Connect Form and Function of Closed Circulatory Systems

11 December 2017 Morse Laboratory

Week 12 - Vertebrate colonization of land: cardiovascular adaptations

Objectives  Connect form and function of closed circulatory systems.  Demonstrate stepwise changes in the circulatory system morphology of vertebrates as increased adaptations to terrestriality.  Reinforce the concept of no universal optimum for function; function only matches environmental requirements.  Address the misconception of linear evolution that leads to successively better forms.

By the end of the lab students should be able to answer:  What makes a double circulation more effective at gas exchange than a single circulation?  If one heart morphology is better than the others, why are there still animals with the less than optimum morphology?  How does a four-chambered, double circulation heart improve life on land?

Activities  Work in groups, share project results with class. Discuss what each circulatory system design does well/not well.  Comparative dissections of perch, frog, and rat to see differences in heart morphology, i.e. find heart, look at vessels coming from it, where they lead. Then dissect the heart open to see chamber morphology. Students are encouraged to work in pairs and teach each other.  Observe dissected calf heart to see chambers and valves.  Group presentations

Cardiovascular System

1. What is the primary purpose of the cardiovascular circulatory system in vertebrates?

2. Think-Pair-Share: Open vs closed circulatory system.

3. Why is a pump necessary?

- Something about resistance: length and diameter of blood vessels dictates how much pressure is needed to push blood through the system

4. Think-Pair-Share: Design a system of tubes for either a rat or a fish that meets the following design criteria:

. Connects the site of oxygen uptake, heart and body.

. Maximizes oxygen delivery to the tissues.

1 11 December 2017 Morse Laboratory

You may add as many components as they need to the ones given to make the most effective system.

5. Calf heart demo - We are going to focus on the respiratory function of the cardiovascular system. The following are parts of the system you should know; most will be demonstrated on a dissected calf heart:

I. Blood

I. Valves

A.1. Atrioventricular A.2. Semilunar valves II. Vessels

1. Aorta 2. Pulmonary Vein 3. Vena cava 4. Pulmonary artery

III. Atria

IV. Ventricles - cardiac muscle

1. Left vs right V. Coronary vessels

6. Comparative Dissections of a Fish, Amphibian and Mammal

 Locate the heart in each of these three specimens.

 Identify the main chambers of the heart and the vessels leading to and from the heart.

 After you have identified all the relevant structures, you may try removing the heart from the body and dissecting it to see its internal anatomy.

Fish representative: the Perch (genus Perca)

To start your dissection locate the anus on the ventral side of the fish, just anterior to the anal fin. Using a pair of scissors, make an incision from the anus to the head. Take special care to only cut the body wall and not to damage any of the organs in the body cavity. You will need to cut through the pectoral girdle bones that connect the pectoral fins, once you are close to the head.

The heart is located near the anterior end of your incision. Enlarge the opening by removing a piece of body wall on each side of your cut. We will focus primarily at looking at the two-chambered heart; see if you can identify any large blood vessels. Where do they lead?

The pericardial cavity is separated from the abdominal cavity by a transverse septum. This septum is NOT homologous to the diaphragm of mammals. The heart has two chambers: a thin-walled atrium and a muscular ventricle. Blood collected from venous system enters the sinus venosus, a thin-walled sac adjoining the atrium posteriorly. Blood then flows into the atrium, and then to the ventricle, which is ventral in position. Finally, the ventricle pumps blood into the short, swollen, bulbus arteriosus, the first part of the ventral aorta. The perch circulatory system features a single circuit;

Anatomy of the teleost fish heart. Kardong Fig. 12.27

Sequence of contractions that move blood into and through and out of the teleost heart. Kardong Fig. 12.28

Amphibian representative: the frog (genus Rana)

Place the frog on its back in your dissection tray. With scissors carefully make a mid- ventral cut through the body wall from the posterior end of the abdomen through the sternum and clavicle to the “neck”. Be careful not to cut too deep! The heart will be wrapped connective tissue, called the pericardial sac. There are two separated atria, the right being bigger than the left, and a single ventricle. Blood flows into the atria from the sinus venosus, and out of the ventricles through a tubular conus arteriosus. The ventral aorta, continuous with the conus arteriosus, is transformed into a bifurcated vessel called the truncus arteriosus.

The pulmonary vein carrying relatively well-oxygenated blood from the lungs and skin, enters the left atrium. The sinus venosus carrying deoxygenated enters the right atrium. At the base of each atrium is an atrioventricular valve regulating the flow of blood into the ventricle. Although the ventricle is undivided, due to slightly different timing in emptying the right and left atria as well as the presence of the trabeculae the two blood streams remain mostly separated. The conus arteriosus receives both streams. A spiral valve in the conus arteriosus directs the oxygen-poor blood and the oxygen-rich blood into the truncus arteriosus. The truncus arteriosus is partitioned into a carotid, a pulmonary, and a systemic channel. The most highly oxygenated blood is shunted into the carotid pathway, mixed blood is shunted into the systemic pathway, and the blood with the lowest oxygen content is shunted into the pulmonary and cutaneous vessels.

Anatomy of the frog heart. Notice the spiral valve and ventricular trabeculae. These structures direct blood flow into the appropriate vessels out of the single ventricle that collects both oxygenated and deoxygenated blood from the left and right atria, respectively. Kardong, Fig. 12.30

Mammalian representative: the Rat (genus Rattus)

Anatomy of the mammalian heart. Kardong, Fig. 12.39

blood into the heart= venous blood blood out of the heart=arterial

precava= superior vena cava postcava=inferior vena cava

Pulmonary circulation pulmonary artery goes to lungs- deoxygenated pulmonary vein comes from lungs- oxygenated

Systemic circulation aorta goes to body- oxygenated vena cavae come from body- deoxygenated

To open your specimen so that you may study the cardiovascular system, place the rat on its back in the dissecting tray. Starting at the middle of the abdomen, pull up some of the loose skin and make a small, midline incision. You may do this either with your scissors or with a scalpel. Be careful not to cut too deeply as you will destroy some of the abdominal organs. Continue your incision anteriorly towards the head so it joins with the incision in the neck where preservative was injected. Over the thoracic region you will be cutting through skin over the ribs. Now, cut from your original incision toward the pelvic region being careful to cut around the external genitalia. By cutting laterally in the region of the armpit and groin, you should be able to peel the skin away to either side in two large flaps. Pin these flaps to the tray.

The body cavity between the ribs is called the thorax or thoracic cavity. To open the thorax you need to cut through the ribs. To do this, cut slightly to one side of the sternum using a pair of stout scissors. Continue your incision up into the neck, but be careful not to cut too deep. This cavity contains the heart and the paired lungs. A large thymus gland covers part of the heart in the anterior portion of the cavity.

Note that the lungs are lobed- 1 lobe on the left and 4 lobes on the right. Moving air from the pharynx to the lungs is the trachea, a tube reinforced with cartilaginous rings. The esophagus lies dorsally to the trachea in the neck (behind the trachea) and continues through the diaphragm to end in the stomach.

In mammals, the heart consists of a right side pumping deoxygenated blood to the lungs and a left side pumping oxygenated blood to the body. Each side of the heart has an atrium (usually with ear-like flaps called auricles) for receiving blood. Blood moves from the atria to the ventricles that pump the blood out of the heart.

The right ventricle pumps blood to the lungs via pulmonary arteries. Note that by definition, arteries carry blood away from the heart, veins carry blood toward the heart. After oxygenation in the lungs, blood returns to the left atrium by the pulmonary veins. Leaving the left ventricle is the aortic arch, which curves to the left then flows down the middle of the body as the dorsal aorta.

Some of the main blood vessels you may be able to see (arteries are stained red, veins are stained blue):

Carotid arteries- supply blood to the head; branch off the aorta; lie on each side of the trachea. Subclavian arteries- supply blood to the forelimbs. Aorta- large vessel leaving the heart; forms a posterior pointing arch. Posterior (inferior) vena cava- brings blood into the heart. Renal artery and vein- supplying and draining the kidneys, two bean shaped structures at the dorsal wall of the abdominal cavity. Common iliac arteries- supply the pelvic region and hind limbs; bifurcate off the aorta.

Cardiovascular System: Matching Design to Environmental Demands

High specialization in mammals and birds actually means less flexibility- for example in amphibians the relative volume of blood sent to the lungs vs the body can be modified because of the single ventricle. In mammals this cannot be done because the left and right side, systemic and pulmonary circuits, are completely separated.