- skeleton is still available

- many of the structures of the mouth will be seen more clearly this week, once the mouth is opened.

- 2 weeks to do circulatory system

- This week, do heart, blood vessels above the heart, respiratory system

- Table 1 - heart to subclavian arteries

- Table 2

Note: gill chamber = gill pouch

- Next week - Table 1 - dorsal aorta to caudal veins

- Next week, do blood vessels below the heart.

- To help with the lab, there are a number of photos and diagrams on the bench.

Start your dissection with the heart. Make a medial incision on the ventral surface of the head between the gill slits.

Remove the skin from the ventral surface then slowly pull away the muscle tissue until you have exposed the pericardium (connective tissue surrounding the heart). Cut the pericardium to expose the heart. Cut through the coracoid bar and pull back to fully open the pericardial cavity. Locate the vessels entering and leaving the heart and the 2 heart chambers - atrium and ventricle.

Look at diagram of blood flow through the heart - Figure 10.9 on page 97 of lab manual.

Next, follow the ventral aorta anteriorly from the heart - no latex.

Pull away tissue to expose the 5 afferent branchial arteries (Figure 5.3).

Later, at end of dissection, cut heart open as described on page 55 (Figure 5.2) and note the interior structure of the heart chambers, semilunar valves, atrioventricular aperture.

Next, cut the buccal cavity open.

Start at the right corner of the mouth, using bone cutters if necessary, and cut along the dorsal margin of the gill slits until you reach the coracoid bar. Cut across the coracoid bar. Cut below the sinus venosus, leaving it intact. Flip the tissue over and pin down. Review the structures in the buccal cavity from last week.

Remove tissue from roof of mouth to expose the efferent branchial arteries and the dorsal aorta. These vessels should all be injected with pink latex.

Locate the rest of the vessels listed in Table 1 and shown in Figure 5.3.

Holobranch - entire gill (Figure 4.6)

3 elements:

interbranchial septum, supported by gill ray, forms framework of gill

2 demibranchs on either side of septum

In shark, 9 demibranchs on each side, arranged as 4 holobranchs and 1 demibranch

- demibranch being located anterior to 1st gill chamber

- no demibranch on porterior wall of last gill chamber

- see handout

Blood flows from heart into afferent branchial arteries. Each afferent branchial artery flows into the interbranchial septa and sends numerous small branches into the gill lamellae. Oxygenated blood is collected from the gill lamellae by a system of efferent branchial arteries. The first portion of this system is a series of collector loops. Each arterial collector loop is formed from the union of a pretrematic artery from the anterior side of a gill slit with a posttrematic artery from the posterior side of the gill slit. The pre and posttrematic arteries receive tiny branches from the adjacent gill lamellae. They also are connected by many larger branches (cross trunks) that pass through the interbranchial septum (from pre to post). The efferent branchial arteries all empty into the dorsal aorta.

Functional anatomy of circulatory and respiratory system is important. Think carefully about relation between circulation and oxygenation of blood in the gill. Consider the handout and look at Figure10.8 on page 97. Read discussion of respiratory and circulatory system on pages 96-98.

Flow of water over gill runs countercurrent to flow of blood through gill capillaries. When blood first enters the gill, it contacts oxygen poor water. Diffusion of oxygen into oxygen depleted blood. As blood moves through the gill, it encounters water that is increasingly oxygen rich. Diffusion continues as blood flows through lamellae, resulting in maximum oxygen exchange.