Blood flow and volume Flashcards
In what 2 ways can blood flow to an area be varied?
- Altering the vascular resistance
- Altering the perfusion pressure
What make up the ‘essential’ organs?
The brain
Coronary circulation
Working skeletal muscle
What is active hyperaemia?
An increase in metabolic rate brings about an increased blood flow
Increased metabolic rate in the cells of the tissue results in …, … and … ?
Increased oxygen consumption
Increased production of waste products including carbon dioxide and lactic acid
Increased potassium outflow from cells
Is oxygen a vasodilator of vasoconstrictor?
Vasoconstrictor
Describe metabolic autoregulation
- intrinsic control of blood flow
- An increase in blood pressure leads to increased perfusion of tissue
- This delivers more oxygen and removes waste products more rapidly which causes vasoconstriction thereby decreasing the perfusion
What is reactive hyperaemia?
- blood flow to an area is completely interrupted
- depletion of oxygen and build up of waste products
- when blood flow is re-established it increased above normal to re-pay the oxygen debt
Give the names of the following:
- reduced blood flow to tissues
- cell damage
- cell death
1 = ischaemia 2 = infarction 3 = necrosis
What are the 3 ways the body tries to limit ischaemia?
- causes pain
- a reflex increase in arterial blood pressure which increases perfusion pressure to the muscle
- reduces the strength of the muscular contraction so the ischaemic exercise cannot be performed
What is paracrine control of blood flow?
Locally acting chemicals which affect the local blood flow in response to the local environment
Increase in blood flow velocity in an area causes endothelial cells to release … ? What is the function of this substance?
Nitric oxide which is a vasodilator
Which systems are able to cope with being compromised for a period of time?
Renal, splanchnic and resting skeletal muscle circulations, and the circulation to bone and skin
What is the role of the medulla oblongata in extrinsic control?
Contains the cardiovascular centre which coordinates the blood flow of the non-essential organs
What does the cardiovascular centre maintain?
Cardiac output and vascular resistance
What is the first system to act in response to changes in blood pressure?
Baroreflex
Describe how the baroreflex works
- Blood pressure is detected by stretch receptors
- These baroreceptors deliver action potentials to the CV centre in response to stretch
- The CV centre compares the information received to its reference value and makes changes as necessary – this response is known as the baroreflex
Where are stretch receptors located?
In the aortic arch and carotid sinuses
In response to a decrease in blood pressure, the response of the baroreflex is … ?
- decreased stretch detected by baroreceptors
- decreased frequency of AP sent to the brain
- CV centre causes increased sympathetic activity
- Increased contractility, heart rate and faster conduction speed
- Vasoconstriction of peripheral blood vessels and dilation of vessels supplying essential organs
- These changes cause increased TPR and CO which raises the arterial blood pressure
What is blood volume detected by?
Stretch receptors in the left and right atrial walls and the large thoracic veins. These are called atrial volume receptors
Which hormone is released in response to the increase in sympathetic activity caused by the baroreflex?
Renin
Where is renin released from?
Cells known as the juxtaglomerular apparatus (JGA)
What is the function of renin?
Renin causes a substance called angiotensinogen to be converted to angiotensin I in the liver
What is the function of angiotensin II?
Angiotensin II causes vasoconstriction, and causes release of aldosterone from the adrenal gland.
What is the function of aldosterone?
Causes the kidney to conserve sodium and water which increases the blood volume
What effect does angiotensin II have on the pituitary gland?
Causes it to release ADH which causes the kidney to conserve water, increasing blood volume, causing further vasoconstriction
What effect does vasoconstriction have on the hydrostatic pressure in capillaries?
Reduces it which favours reabsorption of water from the ISF back into circulation
Long term blood pressure is mediated by which organ?
Kidney
