1. Digestive System

2. The main role of the digestive system is to metabolize food
2 roles of metabolism are:
Catabolic reactions: breakdown of molecules, energy is released
Anabolic reactions: the making/formation of a molecule, energy is required
In the digestive tracts the following occurs:
Polmersmonomersabsorbed into the bloodcellsmitcondriaenergy (ATP)

3. Unlike plants, heterotrophs must consume large organic molecules and break them down into smaller molecules that can be transported by the blood, absorbed and used in the body. This process of digestion involves four distinct stages:
Ingestion: ‘eating,’ taking in food
Digestion: 2 types:
Mechanical: Physical breakdown of food into smaller pieces to increase surface area
Chemical: breaking of the bonds by enzymes to make something new
Absorption: movement of food particles into the blood
Egestion: ‘pooping,’ removing waste

4. The digestive tract of adults is about 6-9 m long
The digestive tract of adults is about 6-9 m long. It is responsible for taking in, storing, breaking down, and absorbing food as well as removing waste materials. 2 ended: mouth  anus Food moves through this system by peristalsis, which is just a contractile motion

5. Ingestion
Ingestion involves the taking in of nutrients by the mouth. The early stages of chemical and mechanical digestion also occur in the mouth as food is taken in.
Food is taken into the mouth, combined with saliva and chewed into a soft, slippery mass called a bolus.

6. Saliva – is a watery, slippery fluid produced by the salivary glands that contains the enzyme amylase, responsible for chemical digestion. This enzyme breaks down complex carbohydrates into simpler sugars. The saliva also dissolves food particles so that they can stimulate the taste buds, and it lubricates the food bolus so it can travel through the digestive system more easily.

7. Mechanical Digestion
Teeth – are important for the physical digestion of foods in the mouth. The tongue pushes food toward the roof of the mouth, and the teeth break it up into smaller bits. The canine and incisor teeth are sharper and designed for chopping and tearing food while the molars are flat and broad, designed for grinding food.

8. Through the teeth, past the gums, look out stomach, here it comes!
Esophagus – is a long muscular tube that contracts in a rhythmic motion called peristalsis. These contractions push the food bolus towards the stomach and the remainder of the gastro-intestinal tract.

9. Stomach – the stomach is a J-shaped sac with a capacity of about 1
Stomach – the stomach is a J-shaped sac with a capacity of about 1.5 L that is also the site of food storage and digestion. As food enters the stomach from the esophagus, the cardiac sphincter contracts, and closes, preventing the stomach contents from moving back into the esophagus. At the bottom of the stomach, the pyloric sphincter regulates the exit of digested food into the small intestine. The stomach secretes a number of digestive enzymes and gastric juices to help in the digestion of food particles.

11. Digestive Secretions of the Stomach
Mucus – Comes from the mucous cells. coats the inner lining of the stomach, protecting it, from its own digestive juices.
Hydrochloric Acid (HCl) – comes from the parietal cells. kills harmful bacteria in the stomach. ***HCl is also important in activating the protein digesting enzyme pepsinogen to become pepsin. As a result, the pH of the stomach is about 1 – 2.
Pepsin – comes from the chief cells. enzyme responsible for the digestion of proteins. Pepsin, secreted as pepsinogen, is activated by the presence of HCl. In the active form, pepsin breaks down long chain amino acids into shorter chain polypeptides.

12. Rennin – an enzyme that causes milk to curdle
Rennin – an enzyme that causes milk to curdle. Because milk is a liquid, it would pass through the digestive tract too quickly for nutrients to be absorbed.
Also, it is at the stomach where alcohol, some drugs (Such as asprin) and vitamin B is absorbed into the blood
When food finally exits the stomach and enters the small intestine, it is now known as chyme.

13. Digestive Disorders
Acid Reflux – aka “heartburn” is caused by the movement of gastric juices (acidic) back into the esophagus. This is usually caused by failure of the cardiac sphincter to close.
General Acid Reflux Shockwave™ Animation

14. Peptic Ulcers – are caused by a breakdown of the protective mucous lining in the stomach. This causes lesions (sores) on the stomach lining that are irritated by the acidic secretions in the stomach. Ulcers are caused by stress, diet and the bacteria Heliobacter pylori.
The stomach can be removed with any real harm occurring

15. Digestion
Digestion involves further chemical breakdown of macromolecules into smaller components. Most digestion takes place in the first cm of the small intestine, called the duodenum. Digestion is primarily a chemical process that is helped by a number of enzymes secreted by the pancreas, liver and gallbladder.
Animations

16. The Pancreas
Pancreas – when acids enter the small intestine, a hormone called secretin is released from the duodenum. This hormone stimulates the pancreas to secrete enzymes that break down the three major components of food: proteins, carbohydrates and lipids.
zeroBio
Proteins – the inactive enzyme trypsinogen is converted to an active enzyme, trypsin, by the enzyme enterokinase. Trypsin breaks down long chain polypeptides into shorter chain peptides called peptones. A second enzyme called erepsin is released form the pancreas to complete digestion of proteins into amino acids.

17. Carbohydrates – the pancreas also releases the amylase enzymes to continue with carbohydrate digestion in the small intestine.
Lipids – lipase enzymes are also secreted from the pancreas to digest fats into fatty acids and glycerol.
Zoo 202: Digestive System
Also, the pancreas releases bicarbonate ions which neutralize the stomach acids that flow into the small intestine, so that it does not denature the pancreatic enzymes

18. Liver and Gallbladder
Liver and Gallbladder – the liver continually produces a fluid called bile that helps with fat digestion. This fluid is stored in the gall bladder. Fats in the small intestine stimulate the release of a hormone cholecystokinin (CCK), which in turn triggers the gall bladder to release bile salts. These bile salts act as an emulsifying agent (like soap), causing the fat droplets to be broken apart into smaller particles. The increased surface area produced by smaller droplets allows the lipase enzymes to work more effectively.
Concepts in Biochemistry - Interactive Animations

19. Other Liver Functions
The liver breaks down hemoglobin from red blood cells and stores the products in the gallbladder. The resulting pigments give feces its characteristic color. The liver also stores glycogen and vitamins A, B12, and D. The liver also removes many toxins and harmful substances from the body (like alcohol).

20. More digestive problems…
Gallstones – crystals of bile salt the form in the gallbladder. These may block the bile duct causing pain and impairing fat digestion.
Jaundice – yellowing of the skin and tissues due to an accelerated destruction of red blood cells. Bile pigments are not excreted and accumulate in the body.
Cirrhosis – chronic inflammation of the liver caused by nutritional deprivation or infection.

21. Absorption
The stomach absorbs some water, some vitamins, medications and alcohol. Most absorption however, occurs in the small intestine. The small intestine is folded on the inside, creating fingerlike projections called villi. The villi are also lined with individual cells arranged in long extensions of the membrane called microvilli. Some of the nutrients are absorbed into the capillary network by active transport other nutrients are absorbed by diffusion. Only amino acids, and monosaccharides can be absorbed here!

22. Each villus is supplied with a capillary network that intertwines with lymph vessels called lacteals, where fats are absorbed. Only glycerol and the 3 fatty acids are absorbed here!

23. Egestion
Once food reaches the large intestine (colon), chemical digestion is complete. The large intestine then re-absorbs water, minerals and some vitamins. Bacteria in the large intestine use waste materials to make vitamins B and K. Undigested waste materials accumulate in the large intestine until a bowel movement is made. The movement removes potentially toxic waste from the body and is stimulated by un-digestible fibrous material in the colon such as plant fiber.

25. Overview of Digestive Hormones