Chapter20 Circulatory Flashcards
1
Q
Capillaries
A
Connect smallest arteries to smallest veins
2
Q
Tunica interna
A
Consists of simple squamous endothelium that acts as a selectively permeable barrier, secretes chemicals for vasoconstriction/vasodilation, and repels blood cells and platelets
3
Q
Tunica media
A
The thickest layer that consists of smooth muscle, strengthens vessels and prevents blood pressure from rupturing them, and regulates the diameter of blood vessels
4
Q
Tunica externa
A
Loose connective tissue that anchors the vessel and provides passage for small nerves and lymphatic vessels
5
Q
Vasa vasorum
A
Small vessels that supply blood to at least the outer half of the larger vessels
6
Q
A
Strong, resilient tissues that resist high blood pressure
7
Q
What are conducting arteries
A
The thickest/strongest arteries that expand during ventricular systole and recoil during ventricular diastole which lessens fluctuations in blood pressure and takes stress off arteries downstream
8
Q
What are examples of conducting arteries
A
Aorta, common carotid, subclavian, pulmonary trunk, common iliac arteries
9
Q
What are distributing arteries
A
Distribute blood to specific organs; smooth muscle layers constitute majority of vessel wall
10
Q
What are examples of distributing arteries
A
Brachial, femoral, renal, and splenic arteries
11
Q
What are resistance (small) arteries
A
They are arterioles - the smallest arteries - that control the amount of blood that goes to various organs
12
Q
What are metarterioles
A
Known as thoroughfare channels; short vessels that link arterioles to capillaries and allow blood to bypass capillary bed
13
Q
What is an aneurysm
A
Thin-walled, bulging sac that pulsates with each heartbeat; may rupture at any time causing hemorrhage
14
Q
Where are the most common sites of aneurysm
A
Abdominal aorta, renal arteries, arterial circle at the base of the brain
15
Q
What causes an aneurysm
A
Congenital weakness of blood vessels, trauma, bacterial infections; most common cause is combination of atherosclerosis and hypertension
16
Q
What happens in the walls of the major arteries above the heart?
A
Blood pressure and composition is monitored, information is transmitted to the brain stem that serves to regulate heartbeat, blood vessel diameter, and respiration
17
Q
What do the baroreceptors in the carotid sinuses do?
A
Monitors blood pressure, decreases heart rate and causes vasodilation in response to high BP; located in the internal carotid artery
18
Q
What do the chemoreceptors in the carotid bodies do?
A
Monitor blood composition and transmit signals to brain stem respiratory centers; adjust respiratory rate to stabilize pH as well as CO2 and O2 levels; oval bodies near branch of common carotid
19
Q
What do the chemoreceptors in the aortic bodies do?
A
They have the same function as carotid bodies (monitoring and adjusting) but are located in the walls of aortic arch near arteries to head and arms
20
Q
What are capillaries
A
Site where nutrients, wastes, and hormones pass between blood and tissue fluid; known as the “business end” of the cardiovascular system
21
Q
What are capillaries made of
A
Only endothelium and basal lamina so exchange can occur at a very fast rate
22
Q
Where are capillaries absent from
A
Tendons, ligaments, epithelia, cornea, and lens of eye
23
Q
What are the most common capillaries
A
Continuous capillaries
24
Q
What are continuous capillaries
A
Endothelial cells held together by tight junctions forming a continuous tube with intercellular clefts
25
What do intercellular clefts do
Allow passage of solutes such as glucose, restrict passage of large molecules such as plasma proteins, platelets, and blood cells
26
What are pericytes
They wrap around the capillaries to contract and regulate blood flow
27
Where are fenestrated capillaries
They are found in organs that require rapid absorption or filtration such as the kidneys and small intestines
28
What are fenestrated capillaries
Endothelial cells riddled with holes called filtration pores (fenestrations) that allow passage of only small molecules; retain most proteins and larger particles in bloodstream
29
What are sinusoids
Endothelial cells separated by wide gaps that occur in the liver, bone marrow, and spleen; irregular blood filled spaces with large fenestrations
30
What do sinusoids do
Allow proteins (albumin), clotting factors, and new blood cells to enter circulation
31
What are capillary beds
Organized networks of capillaries supplied by a single arterioles or metarteriole; transition to venules or drain into a thoroughfare channel at the distal end
32
What are precapillary sphincters
They control which beds are well perfused
33
What happens when precapillary sphincters are relaxed
Capillaries are well perfused with blood and engage in exchanges with tissue fluid
34
What happens when precapillary sphincters contract
Blood bypasses capillaries, flows through thoroughfare channel to venule
35
What do veins have more of than arteries
Greater capacity for blood containment than arteries
36
Describe veins compared to arteries
Thinner walls, flaccid, less muscular, elastic tissue; collapse when empty, expand easily; have steady blood flow; merge to form larger veins; subjected to relatively low blood pressure
37
What are the smallest veins
Post capillary venules
38
What do post capillary venules do
Receive blood directly from capillaries or by distal end of thoroughfare channels
39
Describe postcapillary venules
Porous; fluid exchange with surrounding tissues; most leukocytes emigrate from bloodstream through venule walls
40
Describe muscular venules
Receive blood from postcapillary venules; 1 or 2 layers of smooth muscle in tunica media
41
Describe medium veins
Tunica interna forma venous valves; skeletal muscle pump propels venous blood back toward the heart
42
Describe venous sinuses
Veins with especially thin walls, large lumens, and no smooth muscle; dural venous sinus of brain and coronary sinus of the heart; not capable of vasomotion
43
Describe large veins
Some smooth muscle in all 3 tunics; tunica externa thickest layer and contains longitudinal bundles of smooth muscle; vena cavae, pulmonary veins, internal jugular veins, renal veins
44
What are varicose veins
Blood pools in lower legs of people who stand for long periods stretching the veins
45
What is the physiology of varicose veins
Cusps of valves pull apart in enlarged superficial veins, further weakening the vessels. Blood back flows and further distends vessels, their walls grow weak and develop into varicose veins
46
What can contribute to varicose veins
Hereditary weakness, obesity, pregnancy
47
What is the simplest and most common circulatory route?
Heart to arteries to arterioles to capillaries to venules to veins; passes only one network of capillaries from time it leaves the heart until the time it returns
48
Describe a portal system
Blood flows through 2 consecutive capillary networks before returning to the heart; found between hypothalamus and anterior pituitary as well as in kidneys between intestines and liver
49
Describe arteriovenous anastomosis
Shunt; artery flows directly into vein by passing capillaries
50
What is venous anastomosis
One vein empties directly into another
51
What is arterial anastomosis
Two arteries merge providing collateral routes of blood supply to a tissue; coronary circulation and common around joint
52
Define blood flow
The amount of blood flowing through an organ, tissue, or blood vessel in a given time (mL/min); at rest, total flow is equal to the cardiac output (5.25 L/min)
53
Define perfusion
The flow per given volume or mass of tissue in a given time (mL/min/g)
54
What is perfusion important for
Delivery of nutrients and oxygen, and removal of metabolic wastes
55
How are pressure and flow related
The greater pressure difference between 2 points, the greater the flow; the greater the resistance the less the flow
56
Describe blood pressure
The force that blood exerts against a vessel wall; use sphygmomanometer at brachial artery
57
What are the two pressure recorded when taking blood pressure
Systolic - peak arterial BP taken during ventricular systole - and diastolic - minimum arterial BP taken during ventricular diastole between heart beats
58
What is the normal BP in a healthy adult
120/75 mm Hg
59
What is peripheral resistance
Opposition to flow that blood encounters in vessels way from the heart
60
What are the 3 variables that effect resistance
Blood viscosity, vessel length, vessel radius
61
What effects blood viscosity
RBC count, albumin concentration, anemia and hypoproteinemia (decrease viscosity), polycythemia and dehydration (increase viscosity)
62
What effect does vessel radius have on peripheral resistance
Most powerful resistance; vasoreflexes changes laminar flow (flows in layers, faster in center)
63
How does blood velocity change from aorta to capillaries and why
Decrease due to greater distance, smaller radii, and farther from heart (total cross sectional area gets greater and greater)
64
How does velocity change from capillaries to vena cava and why?
Increases due to larger veins/less resistance, large amount of blood forced into smaller channels, noteworthy that it never regains velocity of large arteries
65
What are arterioles role in peripheral resistance
Most significant point of control over peripheral resistance and flow; best positioned to regulate flow into capillaries, most numerous control points, more muscular in proportion to their diameters; highly capable of changing radius
66
What are vasoreflexes
Quick and powerful ways of altering blood pressure and flow; vasoconstriction and dilation
67
What are the 3 ways of controlling vasomotor activity
Local control, neural control, hormonal control
68
What are the components of local control
Auto regulation, vasoactive chemicals, reactive hyperemia, angiogenesis
69
What is autoregulation
Ability of tissue to regulate their own blood supply
70
What is the metabolic theory of autoregulation
If tissue is inadequately perfused, wastes accumulate, stimulating vasodilation which increases perfusion; blood stream delivers oxygen and removes metabolites, when wastes removed vessels constrict
71
What are vasoactive chemicals
Substances secreted by platelets, endothelial cells, and peri vascular tissue to stimulate vasomotion; histamine, prostacyclin, nitric oxide
72
What is reactive hyperemia
If blood supply is cut off and then restored, flow increase above normal
73
What is angiogenesis
Growth of new blood vessels; controlled by growth factors and inhibitors; occurs in regrow that of uterine lining, around coronary artery obstructions, in exercised muscle, and malignant tumors
74
Describe neural control
Vessels under remote control by CNS and ANS; vasomotor center exerts sympathetic control over blood vessels
75
What effect does the vasomotor center have on vessels
Stimulates most vessels to constrict, but dilates vessels in skeletal and cardiac muscle to meet demands of exercise; vasomotor center is the integrating center for 3 autonomic reflexes: baroreflexes, chemoflexes, medullary ischemic reflex
76
Describe the baroreflex
Automatic, negative feedback response to a change in BP
77
What detects the increases and decreases in BP
Carotid sinuses
78
Where are baroreflex signals sent
to brainstem
79
What type of BP change are baroreflexes important for
Short-term; not cases of chronic hypertension
80
Described the chemoreflex
Autonomic, response to changes in blood chemistry (pH, O2, and CO2 concentrations)
81
where are chemoreceptors found
Aortic and carotid bodies in aortic arch, subclavian arteries, and external carotid arteries
82
What is the primary role of the chemoreflex
adjust respiration to changes in blood chemistry
83
What is the secondary role of the chemoreflex
Vasomotion: Hypoxemia, hypercapnia, and acidosis stimulate chemoreceptors causing widespread vasoconstriction, increases in BP, lung perfusion, and gas exchange; also stimulates breathing
84
Describe the medullary ischemic reflex
Autonomic response to a drop in perfusion of the brain; Medulla oblongata monitors its own blood supply and activates corrective reflexes when ischemia is detected
85
How does the medulla oblongata activate corrective reflexes
Cardiac and vasomotor centers send sympathetic signals to heart and blood vessels which increases heart rate and contraction force, causes widespread vasoconstriction, and raises BP and restores normal perfusion to the brain
86
What is angiotensin II
A type of hormonal control that is a potent vasoconstrictor; it raises blood pressure by promoting Na+ and water retention by kidneys and increases blood volume and pressure
87
What is aldosterone
Hormonal control that promotes Na+ retention by kidneys which promotes water retention; maintains BP
88
What is Natriuretic peptide
Hormonal control that increases urinary sodium excretion by reducing blood volume and promoting vasodilation; lowers blood pressure
89
What is ADH
Hormonal control that promotes water retention and raises BP
90
What is epinephrine and norepinephrine
Hormonal control that causes most blood vessels to vasoconstrict except skeletal and cardiac muscle blood vessels that vasodilate
91
What are two purposes of vasomotion?
Generalizes raising or lowering of BP throughout entire body; Selectively modifying perfusion of a particular organ and rerouting blood from one body region to another
92
What are capillaries
only place where exchanges between blood and surrounding tissue occur
93
Define capillary exchange
two-way movement of fluid across capillary walls; water, oxygen, glucose, amino acids, lipids, minerals, antibodies, hormones, wastes, carbon dioxide, ammonia
94
Mechanisms for capillary exchange
Diffusion, transcytosis, filtration and reabsorption
95
When can diffusion occur in capillary exchange
Only if solute can permeate plasma membrane of endothelial cell (lipid soluble); use filtration pores and intracellular clefts; Large particles such as proteins are held back
96
Describe transcytosis in capillary exchange
Endothelial cells pick up material on one side of plasma membrane, transport vesicles cross cell, and discharge material on other side; important for fatty acids, albumin, and some hormones (insulin)
97
Define filtration and reabsorption
Fluid filters out of arterial end of capillary and osmotically reenters at venous end
98
Define hydrostatic pressure
physical force exerted against a surface (capillary wall) by a liquid (blood) that drives fluid out of a capillary; high on arterial end of capillary, low on venous end
99
What are the opposing forces to hydrostatic pressure
Colloid osmotic pressure (COP) and Oncotic pressure
100
What is COP
draws fluid into capillary; results from plasma proteins (albumins) - more in blood than surrounding tissue fluid
101
What is oncotic pressure
net COP (blood COP - tissue COP); this pressure draws H20 into capillary by osmosis
102
What is edema
Accumulation of excess fluid in a tissue; fluid filters into a tissue faster than it is reabsorbed
103
What are the 3 primary causes of edema
Increased capillary filtration (kidney filtration, histamine release, old age, poor venous return), Reduced capillary reabsorption (hypoproteinemia, liver disease, dietary protein deficiency), and Obstructed lymphatic drainage or surgical removal of lymph nodes (fluid accumulation distal to obstruction)
104
What are some consequences of edema
Tissue necrosis, pulmonary edema, cerebral edema, circulatory shock or severe edema
105
What is venous return
flow of blood back to heart
106
What are the mechanisms of venous return
Pressure gradient, Gravity, skeletal muscle pump, thoracic (respiratory) pump, and cardiac suction
107
How does exercise increase venous return
Heart beats faster and harder, increasing CO and BP; Vessels of skeletal muscles, lungs and heart dilate to increase flow; increased respiratory rate, increased action of thoracic pump; increased skeletal pump
108
What occurs with inactivity
Venous pooling - accumulation of blood in the limb
109
What is circulatory shock
Any state in which cardiac output is insufficient to meet body's metabolic needs
110
What are some examples of circulatory shock
Cardiogenic shock, Low venous return (hypovolemic shock, obstructed venous return shock, venous pooling shock), neurogenic shock, septic shock, anaphylactic
111
What are the two types of responses to circulatory shock
Compensated shock and decompensated shock
112
What is compensated shock
several homeostatic mechanisms bring about spontaneous recovery; example is fainting
113
What is decompensated shock
Triggered when compensated shock mechanism fails; life-threatening positive feedback loop occurs; Condition gets worse causing damage to cardiac and brain tissue
114
What is the brains role in its own regulation of BP and chemistry
Regulates its own blood flow to match changes in BP and chemistry
115
What are transient ischemic attacks
brief episodes of cerebral ischemia caused by spasms of diseased cerebral arteries
116
What is a CVA or stroke?
Sudden death of brain tissue caused by ischemia
117
What is the state of arterioles in skeletal muscles at rest
Arterioles constrict, most capillary beds shut down
118
What is the state of arterioles in skeletal muscles when exercising
Arterioles dilate in response to epinephrine and NE, precapillary sphincters dilate due to muscle metabolites like lactic acid, CO2, blood and flow can increase 20 fold
119
Is capillary pressure high or low in the lungs
Low pulmonary pressure so that there is more time for has exchange
