5 structures that occupy the thoracic cavity
- heart, aorta, pulmonary trunk, trachea, oesophagus, thymus gland, lungs.
alternate names of valves: Right + left AV valves, aortic + pulmonary valves
- Right AV valve: tricuspid
- Left AV valve: mitral/bicuspid
- aortic + pulmonary: semilunar valves
Which heart chamber receives blood from the coronary sinus?
- right atrium
Describe the function of both the fibrous + serous pericardium layers
- fibrous: protects the heart + anchors it to surrounding tissues
- serous: lubricate heart + minimise friction
Palpation of pulses: analysed in respect to:
a) volume; gives an assessment of the amplitude + therefore the pulse pressure
b) rate: gives an assessment of the ventricular rate assuming each ventricular ejection is effective
c) rhythm: gives an idea of whether the ventricular contraction are regular or irregular
Measurement of arterial blood pressure
Key concepts:
• Measuring the blood pressure using the sphygmomanometer relies on the fact that turbulent blood flow in a blood vessel is noisy
•Turbulent blood flow occurs when an artery is partly occluded
•Externally applied pressure can be used to occlude an artery
•Normal blood flow in the artery is laminar, and therefore silent.
Why is it important to regulate blood pressure?
- The blood pressure is the “driving force” for blood flow. (Pressure = QR) = as fundamentally pressure is what is determining the flow
- Blood flow is mostly regulated by local changes to resistance (radius of arterioles)
- However, if BP is not stable, then changing resistance to regulate flow becomes much more complicated
- BP can fluctuate dramatically. One major factor that affects BP is gravity.
How is the short-term control of blood pressure achieved?
- MAP = CO x TPR = HR x SV x TPR
- Therefore BP is regulated by changes to HR, SV, TPR
- Short term control of BP is by change in sympathetic and parasympathetic activation
How is BP controlled in the longer term?
- Mostly by changes in blood volume (inc. BV → inc. BP)
- Balance of fluid intake and fluid output (largely urination)
- Controlled neurally and hormonally (vasopressin, angiotensin II and aldosterone)
- The hormones increase salt and water reabsorption from the kidney → increase blood volume (i.e. conserve water)
Define the following terms and explain the effects of an increase in each variable on the arterial blood pressure: CO, SV, preload, contractility, afterload, TPR
a. cardiac output: volume of blood ejected by the ventricle per min (CO = HR x SV)
- Will increase BP / MAP
b. stroke volume: volume of blood ejected per contraction of the ventricle
- Will increase BP / MAP
i. Preload: degree of stretch of ventricle prior to systole (i.e. end diastolic volume, EDV)
- Will increase BP / MAP
ii. Contractility: force generated by myocardium independent of EDV (related to [Ca2+]
- Increase BP / MAP
iii. Afterload: resistance against which the ventricle has to eject
- Reduces SV (+ therefore CO) + therefore MAP
c. total peripheral resistance: resistance to blood flow in entire circulation (mostly arterioles)
- Arterioles are a “bottleneck”
- Will increase BP / MAP
Describe the structure of the arteries and the arterioles and how they differ.
- Arteries are principally elastic
- Can stretch + recoil as each ejection of blood passes through them
- As they stretch, the increase in BP during systole is lessened
- As people age their arteries become less elastic, causing their systolic BP to be higher
- As arteries recoil the force (BP) is maintained by pushing on the blood → drives flow
- Also as arteries recoil, the decrease in BP during diastole is also lessened
- Elastic arteries - reduced SBP, increased DBP → pulse pressure is reduced and flow becomes more laminar
- Arterioles have large amounts of smooth-muscle in their walls
- By regulating the contraction of the smooth-muscle, the arteriole radius and hence blood flow through the vessel can be controlled
- Overall, arterioles make up the major component TPR (~70%)
- As the blood flows through the arterioles there is a significant reduction in BP (in the arterioles) due to the energy loss
CASE STUDIES: The effects of stress on the CVS
- Any form of stress increases sympathetic nervous system activity
- This can be a physical stress (e.g. exercise, injury), or emotional stress, such as anger or fear
- Recall: sympathetic is the flight or fight response - readies the animal for action
- the effects of activation of the sympathetic nervous system on BP and how they occur:
- Increase MAP (MAP = HR x SV x TPR)
- Sympathetic Activation:
- increased heart rate
- increased stroke volume
- increased TPR
- Activation of sympathetic from stress is mediated via the hypothalamus
which relays to cardiovascular control centres in medulla oblongata - Activation of the sympathetic can occur reflexively
- arterial baroreceptor reflex in response to drop in BP = is the negative feedback reflex that tries to maintain a steady BP
The likely r/s b/w postural hypotension and a decreased cold pressor response
- A decreased cold pressor response suggests reduced ability for the sympathetic to influence BP (in response to cold).
- What about the influence of the sympathetic in regulating BP responses to ∆ posture (gravity).
- Standing up decreases CO & BP, causing decreased blood flow to brain
= risk of fainting - Normally rapidly compensated by baroreceptor reflex
- inc. HR & TPR → inc BP.
- Often if sympathetic has a reduced response to cold, it also has a reduced response to postural changes
