Page 157 - Essential Haematology

Chapter 10 Spleen / 143

The spleen has an important and unique role in the vasculature is closed in which the arterial and
function of the haemopoietic and immune systems. venous systems are connected by capillaries with a
As well as being directly involved in many diseases continuous endothelial layer.

of these systems, a number of important clinical The central arterioles are surrounded by a core
features are associated with hypersplenic and hypo- of lymphatic tissue known as white pulp which has
splenic states. an organization similar to lymph nodes (Fig. 10.1 ).
Th e periarteriolar lymphatic sheath (PALS) lies
directly around the arteriole and is equivalent to the
The a natomy and c irculation of
T zone of the lymph node (see p. 128 ). B - cell fol-
the s pleen
licles are found adjacent to the PALS and these are
The spleen lies under the left costal margin, has a surrounded by the marginal zone and perifollicular

normal weight of 150 – 250 g and a length of between zone which are rich in macrophages and dendritic
5 and 13 cm. It is normally not palpable but cells. Lymphocytes migrate into white pulp from
becomes palpable when the size is increased to over the sinuses of the red pulp or from vessels that end
14 cm. directly in the marginal and perifollicular zones.

Blood enters the spleen through the splenic There are both rapid (1 – 2 min) and slow (30 –
artery which then divides into trabecular arteries 60 min) blood circulations through the spleen. Th e
which permeate the organ and give rise to central slow circulation becomes increasingly important in
arterioles (Fig. 10.1 ). The majority of the arterioles splenomegaly.

end in cords which lack an endothelial lining and
form an open blood system unique to the spleen The f unctions of the s pleen
with a loose reticular connective tissue network

lined by fibroblasts and many macrophages. Th e The spleen is the largest filter of the blood in the
blood re - enters the circulation by passing across the body and several of its functions are derived from
endothelium of venous sinuses . Blood then passes this.
into the splenic vein and so back into the general

circulation. The cords and sinuses form the red
Control of r ed c ell i ntegrity
pulp which forms 75% of the spleen and has an
essential role in monitoring the integrity of red The spleen has an essential role in the quality
‘

blood cells (see below). A minority of the splenic control ’ of red cells. Excess DNA, nuclear remnants
Capsule
Splenic artery

Trabecular artery

Marginal zone White
Follicle pulp
Trabecular T-cell zone
vein
Central arteriole
Figure 10.1 Schematic represen-

tation of the blood circulation in
the spleen. Most blood fl ows in an
Cords Red
‘ open ’ circulation through splenic pulp
Venous sinuses
cords and regains entry into the
circulation through the venous
sinuses.