Alveolar capillary bed

Looks like

A dense mesh of the finest blood vessels wrapped around every air sac, their walls a fraction of a micrometre from the air.

What it does

Where oxygen crosses into the blood and carbon dioxide leaves it.

Keeping it well

Scarring (pulmonary fibrosis), fluid from heart failure or blocked vessels from clots all thicken or cut off this barrier; breathlessness on effort with low oxygen readings, or crackles heard in the lungs, needs investigation.

Related conditions

• Acute respiratory distress syndrome
• Alpha-1 antitrypsin deficiency
• Altitude sickness
• Asbestosis and asbestos-related disease
• Aspergillosis
• Asthma
• Breathing pattern disorder
• Bronchiectasis
• Bronchiolitis & RSV
• COPD
• COVID-19
• Cystic fibrosis
• Drowning
• Echinococcosis (hydatid disease)
• Endemic fungal infections (histoplasmosis, coccidioidomycosis)
• Hantavirus infection
• High blood pressure
• High cholesterol
• Hypothermia & frostbite
• Idiopathic pulmonary fibrosis
• Influenza
• Kawasaki disease
• Legionnaires' disease
• Leptospirosis (Weil's disease)
• Long COVID (post-viral syndrome)
• Lung abscess
• Lung cancer
• Measles
• Mesothelioma
• Metabolic syndrome
• Molar pregnancy and gestational trophoblastic disease
• Neonatal sepsis
• Neuroendocrine tumours (carcinoid)
• Orthostatic hypotension & POTS
• Peripheral artery disease
• Phaeochromocytoma & hyperaldosteronism
• Pleural effusion
• Pleurisy
• Pneumocystis pneumonia (PCP)
• Pneumonia
• Pneumothorax
• Pre-eclampsia
• Pulmonary embolism
• Pulmonary hypertension
• Pulmonary oedema
• Raynaud's phenomenon
• Respiratory distress syndrome of the newborn
• Sarcoidosis
• Sepsis
• Shock (circulatory failure)
• SIADH (inappropriate antidiuretic hormone)
• Silicosis and coal workers' pneumoconiosis
• Sudden infant death syndrome
• Systemic sclerosis (scleroderma)
• Tuberculosis
• Vasculitis (GCA & others)
• Whooping cough