Week 1 Flashcards
Describe the elements of contractile cardia cells.
- Striated like skeletal muscle
- Short, fat and branched
- Interconnected
- Cardiac cells interlock - intercalated discs
- 25-34% of cardia cells are large mitochondria
What type of respiration does the heart rely on?
Almost exclusively on Aerobic respiration
What is the difference between cardiac and skeletal muscle?
Skeletal
- Striated, long, cylindrical, multinucleated
- No gap junctions between cells
- Stimulated individually
- Many T Tubules
- Elaborate sarcoplasmic reticulum
- Calcium binds to troponin
- Supply of ATP through aerobic and anaerobic
Cardiac- striated, short, branched, 1-2 nuclei per cell
- Has gap junctions
- Fewer and wider T Tubules
- Less elaborate sarcoplasmic reticulum
- Calcuim binds to troponin
- Supply of ATP through Aerobic respiration only
Are pacemaker cells extrinsic or intrinsic?
Intrinsic - they are self-excitable
- Spontaneously depolarise
-> cardia cells are connected through gap junction so they when pacemaker cells depolarise, it can depolarise all the cells.
Define cardiac contractility
Ability of fibres to shorten when stimulated
Define cardiac conductivity
Fibres transmit action potential easily
Define cardiac Excitability
Capactity to respond to a stimulus
Define cardiac Automaticity
Ability of heart to spontaneously depolarise without neuro-humoral control
What is the refractory period?
The time that the cell will not respond to a stimulus
What is expansibility?
The ability of the heart to stretch as it fills
What is the sequence of excitation in cardiac muscles?
- SA node generates impulse
- The impulse pauses (0.1s) at AV node
- AV bundle connects atria to ventricles
- Bundle branches conduct impulses through the inter-ventricular septum
- The subendocardial conducting network depolarises the contractile cells of both ventricles
What is the resting membrane potential of the cardiac muscles?
-90mV
- high concentration of Na+ outside cell
- Inside cell is negatively charges due to presence of high concentrations on anion (some cations are present in K+)
What is the threshold potential?
-70mV
How is resting membrane potential maintained?
RMP is maintained by Na+/K+ pump, using energy to move ions against concentration gradient
3Na+ out, 2K+ in
What happens during an action potential?
- AP stimulation results in cell membrane becoming permeable to Na+ ions
- As cell interior becomes less negative, fast sodium channels open at about -60mV to allow even more Na+ to enter cell
- Depolarisation occurs when interior of cell reaches +20-+30mV compared to outside of cell
- The depolarisation stimulates depolarisation in adjacent cell
- Once depolarisation occurs, K+ begins moving into cell, restoring the negative environment through repolarisation`
When does depolarisation occur during an AP?
Depolarisation occurs when interior of cell reaches +20-+30mV compared to outside of cell
What occurs at Phase 0?
Rapid depolarisation
- Na+ into cell till +20-+30mV
- occurs in 2ms
What occurs at Phase 1?
Beginning of repolarisation
- Na+ channels close
- K+ channels open
What occurs at Phase 2?
Plateau phase
- K+ moving in
- Slow Ca+ channels are opened
- Cl- channels open in response to Ca+
- Balances electrical signal for short period
What occurs at Phase 3?
Repolarisation
- K+ channels remain open
- Na+/Ca+ exchanger open
- Na+/K+ pumps open
Net outward current flow creating negative membrane potential
What are the two parts to the refractory period?
Absolute refractory period (ARP)
Relative refractory period (RRP)
When does the ARP start and finish?
Begins with phase 0
Ends half way through Phase 3
- Approximately peak of T wave on ECG
- Makes up 2/3 the overall refractory period
- Because cardiac cells have not repolarised to their threshold potential (-60 to -70mV) they cannot pass on another action potential and contract.
When does the RRP start and finish?
Half way through phase 3 to the end of phase 3
- Downstroke of T wave on ECG
- cardia cells have repolarised to their threshold potential and can be stimulated but another AP
Describe the 3 steps on a pacemaker cells action potential
Pacemaker cells have unstable resting potential
- PACEMAKER POTENTIAL Slow depolarisation due to both opening of Na+ and closing of K+ channels
- DEPOLARISATION the AP begins when pacemaker potential reaches threshold.
Depolarisation is due to Ca2+ influx through Ca2+ channels - REPOLARISATION is due to Ca2+ channels inactivating and K+ opening, bringing membrane potential back to it’s most negative voltage
What is the threshold potential for pacemaker cells?
-40mV
What nervous system is the vagus nerve in?
Parasympathetics
Where does the Cardioinhibitory and cardioaccelatry centres sit?
Medula oblongata
Why is there no AP over the P wave?
P wave is passive
What is perfusion?
The circulation of blood through the a vascular bed of tissue
-> The level of perfusion is determined by the ability to provide adequate blood supply to tissue or organs to provide nutritional demands and remove waste.
What is the function of the cardiovascular system
- Distribute oxygen and glucose
- collect waste and return to elimination sites
- thermoregulation
- hormone distribution
What are the components of the CV system?
Heart - pumping force Arteries - Distribution Arterioles - Flow & pressure regulation Capillaries - Exchange Veins - Collection
What is Hydrostatic pressure?
Force exerted by fluid pressing against a wall
What is osmotic pressure?
The force that opposes hydrostatic pressure.
Movement of solutes
What is the formula for Cardiac Output?
CO = HR x SV
What is the formula for BP?
CO x R
What are the four perfusion factors?
- Heart Rate
- Stroke Volume
- Resistance
- Viscocity
What is the formula for Mean arterial pressure?
MAP = diastoilic pressure + (pulse pressure/3)
How do you calculate pulse pressure?
Difference between systolic and diastolic pressure.
What are the elements for blood pressure regulation?
- Cardiac Centre
- Vasomotor centre
- Baroreceptors
- Chemoreceptors
- Adrenal medulla
- Angiotensin II
- Antidiuretic hormones
Where does the parasympathetic and sympathetic NS originate
Parasympathetic - Medulla oblongata
Sympathetic - spinal cord
Explain Starlings law
- Increased venous return increases end diastolic vol.
- Increased end diastolic volume causes stretching of ventricular wall
- This results in an increase in the force of cardiac contraction
- With all other factors remaining constant, the result is an increase in stroke vol, CO, and BP
What diseases is hypertension a risk factor for?
- Stroke
- Renal failure
- Chronic/congestive heart failure
- Acute myocardial infarction
What’s classes as normal BP?
<120 / <80
What’s classed as high to normal BP?
120-139 / 80-89
What’s classed as mild (Grade 1) hypertension?
140 - 159 / 90 - 99
What’s classed as moderate (Grade 2) hypertension?
160 - 179 / 100 - 109
What’s classed as severe (Grade 3) hypertension?
180/110
