Lymphatic System

The class book serves as a handout for online Panopto lectures, replacing uploaded slides.
Students are encouraged to review Ross & Wilson's Anatomy and Physiology in Health and Illness, available in E-book and physical format at the library.
Learning Outcomes:
- Identify anatomical structures/components of the lymphatic system.
- Describe physiological functions and mechanisms of the lymphatic system.
- Explain pathophysiological changes due to common illnesses, diseases, injuries, and well-being conditions associated with the lymphatic system.

Components:
- Lymph
- Lymph vessels
- Lymph nodes
- Lymph organs
- Mucosal-associated lymphoid tissues
- Bone marrow
Role:
- Protects the body from diseases and infections.
- Lymph consists of excess interstitial fluid and particulate matter, including cell debris and bacteria drained from tissues by lymphatic capillaries.
- Lymphatic capillaries unite to form larger vessels connected through lymph nodes and organs like the thymus and spleen.

Lymph:
- Clear, watery fluid similar to interstitial fluid and plasma (with less protein).
- Transports plasma proteins and larger particles (cell debris, bacteria) to lymph nodes.
- Contains lymphocytes that patrol the body's tissues.
Lymph Vessels:
- Start as blind-ended tubes in interstitial spaces, with a structure similar to blood capillaries but more permeable to proteins and debris.
- Join to form larger lymph vessels, often alongside arteries and veins.
- Have a similar wall structure to small veins, with valves to ensure one-way flow.
- Include the thoracic duct and right lymphatic duct, which empty into subclavian veins.

Lymph typically flows through 8 to 10 nodes before returning to venous circulation.
Nodes are grouped along lymph vessels, especially in infection-prone areas (e.g., respiratory system).
Size ranges from 1 to 25 mm, shaped bean or oval.

The largest lymph organ, slightly oval in shape, located in the left hypochondriac region (12 x 7 x 2.5 cm, approx. 200g).
Surrounded by a fibroelastic capsule forming trabeculae, with splenic pulp (red and white) composed of macrophages and lymphocytes.
Blood flows via sinusoids, enabling effective removal of damaged cells from the bloodstream.
Major vessels entering at the hilum: splenic artery, splenic vein, efferent lymph vessels, and nerves.

Located in the upper mediastinum, behind the sternum, extending into the neck.
Grows until puberty followed by atrophy, returning to approximate weight by middle age.
Composed of two lobes enclosed by fibrous capsule, divided into lobules containing lymphocytes and epithelial cells.

Major components: tonsils and Peyer’s patches in the small intestine.
Composed of lymphoid tissue collections not enclosed like thymus or spleen.
Contains B and T cells; they are crucial for detecting invasions but do not filter lymph, avoiding certain diseases affecting other lymphatic organs.

Functions categorized as:
1. Tissue drainage
2. Absorption in the gastrointestinal tract
3. Immunity
Significant interactions with circulatory, digestive, and immune systems.

Approximately 21 liters of plasma fluid escape into tissues daily; most returns through venous capillaries, with 3-4 liters drained by lymphatics.
Prevents cardiovascular failure due to lowered blood volume; also removes pathogens and debris from tissues, ensuring they do not become oedematous.
Lymph is filtered through lymph nodes housing lymphocytes and macrophages before returning to the bloodstream.

Villi in the small bowel aid absorption, containing blood vessels and lymph capillaries known as lacteals (responsible for milky appearance from fat absorption).
Peyer’s patches help identify and neutralize ingested pathogens.

Thymus is essential for T-cell lymphocyte maturation, with shrinking starting post-puberty leading to increased vulnerability to infections.
Lymph nodes play key roles in defense and lymphocyte maturation; lymph is filtered through them, destroying organic matter using antibodies and macrophages.
The spleen’s roles include:
- Immune Response: White pulp contains T & B lymphocytes for immunity; splenectomy increases infection risk.
- Phagocytosis: Red pulp removes pathogens, damaged erythrocytes, and debris from the bloodstream.

Blood Storage: Contains up to 350 mL of blood, returning it to circulation in response to sympathetic stimulation (e.g., hemorrhage).
Erythropoiesis: Essential in fetal development and can occur in adults during significant need; retains the role when necessary.

Covers pathology of lymph vessels, diseases of lymph nodes and thymus, and disorders of the spleen.
Common terms:
- Lymphangitis: Inflammation of lymph vessels.
- Lymphadenitis: Infection of lymph nodes.
- Lymphadenopathy: Enlargement of lymph nodes.
- Splenomegaly: Enlargement of the spleen.
- Lymphoedema: Swelling due to obstructed lymphatic drainage.

Lymphatic Obstruction: Can lead to secondary lymphoedema, often caused by tumors or radical treatments; prevalent in head and neck cancer cases.
Lymphangitis: Occurs when bacteria spread along lymph vessels, visible as a classic red line.
Spread of Disease: Malignant cells can enter lymphatic vessels and spread to the nearest nodes, posing a risk for bloodstream involvement.

Lymphadenitis: Nodes become enlarged due to infections, potentially leading to abscesses; can arise acutely or chronically.
Infectious Mononucleosis: Highly contagious; caused by Epstein–Barr virus. Symptoms include fatigue, malaise, tonsillitis, lymphadenopathy, and splenomegaly.
Lymphomas: Cancers originating in lymphatic cells; classified as Hodgkin's (typically rarer) and Non-Hodgkin's (more common and varies in malignancy). Complications may include depression of lymphocyte function and anemia.

Autoimmune conditions linked to thymus enlargement include Addison’s disease and Myasthenia gravis.
Thymic hyperplasia and thymoma can impact nearby structures, causing various respiratory issues.

Splenomegaly: Enlargement can arise from infections (local or blood-borne), circulatory disorders, or tumors.
Acute infections are rare but severe; chronic infections are more common and usually less severe. Examples include malaria, tuberculosis, and glandular fever.