Download The Lymphatic System

UNIT B
Chapter 10: Circulatory System and Lymphatic System
The Lymphatic System
Consists of lymphatic vessels and the lymphoid organs.
The lymphatic system has three main functions:
1. Return excess tissue fluid to circulation
2. Absorb fats from the digestive tract
3. Defend the body against disease
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Section 10.6
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Chapter 10: Circulatory System and Lymphatic System
Section 10.6
Figure 10.21 Lymphatic
system. Lymphatic vessels
drain excess fluid from the
tissues and return it to the
circulatory system. Lymphatic
vessels, like circulatory veins,
have valves to prevent
backward flow.
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Chapter 10: Circulatory System and Lymphatic System
Lymphatic Vessels
Lymphatic vessels form a oneway system that begins with the
lymphatic capillaries.
Lymphatic capillaries (tiny,
closed-ended vessels) absorb
excess tissue fluid called lymph.
• Tissue fluid contains water,
solutes (nutrients, electrolytes,
oxygen), and cellular products
(hormones, enzymes, wastes)
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Section 10.6
Compare Lymphatic Capillaries to Blood
Capillaries
Lymphatic Capillaries
• have valves,
• are slightly larger in diameter,
• have closed ends (unlike the loop structure of blood
capillaries).
• Unique structure permits interstitial fluid to flow in but not
out.
• The ends of the endothelial cells that make up the wall of a
lymphatic capillary overlap.
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Chapter 10: Circulatory System and Lymphatic System
Movement of Lymph in Lymphatic Vessels
• dependent on skeletal muscle
contraction
• One-way valves in the vessels
prevent lymph from flowing
backward
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Section 10.6
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Movement of Lymph in Lymphatic Vessels
The lymphatic capillaries join to
form lymphatic vessels that
merge before entering one of two
ducts:
• Thoracic duct: returns lymph
collected from the left side of
the body into the left
subclavian vein
• Right lymphatic duct: returns
lymph collected from the right
side of the body into the right
subclavian vein
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Section 10.6
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
Edema
Edema is localized swelling caused by the accumulation
of tissue fluid that has not been collected by the
lymphatic system.
• Occurs if too much tissue fluid is made and/or if not
enough is drained away
• Can lead to tissue damage and death
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Chapter 10: Circulatory System and Lymphatic System
Section 10.6
Lymphoid Organs
Lymphoid organs contain large numbers of lymphocytes
(white blood cells involved in adaptive immunity).
There are two types of lymphoid organs:
• Primary lymphoid organs: red bone marrow and
thymus, where lymphocytes develop and mature
• Secondary lymphoid organs: lymph nodes and spleen,
where lymphocytes become activated
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UNIT B
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Chapter 10: Circulatory System and Lymphatic System
Section 10.6
Figure 10.22 The lymphoid organs. The thymus (a) and red bone marrow (b)
are the primary lymphoid organs. Blood cells, including lymphocytes, are
produced in red bone marrow. B cells mature in the bone marrow. T cells mature
in the thymus. The lymph nodes (c) and the spleen (d) are secondary lymphoid
organs. Lymph is cleansed in the nodes, and blood is cleansed in the spleen.
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Chapter 10: Circulatory System and Lymphatic System
Primary Lymphoid Organs
Red bone marrow
• Contains a network of connective
tissue fibres, along with stem cells
that can divide and produce blood cells
• Lymphocytes begin development in the
• bone marrow
o B lymphocytes (B cells) begin in bone marrow and
then migrate to secondary lymphoid organs to
mature
o T lymphocytes (T cells) in bone marrow and then
migrate to the thymus, where they mature and
differentiate
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Section 10.6
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Chapter 10: Circulatory System and Lymphatic System
Primary Lymphoid Organs
Thymus
• lobules, filled with T cells and
supporting cells
• Lobules are lined with epithelial
cells that secrete hormones called
thymosins, which are involved in
the differentiation of T cells
• T cells that react to the body’s own
cells undergo apoptosis
(programmed cell death)
• T cells that leave the thymus can
react to foreign molecules
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Section 10.6
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Chapter 10: Circulatory System and Lymphatic System
Secondary Lymphoid Organs
Spleen
• Cleanses blood
• Thin capsule surrounding white
(filters debris and bacteria) and
red pulp ( macrophages filter worn
out RBC)
• May be surgically removed due to
trauma or disease, however the body
becomes more susceptible to certain
types of infections
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Section 10.6
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Secondary Lymphoid Organs
Lymph nodes
• Cleanse lymph
• Occur along lymphatic vessels
• Connective tissue divides nodes into
nodules, each of which contain B
cells, T cells, and a sinus
• As lymph passes through the sinuses,
macrophages engulf pathogens.
• Cancer cells can enter the lymph nodes
and lymphatic vessels and move
through to other regions of the body,
where they produce secondary tumours
(metastasis)
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Section 10.6