Respiratory System Functions

• The major function of the respiratory system is to supply O2 and remove carbon dioxide.
• Build up of waste causes blood pH to decrease and become more acidic
• The respiratory system is responsible for both pulmonary ventilation and external respiration.

Respiration Accomplished By

• Pulmonary ventilation (breathing).
• External respiration takes place.
• Respiratory gases are transported.
• Internal respiration occurs.

Pulmonary Ventilation (Breathing)

• Ventilation consists of both inspiration and expiration.
• Inspiration moves air into the lungs, inhaling.
• Expiration moves air out of the lungs exhaling.

External Respiration

• O2 diffuses from the lungs to the blood.
• CO2 diffuses from the blood to the lungs.

Transport of Respiratory Gases

• The cardiovascular system transports gases using the blood as the transporting fluid.
• O2 is transported from the lungs to the tissue cells of the body.
• CO2 is transported from the tissue cells to the lungs.

Internal Respiration

• O2 diffuses from blood to tissue cells.
• CO2 diffuses from the tissue cells to blood.

Major Respiratory Organs

• Upper respiratory system warms, humidifies, and filters air.
• The upper respiratory system consists of the nose, paranasal sinuses, and pharynx (throat).
• Lower respiratory system is the conducting & respiratory zones.
• Lower respiratory system consists of the larynx, trachea, bronchial tree, alveoli, lungs, pleurae (voice box).

Nose & Nasal Cavity

• Nose functions as an airway, moistens warms & filters air.
• The Nose functions as a resonating chamber for speech - affects quality of speech
• The Nose houses olfactory receptors - smell.
• The framework of the nose is bone and cartilage, both internally and externally.
• External openings are nostrils (nares).
• The nasal cavity is internal and is divided by a bony septum (wall)
• The nasal cavity is continuous with the pharynx (throat).
• The area just inside nostrils is lined with sweat and sebaceous glands, and hair.
• Sweat glands, sebaceous glands, and hair secrete oils.
• The two types of mucous membranes in the nose are olfactory mucosa and respiratory mucosa.
• Olfactory mucosa functions for smell.
• Respiratory mucosa is pseudostratified ciliated columnar and produces mucus.

Pharynx (Throat)

• The Nasopharynx is the most superior portion, and the uvula covers the opening when swallowing, stopping food from entering.
  • The auditory tube connects to the middle ear to equalize pressure as necessary.
  • Only air passes through the nasopharynx.
• The Oropharynx is continuous with the oral cavity, air and food pass through the oropharynx.
• The Laryngopharynx is where respiratory and digestive pathways diverge and is continuous with the esophagus
  • Air and food pass through the Laryngopharynx.

Larynx

• The larynx is the "voice box".
• It is superior to the trachea and is composed of nine cartilages connected by membranes and ligaments.

Larynx Three Functions

• Provides a patent (open) airway.
• Routes air and food properly
• It houses the vocal cords for voice production.
• The epiglottis is elastic cartilage that covers the entrance to the trachea during swallowing.

Trachea

• The trachea is the wind pipe.
• It is a flexible tube descending from the larynx to mid-thorax, where it divides into two main bronchi.
• The trachea cleans, warms, and moistens incoming air.
• The trachea is lined by mucous membrane, which produces mucous that traps pathogens, dirt, and debris, and cilia move it up and out.
• The trachea is reinforced by 20 C-shaped rings of hyaline cartilage to prevent collapse.

Bronchi: Conducting Zone Structures

• Serve as passages that move air from the nose through bronchi.
• A bronchial Tree serve as passageways in the lungs that branch repeatedly.
• Order of air flow: Trachea > R&L main > Secondary bronchi > Tertiary bronchi > Bronchioles > Terminal bronchioles.

Respiratory Zone Structures

• The actual site of gas exchange is in the respiratory zone.
• Microscopic structures that begin at the entry of terminal bronchioles.
• Respiratory bronchioles lead into Alveoli (thin-walled air sacs covered with capillaries for gas exchange)
• Cells of Alveoli secrete surfactant, which is antimicrobial and increases elasticity (compliance) of lungs, improving the efficiency of breathing.
• Macrophages are be present to phagocytize pathogens, dirt, & debris.

Gross Anatomy of Lungs

• The lungs are paired organs in the thorax.
• The lungs are cone shaped with a hilum (concave area on medial surfaces for entry and exit of vessels, bronchi & nerves).
• The left lung is slightly smaller than the right to accommodate the heart in the cardiac notch.
• The left lung has two lobes (superior & inferior) with an oblique fissure between them.
• The right lung has three lobes (superior, middle, and inferior) with horizontal and oblique fissures between them.
• Stroma is lung tissue which is elastic CT, allowing lungs to recoil passively during expiration.

Pleurae

• The pleurae are thin, double layered membranes that surround the lung but are not open to the outside.
• The parietal pleura lines the thoracic wall and the superior surface of the diaphragm.
• Visceral pleura covers the lung surface and lines fissures between lobes.
• Pleural Cavity is space (between parietal and visceral pleura) filled with pleural fluid which prevents friction.
• Fluid causes serosa to cling to each other and causes the parietal pleura to cling to the wall of the thorax.
• The creates surface tension of fluid molecules attracted to each other
• Keeps lung from collapsing.

Pressure Relationships

• Intrapulmonary pressure (Ppul) is the pressure within the lungs; rises and falls with breathing
  • Intrapulmonary pressure always equalizes with P atm.
• Intrapleural pressure (Pip) is the pressure in the pleural cavity; rises and falls with breathing - always about 4 mm Hg less than Ppul (negative relative to Ppul).
• Transpulmonary pressure (Ppul - Pip) keeps air spaces in lungs open and keeps lungs from collapsing.
• Any condition that causes Pip to equal Patm causes lungs to collapse.

Pulmonary Ventilation

• Consists of inspiration and expiration.
• Depends on volume changes in the thoracic cavity.
• Volume changes lead to pressure changes (as volume increases, pressure decreases; as volume decreases, pressure increases)
• Pressure gradients lead to flow of gases (just like blood flow).

Inspiration

• Inspiration causes pressure inside the lungs to drops below atmospheric pressure.
• Air moves into the lungs during inspiration.

Expiration

• Expiration causes the pressure inside the lungs to rises above atmospheric pressure.
• Air moves out of lungs during expiration.

Respiratory Volumes

• Respiratory volumes and capacities are measured to gain information about a person’s respiratory status.
• RV keeps alveoli open and prevents lung collapse.

Dead Space

• Anatomical dead space is the inspired air that fills conducting passages but never makes it to alveoli for gas exchange; is normally about 150 ml.
• Alveolar dead space is when air that makes it to alveoli but no gas exchange occurs due to alveolar collapse or obstruction; which is not normal.
• Total dead space is the sum of anatomical dead space + alveolar dead space.
• Minute ventilation is the amount of air flowing into and out of respiratory tract in one minute; typically 6,000 ml/min (500 ml * 12 breaths per minute); does not account for dead space.
• Alveolar Ventilation Rate (AVR) measures the flow of air into and out of lungs but accounts for dead space; 12 breaths per minute * (500 - 150 ml) = 4200 ml/min

Test Questions

• Food should not enter the nasopharynx.
• The respiratory & digestive systems diverge in the laryngopharynx.