Human Lungs Anatomy

Lungs Structure

• Paired, cone-shaped organs in thoracic cavity, separated by heart and other structures in mediastinum
• Divided into two anatomically distinct chambers by mediastinum

Pleural Membrane

• Double layer of serous membrane that encloses lungs
• Parietal pleura lines wall of thoracic cavity, visceral pleura lines lungs
• Pleural cavity space between parietal and visceral pleura contains lubricating fluid secreted by membranes
• Pleural fluid reduces friction between membranes during breathing and adheres to membrane surface tension

Position and Hilum

• Concave base of lungs sits on convex area of diaphragm
• Anterior, lateral, and posterior surface of lungs lie against ribs, costal surface matches rounded curvature of ribs
• Hilum is at mediastinal surface where bronchi, pulmonary blood vessels, lymphatic vessels, and nerves enter and exit
• Held by pleura and connective tissue root

Cardiac Notch and Fissures

• Medial concavity at left lung due to heart, making left lung ~10% smaller than right lung
• Fissures divide lungs into lobes
• Oblique fissure separates superior lobe from inferior lobe (left lung), and superior lobe from inferior lobe and inferior lobe from middle lobe (right lung)
• Horizontal fissure separates superior lobe from middle lobe (right lung)

Lobes and Bronchopulmonary Segments

• Each lobe receives a 2º bronchus
• Bronchopulmonary segment receives a 3º bronchus and contains many lobules

Lobules and Alveoli

• Lobules contain a lymphatic vessel, an arteriole, a venule, and a branch from terminal bronchiole
• Alveoli are cup-shaped outpouchings lined by simple squamous epithelium and supported by a thin elastic basement membrane
• Alveoli are the main site for gas exchange

Alveolar Cells and Macrophages

• Type I alveolar cells are simple squamous epithelium and the main site for gas exchange
• Type II alveolar cells (septal cells) are rounded or cuboidal epithelium with microvilli, secrete alveolar fluid, and contain surfactant
• Alveolar macrophages remove fine dust particles and other debris from alveolar spaces

Respiratory Membrane

• Exchange of O2 and CO2 between alveolar air space and blood by diffusion
• Consists of alveolar wall (type I, II, and macrophages), basement membrane of alveolar wall, capillary endothelium, and basement membrane of capillary endothelium

Blood Supply

• Pulmonary arteries come from right ventricle and pulmonary trunk, and branch into right and left pulmonary arteries
• Pulmonary veins return oxygenated blood to left atrium
• Unique feature: constriction in response to localized hypoxia, diverting pulmonary blood from poorly ventilated area to well-ventilated area
• Bronchial arteries branch from aorta and perfuse muscular walls of bronchi and bronchioles, delivering oxygenated blood to lungs

Bronchial Tree

• Trachea divides into 1˚ bronchi, 2˚ bronchi, 3˚ bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, and alveolar ducts

Epithelial Changes

• Epithelial changes occur along the bronchial tree, from pseudostratified ciliated columnar (trachea, 1˚, 2˚, 3˚) to simple squamous (alveoli)

Lungs Structure

• Paired, cone-shaped organs in thoracic cavity, separated by heart and other structures in mediastinum
• Divided into two anatomically distinct chambers by mediastinum

Pleural Membrane

• Double layer of serous membrane that encloses lungs
• Parietal pleura lines wall of thoracic cavity, visceral pleura lines lungs
• Pleural cavity space between parietal and visceral pleura contains lubricating fluid secreted by membranes
• Pleural fluid reduces friction between membranes during breathing and adheres to membrane surface tension

Position and Hilum

• Concave base of lungs sits on convex area of diaphragm
• Anterior, lateral, and posterior surface of lungs lie against ribs, costal surface matches rounded curvature of ribs
• Hilum is at mediastinal surface where bronchi, pulmonary blood vessels, lymphatic vessels, and nerves enter and exit
• Held by pleura and connective tissue root

Cardiac Notch and Fissures

• Medial concavity at left lung due to heart, making left lung ~10% smaller than right lung
• Fissures divide lungs into lobes
• Oblique fissure separates superior lobe from inferior lobe (left lung), and superior lobe from inferior lobe and inferior lobe from middle lobe (right lung)
• Horizontal fissure separates superior lobe from middle lobe (right lung)

Lobes and Bronchopulmonary Segments

• Each lobe receives a 2º bronchus
• Bronchopulmonary segment receives a 3º bronchus and contains many lobules

Lobules and Alveoli

• Lobules contain a lymphatic vessel, an arteriole, a venule, and a branch from terminal bronchiole
• Alveoli are cup-shaped outpouchings lined by simple squamous epithelium and supported by a thin elastic basement membrane
• Alveoli are the main site for gas exchange

Alveolar Cells and Macrophages

• Type I alveolar cells are simple squamous epithelium and the main site for gas exchange
• Type II alveolar cells (septal cells) are rounded or cuboidal epithelium with microvilli, secrete alveolar fluid, and contain surfactant
• Alveolar macrophages remove fine dust particles and other debris from alveolar spaces

Respiratory Membrane

• Exchange of O2 and CO2 between alveolar air space and blood by diffusion
• Consists of alveolar wall (type I, II, and macrophages), basement membrane of alveolar wall, capillary endothelium, and basement membrane of capillary endothelium

Blood Supply

• Pulmonary arteries come from right ventricle and pulmonary trunk, and branch into right and left pulmonary arteries
• Pulmonary veins return oxygenated blood to left atrium
• Unique feature: constriction in response to localized hypoxia, diverting pulmonary blood from poorly ventilated area to well-ventilated area
• Bronchial arteries branch from aorta and perfuse muscular walls of bronchi and bronchioles, delivering oxygenated blood to lungs

Bronchial Tree

• Trachea divides into 1˚ bronchi, 2˚ bronchi, 3˚ bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, and alveolar ducts

Epithelial Changes

• Epithelial changes occur along the bronchial tree, from pseudostratified ciliated columnar (trachea, 1˚, 2˚, 3˚) to simple squamous (alveoli)

This quiz covers the structure and function of human lungs, including the thoracic cavity, pleural membrane, and pleural cavity.