Understanding the Human Immune and Respiratory Systems

Posted on May 12, 2024 in Biology

Innate and Adaptive Immunity

What is Immunity?

1. Innate immunity refers to the body’s natural defense mechanisms that are present from birth and provide immediate, non-specific protection against pathogens. Adaptive immunity, on the other hand, is a specific immune response that develops over time as the body encounters and recognizes specific pathogens.

What is a Pathogen?

2. A pathogen is a disease-causing microorganism, such as bacteria, viruses, fungi, or parasites.

Barriers of Innate Immunity

3. The three barriers of innate immunity are physical barriers, chemical barriers, and biological barriers.

  1. Physical barriers, like the skin and mucus, act as the first line of defense by preventing pathogens from entering the body and trapping them to be expelled.
  2. Chemical barriers include substances like interferons, which are proteins that help inhibit viral replication, and the complement system, which is a group of proteins that enhance the immune response.
  3. Biological barriers involve processes like phagocytosis (engulfing and destroying pathogens), chemotaxis (movement towards chemical signals), ameboid movement (cellular movement), and diapedesis (migration of immune cells from blood vessels to tissues).

Inflammation and Fever

  1. Inflammation is a response to tissue damage or infection. It is characterized by redness, swelling, heat, and pain. Chemicals like histamine and prostaglandins are released, causing blood vessels to dilate and become more permeable, allowing immune cells to reach the site of infection or injury. Inflammation helps to contain and eliminate pathogens, and promote tissue repair.
  2. Fever is a rise in body temperature that can occur as a response to infection. It is triggered by chemicals called pyrogens, which reset the body’s thermostat in the hypothalamus. Fever can help enhance immune function and inhibit the growth of certain pathogens.

Antigens and Immune Responses

4. Antigens are substances that can elicit an immune response. Antigen determinants, also known as epitopes, are specific regions on antigens that are recognized by immune cells.

  1. Molecules trigger immune responses based on their size and complexity. Large and complex molecules tend to be more immunogenic, meaning they are more likely to trigger an immune response.
  2. Pathogens carry antigens on their surfaces, and these antigens can have different antigenic determinants. The immune system recognizes these antigens as foreign and mounts an immune response against them.
  3. Self-antigens are antigens present on our own cells, while non-self antigens are foreign.

Lymphocytes: B Cells and T Cells

6. B lymphocytes are formed in the bone marrow and mature in the bone marrow or lymphoid tissues. T lymphocytes are formed in the bone marrow but mature in the thymus. They both become activated when they encounter antigens.

  1. Immunocompetence refers to the ability of lymphocytes to recognize specific antigens. Self-tolerance is the ability of the immune system to distinguish between self and non-self antigens. Clonal selection is the process by which lymphocytes with receptors specific to an antigen are selected for activation and proliferation.
  2. B cells transition from the bone marrow to becoming naïve cells, which circulate in the blood and lymphoid tissues. When they encounter an antigen, they become activated and differentiate into plasma cells or memory B cells.

Humoral Immunity

7. Humoral immunity involves the activation of B cells and the production of antibodies.

  1. B cells are activated when their surface receptors bind to specific antigens.
  2. An activated B cell produces antibodies, also known as immunoglobulins, which are proteins that target specific antigens.
  3. Plasma cells are effector B cells that produce a large amount of antibodies. Memory B cells are long-lived cells that “remember” the antigen and can quickly respond to future exposures.
  4. Antibodies are Y-shaped proteins that can bind to antigens. They can neutralize pathogens, mark them for destruction by other immune cells, or activate other components of the immune system.
    1. The shape of antibodies allows them to bind to specific antigens, like a lock and key.
    2. There are five classes of antibodies: IgM, IgG, IgA, IgE, and IgD. Each class has a different function, such as neutralizing pathogens, promoting phagocytosis, or activating other immune cells.
    3. Antibodies can directly neutralize pathogens or indirectly activate other immune responses, such as complement activation or antibody-dependent cell-mediated cytotoxicity.
  5. The surface antigen binding sites on activated B cells, plasma cells, and antibodies allow them to specifically bind to antigens.
  6. Primary responses occur when the immune system encounters an antigen for the first time, resulting in the production of antibodies. Secondary responses occur upon re-exposure to the same antigen and are faster and stronger due to the presence of memory B cells.
  7. Passive humoral immunity involves the transfer of pre-formed antibodies, such as through breastfeeding or receiving immune globulin injections. Active humoral immunity develops when the body produces its own antibodies in response to an antigen.

Cellular Immunity

8. Cellular immunity involves the activation of T cells, which are responsible for directly attacking and destroying infected or abnormal cells.

  1. Antigen presenting cells (APCs) are immune cells that capture, process, and present antigens to activate T cells. They work by engulfing pathogens or antigenic material, breaking it down, and displaying fragments of the antigen on their surface using major histocompatibility complex (MHC) molecules.
  2. T cells have surface receptors called T cell receptors (TCRs) that recognize specific antigens. CD4 receptors are found on helper T cells, while CD8 receptors are found on cytotoxic T cells.
  3. T cells are activated when their TCRs recognize antigens presented by APCs. This interaction, along with co-stimulatory signals, triggers T cell activation.
  4. CD4 cells bind to MHC class II molecules on APCs, resulting in the activation of helper T cells.
  5. CD8 cells bind to MHC class I molecules on infected or abnormal cells, resulting in the activation of cytotoxic T cells.
  6. Helper T cells assist in immune responses by releasing cytokines and activating other immune cells. Cytotoxic T cells directly kill infected or abnormal cells.
  7. Effector Helper T cells primarily release cytokines to coordinate immune responses.
  8. Effector Cytotoxic T cells directly kill infected or abnormal cells.

T Cell Dependent Activation of B Cells

9. T cell dependent activation of B cells occurs when activated helper T cells interact with B cells presenting antigens. This interaction stimulates B cells to differentiate into plasma cells, which produce antibodies.

  1. Effector B cells are called plasma cells, and they produce antibodies to target specific antigens.

Humoral vs. Cellular Immunity

10. Humoral immunity involves the production of antibodies by B cells, while cellular immunity involves the activation of T cells to directly eliminate infected or abnormal cells.

Organ Transplants and Rejection

11. Organ transplants involve the transplantation of organs from one individual to another. Rejection occurs when the recipient’s immune system recognizes the transplanted organ as foreign and mounts an immune response against it.

Immunodeficiencies

12. Common immunodeficiencies are conditions where the immune system is compromised, leading to increased susceptibility to infections. Examples include primary immunodeficiency disorders and acquired immunodeficiency syndrome (AIDS).

HIV and AIDS

13. HIV (human immunodeficiency virus) is the virus that causes AIDS (acquired immunodeficiency syndrome). HIV attacks and weakens the immune system, making individuals more susceptible to infections and diseases.

Autoimmune Diseases

14. Autoimmune diseases occur when the immune system mistakenly attacks healthy cells and tissues in the body. Common treatments include immunosuppressants, which suppress the immune response.

The Respiratory System

Categories of Respiration

1. The five categories of respiration are pulmonary ventilation, external respiration, internal respiration, transport, and cellular respiration.

Functions of the Respiratory System

2. The respiratory system has several functions, including the exchange of oxygen and carbon dioxide, regulation of blood pH, production of sound, and the sense of smell.

Tissues of the Respiratory System

3. The respiratory system is made up of different types of tissues. The nasal passages, pharynx, larynx, trachea, and bronchial tree are lined with respiratory epithelium, which contains ciliated cells and goblet cells. The alveoli are made up of simple squamous epithelium.

Path of Air Through the Respiratory System

4. The path of air through the respiratory system starts in the nasal passages, which warm, humidify, and filter the air. Then it moves through the pharynx, where it is further filtered and moistened. Next, it enters the larynx, where the epiglottis prevents food and liquid from entering the airway. From there, it travels through the trachea and bronchial tree, which branch into smaller bronchioles. Finally, the air reaches the alveoli, where gas exchange occurs.

  1. Nasal Passage: Functions to filter, warm, and humidify the air. The olfactory mucosa is responsible for the sense of smell, while the respiratory mucosa produces mucus to trap particles.
  2. Pharynx: Has three divisions: the nasopharynx, oropharynx, and laryngopharynx. It serves as a common pathway for air and food, and it plays a role in swallowing and speech.
  3. Larynx: Contains the epiglottis, which prevents food and liquid from entering the airway. The vocal folds are responsible for sound production, while the vestibular folds help protect the airway.
  4. Trachea: Also known as the windpipe, provides a rigid tube for air to pass through. It is lined with ciliated cells and goblet cells that help move mucus and particles out of the airway.
  5. Bronchial Tree: Consists of bronchi and bronchioles. As the bronchi progress to bronchioles, the tissue changes from pseudostratified columnar epithelium to simple columnar epithelium, and finally to simple cuboidal epithelium. The diameter of the tube is controlled the most in the bronchioles.

Pulmonary Ventilation

Pulmonary ventilation refers to the process of breathing, which involves the movement of air into and out of the lungs. The muscles involved in breathing include both involuntary and voluntary muscles. The diaphragm and intercostal muscles are the main players. Changes in pressure cause pulmonary ventilation. When the diaphragm contracts and the intercostal muscles expand the chest cavity, the volume increases, and intrapulmonary pressure decreases. This creates a pressure gradient that allows air to rush into the lungs during inhalation. Atmospheric pressure is the pressure exerted by the air around us. It’s important because it determines the direction of air movement. When the intrapulmonary pressure is lower than atmospheric pressure, air flows into the lungs. Conversely, when the intrapulmonary pressure is higher, air flows out of the lungs during exhalation. Pneumothorax is the presence of air in the pleural cavity, which can disrupt the pressure balance and cause lung collapse. Atelectasis is the collapse of a lung or part of a lung due to a blockage or loss of air. Boyle’s law states that the pressure of a gas is inversely proportional to its volume. During inhalation, the increase in chest volume decreases intrapulmonary pressure, causing air to flow in. During exhalation, the decrease in chest volume increases intrapulmonary pressure, causing air to flow out.

Tissue Gas Exchange

Tissue gas exchange occurs in the capillaries of body tissues. Oxygen-rich blood from the lungs is delivered to the tissues, and carbon dioxide produced by the tissues is removed. Partial pressures play a role in gas transport. Oxygen moves from areas of higher partial pressure (in the blood) to areas of lower partial pressure (in the tissues), while carbon dioxide moves in the opposite direction. The tissue membrane consists of capillaries that are in close proximity to the body’s cells. This allows for the exchange of gases, nutrients, and waste products between the blood and the tissues.

Transport of Oxygen

Transport of oxygen in the blood occurs in two ways. Most of it binds to hemoglobin in red blood cells, forming oxyhemoglobin. Some oxygen dissolves directly in the plasma. Oxyhemoglobin refers to hemoglobin bound to oxygen, while deoxyhemoglobin is hemoglobin without oxygen. Carbaminohemoglobin is formed when carbon dioxide binds to hemoglobin. Affinity refers to the attraction between hemoglobin and oxygen. Factors like temperature, pH, and carbon dioxide levels can affect hemoglobin’s affinity for oxygen. Changes in these factors can influence pulmonary ventilation.

Blood pH and Respiration

Blood pH is controlled by carbon dioxide through the bicarbonate buffer system. An increase in CO2 can alter blood pH. Bicarbonate acts as a buffer, helping to maintain a stable pH by absorbing excess hydrogen ions. Changes in pH can affect pulmonary ventilation.

Regulation of Breathing

The medulla oblongata and pons in the brain help regulate steady breathing and respond to changes in breathing.

There are different types of hypoxia, including hypoxic hypoxia (low oxygen levels in the blood), anemic hypoxia (reduced ability of blood to carry oxygen), circulatory hypoxia (poor blood flow to tissues), and histotoxic hypoxia (inability of tissues to use oxygen)