Chapter 19 - Blood vessels Flashcards
What is the difference between arteries, capillaries and veins regarding blood flow?
A - blood away from heart (towards capillaries) ; umbilical arteries transport oxygen-poor blood from fetus to placenta
C - exchange vessels, directly serving cellular needs
V - blood to the heart (away from capillaries) - happens when venules join together
What are capillaries called when they unite and what are their characteristics?
postcapillary venules
- smaller venules contain only endothelium and pericytes
- very porous; fluids and WBC move into tissue
What are the characteristics of larger venules?
have a thin tunica media and tunica externa
What is the composition difference between tunica media and tunica external in venues?
TM - thin (little smooth muscle or elastic)
TE - thicker (thick collagen fibers and elastic network)
Why can veins accommodate large amounts of blood relative to low pressure?
called capacitance vessels and blood reservoirs because they contain up to 65% of blood supply at any time
Why is blood pressure low in the arteries?
so adaptation ensure that blood returns to the heart
- large diameter lumens offer little resistance
What do vessels consist of?
- lumen
- central blood-containing space
- wall
What are the layers of wall in vessels?
- tunica intima
- tunica media
- tunica externa
what are capillary walls made of?
endothelium with thin basal lamina
Why is the structure of the tunica intima important?
simple squamous epithelium lines lumen of all vessels
- continuous with the endocardium and reduces friction
- subendothelial layer: basement membrane and loose connective tissue - support endothelium
What are the characteristic of tunica media?
- bulkiest layer in arteries
- smooth muscles regulate sympathetic vasomotor nerve fibers; vasoconstriction and vasodilation
What are the characteristics of tunica externa?
- mostly collagen fibers to protect wall and anchors to surrounding
- contains elastics in large veins
- networks with nerve fibers, lymphatic vessels and blood vessels
- has vasa vasorum
What are the three groups of arteries?
- elastic arteries
- muscular arteries
- arterioles
What are the characteristics of elastic arteries also known as conducting arteries?
- thick walled near the heart: pulmonary truck/ aorta and major branches
- large lumen = low resistance
- contains more elastin and smooth tissue(inactive in vasoconstriction)
How do arteries act as pressure reservoirs?
- expand and recoil as blood is ejected from the heart
- allows for continuous blood flow downstream, even with heart beat
Why are muscular arteries also called distributing arteries?
- deliver blood to specific body organs
- diameter ranges from pinky finger to pencil lead size
- thickest tunica media and less stretchy and more vasoactive than elastic fibers
What are the characteristics of arterioles also called resistance vessels?
- smallest of all arteries
- large one: contains all layers of tunica; small one: contains single layer of smooth muscle around endothelium
- controls flow into capillary beds via vasodilation and constriction
What are the characteristics of capillaries?
smallest blood vessel and act as exchange vessels between blood and interstitial fluid
- consists of only thin tunica intima and single endothelial cells
- RBC pass through in single file
Why do some capillaries have pericytes?
P- contractile cells
- can generate new vessels or scar tissue and stabilize wall/ control permeability
Which tissues lack capillaries?
- some tendons/ ligaments
- avascular cartilage/ epithelia/ cornea/ lens
What are capillary beds?
network of capillaries between arterioles and venules
What is microcirculation?
flow of blood through capillary bed and arteriole to venule
- capillary drains into postcapillary venule (helps with exchange)
What controls blood flow into capillary beds?
local chemicals and arteriolar vasomotor nerve fibers
what does the vascular shunt consist of?
metarteriole and thoroughfare channel
What is the function of the intestinal mesenteries?
vascular shunts: channel that directly connects terminal arteriole with postcapillary venule
What is the precapillary sphincter?
smooth muscle surrounding each true capillary that branches off metarteriole
- acts as valve regulating blood flow
- controlled by local chemicals
Where is most of the blood in the body at any given time and percentage?
systemic veins and venules
- 60%
What is vascular anastomoses, subcategory, and location?
interconnection of blood vessels
- interconnected arteries form arterial anastomoses (alternate pathway - collateral channel - to same tissue to ensure continuous blood flow)
- in joints, abdominal organs, brain, heart
What is arteriovenous anastomoses and subcategory and characteristic?
shunts across capillary beds (ex. metarteriole-thoroughfare channel)
- venous anastomoses
- so abundant that occluded veins rarely block blood flow or tissue death
What is blood flow and characteristics?
amount of blood flowing through vessel, organ, or entire circulation in a given period of time
- equivalent to CO
- flow is based on organ need
What is blood pressure and characteristics?
force per unit area exerted on vessel wall by blood
- in mm Hg
- measured as systemic arterial BP in large arteries near heart
- pressure gradient provides driving force that keeps blood moving
What is resistance and characteristics?
opposition to flow; measure of friction blood encounters along vessel walls
- mostly in peripheral (systemic) circulation, also called total peripheral resistance (TPR)
- contributing factors: blood viscosity, vessel length and diameter
What is blood viscosity and characteristics?
the internal resistance to flow in fluids
- thickness/ stickiness
- contributing factors: too many RBC
What is the total blood vessel length characteristics?
constant, but when tissue grows so does its blood supply
- greater vessel length means more resistance
What are the blood vessel diameter characteristics?
- smaller diameter = more resistance (more contact with wall)
- frequently changes
- radius reduces by half (resistance rises 16 times); radius doubles (resistance decreases by 1/16)
What is the relationship between blood flow (F) and pressure (P) and the equation?
- if delta P increase, blood flow increase (vice versa)
- if TPR increases, blood flow decreases (vice versa)
- F= delta P/ TPR
What is the order of blood pressure in various blood vessels from highest to lowest?
- aorta (80 -120)
- arteries
- arterioles (steepest fall)
- capillaries
- venules
- veins
- vena cava (0)
What is a vital sign and pressure points?
VS - pulse and blood pressure, along with respiratory rate and body temperature
PP - areas where arteries are close to skin
What is the difference between systolic and diastolic pressure?
SP - pressure when first sounds heard, as blood starts to spurt though artery
DP - pressure at which sounds disappears, as artery no loner constricted, blood flows freely
What is the BP range from the beginning to end of the capillary bed and why is low BP desirable?
35- 17
- high BP ruptures fragile, thin-walled capillaries
- capillaries are extremely permeable, so even low pressure forces filtrate into interstitial spaces
What are the characteristics of venous pressure?
- steady (non pulsatile)
- low BP causes blood to flow steadily out of cut and helps distribute (cool down) heat
What are the 3 functional adaptations that assist venous return?
- muscular pump: contracts/ relaxes skeletal muscle around deep veins to prevent back flow
- respiratory pump: pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand
- sympathetic venoconstriction: SNS triggers contraction of veins, reducing their capacitance (and blood reservoir) as blood is pushed towards the heart
What are the 3 factors regulating BP?
- cardiac output (CO)
- Total peripheral resistance (TPR)
- Blood volume
what is the calculation to find MAP and CO?
CO = SV x HR
MAP = CO x TPR
MAP = SV x HR x TPR
What are the 2 mechanisms regulating BP?
- short term: alters TPR and CO
- long term: alters blood volume (via kidneys)
What is the TPR main goals through neural controls?
- maintain adequate MAP moment-by-moment by altering vessel diameter
- after blood distribution to organs as the metabolic demands change (distributing blood to needed organs)
What is the difference between baroreceptors reflex and chemoreceptor reflex?
BR - neural controlled; monitor changes in stretch of vessel walls (pressure changes)
CR - neural controlled; influenced by higher brain centers and chemoreceptors that monitor blood levels of CO2, H+ and O2
What is the cardiovascular center?
in medulla receives/ integrates inputs from baroreceptors, chemoreceptors and higher brain centers
What is the roll of the cardiovascular center?
consist of three groups of neurons in the medulla that work together to adjust CO (via HR and SV) and TPR (via vessel diameter) to regulate MAP
- has inhibition and contractile centers
What is the vasomotor center?
sends impulses via sympathetic vasomotor fibers to blood vessels (mainly arterioles)
- continuous moderate constriction is called vasomotor tone
Where are baroreceptors located?
carotid sinus, aortic arch, and walls of large arteries of neck and thorax
How are chemoreceptors in the aortic arch and large arteries stimulated by and what do they stimulate?
- rise in blood CO2 or drop in bloop pH or O2
- send AP to cardiovascular center at high frequency to increase CO and MAP by: simulating the cardio acceleratory center (increase HR and SV) and the vasomotor center (increase TPR via vasoconstriction)
What influence does the higher brain center have?
hypothalamus and cerebral cortex can modify arterial pressure via relays to the cardiovascular center in the medulla
- hypo mediates fight/ flight and increased blood flow in exercise
What regulates MAP?
short term - hormone regulation via TPR
long term - via changes in blood volume
What is the function of the adrenal medulla hormones?
E and NE from adrenal gland increase CO and vasoconstriction
- angiotensin 2 stimulates vasoconstriction, release of adenosine and ADH (all increase blood volume)
what is atrial natriuretic peptide (ANP)?
decreases MAP by antagonizing aldosterone, causing decreased blood volume; also by causing generalized vasodilation
What is ADH - vasopressin?
stimulates kidneys to conserve water
- also stimulates vasoconstriction
How do the kidneys regulate MAP?
- direct renal mechanisms
- indirect renal mechanism (renin-angiotensin- aldosterone system)
What is the direct renal mechanism?
alters blood volume independent of hormone
- rise in blood pressure or volume causes kidneys to eliminate more water in the body (reducing BV and P)
- fall in P causes kidneys to conserve more water (increases BV and P)
What is the indirect renal mechanism?
use of the renin-angiotensin-aldosterone system
- drop in MAP triggers kidneys to release enzymes called renin into blood
- catalyzes conversion of angiotensinogen to angiotensin 1
- angiotensin-converting enzyme (ACE) converts angiotensin 1 to angiotensin 2
How does angiotensin 2 act to increase MAP and ECF volume?
- triggers aldosterone secretion (kidneys conserve Na+ and water)
- causes ADH conserve water
- activates hypothalamic thirst center (increased water intake)
- acts as a potent vasoconstrictor to increase TPR (directly increases MAP)
What is primary hypertension?
- 90% of hypertensive people have it
- no underlying cause identified; results from genetics or environment
- no cure
- risk factors: obesity, genetics, diet, age, stress, smoking, diabetes mellitus
What is secondary hypertension?
- 10% of hypertensive people
- due to identifiable disorders (obstructed renal arteries, kidney disease)
- treatment available
What is hypertension?
systolic BP above 130 or diastolic BP above 80
- slowly damages heart and vessels (silent killer)
- causes heart failure, vascular disease, renal failure and stroke
- heart must work harder
What is hypotension?
low BP between 90/60 mm Hg
- may cause inadequate blood flow to tissues
- associated with long life and lack of cardiovascular illness
What is tissue perfusion (blood flow through body tissue) involved in?
- delivery of o2 and nutrient to and removal of wastes from tissue cells
- gas exchange (lungs)
- absorption of nut (digestive system)
- urine formation (kidney)
What is the rate of tissue/ organ perfusion dependent on?
metabolic needs to meet supply and demands
- regulated by intrinsic controls (autoregulation) that acts automatically in the smooth muscle of arterioles
What is the extrinsic controls?
sympathetic and endocrine
- act on smooth muscles of arterioles to maintain MAP (not to regulate tissue perfusion)
- SNS and certain hormones reduce flow to regions that least need it (constriction) to maintain MAP
What is the difference between intrinsic and extrinsic controls?
IC - uses paracrine or properties of muscle tissue (autoregulation or local control)
EC - uses hormones
How do organs regulate their own blood flow and what allows it to happen?
intrinsically by varying the diameter (thus resistance) of their arterioles
- based on local tissue conditions
- form autoregulation because no nerves or hormones
What is the types of intrinsic mechanisms determine final autoregulatory responses?
- metabolic (chemical)
- myogenic (physical)
What are the metabolic controls and what are the effects of changing the levels or local chemicals?
increase in tissue metabolic activity due to
- decreased O2 or increased metabolic factors
- direct relaxation of arterioles and precapillary sphincters
- NO and inflammatory chemicals (vasodilator)
- endothelin (vasoconstrictor)
- NO and endo is balanced but when not enough blood, NO is more powerful
Myogenic controls: what is myogenic responses and what are the factors that change it?
vascular smooth muscle responds to changes in intravascular pressure to keep perfusion relatively constant
- if pressure increases: vessel walls stretch (smooth muscle contracts to constrict the vessel and reduce flow)
- if pressure decreases: vessel walls stretch less (smooth muscle relaxes/ dilates vessel, allowing blood flow)
Why does long-term autoregulation happen and what are the effects?
when short-term controls can’t meet tissue demands
- existing vessels enlarge and new vessels form (angiogenesis); takes months
- common in heart when coronary vessels partially occluded; throughout people in high altitude
What is active hyperemia in regards to skeletal muscle?
blood flow increases in direct proportion to metabolic activity, a form of metabolic regulation
- local controls override sympathetic vasoconstriction; blood flow increases 10X
How does velocity change throughout the systemic system and what is speed related to?
- aorta: fastest
- capillaries: slowest
- veins: increases again
total cross-sectional area
- capillaries have the largest, so it moves the slowest allowing for proper exchange
What is vasomotion and what is it due to?
intermittent flow of blood through capillaries
- alternating dilation and constriction of arterioles and precapillary sphincters in response to local chemical conditions (intrinsic control)
What are the 4 routes molecules move through capillaries?
- liquid-soluble molecule: endothelial cell membrane (respiratory gases)
2/3. water-soluble molecules: intercellular cleft or fenestrations (amino acids/ sugar) - larger molecule: actively transported in vesicles via endocytosis and transcytosis (proteins)
Explain what bulk flow is, the filtration, reabsorption and results?
continuous movement of fluid across capillary walls mixes blood plasma and interstitial fluid
F: 20 L of fluid filters from cap at arteriolar end to interstitial space
R: 17L of fluid reabsorbed
R: maintain composition of inter fluid ensure proper fluid balance
What is the difference between hydrostatic pressure and osmotic pressure?
HP - fluid pressing against a boundary until it “pushes” some of the fluid across the boundary
OP - non-diffusible solutes that cannot cross the boundary. “pulls” fluid a cross the boundary
what is edema and how does it affect capillary filtrate?
an abnormal increase in interstitial fluid volume
- rise in outward directed pressures, leading to more filtrate (high NFP)
- drop in inward directed pressure (high NFP)
How is capillary hydrostatic pressure increased?
through fast fluid build up
- due to incompetents venous valves, localized vessel blockage, cong. heart failure or high BP
How is osmotic pressure increased?
due to inflammatory response
- inflammation increases capillary permeability and allows proteins to leak into interstitial fluid
How is capillary colloid osmotic pressure decrease hinder fluid return to blood?
Hypoproteinemia (low protein levels): results from malnutrition, liver disease or glomerulonephritis
What is the venous system?
consists of two main circulations
- pulmonary: short loop that runs from heart to lungs and back
- systemic: long loop to all parts of body and back
What is the difference in depth between arteries and veins?
A - run deep
V - run superficial and deep; most veins share same name with artery but superficial veins don’t share names
Is the venous pathway more interconnected then the arteriole?
Yes
How is the venous drainage system different in the brain and digestive system?
B: blood from brain enters dural venous sinuses (rather than veins)
DS: blood enters hepatic portal system, passing through the liver before getting to the heart
What are the 3 types of capillaries?
- continuous (least permeable - skin, muscle, lungs, CNS)
- fenestrated (pores - active filtration and absorption - kidney)
- sinusoid (most permeable - liver, bone marrow, spleen and adrenal medulla)
