Respiratory System Structure and Function

• Cells require energy to survive, which comes from ATP produced by mitochondria.
• Mitochondria need oxygen and glucose to create ATP.
• The primary function of the respiratory system is to deliver oxygen to cells and remove carbon dioxide waste.
• The system uses ventilation to facilitate oxygen intake and carbon dioxide removal.
• Secondary functions include regulating blood pH, vocalization, smell, and aiding circulation.

Structure and Function

• The main function is to ventilate air into the lungs and exchange oxygen and carbon dioxide between the lungs and cells.
• Three major components of the respiratory system are airways for ventilation, muscles for ventilation, and alveoli for gas exchange.

Nostrils, Nasal Cavity, and Sinuses

• These structures channel air into the pharynx.
• They warm, moisten, and filter air.
• They connect to olfactory bulbs, which are involved in smell.
• These structures are mucous membranes and are highly vascular.

Pharynx

• Channels air into the larynx.
• Warms, moistens, and filters air.
• Is made of mucous membranes, is highly vascular, and has an L-shaped bend.

Larynx

• Channels air into the trachea.
• Modulates vocalizations.
• Excludes solids and liquids from the trachea.
• Is a cartilaginous chamber with rings of muscle, glottis, epiglottis, and laryngeal muscles.

Trachea

• Channels air into the lungs.
• Is a flexible tube about 12cm long.
• Is anterior to the esophagus.

Lungs

• Large sacs containing airways and blood vessels.
• Divided into lobes by fissures.
• The right lung has three lobes.
• The left lung has two lobes to accommodate the cardiac notch for the heart.

Bronchial Tree

• Air flows through the trachea, bronchi, lobar bronchi, and segmental bronchi (all surrounded by cartilage).
• The air further splits into bronchioles, terminal bronchioles, respiratory bronchioles, and alveolar ducts (surrounded by smooth muscle lining).

Alveoli

• Alveolar sacs consist of multiple alveoli in a "bunch of grapes" arrangement.
• Individual alveoli are like individual grapes in the bunch.
• They have a thin film of liquid on the inside.
• Structure includes a thin membrane with a capillary network.

Defense Systems

• The body must defend against moisture, temperature, pathogens, and particulates in the atmosphere.

Temperature and Moisture Regulation

• Very dry or cold air can irritate alveoli.
• Vascular epithelium warms cold air.
• Mucous membranes moisten the air.
• Nasal conchae slow down and disrupt airflow, increasing contact with the mucous membrane for moistening and warming.

Particulates and Pathogens

• Nasal conchae, nasal hairs, and the L-shaped bend in the pharynx slow airflow.
• This increases the likelihood of particulates and pathogens interacting with and sticking to the mucous membrane.

Sneeze Reflex

• Triggered by chemical or physical irritants in the nasal mucosa.
• Expels irritants from the body.

Mucociliary Escalator

• Goblet cells in the mucous membrane produce mucus, which traps debris.
• The mucociliary escalator sweeps debris toward the pharynx.
• Coughing expels the debris, or it is swallowed.

Tonsils

• Located in the mucous membrane of the pharynx.
• Detect and trap inhaled pathogens.
• Pathogens are flushed via the lymph system once a certain amount is collected.

Trachea Form

• C-shaped cartilaginous rings with muscles in between allow expansion and prevent blockages.

Alveolar Macrophages

• Phagocytic cells in alveoli walls.
• Destroy particulates and pathogens.
• Collect dust particles.

Ventilation

• Pressure is the force exerted on a container by its contents.
• A pressure gradient moves contents from a higher-pressure container to a lower-pressure one to equalize pressure.

Process of Ventilation

• Two stages include inhalation and exhalation.

Inhalation/Inspiration

• The diaphragm contracts and ribs expand, increasing pressure in the intrapleural cavity.
• This causes the lungs to expand.
• A pressure gradient is created between the lungs and the atmosphere, causing air to enter the lungs.

Expiration/Exhalation

• Ribs and diaphragm relax, causing the lungs to contract.
• Air escapes the lungs due to the pressure difference with the atmosphere.

Forced Breathing

• Used when more oxygen is needed.
• Extra muscles are engaged during inhalation to expand the ribs more than usual.
• Extra muscles are engaged during exhalation to contract ribs more than usual.

Surface Tension in the Alveoli

• A liquid layer inside alveoli assists with gas exchange, provides a barrier, and prevents drying out.
• Surface tension exerts inward pressure.
• Without air remaining, surface tension could cause collapse upon exhalation (making inflation difficult).
• Surfactant reduces the surface tension of water, which makes it easier to inflate the alveolus.

Airway Resistance

• Airflow through airways is driven by pressure gradients.
• Resistance, or friction against the walls of airways, slows airflow.
• Airways are surrounded by smooth muscle.
• Bronchoconstriction and bronchodilation alter resistance.
• Constrictive lung diseases increase airway resistance, making inhalation difficult.

Gases, Location, and Purpose

• Total pressure is the sum of all partial pressures in a mixed gas.

Partial Pressure Gradients

• Partial pressures equalize overall pressure.

Types of Gas Exchange

• Both types are driven by diffusion across membranes down partial pressure gradients.

External Respiration

• Occurs between the alveoli in the lungs and the atmosphere.
• Alveoli in lungs have high oxygen and low carbon dioxide.
• Deoxygenated blood has low oxygen and high carbon dioxide.
• Oxygen diffuses into the blood, and carbon dioxide diffuses out.

Internal Respiration

• Occurs between the cells interior and oxygenated blood.
• Cell interior has low oxygen and high carbon dioxide.
• Oxygenated blood has high oxygen and low carbon dioxide.
• Oxygen enters the cell, and carbon dioxide enters the blood.

Conducting Zone

• Passage for moving air into and out of lungs where gas exchange does not occur.
• Anatomical dead space in males is about 150ml

Anatomical Dead Space

• Volume of air in the conducting zone, ~150ml in males.

Physiologic Dead Space

• Combination of anatomical dead space and alveolar dead space.
• Alveolar dead space is the volume of air in the respiratory zone not involved in gas transfer.
• Alveolar dead space is usually negligible in healthy people.

Alveolar Ventilation

• Air volume available for gas exchange per breath = (tidal volume - physiological dead space) x breaths per minute = liters per minute

Respiratory Zone

• Surfaces involved in gas exchange.

Gas Transport in Blood

• Arterial blood concentration = ~20ml O2 / 100ml blood.