Chapter 21: Blood vessels Flashcards
How many layers to blood vessels have with the exception of capillaries
3 layers:
1. tunica interna (innermost)
2. Tunica media ((middle)
3. tunica externa
What layer of blood vessels helps to constrict them
Tunica media: the smooth muscle
Endothelium for blood vessels is
one layer; gas exchange is easier
are arteries or veins thicker
arteries are thicker because they have more smooth muscle
The walls of arteries are elastic which allow…
them to absorb pressure created by the ventricles of the heart as they pump blood into the arteries eg. aorta
What are the different types of arteries
- elastic arteries
- muscular arteries
Elastic arteries (conducting arteries)
- large diameter
- more elastic fibers, less smooth muscle
- function as pressure reservoirs
Example of elastic artery
aorta: a lot more elastic fibers and less smooth muscle
Muscular arteries ( distributing arteries)
- medium diameter
- more smooth muscle, fewer elastic fibers
- distribute to various parts of the body
As arteries branch they become …
muscular arteries
Anastomoses
the union of the branches of two or more arteries supplying the same region of the body
Anastomosis results in
collateral circulation
- provides an alternate route for blood flow
- example: circle of willis
Arteries that do not form anastomosis is called
end arteries
- if an end artery is blocked, blood cannot get to that particular region of the body and necrosis occurs
Capillaries
- are microscopic vessels that usually connect arterioles and venules
- composed of a single layer of cells and basement membrane
- because their walls are so thin, they allow gas exchange
capillary networks are found near
almost every cell in the body
Continuous capillaries
individual cells join to one another
- not much space between cells
What is the intercellular cleft
space which allows wbcs to squeeze through to emigrate
Fenestrated capillaries
- they have pores
- allow arteries to exchange substances
- present in the kidneys
Sinusoid capillaries
- has incomplete basement membrane
- allows for greater exchange
- has bigger holes than fenestrated capillaries and allows red blood cells to squeeze through
- wbcs can freely enter
- present in the liver
Venules
are small vessels that are formed by the union of several capillaries
- drain blood from capillaries into veins
Veins
- formed by the union of several venules
- less elastic tissue and smooth muscle than arteries
- have thicker tunica externa and thinner tunica interna and media
Varicose veins
are formed when venous valves become weak of damaged
- cannot prevent backwards flow and veins will buldge
- dilated and twisted in appearance
Spider veins
are dilated venules close to the skin, especially in the lower limb and face
- spider veins appear red, blue or purple, resembling a spider web
At rest, the largest portion of the blood is in systemic..
veins and venules, which are considered blood reservoirs
Substances cross capillary walls by …
- diffusion
- transcystosis
- bulk flow
Diffusion in capillaries
substances move from an area of high concentration to an area of low concentration
- substances in blood or interstitial fluids can cross the capillary walls by: intercellular clefts, fenestrations and diffusion through the plasma membrane of the endothelial cells
Transcytosis in capillaries
combination of endo and exocytosis
- example: insulin
Bulk flow in capillaries
movement of liquid plasma and small particles
- everything goes in the same direction unlike diffusion
Bulk flow occurs from an area of
higher pressure to an area of lower pressure and it continues as long as there is a pressure difference between two areas
What is bulk flow important for
important for regulation of the relative volumes of blood and interstitial fluid
- in contrast diffusion is the regulation of movement of solutes
Bulk flow is calculated by
filtration and absorption
Filtration in bulk flow
the pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid
What promotes filtration
blood hydrostatic pressure (BHP) and intersitital fluid osmotic pressure (IFOP) promote filtration
Reabsorption in bulk flow
the pressure-driven movement of fluid and solutes from interstitial fluid into blood capillaries
What promotes reabsorption
interstitial fluid hydrostatic pressure (IFHP) and blood colloid osmotic pressure (BCOP) promote reabsorption
Net filtration pressure
NFP = (BHP + IFOP) - (BCOP + IFHP)
Blood flow
the volume of blood that flows through any tissue in a given time period (in mL/min)
Total blood flow is represented by…
cardiac output
Cardiac output equals
- heart rate X stroke volume (mL of blood pushed out by ventricles in each contraction)
- mean arterial pressure (MAP) divided by resistance
Vascular resistance
is the opposition to blood flow due to friction between blood and the walls of blood vessels
- the higher the resistance the lower the blood flow
Vascular resistance depends on 3 factors…
- the size of the blood vessel lumen
- arteries and veins have larger diameters and lower resistance
- arterioles, venules and capillaries contribute to the most resistance - blood viscosity
- total blood vessel length
What is a major function of arterioles
to control systemic vascular resistance through vasodilation or vasoconstriction
Velocity of blood flow
is inversely related to the total cross-sectional area of blood vessels
(blood flow is the volume of blood that flows through a tissue in a given period of time)
Venous return
is the volume of blood flowing back to the heart through the systemic veins.
- it occurs due to the pressure generated by contractions of the heart’s left ventricle
What 3 factors affect venous return
- contraction and relaxation of the heart
- skeletal muscle pump
- respiratory pump
How does contraction and relaxation affect venous return
relaxation causes return at diastole; the volume is higher and the pressure is lower which helps blood return from the vena cava to the right atrium. The pressure difference causes it
What controls blood pressure and blood flow
Medulla oblongata contains the cardiovascular center which is a group of neurons that regulates the heart rate, contractility and blood vessel diameter
Homeostasis - negative feedback loop for decreased blood pressure explained
- stimulus: decreased blood pressure
- controlled condition: blood pressure
- receptors: baroreceptors in the carotid sinus and aortic arch
- input: stretch less and decrease the rate of nerve impulses
- control centers: cardiovascular center
- Output: increased sympathetic and decreased parasympathetic responses.
- Effectors: heart and blood vessels which increase stroke volume, hr and vasoconstriction
- Response: blood pressure is increased and returns to homeostasis
ANP (atrial natriuretic peptide) is made during
high blood pressure to decrease it
What is shock
shock is failure of a cardiovascular system to deliver enough oxygen and nutrients to meet the metabolic demands for delivery of oxygen and nutrients and removal of wastes
what are the four different types of shock
- hypovolemic
- cardiogenic
- vascular (distributive)
- obstructive
Homeostatic responses to shock
- activation of renin-angiotensin-aldosterone system (constricts blood vessels, increases resistance and blood pressure)
- secretion of ADH
- release of local vasodilators
signs and symptoms of shock
- low systolic bp
- tachycardia (due to sympathetic stimulation from release of epinephrine and norepinephrine)
- weak pulse (reduced cardiac output)
- skin is cool and clammy (vasoconstriction to nonvital organs)
- mental state is altered
- urine formation reduced (dark and concentrated urine)
- thirst
- pH is low due to acidosis (build up of lactic acid) –> not enough O2 going to cells of the body
- nausea; vasoconstriction of blood vessels of the digestive system
What is the source of the hepatic portal system
venous system returns blood from the digestive tract and spleen into the liver where raw nutrients are processed before they return to the heart
Age related changes to the CV system
- loss of compliance (elasticity) of aorta
- reduction in cardiac muscle fiber size
- decline in maximal heart rate
- increased systolic bp
