2.1. Blood & Cardiovascular System Flashcards
Describe the clotting cascade (Haemostasis)
- Vasoconstriction occurs, reflexive contraction that causes a decrease in blood flow to the area
- Platelets aggregate near injury site and form a plug
- Circulating prothrombin is converted to thrombin, which promotes the formation of insoluble fibrin from fibrinogen
- Fibrin adheres to the plug to form an insoluble clot
What is physiological anaemia of pregnancy?
Plasma volume increases more quickly than red blood cell mass, this causes haemodilution and therefore a decrease in haemoglobin concentration
What are other causes of anaemia in pregnancy?
- Sickle cell trait
- Thalassaemia
- Sickle cell anaemia
- Inheritable disease
What are the signs/symptoms and risk of sickle cell anaemia?
- Pain crises-> sickle cells block blood flow in tiny blood vessels and causes oedema of peripheries
- Delayed growth
- Infections-> spleen damage
- Anaemia-> life span of sickle cells is shorter so there are fewer RBCs in body
- Vision problems-> blood vessels in eyes can become plugged with sickle cells which damages retina
Which blood group is the universal recipient?
AB
Which blood group is the universal donor?
O
Describe the pump system of the heart
Blood from the right side of heart enters the pulmonary circulation to the capillaries surrounding the alveoli of the lungs where the blood is oxygenated.
This oxygenated blood returns to the left side of the heart in the pulmonary veins.
Oxygenated blood is then pumped from the left side of the heart around the body, and then back to the right side of the heart. This is known as the systemic circulation.
Arteries:
- Direction of blood flow
- Oxygen concentration
- Pressure
- Key structural features
- Valves?
- Away from heart
- Oxygenated (except pulmonary artery)
- High
- Elastic; thick outer walls
- No valves
Veins:
- Direction of blood flow
- Oxygen concentration
- Pressure
- Key structural features
- Valves?
- Towards heart
- Deoxygenated (except pulmonary vein)
- Low
- Elastic; thin outer walls
- Valves
Capillaries:
- Oxygen concentration
- Key structural features
- Valves?
- Oxygen diffuses into capillaries at lungs and out to body cells
- One cell thick- allows rapid diffusion
Stroke volume
Volume of blood pumped from the left ventricle per beat
Heart rate
Number of times the heart beats per minute
Cardiac output
Amount of blood the heart pumps through the circulatory system in 1 min
Blood pressure
The force exerted on the wall of a blood vessel by the blood
What does blood pressure depend on?
- Cardiac output
- Peripheral vascular resistance
Systolic blood pressure
Pressure in the vessels as the left ventricle expels blood into the aorta.
Diastolic blood pressure
When the aortic valve closes
What are the 5 ways in which blood pressure is controlled?
- Diameters of vessels- altered by relaxation or constriction of smooth muscle
- Baroreceptors- maintain BP sitting to standing, slows heart rate
- Blood carried hormones- eg. adrenaline
- Endothelial cells
- Kidney- anti-diuretic hormone, renin-angiotensin balance
What is supine hypotension syndrome?
Why does it occur?
The gravid uterus compresses the aorta and vena cava, thus obstructing the flow of blood circulation.
Hypotension and bradycardia are signs, this happens when a woman lies on her back after 28wks.
Compression is relieved by tilting woman on her LEFT side.
Pregnancy is a ……….. state, with reduced……… activity
pro-coagulant
fibrinolytic (slower breakdown of clots)
How much does blood plasma volume increase by?
40-50%
What happens to the heart?
It enlarges and moves upwards and laterally
What happens to cardiac output and why?
Increases by 30-50%
To accommodate increased blood volume circulating
How much does RBC mass increase by?
20-30%
The increase in plasma volume is greater than RBC mass, what does this result in?….
Haemodilution and an apparent decrease in haemoglobin concentration
How much does heart rate increase by?
10-20%
How much does stroke volume increase by?
10%
How much does peripheral resistance decrease by?
35%
What are 2 functions of pregnancy-induced hypervolemia?
- Increased blood volume facilitates maternal and fetal exchange of respiratory gases, nutrients, metabolites
- The impact of maternal blood loss at birth is reduced
Blood volume increases by…..%
why?
20-50%
flows to uterus, skin, breasts, kidneys
When would you treat a woman for anaemia in 1st trimester?
Hb < 100g/L
When would you treat a woman for anaemia in 2nd/3rd trimester?
Hb < 100g/L
What could be causes of low blood pressure?
- Infection
- Dehydration
- Anaemia
- Heart condition
- Malnutrition
