Structure and function of spleen- anatomy, physiology

2. Spleen
• Lymphatic organ connected to blood vascular system
• Part of mononuclear phagocyte system.
• Wedge shaped

3. Spleen
• situated
principally in
the left
hypochondriac
region, but its
superior
extremity
extends into
the epigastric
region

4. • it lies between the
fundus of the
stomach and the
diaphragm.
• the largest of the
ductless glands, and
is of an oblong,
flattened form, soft,
of very friable
consistence, highly
vascular, and of a
dark purplish color.

5. • 1" (2.5 cm) by
3“(7.5cm) by
5“(12.5cm)
• 150 grams (5.3 oz)
to 200 grams
(7.1 oz)
• lies between the
9th and 11th ribs
on the left hand
side.

7. Development
• Appears about the fifth week
• It arises in a series of hillocks, of
the mesoderm in the dorsal
mesogastrium above the tail of
pancreas.
• With the change in position of
the stomach the spleen is carried
to the left, and comes to lie
behind the stomach and in
contact with the left kidney.
• The part of the dorsal
mesogastrium between the spleen
and the greater curvature of the
stomach forms the gastrosplenic
ligament.

8. • When the hillocks fail to unify
• 20% of persons.
• especially in the gastrolienal ligament and
greater omentum,
• vary in size from that of a pea to that of a plum.

9. Relations
Diaphragmatic
surface (external or
phrenic surface)
• convex, smooth
• Relation -under surface of
the diaphragm, which
separates it from the ninth,
tenth, and eleventh ribs of
the left side, and the
intervening
costodiaphragmatic recess

10. Visceral surface
divided by a ridge
Gastric surface
• broad and concave
• is in contact with the
posterior wall of the
stomach; and below this
with the tail of the pancreas.
• It presents near its medial
border a long fissure,
termed the hilum. This is
pierced by several irregular
apertures, for the entrance
and exit of vessels and
nerves.

11. Renal surface
• somewhat
flattened, is
considerably
narrower than the
gastric surface
• upper part of the
anterior surface of
the left kidney and
occasionally left
suprarenal gland.

12. Colic surface
• flat, triangular in
shape, and rests upon
the left flexure of the
colon and the
phrenicocolic ligament,
and is generally in
contact with the tail of
the pancreas.

14. • anterior border -is free, sharp,
and thin, and is often notched,
especially below
• posterior border- more rounded
and blunter than the anterior,
corresponds to the lower
border of the eleventh rib and
lies between the diaphragm
and left kidney.
• The intermediate margin is
the ridge which separates the
renal and gastric surfaces.
• inferior border- rounded

15. Peritoneal relations
• Gastrosplenic ligament :
• from the hilum of the spleen to
the greater curvature of the
stomach; it contains short gastric
vessels and associated
lymphatics and sympathetic
nerves.
• Splenorenal ligament : from the
hilum of the spleen to the
anterior surface of the left
kidney; it contains the tail of the
pancreas and splenic vessels,ln
• Phrenicocolic ligament :from the
splenic flexure of the colon to
the diaphragm along the
midaxillary line

16. Structure
External or serous coat (tunica serosa)
• from the peritoneum
• thin, smooth, and intimately adherent to the fibroelastic
coat. It invests the entire organ, except at the hilum and
along the lines of reflection of the phrenicolienal and
gastrolienal ligaments.
Fibroelastic coat (tunica albuginea) invests the organ, and at
the hilum is reflected inward upon the vessels in the form of
sheaths. From these sheaths, as well as from the inner
surface of the fibroelastic coat, numerous small fibrous
bands, trabeculae are given off in all directions

17. • The fibroelastic coat, the
sheaths of the vessels, and
the trabeculæ, are
composed of white and
yellow elastic fibrous
tissues
• spleen possesses a
considerable amount of
elasticity, which allows of
the very great variations in
size
• small amount of non-
striped muscular fiber
The spleen consists of a number of small spaces,
formed by the trabeculæ which contain the
splenic pulp.

19. • The spleen is made of red pulp and white
pulp, separated by the marginal zone; 76-
79% of a normal spleen is red pulp

20. red pulp
• Red blood–filled sinusoids and reticuloendothelial cell–
lined cords of Billroth (connective tissue )
• Splenic cords -reticular fibers, reticular cells, and associated
macrophages
Sinusoids
• wide vessels that drain into trabecular veins.
• Gaps in the endothelium lining the sinusoids mechanically
filter blood cells as they enter the spleen.

21. Venous sinuses →a lining of endothelial cells that are positioned in
parallel and connected by stress fibres to annular fibres,
Contractility of the stress fibres allows the formation of slits between
the endothelial cells, regulating the passage of blood
Worn-out or abnormal red cells attempting to squeeze become
damaged, and are devoured by macrophages

22. • Splenic cells-Large rounded cells, ameboid movement,
often contain pigment and red-blood corpuscles in
their interior.
• Cells of the reticulum may contain pigment granules in
their cytoplasm
•B and T lymphocytes
•Erythrocytes
• granulocytes
•plasma cells
•hematopoietic cells
•plasmablasts that migrate from the follicles and the
outer PALS after antigen specific differentiation
•macrophages

24. • white lymphoid follicles arrayed within the red
pulp matrix
• Contains lymphocytes and macrophages,
dendritic cells, plasma cells, arterioles, and
capillaries in reticular connective tissue
meshwork
Periarterial lymphatic sheaths (PALS)-Lymphatic
tissue sheath that surrounds central artery
• Most of the T cells are CD4+

26. Malpighian bodies, splenic lymphoid nodules:
• hemispherical accumulations of B lymphocytes
attached to the PALS at intervals.
• 0.25 mm. to 1 mm. in diameter
Secondary follicles
•Follicles with a germinal centre
•arise when antigen specific B-
cell immune reactions occur in
the spleen
•existence is of limited duration.
•attached to the smaller
ramifications of the splenic artery.

27. Germinal centre
• Antigen specific larger B cells
• pale-staining nuclei and abundant cytoplasm
Mantle zone or corona.
• The expanding germinal centre displaces the small, dark
recirculating B lymphocytes to the periphery of the
follicle
Marginal Zone
• broad region primarily occupied by relatively large
memory B cells.
• light impression after routine staining
• delimited from the PALS and the follicles by a very
irregular capillary blood vessel called the marginal sinus.

28. • white pulp of the spleen is seen in a lymphoid follicle, outlined by the
dashed line found. The lymphoid follicle has a pale-staining germinal center
(GC) in which B cells are proliferating. mantle zone (ManZ) contains small
lymphocytes and an outer marginal zone that contains larger lymphocytes
that are less densely packed than cells in the mantle zone.

30. Blood supply
Blood flow is
about 150
mL/min
Splenic A.
• large size in
proportion to
the size of the
organ
• tortuous course

31. •Passes through
leinorenal ligament
to reach the hilum
where it divides into
six or more branches
•receive sheaths the
external fibrous
tissue
•branches into
numerous arterioles

32. • When arterioles acquire
a coating of T cells, they
are called central arteries
and the surrounding
lymphoid tissue is called
the PALS, i.e., the
periarteriolar lymphoid
sheath.

34. • The arterioles end by opening freely into the splenic pulp; their walls
become much attenuated, they lose their tubular character, and the
endothelial cells become altered, presenting a branched appearance,
and acquiring processes which are directly connected with the
processes of the reticular cells of the pulp
•

37. The spleen comprises many units of red and
white pulp centered around small branches of
the splenic artery, called central arteries.
White pulp is lymphoid in nature and contains
B cell follicles, a marginal zone around the
follicles, and T cell–rich areas sheathing
arterioles. The red pulp areas include pulp
sinuses and pulp cords.
The cords are dead ends. In order to regain
access to the circulation, red blood cells must
traverse tiny openings in the sinusoidal lining.
Stiff, damaged, or old red cells cannot enter
the sinuses.

38. Pitting
Red cell–inclusion bodies such as parasites ,nuclear
residua (Howell-Jolly bodies), or denatured hemoglobin
(Heinz bodies) are pinched off in the process of passing
through the slits
The culling of dead and damaged
cells and the pitting of cells with
inclusions appear to occur without
significant delay because the blood
transit time through the spleen is
only slightly slower than in other
organs

40. Splenic vein and tributaries

41. Open circulation

42. Closed circulation

43. Nerve supply
• Sympathetic fibres derived from the celiac
plexus
• They are distributed to the blood vessels and
to the smooth muscle of the capsule and
trabeculae.

44. Lymphatic vessels
• Splenic tissue proper
has no lymphatics
• Lymphatics from
connective tissue drain
into pancreaticosplenic
lymph nodes along
splenic artery

45. • Red pulp- Mechanical filtration of red blood cells.
• white pulp -Active immune response through
humoral and cell-mediated pathways.
• Production of opsonins, properdin, and tuftsin.

47. Storage
• contains approximately one-third of the total
body platelets and a significant number of
marginated neutrophils.
• sequestered cells are available when needed
to respond to bleeding or infection.
• the normal human spleen does not sequester
or store red blood cells

48. Removal of Red Blood Cells
• Removes senescent and defective red blood cells
• through a unique organization of its parenchyma
and vasculature
• After normal lifespan
RBC will be broken down
and some parts recycled.
•Removes all abnormal
red blood cells.

49. • The removal of antibody-coated bacteria and
antibody-coated blood cells from the
circulation.
Phagocytes:
1. Reticular cells and free macrophages of red
pulp
2. Modified reticular cells of ellipsoid
3. Free macrophages and endothelial cells of
venous sinusoids
4. Surface reticular cells of lymphatic follicle

50. • (1) clearance of bacteria and particulates
from the blood
• (2) the generation of immune responses to
certain pathogens
• (3) the generation of cellular components of
the blood under circumstances in which the
marrow is unable to meet the needs (i.e.,
extramedullary hematopoiesis).