circulation

Question 1

artery lumen:

Answer 1

lined by endothelial cells

endothelial cells make basal lamina (basement membrane) o adhere to and sit on

Smooth muscle cells surround the basal lamina

Interstitial collagen fibres surround the smooth muscle cells

Question 2

the lumen of the artery contains:

Answer 2

Plasma - water & proteins

• Red blood cells
• White blood cells
• Platelets
• Fibrin

Question 3

platelets:

Answer 3

Platelets aren’t normally exposed to interstitial collagen fibres around the vessel

produced in bone marrow from a cell
called megakaryocyte (large cell & many nuclei)

They bud off as fragments from cytoplasmic extensions

Megakaryocytes undergo nuclear division but not cell division
→ get huge with many nuclei

Question 4

the function of platelets:

Answer 4

Trauma to vessel

Exposure of platelets to interstitial collagen

Adhere together to try and form a bridge to close the gap

Question 5

plasma vs serum:

Answer 5

Plasma contains clotting factors

Serum is plasma but without clotting factors

Question 6

clotting factors:

Answer 6

Clotting factors are an amplification system, resulting in thrombin production

• Thrombin converts soluble fibrinogen into insoluble fibrin
• Fibrin forms a mesh of strands

produced in the liver (but also by endothelial cells)

Question 7

initial damage (trauma)

Answer 7

1. Exposure of interstitial collagens to Plasma
2. Release of Tissue Factor (TF)

Initiation of clotting cascade:

———–Simple Clotting Cascade———

1 - TF (released by smooth muscles)

2 - Prothrombin → Thrombin

3 - Fibrinogen → insoluble Fibrin
Enzyme: Thrombin

Question 8

activation of clotting factors:

Answer 8

Clotting factors use serine proteases to cleave other clotting factors and form the active molecule.

Question 9

coagulation:

Answer 9

solidification of blood.

Two types:

1- Thrombus formation

2- Clot formation

Question 10

Why does a thrombus of platelets and fibrin occur in flowing blood?

Answer 10

Platelets have molecules on their surfaces which allow adherence to interstitial collagen,
even when blood is flowing past them.

von willebrand Factor VIII enhances this process.

Question 10

thrombosis

Answer 10

Thrombus formation is a type of blood coagulation that:

→ occurs in flowing blood

→ pale cream coloured

→ consists of platelets and fibrin strands

Thrombosis - the process of thrombus formation which occurs in flowing blood

Question 11

typical wound:

Answer 11

[1] Trauma disrupts vessel

[2] Leakage of blood

[3] The clotting system is activated by collagen and by the stagnant blood, forming a clot

[4] The wound may continue to bleed

[5] Vasoconstriction to decrease blood loss

[6] Platelet and Fibrin thrombus formation
to bridge the gap between the ends of the vessel adjacent to the flowing blood

[7] Skin now stops bleeding – haemostasis has been achieved

Question 11

clot formation:

Answer 11

a type of blood coagulation where blood leaks out of a vessel and becomes stationary/stagnant

→ Within the stagnant blood, sitting next to interstitial collagen, the clotting cascade is activated

→ consists of a network of fibrin strands and red blood cells

Question 12

removal of thrombus:

Answer 12

Plasma protein called plasminogen → Plasmin

Plasmin cuts up fibrin into smaller fragments.

This process is called thrombolysis

Question 13

virchow’s triad:

Answer 13

1. Changes in the intimal surface of a vessel
2. Changes in the pattern of blood flow
3. Changes in the blood constituents

Question 14

physiological vs pathological thrombosis:

Answer 14

Physiological → Normal after a cut or other injury

Pathological → Occurs in the absence of cut or traumatic injury

Question 15

pathological thrombosis (e.g. Coronary artery thrombosis):

Answer 15

[1] Changes in the intimal surface of a vessel
e.g. atheroma lipid coming through the surface

[2] Changes blood flow pattern
e.g. a bulge of atheroma changing the flow of blood

[3] Changes in the blood constituents
e.g. smoking → sticky platelets → platelets aggregate
e.g. more abundant platelets

Question 16

atheroma:

Answer 16

a disease of coronary arteries

results in a build-up of lipids under the intimal surface
→ slow & turbulent flow

Question 17

How do cigarettes make it more likely that a thrombosis occurs?

Answer 17

Smoking cigarettes increases the ‘stickiness’ of platelets

→ easier to aggregate

Question 18

lines of Zahn:

Answer 18

are multiple layers of thrombus (platelets & fibrins) and clot (RBCs).

Question 19

embolism:

Answer 19

blockage of a blood vessel by a foreign substance or a blood clot that has traveled through the bloodstream from another location in the body

Question 19

consequences of thrombus blockage:

Answer 19

[1] Complete obstruction
→ tissue receives no flow ischaemia
→ no oxygenation (hypoxia)
→ localised area of tissue dies (infarct/infarction)

[2] Partial obstruction
→ tissue receives poor flow (ischaemia)
→ decreased oxygenation (:hypoxia)

Question 20

thromboembolism e.g. pulmonary embolism beginning with leg vein:

Answer 20

When a thrombi/clot embolises

e.g. Pulmonary embolism

[1] Sluggish flow in leg veins leads to thrombosis and clot formation

[2] Part of the thrombus and clot breaks off and travels up the vein

[3] The embolus passes into the inferior vena cava, then the right heart, then the pulmonary trunk, and lodges in the pulmonary artery branch

[4] The embolus blocks the pulmonary artery and gets pulmonary infarct

Question 21

marrow and air embolism:

Answer 21

air - Air bubbles enter the bloodstream

due to trauma, surgery, or medical procedures like intravenous injections.

marrow - bone marrow fragments in the bloodstream, which can block blood vessels and impair circulation.

Question 22

detection of blood pressure and oxygen:

Answer 22

carotid bodies - sense the partial pressure of oxygen

sinus - respond to blood pressure:

Question 23

circulatory shock:

Answer 23

a profound circulatory failure causing poor perfusion of vital organs.

Features:
→ Low blood pressure (hypotension) and its physiological consequences
e.g. 60/40

→ Fast pulse (Tachycardia)
e.g. >100

Question 24

function of brainstem:

Answer 24

Stimulates SNS which leads to:

[1] Increased heart rate

[2] Increased vascular tone in vessels located in limbs and abdomen

→ blood pushed to chest and head

→ results in circulation of remaining blood around vital organs (heart, lungs, brain)

[3] Adrenal glands secrete catecholamine (adrenaline)

→ results in faster & stronger heart rate

Question 25

main causes of circulatory shock:

Answer 25

Main Causes of Circulatory Shock:

[1] Hypovolaemic → low volume of blood

[2] Septic→ infection causing generalised vasodilation

[3] Cardiogenic → heart function failure

Question 25

bradycardia:

Answer 25

In severe septic shock, Bradycardia occurs in the heart muscles; the heart loses its tone and has a slow heart rate.

Question 26

complications of shock:

Answer 26

[1] Decreased perfusion of the brain (ischaemia)
→ initially reversible but then permanent (infarction)
→ brain injury

[2] Decreased perfusion of kidneys (ischaemia)
→ initially reversible, then more severe
(ischaemic necrosis of renal tubules)

Question 26

hypovolaemic:

Answer 26

Low blood pressure - severe reduction in the amount of blood in circulation

The high pulse - physiological response to low blood pressure

Question 27

A 35-year-old man walking across the road.
Hit by a car.
The fractured left rib goes through the spleen.
Spleen ruptures with loss of 3 litres (of his 5 litre blood volume) into the abdominal cavity.
complains about Abdominal pain.

Explain the steps of hypovolaemic shock.

Answer 27

[1] rib penetrated spleen → internal haemorrhage (3L loss)

[2] vessels collapse due to no blood

[3] collapse of inferior vena cava (venous BP falls to zero)

[4] no blood enters the right side of the heart

[5] very little blood goes to the lungs, brain, and rest of the body

[6] drop in systemic BP

[7] carotid sinuses sense a drop in systemic BP

[8] stimulate brainstem → activates SNS

• Patient usually feels very ‘ill’
• Rapid breathing.
• Fast heartbeat – pulse fast and may be weak
• Pale, cold, sweaty skin

Diagnosis:

• Tender abdomen
• Blood pressure 60/40, pulse 120 = Shock
• Diagnosis of abdominal trauma with hypovolaemic shock.
• Transfused blood to restore blood volume.

An operation to remove the spleen

Question 27

70-year-old man with heart disease

Heart starts failing and eventually can no longer pump enough blood to maintain blood pressure

Answer 27

Blood pressure falls, pulse rate goes up

Diagnosis:
→ cardiogenic shock
(not due to blood loss – so venous pressure is normal or even increased)

Treatment:
→ drugs to increase heart function

Question 28

A 30-year-old woman gets a urinary tract infection
which then causes kidney infection then bacteria go into the blood (= septicaemia)

Explain what happens in Septic shock

Answer 28

Eventually, molecules released cause generalised vasodilatation

[1] Vasodilatation is general and results in the pooling of blood in veins

[2] Not enough blood gets back to the heart
(venous pressure and filling are low)

[3] Not enough blood can now go to the brain and the rest of the body