Chapter 11: Keeping Up Your Defenses: The Lymphatic System Summary

The lymphatic system

The lymphatic system filters and destroys pathogens hence protecting the body.

The lymphatic system absorbs and breaks down excess fats and regulates the blood volume.

Lymph and ducts

The lymphatic system starts within body tissues and proceeds to blood capillaries where plasma proteins, plasma, and nutrients leak into the cells while wastes including carbon dioxide move into the lymphatic system.

The lymphatic vessels collect, transports, clean, and return the lymph fluid to the bloodstream. Lymph capillaries collect the lymph fluid from the whole body. The capillaries terminate in tissues.

Lymph is the fluid trapped within capillaries which then moves to the wider capillaries called lymphatic vessels.

The lymphatic vessels are wide, thin-walled, and have many valves. They also contain lymph nodes which are bean-shaped structures on the vessels.

Ducts are formed when lymphatics merge to form large lymphatic vessels. The thoracic duct (left lymphatic duct) is the largest. The lymphatic duct and the right lymphatic duct empty into the subclavian region.

Lymph nodes

Lymph nodes are the lymphatic system filtration sites. They are covered with connective tissues and are kidney-shaped in shape.

The lymph nodes have macrophages that destroy cancer cells and bacteria. Lymphocytes in lymph nodes generate immune responses to bacteria. The nodes contain a cortex for collecting lymphocytes while the medulla is found at the center and contains lymphocytes too.

Lymphocytes are aligned on the outer cortex in large numbers to form lymphatic nodules that contain germinal centers that produce lymphocytes.

Many nodes exist in groups especially in the armpit, groin, and areas of the mammary gland.

• The primary lymph node areas include:
  • Neck
  • Head
  • Lower extremities
  • Upper extremities
  • Thorax
  • Viscera
  • Pelvis and abdomen
• The lymph node cortex contains B and T lymphocytes and monocytes.
  • Monocytes in lymph nodes mature into macrophages that destroy bacteria and cancer cells.
  • B cells produce antibodies that stimulate phagocytes to attack the pathogens or activate the complement pathway.
  • T cells mature in the thymus and are produced in the bone marrow. They kill pathogens directly or produce cytokines for cell pathogen destruction.

The spleen

It is the biggest lymphatic organ that is egg-shaped in shape.

Blood moves within the spleen slowly to enhance the removal of tired erythrocytes, microorganisms, and foreign substances available in the blood.

The spleen can store blood. When the body is at rest, the blood volume in circulation reduces, the vessels in the spleen dilate and reserves more blood.

The spleen also generates erythrocytes in embryonic development and stops after delivery. In anemic conditions, the spleen begins the production of the erythrocytes again.

Thymus gland

The thymus gland educates T lymphocytes in the fetal development stage and even for the initial years of life.

The bone marrow of the fetus produces lymphoblasts that are taken to the thymus. Between birth and adolescence, thymosin hormone is produced by the thymus and the hormone facilitates the maturity of T cells making them immunocompetent.

A fibrous capsule surrounds the thymus to form chambers called lobules. Every lobule contains a T cell cortex bound together by reticular fibers.

Tonsils and Peyer’s patches

• Peyers patches are lymph tissue groups found beneath the ileum. The Peyer’s patches can accumulate many macrophages and B cells to destroy pathogens.
• Tonsils are the largest at puberty and reduce in size with age. The tonsils don’t produce hormones and but synthesizes antibodies and lymphocytes that destroy microorganisms that get into the body.
• There are 6 tonsils: The palatine tonsils are two, two are pharyngeal or adenoid tonsils and two are lingual tonsils.
• Tonsil invaginations form structures called crypts that absorb bacteria and foreign molecules.

Revision

What is the order in which the lymph travels through the body?
Lymphatic capillaries -> Lymphatic collecting vessels
-> Lymphatic trunks -> Ducts.

In what direction does the lymph travel through the body?
One way, towards the heart.

Lacteals
Specialized lymphatic capillaries that are found in the villi of the intestinal mucosa. They play a large role in absorbing digested fats from the intestine.

What is the name of the fat absorbed by the lacteals?
Chyle

What are the names of the lymphatic trunks?
Lumbar, bronchomediastinal, subclavian, jugular, and intestinal.

What are the lymph ducts, and where do they receive lymph from?
Right lymphatic duct – receives lymph from the right upper limb, right side of the head, and thorax.
Thoracic duct – receives lymph from the rest of the body.

Where is the lymph emptied into the venous circulation?
At the junction of the internal jugular vein and the subclavian vein.

What are the 3 main functions of the lymphatic vessels?

1. Return excess fluid to the bloodstream.
2. Return leaked proteins to the blood.
3. Carry absorbed fat (chyle) from the intestine to the blood (via lacteals).

What are the ways in which lymph is ‘pumped’ through the lymphatic vessels?
By contraction of near by skeletal muscle, pressure changes in the thorax due to breathing, and pulsations of nearby arteries.

What types of cells are found in lymphoid organs?
Lymphocytes, macrophages, dendritic cells, and reticular cells.

What types of cells do lymphocytes differentiate into?
T cells
B cells – produce plasma cells, which secrete antibodies.

What is the function of macrophages?
They phagocytize foreign substances.

What is the function of dendritic cells?
They capture antigens and bring them back to the lymph nodes for phagocytosis.

What is the function of reticular cells?
They produce the reticular fiber stroma of the lymphatic system.

What type of tissue composes all lymphoid organs, other than the thymus?
Reticular connective tissue.

Where are lymph nodes found?
Clustered along lymphatic vessels.

What are the main functions of lymph nodes?
They act as lymph filters as lymph travels through them, and they help to activate the immune system.

Where does the lymph enter and exit the lymph node?
It enters via the afferent lymphatic vessels on the convex side of the node, and exits via the efferent lymphatic vessels at the hilum.

What are the other lymphoid organs found in the body?
The spleen, thymus, tonsils, Peyer’s patches of the intestine, and bits of lymphatic tissue scattered throughout the body.

What are the functions of the spleen?
It provides a site for lymphocyte proliferation, it stores some of the breakdown products of RBC’s for later use, restores platelets, and is thought to be the site of erythrocyte production in the fetus.

When is the thymus most functional?
During the early years of life.

What is the function of the thymus?
It is the site of T lymphocyte maturation.

What is the simplest lymphoid organ?
The tonsils.

What is the key function of the tonsils?
To gather and remove many of the pathogens entering the pharynx in food and inhaled air.

What are the 4 tonsils?
The paired palatine tonsils, the lingual tonsil, the pharyngeal tonsil, and the tubal tonsils.

How do the tonsils trap bacteria?
They form tonsillar crypts.

What are Peyer’s Patches?
Large clusters of lymphoid follicles that are loacted at the portion of the small intestine.

What is another name for Peyer’s Patches?
Aggregated lymphoid nodules.

How are lymphatic vessels and lymph nodes formed?
They arise from budding from developing veins.

What type of cells do lymphoid organs stem from?
Mesenchymal cells.

Elephantitis
A typically tropical disease in which the lymphatics become clogged with parasitic roundworms. There is enormous swelling.

Hodgkin’s Disease
A malignancy of lymphoid tissue. Symptoms include swollen, non-painful lymph nodes, fatigue, intermittent fever, and night sweats. It is characterized by the presence of giant malignantly transformed B cells, called Reed-Sternberg cells. It is treated with chemotherapy and radiation.

Lymphadenopathy
Any disease of the lymph nodes.

Lymphangiography
A diagnostic procedure in which lymphatic vessels are injected with radiopaque dye then visualized with x-rays.

Lymphoma
Any neoplasm (tumor) of the lymphoid tissue, whether it be benign or malignant.

What are the levels organization in the body – smallest to largest.
chemical level – cellular level – tissue level – organ level – organ system level.

What are the processes to maintain life?
Movement, responsiveness, digestion, metabolism, excretion of waste, and reproduction.

Pathology
The study of changes in organs and tissue by diseases.

Autopsy
Examination of a body after death o determine the COD. Aka: postmortem examination and necropsy.

Ionic Balance
The balance of ions in the body that is necessary for proper function. It is mostly maintained by the urinary system and integumentary system.

Acidosis
Low pH.

Ketosis
Results from excessive ketones (breakdown of fats) in the blood. It is common during starvation and attacks of diabetes mellitus.

Alkalosis
High pH.

Tonicity
The ability of a solution to change the tone or shape of cells.

Anaplasia
Cells with abnormal structure.

Apoptosis
Programmed cell death. Intracellular enzymes destroy cellular structures and the cell remains are phagocytized by nearby cells.

Necrosis
Uncontrolled cell death – due to injury or disease.

Dysplasia
Abnormal size, shape, or arrangement of cells; non-cancerous.

Neoplasms
Uncontrolled growth of cells – cancerous or not.

Hyperplasia
Increase in the number of cells – non-cancerous.

Hypertrophy
Growth in organ due to increase in size of cells.

Edema
Swollen tissue.

Benign neoplasm
a nonmalignant tumor; local.

Malignant neoplasm
A malignant tumor.

Metastasis
A part of a tumor breaking off, and traveling to other parts of the body.

Carcinoma
Cancer arising in the epithelium.

Sarcoma
Cancer arising in mesenchyme-derived tissue.

Scurvy
A nutritional deficiency caused by a lack of vitamin C, which is needed to synthesize collagen.

Lesion
An injury, wound, or infection that affects tissue over an area of definite size.

Mononucleosis
A viral disease common in adolescents and young adults. Symptoms include fatigue, fever, sore throat, and swollen lymph nodes. It is caused by the Epstein-Barr virus. It specifically attacks B cells, which leads to a massive activation of T cells.

Non-Hodgkin’s Lymphoma
Includes all cancers of lymphoid tissues except Hodgkin’s disease. It involves uncontrolled multiplication and metastasis of undifferentiated lymphocytes. Causes swelling of lymphoid organs.

Sentinel Node
The first node that receives lymph drainage from a body area suspected of being cancerous. It is the best node to examine for indication if metastasis has occurred.

Splenomegaly
Enlargement of the spleen due to accumulation of infectious microorganisms. Typically caused by septicemia, mononucleosis, malaria, or leukemia.

Tonsillitis
Inflammation of the tonsils, typically due to bacterial infection. They become red, swollen, and sore.

What are the functions of the lymphatic system?
Drain excess interstitial fluid, transport dietary lipids, and carry out immune responses

What happens to lymph once it finishes circulating through the body?
Lymph returns to venous circulation

Which lymphatic organ has the largest amount of lymphatic tissue?
Spleen

How does the thymus change size throughout life?
Grows during childhood and shrinks after puberty

What is the function of the lymph nodes?
Filters lymph

Which lymphatic organ is effective against airborne pathogens?
Tonsils

How is innate immunity different from adaptive immunity?
Innate- Born with
Adaptive- Developed

What is considered to be your first line of defense against pathogens?
Physical barriers (skin, mucus, saliva, hair, sweat, body fluids)

Which types of cells are responsible for cell-mediated immunity?
Tcells

Which types of cells are responsible for humoral (anti-body) mediated immunity?
Bcells

How are T cells activated?
Being exposed to antigens

How will T cells activate B cells?
Tcells will divide to make Active T helper cells which can activate either more Tcells or Bcells

How is active immunity different from passive immunity?
Active- able to make anti-bodies
Passive- antibodies are given to us

Lymphatic capillaries and blood capillaries are always found __ (near, far) from each other?
Near

What special characteristic do lymphatic vessels have and what for?
Have overlapping structures (like valves) to ensure one-way flow

What happens at the Lymphatic ducts?
Lymph is returned to venous circulation

What are found in the center of lymph nodes?
(1) Macrophages, (2) Tcells, (3) Plasma cells, and (4) Bcells

What is inflammation?
A localized tissue response to injury