Chapter 20 - Blood Vessels Flashcards
Arteries
- Carry blood away
- Are oxygenated except for pulmonary circulation and umbilical vessels of fetus
Capillaries
- Contact tissue cells
- Connect arterioles to venules
- Directly serve cellular needs and exchange of gases, nutrients, wastes, hormones, etc. between blood and ISF
- Exchange substances between blood and tissues
- Pericytes: Help stabilize their walls and control permeability –> located in random places and doesn’t form continuous layer
- Diameter = 1 RBC at a time
- In all tissues except cartilage, epithelia, cornea, and lens of eye
- 3 types
- Single squamous epithelium lining on basement membrane
Veins
- Carry blood from capillaries toward heart
- Formed when venules converge
- Small and medium-sized veins (ex: radial and femoral veins) are companion vessels with muscular arteries
- Largest veins (ex: common iliac, IVC) travel with elastic arteries
- Called capacitance vessels (blood reservoirs); has up to 65% of blood supply because they can’t vasoconstrict well
- Most have valves that are primarily of tunica intima and strengthened by elastic and collagen fibers –> most abundant in veins of limbs
Arteries, compared to veins…
- Thicker tunica media –> allows for better vasoconstriction/dilation –> arteries mainly help to regulate blood flow and blood pressure
- Narrower lumen
- More elastic and collagen fibers
- Are more resistant than veins in BP change
- Remain open even without blood in it –> veins collapse without blood
- Don’t have valves (veins do)
Companion vessels
- Arteries and veins that supply the same body region and tend to lie next to each other
What is the lumen?
- Central blood-containing space
What are the 3 wall layers in arteries and veins?
- Tunica interna
- Tunica media
- Tunica externa (tunica adventitia)
Tunica intima
- Innermost layer
- Simple squamous endothelium lines lumen of all vessels –> continuous with endocardium –> slick surface reduces friction
- Subendothelial layer in vessels larger than 1 mm –> connective tissue basement membrane
- Releases substances to regulate contraction/relaxation of smooth muscle within tunica media
- Blood supplied through blood passing through lumen
Tunica media
- Middle layer of vessel
- Smooth muscle and sheets of elastin
- Sympathetic nerve fibers control vasoconstriction/dilation
- Made of layers arranged in a circular way
Tunica externa (tunica adventitia)
- Made of areolar connective tissue that contains elastic and collagen fibers –> Collagen fibers protect and reinforce –> anchor to surrounding structures
- Contains nerve fibers, lymphatic vessels
- Large blood vessels need their own supply to the tunica external –> Vasa vasorum is a small network of small arteries that extends through tunica external and can also supply tunica media
Layers of capillaries
- Basement membrane
- Endothelial cells
Valves in veins
- Valves don’t have cordinae tendineae
- Because veins can’t vasoconstrict the best, they prevent backflow
- Not in all veins, only in certain sites
How do arteries changes as they go from heart to capillaries?
- Progressively branch into smaller vessels
- Decrease in diameter
- Change in tunic wall that includes a decrease in elastic fibers and an increase in amount of smooth muscle
Order of arteries as they move towards capillaries (biggest to smallest)
- Elastic artery
- Muscular artery
- Arteriole
Order of veins as they move towards capillaries (biggest to smallest)
- Large vein
- Small to medium-sized vein
- Venule
Elastic (conducting) arteries
- Large thick-walled arteries with elastin in all 3 tunics, especially tunica media
- Ex:Aorta, pulmonary trunk, common carotid, common iliac arteries
- Large lumen –> low resistance
- Inactive in vasoconstriction
- Acts as pressure reservoir (expands and recoils as blood is ejected from heart)
Muscular (distributing) arteries
- Deliver blood to body organs
- Thick tunica media with more smooth muscle
- Active in vasoconstriction
- More smooth muscle and lesser amount fo elastic fibers –> better ability to vasoconstrict/dilate but lessened ability to stretch compared to elastic arteries
- Ex: Brachial, anterior tibial, coronary, and inferior mesenteric
- Elastic tissue in 2 layers
1.) Internal elastic lamina: Between tunica intima and tunica media
2.) External elastic lamina: Between tunica media and tunica externa
Arterioles
- Smallest arteries and leads to capillary beds –> Control flow into them through vasoconstriction/dilation
- Not named
- Larter arterioles have all 3 layers, smaller ones only have tunica intima with a single layer of smooth muscle cells on the outside
Vasomotor tone: The concept that the smooth muscle in the arterioles are slightly contracted –> regulated by vasomotor center in medulla oblongata - Have the biggest drop in blood pressure –> constrict to protect the capillaries
What are the 3 structural types of capillaries?
1.) Continuous capillaries
2.) Fenestrated capillaries
3.) Sinusoid capillaries
Continuous capillaries
- Least permeable and most common
- Abundant in skin and muscles
- TIght junctions connect endothelial cells but don’t completely seal –> intercellular clefts allow passage of fluids and small solutes (ex: glucose or <5 nanometers) but not larger particles (ex: cells, proteins)
- Continuous capillaries of brain are unique –> right junctions form a complete blood-brain barrier
- In muscle, skin, thymus, lungs, brain, and spinal cord
Fenestrated capullaires
Fenestrations: Pores where small regions of the endothelium are thin
- More permeable than contunous capillaries
- Function in absorption or filtrate formation (small intestines, endocrine glands, kidneys)
- In areas where much fluid transport happens (ex: kidney capillaries filtering blood to form urine)
Sinusoid capillaries/ discontinuous capillaries
- Fewer tight junctions
- Usually fenestrated, larger intracellular clefts, and large lumens
- Base membrane is incomplete or absent
- Flood flow sluggish and allows modification –> openings allow large molecules and blood cells to pass between blood and tissue
- Only in the liver, bone marrow, spleen, surrounding tissues, and some endocrine glands
- Macrophages in lining to destroy bacteria
Capillary beds
- Interwoven networks of capillaries between arterioles and venules
- Precapullary sphincter (smooth muscle ring) may control blood flow into the true capillaries –> relaxed will cause blood flow into capillaries and constriction will cause blood flow directly from metarteriole and thoroughfare channel into postcapillary venule by passing capillary bed
- Precapularry sphincters are regulated by local chemical conditions and vasomotor nerves
Microcirculation
- Flow of blood through bed from arteriole to venule
- The terminal arteriole has metarteriole and is how a capillary bed has blood delivered
- The distal part of metarteriole has thoroughfare channels (intermediate between capillary and venule) with no smooth muscle and connects to postcapillary venule –> drains blood from capillary bed
- True capillaries make up the bulk of capillary bed and branch off metarterole or terminal arteriole
What is the vascular shunt?
- Made of metarteriole and thoroughfare channel
- Allow blood to be directly shunted to the venous side
True capillaries normally branch from ________ and return to __________
Metarteriole, thoroughfare channel
Venules
- Larger venules have all 3 tunics
- Companion vessels with arterioles
- Formed when capillary beds unite
- Very porous; allow fluids and WBC into tissues
- Consists of endothelium and a few pericytes
- Merge to form veins
What are the % of total blood in each part of cardiovascular system at rest?
- Pulmonary circulation ~18%
- Heart ~ 12%
- Systemic circulation ~70% –> 55% is within systemic veins
Venous sinuses
Flattened veins with extremely thin walls (ex: coronary sinus of the heart and dural sinuses of the brain)
What is the simple pathway of blood vessels?
- Has 1 artery, 1 capillary bed, and 1 vein
- End arteries: Arteries that provide only one pathway through which blood can reach an organ
What are the alternative pathways of blood vessels?
1.) Venous anastomoses
2.) Arterial anastomoses
3.) Arteriovenous anastomosis (shunt)
4.) Portal system
Alternative pathways differ in what?
- Number of arteries, capillary beds, or veins
Anastomosis
The joining together of blood vessels
- Provide an alternative route in case a vessel is compressed or blocked
- Arterial anastomosis is common in joints, abdominal organs, heart –> none in retina, kidneys, spleen
- Vascular shunts of capillaries are examples of arteriovenous anastomoses
Functional end arteries
Other vessels (ex: coronary arteries) that are so small, the function of the arteries may almost be considered end arteries
Arterial anastomoses
- Includes 2 or more arteries converging to supply the same body region
Venous anastomoses
- 2 or more veins draining into the same body region
- There are more venous anastomoses than arterial anastomoses
- Ex: veins that drain upper limb like basilic, brachial, and cephalic veins
Arteriovenous anastomoses (shunt)
- Transports blood from an artery directly into a vein, bypassing the capillary bed
- In fingers, toes, palms, and ears –> allow these areas to be bypassed if the body is becoming hypothermic –> bypassing these structures makes them more vulnerable to frostbite
Cross-sectional area of a vessel
Diameter of the vessel’s lumen
Total cross-sectional area
Aggregate lumen diameter across total number of a given type of blood vessel if they were positioned side by side
- Measures area of lumen
- Influences blood flow velocity
Arteries and their total/ cross-sectional area
- Cross-sectional area –> relatively large
- Total cross-sectional area –> Smallest
veins and their total/ cross-sectional area
- Total cross-sectional area –> relatively small
capillaries and their total/ cross-sectional area
- Cross-sectional area –> relatively large
- Total cross-sectional area –> Largest (~60,000 miles or ~4,500cm^2)
Blood flow velocity
- The rate of blood transported per unit time (cm/sec)
- Inverse relationship between total cross-sectional area and blood flow velocity –> Capillaries with largest total cross-sectional area –> slowest flow
- Changes as it moves through different vessel type –> Fastest in aorta; slowest in capillaries; increases in veins
- Ex: flow of a narrow river = faster
- Slower rate allows for sufficient time for capillary exchange between body tissues and blood
Which is the order of highest to lowest velocity of blood flow of these?
- Elastic arteries
- Muscular arteries
- Arterioles
- Capillaries
- Venules
- Veins
- Venae cavae
- Elastic arteries (e.g., aorta) → Fastest
- Muscular arteries
- Venae cavae
- Veins
- Arterioles
- Venules
- Capillaries → Slowest
Blood flow
Volume of blood flowing through vessel, organ, or entire circulation in given period
- mL/min
- Equivalent to cardiac output (CO- Amount of blood ejected from heart in 1 min) for entire vascular system
- Constant at rest
- Can vary through individual organs based on needs
Blood pressure (BP)
Force per unit area exerted on wall of blood vessel by blood
- mm Hg
- Measured as systemic arterial BP in large arteries near heart
- Pressure gradient provides driving force that keeps blood moving from higher to lower pressure areas –> BP is highest in arteries as heart contracts and lowest in veins
- Measured indirectly by auscultatory method using a sphygmomanometer –> pressure increased in cuff until it exceeds systolic pressure in brachial artery –> pressure released slowly and examiner listens for sounds of Korotkoff (sounds of blood flow) with stethoscope
Blood flow equation
F = (Pressure of blood coming into vessel - Pressure of blood coming out vessel)/ Resistance = ΔP/ R
Resistance equation
R = (Viscosity of blood x length of blood vessel)/ radius of blood vessel^4
What is the most important aspect that impacts resistance?
- Radius of blood vessel
If a blood vessel is blocked by 50%, ______ blood is getting to the area (how much?)
r^4 –> r^4/2 (bc half is blocked) –> r^4/2^4 = r^4/16 –> 16x less blood is getting to the area
Resistance
- The friction blood encounters
- Opposite to flow
- Due to contact between blood and vessel wall
Peripheral resistance
- Measure of amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation
- 3 sources of resistance
1.) Blood viscosity
2.) Total blood vessel length
3.) Blood vessel diameter (lumen size)
For resistance, which are the factors that remain relatively constant?
- Blood viscosity
- Blood vessel length
Blood viscosity in relation to resistance
- Resistance of blood to its flow –> the thickness of a fluid
- The stickiness of blood due to formed elements and plasma proteins
- Increased viscosity –> increased resistance
- Depends on percentage of particles in fluid and their interactions –> anemic person has a lower blood viscosity and less resistance
- Blood is ~5x more viscous (thicker) than water
Blood vessel length in relation to resistance
- Longer vessel = greater resistance as friction occurs along the length
- Weight gain or loss can change vessel length
- Weight gain –> associated with angiogenesis (increased resistance)
- Weight loss –> associated with vessel regression (decreased resistance)
Blood vessel diameter in relation to resistance
- Greatest influence on resistance
- Blood has laminar flow (different flow rate within vessel) –> flow is faster in center of lumen and slower new vessel wall
- Varies inversely with fourth power of vessel radius –> F ∝ r^4 –> if radius is doubled, the resistance is 1/16 as much
- Fatty plaques from atherosclerosis can increase resistance
- Disrupt laminar flow and cause turbulent flow –> irregular fluid motion = increased resistance
Relationship between blood flow, blood pressure, and resistance
- Blood flow (F) is directly proportional to blood pressure gradient (ΔP = systemic blood pressure gradient = P1-P2) divided by resistance = F ∝ ΔP/R
- Systemic blood pressure gradient increases –> blood flow speeds up
- R increases, blood flow decreases
- F = ΔP/R
- R more important in influencing local blood flow
What is local blood flow and what factors influence it?
Local blood flow: Blood delivered locally to the capillaries of a specific tissue (bc blood is directed where it is most needed)
Dependent on…
1.) Degree of vascularization
2.) The myogenic response
3.) Local regulatory factors (vasoactive chemicals, autoregulation, etc.)
4.) Total blood flow
Myogenic response
The contraction and relaxation of smooth muscle within blood vessels i response to changes in stretch of blood vessel wall
- Can cause blood flow to be relatively constant
- EX: Higher systemic BP –> increase in blood vessel –> increase in stretch of smooth muscle cell in vessel wall –> smooth muscle contract –> vasoconstriction
What are vasoactive chemicals and what are the 2 types?
Vasoactive chemicals: The certain chemicals that change in concentration and stimulate regulation
1.) Vasodilators: substances that cause smooth muscle relaxation and results in vasodilation of arterioles and opening of precapillary sphincters –> increase blood flow into capillary bed
2.) Vasoconstrictors: Substances that cause smooth muscle contraction –> arterioles vasoconstrict and precapillary sphincters close –> blood flow decreases in capillary bed
Autoregulation
The idea that a tissue regulates its local blood flow in response to its changing metabolic needs
- Initial stimulation is typically inadequate perfusion because of increased metabolic activity of the tissue –> oxygen and nutrients are low and high level of CO2, H+, and K+
- Negative feedback loop controlled intrinsically by modifying the diameter of local arterioles feeding capillaries (independent of MAP, which is controlled as needed to maintain constant pressure)
- Reactive hyperemia: A condition in which local blood flow is restored and there is an increase in blood flow to tissue –> ex: cheeks getting warm after cold
- Short term regulation as part of the body defense system or because of damaged tissue (organs can also regulate their own blood flow by varying resistance of own arterioles)
- Histamine (increases capillary permeability and causes vasodilation) and bradykinin are inflammatory mediators
Two types that determine final autoregulatory response –> metabolic controls and myogenic controls
What are local substances v. hormones and neurotransmitters that cause vasodilation
Local
- Decreased O2 levels
- Decreased nutrient needs
- Increased CO2, H+, K+, and lactate levels
- Histamine
- Bradykinin
- Nitric oxide
- Prostaglandins
Hormones and neurotransmitters
- Atrial natriuretic peptide (ANP)
- Epinephrine (bound to β2 receptors within coronary and skeletal muscle blood vessels)
What are local substances v. hormones and neurotransmitters that cause vasoconstriction
Local
- increased O2 levels
- increased nutrient needs
- decreased CO2, H+, K+, and lactate levels
- Leukotrienes
- Thromboxanes
- Endothelins
Hormones and neurotransmitters
- Angiotensin II
- Aldosterone
- Antidiuretic hormone (ADH)
- Norepinephrine and to a lesser extent epinephrine (bound to Local
- Decreased O2 levels
- Decreased nutrient needs
- Increased CO2, H+, K+, and lactate levels
- Histamine
- Bradykinin
- Nitric oxide
- Prostaglandins
Hormones and neurotransmitters
- Atrial natriuretic peptide (ANP)
- Epinephrine (bound to ⍺1 receptor in most blood vessels, including skin and abdominal organs)
Highest BP is generated in the arteries is during ventricular ______ when ______
Ventricular systole (contraction) when artery is maximally stretched (systolic pressure)
Lowest BP is during ventricular ________ when artery _______
During ventricular diastole (relaxation) when artery recoils no further (diastolic pressure)
Pulse pressure
The additional pressure placed on the arteries when the heart is resting (diastolic bp) to when the heart is contracting (systolic bp)
- Pulse pressure = Systolic bp - diastolic bp
- A measure of the elasticity and recoil of arteries as it is a pressure wave caused by the expansion and recoil of arteries –> healthy arteries expand and recoil easily
- Highest closest to the heart and decline with increasing distance
- Radial pulse (taken at wrist) is commonly used
- Pressure points where arteries close to body surface can be compressed to stop blood flow
Systemic blood pressure
- Pressure results when flow is opposed by resistance in the body
- Highest in the aorta and declines throughout pathway
- 0 mm HG in right atrium –> the end point where blood returns to the heart
What two factors of arteries does arterial blood pressure reflect?
1.) Elasticity (compliance or distensibility)
2.) Volume of blood forced into them at any time
Systolic pressure
Pressure exerted in aorta during ventricular contraction
- About 120 mm Hg or less in normal adult
- Pressure when sounds first occur as blood starts to spurt through artery
- Artery is maximally stretched during ventricular systole
Diastolic pressure
Lowest level of aortic pressure
- Normally less than 80 mm Hg
- Pressure when sounds disappear because artery is no longer constricted and recoils no further in ventricular diastole –> blood flowing freely
Pulse
Throbbing of arteries
Mean arterial pressure (MAP)
The average measure of BP in the arteries
- Pressure that propels blood to tissues
MAP = Diastolic pressure + (1/3) pulse pressure
- Decline with increasing distance from heart
Ex: BP= 120/80 –> MAP= 80 + ((1/3)x(120-80)) –> 80+(1/3)(40) –> 93 mm Hg
- Takes into account the fact that diastolic pressure usually lasts slightly longer than systolic pressure
- Numeric value for how well body tissues and organs are perfused –> high MAP value –> possible edema
- During stress, cardioacceleratory center increases heart rate and stroke volume via sympathetic –> ESV decreases and MAP increases
Capillary blood pressure
- Ranges from 17 to 35 mm Hg
- By the time the blood preaches capillaries, fluctuations between systolic and diastolic BP disappear
- ~40 mm Hg on atrial end of capillary
- ~20 mm Hg on venous end of capillary
- Venous and atrial end pressure of capillary is used to determine net filtration pressure for capillary exchange
Venous blood pressure
- changes little during cardiac cycle
- Small pressure gradient (~15 mm Hg)
- Low pressure bc of cumulative effects of peripheral resistance –> bp energy lost as hear during each circuit –> ~20 mm Hg in venules and almost 0 mm Hg by the time the blood is transported through the IVC
- Venous return of blood to the heart depends on…
1.) Pressure gradient
2.) Skeletal muscle pump
3.) Reparatory pump
Muscular pump (venous blood pressure)
Contraction of skeletal muscles “milks” blood toward heart
- Valves prevent blood backflow
- Assists with movement of blood primarily within limbs
- Circulates blood faster and more efficiently when more active
- Extended inactivity –> blood pooling –> higher risk for deep vein thrombosis
Respiratory pump (venous return)
- Pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand
- Assists with movement of blood within thoracic cavity
Venoconstriction under __________ control pushes blood toward heart
Sympathetic control
Maintaining blood pressure requires…
1.) Cooperation of heart, blood vessels, and kidneys
2.) Supervision by brain
The main factors influencing blood pressure…
1.) Cardiac output (CO)
2.) Peripheral resistance (PR)
3.) Blood volume
Short term regulation of BP occurs through…
- Autonomic reflexes involving nuclei within the medulla oblongata
Cardiovascular center is within the _____________
- Within medulla oblongata
What are the parts of the cardiovascular center?
Cardiac center –> Regulates heart activity and cardiac output
1.) Cardioacceletory center: Sympathetic division pathways extend from the cardioacceletory center to both SA and AV node –> causes release of NE from ganglionic neurons –> increases firing rate of SA and shortens the AV delay
- Also extends to myocardium to cause more forceful contractions and increase stroke volume
2.) Cardioinhibitory center: Parasympathetic decreases heart rate –> CO decreases
- Doesn’t extend to myocardium
Vasomotor center: Controls degree of vasoconstriction/dilation –> thus, resistance
- Unlike the heart, blood vessels don’t have dual innervation and are typically only innervated by sympathetic division –> sends steady impulses via sympathetic efferents to blood vessels
- NE released from ganglionic neurons here
- Recieves input from baroreceptors, chemoreceptors, and higher brain centers
Where are baroreceptors that regulate bp located?
- Carotid sinus
- aortic arch
- within right atrium
Where are chemoreceptors that regulate bp located?
- Carotid body
- Aortic body
What are baroreceptors?
- Specialized sensory nerve endings that respond to stretch
- Increased blood pressure stimulates baroreceptors to increase input to vasomotor center –> inhibits vasomotor and cardioacceleratory centers to cause arteriole dilation and venodilation –> stimulates cardioinhibitory center
- If MAP is low –> reflex vasoconstriction –> increased CO –> increased blood pressure
Baroreceptor (carotid sinus)
- Within each carotid artery, near artery’s initial bifurcation
- Transmit nerve signals to cardiovascular center through glossopharyngeal nerve (CN IX - 9)
- Monitor bp changes in head and neck and are more sensitive to changes than those in arch
- Best for short term changes
What are chemoreceptors?
Peripheral sensory receptor or specialized cells that detect specific chemicals in fluid
- Most important in regulating repsoration
- Negative feedback loop
- Stimulated by high CO2 levels, low pH, and very low O2 levels
- Increased firing stimulates vasomotor center –> increases nerve signals along sympathetic pathways to blood vessels –> increases resistance and venous return –> bp and blood flow increase and blood flow to lungs for gas exchange –> blood gas levels return to normal
- Causes increase in bp by signaling cardioacceletory center –> increase CO and also signaling vasomotor center –> increase vasocontriction
Chemoreceptors in carotid body
- At the bifurcation of each common carotid as it splits into an external carotid and internal carotid artery
- Sends sensory input to cardiovascular center via glossopharyngeal nerve (CN IX - 9)
Chemoreceptors in aortic body
- Sends sensory input to cardiovascular center via vagus nerve (CN x -10)
Baroreceptors in aortic arch
- Transmit nerve signals to the cardiovascular center through vagus nerve (CN x -10)
- Helps regulate systemic bp
- best for short term change
Variations in response of blood vessels (vasoconstriction/dilation) is dependent on _________
- Subtypes of receptors in the smooth muscle cells within tunica media
Smooth muscle in vessel wall with ⍺1 receptors do __________
- Contract in response to NE –> vasoconstriction
- Most blood vessels in the body
Smooth muscle in vessel wall with β2 receptors do _________
- Relax in response to epinephrine –> vasodilation
- Ex: coronary arteries and arteries supplying skeletal muscle
Activation of sympathetic division and stimulation of adrenal medulla causes what 3 things?
1.) Increased peripheral resistance as vessels constrict since there are more with ⍺1 than β2
2.) Larger circulating blood volume –> vasoconstriction of veins shifts blood from venous reservoirs
3.) Redistribution of blood flow –> More blood flow reaches skeletal muscle and heart
Blood pressure formula
- BP measures cardiovascular –> Heart + blood vessels
BP = CO x PR - CO depends on blood volume
Cardiac Output
- CO x SV x HR
- SV controlled by venous return (EDV) –> affected by preload, contractility with Ca2+, and afterload
- Normal = 5.0 - 5.5 L/min
- Determined by venous return, and neural and hormonal controls
- Resting heart rate maintained by cardioinhibitory venter via parasympathetic vagus nerves
Short-term neural controls of blood pressure
- Neural controls of peripheral resistance
- Maintain MAP by altering blood vessel diameter –> if low blood volume all vessels constrict except those in heart and brain and alters blood distribution
- Operate via reflex arcs that involve…
1.) Baroreceptors
2.) Cardiovascular center of medulla
3.) Vasomotor fibers to heart and vascular smooth muscle
4.) Sometimes input form chemoreceptors and higher brain centers
Short term controls of bp controls include…
Counteract fluctuations in blood pressure by altering peripheral resistance and CO
- Neural controls
- Hormonal controls
Influence of higher brain centers with short term maintenance of bp
- Reflexes in medulla
- Hypothalamus and cerebral cortex can modify arterial pressure via relays to medulla
- Hypothalamus increases blood pressure during stress
- Hypothalamus mediates redistribution of blood flow during exercise and changes in body temperature
Short term hormonal control of bp
- Via changes in peripheral resistance and cardiac output
- Cause increased np
- Epinephrine and norepinephrine from adrenal gland –> increased CO and vasoconstriction
- Anginotensin II stimulates vasoconstriction
- High ADH levels causes vasoconstriction
- Atrial natriuretic peptide causes decreased blood volume by antagonizing aldosterone
Atrial natriuretic peptide
- Natrium = sodium
- Helps put Na+ in urine –> wherever Na+ goes, water will follow
- Stimulates vasodilation –> decrease peripheral resistance
- Increases urine output –> decreases bp
Long term renal regulation of bp - urinary system
- Counteracts fluctuations in blood pressure by altering blood volume via kidneys
- Baroreceptors quickly adapt to chronic high or lo bp so are ineffective
- Kidneys regulate arterial blood pressure –> direct renal mechanism and incirect renal (renin-angiotensin-aldosterone) mechanism
Direct renal mechanism of long-term renal regulation in bp regulation
- Alters blood volume independently of hormones
- Increased BP or blood volume causes elimination of more urine –> reduces BP
- Decreased BP or blood volume causes kidneys to conserve water –> BP rises and MAP rises
Indirect renal mechanism (renin-angiotensin-aldosterone mechanism steps) of long-term renal regulation in bp regulation
1.) Kidney receptors detect low blood pressure or are stimulated by the sympathetic decision
- Renin enzyme is released from the kidney
2.) Renin converts angiotensinogen into angiotensin I
- Angiotensinogen: A plasma protein that is continuously produced by the liver and circulates within the blood –> an inactive hormone
3.) ACE (Anginotensin Converting Enzyme- enxyme in capillaries of the lung) converts angiotensin I (an inactive hormone) into Angiotensin II (active hormone)
- Most conversion occurs within blood vessels of lungs
4.) Angiotensin II increases blood pressure by…
- Causing vasoconstriction –> thus, increase in peripheral resistance and increase bp
- Stimulating thirst center within hypothalamus –> an increase in fluid intake is an increase in BP
- Decreasing urine formation through the stimulus of aldosterone and antidiuretic hormone –> Aldosterone increases absorption of Na+ and water in kidney while ADH increases water absorption in kidney
Describe blood flow during exercise
- Blood flow changes from 5.25 L/mm –> 17.5 L/mm
- Blood flow to coronary arteries of heart increase by 3-fold for sufficient O2 (250 –> 750 mL/min)
- Skeletal muscle blood flow increases by 11-fold (1,100 –> 12,500 mL/min)
- Percent of blood flow to skin increases to almost 5x resting level (400 mL –>1,900 mL/min) to dissipate heat
- Less total blood flow distributed to abdominal organs
Which organs increase and decrease in blood flow during exercise?
Increase
- Brain
- Heart
- Skin
- Skeletal muscles
Decrease
- Kidney
- Abdominal organs
- Other (400 mL/min)
Vital signs
- Pulse and blood pressure, along with respiratory rate and body temperature
Tissue perfusion involved in…
- Delivery of O2 and nutrients to, and removal of wastes from, tissue cells
- Gas exchange (lungs)
- Absorption of nutrients (digestive tract)
- Urine formation (kidneys)
Autoregulation - Metabolic controls
- Vasodilation of arterioles and relaxation of precapillary sphincters occur in response to declining tissue O2 or substances from metabolically active tissues (H+, K+, adenosine, and prostaglandins) and inflammatory chemicals
- Causes relaxation of vascular smooth muscle
- Causes release of Nitric Oxide (a powerful vasodilator) by endothelial cells
- Endothelins released from endothelium are potent casoconstritors
- NO and endothelins balanced unless blood flow inadequate, then NO wins
Autoregulation - Myogenic controls
- Myogenic responses keep tissue perfusion constant despite most fluctuations in systemic pressure
- Vascular smooth muscle responds to stretch
1.) Passive stretch: Increased intravascular pressure –> promotes increased tone and vasoconstriction
2.) Reduced stretch –> promotes vasodilation and increases blood flow to the tissue
Long-term autoregulation
- Occurs when short-term autoregulation can’t meet tissue nutrient requirements
- Include angiogenesis
Angiogenesis
When the number of vessels to a region increases and existing vessels enlarge
- Common in heart when coronary vessel occluded, or throughout body in people in high-altitude areas
- Over weeks to months to increase potential perfusion
- Ex: skeletal muscle (bc of aerobic training), adipose tissue (weight gain), coronary vessels (blockage)
Vasomotion
Blood flow through capillaries
- Slow, intermittent flow
- Reflects on/off opening and closing of precapillary sphincters
What are the different types of capillary exchange?
1.) Diffusion
2.) Vesicular transport
3.) Bulk flow (filtration/reabsorption)
Diffusion
Random movement of molecules down concentration gradient
- Move from high concentration in the blood into ISF and then into tissue cells where the concentration is lower
- O2 and nutrients –> Blood to tissues
- CO2 and metabolic wastes –> from tissue to blood
- Lipid-soluble molecules diffuse rectly through endothelial membranes
- Very small solutes (water-soluble solutes) (O2,CO2, glucose, ions, et.c) and fluids may diffuse via the endothelial cells or intercellular clefts
- Larger solutes (water-soluble solutes) (ex: small proteins) must pass through the fenestrations in fenestrated capillaries or gaps in sinusoids
- Larger molecules (ex: larger proteins) are actively transported in pinocytotic vessels (small membrane-bound sacs in endothelial cells that transport stuff across cell via a type of endocytosis called pinocytosis) or caveolae
Vesicular transport
Occurs when endothelial cells use pinocytosis to form fluid-filled vesicles and those are transported to the other side fo the cells and released by exocytosis
- Substances may be moved either from the blood into the ISF or vise versa
- Used by larger solutes (ex: insulin)
Bulk flow
The movement of large amounts of fluids and their dissolved substances in one direction down a pressure gradient
- Important in determining relative fluid volumes in blood and interstitial space
- Direction and amount of fluid flow depend on two opposing forces –> hydrostatic and colloid osmotic pressures
Two main types:
1.) Filtration: A process that occurs on the arterial end of a capillary in which the fluid bulk flows out of the blood through the openings of capillaries (ex: intracellular clefts, fenestrations)
- Fluids and small, dissolved solutes flow through easily
- Formed elements and proteins are generally blocked
2.) Reabsorption: Occurs at venous end of a capillary and is the movement of fluid by bulk flow in the opposite direction –> back into blood
Hydrostatic pressures
Physical force exerted by a fluid on a structure
- Can include blood hydrostatic pressure (HPb)/ blood pressure: Force exerted per unit area by the blood as it presses against the internal surface of the vessel wall
- Promotes filtration from the capillary
- Main hydrostatic pressure
1.) Capillary hydrostatic pressure (HPc) (capillary blood pressure)
- Tends to force fluids through capillary walls
- Greater at arterial end (35 mm Hg) of bed than at venule end (17 mm Hg)
2.) Interstitial fluid hydrostatic pressure (HPif): The force of the interstitial fluid on the external surface of the blood vessel
- Pressure that would push fluid into the vessel
- Usually assumed to be 0 because of lymphatic vessels
Colloid osmotic pressure
Refers to the pull of water back into a tissue by the tissues concentration of proteins (colloid)
- Blood colloid osmotic pressure (COPb): The force that draws fluid back into the blood due to proteins in the blood (ex: albumin)
- Opposes hydrostatic pressure –> COP promotes reabsorption
- Ranges from 26 - 28 mm Hg
- Also called oncotic pressure
1.) Capillary colloid osmotic pressure/ oncotic pressure (OPc) –> Created by non diffusible plasma proteins, which draw water toward themselves
- ~26 mm Hg
2.) Interstitial fluid osmotic pressure (OPif)
- Low (~1 mm Hg) due to low protein content
- Can range from ~ 0-5 mm Hg
Net filtration pressure (NFP)
- NFP comprises all forces acting on capillary bed –> based on idea that hydrostatic and osmotic forces work against one another to regulate filtration and reabsorption of materials in capillary wall
- NFP = (HPc - HPif) - (OPc - OPif)
- Difference between net hydrostatic pressure (bw blood and ISF) and net colloid osmotic pressure (bw blood and ISF)
- Net fluid flow out at arterial end
- Net fluid flow in at venous end
- More leaves than is returned
- Excess fluid is returned to blood via lymphatic system –> capillary only absorbs ~ 86% of fluid that’s passed from blood to ISF –> lymphatic picks up excess 15% and returns it to blood after filtering
- If NFP at venous end is (-) –> reabsorption is occurring so fluid moves from ISF into capillary
- If NFP is (+) –> outward pressure
What are the two circulatory pathways for the blood vessels?
Pulmonary circulation: Short loop that runs from heart to lungs and back to heart
- Pulmonary trunk divides into L and R pulmonary artery –> divide into smaller arteries and then form arterioles
- CO2 diffuses from blood –> alveoli (air sacs)
- O2 moves from alveoli –> blood
- Capillaries drain into venules and then pulmonary veins
- Pulmonary arteries have less elastic connective tissue and wider lumens than systemic arteries
- Compared to systemic circulation, pulmonary vessels are short with less resistance to blood flow because lungs are closer to heart –> lower bp
Systemic circulation: Long loop to all parts of body and back to heart
