Respiratory System: Upper Tract & Nose

• Oxygen enters the body and carbon dioxide leaves via the respiratory system.
• Air moves from the atmosphere to the lungs through cavities and tubes during breathing in (inspiration).
• Air moves from the lungs to the atmosphere via the same structures during breathing out (expiration).
• Ventilation or breathing is the process of inspiration and expiration.
• The cardiovascular system transports oxygen from the lungs to the tissues and carbon dioxide in the other direction.
• During cellular respiration, cells use oxygen and produce carbon dioxide.

The Upper Respiratory Tract

• The nasal cavities, pharynx, and larynx form the upper respiratory tract.

The Nose

• The nose begins at the nares (nostrils), which lead to the nasal cavities.
• The nasal cavities are separated by a septum made of bone and cartilage.
• Hairs filter the air, trapping small particles.
• The nasal cavities are lined with a mucous membrane.
• Mucus traps particles and moves them to the pharynx to be swallowed or expectorated.
• The submucosa, under the mucous layer, has many capillaries that help warm and moisten the incoming air.
• The abundance of capillaries makes the nose susceptible to nosebleeds.
• The nasal cavities contain odor receptors.
• Tear glands drain into the nasal cavities, explaining why crying causes a runny nose.
• The nasal cavities connect with the sinuses of the skull.
• Fluid accumulation in the sinuses causes an increase in pressure and sinus headaches.
• Air from the nasal cavities passes into the nasopharynx, the upper portion of the pharynx.

Auditory Tubes

• Auditory (eustachian) tubes connect the nasopharynx to the middle ear.
• Auditory tube openings may create a "popping" sensation as air pressure equalizes inside the middle ear with the air pressure in the nasopharynx.

The Pharynx

• The pharynx, or throat, is a funnel-shaped cavity that connects the nasal and oral cavities to the larynx.
• The pharynx has three portions: the nasopharynx, oropharynx, and laryngopharynx.
• Tonsils are made of lymphoid tissue at the junction of the oral cavity and pharynx.
• The pharynx functions to provide defense against inhaled pathogens.

The Larynx

• The larynx is a cartilaginous structure between the pharynx and the trachea.
• The Adam's apple (laryngeal prominence) is located at the front of the neck.
• The larynx houses the vocal cords, which are mucosal folds supported by elastic ligaments.
• The slit between the vocal cords is called the glottis.
• When air passes through the glottis, the vocal cords vibrate, producing sound.
• Greater tension in the vocal cords results in a higher pitch, while a wider glottis causes lower pitch.
• Loudness depends on the degree to which the vocal cords vibrate.
• When food is swallowed, the larynx moves upward against the epiglottis, a flap of tissue that prevents food from entering the larynx.

The Lower Respiratory Tract

• The trachea, bronchial tree, and lungs make up the lower respiratory tract.

The Trachea

• The trachea is commonly called the "windpipe."
• The trachea connects the larynx to the primary bronchi.
• Its walls are reinforced by C-shaped cartilaginous rings, preventing collapse.
• The C shape allows the esophagus to expand into the trachea during swallowing.
• The trachea is lined with pseudostratified ciliated columnar epithelium and goblet cells.
• Mucus, produced by goblet cells, traps debris from the air.
• Cilia sweep the mucus toward the pharynx.
• Smoking damages cilia, causing smokers' cough.
• A tracheostomy involves inserting a breathing tube into the trachea.

The Bronchial Tree

• Two primary bronchi lead from the trachea into the lungs.
• The primary bronchi branch into secondary bronchi, which continue to branch into smaller bronchioles (about 1 mm in diameter).
• Bronchi have cartilage, similar to the trachea, which disappears as they get smaller.
• During an asthma attack, the smooth muscle of the bronchioles contracts, causing constriction and wheezing.
• Each bronchiole leads to an elongated space enclosed by air sacs called alveoli.

The Lungs

• The lungs are made of secondary bronchi, bronchioles, and alveoli.
• The right lung has three lobes, while the left lung has two lobes.
• Each lobe is divided into lobules.
• Each lung is enclosed by pleurae, two layers of serous membrane that produce serous fluid.
• Pleural fluid has surface tension, adhering the parietal and visceral pleurae.
• Surface tension, due to hydrogen bonds between water molecules, is the reason when the thoracic cavity enlarges, the parietal pleura pulls the visceral pleura, and therefore the lungs, outward.
• This increases the size of the lungs.
• Pleurisy is inflammation of the pleurae and is painful.

The Alveoli

• The lungs have about 300 million alveoli.
• Each alveolar sac is surrounded by blood capillaries.
• The walls of alveolar sacs and capillaries are made of simple squamous epithelium.
• Gas exchange occurs between air in the alveoli and blood in the capillaries.
• Oxygen diffuses across the alveolar wall and enters the bloodstream, while carbon dioxide diffuses from the blood into the alveoli.
• Alveoli are lined with surfactant, a lipoprotein film that lowers water's surface tension and prevents the alveoli from closing.
• Infant respiratory distress syndrome occurs when premature infants do not produce enough surfactant, leading to alveolar collapse.

Mechanism of Breathing

• Ventilation has two phases: inspiration (inhalation) and expiration (exhalation).
• Inspiration moves air into the lungs, while expiration moves air out of the lungs.
• Lungs lie within the sealed thoracic cavity.
• The rib cage forms the top and sides while Intercostal muscles lie between the ribs and the diaphragm forms the floor of the thoracic cavity.
• The lungs adhere to its wall via the pleura.
• The two pleural layers contain minimal space and is filled with pleural fluid.
• At a constant temperature, pressure of a gas is inversely proportional to its volume, as stated by Boyle's Law.
• Such relationship controls exhalation and inhalation.
• The diaphragm and external intercostal muscles contract during the active phase of ventilation.
• The diaphragm becomes flat and contracts, while the external intercostal muscles cause the rib cage to move upward and outward during inhalation.
• Expiration is the passive phase; the diaphragm and external intercostal muscles relax.
• The rib cage returns to its resting position moving down and inward, as air pressure inside increases and lungs recoil as air flows out.
• Surfactant keeps the aveoli open as the pressure between the pleura decreases, and during expiration to keep the alveoli open.
• In an accident, if the thoracic cavity is punctured air enters between the two pleurae, causing the lung to collapse.
• Breathing hard uses muscles of the back, chest, and neck to increase thoracic cavity size.
• Expiration can also be forced, such as during singing or blowing air.
• Contraction of the internal intercostal muscles forces the rib cage downward and inward, and abdominal muscles contract, forcing air out.
• The respiratory control center automatically sends nerve signals to the diaphragm and the external intercostal muscles of the rib cage causing inspiration.
• Expiration occurs when the respiratory center stops sending nerve signals.
• Sudden infant death syndrome (SIDS), is when a seemingly healthy infant stops breathing, with the cause being not known.
• Although the respiratory center controls the rate and depth of breathing, it is influenced by the nervous system and can voluntarily change such pattern.
• Stretch receptors in the airway walls initiate inhibitory nerve impulses that stop the respiratory center from sending out nerve signals following forced inspiration.

Chemical Control of Breathing

• Cells produce carbon dioxide during cellular respiration.
• Carbon dioxide enters the blood, combines with water, and forms carbonic acid that then gives off hydrogen ions thus decreasing the pH of the blood.
• Chemoreceptors which are sensitive to the chemical composition of body fluids can cause breathing to speed up with increased levels of pH.
• One set is in the medulla oblongata of the brain stem, the other is the carotid bodies of the carotid arteries and aortic bodies of the aorta
• These chemoreceptors mostly respond to carbon dioxide levels of the blood.
• The respiratory center increases the breathing rate and depth to remove carbon dioxide when the blood pH decreases.
• This increases the pH, so the breathing rate returns to normal.
• Carbon dioxide accumulates and decreases the pH when you hold your breath.
• The respiratory center is able to override a voluntary inhibition of respiration, forcing breathing.

Gas Exchange in the Body

• Oxygen is needed to produce ATP.
• Respiration includes the exchange of gases not only in the lungs but also in the tissues.
• The principles of diffusion govern the movement of oxygen and carbon dioxide in or out of the blood.
• Gas pressure is called its partial pressure, symbolized as PCO2 or PO2.
• Gases diffuse from higher to lower partial pressure across a membrane.

External Respiration

• Exchange of gases between the lung alveoli and the blood capillaries
• PCO2 is higher in the lung capillaries than the air; thus, C O2 diffuses out of the blood into the lungs as oxygen moves in the opposite direction.
• Most of carbon dioxide is carried in plasma as bicarbonate ions
• In the low-PC 02 environment of the lungs, this reaction proceeds to the right
• Hyperventilation (breathing at a high rate) pushes the reaction to the right resulting in less hydrogen ions resulting in alkalosis (high blood pH).
• Hypoventilation (breathing at a low rate) pushes the reaction to the leftresulting in acidosis (low blood pH).
• Oxygen in pulmonary capillary blood diffuses into plasma and then into red blood cells in the lungs.
• Hemoglobin then takes up oxygen into oxyhemoglobin (HbO2).

Internal Respiration

• Gases exchange between the blood in systemic capillaries and the tissue cells.
• Blood entering systemic capillaries is bright red because red blood cells contain oxyhemoglobin.
• HbO2 gives up oxygen, it diffuses out of the blood into the tissues as P02 is lower than that in the blood.
• Carbon dioxide diffuses into the blood from the tissues because the P02 is higher than that of blood being produced during cellular respiration.

Upper Respiratory Tract Infections

• Upper respiratory tract infections can spread from the nose, nasal cavities, pharynx, and larynx, to the sinuses, middle ears.
• The upper respiratory tract is susceptible to viral and bacterial infections because it filters out pathogens and other materials in the air.
• Viral infections cause colds such as with with symptoms of sneezing, runny nose, mild fever.
• Sinusitis is the blockage of sinuses.
• Tonsillitis is inflammation of the tonsils.
• Tonsillectomy is surgical removal of the tonsils.
• Laryngitis is an infection of the larynx leading to voice loss.

Lower Respiratory Tract Disorders

• Lower respiratory tract disorders include: infections, restrictive pulmonary disorders, obstructive pulmonary disorders, and lung cancer.
• Acute bronchitis is an infection of the primary and secondary bronchi.
• Pneumonia is a bacterial or viral infection that fills the bronchi and alveoli with thick fluid.
• Tuberculosis is a bacterial infection leading to tubercles (encapsulated bacteria).

Restrictive Pulmonary Disorders

• Vital capacity is reduced and the lungs have lost elasticity.
• Pulmonary fibrosis causes fibrous connective tissue to build up in the lungs because of inhaled particles.
• Lungs cannot inflate properly and may lead to cancer.

Obstructive Pulmonary Disorders

• Air does not flow freely in the airways when one suffers from such disorders.
• Chronic bronchitis, emphysema, and asthma are referred to as chronic obstructive pulmonary disease (COPD) because they tend to recur.
• Chronic bronchitis refers to airways that are inflamed and filled with mucus.
• Bronchi undergo degenerative changes including the loss of cilia most often triggered by smoking.
• Exposure to other pollutants can also cause restrictive pulmonary disorders.

Emphysema

• Emphysema is chronic and incurable.
• Alveoli are distended and their walls are damaged, reducing the surface area for gas exchange, therefore, less oxygen reaches the heart and the brain.
• It can be caused by smoking reducing the elastic recoil of the lungs and the driving force behind expiration is also reduced.
• Lack of oxygen in the brain can make the person feel depressed, sluggish, and irritable.
• Severe emphysema may be treated by lung transplantation or lung volume reduction surgery (LVRS).

Asthma

• Asthma symptoms include wheezing, breathlessness, and sometimes a cough with mucus.
• The smooth muscle in the bronchioles spasms when exposed to an irritant like pollen or tobacco smoke.
• Asthma is not curable, but it is treatable with special inhalers.

Lung Cancer

• Lung cancer is more prevalent in men than in women.
• The thickening of the lining of the bronchi is the first event in lung cancer losing cilia, therefore, unable to prevent dust and dirt from settling.
• The cells with atypical nuclei appear in the lining turning into a tumor made of itself in situ.
• Some cells break loose and penetrate other tissues; this is the final step (metastasis).
• The original tumor grows until it blocks a bronchus, cutting off the supply of air to that lung.
• Removing a lobe or the whole lung is needed performed before metastasis aka pneumonectomy.