Cardiac Cycle + Blood vessel regulation Flashcards
What does a pressure volume loop describe? In general, describe the phases of activity in the left ventricle on the pressure-volume loop below.
Define contractility. What woud be the effect on inreasing contractility on a Frank-Starling curve?
For the same pre-load, increasing contractility leads to increasing stroke volume.
Explain the Frank-Starling mechanism. Define preload in the context of this mechanism.
The Frank-Starling mechanism basically describes the relationship between forceof contraction and lengthening of the sarcomeres of a myocyte. As the myocyte is stretched, its sarcomeres get stretched as well, allowing actin to bind myosin with the correct polarity. Troponin C gets stretched as well, which increases its affinity for Ca2+ binding, thereby promoting cross-bridge formation.
Thus, increasing sarcomere length (preload) causes an increase in force of contraction.
Describe the concept of vascular tone. What are 4 ways thorugh which tone can be regulated?
Vascular tone:relative state of contraction of a blood vessel OR the degree of contraction of a blood vessel that determines its diameter when its fully dilated.
Ways to regulate vascular tone:
Neurogenic (the action of neurotransmitters e.g. norepinephrine/epinephrine)
Endothelial (shear stress)
Metabolic (metabolite release)
Myogenic (pressure)
Describe the role of norepinephrine in regulating blood vessel tone. Which receptor does it bind? What is the action of norpinephrine when bound to alpha 1 receptors vs beta receptors?
When bound to alpha 1 receptors, NE promotes vascular smooth muscle contraction.
When bound to beta receptors, NE promotes vasodilation; myocardial contraction
Basically NE works by binding to alpha 1 receptor >> PLC activation >> PIP2 cleaved into IP3 and DAG >> IP3 promotes Ca2+ release from SR
Interpret the graph below. What does the data say about the relationship between sympathetic system activation and blood flow in the arteries/venous reserve in the tissues?
Sympathetic stimulation (i.e. release of NE and E) causes vasoconstriction, thus there’ll be reduced blood flow in the arteries, and reduced blood volume in the venous system.
Describe the concept of metabolic vasodilation. What are some of the metabolites released that impact vasodilation?
Metabolic vasodilation is the idea that during normal metabolic conditions, metabolites are released that act secondarily to inducse vasodilation, which increases blood flow.
Local vasoactive factors:
ATP
NO
Prostaglandins
Extracellular K+
T/F:Metabolic vasodilation results in an ultimate increase in the rate of oxygen consumption?
True. Metabolic vasodilation >> increased blood flow >> increased O2 consumption/O2 delivery rate
Describe the myogenic effect of modulating vascular tone. What is the role of the endothelium in the myogenic response?
Explain the graph below. What happens when you release the pressure in the artery?
Myogenic response = vascular smooth muscle first expands then it contracts following an increase in pressure
When pressure is released, the vessel undergoes passive collapse first, followed by active relaxation.
The endothelium is not involved in the myogenic response.
What is “shear stress” and what is its role in regulating vascular tone?
Shear stress is the force of blood/pressure exerted on the endothelial layer of blood vessels.
Shear stress triggers the release of Nitric Oxide and Endothelial dependent hyperpolarizing factor. NO promotes release of cGMP >> PKG >> Rho-P >> blocks ROK, can’t inactivate MLCP >> MLCP removes P from Myosin regulatory light chain >> muscle relaxation (i.e. cross bridge detachment)
Explain flow-induced vasodilation.
Upon muscle contraction, metabolic rate increases which causes release of metabolites that promote vasodilation of downstream arterioles >> increases blood flow >> endothelial shear stress >> increased vascular sm ms relaxation >> blood flow >> O2 delivery
Define autoregulation. How does this work?
Autoregulation: Maintenance of constant flow despite changes in blood pressure. Changes in flow rate are, for the most part, transient
Mechanisms: myogenic = constrict when pressure increases
Metabolic = constrictor response to washout
