OBJECTIVES
When you complete this lab, you will be expected to:
1.Describe the functions of the cardiovascular system in vertebrates.
2.List the major components of the cardiovascular system and describe its role in the functioning of the system.
3.Describe the functions of the respiratory system in vertebrates.
4.Describe the various respiratory organs of vertebrates and indicate which are used in and out of water.
5.Compare the structures of the cardiovascular systems in the 5 major vertebrate groups.
6.Discuss how the differences in these groups are adaptations to various habitats and metabolic needs.
7.Discuss why convergent evolution is likely the reason for the similarities between the cardiovascular systems of birds and mammals.
8.Identify the major structures of a mammalian heart and describe the flow of oxygen-rich and oxygen-poor blood through the heart.

INTRODUCTION
In this lab, we will explore the evolutionary relationships of the animals classified as vertebrates by identifying adaptations vertebrate groups have in their respiratory and cardiovascular systems that adapts these groups to their habitats and other ways of life. Models and dissections of animals will be used to illustrate these adaptations in the various vertebrate groups.
Vertebrates are animals that possess heads and spinal cords protected in vertebral columns (backbone). Like all animals, each of their cells require nutrients and oxygen (O2) and produce metabolic wastes and CO2. The organ systems of vertebrates: the respiratory system, digestive system, excretory system, and cardiovascular system (a circulatory system) ensure that nutrients and O2 as well as wastes and CO2 are transported to the correct parts of the body to maintain homeostasis and keep cells and the body alive (Fig. 1).
Cardiovascular System: Mechanisms for Circulating Materials Between Cells
The large bodies of vertebrates require a system for circulating nutrients, wastes, and respiratory gases between the cells of the body and the systems that allow them to exchange materials with their environment. The cardiovascular system in vertebrates and many other animals (such as earthworms depicted in the Fig. 2b) is a closed circulatory system that comprises a heart that pumps blood through a network of branching vessels. However, many animals such as arthropods and molluscs possess an open circulatory system that circulates the hemolymph (not blood) using a heart through open-ended vessels into a body cavity to surround cells for exchange of materials before being collected and brought back to the heart (Fig. 2a).
Winter 2020
In a closed circulatory system, chemicals transferred
between blood and cells must pass through the Away from heart interstitial fluid that surrounds cells. The cardiovascular Arteriole
system of vertebrates also transports white blood cells that are part of the immune system, platelets that play a role in blood clotting, and hormones that act as longdistance chemical messengers in cell-to-cell communication.
The heart is a muscular pump that contains cavities called chambers that pool blood and contract their walls to create pressure that pushes blood through the heart and into circulation. Blood leaves the heart through arteries, that branch into narrower arterioles and bring blood to the cells of the body through microscopic vessels called capillaries that form a network (bed) around organs (Fig. 3). Capillaries have thin walls that allow for materials to be exchanged between the blood and the cells of the body. Blood from these capillary beds is collected in venules that pool blood into veins and bring blood back to the heart.
The flow of blood through the heart is unidirectional due to the valves of the heart. These valves are flaps of connective tissue that open to let blood travel from one chamber to the next or from a chamber to the major artery leaving the heart but close off the path for blood to travel back where it came from when the chambers contract.
Respiratory Systems: Mechanisms for Gas Exchange with the Environment
Vertebrates rely on specialized respiratory organs for exchange of O2 and CO2 between the environment and their cardiovascular systems. These organs work by providing a respiratory surface that allows 1) O2 from water or air to diffuse into the organism’s blood and 2) CO2 to diffuse out of the organism’s blood back into the air or water. Vertebrates use gills for respiration in water and lungs for respiration on land. Amphibians can complement their lungs by using the lining of their mouths and skin as a respiratory organ. The structure and function of lungs are shown in Fig. 4. All respiratory surfaces have the following characteristics: 1) A structure that provides a large, thin surface area for exchange, 2) An extensive network of capillaries that surrounds the surface. All respiratory surfaces must be kept moist or
the organism will suffocate. Oxygen and carbon dioxide can only diffuse through an aqueous medium (water). Most animals that are more complex than a roundworm possess either gills or lungs depending on whether they are aquatic or terrestrial.

Insects and some other arthropods have a tracheal system for respiration. This system provides a network of microscopic tubules that extend from openings in the exoskeleton to body cells and allow for direct exchange of respiratory gases between body cells and the environment.
The Evolution of these Systems in Vertebrates
All tetrapods (amphibians, mammals, reptiles, and birds) and fish are thought to have evolved from a common fishlike ancestor millions of years ago (Fig. 5). The differences in the respiratory and circulatory systems of these groups represent evolutionary adaptations to various habitats and ways of life as these groups diverged.

Blood circulation in a closed cardiovascular system is illustrated in Fig. 6 using a fish as an example. In the systemic capillary beds, oxygen (and nutrients) are delivered from the blood to body cells and carbon dioxide is removed from body cells to the blood. The oxygen-poor blood (colored blue in circulation diagrams) is transported by vessels towards the respiratory organ of the organism (gills in fish). In the respiratory capillary bed, carbon dioxide is removed from the blood and transferred to the air or water. Oxygen is taken up from the water or air into the blood. The oxygen-rich blood (colored red in circulation diagrams) is transported by vessels to the body cells to repeat the cycle.
The cardiovascular systems of all vertebrates are quite similar. The principal differences reside in:
A. The number of heart chambers B. The number of circulation circuits (loops) C. The division between the circulation circuits

As mentioned previously, chambers are muscular cavities within the heart. There are two types of heart chambers:
A.Atrium: Collects blood from a vein and pumps blood to a ventricle.
B.Ventricle: Pumps blood to an artery.

A circulatory circuit is a series of connected blood vessels that carried blood away from the heart via an artery and brings blood back to the heart via a vein. Vertebrates either have a single circuit called the systemic circuit to deliver blood to the entire body or two separate circuits: the systemic circuit and the respiratory circuit. Specifically, a separate respiratory circuit is only seen in vertebrates with lungs and this second circuit is referred to as the pulmonary circuit.

Blood mixing (generally colored purple in circulation diagrams) can happen in vertebrates that have a systemic circuit and a pulmonary circuit that are not completely divided. Oxygen-rich blood from the pulmonary circuit mixes with the oxygen-poor blood from the systemic circuiting in the single ventricle of the heart. When blood mixing occurs, the blood pumped out towards the systemic circuit is not oxygen saturated (i.e. not filled to capacity).
N.B. the purple blood in the capillary beds of a circulation diagram does not signify blood mixing but a transition between oxygen-rich and oxygen-poor blood as blood flows through these vessels.
A. FISH

1. Respiratory System
   All fish (jawless, cartilaginous, and, bony) use gills for respiration. Gills are structures specialized for gas exchange in aquatic environments. When water passes over the gill filaments, a large portion of the O2 that is dissolved in the water diffuses into the blood that’s circulating through the gill filaments’ capillaries (Fig. 7).

In fish, breathing occurs in two phases: 1. the fish closes its gill slits (openings) and water is drawn into the mouth as it is opened and as the
pharynx (the throat) expands. 2. the gill slits open while the pharynx contracts (the space becomes smaller), forcing oxygenated water to flow over the gill and its filaments. In the process of exiting through the slits, the water exchanges gases with the blood passing through capillaries in the gills; water leaving the gill slits is therefore lower in O2 and higher in CO2 compared to when it entered the mouth.

1. Cardiovascular System
   Lab Exercises:
   1.Label the structures of the fish cardiovascular system in Fig. 8 using the letters from the list.
   2.Fill-in the blanks below BY INDICATING THE NUMBER FOR EACH COMPONENT.

Fish have 2__ heart chambers:1 __ atrium(a) and __1 ventricle(s).

Division of circuits and blood mixing does not apply because fish only have __ circuit.

Oxygen-poor blood coming from the systemic capillaries collects in the atrium of the heart. The atrium then pumps blood into the ventricle, which in turn pumps the blood to the gill capillaries via the ventral aorta (ventral = towards the front) and its linked arteries. The oxygen-rich blood is then transported to the various systemic capillaries:
capillary beds of the body’s organs (e.g. intestines, kidney, muscle, etc.) via the dorsal aorta (dorsal = towards the back) and its linked arteries. The oxygen-poor blood leaving the systemic capillaries is collected into veins and then a ventral vein that brings blood back to the heart.
Fish only have one (1) circulation circuit. In a system with only one circuit, blood only passes through the heart once and so only gets pumped once. Blood pressure drops as the blood goes through the various blood vessels on its way back to the heart. This drop in pressure can be a problem since it might limit the return of blood back to the heart. However, fish can compensate for this lowered pressure by using their muscles to swim. The contraction and relaxation of the muscles creates additional pressure that helps bring blood back to the heart.

1. Summary of Adaptations in Fish
   A.2 heart chambers and 1 circulation circuit.
   B.Gills for respiration in water.
   C.Use of muscle contractions to compensate for loss of blood pressure in a cardiovascular system with 1 circuit.

The cardiovascular and respiratory system of fish fits the way of life of these aquatic animals.

B. AMPHIBIANS

1. Respiratory System
   Adult amphibians can have a structurally simple pair of lungs that it can use for respiration while out of water. The lungs provide an internal surface lined with capillaries for gas exchange. An internal surface can be kept moist when out of water (unlike gills). The simple lungs of amphibians are not efficient enough and are complemented with other respiratory organs (Fig. 9). Amphibians can also exchange gases with the environment and its blood through the lining of its mouth and its skin. The lining of the mouth is primarily used during rest while out of water. The skin can be used out of water to complement the other respiratory organs but is the only organ used while the amphibian is underwater.
2. Cardiovascular System
   Lab Exercises:
   1.Label the structures of the amphibian cardiovascular system Fig. 10 using the letters from the list.
   2.Fill-in the blanks below BY INDICATING THE NUMBER FOR EACH COMPONENT OR CHOOSING FROM THE CHOICES THAT PRECEED THE BLANK.

Amphibians have 3 heart chamber(s): 2 atrium(a) and 1__ ventricle(s) and __2 circulation circuit (s).

Blood mixing [circle one: does or does not] occur as the _ circuits are [circle one: partially or completely] _ separated.

All amphibians have two (2) circulation circuits: systemic and pulmocutaneous (pulmo = lungs; cutaneous = skin). In a cardiovascular system with 2 circuits, blood passes through the heart twice to complete a cycle which increases the blood pressure in the organism. Notice that blood from the two circuits are deposited into the single ventricle of the heart. However, oxygenrich and oxygen-poor blood coming from the separate circuits are not completely mixed. A ridge within the ventricle and precisely timed contractions of the heart chambers helps to “direct” blood flow out of the heart towards the appropriate circuits. Even with the potential for complete blood mixing, these mechanisms direct most of the oxygen-poor blood that comes into the ventricle to the pulmocutaneous circuit to be oxygenated and most of the oxygen-rich blood to the systemic circuit to deliver its oxygen to body cells.

1. Summary of Adaptations in Amphibians
   A.3 heart chambers and 2 circulation circuits.
   B.Lungs for respiration on land.
   C.Skin for respiration in water and to compensate for inefficient lungs.
   D.Mechanisms to direct blood to the appropriate circuits to limit the effects of blood mixing.

The cardiovascular and respiratory system of amphibians fits the way of life of these semiaquatic animals.

C. REPTILES

1. Respiratory System
   The thick, scaly skin of reptile make using the skin as a respiratory organ impossible. Reptile have lungs that are more efficient than amphibian’s and do not need another respiratory organ to compensate. Their lungs have a surface of microscopic air-filled sacs called alveoli that are surrounded by capillaries for exchange (similar to that of mammals shown in Fig. 4). Consequently, reptiles cannot breathe underwater like amphibians.
2. Cardiovascular System
   Lab Exercises:
   1.Label the structures of the reptile cardiovascular system in the illustration in Fig. 11 using the letters from the list.
   2.Fill-in the blanks below BY INDICATING THE NUMBER FOR EACH COMPONENT OR CHOOSING FROM THE CHOICES THAT PRECEED THE BLANK.

Non-crocodilian reptiles have 3 heart chamber(s): 2 atrium(a) and 1.5 ventricle(s) and 2_ circulation circuit (s).

Blood mixing [circle one: does or does not] Figure 11. The cardiovascular system of non_______ occur as the _ circuits are [circle one: crocodilian reptiles. partially or completely] separated.
As in amphibians, all reptiles (non-crocodilian and crocodilian) have two (2) circulation circuits: systemic and pulmonary. However, there are some distinct differences in the structure of the reptile heart and vasculature when compared to the amphibian system.

Non-crocodilian reptiles have an incomplete separation in the ventricle of their heart called a septum. The septum partially divides the ventricle into two halves and keeps most of the oxygen-rich blood from the pulmonary circuit and oxygen-poor blood from the systemic circuit from mixing in the ventricle before it is pumped out into the appropriate circuits via arteries.

Crocodilian reptiles (i.e. crocodiles, alligators, and caimans) have a 4-chambered heart: 2 atria and 2 ventricles similar to birds, which are their closest relative within the groups of vertebrates discussed here. The complete separation of the heart prevents oxygen-rich blood on the left side of the heart from mixing with oxygen-poor blood from the right side of the heart.

All reptile systems have 2 aortae: a main aorta and a bypass aorta. Both vessels can bring oxygen-rich blood from the heart towards the systemic circuit when the lungs are active and can re-oxygenate blood. However, when the lungs are not being used due to a period of apnea (breathing stops), oxygen-poor blood from the systemic circuit returned to the ventricle (right ventricle in crocodiles) can be directed out through the bypass aorta bringing it right back to the systemic circuit in a process called shunting. Reptiles go through apnea when they slowly ingest large prey (e.g. snake) or semi-aquatic reptiles go underwater (e.g. crocodile) and so shunting bypasses the pulmonary circuit and recycles the blood in the systemic circuit when the lungs cannot be used.

When observing the crocodile heart model in this lab, you’ll notice that a blood vessel is colored purple to signify mixed blood. So why is there still some blood mixing in the crocodilian cardiovascular system? Although crocodilian reptiles have a 4-chambered heart and complete separation of oxygen-rich and oxygen-poor blood at the level of the heart, oxygen-poor blood from the bypass aorta during periods of apnea can mix with oxygen-rich blood from the main aorta via a hole between these aortae called the foramen of Panizza.

1. Summary of Adaptations of Reptiles
   A.3 (or 4 for crocodilians) heart chambers and 2 circulation circuits.
   B.Partial (or complete for crocodilian) septum to help limit blood mixing.
   C.Shunting can divert blood to where it is needed most when lungs are not used.
   D.Efficient lungs for respiration on land.
   The cardiovascular and respiratory system of reptiles fits the way of life of these animals. Reptiles have lower metabolic needs than birds and mammals so their tissues do not need as much O2 or buildup as much CO2. Their lower metabolic needs are explained by 1. they do not use muscles to the same extent as some other animals (e.g. reptiles are “sit-and-wait” predators and do not chase their prey) and 2. do not use internal mechanisms to regulate their body temperature. These lower metabolic needs and blood mixing through a shunt allows semiaquatic reptiles such as crocodiles to remain underwater for long periods of time and cycle the oxygen in their blood before having to come up for air.

D. BIRDS AND MAMMALS

1. Respiratory System
   Birds and mammals possess the most efficient lungs in the animal kingdom. The anatomy and physiology of avian (bird) lungs differ significantly from that of mammalian lungs but the basic principle remains the same. Compared to reptilian lungs, mammalian lungs possess a much more extensive network of branching tubes reflecting a much greater surface area for gas exchange (Fig. 12). However, exchange is still performed in the alveoli at the ends of the respiratory tree and the pulmonary capillaries that surround them
   (Fig. 4).
2. Cardiovascular System
   Lab Exercises:
   1.Label the structures of the bird/mammal cardiovascular system in Fig. 13 using the letters from the list.
   2.Fill-in the blanks below BY
   INDICATING THE NUMBER FOR
   EACH COMPONENT OR CHOOSING FROM THE CHOICES THAT PRECEED THE BLANK.

Birds/Mammals have 4 heart chamber(s): _2 atrium(a) and 2 ventricle(s) and _2 circulation circuit (s).

Blood mixing [circle one: does or does not] occur as the _ circuits are [circle one: partially or completely] _ separated.

1. Summary of Adaptations
   A.4 heart chambers and 2 circulation circuits.
   B.Complete septum that separates the circulation loops and prevents blood mixing.
   C.Most efficient lungs for respiration on land.

The cardiovascular and respiratory system of mammals and birds fits the way of life of these animals. Both the complete separation of the pulmonary and systemic circuit and highly efficient lungs ensure that the blood of birds and mammals can provide oxygen saturated blood to its highly metabolic tissues to satisfy its needs. Birds and mammals have high metabolic demands as 1. they use muscles extensively (i.e. flying or running) and 2. are endotherms (regulate their body temperature via internal mechanisms).

The similar systems between birds and mammals are thought to be a product of convergent evolution. In convergent evolution, organisms develop similar adaptations independently as a result of similar habitats and/or similar ways of life. Indeed, data suggest that efficient lungs and a four-chambered heart that prevents blood mixing was not inherited from a common ancestor and are not homologies. A similar adaptation that arises through convergent evolution is referred to as an analogy.

Lab Exercises: Label the various structures in the diagrams using the list at the right.
The Mammalian Heart
The heart is located in the thoracic (chest) cavity and is protected by a bone called the sternum and by the rib cage. The heart is about the size of an adult’s fist and has a mass of approximately 300g.

The heart is a hollow cavity with muscular walls, composed of very special muscle tissue (cardiac muscle) capable of contracting without an external stimulus. The continuous flow of blood throughout the body is brought about by the rhythmic contraction and relaxation of these heart muscle cells.

A thick partition divides the heart into a right and left side. The right side of the heart is responsible for collecting oxygen-poor blood from the body via the vena cavae (systemic veins) and then pumping it to the lungs via the pulmonary arteries. The left side of the heart is responsible for receiving oxygen-rich blood from the lungs via the pulmonary veins and then pumping it to the rest of the body, via the aorta (systemic artery).

Each side of the heart contains 1 atrium and 1 ventricle for a total of 4
chambers. The smaller atria are about 1/3 the size and volume of the ventricles. The atria are thin-walled chambers that lie above the ventricles. Their main function is to collect blood from large vessels and pass it into the ventricles. The ventricles have much thicker walls and are responsible for passing the blood to the arteries of the Figure 14. The mammalian heart and its circuits. heart.
Names: _____ _____

Lab Section: _

LAB REPORT

Part A: Comparison of Vertebrate Hearts

1.Based on expected characteristics, compare the hearts in part 1 of the Lab 7 Appendix document and match each of the model hearts to a vertebrate group and complete the table below.
Please note that the relative sizes and colour of the hearts are not true to life. You are not expected to memorize the direction of blood flow or the names of the structures of the hearts in the appendix
In the last column of the table, Defining Features, please list a characteristic that helps you distinguish different 3 chambered hearts from each other, or different 4 chambered hearts from each other. ie. Don’t just write “4 chambered hearts” for both humans and owls.

Animal Vertebrate Group Heart
(use # label) Heart Chambers Blood
Mixing in the CV
System?
[Yes or No] Defining Feature(s)
Used to identify heart.

Atrium(a)

Ventricle(s)

Human Mammal 1 2 2 No It has 2 chambers and are separated properly
Owl Bird 2 2 2 No Smaller in size as compared to body mass and inside wall for ventricle and atria are smoother
Turtle Reptiles 6 2 1 Yes 3.5 chambered heart. Ventricle partially divided
Dog Mammal 5 2 2 No The left atrial appendage are triangular shaped as well as is lesser than the right atrial (Kozlovsky & Larin, 2019)
Bullfrog Amphibians 4 2 1 Yes The septum develops at a point where ventricle separate and receive oxygen rich blood
Crocodile Reptiles 3 2 2 No This reptile have left aorta exit the heart separately
Dogfish Fish 7 1 1 Yes Fish have only one atria as well as one ventricle

2.Complete the following phylogenetic tree to illustrate the evolutionary relationships between the 7 organisms from the table above. Use the appearance of adaptations in the cardiovascular system listed to help you label the tips. Assume that convergent evolution produced the similarities in the respiratory and cardiovascular systems of birds and mammals.

3.Answer the following questions concerning the evolution of vertebrates.
a)Which current group (of the 7 in this tree) might the first tetrapod (ancestor to all future tetrapods, now extinct) have resembled?

The Amphibian would be the first tetrapod among the all the tetrapods in the above group.

b)Which characteristic(s) would you have expected in the cardiovascular system of this tetrapod ancestor?
The ancestor Amphibian might have 3 chambers such as 2 atria and one ventricle and there was no ventricular partial partition (Kozlovsky & Larin, 2019).

c)Which characteristic(s) would you have expected in the respiratory system of this tetrapod ancestor? Add this (these) characteristic(s) as adaptations to this tree.

The amphibian tetrapod ancestor would have gills to respire in water and lungs to respire on land. Initially there was only gills for water respiration as life began in water; with adaptation the development of lungs took place and these group got the ability to respire in land, however slowly the gills became obsolete due to evolution (Chen et al., 2017).

d)Sometimes adaptations in extant/extinct organisms can be viewed as a transitional
(intermediate) form between two distinct adaptations in other organisms and gives us insight on how evolution occurred. Which adaptation in the hearts of reptiles can be viewed as a transitional form in the evolution of the vertebrate heart?

In reptiles the heart is 3.5 chambered which means that their ventricles are partially divided. Before adaptation there was no partial partition for ventricles. Hence. This partial partition proved adaptation or evolution (Chen et al., 2017).

e)How do we know that the similarities between the respiratory and cardiovascular systems of mammals and birds are analogies and not homologies?

Respiratory: their function is same however there is difference in the air flow, for bird it is unidirectional and mammal it is bidirectional (Yanagida & Hla, 2017).
Cardiovascular: Mammal and bird have 4 chambered heart but partition between atria and ventricle are smooth for birds.

f)If convergent evolution produced the similarities in the heart structures of birds and mammals, would you expect the anatomy of the blood vessels (network of arteries and veins) and other anatomical traits of a bird to more closely resemble that of a crocodile or a dog? Briefly explain.

The anatomical feature of bird’s heart will match with dog more than crocodile. As crocodile is a reptile that comes before bird in evolutionary history. Moreover, bird and dog both have smaller heart (Bozkurt, 2020).

g)Draw TWO (2) phylogenetic trees for the following groups: A. Fish, B. Mammals, C. Reptiles, D. Birds, and E. Amphibians. Indicate (where each important adaptation in the cardiovascular system appeared for the first time at the appropriate node (representing an ancestor in this lineage; use a perpendicular line just below the node for each adaptation).
One tree should represent the hypothesis that convergent evolution has played a role in the similarities of bird and mammal hearts (accepted hypothesis; now considered a theory), while the other should represent the alternative hypothesis that the similarities of bird and mammal hearts have been inherited from a common ancestor (refuted hypothesis).

Convergent Evolution Hypothesis

The perpendicular line demonstrates the point when evolution occurred. This proves the hypothesis that the convergent evolution has played a major role in cardiovascular system evolution (Duke et al., 2016).
Common Ancestor Hypothesis

This phylogenetic tree shows that all the groups have common ancestry however, evolution occurred during the process of development. This tree also demonstrates which species are closely related and which species are distantly related to each other (Misra et al., 2017).

Part B: Mammalian Heart

As you explore the mammalian heart, answer the following questions. Please refer to part 2 in the Lab 7 Appendix document for guidance.

1.Many students think that arteries always carry oxygen-rich blood and veins carry oxygen-poor blood. Is this correct? Briefly explain and give an example.
No it is not true. It is normal that arteries carry orxugentaed blood and vein carry deoxygenated blood. However, there are some exceptions where it is seen that deoxygenated blood is carried by pulmonary artery from right ventricle to the lungs and oxygenated blood by pulmonary vein (Pediatrics, 2015). This pulmonary vain is present in all the 4 chambers of the heart and this vein carries oxygenated blood from lungs to the heart (left atrium).
2.The terms oxygenated and deoxygenated blood is often used in anatomy and physiology when describing the cardiovascular system. Why might the term deoxygenated be considered inaccurate?
Deoxygenated means remove oxygen. On the other hand, this term is considered inaccurate because, in case of deoxygenated blood the meaning is there is less oxygen present as compared to oxygenated blood. The deoxygenated blood has lesser content of oxygen hence it is called de-oxygenated but the term itself means no oxygen (Wright et al., 2014). There is no blood in body without oxygen. Therefore, the term de-oxygenated is considered inaccurate in this case.

3.What is the function of the right AV valve? How about the left (aortic) semilunar valve? Be specific.
The AV (atrioventricular) valve discrete the atrium from the ventricles on every side of the heart, hence preventing the flow of blood from ventricles to the atrium during the systolic moment. The right atrioventricular valve is also known as tricuspid valve, and the left valve is called a mitral valve (Menga & Ghirardi, 2019). The blood flow is permitted by the pulmonary valve where the flow of blood occurs from right ventricles to the pulmonary artery as well as aortic valve that allows the blood flow from left ventricle to the aorta. The main function of AV valve is that it closes during systole (ventricular) to stop spewing of blood from the right ventricle into the right atrium. It unlocks in the time of ventricular diastole that allows the blood to drift from the right atria into the right ventricle.
4.Why does it make sense that the left ventricle is more muscular than the right ventricle?
Left ventricle is more muscular than right ventricle because left ventricle have to pump more blood and with more force through the circuit system in comparison to the pulmonary circuit. Hence, more muscular force are required, therefore they are more muscular (Lukyanchenko, 2016). On other hand, ventricles have to work more, more blood pumping hence, the ventricular muscles are stronger than arterial.

Part C: Final Questions (Formerly pre-lab exercise)

A. Respiratory Systems
1.In your own words, describe the functions of a respiratory system?
The respiratory system helps all living organism to breath, hence the exchange of gases like carbon dioxide and oxygen takes place. All living organism takes in oxygen and releases carbon dioxide. The main organ performing all these function is lungs, that carry out gas exchanges when there is breathing. Along with gaseous exchange respiratory system has an important role such as olfactory assistance such as smell, sound production and protection from microbes and dust that enters our body by production of mucus, coughing and cilia (Misra et al., 2017).

2.Although there are many types, which characteristics do all respiratory surface organs have in common that helps them accomplish these functions?
The common characteristics of respiratory system that is present in all organism are large surface area so that enough oxygen can be received. All the respiratory organ irrespective of species have thin walled organ system so that easy gas diffusion can take place (Wright et al., 2014). Various kinds of respiratory organs are lungs, skin and gills all have high source of blood supply that helps in transporting respiratory gases. The most common feature among lungs and gills are to play an important role in the air purification. All these respiratory organs are well supplied with blood cells. Both of these organs helps in breathing and they have respiratory part that allows the gases to pass through their membrane.

3.Would a bullfrog suffocate if it dries out? Briefly explain.
Yes, bull frog would suffocate if it dries out. However, the bull frog does not immediately dry up once they are on land because frog gets oxygen and water from their skin. This whole process works till the skin of the frog is moist but the moment the skin starts to dry up they suffocate as they do not get enough oxygen or can release carbon dioxide (Wright et al., 2014). Slowly they die.

4.Can a reptile breathe underwater like a fish or an amphibian? Briefly explain.
No, reptile cannot breathe inside water. They come to the land surface to get air so that they can breathe. In some cases, it has been observed that they can hold the breathe for a long time but they cannot continue it for long.

B. Cardiovascular Systems
1.In your own words, describe the functions of a cardiovascular system?

The cardiovascular system comprises of blood, blood vessels and heart. This system helps in transport of hormones, oxygen and nutrients. They transfer all these elements to the cells of the body and hence helps in the removal of all the metabolic wastes such as nitrogen wastes and carbon-di-oxide (Misra et al., 2017)
2.What are the specific functions of?
a)The heart: The main function of heart is to pump oxygen all over the body through the circulatory system. The blood carries nutrient and oxygen to the cells of the body and brings back waste back to the heart for purification. The tissues of the organism require supply of oxygen and nutrients continuously to stay active all through out.

b)Arteries: Arteries carries oxygenated blood from heart to other parts of the body. It carries all the essential nutrients to the cells of the body (Misra et al., 2017).

c)Veins: The veins carry impure blood/ deoxygenated blood from the cells, tissues to the heart for purification.

d)Capillaries: It edge body cells in addition to tissues to transport in addition to engross nutrients, oxygen in addition to additional substances. The capillaries also link the arteries branches along with the veins branches.

C. Convergent Evolution in Birds and Mammals

1. In this lab, we will discuss the high efficiency of the respiratory and cardiovascular systems of mammals and birds. Although both systems are efficient in these vertebrate groups, the anatomy and physiology of these systems have arisen by convergent evolution due to similar metabolic needs. a) What is convergent evolution?
   Convergent evolution can be defined as an independent evolution of parallel characters in species of diverse eras or periods in time. It creates equivalent structures, which have comparable arrangement or purpose on the other hand were absent in the former common ancestor of these groups (Menga & Ghirardi, 2019).
   b)Based on the functions of the respiratory and cardiovascular systems, what is the outcome of efficiency in these systems?
   Both of these systems are highly efficient as they are prime system for survival. An organism cannot survice without these two system. One system helps in gaseous exchange and another system helps in transferring the nutrient to every parts of the body (Misra et al., 2017).

c)Describe TWO (2) shared aspects of their respective metabolisms that create a need for higher metabolic needs?
The circulatory system transfers essential gases as well as nutrients all over the body and removes unwanted products from tissues that are produced due to metabolism and hence carries these metabolic products to excretory organ (Menga & Ghirardi, 2019). On other hand, respiratory system along with circulatory system supplies oxygen and removes metabolic wastes. Hence, the blood is easily maintained.

References
Bozkurt, S. (2020). Computational Simulation of Cardiac Function and Blood Flow in the Circulatory System under Continuous Flow Left Ventricular Assist Device Support during Atrial Fibrillation. Applied Sciences, 10(3), 876. https://doi.org/10.3390/app10030876
Chen, Y., Chan, H., Michael, S., Shen, Y., Chen, Y., & Tian, Q. et al. (2017). A microfluidic circulatory system integrated with capillary-assisted pressure sensors. Lab On A Chip, 17(4), 653-662. https://doi.org/10.1039/c6lc01427e
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