# Splenic Function Physiology

> Splenic function in MBBS Physiology: red pulp filtration, white pulp immunity, post-splenectomy changes and OPSI prevention.

- Canonical URL: https://prepelephant.com/topics/mbbs/physiology/splenic-function-physiology
- Exam / course: MBBS · Subject: Physiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Splenic Function Physiology", PrepElephant, https://prepelephant.com/topics/mbbs/physiology/splenic-function-physiology

## Direct answer

The spleen — about 12 cm long and 150 grams in adults, receiving 5 per cent of cardiac output — runs two operations in one organ: the red pulp filters blood through the Billroth cords, where sluggish flow lets macrophages remove opsonised particles, pit intra-erythrocytic inclusions (Howell-Jolly bodies, Heinz bodies) and cull aged erythrocytes; the white pulp mounts immune responses, with T-cells in the periarteriolar lymphoid sheath and B-cell follicles around central arterioles. Splenic macrophages are the body's specialist defence against encapsulated bacteria — pneumococcus, Haemophilus influenzae type b, meningococcus — because IgG and C3b opsonisation is exactly what the cords capture. After splenectomy, Howell-Jolly bodies appear in smears, platelets transiently exceed 400,000 per microlitre, and the lifetime risk of overwhelming post-splenectomy infection (OPSI, about 5 per cent lifetime, highest in the first two years, mortality near 50 per cent) makes vaccination and penicillin prophylaxis mandatory.

## What you must remember

- **Architecture:** white pulp (PALS T-zone around central arterioles, B-follicles, marginal zone macrophages and B cells) for immunity; red pulp (cords of Billroth and venous sinuses) for filtration — a one-line answer worth full marks.
- **Filtration functions:** removal of aged and antibody-coated erythrocytes, pitting of inclusions (Howell-Jolly bodies, Heinz bodies, malarial pigment), spherocyte destruction in hereditary spherocytosis, and culling of intraerythrocytic parasites — hence splenic protection in malaria.
- **Immune functions:** antibody production against polysaccharide antigens, marginal-zone memory B cells, tuftsin and properdin production (opsonin support), and the main site of IgM response to encapsulated organisms.
- **Encapsulated organism triad:** Streptococcus pneumoniae, Haemophilus influenzae type b, Neisseria meningitidis — the OPSI pathogens; pneumococcus accounts for most cases.
- **Post-splenectomy smear:** Howell-Jolly bodies, target cells, acanthocytes, pitted erythrocytes; counts show transient thrombocytosis (platelets often above 400,000, normalising over weeks to months) and mild lymphocytosis.
- **OPSI numbers:** lifetime risk about 5 per cent, greatest within two years; presentation is fulminant septicaemia, commonly pneumococcal, with adrenal haemorrhage (Waterhouse-Friderichsen picture); mortality around 50 per cent.
- **Prevention protocol:** vaccination at least two weeks before elective splenectomy (or about two weeks after emergency surgery) — pneumococcal conjugate then polysaccharide, Hib, meningococcal ACWY plus B; antibiotic prophylaxis (oral penicillin or amoxicillin) especially for children, commonly for at least 2-5 years and often lifelong in high-risk Indian practice.
- **Platelet pool:** about a third of the body's platelets reside in the splenic pool, exchangeable with circulation; massive splenomegaly can sequester most of the platelet mass (and red cells) causing pancytopenia — hypersplenism.

## A worked case from elective splenectomy

A 19-year-old with hereditary spherocytosis is listed for splenectomy. Physiology writes the preoperative checklist: vaccinate at least two weeks ahead — conjugate pneumococcal, Hib, meningococcal ACWY and B — because the postsplenectomy immune defect is specifically against polysaccharide antigens, which the spleen's marginal-zone B cells were built to answer. Postoperatively the smear tells the story: Howell-Jolly bodies (the pitting function is gone), platelets climbing past 500,000 before settling over weeks.

Then fast-forward two years to fever with rigors in the same patient. In anyone else this is a viral illness; in a splenectomised patient it is OPSI until proven otherwise — immediate blood culture and empirical antibiotics, because pneumococcal bacteraemia in this setting can kill within hours. The educational asymmetry is the point: the operation is curative for spherocytosis's anaemia yet purchases a permanent, quantifiable infection risk, and the physiology justifies both the surgery and the lifelong caution.
## Where students slip

The commonest slip is calling the spleen a blood filter only — half the organ is lymphoid tissue, and the marginal-zone B cell is the cell type to name for encapsulated organisms. The second is dating OPSI risk to the recovery period alone; the risk is lifelong, though front-loaded in the first two years, and vaccination does not abolish it — patients are still taught to treat fever as an emergency. Third, every spleen pools platelets; only an enlarged spleen pools enough to cause cytopenias — physiological sequestration versus pathological hypersplenism. Indian viva bonus: the huge splenomegalies — chronic malaria (hyperreactive malarial splenomegaly), kala-azar, portal hypertension and myeloproliferative disease.

## Frequently asked questions

### Which organisms cause overwhelming post-splenectomy infection?

Encapsulated bacteria, chiefly Streptococcus pneumoniae, then Haemophilus influenzae type b and Neisseria meningitidis, because splenic macrophages and marginal-zone B cells specialise in clearing IgG-C3b-opsonised encapsulated organisms.

### What smear findings indicate hyposplenism or asplenia?

Howell-Jolly bodies, target cells, acanthocytes and pitted erythrocytes — remnants the red pulp can no longer pit out — with thrombocytosis and lymphocytosis.

### Why does thrombocytosis occur after splenectomy?

The spleen normally sequesters about a third of circulating platelets; its removal releases the pooled platelets, commonly pushing counts above 400,000 per microlitre before normalising over weeks.

### What is the vaccination schedule before elective splenectomy?

Pneumococcal conjugate followed by polysaccharide vaccine, Haemophilus influenzae type b and meningococcal ACWY with B, all given at least two weeks preoperatively; emergency cases about two weeks after.

### Why is splenectomy delayed until after five years of age in children?

OPSI risk and mortality are highest in young children, whose polysaccharide antigen responses are immature even with a spleen; deferring surgery lowers the window of greatest vulnerability.