEEN AND RETICULOENDOTHELIAL SYSTEM
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Transcript of SPLEEN AND RETICULOENDOTHELIAL SYSTEM
DR NILESH KATE
MBBS,MDASSOCIATE PROF
DEPT. OF PHYSIOLOGY
SPLEEN
OBJECTIVES At the end of the lecture you should know:
The functional anatomy of the spleen. The histological structure of spleen (red & white
pulp) How to draw the schematic diagram of histological
structure. Functions of spleen. Definition & causes for splenomegaly &
hypersplenism. Definition, components & function of RES.
INTRODUCTION Spleen is the largest
lymphoid tissue in the body.
The spleen is to the circulatory system as the lymph nodes are to the lymphatic system.
STRUCTURE Bean shaped organ. Situated in left
hypochondrium, just below the diaphragm, above the left kidney & descending colon.
Highly vascular organ. Measures about 12 x 7 x 3 cm. Weights about 150 gm in an
adult.
THE NINE ABDOMINAL REGIONS
Wednesday, May 3, 2023
ANATOMICAL LOCATION OF SPLEEN
STRUCTURE
STRUCTURE The spleen is covered with a dense connective
tissue capsule.
The fibrous tissue of the capsule extends into the spleen to form a series of trabeculae between which lies the splenic pulp (parenchyma).
The parenchyma is divided into: White pulp Red pulp
WHITE PULP Collection of lymphoid cells surrounding medium-
sized splenic arteries. The artery is surrounded by a collar of T
lymphocytes, k/a “periarteriolar lymphatic sheath”.
At intervals, this lymphatic sheath expands, usually on one side of the artery, to form ‘lymphoid nodules’ composed principally of B lymphocytes.
On antigenic stimulation, typical ‘germinal centers’ form within these B-cell areas.
RED PULP Contains thin-
walled ‘vascular sinusoids’, separated by the ‘splenic cords’, or ‘cords of Billroth.’
RED PULP The endothelial lining
of the sinusoid is of the open or discontinuous type, providing passage of blood cells between the sinusoids and cords.
RED PULP Blood reaching the capillaries in red pulp may
take one of two routes: Open route: filters into the splenic cords. Closed route: passes directly into
sinusoides.
The splenic cords are lined by macrophages and function as seive through which blood in red pulp filters into sinusoides.
CLOSED ROUTE OPEN ROUTE
FUNCTIONS OF SPLEEN
Formation of RBC Removal of unwanted elements from
the blood. Reservoir function Role in defense mechanism Storage and metabolism of iron
FORMATION OF RBC During fetal life (3-
5m IUL) spleen along with liver act as an important hemopoietic organ.
Lymphocytes are also formed in the white pulp.
REMOVAL OF UNWANTED ELEMENTS FROM THE BLOOD.
By splenic phagocytes in the cord. Removes:
Old effaced RBCs Damaged RBCs & leucocytes Abnormal RBCs (e.g. Hereditary spherocytes) Bacteria, cell debris etc.
RBCs undergo extreme deformation during passage from the cords into the sinusoids.
↓ RBC elasticity RBC entrapped in cords phagocytosed by cordal macrophages.
RESERVOIR FUNCTION More important in animals with contractile
spleen (e.g. Dog). Human spleen is non-contractile.
It contains about 30-40 ml of RBCs. Also contains 30-40% of total platelet mass in the body.
Enlarged spleen can trap 80-90% of platelets and can cause thrombocytopenia.
ROLE IN DEFENSE MECHANISM Macrophages of spleen
engulf bacteria and other infectious agents.
Lymphoid cells of the spleen react against infections by formation of antibodies.
Contains about 25% of T & 15% of B lymphocytes
STORAGE AND METABOLISM OF IRON
SPLENOMEGALY(A CLINICALLY PALPABLE SPLEEN IS CALLED
SPLENOMEGALY). HEMATOLOGICAL
CAUSES: Haemolytic anaemias Haemoglobinopathies Leukemias Lymphomas
INFLAMMATIONS: Rheumatoid Arthritis
INFECTIONS: Acute: typhoid Chronic: tuberculosis Parasitic: malaria, kala
azar
OTHERS: Portal hypertension Cancers
HYPERSPLENISM(INCREASED ACTIVITY OF SPLEEN IS KNOWN AS
HYPERSPELNISM)
Characterized by: splenomegaly cytopenia(s) normal or hyperplastic bone marrow responds to splenectomy.
All possible causes of splenomegaly cause hypersplenism.
RETICULOENDOTHELIAL SYSTEM Also known as:
Monocyte-Macrophage System Mononuclear Phagocytic System Lymphoreticular system.
Collection of cells united by the common property of phagocytosis.
It is a generalized phagocytic system located in all tissues.
Especially in those tissues where large quantities of particles, toxins, and other unwanted substances must be destroyed.
RETICULOENDOTHELIAL SYSTEM
System of cells which have highly phagocytic properties.
RES consists of: Monocytes Mobile (wandering) tissue macrophages Fixed tissue macrophages.
MONOCYTES Largest leucocytes.
Immature cells present in blood, with little ability to fight infectious agent.
After 72 hours they enter the tissues to become ‘tissue macrophages’.
In the tissue they swell to become large in size and cytoplasm is filled with lysosomes.
FUNCTIONS OF MONOCYTES1. Enter tissue and form tissue macrophages – act as scavengers.
2. Phagocyte several bacteria. (up to 100)
3. Engulf large particulate matter, dead tissue cells and senile cells.
4. Along with macrophage involved in phagocytosis & destruction of necrotic material.
5. Co-operate with B & T lymphocyte in both Humoral & Cellular immunity.
WANDERING TISSUE MACROPHAGES Monocytes leaving the blood become
activated and differentiate into macrophages.
Those that have recently left the blood are sometimes referred to as wandering macrophages.
Monocyte changes during maturation: A. Increase in cell size B. Number and complexity of intracellular
organelles increase, i.e., Golgi, mitochondria, lysosomes
C. Increase in intracellular digestive enzymes
FIXED TISSUE MACROPHAGES(KNOWN BY DIFFERENT NAMES IN DIFFERENT SITES)
LiverLiver Kupffer cellsKupffer cells
LungsLungs Alveolar macrophagesAlveolar macrophages
SkinSkin Langerhans cellsLangerhans cells
Connective tissueConnective tissue HistiocytesHistiocytes
CNSCNS MicrogliaMicroglia
BonesBones OsteoclastsOsteoclasts
Spleen/Bone Spleen/Bone marrow/Lymph nodesmarrow/Lymph nodes
Reticular or Dendritic Reticular or Dendritic cellscells
CNS MICROGLIA
BONE OSTEOCLAST
SKIN LANGERTHAN
CELLS
FUNCTIONS OF MACROPHAGES1. Engulf inorganic particulate matter (carbon & dust
particles).2. When confronted with large insoluble particle, plenty
of macrophage fuse together to become ‘Multinucleated Giant Cell’
3. Organic foreign matter such as thorn, fish bone, catgut are destroyed by enzyme action & lysis.
4. Engulf micro-organism, senile WBC, RBC, tissue debris & some parasites.
5. Help ‘T’ & ‘B’ lymphocyte in the acquired immunity by presenting antigens.
FUNCTIONS OF THE RES Phagocytic Function:
Bacteria, other foreign bodies and tissue debris are engulfed and digested by the lysosomes of the macrophages.
Destruction of senile red cells. Storage and metabolism of iron. Formation of bile pigments.
SUMMARY In this lecture we have seen that:
Spleen is divided into red & white pulp and plays an important role in defense mechanism.
RES is an innate defense mechanism of the body and is located in all the tissues of the body.
Thank You