Lesson 32

◊ Lesson Outline: ♦ Phylogenetic Trends in Circulatory System Form and Function

◊ Objectives: Throughout the course what you need to master is an understanding of:

1) the form and function of structures,

2) the phylogenetic and ontogenetic origins of structures, and

3) the extend to which various structures are homologous, analogous and/or homoplastic.

References: Chapter 14: 314-350

Reading for Next Lesson: Chapter 15: 351-386 Exercise #1 List the basic functions of the circulatory system:

The role of the circulatory system is to transport substances between sites in the body.

The circulatory system also distributes hormones that play a key role in regulatory processes, and transports the chemicals of the immune system that defend the body from foreign organisms.

Exercise #2 Describe the evolutionary trends that we see in the hearts and major arteries of the different vertebrate groups:

Phylogenetically, the heart probably began as a contractile vessel with no distinct chambers or valves - as is still the case in amphioxus. While this may seem inefficient, at this point in evolution, organisms were sessile and most exchange still took place across the general body surface. Under these conditions, such a form of circulation was more than adequate to meet their needs.

The phylogenetic trends that we see throughout the remainder of the chordates were covered in detail in the last lecture (lecture 29) and are summarized schematically in the next figure:

Exercise #3 – Comparisons –

Case 1 What class of vertebrate is each heart from?

What evidence did you use in deriving your conclusions?

a) This is an amphibian heart. It has a single ventricle from which the conus arteriosus and truncus arteriosus stem. The aortic arches are symmetrical and arches 3 (commom carotid), 4 (systemic), and 6 (pulmonary) are present, which is typical of amphibians. b) This is a reptile heart. There are three major vessels stemming off the ventricle, which is characteristic of reptiles. They have both a right and a left systemic arch (arch #4) which runs to the body. Arch 3 and 6 also are present. c) This is a bird. They have a divided ventricle. The systemic arch branches and runs down the right side of the body. The subclavians branch off of the 3rd aortic arch. d) This is a mammal. They also have a divided ventricle. The systemic arch branches and runs down the left side of the body. The subclavians branch off of the aortic trunk.

Case 2

Based on these three diagrams, describe the flow of systemic venous blood from the heart to the lung.

Then discuss whether the pulmonary artery in the mudpuppy is homologous to the pulmonary artery in a human or not

Systemic venous blood returns to the right atrium and then gets pumped to the common, undivided ventricle. From here, it is pumped into the conus arteriosus, through the bulbous arteriosus and off to the gills where they pick up oxygen and remove CO2 form the blood if the animal is respiring through the gills. From here, some of the oxygenated blood runs through the pulmonary artery to the lungs. The rest of the blood continues on to the rest of the body. The blood from the pulmonary artery runs to the lungs and then returns to the left side of the heart via the pulmonary vein.

The mudpuppy pulmonary artery is not homologous with that in a mammal because it does not branch off from the truncus arteriosus. Rather, it branches off and diverges to the lungs only after it has passed through the gills. Thus, the pulmonary artery does not branch off from the heart, as it does in most other terrestrial vertebrates.

Case 3

A rete is a vascular complex in which arteries and veins break up into small vessels that intermingle to form a complex structure. There is no direct communication between the arteries and the veins – they simply intermingle. What might retes be used for and what might be the specific function of the ones shown in figure b?

Summer 2005 – You are not responsible for this question.