1. The Lymphatic System UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
The Lymphatic System
Consists of lymphatic vessels and the lymphoid organs.
The lymphatic system has three main functions:
Return excess tissue fluid to circulation
Absorb fats from the digestive tract
Defend the body against disease
lymphatic system: a type of organ system consisting of lymphatic vessels, lymph nodes, and other lymphatic organs; transports lymphs and lipids, and aids the immune system
The lymphatic system has three main functions:
Lymphatic capillaries absorb excess tissue fluid and return it to the bloodstream
Lymphatic capillaries absorb fats from the digestive tract and transport them to the bloodstream
Lymphoid organs defend the body against disease
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2. UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
Figure 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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3. Lymphatic Vessels UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
Lymphatic Vessels
Lymphatic vessels form a one-way 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)
lymphatic vessels: a one-way system that carries lymph
lymphatic capillaries: collect excess tissue fluid called lymph
lymph: tissue fluid contained within lymphatic vessels
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4. Compare Lymphatic Capillaries to Blood 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.
Both have valves

5. Movement of Lymph in Lymphatic Vessels
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
Movement of Lymph in Lymphatic Vessels
dependent on skeletal muscle contraction
One-way valves in the vessels prevent lymph from flowing backward
Lymph percolates through various lymph nodes, where foreign material can be recognized by the immune system
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6. Movement of Lymph in Lymphatic Vessels
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
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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7. 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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8. UNIT B
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
lymphoid organs: organs that contain large number of lymphocytes; can be primary or secondary lymphoid organs
lymphocytes: have two major types: B lymphocytes produce antibodies, T lymphocytes can either regulate the responses of other cells or can kill other cells
primary lymphoid organs: organs where lymphocytes develop and mature; includes red bone marrow and thymus
secondary lymphoid organs: organs in which some lymphocytes become activated; includes lymph nodes and spleen
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9. UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
Figure 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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10. Primary Lymphoid Organs
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
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
B lymphocytes (B cells) begin in bone marrow and then migrate to secondary lymphoid organs to mature
T lymphocytes (T cells) in bone marrow and then migrate to the thymus, where they mature and differentiate
red bone marrow: a primary lymphoid organ where lymphocytes begin their development; contains a network of connective tissue fibres, along with stem cells that are able to divide and produce blood cells
B cells: lymphocytes that remain in bone marrow until mature; also called B lymphocytes
T cells: lymphocytes that migrate from bone marrow to the thymus where they mature and differentiate
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11. Primary Lymphoid Organs
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
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
thymus: a primary lymphoid organ that secretes the hormone thymosins, which aids in the differentiation of T cells
Thymus
Connective tissue divides the thymus into lobules, which are 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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12. Secondary Lymphoid Organs
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
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
spleen: a secondary lymphoid organ that removes old and defective blood cells, as well as reacts to foreign invaders
Thin capsule can burst from injury. Surgical removal may lead to susceptibility to infections
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13. Secondary Lymphoid Organs
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.6
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)
lymph nodes: masses of lymphatic tissue located along the course of a lymphatic vessel
pathogens: disease-causing agents such as viruses and bacteria
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