Hypertension Flashcards
What is the arterial pressure equation?
Arterial Pressure = CO X TPR
How can arterial pressure increase?
- Constricting almost all arterioles of the body, which increases total peripheral resistance
- Increasing blood volume which increases venous return and cardiac output
- Constricting large vessels of the circulation, thereby increasing venous return and cardiac output
- Directly increasing cardiac output by increasing heart rate and contractility
What class of drugs affects vascular tone?
Vasodilators
What are the levels of vascular resistance regulation?
- Neural controls
- Local controls
- Humoral controls
List the vasoconstrictors and vasodilators at each level of vascular resistance regulation:
-
Neural controls
- Vasoconstrictors - Sympathetic system
- Vasodilators - Parasympathetic system
-
Local controls
- Vasoconstrictors - Myogenic response
- Vasodilators - PO2 reduction; K+, CO2, H+ osmolality; NO; Adenosine
-
Humoral controls
- Vasoconstrictors - NE; AngII; Vasopressin; Endothelin; Thromboxanes
- Vasodilators - Epinephrine; ANP; Bradykinin; Histamine; Prostaglandins
How does the nervous system globally regulate circulation?
- Redistribution of blood flow to different areas
- Affects heart rate and pumping activity of the heart
- Essential for the very rapid control of arterial pressure.
Be able to describe the signal transduction that modulate calcium in vascular smooth muscle:
What are areas of the brain that play important roles in the nervous regulation of the circulation?
-
Reticular substance:
- lateral and superior portions ~ excitation
- medial and inferior portions ~ inhibition
-
Hypothalamus:
- posterior-lateral portions cause mainly excitation
- anterior portion can cause mild excitation or inhibition
-
Motor cortex:
- excitation or inhibition depending on region stimulated
Where is the vasomotor center?
Located bilaterally in the reticular substance of the medulla and lower third of the pons
Describe the specific task of each vasomotor center area:
-
Vasoconstrictor area “C-1” anterolateral upper medulla:
- sympathetic discharge
-
Vasodilator area “A-1” anterolateral lower medulla:
- inhibits C-1 area
-
Sensory area “A-2” bilateral in nucleus tractus solitarii:
- receive sensory signals from vagus and glossopharyngeal from baroreceptors
- Control C-1 and A-1 areas
-
Cardiac center
- heart rate and contractility
- What does the sympathetic nervous system innervate?
- How is the parasympathetic nervous system involved?
Sympathetic nerve fibers:
- Innervate all vessels except capillaries and precapillary sphincters and some meta arterioles
- Innervation of small arteries and arterioles allow sympathetic nerves to increase vascular resistance
- Large veins and the heart are also sympathetically innervated
Parasympathetic nervous system
- mainly important in control of heart rate via the vagus nerve
What is responsible of vasomotor tone?
Sympathetics are responsible for “vasomotor tone”
What is the function of α1 and α2 adrenergic receptors?
-
α1:
- vasoconstriction (vascular smooth muscle)
-
α2:
- inhibit NE release (increase venous tone)
What do adrenergic receptor agonists activate?
Signal transduction pathways
What is the function of the β1 adrenergic receptor?
↑ HR and contractility
Where are α and β adrenergic receptors generally located?
-
α:
- α1: vascular smooth muscle
- α2:** **sympathetic neuron
-
β:
- β1: myocardium
Where are baroreceptors located?
How are the signals transferred between each baroreceptor?
- Baroreceptors are located in the walls of the carotid bifurcation called the carotid sinus and in the walls of the aortic arch
- Signals from the carotid sinus are transmitted by the Hering’s nerve to the glossopharyngeal nerves and then to the nucleus tractus solitarii (NTS) of the medulla
- Signals from the arch of the aorta are transmitted through the vagus into the NTS
What type of feedback is the baroreceptor system?
Negative feedback control system
What is feedback gain (G)?
“Feedback gain” (G) represents the strength of the feedback
G = Correction of error signal / Error (abnormality still remaining)
How does the baroreceptor system respond to a fall in carotid sinus pressure?
Constrict Common Carotids → ↓ Pressure at Carotid Sinuses → ↑ Arterial Pressure
Baroreceptors respond to:
Arterial Pressure Changes
As pressure increases, the number of impulses from carotid sinus increases; this results in:
- inhibition of the vasoconstrictor
- activation of the vagal center
At what pressure are the baroreceptors most sensitive?
100 mmHg
What happened to arterial pressure after the baroreceptors were denervated in a dog?
Extreme fluctuations in arterial pressure
Why are baroreceptors reset?
- thought to prevent the reflex from functioning as a control system for changes in pressure that last more than a day
- However, resetting is not complete