Blood Vessels Flashcards
5 main types of blood vessels:
- arteries
- arterioles
- capillaries
- venules
- veins
Arteries:
- carry blood away from heart
- pressure reservoir
- large radius, which leads to little resistance to blood flow
Arterioles:
- deliver blood to capillaries
- known as resistance vessels
- regulate distribution of cardiac output
- produce rapid decrease in pressure
Arterioles create resistance by…
changing the diameter
Large arteries branch off into…
smaller vessels like arterioles
CT for arteries has…
- collagen fibers: provide tensile strength
- elastin fibers: provide elasticity to arterial walls
Arterioles don’t have…
elastic and fibrous tissue
Arterioles are made up of…
smooth muscle
Arterioles are the main contributors to…
total peripheral resistance (TPR)
Capillaries:
- site of nutrient exchange
- has thin and porous walls
- form beds at tissues
Flow of capillaries is controlled by…
- metarteriole
- precapillary sphincters
Continuous capillaries are made of…
plasma membrane of cells w/ intercellular clefts
- most abundant
Continuous capillaries are permeable to…
- h2o
- glucose
- small solutes
Different types of capillaries:
- continuous
- fenestrated
- sinusoids
Fenestrated capillaries:
- have pores (fenestrations)
- more permeable than continuous
Fenestrated capillaries are found in…
- kidneys
- small intestines
- endocrine organ
Sinusoids:
- wider and more winding
- has unusually large fenestrations
- allows movement of large substances
Layers in the blood vessels dictate…
function
Layers of blood vessels:
- endothelium
- smooth muscle
- connective tissue
Function of endothelium:
- thin layer of epi cells supported by basal lamina that are innermost
- provide physical barrier and other vascular functions
Function of smooth muscle:
controls vasodilation and vasoconstriction
Function of CT:
- elastic: allows for blood vessels to stretch
- fibrous: provides blood vessel with tensile strength
Function of venules:
drain blood from capillaries
Function of veins:
- carry blood back to heart
- aided by valves and pumps (skeletal and respiratory)
Venules and veins function as…
blood volume reservoirs
Capillaries are also known as…
tunica intima
- low pressure
- built for exchange
Capillaries in the kidney, intestine, liver, and bone marrow:
- large pores
- unlimited exchange
- fenestrated capillaries
Capillaries in cardiac and skeletal muscle:
- small pores
- limited exchange
Capillaries in brain:
- no pores
- blocks entry of many small molecules
- has blood brain barrier
Tissues that don’t have capillary beds:
- bone marrow
- liver
- spleen
- they will have sinusoids instead
Capillary bed is arranged for…
max exposure of tissues to blood for max exchange of nutrients and waste
- parallel arrangement
Precapillary sphincter guards…
entrance to capillaries
- regulates blood entry via myogenic control
- determined by metabolic state of capillary bed
Capillary bed is made up of…
- metarterioles
- capillaries
- venules/veins
- surrounded by pericytes
Capillary density in capillary beds:
- high in metabolically active tissues
- low in metabolically inactive tissues
Examples of metabolically active tissues:
- cardiac
- skeletal
- glandular
Examples of metabolically inactive tissues:
- subcutaneous tissue
- cartilage
Microcirculation/nutritional flow:
- blood flow within capillary
- dependent on contractile state of arteriole feeding the capillaries
Capillary beds are able to withstand…
large internal pressure
Function of pericytes:
- decreases the size of filtration slits
- tightens capillary beds
Two ways blood can flow w/ capillary beds:
- flow to capillary beds: regulated by arterioles
- flow through capillary beds
Flow to capillary bed sets the…
basal (resting) vascular tone
- generally smooth muscle are partially contracted
Decrease in basal vascular tone leads to…
- decrease in resistance
- increase in diameter and flow
Increase in basal vascular tone leads to…
- increase in resistance
- decrease in diameter and flow
Flow to capillary bed can be altered by:
intrinsic and extrinsic factors
- neural and local control
Neural control dominates:
skin and splanchnic
Local control dominates:
heart, brain, and skeletal muscle
Flow through capillary beds is regulated by:
oncotic and hydrostatic pressure
Examples of passive exchange in capillary endothelium:
- diffusion
- bulk flow
- vesicular transport
Diffusion:
- most important
- movement across and between endo cells
- solubility is major factor for movement
Diffusion follows what law?
Flick’s
Diffusion of nonlipid soluble substances:
- can’t pass through membrane
- restricted to pores
- ex: nutrients and fluid
Small nonlipid soluble substances and diffusion:
- flow limited: goes as fast as blood arrives
- increased diffusion distance means that diffusion is limited
Large nonlipid soluble substances are transported via…
transcytosis
- pore size restricts diffusion
- minimal movement when MW is big
Diffusion of lipid soluble substances:
- materials are soluble in membrane
- occurs all over membrane, so not limited to pores
- has greater SA for exchange
- rate depends on solubility of substance
Bulk flow (filtration):
- not as important as diffusion
- moves large volumes of solutes through endothelium pores in response to pressure gradient
- same direction
- uses starling forces
What is unfiltered via bulk flow returns to…
vascular system via lymph
What is filtered via bulk flow is reabsorbed in…
capillaries and venules
Permeability of capillary membrane in bulk flow varies w/…
- # and size of pores
- location: venous ends are more porous and permeable than arterial end
Starling forces:
sum of hydrostatic and osmotic pressure across membrane
- determines direction and magnitude of h2o movement
Hydrostatic pressure:
- fluid pressure w/in capillary (Pc)
- principle force in capillary filtration
- varies in tissues and body position
- push
Hydrostatic pressure depends on arterial and venous…
- pressure
- resistance
Increase in arterial and venous pressure leads to…
increase in hydrostatic pressure
Increase in arterial resistance leads to…
decrease in capillary hydrostatic pressure
Decrease in arterial resistance leads to…
increase in capillary hydrostatic pressure
Difference in hydrostatic pressure between tissues is due to…
resistance and loss of fluid
Interstitial hydrostatic pressure (Pi):
- opposes capillary filtration
- usually close to 0
- rises w/ edema
Osmotic forces:
- key factor that limits fluid loss from capillaries
- pull
- due to colloid osmotic pressure
- oncotic pressure and osmotic pressure of plasma membrane
Positive sum of starling force equation:
filtration occurs
- usually at arterial end
Negative sum of starling force equation:
absorption occurs
- usually at venous end
Renal glomerus filters/absorbs
filters
Intestinal mucosa filters/absorbs
absorb
Transcytosis:
- moves substance w/in tiny vesicles
- transfers across capillary endothelium cells by endocytosis and exocytosis
- spends ATP
- important for large NLS molec
Venous system returns…
blood from tissues
- valves prevent backflow
Venous system is a…
low pressure system
- has to be lower than capillary or blood won’t flow
- decreases hydrostatic pressure
- responsible for preload
In the venous system, the pressure in the right atrium has to be…
lowest otherwise blood won’t return to heart
Venous system has a high…
compliance, which leads to low resistance
- varies with body position
Veins in the lower limbs are…
thicker and less compliant than those above the heart
Venous system is a reservoir that contains…
up to 70% of blood vessels
- has capacitance vessels
What causes variations in venous return?
- venomotor tone
- respiratory activity
- orthostatic stress
- muscle pump
Venomotor tone:
- controlled by basal SNS output
- usually low so it can hold greater amount of volume
Increase in venomotor tone leads to…
greater volume of blood is moved toward heart
Respiratory activity is when…
diaphragm generates negative inter-thoracic pressure
Respiratory activity facilitates…
return of blood toward heart by pulling blood into thoracic cavity
Orthostatic stress:
- gravity or posture change
- ex: standing up leads to increased pressure in veins of lower legs
Muscle pump and one way valves:
- exercise leads to low venous pressure in legs b/c of pressure exerted by leg muscles
Contracting leg muscles…
- push veins against bones
- blood forced toward heart
- valves prevent backflow
Structure of lymphatic system:
- widely distributed network of closed-ended lymph capillaries
- no delivery system
- single layer endo cells w/ no tight junctions
- fine filaments anchor lymph vessels to surrounding CT
- extensive series of one way valves
Function of lymphatic system:
- maintain blood volume
- transports dietary fat and fat soluble vitamins from GI system
- conducts immune surveillance
Lymphatic system maintains blood volume by…
returning ISF fluid that leaked out of capillaries back to veins
Lymph vessels pass through…
lymph nodes
Lymphatic system is packed with…
lymphocytes and phagocytes, which help recognize foreign material
Lymph:
fluid that enters lymphatic vessels
- same fluid after it becomes ECF and lymph again, just with different substances in it
Lymph travels through…
blood vessels -> filtered into tissue bed by hydrostatic pressure (ECF) -> picked up by bind end lymph capillaries (lymph)
Lymphatic capillaries drain into…
lymphatic vessels and then ducts
Lymphatic system returns fluid back to…
large veins (ex: subclavian) close to the heart - aided by skeletal muscle
When transport of the lymphatic system is overwhelmed or when lymphatic vessels are blocked, it leads to…
fluid accumulation in the tissues (edema)
Failure of the lymphatic vessels occurs b/c of…
- increased hydrostatic and venous P and interstitial protein
- decreased plasma protein [ ]
Distribution of lymphatics is extensive in the…
GI and lungs
No distribution of lymphatics in…
- bone
- epithelia
- tissues of CNS
Resistance of blood flow to organs increases as…
- radius of vessels decrease
- length of vessels increase
- viscosity of blood increase
Blood flow of the organ at rest is based on…
metabolic activity of organ
Blood flow of the organ during stress is…
reduced for most organs
Vascular tone is the partial contraction of…
arteriole smooth muscle
- baseline for constriction and dilation
Vascular tone can be changed by:
intrinsic factors: - physical changes - local mediators - hyperemia extrinsic factors: - nerves - hormones
Cardiac output (CO):
- very sensitive to changes in end diastolic volume (EDV)
Ideal cardiac output:
amount leaving heart = amount coming to heart
Factors that affect ventricular return:
- starting cardiac output
- total blood volume
- vasomotor tone
- distribution of blood within vascular system
- resistance to ventricular return
At rest, the metabolic demand for the body is…
low
- blood sits in spleen and veins
During high metabolic demand in the body…
blood from spleen and veins are mobilized
- ventricular return rises
- cardiac output increases
Cardiovascular reflexes:
- adjust flow to meet immediate demand
- monitors conditions in specific locations in cardiovascular system
Control mechanisms of blood flow:
- systemic
- changes cardiac output and total peripheral resistance
Cardiovascular reflex center:
- located in medulla oblongata
- gets input from peripheral baroreceptors, chemoreceptors, and hypothalamus
- output is ANS to heart and blood vessels
Cardiovascular reflex center outputs via…
changes in PNS and SNS to heart and blood vessels
Hypothalamus:
provides behavioral and thermal input to CV center
- increase of SNS leads to decrease of PNS
- increase HR, SV = venoconstriction that increase VR / vasoconstriction that increases TPR and MAP
Thermal input comes from…
thermoreceptors in skin and blood perfusing hypothalamus
For thermal input, SNS output to peripheral blood vessels of skin lead to…
redistribution of blood flow
Cold thermal input leads to…
increased SNS output to skin
- constricts surface vessels
- reduce flow and limit heat loss
Warm thermal input leads to…
decreased SNS output to skin
- surface vessels dilate increasing surface flow and promoting heat loss
Arterial baroreceptors are located in…
carotid sinuses and aortic arch
Arterial baroreceptors: increased MAP leads to…
- increased pressure on vessel wall
- increased vascular stretch and deformation
- eventually leads to firing
Changes in output from CV center in response to…
- hypothalamic input
- change in firing of baroreceptors, peripheral and chemical chemoreceptors
