Lung Histology Objective To describe the gross anatomy and structure of lung tissue

Different levels of airways

Lung and airway structure

The structure of an alveolus

The relationship between a capillary and an alveolus

Alveoli – key structural features Surrounded by capillaries –Originating from pulmonary artery –Rejoining pulmonary vein Moist squamous epithelium –Flattened cells –Collagen & elastic fibres (for stretch and recoil) Surfactant

Epithelial Cells Referred to as Type I and Type II pneumocytes. Type I are large flattened cells and make up most of the alveolar wall. Type II secrete surfactant Barrier between the alveolus and the blood is called the respiratory membrane and is of minimal thickness.

Surfactant a mixture of lipids and proteins which helps reduce the surface tension of liquid lining inner surface of alveoli Speeds up transport of gases between the air and the liquid lining the alveolus Kills bacteria

“Thickness of the layers” Endothelium of capillary um Interstitial space um Alveolar epithelium um Surfactant layer 0.01um Therefore the total distance for gases to travel between blood and cells is um

Blood Vessels Mostly pulmonary capillaries Form a dense network around each alveolus. alveolar macrophages (a type of phagocytic white blood cell) digest any foreign particles that have reached the alveoli.

What allows efficient diffusion of gases across the alveoli? Large surface area Short distance to travel –One-cell thick walls (alveoli & capillaries) Steep diffusion gradient maintained by: –Ventilation –Good blood supply –Haemoglobin Surfactant RBC squeezing through narrow capillaries expose more surface area to alveolus

Connective Tissue Forms a supporting layer beneath the epithelium. Consists of fine collagen and elastin fibres together with fibroblast cells. Allows stretch and recoil of lung tissue with breathing

Uninflated lung tissue Inflated lung tissue

HOMEWORK Use pages 46 and 47 of your text book and suitable images from the internet produce an A4 page summary titled “How the lungs are adapted for efficient gaseous exchange”