Human Respiratory System Overview

Respiratory System

• Divided into upper and lower respiratory tracts
• Upper tract: structures outside the thoracic cavity (nasal cavity, pharynx, larynx)
• Lower tract: structures inside the thoracic cavity (trachea, bronchi, lungs)

Upper Respiratory Tract Functions

• Conditions air (warming and humidifying)
• Responsible for smell and taste
• Facilitates swallowing
• Cilia filter dust and large particles

Nasal Cavity

• Separated into two halves by the septum
• Lined with epithelium rich in goblet cells, producing mucus

Obstructive Sleep Apnea

• Muscles supporting the soft palate and uvula relax

Pharynx

• Muscular tube behind nasal and oral cavities
• Divided into three regions (nasopharynx, oropharynx, laryngopharynx)

Nasopharynx

• Extends from posterior nares to the soft palate
• Contains openings for the auditory tubes

Oropharynx

• Space between soft palate and base of the tongue
• Contains palatine and lingual tonsils

Laryngopharynx

• Passes dorsal to the larynx, connecting to the esophagus
• Chamber formed by cartilage and muscle

Pharynx Functions

• Prevents food and liquids from entering the trachea
• Acts as an air passageway
• Produces sound (larynx is responsible)

Larynx

• Located between the root of the tongue and the upper end of the trachea
• Chamber formed by cartilage and muscle
• Known as the voice box

Epiglottis

• Closes over the larynx during swallowing, directing food and liquids into the esophagus

Thyroid Cartilage

• Largest piece of cartilage in the larynx
• Known as the Adam's apple

Lungs and Alveoli

• Lung passages serve the alveoli, as gas exchange occurs within them
• Deoxygenated blood flows into alveoli through pulmonary arterioles, oxygenated leaves via venules
• Alveoli inflate like balloons during inhalation
• Oxygen enters and carbon dioxide exits during exhalation

Lungs

• Large, spongy, cone-shaped organs filling the pleural cavity
• Extend from above the clavicles to the diaphragm
• Lie against the anterior and posterior ribs
• Hilum is an opening on the medial surface where bronchi and blood vessels enter
• Right lung: shorter, broader, and larger than the left, with three lobes (superior, middle, inferior)

Pleural Cavity

• Space between the visceral and parietal pleurae
• Potential space, only existing when lungs are not inflated
• Contains fluid that lubricates surfaces, enabling smooth expansion and contraction

Pneumothorax

• Loss of negative pressure in the pleural cavity
• Causes lung recoil and collapse

Left Lung

• Handles about 55% of gas exchange
• Contains two fissures: horizontal and oblique
• Has two lobes (superior and inferior) due to the heart pushing on the lung structure
• Features a cardiac notch, accommodating the heart
• Handles 45% of gas exchange

Lung Components

• Apex: top of the lung
• Base: bottom of the lung

Asthma

• Common chronic disease in childhood

Bronchodilator

• Inhaler used for asthma

Pleura

• Serous membrane covering the lungs

Visceral Pleura

• Covers the surface of the lungs and extends into the fissures

Parietal Pleura

• Lines the entire thoracic cavity

Trachea and Bronchi

• Distribute air into the lungs
• Trachea: rigid tube located in front of the esophagus
• C-shaped cartilage rings reinforce the trachea, preventing collapse during inhalation
• The trachea extends from the larynx to the carina

Bronchial Tree

• The trachea branches into two primary bronchi: right bronchus is wider and more vertical

Secondary Bronchi

• Branch into secondary bronchi, one for each lobe of the lung

Tertiary Bronchi

• Branch from secondary bronchi, further subdividing into bronchioles

Bronchioles

• Branch into thin-walled passages called alveolar ducts

Alveolar Ducts

• Terminate in clusters of alveolar sacs

Alveoli

• Primary structures for gas exchange

Respiration

• Cerebral cortex allows for voluntary control of breathing rate and rhythm
• Carbon dioxide is the primary regulator of respiration
• Atmospheric pressure drives respiration

Inspiration

• Pressure within the lungs drops below atmospheric pressure

Expiration

• Pressure within the lungs rises above atmospheric pressure

Surfactant

• Infants, born before 28 weeks, commonly lack surfactant, meaning lungs are not fully developed

Emphysema

• A form of COPD, a lung condition
• Easy to inhale, hard to exhale
• Causes a "barrel chest"

Spirometer

• Device used to measure lung volumes and capacities

Tidal Volume

• Amount of air inhaled and exhaled during quiet breathing (500mL)

Breathing Mechanism

• Internal intercostals help elevate ribs
• Diaphragm contracts, flattens, and drops during inhalation
• Intercostal muscles relax pulling ribs downward during exhalation
• Diaphragm relaxes, bulging upward and pressing against lungs during exhalation

Deep Inspiration

• Uses muscles of the neck

Forced Expiration

• Uses abdomen muscles

Neural Control of Breathing

• Skeletal muscles require nervous stimulation to contract
• Medulla contains two interconnected centers controlling breathing: inspiratory and expiratory centers
• Pons contains two centers that influence breathing rhythm

Respiratory Volumes and Capacities

• Inspiratory Reserve Volume: 3000 mL
• Expiratory Reserve Volume: 1200 mL
• Residual Volume: 1300 mL
• Vital Capacity: 4700 mL
• Total Lung Capacity: 6000 mL

Common Respiratory Terms

• Apnea: temporary cessation of breathing
• Bradypnea: abnormally slow breathing
• Cheyne-Stokes Respiration: cyclical breathing pattern
• Dyspnea: labored or difficult breathing
• Hyperpnea: Increased rate of breathing, often due to exercise
• Hyperventilation: increased rate of respiration resulting in lowered carbon dioxide levels

Pulmonary Ventilation

• External intercostal muscles pull ribs upward and outward during inhalation
• Lungs rely on skeletal muscles to expand and contract during expiration
• Diaphragm is the main muscle of ventilation
• Normal respiratory rate is 12-20 breaths per minute

Pleural Cavity

• Space between the visceral and parietal pleurae
• Contains fluid that lubricates surfaces and helps with lung inflation
• Loss of negative pressure causes pneumothorax and lung collapse