Revised 11/5/2007
INTRODUCTION TO RESPIRATION:
Our cells use oxygen and glucose to produce ATP energy. What organelles produce ATP? ________________________________________ This cellular process that produces ATP also results in the production of carbon dioxide, which is a toxic cellular waste product. When carbon dioxide dissolves in water, it reacts with the water to produce carbonic acid. This lowers the blood's pH (i.e. makes the blood more acidic), which can be deadly if the body does not get rid of the carbon dioxide.
The major function of the respiratory system (Fig. 24.1) is to supply the body with oxygen and get rid of carbon dioxide. Respiration is the overall exchange of gases between the air you breathe, your blood, and the cells of your body. The following processes are involved in respiration:
1) Pulmonary ventilation (breathing) involves inspiration (inhalation) and expiration (exhalation).
2) External respiration is the gas exchange between the air sacs of the lungs and the blood.
3) Respiratory gas transport: The cardiovascular system must transport oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. The cardiovascular system uses blood as the transporting fluid. Oxygen is carried by the ___________________________________ and carbon dioxide is carried in the ________________________ of the blood. (Fill in the blanks)
4) Internal respiration is the gas exchange between the blood and tissue cells.
THE NOSE AND THE NASAL CAVITIES: Fig. 24.2
The supporting framework of the nose consists of NASAL bones that form the bridge of the nose & MAXILLAE that form the lateral sides of the nose. Flexible HYALINE CARTILAGE forms the anterior portion of the nose.
EXTERNAL NARES (NOSTRILS) are the external openings of the nose. Inside each EXTERNAL NARIS is the VESTIBULE, which is lined with skin that contains coarse hairs called VIBRISSAE, which filter large particles from inhaled air.
Internal to the vestibule are two NASAL CAVITIES. A wall called the NASAL SEPTUM separates the nasal cavities. See FIG. 7.11, p. 181. HYALINE CARTILAGE forms the anterior nasal septum; the VOMER bone and the PERPENDICULAR PLATE OF THE ETHMOID form the posterior nasal septum.
The nasal cavities lie inferior to the cranium and superior to the mouth. The CRIBRIFORM PLATE OF THE ETHMOID forms the roof of the nasal cavities (see FIG. 7.8, p. 176). The floor of the nasal cavities is formed by the PALATE, which separates the nasal cavities from the ORAL CAVITY. The anterior palate is called the HARD PALATE and is supported by the PALATINE PROCESSES OF THE MAXILLAE and the PALATINE bones (see FIG. 7.7, p. 174). The unsupported posterior part of the palate is the SOFT PALATE (see FIG. 25.4, p. 771).
Nasal cavities are lined with MUCOUS MEMBRANE, which consists of CILIATED PSEUDOSTRATIFIED COLUMNAR EPITHELIUM (see Table 3.1, p. 65) with many GOBLET CELLS. Each day, the goblet cells secrete about a quart of sticky mucus. The MUCUS traps dust, bacteria and other debris; it also contains an antibacterial enzyme that destroys bacteria. The ciliated cells create a gentle current that moves contaminated mucus back toward the throat, where it is swallowed. The mucus also moistens the air as it is inhaled.
A rich supply of capillaries are located in the connective tissue layer of the nasal cavity's mucous membrane. The blood in the capillaries heats incoming air as it flows over the mucous membranes.
OLFACTORY EPITHELIUM lines the superior region of the nasal cavity & contains OLFACTORY SENSORY RECEPTORS that detect smells. The olfactory nerves pass through the FORAMINA of the CRIBRIFORM PLATE OF THE ETHMOID BONE, carrying olfactory sensory information to the brain (see FIG. 22.1, p. 673).
Projecting medially from the lateral wall of each nasal cavity are three mucous membrane covered lobes, the SUPERIOR, MIDDLE & INFERIOR NASAL CONCHAE. The depression or groove below each concha is called a MEATUS (SUPERIOR, MIDDLE & INFERIOR NASAL MEATUSES). See FIG. 7.9, p. 179. The conchae and meatuses increase the air turbulence in the nasal cavity. This air turbulence helps clean, moisten and warm incoming air before it reaches the throat.
The nasal cavities are surrounded by a ring of PARANASAL SINUSES located in the FRONTAL, SPHENOID, ETHMOID, and MAXILLAE bones. See FIG. 7.13, p. 184. The sinuses lighten the skull, produce mucus that drains into the nasal cavities and serve as resonating chambers for sound.
Two INTERNAL NARES serve as openings between the nasal cavities and the pharynx (throat).
THE PHARYNX: Figs. 24.2 & 24.3
The PHARYNX (throat) is about 13 cm (5 inches) long. It is subdivided into 3 regions: NASOPHARYNX, OROPHARYNX & LARYNGOPHARYNX.
The NASOPHARYNX is posterior to the nasal cavities. The nasopharynx extends inferiorly to the level of the soft palate. Mucous membrane consisting of CILIATED PSEUDOSTRATIFIED COLUMNAR EPITHELIUM (Table 3.1, p.65) lines the nasopharynx.
The posterior wall of the nasopharynx contains the PHARYNGEAL TONSIL or ADENOID. What is its function?
The EUSTACHIAN TUBES open into the lateral walls of the nasopharynx. See FIG. 22.10, p. 685. Air is exchanged between the eustachian tubes and the nasopharynx so that air pressure inside the MIDDLE EAR equals the atmospheric air pressure of the air entering the nose and mouth.
The OROPHARYNX is posterior to the oral cavity and extends from the soft palate inferiorly to the level of the hyoid bone. It is a common passageway for air, food & fluids. The FAUCES (See also FIG. 25.4, p. 771) is the opening between the oral cavity & oropharynx. The mucous membrane of the oropharynx consists of NONKERATINIZED STRATIFIED SQUAMOUS EPITHELIUM (Table 3.1, p.65). WHY?
PALATINE TONSILS are located posterior to the soft palate (FIGS. 24.2 & 24.3, & 25.4, page 771) & LINGUAL TONSILS are at the base of the tongue (FIGS. 24.2 & 24.3).
The LARYNGOPHARYNX is inferior to the oropharynx, extending from the hyoid bone to the larynx. Since it is also a common passageway for food, liquids and air, it is also lined with NONKERATINIZED STRATIFIED SQUAMOUS EPITHELIUM (Table 3.1, p. 65).
The laryngopharynx splits to form the esophagus and the larynx. The ESOPHAGUS is posterior to the LARYNX. The esophagus conducts food & fluids to the stomach.
THE LARYNX: Figs. 24.2, 24.3, 24.4, & 24.5
The wall of the LARYNX (voice box) is composed of 9 pieces of cartilage, most of which are made of HYALINE CARTILAGE. The anterior wall of the larynx consists of a large, triangular plate of hyaline cartilage called the THYROID CARTILAGE (Adam's apple).
The EPIGLOTTIS is a flexible, leaf-shaped piece of ELASTIC CARTILAGE that sits on top of the larynx. The stalk of the epiglottis is attached to the inside, anterior wall of the thyroid cartilage. The leaf-shaped portion of the epiglottis is unattached and free to move up and down like a trap door. During inhalation, the free edge of the epiglottis projects upward, leaving the larynx open. During swallowing, the larynx moves up and the free edge of the epiglottis moves down to form a lid over the larynx entryway.
The mucous membranes of the larynx are arranged into 2 pairs of folds. See FIG. 24.5. The upper pair, VENTRICULAR FOLDS or FALSE VOCAL CORDS, play no part in sound production. They help you hold your breath when they are brought together. The lower pair, the VOCAL FOLDS or TRUE VOCAL CORDS, vibrate and produce sound as air rushes upward from the lungs. Because the vocal folds are avascular, they appear pearly white. Skeletal muscles of the larynx are attached to the vocal folds. When the muscles contract, they stretch the vocal folds so that the RIMA GLOTTIDIS (opening) is narrowed. As tension of the vocal cords change, the pitch of the sound changes. The tenser the vocal folds, the faster they vibrate and the higher the pitch. Deeper sounds are produced by decreasing the muscular tension on the vocal folds. The rima glottidis is wide when we produce deep tones and narrows to a slit for high-pitched sounds. Vocal folds are thicker and longer in males than females, so they vibrate slower. Therefore, men have a lower range of pitch than women.
Loudness of sound is due to the force of air on the vocal cords. The greater the force of air on the vocal folds, the stronger the vibration of the vocal cords and the louder the sound.
The PHARYNX, ORAL CAVITY, NASAL CAVITIES, and PARANASAL SINUSES act as resonating chambers for sound. They amplify and enhance the quality of sound.
The skeletal muscles in the PHARYNX, TONGUE, SOFT PALATE, CHEEKS, and LIPS shape sounds into consonants and vowels.
THE TRACHEA: Figs. 24.2, 24.3, 24.4, 24.6, & 24.7.
The TRACHEA (windpipe) is 12 cm (about 5 inches) long and 2.5 cm (one inch) in diameter. The trachea lies anterior to the esophagus. It extends from the larynx to the level of the STERNAL ANGLE, where it divides into the right and left PRIMARY BRONCHI.
The trachea is lined with mucous membrane consisting of CILIATED PSEUDOSTRATIFIED COLUMNAR EPITHELIUM (See Table 3.1, p. 65). The tracheal wall is reinforced with 16-20 horizontal C-shaped rings of HYALINE CARTILAGE. The open parts of the C-shaped cartilage face the esophagus, allowing the esophagus to expand during swallowing. See FIG. 24.6.
THE BRONCHIAL TREE: Figs. 23.7 & 23.10
The trachea divides into the RIGHT and LEFT PRIMARY BRONCHI at the level of the STERNAL ANGLE. The RIGHT PRIMARY BRONCHUS runs diagonally to the right lung. The LEFT PRIMARY BRONCHUS runs diagonally to the left lung. The right primary bronchus is wider, shorter and more vertical than the left.
Once inside the lungs, each primary bronchus subdivides into SECONDARY (LOBAR) BRONCHI, one for each lobe of the lung. Three secondary bronchi serve the right lung and two serve the left lung. The secondary bronchi branch within each lobe of the lung to form the smaller TERTIARY BRONCHI, which lead to BRONCHOPULMONARY SEGMENTS. See FIG. 24.10.
The bronchial walls are reinforced by rings of cartilage, like the trachea, and are lined with mucous membrane.
The tertiary bronchi divide repeatedly into smaller and smaller BRONCHIOLES, eventually branching into tiny TERMINAL BRONCHIOLES, which are less than 0.5 mm in diameter. See FIG. 24.11. The terminal bronchioles branch into microscopic branches called the RESPIRATORY BRONCHIOLES. The respiratory bronchioles branch into several ALVEOLAR DUCTS, which lead directly into ALVEOLAR SACS or ALVEOLI. It has been estimated that the lungs contain 300 million alveoli.
See FIG. 24.12. The walls of the alveoli are composed of SIMPLE SQUAMOUS EPITHELIUM. The external surfaces of the alveoli are densely covered with a "cobweb" of PULMONARY CAPILLARIES, providing a large surface area for gas exchange. Together, the alveolar and capillary walls form the RESPIRATORY (ALVEOLAR-CAPILLARY) MEMBRANE. Since both the alveolar and capillary walls are made of simple squamous epithelium, the respiratory membrane is only about 0.5 micrometer thick (remember, there are 1,000 micrometers in a single millimeter). Inside the alveolar sacs are ALVEOLAR MACROPHAGES that engulf and remove dust and debris from the alveolar space. Also found in the alveoli are SEPTAL CELLS which produce an alveolar fluid that contains a surfactant. The surfactant lowers the surface tension of the alveolar fluid. This surface tension, which is due to the attraction of water molecules to other water molecules, could cause the alveoli to collapse. The surfactant, which is a mixture of lipids, lowers the surface tension of the alveolar fluid and, therefore, prevents the collapse of the alveoli.
GROSS ANATOMY OF THE LUNGS: Fig. 24.9 & Fig. 1.7, page 13.
The narrow superior portion of the lung is the APEX. The inferior surface that rests on the diaphragm is the BASE. The base is concave so that it fits snuggly over the convex diaphragm.
The anterior, lateral and posterior sides of the lungs lie in close contact with the ribs, forming a continuously curving surface called the COSTAL SURFACE. See FIGS. 1.7 & 24.9.
On the medial surface of each lung is the indentation called the HILUS, where the pulmonary arteries enter the lungs and pulmonary veins exit the lungs. The hilus is also where the primary bronchi enter the lungs.
The right lung is thicker, broader and shorter than the left lung. The liver, which is below the diaphragm on the right side, pushes the diaphragm up, causing the right lung to be shorter than the left lung.
In the medial portion of the LEFT LUNG is the CARDIAC NOTCH, a concave area that accomodates the heart. See FIGS. 1.7 & 24.9.
The HORIZONTAL & OBLIQUE FISSURES divide the RIGHT lung into 3 lobes: SUPERIOR, MEDIAL and INFERIOR LOBES. The OBLIQUE FISSURE divides the LEFT lung into 2 lobes: SUPERIOR and INFERIOR LOBES.
THE PLEURAL MEMBRANE: Fig. 1.7, page 13; Figs. 24.7, 24.8, & 24.11
The PLEURA is the SEROUS MEMBRANE associated with the lungs. The PARIETAL PLEURA lines the wall of each PLEURAL CAVITY. The VISCERAL PLEURA covers the surface of the lungs. The PLEURAL CAVITY is the potential space between the parietal and visceral pleura. It contains PLEURAL FLUID, which lubricates the pleural membranes so that they glide easily over each other during breathing movements.
MECHANICS OF BREATHING: Fig. 24.13
Breathing, or pulmonary ventilation, consists of 2 phases: Inspiration (inhalation) and expiration (exhalation). Ventilation depends upon a pressure difference between the lungs and the outside atmosphere.
Inspiration: Because of the pleural membrane, the lungs cling to the thoracic cavity wall, so that when the thoracic cavity expands, the lungs expand. The DIAPHRAGM and EXTERNAL INTERCOSTAL MUSCLES are the prime movers of inspiration. When the DIAPHRAGM is relaxed it is dome-shaped. When it contracts, it flattens. This causes the lungs to be pulled down, increasing the internal volume of the lungs. The EXTERNAL INTERCOSTALS are located in the intercostal spaces between the ribs. When the external intercostals contract, they pull the ribcage up and out. This also increases the internal volume of the lungs. If the volume of the lungs is increased, the pressure inside the lungs (intrapleural pressure) decreases with respect to the atmospheric pressure, and air from the outside rushes into the lungs to equalize the intrapleural pressure with the external atmospheric pressure.
Forced inspiration is caused by the contraction of muscles in the upper chest, such as the sternocleidomastoids & scalenes. These muscles pull the chest up and out even more, further decreasing the intrapleural pressure so that even more air will rush into the lungs to fill the void.
Expiration: When the DIAPHRAGM and EXTERNAL INTERCOSTALS relax, the lungs recoil to their resting state and the internal volume of the lungs decreases. When the volume of the lungs decreases, the intrapleural pressure increases to a level above the atmospheric pressure, forcing air out of the lungs.
Forced expiration is caused by the contraction of the INTERNAL INTERCOSTALS and the ABDOMENAL MUSCLES. The INTERNAL INTERCOSTAL muscles are between the ribs, located deep to the external intercostal muscles. The internal intercostals push the chest down further and the abdominal muscles push against the diaphragm. This helps force even more air out of the lungs than quiet expiration alone.