Module 3: Frog Heart Comparisons

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Questions and Answers

Name 2 comparisons between frog and human hearts.

Frog heart has 3 chambers instead of 4 with 2 atria and 1 ventricle. 2. Pacemaker cells are located in the Sinus Venosus (SV) node instead of SA and AV.

Where does the mixing of oxygenated and deoxygenated blood occur in the frog?

Ventricle

What are two frog heart structures that try to prevent mixing?

Trabeculae: site of attachment for papillary muscles which reduce suction against heart wall to prevent mixing. 2. Spiral folds: help guide blood flow from atria to the systemic and pulmonary arteries while maintaining separation.

What are the simplified steps of blood circulation in the frog model?

<ol> <li>Deoxygenated blood enters right atrium via SV whereas oxygenated blood from lungs enters left atrium through pulmonary veins. 2. Blood remains separate until ventricle and then pumps out via 1 artery.</li> </ol> Signup and view all the answers

Where does oxygenated blood flow to after leaving the frog heart?

To brain and internal tissues Signup and view all the answers

Where does deoxygenated blood flow to after leaving the frog heart?

To lungs and skin Signup and view all the answers

Where is the ground electrode placed on the frog?

Left leg Signup and view all the answers

Where is the positive electrode placed on the frog?

Right shoulder Signup and view all the answers

Where should you hook the negative electrode in?

Ventricle of the frog Signup and view all the answers

What are the 5 factors that affect cardiac function?

<ol> <li>Temperature 2. Ionic concentration 3. Parasympathetic and sympathetic innervation 4. Mechanical stretch 5. Refractory period</li> </ol> Signup and view all the answers

What is the effect of temperature on cardiac function?

Quantified by q10 (temp coefficient) Signup and view all the answers

What is Q10?

Measurement of how much the rate of process increases with a temperature change of 10 degrees. The most common Q10 is about 2-3. Signup and view all the answers

What is the effect of ionic concentration (Potassium specifically) on cardiac function?

Increase in EK should decrease concentration gradient because it will bring the membrane closer to equilibrium. High doses of K will reverse the equilibrium potential and the AP will be unable to depolarize and contraction will stop. Signup and view all the answers

What is the effect of ionic concentration (Calcium specifically) on cardiac function?

Enters cytoplasm via L-type Ca channels which then binds to RyR receptors on SR; this is known as Calcium-induced Calcium release. Signup and view all the answers

What is the effect of parasympathetic and sympathetic innervation on cardiac function?

Para: ACh release. Sym: NE release. Signup and view all the answers

What is atropine?

Cholinergic antagonist that prevents the activation of mAChRs. Signup and view all the answers

What is Isoproterenol?

Synthetic amine agonist for Beta receptors. Signup and view all the answers

What is Frank-Starling Law?

Relationship between the degree of stretch of ventricular muscle (length) and strength of contraction (tension). Signup and view all the answers

What is the effect of the refractory period?

Due to plateau of AP, blocking of Na channels is almost complete; the removal or blocking gates from Na channels on repolarization is delayed. Signup and view all the answers

What is truncus arteriosus?

The single ventricle of the frog receives blood from both atria and pumps it out through this 1 artery. Signup and view all the answers

In the frog, there is only one electrical connection between the atria and ventricles via?

AV node. Signup and view all the answers

What does the vagus nerve inhibit?

The SA nodes so the resting heart rate is slower than the spontaneous rate that cells would generate. Signup and view all the answers

What does the Frank-Starling Mechanism involve?

Increasing venous return to the left ventricle increases LVEDP and volume, thereby increasing stroke volume. Signup and view all the answers

Cholinergic drugs have ____ effects.

Decrease the rate and force of atrial contraction, but have no effect on force of ventricular contraction. Signup and view all the answers

Why is there a delay between the peak of the QRS complex and ventricular contraction?

There is a delay between the atrial and ventricular contractions. Signup and view all the answers

How do you think increased extracellular K+ will affect cardiac function (rate/contractile strength)?

Increased extracellular potassium decreases the concentration gradient and brings the membrane closer to threshold, increasing the rate of firing. Signup and view all the answers

How do you think increased extracellular Ca2+ will affect cardiac function (rate/contractile strength)?

Increased extracellular calcium will flow into the cell more often and strengthen the force of contraction. Signup and view all the answers

Name two structures that are dramatically different between mammalian and frog hearts.

One of the major differences is the number of chambers; frogs have three (two atria and one ventricle) while mammals have four. Pacemaker cells in frogs are found in the sinus venosus (SV node) instead of the SA and AV nodes. Signup and view all the answers

Indicate what peaks 1 and 2 represent in the trace depicting mechanical activity of the frog heart.

Peak 1 represents atrial contraction (depolarization), while Peak 2 depicts ventricular contraction (depolarization). Signup and view all the answers

Describe the mechanism for how cold Ringer's decreased heart rate.

Cold Ringer's reduces heart rate due to a decrease in open L-type calcium channels, leading to reduced calcium influx. Signup and view all the answers

Which frog Ringer's treatment should show the largest force of contraction?

Ringer's with moderately high calcium should show the largest force of contraction. Signup and view all the answers

What effects do Isoprel (Isoproterenol) and Acetylcholine (ACh) have on heart rate?

Isoprel increases heart rate by activating the sympathetic nervous system, while Acetylcholine decreases heart rate by activating the parasympathetic nervous system. Signup and view all the answers

What receptor does atropine block to increase heart rate?

Atropine blocks mAChRs. Signup and view all the answers

Study Notes

Frog Heart Anatomy and Function

Frog heart consists of 3 chambers: 2 atria and 1 ventricle, unlike the 4 chambers of a human heart.
Pacemaker cells in frogs are found in the Sinus Venosus (SV) node rather than the SA and AV nodes in humans.
Mixing of oxygenated and deoxygenated blood occurs in the ventricle.

Blood Flow Mechanics

Blood from the right atrium enters via the Sinus Venosus, while oxygenated blood from the lungs enters the left atrium through pulmonary veins.
Blood remains separated until it reaches the ventricle which then pumps through a single artery.

Structures Preventing Blood Mixing

Trabeculae provide structural support and reduce suction against the heart wall, helping to minimize blood mixing.
Spiral folds guide blood flow from the atria to both systemic and pulmocutaneous arteries, facilitating some separation of blood types.

Cardiac Function Influencers

Five key factors affecting cardiac function include temperature, ionic concentration, innervation (both parasympathetic and sympathetic), mechanical stretch, and the refractory period.

Effects of Temperature and Ionic Concentration

Q10 quantifies the increase of biological process rates with a 10-degree temperature change; common values are between 2 and 3.
Increased extracellular potassium lowers concentration gradients, causes depolarization, and can, at high doses, prevent contraction by reversing equilibrium potential.
Calcium influx through L-type Ca channels causes calcium-induced calcium release, critical for cardiac contraction.

Nervous System Influence

Parasympathetic innervation releases ACh, slowing heart rates. Sympathetic innervation releases NE, increasing heart rates.
The vagus nerve inhibits SA nodes, leading to a slower resting heart rate; overstimulation may cause "vagal escape."

Contraction Mechanisms

Frank-Starling law connects ventricular muscle stretch (length) to contraction strength (tension); influenced by epinephrine.
The refractory period, due to plateau potentials, delays Na channel repolarization, impacting contraction and relaxation timings.

Unique Frog Heart Features

The truncus arteriosus is the single vessel through which the frog's heart pumps blood.
The AV node is the sole electrical connection between the atria and ventricles, facilitating sequential contractions.

Ringer's Solutions and Their Effects

Cold Ringer's decreases heart rate due to fewer open L-type calcium channels, impacting contraction.
Ringer's with high calcium enhances contraction strength, while high potassium prevents contractions due to significant repolarization.

Pharmacological Effects

Isoproterenol (Isuprel) stimulates beta receptors, enhancing heart rate and contractions via sympathetic activation.
Acetylcholine activates potassium channels, leading to increased repolarization and reduced heart rate.

Clinical Relevance of Atropine

Atropine blocks mAChRs, allowing increased heart rate by inhibiting parasympathetic activity; useful in cases of bradycardia or asystole during emergencies.

Electrophysiology Insights

The delay between the QRS complex and ventricular contraction allows for complete atrial depolarization before ventricular activation.
Increased extracellular Ca2+ leads to stronger contractions by enhancing the influx of calcium into cardiac cells.

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Description

Test your knowledge on the anatomical and functional differences between frog and human hearts with this quiz. Explore concepts such as heart chambers, blood mixing, and the specific structures that prevent blood mixing in frogs. Perfect for students studying comparative anatomy!