Heart and Blood Vessel Physiology Flashcards
Where is the heart?
In the mediastinum between 3rd and 4th rib
What are desmosomes?
Intercolated discs that keep muscle cells together and uniform
Why is it important for the heart to have gap junctions?
Ions can pass more quickly from cell to cell, making depolarization faster
Why is the left wall of the heart thicker?
It needs to generate greater contractive force for higher pressure in vessels
True or False: Blood requires a lot of ATP to move throughout the body
False. Blood requires bo energy to move throughout the body. It follows pressure gradients
True or False: The right side of the body and left side pump equal amounts of blood.
True
On average, how much blood does the human body contain and how often is it circulated through the body?
5L; once a minute
What are the two kinds of myocardial cells?
Contractile (99%) and Autorhythmic
Describe autorhythmic cells
1% of myocardial cells
Able to generate APs spontaneously
Found in nodes, bundles, and fibers
Never rest (reach -70mV), go to about -60mV via slow depolarization due to leaky Na+ channels
Describe the electrical activity of contractile cells
Rest at -90mV and remain at constant membrane potential for a long time in a plateau phase because voltage-gated Ca2+ channels stay open
Are cardiac action potentials voluntary or involuntary?
Involuntary
How does the absolute refractory period of the heart compare to skeletal muscles? Why is this significant?
The heart has a relatively long refractory period, which allows it to relax, lower pressure, and allow blood back into it
What is the intrinsic conduction system?
Siniatrial Node (SA), 70-75bpm
Atrioventircular Node (AV) 50bpm
AV bundle (intraventricular space) 35bpm
-Goes left to right
Bundle Branches
Purkinje Fibers (30bpm)
Individual fibers can generate their own rhythm as a last resort
What is arrhythmia?
An irregular heartbeat
What is fibrillation?
Rapid irregular contractions, which are useless for pumping blood
What is the pacemaker of the heart?
The Sinoatrial Node
What happens if the SA node fails?
Ecoptic focus: the AV takes over and the heart assumes slowed junctional rhythm
What happens if the AV node is defective?
Heart block
What is tachycardia?
An abnormally fast heartrate (more than 100bpm)
What is bradycardia?
An abnormally slow heartrate (less than 60bpm)
Note: This is desirable result of endurance training
What’s ectopic focus?
Abnormally excitable areas depolarize faster than the SA node (can lead to accelerated heartrate)
What is the difference between systole and diastole?
Systole: Contraction
Diastole: Relaxation
When does ventricular filling occur?
Mid to late diastole, when ventricles are relaxes and AV valves are open
What is EDV?
End Diastolic Volume: The blood left in the ventricle after diastole, about 20% of capacity
When do Ventricular Systole and Atrial Diastole take place?
At the same time.
What causes AV valves to close?
Rising ventricular pressure during systole exceeding atrial pressure
What is true about valves during the isovolumetric phase?
They are closed
What causes the semilunar valves to open?
Ventricular pressure exceeds pressure in the large arteries during “Ejection Phase”
What is ESV?
End Systolic Volume - Blood remaining in ventricles at end of ejection phase
What causes a dicrotic notch?
Backflow of blood in aorta and pulmonary trunk when SL valves close
What are the heart sounds and when do they occur?
Lub - When AV valves close, beginning of systole
Dubb - When SL valves close, beginning of diastole
What are heart murmurs and what do they indicate?
Abnormal heart sounds – most often indicate valve problems
What is Cardiac Output (CO)?
Heart Rate x Stroke Volume
(xxx bpm) x (70mL/beat)
What is the cardiac reserve?
The difference between resting and maximal CO
What are the effects of the SNS on heartrate?
Hormones & Autonomic Innervation
-Emotional or Physical stressors activate
-NE causes pacemaker to fire more rapidly
-Epinephrine depolarizes autor. cells and increases contractility and HR
-Positive cronotropy
-Thyroxine enhances effects of NE/Ep
What are the effects of the PSNS on Heart Rate
ACh hyperpolarizes pacemaker cells by opening ligand-gated K+ channels
Negative cronotropy
What is Starling’s Law?
The heart will pump out whatever volume is pumped in
What are the factors affecting stroke volume?
Preload
Contractility
Afterload
What is “Preload”?
Ventricular stretching during diastole, specifically the degree of stretch of cardiac muscle cells before they contract
True or False: At rest cardiac muscles are shorter than optimal length
True
What is contractility?
The force produced during contraction at a given preload
The contractile strength at a given muscle length independent of muscle stretch and EDV
What can increase contractility?
Increased Ca2+
Hormones (thyroxine, glucagon, epinephrine)
What can decrease contractility?
Negative intropic agents
Acidosis
Extracellular K+
Ca2+ blockers
What is afterload?
Blood pressure in major arteries which must be overcome to eject blood from heart
What effect does hypertension have on Stroke Volume?
Increases afterload, decreasing stoke volume
What are the results of increased venous return?
Distended ventricles, therefore increased contraction force, therefore increased Stroke Volume
What is the Bainbridge Reflex?
Atrial walls stretch and stimulate SA node and atrial stretch receptors
What factors affect heart rate?
Age, Sex, Exercise, Body Temp
True or False: The heart can only use glucose as an energy source?
False, it is adaptable to a number of food sources including fatty acids and lactic acid
What is Congestive Heart Failure?
A progressive condition where cardiac output is so low that circulation is inadequate for tissue needs
What are some possible causes of Congestive Heart Failure?
Coronary Atherosclerosis
Persistent Hypertension
Multiple Myocardial Infarctions
Dilated Cardiomyopathy
True or false: arteries have thicker muscle, veins have a wider diameter
True
True or False: The wider the diameter if a blood vessel the faster the flow
True
Where are the elastic arteries, why are they important?
Nearer to the heart, can expand as heart expels blood, accommodating for pressure changes
What is tissue perfusion?
Blood flow. Rate of flow is important to provide proper function:
Important for delivery of O2, removal of waste, absorption of nutrients, urine formation
True or False: Blood travels at a rate inverse to the total cross-sectional area?
True. (Wider/Bigger = Faster)
What is blood flow?
The volume in a vessel organ or system during a given period, measured in ml/min
Equivalent to the total cardiac output of the entire vascular system
How is blood flow calculated?
Flow Rate = deltaP/R
As resistance increases flow rate decreases
P - Pressure Gradient
R - Vascular Resistance (opposition to flow through a vessel)
