Thymic macrophages help clear out debris of dead and


Thymic macrophages – help clear out debris of
dead and dying cells

Surviving T cells enter medulla

medulla – consists of widely scattered, more
mature T cells, epithelial cells, dendritic cells, and
macrophages

T cells that leave thymus via blood migrate to
lymph nodes, spleen, and other lymphatic tissues
where they colonize parts of these organs and
tissues


~ 600 lymph nodes scattered along lymphatic
vessels (in superficial and deep groups) that serve
as filters to trap and destroy
foreign objects in lymph fluid

Important group of regional
lymph nodes include:
◦
Submandibular
◦
Cervical
◦
Axillary
o
Mediastinal
o
Inguinal


Lymph nodes make immune cells that help the body
fight infection
◦
Filter the lymph fluid and remove foreign material such as
bacteria and cancer cells
◦
When bacteria are recognized in the lymph fluid , the lymph
nodes make more infection-fighting white blood cells, which
cause the nodes to swell
◦
Swollen nodes are sometimes felt in the neck, under the arms,
and groin


Contain T cells, macrophages, follicular dendritic cells, and B cells

Like thymus, lymph nodes are covered by capsule (connective
tissue)

Capsular extensions called trabeculae divide the node into
compartments, provide support, and provide a route for blood
vessels into interior of node


stroma (supporting framework) - Capsule, trabeculae,
reticular fibers (inside capsule), and fibroblasts (inside
capsule)

parenchyma (functioning part) is divided into cortex and
medulla


Outer Cortex:
◦
B cells
◦
Follicular dendritic cells
◦
macrophages


follicular cells “present” an
antigen

B cells proliferate and develop
into antibody-producing plasma
cells or develop into memory B
cells

Memory B cells “remember”
having encountered a
specific antigen (fight
second infection faster!)


Inner cortex
◦
Consists mainly of T cells and
dendritic cells that enter lymph
node

Dendritic cells present
antigens to T cells ( antigen-
presenting cells), causing them
to proliferate

Newly formed T cells migrate
from lymph node to areas of
body where there is antigenic
activity


Medulla of lymph node
◦
Contains B cells, antibody producing plasma cells that
have migrated out of cortex into medulla, and
macrophages


Lymph nodes function as a filter

As lymph enters one end of a lymph node, foreign
substances are trapped by reticular fibers within
sinuses of node

Macrophages then destroy foreign substances by
phagocytosis

Lymphocytes destroy others by immune responses

Filtered lymph then leaves
other end of lymph node

Afferent lymphatic vessels have valves pointing inward, to keep lymph
flowing in one direction
Efferent have valves point out (fewer than afferent, which slows the flow
through so more time to filter)


Largest mass of lymphatic tissue in the body

found in the left hypochondriac region between the fundus
of the stomach and the diaphragm


Superior surface of spleen is smooth and convex and conforms to
the concave surface of the diaphragm

Like lymph nodes, spleen has a hilum
◦
Through the hilum passes the splenic artery and vein, and
efferent lymphatic vessels

Neighboring organs make impressions