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