Blood flow and pressure Flashcards
Blood flow is defined as the volume of blood that flows through any tissue in a given time period.
The total blood flow is called the cardiac output (volume of blood that circulates through systemic blood vessels each minute).
The formula to calculate cardiac output is…?
Cardiac output = stroke volume x heart rate
Name some factors that affect blood pressure (4).
- cardiac output
[an increase in heart rate or stroke volume increases cardiac output which leads to an increase in blood pressure] - blood volume
- vascular resistance
- elasticity of arteries
Describe systolic or diastolic blood pressure.
Systolic blood pressure is the highest pressure attained in the arteries during systole.
Diastolic blood pressure is the lowest pressure attained in the arteries during diastole.
Factors affecting vascular resistance?
- size of blood vessel lumen
- blood viscosity
- total vessel length
(these can be influenced by factors such as polycythemia or obesity)
Venous return (volume of blood flowing back to the heart through systemic veins) occurs through…?
- pressure generated by left ventricular contractions
- skeletal muscle pump
- respiratory pump
Blood velocity is inversely related to the total cross-sectional area of blood vessels. Where does blood flow slowest in the cardiovascular system?
Capillaries
(the slow rate aids the exchange of materials between blood and interstitial fluid)
Circulation time is the time required for a drop of blood to pass from the right atrium, through the pulmonary circulation, back to the left atrium, through the systemic circulation down to the foot, and back again to the right atrium. What is the average circulation time in a resting person?
1 minute
Blood pressure and blood flow are controlled by adjusting the heart rate, stroke volume, systemic vascular resistance, and blood volume.
This is done through 4 interconnected negative feedback mechanisms. What are they?
- Cardiovascular centre
- Nervous system
- Hormones
- Auto regulation
Input into the cardiovascular centre (a group of neurons in the medulla oblongata) comes from the higher brain regions and also three sensory receptors. What are these receptors?
- proprioceptors (monitor joint/muscle movements)
- baroreceptors (monitor blood pressure)
- chemoreceptors (monitor chemical concentrations)
Do parasympathetic impulses (from the cardiovascular centre) increase or decrease heart rate?
Decrease
Do sympathetic impulses (from the cardiovascular centre) increase or decrease heart rate?
Increase
Baroreceptors are pressure-sensitive sensory neurons located in the aorta, internal carotid arteries, and other large arteries in the neck/chest.
They monitor the stretching of the walls of blood vessels and the artia.
There are two main baroreceptors reflexes…
- carotid sinus reflex - maintains normal blood pressure in the brain
- aortic reflex - maintains general systemic blood pressure (initiated from the arch of the aorta)
Chemoreceptors are sensory receptors that monitor the chemical composition of blood and are located close to the baroreceptors of the carotid sinus and arch of aorta.
Their main function is to detect changes in blood levels of O2, CO2 and H+ which provides input to adjust breathing accordingly.
Several hormones help regulate blood pressure and flow. How do they do this?
(Renin-angiotensin-aldoserone system; epinephrine/norepinephrine; ADH [antidiuretic hormone]; and ANP [antrial natriuretic peptide]
- alter cardiac output
- change systemic vascular resistance
- adjust total blood volume
Auto regulation is the ability of a tissue to automatically adjust its own blood flow to match its metabolic demand for the supply of oxygen and nutrients, and the removal of wastes.
What are the 3 stimuli that cause autoregulatory changes?
- Physical changes (e.g. warming/cooling)
- Vasodilating and vasoconstricting chemicals (e.g. lactic acid, histamines)
- Changes in oxygen level