Lymphatic, Immune, and Respiratory Systems: Study Guide (Chapters 20–22)

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Lymphatic System

Main Functions and Components

The lymphatic system is essential for maintaining fluid balance, defending the body against pathogens, and facilitating the absorption of dietary fats. Its main components include:

Bone marrow: Site of lymphocyte production.
Thymus: Site of T lymphocyte maturation.
Lymph nodes: Filter lymph and house immune cells.
Lymphatic vessels: Transport lymph throughout the body.

Major Lymph Node Locations

Cervical lymph nodes: Neck region
Axillary lymph nodes: Armpits
Inguinal lymph nodes: Groin area

Lymph Node Anatomy

Afferent vessels enter at the convex surface.
Efferent vessels exit at the concave surface (hilum).
Cortex: Contains lymph follicles with germinal centers (active B cell division).
Medulla: Contains medullary cords and sinuses.

Tonsils and Lymphatic Nodules

Lingual tonsils: Base of the tongue.
Tubal tonsils: Around the auditory tube.
Palatine tonsils: Oropharynx; lined by stratified squamous non-keratinized epithelium.
Pharyngeal tonsil (adenoids): Nasopharynx.
Peyer's patches: Isolated lymphatic nodules in the small intestine.

Thymus

Site of T lymphocyte immunocompetence development.
Located in the thorax; largest in children, atrophies after adolescence.
Contains thymic corpuscles (Hassall's corpuscles) in the medulla.
Self-reactive T cells are destroyed during selection to prevent autoimmunity.

Lymphatic Ducts

Thoracic duct: Begins at the cisterna chyli, drains lymph from the left side of the body into the junction of the left internal jugular and subclavian veins.
Right lymphatic duct: Drains lymph from the right upper torso into the junction of the right internal jugular and subclavian veins.

Spleen

Located in the left hypochondrium, lateral to the stomach.
Highly vascular, covered by peritoneum.
Site of red blood cell destruction.
Histology: Contains red pulp (RBC destruction) and white pulp (immune function).

Immune System

Overview of Immune Response

The immune system protects the body from pathogens using innate (nonspecific) and adaptive (specific) defenses.

Innate Immunity

First line of defense: Physical and chemical barriers (skin, mucous membranes, secretions).
Second line of defense: Internal defenses (phagocytes, natural killer cells, inflammation, antimicrobial proteins, interferons, fever).

Complement activation leads to cell lysis.

Inflammation

Triggered by trauma, heat, infection.
Results in redness, swelling, heat, and pain.

Antigens

Substances that provoke an immune response.
Located on cell surfaces; can be pathogens or foreign cells.

Adaptive Immunity

Humoral immunity: B lymphocytes produce antibodies; targets extracellular pathogens.
Cellular immunity: T lymphocytes target intracellular pathogens.

Cytotoxic T Lymphocytes

Attack infected or abnormal cells (e.g., cancer, virus-infected, graft rejection).
Require antigen presentation via MHC proteins.
Stimulated by helper T cells.

Antibodies (Immunoglobulins)

Proteins produced by plasma cells (from B lymphocytes) in response to antigens.
Mechanisms: Neutralization, agglutination, precipitation, complement fixation, cell lysis.

Antibody	Main Function
IgM	First antibody secreted in primary response
IgA	Found in secretions (saliva, sweat, milk, etc.)
IgD	B cell antigen receptor
IgG	Most abundant in plasma; crosses placenta
IgE	Allergic reactions; binds mast cells/basophils

Types of Immunity

Type	How Acquired	Example
Active, natural	Exposure to antigen	Measles infection
Active, artificial	Vaccination	Flu shot
Passive, natural	Antibodies from mother	Placental transfer
Passive, artificial	Injection of antibodies	Antibody shot before travel

Primary vs. Secondary Immune Response

Primary response: First exposure, lag time 3–6 days.
Secondary response: Faster, stronger due to immunological memory.

Immune Disorders

AIDS: Destroys helper T lymphocytes.
Autoimmune diseases: Immune system attacks self (e.g., rheumatoid arthritis, multiple sclerosis, Graves’ disease, Type 1 diabetes, lupus, glomerulonephritis).
Hypersensitivity reactions: Overreaction to harmless substances; involves IgE, mast cells, basophils, and histamine release (allergic reactions).

Respiratory System

Anatomy of the Respiratory System

Olfactory epithelium: Roof of the nasal cavity.
Nasal septum: Formed by cartilage, vomer, and ethmoid bone.
Palatine tonsils: Located in the oropharynx.
Laryngeal cartilages: Arytenoid (paired), epiglottis (elastic cartilage, prevents food entry).
Trachea: Largest tube, hyaline cartilage rings.
Bronchioles: Small tubes (<1 mm), smooth muscle, no cartilage.
Vocal cords: Shorter/thinner in women (higher pitch).
Narrowest larynx region: Between the vocal folds.
Pharynx divisions: Nasopharynx, oropharynx, laryngopharynx (superior to inferior).
Auditory tube: Connects middle ear to nasopharynx (route for infection spread).
Paranasal sinuses: Frontal, sphenoid, ethmoid, maxillary (located in respective bones).

Respiratory Zones

Respiratory zone: Respiratory bronchioles, alveolar ducts, alveoli (site of gas exchange).
Conducting zone: Nasal cavity, pharynx, trachea, bronchi, bronchioles, terminal bronchioles (air passageways).

Respiratory Membrane

Composed of alveolar wall, capillary wall, and fused basement membranes.

Lung Anatomy

Hilum: Indentation where vessels, bronchi, lymphatics, and nerves enter/exit lung.
Carina: Cartilage at tracheal bifurcation.
Right primary bronchus: Shorter, wider, more vertical (more likely for foreign body entry).

Mechanics of Breathing

Inspiration: Thoracic volume increases, intrapulmonary pressure decreases.
Expiration: Thoracic volume decreases, intrapulmonary pressure increases.
Muscles for inspiration: External intercostals, diaphragm.
Muscles for expiration: Internal intercostals, diaphragm.
Thoracic diameter increases in transverse and anteroposterior directions during inspiration.

Gas Exchange and Transport

External respiration: Gas exchange between alveoli and blood.
Internal respiration: Gas exchange between blood and tissues.
Oxygen transport: 98.5% bound to hemoglobin, 1.5% dissolved in plasma.
Carbon dioxide transport: 70% as bicarbonate, 20% bound to hemoglobin, 7–10% dissolved in plasma.
CO2 is more soluble in plasma than O2 (20x).

Enzyme in CO2 Transport

Carbonic anhydrase: Catalyzes ; present in red blood cells (RBCs).

Lung Compliance

Describes the stretchiness of the lungs.
Depends on lung tissue distensibility and alveolar surface tension.

Surfactant

Produced by type II alveolar cells.
Reduces alveolar surface tension, preventing collapse.

Respiratory Volumes

Volume	Definition	Typical Value
Tidal Volume (TV)	Air in/out during normal breath	500 mL
Vital Capacity (VC)	Max air exhaled after max inhalation (TV + IRV + ERV)	3100 mL (women), 4800 mL (men)

Partial Pressures of Gases

Blood Vessel	O2 (mmHg)	CO2 (mmHg)
Pulmonary arteries	40	45
Pulmonary veins	100	40
Systemic arteries	100	40
Systemic veins	40	45

Acid-Base Balance and CO2

As PCO2 increases, pH decreases (more acidic).
As PCO2 decreases, pH increases (more basic).
Hyperventilation decreases CO2 in blood, raising pH (alkalosis).

Factors Affecting Pulmonary Gas Exchange

Gas solubility and partial pressure gradients.
Ventilation-perfusion ratio.
Respiratory membrane thickness (should be <0.5 μm).
Surface area for gas exchange.

Respiratory Chemoreceptors

Located in aortic and carotid bodies, and medulla.
Stimulated by increased H+ or decreased O2 partial pressure.

Dead Space

Volume of air not involved in gas exchange (conducting zone).
Typical value: 150 mL (or 1 mL per pound of ideal body weight).
Increased dead space may indicate alveolar damage.

Pneumothorax

Presence of air in the pleural cavity, causing lung collapse.

Additional info:

Vital capacity (VC) formula:
IRV: Inspiratory Reserve Volume; ERV: Expiratory Reserve Volume
Alveolar ventilation = Tidal volume – Dead space