2B Flashcards
Describe veins
- take blood towards the heart
- drains blood from capillaries
- has a larger lumen than arteries
- has valves
-collapses when not filled
-has largest amount of blood in the systemic veins
-defined by size (small, medium, large, small arteries and arterioles)
Describe arteries
- moves blood away from heart
- smaller lumen than veins
- retains shape/ stays open when empty
- vessels with highest bp
- thickest vessels with large amounts of elastic fiber and smooth muscle
Why are arteries made of large amounts of elastic fibers and smooth muscle
allows for vasoconstriction
What is vasoconstriction
- shrinking of the lumen
What is vasodilation
-growing of the lumen
What are the three types of arteries?
- elastic (aorta)
- muscular (coronary)
- arterioles
What does the tunica intima do?
has protrusions that form valves and prevent backflow
What are capillaries?
smallest blood vessels with a thin narrow wall (endothelium) that supports the exchange of materials between the body and blood
Where do CO2 and O2 go
they diffuse through the capillaries
Describe continuous capillaries
- lining of the endothelial cell is complete around the lumen (no openings)
- basement membrane is complete
- intercellular clefts between endothelial cells
- least leaky
- most common type
Describe fenestrated Capillaries
- same as continuous capillary but contains fenestrations
- somewhat leaky
- acts as a filter
- found in most endocrine organs, kidneys, small intestines
Describe Sinusoid capillaries
-the lining of the endothelial cell is incomplete around the lumen
- basement membrane is incomplete or absent
- most leaky
- found in red bone marrow, liver, spleen, some endocrine organs
How do capillary beds work?
-most follow a simple pathway where blood enters the capillary bed from an arteriole and is drained by a venule
-blood enters the capillary bed from an arteriole
through metarteriole, the proximal part is encircled by the scattered smooth muscle cells and the distal part forms the thoroughfare channel which has no smooth muscle cells and leads to venules
What is a true capillaries?
capillaries that branch from the metarteriole and thoroughfare channel and makeup most of the capillary bed
What do precapillary sphincters do?
- control blood flow through the capillaries perfusing the tissues when open
- cycle through contraction and relaxation phases called vasomotion with approx. 25%of capillary beds open at any given time
What is vasomotion?
alternating between contraction and relaxation
When does blood go to the true capillaries?
when the precapillary sphincter is relaxed
How do alternative pathways of circulation differ from simple pathways?
-differ in the number of arteries, capillaries, or venules that serve organ/region
What are the types of anastomosis?
-venule
-arteriole
-arteriovenous
What is venule anastamoses?
-multiple veins collectively drain into a single body region
- most common type
- basilic, brachial, cephalic
What is arteriole anastomosis?
multiple arteries converge into a single body region
What is arteriovenous anastomosis?
- shunt
- moves blood directly from an artery to a vein bypassing the capillary bed
What is a portal system?
when blood flows through two capillary beds connected by a portal vein
- ex hypothalamic-hypophyseal portal system
What determine venous return of blood to the heart?
-pressure gradients
- assisted by two pumps (skeletal muscle pump and respiratory pump)
- low with a small gradient (20 mm HG)
-non-pulsatile ( remains constant)
How does the skeletal muscle pump work?
- as muscles contract veins are squeezed
- blood is pushed and valves prevent backflow (muscle sends blood both ways but valves make it only go to the heart)
- blood is moved quickly during excercise
- blood pools in leg veins with prolonged inactivity
How does the respiratory pump work?
- assists venous return in thorax
- in inspiration: diaphragm contracts so abdominal pressure increases and thoracic pressure decreases
- blood in abdominal veins is driven toward the thoracic cavity
- in expiration diaphragm releases so that thoracic pressure increases while abdominal pressure decreases
- blood in thoracic veins is driven towards the heart
- blood in lower limbs allowed into abdominal veins
- gives larger volume in thoracic cavity during inspiration
What is the relationship between volume and pressure?
increased volume= increased pressure
What is total cross-sectional area?
- the sum of diameters of all vessels of a certain type (artery, capillary, vein)
- collectively cross-sectional area of capillaries is largest because there are so many capillaries
How is blood flow velocity related to cross-sectional area?
-inversely related, blood flow is slow in capillaries allowing for exchange between blood and fluid tissue
What is bulk flow?
the movement of large amounts of fluids and dissolved substances along a gradient
- 15% of remaining materials remain in tissues and are picked up by the lymphatic system
- 55% of materials are reabsorbed
What do negative arrows on the picture represent?
more going out than going in
What is net hydrostatic pressure?
pushes blood out
What is net colloid osmotic pressure
- pushes blood in
What is net filtration?
- net hydrostatic- net coloid
What does negative net filtration mean?
reabsorbtion
What does positive net filtration mean?
filtration
What is myogenic response
- smooth muscle in artery/ arteriole wall responds to changes in bp to keep local flow relatively constant
- we want amount of blood going into the tissues to be constant regardless of bp
What is the relation chip between bp, circumference and bloodflow
- all are positively correlated
What happens if systemic bp rises?
there is an increase in blood flow
- as more blood moves into the arteriole its wall will stretch and smooth muscle in the arteriole wall will respond by constricting
- increased pb = vasoconstriction, decreasing blood flow and returning it to normal levels
What happens if bp lowers?
- there is a decrease in blood flow
- as less blood moves into arterioles there is a decreased stretch and smooth muscle relaxes (vasodilation)
-vasodilation increases blood flow returning flow to normal levels
What do vasodilators do?
– dilate arterioles and relaz precapillary sphincters
-increase blood flow through arterioles and into capillary beds
What are examples of vasodilators?
- increased body temp, co2 levels, H+, K+, lactate ANP
- decreased O2 and nutrient levels
What do vasoconstrictors do?
- constrict arterioles and cause contraction of precapillary sphincters
- decrease blood flow through arterioles into capillary beds
What are examples of vasoconstrictors?q
- increased o2, nutrient levels, aldosterone, adh
- decreased body temp, CO2, lactate, H+ K levels
What is blood pressure?
force of blood pushing against vessel wall
What is blood pressure gradient?
change in pressure from 2 end of the vessel to the other
What does a blood pressure gradient do?
- propels blood through vessels
- the pressure is highest in arteries and lowest in veins
- arterial bp varies in between systole and diastole
- at capillaries, there is no difference between systolic and diastolic but there is a gradient between atrial (higher) and venule (lower)
Describe atrial bp
- pulsatile bc of alternating stretching and recoiling of vessel walls
- varying
What is systolic pressure?
when ventricles contract
What is diastolic pressure?
- when ventricles relax
What is pulse pressure?
difference between systolic and diastolic pressure
What is mean arterial pressure?
average arterial bp across the entire cardiac cycle in which diastole lasts longer
1/3 pulse pressure + diastolic pressure
What is total blood flow?
amount of blood moving through system per one unit time
How is total blood flow calculated?
pressure gradient established by heart/ resistance experienced by blood as it moves through the heart
What is systemic blood pressure gradient
delta p
as the gradient increases blood flow increases
the gradient is increased by increasing cardiac output
What is resistance?
r
as resistance increases total blood flow decreases
resistance is friction blood encounters due to contact between blood and vessel, opposing blood flow
What does a steeper blood pressure gradient mean?
bigger push and blood flow
What does a smaller blood pressure gradient mean?
less blood flow, potential problem
