Respiratory System - Anatomy

Respiratory SystemAnatomyOverviewOf all the substances that cells and thewhole body must have to survive, O2 is byfar the most crucial A person can live a few weeks withoutfood, a few days without water, but only afew minutes without O2 Constant removal of carbon dioxide fromthe body is just as important for survivalas a constant supply of O2 Functions The organs of the respiratory systemperform several functions:– Gas exchange via diffusion Deliveryof O2 to body cellsof CO2 produced by body cells Elimination– Regulation of blood pH– Filter, warm & humidify the air we breathe– Contain receptors for the sense of smell– Production of vocal sounds– Excretion of heat & water1

Respiration EnsuresO2 is supplied to body cellsis removed from the body cells Respiration CO2 homeostatic mechanism– Helps maintain a constant environment body cells to function effectivelyRespiratory Organs Organsof the respiratory system– Nose & nasal cavities– Pharynx– Larynx– Trachea– Bronchi– Lungs– Alveoli Basic structure is that of a tube with many branches endingin millions of extremely tiny, very thinthin-walled sacs calledalveoliConsists of passageways that filter incoming air & carry itinto the lungs2

Respiratory Tract Divisions Assist in thedescription ofsymptoms associatedwith commonrespiratory problemssuch as a coldNose Upper respiratory tract-Nose-Pharynx-Larynx PharynxLarynxLower respiratory tract in the thorax– trachea, bronchial tree & lungsRespiratory Tract Nose, pharynx, larynx, trachea, bronchi &bronchioles are hollow tubes– Form air passageways– Constitute conducting portion of respiratorysystem Air sacs & alveoli– Respiratory portion of the respiratory system– Gas exchange occurs in the alveoli (largesurface area)– Alveoli sacs are delicate elastic membraneswith extensive capillary network of thepulmonary circulation3

Anatomy of theRespiratory SystemUpper Respiratory TractNose Air enters the respiratorytract through the externalnares or nostrilsFlows into the right & leftnasal cavities, (lined byrespiratory mucosa)A partition called the nasalseptum separates thesetwo cavitiesAir may also enter via themouth - the nasal cavities& mouth meet at theregion at the back of themouth pharynxSurface is moist frommucus & warm fromblood flowNerve endingsresponsible for thesense of smell(olfactory receptors)are located in thenasal mucosaThree conchaeprotrude into thenasal cavityThese increase surfacearea over which airmust flow as it passesthrough the nasalcavity4

NoseThe structure of the conchae increases the surface area overwhich inhaled air travels ensuring that it is thoroughlywarmed & filteredNose Blood vessels in the nasal mucosa cool hot air &warm cold airAir entering the nose is generally contaminatedwith one or more common irritants such asinsects, dust, pollen & bacteriaAir is purified removing almost all contaminantsbefore inspired air reaches the lungsMucus secreted by mucosa adds moisture to dryair while trapping fine dust particles & micromicroorganismsCiliated cells of the mucosa move contaminatedmucus into the throat where it is swallowed ClinicalExample:– Because the mucosa lines the nose,sinus infections often develop fromcolds in which the nasal mucosa isinflamed– When the nasal cavity is blocked, the airin the sinuses is absorbed– Sometimes a sinus headache is incurred& localised over the inflamed area5

Paranasal SinusesFour paranasal sinusessinuses- the frontal,maxillary, sphenoidal & ethmoidal – draininto the nasal cavities Paranasal sinuses are lined with mucousmembrane that assists in the productionof mucus for the respiratory tract Hollow spaces help to lighten the skull &serve as resonant chambers for theproduction of sound Paranasal SinusesYou can see how a sinus headache would be quite uncomfortable asthe pressure within the cavity would build up & be unable to escape(see slide 15)Pharynx Extendsfrom the nasal cavities tothe larynx Behind the nasal cavities & abovethe soft palate is the nasopharynx Dorsally is the oropharynx digestive & respiratory passagewaysmeet Inferior to oropharynx lies thelaryngopharynx immediately beforethe larynx6

Three regions of the pharynxPharynx Twoauditory tubes, the Eustachiantubes open from the middle ear intothe lateral walls of the nasopharynx– Equalise air pressure between thenasopharynx & the middle earPharynx Pharyngeal tonsils lie on posterior wall ofnasopharynx– Traps airborne infectious agents– Swollen tonsils are referred to as adenoids which mayobstruct the passage of air Palatine tonsils lie on the lateral aspects of thepharynx behind the mouth– Function same as pharyngeal tonsil– Tonsillitis inflammation of the palatine tonsils obstructs nasopharynx, forcing mouth breathing air is not properly moistened, warmed or filtered beforereaching the lungs7

Question:How might the position of the tonsils assist in performing their immunefunction of trapping and destroying pathogens?Pharynx Thepharynx is a passageway forboth the digestive & respiratorysystems Distally, the pharynx branches intotwo tubes– Oesophagus stomach– Larynx Larynx lungsLarynxCartilaginous structure connecting thepharynx & trachea at the level of thecervical vertebrae Connective tissue containing nine pieces ofcartilage arranged in boxbox-like formation Largest cartilage is the thyroid cartilage,AKA "Adam's apple" – Thyroid cartilage is visible in the ventral aspectof the throat and is more pronounced in adultmales than adult females8

The cricoid cartilage resembles a signet ring– Connects larynx & trachea The epiglottis, a leafleaf-shaped "lid" at the entry tothe larynx– Seals off the respiratory tract when food passes into theoesophagus Opening to the larynx is called the glottis– During swallowing the larynx is pulled upward, theepiglottis closes to route food/fluid to the stomach– If anything other than air enters the larynx, a coughreflex is triggered to expel the substance & prevent itgoing to the lungsThe larynxQuestion:What is the advantageof having cartilaginousrings in the airways?Transvere sectionthrough the tracheaLarynxLarynx is a passageway for air & produces soundTwo folds of tissue project from the lateral wallsof the larynx vocal cords Exhalation vocal cords vibrate produce sounds that can be modified into wordsby muscles of the neck, lips, tongue, & cheeks Length of vocal cords determines pitchfemales & children have shorter vocal cords voices of a higher pitch – Read page 842 Jenkins, Kemnitz & TortoraStructures of voice production9

Trachea Larynx opens into a rigid tube tracheaTrachea is 12 to 15cms long in the midline ofthe neckSupported & held open by a stack of CC-shapedrings of cartilage open at the dorsal aspectThe area between adjacent cartilages & the tipsof cartilage contains connective tissue & smoothmuscleThe trachea is an open passageway for incoming& outgoing airCiliated cells filter air before it enters the bronchiTracheaBy pushing against your throat about aninch above the sternum, you can feel theshape of the trachea Only if you use considerable force can yousqueeze it closed Air has no other way to get to the lungs, &complete tracheal obstruction can squeezethe trachea shut & cause death in amatter of minutes – Eg. choking on food, tumour or infectioncausing inflammation of the lymph nodes ofthe neckBronchi The trachea branches into two primary bronchi– Same structure as the trachea– Right bronchus is slightly larger & more vertical than theleft Bronchi become smaller & smaller secondarybronchi then tertiary bronchiAs they extend further into the lungs diameter isreduced to about one millimetreBronchi are now called bronchiolesThe amount of cartilage reduces as the tubesbecome smaller & smaller disappearing in thedistal bronchioles10

Note the branching structure of the bronchi as the tubes becomesmaller & smallerBronchioles Bronchioles are composed of smooth musclesupported by connective tissueSubdivide until they form the smallest airpassageways terminal bronchiolesTerminal bronchioles extend into the alveoliAlveoli resemble a single grape & are effective in gasexchange as they are thinthin-walled & in contact with ablood capillaryMembrane inside each alveoli is covered in surfactantwhich reduces surface tension, keeping them fromcollapsing as air moves in & out during respirationBranching & rebranching of the bronchi & bronchioleswithin the lungs is called the bronchial treeBronchiClinical Examples: Inflammation of the bronchial tree is commonlyknown as bronchitis Asthma also affects the bronchial tree– Asthma is accompanied by periodic attacks of wheezing& difficult breathing– Caused by spasms of the smooth muscles (as there is nocartilage to hold them open)– Often triggered by allergens in the environment– Read page 844844-845 Jenkins, Kemnitz & TortoraBronchi11

Lungs Paired organs occupying most of the space of thethoracic cavityConsist of millions of small, cupcup-shaped outpockets (sacs) called alveoliRespiratory membranes of alveoli are a thinbarrier in which gases can pass by diffusion 300 million alveoli in an average adultLungs are separated from one another by amedian dividing wallCalled the mediastinum– contains the heart, thymus, oesophagus, large bloodvessels embedded in connective tissueLungs Lungsare conical shaped withelastic, spongy texture due to thenature of the alveoli Right lung is subdivided into threelobes Left lung is subdivided into two lobes Each lobe is divided into smallerlobules, each lobule is serviced by alarge bronchiole12

Microscopic Anatomy of theLungs The walls of the alveoli are one cellsthick The surface area of the alveoli ishuge 70m2 As the capillary network is soclosely associated with the cell wallrespiratory gases are easily diffusedacross the surfaceRespiratory MembraneRespiratory membrane separates the airin the alveoli from the blood insurrounding capillaries Consists of four cell layers – Alveolar wall of Type I & Type II alveolar cells– Epithelial basement membrane– Capillary basement membrane– Capillary endothelium– Read page 849849-850 Jenkins, Kemnitz & TortoraAlveoliHistology of AlveoliEpithelial spiratory/alveoli.jpg13

PleuraTwoTwo-layered membrane surrounding eachlung Inner layer visceral pleura – covers the surface of each lung– reaches into the fissures between the lobes ofthe lung– encloses the mediastinum Outer layer parietal pleura– lines the inner surface of the thoracic cavityWho remembers Fred Dagg & his song ‘If it weren't for yourgumboots’? The pleurisy mentioned in the song is an inflammation ofthe pleurae. It is a very painful condition as it reduces the ability ofthe pleural surfaces to move over each other causing rubbing/frictionwith each breath.PleuraVisceral & parietal pleura are continuouswith one another where the primarybronchus, blood vessels & nerves entereach lung Two layers of the pleura form a collapsedsac Area within the sac pleural cavity – Fluid in the cavity keeps the twotwo-pleural membranes inclose contact with each other & allows them to glidesmoothly over each other– Fluid adheres the two layers of the pleura to one another14