cardiac action potentials in the SA Nodal cells, atrial cells, and ventricolar c
ID: 3514200 • Letter: C
Question
cardiac action potentials in the SA Nodal cells, atrial cells, and ventricolar cells. (Hint: Think of the molecular mechanisms that regulate cardiae ces 17. Explain how the sympathetic and parasympathetic nervous systenm 18. List and describe the passive mechanisms used to exchange materials across the capillary wall 19. Which of the following substances would be expected to directly increase arteriolar resistance to blood flow? (There can be more than one) a. Angiotensin I b. Adenosine c. Norepinephrine d. Bradykinin e. Histamine 20. Explain why you chose your answer in question #19.Explanation / Answer
17. ANS: Sympathetic and Para Sympathetic Nerves system effect on the heart and the vasculature:
Autonomic nervous system:
Sympathetic Nerve system:
It is represented by a chain of 21 Sympathetic ganglia on either side of spinal cord. It receives pre-ganglionic Sympathetic fibers from spinal cord , exit along with thoriac and lumbar nerves.
Post-ganglionic Sympathetic fibers are adrenergic (release nor adrenaline) and pre-ganglionic Sympathetic fibers are cholinergic (liberate Acetyl choline).
The action of Sympathetic system results in accelerated heart rate, Increase blood pressure and takes blood flow away from peripheral and digestive system to towards brain, heart & skeletal muscles. It also causes adrenaline to be released.
Sympathetic system can release the epinephrine and nor epinephrine, these hormones can increase the heart rate.
Para Sympathetic Nerves system:
It brings the body back to a state of equilibrium, comfort, relation state. It decrease heart rate and release of hormones into blood.
Para Sympathetic Nerves system slows the heart rate by releasing by acetylcholine.
Effects of sympathetic stimulation:
Heart SA node Increase heart rate
Atria Increase heart rate and force
AV node Increase conduction velocity
Purkinje system Increase conduction velocity
Ventricles Increase heart rate and force
Effects of parasympathetic stimulation:
Heart SA node Decrease heart rate
Atria Decrease heart rate and force
AV node Decrease conduction velocity
The SA node of the heart is innervated by both sypathetic and parasympathetic nerve fibers.
=> Under rest conditions, the parasympathetic fibers release acetlycholine (a neurotransmitter), which acts to slow the pacemaker potential of the SA node and thus reduce heart rate.
=> Under physically and emotionally active condition, sympathetic nerve fibers release norepinephrine, which acts to speed up the pacemaker potential of the SA node, thus increasing heart rate.
Released acetylcholine (neurotransmitter) molecules diffuse into the gap and binds briefly to receptor molecules on ion- channels in the postsynaptic membrane. When an action potential arrives at a terminal knob, causes an inward movement of calcium (Ca+) ions through voltage - gated channels in the synaptic knob membrane. The change in membrane potential causes voltage-gated Na+ channels to open suddenly, permitting Na+ to diffuse into the axon from the outside, moving down the concentration gradient for Na+. They remain open for less than a millisecond and causes depolarization of the membrane. Then, as the Na+ channels close, the membrane quickly regains its resting properties as K+ ions quickly diffuse out through voltage-gated K+channels that open briefly in reponse to the membrane depolarization. Factors such as stress , caffeine and excitment can temporarily increase the heart rate . Excercise for any duration can also increase the heart rate release of acetylcholine , decrease in body temperature decreased sodium ion concenteration and increased pottasium ion can decrease the heart rate and increase level of oxygen and carbon dioxide also decreasing the heart rate.
18. ANS: The net filtration of fluid out of the capillaries into the interstitial compartment is greater than the net absorption of fluid back into the capillaries. But when the concentration of plasma proteins drops, the osmotic potential of plasma drops, thus less interstitial fluid is absorbed into the capillaries. Thus, there must be a balance between the hydrostatic pressure of the blood in the capillaries and the osmotic attraction of the blood for the surrounding fluids.
The four Starling's forces are:
1. Hydrostatic pressure in the capillary (Pc).
2. Hydrostatic pressure in the interstitium (Pi).
3. Oncotic pressure in the capillary (Pc).
4. Oncotic pressure in the interstitium (Pi).
Capillary Exchange Passive Diffusion Ultrafiltration:
Permeability
Concentration gradientUltrafiltration
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