English: Dental pad of domestic livestock. Note the lack of upper incisors and canine teeth. (Photo credit: Wikipedia)
This week we’ll be looking at cow mouths. Cows have 32 teeth. They have 6 incisors and 2 canines on the bottom. The canines are not pointed, but look like incisors. Also, there are no incisors on the top; instead cattle have a dental pad. Cows have 6 premolars and 6 molars on both top and bottom jaws for a total of 24 molars. In addition, there is a large gap between the incisors and molars. This configuration allows cattle to harvest and masticate large amounts of fibrous feed. Because their teeth are primarily for grinding, cattle use their tongues to grasp or gather grass and then pinch it off between their incisors and dental pad. Since they lack upper incisors, cattle cannot bite off grass very well, and they are inefficient at grazing closely. The inside of the cheeks and palate are rough which helps hold feed in while cattle chew with a side to side motion. In addition to reducing the size of feed particles, the mouth aids in digestion by adding saliva to the feed. Cows will produce 20-35 gallons of saliva a day. The saliva helps moisten the feed. Saliva also contains sodium bicarbonate to keep the rumen at the proper neutral pH (6.5-7.2) for good microbial growth. Much of the water contained in saliva is then recycled by the cow. In conclusion, compared to horses or humans, cows do not have the best mouth configuration. But, it does serve them well.
To watch my video, click here.
Horse mouth (royalty free)
For the next few weeks, I’ll be writing about different animal mouths. Starting with the horse mouth. Horses grasp food using a combination of the lips, tongue, and teeth. Horses’ lips are extremely tactile when it comes to consuming feed. Feeds are mixed with saliva in the mouth to make a moist bolus that can be easily swallowed. There are three pairs of glands that produce saliva – the parotid, the submaxillary, and the sublingual. Horse saliva contains bicarbonate, which buffers and protects amino acids in their highly acidic stomach. Saliva also contains small amounts of amylase which assist with carbohydrate digestion. The mouth contains 36 – 40 teeth. Wolf teeth are not included as not all horses have them. The horse’s upper jaw is wider than the bottom jaw to allow for a chewing motion that is quite complex. The chewing action of the horse is a sweeping action which incorporates both lateral, forward, backwards, and vertical motions. This allows the feed to be effectively ground and mixed with saliva to initiate the digestive process. The texture of the feeds will dramatically influence the chewing rate (jaw sweeps) and rate of ingestion. An average horse will generally take 60,000 jaw sweeps per day when grazing. This amount will be dramatically reduced when confined to a stable and large amounts of grain are fed. When horses chew fibrous feeds such as hay or pasture it is a long jaw sweep action. This is why horses continually out on pasture rarely develop sharp edges on their teeth. Grains are consumed in a shorter sweep which does not extend past the outer edge of the teeth. When large amounts of grain are given, horses chewing action will be changed and the teeth will not be worn evenly. Hooks or sharp edges will start to form on the outside edge of the teeth. Conclusively, mouths are essential for digestion and a discussion about the digestive system would not be complete without them.
To see where the “wolf teeth” are positioned and what a horse’s skull looks like, click here to watch my video
Chicken stomach (photo credit nutrenaworld.com)
This week we’ll look at the chicken stomach. Bird stomachs are different from mammal stomachs in many ways. Today we will be looking at the Crop, the Proventriculus, and the Gizzard. The crop is an out-pocketing of the esophagus and is located just outside the body cavity in the neck region. Any swallowed food and water is stored in the crop until it is time to pass it on to the rest of the digestive tract. When the crop is empty, or nearly empty, it sends hunger signals to the brain so that the chicken will eat more. Although salivary glands of the mouth secrete the digestive enzyme amylase, very little digestion actually takes place in the crop, it is simply a temporary storage pouch. The proventriculus (also known as the ‘true stomach’) is the glandular stomach where digestion begins. As with human stomachs, hydrochloric acid and digestive enzymes (like pepsin) are added to the food here. At this point however, the food has not yet been ground up. The term ‘proventriculus’ is used since it comes before the ‘ventriculus’ or gizzard, with ‘pro’ being the Latin term meaning before. And finally, the gizzard. The gizzard, or ventriculus, is a part of the digestive tract unique to birds. It is often referred to as the ‘mechanical stomach’. It is made up of two sets of strong muscles which act as the bird’s teeth. Consumed food and the digestive juices from the salivary glands and the proventriculus pass into the gizzard for grinding, mixing, and mashing, which is aided by the small stones or grit the bird consumes. These stones remain in the gizzard until they become ground into pieces small enough to pass through to the rest of the digestive tract. The stones/grit are weakened by the acidic environment created in the proventriculus and then are ground into tiny pieces by the strong muscles of the gizzard. This is how chickens can eat a lot of hard seeds and not get digestive issues like humans. Ultimately, Chicken stomachs are designed to ingest the bugs and seeds which chickens need to survive. If any part of the stomach did not work correctly, the chicken might die. Which just goes to show how intricate the whole system is.
To see more chicken anatomy, click here to watch my video.
Dog stomach (Photo credit Hill’s Pet Nutrition)
Now, no talk of stomachs can be complete without finding out how dogs can eat carrion and excrement. A dog’s stomach is like an accordion in that it folds to almost a thin intestine-like organ when it is empty, and when filled, it expands to full size, unfolding all the wrinkles. While a human stomach is simply a bag, not folding at all. The stomach has some very strong muscle in its lining, and it will constantly massage the food, thus making sure the digestive juices get into close contact with all the food. Accordingly, the dog’s stomach will take up some 70-75% of the total volume of the entire gastrointestinal system. It is huge. The human stomach will be only a small fraction of the system, taking up only about 20% of its total volume. In general, all this is geared towards the stomach handling big portions of food at a time -and being given the opportunity to finish a meal before being filled again. It is like a washing machine running through its program and then waiting for the next load. This is a huge difference compared to the human system that is much more like a septic tank where the food seeps through all the time. Another important aspect that is often ignored is that a dog’s stomach is not supposed to be working constantly. It is meant to do a lot of hard work for some time – and then rest for a long period of time. It makes sense that it needs rest, considering how much harder it has to work, compared to a human stomach. Yet, a human stomach generally gets some serious rest every night. Our meals typically take no more than about 3-4 hours for the stomach to finish and hand over to the intestine, so even if we get a “good night snack” just before bedtime, there will still be 4-6 hours rest available for the stomach before breakfast. For the dog, digestion of a full meal can easily take more than 24 hours. Conclusively, the dog’s stomach is a depot organ – the human stomach is merely a transit station. This is why a dog can ingest excrement. And as said before, humans cannot ingest excrement without painful consequences. So I would advise against eating anything rotten, or something that has already been digested, and anyway, who would want to?
To see what the inside of a dog stomach looks like and where it is in a dog’s body, click Here to watch the video
Pig stomach (photo credit) pigsite.com
This week I will be writing about the pig stomach. It is very different from the cow and horse stomach, being an omnivore’s stomach. The pig stomach has four distinct areas called the Esophageal region, the pyloric region, the fundic region, and the cardiac region. The esophageal region is located at the entrance of the stomach, connecting it to the esophagus. This region of the stomach does not secrete digestive enzymes, but has significance in that this is where ulcer formation in pigs occurs. Irritation in this area due to fine particle size, stress or other environmental factors can contribute to ulcer formation in swine. Once food passes through this region, it enters the cardiac region. In the cardiac portion of the stomach, mucus is secreted and mixed with the digested food. Food then passes into the fundic region, which is the first major portion of the stomach that begins the digestive process. In this region, gastric glands secrete hydrochloric acid, resulting in a low pH of 1.5 to 2.5. This reduced pH kills bacteria ingested with the feed. Other secretions in this region are present in the form of digestive enzymes, specifically pepsinogen. Pepsinogen is then broken down by the hydrochloric acid to form pepsin, which is involved with the breakdown of proteins. Finally the digesta moves to the bottom of the stomach, which is the pyloric region. This region is responsible for secreting mucus to line the digestive membranes to prevent damage from the low pH digesta as it passes to the small intestine. The pyloric sphincter regulates the amount of chyme (digesta) that passes into the small intestine. This is an important function so as not to overload the small intestine with chyme so proper and efficient digestion and absorption of nutrients occurs. In addition, once the chyme leaves the stomach, the material is quite fluid in consistency. As you probably know, pigs are notorious for eating anything and everything. So their stomachs must be able to digest a vast variety of foods and non-food items. Conclusively, the stomach is a very sophisticated organ that shows great design, and if it was just slightly off, the animal could die.
To see what a pig stomach looks like, watch my video at http://youtu.be/IxN92Xzf8pk