Physiology Lecture Exam 3
Why do AV valves close?
- Because of a pressure gradient
- Not due to papillary muscle contraction
Why are intercalated discs important in the heart?
- It allows the heart muscle to beat on syncytium
What are intercalated discs?
- Modified desmosomes and gap junctions that allow quick movement of ion between the individual muscle cells
Fetal oxygenated blood bypasses the liver and the blood is shunted through here to go into the inferior vena cava. What is the structure called?
- Ductus venosus
What structure does blood go through to get from the right atrium to the left atrium directly?
- Foramen ovale
What circuit does the fetal circulation by pass?
- Pulmonary circuit
What shunt bypasses the lungs due to high resistance in the pulmonary artery?
- Ductus arteriosus
Why does the foramen ovale close in newborn circulation?
- Closes due to the high pressure in newborn’s left atrium
Why does the ductus arteriosus close in newborn circulation?
- Closes due to high oxygen levels and a decrease in prostaglandin levels
What kind of shunt does Patent Ductus Ateriosus have?
- Left to right shunt
What happened to the ductus arteriosus in Patent Ductus Arteriosus?
- The ductus arteriosus didn’t close and the high pressure in the aorta forces blood through the ductus arteriosus and into the pulmonary artery
What happens to blood volume and cardiac output in Patent Ductus Arteriosus?
- Blood volume increases to compensate for the decrease in cardiac output
What is heard during diastole and systole in Patent Ductus Arteriosus?
- A murmur
How will cyanosis be presented in a child who has Patent Ductus Arteriosus?
- Cyanosis will be presented on the left side of the skull, left upper body member and lower membrane
Why does left ventricular hypertrophic and right ventricular occur in Patent Ductus Arteriosus?
- Left - occurs because of the extra blood the left ventricle must pump harder
- Right - High pulmonary pressure
What kind of shunt occurs in Tetralogy of Fallot?
- Right to left shunt
How will cyanosis be presented in a child who has Tetralogy of Fallot?
- The baby will be blue all over
- Blue baby syndrome
What are the four heart defects that occur in Tetralogy of Fallot?
- Overriding aorta
- pulmonary valve stenosis
- Ventricular septal defect
- Right ventricular hypertrophy
What are the “leading cells” in the heart?
- Specialized cells
What are the “following cells” in the heart?
- Contractile cells
How can specialized fiber spontaneously initiate an AP on there own?
- They can reach threshold on their own because of leaky Na+ and less leaky to K+
- The inside of the cell becomes more + which causes cells to depolarize
How does the fibrous skeleton help in the separation between the atria and ventricules?
- Allows an delay between the AV node and AV bundle so the atria can contract and assist in ventricular filling before the ventricles can depolarize and contract
How do papillary muscles help during ventricular systole?
- Produce counter tension so that the valves do not bulge back toward the atria and allow regurgitation into the atria
What is the pathway of conduction through the heart?
- SA node
- AV node
- AV bundle (bundle of His)
- Purkinje fibers
Why is the SA node known as the pacemaker?
- SA node depolarizes first
- It is the most leaky to Na+ and less leaky to K+
What is the reason the AV node is delayed?
- Because it has a small diameter (more resistance) and fewer gap junctions
What would happen if the SA stops working?
- The AV node would take over and the heart rate would decrease because it reaches threshold slower
What is the reason there is a delay in the Bundle of His?
- Due to the fibrous skeleton
Which specialized cells have a faster conduction?
- Purkinje fibers
What happens during the the pre-potential of a specialized cells?
- Leaky to Na+ and less leaky to potassium
What happens during the upstroke of a specialized cell?
- Slow Ca+ VGC open at threshold
What happens during downstroke of a specialized cell?
- K+ channels open more
What is the NT and receptor of the heart in the sympathetic system?
- Beta 1 receptor
What is the NT and receptor of the heart in the parasympathetic system?
- muscarine receptors
How does the sympathetic system increase heart rate?
- Faster depolarization rate
- Increasing Ca2+ and Na+ channel influx and decreasing K+ permeability
- trapping positive charges and leading to threshold faster
How does the parasympathetic system decrease heart rate?
- Hyperpolarizes the membrane potential
- Increasing K+ efflux (flowing out) and decreasing Ca2+ influx
Which system of the ANS has little to no influence on inotropy?
- Parasympathic System
What are the effects of chronotropy and inotropy in the sympathetic system?
- Positive chronotropy and positive inotropy
What fibers are innervated by the sympathetic nervous system?
- Specialized and contractile cells
What fibers are innervated by the parasympathetic nervous system?
- The specialized cells in the atria only
- SA node and AV node
What refractory period does the contractile cell repolarize?
- During the absolute refractory period
Why does the contractile cell repolarize during the absolute refractory period?
- Repolarization leads to relaxation
- it ensures that the heart can’t reach tetany
What does cardiac muscle have an extracelluar source of?
- Calcium that is created by calcium sodium exchanger
What occurs in phase 0 in contractile cells?
- Fast Na+ VGC open
What occurs in phase 1 in contractile cells?
- Early repolarization
- Fast Na+ VGC close
What occurs in phase 2 in contractile cells?
- Plateau phase
- Slow Ca2+ VGC open and decreased K+ permeability
- Peak force of contraction
What occurs in phase 3 in contractile cells?
- K+ channels open and Ca2+ close
What channels open in depolarization in the specialized cells and contractile cells?
- Specialized cells - slow Ca2+ channels open
- Contractile cells - fast Na+ channels open
What is cardiac output?
What regulates heart rate?
- Parasympathetic system
- Sympathetic System
What is the MAP of hypertension?
- MAP is greater than 110 mmHg
What is the problem with hypotension?
- CO doesn’t maintain perfusion