Flashcards in Module three - The Circulatory System Deck (28):
What is the overall purpose of the cardiovascular system?
To provide adequate blood flow to all tissues/ organs according to their immediate needs.
What are the three tunics called?
intima, media and externa
Vessels with specific structures for specific functions
Elastic arteries: conducting vessels
Muscular arteries: distributing vessels
Arterioles: resistance vessels
Capillaries: exchange vessels
Venules and veins: capacitance vessel
What determines the dynamics of circulation?
Blood flow, blood pressure and resistance
What is bood flow?
The volume of blood flowing through a vessel, organ or the entire circulation in a given time period. It is determined by blood pressure and resistance
What is blood pressure?
The force exerted on a vessel wall by the blood in that vessel. expressed in mmHg. It is the force generated by the pumping of the heart that keeps blood moving (maintains blood flow)
What is resistance?
Opposite to blood flow. A measure of the amount of friction blood encounters as it flows through a vessel. There are three types of resistance.
What are the three types of resistance?
Blood viscosity, total blood vessel length and blood vessel diametre.
What does viscosity refer to?
The thickness or stickiness of a fluid, due to formed elements (cells) and plasma proteins.
How does vessel length change resistance?
resistance to flow increases as the vessel length increases.
How does vessel diametre affect resistance?
The amount of contact between two surfaces determines the amount of friction - friction determines ease of movement.
The more contact the blood has with the walls of the vessel, the more friction between the blood and the vessel wall = more resistance.
As diametre changes, the degree of resistance to blood flow changes, depending on how much of the blood is contacting the vessel walls
What is the primary means of altering local blood flow?
Changes in arteriole diametre.
vasoconstriction: decreased diametre - increased resistance - decrease blood flow.
Vasodialation: increase diametre - decrease resistance - increase blood flow.
How is blood flow determined? (equation)
What is sytemic blood pressure?
the pumping action of the heart generates pressure, which in turn drives blood. Highest in the aorta, lowest i venae cavae/ veins
What is arterial blood pressure?
Reflects two factors;
1. how much elastic arteries can be stretched
2. the volume of blood forced into the elastic arteries by ventricular contraction i.e. stroke volume
Two types of arterial BP (systolic and diastolic)
What are the two types of arterial blood pressure?
Systolic pressure: peak pressure generated in large arteries when the ventricles contract (average 120mmHg)
Diastolic pressure: pressure in large arteries during ventricular relaxation (average 80mmHg)
What is pulse pressure?
PP= systolic pressure- diastolic pressure. i.e. 120-80 = 40mmHg. Felt as throbbing sensation in the artery, declines with increasing distance from heart
What is mean arterial pressure?
MAP = the pressure that propels blood through the vessels.
MAP = diastolic pressure + (1/3 X pulse pressure)
= 80+ (1/3 X 40)
What is hypotension?
Systolic pressure is below 100mmHg. May result in dizziness and fainting
What is hypertension?
transient elevation due to exercise, illness, or emotional states. Chronis hypertension is sustained systolic pressure above 140mmHg: major cause of heart failure, vascular disease and stroke.
What is capillary blood pressure
Blood pressure in capillaries. ranges from 35mmHg in the arterial end of capillary bed to 15mmHg at venous end.
** Low capillary pressure is required due to fragile capillary walls and the permeability of capillaries, so low pressure is adequate for fluid exchange
What is venous return?
involves numerous factors:
1. valves (compartmentalise blood to move it and prevent backflow)
2. muscular pump (muscle contraction squeezes veins = pushes blood)
3. respiratory pump (squeezing of abdominal veins as thoracic veins expand... helps blood move toward heart due to pressure changes)
4. Pulsation (in nearby arteries)
5. Venoconstriction (tunic media)
What are the factors that influence blood pressure?
1. cardiac output (rapid, short term regulation)
2. Peripheral resistance (rapid, short term regulation)
3. Blood volume (slower, long term regulation)
How is blood pressure regulated?
1. autoregulation: occurs within tissues and is dependent on local conditions
2. neural regualtion: involves cardiovascular centres and ANS
3. renal mechanisms
4. endocrine regulation
How does local regulation (autoregulation) of blood flow occur?
tissues can regulate their own blood flow and pressure in response to local conditions by:
1. altering arteriole diametre
2. opening or closing pre-capillary sphincters (alters blood flow into capillary beds)
What is neural regulation?
the brains control of cardiovascular activity. three centres:
1. cardioinhibitory centre
2. cardioaccelatory centre
3. vasomotor centre
Located in medulla oblongata.
Input from hypothalamus includes:
- regularion of blood flow by maintaining temp.
- fight or flight initiation.
What is the vasomotor centre?
in medulla oblongata and involved in neural regulation.
sympathetic vasomotor fibres to the smooth muscle of arterioles - changes in vasomotor tone - changes in vessel diametre