Introduction to CVS Flashcards
Why do we need a cardiovascular system?
All living cells are metabolically active so they use O2 and produce CO2
Single-celled or tiny organisms can get O2 and nutrients directly by diffusion from environment
Larger organisms need a system for getting the
oxygen and nutrients close to the cells
The heart needs a blood supply. What are the consequences of blocked heart vessels that supply the heart with oxygen?
The left ventricle is filled with oxygenated blood
BUT - The distance of the cells from the source of O2 and nutrients means that the muscle wall of the left ventricle will be seriously damaged if the vessels supplying it are blocked
Where does diffusion take place? Why is that place suitable for diffusion?
The cardiovascular system carries oxygen and nutrients to the capillaries to allow diffusion to take place
Capillaries are composed of a single layer of endothelial cells surrounded by basal lamina
What three factors affect diffusion in the cardiovascular system?
1) Area available for exchange (the bigger, the better)
2) Diffusion resistance (Nature of the molecule, the barrier, the path
length)
3) Concentration gradient
Explain how the area for diffusion affects the rate of diffusion.
Area for exchange between capillaries and tissues is generally
very large
– it depends on capillary density
A tissue which is more metabolically active will have more
capillaries
– And a Higher capillary density means faster rate of diffusion
Explain how the concentration gradient affects the rate of diffusion.
What affects the concentration of O2 and nutrients in tissues?
The larger the conc grad, the faster the rate of diffusion.
If a tissue is more metabolically active, the higher the blood flow. The blood flow must reach the metabolic needs of the tissue.
A substance which is used by the tissues will have a lower concentration in capillary blood than arterial blood
How much lower depends on
– rate of use by the tissue
– rate of blood flow through the capillary bed
The lower the blood flow, the lower the capillary concentration
Blood flow must be high enough to maintain a sufficient concentration gradient
The rate of blood flow determines the concentration gradient driving O2
diffusion into the cells
What are the 3 principles of supply and demand?
Blood flow must match the tissues’ metabolic needs
– the higher the rate of metabolism the greater the demand for O
– increases in metabolism must be met by increases in blood flow
– the rate of blood flow is known as the perfusion rate
What are the main tissues that require constant blood flow? And briefly explain why.
Brain and kidneys
Lack of or reduced blood flow could lead to loss of conscienceness and eventually death of neurons in the brain.
The kidneys’ function is dependent on a constant blood supply, so interruptions in the blood flow to the kidneys may result in tissue death and loss of kidney function.
Kidney function is highly dependent upon sufficient blood pressure in the glomeruli.
The arteries and arterioles that provide blood flow to the kidneys must maintain sufficient blood flow to
1) keep the tissues of the kidneys alive
2) maintain sufficient blood pressure to allow wastes to be separated from the blood.
Interruption of the blood flow through one of the segmental arteries or their branches results in kidney infarction and kidney failure where kidney tissue dies and ceases to function. Interruption of the blood flow to the entire kidney results in kidney failure.
Outline some tissues that require blood flow and explain when it is required more or less.
Brain needs high, constant flow
– 0.5 ml.min-1.g-1
Heart muscle needs high
flow which increases during exercise
– 0.9 to 3.6 ml.min-1.g-1
Kidneys need high, constant flow
– 3.5 ml.min-1.g-1
Blood flow to skeletal muscle can be very high during exercise and gut blood flow is high after a meal
What is the difference between blood flow at rest and during exercise?
Blood flow must adjust to meet requirements so at rest, total blood flow is about 5 l.min-1.
During exercise, this can rise to 25 l.min-1
What is the structure and function of the pericardial sac?
The pericardium is a double-walled sac containing the heart and the roots of the great vessels.
The pericardial sac has two layers, The inner serous layer and the outer fibrous layer.
It encloses the pericardial cavity which contains pericardial fluid.
It is also attached to the diaphragm and great vessels.
What are the layers of the pericardium?
The fibrous layer
The outer serous layer (Parietal layer)
Pericardial cavity
The Inner Serous layer (Visceral Layer/Epicardium)
Myocardium (Heart Muscle)
Why is there fluid present in the pericardium? What is the consequence of excess fluid?
Pericardial fluid is the serous fluid secreted by the serous layer of the pericardium into the pericardial cavity.
There is normally only a very thin film of fluid.
The pericardial fluid reduces friction within the pericardium by lubricating the epicardial surface allowing the membranes to glide over each other with each heart beat.
If excess fluid builds up relatively rapidly this can compress the heart due to the inextensible fibrous pericardial layer
Compression of the heart can lead to cardiac tamponade which means the heart cannot relax and fill at diastole.
Fluid may need to be removed for testing or to relieve compression
– pericardiocentesis
Where is the transverse pericardial sinus?
What is the significance of it?
It is the passage between the aorta and pulmonary artery anteriorly and the superior vena cava posteriorly.
It can be used to pass ligature during cardiac surgery.
Where is the oblique sinus?
What is the significance of it?
The cul-de-sac sinus, enclosed between the limbs of the inverted U of the venous mesocardium lies posterior to the left atrium and is known as the oblique sinus.
