92 BIOLOGICAL INQUIRY: A Workbook of investigative Cases Core Investigations I.
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92 BIOLOGICAL INQUIRY: A Workbook of investigative Cases Core Investigations I. Critical Reading Before beginning the investigations, read Chapter 41 Animal Nutrition in your text. You may also have to refer to other chapters in Unit Seven and Chapter 24 The Origin of Species to learn the most from this investigative case t. Compare the digestive systems of cattle (in this instance a cow), horses, and humans using Figure 7 2, as well as Figures 41 18 and 41.9 in your text Large intestine (46%) Rectum Stomach (9%) Cecum (1796) Small intestine (28%) Figure 7.2 Idealized digestive system of the horse-a postgastric fermenter. The percentages refer to the relative capacities of each structure a. How does the structure of the stomach in these three organisms differ? b. Examine Figure 7.3. Note the significant difference in the relative capacity of the stom- ach when comparing a horse with a cow. What do you think this indicates about the location of digestion in both animals?Explanation / Answer
The horse is a non-ruminant herbivore. Non-ruminant means that horses do not have multi-compartmented stomachs as cattle do. Instead, the horse has a simple stomach that works much like a human’s.
The stomach of the horse is proportionally very small and makes up only 10% of the capacity of the digestive system or 9-15 litres in volume. The stomach of the horse is divided into two sections, a glandular and a non-glandular (squamous) section, separated by a demarcation called the margo plicatus. The stomach has 3 main areas; the saccus caecus, fundic and pyloric regions. Each is quite unique in structure and function. The saccus caecus region is located at the entrance of the stomach and the oesophagus. As the feed moves through the stomach the next section of the stomach is the fundic region. The final section of the stomach is the pyloric region where the stomach joins the small intestine. The proteolytic activity (protein digestion) in this area is 15-20 times that of the fundic region.
Humans have a uniform stomach similar to that of pigs.
The human stomach is subdivided into four regions: the fundus, an expanded area curving up above the cardiac opening (the opening from the stomach into the esophagus); the body, or intermediate region, the central and largest portion; the antrum, the lowermost, somewhat funnel-shaped portion of the stomach; and the pylorus, a narrowing where the stomach joins the small intestine. Each of the openings, the cardiac and the pyloric, has a sphincter muscle that keeps the neighbouring region closed, except when food is passing through. In this manner, food is enclosed by the stomach until ready for digestion.
The stomach of the cow is divided into four compartments
Rumen – The rumen is the largest part of the cow's stomach, holding up to 50 gallons of partially digested food at any given time. It contains enzymes that start the digestion process, breaking down the hard food and cellulose. The food may spend 15 to 48 hours in and out of the rumen being chewed, swallowed, regurgitated and swallowed again and again before it moves on to the second part of the stomach, the reticulum.
Reticulum – The reticulum traps anything that the cow should not have eaten, such as pieces of fencing, rocks and pieces of wire. Here the food mixes with the cow’s saliva and produces cud. Cows burp up the cud into their mouths and chew it to help break it down more. When a cow looks like she is chomping on bubble gum, really she is chewing her cud.
Omasum – The omasum has many folds to filter the food, squeeze out the water and further break down the cud.
Abomasum – The abomasum completes the digestion process. It passes essential nutrients to the bloodstream and sends the rest through the intestines.
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