Neurohumoral Control Of The Heart And Circulation Flashcards
This operates the visceral reflexes
Autonomic nervous system
__________ primarily controls the heart, and _______ controls the vasculature and excitatory functions of the heart
Parasympathetic nervous system
Sympathetic nervous system
This receives input from baro and chemo receptors
NTS
Parasympathetic is excitatory or inhibitory?
Inhibitory
Extrinsic control of peripheral blood flow is mainly mediated by what?
Sympathetic nervous system
Nervous control of the circulation affects what global functions?
- Redistributing blood flow
- Increasing pump activity of the heart
- providing rapid control of blood pressure
During sympathetic stimulation, sympathetic nerves release what?
Norepinephrine
-acts directly on alpha adrenergic receptors
During sympathetic stimulation the adrenal glands release what?
- mostly epinephrine (80%)
- lesser amount of norepinephrine (20%)
Norepinephrine released fro the sympathetic nerves has a long or short period of action
Short
____________ is a principle vasoconstrictor
Norepinephrine
T/F: epinephrine will cause vasodilation in a few tissues due to beta 2 adrenergic stimulation
True
Dose dependent. Will become vasoconstrictor at higher doses
What do the adrenergic receptors do when stimulated?
Alpha: -vasoconstriction Beta 1: -increased heart rate -increased contractility Beta 2: -vasodilation -bronchodilation -uterine relaxation -glycogenolysis
Sympathetic activation of the heart does what?
- chronotropy = HR
- inotropy = contractility
- dromotropy = conduction velocity
- lusitropy = relaxation
Cardiac contraction and relaxation are both accelerated by activation of what 2 things?
- catecholamines
- adenylyl cyclase
Increase in cAMP activates a protein kinase which phosporylates the ca++ channel in the sarcolemma resulting in a greater influx of what?
Calcium
This causes an increase in contractility
When contractility is increased, relaxation is also enhanced (lusitropy) by the uptake of what by the sarcoplasmic reticulum?
Calcium
Name the 6 cardiovascular reflexes
- Baroreceptor reflex
- Atrial trench receptor reflexes (bainbridge reflex)
- Behold-jarisch reflex (ventricular receptor reflex)
- Chemoreceptor reflex
- CNS ischemic response (Cushing response)
- Diving reflex
Where are baroreceptors located?
Carotid sinus
Aorta arch
Baroreceptor reflex
- responsible for rapid adjustments in BP
- Stimulated when stretched
- signals transported through herings nerve to glossopharangel nerve, NTS
-aortic transported by vagus nerve to NTS
Baroreceptor reflex reduces the daily variation in BP by how much from that which would occur if this system was not present?
1/2 - 1/3
This helps with postural changes in BP
Baroreceptor reflex
*this functions well within normal BP range, if out of range have difficulty
Atrial stretch receptors are sensitive to what?
Volume
Stretching—>increased water and sodium excretion
Baroreceptors are sensitive to what?
Pressure
Atrial stretch receptors are located where?
- vena cava: right atrial junction
- pulmonary vein: left atrial junction
Bainbridge reflex
- Increased intravascular volume
- atrial stretch receptors
- medullary activation (via vagus nerve)
- increased sympathetic activity to SA node
- increased HR
If you give a volume of fluid fast what will happen to HR?
If will increase due to the bainbridge reflex
- degree and direction of HR change depends on the prevailing HR
- slow baseline HR->see increased HR with infusion
- high baseline HR-> see decreased HR with infusion
What are some of other cardiac reflexes due to atrial stretch receptor activation?
- decreased sympathetic activity to kidney -> increased UO
- decreased vasopressin (ADH) -> increased UO and decreased water reabsorption, decreased BP
- increased atrial natriuretic peptide -> increased natriuresis, increased UO, decreased BP
Behold-Jarisch Reflex is AKA
Ventricular receptor reflex
What is the ventricular receptor reflex?
Responds to noxious ventricular stimuli
negative reflex
Will see:
- hypotension
- bradycardia
- coronary artery dilation
What elicits the ventricular receptor reflex?
Strong contraction of an underfilled ventricle
Peripheral chemoreceptors are located where?
Aortic and carotid bodies
Peripheral chemoreceptors are primary concerned with what?
Regulation of respiration
- decreased in arterial blood O2 tension, CO2 excess, and/or hydrogen excess results in excitation of the vasomotor center
- this may occur whenever the atrial pressure falls below a critical level (inadequate blood flow to the chemoreceptors)
- this reflex helps to return the BP back to normal level
The peripheral chemoreceptors are not stimulated strongly until atrial pressure falls below what?
80mmHg
Pathway of baroreceptor and chemoreceptor msgs
Hering’s nerve
Vagus nerve
Vasomotor center of the brain
What stimulates the CNS ischemic response?
- Decrease blood flow to vasomotor center in medulla
- increased local concentration of CO2 results in stimulation in the medulla
- results in increased BP
- very poor activator of the sympathetic nervous system
What caused a Cushing response?
Increased intra-cranial pressure
- special type of CNS ischemic response
- increased ICP results in increased BP until blood flows once again in the vessels of the brain
What activates the diving reflex?
Cold water on face
-information relayed to brain stem via facial nerve afferents
Survival mechanism. Body shuts down “less important” parts trying to conserve O2 for heart and brain
How can HR change with respirations?
HR increases with inspiration and slows with expiation
- increased sympathetic activity with inspiration
- increased parasympathetic activity with expiration
What are circulating catecholamines?
Epinephrine
Norep
Epinephrine will increase what and decrease what?
Increase: Cardiac -HR -Inotropy -Dromotropy Vasculature -Resistance
Decrease:
Vasculature
-resistance — some vascular beds constrict, others dilate
-Capacitance
Norepinephrine increases and decreases what?
Increases: Cardiac -HR -Inotropy -Dromotropy
Vasculature
-Resistance
Decreases:
Cardiac
-HR - will get rebound bradycardia
-Capacitance
How does the Renin-Angiotensin-Aldosterone System help regulate BP
Hypotension, decreased Na delivery, and sympathetic stimulation cause the kidney to release renin
Renin->angiotensin -> adrenal cortex + aldosterone = renal sodium and fluid retention
-this will cause an increase in blood volume, will increase CO, and increase arterial pressure
How does atrial Natriuretic peptide work to help control BP?
ANP is release by stretch receptors out of the atria
ANP -> affects kidney, decrease release of renin -> natriuesis diuresis -> decrease blood volume and decreased arterial pressure
How does vasopressin help to control BP
AKA: antidiuretic hormone
Angiotensin II, hyperosmolarity, decreased atrial receptor firing, and sympathetic stimulation -> pituitary to release vasopressin -> vasoconstriction and renal fluid absorption -> increased blood volume and increased arterial pressure
Where is vasopressin formed, stored, and excreted?
- Formed in nerve cells in hypothalamus
- Transported by nerve axons to and stored in posterior pituitary. It is the excreted from there
An increase in what ion concentration causes vasoconstriction and why
Calcium ion concentration
The generally effect of calcium to stimulate smooth muscle contraction
An increase in what ion concentration within the physiological ranges, causes vasodilation and why?
Potassium ion
The effect results from the ability of potassium ions to inhibit smooth muscle contraction
An increase in what ion concentration causes powerful vasodilation and why?
Magnesium ion
Bc magnesium ions inhibit smooth muscle contraction
An increase in hydrogen ion concentration (decrease in pH) causes what?
Dilation of the arterioles
A slight decrease in hydrogen ion concentration causes what?
Arteriolar constriction
An increase in CO2 concentration causes moderate ___________ in most tissues, but marked ________ in the brain
Vasodilation
Vasodilation
*however, CO2 in the blood, acting on the brain vasomotor center, has an extremely powerful indirect effect, causing widespread vasoconstriction throughout the body
Effects of moderate hypoxia on cardiac performance
Indirect effects:
Sympathetic nervous system activation -> increased HR, increased CO, increased contractility
Effects of severe hypoxia on cardiac performance?
Direct effects:
Depressed myocardial contractility
Indirect and direct effects of hypercarbia on cardiac performance
Indirect
- sympathetic nervous system activation
- increased HR, increased CO, increased contractility
Direct
-depressed myocardial contractility
