Lecture 10 Flashcards
What are two major functions of arteries?
- rapid transit passageways for blood from the heart to the tissues
- a pressure reservoir to provide the driving force for blood when the heart is relaxing
What is the structure of arteries?
- wide
- total cross-sectional area is lower than those of the downstream arterioles and capillaries=so blood can travel faster there
What are the tissue layers in arteries?
- endothelial lining
- thick smooth muscle layer
- collagen and elastin
What is the purpose of elastin and collagen fibres arteries?
elastin-elasticity so the walls behave like a ballon
collagen- tensile strength against the high pressure of blood ejected from the heart
What is the main function of arteries?
passageway from heart to organs serve as pressure reservoir
What are the tissue layers in arterioles?
- highly muscular, well innervated walls small radii
- less smooth muscle than arteries
- some connective tissue= mainly collagen almost no elastin
What is the main function of arterioles?
- primary resistance vessels, determine distribution of cardiac output
- variably distribute the cardiac output among the systemic organs depending on the body’s needs
- to help regulate bodywide arterial blood pressure
What are the tissue layers in capillaries?
- very thin walled, large total cross sectional area
- only endothelial layer (+basement membrane as all of them have= all the tubes)
What is the main function of capillaries?
- site of exchange, determine distribution of extracellular fluid between plasma and interstitial fluid
- diffusion into interstitial fluid
What are the tissue layers in veins?
- thin walled compared to arteries, highly distensible= can be stretched, large radii
- smooth muscle with collagen= not very elastic
What is the main function of veins?
-passageway to heart from organs, serve as blood reservoir
What is the main driving force of blood flow in arteries?
- mean pressure=average pressure responsible for driving blood forward
- not halfway between diastolic and systolic
- as 2/3 are spent in diastole and 1/3 in systole
What do arteries do in systole?
they stretch to accommodate the extra blood
What do arteries do in diastole?
-the smooth muscle naturally flexes back (elastin) as less blood is in arteries then
3What is the pressure in arterioles in comparison to the arteries?
-much lower and arterioles convert the pulsating blood into steady flow
What are the metabolic factors in vaso-regulation?
O2-decreased, during exercise= local concentration drops=relaxation of smooth muscle=more flow
CO2-increased when increases activity=relaxed smooth muscle of arterioles
pH-increased acid-more as exercise more=relaxation of smooth muscle
K+-increase= more K during exercise as Na/K+ pump can’t keep up= relaxation of arteriole smooth muscle
What are the chemical factors in vaso-regulation?
adenosine-release when increased activity= relax arteriole smooth muscle=more flow
prostaglandin-
NO-causes vasodilation by inducing relaxation of arterial smooth muscle
histamine-released by local immune cells when injured=increase in blood flow to the are= relax smooth muscles
What are the physical factors in vaso-regulation?
hot-vasodilation
cold-vasonstriction
stretch-more stretch= vasoconstriction, less stretch= vasodilation
What are the autonomic nervous innervation factors in vaso-regulation?
-sympathetic nerve influence
NE -vasoconstriction
What are the hormonal factors in vaso-regulation?
vasopressin-
angiotensin II-
adrenalin-vasodilation
What is total peripheral resistance?
- how dilated arterioles are
- many factors determine the constriction and dilation
How fast is the blood in capillaries in comparison to all the other blood vessels?
-the slowest
What is the total cross sectional area of capillaries in comparison to other blood vessels?
-largest, there are so many of them! billions!
What is capillary blood pressure?
- the hydrostatic pressure exerted by blood in the inside of the capillary wall
- forces the fluid out
- lower mean blood pressure here
What is plasma colloid osmotic pressure?
- force caused by the colloidal dispersion of blood proteins, it arises as the plasma proteins remain in the plasma and don’t cross into the interstitial fluid
- thus there is osmotic difference causing water movement from the interstitial fluid into the capillaries by osmosis
What is interstitial fluid hydrostatic pressure?
-the fluid pressure exerted on the outside of the capillary wall by the interstitial fluid, this pressure tends to force fluid into capillaries
What is the interstitial fluid colloid osmotic pressure?
-results from the small fraction of plasma proteins that leak across the capillary walls into the interstitial fluid (normally returned to the blood via the lymphatic system), this protein concentration is very low= so this pressure close to zero can change when proteins leak in= like histamine=promotes fluid moving into capillaries
How does blood flow increase in veins?
- as the blood gets closer to the heart the overall cross sectional area decreases so the flow increases
Why are veins so stretchable?
- collagen and not much elastin=stretch easily
- smooth muscle doesn’t have myogenic tone= easily stretched
How are veins the blood reservoir?
- when demand for blood low, blood stays in veins that can stretch a lot
- in rest conditions veins have 60% blood in a body
What is venous return?
venous return=volume of blood entering each atrium per minute
How is venous return affected by sympathetic activity?
-sympathetic stimulation = tone in smooth muscle= vasoconstriction= increase in venous pressure= drives more blood to the atrium(as atrium has lower pressure)
How is venous return affected by musculo-skeletal activity?
-many large veins in the extremities lie between skeletal muscles so when those contract= veins compressed=decrease in venous capacity and increase in venous pressure = squeezing the blood towards the heart= skeletal muscle pump
How is venous return affected by venous valves?
- large veins have one way valves which permit blood to move towards the heart but prevent it from moving back
- helps defeat gravity as well
How is venous return affected by respiration?
- respiration brings pressure within body cavity below atmospheric pressure so pressure gradient between the lower veins (atmospheric pressure) and chest veins (less than atm pressure)
- increase respiration =enhance venous return during movement
How is venous return affected by cardiac suction?
- heart sucks the blood in enhancing venous return
- minor effect in venous return
What are the functions of the lymphatic system?
- reabsorb the interstitial fluid and return it to blood as more is filtered out of the capillaries than is reabsorbed
- immune system
- fat metabolism
What does the lymphatic system consist of?
one way vessels to return interstitial fluid to the blood
-at first called initial lymphatics and then lymphatic vessels
What is lymph?
-interstitial fluid when in a lymphatic vessel
movement assisted by skeletal muscle and lungs
What are lymph nodes and why are they important?
- in the lymphatic system
- passage of the fluid important for immunity and absorption of fat from digestive tract
Which blood pressure regulated by baroreceptors and what are they?
-the arterial pressure is controlled by those,
they are located in the aortic arch and carotid sinus
-sensitive to change in mean arterial pressure and pulse pressure
What do the baroreceptors in the carotid sinus do?
- in vessels leading to the brain
- information about arterial blood pressure
What do the baroreceptors in the aortic arch do?
- information about arterial blood pressure
- in the major arterial trunk before it gives off branches that supply the rest of the body
What is the cardiovascular control center?
- in the medulla
- can regulate cardiac output and arterial resistance
- integrator= receives input from sensors
Does blood viscosity affect arterial pressure?
- yes
- viscosity is the number of red blood cells and how many proteins
