Shark anatomy
This picture shows the dissected shark specimen that you can see in the lab. The numbers in the accompanying text refer to the numbers on that specimen. The numbers are hidden in this image, but you'll see them on the actual specimen.
Heart & Circulation
In sharks, as in bony fish, the blood is pumped only once as it makes its passage through the gills and then through the systemic circulation before coming back to the heart. You should be able to make out three separate parts of the shark’s heart:
1. Ventricle: muscular, thick-walled chamber that pumps the blood.
2. Auricle: (also called atrium) thin-walled, stretchy chamber that receives the deoxygenated blood before it passes to the ventricle.
3. Conus arteriosus: receives blood pumped from the ventricle. Contains valves that prevent backflow of blood. This chamber apparently helps even out the blood pressure coming from the heart.
4. Ventral aorta: large artery that receives blood from the heart. The blood flow goes: auricle→ventricle→conus arteriosus→ventral aorta. The ventral aorta branches into two main arteries that carry blood to the gills.
5. Gills: perform gas exchange, aided by the countercurrent flow of blood and water and by the large surface area and short diffusion distance. In addition to gas exchange, gills also perform important roles in eliminating excess ions and nitrogenous waste and in regulating pH.
7. Spleen: functions in producing and maturing some kinds of blood cells.
14. Dorsal aorta: carries oxygenated blood from the gills to the systemic circulation.
Digestion & absorption
6. Stomach. The main region (also called “cardiac region”) of the shark’s stomach is muscular and stretchy, with thick folds. The diagram at right is an illustration of the shark stomach from an 1893 edition of the Encyclopedia Britannica (courtesy of Clipart ETC http://etc.usf.edu/clipart).
8. Pylorus. The food passes from the main region of the stomach into the lower pyloric region. At the downstream end of the pyloric region, there is a pyloric sphincter that regulates the passage of chyme (partially digested food) into the intestine.
9. Ventral lobe of pancreas: secretes digestive enzymes into the stomach (this is a little different from mammals, in which pancreatic enzymes are secreted into the duodenum).
10. Bile duct: carries bile from the liver to the duodenum.
11. Hepatic portal vein: carries blood from the intestine and spleen to the liver.
15. Duodenum: The first part of the intestine, in which much of the digestion occurs.
16. Intestine and 17. Valvular region of intestine: the intestine. Sharks have short intestines. At first glance, the intestine doesn’t seem long enough to provide adequate surface area for absorption. However, inside the valvular region of intestine, there is a spiral valve (similar to a spiral staircase) that provides additional surface area and slows down the passage of food.
10. Bile duct: carries bile from the liver to the duodenum.
11. Hepatic portal vein: carries blood from the intestine and spleen to the liver.
12. Liver: As in mammals, the liver performs some functions related to digestion and absorption:
- Produces bile to aid in fat digestion.
- Helps control blood sugar level.
- In addition, the livers of sharks also help to regulate buoyancy for swimming. Unlike bony fish, sharks don't have a gas-filled swim bladder. Instead, they regulate buoyancy largely by storing squalene, a low-density hydrocarbon. Containing large amounts of squalene, the liver becomes less dense than the surrounding seawater, making it easier for the shark to avoid sinking like a stone. Sharks have large livers in relation to body size. Nevertheless, sharks are generally denser than water, and must do some work to avoid sinking. This is in contrast to bony fish, which can adjust the size of the swim bladder to become neutrally buoyant.
13. Gall bladder: stores bile produced by the liver before it is delivered to the duodenum via the bile duct.
Osmoregulation
18. Rectal gland: concentrates salt ions (particularly Na+ and Cl-) in the urine before the urine is eliminated via the cloaca.
20. Kidney: Eliminates excess water and salts, but very little urea. Urine passes from the kidney to the rectal gland.
Other structures
19. Testis: produces sperm.
26. Seminal vesicle: stores sperm.
27. Clasper: A structure alongside each pelvic fin that is used to insert sperm into a female. (Sharks have internal fertilization.) Claspers are only found in males.
28. Cloaca: The single opening through which urine, gametes, and feces leave the body.
References & further reading:
Reefquest center for shark research. A site with lots of shark information, including physiology.
Canadian shark research laboratory (internal anatomy page). Detailed dissection photos.
Virtual Shark Lab from Philip Pepe at Maricopa. Click on the links in the main page to see labeled dissection photos.
Wikipedia shark page. General information, some of which may be true.
Differences between sharks and bony fish: more than just the skeleton from Shark Savers.