Chapter 20: Blood Vessels Flashcards
________________ carry blood away from heart
______________ carry blood back to heart
Arteries carry blood away from heart
Veins carry blood back to heart
_________ connect smallest arteries to smallest veins and directly serve tissue cells
Capillaries
Define lumen
central blood-containing space
The walls of arteries and veins composed of what?
3 tunics
What are the 3 tunics of blood vessels?
Tunica interna, tunica media, and tunica externa
Describe tunica interna of blood vessels
- Endothelium: simple squamous epithelium overlying basement membrane
- Acts as a selectively permeable barrier
- Secretes chemicals that stimulate dilation or constriction
- Normally repels blood cells and platelets
Describe tunica media
- Consists of smooth muscle, collagen, and elastic tissue
- Regulated in part by sympathetic nervous system
- Controls vasoconstriction (muscle contracts) and vasodilation (muscle relaxes)
Describe tunica externa
- Collagen fibers that protect and reinforce vessels
- Anchors the vessel and provides passage for small nerves, lymphatic vessels
- Vasa vasorum (**): small vessels that supply blood to outer part of the larger vessels
What are the 4 types of arteries?
1) Conducting (elastic or large) arteries
2) Distributing (muscular or medium) arteries
3) Resistance (small) arteries
4) Metarterioles
Describe conducting (elastic or large) arteries
- Biggest arteries
- Aorta, common carotid, subclavian, pulmonary trunk, and common iliac arteries
- Have layers of elastic tissue
- Expand during systole, taking pressure
- Recoils during diastole maintains pressure and keeps blood flowing
Describe distributing (muscular or medium) arteries
- Distributes blood to specific organs
- Brachial, femoral, renal, and splenic arteries
- Smooth muscle layers constitute three-fourths of wall thickness
Describe resistance (small) arteries
- Arterioles**: smallest arteries
- Thicker tunica media in proportion to their lumen and very little tunica externa
Describe metarterioles
- In some places, short vessels that link arterioles to capillaries
- Have a precapillary sphincter
Describe an aneurysm and list its most common sites
- Weak point in artery or heart wall
- Forms a thin-walled, bulging sac that pulsates with each heartbeat and may rupture at any time
- Most common sites: abdominal aorta, renal arteries, and arterial circle at base of brain
Describe arterial sense organs
- Sensory structures in walls of major vessels that monitor blood pressure and chemistry
- Transmit information to brainstem to regulate heart rate, blood vessel diameter, and respiration
Carotid and aortic bodies are ____receptors, whereas carotid sinuses are ____receptors
Carotid and aortic bodies are chemoreceptors, whereas carotid sinuses are baroreceptors
Name 3 arterial sense organs
1) Carotid body
2) Carotid sinus
3) Aortic body
Define capillaries and what they’re composed of
- Defined as exchange vessels
- Composed of endothelium and basal lamina
Name the 3 types of capillaries
1) Continuous capillaries
2) Fenestrated capillaries
3) Sinusoids
Describe continuous capillaries
- Occur in most tissues
- Endothelial cells have tight junctions forming a continuous tube
- Intercellular clefts allow passage of small solutes such as glucose
- Blood-brain barrier do not have the clefts
- Least permeable, most common
What is the least permeable but most common type of capillary?
Continuous capillaries
Describe fenestrated capillaries and where they’re found
-Found in organs that require rapid absorption or filtration (Kidneys, small intestine)
=Endothelial cells riddled with holes called filtration pores (fenestrations)
Describe sinusoids (discontinuous capillaries) and where they’re found
- Found in liver, bone marrow, spleen
- Irregular blood-filled spaces with large fenestrations
- Allow proteins (albumin), clotting factors, and new blood cells to enter the circulation
- Most permeable
What is the most permeable type of capillary?
Sinusoids (discontinuous capillaries)
Define and describe capillary beds
- Defined as networks of 10-100 capillaries
- Usually supplied by a single arteriole or metarteriole
- At any given time, three-fourths of body’s capillaries are shut down
- Most control of flow involves constriction of arterioles that are upstream from the capillaries
- Within the capillary bed, precapillary sphincters control flow
Most control of flow involves constriction of _______ that are upstream from the capillaries.
Within the capillary bed, _________ _______ control flow
arterioles; precapillary sphincters
At any given time, _________ of body’s capillaries are shut down
three-fourths
Describe the characteristics of veins
- Greater capacity for blood than arteries
- Thinner walls, less muscular, collapse when empty, expand easily
- ______(**))_____blood pressure
List 4 types of veins and their sizes
- Postcapillary venules: smallest veins
- Muscular venules: up to 1 mm in diameter
- Medium veins: up to 10 mm in diameter
- Large veins: diameter larger than 10 mm
Describe the characteristics of medium veins
- Up to 10 mm in diameter
- Thin tunica media and thick tunica externa
- Tunica interna forms one-way valves
Describe venous sinuses
- Veins with especially thin walls, large lumens, and no smooth muscle
- Dural venous sinus and coronary sinus of the heart
- Not capable of vasoconstriction
Describe large veins
- Diameter larger than 10 mm
- Thin tunica media with thicker tunica externa
- Have venae cavae, pulmonary veins, internal jugular veins, and renal veins
Describe varicose veins and factors that can make them worse
- Blood pools in the lower legs of people who stand for long periods stretching the veins: valves fail in superficial veins, blood backflows and further distends the vessels, walls grow weak
- Hereditary weakness, obesity, and pregnancy also promote problems
Name a type of varicose vein
Hemorrhoids: varicose veins of the anal canal
What is the simplest and most common route for blood? (hint: passes through only one network of capillaries)
Heart > arteries > arterioles > capillaries > venules > veins > Heart
Define a portal system and give 3 examples
- When blood flows through two consecutive capillary networks before returning to heart
- Examples:
1) Between hypothalamus and anterior pituitary
2) In kidneys
3) Between intestines to liver
Define anastomosis
A convergence point between two vessels other than capillaries
Define an arteriovenous anastomosis (shunt)
Artery flows directly into vein, bypassing capillaries
Define a venous anastomosis
- Most common
- Vein blockage is less serious than arterial blockage
Define an arterial anastomosis
- Provides collateral (alternative) routes of blood supply to a tissue
- Coronary circulation and common around joints
Blood supply to a tissue can be expressed in terms of ______ and _______
Blood supply to a tissue can be expressed in terms of flow and perfusion
Define blood flow
The amount of blood flowing through an organ, tissue, or blood vessel in a given time (mL/min.)
Define perfusion
The flow per given volume or mass of tissue in a given time (mL/min./g)
At rest, total flow is quite constant, and is equal to the _______ _______ (5.25 L/min)
cardiac output
What are blood pressure, resistance, and flow needed for?
Delivery of nutrients and oxygen, and removal of metabolic wastes
Physical principles of blood flow based on _______ and _______
pressure and resistance
The greater the _______ difference between two points, the greater the flow.
pressure
The greater the ________, the less the flow
resistance
Define blood pressure (BP)
The force that blood exerts against a vessel wall
What two pressures are recorded in BP?
Systolic and diastolic pressure
What is a normal blood pressure in a young adult?
120/75 mm Hg
Blood flow in arteries is _______, meaning that speed surges from 40 cm/s to 120 cm/s
pulsatile
What property of arterial blood flow explains why blood spurts intermittently from an open artery?
Arterial blood flow is pulsatile
In capillaries and veins, does blood flow at a steady speed, or is it pulsatile?
Blood flows at a steady speed
True or false: BP tends to rise with age
True
What two things can cause BP to rise with age?
Arteriosclerosis and atherosclerosis
Define atherosclerosis
A build up of lipid deposits that become plaques
Define arteriosclerosis
The stiffening of arteries due to deterioration of elastic tissues of artery walls
Define hypertension and describe its consequences
- High blood pressure; a chronic resting BP > 140/90
- Consequences: can weaken arteries, cause aneurysms, promote atherosclerosis
Define hypotension and its causes
- Chronic low resting BP
- Caused by blood loss, dehydration, anemia
What 3 things determine blood pressure?
1) Cardiac output
2) Blood volume
3) Resistance to flow
Define peripheral resistance
- Resistance is opposition to flow
- Measure of the amount of friction blood encounters as it passes through vessels
Resistance hinges on what 3 variables?
Blood viscosity, vessel length, and vessel radius
Define and describe blood viscosity
- The “thickness” of blood
- RBC count and albumin concentration elevate viscosity the most
- Increased viscosity will increase resistance
Define vessel length
The farther liquid travels through a tube, the more cumulative friction it encounters (increase resistance)
What two factors of resistance typically remain relatively constant?
Blood viscosity and vessel length
Define and describe vessel radius
- The most powerful influence over flow
- Changes are frequent and significantly alter peripheral resistance
- Vasoreflexes: Vasoconstriction vs. Vasodilation
- Smaller diameter, increase in resistance
What is the most powerful influence over flow?
Vessel radius
__________ produce half of the total peripheral resistance
Arterioles
__________ is the most important factor in influencing local blood pressure
Resistance
If R (resistance) increases, blood pressure \_\_\_\_\_\_\_\_ and blood flow \_\_\_\_\_\_\_
Blood pressure increases and blood flow decreases
Describe ADH (antidiuretic hormone)
- Released when you are dehydrated
- Increases water reabsorption at kidneys, less water in urine
- More water put back into your blood
Describe aldosterone
- Reabsorb more sodium (water follows)
- Excrete potassium
Define vasomotion
Vasomotion is a quick and powerful way of altering blood pressure and flow
What are the 3 ways of controlling vasomotor activity?
1) Local control
2) Neural control
3) Hormonal control
What are the 4 types of local control of vasomotor activity?
1) Autoregulation (Metabolic theory)
2) Chemicals
3) Reactive hyperemia
4) Angiogenesis
Describe autoregulation (metabolic theory) of local control of vasomotor activity
- The ability of tissues to regulate their own blood supply
- The accumulation of wastes stimulates _(**)__________________ (increases perfusion)
- When wastes are removed, vessels constrict
Describe the local control of vasomotor activity through chemicals
- Chemicals secreted by platelets, endothelial cells, etc.
- Histamine, Bradykinin, and Nitric oxide stimulate vasodilation
What 3 chemicals stimulate vasodialation?
Histamine, Bradykinin, and Nitric oxide
Describe reactive hyperemia (hint: a local mechanism to control vasomotor activity)
If blood supply cut off then restored, flow increases above normal
Describe angiogenesis (a type of local control of vasomotor activity)
- Growth of new blood vessels
- Occurs in regrowth of uterine lining, around coronary artery obstructions, in exercised muscle, and malignant tumors
Vasomotor center of medulla exerts ________________ control over blood vessels throughout the body
vasomotor (**)
The vasomotor center of the medulla stimulates most vessels to ______, but ____vessels in cardiac muscle
constrict; dilates
The vasomotor center is the integrating center for what 3 reflexes?
1) Baroreflexes
2) Chemoreflexes
3) Medullary ischemic reflex
Describe baroreflex
- Short-term regulation:
1) Increases in BP detected by carotid sinuses
2) Glossopharyngeal nerve sends signals to brainstem
3) Results in: 1) inhibition of sympathetic cardiac and vasomotor neurons, and 2) excitation of vagal fibers that slow heart rate and thus reduce BP - Decreases in BP have the opposite effect
Describe the primary and secondary roles of chemoreflex
1) Primary role: adjust respiration to changes in pH, O2 and CO2
2) Secondary role: vasomotion
- Hypoxemia, hypercapnia, and acidosis stimulate vasoconstriction
- This increases BP, lung perfusion, and gas exchange
Describe the medullary ischemic reflex
- An automatic response to a drop in perfusion (ischemia) of the brain
1) Cardiac and vasomotor centers send sympathetic signals to heart and blood vessels
2) Increases heart rate and contraction force
3) Causes widespread vasoconstriction
4) Raises BP and restores normal perfusion to the brain
Name one vasoconstrictor hormone and one vasodilator hormone
1) Angiotensin II: potent vasoconstrictor; promotes Na+ and water retention by kidneys
2) Atrial natriuretic peptide: increases urinary sodium excretion, reduces blood volume, promotes vasodilation
What does ADH do?
ADH promotes water retention
What do epinephrine and norepinephrine do?
- Most blood vessels bind to 𝛼-adrenergic receptors—vasoconstriction
- In cardiac muscle blood vessels bind to 𝛽-adrenergic receptors—vasodilation
What are the two purposes of vasodilation and vasoconstriction?
1) General method of raising or lowering BP
-Requires medullary vasomotor center or a
hormone
2) Rerouting blood from one body region to another
Rerouting blood can be either ______ or locally controlled
centrally
Give 3 examples of blood being rerouted
1) During exercise, sympathetic system reduces blood flow to kidneys and digestive tract and increases blood flow to skeletal muscles
2) Metabolite accumulation in a tissue affects local circulation without affecting circulation elsewhere in the body
3) If a specific artery constricts, the pressure downstream drops, pressure upstream rises
Where is the only place exchanges are made between the blood and surrounding tissues?
Capillary walls
Define capillary exchange and give examples of things that are exchanged
- Two-way movement of fluid across capillary walls
- Exs: Water, oxygen, glucose, amino acids, lipids, minerals, antibodies, hormones, wastes, carbon dioxide, ammonia
What are the 3 routes chemicals use to pass by during capillary exchange?
1) Through endothelial cell cytoplasm
2) Intercellular clefts between endothelial cells
3) Filtration pores (fenestrations) of the fenestrated capillaries
What are the 4 mechanisms involved in the capillary exchange of chemicals?
Diffusion, transcytosis, filtration, and reabsorption
Describe the use of diffusion as a method for capillary exchange
- Most important method
- Lipid-soluble substances and gases (O_2 and CO_2): through plasma membranes
- Water-soluble substances (such as glucose and electrolytes): through filtration pores and intercellular clefts.
- Large particles such as proteins held back
What is the most important method of capillary exchange?
Diffusion
Describe the use of transcytosis as a method for capillary exchange
- Endothelial cells pick up material on one side of their membrane by endocytosis, transport vesicles across cell, and discharge material on other side by ____(**)______________
- Important for fatty acids, proteins, and some hormones (insulin)
Define and describe the purposes of filtration and reabsorption
- Fluid filters out of the arterial end of the capillary and osmotically reenters at the venous end
1) Determines relative fluid volumes of blood and interstitial fluid
2) Delivers materials to cells and removes metabolic wastes
Define and give an example of hydrostatic pressure
- A physical force exerted against a surface by a liquid
- Ex: Blood pressure in vessels is hydrostatic pressure
Capillaries reabsorb about __% of the fluid they filter. The other __% is absorbed by the lymphatic system and returned to the blood
85%; 15%
Capillary ______ at arterial end
Capillary ______ at venous end
Capillary filtration at arterial end
Capillary reabsorption at venous end
Describe the variations in capillary filtration and reabsorption
1) Location
- Glomeruli—devoted to filtration
- Alveolar capillary—devoted to absorption (keeps fluid out of air spaces)
2) Activity or trauma
- Increases filtration
Define edema
The accumulation of excess fluid in a tissue
Describe the 3 primary causes of edemas
1) Increased capillary filtration
- Kidney failure, histamine release, old age, poor venous return
2) Reduced capillary absorption
- Hypoproteinemia, liver disease, dietary protein deficiency
3) Obstructed lymphatic drainage
- Surgical removal of lymph nodes
Describe the effects of edemas
1) Tissue necrosis
- Oxygen delivery and waste removal impaired
2) Pulmonary edema
- Suffocation threat
3) Cerebral edema
- Headaches, nausea, seizures, and coma
4) Severe edema or circulatory shock
- Excess fluid in tissue spaces causes low blood volume and low blood pressure
What is the most important mechanism of venous return?
Pressure gradient
Name the 5 mechanisms of venous return
1) Pressure gradient
2) Gravity
3) Skeletal muscle pump
4) Thoracic (respiratory) pump
5) Cardiac suction
Describe the pressure gradient mechanism of venous return
- Most important
- Pressure at venules (12 to 18 mm Hg) drops to ~5 mm Hg where the venae cavae enters heart
Describe the gravity mechanism of venous return
drains blood from head and neck
Describe the skeletal muscle pump method of venous return
- A pump in the limbs
- Contracting muscle squeezes blood out of the compressed part of the vein; Valves prevent backflow
Describe the Thoracic (respiratory) pump mechanism of venous return
Pressure changes during breathing squeeze veins
Describe the cardiac suction mechanism of venous return
Cardiac suction of expanding atrial space
Describe the 4 ways in which exercise increases venous return
1) Heart beats faster and harder, increasing CO and BP
2) Vessels of skeletal muscles, lungs, and heart dilate and increase flow
3) Increased respiratory rate, increased action of thoracic pump
4) Increased skeletal muscle pump
Describe venous pooling, when it happens, and how to prevent it
- Occurs with inactivity when venous pressure not enough to force blood upward
- With prolonged standing, CO may be low enough to cause dizziness
- Prevented by tensing leg muscles, activate skeletal muscle pump
- Jet pilots wear pressure suits to prevent this
Define circulatory shock and list its 2 basic types
- Defined as any state in which cardiac output is insufficient to meet the body’s metabolic needs
- 2 types: Cardiogenic shock and low venous return (LVR)
Define cardiogenic shock and low venous return (LVR)
- The 2 basic types of circulatory shock
- Cardiogenic shock: inadequate pumping of heart (MI)
- Low venous return (LVR): cardiac output is low because too little blood is returning to the heart
Define the 3 principle forms of LVR shock
!) Hypovolemic shock; most common
- Loss of blood volume: trauma, burns, dehydration
2) Obstructed venous return shock - Tumor or aneurysm compresses a vein
3) Venous pooling (vascular) shock - Long periods of standing, sitting, or widespread vasodilation
The most common type of LVR shock is ________ shock
Hypovolemic shock
Define neurogenic shock
- A type of circulatory shock characterized by loss of vasomotor tone, vasodilation
- Causes from emotional shock to brainstem injury
Define septic shock
-A type of circulatory shock where bacterial toxins trigger vasodilation and increased capillary permeability
