Lecture 31 - Cardiovascular System: Regulation of Blood Pressure in the Short and Long Term Flashcards
What are 2 factors that blood pressure is affected by?
- Total blood volume (how much blood is present)
- Total resistance (what is the diameter of the vessels)
All across blood vessels
What regulates vasoconstriction?
The autonomic nervous system regulates vasoconstriction through (sympathetic) vasomotor fibres that make synapses on vascular smooth muscle. APs in vasomotor fibres lead to enhanced contraction in smooth muscle
What are the general sensors, integrator, and effector of mean arterial blood pressure?
Sensors - neurons in large elastic arteries
Integrator - neurons in hindbrain
Effectors - organs of the cardiovascular system
What are baroreceptors?
They are mechanosensory neurons that monitor mean arterial blood pressure found within the carotid sinus and aortic arch
These neurons send their axons (via CN IX and CN X) to the medulla oblongata
What are the 3 cardiovascular centres that baroreceptor info is integrated?
Integrated within cardiovascular monitoring centres in the brainstem within the medulla oblongata:
- Cardioinhibitory centres
- Cardioacceleratory centres
- Vasomotor
What is the function of the cardiac centres in the medulla oblangata?
They drive changes in cardiac output (CO) by altering activity in ANS inputs to the SA node of the heart and the myocardium
What is the function of the vasomotor in the medulla oblangata?
It drives changes to blood vessel diameter (in both arteries and veins) by altering activity in sympathetic vasomotor fibres
What can cause changes in overall chemical composition of blood in the systemic circuit?
Increased metabolic demands from peripheral tissues, where metabolic demands > current levels of CO:
- decreased PO2
- increased PCO2
- decreased pH (acidosis)
How does blood chemistry restore its levels?
Arterial chemoreceptors - drive homeostatic reflexes that alter blood flow throughout the circulatory system:
Sensors - neurons in large elastic arteries (and hindbrain)
Control center - integrator; neurons in hindbrain
Effectors - organs of the respiratory and cardiovascular system
This leads to blood chemistry being restored
What monitors blood gas composition?
Chemoreceptors - monitor mean arterial pH, P_O2, P_CO2. Found within the carotid bodies and aortic bodies
Where is chemoreceptor info integrated within?
It’s integrated within cardiovascular monitoring centres in the brainstem
Peripheral neurons send axons (via CN IX and CN X) to three cardiovascular centres and respiratory centre within the medulla oblongata
What are the effectors for short term alterations in blood gas composition?
Heart and blood vessel walls
Difference between homeostasis and allostasis in blood pressure regulation
Homeostasis - when BP is disrupted, BP is restored to the set point
Allostasis - when blood chemistry is disrupted, BP is moved to a new set point
T/F? Mechanisms of altering blood pressure over short terms are ideal for long term regulation
False - it is NOT ideal. Why?
- Energy intensive
- Maintain central pressure
What is needed for long-term regulation of BP?
Changes in blood volume - to maintain oxygen delivery at normal rates, blood volume changes must involve changes to both plasma and RBC levels
Adjustments to blood volume are slow, but they can maintain blood pressure throughout the circulatory system without constant energy input
Which organ is the long-term response to low BP, and which 2 hormones do they release?
Kidney; low BP (or blood volume) lead to lower levels of perfusion through kidney tissue, stimulating the release of 2 hormones:
- Renin - leads to increased plasma volume
- Erythropoietin (EPO) - drives RBC production
How does renin play a role in the hormonal axis
It takes part in the hormonal axis Renin-Angiotensin-Aldosterone System (RAAS)
What are the 3 components to RAAS?
1 . Renin is secreted by the kidney (note: it’s not a true hormone)
2a. Angiotensinogen is a plasma protein which is always present in circulation
2b. Angiotensin I is also inactive
2c. Angiotensin II has short-term and long-term effects on BP. It produces vasoconstriction and increase thirst (water intake)
3 . Aldosterone is a mineralocorticoid hormone that acts on the kidney
What does angiotensin II stimulate?
Stimulates the release of aldosterone and ADH/vasopressin
Aldosterone influences Na+ retention by the kidneys, which indirectly contributes to water retention
ADH directly stimulates water retention by the kidney
Which muscle is the long-term response to high BP, and which 2 hormones do they release?
Heart muscle; high BP (or blood volume) leads to increased stretching in heart chamber walls, which leads to the release of:
- ANP - atrial natriuretic peptide, released by the atria
- BNP - brain natriuretic peptide, released by the ventricles
3 functions of natriuretic peptides
- They stimulate the kidneys to increase excretion of Na+, which also leads to water loss
- They also have short term effects on BP; they produce vasodilation in most blood vessels
- Natriuretic peptides are regulatory hormones that inhibit the release of renin (and therefore, aldosterone), ADH, and epinephrine
What do short term responses to blood loss involve?
Neural reflexes and the physiological stress response
Systemic veins can hold large volumes of blood, so venoconstriction can return a large amount of blood from these venous blood reservoirs without affecting perfusion
What will occur in medium to long term loss of blood volume?
Blood contents will be replaced
Medium term - reductions in BP lead to dec. CHP, which leads to recall of fluid in the ISF
Long term - increases in ATII, ADH, aldosterone leads to inc. fluid intake and inc. fluid retention. EPO restores RBCs
What does hypovolemic shock mean and when does it occur?
“Shock” means an acute cardiovascular crisis involving hypotension. Occurs when more than 20% of blood volume is lost (major blood loss) or if the loss of body fluids is faster than physiology can replace them
5 major symptoms of circulatory shock
- Rapid, weak pulse
- Cold
- Pale
- Thirst
- Sweating
