Oxygenation and Ventilation

Upper Respiratory Tract

filters and warms air

Lower Respiratory Tract

handles gas exchange—supplying oxygen to the body and removing carbon dioxide.

nose; paranasal sinuses; pharynx, tonsils and adenoids; larynx; and trachea.

Upper airway structures

Nose

responsible for: passageway for air, filters impurities, warms and humidifies inhaled air

Turbinates

Layers of curved bone within the nasal cavity that increase surface area. Slightly obstruct airflow to enhance air contact with mucosa

Nasal mucosa

warm, moist, vascular, ciliated membrane. Traps dust and pathogens. Moistens & warms air. Contains sensory nerves (detect odors, trigger sneezing)

Paranasal Sinuses

4 pairs of air-filled, bony cavities. Lined with Nasal mucosa & ciliated pseudostratified columnar epithelium. Drains to nasal cavity via ducts. Helps in speech resonance and is a common site of infection

frontal, ethmoid, sphenoid, maxillary

Paranasal Sinuses

Pharynx (Throat)

Tubelike passage connecting nasal & oral cavities to the larynx. Passageway for respiratory and digestive tracts.

Tonsils and Adenoids

Part of lymphoid tissue that encircles the throat. First line of defense—filter and guard against pathogens entering via the nose or mouth

Nasopharynx

Behind nose, above soft palate. Contains adenoids (pharyngeal tonsils)

Oropharynx

Behind mouth. Contains palatine (faucial) tonsils

Laryngopharynx

lower part of the pharynx, just below the oropharyngeal opening into the larynx and esophagus. From hyoid bone to cricoid cartilage.

Epiglottis

A flap of tissue that seals off the windpipe and prevents food from entering.

Larynx (Voice Box)

Cartilaginous, epithelium-lined organ. Connects pharynx → trachea Known as the "watchdog of the lungs". Protects lower airway from foreign substances. Vocalization (sound production). Facilitates coughing. Innervated by C3-C6.

Glottis

space between the vocal folds

Arytenoid Cartilage

Two small cartilages in the larynx, the movements of which abduct and adduct the vocal folds. Anchors the vocal cords

Thyroid cartilage

Largest cartilage; forms the Adam's apple

Cricoid cartilage

Only complete ring of cartilage; located below the thyroid cartilage.

Vocal cords

Folds of connective tissue that stretch across the opening of the larynx and produce a person's voice.

Trachea (Windpipe)

A cylindrical tube about 5 in (10-12 cm) long and 1 in (1.5-2.5) in diameter. composed of smooth muscle and C-shaped cartilaginous rings (incomplete at the back). Open side faces the esophagus (posterior). Rings provide rigidity and prevent collapse during breathing.

Carina

Point at which the trachea bifurcates (divides) into the left and right mainstem bronchi. Highly sensitive, stimulation of this area during suctioning causes vigorous coughing.

angle of Louis (4th-5th T)

Location of Carina

Lungs

Paired, elastic organs in the thoracic cage. Enclosed in an airtight chamber with distensible walls

Right lung

3 lobes → Upper, Middle, Lower. Shorter, wider, and straighter making it more prone to aspiration

Left lung

2 lobes: superior and inferior

pleural fissures

Each lobe divided into 2-5 segments, separated by

Pleura

double-layered membrane surrounding each lung

visceral pleura

inner layer of pleura lying closer to the lung tissue

parietal pleura

outer layer of pleura lying closer to the ribs and chest wall. lines the thoracic cavity, diaphragm, ribs, and mediastinum. Contains pain fibers

Pleural fluid

lies between visceral and parietal layers in the Intrapleural space. Lubricates lungs → allows smooth expansion and movement during breathing. Normally contains 20-25 ml of fluid.

Mediastinum

Center of thorax, between pleural sacs. Extends from sternum to vertebral column. Contains: heart, thymus, aorta and vena cava, esophagus

Main Stem Bronchi

connect the trachea to the lung at the hilum

Lobar Bronchi

Secondary bronchi supplying lung lobes. 3 in right lung, 2 in left lung

Segmental Bronchi

Tertiary bronchi branching from lobar bronchi. 10 on right, 8 on left. Important for postural drainage

Subsegmental Bronchi

4th to 9th generations of the tracheobronchial tree; Surrounded by connective tissue (contains blood vessels, lymphatics, and nerves)

Bronchioles

Branches of subsegmental bronchi. Contain submucosal glands → secrete mucus. Lined with cilia to sweep mucus & debris upward

Terminal Bronchiole

Last part of nonrepiratory conducting airway which then leads into respiratory bronchioles

Respiratory Bronchioles

Transitional zone between conducting and gas exchange airways.

Anatomic Dead space

Volume of air in the trachea and bronchi. does not take part in gas exchange

150 mL

anatomic dead space volume

Trachea - Bronchi - lobar bronchi - segmental bronchi - terminal (non-respiratory) bronchioles - respiratory bronchioles - Alveolar ducts - alveoli

Sequence of structures from conducting airways to gas exchange airways

Bronchial circulation

Does not take part in gas exchange but provides O2 to the bronchi and other lung tissues. starts with the bronchial arteries, which arise from the thoracic aorta

azygos vein into the superior vena cava

Deoxygenated blood returns from the bronchial circulation through the

Alveoli

tiny sacs of lung tissue specialized for the movement of gases between air and blood

Type 1 Alveoli

95% of surface area; gas exchange barrier

Type II Alveoli

5% of surface area; produces surfactant & regenerates type I cells

Surfactant

Lipoprotein produced by Type II alveolar cells. Reduces surface tension, keeps alveoli from collapsing.

Pores of Kohn

small openings in the alveolar walls that allow gases and macrophages to travel between the alveoli

Diaphragm

Primary muscle of respiration. Contracts during inspiration, moving downward → increases intrathoracic volume. Made up of 2 hemidiaphragms.

pulls air into the lungs.

drop in intrathoracic pressure results in

diaphragm, external intercostal and scalene muscles

Muscle responsible During Inspiration

Phrenic nerves

Controls each hemidiaphragm. arise from C3-C5 spinal cord segments

Inspiration

Chest cavity expands → lungs inflate → air enters via trachea to alveoli. Active → requires energy. ~1/3 of respiratory cycle

Expiration

Chest cavity returns to original size → lungs recoil → air expelled. Passive → requires little/no energy. ~2/3 of respiratory cycle

760 mmHg

atmospheric pressure at sea level

Airway Resistance

any obstacle to airflow during inspiration and/or expiration

Airway diameter (primary factor)

Lung volume

Airflow velocity

Airway Resistance depends on

elastin fibers found in the alveolar walls and surrounding the bronchioles and capillaries.

Elasticity of lung tissue is due to

Lung Compliance (distensibility)

Ease with which lungs and thorax expand and stretch

150 to 200 mL/cmH₂O.

Normal Lung Compliance

Increased Compliance

lungs overdistended (too stretchy). Lungs inflate easily but do not recoil properly. Seen in: Emphysema

Decreased Compliance

stiff lungs/thorax. Requires more effort to expand lungs

Tidal Volume

Amount of air that moves in and out of the lungs during a normal breath

500 mL

Tidal Volume

Inspiratory Reserve Volume

Amount of air that can be forcefully inhaled after a normal tidal volume inhalation

3100 mL

Inspiratory Reserve Volume

Expiratory Reserve Volume

Amount of air that can be forcefully exhaled after a normal tidal volume exhalation

1200 mL

Expiratory Reserve Volume

Residual Volume

Amount of air remaining in the lungs after a forced exhalation

1200 mL

Residual Volume

Vital Capacity

The total volume of air that can be exhaled after maximal inhalation. TV + IRV + ERV

4800 mL

Vital Capacity

Inspiratory Capacity

maximum amount of air that can be inhaled after a normal tidal expiration. TV + IRV

3600 mL

Inspiratory Capacity

Functional Residual Capacity

volume of air remaining in the lungs after a normal tidal volume expiration. ERV + RV

2400 mL

Functional Residual Capacity

Total Lung Capacity

the sum of vital capacity and residual volume. TV + IRV + ERV + RV

6000 mL

Total Lung Capacity

Expiratory Capacity

the amount of air one can exhale from the rest position. TV + ERV

1700 mL

Expiratory Capacity

Pulmonary Diffusion

Movement of O₂ and CO₂ across the alveolar-capillary membrane. Follows concentration gradients (high → low)

Pulmonary Perfusion:

Blood flow through the pulmonary circulation

Shunt Circulation

~2% of blood bypasses alveolar gas exchange (normal physiologic shunt) and enters the left heart unoxygenated

Pulmonary Circulation

Low-pressure system capable of adjusting to blood flow changes.

Systolic: 20-30 mm Hg

Systolic pressure in Pulmonary Circulation

Diastolic: 5-15 mm Hg

Diastolic pressure in Pulmonary Circulation

Pulmonary Artery Pressure

Works with gravity and alveolar pressure to regulate regional perfusion.

V/Q ratio

A measurement that examines how much gas is being moved effectively and how much blood is flowing around the alveoli where gas exchange (perfusion) occurs.

Normal V/Q

Ventilation matches perfusion (0.8). Efficient gas exchange

Low V/Q (Shunt)

Perfusion present, but ↓ or no ventilation. may be called shunt-producing disorders. When perfusion exceeds ventilation, a shunt exists. Unoxygenated blood passes to the body leading to hypoxia

High V/Q (Dead space)

Ventilation present, but ↓ or no perfusion. Wasted ventilation; no gas exchange

Shunting

Blood bypasses oxygenation

Main cause of hypoxia after thoracic/abdominal surgery and respiratory failure

> 20%

Severe hypoxia occurs if shunt is

~40 mm Hg

Arterial PCO₂: maintained at

Resting respiration

controlled by cyclic stimulation of respiratory muscles via the phrenic nerve.

Medulla oblongata and Pons

respiratory centers in the brainstem

Medulla

receives chemical and mechanical signals → sends impulses via spinal cord and phrenic nerves to respiratory muscles. Controls rate and depth of breathing to meet metabolic demands

Central Chemoreceptors

Receptors in the medulla that monitor the pH of cerebrospinal fluid to help regulate ventilation rate.

Peripheral Chemoreceptors

Receptors in the carotid arteries and the aorta that monitor blood pH to help regulate ventilation rate.