T3: Circulatory System (cont.) Flashcards
What is the normal blood flow rate of humans?
5L/min
What is the vital function of the cardiovascular system?
Chemical and gaseous exchange between blood and interstitial fluid.
across capillary walls
What is the function of capillaries?
transport gases, nutrients and waste products.
What are the three types of capillaries?
- continuous
- fenestrated
- discontinuous
What is the function of continuous capillaries?
- permit diffusion of water, small solutes and lipid soluble materials into the surrounding interstitial fluid
- prevent the loss of blood and plasma cells
What is the function of fenestrated capillaries?
Exchange of water and solutes (as large as small peptides) between plasma and interstitial fluid.
Where are continuous capillaries located?
all tissues except:
- epithelia
- cartilage
Where are fenestrated capillaries located?
- Kidneys: glomerulus
- GI tract: gut
Where are sinusoidal capillaries located?
- liver
- bone
- spleen
- endocrine glands (pituitary, adrenal glands)
What is microcirculation comprised of?
- arterioles
- capillaries
- venules
- terminal lymphatic vessels
What is a precapillary sphincter? What is its function?
- a circular band of smooth muscle at the entrance to the capillary
- regulates number of perfused capillaries
How do substances pass through the capillary wall?
- diffusion (O2, CO2)
- filtration
- osmosis
What is fluid movement across capillary walls determined by?
- hydrostatic pressure
- osmotic pressure
What is an arteriovenous anastomose? What is its function?
- direct connections between arterioles and venules
- allows blood to bypass the capillary bed and flow directly into the venous circulation
What is the function of capillary beds?
allow gas, nutrient and waste exchange
What is the function of arterioles (in relation to capillaries)?
- regulate capillary hydrostatic pressure
- influence capillary fluid exchange
How do venules play a role in regulating capillary hydrostatic pressure?
Sympathetic innervation of larger venules can alter venular tone which plays a role in regulating capillary hydrostatic pressure.
What is the function of valves?
- keep blood flowing towards the heart
- allow blood flow against the force of gravity
What is the colour of blood flowing through veins? Why?
deep red colour <– lacks oxygen
What is turbulance?
The upset of smooth blood flow caused by:
- high flow rates,
- irregular surfaces
- sudden changes in vessel diameters
which increases resistance and slows the flow of blood.
Where does turbulance usually occur?
- between atria and ventricles
- between ventricles and the aortic/pulmonary tunk
- aorta (high flow rates)
- small vessels (unless the wall is damaged–>plaque –> restricts blood flow)
Is arterial pressure stable?
No!
- rises during ventricular systole
- falls during ventricular diastole
What is a pulse?
The rhythmic pressure oscillation that accompanies each heartbeat.
What is pulse pressure?
The difference between systolic and diastolic pressures.
What is used to report a single blood pressure value?
a MAP (mean arterial pressure)
What is hypertention?
abnormally high blood pressure
What is hypotention?
abnormally low blood pressure
What instrument is used to measure blood pressure?
sphygmomanometer (around arm)
What factors are involved in the regulation of cardiovascular function?
- local factors (AUTOREGULATION: chemical changes in interstitial fluid)
- neural mechanisms (pressure changes or blood gas level changes)
- endocrine mechanisms (releases hormones enhancing short term adjustments and direct long term changes)
What is autoregulation? What does it cause?
causes immediate, localized homeostatic adjustments
State examples of factors promoting autoregulation.
- decreased O2 levels
- increased CO2 levels
- generation of lactic acid
- release of nitric oxide (known as EDRF)
- increased K+
- increased H+
- release of histamine
- elevated local temperatures
EDRF- endothelium derived relaxation factor
What neural centers are responsible for regulatory activities of the cardiac output?
Medulla Oblongata:
- cardiac centers
- vasomotor centers
What does each cardiac center consist of? What are they innervated by?
- cardioacceleratory center (sympathetic innervation)
- cardioinhibitory center (parasympathetic innervation)
What does the neurotransmitter norepinephrine (NE) cause?
- stimulation of smooth muscle cells (arteriole walls)
- vasoconstriction
What neurotransmitter causes vasoconstriction?
norepinephrine (NE)
How do vasodilator neurons function?
- innervate blood vessels in skeletal muscles and brain
- stimulation of vasodilator neurons relaxes smooth muscle cells (arteriole walls)
What is vasodilation triggered by?
appearance of NO in the surroundings
What are the most common vasodilator synapses? What do they release? What does it cause?
Cholinergic:
- releases ACh
- ACh stimulates NO release
- local vasodilation achieved
Nitroxidergic:
- release NO
- local vasodialtion
What do baroreceptor reflexes respond to?
changes in blood pressure
What do chemoreceptor reflexes respond to?
changes in the chemical composition of arterial blood
What are baroreceptor and chemoreceptor reflexes regulated through?
negative feedback loop
Where are baroreceptors involved in cardiovascular regulation located?
- carotid sinuses (regulate blood flow to the brain)
- aortic sinuses (regulate blood flow through the systematic circuit)
What happens when blood pressure falls below normal?
- cardiac output increase (stimulation of heart sympathetic innervation)
- widespread peripheral vasoconsriction (stimulation of sympathetic vasoconstrictor neurons (by vasomotor centers))
What is the function of the antidiuretic hormone (ADH)?
- stimulates water conservation at the kidneys
- prevents a reduction in blood volume (which would reduce blood pressure)
What is the function of the angiotensin II?
- stimulates ADH secretion, Na+ retention, K+ loss, aldosterone production
- stimulates thirst (increased fluid consumption)
- stimulates cardiac output
- triggers vasoconstriction of arterioles
Elevates systemic blood pressure.
- 4-8x more than norepinephrine
What does venous return depend on?
- skeletal muscle action
- respiratory movements
- constriction of smooth muscle in venous walls
Compare the “laminar” and “turbulent” blood flow.
Laminar flow is linear flow, mainly found in the middle of the vessel. Turbulent flow is any disruption in the laminar flow.
