The Respiratory System

PART 1: ANATOMY OF THE RESPIRATORY SYSTEM

Overview

  • Primary Function: Gas exchange (providing constant O₂ while removing CO₂)

  • Two Divisions: Upper Respiratory System and Lower Respiratory System

Upper Respiratory System Structures

Structure

Key Features

Function

Nose

External opening = Nares

Air entry point

Nasal Cavity

Divided by nasal septum; vestibular region with oily hairs; mucus lining

Trap particles; warm incoming air

Olfactory Receptors

Located in roof of cavity

Sense of smell

Conchae Bones

Superior, middle, inferior (scroll-like)

Increase surface area; create turbulence to trap particles

Palate

Hard palate (anterior/bone); Soft palate (posterior)

Separates nasal cavity from mouth

Uvula

Connective/muscle tissue pouch from soft palate

Speech; prevents food from entering nasal cavity

Sinuses

Air-filled spaces around nose with mucus ducts

Lighten head; warm/moisten air; amplify voice

Pharynx

5-inch throat; 3 sections: Nasopharynx, Oropharynx, Laryngopharynx

Passageway for air and food

Tonsils

Lymphatic tissue clusters in pharynx

Trap bacteria and pathogens

Larynx

Triangle-shaped cartilage plates; thyroid cartilage (Adam's apple)

Routes food; contains vocal cords

Epiglottis

Flap of cartilage between tongue and larynx

Covers larynx opening during swallowing

Trachea

Windpipe (4 inches); C-shaped cartilage rings (opening posterior)

Airway; cartilage provides support, opening allows expansion

Lower Respiratory System Structures

Structure

Key Features

Function

Bronchi

Primary tubes to lungs; right is shorter/wider; branch to secondary/tertiary

Air passage to lungs

Bronchioles

Smallest passageways

Form respiratory tree

Alveoli

Air-filled sacs in clusters; thin squamous epithelial cells; coated with surfactant; Pores of Kohn

Main site of gas exchange

Alveoli Surface Area

About size of a tennis court

Maximizes gas exchange

Lungs

Left and right with mediastinum between; apex = upper part

Major respiratory organs

Lung Lobes

Right = 3 lobes; Left = 2 lobes

Division of lung tissue

Pleural Sac

Double-walled sac; Parietal (touches thoracic wall); Visceral (touches lungs); separated by serous fluid

Protects and cushions lungs

Mediastinum

Space between lungs

Contains heart, great vessels, trachea, esophagus, thoracic duct, thymus

PART 2: MECHANICS AND CONTROL OF BREATHING

The Four Key Tasks of Respiration

  1. Pulmonary Ventilation: Air continuously moved in/out of lungs

  2. External Respiration: Gas exchange between alveoli and pulmonary blood

  3. Respiratory Gas Transport: O₂ and CO₂ transported in blood between lungs and tissues

  4. Internal Respiration: Gas exchange inside body between tissues and capillaries

Inhalation vs. Exhalation

Process

Mechanism

Type

Inhalation

Intercostal muscles contract → ribs lift up; diaphragm contracts and pushes down → lungs expand → intrapulmonary pressure lowers → air pulled in

Active

Exhalation

Intercostal muscles relax; diaphragm relaxes → space in thoracic cavity decreases → intrapulmonary pressure rises → air forced out

Passive (normally)

Non-Respiratory Air Maneuvers

Maneuver

Cause/Function

Cough

Clear dust/debris from lower respiratory tract

Sneeze

Clean upper respiratory tract

Hiccup

Spasm of the diaphragm

Yawn

Need for increased oxygen

Control of Breathing

  • Average Rate: 12-15 breaths/minute

  • Influencing Factors: Sex, age, posture, activity

Chemical Factors

Receptor Type

Location

Function

Central Chemoreceptors

Brain

Monitor pH in cerebrospinal fluid (high CO₂ → pH decreases)

Peripheral Receptors

Aorta and carotid artery

Sensitive to blood O₂ levels; send info to brain

Mechanoreceptors

Muscles and joints

Responsible for quick ventilation increase at start of exercise

Neural Factors

Structure

Function

Medulla Oblongata

Sets the pace of breathing

Pons

Controls depth and coordinates breathing

Hering-Breur Reflex

Stretch receptors in bronchioles/alveoli trigger this reflex to prevent overinflation; sends messages to medulla to stop inhalation and start expiration

Lung Volumes

Normal Lung Capacity: About 6 liters

Static Lung Volume (measured with respirometer)

Used to determine if a lung disorder exists through various maneuvers:

Volume

Definition

Tidal Volume (TV)

Amount of air breathed in with a normal breath

Vital Capacity

Total amount of air that can be forcibly expired after maximum inhale

Residual Volume (RV)

Air that remains after maximum exhale (allows gas exchange to continue)

Functional Residual Capacity (FRC)

Amount of air in lungs after normal expiration

Inspiratory Reserve Volume (IRV)

Amount of air that can be inhaled after normal inspirations

Expiratory Reserve Volume (ERV)

Amount of air that can be exhaled after normal expiration

DISEASES AND DISORDERS

Upper Respiratory System

Disease

Description

Nasopharyngitis

Common cold

Pharyngitis

Inflammation of pharynx (sore throat)

Sinusitis

Inflammation of sinuses

Laryngitis

Inflammation of larynx (often losing voice)

Tonsilitis

Inflammation of tonsils

Influenza

Flu

Lower Respiratory System

Disease

Description

Acute Bronchitis

Inflammation of bronchi

Pneumonia

Infection/inflammation of alveoli

Tuberculosis

Bacterial infection of lungs

COPD

Chronic Obstructive Pulmonary Disease (includes emphysema and chronic bronchitis)

Asthma

Airway constriction and inflammation

Lung Cancer

Malignant growth in lung tissue

Key Points to Remember

  1. The upper respiratory system handles air conditioning (warming, filtering) while the lower system handles gas exchange

  2. Alveoli are the functional units where gas exchange actually occurs

  3. Surfactant is crucial for preventing alveolar collapse

  4. Breathing is controlled by a combination of chemical (CO₂/pH levels) and neural (brain stem) factors

  5. Lung volume measurements help diagnose respiratory disorders

  6. The pleural sac protects lungs and reduces friction during breathing