Note
Studied by 2 people
Blood Vessels and Circulation Vocabulary
Blood Vessels and Circulation
Overview of Blood Flow
Pulmonary Circuit:
Blood flow from the right ventricle to the lungs and back to the left atrium.
Systemic Circuit:
Blood flow from the left ventricle to the body and back to the right atrium.
Blood Flow Sequence
Right atrium.
Right ventricle.
Pulmonary arteries.
Capillaries in the lungs.
Pulmonary veins.
Left atrium.
Left ventricle.
Systemic arteries.
Capillaries in the head, neck, upper limbs.
Systemic veins.
Capillaries in the trunk and lower limbs.
Arteries and Veins - Three Layers
Tunica Intima (Tunica Interna):
Innermost layer.
Endothelial cells with connective tissue and elastic fibers.
Tunica Media:
Middle layer.
Concentric sheets of smooth muscle.
Tunica Externa (Tunica Adventitia):
Outermost layer.
Connective tissue sheath.
Anchors vessel to surrounding tissues.
Arterial Wall
Endothelium.
Tunica intima (tunica interna).
Tunica media:
Smooth muscle.
Internal elastic membrane.
External elastic membrane.
Tunica externa.
Elastic fiber
Venous Wall
Endothelium.
Tunica intima.
Tunica media:
Smooth muscle.
Tunica externa.
Five General Blood Vessel Classes
Arteries:
Elastic arteries.
Muscular arteries.
Arterioles
Capillaries
Venules
Veins:
Medium-sized veins.
Large veins.
Blood Vessel Classes Details
Elastic Artery:
Tunica intima.
Tunica media.
Tunica externa.
Muscular Artery:
Internal elastic membrane.
Tunica intima.
Tunica media.
Tunica externa.
Arteriole:
Tunica intima.
Tunica media:
Smooth Muscles cells
Tunica externa.
Capillary:
Endothelium.
Basement membrane.
Pores.
Endothelial cells.
Venule:
Endothelium.
Basement membrane.
Endothelial cells.
Tunica intima.
Tunica media.
Tunica externa.
Medium-Sized Vein:
Tunica intima.
Tunica media.
Tunica externa.
Large Vein:
Tunica intima.
Tunica media.
Tunica externa.
Capillaries
Typical capillary consists of a tube of endothelial cells with a delicate basement membrane
Two major types:
Continuous capillaries
Fenestrated capillaries
Types of Capillaries:
Continuous Capillaries:
Endothelial cell.
Nucleus.
Basement membrane.
Vesicles containing materials transported across the endothelial cell.
Boundary cell between endothelial cells.
Fenestrated Capillaries:
Fenestrations or pores.
Basement membrane.
Boundary between endothelial cells.
Sinusoids
Gap between adjacent cells.
Capillary Beds
Interconnected network of capillaries.
May be supplied by more than one artery.
Collaterals:
Fuse before giving rise to arterioles.
Fusion is an example of arterial anastomosis.
Can be bypassed by arteriovenous anastomosis that directly connects arteriole to venule.
Thoroughfare Channel
Precapillary Sphincters
Vasomotion
Capillary Bed Components
Arterial collaterals.
Arteriovenous anastomosis.
Precapillary sphincter.
Arteriole anastomosis.
Metarteriole.
Thoroughfare Channel.
Capillaries.
Smooth muscle cells.
Small venules.
Venule.
Vein.
Continuous blood flow
Vairable blood flow
Venous Functional Anatomy
Blood pressure in peripheral venules is <10 percent of that in the ascending aorta (largest artery).
Mechanisms are needed to maintain the flow of blood in veins against the force of gravity.
Valves
Contraction of skeletal muscles.
Function of Valves in Veins
Valves superior to the contracting muscle open, allowing blood to move toward the heart.
Valves inferior to the contracting muscle are forced closed, preventing backflow of blood to the capillaries.
Distribution of Blood in the Body
Systemic venous system: 64%
Systemic capillaries: 7%
Systemic arterial system: 13%
Heart: 7%
Pulmonary circuit: 9%
Venous Functional Anatomy - Venoconstriction
Contraction of smooth muscle fibers in veins.
Method of maintaining blood volume in the arterial system even with significant blood loss.
Controlled by the vasomotor center in the medulla oblongata.
Sympathetic nerves stimulate smooth muscles in medium-sized veins.
Cardiovascular Regulation
Accomplished by adjusting both:
Cardiac output
Must generate enough pressure to force blood through miles of peripheral capillaries.
Blood distribution within systemic and pulmonary circuits.
Regulation of cardiovascular function is normally through neural and hormonal mechanisms.
Cardiovascular Regulation - Neural and Hormonal
Makes coordinated adjustments to several areas to ensure cardiac output is sufficient to meet the demands of peripheral tissues.
Affects heart rate and stroke volume in the heart.
Also affects peripheral resistance and venous pressure.
Cardiovascular Regulation - Pressure
Pulsing of the heart generates pressure.
Blood pressure:
Pressure within the cardiovascular system as a whole.
Arterial pressure is much higher than venous pressure.
Must push blood greater distance through smaller vessels.
Flow through blood vessels is influenced by resistance.
Force that opposes movement.
Peripheral resistance:
Resistance of the arterial system as a whole.
Increases as vessels get smaller.
Cardiovascular Regulation - Capillaries
Blood flow in capillaries is very slow.
Capillary pressure is very low.
Allows plenty of time for capillary exchange.
Diffusion between blood and interstitial fluid.
Cardiovascular Regulation - Veins
Blood pressure in veins is maintained by:
Valves
Muscular compression of peripheral veins.
As blood moves toward the heart, vessels get larger, and resistance decreases.
Venous return:
Amount of blood arriving at the right atrium each minute.
On average, equal to the cardiac output.
Sites and Mechanisms of Cardiovascular Regulation
Cardiac Output
Venous Return
Venous Pressure Regulation (Neural and Hormonal)
Arterial Blood Pressure
Peripheral Resistance
Capillary Pressure
Capillary exchange
Interstitial fluid
Factors Affecting Peripheral Resistance
Total Peripheral Resistance:
Resistance of the entire cardiovascular system.
Must be overcome by sufficient pressure from the heart in order for circulation to occur.
Depends on three factors:
Vascular resistance
Viscosity
Turbulence
Total Peripheral Resistance - Vascular Resistance
Vascular resistance:
Opposition to blood flow in vessels.
Largest component of total peripheral resistance.
Primarily results from friction between blood and vessel walls.
Amount of friction depends on two factors:
Vessel length
Vessel diameter
Friction and Vessel Length
Internal surface area = 1, Resistance to flow = 1, Flow = 1
Internal surface area = 2, Resistance to flow = 2, Flow = ½
Friction and Vessel Diameter
Greatest resistance near surfaces, slowest flow
Least resistance at center, greatest flow
Vessel Length versus Vessel Diameter
Diameter = 2 cm, Resistance to flow = 1
Diameter = 1 cm, Resistance to flow = 16
Factors Affecting Peripheral Resistance - Viscosity
Viscosity:
Resistance to flow caused by interactions of solutes and suspended materials in a liquid.
Low-viscosity fluids have lower resistance, so flow at low pressures.
High-viscosity fluids have higher resistance, so flow only at high pressures.
Blood has viscosity ~5 times water.
Due to cells and plasma proteins.
Viscosity is normally stable.
Viscosity Levels and Examples
Water: 1
Blood: 5
Maple syrup: 10
Motor oil: 40
Molasses: 300
Factors Affecting Peripheral Resistance - Turbulence
Turbulence:
Type of fluid flow with eddies and swirls.
Caused by high flow rates, irregular surfaces, and sudden changes in vessel diameter.
Responsible for the production of third and fourth heart sounds.
Increased turbulence = increased resistance = slow blood flow.
Effect of Turbulence on Blood Flow
Plaque deposit causes turbulence.
Factors Affecting Blood Flow
Blood flow:
Directly proportional to blood pressure.
Inversely proportional to peripheral resistance.
More important than absolute pressure is the pressure gradient.
Difference in pressure from one end of the vessel to the other.
Changes in pressure = changes in flow.
Pressure gradient can be altered by the cardiovascular center.
Factors Affecting Blood Flow - Changes in Diameter
From the aorta to capillaries:
Decreasing diameter increases resistance = decreased flow.
From capillaries to venae cavae:
Increasing diameter decreases resistance = increased flow.
Changes in blood pressure:
Highest pressure at the aorta.
Pressure drops at each branching in the arterial system.
Smaller, more numerous vessels produce more resistance, reducing pressure.
At start of peripheral capillaries, pressure is 35 mm Hg
At the venules, pressure is 18 mm Hg
Factors Affecting Blood Flow - Changes in Blood Flow
Highest flow in the aorta:
Highest blood pressure, largest diameter.
Slowest in the capillaries:
Smallest diameter.
Slow flow is important to allow exchange between blood and interstitial fluid.
Flow accelerates in the venous system:
Due to larger diameter vessels = lower resistance.
Changes in Diameter, Pressure, and Flow
Aorta
Elastic arteries
Muscular arteries
Arterioles
Capillaries
Venules
Veins
Venae cavae
Factors Affecting Blood Flow - Changes in Arterial Pressure
Rises during ventricular systole.
Peak pressure = systolic pressure.
Declines during ventricular diastole.
Minimum pressure = diastolic pressure.
Commonly written with a “/” between pressures (e.g., 120/90).
Pulse pressure:
Difference between systolic and diastolic pressure (e.g., 120 – 90 = 30 mm Hg).
Mean arterial pressure (MAP):
Adding 1/3 of the pulse pressure to diastolic pressure (e.g., 90 + (120 – 90)/3 = 100 mm Hg).
Factors Affecting Blood Flow - Capillary Exchange
Involves a combination of diffusion, osmosis, and filtration.
Capillary hydrostatic pressure (CHP)
Capillary Hydrostatic Pressure and Capillary Exchange
Amino acid.
Blood protein.
Glucose.
Ions.
Interstitial fluid.
Hydrogen bond.
Water molecule.
Small solutes.
Endothelial cell 1 & 2.
Capillary exchange - Diffusion
Diffusion:
Net movement of substances from an area of higher concentration to lower concentration.
Occurs most rapidly when:
Distances are short.
Concentration gradient is large.
Ions or molecules involved are small.
Occurs continuously across capillary walls, but the transport mechanism varies for different substances.
Capillary Exchange - Filtration and Reabsorption
At the arterial end of the capillary:
Filtration predominates.
Capillary hydrostatic pressure (CHP) is highest near the arteriole.
As filtration occurs, blood colloid osmotic pressure (BCOP) increases.
CHP > BCOP = fluid forced out of the capillary
Net filtration pressure (NFP):
Difference between capillary hydrostatic and blood colloid osmotic pressure.
NFP = CHP – BCOP
Is positive at the beginning of the capillary: Filtration
Becomes negative by end of capillary: Reabsorption
At roughly 2/3 of the way along the capillary:
No net movement.
Capillary hydrostatic pressure equals blood colloid osmotic pressure.
NFP = CHP – BCOP = 0
At the venule end of the capillary:
Reabsorption predominates.
Capillary hydrostatic pressure falls below blood colloid osmotic pressure.
CHP < BCOP
Water moves into the capillary.
Overall: more water leaves the bloodstream than is reabsorbed
Difference (about 3.6 L/day) enters the lymphatic vessels and is eventually returned to the venous system.
Filtration and Reabsorption in Capillaries
Arteriole
CHP (Capillary hydrostatic pressure) = 35 mm Hg
BCOP (Blood colloid osmotic pressure) = 25 mm Hg
NFP (Net filtration pressure) = +10 mm Hg
Filtration Predominates 24 L/day
Fluid forced out of the capillary
Capillary
CHP (Capillary hydrostatic pressure) = 25 mm Hg
BCOP (Blood colloid osmotic pressure) = 25 mm Hg
NFP (Net filtration pressure) = 0
No Net Movement
No net fluid movement
Venule
CHP (Capillary hydrostatic pressure) = 18 mm Hg
BCOP (Blood colloid osmotic pressure) = 25 mm Hg
NFP (Net filtration pressure) = -7 mm Hg
Reabsorption Predominates 20.4 L/day
Fluid moves into capillary
CHP > BCOP
CHP = BCOP
BCOP > CHP
Capillary Exchange - Variations
Possible variations in capillary exchange
Any condition that affects blood pressure or osmotic pressure of blood or interstitial fluid shifts balance of hydrostatic and osmotic forces
If hemorrhaging occurs:
Blood volume and pressure decline à CHP reduced
Increases capillary reabsorption (= recall of fluids)
If dehydration occurs:
Plasma volume and blood pressure decline à CHP reduced and BCOP increases
If CHP rises or BCOP declines:
Filtration increases
Fluid builds up in peripheral tissues (= edema)
Cardiovascular Regulatory Mechanisms
Homeostatic mechanisms:
Ensure adequate tissue perfusion (blood flow through tissues).
Two regulatory pathways:
Autoregulation
Central regulation
Neural and endocrine control
Cardiovascular Regulatory Mechanisms - Regulatory Pathways
Autoregulation:
Involves changes in blood flow within capillary beds.
Regulated by precapillary sphincters in response to chemical changes in interstitial fluid.
Vasodilators:
Local chemicals that increase blood flow.
Vasomotion
Central regulation:
Involves both neural and endocrine mechanisms.
Neural:
Activation of cardioacceleratory center.
Activation of the vasomotor center.
Peripheral vasoconstriction.
Arteriole vasodilation – in skeletal muscle and the brain.
Can increase cardiac output and reduce blood flow to nonessential or inactive tissues.
Endocrine:
Release of vasoconstrictor (primarily NE) producing long-term increases in blood pressure.
Cardiovascular Regulatory Mechanisms - Flowchart
Start
HOMEOSTASIS DISTURBED
Physical stress (trauma, high temperature)
Chemical changes (decreased O2 or pH, increased CO2 or prostaglandins)
Increased tissue activity
Inadequate local blood pressure and blood flow & Local vasodilators released
Autoregulation
Local decrease in reistance and increase in blood flow
HOMEOSTASIS RESTORED
Normal blood pressure and volume
If autoregulation is ineffective
Central Regulation
Neural mechanisms
Endocrine mechanisms
Stimulation of receptors sensitive to changes in systemic blood pressure or chemistry.
Stimulation of endocrine response
Activation of cardiovascular centers.
Increased cardiac output and peripheral vasoconstriction.
long-term increase in blood volume and blood pressure
Short-term increase of blood pressure by sympathetic stimulation of the heart and peripheral vasoconstriction.
HOMEOSTASIS RESTORED
Normal blood pressure and volume
Cardiovascular Regulatory Mechanisms - Baroreceptor Reflexes
Baroreceptor reflexes (baro-, pressure):
Respond to changes in blood pressure.
Receptors are located in walls of:
Carotid sinuses
Aortic sinuses
Right atrium
The Baroreceptor Reflex - Increasing Blood Pressure
HOMEOSTASIS DISTURBED
Increasing blood pressure
Baroreceptors stimulated.
Cardioinhibitory center stimulated.
Cardioacceleratory center inhibited.
Vasomotor center inhibited.
Decreased cardiac output.
Vasodilation occurs.
HOMEOSTASIS RESTORED
Blood pressure decreases.
HOMEOSTASIS
Normal range of blood pressure.
The Baroreceptor Reflex - Decreasing Blood Pressure
HOMEOSTASIS DISTURBED
Decreasing blood pressure
Baroreceptors inhibited.
Vasomotor center stimulated.
Cardioacceleratory center stimulated.
Cardioinhibitory center inhibited.
Increased cardiac output.
Vasoconstriction occurs.
HOMEOSTASIS RESTORED
Blood pressure increases.
HOMEOSTASIS
Normal range of blood pressure.
Chemoreceptor Reflexes
HOMEOSTASIS DISTURBED
Increased CO2 levels, decreased pH and O2 levels in blood and CSF
Increasing CO2 level & Decreasing pH and O2 levels.
Chemoreceptors stimulated.
Reflex Response
Cardiovascular Responses
Cardioacceleratory center stimulated.
Cardioinhibitory center inhibited.
Vasomotor center stimulated.
Increased cardiac output and blood pressure.
Vasoconstriction occurs.
Respiratory Response
Respiratory centers in the medulla oblongata stimulated.
Respiratory rate increases.
HOMEOSTASIS RESTORED
Decreased CO2 levels, increased pH and O2 levels in blood and CSF.
HOMEOSTASIS
Normal pH, O2, and CO2 levels in blood and CSF.
Endocrine Responses to Changes in Blood Pressure and Volume
Endocrine responses
Endocrine system provides both short-term and long-term regulation of cardiovascular function.
Utilizes endocrine functions of:
The heart
The kidneys
The hypothalamus/posterior pituitary gland
Endocrine Responses to Low Blood Pressure and Volume
Hormonal response to low blood pressure
Immediate response
Release of epinephrine and norepinephrine
Released from the adrenal medullae
Other hormones are important in the long-term response:
Antidiuretic hormone (ADH)
Angiotensin II
Erythropoietin (EPO)
Aldosterone
Endocrine Responses to Low Blood Pressure and Low Blood Volume - Flowchart
Start
HOMEOSTASIS DISTURBED
Blood pressure and volume decrease
Decreasing blood pressure and volume.
Sympathetic activation and release of adrenal hormones E and NE
Short-term & Long-term
Increased blood pressure & Increased blood volume
Increased cardiac output and peripheral vasoconstriction
Angiotensin II Effects
Widespread vasoconstriction
Antidiuretic hormone released
Aldosterone secreted
Thirst stimulated
Increased red blood cell formation
Endocrine Response of Kidneys
Renin (RĒ-nin) is released when renal blood pressure and blood volume decrease. Renin release activates angiotensin I, which is converted in the lung capillaries to angiotensin-converting enzyme (ACE). Several drugs used to control blood pressure inhibit ACE.
Erythropoietin (EPO) is released by the kidneys if blood pressure decreases or if the oxygen content of the blood becomes abnormally low.
Combined Short-Term and Long-Term Effects
HOMEOSTASIS RESTORED
Blood pressure and volume increase
HOMEOSTASIS
Normal blood pressure and volume
Endocrine Responses to High Blood Pressure and High Blood Volume - Flowchart
Start
HOMEOSTASIS DISTURBED
Increasing blood pressure and volume.
Increasing blood pressure and volume
Natriuretic peptides released by the heart
Inhibition of ADH, aldosterone, epinephrine, and norepinephrine release
Peripheral vasodilation
Responses to ANP and BNP
Increased Na^+ loss in urine
Increased water loss in urine
Reduced thirst
Combined Effects
Decreased blood volume
Decreased blood pressure
HOMEOSTASIS RESTORED
Decreasing blood pressure and volume
HOMEOSTASIS
Normal blood pressure and volume
Cardiovascular Adjustments During Exercise
During light exercise:
Three changes take place:
Vasodilation occurs, peripheral resistance drops, and capillary blood flow increases.
Venous return increases with skeletal muscle contraction; increased respiration creates negative pressure in thoracic cavity drawing blood back (respiratory pump).
Cardiac output increases to 9500 mL/min
During heavy exercise:
Cardiac output approaches maximal levels (~17,500 mL/min
Major changes in peripheral blood distribution allow large increase in flow to skeletal muscles without overall decrease in systemic blood pressure
Increased flow to skeletal muscles
Increased flow to the skin (promotes heat loss)
Reduced flow to digestive viscera and kidneys
Brain blood flow remains unchanged
Adjustments to Cardiac Output and Blood Flow During Exercise
At Rest: Cardiac output = 5800 mL/min
Brain: 750 mL/min
Kidney: 1200 mL/min
Abdominal viscera: 1100 mL/min
Skin: 500 mL/min
Skeletal Muscles: 900 mL/min
Other tissues: 1400 mL/min
Light Exercise: Cardiac output = 9500 mL/min
Brain: 750 mL/min
Kidney: 600 mL/min
Abdominal viscera: 400 mL/min
Skin: 1500 mL/min
Skeletal Muscles: 4500 mL/min
Other tissues: 1100 mL/min
Heavy Exercise: Cardiac output = 17,500 mL/min
Brain: 750 mL/min
Kidney: 250 mL/min
Abdominal viscera: 250 mL/min
Skin: 1900 mL/min
Skeletal Muscles: 12,500 mL/min
Other tissues: 1900 mL/min
Cardiovascular Adjustments During Exercise - Training
Cardiovascular performance improves with training
Trained athletes have bigger hearts and greater stroke volumes
Can maintain normal blood flow with lower heart rate (as low as 32 bpm)
Maximal cardiac output can be 50 percent higher than in non-athletes
Fetal Circulation
Umbilical arteries:
Pair of arteries that carry blood from the fetus to the placenta.
Umbilical vein:
Carries blood from the placenta.
Brings oxygen and nutrients.
Drains into the ductus venosus
All umbilical vessels degenerate after birth
Ductus venosus:
Vascular connection to veins within the liver.
Empties into the inferior vena cava
Foramen ovale or interatrial opening:
Allows blood to pass from right atrium to left atrium.
Has one-way valve to prevent backflow
Ductus arteriosus:
Bypass between pulmonary trunk and aorta.
Sends blood from right ventricle to the systemic circuit
Pattern of Fetal Blood Flow
Placenta
Umbilical cord
Umbilical vein
Umbilical arteries
Inferior vena cava
Liver
Aorta
Pulmonary trunk
Ductus venosus
Ductus arteriosus
Foramen ovale
Fetal Circulation - Changes at Birth
Changes in circulation at birth
Occur due to expansion of the pulmonary blood vessels and resulting pressure changes
Increasing pressure in the left atrium closes foramen ovale
Remnant of the foramen ovale is a shallow depression called the fossa ovalis
Rising oxygen levels cause ductus arteriosus to constrict and close
The remnant of the ductus arteriosus is a fibrous cord called the ligamentum arteriosum
Changes in Blood Flow Through the Heart at Birth
Right ventricle
Foramen ovale (closed)
Pulmonary trunk
Ductus arteriosus (closed)
Right atrium
Inferior vena cava
Left atrium
Left ventricle
Fetal Circulation - Congenital Defects
Ventricular septal defects
Patent foramen ovale
Patent ductus arteriosus
Tetralogy of Fallot
Atrioventricular septal defect
Transposition of the great vessels
Ventricular Septal Defect
Ventricular Septal Defect
Ventricular septum
Ventricular septal defect
Patent Foramen Ovale and Patent Ductus Arteriosus
Patent Foramen Ovale and Patent Ductus Arteriosus
Patent foramen ovale
Patent ductus arteriosus
Tetralogy of Fallot
Pulmonary stenosis
Patent ductus arteriosus
Enlarged right ventricle
Ventricular septal defect
Atrioventricular Septal Defect
Atrial defect
Ventricular defect
Transposition of the Great Vessels
Pulmonary trunk
Aorta
Patent ductus arteriosus