How do we get cardiac muscle to contract?
Rise in cystolic calcium which comes from the SR calcium stores = actin / myosin interaction
Pathway of electrical conduction in the heart
- SA node
- AV node
- Bundle of His
- R/L bundle branches
- Purkinje fibres
What is the role of ‘trigger’ calcium in cardiac muscle contraction?
calcium enters the heart cell from calcium channels = activates ryanodine receptor to release enough calcium from the SR to initiate contraction
What does each wave/complex in the electrocardiogram represent?
P wave = atrial depolarisation
QRS complex = ventricular depolarisation
T wave = ventricular repolarisation
What do the heart sounds represent?
Lubb = AV valve closing Dupp = SL valve closing
What are the 4 phases of the ventricular cycle?
- ventricular filling
- isovolumetric ventricular contraction
- ventricular ejection
- isovolumetric ventricular relaxation
Change in pressure and vol. during cardiac cycle?
- Late diastole = chambers are relaxed and ventricles are filled passively
- Atrial systole = atrial contraction
- Isovolumetric ventricular contraction = AV valve close, not enough pressure to open SL valve = EDV
- Ventricular ejection = ventricular pressure increases = SL valve open and blood ejected
- Isovolumetric ventricular relaxed = pressure decreases, SL valve close = ESV
What is the relationship between MABP, CO and TPR?
MABP = CO x TPR
Sympathetic and Parasympathetic autonomic control of the heart
- Sympathetic nerves release NA which bind to beta1 adrenergic receptors = increases heart rate and contractility
- Parasympathetic nerves release Ach which binds to muscarinic receptors = negative effect on heart rate
Intrinsic and extrinsic regulation of stroke volume
Intrinsic:
- Starling’s law
- heart will pump whatever volume of blood it receives
Extrinsic:
- increase in sympathetic activity
- enhances contractility
- enhances stroke volume
- positive iontropic effect
What are the vasodilators and vasoconstrictors of hormonal control?
Vasodilators:
- Histamine
- Kinins
- Nitric oxide
- Adrenaline (beta2)
Vasoconstrictor:
- Angiotensin II
- Vasopressin (ADH)
- Adrenaline (alpha1)
Explain baroreceptor reflex
sensory detectors feed information into control centre about the changes in blood pressure. Control centre regulates input of information to determine what changes need to be made
Location of baroreceptors and what are baroreceptors
Carotid sinus and aortic arch
baroreceptors = are stretch receptors which respond to stretch in the arteries due to change in blood pressure
Mechanisms involved in control of renal blood flow
- increase resistance of afferent arteriole = reduce blood flow to glomerulus
- increase resistance of afferent arteriole = increase blood flow in glomerulus
- decrease resistance of afferent = increase blood to glomerulus
- decrease efferent resistance = increase blood out glomerulus
Formation of concentrated urine
- Anti-duretic hormone = collecting duct is more permeable to H2O
- Countercurrent systems maintain osmotic gradient in medullary interstitum
What are countercurrent systems?
- 2 flows moving opposite each other
- passive transfer of molecules
a countercurrent maintains osmotic gradient for reabsorption of H2O by preventing reduction of osmolarity
Acidosis and alkalosis in the kidneys
acidosis:
- alpha intercalated cells in collecting duct excrete H+ and reabsorb HCO3-
alkalosis:
- beta intercalated cells in collecting duct excrete HCO3- and reabsorb H+
How is ADH released?
- produced in hypothalamus
- stored in vesicles in posterior pituitary gland
- changes in osmolarity are sensed by osmoreceptors in the hypothalamus which cause the release of ADH
- increased osmolarity = increased ADH*
Mechanics of ventilation
Inhalation:
- diaphragm moves down
- external intercostal muscles raise rib cage upwards
Exhalation:
- diaphragm moves up
- intercostal muscles move down
Factors influencing respiratory/ pulmonary ventilation
- Airway resistance = anything that prevents airflow
- alveolar surface tension = gas water boundary
- lung compliance = lungs and chest wall stretch
How does sodium nitroprusside treat angina due to ischaemic heart disease?
produces nitric oxide within the body to cause vasodilation which increases coronary blood flow
What is the immediate physiological response to exercise and what causes it?
increase in ventilation caused by feedforward reflex receptors in muscle
What percentages of Na+ are reabsorbed in the nephron?
66% in proximal convoluted tubule
25% in ascending limb
5% in distal convoluted tubule
3% collecting duct
What is reabsorbed in the proximal convoluted tubule?
66% Na+, K+ and H2O
50% urea, urate
80% HCO3-
100% glucose
