peripheral circulation
Terms
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- ___________ is the common effector for all types of vascular control
- Vascular smooth muscle
- Vascular smooth muscle is Capable of ________ contraction
- graded
- Vascular smooth muscle is Capable of maintaining partial contractions for long periods of time. This gives rise to vascular ____ .
- tone
- __________________Is a property of the muscle cells.
- Spontaneous tone:
- 2. Induced tone: e.g., neural tone is induced by ____________ released from sympathetic noradrenergic nerve endings.
- norepinephrine
- Vascular control depends upon the existence of a _______, upon which can be superimposed relaxation or further contraction of the vascular smooth muscle.
- basal tone
- __________ are independent of vascular innervation and circulating hormones.
- Intrinsic Control Mechanisms:
- Example of intrinsic control responses includes _________ where excess blood flow occurs after a period of reduced flow or zero flow, e.g. due to arterial constriction or occlusion.
- reactive hyperemia:
- Perfusion Pressure =
-
Arterial Pressure-Venous Pressure,
measured distal to occlusion. - Example of intrinsic control responses includes, ________ increased blood flow accompanies an increase in metabolic activity, even with a constant perfusion pressure
- Functional hyperemia (or active hyperemia):
- Autoregulation of blood flow in response to changes in perfusion pressure _______ blood flow tends to remain nearly constant over a wide range of arterial pressure.
- steady state
- A Possible mechanisms of intrinsic vascular control, includes the ______ mechanism. Where increased stretch of vascular smooth muscle cells causes contraction (e.g., following an increase in arterial pressure). This results in vascular constriction. Decr
- Myogenic
- A Possible mechanisms of intrinsic vascular control, includes the ______ mechanism. Where direct effects of vasoactive metabolites on have an effect on arterioles.
- Metabolic mechanism:
-
Metabolic mechanism: increase in Tissue Cell Metabolic Rate leads to increase in Interstitial Fluid Concentrations of
K+, H+, CO2, inorganic phosphate, adenosine, ATP , ADP, AMP and increase in Total Osmolarity & a decrease in Interstitial Fluid - Relaxation
-
Effects of vasoactive metabolites on _______ neurons innvervating arterioles:
increase Tissue Cell Metabolic Rate leads to increase in Interstitial Fluid Concentrations of
K+, H+, adenosine, ATP , ADP, AMP and increase in Total Osmolarity. This - sympathetic
- Both myogenic and metabolic mechanisms are probably involved to varying degrees in different organs. The normal ratio of ___________ determines which mechanism dominates.
- blood flow to metabolic rate (BF/MR)
- High BF/MR: usually associated with larger _____ component. (e.g., intestine, kidney, resting skeletal muscle).
- myogenic
- Lower BF/MR: usually associated with larger _______ component. (e.g., brain, heart, exercising skeletal muscle).
- metabolic
- Intrinsic mechanisms affect primarily the _______ side of the microcirculation. The venular side usually dilates or constricts passively following arteriolar dilation or constriction
- arteriolar
- Extrinsic Control Mechanisms are _____
- Neural
- Sympathetic Noradrenergic Innervation (Also commonly termed “Adrenergic†Innervation use the Neurotransmitter: ____________
- norepinephrine (NE)
- NE stimulates predominately _____ adrenergic receptors in vascular smooth muscle, which cause constriction.
- alpha
- Beta-2 adrenergic receptors are also present in some vessels, but increased sympathetic nerve activation normally causes ________
- net constriction
- The physiological importance of neural activation of any vascular _____ receptors is uncertain. They may be activated primarily by epinephrine from the adrenal medullae.
- beta-2
- Arterioles and venules receive sympathetic ________ innervation. Precapillary sphincters also may be innervated in some tissues.
- noradrenergic
- Sympathetic noradrenergic neurons are __________ at rest.
- tonically active
-
Effects of increased activation of sympathetic noradrenergic neurons:
a. Arteriolar ________, with increased precapillary resistance and decreased blood flow to downstream capillaries.
b. Decreased capillary ______ downstream from i -
a. constriction
b.pressure
c.Constriction -
During vasoconstriction:
1) Venous _____capacity decreases.
2) Venous blood is displaced toward the _____.
3) Venous ______ and ventricular filling increase.
d. Vascular beds in different organs differ in degree of constri -
1. volume
2.heart
3.return - Most neurally mediated vaso- and venodilation results from ______ sympathetic noradrenergic activation ("passive dilation").
- reduced
- Sympathetic Cholinergic DILATOR Innervation Occurs primarily in _______vessels supplying skeletal muscle.
- precapillary
- Sympathetic Cholinergic DILATOR Innervation, Neurotransmitter is ________
- acetylcholine (ACh)
- Increased activation causes of Sympathetic Cholinergic DILATOR Innervation causes ________
- vasodilation
- Mechanism of dilation in Cholinergic DILATOR Innervation appears to involve prejunctional inhibition of ____ release from noradrenergic neurons innervating the same vessels.
- NE
- Sympathetic cholinergic dilator neurons are not _____ active, and innervate only precapillary vessels.
- tonically
- Sympathetic cholinergic dilator neurons may be activated at the beginning of ______ . Activation in highly emotional states could result in _______.
-
exercise
fainting - . In humans, some sympathetic dilator neurons may release ______ , which would stimulate vascular _____ receptors to dilate the vessels.
-
epinephrine
beta-2 - "Active dilation" by beta-2 adrenergic receptors may result primarily from circulating ______ released by the adrenal medullae. Physiological importance is uncertain, but it may modulate alpha receptor mediated constriction. Beta-2 receptors ar
- epinephrine
-
a. Genitals (erectile tissues; some fibers release nitric oxide as transmitter.)
b. Bladder
c. Large intestine
d. Heart
e. Brain
all have vessels that receive _________innervation (note: This is quite limited compared to sy - parasympathetic
- In most cases, the parasympathetic neurotransmitter is ____, which appears to inhibit release of NE from noradrenergic neurons innervating the same vessels, resulting in _________.
-
ACh
vasodilation - In erectile tissues of the genitals, ACh may cause endothelial release of ___
- NO
- . In salivary glands, ACh release appears to cause formation of ______ from a plasma protein. ______ then causes dilation of salivary gland vessels.
-
bradykinin
Bradykinin - “Nitroxidergic†Innervation: cerebral and other vessels may receive vasodilator fibers which release ______. These neurons may have tonic activity.
- nitric oxide (NO)
- __________ is the primary adrenal medullary hormone released in humans.
- Epinephrine:
- Epinephrine is released during increased _______ activity
- sympathetic
- the ______ mechanisms described above usually dominate over the effects of epinephrine released during increased sympathetic discharge
- neural
- Circulating levels of epinephrine are normally low. Increases in epinephrine cause dilation of vessels in _________ & constriction of vessels in the ____.
-
skeletal muscle
skin - Angiotensin II (ANG-II) is A powerful _________
- vasoconstrictor
- Formation of Ang II is initiated by low plasma _____ concentration and low blood _______
-
sodium
pressure - Formation of ANG-II continues when the kidney releases ______. This acts on a plasma protein to form __________. This converted to ANG-II by __________
-
renin
angiotensin I
(ANG-I)angiotensin converting enzyme (ACE) - ANG II is normally involved in ____and ____ balance rather than vascular control.
-
salt
water - Antidiuretic hormone (arginine vasopressin in humans) is a _________.
- Vasoconstrictor
- ADH is Released by _______ in response to lowered blood volume and increased extracellular osmolarity.
- posterior pituitary
- ADH May be important in the compensatory response to _______, and possibly in maintaining normal blood pressure
- hemorrhage
- Hormones of the adrenal cortex are ________
- steroids
- The role of steroids seems to be ________. Normal reactivity of vessels to neurotransmitters and hormones seems to depend upon normal levels of steroids.
- "permissive"
- Histamine ______ arterioles
- dilates
- Histamine eleased by _____ cells following injury and allergic reactions.
- mast
- histamine _______ capillary permeability
- increases
- histamine _____ edema formation
- Promotes
- Atrial natriuretic peptide (ANP, atriopeptin) and B-type natriuretic peptide (BNP, first found in the Brain Stored in and secreted from atrial (ANP) and ventricular (BNP) cells in response to increased _____ of the cardiac chambers.
- distension
- Additional stimuli for ANP release: cardiac ______ nerve activation, Angiotensin II, Endothelin, and possibly others. May also apply to BNP release
- sympathetic
- ANP and BNP cause ______ and reduce vascular resistance.
- vasodilation
- . ANP and BNP increase urinary excretion of ____ , which lowers blood volume.
- Na+
- ANP and BNP participate in the long-term regulation of ______ pressure and extracellular fluid volume, via additional mechanisms
- arterial
- ANP and BNP degradation is via neutral _______.
- endopeptidase
-
Endothelium-Dependent Vasodilation. General Mechanism:
Blood-Borne Vasoactive _____
V
Endothelial Membrane ______
V
Endothelial Cell Synthesis and Release
of ___________
V
Arteriolar Smooth Muscle _______
-
Substances
V
Receptors
V
Endothelium-Derived Relaxing Factor(s)
(EDRFs)
V
Relaxation -
Examples of vasoactive substances which appear to cause _____ release:
1. Acetylcholine (especially exogenous ACh injected into the bloodstream).
2. Vasopressin: (reduces constriction due to vasopressin.)
3. Bradykinin
4. Serot - EDRF
- Increased rate of blood _____ also stimulates EDRF release and causes dilation (flow-induced vasodilation), which would enhance the flow increase.
- flow
- A major EDRF is _______.
- nitric oxide (NO)
- There appears to be a _______-dependent vasodilator tone existing in many, if not all, vascular beds.
- nitric oxide
- __________ is also a dilator released by endothelial cells.
- Prostacyclin (PGI2)
- ________ is a powerful constrictor peptide released by endothelial cells. Other endothelium-derived constricting factors (EDCFs) appear to exist. Some may be released under pathological conditions such as anoxia and hypertension.
- Endothelin
- Hypertension and atherosclerotic damage to the vascular endothelium may reduce release of ___ and other EDRFs and enhance release of endothelin and other EDCFs, promoting arterial spasm. These possibilities are still being investigated.
- NO
- The _________ is the"Vasomotor Center":
- Medulla Oblongata
- The Medulla Oblongata contains the Vasoconstrictor ("Pressor") Area called area _____ in some books.
- "C-1"
- Activation of C1 results in vaso- and veno _______.
- constriction
- C1 neurons project to sympathetic preganglionic neurons in the spinal cord, and ______ their activities.
- increase
- Tonic activity of C1 at rest results in sympathetic noradrenergic neural ____ of blood vessels and heart.
- tone
- Spontaneous rhythmic changes in tonic activity produce oscillations in resting arterial blood ______
- pressures
- Vasodilator ("Depressor") Area is also called area ____ in some books.
- "A-1"
- A1 neurons project to and _____ the activity of the vasoconstrictor area. The pathways may involve more than one inhibitory interneurons.
- inhibit
- Nucleus Tractus Solitarius (NTS) Receives sensory input from the vagus and glossopharyngeal nerves, including afferent impulses from the _______
- baroreceptors
- ________ interneurons project from the NTS to the vasoconstrictor area
- Inhibitory
- Increased activation of the NTS by increased afferent input from the baroreceptors ________ the vasoconstrictor area. (The vasodilator area may be simultaneously activated.) Diminished afferent input from the baroreceptors has the opposite effects.
- inhibits
-
Medulla Oblongata: Nucleus Ambiguus and Related Areas Near the Dorsal Motor Nucleus of the Vagus Nerve.
These are called the _______ or "cardioinhibitory area" in many books. - "vagal area"
- The vagal area is the origin of the vagal parasympathetic preganglionic neurons which innervate the heart. The area is ______ active at rest.
- tonically
- The VA receives _______ neurons from the NTS. May also receive afferent input from baroreceptors directly.
- excitatory
- Increased activation of the VA by increased afferent input from the baroreceptors _______ parasympathetic impulses to the heart. Diminished baroreceptor input has the opposite effect.
- increases
- Some books include the VA area as part of the of the __________ medulla.
- "vasomotor center"
- There is evidence that the vagal and pressor areas ______ the other when active E.g., increased pressor area activity inhibits vagal area activity.
- inhibit
- Hypothalamus is an important ________ center for body temperature control, and other functions
- integrative
- Activation of the anterior region of the hypothalmus causes ______blood pressure, vaso_______ , _____cardia.
-
decreased
dilation
brady - Activation of posterolateral region of the hypothalmus causes ____ blood pressure, vaso______ , ____ cardia
-
increased
constriction
tachy - The hypothalamus receives input from cutaneous temperature receptors. Causes reflex cutaneous vaso______ in response to heat, and vaso______ in response to cold.
-
dilation
constriction -
Cerebral Cortex:
Activation of some regions results in vasodilation, while activation of others results in vasoconstriction.
It is involved in vascular actions producing _____ ,_____ and ______. -
blushing
fainting
sexual arousal - The Cerebral Cortex is the origin of neurons which project to the sympathetic postganglionic dilator neurons innervating vessels in _______.
- skeletal muscle
- Baroreceptors are sensory nerve terminals which respond to stretch by ________ action potential generation.
- increased
- Major baroreceptors involved in continuous, short-term adjustments of _____ pressure.
- arterial
- Major baroreceptors include, the _______; afferent fibers in the sinus nerve and glossopharyngeal nerves. And the _______ ; afferent nerve fibers in the vagus nerves.
-
Carotid sinus
Aortic arch - The afferent fibers of baroreceptors have terminals in the __________
- nucleus tractus solitarius (NTS).
- Baroreceptors adapt to sustained stretch, so they respond more to _____ changes in pressure than to slow or sustained changes.
- rapid
- Baroreceptors respond to changes in _______ as well as mean arterial pressure
- pulse pressure
- The normal range of pressures they respond to is about 50 to 200 mm Hg. This can be altered by disease states such as ______ .
- hypertension
- The __________ results when changes in arterial mean and/or pulse pressure elicit reflex responses which attempt to return pressure toward normal (may not actually reach normal).
- Baroreceptor Reflex
- Since mean arterial pressure (MAP) = cardiac output (CO) x total peripheral resistance (TPR), MAP can be altered by adjustments in CO (stroke volume x heart rate) and/or TPR. All these are under control of the ________.
- autonomic nervous system
-
An initial increase in arterial pressure results in _________ of carotid and aortic baroreceptors (increased action potential frequency).
Vasodilator area may also be activated. - Stimulation
- An initial increase in arterial pressure results in increased frequency of afferent impulses to the _____.
- medulla
- An initial increase in arterial pressure results in Inhibition of ________ area of medulla and activation of "______ area".
-
vasoconstrictor
vagal -
An initial increase in arterial pressure results in decreased tone in sympathetic fibers to blood vessels and heart, resulting in:
1) Vaso-______(decreases TPR)
2) Cardiac _____ 3) Decreased cardiac ________(decreases SV and CO) -
1. dilation
2. slowing
3. contractility - An initial increase in arterial pressure results ine. Increased tone in _______ fibers to heart decreases HR.
- parasympathetic
- An initial increase in arterial pressure results in _____ being decreased toward the original value (may not actually reach original value).
- MAP
- The ________ involves Carotid and aortic body sensors for changes in arterial PO2, PCO2, and pH. It has afferents in glossopharyngeal and vagus nerves, respectively. It is stimulated by hypoxia, hypercapnia and acidosis.
- Chemoreceptor reflex
- Primary reflex activity of chemoreceptors is in regulation of ________
- ventilation
- Chemoreceptor stimulation sends impulses to vasomotor center, resulting in reflex vaso-_________ .
- constriction
- Chemoreceptor stimulation potentiates baroreceptor reflex in response to decreased _____ (it then increased toward normal).
- pressure
- When chemoreceptor stimulation and increased pressure occur simultaneously, the _______ dominates (pressure is reduced toward normal).
- baroreceptor reflex
- ______ and _______pressoreceptors are also called cardiopulmonary baroreceptors
-
Atrial
pulmonary - Increased volume of the atria causes reflex vasodilation and decreased blood pressure. Atrial pressures are normally much lower than those in systemic arteries, so these are low pressure receptors responsive to ______ changes.
- volume
- Collapse of lungs causes reflex vaso______ , via stretch receptors in the lungs
- constriction
- Direct stimulation of the vasomotor center by increased arterial PCO2 and decreased pH, results in vaso__________ .
- constriction
- _________ decreases in arterial PO2 may activate vasomotor center by releasing neurotransmitters.
- Moderate
- _____ decreases in arterial PO2 depress vasomotor center activity.
- Large
- _______, resulting in strong vasoconstriction is probably due to local increases in PCO2 and decreases in PO2, which transiently stimulate the vasomotor center of the medulla.
- Cerebral ischemic response
- Distension of viscera often causes diffuse pain and vaso______ .
- dilation
- Cutaneous pain usually causes vaso______ , but deep cutaneous pain may cause vaso_______ .
-
constriction
dilation