lymphatic system

Fluid balance  

1. Returns excess interstitial fluid and proteins to the bloodstream 

2. Prevents edema

Absorption of dietary lipids  

1. Lacteals (lymphatic capillaries in small intestine) absorb fats 

2. Fats enter lymph → bloodstream 

Immune defense

1. Filters lymph and blood 

2. Houses immune cells (lymphocytes, macrophages)

Lymph

clear fluid with lymphocytes 

Lymphatic vessels

transport lymph 

Lymph nodes

filter lymph 

Spleen

filters blood

Thymus

T‑cell maturation 

Tonsils

trap pathogens 

Formation & Movement of Lymph

• Derived from interstitial fluid 

• Moves one direction toward heart 

Driven by:  

• Skeletal muscle pump 

• Breathing movements 

• Valves 

Capillaries 

• vessels that collect the excess tissue fluid and are located near the blood capillaries

• allows any bacteria, viruses, or cancer cells to enter easily →lymph nodes to destroy

Collecting vessels 

• more valves than the veins → direct the flow of lymph

Lumbar trunks

• paired and lies along the side of the
  abdominal aorta → receives lymph draining from the lower
  limbs, pelvic organs

Intestinal trunk

• unpaired and lies posterior to the
  abdominal wall in the midline → receive fatty lymph (chyle)
  from the stomach, intestines

Broncho mediastinal trunks

• paired near the sides of the
  trachea → receives lymph from the thoracic organs and
  wall

Subclavian trunks

• paired near the base of the neck →
  receives lymph from the upper limb and the superior thoracic
  wall

Jugular trunks

paired located at the base of each
internal jugular vein and drain the head and neck

ducts

Drains the lower extremities

Thoracic duct  

Drains entire body except right upper quadrant

Right lymphatic duct 

Drains right head, arm, and chest 

Lymph nodes

filter lymph

Spleen

filters blood, removes RBCs

Thymus

T‑cell development

Tonsils

immune surveillance 

Primary organs

• Bone marrow, thymus 

• Where lymphocytes mature 

Secondary organs

• Lymph nodes, spleen, tonsils 

• Where immune responses occur 

Red bone marrow

Lymphocytes (T cells and B cells) (b cells= bone marrow, T cells= Thymus)

Thymus

• turn into Helper T cells and Cytotoxic T cells

• disappear after puberty

Lymph nodes

One way flow of lymph through node
• More entering vessels than exiting → increased exposure time
• Exit: hilum

Spleen

• Largest lymphatic organ

Two regions filter blood:
•White pulp: lymphocytes and
Macrophages carry out immune function
• Red pulp: removes dead blood cells and platelets

Tonsils

gather and remove many pathogens that enter the pharynx in inspired air and swallowed food.

Innate Immunity

A defense system you are born with. It protects you against all
antigens (1st line and 2nd line of defense)

First Line of Defense

• Skin – physical barrier 

• Mucous membranes – trap pathogens 

• Secretions – lysozyme, acid, sweat 

Second Line of Defense

• Inflammation – redness, heat, swelling 

• Fever – inhibits pathogens 

• Phagocytosis – neutrophils, macrophages 

• Natural killer cells – destroy abnormal cells 

• Antimicrobial proteins – complement, interferons 

Phagocytosis

1. Chemotaxis - attraction to the pathogen

2. Adherence - attachment to the pathogen

3. Ingestion - engulfing the pathogen

4. Digestion - breaking down the pathogen

5. Exocytosis - exspulsion of debris

Inflammation

• Vasodilation 

• Increased permeability 

• Attracts immune cells 

Adaptive Immunity 

Effective against:
1- intracellular pathogens (viruses, bacteria, fungi)
2- some cancer cells
3- foreign tissue transplants

• has memory

• Recognizes self vs non‑self 

Humoral immunity

Humoral immunity involves B cells producing antibodies to fight extracellular pathogens in bodily fluids

Cell-mediated

employs T cells to destroy intracellular pathogens, tumor cells, and transplanted tissues

B cells

Create antibodies to target bacteria

T cells

Attack viruses, fungi, some cancer cells directly

• Helper T → activate immune response 

• Cytotoxic T → kill infected cells 

Antibodies 

• a protein component of the immune system that circulates in the blood

• Bind antigens 

• Neutralize pathogens 

• Opsonization (acts as a marker, making the pathogen more visible)

• Activate complement 

Important Immune Cells 

• Helper T cells (CD4) 

• Cytotoxic T cells (CD8) 

• Plasma cells 

Antigens 

• Substances that trigger immune responses 

• Usually proteins or polysaccharides 

Immunodeficiency

weak immune system 

Autoimmunity

body attacks itself 

Hypersensitivity

exaggerated response 

Graves’ disease

thyroid stimulation 

Celiac disease

gluten damages intestine

Allergies & Hypersensitivity

• IgE‑mediated 

• Histamine release 

• Symptoms: swelling, itching, bronchoconstriction

Active immunity

• Body makes antibodies 

• Long‑lasting 

Passive immunity

• Antibodies received 

• Temporary