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10.01 Digestive System Anatomy

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  1. General Structures
    1. Mouth → Oropharynx → Esophagus → Stomach → Small Intestine → Large Intestine → Anus
    2. Ancillary Glands
      1. Salivary
      2. Pancreas
      3. Liver
  2. General Functions
    1. Physical & chemical breakdown of large food stuffs into smaller nutrients
    2. Absorption – organic nutrients, vitamins, water, electrolytes
    3. Elimination of wastes (feces)

Nursing Points


  1. Physical / Chemical Digestion Process
    1. Mouth
      1. Mastication – chewing (physical breakdown)
      2. Salivary glands – release amylase
        1. Starches partially broken down into maltose
        2. Enzyme deactivated in stomach
      3. Deglutition – swallowing
        1. Bolus of food rolled by tongue to oropharynx
        2. Skeletal muscles contract (reflex)
        3. Bolus pushed into esophagus
        4. Pushed into stomach by peristalsis
    2. Stomach
      1. Gastric glands secrete gastric juices
        1. Hydrochloric Acid
        2. Pepsinogen converts to Pepsin
        3. pH 1.5 – 2.5
        4. Kills bacteria in food
        5. Pepsin + HCl digest proteins into proteoses and peptones
      2. Infants secrete rennin, which curdles milk in stomach
      3. Muscular contractions
        1. Mix and churn food with gastric juices → chyme
          1. pH 2.0
        2. Pushes chyme through pyloric sphincter to duodenum
    3. Small Intestine – majority of digestion and absorption happens here
      1. Pancreatic secretions
        1. Duodenum
        2. Inactive enzymes
        3. Sodium Bicarb → neutralizes chyme
      2. Duodenal cells secrete enteropeptidase
        1. Activate digestive enzymes from pancreas
      3. Chemical digestion
        1. Proteoses and peptones into peptides by Trypsin
        2. Starches fully broken down into maltose by Amylase
        3. Lipids emulsified by Bile
        4. Lipids broken down into fatty acids and glycerol by Lipase
      4. Succus entericus secreted from glands in small intestine → Enzymes
        1. Break down peptides into Amino Acids
          1. Dipeptidase
          2. Aminopeptidase
          3. Carboxypeptidase
        2. Maltose → 2 glucose by Maltase
        3. Sucrose → glucose + fructose by Sucrase
        4. Lactose → glucose + galactose by Lactase
      5. Muscular movements move food
        1. Segmental contractions (mix)
        2. Peristalsis (move)
      6. Absorption
        1. 10-20% of monosaccharides, fatty acids, and glycerol absorbed into capillaries
        2. 80% synthesized back into triglycerides and absorbed into lacteals (lymph) along with fat-soluble vitamins
    4. Large Intestine
      1. Bacteria and cellulose moved along tract
      2. Muscular movements – same as small intestine
      3. Absorption – in ascending colon
        1. Water
        2. Vitamin B complex
        3. Vitamin K
        4. NaCl
      4. Defecation – elimination of solid wastes
        1. Peristalsis moves fecal matter into rectum
        2. Stretch receptors → reflex
          1. Peristalsis
          2. Relax anal sphincter
        3. Abdominal muscles contract to help
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Video Transcript

All right in this lesson we’re going to take a look at the digestive system, and its major structures and functions.

The gastrointestinal tract or the alimentary canal as some people call it has lots of different parts. It’s basically a long tubing system and its main purpose is the physical breakdown of food into nutrients and then the absorption of those nutrients vitamin water and electrolytes.Not everything that we eat gets absorbed, so there are always some waste and these wastes are eliminated through feces.

When we look at the general structure of the GI tract the basic structures are the mouth, oropharynx, esophagus, stomach, small intestine, large intestine, and anus. There’s also some ancillary glands which help to produce enzymes that help the chemical breakdown of food. These glands are the salivary glands, pancreas, and also liver.

When we start at the mouth, the main purpose of the mouth when it comes to food is for chewing or mastication. It is literally the physical breakdown of food. There are some ancillary glands in the mouth, the salivary glands, and they released amylase. Amylase is an enzyme that breaks down starches and then as the food gets to the stomach that amylase is deactivated. There’s another process called deglutition which is the process of swallowing. As we chew our food, that bolus of food gets pushed back to the oropharynx with a tongue. Skeletal muscle contracts, and then that bolus is pushed down into the esophagus which is the main tube that connects the mouth to the stomach. As the bolus of food starts to go down the esophagus peristalsis happens and that bolus of food moves into the stomach.

As food moves from the esophagus to the stomach, glands in the stomach starts to secrete the gastric juices. The primary juice that secreted is hydrochloric acid. There’s also an enzyme called pepsinogen that secreted by the stomach cells, and that’s converted to pepsin. Pepsins main purpose is to break down proteins into smaller peptide chains. Because of the presence of hydrochloric acid the pH in the stomach is about 1.5 to 2.5. And what happens is with such a low PH, that helps to kill bacteria in the food. When we look at pepsin, and we add that to hydrochloric acid, that helps to digest the proteins by converting them into things called proteoses and peptones.

In infants, they also have another enzyme called renin which helps to curdle the milk in the stomach. This helps the infant to stay fuller for a longer period of time, and it also helps for better absorption for the infant.

In the stomach, the muscle walls contract to mix and turn the food and it also helps to combine the food that’s in there with gastric juices to create something called kind. Once chyme is pushed through the pyloric sphincter at the lower end of the stomach, into the first part of the small intestine called the Duodenum

Now that the food is in the small intestine, this is where the majority of digestion happens.

There’s going to be a lot of things that happen in the small intestine, but these are the big main points. It’s much easier for the body to absorb the nutrients if they’re in its simplest form. And that goes for all the macronutrients that we have. So it’s much easier for fat if they’re broken down into fatty acids to be absorbed in the GI tract. So in the small intestine the small intestine focuses on converting fats to fatty acids, proteins being converted into amino acids, and then your carbohydrates or starches, being converted into monosaccharides.

When we look at what happens in the GI tract, as the food comes down to pancreatic enzymes are released from the pancreas into the duodenum. They’re actually inactivated enzymes. But once they get into the duodenum, those enzymes are going to be activated. Muscular movement helps to move the food down, so these are segmental contractions would help to mix food, and peristalsis which helps to move the food. In the resources attached to this lesson, there is an outline which helps to explain which enzymes are related to breaking down all of these macronutrients into micronutrients, so I encourage you to check that out so you have a greater understanding of it. But what you need to know is that these large complex macronutrients are broken down into smaller counterparts. Once they’re ready to be absorbed, about 10 to 20% of them are absorbed as monosaccharides, fatty acids, and glycerol. The other 80% are synthesized back and absorbed by the lacteals, or the lymph portion of the GI tract.

Once the remaining unabsorbed food moves down into the GI tract, this isn’t mainly bacteria and cellulose, this middle contraction and peristalsis propels that bolus, or the remaining waist down. The movement is exactly the same as in the small intestine. The only difference here in the large intestine, is that the large intestine is primarily responsible for the absorption of a lot of things. This includes water, vitamin B complex, vitamin K, and sodium chloride. Once this bolus has moved into the rectum, the defecation process starts. What happens is the stretch receptors inside the rectum initiate the defecation reflex. When this happens, the anal sphincter relaxes, and peristalsis will move the feces out of the rectum and out of the body.

Okay so let’s recap.

The major functions of the GI tract are the chemical and physical breakdown of food into those nutrients and vitamins so that we can observe them.

The mouse main responsibility is to physically break down the food in this is the process of mastication.

The stomach is responsible for utilizing the physical and chemical mixing of food which helps to Initiate breaking down those macronutrients.Don’t forget that the stomach is an extremely acidic environment with a pH of about 1.5 to 2.5.

The small intestine is where the majority of digestion happens with a lot of enzymes breaking these macronutrients down even further.

In the large intestine versus where the major absorption of water, vitamin B, vitamin K, and sodium chloride happen, and this is the part of digestion where the wastes are eliminated through feces.

And that’s it for our lesson on the digestive system. Make sure you check out all the resources attached to this lesson. Now, go out and be your best selves today, and as always, happy nursing!