Blood Pressure Regulation Flashcards
Regulation of BP occurs through which 2 mechanisms?
- Hormonal
- Neural
Hormonal and neural mechanisms that effect BP respond to changes in?
CO, SVR & BV
The cardiovascular control centre is located in which part of the brain?
The medulla oblongata.
The medulla oblongata receives input from the sensory repcetpors (3) and higher brain centres (3). Describe these.
Sensory inputs include:
-Baroreceptors: detect changes in BP
-Chemoreceptors: Detect chemical changes in the blood (pH, O2 and CO2)
-Proprioceptors: detect changes of limb and muscle position
Higher brain centers include:
-Cerebral cortex
-Limbic system: monitors emotions and anticipation of activity
- Hypothalamus: monitors body temperature
The medulla oblongata sends what kind of signals where (3)?
Sends autonomic motor output to:
- pacemaker cells
- myocardium
- blood vessels.
Describe the sympathetic innervation of the heart as part of motor output from the medulla oblongata.
Sympathetic innervation (via cardiac accelerator nerves): of pacemaker and myocardial cells increases HR and contractility.
Sympathetic neurons exit the spinal cord in the upper thoracic region.
Innervate:
- the SA and AV nodes
- atrial and ventricular myocardium
What are baroreceptors and where are they located? How are they stimulated?
Pressure-sensitive sensory receptors (mechanoreceptors) located in the wall of the aortic arch and the carotid sinuses.
Stimulated when mechanoreceptors are stretched with increased BP
Carotid sinus baroreceptors monitor blood flow to… and nerve impulses are carried to the medulla oblongata via the…?
to the brain
by the Glossopharyngeal nerve (CN IX)
Aortic arch baroreceptors monitor blood flow to… and nerve impulses are carried by the…?
to the systemic circulation
by the Vagus nerve (CN X)
What is the baroreceptor reflex?
Change in BP is detected by the mechanoreceptors in the aortic arch and the carotid sinuses.
Nerve impulses travel to the medulla oblongata by the vagus and glossopharyngeal nerves.
The medulla oblongata has a sympathetic (low BP) or parasympathetic (high BP) response.
Describe the sympathetic cardiac effects on HR.
NE released form sympathetic neurons binds to B1-adrenergic receptors in pacemaker cells
Causing an increase in Na+ and Ca2+
Pacemaker cells reach threshold more quickly = increased HR
Describe sympathetic cardiac effects on contractility.
NE binds to B1-adrenergic receptors on cardiac muscle cells
Opens Ca2+ channels
Ca2+ influx increases contractility
Describe the parasympathetic innervation of the heart as part of the motor response of the medulla oblongata.
Parasympathetic innervation (via vagus nerve): of pacemaker and myocardial cells decreases HR.
Innervates:
- SA and AV nodes
- Atrial myocardium
Ach released from parasympathetic neurons binds ot cholinergic receptors on pacemaker cells
Results in the efflux of K+ causing hyperpolarization
Pacemaker cells reach threshold more slowly = decreased HR
Describe the vasomotor effects.
Vasomotor centre in the medulla oblongata receives input from baroreceptors.
Sympathetic vasomotor nerves exit the spinal cord through all thoracic and the first two lumbar spinal nerves
Vascular smooth muscle cells contain adrenergic receptors
Alpha-1 receptors (most blood vessels):
- bind NE
- stimulates smooth muscle contraction and vasoconstriction
Beta-2 receptors (coronary and skeletal muscle vessels):
- greater affinity for epinephrine
- stimulates smooth muscle relaxation and vasodilation
Stimulation of the vasomotor centre causes venoconstriction and the mobilization of venous reserve
Adrenal catecholamines (epinephrine and norepinephrine) and antidiuretic hormone are stimulated to release in response to?
The baroreceptor reflex. These aid in regulation of BP.
What happens to the baroreceptor reflex with age?
Baroreceptors become less sensitive with age (less effective and lead to a slower response).
Change in position from sit to stand, receptors don’t respond as quickly (BP does not rise) and hypotensive signs occur (dizziness or blurred vision) = orthostatic hypotension.
What are the 4 hormonal mechanisms for BP regulation?
- renin-angiotensin-aldosterone system (RAAS)
- antidiuretic hormone (ADH)
- Adrenal catecholamines
- Natriuretic peptides
The RAAS is activated by (2)?
- reduced renal perfusion (e.g. decreased BV or BP)
- sympathetic activation of juxtaglomerular cells
What happens when the RAAS is activated?
Juxtaglomerular cells release renin into the blood
Renin converts angiotensinogen (from the liver) to angiotensin I
Angiotensin I enters lung capillaries containing angiotensin-converting enzyme (ACE) and is converted to angiotensin II (AII)
What does angiotensin II (AII) do (3)?
- potent vasoconstrictor
- stimulates aldosterone release (adrenal gland)
- stimulates ADH release (posterior pituitary gland)
What does aldosterone do?
Mainly targets tubule cells of the kidney.
Stimulates synthesis of Na+ channels and Na+/K+ pumps = Na+ reabsorbed, water follow by osmosis, and K+ excreted.
Where is antidiuretic hormone released from and how is it simulated (3)?
Released from the posterior pituitary in response to:
- Activation of osmoreceptors (increased blood osmolality)
- Increased angiotensin II (activation of the RAAS)
- sympathetic activation of the hypothalamus
What does antidiuretic hormone (ADH) do (2)?
- Aquaporins
- Vasoconstrictor
Stimulates the insertion of aquaporins (water channels) into the plasma membrane of kidney tubule cells = stimulates water reabsorption = increases blood volume.
Is a vasoconstrictor (also called a vasopressin).
What is the RAAS effect on the hypothalamus?
Increases thirst
