Week 1/2 - B(3) - Physiology 6,7,8 - Vasomotor tone, Adrenaline Shock (hypovalaemic, cardiogenic, obstructive, distributive), Syncope (vasovagal, reflex, carotid sinus)

Question 1

We have established the dominant control of the heart under resting conditions is the vagus nerve is vasomotor tone sympathetic or parasympathetic?

Answer 1

Vasomotor tone is under sympathetic control - at rest the vascular smooth muscles are partially constricted

Question 2

Vascular smooth muscle are controlled by both intrinsic and extrinsic mechanisms Extrinsic control of the vascular smooth muscle involves nerves and hormones * Have already dscussed baroreceptor reflex - stretching cause signal to medulla which cause changes in autonomics The vascular smooth muscles are supplied by SYMPATHETIC nerve fibers. The neurotransmitter is NORADRENALINE Which vascular smooth muscles also have parasympathetic innervation?

Answer 2

There is no significant parasympathetic innervation of arterial smooth muscles - exceptions include penis and clitoris

Question 3

Where is adrenaline released from? What effect does adrenaline have on alpha and beta receptors? Where are they predominant?

Answer 3

Adrenaline is released from the adrenal medulla Adrenaline acts on alpha receptors (skin, gut, kidneys) * a1 causing vasoconstriction Adrenaline works on beta receptors (cardiac, lungs) * B1 causing increased cardiac contractile force and increased heart rate * B2 cause bronchodilation in the lungs

Question 4

Intrinsic control of vascular smooth muscles are due to chemical agents and physical factors Which chemical agents cause vasodilation? Which chemical agents cause vasoconstriction?

Answer 4

Chemical agents causing vasodilation - histamine, bradykinin (both released during allergic attacks), nitric oxide Chemical agents causing vasoconstriction - serotonin, thromboxane A2, leukotrienes, endothelin

Question 5

What is the abnormality of the circulatory system resulting in inadequate tissue perfusion and oxygenation? State the different types

Answer 5

Shock is the abnormality of the circulatory system resulting in inadequate tissue perfusion Hypovalaemic, cardiogenic, obstructtive, distributive

Question 6

Describe how hypovalaemic shock leads to inadequate tissue perfusion? State different causes of hypovalaemic shock

Answer 6

Hypovalaemic shock Haemorrhagic Non-haemorrhagic - eg vomiting/diarrhoea, sweat, diuresis * Loss of blood volume * Decreased venous return * Decreased end diastolic volume * Decreased stroke volume * Decreased cardiac output and blood pressure * INADEQUATE TISSUE PERFUSION

Question 7

Describe how cardiogenic shock leads to inadequate tissue perfusion? State different causes of cardiogenic shock

Answer 7

Cardiogenic shock Sustained hypotension due to decreased cardiac contractility eg myocardial infarction * Decreased cardiac contractitlity * Decreased stroke volume * Decreased cardiac output and blood pressure * INADEQUATE TISSUE PERFUSION

Question 8

Describe how obstructive shock leads to inadequate tissue perfusion? State different causes of obstructive shock

Answer 8

Obstructive shock Things that increase intrathoracic pressure eg PE, tension penumothorax, cardiac tamponade * Increased intrathoracic pressure * Decreased venous return * Decreased EDV * Decreased SV * Decreased CO and BP * INADEQUATE TISSUE PERFUSION

Question 9

Distributive shock results from excessive systemic vasodilatation and leakage of fluid from capillaries into surrounding tissue

What are the different types of distributive shock?

Answer 9

Distributive shock

• * Neurogenic shock
• * Vasoactive shock -
  
  • * Anaphylactic
  • * Septic
  • Adrenal crisis

Question 10

Describe how neurogenic shock leads to inadequate tissue perfusion? State different causes of neurogenic shock

Answer 10

Neurogenic shock Eg brain injury, spinal cord injury - trauma that causes a sudden loss of brackground sympathetic stimulation to blood vessels Massive venous and arteriolar dilatation –> * decrease in venous return, EDV, SV, CO,BP * decreased in SVR, and BP * decreased HR, CO, BP INADEQUATE TISSUE PERFUSION

Question 11

Describe how vasoactive shock leads to inadequate tissue perfusion? State different causes of vasoactiveshock

Answer 11

Vasoactive shock Vasoactive mediators (eg histamine/bradykinin in ananphylaxis or cyotkines in septic) Increased capillary permability Massive venous and arteriolar dilatation –> decrease in venous return, EDV, SV, CO,BP decreased in SVR, and BP decreased HR, CO, BP INADEQUATE TISSUE PERFUSION

Question 12

Syncope can be classified into three categories * Reflex syncope * Vasovagal * Situational * Carotid sinus syncope Orthostatic hypotension Cardiac syncope What is syncope defined as?

Answer 12

Syncope is a transient loss of conscsiousness due to cerebral hypoperfusion, characterized by rapid onset, short duration, and spontaneous complete recovery

Question 13

Reflex syncope Vasovoagal syncope Situiational syncope Carotid sinus syncope What happens in vasovagal reflex syncope ie what is the trigger and how does the fainting occur?

Answer 13

In vasovagal syncope, your body reacts to certain triggers such as pain, fear or blood phobia or standing for too long There is simultaneous * enhancement of the vagal tone leading to a drop in heart rate and * withdrawal of sympathetic tone leading to arteriolar vasodilation * Results in decreased cerebral perfusion

Question 14

What are the symptoms of vasovagal syncope? How is treated?

Answer 14

Symptoms include - pallor, sweating , nausea Treatment - reassurance, avoidance of triggers, adequate hydration, lying flat - can increase venous return to heart

Question 15

What happens in situational syncope? What are the symptoms? how is it treated?

Answer 15

Situational syncope - same symptoms as vasovagal (pallor, sweating, nausea) - CLEAR PRECIPITANT * Usually occurs due to a vasavagal response * Effort syncope - exercise * Cough syncope - broght on during paroxysms of coughing * Micturition syncope - happens during or after urination Treat the same as vasovagal - reassurance, hydration, lie down, avoidance

Question 16

What happens in carotid sinus syncope?

Answer 16

Hypersensitive carotid sinus baroreceptors results in increased parasympathetic activity and decreased sympathetic Usually occurs in elderly males eg during shaving or tight collar - cause vasodilation of carotid sinus on minimal stimulation

Question 17

What is the treatment of carotid sinus syncope?

Answer 17

Medications may be helpful eg fludricortisone (decreases Na/water excretion) or midodrine (sympathomimetic - alpha-1 agonist- increases vasoconstriction) Cardiac permanent pacing is generally recommended

Question 18

We have discussed reflex syncope * vasovagal - pain, blood, standing too long * Situational - clear precipitant eg cough, exercise, micturition, defecation * Carotid sinus - increased sensitivity We have discussed postural hypotension in previous cards (baroreceptor dysfunction) NOW WE discuss cardiac syncope What is this caused by?

Answer 18

Cardiac syncope is caused by cardiac events that result in a sudden drop in cardiac output eg * Arrhytmias - brady or tachycardia causing * Acute MI * Structural cardiac disease - eg aortic stenosis