Exam #3 Review Outline: Immune and Respiratory Systems

Comparison of Adaptive and Innate Immune Systems

Specificity:

• Adaptive Immunity: This system is highly specific, capable of recognizing and specifically targeting particular antigens, which are distinct molecules found on pathogens such as viruses, bacteria, and fungi.

• Innate Immunity: This response is non-specific, reacting broadly to a wide range of pathogens and relying on general mechanisms to protect the body from infection.

Time to Initiate Protection:

• Adaptive Immunity: The response is slower, taking days to weeks to mount an effective defense due to the time required for antigen recognition and the selection and proliferation of specific lymphocyte clones.

• Innate Immunity: Provides an immediate response, within minutes to hours, to potential threats.

Memory Responses:

• Adaptive Immunity: Utilizes memory cells formed after the initial exposure to an antigen, enabling a quicker and more robust response upon subsequent encounters with the same pathogen.

• Innate Immunity: Lacks memory; the reaction remains the same regardless of the number of exposures to a given pathogen, making it less efficient in mounting a rapid response upon re-exposure.

Cells Involved:

• Adaptive Immunity: Primarily involves B cells (which produce antibodies) and T cells (which include helper T cells that assist in activating other immune cells and cytotoxic T cells that directly kill infected cells).

• Innate Immunity: Composed of various cell types such as phagocytes (including macrophages and neutrophils that engulf and digest pathogens), natural killer (NK) cells (which kill infected or cancerous cells), and dendritic cells (which present antigens to T cells and help initiate adaptive responses).

Classification of Immune Response

To determine if an immune response is primarily adaptive or innate, one must assess its characteristics such as specificity, response time, memory capability, and cell types involved.

Functions of the Lymphatic System

Functions:

• Fluid Balance: The lymphatic system drains excess interstitial fluid that can accumulate in tissues, thus maintaining fluid homeostasis.

• Immune Function: It is crucial for immune responses as it serves as a site for lymphocyte storage and maturation (including B cells and T cells) and allows for the transport of immune cells throughout the body.

• Lipid Transport: Transports dietary lipids from the gastrointestinal tract to the bloodstream through specialized lymphatic vessels called lacteals.

Histological Structure:

• Lymphatic vessels possess thin walls featuring a simple squamous epithelium and valves to prevent the backflow of lymph. These anatomical features ensure the unidirectional flow of lymph towards the thoracic duct and right lymphatic duct, where lymph rejoins the circulatory system.

Immunological Tolerance

Immunological tolerance is a critical mechanism preventing the immune system from attacking the body’s own tissues. Key processes include:

• Negative Selection: During T cell development in the thymus, T cells that are strongly reactive to self-antigens are induced to undergo apoptosis to eliminate potentially harmful cells.

• Peripheral Tolerance Mechanisms: Additional mechanisms such as anergy (a functional inactivation of T cells) and deletion (removal of autoreactive lymphocytes from circulation) help maintain tolerance in mature lymphocytes.

Innate Immune System Mechanisms

• Physical Barriers: The first line of defense includes skin and mucous membranes that form a physical barrier to pathogen entry.

• Phagocytosis: Immune cells like macrophages and neutrophils actively engulf and digest pathogens to eliminate infection.

• Immunological Surveillance: Natural killer (NK) cells play a pivotal role in identifying and destroying cells that are infected or malfunctioning.

• Interferons: These cytokines are important for inhibiting viral replication and activating neighboring immune cells to bolster antiviral responses.

• Complement System: A series of proteins that enhance the ability of antibodies and phagocytes to clear infections, known for two main pathways:

  • Classical Pathway: Initiated by the interaction of antibodies with antigens.

  • Alternative Pathway: Activated spontaneously on pathogen surfaces without prior antibody binding.

• Inflammatory Response: Characterized by redness, heat, swelling, and pain, this response is essential for containing infections and initiating the healing process.

• Fever: An elevated body temperature that not only enhances immune function but also inhibits the growth of pathogens by creating an unfavorable environment.

Forms of Immunity

Types of Immunity:

• Innate Immunity: Consists of natural defenses that are present at birth, providing immediate but non-specific protection against pathogens.

• Adaptive Immunity: Acquired immunity resulting from exposure to pathogens or vaccination, characterized by specificity and the ability to remember previous infections.

Examples:

• Active Immunity: Results from infection or vaccination that leads to the formation of antibodies and memory cells.

• Passive Immunity: Involves the transfer of antibodies from one individual to another, such as maternal antibodies passed to a child during breastfeeding.

Cell-Mediated vs. Humoral-Mediated Immunity

Cell-Mediated Immunity:

• This immunity involves mainly T cells, including cytotoxic T cells (which kill infected or cancerous cells) and helper T cells (which assist other immune cells).

Humoral-Mediated Immunity:

• Involves B cells, which produce antibodies that bind to pathogens and neutralize them. B cells can differentiate into plasma cells that secrete these antibodies.

Key Cell Types:

• B cells: Responsible for antibody production and differentiation into plasma cells.

• Cytotoxic T cells: Integral for attacking and destroying infected or malignant cells.

• Helper T cells: Essential in the activation and regulation of both B cells and cytotoxic T cells.

• Regulatory T cells: Crucial for maintaining tolerance and preventing autoimmune reactions.

Antigen Presentation

Types of Antigen-Presenting Cells (APCs):

• APCs include dendritic cells, macrophages, and B cells. They are vital in processing and presenting antigens to T cells to initiate adaptive immune responses.

MHC Class I and II:

• MHC Class I: Presents endogenous antigens (e.g., proteins from viruses) to CD8+ cytotoxic T cells, which are responsible for killing infected or altered cells.

• MHC Class II: Presents exogenous antigens (e.g., proteins from external pathogens) to CD4+ helper T cells, which assist in activating B cells and other immune responses.

Antigen Types:

• Endogenous Antigens: Typically produced within the cells (e.g., viral proteins).

• Exogenous Antigens: Derived from outside the cell (e.g., bacterial components).

Antibody Structure and Functions

Basic Structure:

• Antibodies, or immunoglobulins, are composed of two heavy and two light chains, forming a Y-shaped molecule that can recognize specific antigens.

Five Classes of Antibodies:

• IgG: The most abundant antibody in circulation, playing a significant role in secondary immune responses.

• IgM: The first class of antibody produced in response to an infection; effective in forming immune complexes.

• IgA: Found in mucosal areas, such as the gastrointestinal tract and respiratory system, playing a protective role on epithelial surfaces.

• IgE: Involved in allergic reactions and response to parasitic infections.

• IgD: Primarily functions as a surface receptor on B cells, involved in B cell activation.

Immune Response Comparison

• Primary Response: The first time the immune system encounters a pathogen, the response is slower, less intense, and produces fewer antibodies as the body learns to recognize the invader.

• Secondary Response: Upon re-exposure, the memory cells lead to a much faster and stronger response, resulting in a greater quantity of antibodies being produced due to the body's prior experience.

Immune Disorders

• Autoimmunity: Occurs when the immune system mistakenly attacks the body's own tissues as if they were foreign invaders, leading to autoimmune diseases such as rheumatoid arthritis or lupus.

• Severe Combined Immunodeficiency Disease (SCID): A rare genetic disorder that results in a lack of functional immune responses due to the absence of both T and B lymphocytes.

• Acquired Immune Deficiency Syndrome (AIDS): Caused by the Human Immunodeficiency Virus (HIV), which specifically targets and destroys helper T cells, severely compromising the immune system.

• Allergies: Overreactions of the immune system to generally harmless substances (allergens), which may cause symptoms ranging from mild to life-threatening responses such as anaphylaxis.

Effects of Stress and Aging on the Immune System

• Stress: Chronic stress can lead to the release of stress hormones that suppress immune function, making individuals more susceptible to infections and illnesses.

• Aging: As individuals age, their immune responses often decrease in efficiency; this includes diminished production of new immune cells and a reduced response to vaccinations, contributing to increased vulnerability to infections and a higher incidence of autoimmune diseases.

1. Pathway of Air Through the Respiratory System

• External Nostrils (Nares): Air enters through the external nares, which are the openings of the nose. The nasal cavity, lined with vibrissae (nose hairs), filters large particles from the inspired air.

• Nasal Cavity: Warms and moistens air; contains olfactory receptors for smell. The structure includes:

  • Gross Anatomy: Divided by the nasal septum; has three conchae (superior, middle, inferior) that increase surface area for warming and humidification.

  • Micro Anatomy: Lined with ciliated pseudostratified columnar epithelium, which traps particles in mucus and uses cilia to move it towards the throat.

• Pharynx: Commonly known as the throat, it consists of three sections:

  • Nasopharynx: Located behind the nose; contains the pharyngeal tonsils.

  • Oropharynx: Located behind the mouth; shared pathway for air and food, contains palatine tonsils.

  • Laryngopharynx: Leads to the esophagus and larynx.

• Larynx: The voice box, contains vocal cords; functions in sound production.

  • Gross Anatomy: Composed of cartilage (thyroid, cricoid, arytenoid).

  • Micro Anatomy: Lined with ciliated columnar epithelium and non-keratinized stratified squamous epithelium (over vocal cords).

• Trachea: The windpipe; extends from the larynx to the bronchi.

  • Gross Anatomy: Supported by C-shaped cartilaginous rings; bifurcates into left and right bronchi.

  • Micro Anatomy: Lined with ciliated pseudostratified columnar epithelium and goblet cells producing mucus.

• Bronchi: Branching tubes leading into each lung.

  • Gross Anatomy: Primary bronchi branch into secondary (lobar) and tertiary (segmental) bronchi.

  • Micro Anatomy: Structure transitions from cartilage to smooth muscle as bronchi branch out.

• Bronchioles: Continued branching of bronchi, leading to alveolar ducts.

  • Gross Anatomy: Small and less than 1mm in diameter.

  • Micro Anatomy: Lined with simple cuboidal epithelium and lacks cartilage, contains Clara cells that protect the epithelium and produce surfactant.

• Alveoli: Tiny air sacs where gas exchange occurs.

  • Gross Anatomy: Clusters of alveolar sacs.

  • Micro Anatomy: Composed of thin walls (simple squamous epithelium) and surrounded by capillary networks; type I and type II alveolar cells are present; type II cells produce surfactant.

2. Functions of the Respiratory System

• Main Functions:

  • Gas Exchange: Oxygen uptake and carbon dioxide removal.

  • Regulation of Blood pH: Through CO2 levels affecting carbonic acid concentration.

  • Protection: Filtration of airborne pathogens and particles.

  • Sound Production: Via the larynx.

  • Olfaction: Sense of smell via nasal cavity receptors.

• Components:

  • Upper Respiratory System: Includes the nasal cavity, pharynx, and larynx.

  • Lower Respiratory System: Includes the trachea, bronchi, bronchioles, and alveoli.

3. Maintenance of Sterile Environment in the Lungs

• Ciliary Action: Cilia on respiratory epithelium move mucus with trapped particles and pathogens upward to the pharynx for expulsion or swallowing.

• Mucus Production: Goblet cells throughout the respiratory tract produce mucus to trap contaminants.

• Alveolar Macrophages: Immune cells in the alveoli that engulf and digest microorganisms and debris.

4. Role of the Larynx in Swallowing and Sound Production

• Sound Production: Vocal cords in the larynx vibrate as air passes through them, producing sound.

• Swallowing: During swallowing, the larynx moves upward and the epiglottis folds down to cover the trachea, preventing food from entering the airway.

5. Forces and Features for Lung Expansion and Contraction

• Lung Expansion: The contraction of the diaphragm and intercostal muscles increases thoracic cavity volume, allowing air into the lungs.

• Lung Contraction: Relaxation of these muscles reduces thoracic volume, expelling air from the lungs.

• Surfactant: A substance produced by type II alveolar cells that reduces surface tension in the alveoli, preventing collapse during expiration.

• Pleural Fluid: Found between the visceral and parietal pleura, provides lubrication and keeps the lung surfaces adhered to the thoracic wall, aiding in expansion and contraction.

• Musculoskeletal System: The skeletal structure, including the rib cage, supports the lungs, and the muscular system (diaphragm and intercostal muscles) facilitate breathing movements.

6. Measurements of Respiratory Function

• Respiratory Rate: This measures the number of breaths taken per minute. It typically ranges from 12 to 20 breaths per minute in a resting adult. It can vary based on factors such as activity level, emotional state, and health conditions.

• Respiratory Minute Volume: This is the total volume of air inhaled or exhaled from the lungs in one minute. It is calculated as the product of the respiratory rate and tidal volume (the amount of air exchanged in each breath). The formula is:
  \text{Minute Volume (MV)} = \text{Tidal Volume (TV)} \times \text{Respiratory Rate (RR)}

• Alveolar Ventilation Rate: This measures the volume of fresh air that reaches the alveoli per minute, which is more relevant for effective gas exchange. It is calculated as:
  \text{Alveolar Ventilation (AV)} = (\text{Tidal Volume (TV)} - \text{Dead Space Volume (DSV)}) \times \text{Respiratory Rate (RR)}
  This calculation accounts for the volume of air that does not participate in gas exchange (dead space).

• Standard Pulmonary Volumes/Capacities: Standard measurements include:

  • Tidal Volume (TV): The volume of air inhaled or exhaled in a normal breath (approximately 500 mL).

  • Inspiratory Reserve Volume (IRV): The additional air that can be inhaled after a normal inspiration (about 3000 mL).

  • Expiratory Reserve Volume (ERV): The additional air that can be exhaled after a normal expiration (about 1200 mL).

  • Residual Volume (RV): The volume of air remaining in the lungs after a maximal exhalation (about 1200 mL).

  • Vital Capacity (VC): The maximum amount of air that can be exhaled after a maximum inhalation; calculated as ( VC = TV + IRV + ERV ) (approximately 4800 mL).

  • Total Lung Capacity (TLC): The total volume of air in the lungs after a maximal inhalation; calculated as ( TLC = VC + RV ) (approximately 6000 mL).

7. Role of Hemoglobin in Gas Exchange

• Oxygen Transport: Hemoglobin, a protein found in red blood cells, binds to oxygen in the lungs, forming oxyhemoglobin. It can carry up to four molecules of oxygen per hemoglobin molecule. When oxygen-rich blood travels to tissues, hemoglobin releases oxygen, which diffuses from the blood into the cells for cellular respiration.

• Carbon Dioxide Transport: Hemoglobin also facilitates the transport of carbon dioxide (CO2) from the tissues back to the lungs. It can bind to CO2 (forming carbaminohemoglobin) and transport it in the blood. Additionally, a portion of CO2 is transformed into bicarbonate ions in plasma, contributing to the buffering of blood pH.

• Bohr Effect: This physiological phenomenon describes how increased levels of carbon dioxide and lower pH in tissues promote the release of oxygen from hemoglobin, enhancing the oxygen delivery where it is needed most, during high metabolic activity.

• Reverse Bohr Effect: In the lungs, where CO2 concentration is lower and pH is higher, hemoglobin's affinity for oxygen increases, facilitating loading of oxygen onto hemoglobin at the alveolar level.

8. Oxygen-Hemoglobin Saturation Curve

• The oxygen-hemoglobin saturation curve is sigmoidal (S-shaped) due to the cooperative binding of oxygen molecules to hemoglobin. When the first oxygen molecule binds to hemoglobin, it induces a conformational change in the protein, making it easier for subsequent oxygen molecules to bind. This results in a steep increase in saturation at moderate partial pressures of oxygen.

• Factors Affecting the Curve:

  • Temperature: An increase in temperature shifts the curve to the right (Bohr effect), indicating decreased affinity of hemoglobin for oxygen, enhancing oxygen unloading in tissues during active metabolism.

  • pH: A decrease in pH (more acidic conditions) also shifts the curve to the right, further decreasing hemoglobin's affinity for oxygen (this is known as the Bohr effect), facilitating oxygen release when acidity increases as a result of increased carbon dioxide from cellular respiration.

  • Rate of Glycolysis: Higher rates of glycolysis increase levels of lactic acid and carbon dioxide, lowering pH and contributing to a rightward shift in the saturation curve.

  • Stage of Life: Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA), allowing efficient oxygen transfer from maternal circulation to the fetus. The oxygen-hemoglobin curve for fetal hemoglobin is shifted to the left compared to adult hemoglobin, facilitating increased oxygen uptake in the placenta.

9. Control of Respiration

• The control of respiration is primarily managed via the respiratory centers located in the brainstem, including:

  • Medulla Oblongata: Contains the dorsal respiratory group (DRG), which stimulates contraction of the diaphragm and external intercostal muscles during inhalation, and the ventral respiratory group (VRG), which is active during forceful breathing.

  • Pons: Involved in regulating the rate and depth of breathing through the pneumotaxic center, which modulates signals from the medulla to control the transition between inhalation and exhalation.

• Respiratory Reflexes:

  • Chemoreceptors in the carotid and aortic bodies respond to changes in blood pH, CO2, and oxygen levels. An increase in CO2 stimulates a stronger respiratory drive, while low oxygen levels can also trigger increased ventilation rates.

  • Stretch receptors in the lungs prevent over-inflation via the Hering-Breuer reflex, sending signals to inhibit inspiration as lung volume reaches a certain threshold.

10. Decline in Respiratory Performance with Age

• Respiratory performance typically declines with age due to several factors:

  • Decreased Elasticity: The elastic recoil of the lungs reduces, making it harder to expel air and leading to conditions like chronic obstructive pulmonary disease (COPD).

  • Reduced Surface Area: There is a loss of alveolar surface area, which diminishes the efficiency of gas exchange.

  • Decreased Strength of Respiratory Muscles: The strength and endurance of respiratory muscles, such as the diaphragm and intercostals, can decrease, leading to a reduced ability to ventilate the lungs effectively.

  • Increased Risk of Infections: Aging is associated with a decline in immune function, increasing susceptibility to respiratory infections.