circulation Flashcards
artery lumen:
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
the lumen of the artery contains:
Plasma - water & proteins
- Red blood cells
- White blood cells
- Platelets
- Fibrin
platelets:
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
the function of platelets:
Trauma to vessel
Exposure of platelets to interstitial collagen
Adhere together to try and form a bridge to close the gap
plasma vs serum:
Plasma contains clotting factors
Serum is plasma but without clotting factors
clotting factors:
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)
initial damage (trauma)
- Exposure of interstitial collagens to Plasma
- 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
activation of clotting factors:
Clotting factors use serine proteases to cleave other clotting factors and form the active molecule.
coagulation:
solidification of blood.
Two types:
1- Thrombus formation
2- Clot formation
Why does a thrombus of platelets and fibrin occur in flowing blood?
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.
thrombosis
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
typical wound:
[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
clot formation:
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
removal of thrombus:
Plasma protein called plasminogen → Plasmin
Plasmin cuts up fibrin into smaller fragments.
This process is called thrombolysis
virchow’s triad:
- Changes in the intimal surface of a vessel
- Changes in the pattern of blood flow
- Changes in the blood constituents
physiological vs pathological thrombosis:
Physiological → Normal after a cut or other injury
Pathological → Occurs in the absence of cut or traumatic injury
pathological thrombosis (e.g. Coronary artery thrombosis):
[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
atheroma:
a disease of coronary arteries
results in a build-up of lipids under the intimal surface
→ slow & turbulent flow
How do cigarettes make it more likely that a thrombosis occurs?
Smoking cigarettes increases the ‘stickiness’ of platelets
→ easier to aggregate
lines of Zahn:
are multiple layers of thrombus (platelets & fibrins) and clot (RBCs).
embolism:
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
consequences of thrombus blockage:
[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)
thromboembolism e.g. pulmonary embolism beginning with leg vein:
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
marrow and air embolism:
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.
detection of blood pressure and oxygen:
carotid bodies - sense the partial pressure of oxygen
sinus - respond to blood pressure:
circulatory shock:
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
function of brainstem:
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
main causes of circulatory shock:
Main Causes of Circulatory Shock:
[1] Hypovolaemic → low volume of blood
[2] Septic→ infection causing generalised vasodilation
[3] Cardiogenic → heart function failure
bradycardia:
In severe septic shock, Bradycardia occurs in the heart muscles; the heart loses its tone and has a slow heart rate.
complications of shock:
[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)
hypovolaemic:
Low blood pressure - severe reduction in the amount of blood in circulation
The high pulse - physiological response to low blood pressure
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.
[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
70-year-old man with heart disease
Heart starts failing and eventually can no longer pump enough blood to maintain blood pressure
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
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
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
