CRS 3 Flashcards
Describe the clinical signs of lower airway disease
- Coughing
- Tachypnoea
- Increased depth of breathing
- Listlessness
- Dyspnoea
- Secretions
- Crackling or wheezing on auscultation
List the diagnostic tools which may be of use in investigating lower respiratory disease
- Ultrasonography
- Radiography
- MRI and CT
- Swabs
- Endotracheal wash
- Biopsy
- Fine needle aspirate
- Bronchoalveolar lavage
- Top 3: radiograph, guarded swab, endotracheal wash
Describe how you would carry out a radiograph of the lower respiratory system of a dog or cat
- Left and right lateral
- Dorsoventral
- Label, contast, Kv and Mv
- Hold lungs at full inflation
- Consider safety of person inflating lungs
- Must include cranial part of diaphragm
Describe the effects of bronchoconstriction on ventilation/lung parameters including compliance, resistance, tidal volume, work of breathing, gas exchange and arterial oxygenation
- Less air reaching alveoli
- Compliance reduced
- Resistance increased
- Tidal volume decreased
- Work of breathing increased
- Gas exchange decreased
- Arterial oxygenation may be lowered in an attack
- Closing capacity becomes an active process in an asthma attack
List the effects of restrictive bronchial disease which may increase the risk of general anaesthesia
- Rate of oxygen uptake is reduced
- Reduction of tidal volume and lumen of small airways
- Great risk of asphyxiation
- Reduction in gas exchange rate
- Greater risk of oxygen starvation
- Severe reduced arterial oxygen
Explain the effects of recumbency on respiratory function
- In VD, lungs pushed against dorsal side of animal
- Reduces capacity to inflate
- Problematic if at risk or already in respiratory distress
Describe the effects of anaesthetic agents on respiratory function
- Airway obstruction (relaxation of muscles)
- Reduced ventilation (due to reduced tidal volume or rate of respiration)
- Decreased functional residual capacity (relaxation of diaphragm and intercostal muscles)
- Increased V/Q mismatch and shunting
State the methods by which anaesthetic risks to threspiratory function can be minimised before and during eh procedure
- Pre-oxygenating to maximise FRC
- Antimuscarinic drugs before to reduce saliva production
- Mechanical ventilation
- Not using 100% oxygen
- Maintaining perfusion pressure by giving fluids
Describe the relevance of circuit factors for calculating fresh gas requirements under anaesthesia
Needed to calculate flow rate for gas, to ensure patient is not breathing in the CO2 it has exhaled
Describe possible radiographic changes associated with feline asthma including air trapping, bronchial pattern and consolidation
- Bronchial thickening - doughnuts on DV view
- Consolidation and air trapping also common
- See as flattened diaphragm, increased distance between cardiac silhouette and diaphragm
Outline the pharmacologial therapeutic options for the management of inflammatory restrictive airway disease and how each works
- 2 classes
- Steroids and bronchodilators
- Can be used in feline inhaler
- Steroids: anti-inflammatory, reduce mucus production (prednisolone, dexamethosone and fluticasone)
- Bronchodilators: stabilise mast cell membrane, inhibit ACh release, promote mucus clearing (albuterol)
Outline non-pharmacological therapeutic options for the management of inflammatory restictive airway disease
- Control weight
- Limit use of pollutants
Explain how the structure of the thorax facilitates breathing
- Air flows from high to low pressure
- Thorax must have lower pressure than atmospheric to have air flow in
- Increas lung volum by thoracic expansion
- Inspiratory muscles
- Diaphragm contracts - flattens and moves caudally
- External intercostals contract, ribs cranially and outwards
- Increases volume of thoracic cavity
- In expiration, inspiratory muscles relax, dome of diaphragm pushed back by inspiratory pressure, ribs recoil
- Pleural membranes attach lungs to thoracic wall
- When thorax expands, pleural membranes expand, lungs expand
Explain how the calibre of the airways affects air flow
- 2 factors to increase resistance to flow in airways: calibre of airways and turbulence
- Calibre decreases as go down, maintains resistance to flow at a constant level
- Combined cross sectional area of 2 daughter airways always exceeds that of parent airways
- Air flow remains constant
- Laminar or turbulent air flow
Explain how laminar and turbulent air flow occur
- Laminar: resistance is directly proportional to length of tube and inversely proportional to internal radius of tube
- Increased resistance means pressure must be increased to maintain flow
- Turbulence can also occur
- Is greatest in trache and bronchi
- Increasing branching along airway increases overall diameter and therefore turbulence decreases
Define anatomical dead space
An airway in which no appreciable gas exchange can occur
Describe how smooth muscle in airways regulates dead space and resistance to flow
- Bronchial muscle consists of spiral bands of smooth muscle
- Criss cross left and right around bronchi and bronchioles
- Particularly well developed in wall of bronchioles
- Sympathetic system relaxes smooth muscle and spiral design allows reduction of airway length and diameter
- Enables normal lung to balance dead space against resistance to air flow
- Internal radius of conducting airways must not be too small
- Increases resistance to air flow and turbulence
- Volume of CAs must not be too great
- Would enlarge anatomical dead space and lead to unecessary energy expenditure
Explain the role of the pleura in ventilation of the lungs
- Pleura connects lungs to thoracic wall
- When thorax expands so do pleura and lungs
- Draws in air
- When thorax collapses, so do pleura and lungs pushing air out
Outline the importance of complaince and surface tension in lung function
- Compliance = change in volume of a structure for each unit change in pressure
- Elastance is retractive force that distension of structure generates
- All tubes within lung are subject to transverse and longitudinal traction
- Increases volume of airways
- Compliance must be great enough to allow maximum passage of air
- Surface tension increases in smaller spheres
- Reduced by production of surfactant
- More surfactant in smaller alveoli so pressure is same between smaller and larger alveoli
Describe the structural defence mechanisms of the pulmonary system
- Branching airways: turbulence, irritant receptors, cough reflex initiated
- Bronchi surrounded by cartilaginous rings and smooth muscle: bronchi constrict, held open a little
- Intimate relationship between blood and airways: rapid resopnse to particle deposition, lymphocytes adjacent to site of deposition
Describe the functional defence mechanisms of the pulmonary system
- Mucociliary escalator
- Secreteory fluid: mucin and surfactant ensure lungs stay inflated, mucociliary escalator
- Cough reflex: expel particles
- Bronchoconstriction and dilation: entrance of particles, more open in exercise
Describe the cellular components of host defencesystem in teh lungs
- Intraepithelial lymphocytes: adjacent to site of particle deposition, fast response
- MALT/BALT: located in areas where fast drainage is importat
- Drainage lymph nodes: 4 lymphoid centres, important sites of drainage
- Bronchoalveolar lymphocytes: destroy pathogens on site, prevent infection
Describe how inflammatory mediators interact with mechanisms of bronchiolar spasm
- Inappropriate release of inflammatory mediators causes bronchiolar spasm
- Inflammaory mediators: histamine, prostaglandins, leukotrienes, bradykinins, cytokines
- Simulate CNS to react and cause bronchiolar spasm
- CNS excites vagus
- Innervated from trachea to bronchioles
- NTs released
- Excite SMCs
- Excitation results in bronchoconstriction
Describe the broad mechanisms of action by potential therapeutic targets to resolve bronchospasm
- Intervene in efferent response with drugs
- Binding of catecholamines to beta adrenergic receptors on smooth muscle cells = bronchodilation
- Clenbuterol: agonistic for beta adrenergic receptors
- INhibit Ach receptors
- Anti-inflammatory drugs
- Cholinergic to stimulate mucus and ciliary motility
Describe the suspencion of the larynx and articualtion with hyoid apparatus
- Larynx suspended by hyoid bones
- Articulate with base of skull - temporal bone
- Lies below pharynx behind mouth
- Suspended from cranial base
- Thyrohyoid bone (hyoid apparatus) and thyroid cartilage (larynx) articulate to hold up larynx
Explain the innervation and function of the larynx and its effects on conduction of air to lungs and deglutition
- 2 nerves either side
- Cranial laryngeal nerve = sensory of laryngeal mucus membrane, motor innervation of cricothyroideus
- Caudal laryngeal = innervates all laryngeal muscles except cricothyroideus
- Larynx is connection of nasal part of pharynx and trachea
- Involved in breathing, protection of lower airways, swallowing and phonation
- Protected by epiglottis
- Inhibited respiration during swallowing
Name the 4 cartilage structures of the larynx
- Epiglottic
- Arytenoid
- Thyroid
- Cricoid
Describe the thyroid cartilage of the larynx
- Largest
- 2 lateral plates that fuse ventrally to varying degrees
- Most rostral part is thickened = Adam’s apple
- Rostral and caudal extremities of dorsal edge of each lamina articualte with thyrohyoid and arch of cricoid respectively
- Cartilage is hyaline
- Susceptible to aging
Describe the cricoid cartilage
- Expanded dorsal lamina
- Narrow ventral arch
- Signet ring
- Dorsal carries median crest and on rostral rim 2 facts on each side for arytenoid cartilages
- Arch carries facet on each side for articulation with thyroid cartilage
- Hyaline
- Subject to aging
Describe the arytenoid cartilages
- Irregular shape
- Caudal facet articulates with rostral margin of cricoid lamina
- From this radiate vocal process ventrally into laryngeal lumen to which vocal fold attaches, muscular process that extends laterally, corniculate process that extends dorsomedially
- Forms caudal margin of laryngeal entrace
- Mostly hyaline
- Corniculate is elastic
Describe the epiglottic cartilage
- Most rostral
- Stalk and leaf
- Stalk embedded between root of tonge, basihyoid and body of thyroid cartialge
- Attached to all
- Can be tilted backward to partially cover entrance to larynx when animal swallows
- Elastic cartilages
- Flexible
Describe the cartilaginous structures of the larynx and their articulation in birds
- Only cricoid and arytenoid
- No vocal folds = no creation of sound
- Sound created in syrinx
- Glottis can be closed to prevent food particles entering larynx or trachea
Explain how ventilation is regulated
- Distribution regulated by pleural pressure gradient
- Lower portions ventilated more than upper
- Lung easier to inflate at lower volumes
- Apex has large expanding pressure
- Big resting volume
- Small change in volume on inspiration
- Regional differences in ventilation are equal to change in volume per unit resting volume
- Also applies to lower most section of lung
- High CO2 concentration detected incrased respiration rate and volume to increase gas exchange and remove waste from body
Outline the mechanisms that limit ventilation regionally
- Resistance to flow in airways
- Lung compliance
- Alveolar tension
Explain how perfusion of the lung is affected by posture.
- Half volume of lung is dorsal to pulmonary trunk
- Pulmonary systolic arterial pressure is only 20-40mmHg
- Dorsal parts less well perfused and reduction in ventilation of dorsal parts
Explain how perfusion if affected by cardiac function
- If obstruction of blood vessel then that area will not be perfused
- Less blood returing to heart but blood returning is normal
- Muscle mass of heart is smaller on RHS - if cardiac pressure falls may not be able to perfuse lungs properly
- Gaseous exchange will not be able to take place
Explain how perfusion of the lung is affected by lung disease
- Alveoli not function due to infection or mucus blocking alveolis
- No ventilation in that area
- Gas exchange cannot take place
- Drop in blood oxygen concentration
Describe the effects of ventilation perfusion mismatching in animals
Impairs gas exchange and can lead to hypoxia, hypercapnia and costs energy
How is tidal volume calculated?
Volume of air fowing through airways each inspiration and expiration
How is minute volume calculated?
Volume of air inhaled or exhaled in one minute. Tidal volume x breathing rate
Describe the passage of carbon dioxide from the atmosphere to the tissues
- CO2 enters RBCs
- Reacts with water to form carbonic acid
- Carbonic acid dissociates to bicarbonate ions and hydrogen ions
- Diffuse into plasma
- H+ buffered by Hb (HHb)
- carbon dioxide carried to lungs in plasam as bicarbonate ions
- Diffuse into lungs as CO2 again
- Ventilation stimulated by drop in blood pH, due to high blood concentration of H+ and HCO3- ions
Define the driving forces for oxygen and carbon dioxide transport
- O2 tension in pulmonary capillaries (normally = PAO2)
- Haldene effect: deoxygenation of blood increases ability of Hb to carry CO2. More effective buffer of H+ than HbO, has protective effect
- Affinity for Hb is inversely related to the P50
Explain the principles of diffusion and the factors affecting pulmonary perfusion of respiratory gases
- For oxygen to pass through respiratory membrane must first dissolve then diffuse in to plasma
- Oxygen then diffuses into the RBCs and combines reversibly with iron atoms of Hb
- Deoxyhaemoglobin +O2 = oxyhaemoglobin
- PAO2 in pulmonary capillary is higher than PO2 in pulmonary artery
- Therefore oxygen will diffuse into pulmonary blood
- Dissolves in plasma and binds to Hb
What is Fick’s Law of Diffusion?
Rate of transfer of a gas through a tissue sheet is directly proportional to tissue area and difference in partial pressure between the 2 sides
List the changes in oxygen in carbon dioxide composition between inspired and expired gas and arterial and mixed venous blood
- PO2 decreases through system, PCO2 increases
- Inspired gas has more oxygen and less CO2 than expired gas
- pO2 = barometric pressure x fraction of oxygen present
List the factors governing diffusion at tissues
- Partial pressure of oxygen
- Partial pressure of carbon dioxide
- Ventilation/perfusion ration
- Carboxyhaemoglobin (carbon monoxide has a higher affinity and binds irreversibly to Hb, removes proportion of Hb)
Distinguish between hypo- and hyperventilation and describe the effects of these on blood acid-base balance
- Hypo: reduced ventilation, increases blood CO2 as is triggere by reduced CO2 in CSF
- Hyper: increased ventilation, decreases blood CO2, triggered by increase in CO2 in CSF
- Ensures blood acid-base balance changes around set point between set limits
Describe how blood acid-base balance affects the ventilation rate
- Central chemoreceptors in ventral surface of medulla
- Sensitive to H+ ion concetration in CSF
- Indirect as charged ions to not cross BBB
- CO2 highly soluble and does cross barrier
- Hydrated to carbonic acid -> H+ and HCO3-
- Increase in CO2 in CSF causes chemoreceptors to stimulate respiration while fall in CO2 would inhibit respiration
Describe the mechanism of bronchodilation
- Sympathetic stimulation
- Beta2 adrenoceptors stimulated by agonist
- NE causes dilation by increasing cAMP
Describe the mechanisms of bronchoconstriction
- Parasympathetic stimulation
- Muscarinic receptors stimulated (M1 and M3)
- Stimulation of M3 receptors decrease cAMP
- Increased mucus secretion and causes contraction of bronchial smooth muscle
- Stimulation of M1 increases mucus secretion
Explain how the function of the normal lung can be altered by inappropriate release of NTs or inflammatory mediators
- Inappropraite release of NTs: muscarinic mediated bronchospasm, feline asthma, equine recurrent airway obstruction
- Overstimulation of PSNS: excessive bronchoconstriction
- Inflammatory mediators: excessive mucus, oedmea and fibrosis, increase resistance, narrow airways
- All reduce respiratory function
Describe the neurological control of lungs and ventilation
- Medulla oblongata
- Due to CO2/H+ concentration
- Regular intervals action potentials in inspiratory neurons of MO
- Excitatory synapses with motor neurons innervating inspiratory muscle = contraction
- Forced inspiration
- Expiratory neurons stimulate motor neurons to expiratory muscles
- Rhythm influenced by central pattern generator
- Stretch sensitive sensory cells located on surface of bronchial smooth muscle respond to increase with transpulmonary pressure
- When activated by stretch, inhibit impulse generation
What are the non-respiratory function of the lungs?
- Vascular reservoir
- Recruitment and distension
- Postural and ventilator cahnges
- Filter for blood born substances
- Physical filtration
Describe the lungs as a vascular reservoir
Blood not used for gas exchange is held within pulmonary vasculature
Describe the lungs’ funtion in recruitment and distension
- Able to alter lung blood volume to accomodate ncreased blood flow due to posture, exerciser and increased intravascular volume
Explain how the lungs can act as filters for blood borne substances
- Ideally positioned
- particulate matter such as clots, fibrin clumps and other endogenous and exogenous material from systemic circulation
- Prevents ischaemia and infarction
Explain how the lungs can carry out physical filtration
- Act as physical barrier to blood borne substances
- Not completely efficient in protecting systemic circulation
- Pulmonary microcirculation designed to maintain alveolar perfusion
- Prevents exo and endogenous emboli accessing systemic circualtion
Describe respiratory clearance and identify cell types responsible for this function
- Mucociliary escalator
- Reflex responses
- Head position important in respiratory clearance
- Goblet cells and ciliated epithelial cells
- Tiny particles breathed out
- Sensory cells detect particles and stimulate coughing and sneezing
Describe the air flow through the upper respiratory system, the lungs and the air sacs or the avain lung
- Air inhaled through nose
- Passes through larynx into trachea
- Past syrinx
- Into lungs and air sacs
- Half passes into caudal air sacs, half into lungs for gas exchange
- Air in cranial air sac expired, lung air into cranial air sac, caudal air into lungs
- Ensures there is alwyas fresh air on gas exchange surfaces
Describe the structure of the avian lung
- Stiff and non-complaint
- Unidirectional flow of air
- 8 or 9 air sacs
- Highly vascularised
- Lung branches into primary bronchus (runs through lung), 4 sets of secondary bronchi and parabronchi
- Are for gas exchange
- Paleopulmonic bronchi make up most of parabronchi, parallel tubes
- Neopulmonic bronchi are fewer in number irregularly branched, bidirectional flow
- Number of parabronchi depends on how much gas exchange is needed
- Parabronchi have hexagonal shape
- Connect to air capillaries
- Constant volume
Describe the structure and function of the avian air sac system
- Ensure always fresh gas on exchange surfaces
- Act as bellows
- 8 or 9 sacs (depends)
- 3 pairs and 2 singles or 4 pairs and 1 single
- Divided into cranial and caudal
- Cranial: cervical (pair), thoracic (pair) and interclavicular (single)
- Caudal: thoracic (pair) and abdominal (pair)
- Also used for evaporative heat loss and sound protection
Describe the role of the skeletal system in avian respiration
- Pneumatic
- Connected to respiratory system
- Fracture can decrease efficiency of respiration
Describe the function of the nasal cavity in the bird, including water and thermoregulation
- Filtration of air
- Humidification
- Olfaction
- Thermoregulation
- Nasal conchae act as heat exchangers by evaporative cooling
- As temperature increases, so does water saturation of air exhaled
- During exhalation and as temperature decreases, water condenses
- Leads to reclaiming of water
Describe the counter current exchange system and gas exchange in the avian lung
- Blood and gas flow in opposite directions (both unidirectional)
- Always higher concentration of O2 in the air than in the blood, so diffusion into blood will always occur
- Gas exchange is continuous due to continuous supply of fresh gas on exchange surfaces
Describe the structure of the primitive heart and contortional changes during early development
- From cardiogenic plate of mesodermal tissue at head of embryonic disc
- Rapid development and flexion lead to cardiac disc lying below head and mouth, but cranail to foregut (will become lungs, endoderm)
- Primitive cardiac tube made of 2 lateral extensions of cardiac discs, hollowed out, fold laterally
- Primitive tube has 5 zones: truncus arteriosus, bulbus cordis, ventricle, atrium, sinus venosus
- Folds and falls to right = d-looping
- Atria migrate to left and right and fuse to ventricle
- Sinus venosus still connected to atria
- Chambers form due to blood pressure and flow
- Heart partitions in order: atria, AV canal, bulboventricular loop, truncus arteriosus, aorticopulmonary septum
- Blood to heart from sinus venosus into atria
- Into common ventricle then out via truncus arteriosus
- Right horn os SV incorporated into atrial wall, left horn = coronary sinus
- AV endocardial cushion develops between left and right AV orifices
- Atria and ventricles divided by proliferation of atrial cushions
- Fuse
- Interventricular septum and setpum primum of atria develop
- Septum secundum forms foramen ovale
- Right to left shunting continues
- Do not fuse until increase presure in LA and reduced pressure in RA
- Secondary interventricular forament closes due to further growth of muscular interventricular septum , endocardial cusions tissue and spiral rides from septation of truncus and pulmonary arches
- Plugs hole
- Blood enters right atrium from sinus venosum via septum spurium
Explain the importance of the endocardial cushions in heart development
- Provide basis for division of heart into chambers
- To divide atria septum primum grows down towards cushion, septum secundum grows up out of cushion, to meet in the middle
- Forms foramen ovale
Explain how the bulbus cordis divides to for the aorta and pulmonary artery, and how vessels communicate with the ventricles
- Bulbus cordis and truncus arteriosus need to split
- True septation
- Bulbar cushions in bulbus cordis and truncal cushions in TA fuse to form aorticopulmonary septum, move up TA
- Forms a sprial, rotates down clockwise to form truncal septum
- From middle of bulbus cordis to 6th aortic arch and 3rd and 4th arches
- Vessel lumens enlarge, truncus expands and 2 cahnnels completely separate into pulmonary trunk and aorta
- Aorta arches over pulmonary artery
- Aorta is from LV, pulmonary artery is from RV
Describe the process of trabeculation in cardiac embryology and its importance
- Occurs due to mesencymal and myocardial cells dividing
- Endocardial cells undergo apoptosis
- Give rise to uneven surface of ventricles
- Important for retention of muscular and tendinous cords including papillary muscles
- Support AV-valves
Describe the formation of the AV valves
- Reshaping and tissue loss within ventricular walls
- Ventricle dilates and walls hypertrophy
- Trabeculation occurs
- Strands of cardiac wall mesenchyme from AV cushions to ventricle wall remain
- Form cusps of AV valve and chorda tendinae
Describe the formation of the pulmonary artery and aorta
- True septation of bulbus cordis and truncus arteriosus
- Following formation of truncal ridges get 3 swellings in walls of aorta and pulmonary artery trunks
- Expand into lumen of each vessel
- Very broad then become thin with cellular degradation
Describe the cardiac anatomy of fish
- One atrium, one ventricle
- Rudimentary valve between the 2
- Conus arteriosus runs to gills
- Sinus venosus remains in fish
Describe the cardiac anatomy of amphibia
- Single ventricle (funtionally but not anatomically divided), 2 atria
- Sinoatrial valves and sinus venosus reamians
- Also possess rudimentary semilunar valves
- Flap of tisse separating right and left TA
Describe the cardiac anatomy of reptiles
- Heart position dependent on breed
- Iguanids heart in thoracic inlet
- Monitors more conventional heart position
- 2 atria, right and left ventricle
- Sinus venosus remains
- Blood enters from 2 anterior vena cava, hepatic veins and coronary arteries
- Right and left aortic archa and 1 pulmonary vein
Describe the cardiac anatomy of chelonians
- Single venticle (functionally but not anatomically divided), 2 atria
- 2 large carotid and subclavian arterial trunks
Describe the cardiac anatomy of birds
- Larger than mammals
- Larger left ventricle
- Atrioventricular valve is muscular flap
Describe the cardiac anatomy of snakes
- 3 chambered heart
- 2 atria, one ventricle with partial septation
- Caudal ventricle and 2 cranial VC drain into sinus venosus
- Sinoatrial valve between SV and RA
- Paired AV valves
- 2 aortic arches
- Right goes to bicarotid trunk then fuses with left aortic arch caudally in midline
Define the functional role of the heart in the mammmalain circulatory system
- Transport (oxygen, CO2 nutrients, waste, heat, hormones)
- Homeostasis (pH, osmolarity, electrolytes, infection)
- Other (generate pressure - renal filtration and reproduction), protection as transport WBC and Ig
Describe the principal functions of a cardiorespiratory system and appreciae how the various components of such a system are structure to fulfil these function
- Pump blood, provide oxygen, remove waste
- Deoxygentated blood pumped through RHS of heart to lungs to be oxygenated
- Oxygenated then passes through LHS of heart to be pumped into the body
- Here capillaries perfuse tissues and provide a large surface area for exchange of nutrients
Describe the structures of the cardiorespiratory system and how these are integrated
- Heart: main pushing force for blood to move around body
- Lungs: site for gas exchange in order to remove waste gases such as CO2 and re-oxygenate the blood
- Veins: carry blood back to heart once gas exchange has taken place in tissues
- Arteries: carry blood to the tissue from the heart in order to provide the oxygen
- Capillaries: increase surface area for maximised diffusion in tissues
- Portal veins: run between 2 capillary beds
Describe the basics of the cardiac cycle
- Systole: contraction of ventrilces. Cardiac output and produces “lub” sound by blood hitting valves = S1
- Diastole: relaxation of ventricles and ventricular filling, “Dub” sound, involves semilunar valves at base of PA and aorta, loudest over base = S2 (closure of semilunar valves)
- S3 = sound made by ventricular filling
- ## S4 = sound made by atrial contraction
Describe the necessity for a dual circulatory system in the adult mammal
- Prevents mixin go f oxygenated and deoxygenated blood
- Ensure highest concenration possible of oxygenated blood pumped into systemic circulation
Desribe the structure and function of the cardiac skeleton
- Separates atria and ventricles from one another
- Insulates the heart so only AV bundle can get through
- Means contraction is synchronised
- Maximises pumping ability
- Called ossa cordis
Describe the structure and function of the atrioventricular valves
- Tricuspid on right, mitral on left
- Prevent leakage of blood into ventricles before atrial contraction
- Prevents back flow of blood into atria during ventricular systole
Describe the structure and function of the semilunar valves
- Sit at base of PA and aorta
- Prevent backflow into ventricles during diastole
- Pause where pressure in ventricles great enough to close AV valves but not high enough to open semilunar valves
Describe the flow of blood through the adult mammalian heart
- Into RA from body via cranial and caudal vena cava
- Atria contract
- Blood into RV through tricuspid valve
- Contract
- Blood into PA through semilunar valve
- Blood into LA from lungs through pulmonary veins
- Atria contrac
- Blood into LV through mitral valve
- Ventricles contract
- Blood into aorta to body via semilunar valve
Compare structure and function of cardiomyocytes with skeletal muscle cells
- Cardiomyocytes cylindrical and striated
- Short branched fibres with many mitochondria
- At Z-lines have intercalated discs which are gap junctions
- Desmosomes for force transfer
- Functional syncitium
- Facilitates fast AP passage due to presence of T-tubules and sarcoplasmic reticulum
- Cannot regenerate if damaged
- Myogenic
Describe coronary circulation
- Right and left coronary arteries
- Left bigger
- Coronary arteries arise from coronary sinus above aortic valve
- Perfusion occurs during ventricular diastole
- Great cardiac vein is coronary sinus
Describe the landmarks of the heart
- Ventral border of lungs at cardiac notch (which is bigger on the left)
- Lungs also lateral with thymus cranially
- Diaphragm caudally
Describe the relative positions of the heart
- LA sits in back and in the middle
- Aorta out of middle of heart
- RA right side of heart
- RV in front of LV
- LV is bigger
- PA is on left side of animal
Give the key points about the right atrium
- Blood enters via cranial and caudal vena cava
- Intervenous tubercle on roof of atrium causes blood to be diverted into atrium
- Contains SAN and coronary sinus
- Azygous vein transports deoxygenated blood from posterior walls of thorac and abdomen into the superior vena cava
- Foramen ovale present in RA
Give the key points about the left atrium
- Dorsal and caudal to right atrium
- Under tracheal bifurcation
- Blood enters via groups of pulmonary veins in 2 or 3 sites
- In septal wall scar of valve of foramen ovale
Give the key points about the right ventricle
- In front of left ventricle
- Cresenteric in section
- Wraps around left ventricle cranially and to the right
- Pulmonary artery is cranial and to left of aorta
- 1/3 of size of LV
- Lower pressure than in LV
- Volumes roughly equal
Give key points about the left ventricle
- Circular in section
- Occupies entire apex
- Prominent papillary muscles
- Aorta is ventral
- Most easily seen when ultrasounding heart
Describe the sequence of valve positions in the four pahses of the cardiac cycle and the corresponding changes in volume and presure in each chamber
- Atrial systole: AV open, semilunar closed
- Isovolumetric contraction: AV closed, semilunar closed
- Ventricular systole: AV closed, semilunar open
- Isovolumetric relaxation: AV closed, semilunar closed
Describe the distribution of ions across the membranes of excitable cardiac cells
- Cell has negative charge - protein anions
- Permeable to K+ at rest, enters down electrical gradient
- Results in efflux of potassium
- Negative resting membrane potential
- Draws K+ back into cell (1K+ enters as 1K+ leaves)
- Na+ also attracted down electrical gradietn
- Active transport keeps Na+ low
- Na+/K+ ATPase pump (3Na+ out for 2K+ in)
- Na+/Ca2+ antiporter removes calcium from cytosol
- Energy obtained from sodium passing down electrochemical gradient
- High conc of anions, moderate K+, low Na+, low Ca2+ in cell
- Low K+, moderate Na+ and high Ca2+ outside cell
Define the term transmembrane potential
Potential difference between the interior of a cell and the intersittial fluid beyong the membrane
Name the types of gateed channels in the cardiac cell membrane and describe how they exert their effects
- Voltage gated K+ channels: activated by specific depolarising voltage change. Allow efflux of potassium to repolarise cell
- Voltage gated Na+ channels: activated by localised depolarisation from neighbouring cells, allow rapid influx of NA+ to depolarise and cause AP
- L-type calcium channel: long lasting, maintain AP, respond to higher membrane potentials, open more slowly, allow influc of Ca2+
- T-type calcium channel: transient voltage gated calcium channels, shorter time open, initiation of AP, found in pacemaker cells, SAN and AVN primarily
Outline the cellular and ionic events leading to cellular depolarisation
- Pacemaker cells spontaneously depolarise
- Occurs when cations enter polarised cell
- AP in contractile cells initiated when AP from SAN reaches them
- Occurs rapidly due to an increase in membrane permeability of Na+
- Opening of voltage gated Na+ channels
- Closing of voltage gated K+ channels
- First sodium, then calcium, then repolarised with potassium
- 5 phases
- Rapid depolarisation, incomplete repolarisation, plateau phase, rapid repolarisation, electrical diastole
Describe what occurs during rapid depolarisation (phase 0) of the cardiac action potential
- At threshold potential of ~-60mV voltage sensitive fast Na+ channels open quickly
- More Na+ in
- Overcomes outward current through K+ channels = rapid upstroke
- T-type Ca2+ channels open at membrane potentials between -70mV and -40mV
- Calcium influx
- Influx of Na+ has positive feedback effect and more Na+ channels open
Describe what occurs during incomplete repolarisation (phase 1) of the cardiac action potential
- Depolarisatio of ~0.5mx inactivates Na+ channels
- No inward current of Na+
- K+ ions leave cell via transient outward channels
- Cell dows not repolarise as Ca2+ channels still open
