Physiology Exam Sem 1 content Flashcards
Describe how electrical excitation leads to muscle contraction
- Electrical impulse at SAN
- Impulse travels to AV node
- Travels across bundle of His, to the purkinje fibres then to the apex where it contracts the ventricular muscle
What is cardiac output incl it’s equation?
the volume of blood ejected from the left side of the heart in one minute. CO = HR x SV
What is stroke volume?
the amount of blood ejected from the heart in one contraction
What are the 3 lifestyle changes that can reduce CV death rate?
reduce smoking, improve diet, increase exercise
How do drugs that reduce CVD work?
controlling hypertension, preventing blood clots and controlling blood cholesterol
What is the volume of blood in the system controlled by?
kidneys
What’s the pharmacist’s role in CVD?
disease prevention & supporting patients with established disease
What’s the refractory period and its role in conduction?
caused by inactivation of sodium channels, critical to conduction of action potential, prevents action potential form travelling backwards. Influx of potassium ions as vgkc slow to close.
What is ECG, how is it recorded and what does it tell us?
it’s a machine that records conduction through the heart / 10 electrodes and 12 leads, 6 on the chest, 1 on each wrist and 1 on each ankle / each lead records the potential difference between 2 electrodes to detect the direction of current flow
What is the isoelectric line and what does it represent?
a straight line (baseline) which represents the absence of electrical activity in the cardiac tissue
Describe what each element of the PQRST cycle represent
p wave: atrial repolarization, QRS complex: ventricular depolarization, T wave: ventricular repolarisation
What does an absent P wave represent
problem in atria or SAN
What does an absent QRS complex signify
problem in ventricles or conducting tissue supplying ventricles
What are the 6 disorders of rhythm?
sinus tachycardia, sinus bradycardia, atrial flutter, atrial fibrillation, ventricular fibrillation, torsade de pointes
How can you identify heart block on an ECG?
1st degree: long pq interval 2nd degree: missed QRS complex 3rd degree: p wave disconnected from QRS complex or absent
How can you identify a myocardial infarction on an ECG?
- the more leads on ECG the larger the infarct size
- abnormal Q wave and heightened T wave
- ST segment elevated or depressed
How does atrial flutter present on an ECG?
Absent P wave, sawtooth pattern
How does atrial fibrillation present on an ECG?
no P waves, irregularly spaced QRS waves
How does ventricular fibrillation present on an ECG?
irregular unformed QRS complexes without any clear P waves
How does Torsade de Pointes present on ECG?
QRS peaks transition back and forth across isoelectric line
Explain how excitable and non-excitable cells differ and give some examples of each
non-excitable cells do not generate action potential, they have higher resting potential
Non-excitable cell: RBCs, epithelium , endothelium, adipose
Excitable: SAN, skeletal muscle, neurone, cardiac muscle
What is automaticity?
The ability of the heart to start and maintain rhythmic activity without the use of the nervous system or without external control
Which two factors determine membrane potential?
Gradients of ions across membrane
Selectively permeable ion channels in membrane
What is excitation-contraction coupling?
The mechanism that ensures that skeletal muscle contraction does not occur without neural stimulation (excitation). At rest, cytosolic [Calcium] is low, and the troponin, tropomyosin complex covers the myosin-binding sites on actin. When the muscle is stimulated by a neuron, calcium is released from the sarcoplasmic reticulum into the cytosol of the muscle cell. Calcium binds to troponin, causing a conformation change in the troponin-tropomyosin complex that shifts it away from the myosin-binding sites. This allows myosin and actin to interact according to the sliding filament theory.
Describe the arrangement of cardiac conductive tissue
myocytes, gap junctions: large pores spanning that allow ions to pass between them allowing APs to spread between cells. Intercalated discs: hold cells together and gap junction found here, nexus: where gap junction is found
Explain the concept of calcium induced calcium release
the process whereby calcium promotes its own release from intracellular calcium stores. Provides a means for amplification of microscopic initiation events into propagating calcium signals. During each heartbeat an influx of calcium through L-type voltage gated channels provides the trigger to induce CICR from receptors on the SR resulting in cardiac contraction
How does input form the autonomic nervous system affect cardiac function?
it alters rate and force of heartbeat but not required for heart to function
Describe nerve axon APs
simplest and fastest / specialised for rapid conduction over long distance / starts with depolarization to threshold for opening voltage gated Na+ channels / at peak Na+ influx falls, eqm is approached and Na+ channels closes and creates opposing outward flux of K+ and repolarisation occurs / brief hyperpolarization before membrane goes back to resting potential
Describe cardiac ventricular muscle APs
triggers ventricular muscle contraction / calcium entry during AP causes release of calcium from SR to stimulate contraction / much longer duration than axon AP
What are the 2 important consequences of the long plateau?
keeps sodium channels activated / allows time for calcium to enter, trigger contraction and replenish stores