LESSON 4: VARIATION IN MAMMALIANS DIGESTIVE SYSTEM

• Digestive system


  Made up of the digestive tract (the gut) and other organs like the liver, pancreas and gall bladder. It is where your body breaks down food and absorbs nutrients.
• Digestive system


  Starts at the mouth and goes through the esophagus, stomach, small intestine, large intestine and ends at the anus
• Digestive system

  Breaks down food into simple nutrients such as carbohydrates, fats and proteins. These can then be absorbed into your blood, so your body can use them for energy, growth and repair. Anything that isn't used is waste, and leaves the body as faeces (poo).
• Mouth


  • Food starts its journey from the mouth or the oral cavity. There are many other organs that contribute to the digestion process, including teeth, salivary glands, and tongue.
• Pharynx

  • A fibromuscular y-shaped tube attached to the terminal end of the mouth. It is mainly involved in the passage of chewed/crushed food from the mouth through the esophagus.
• Esophagus


  • A muscular tube that connects the pharynx, which is a part of an upper section of the gastrointestinal tract. It supplies swallowed food along with its length.
• Stomach

  • Acts as a storage for the food and provides enough time to digest meals. It produces digestive enzymes and hydrochloric acid that maintains the process of digestion.
• Small intestine

  • A thin, long tube of about 10 feet long and a part of the lower gastrointestinal tract, coiled and the inner surface consists of folds and ridges. DUODENUM, JEJUNUM, ILEUM
• Large intestine

  • A thick, long tube measuring around 5 feet in length. Wraps over the edges of the small intestine. Absorbs water and consists of bacteria (symbiotic) to fetch nutrients.
• Rectum

  • At the end of your colon and on the other side of your anal canal. This is where your poop collects just before it's ready to come out.
• Anus


  • The end of your large intestine, where food waste completes its journey through your digestive tract and makes its exit
• Pancreas

  • A large gland present just behind the stomach. The pancreas releases digestive enzymes to complete the process of chemical digestion.
• Liver

  • A roughly triangular, reddish-brown organ located to the right of the stomach. It produces bile, which helps in the digestion of fat in the small intestine.
• Gall bladder

  • A small, pear-shaped organ which is located just next to the liver.
• Other organs

  • Tongue
  • Teeth
  • Salivary glands
• How our digestive system works

  1. Food's journey begins in the mouth. Teeth tear and break the food into smaller pieces.

  2. Saliva starts to break down the food and turn it into a ball-like mixture of food and digestive juices. Saliva also moistens our food, making it easier to swallow.

  3. Food travels down the esophagus as it encounters powerful squeezes and squishes.

  4. Food enters the stomach, a stretchy bag that squishes and mixes the food with stomach juices.

  5. Ball-like mixture turns into a frothy liquid, ready to move into the intestine. The intestine has two sections: the small intestine and the large intestine.

  6. Food gets broken down even more in the small intestine, and the body takes all the nutrients from it.

  7. Liver, pancreas and gallbladder release digestive juices that help break down fats, proteins and carbohydrates.

  8. Large intestine takes out all the water from what was left of the food. The result is a solid mass called stool.

  9. Stool enters the rectum for temporary storage before it comes out of the body through the anus.
• Four functions of the digestive system

  • Ingestion
  • Digestion
  • Secretion
  • Absorption
• Ingestion

  The process of taking food into the body through the mouth. It involves the intake of food and liquids, which are then prepared for digestion. The teeth and tongue help in chewing and swallowing food, breaking it down into smaller particles that can be easily digested.
• Digestion

  The process of breaking down food into smaller molecules that can be absorbed by the body.
• Types of digestion

  • Mechanical digestion
  • Chemical digestion
• Mechanical digestion

  Involves the physical breakdown of food into smaller pieces, such as through chewing and the muscular contractions of the stomach and intestines.
• Chemical digestion

  Involves the breakdown of food molecules into smaller nutrients through the action of enzymes and acids.
• Secretion

  The release of digestive juices and enzymes that aid in the digestion process. These secretions come from various organs in the digestive system, including the salivary glands, stomach, liver, gallbladder, and pancreas.
• Absorption

  The process by which nutrients from the digested food are taken up by the body and transported to the cells for energy, growth, and repair. Most absorption occurs in the small intestine.
• Four basic types of digestive system in animals

  • Monogastric
  • Avian
  • Ruminant
  • Pseudo-ruminant
• Monogastric

  • Has one simple stomach. The stomach secretes acid, resulting in a low pH of 1.5 to 2.5. The low pH destroys most bacteria and begins to break down the feed materials. Animals with this type of digestive system are better adapted to eat rations high in concentrates.
• Monogastric

  • Pigs, Cats, Dogs, and Humans
• Avian

  • Food passes from the crop to the first of two stomachs, called the proventriculus, which contains digestive juices that break down food. From the proventriculus, the food enters the second stomach, called the gizzard, which grinds food. Some birds swallow stones or grit, which are stored in the gizzard, to aid the grinding process. Uric acid from the kidneys is secreted into the large intestine and combined with waste from the digestive process. This waste is excreted through an opening called the cloaca.
• Avian

  • Parrots, Chickens, Penguins, Owl, Crows
• Ruminant

  • Eat feed rations that are high in roughages and low in concentrates. They swallow their food in large quantities with little chewing. Later they will ruminate, or belch up the feed, chew, and swallow it again. The regurgitated feed is called a cud.
• Ruminant

  • Cow, Goat, Sheep, Deer
• Compartments of ruminant stomach

  • Rumen
  • Reticulum
  • Omasum
  • Abomasum
• Pseudo-ruminant

  • Animals that eats large amounts of roughage but does not have a stomach with several compartments. The digestive system does some of the same functions as those of ruminants. For example, in the horse, the cecum ferments forages.
• Pseudo-ruminant

  • Horse, Kangaroo
• Differences between ruminant and pseudo-ruminant

  • Ruminant: Four compartment stomach, predominantly herbivorous, higher nutrient absorption, fermentation in rumen
  • Pseudo-ruminant: Three or monogastric, can be omnivorous, lower nutrient absorption, fermentation in intestines