MMED1005 Lecture 23: Week 11 lecture 2
7 Jun 2018
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Cardiovascular system IV: blood flow and blood pressure
Learning objectives:
- Define blood flow, blood pressure and resistance and explain the relationships between
these factors
- Explain how blood flow is regulated in the body
- Explain the difference between systolic, diastolic and mean arterial blood pressure
- Explain how blood pressure is measured using a sphygmomanometer
- Describe how blood pressure is regulated in the short-term
Main points:
- Blood flow = P/R
- Mean arterial blood pressure is dependent upon CO and SVR (and CVP)
- CO is strongly influenced by changes ins systemic vascular function
- Arterial pressure changes are sensed by baroreceptors that signal changes in the autonomic
nervous system, resulting in blood pressure being restored to normal levels
find more resources at oneclass.com
find more resources at oneclass.com
Blood flow:
- Definition: volume of blood flowing through a vessel, an organ or the entire circulation in a
given period of time
- In the entire circulation, blood flow is equal to the cardiac output (relatively constant at rest)
- Blood flow through individual organs can vary depending upon need
Blood flow through vessels:
- Blood vessels have a layer of endothelial cells which are in direct contact with the blood
- Blood is moving through the lumen of the vessel, moving parallel to the wall of the blood
vessel – alled laiar flow
- Endothelial cells try to minimise friction but still slows down a little despite this
Blood flow through tissues:
- Blood flow (tissue perfusion) is involved in:
o Delivery of O2 and nutrients to, and removal of wastes from, tissue cells
o Gas exchange (lungs)
o Absorption of nutrients (digestive tract)
o Urine formation (kidneys)
- Rate of flow is precisely the right amount to provide for proper function
Blood flow through organs:
- A percentage of the cardiac output will flow through individual organs
- Most major organ systems are in parallel with each other so that blood flow in one organ
has relatively little influence on blood flow in another organ
- The diagram shows that there is a percentage of blood being ejected from the heart. Think
of this as the total volume of blood. A percentage of this moves to each of the individual
organs (kidney, digestive system, etc.). they are arranged parallel with each other. this
means that if for example you need to increase amount of blood flow to the skeletal muscle,
it doest hage, for example, the blood flow to the brain.
- The rate of blood flow can also vary depending upon need
o for example, during exercise flow to skeletal muscle can increase 10-fold during
exercise
Velocity of blood flow:
- definition: distance per unit time with which blood flows through a given segment of the
circulation
- it is inversely related to the total cross-sectional area
- it is fastest in the aorta, slowest in the capillaries, increases again in veins
- slow capillary flow allows adequate time for exchange between blood and tissues
Blood pressure: (BP)
- force per unit area exerted on the wall of a blood vessel by the blood:
o expressed in mm Hg
o measured as systemic arterial BP in large arteries near the heart
- the pressure gradient provides the driving force that keeps blood moving from higher to
lower pressure areas
Resistance: (peripheral resistance)
- opposition to flow
- measure of the amount of friction blood encounters
- generally encountered in the peripheral systemic circulation
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Cardiovascular system iv: blood flow and blood pressure. Define blood flow, blood pressure and resistance and explain the relationships between these factors. Explain how blood flow is regulated in the body. Explain the difference between systolic, diastolic and mean arterial blood pressure. Explain how blood pressure is measured using a sphygmomanometer. Describe how blood pressure is regulated in the short-term. Mean arterial blood pressure is dependent upon co and svr (and cvp) Co is strongly influenced by changes ins systemic vascular function. Arterial pressure changes are sensed by baroreceptors that signal changes in the autonomic nervous system, resulting in blood pressure being restored to normal levels. Definition: volume of blood flowing through a vessel, an organ or the entire circulation in a given period of time. In the entire circulation, blood flow is equal to the cardiac output (relatively constant at rest) Blood flow through individual organs can vary depending upon need.
