chapter 22 the respiratory system the respiratory system is comprised of a tract which is an elongated passage or pathway the function of the respiratory tract is to serve as a series of air distribution or air conduction tubes the respiratory system is often described as a respiratory tree a tree that is inverted and Hollow where the trachea or windpipe represents the trunk or the base of the respiratory tree and the bronchi represent the branches of the respiratory tree the microscopic air sacs called alvioli represent the leaves of the respiratory tree now this respiratory tract is subdivided into two parts an upper and lower portion generally the larynx and any respiratory organ located Superior or above the larynx is classified as part of the upper respiratory tract therefore the nasal cavity and the fairings or the throat constitutes part of the upper respiratory tract and generally the trachea and any respiratory organ inferior to or below the trachea is classified as part of the lower respiratory tract so the lower respiratory tract also includes the lungs as well as the primary right and left bronchi and the alvioli since the respiratory tract opens to the exterior or is continuous with the external environment the respiratory tract is also aligned with mucous membrane or mucosa now the metabolic purpose for breathing or respiration is twofold one reason is to supply body cells with oxygen so that they can carry out aerobic respiration to convert nutrients such as glucose into energy or ATP molecules now the second reason is to eliminate carbon dioxide waste produced by body cells during the execution of these biochemical reactions now diffusion is a passive mode of transporting substances across cell membranes passive indicates there is no investment of energy or ATP required by body cells because gas molecules are moving down their concentration gradient from a region of high concentration towards a region of low concentration now oxygen concentration in the Alvi or air saxs is higher compared to oxygen concentration in the blood therefore the natural tendency will be for oxygen molecules to passively diffuse down their concentration gradient from a region where they are highly concentrated in the alveoli towards a region where they are less concentrated in the blood conversely carbon dioxide concentration in the blood is higher compared to carbon dioxide concentration in the alvioli therefore the natural tendency will be for carbon dioxide molecules to passively diffuse down their concentration gradient from a region where they are highly concentrated in the blood towards a region where they are less concentrated in the Alvi now diffusion is the process by which oxygen molecules from alvioli move into red blood cells for Cellular use diffusion is also the process by which carbon dioxide molecules move from red blood cells into alv ey for elimination through the process of exhalation now what drives the direction of gas movement is the concentration gradients or concentration differences of these gases across cell membranes here is another figure illustrating the upper and lower respiratory tracts now at increased magnification we can see the alvioli enclosed by a network of blood capillaries the Alvi and blood capillaries are the site of gas exchange now the alvioli or air saxs are aligned with simple squamous epithelium in other words a single layer of flattened cells hence the microscopic size of Alvi the simple squamous epithelium accounts for why alvioli are not visible to the naked eye now recall that the morphology and arrangement of a body tissue determines the function of that particular body tissue owing to its single layered arrangement of cells and the exceedingly thin nature of those cells the alvioli are well suited for facilitating diffusion of gaseous molecules such as oxygen and carbon dioxide now a bulky or stratified arrangement of cells on the other hand would actually hinder or impede the passage or diffusion of substances across alveolar walls the tissue class that dominates the majority of the respiratory tract specifically the trachea and the nasal cavity is pseudostratified columnar epithelium with cyia and goblet cells now pseudo stratified translates to false or phony layering where you have columnar cells in a simple arrangement masquerading or pretending to be stratified or layered it's the nuclei scattered at different or varying levels that give the false appearance of stratification in pseudo stratified columnar epithelium the nuclei are not arranged in a single row but rather scattered at various levels now the special ized and abbreviated term for pseudostratified columnar epithelium with goblet cells and cyia is respiratory epithelium now pseudostratified columnar epithelium is assigned this specialized term respiratory epithelium because it is so prevalent throughout much of the respiratory tract now recall that a class of of connective tissue known as loose areolar connective tissue is widely distributed underneath epithelial tissue so when describing the respiratory epithelium in combination with its underlying loose areolar connective tissue we must then assign the term respiratory mucosa or respiratory mucus membrane instead if we are collectively referring to the respiratory epithelium plus its underlying connected tissue now the goblet cells and cyia work in Tandem and corination to prevent inhaled irritants such as dust or pollen from breaching the lung tissue now goblet cells secrete a mucous blanket or coat over much of the the respiratory tract the mucus serves as a purification mechanism by trapping inhaled irritants hairlike projections called cyia will then beat unidirectionally to move or Propel this mucus and all of its trapped irritants towards the fairings for eventual removal now the iial tissue encountered throughout various locations of the respiratory system will vary we've already established that the trachea as well as the nasal cavity both contain respiratory mucosa however in areas of the respiratory system subject to more abrasion such as the inferior portion of the fering which comes into constant contact with food particles and liquids respiratory mucosa is replaced by stratified squamous epithelium Instead This is for increased protection in the lower regions of the ferx now the primary broni are lined with simple columnar epithelium the primary broni diverge from the main trachea and project into the respective lung on its own side of the body for instance the left primary broncus will project into the left lung and the right primary bronchus will project into the right lung as the primary bronchi progressively decrease in size into smaller tubes called bronchioles we can see there is a gradual transition to simple cuboidal epithelium finally in the alvioli the tissue type transitions to simple squamous epithelium the lung tissue itself is comprised of dense elastic connective tissue which contains a high concentration of elastic fibers to allow for expansion and recoil of the lungs during breathing phases the nasal septum is a partition of bone that subdivides the nose into corresponding right and left nasal cavities now bordering both sides of the nose are air filled cavities called paranasal sinuses these paranasal sinuses are located within four skull bones the frontal maxillary sphenoid and ethmoid bones these paranasal sinuses are also lined with mucosa now individuals are often susceptible to infection of the sinuses because the mucosa of the sinuses is continuous with the mucosa lining of the nasal cavity which is open to the external environment therefore any foreign particles from the external environment that enter the nasal cavity can potentially breach the deeper sinuses causing the sinuses to become easily inflamed or irritated in addition to the respiratory epithelium another specialized type of pseudostratified colomar epithelium called o Factory epithelium is also present in the nasal cavity now o Factory receptor cells also known as oao neurons responsible for smell Sensations are integrated into the olfactory epithelium now the location of olfactory epithelium is strictly localized to the dorsal roof of the nasal cavity near the ethmoid bone now in addition to the perception of smell the nose also functions in warming moistening and cleansing inhaled air as well the larynx or throat is another mucosa lined air distribution tube several structures are continuous with the fings and open into the fs for this reason the ferx can be subdivided into three anatomical regions the superior nasal fering where the fering connects with the nasal cavity the intermediate oral fings where the ferx connects with the oral cavity or mouth and the inferior Leno ferx where the ferx connects with the larynx and also the esophagus now the nasal fings is where the auditory or ustation tube of the Middle Air cavity opens into the fer and a pair of tonsils called the Fingal tonsils are also located in the naso ferins if the Fingal tonsils become inflamed this can actually obstruct air Passage through the fings and ultimately impair breathing potentially causing symptoms associated with sleep apnea such as excessive daytime sleepiness loud snoring or abrupt Awakenings at night often accompanied by gasping now the two remaining pairs of t tonsils called the Palatine and the lingual tonsils are located in the Oro fering the larynx or voice box is another mucosal lined air distribution tube that is heavily reinforced by several pieces of cartilage the largest piece of cartilage in the larynx is the thyroid cartilage which is commonly referred to as the atoms Apple now the thyroid carage is located on the anterior aspect of the larynx and it is comprised of reinforcing hyolin cartilage note that the thyroid cartilage is indeed present in both genders although the thyroid cartilage may appear or show up more prominently in males than females the fact that males have much longer vocal cords accounts for why their thyroid cartilages protrude more anteriorly another piece of cartilage found in the larynx is the epig glotus which is comprised of elastic cartilage the epiglottis partially covers the opening between the vocal cords in the larynx called the glotus the epig glotus will seal off this opening called the glotus during swallowing to prevent entry of foods Andor liquids into the lower trachea this is a mid sagittal section of the head and neck now here we can see that the nasal cavity is comprised of three fleshy loes called nasal con the superior nasal cona the middle nasal cona and the inferior nasal cona now con refer to a body part that resembles a spiral shell and the function of the nasal conqu is to increase the surface area available in the nasal cavity this increase in surface area maximum maximizes the amount of inhaled air that can be moistened warmed and cleansed at a given time increasing the surface area in the nasal cavity does not result in an increase in the overall volume or size of the nasal cavity in this mid sagittal view we can also note the location of the trachea as anterior to the esophagus or food pipe this brings us to the first checkpoint question of this lecture recording now immediately inferior to the larynx is the trachea which is also reinforced by highin cartilage rinks we call these TR cartilage note these highin cartilage rings or tracheal rings are incomplete and c-shaped therefore they do not enclose the entire circumference of the trachea and these tracheal carage Rings actually leave the posterior aspect of the trachea uncovered by cartilage instead the posterior aspect of the trachea is lined with a smooth muscle called the trachealis muscle the trachealis muscle Bridges the gap between the free ends of the c-shaped tracheal cartilage rings however the very first tracheal ring known as the cricoid cartilage is the only complete ring of Highland cartilage that completely encircles the entire trachea in the posterior view of the trachea on the right we can see that the criid cartilage fully covers the posterior aspect of the trachea the structure known as the CCO thyroid ligament connects the cricoid cartilage to the thyroid cartilage another structure known as the Cyro muscle actually contracts to elongate and tense up the vocal cords producing high pitch sounds the cricothyroid muscle also undergoes relaxation to produce more low pitch or deeper sounds lastly the thyrohyoid membrane is a membranous sheet that connects the thyroid cartilage to the hyoid bone now Highland cartilage lends strong structural support and reinforcement properties to any structure specifically Highland carage lends these properties to the tracheal cartilages if the posterior trachea had been completely covered by tracheal cartilage this would render the posterior aspect of the trachea quite stiff and rigid effectively impeding or even hindering food Passage through the esophagus a rigid and stiff trachea completely reinforced on all sides by Highland cartilage would prevent partially digested food from bulging anteriorly as that food Journeys through the the esophagus and this accounts for why tracheal cartilages are incomplete and c-shaped with the exception of the very first tracheal cartilage ring known as the cricoid cartilage this brings us to the next checkpoint question of this lecture recording the trachea also known as the windpipe is a mucosa Lin a distribution tube that extends from the larynx all the way down into the thoracic cavity we've established that the trachea is reinforced by tracheal cartilage ring this is to prevent the collapse of the trachea during pressure changes that occur with breathing to illustrate the process of air distribution in the respiratory tract we will trace the trajectory of inhaled oxygen molecules as they enter the respiratory tract by way of the nasal or oral cavity the oxygen molecules will then enter the fings then the larynx and subsequently the trachea now the trachea diverges or branches into right and left primary broni which project into the respective lung on its side of the body broni will then Branch into progressively smaller tubes called bronchioles now the two smallest types of bronchol are termed terminal bronchioles and respiratory bronchioles the respiratory bronchioles being the smaller of the two this indicates that oxygen molecules will enter the terminal bronches before they enter the respiratory bronches respiratory bronches will then Branch into Alvar ducts now alveolar ducts constit to the smallest air distribution tube in the entire respiratory tract the alol duct will then distribute or conduct the oxygen molecules towards the alveoli which are enclosed by surrounding blood capillaries called pulmonary capillaries the alveoli and Pulmonary capillaries serve as sites of gas exchange where oxygen from Alvi diffused into red blood cells to be delivered back to the Heart by way of pulmonary venules which then Branch into larger versions called pulmonary veins pulmonary veins will eventually deliver this oxygenated blood to the left atrium of the heart both divisions of the autonomic nervous system known as the parasympathetic and the sympathetic nervous system produce antagonistic or opposing effects on various internal organs we are particularly concerned with parasympathetic and sympathetic effects on the broni or air waste now since the parasympathetic nervous system promotes rest and and digestion essentially a conservation of energy activation of the parasympathetic nervous system results in shallow breathing and decreased breathing rate this is the results of Bronco constriction during Bronco constriction smooth muscles contract in order to constrict or narrow broni now AC ation of the sympathetic nervous system on the other hand promotes the body's rapid involuntary fight or flight response to stressful situations this will result in a flood of adrenaline or epinephrine hormone release that brings about Bronco dilation during Bronco dilation smooth muscles relax to open up or widen the bronchi now asmatic inhalers containing ingredients such as albuterol will mimic the sympathetic action of our naturally occurring adrenaline or epinephrine hormone these inhaler ingredients will effectively copy the Bronco dilation effects of our naturally occurring adrenaline or epinephrine hormone to effectively open up the bronchi and ease breathing during episodes of asthmatic attacks here is the next checkpoint question the walls of Al Oli are lined with a thin layer of water this can create a potential problem known as surface tension because water molecules have a stronger attraction or affinity for each other than they do for gases in the air this strong attraction between water molecules results results in the phenomenon known as surface tension now during the exhalation process air leaves alveoli causing the alveoli to become smaller this decrease in the size of the Alvi effectively draws the water molecules even closer together increasing their inward attraction or surface tension to the point where the alveolar walls May cave in and collapse altogether with collapse alvioli there is no oxygen available to diffuse into blood collapsed alvioli can also increase difficulty breathing as the Alvi must now completely reinflated from scretch following each exhalation episode now fortunately the alveoli possess a safeguard against surface tension the alioli secrete a lipidlike liquid substance known as surfactant to interfere with the strong attraction between these water molecules and thus reduce surface tension in the alveoli when surface tension is reduced the lungs can inflate and deflate properly without the possibility of collapse from surface tension now premature infants born before term have underdeveloped lungs and therefore often lack surfactant production as a result premature infant lungs are supplemented with synthetic surfactin they are often treated with doses of synthetic surfactant following birth to increase blood oxygen saturation levels here is the next checkpoint question alveoli are comprised of two epithelial cell types simple squamous epithelial cells are denoted as type one they form the framework of the Alvar walls simple cuboidal epithelial cells are denoted as type two they function strictly in surfactin production now the alveoli exclusively function in gas exchange they do not serve as air conducting or air distribution tubes now in order for gas G exchange to efficiently occur between pulmonary blood capillaries and alvioli a structure known as the respiratory membrane must be no greater than 0.5 to 1 micrometer in thickness which is very microscopically thin the respiratory membrane is comprised of the simple squamous epithelial wall of alvioli plus the simple squamous epithelial wall of the pulmonary blood capillaries plus their fused basement membranes the respiratory membrane must be exceedingly thin so that inhaled oxygen from inside the alvioli can diffuse across this respiratory membrane into the red blood cells inside the pulmonary blood capillaries at the same time the respiratory membrane must be thin enough to allow carbon dioxide carried by red blood cells inside the pulmonary capillaries to diffuse across the respiratory membrane into the alvioli for removal through exhalation now the respiratory membrane is not not the same structure as the respiratory mucosa lining air distribution tubes here is the next checkpoint question now the narrowest portion of the lungs known as its apex is located ated on the superior aspect of the lungs the widest or broadest portion of the lungs known as its Base is located on the inferior aspect of the lungs the base is immediately above or superior to the diaphragm now the plura represents one of the double layered cus membranes of the body the plura is comprised of two layers an inner deeper layer known as the visceral plura and the outer superficial layer known as the parial plura now the visceral plura directly encloses the surface of the lungs the parial plura lines the thoracic cavity wall now situated in between the visceral and parietal plura is the plural cavity the plural cavity contains lubricating plural fluid to absorb the shock and impact of the visceral plura sliding against the parial plura with each inhalation episode in terms of macroscopic lung an the right lung contains two slitlike openings called fissures the fissure that runs across the right lung is known as the horizontal fissure and the fissure that runs along the diagonal at an angle is known as the oblique fissure these two fissures subdivide the right lung into three respective loes the right Superior lobe the right middle lobe and the right inferior lobe the left lung only contains a single oblique fissure which subdivides the left lung into two loes the left Superior lobe and the left inferior lobe