Chapter 30 Flashcards
Hemodynamics
Refers to the numerous mechanisms that influence the dynamics of the circulation of blood
Essential for health and survival
Circulation control mechanisms must:
Maintain circulation
Vary the volume and distribution of blood circulated
Primary principle of circulation
Blood moves, or flows, due to a pressure gradient along its pathway, according to the following principles:
A fluid doesn’t flow when the pressure is the same throughout the system
A fluid flows only when its pressure is higher in one area than in another, and it flows from its higher pressure area to its lower pressure area
Blood flow between any two points in the circulatory system can always be predicted by the pressure gradient
Arterial blood pressure (BP)
BP is the push or force of blood in the blood vessels
Must be highest in arteries, lowest in veins to allow for proper circulation of blood
Arterial BP is directly proportional to arterial blood volume
Main factors determine arterial BP (2)
Cardias output
Peripheral resistance
Cardiac output
The amount of blood that flows out of a ventricle of the heat per unit time
Resting CO2 from the left ventricle
5000ml/min
Co2 influenses
The flow rate to various organs of the body
Cardio output is determined by
The volume of blood pumped out of a ventricle by each beat= stroke volume (SV) and by heart rate (HR)
The great the SV the greater the
CO
CO=
SV x HR
Anything that changes either HR or SV will to to impact
CO
Factors affecting Stroke volume (SV)
Strength of myocardial contractions
- Recall length-tension relationship re: muscle fibre contraction. The more ‘stretched out’ heart muscle fibres are at the beginning of a contraction, the stronger the contraction will be (relative to the amount of blood in the heart – provided it is not ‘hyperextended’) = Starling’s Law of the Heart
- Neurotransmitters
- Hormones
Autonomic nervous system innervation
Sympathetic vs parasympathetic
Cardiac pressoreflexes
control centers that receive information from stretch receptors in the aorta and carotid sinuses. If high BP is detected, a motor message will be sent to the SA-node to decrease HR
Other factors the that influence heart rate and what they as a group are called
Emotions – e.g. anxiety, fear, anger vs grief
Exercise
Hormones
Blood temperature – increased blood temp tends to increase HR
Pain – can result in decreasing the heart fainting
Stress response/Sympathetic NS
All called: Peripheral resistance
Peripheral resistance is
Any force that acts against the flow of blood
Blood viscosity
comes mainly from the proportion of RBCs and partly from blood protein concentration (e.g. polycythemia, anemia, hemmorhage)
Tension in the muscles of the blood vessel walls
Vasomotor mechanism
Vascomotor center located in the medulla can
Stimulate constriction of blood vessels
Vasomotor pressorelexes
the stretch receptors in the aorta and carotid sinuses response to increased BP and messages are sent to inhibit the vasomotor center; and vice-versa
Vasomotor chemoreflexes
same location as stretch receptors; are sensitive to excess carbon dioxide in the blood, as well as low oxygen and decreased arterial pH vasoconstriction
Varying normal range of blood pressure can be affected by
Strenuous exercise, stress increased BP
Fitness level
Age, gender, race, weight
Stress, emotions
Hormones (e.g. renin, angiotensin II, aldosterone, ANH, ADH)
Diseases (e.g. diabetes, CVD)
Tobacco, alcohol, caffeine and other drugs
Feedback mechanisms work to go back to homostasis
Hypertension
Higher than normal blood pressure reading
If BP is too high, it can cause the rupture of blood vessels
Silent killer- no symptoms
Hypotension
Lower than normal blood pressure
If BP is too low, blood may stop flowing
Blood pressure being measured with a
Sphygmomanometer
Central venous pressure
Definition: The venous blood pressure within the right atrium (close to zero!)
Influences the pressure that exists in the large peripheral veins
Strong heart beat blood is entering and exiting the heart effectively low central venous pressure
Weak heart beat is weak flow of blood into the right atrium will be slowed increased/high central venous pressure
Mechanisms that help keep venous blood moving through circulatory system
Continued beating of the heart
Adequate BP in the arteries to push blood to and through the veins
Semilunar valves in veins that ensure blood flow in one direction (towards the heart)
Contraction of skeletal muscles – produces a ‘pumping’ action which squeezes veins
Changing pressures in the chest cavity during breathing also produces a kind of ‘pumping’ action in the veins in the thorax
Pulse
Alternate expansion and recoiling of an arterial vessel wall
Possible due to pressure changes within arteries and the elasticity of arterial walls
Provides info re: the cardiovascular system, blood vessels, and circulation (e.g. rate, strength and rhythm of heart beat
Nine major pulse points
