BIO127 – Lymphatic System (Part I)

Objectives & Learning Outcomes

  • BIO127 – Chapter 11, Part I will help you understand:

    • What the lymphatic/immune systems do in general and specifically.

    • Important medical words, shortcuts, and parts of words used for these systems.

    • How to spot the parts like vessels, ducts, nodes, organs, and cells.

    • How things work: where lymph comes from and how it travels, the body's three layers of defense, the difference between general and specific protection, and how the body fights sickness with antibodies or special cells.

    • Real-world skills: tests, sicknesses, how aging affects the system, and different ways we get immunity.

Core Medical Terminology

  • immun/o = protection

  • lymph/o = lymph (the fluid)

  • lymphaden/o = lymph node (a filtering station)

  • splen/o = spleen (an organ)

  • thym/o = thymus gland (another organ)

Two Fluid-Circulating Systems

  • Cardiovascular System

    • A closed loop (heart and blood vessels) that moves blood around.

    • Path: \text{Right Heart} \to \text{Lung Arteries} \to \text{Lungs} \to \text{Lung Veins} \to \text{Left Heart} \to \text{Main Arteries} \to \text{Smaller Arteries} \to \text{Tiny Capillaries} \to \text{Tiny Veins} \to \text{Larger Veins} \to \text{Right Heart}.

  • Lymphatic System

    • An open network that carries lymph (a fluid like blood plasma but with less protein).

    • It works with the blood system to pick up extra fluid from tissues, take in fats, and fight off sickness.

Lymph: Where it Comes From, What it's Made Of, & Its Journey in Tissues

  • Blood plasma leaks out of tiny blood vessels (capillaries) → becomes interstitial fluid (tissue fluid) between cells.

  • What interstitial fluid does:

    • Delivers food and oxygen to cells.

    • Cleans tissues by picking up waste, broken bits, germs, or loose cancer cells.

  • When there's too much fluid in tissue spaces → tiny, flap-like valves in lymphatic capillaries open → fluid enters and is now called lymph.

  • Lymph is colorless, rich in white blood cells (WBCs), and has less protein than blood plasma.

Lymphatic Vessels & Valves

  • Lymphatic capillaries

    • They are closed at one end, have thin walls, and wide openings.

  • They gradually join together to form larger lymphatic vessels that have one-way valves (like veins, they stop fluid from flowing backward).

  • Muscle squeezes and pressure differences push lymph towards the heart.

Major Lymphatic Pathways

  • Two main tubes collect all the lymph from the body: 1. Right Lymphatic Duct → empties into the right subclavian vein; drains the right side of the head, right arm, and right chest (thorax)

    1. Thoracic Duct (the biggest) → empties into the left subclavian vein; drains about 75\% of the rest of the body. (drains whatever is left)

  • Final stop: The lymph goes back into the blood system and returns to the right side of the heart, helping to keep fluid levels balanced.

  • Subclavian Veins - (right and left) where it joins the venous blood returning to the right heart.

Lymph Nodes

  • Small, bean-shaped filters found along the lymphatic vessels.

  • Structure: Many nodules packed with immune cells (lymphocytes and macrophages); lymph flows in through many vessels, filters through, and flows out through one vessel. They also have special areas where B-cells are made.

  • Function, like a “water filter” for lymph: They remove trash, germs, and abnormal cells before the lymph goes back into the blood.

  • Groups of nodes in different body areas:

    • Cervical – clean lymph from the head and neck. - in the neck

    • Axillary – clean lymph from the breasts and arms. - in axillary area at the lateral margin of breast.

    • Thoracic (in the chest) – clean lymph from organs in the chest. - trachea & bronchi

    • Abdominal / Mesenteric / Intestinal – clean lymph from organs in the abdomen, like urinary and reproductive parts. - in posterior wall of the abdominopelvic cavity.

    • Inguinal & Popliteal (shown in image) – clean lymph from the lower legs.

Lymphoid Tissues & Secondary Organs

  • MALT (Mucosa-Associated Lymphatic Tissue)

    • Immune cells spread out in the moist linings of the respiratory, digestive, urinary, and reproductive tubes.

  • purpose is to guard and fight pathogens trying to enter the body.

    • They are the first to react when germs try to enter through these openings.

    • A special type: Peyer’s Patches - Patches of lymphatic tissue (densely packed pockets of lymph “modules”) in the lower small intestine; they watch for gut bacteria and stop bad germs from getting in.

  • Tonsils (ring of tissue in the throat) lymphoid tissue, high concentration of lymphocytes.

    • Include Pharyngeal (adenoids), Palatine (“regular” tonsils), and Lingual.

    • Have many immune cells; small pockets in the tonsils trap germs so the immune system can learn about them.

  • Thymus

    • A two-part gland located over the heart; it’s big in children but shrinks with age.

    • This is where T-lymphocytes (a type of immune cell) grow up and learn to tell the difference between healthy body cells and invaders.

  • Create WBC

  • Spleen

    • The largest immune organ; located in the upper left part of the belly under the diaphragm.

    • Jobs: filters blood (removes old red blood cells), stores extra blood, controls blood volume, helps make blood cells in babies before they are born, and watches for sickness.

    • Parts: Red pulp (stores red blood cells, cleans up old ones) vs. White pulp (where immune cells multiply).

Cells of the Lymphatic / Immune System

  • Natural Killer (NK) Cells

    • Large immune cells with granules; they are a general defense: they destroy bacteria, virus-infected cells, cancer cells, and transplanted cells that don't belong.

  • T-Lymphocytes (start in bone marrow, finish maturing in the thymus) come from stem cells in red bone marrow, sent to thymus gland where they mature. Protect the body from infection; may help fight cancer

    • T(Helper) – Like “quarterbacks”; they activate both general and specific immune responses; they help B-cells, other T cells, and macrophages by sending out chemical signals.

    • T(Cytotoxic) – Directly kill cells infected with viruses and cancer cells.

    • T (Memory) – Stay in the body for a long time; they make the body react faster to a second exposure to the same germ. remember pathogens that had previously been introduced into the body. allowing response to repeat.

    • T(Regulatory/Suppressor) – Release chemicals that stop other T-cells from being too active; they prevent the immune system from attacking the body’s own healthy tissues. Keep other cells in check

    – If they don't work right → autoimmune disease (the body attacks itself).

  • B-Lymphocytes - WBC

  • (grow and mature in bone marrow) develop from stem cells in the bone marrow, produce antibodies which bind to pathogens and toxins and inactivate them, also serve as antigen presenting cells (APC’s)

  • Dedicated APC- present foreign antigen to T-helper cells

  • Virus infected cells- (cancer cells) can present antigens originating inside the cell to the T-cytotoxic cells

  • EXTREMELY important in effective adaptive immune response

    • They change into:

    ◦ B Plasma Cells – Make and release specific antibodies into the blood (this is called humoral immunity). dissolved in plasma.

    ◦ B Memory Cells – Long-lasting cells that remember how to quickly make antibodies in the future.

    • They also act as Antigen-Presenting Cells (APCs), showing parts of germs to T cells.

  • Antigen-Presenting Cells (APCs)

    • Special cells: dendritic cells, macrophages, B-cells.

    • Also, infected or cancer cells can show parts of themselves to T cells.

    • They are key for starting the body's specific immune response.

  • Macrophages

    • Large eating cells made from monocytes; they are a general defense – they swallow germs, debris, and dead immune cells; they are also APCs.

  • Dendritic Cells

    • Guard cells in the skin and lining of tissues; they capture germs, travel to lymph nodes, and show them to T cells; they also make antibodies. These also act as APCs

Functional Summary of the Lymphatic System

  • Fluid Balance

    • Returns about 3\,L/\text{day} of fluid (that came from plasma) back to the bloodstream, stopping swelling caused by too much fluid.

  • Immunity

    • Provides monitoring, filtering, and a place to start both general (innate) and specific (adaptive) immune responses.

  • Lipid Absorption

    • Special vessels (lacteals) in the small intestine absorb fatty fluid (chyle) into the thoracic duct.

  • Defense Against Disease • Three levels of protection: 1. Outside barriers (skin, moist linings).

    1. General internal defenses (NK cells, macrophages, inflammation, special proteins called complement).

    2. Specific immunity (T-cells for cell-based defense; B-cells and antibodies for fluid-based defense).

  • Ageing Effects (more in Part II)

    • The thymus shrinks, T-cell production goes down, less effective response to vaccines, and more autoimmune diseases.

Analogies & Real-World Connections

  • Lymph node is like a household water filter that cleans impurities before the water (lymph) goes back into the main supply (blood).

  • Traffic system: the blood system is the “highway” while the lymphatic system is the “service roads” that collect spills and garbage to disposal centers (nodes/spleen).

  • Clinical use: In breast cancer, checking the sentinel node (the first lymph node to which cancer cells are likely to spread) helps predict how far the cancer has spread.

  • Ethical/philosophical: Too much suppression by T$_{\text{Reg}}$ cells might let tumors grow; too little suppression can lead to autoimmune diseases. Balancing immunity is crucial in treatments (e.g., cancer drugs, anti-rejection drugs after organ transplants).

Key Numbers & Facts to Memorize

  • The \text{Right Lymphatic Duct} drains about 25% of the body (upper right area).

  • The \text{Thoracic Duct} is about 38–45 cm long; it starts at a pouch called cisterna chyli (not yet discussed in detail).

  • On average, 2.0\text{–}3.0\,L of lymph are returned to the blood each day.

Common Abbreviations

  • APC – Antigen-Presenting Cell (a cell that shows invaders to immune cells)

  • MALT – Mucosa-Associated Lymphatic Tissue (immune tissue in moist body linings)

  • NK – Natural Killer (a type of immune cell)

  • WBC – White Blood Cell (immune cell)

  • RBC – Red Blood Cell (carries oxygen)

  • T$_{\text{H}}$ – T Helper (a type of T-cell that helps other immune cells)

  • T$_{\text{C}}$ – T Cytotoxic (a type of T-cell that kills bad cells)

  • T$_{\text{Reg}}$ – T Regulatory (a type of T-cell that balances the immune response)

Sample Word-Building

  • lymph/o + aden + itis → lymphadenitis = swelling/inflammation of a lymph node.

  • splen/o + megaly → splenomegaly = enlarged spleen.

  • immun/o + suppress + ant → immunosuppressant = a substance that lowers immune activity.

Take-Home Messages

  • The lymphatic system is essential for keeping fluid levels balanced and