Human Respiratory System: An Overview

• Human respiratory system facilitates efficient gas exchange, delivering oxygen to the body and removing carbon dioxide.

Respiratory System Components and Functions

• Nose/Nasal Cavity filters, warms, and moistens inhaled air, trapping particles with mucus and cilia.
• Pharynx (Throat) serves as an airway from the nose to the larynx and aids in swallowing by directing food to the esophagus.
• Larynx (Voice Box) contains vocal cords for sound production and prevents food/liquids from entering the trachea.
• Trachea (Windpipe) provides a clear airway to the lungs and is lined with cilia and mucus for filtering.
• Bronchi divide from the trachea, directing air into the left and right lungs.
• Bronchioles are smaller branches of the bronchi that distribute air to the alveoli (air sacs).
• Alveoli are tiny sacs where oxygen is absorbed into the blood, and carbon dioxide is removed.
• Lungs house the alveoli and facilitate gas exchange.
• Diaphragm is a muscle that contracts and relaxes, changing lung volume for breathing.
• Intercostal Muscles between the ribs expand/contract the ribcage, aiding inhalation/exhalation.

Gas Exchange and Diffusion

• Diffusion is the movement of particles from an area of higher concentration to lower concentration.
• Oxygen and carbon dioxide move across the respiratory membrane through diffusion.
• Oxygen diffuses from the alveoli (high concentration) into the blood (low concentration).
• Carbon dioxide diffuses from the blood (high concentration) into the alveoli (low concentration) for exhalation.
• Diffusion is driven by concentration gradients across the alveoli and capillaries.

Breath Rate Factors

• During intense physical activity, muscles consume more oxygen and produce more carbon dioxide. The body increases breathing rate to meet these demands.
• Fear triggers the sympathetic nervous system, releasing adrenaline, increasing heart rate and breathing rate for quick action.

Inspired vs. Expired Air

• Inspired air is inhaled from the atmosphere and contains more oxygen and less carbon dioxide/water vapor than expired air.
• Typical composition of inspired air: 21% oxygen, 0.04% carbon dioxide, 78% nitrogen, and variable water vapor.
• Expired air is exhaled after gas exchange, containing less oxygen and more carbon dioxide/water vapor than inspired air.
• Typical composition of expired air: 16-17% oxygen, 4-5% carbon dioxide, roughly the same nitrogen, and more water vapor.
• Inspired air is fresh air breathed in, while expired air is air breathed out after gas exchange.

Skin Respiration

• Thin skin ensures a short distance for efficient gas diffusion.
• Large surface area maximizes the area for gas exchange, often with folds or wrinkles.
• Moist skin allows gases like oxygen and carbon dioxide to dissolve and diffuse easily.
• Rich blood supply provides a network of capillaries close to the skin for gas transport.
• Permeable skin allows gases to pass through, facilitating respiration in animals like amphibians.

Red Blood Cells (Erythrocytes)

• Biconcave disc shape increases surface area for gas exchange.
• They lack a nucleus (in mammals), allowing more room for hemoglobin.
• Flexible structure allows them to squeeze through capillaries.
• Hemoglobin in RBCs binds oxygen in the lungs and delivers it to tissues.
• Transports CO₂ from tissues to the lungs for exhalation.
• Help regulate pH by buffering blood.
• Lifespan is about 120 days; broken down in the spleen and liver

White Blood Cells (Leukocytes)

• Protect the body against infections, foreign invaders, and diseases.
• Lifespan varies.

Granulocytes

• Neutrophils (50-70% of WBCs) are first line of defense against bacteria and fungi that engulf and kill microbes through phagocytosis with a short lifespan.
• Eosinophils (1-4% of WBCs) are involved in allergic reactions and parasitic infections, releasing enzymes to break down allergens and accumulate in inflamed tissues.
• Basophils (<1% of WBCs) release histamine and other chemicals during allergic reactions and help in inflammatory response.