Functions of the Respiratory System

Functions of Respiratory System

• The respiratory system facilitates gas exchange between blood and air
• It moves air to and from exchange surfaces
• Protects exchange surfaces from environmental variations and pathogens
• Produces sound
• Detects olfactory stimuli

The Respiratory Tract

• Conducting portion: conducts air movement from nares to small bronchioles
• Respiratory portion: gas exchange region, comprising respiratory bronchioles and alveoli

Respiratory Mucosa

• Comprises respiratory epithelium, supporting connective tissue, and mucous glands
• Lines nasal cavity and most airways
• Goblet and gland cells secrete mucus
• Mucus traps inhaled dirt, pathogens, etc.
• Ciliated cells sweep the mucus out of the airways into pharynx
• Irritants stimulate secretion, causing “runny nose”

The Larynx

• Also known as the “voice box”
• Made of nine cartilages
• Air passes through glottis
• Covered by epiglottis during swallowing
• Keeps solids, liquids out of airways
• Made of elastic cartilage
• Supports true vocal cords
• Exhaled air vibrates true vocal cords to make sound

The Trachea

• Also called “windpipe”
• Stiffened by C-shaped cartilage rings
• Esophagus stuck to posterior surface
• Cartilage missing there
• Trachea distorted by balls of food as they pass down esophagus to stomach

The Bronchi

• Trachea forms two branches: right and left primary bronchi
• Primary bronchi branch to form secondary bronchi
• Each secondary bronchi ventilates a lobe
• Secondary bronchi branch to form tertiary bronchi
• Tertiary bronchi branch repeatedly
• Cartilage decreases, smooth muscle increases

The Alveolar Ducts and Alveoli

• Gas exchange regions of the lung
• Respiratory bronchioles lead into alveolar ducts
• Ducts lead into alveolar sacs
• Sacs are clusters of interconnected alveoli
• Gives the lung an open, spongy look
• Approximately 150 million alveoli per lung

Anatomy of the Alveolus

• Respiratory membrane: simple squamous epithelium, capillary endothelium, and shared basement membrane
• Septal cells produce surfactant to reduce collapse
• Alveolar macrophages engulf foreign particles

Air Flow

• Determined by the relationship of atmospheric pressure and pressure inside the respiratory tract
• Flow is always from higher to lower pressure

Muscles of Respiration

• Primary inspiratory muscles: diaphragm and external intercostals
• Relaxed normal expiration is a passive process
• Muscles of inspiration elevate the ribs and sternum
• Muscles of expiration depress the ribs and sternum
• Forceful expiration involves internal intercostals and abdominal muscles

Gas Exchange

• External respiration: diffusion of gases between alveolar air and pulmonary capillary blood across the respiratory membrane
• Internal respiration: diffusion of gases between blood and interstitial fluids across the capillary endothelium
• Hemoglobin binds most oxygen in the bloodstream, releasing more oxygen as PO2 decreases, pH falls, or temperature rises

Carbon Dioxide Transport

• Aerobic metabolism produces CO2
• 7% of CO2 travels dissolved in plasma
• 23% of CO2 travels bound to hemoglobin as carbaminohemoglobin
• 70% of CO2 is converted to H2CO3 (carbonic acid) in RBCs

Respiratory Control

• Respiratory centers in brainstem: three pairs of nuclei (two in pons, one in medulla oblongata)
• Control respiratory muscles and set rate and depth of ventilation
• Respiratory rhythmicity center in medulla sets the basic rhythm of breathing

Respiratory Mucosa

• Respiratory epithelium plus supporting connective tissue with mucous glands
• Lines nasal cavity and most airways
• Goblet and gland cells secrete mucus, which traps inhaled dirt, pathogens, etc.
• Ciliated cells sweep mucus out of airways into pharynx
• Irritants stimulate mucus secretion, causing a "runny nose"
• Smooth muscle in wall controlled by ANS (Sympathetic: bronchodilation, Parasympathetic: bronchoconstriction)
• Excess bronchoconstriction is asthma