Blood Vessels I
What are the 3 blood vessel layers from deep to superficial?
- tunica intima
- tunica media
- tunica externa/adventitia
In which type of blood vessel is most of the body's blood supply found in at any given point in time?
- veins = up to 65% of the body's blood volume is there at any given time
What 3 factors affect circulation?
- blood flow (cardiac output, how much blood is moving through the body and at what rate, mL/min)
- blood pressure (with how much force is the blood moving, always moves from high to low pressure, mmHg)
- resistance (how easily is the blood moving through the vessels)
Which type of blood vessel has the highest blood pressure and why?
- arteries have the highest blood pressure because they bring blood directly from the heart where pressure is highest and veins are post-capillary beds, meaning that they can't have but so much pressure because capillary beds can't have high pressure
Which organs to the brain use to regulate blood pressure?
- heart
- blood vessels
- kidneys
Which type of blood vessel does not have all 3 layers and which layer does it have?
- capillaries = tunica intima only
Why is it important for capillaries to have only 1 blood vessel layer/ be so thin?
- capillaries are where gas exchange takes place, oxygen and nutrients diffuse from capillaries into the interstitial space & carbon dioxide and waste products diffuse from the interstitial space into the capillaries
- this could not happen through the thick walls of arteries or veins
What is the relationship between the 3 factors affecting circulation?
- as resistance increases, blood flow decreases
- as blood pressure increases, blood flow increases
- as resistance increases, blood pressure increases
What is mean arterial pressure (MAP) and how is it calculated?
- mean arterial pressure = the average pressure in one cardiac cycle, taken since aortic pressure fluctuates so much
- MAP = DBP + PP/3 --> diastolic BP + (systolic - diastolic)/3 = MAP
What changes in the amount of blood flow to different organs occur during exercise?
- heart = increases to meet demands for oxygen and glucose
- brain = no changes *brain never gets blood supply lessened*
- kidneys = decreases, those processes aren't crucial
- skin = increases to allow heat to leave the body
- GI system/liver = decreases, these processes aren't crucial
- skeletal muscle = increases to meet demand for oxygen and glucose
Name 3 differences between arteries and veins.
- arteries carry blood away from the heart, veins carry blood back to the heart
- arteries have higher blood pressure compared to veins
- arteries carry oxygenated blood, veins carry deoxygenated blood
- arteries branch to become smaller and smaller, veins join together to become bigger and bigger
What is responsible for regulating the flow of blood into the capillaries so that it is not continuous?
- precapillary sphincters = regulated by sympathetic nervous system to send blood either through the true capillaries of the capillary bed or through the metarteriole
What is the difference between systolic and diastolic blood pressure and what are the normals for each?
- systolic = pressure on ventricular systole/contraction, average is 120 mmHg *above 127 mmHg is damaging
- diastolic = pressure on ventricular diastole/relaxation, average is 80 mmHg
What adaptations to veins have in order to compensate for the lower blood pressure within them?
- muscle pumps = deeper veins are between layers of muscle, when the muscles contract they help squeeze blood up through the veins to improve venous return
- respiratory pump = veins in the thorax are surrounded by muscles that aid in respiration, when those muscles contract during inspiration they squeeze those blood vessels to help get blood back to the heart
- sympathetic vasoconstriction = veins experience vasoconstriction, thus moving blood forward to the heart
Name at least 1 hormone involved in blood pressure regulation.
- epinephrine/norepinephrine = increased vasoconstriction & cardiac output, sympathetic NS
- angiotensin II = stimulates vasoconstriction & release of aldosterone and ADH (blood volume)
- atrial natriuretic peptide (ANP) = produced by heart, decreases blood volume and BP
- antidiuretic hormone (ADH) = water reabsorption to increase blood volume and BP
What are the 3 types of arteries and where you would find each type (if applicable)?
- elastic arteries = closest to the heart, ex. aorta and major branches
- muscular arteries = leading directly into major organs, ex. hepatic artery, splenic artery, etc.
- arterioles = leading directly into capillary beds, ex. literally everywhere capillary beds are
What are the 3 types of capillaries, how permeable is each type, and where would you find each type?
- continuous capillaries = least permeable type to closely regulate what comes in and out of the tissues; found in the brain (blood brain barrier), lungs, muscles, and skin *most common type*
- fenestrated capillaries = middle of the road permeability to allow for filtration, absorption, and hormone secretion; found in the kidneys, small intestines, and most endocrine glands
- sinusoid capillaries = most permeable with big gaps to allow large molecules and other things to move through; found in the spleen, bone marrow, adrenal medulla, and liver
What 2 things affect arterial blood pressure?
- compliance of elastic arteries closest to the heart (how easily to the elastic arteries stretch and recoil to meet the demands put on them) *compliance of large arteries closest to heart is what makes BP pulsatile
- volume of blood pumped into elastic arteries (more blood volume = higher blood pressure)
What factors are affected by blood pressure regulation systems?
- cardiac output = heart pumps out more blood to increase pressure
- peripheral resistance = blood vessels constrict to increase blood pressure
- blood volume = body retains more fluid to increase blood volume, thereby increasing pressure through how much is pumped out
What are the 3 categories of neural controls over blood pressure and what do they react to?
- baroreceptors = react to arterial pressure changes and stretch in arterial walls
- chemoreceptors = respond to changes in carbon dioxide, oxygen, and pH
- higher brain centers = hypothalamus reacts to fight or flight input from medulla oblongata
What are vascular anastomoses, what is there purpose, and what is an example of it/where would you expect to find them?
- vascular anastomoses are interconnections of blood vessels
- arterial anastomoses provide redundant blood flow to an area so if one artery is compromised the area can still receive oxygenated blood
- venous anastomoses are more common and drain the blood supplied to prevent excessive blood build up
- circle of willis (in the brain), around the joints, dorsal venous arches of hands
What are the two forces that regulate fluid flow through the capillaries and describe each?
- hydrostatic pressure = force pushing fluid against the capillary walls, forcing fluid out of the capillaries to create filtration, also called capillary blood pressure
- colloid osmotic pressure = force created by large non-diffusible molecules (i.e. albumin) that pulls fluid into the capillaries, opposes hydrostatic pressure *molecules like albumin create a lower fluid volume in the capillaries which cause fluid to flow into them to move down their concentration gradient
- net filtration pressure = hydrostatic pressure + colloid osmotic pressure
What 3 factors affect resistance and how do they do so?
- blood viscosity (how thick the blood is) = if blood is thicker, the body has to work harder to push it through, thus increasing resistance *think how easily it is for water to move compared to molasses or honey* (polycythemia vera)
- blood vessel length = a longer blood vessel means that the blood has to travel more, which leads to a higher resistance to it moving *sprinting vs marathon*
- blood vessel diameter = the smaller the blood vessel diameter, the less clearance the blood has to flow through, thus increasing resistance *think a tractor trailer trying to go through a drive through and under that bar they have hanging* (atherosclerosis)
There are 2 divisions of blood pressure regulation, what are they, which mechanisms do they include, and what aspect do they affect?
- short term regulation = affects peripheral resistance and cardiac output; includes neural controls (NS and brain) and hormonal controls
- long term regulation = affects blood volume; includes renal/kidney mechanisms
The kidneys regulate BP long term, what do they respond to and what is their goal in changes?
- kidneys respond to changes in blood volume (ex. blood loss, high sodium consumption, dehydration, exercise, etc.)
- their goal is to keep our blood volume around 5 liters (give or take depending on your size) and to keep our blood pressure within a safe, narrow range *BP too low and nothing is perfused properly, too high and capillaries can burst and major damage is done (even potential hypertensive crisis)*