Anatomy

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The Respiratory System

Objectives • Describe the primary functions of the respiratory system. • Identify the organs of the respiratory system and describe their functions. • Define and compare the processes of external and internal respiration. • Summarize the physical principles governing the movement of air into the lungs and

the diffusion of gases into the blood. • Explain the important structural features of the respiratory membrane. • Describe how O2 and CO2 are picked up, transported, and released in the blood.

Functions of the respiratory system • Gas exchange between air and circulating blood • Moving air across the exchange surface of the lungs • Protection of respiratory surfaces • Production of sound • Provision for olfactory sensations

Organization of the respiratory system • Upper respiratory system

• Nose, nasal cavity, paranasal sinuses, pharynx • Lower respiratory system

• Larynx, trachea, bronchi, bronchioles, alveoli

The Respiratory tract • Passageways carrying air to and from the alveoli

• Upper respiratory passages filter and humidify incoming air • Lower passageways include delicate passages and alveolar exchange surfaces

Respiratory mucosa • Respiratory epithelium and underlying connective tissue supported by lamina propria • Lines conducting portion of respiratory tract • Protected from contamination by respiratory defense system

The nose and nasal cavity consists of • External nares • Nasal cavity • Vestibule • Superior, middle, and inferior meatuses • Hard and soft palates • Internal nares • Nasal mucosa

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The Pharynx • Shared by the digestive and respiratory systems • Divided into three sections:

• Nasopharynx – superior portion • Oropharynx – continuous with the oral cavity • Laryngopharynx – between the hyoid bone and the esophagus

The Larynx • Air passes through the glottis on the way to the lungs • Cartilages of the larynx

• Three large cartilages • Thyroid, cricoid, and epiglottis

• Paired cartilages • Arytenoids, corniculate, and cuneiform

• Folds of the larynx • Inelastic vestibular folds • Delicate vocal folds

Sound production • Air passing through the glottis vibrates the vocal folds producing sound waves • Pitch depends on conditions of vocal folds

• Diameter • Length • Tension

The laryngeal musculature • Muscles of the neck and pharynx position and stabilize the larynx

• When swallowing, these muscles • Elevate the larynx • Bend the epiglottis over the glottis

The Trachea • Extends from the sixth cervical vertebra to the fifth thoracic vertebra • A tough, flexible tube running from the larynx to the bronchi • Held open by C-shaped tracheal cartilages in submucosa • Mucosa is similar to the nasopharynx

The primary bronchi • Trachea branches in the mediastinum into right and left bronchi

• Bronchi enter the lungs at the hilus

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The Lungs

Lobes and surfaces of the lungs • Lobes of the lung are separated by fissures

• Right lung has three lobes • Left lung has two lobes

• Concavity on medial surface = cardiac notch

The bronchial tree • System of tubes formed from the primary bronchi and their branches

• Primary bronchi branch into secondary or lobar bronchi • Secondary bronchus goes to each lobe of the lungs • Secondary bronchi branch into tertiary bronchi • Tertiary bronchi supply air to a single bronchopulmonary segment

The bronchioles • Ultimately branch into terminal bronchioles

• Delivers air to a single pulmonary lobule • Terminal bronchiole becomes respiratory bronchioles

Alveolar ducts and alveoli • Respiratory bronchioles end in ducts and sacs

Respiratory membrane • Simple squamous epithelium • Endothelial cell lining an adjacent capillary • Fused basal laminae

Cells of the respiratory membrane include • Septal cells

• Produce surfactant which keep alveoli open • Alveolar macrophage

• Patrol epithelium and engulf foreign particles

The pleural cavities and pleural membranes • Each lung covered by one pleura

• Pleura—serious membranes lining the pleural cavity • Parietal—attaches to the walls of the pleural cavity • Visceral—adheres to the surface of the lungs

• Pleural fluid—fills and lubricates the space between the pleura

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Respiratory physiology • External respiration

• Exchange of gases between interstitial fluid and the external environment • The steps of external respiration include

• Pulmonary ventilation – moving air between external environment and lungs • Gas diffusion – moving gases across respiratory membrane and into blood • Transport of O2 and CO2 – in blood from lungs into the systems

• Internal respiration • Exchange of gases between interstitial fluid and cells

Pulmonary ventilation • Movement of air depends upon

• Boyle’s law • Pressure and volume inverse relationship • Volume depends on movement of diaphragm and ribs

• Pressure and airflow to the lungs • Compliance – an indication of the expandability of the lungs

Respiratory volumes - Spirometry • Tidal Volume (VT)

• Amount of air inhaled or exhaled with each breath • Inspiratory Reserve Volume (IRV)

• Inhaled air above VT • Expiratory Reserve Volume (ERV)

• Exhaled air below VT • Vital Capacity (VC)

• VT + IRV and ERV • Residual Volume (RV)

• Air left in lungs after maximum exhalation • Total Lung Capacity (TLC)

• VC + RV

Gas Diffusion • Dalton’s law and partial pressure

• Individual gases in a mixture exert pressure proportional to their abundance

Atmospheric pressure (760 mm Hg) = PO2 + PCO2 + PN2 + PH2O

Atmospheric PO2 = 21% .21 x 760 mm Hg = 160 mm Hg

Atmospheric PCO2 = .04% .0004 x 760 mm Hg = .3 mm Hg

Atmospheric PN2 = 78.5% .785 x 760 mm Hg = 597 mm Hg

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Transportation of O2 and CO2

Oxygen transport

• 3% dissolved in plasma • 97% carried in hemoglobin (heme portion) as oxyhemoglobin (HbO2) • The amount of oxygen hemoglobin can carried is dependent upon

• PO2 • pH – higher values result in less saturation • temperature – higher temps cause Hb to release O2

Carbon dioxide transport • 7 % dissolved in plasma • 23 percent bound to hemoglobin

• carbaminohemoglobin • 70 % carried as carbonic acid, which dissociates into a hydrogen ion and bicarbonate

ion • Carbon dioxide plus water reversibly reacts to form a hydrogen ion and

bicarbonate ion • CO2 + H2O ⇔ H+ + HCO3-

• Most of the H+ is taken up by Hb, which therefore serves as a buffer • The + HCO3- move out of RBC and into plasma in exchange for a Cl-, this is

the chloride shift

The efficiency of the respiratory system decreases with age as: • Elastic tissue deteriorates causing lower lung compliance and vital capacity • Chest movements are restricted by arthritic changes • Some degree of emphysema normally occurs