RESPIRATORY SYSTEM

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Slide 1 :

RESPIRATORY SYSTEM RAJESH PARIKH

Slide 2 :

RESPIRATORY SYSTEM RESPIRATORY ZONE CONDUCTING ZONE

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Respiratory System Consists of the respiratory and conducting zones Respiratory zone Site of gas exchange Consists of bronchioles, alveolar ducts, and alveoli

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Respiratory System Conducting zone Provides rigid conduits for air to reach the sites of gas exchange Includes all other respiratory structures (e.g., nose, nasal cavity, pharynx, trachea) Respiratory muscles – diaphragm and other muscles that promote ventilation

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Respiratory System Figure 22.1

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Major Functions of the Respiratory System To supply the body with oxygen and dispose of carbon dioxide Respiration – four distinct processes must happen Pulmonary ventilation – moving air into and out of the lungs External respiration – gas exchange between the lungs and the blood

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Major Functions of the Respiratory System Transport – transport of oxygen and carbon dioxide between the lungs and tissues Internal respiration – gas exchange between systemic blood vessels and tissues

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Function of the Nose The only externally visible part of the respiratory system that functions by: Providing an airway for respiration Moistening and warming the entering air Filtering inspired air and cleaning it of foreign matter Serving as a resonating chamber for speech Housing the olfactory receptors

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Nasal Cavity Lies in and posterior to the external nose Is divided by a midline nasal septum Opens posteriorly into the nasal pharynx via internal nares The ethmoid and sphenoid bones form the roof The floor is formed by the hard and soft palates

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Nasal Cavity Respiratory mucosa Lines the balance of the nasal cavity Glands secrete mucus containing lysozyme and defensins to help destroy bacteria Ciliated mucosal cells remove contaminated mucus

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Nasal Cavity Superior, medial, and inferior conchae: Protrude medially from the lateral walls Increase mucosal area Enhance air turbulence and help filter air Sensitive mucosa triggers sneezing when stimulated by irritating particles

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Functions of the Nasal Mucosa and Conchae During inhalation the conchae and nasal mucosa: Filter, heat, and moisten air During exhalation these structures: Reclaim heat and moisture Minimize heat and moisture loss

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Paranasal Sinuses Sinuses in bones that surround the nasal cavity Sinuses lighten the skull and help to warm and moisten the air

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Pharynx Funnel-shaped tube of skeletal muscle that connects to the: Nasal cavity and mouth superiorly Larynx and esophagus inferiorly Extends from the base of the skull to the level of the sixth cervical vertebra

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Pharynx It is divided into three regions Nasopharynx Oropharynx Laryngopharynx

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Nasopharynx Lies posterior to the nasal cavity, inferior to the sphenoid, and superior to the level of the soft palate Strictly an air passageway Closes during swallowing to prevent food from entering the nasal cavity Pharyngotympanic (auditory) tubes open into the lateral walls

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Oropharynx Extends inferiorly from the level of the soft palate to the epiglottis Opens to the oral cavity via an archway called the fauces Serves as a common passageway for food and air

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Laryngopharynx Serves as a common passageway for food and air Lies posterior to the upright epiglottis Extends to the larynx, where the respiratory and digestive pathways diverge

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Larynx (Voice Box) Attaches to the hyoid bone and opens into the laryngopharynx superiorly Continuous with the trachea posteriorly The three functions of the larynx are: To provide a patent airway To act as a switching mechanism to route air and food into the proper channels To function in voice production

Slide 20 :

Framework of the Larynx Cartilages (hyaline) of the larynx Shield-shaped anterosuperior thyroid cartilage with a midline laryngeal prominence (Adam’s apple) Signet ring–shaped anteroinferior cricoid cartilage Epiglottis – elastic cartilage that covers the laryngeal inlet during swallowing

Slide 21 :

Sphincter Functions of the Larynx The larynx is closed during coughing, sneezing, and Valsalva’s maneuver Valsalva’s maneuver Air is temporarily held in the lower respiratory tract by closing the glottis Causes intra-abdominal pressure to rise when abdominal muscles contract Helps to empty the rectum Acts as a splint to stabilize the trunk when lifting heavy loads

Slide 22 :

Trachea Flexible and mobile tube extending from the larynx into the mediastinum Composed of three layers Mucosa – made up of goblet cells and ciliated epithelium Submucosa – connective tissue deep to the mucosa Adventitia – outermost layer made of C-shaped rings of hyaline cartilage

Slide 23 :

Conducting Zone: Bronchi The carina of the last tracheal cartilage marks the end of the trachea and the beginning of the right and left bronchi Air reaching the bronchi is: Warm and cleansed of impurities Saturated with water vapor Bronchi subdivide into secondary bronchi, each supplying a lobe of the lungs Air passages undergo 23 orders of branching in the lungs

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Conducting Zone: Bronchial Tree Tissue walls of bronchi mimic that of the trachea As conducting tubes become smaller, structural changes occur Cartilage support structures change Amount of smooth muscle increases

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Conducting Zone: Bronchial Tree Bronchioles Have a complete layer of circular smooth muscle Lack cartilage support and mucus-producing cells

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Respiratory Zone Defined by the presence of alveoli; begins as terminal bronchioles feed into respiratory bronchioles Respiratory bronchioles lead to alveolar ducts, then to terminal clusters of alveolar sacs composed of alveoli Approximately 300 million alveoli: Account for most of the lungs’ volume Provide tremendous surface area for gas exchange

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Respiratory Zone Figure 22.8a

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Respiratory Zone Figure 22.8b

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Respiratory Membrane This air-blood barrier is composed of: Alveolar and capillary walls Their fused basal laminas Alveolar walls: Are a single layer of type I epithelial cells Permit gas exchange by simple diffusion Secrete angiotensin converting enzyme (ACE) Type II cells secrete surfactant

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Alveoli Surrounded by fine elastic fibers Contain open pores that: Connect adjacent alveoli Allow air pressure throughout the lung to be equalized House macrophages that keep alveolar surfaces sterile

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Respiratory Membrane Figure 22.9b

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Gross Anatomy of the Lungs Lungs occupy all of the thoracic cavity except the mediastinum Root – site of vascular and bronchial attachments Costal surface – anterior, lateral, and posterior surfaces in contact with the ribs Apex – narrow superior tip Base – inferior surface that rests on the diaphragm Hilus – indentation that contains pulmonary and systemic blood vessels

Slide 33 :

Lungs Cardiac notch (impression) – cavity that accommodates the heart Left lung – separated into upper and lower lobes by the oblique fissure Right lung – separated into three lobes by the oblique and horizontal fissures There are 10 bronchopulmonary segments in each lung

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Blood Supply to Lungs Lungs are perfused by two circulations: pulmonary and bronchial Pulmonary arteries – supply systemic venous blood to be oxygenated Branch profusely, along with bronchi Ultimately feed into the pulmonary capillary network surrounding the alveoli Pulmonary veins – carry oxygenated blood from respiratory zones to the heart

Slide 35 :

Blood Supply to Lungs Bronchial arteries – provide systemic blood to the lung tissue Arise from aorta and enter the lungs at the hilus Supply all lung tissue except the alveoli Bronchial veins anastomose with pulmonary veins Pulmonary veins carry most venous blood back to the heart

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Pleurae Thin, double-layered serosa Parietal pleura Covers the thoracic wall and superior face of the diaphragm Continues around heart and between lungs

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Pleurae Visceral, or pulmonary, pleura Covers the external lung surface Divides the thoracic cavity into three chambers The central mediastinum Two lateral compartments, each containing a lung

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Breathing Breathing, or pulmonary ventilation, consists of two phases Inspiration – air flows into the lungs Expiration – gases exit the lungs

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Pressure Relationships in the Thoracic Cavity Respiratory pressure is always described relative to atmospheric pressure Intrapulmonary pressure (Ppul) – pressure within the alveoli Intrapleural pressure (Pip) – pressure within the pleural cavity

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Pressure Relationships Intrapulmonary pressure and intrapleural pressure fluctuate with the phases of breathing Intrapulmonary pressure always eventually equalizes itself with atmospheric pressure Intrapleural pressure is always less than intrapulmonary pressure and atmospheric pressure

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Pressure Relationships Two forces act to pull the lungs away from the thoracic wall, promoting lung collapse Elasticity of lungs causes them to assume smallest possible size Surface tension of alveolar fluid draws alveoli to their smallest possible size Opposing force – elasticity of the chest wall pulls the thorax outward to enlarge the lungs

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Pressure Relationships Figure 22.12

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Inspiration The diaphragm and external intercostal muscles (inspiratory muscles) contract. The lungs are stretched and intrapulmonary volume increases Intrapulmonary pressure drops below atmospheric pressure (?1 mm Hg) Air flows into the lungs, down its pressure gradient, until intrapleural pressure = atmospheric pressure

Slide 44 :

Expiration Inspiratory muscles relax and the rib cage descends due to gravity Thoracic cavity volume decreases Elastic lungs recoil passively and intrapulmonary volume decreases Intrapulmonary pressure rises above atmospheric pressure (+1 mm Hg) Gases flow out of the lungs down the pressure gradient until intrapulmonary pressure is 0

Slide 45 :

Respiratory Volumes Tidal volume (TV) – air that moves into and out of the lungs with each breath (approximately 500 ml) Residual volume (RV) – air left in the lungs after strenuous expiration (1200 ml) Vital capacity (VC) – the total amount of exchangeable air.

Slide 46 :

Basic Properties of Gases: Dalton’s Law of Partial Pressures Total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture The partial pressure of each gas is directly proportional to its percentage in the mixture

Slide 47 :

Partial Pressure Gradients and Gas Solubilities The partial pressure oxygen (PO2) of venous blood is 40 mm Hg; the partial pressure in the alveoli is 104 mm Hg This steep gradient allows oxygen partial pressures to rapidly reach equilibrium (in 0.25 seconds).

Slide 48 :

Partial Pressure Gradients and Gas Solubilities Although carbon dioxide has a lower partial pressure gradient: It is 20 times more soluble in plasma than oxygen It diffuses in equal amounts with oxygen

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Oxygen Transport Molecular oxygen is carried in the blood: Bound to hemoglobin (Hb) within red blood cells Dissolved in plasma

Slide 50 :

Oxygen Transport: Role of Hemoglobin Each Hb molecule binds four oxygen atoms in a rapid and reversible process The hemoglobin-oxygen combination is called oxyhemoglobin (HbO2) Hemoglobin that has released oxygen is called reduced hemoglobin (HHb) HHb + O2 Lungs Tissues HbO2 + H+

Slide 51 :

Carbon Dioxide Transport Carbon dioxide is transported in the blood in three forms Dissolved in plasma – 7 to 10% Chemically bound to hemoglobin – 20% is carried in RBCs as carbaminohemoglobin Bicarbonate ion in plasma – 70% is transported as bicarbonate (HCO3–)

Slide 52 :

Influence of Carbon Dioxide on Blood pH Changes in respiratory rate can also: Alter blood pH Provide a fast-acting system to adjust pH when it is disturbed by metabolic factors

Slide 53 :

Control of Respiration: Medullary Respiratory Centers The dorsal respiratory group (DRG), or inspiratory center: Appears to be the pacesetting respiratory center Excites the inspiratory muscles and sets eupnea (12-15 breaths/minute) Becomes dormant during expiration The ventral respiratory group (VRG) is involved in forced inspiration and expiration

Slide 54 :

Control of Respiration: Pons Respiratory Centers Pons centers: Influence and modify activity of the medullary centers Smooth out inspiration and expiration transitions and vice versa The pontine respiratory group (PRG) – continuously inhibits the inspiration center to prevent over inflation of the lungs.

Slide 55 :

Depth and Rate of Breathing: PCO2 Changing PCO2 levels are monitored by chemoreceptors of the brain stem Carbon dioxide in the blood diffuses into the cerebrospinal fluid where it is hydrated PCO2 levels rise (hypercapnia) resulting in increased depth and rate of breathing

Slide 56 :

Depth and Rate of Breathing: PCO2 Hyperventilation – increased depth and rate of breathing that: Quickly flushes carbon dioxide from the blood Occurs in response to hypercapnia Though a rise CO2 acts as the original stimulus, control of breathing at rest is regulated by the hydrogen ion concentration in the brain

Slide 57 :

Depth and Rate of Breathing: PCO2 Hypoventilation – slow and shallow breathing due to abnormally low PCO2 levels Apnea (breathing cessation) may occur until PCO2 levels rise

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Depth and Rate of Breathing: PCO2 Arterial oxygen levels are monitored by the aortic and carotid bodies Substantial drops in arterial PO2 (to 60 mm Hg) are needed before oxygen levels become a major stimulus for increased ventilation If carbon dioxide is not removed (e.g., as in emphysema and chronic bronchitis), chemoreceptors become unresponsive to PCO2 chemical stimuli In such cases, PO2 levels become the principal respiratory stimulus (hypoxic drive)

Slide 59 :

Depth and Rate of Breathing: Arterial pH Acidosis may reflect: Carbon dioxide retention Accumulation of lactic acid Excess fatty acids in patients with diabetes mellitus Respiratory system controls will attempt to raise the pH by increasing respiratory rate and depth

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Respiratory Adjustments: High Altitude The body responds to quick movement to high altitude (above 8000 ft) with symptoms of acute mountain sickness – headache, shortness of breath, nausea, and dizziness

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Respiratory Adjustments: High Altitude Acclimatization – respiratory and hematopoietic adjustments to altitude include: Increased ventilation – 2-3 L/min higher than at sea level Chemoreceptors become more responsive to PCO2 Substantial decline in PO2 stimulates peripheral chemoreceptors

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RESPRIATORY SYSTEM BASICS
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