Biology 211
Size: 250-350 grams
Location: extends 12-14 cm within mediastinum, from 2nd rib to 5th intercostal space
Orientation: anterior to vertebral column; posterior to sternum; intermediate to lungs
- base: posterior aspect; mainly left atrium
- apex: inferolateral aspect
Pericardium: double-walled sac enclosing heart
- Fibrous pericardium: outer dense connective tissue layer
o anchors heart to surrounding structures (diaphragm, vessels)
o prevents overfilling with blood
- Serous pericardium: deep to fibrous pericardium
o parietal layer: lines internal surface of fibrous pericardium
o visceral layer (epicardium) – deep to parietal layer; outer layer of heart wall
Layers of heart wall:
- epicardium: visceral layer of serous pericardium; often accumulates fat
- myocardium: cardiac muscle deep to epicardium; bulk of heart tissue
o branched cardiac muscle cells linked by connective tissue fiber bundles (collagen & elastin) – fibrous skeleton of heart
- endocardium: thin inner myocardial surface; sheet of endothelium (squamous epithelium) resting on connective tissue
o lines chambers & valves; continuous with endothelial linings of major vessels
- 2 superior atria separated by interatrial septum
- 2 inferior ventricles separated by interventricular septum
- atrioventricular groove (coronary sulcus): encircles junction of atria & ventricles
- anterior & posterior interventricular sulcus: slight depression that superficially marks position of interventricular septum on heart surface
- Atria: receiving chambers for blood
o auricles: small protruding appendages that slightly increase atrial volume
o pectinate muscles: bundles of muscle on posterior walls
o fossa ovalis: depression at interatrial septum that marks previous location of the foramen ovale (atrial pulmonary circuit bypass) in fetal heart
o right atrium receives deoxygenated blood from superior vena cava (from areas above diaphragm), inferior vena cava (from areas below diaphragm), & coronary sinus (from myocardium)
o left atrium receives oxygenated blood from pulmonary veins (4, from lungs)
- Ventricles: discharging (pumping) chambers for blood
o trabeculae carneae: muscle ridges on internal walls of ventricles
o papillary muscles: conelike muscle bundles in ventricular cavity; attached to tendon (chordae tendineae) that play a role in valve function
o right ventricle pumps blood into pulmonary trunk (to lungs)
o left ventricle pumps blood into aorta (to systemic circulation/body tissues)
Pathway of blood through heart:
- pulmonary circuit: blood vessels that carry blood to & from the lungs
- systemic circuit: blood vessels that carry oxygenated blood to & from body tissues
- superior & inferior vena cava and coronary sinus ® right atrium ® (tricuspid valve) ® right ventricle ® (pulmonary semilunar valve) ® pulmonary trunk ® pulmonary arteries ® lungs ® pulmonary veins ® left atrium ® (bicuspid valve) ® left ventricle ® (aortic semilunar valve) ® aorta ® body tissues
Coronary Circulation: functional blood supply of heart (myocardium)
- coronary arteries: arise from the base of the aorta; carry oxygenated blood to myocardium of atria & ventricles
o left coronary artery: runs toward left side of heart; branches to anterior interventricular artery & circumflex artery
o right coronary artery: runs toward right side of heart; branches to posterior interventricular artery & marginal artery
- cardiac veins: carry deoxygenated blood from myocardium to coronary sinus, which empties into right atrium
- proper circulation to myocardium is critical; blockage of coronary arterial circulation can be serious/fatal
o angina pectoris: chest pain due to short deficiency of blood supply to myocardium
o myocardial infarct (MI, heart attack or coronary): can result from prolonged blockage
- atrioventricular (AV) valves: prevent backflow of blood from ventricles to atria
o tricuspid valve: right AV valve; has 3 cusps (flaps of endocardium reinforced with CT)
o bicuspid (mitral) valve: left AV valve
o chordae tendineae: collagen cords attached to AV valve flaps; anchor cusps to papillary muscles
§ papillary muscles contract & allow chordae tendineae to anchor valve flaps to prevent backflow of blood to atria during ventricular contraction
- semilunar (SL) valves: prevent backflow of blood from great vessels to ventricles
o aortic semilunar valve: prevents blood from flowing back into left ventricle following ventricular contraction
o pulmonary semilunar valve: prevents blood from flowing back into right ventricle following ventricular contraction
Cardiac muscle:
- striated, branched muscle; usually uninucleate cells
- contracts by sliding filament mechanism
- fibrous connective tissue skeleton: anchored to endomysium; strengthens & holds tissue together
- intercalated discs: connections between plasma membranes of adjacent cells
o desmosomes: proteins that hold cells together during contraction
o gap junctions: channel proteins allow ions to pass from cell to cell; allows depolarization to move across entire heart (coordinated contraction – functional syncytium)
o large numerous mitochondria – for aerobic cellular respiration
o myofibrils composed of sarcomeres
Mechanisms & Events of Contraction:
- autorhythmic cells: spontaneously depolarize to begin depolarization wave across heart (nervous system stimulation not required
- cardiac muscle contracts as an organ unit (all or none)
- cardiac muscle has sustained intervals between contraction (absolute refractory period of ~ 250 ms, compared to 1-2 ms for skeletal muscle)
- contraction events:
o influx of sodium ions (from depolarization wave generated by autorhythmic cells) generates action potential by opening sodium channels
o sodium channels quickly close, & depolarization progresses to T tubules
o influx of calcium ions causes calcium ion release from ER (sarcoplasmic reticulum)
o calcium ion channels remain open for ~ 200 ms, prolonging contraction
o eventually calcium ion channels close & potassium ion channels open, allowing potassium to exit cell & restoring resting membrane potential
- cardiac muscle can use carbohydrates as well as alternative sources of energy (lipids)
- since lactic acid buildup from anaerobic respiration impairs function of cardiac muscle cells, they rely almost exclusively on aerobic cellular respiration (need constant supply of oxygen)
- Intrinsic conduction system: noncontractile cardiac cells specialized to initiate & distribute impulses throughout the heart
- Autorhythmic cells: cardiac cells with an unstable resting potential
o spontaneously depolarize due to pacemaker potentials caused by gradual influx of sodium ions
o when threshold is reached, fast calcium ion channels open & calcium ions flood into cell causing action potential
o the impulse is transferred from atria to ventricles in a defined sequence through gap junctions between cells
- sequence of excitation:
o sinoatrial (SA) node: autorhythmic cells here are the fastest to generate impulses (~75/min, called sinus rhythm); hence, this is the heart¹s pacemaker
o atrioventricular (AV) node: receives impulses from SA node; fewer connections between cells delay impulse long enough for atria to complete contraction; also autorhythmic cells here, but slower impulses (~50-60/min, called junctional rhythm), so these cells do not set the pace unless there is damage to SA node cells
o atrioventricular (AV) bundle (bundle of His): electrical connection between atria & ventricles; transmits impulse to ventricles
o right & left bundle branches: sends impulse along cells of interventricular septum toward apex
o Purkinje fibers: extend from inferior aspect of interventricular septum to apex & into outer walls of ventricles
- irregular heart rhythms (arrhythmias):
o fibrillation: rapid & irregular contractions
§ defibrillation: electrical shock to heart to reset rhythm
o ectopic focus: abnormal pacemaker; may be caused by drugs (caffeine, nicotine) or SA node damage
o heart block: damage to AV node interferes with impulse transmission to ventricles
§ artificial pacemakers can be used to deliver impulses
- Electrocardiography
o Electrocardiograph: measures electrical currents generated during heart contraction with a series of electrodes placed on 12 body regions
o Electrocardiogram (ECG or EKG): recording from electrocardiograph
§ P wave: atrial depolarization
§ QRS complex: ventricular depolarization
§ T wave: ventricular repolarization
§ P-Q interval: beginning of atrial depolarization until beginning of ventricular depolarization
§ Q-T interval: beginning of ventricular depolarization until beginning of ventricular repolarization
- Cardiac cycle: all events associated with blood flow through heart
o Systole: contraction
o Diastole: relaxation (dilation or expansion)
o Sequence:
§ ventricular filling (mid to late ventricular diastole)/atrial systole
§ ventricular systole/atrial diastole
§ early ventricular diastole
o quiescent period: period of total heart relaxation (~0.4 sec. of total 0.8 sec. of cycle)
- Heart sounds: lub-dup sound
o AV valves close
o SL valves close
o Murmurs: sounds often indicative of valve problems
- Cardiac output (CO): CO = Stroke Volume (SV) x Heart Rate (HR)
o normal resting values: SV = 70 ml/beat; HR = 75 beats/min; CO = 5250 ml/min
§ SV = end diastolic volume (EDV) – end systolic volume (ESV)
· Normal resting values: EDV = 120 ml; ESV = 50 ml
o cardiac reserve: difference between resting & maximal CO
o regulation of stroke volume:
§ preload: degree of stretch of cardiac muscle cells just before contraction
§ contractility: increase in contractile strength
§ afterload: back pressure exerted by arterial blood
- Regulation of heart rate:
o Sympathetic division of ANS (cervical & upper thoracic chain ganglia): increases heart rate
§ stimulated by cardioacceleratory center in medulla oblongata
o Parasympathetic division of ANS (vagus nerve): decreases heart rate
§ stimulated by cardioinhibitory center in medulla oblongata
o hormones:
§ epinephrine & norepinephrine: increases heart rate
§ thyroxine: slow sustained increase in heart rate
o ions: calcium, sodium & potassium
- heart rate abnormalities:
o tachycardia: abnormally rapid heart rate (> 100 beats/min)
o bradycardia: abnormally slow heart rate (< 60 beats/min)
o congestive heart failure (CHF): abnormally low cardiac output; due to many factors (weakening of heart muscle)
Developmental aspects of heart:
- pulmonary circuit bypasses due to incomplete lung development in fetus
o foramen ovale: sends blood from right atrium to left atrium
§ closes to become fossa ovalis after birth
o ductus arteriosus: sends blood from pulmonary trunk to aorta
§ closes to become ligamentum arteriosum after birth
Chapter 19: The Cardiovascular System: Blood Vessels
Structure of Blood Vessel Walls:
- tunica interna (tunica intima): innermost tunic (layer)
o endothelium (simple squamous epithelium) lining lumen of all vessels
o larger vessels have basement membrane
- tunica media: middle tunic
o mostly smooth muscle cells & sheets of elastin fibers
o generally thickest layer in arteries
o smooth muscle innervated by vasomotor fibers of sympathetic division of ANS
§ vasoconstriction: reduction in lumen diameter due to smooth muscle contraction
§ vasodilation: increase in lumen diameter due to smooth muscle relaxation
- tunica externa (tunica adventitia): outermost tunic
o mostly loose collagen fibers; protect & reinforce vessel wall & anchor it to surrounding structures
o contains nerve fibers, lymphatic vessels, & elastin in larger veins
o vasa vasorum: system of blood vessels nourishing tunica externa in larger vessels
- arteries: transport blood away from the heart
o elastic (conducting) arteries: thick-walled arteries near heart (aorta & major branches)
§ large diameter, low resistance
§ most elastic arteries; elastin present in all 3 tunics (mostly in tunica media)
§ fairly continuous blood flow; passively expand & contract to accommodate blood volume
o muscular (distributing) arteries: branch from elastic arteries to distribute blood to body organs
§ includes most named arteries
§ proportionately thickest tunica media; more active than elastic Arteries in vasoconstriction
o arterioles: vary in size; lead from muscular arteries to capillary beds
§ blood flow into capillary beds determined by arteriole diameter
· if arterioles constrict, tissue is largely bypassed
Capillaries: smallest blood vessels; exchange materials (gases, nutrients, hormones, etc.) in blood with tissues
- only tunica interna (endothelium)
- pericytes: smooth muscle-like cells at intervals to stabilize capillary wall
- capillary types:
o continuous capillaries: most common type; abundant in skin & muscles
§ endothelial cells joined by incomplete tight junctions – leave gaps between cells called intercellular clefts
§ gaps large enough to allow fluids & small solutes to pass through
§ in brain, tight junctions are complete (blood-brain barrier)
o fenestrated capillaries: similar to continuous; some endothelial cells contain pores or fenestrations
§ pores allow greater permeability to fluid & small solutes
§ found where active absorption or filtration occurs (digestive system, kidneys)
o sinusoidal capillaries (sinusoids): highly modified, leaky capillaries found only in certain organs (liver, bone marrow, lymphoid tissue & endocrine organs)
§ fenestrated with fewer tight junctions & larger intercellular clefts
§ allow larger molecules (proteins, etc.) & blood cells to pass through
§ phagocytes often aggregate around endothelial cells
- Capillary Beds:
o Microcirculation: flow of blood from arteriole to venule
o capillary bed consists of:
§ Vascular shunt (metarteriole-thoroughfare channel): short vessel that connects the arteriole & venule at opposite sides of the bed
· metarteriole: intermediate between arteriole & capillary
· thoroughfare channel: intermediate between capillary & venule
§ True capillaries: exchange vessels
o flow of blood: terminal arteriole->metarteriole->thoroughfare channel-> postcapillary venule
o precapillary sphincter: at root of metarteriole & capillary; acts as valve to regulate blood flow into capillary (constricts to send blood through bed (using vascular shunt))
Venous System:
- veins: transport blood toward heart
o venules: smallest veins; range from postcapillary venules (only tunica interna) to larger venules with additional one or two layers of smooth muscle cells & thin tunica externa
o veins: large vessels with all 3 tunics; vessel walls smaller & larger lumens than corresponding arteries
§ capacitance vessels (blood reservoirs): at any given time, most blood in the body is within veins
§ venous valves: formed from folds of tunica externa; flaps that prevent backflow of blood, especially in limbs
Vascular Anastomoses: joining of vascular channels
- arterial anastomoses: provide alternative blood route (collateral channel)
- venous anastomoses: more common than arterial
- arteriovenous anastomoses: vascular shunt (see capillaries)
Blood Flow: volume of blood flowing through a vessel, organ, or circulation in a given period (ml/min)
Blood Pressure: pressure (force per unit area) exerted on the walls of a vessel by blood
Resistance: opposition to blood flow (friction)
- peripheral resistance (PR): resistance in systemic circulation; contributed by:
o Blood viscosity: thickness of blood (high viscosity in polycythemia; low viscosity in anemia)
§ more viscosity = greater resistance
o Blood vessel length: longer vessel length = greater resistance
o Blood vessel diameter: most likely to alter resistance
§ smooth muscle fibers control blood vessel diameter
§ decreased diameter = greater resistance
- Arterial Blood Pressure:
o Systolic pressure: pressure generated in aorta following (left) ventricular systole (~120 mm Hg)
o Diastolic pressure: pressure in aorta following ventricular diastole (70-80 mm Hg)
o Pulse pressure: systolic pressure – diastolic pressure
o Mean arterial pressure (MAP): average pressure in arterial system
- Capillary Blood Pressure: ~ 20-40 mm Hg; good intermediate pressure range (facilitates exchange without rupturing thin walls)
- Venous Blood Pressure: decreases to ~ 20 mm Hg due to peripheral resistance
o pressure built up during breathing & skeletal muscle contraction aid in venous blood return
Maintaining Blood Pressure:
- Short Term Regulation
o Neural Controls:
§ Vasomotor center: sympathetic neurons in medulla integrate blood pressure control by altering cardiac output & blood vessel diameter
§ Baroreceptor-initiated reflexes: baroreceptors = pressure-sensitive mechanoreceptors that respond to changes in arterial pressure & stretch
§ Chemoreceptor-initiated reflexes: chemoreceptors respond to changing blood levels of oxygen, carbon dioxide & acidity
§ Higher brain centers: hypothalamus (e.g.: fight or flight response) via medulla
o Chemical controls:
§ Adrenal medulla hormones
§ Atrial natriuretic peptide (ANP)
§ Antidiuretic hormone
§ Angiotensin II
§ Endothelium-derived factors (endothelin, PDGF)
§ Nitric oxide (NO)
§ Inflammatory chemicals
§ Alcohol
- Long Term Regulation: Renal regulation
o Direct renal mechanism: blood volume altered through filtration in kidneys
o Indirect renal mechanism: renin-angiotensin mechanism leads to aldosterone production
Pulse: indirect measure of heartbeat/heart rate (measures arterial pressure during cardiac cycle)
- often for convenience radial artery is monitored (radial pulse)
Blood Pressure: measured from brachial artery with sphygmomanometer
- uses auscultatory method (listening for filling of artery as pressure in cuff drops below arterial pressure)
- normal resting ranges: systolic BP: 110-140 mm Hg; diastolic BP: 75-80 mm Hg
- Hypotension: low blood pressure (systolic BP below 100 mm Hg)
o often due to individual variations, fluctuations
o chronic hypotension may be indicative of poor nutrition
- Hypertension: high blood pressure (sustained arterial pressure > 140/90)
o Acutely due to exercise, illness
o Chronic hypertension may be indicative of increased peripheral resistance (often due to vessel blockage)
§ Primary hypertension: most cases; no known causeŠ factors include diet, obesity, age, race heredity, stress & smoking
§ Secondary hypertension: ~ 10% of cases; due to disorders such as arteriosclerosis & hyperthyroidism
Blood Flow Through Tissues (tissue perfusion)
- reasons: delivery of oxygen & nutrients to tissue cells & removal of wastes, gas exchange in lungs, absorption of nutrients from digestive tract, urine formation by kidneys
- velocity of blood flow: velocity inversely proportional to diameter of blood vessel
o aorta = 40-50 cm/s; capillary = ~ 0.03 cm/s; venae cavae = 10-30 cm/s
- autoregulation: local regulation of blood flow
o organs regulate blood flow by varying resistance of arterioles
o metabolic controls: vasodilation by inflammatory mediators (histamine) or nitric oxide
o myogenic controls: vasoconstriction & vasodilation by vascular smooth muscle to keep tissue perfusion constant despite pressure variations
o long-term autoregulation: angiogenesis creates new vessels & enlarges vessels to increase blood flow or bypass occluded vessel
- vasomotion: slow blood flow through capillaries
- capillary exchange of respiratory gases & nutrients: oxygen, carbon dioxide, most nutrients & cellular wastes pass between blood & interstitial fluid by diffusion
- fluid movement: pressure & capillary pores allow fluid to leave capillaries at arterial end of capillary bed, but most returns at venous end
o hydrostatic pressure: force exerted by fluid pressing against a wall
§ in capillaries, same as capillary blood pressure
§ capillary hydrostatic pressure tends to force fluids through capillary walls
§ interstitial fluid hydrostatic pressure pushes fluid back in
- colloid osmotic pressure: large non-diffusible molecules (proteins) draw fluid toward them through osmosis
o capillary colloid osmotic pressure: large molecules cannot move through capillary membrane; draw fluid in
- net filtration pressure: considers all forces acting at the capillary bed
Circulatory Shock: condition in which blood vessels are inadequately filled & blood cannot circulate properly; results in inadequate blood flow to tissues
- hypovolemic shock: due to low blood volume (injury, hemorrhage, burns, emesis)
- vascular shock: usually due to vasodilation (anaphylaxis/histamine release)
- cardiogenic shock: usually due to myocardial damage (heart attack)
Systemic Circulation:
- major systemic arteries:
o aorta, aortic arch, descending aorta (thoracic & abdominal aorta)
o 3 branches from aortic arch: brachiocephalic artery, left common carotid artery & left subclavian artery
o common carotid arteries: serve head
§ vertebral & internal carotid arteries give off branches to form Circle of Willis in brain (several paths for blood to brain tissue)
o subclavian arteries: serve arms
o common iliac arteries: branch to internal iliac arteries (serve pelvic organs) & external iliac arteries (serve legs)
- major systemic veins:
o external & internal jugular veins: drain blood from brain, head & neck
o subclavian arteries: drain blood from arms
o brachiocephalic arteries: receive blood from jugular & subclavian veins & enter superior vena cava
o hepatic portal vein: receives blood from abdominal (digestive) organs & enters liver (metabolism & detoxification)
o common iliac veins: receive blood from internal iliac veins (from pelvic organs) & external iliac veins (from legs)
§ common iliac veins merge to form inferior vena cava
- pulmonary ventilation: ventilation or breathing; movement of air into & out of lungs (refreshes air in alveoli)
- external respiration: gas exchange (O2 loading & CO2 unloading) between blood & alveoli
- transport of respiratory gases: transport of O2 & CO2 between lungs & body tissues (in blood)
- internal respiration: gas exchanges (O2 unloading & CO2 loading) between systemic blood & tissue cells
- requires cooperation of respiratory system & circulatory system
- respiratory zone: site of gas exchange; includes respiratory bronchioles, alveolar ducts & alveoli
- conducting zone: all other passageways of respiratory system; cleanse, warm & humidify incoming air
Nose: provides an airway for respiration, moistens & warms incoming air, filters & cleanses inspired air, serves as a resonating chamber for speech, houses the olfactory (smell) receptors
- external nose
o surface features: root, bridge, dorsum nasi & apex
o other features: philtrum, external nares (nostrils), alae (flared lateral walls of external nares)
o skeletal framework: frontal & nasal bones superiorly; maxillary bones laterally; plates of hyaline cartilage (lateral, septal & alar cartilages) inferiorly
- nasal cavity: posterior to external nose
o divided by midline nasal septum (formed by septal cartilage anteriorly & vomer bone & perpendicular plate of ethmoid bone posteriorly)
o continuous with nasopharynx through internal nares (posterior nares or choanae)
o palate: floor of the nasal cavity; formed by anterior hard palate (palatine bone & maxillary palatine process) & posterior muscular soft palate
o vestibule: just superior to nostrils; contains hairs (vibrissae) to filter particles (dust, pollen) from inspired air
o olfactory mucosa: contains smell receptors
o respiratory mucosa: pseudostratified ciliated columnar epithelium containing goblet cells (secrete mucus) resting on a lamina propria with mucus & serous glands
§ glands secrete mucus with lysozyme (antibacterial enzyme)
§ epithelial cells also secrete defensins (natural antibiotics)
§ ciliated cells sweep mucus posteriorly toward throat (pharynx) to be swallowed
§ mucus humidifies air & rich capillary plexuses warm air
§ nasal conchae (superior, middle & inferior): mucosa-covered projections in walls of nasal cavity aid in trapping particles in air in mucus as air swirls through them
§ mucosal sensory nerve endings trigger a sneeze reflex following contact with irritating particles
§ rhinitis: inflammation of nasal mucosa; can be caused by cold viruses, bacteria (streptococcus) & allergens
Paranasal sinuses: air spaces surrounding nasal cavity located in frontal, sphenoid, ethmoid & maxillary bones
- help to warm & moisten air
- mucus secreted ordinarily flows into nasal cavity
- sinusitis: inflamed sinuses; can be caused by spread of infection from nasal mucosae
Pharynx (throat): connects nasal cavity & mouth superiorly with larynx & esophagus inferiorly
- nasopharynx: posterior to nasal cavity; continuous with nasal cavity through internal nares
o air passageway
o mucosa of pseudostratified ciliated columnar epithelium
o uvula: extension of soft palate that closes off nasopharynx from rest of pharynx during swallowing
o pharyngeal tonsil (adenoids): located on superior aspect of posterior wall of nasopharynx; lymphatic tissue that destroys pathogens entering nasopharynx
o auditory (pharyngotympanic) tubes: open into lateral walls of nasopharynx; drain middle ear cavities
§ tubal tonsils: located over auditory tube openings; protect against middle ear infections
- oropharynx: posterior to oral cavity; continuous with oral cavity through fauces; extends from soft palate to epiglottis
o air & food passageway
o mucosa of stratified squamous epithelium
o palatine tonsils: located in lateral walls of fauces
o lingual tonsil: covers base of tongue
- laryngopharynx: posterior to epiglottis; extends to larynx; continuous with esophagus posteriorly
o air & food passageway
o mucosa of stratified squamous epithelium
o food enters esophagus; air enters larynx
Larynx (voice box): superiorly attaches to hyoid bone & opens into laryngopharynx; inferiorly continuous with trachea
- provides a patent (open) airway
- acts as switching mechanism to route food & air into appropriate passageways
- houses vocal cords for speech production
- framework of nine cartilages held together by membranes & ligaments
o thyroid cartilage: hyaline cartilage; largest cartilage
§ laryngeal prominence (Adam¹s apple): midline fusion of cartilage plates
o cricoid cartilage: hyaline cartilage inferior to thyroid cartilage
o three pairs of small hyaline cartilages in lateral & posterior walls
§ arytenoid, cuneiform, & corniculate cartilages
- epiglottis: flexible elastic cartilage extending from posterior aspect of tongue to thyroid cartilage
o covered by mucosa with scattered taste buds
o switching mechanism for air & food passageways
§ during swallowing, the larynx is pulled superiorly & epiglottis tips to cover the laryngeal opening into laryngopharynx
- vocal folds (true vocal cords): vibrate from air moving up from lungs to produce sounds
o core formed from vocal ligaments surrounded by laryngeal mucosa
o glottis: medial opening through which air passes
o laryngitis: inflammation of vocal folds; can be caused by overuse of voice, bacterial infection, dry air or tumors
- vestibular folds (false vocal cords): mucosal folds superior to vocal folds; play no role in voice production
- mucosa of stratified squamous epithelium above vocal folds & pseudostratified ciliated columnar epithelium below vocal folds
- voice production: involves intermittent release of expired air and opening & closing of glottis
o intrinsic laryngeal muscles affect the length of the vocal folds & size of glottis
o higher pitches from narrow glottis opening & tenser vocal folds
- sphincter functions of larynx: vocal folds can act as a sphincter during cough & sneeze reflexes, closing glottis
Trachea (windpipe): descends from larynx through neck into mediastinum
- inferiorly divides into primary bronchi
- wall composed of mucosa (pseudostratified ciliated epithelium with goblet cells), submucosa (connective tissue with seromucous glands) & adventitia (connective tissue reinforced with hyaline cartilage rings)
- trachealis muscle: smooth muscle in posterior wall; contracts to narrow trachea during expiration & expel mucus during coughing
- carina: extension of last tracheal cartilage; marks split of trachea into primary bronchi
- Heimlich maneuver: uses air in lungs to force food trapped in trachea up into oral cavity
- Conducting Zone
o right & left primary (principal) bronchi
o secondary (lobar) bronchi
o tertiary (segmental) bronchi
o bronchioles
§ terminal bronchioles
o tree-like pattern: bronchial or respiratory tree
o tissue composition of wall changes as tubes become smaller
§ cartilage support structures change from rings to irregular plates
§ epithelium changes from pseudostratified columnar to columnar to cuboidal in terminal bronchioles
§ amount of smooth muscle increases
- Respiratory Zone:
o terminal bronchioles feed into respiratory bronchioles, which lead into alveolar ducts that end in clusters of alveoli called alveolar sacs (grape-like clusters of alveoli)
o respiratory membrane: walls of alveoli together with pulmonary capillaries & their fused basal laminas (also known as air-blood barrier or alveolar-capillary membrane)
§ type I cells: very thin simple squamous epithelium
· participate in gas exchange with pulmonary capillaries
· secrete angiotensin converting enzyme (ACE), which plays a role in blood pressure regulation
§ type II cells: cuboidal cells scattered among the type I cells
· secrete a fluid containing surfactant that coats the alveolar walls
o other features of alveoli:
§ surrounded by fine elastic fibers
§ alveolar pores connect adjacent alveoli (provide alternate air routes if alveoli collapse)
§ alveolar macrophages (dust cells) along internal alveolar surfaces
- Lungs:
o occupy most of thoracic cavity (all except mediastinum)
o root: vascular & bronchial attachments to mediastinum
o apex: superior tip just deep to clavicle
o base: inferior surface resting on diaphragm
o hilus: medial indentation where blood vessels enter & leave lung & primary bronchus enters
o left lung: 2 lobes
§ cardiac notch (impression): concave depression in left lung to accommodate heart
o right lung: 3 lobes
o bronchopulmonary segments: pyramid shaped tissue segments within each lung (10 in each lung)
o lobule: small hexagonal subdivisions of bronchopulmonary segments
o most of the volume of lung is air spaces
§ stroma: elastic connective tissue binding together air spaces within lungs
- Blood Supply & Innervation of Lungs:
o pulmonary arteries: deliver systemic venous blood to lungs to be oxygenated
o pulmonary capillary networks: pick up oxygen from alveoli
o pulmonary veins: deliver freshly oxygenated blood from respiratory zones of lungs to heart
o bronchial arteries: provide systemic blood to lung tissues
§ supply blood to all lung tissues except alveoli (alveoli are served by pulmonary circulation)
o pulmonary plexus: delivers parasympathetic (& sympathetic) motor nerve fibers & visceral sensory fibers to lungs
- Pleurae:
o parietal pleura: follows around lungs covering thoracic wall & superior face of diaphragm, & lateral walls of mediastinum
o visceral (pulmonary) pleura: covers external lung surface
o pleural fluid: fills pleural cavity (between parietal & visceral pleura)
o pleurisy: inflammation of pleura; often caused by pneumonia
§ less or more pleural fluid may be produced causing friction during breathing (less) or increased pressure (more)
o pleural effusion: accumulation of fluid (pleural fluid, blood)in pleural space
Mechanics of Breathing:
- breathing (pulmonary ventilation) consists of:
o inspiration: period when air flows into lungs
o expiration: period when gases exit lungs
- pressure relationships in thoracic cavity
o respiratory pressures always described relative to atmospheric pressure
§ atmospheric pressure (Patm): pressure exerted by air (gases) surrounding body
· normal Patm at sea level is 760 mm Hg
- negative respiratory pressure indicates pressure in that area is lower than atmospheric pressure
- intrapulmonary (intra-alveolar) pressure (Palv): pressure within alveoli of lungs
o rises & falls with breathing, but always equalizes with Patm
- intrapleural pressure (Pip): pressure within pleural cavity
o also varies with breathing, but is always about 4 mm Hg less than Palv (negative with respect to both intrapulmonary & atmospheric pressures)
o 2 forces lead to lung collapse:
§ natural tendency of lungs to recoil
§ surface tension of alveolar fluid (draws alveoli to smallest dimension)
o these forces are opposed by the elasticity of chest wall (so thoracic cavity expands, preventing lung collapse)
o any condition that equalizes intrapleural pressure with intrapulmonary or atmospheric pressure can cause immediate lung collapse
o transpulmonary (transpulmonic) pressure: Palv - Pip
§ keeps lungs from collapsing
- pulmonary ventilation: inspiration & expiration
o volume changes lead to pressure changes, which leads to flow of gases to equalize pressure
o Boyle¹s Law: pressure of gas inversely proportional to its volume
o Inspiration:
§ diaphragm contracts & moves inferiorly to lengthen thoracic cavity
§ intercostal muscles contract to lift rib cage & pull sternum forward, so that the diameter of the thoracic cavity increases
§ lungs are stretched out & intrapulmonary volume increases; as volume increases, pressure decreases ® flow of gases into lungs to equalize pressure
§ sternocleidomastoid, scalenes & pectoralis minor muscles contract to allow forceful inhalation
o Expiration:
§ diaphragm relaxes & moves superiorly to shorten thoracic cavity
§ intercostal muscles relax & rib cage descends due to gravity, so that the diameter of the thoracic cavity decreases
§ elastic lungs passively recoil & intrapulmonary volume decreases; as volume decreases, pressure increases ® flow of gases out of lungs to equalize pressure
§ abdominals & internal intercostals contract to allow forceful exhalation
- Physical factors influencing pulmonary ventilation
o Airway resistance (friction or drag): determined mostly by diameters of conducting tubes (trachea, bronchi,Š)
§ mostly insignificant since diameters of tubes generally very large & diffusion is main driving force for smaller tubes (rather than gas flow)
o alveolar surface tension forces
§ surface tension at gas-liquid boundary caused by greater liquid-liquid attraction than liquid-gas attraction
§ surface tension draws liquid molecules closer together & resists increases in surface area (draws alveoli to smallest possible size)
§ surfactant produced by type II alveolar cells interferes with cohesiveness of water molecules, reducing surface tension
o lung compliance: ease of lung expansion due to elasticity
§ lung compliance diminished by factors that: reduce elasticity, block respiratory passageways, reduce surfactant production, decrease ability of thoracic cavity to expand
§ lower lung compliance = more energy needed to breathe
Respiratory volumes:
- respiratory volumes measured with spirometer
- tidal volume (TV): air volume that moves into & out of the lungs with each breath (~ 500 ml)
- inspiratory reserve volume (IRV): air volume that can be forcibly inspired beyond tidal volume (~ 1900-3100 ml)
- expiratory reserve volume (ERV): air volume that can be forcibly expired beyond tidal volume (~ 700-1200 ml)
- residual volume (RV): air remaining in lungs after forced exhalation (~ 1200 ml)
Respiratory capacities:
- inspiratory capacity (IC): TV + IRV
- functional residual capacity (FRC): RV + ERV
- vital capacity (VC): TV + IRV + ERV
- total lung capacity (TLC): VC + RV
Dead Space: portions of the respiratory passageways where air remains & does not take part in gas exchange in the lungs (~ 30% or 150 ml of 500 ml tidal volume )
- anatomical dead space: in nose, pharynx, larynx, trachea, bronchi, bronchioles
- alveolar dead space: in alveoli & respiratory zone
- total dead space: anatomic + alveolar dead space
Pulmonary Function Tests:
- minute or total ventilation: total amount of gas that flows into or out of the respiratory tract in 1 minute
o during normal quiet breathing, ~ 6 L/min. (500 ml/breath x 12 breaths/min.)
- forced vital capacity (FVC): measures amount of gas expelled following deep breath & forceful exhalation
o forced expiratory volume (FEV): determines amount of air expelled during specific intervals or FVC test
Alveolar ventilation: AVR = frequency (breaths/min.) x (TV – dead space)
- measures respiratory efficiency taking dead space into account
- normally ~ 4200 ml/min.
Nonrespiratory air movements: processes other than breathing that affect air entrance or exit from lungs
- examples: laughing, sneezing, coughingŠ
- mostly reflex, sometimes voluntary
Dalton¹s Law of partial pressures: total pressure exerted by a gaseous mixture is the sum of the pressures exerted by each gas in the mixture (PT = P1 + P2 + P3Š)
- example: partial pressure of oxygen in air (P02 = 760 mm Hg x .209 (fraction of air occupied by oxygen) = 159 mm Hg
Henry¹s Law: when a mixture of gases contacts liquid, each gas dissolves in liquid in proportion to its partial pressure
- volume of a gas that will dissolve in a liquid also depends on its solubility in the liquid & temperature of liquid
- hyperbaric oxygen chambers use oxygen at pressures higher than atmospheric pressure to force more oxygen into a patient¹s blood to treat carbon monoxide poisoning or hypoxia
- if Po2 > 2.5 mm Hg, oxygen toxicity can result as harmful free radicals form
Composition of Alveolar Gas: alveolar gas contains more carbon dioxide and less oxygen than the atmosphere due to oxygen leaving and carbon dioxide entering alveoli and leftover gases (mostly carbon dioxide) in the lungs between breaths
- external respiration (pulmonary gas exchange): Po2 in pulmonary arteries much less than in alveoli, so oxygen flows into pulmonary circulation to equalize
o ventilation-perfusion coupling: close matching between gas entering alveoli & blood flow in pulmonary capillaries
§ changes in alveolar Po2 cause changes in diameter of pulmonary capillaries, so that blood flow is directed to alveoli with high Po2
§ changes in alveolar Pco2 cause changes in diameter of bronchioles, so that alveoli with high Pco2 can expedite its removal (by dilating associated bronchioles)
o in general, the thinner the respiratory membrane & the greater its surface area, the more gas can be exchanged
§ disorders that thicken the respiratory membrane (pneumonia) or decrease surface area by breaking down or blocking alveoli (emphysema) decrease effective gas exchange
- internal respiration (capillary gas exchange in body tissues): Po2 in tissues is always lower than in systemic blood (40 mm Hg vs. 104 mm Hg), so oxygen moves from blood into tissues
Transport of Respiratory Gases by Blood:
Oxygen Transport: since oxygen is poorly soluble in water, most (> 98%) of oxygen transported by blood is bound to hemoglobin
- association & disassociation of oxygen with hemoglobin: hemoglobin with bound oxygen is oxyhemoglobin (HbO2); hemoglobin without bound oxygen is reduced hemoglobin or deoxyhemoglobin (HHb)
o cooperation: each hemoglobin can bind 4 oxygen molecules; after first oxygen is bound, binding of other 3 is facilitated
o hemoglobin with 4 oxygens bound is fully saturated with oxygen
o the oxygen-hemoglobin dissociation curve shows that hemoglobin is almost completely saturated with oxygen at Po2 of 70 mm Hg
§ since normal breathing can increase alveolar & systemic Po2 > 104 mm Hg, oxygen levels can decrease somewhat (high altitudes, exercise) & adequate oxygen is still available for tissues
§ increases in temperature, pH, & Pco2 in general will decrease hemoglobin affinity for oxygen & enhance oxygen unloading from the blood
§ BPG (2,3-biphosphoglycerate, a breakdown product of glucose in RBCs that binds hemoglobin) will also decrease hemoglobin affinity for oxygen & enhance unloading of oxygen
§ nitric oxide (NO), secreted by lung cells & vascular endothelial cells, is a vasodilator that regulates blood pressure
· ordinarily, NO is destroyed by hemoglobin, but as oxygen binds hemoglobin in lungs, NO binding to hemoglobin is facilitatedŠ this allows hemoglobin to unload both oxygen & NO at tissues
- hypoxia: inadequate oxygen delivery to tissues
o classes: anemic, ischemic, histotoxic & hypoxemic (hypoxic) hypoxia
Carbon dioxide Transport: carbon dioxide transported in blood from tissue cells to lungs in 3 forms:
- gas dissolved in plasma (~7-10%)
- chemically bound to hemoglobin (~20%): hemoglobin with bound CO2 is carbaminohemoglobin (since CO2 binds to amino acids of hemoglobin while oxygen binds to iron of the heme group, CO2 does not compete with O2 for binding)
- as bicarbonate ion in plasma (~70%): most carbon dioxide that diffuses into RBCs combines with water, forming carbonic acid, which dissociates into hydrogen & bicarbonate ions
o this acts as part of the carbonic acid-bicarbonate buffering system in blood
The Haldane effect: the lower the Po2 and hemoglobin saturation with oxygen, the more carbon dioxide can be carried in blood
- reduced hemoglobin (deoxyhemoglobin) more able to form carbaminohemoglobin
Neural mechanisms: medullary & pons respiratory centers
- medullary centers generate the basic respiratory rhythm (may involve pacemaker neurons in inspiratory center), while pons centers modify activity of medullary neurons
- pulmonary irritant reflexes: inhaled irritants & debris promote constriction of air passages
- inflation reflex: stretch receptors in lungs inhibit inspiration & begin expiration
- higher brain centers: hypothalamic & cortical controls
- chemical factors: chemoreceptors in medulla & vessels of neck
o Pco2: increase can lead to hyperventilation; decrease can lead to hypoventilation
o Po2: very low levels (< 60 mm Hg) require increased ventilation
o pH: falling arterial pH leads to increased ventilation (as with increased Pco2)
- Exercise: during exercise, breathing becomes deeper & more vigorous without significantly changing rate (hyperpnea)
o results in increased ventilation
o caused by psychic factors (anticipation), motor activation of skeletal muscles with respiratory centers, & excitation of proprioceptors
- High Altitude effects: acclimatization (adaptation to decreased oxygen levels) involves increased ventilation as respiratory volumes are increased
o Hemoglobin saturation with oxygen is much less than at sea level, but still sufficient for adequate oxygen delivery to tissues
- Chronic Obstructive Pulmonary Disease (COPD):
o obstructive emphysema: marked by enlargement of alveoli & destruction of alveolar walls
§ Leads to lung fibrosis & loss of elasticity
o chronic bronchitis: chronic excessive mucus production by lower respiratory tract as well as inflammation & fibrosis
- asthma (bronchial asthma): characterized by episodes of coughing, dyspnea (difficult breathing), wheezing & chest tightness
o periods of acute symptoms followed by symptom-free periods
o treatments changed from inhaled bronchodilators to inhaled steroids
- tuberculosis (TB): infectious disease caused by the bacterium Mycobacterium tuberculosis
o spread by exposure to airborne bacteria usually from coughing
o 12-month course of antibiotics for treatment
- lung cancer: incidence strongly associated with cigarette smoking
o squamous cell carcinoma, adenocarcinoma & small cell carcinoma
o treated with surgical removal of cancerous lung tissue, radiation & chemotherapy