BLOOD PRESSURE AND CARDIAC OUTPUT - Coggle Diagram
BLOOD PRESSURE AND CARDIAC OUTPUT
: Blood Pressure is the force blood exerts on the artery wall. Reflects: How compliant the arteries are. The volume of blood forced into them. Blood moves forward because the pressure in the aorta is higher than pressure in distal arteries.
FUNCTIONS OF BLOOD PRESSURE:
Blood pressure pushes blood through blood vessels. Filtration of blood in the kidneys. Drives capillary exchange between blood and cells (gas exchange).
MEASUREMENT OF BLOOD PRESSURE:
is the higher pressure measured during left ventricular systole.
is the lower pressure measured during left ventricular diastole.
Mean arterial pressure
is a calculation to check if there is enough blood flow, resistance and pressure to supply blood to all the major organs.
Factors that effect BP:
Peripheral resistance. Blood vessel diameter. Blood viscosity. Blood vessel length. Cardiac output.
The opposition to blood flow.
Caused by friction between blood and vessel wall. Most resistance in arterioles in peripheries. Narrower vessels have higher resistance.
BLOOD VESSEL DIAMETER:
Blood vessel diameter is the most important influencer on BP. Changes frequently. Aorta has little resistance due to minimal diameter changes. Arterioles are the major influencer on peripheral resistance.
Viscosity is the thickness of blood. Increased blood viscosity increases BP. Dehydration increases BP. Haemorrhage or low levels of plasma proteins lowers BP.
TOTAL VESSEL LENGTH INFLUENCES BP
: The longer the blood vessel the greater resistance.
Cardiac output (CO) is the amount of blood pumped out by a ventricle in one minute. Cardiac output must be adequate to maintain homeostasis. Stroke volume is the volume of blood ejected from one ventricle every beat.
CO = SV x HR
FACTORS THAT AFFECT STROKE VOLUME:
- The amount of blood in the ventricle before it contracts, also knows as end diastolic volume.
- The resistance that ventricles must overcome to circulate blood.
- How strongly the ventricle can contract.
The cardiac centre in the medulla oblongata controls the rate and force of the heart contraction. The vasomotor centre in the medulla oblongata controls the diameter of blood vessels.
ROLE OF THE VASOMOTOR CENTRE:
stimulates smooth muscle in walls of arterioles to constantly maintain tone. Increase in sympathetic stimulation leads to vasoconstriction & raises BP.
of veins reduces the volume of blood in veins. This blood is pushed towards the heart – venous return increases.
Baroreceptors are in: Carotid arteries. Aortic arch. Other large arteries in the neck & thorax. Baroreceptors are pressure receptors that respond rapidly to maintain homeostasis during short-term or acute changes in the blood pressure.
ROLE OF BARORECEPTORS IN RAISED BP:
Baroreceptors stretched with increased BP, send impulses to cardiac and vasomotor centres
Sympathetic NS stimulation reduced
Arterioles Dilate (PVR lowered)
CO and MAP decrease -> Parasympathetic stimulation of heart reduced HR and force of contraction
Veins Dilate- increasing blood reservoir, VR and CO fall.
ROLE OF BARORECEPTORS IN LOW BP:
Baroreceptors send less impulses to vasomotor and cardiac centres
Sympathetic NS fired to increase HR, vasomotor system sends messages to vessels
HR increased, therefore CO increased
Arterioles vasoconstrict, increasing PVR and BP
Veins constrict which increases Venous return
SV, CO and therefore BP increase.
in carotid and aortic bodies, as well as vasomotor centres detect changes in CO2, O2 and H+. When O2 drops, CO2 increases and/or pH drops, sympathetic impulses are dominant leading to increased heart rate and stroke volume and constricts reservoir vessels in response.
ROLE OF ADRENALINE AND NORADRENALINE
: Adrenaline and noradrenaline are released in emergency situations. These are hormones which enhance the response of the sympathetic nervous system. They raise blood pressure by - increasing heart rate and force of contraction. Constricting many arterioles. Increasing venous pressure.
THE RENAL SYSTEM AND BP:
Blood volume is a major determinant of cardiac output.The kidneys control blood volume by increasing urine output when blood volume is higher. RAAS- changes blood plasma volume. ADH and RASS tend to increase water retention and increase total plasma volume. ANP antagonises mechanisms by promoting water loss and decrease in total plasma volume.
AGE RELATED CHANGES:
1. Decreased compliance of the aorta. 2. Loss of cardiac muscle size & strength
decreased cardiac output. 3. Increase in systolic BP. 4. Increase in total blood cholesterol. 5. Increase in coronary artery disease (major cause of death)