Circulation 3: Circulatory shock

Question 1

Describe what shock is.

Answer 1

Shock:
- Low blood pressure
(+ its physiological consequences)

Question 2

Describe circulatory shock.

Answer 2

Circulatory shock is profound circulatory failure causing poor perfusion of vital organs.
(ultimately causing poor perfusion)

Question 3

State the normal values for blood pressure.

Answer 3

120/80 = normal blood pressure

Question 4

Describe how a normal blood pressure is maintained

Answer 4

1) Enough blood in the system
2) Smooth muscle vessels in having a certain ‘tone’
3) Heart pumping blood

Question 5

Describe a carotid body.

Answer 5

The 2 carotid bodies (at the bifurcation of the carotid artery) is important in sensing the partial pressure of oxygen and CO2.

Question 6

Describe the function of carotid sinuses.

Answer 6

Sense changes in blood pressure.
Respond by sending nerve signals through the sympathetic nervous system to the brain stem.
- animal pharmacology, animal toxicology, tissue culture

Question 7

Describe a mechanism by the brainstem to keep a person suffering from low blood pressure alive (Tone)

Answer 7

The brain stem stimulates the sympathetic nervous system causing:
- Increased vascular tone in vessels in limbs and abdomen
- Blood pushed up to chest and head.

Results in circulation of remaining blood around heart, lungs and brain - keeps vital organs alive.

Question 8

Describe the (hallmark) presentation of shock clinically.

Answer 8

Hypotension and tachycardia
(Low blood pressure and fast pulse)

Question 9

State the 3 main causes of circulatory shock.

Answer 9

1) Hypovolaemic or Haemorrhagic shock

Question 10

Describe hypovolaemic shock

Answer 10

An injury causes a major bleed in a an area of the body (e.g. spleen).
For first wee while, the systemic (arterial) pressure stays the same but then the lack and loss of blood causes the vessels to collapse as they have no blood in them.
Eventually there is less blood in inferior vena cava - which will then also collapse.
Systemic blood pressure drops.

Question 11

Describe septic shock.

Answer 11

Septic shock is an immune response by the body to widespread infection and inflammation (septicaemia - bacteria in circulation).
This reduces the tone in the smooth muscle of the blood vessels - resulting in vasodilatation.
The blood flow increases and can pool in these dilated blood vessels.
This pooling means that not enough blood is returning to the heart and the venous pressure in the right side of the heart is low.
This means that blood cannot reach the rest of the body.

Question 12

Describe cardiogenic shock.

Answer 12

Shock where there is tachycardia and hypertension that is NOT due to blood loss.
So , venous pressure is normal of increased - so no change in preload.
However, there is a change in afterload, contractility and stroke volume.

Question 13

Describe the effect of shock on the brain.

Answer 13

Shock can lead to reduced perfusion of the brain - this is initially reversible but could also be permanent - i.e. infarction.
**ischaemia

• Confusion, reduced consciousness, coma

Question 14

Describe the effect of shock on the kidneys.

Answer 14

The perfusion of the kidneys is decreased - this is initially reversible but can become more severe (ischaemic necrosis of renal tubules)

• Reduced urine output, reduced excretion of toxic substances.

Question 15

Describe the importance of having enough blood in your cardiovascular system

Answer 15

It is important to have enough blood because, if there was no blood in the vessel that causes it to collapse and the blood pressure becomes low and then unrecordable

Question 16

Describe the importance of the ‘tone’ of smooth muscle.

Answer 16

It is important that smooth muscle cells have a certain ‘tone’ because if the tone is decreased then the vessel will dilate - if enough vessels are affected by this an also dilate then blood pressure may fail.
(Blood can pool/pull - usually peripherally)

Question 17

Describe the mechanism of the physiological response to low blood pressure

Answer 17

Brain stem sends signals (via sympathetic nerve signals) to the heart, instructing it to beat harder and faster.
The heart beating faster = increased pulse rate peripherally.
So, physiological response to low blood pressure = faster heart rate (pulse)

Question 18

Describe the mechanism by the brain stem that keeps a person with low blood pressure alive (Adrenal glands)

Answer 18

(by the sympathetic nervous system) - the adrenal glands secrete adrenaline which causes the heart to pump harder and faster.

Question 19

Describe the role of the carotid sinuses in hypovolaemic shock.

Answer 19

Carotid sinuses recognise the low blood pressure - they upregulate the sympathetic nervous system, leading to various different signs;
- Rapid breathing
- Fast heartbeat (fast and weak pulse)
- Pale, sweaty skin
- Tender abdomen

Question 20

Describe severe septic shock.

Answer 20

In severe septic shock, the muscles of the heart - just like the muscles in vessels - loose their tone.
This can lead to a slow heart = bradycardia.