Chapter 10 BIO105

The Respiratory System

Overview

  • The respiratory system is critical for gas exchange, ensuring the intake of oxygen and expulsion of carbon dioxide from the body.

  • Key Processes:
      - Inspiration (Inhalation): Air flows from the atmosphere into the lungs through cavities and tubes.
      - Expiration (Exhalation): Air is expelled from the lungs back into the atmosphere using the same structures.

Ventilation (Breathing)

  • Ventilation encompasses both inspiration and expiration.

  • The respiratory system collaborates with the cardiovascular system:
      - Function: Transports oxygen from the lungs to tissues and removes carbon dioxide from tissues back to the lungs.

  • During cellular respiration, cells utilize oxygen, generating carbon dioxide as a byproduct.

The Human Respiratory Tract

  • Components: The respiratory tract comprises various structures through which air passes, categorized into upper and lower sections.

Upper Respiratory Tract

  • Includes: Nasal cavities, pharynx, and larynx.

  • Structure of the Nose:
      - Opens at the nares (nostrils) which lead to nasal cavities.
      - Nasal cavities are divided by a septum made from bone and cartilage.
      - Hairs in the nostrils filter air, trapping particles.

Nasal Cavities

  • Characteristics:
      - Lined with mucous membrane that helps trap particles and transport them to the pharynx.
      - Beneath the mucous layer is the submucosa, rich in capillaries for warming and moistening incoming air, leading to susceptibility to nosebleeds.
      - Contains odor receptors and connects to the sinuses and tear ducts, causing a runny nose when we cry.

Pharynx

  • The pharynx is a funnel-shaped cavity connecting the nasal and oral cavities to the larynx.

  • Divided into three regions:
      1. Nasopharynx
      2. Oropharynx
      3. Laryngopharynx

  • Contains tonsils, lymphoid tissues that provide defense mechanisms against inhaled pathogens.

Larynx

  • Cartilaginous structure linking the pharynx to the trachea:
      - The Adam's apple is a prominent feature located in the front of the neck.
      - Houses the vocal cords, mucosal folds supported by elastic ligaments, responsible for sound production:
        - The opening between vocal cords is referred to as the glottis.
        - Sound pitch variations depend on vocal cord tension; louder sound correlates with increased vibrations of vocal cords.
      - The larynx also prevents food from entering the respiratory tract via the epiglottis during swallowing.

Lower Respiratory Tract

  • Comprises: Trachea, bronchial tree, and lungs.

Trachea

  • Commonly known as the windpipe, it connects the larynx to the primary bronchi.

  • The trachea is reinforced by C-shaped cartilaginous rings to avoid collapse, allowing the esophagus to expand during swallowing.

  • Lined with pseudostratified ciliated columnar epithelium containing goblet cells that secrete mucus, trapping air debris and moving it toward the pharynx.
      - Smoker’s cough is a consequence of cilia damage due to smoking.

  • Tracheostomy: A process that involves inserting a breathing tube into the trachea for those who cannot breathe adequately.

Bronchial Tree

  • Features two primary bronchi branching from the trachea into the lungs, further dividing into secondary bronchi and smaller bronchioles, ultimately leading to alveolar spaces.

  • During an asthma attack, bronchial smooth muscles constrict, leading to wheezing sounds.

Lungs

  • Comprised of secondary bronchi, bronchioles, and alveoli:
      - The right lung consists of three lobes, while the left lung has two to accommodate the heart.
      - Each lobe is subdivided into lobules; they are enclosed by pleurae that secrete pleural fluid.
      - Pleural fluid creates surface tension helping to adhere pleurae together, facilitating lung expansion during thoracic cavity enlargement.
      - Pleurisy: An inflammation condition of the pleurae causing pain.

Alveoli

  • Important structures for gas exchange, approximately 300 million alveoli are present in the lungs.

  • Each alveolar sac is surrounded by blood capillaries, both made of simple squamous epithelium, enabling effective gas exchange:
      - Oxygen diffuses into the bloodstream while carbon dioxide diffuses from the blood into the alveoli.

  • Alveoli are coated with surfactant, a lipoprotein film that reduces surface tension and prevents collapse:
      - Inadequate surfactant in premature infants can lead to respiratory distress syndrome due to alveolar collapse.

Ventilation (Breathing Process)

  • Phases: Two primary phases exist in ventilation: inspiration (inhalation) and expiration (exhalation).

  • Anatomy of Ventilation:
      - The lungs reside in a sealed thoracic cavity bordered by the rib cage (top and sides), intercostal muscles (between ribs), and diaphragm (base).
      - The pleura secures the lungs to the thoracic wall with minimal pleural fluid between them.

Boyle's Law

  • Fundamental principle underlying ventilation:
      - At constant temperature, the pressure of a gas is inversely proportional to its volume.

Inspiration Process

  • Active Phase: This process involves the contraction of the diaphragm and external intercostal muscles:
      - In a relaxed state, the diaphragm is dome-shaped; during contraction, it flattens out.
      - The rib cage elevates outward due to the intercostal muscles, increasing thoracic cavity size.

  • Increased thoracic cavity volume results in diminished alveolar pressure, allowing air to flow into the lungs.

Expiration Process

  • Passive Phase: This phase occurs when the diaphragm and external intercostal muscles relax:
      - The rib cage moves down and inwards to reclaim resting position, leading to lung recoil and increased air pressure, thus expelling air.

  • Surfactant functionality maintains alveoli patency during expiration.
      - Puncturing the thoracic cavity can lead to collapsed lungs due to air entering pleural space.

Maximum Inspiratory Effort and Forced Expiration

  • Forced expiration necessitates the contraction of internal intercostal muscles, pulling the rib cage down and inwards:
      - Abdominal muscles engage to push abdominal organs upward against the diaphragm, aiding in air expulsion.

Volumes of Air Exchanged During Ventilation

  • Tidal Volume: Amount of air exchanged in normal breath.

  • Vital Capacity: Maximum volume possible to inhale and exhale in one breath.

  • Inspiratory and Expiratory Reserve Volume: Extra volume of air that can be inhaled or exhaled with force.

  • Dead Air Space: Air in passages not involved in gas exchange, such as nasal cavities and trachea.

  • Residual Volume: The volume of air left in the lungs post-exhalation.

Control of Ventilation

  • Breathing regulation is influenced by the nervous system and chemical signals:
      - The respiratory control center in the brain manages diaphragm and intercostal muscle activity for inspiration and expiration.
      - Sudden Infant Death Syndrome (SIDS): Sudden cessation of breathing in an infant, possibly due to miscommunication between the brain's respiratory center and lungs.

Nervous Control of Breathing

  • The respiratory center automatically modulates breathing but can be voluntarily altered for activities such as speaking, singing, or swimming.

  • Activation of stretch receptors halts respiratory signals during excessive lung stretching, preventing lung overexpansion.

Chemical Control of Breathing

  • Carbon dioxide production during cellular respiration influences blood pH:
      - Carbon dioxide combines with water to form carbonic acid, which dissociates and releases hydrogen ions (H+), lowering pH.

  • Chemoreceptors in the medulla oblongata and carotid/aortic bodies detect these pH changes and influence ventilation rate accordingly.

  • Increased blood CO2 prompts the respiratory center to elevate breathing depth/rate.
      - Oppositely, breath-holding leads to CO2 accumulation and decreased pH, stimulating the respiratory center to resume breathing despite voluntary breath inhibition.

Gas Exchanges in the Body

  • Necessary for supplying oxygen for ATP production and removing carbon dioxide:

  • Governs gas diffusion principles between pulmonary and tissue levels:
      - Partial Pressure: The pressure exerted by an individual gas component. Diffusion occurs from areas of higher to lower partial pressure.

External Respiration

  • Process: Gas exchange between alveoli and blood capillaries:
      - Higher PCO2 in capillaries causes CO2 to diffuse out into the lungs, while higher PO2 in alveoli prompts O2 to enter red blood cells.

  • CO2 is primarily transported as bicarbonate ions (HCO−3) in plasma.

  • The enzyme carbonic anhydrase catalyzes the breakdown of carbonic acid within red blood cells.
      - Hyperventilation leads to blood alkalosis; hypoventilation leads to acidosis.

Internal Respiration

  • Process: Gas exchange occurring between systemic capillaries and tissue cells:
      - Blood is bright red due to oxyhemoglobin presence. Oxygen segregates from hemoglobin and diffuses into tissues, fueled by continuous oxygen consumption in cellular respiration.

Respiratory Health Issues

  • Restrictive Pulmonary Disorders: Characterized by reduced vital capacity, such as pulmonary fibrosis caused by exposure to inorganic dust, potentially leading to cancer.

  • Obstructive Pulmonary Disorders: Include chronic bronchitis, emphysema, and asthma, collectively termed COPD due to their recurring nature.

Chronic Bronchitis

  • Characterized by inflammation and mucus accumulation in the airways, often exacerbated by smoking/environmental pollutants, leading to degenerative tissue changes.

Emphysema

  • Irreversible condition where the alveoli are damaged, decreasing gas exchange surface area and impairing oxygen delivery:
      - Symptoms may include fatigue, cognitive slowdowns, and mood changes with treatment options such as lung transplantation or surgery being available for severe cases.

Smoking and Respiratory Health

  • Tobacco use leads to adverse health outcomes:
      - Increases risk for diverse cancers and is linked to COPD and heart diseases. Passive smoke endangers non-smokers through pneumonia and lung cancer risk increases.