CO and blood flow Flashcards
(38 cards)
What organs ALWAYS receive blood even at the expense of other organs/
Brain and heart
Name the various mechanisms that exist to match blood flow to demand
- special receptors
- metabolic controls
- oxygen deficiency
- nitric oxide
- long term control mechanisms
How do special receptors work to match blood flow to demand?
Skeletal muscle arterioles dilate in response to moderate levels of adrenaline
How does metabolic control contribute to blood flow?
Diffusion of metabolic products e.g. adenosine, lactate, Co2, K+ from active cells causes vasodilation
How does nitric oxide contribute to blood flow?
Shear stress from increased blood flow in arteries and arterioles causes their lining endothelial cells to release EDRF which leads to vasodilation
What are some the longer term control mechanisms that exist to regulate blood flow?
Capillary density changes (certain organs can grow more capillaries e.g. skeletal muscle. Muscle mass increases, so oxygen demands increase, capillaries are grown to match the demand)
What is autoregulation?
The intrinsic ability of an organ to maintain a constant blood flow despite changes in BP
What are the two mechaisms of autoregulation?
Metabolic and myogenic
Describe the metabolic mechanism
Diffusion of metabolic products (e.g. adenosine, lactate, Co2, K+) from active cells causes vasodilation
oxygen removal from blood by active cells reduces local blood oxygen, also leading to vasodilation
Describe the myogenic mechanism of autoregulation
Stretch induces a reflex in vascular smooth muscle constriction (prominent in the arterioles).
The muscles can recoild/dilate/restrict to maintain the BP of the vessels they surrounde/supply
Does not require SNS or metabolic input and is a rapid mechanism for larger arteries and arterioles
How much can autoregulation adjust BP by?
Up to 100mmHg
Total systemic blood flow is the sum of all blood flow to organs ONLY IF….
1: organ circulations are arranged in parallel
2: CO is the sum of all organ blood flows
if systemic blood flow increases or decreases, what happens to the blood flow to the brain?
Nothing. it stays the same. Percentage of overall flow may be different but the raw value always stays the same
What is vasomotion?
Blood flow regulation at the tissue level.
Rhythmic distribution of blood flow in a tissue driven by changes in metabolism
What is a mechanism that exists to regulate capillary blood flow (e.g. when skeletal muscles ar at rest and capillary flow only acts to meet nutrient demand)
Pre-capillary sphincters
What are the three variables relating to stroke volume that can be altered?
Preload, afterload and contractility
What is preload? Why is it relevant?
Preload is the amount of blood that fills the heart before it contracts.
Why does increasing sarcomere length increase the tension of the next contraction?
Placing the sarcomere under more tension increases the sensitivity of troponin C to Ca2+
In other words it increases the efficiency of E-C coupling in cardiomyocytes
What is preload proportional to?
the volume of the ventricle at the end of diastole (EDC)
What does a high EDV lead to?
increased cardiomyocyte stretch and increased force of contractionQ
What is the Frank-Starling mechanism?
If venous return increases, stroke volume and therefore CO, increases to match
How can you increase venous return e.g.during exercise to maintain a higher CO
Skeletal muscle pump: contraction of muscles helps to squeeze the veins and propel blood back to the heart
Respiratory pump: inhalation moves the diaphrgam and causes the vena cava to constrict.On exhalation, the vena cava relaxes
What is afterload?
The pressure the heart has to work against during ejection.
It is analagous to the force that a skeletal muscle works against when it shortens
What is the law of LaPlace? How does it apply to ventricles?
Wall stress = pressure x radius / 2 x wall thickness
Ventricular muscle is roughly a sphere shape, s the force it has to oppose when contracting is the wall stress
