Digestive System: Organs, Functions, and Digestion

• The digestive system includes the parts and functions and the disorders
• It is a group of organs digesting food, providing molecules for body use
• Hunger is when cells signal the brain of energy needs
• The digestive tract known as the alimentary canal, is a series of tube-like organs joined end to end, measuring about 9 meters
• The digestive tract consists of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus
• Food is digested as it moves through the digestive tract
• The stomach does not do all of the digesting
• The digestive tract is one of the most important immune support organs with islands of immune cells that intercept potentially illness-creating organisms
• The most important area of the digestive tract is the small intestine, including the duodenum, jejunum, and ileum
• The liver, gallbladder, pancreas, and salivary glands secrete substances used in digestion

About Digestion

• Digestion breaks down food into chemicals that can move from the digestive system into the bloodstream
• There are two types of digestion, mechanical which crushes food and chemical which with enzymes help break items down
• Nutrients, substances in food required for normal growth, maintenance, and repair include fats, proteins and carbohydrates
• Enzymes are proteins, that are made of amino acids, they break nutrients into smaller particles for absorption

Mouth

• Digestion starts in the mouth through chewing, which makes food slippery and easy to swallow and digest

Teeth

• The teeth aid in mechanical digestion
• Molars grind food; premolars mash food and incisors and canines shred food
• Enamel on the outside of the tooth is the hardest material in the body, protecting nerves

Saliva

• Chewing mixes the food with saliva
• Saliva contains amylase, an enzyme that breaks down complex carbohydrates like starch into simple sugars like glucose
• Salivary glands are in and around the mouth

Pathway of Digestion

• Teeth with the help of jawbones/muscles, turn food into a soft mush
• The tongue then pushes the mush down the pharynx to the esophagus
• The esophagus squeezes food with rhythmic muscle contractions called peristalsis to get to the stomach
• Gravity is not responsible for this movement

Stomach

• A muscular, bag-like organ at the end of the esophagus
• Mechanical digestion continues as the stomach squeezes contents
• Chemical digestion also occurs as acid and enzymes are released into the stomach
• Sphincters are located at both ends of the stomach
• Gastric acid in the stomach kills bacteria
• After a few hours, food turns into chyme, a soupy mixture

Chyme

• The pulpy acidic fluid that passes from the stomach to the small intestine, consisting of gastric juices and partly digested food.

The Small Intestine

• The small intestine is a muscular tube with a diameter of 2.5 cm, and a length of about 6 meters
• Most chemical digestion takes place in the small intestine
• Nutrients are absorbed through fingerlike projections called villi
• No mechanical digestion occurs in the small intestine
• Chyme is moved through the small intestine by peristalsis

Villi

• Microscopic fingerlike projections lining the inner wall of the small intestine
• Nutrients are absorbed into the body through the villi
• Nutrients are absorbed into blood capillaries and lymphatic vessels(lacteals)
• From the blood, nutrients are later taken/assimilated by cells for their use
• The lining of the small intestine has circular folds, that are rich in villi
• Each villus has absorptive cells that contain microvilli
• All structures increase the absorption surface area of the intestine

Function of Small Intestine

• The small intestine is made up of three parts: the duodenum, jejunum and ileum.
• Chyme enters the duodenum through the pyloric sphincter
• Enzymes and acid neutralizers from the pancreas and liver, are released to breakdown nutrients
• Chemical digestion continues here in the duodenum
• The jejunum absorbs the majority of nutrients
• Nutrients pass into the capillaries and lymphatic vessels in the wall of the intestine
• The ileum connects with the large intestine (LI) and any undigested food passes into the LI

Pancreas

• The pancreas is a fish-shaped organ located between the stomach and small intestine
• Pancreatic juice released into the small intestine contains:
• Enzymes and bicarbonate, that help protect the small intestines by neutralizing acids
• These enzymes help digest carbohydrates, protein, and fat

Liver and Gallbladder

• The liver is a large reddish-brown organ which functions in digestion and is located on the right side of the abdomen
• The liver makes bile used in fat digestion
• The liver stores nutrients for later use
• The liver breaks down toxic substances like drugs and alcohol in blood
• and, the liver makes cholesterol (lipid) for cell membranes
• The gallbladder stores bile made in the liver
• Bile from the gallbladder is squeezed into the small intestine to break up fat into smaller pieces for further digestion

Large Intestine

• The large intestine stores, compacts, and eliminates indigestible material, with a diameter of 7.5 cm, and a length of 1.5 m
• Undigested material enters the large intestine as a soupy mixture
• The large intestine absorbs most of the water, forming a solid mass called feces
• Fiber is indigestible, keeps feces soft, and helps with elimination
• Fiber/cellulose is found in cell walls of plants, especially in fruits and vegetables

Rectum

• In the last section of the large intestine
• Stores feces until it is expelled

Anus

• Is the opening at the end of the rectum where waste is released
• Each meal has taken about 24 hours for the journey through this system

Steps in Digestion

• It begins with ingestion in the mouth
• Teeth chew and mix food with saliva, which starts breaking down carbohydrates in the mouth
• This starts with mechanical and chemical digestion
• The tongue pushes food into the pharynx and esophagus
• Then peristalsis pushes down the esophagus into the stomach
• The stomach mechanically and chemically digests food, forming chyme
• Chyme is released into the small intestine (SI)
• The pancreas and liver secrete enzymes into the small intestine to continue chemical digestion of carbohydrates, protein, and fat
• Chyme move through small intestine via peristalsis
• From here absorption and assimilation take place
• Undigested material enters the large intestine (LI) which absorbs water, forming feces
• Feces moves into the rectum and is stored, ready for elimination
• Elimination or egestion of feces occurs through the anus

Role of Amino Acids

• Chewing starts mechanical breakdown in the mouth
• In the stomach, chemical digestion of protein begins
• HCL and pepsin are found in the stomach
• Polypeptides are broken down into amino acids, by protein digesting enzymes by protein secreting
• Amino acids share the same transport system, used by a variety of different transport proteins
• Dipeptides and tripeptides can enter the mucosal cell
• They are broken down into single amino acids inside
• Amino Acids then pass from the mucosal cell into the blood, and then to the liver

Other Organs

• The appendix sits at the junction of the small intestine and large intestine
• It's a thin, four-inch tube in the lower right abdomen
• The function of the appendix is unknown

Digestive Disorders

• Disorders of the digestive system are caused by eating too much or consuming highly acidic foods, drugs, caffeine, and alcohol
• Disorders are treated by lifestyle changes and medications like antacids
• Heartburn is when the stomach is blocked off at either end by bands of muscles called sphincters
• Backflow of chyme from the stomach to the esophagus causes a burning pain in the chest
• Constipation is caused by lack of fiber, water, or exercise which causes the contents of the large intestine to become dry
• Diarrhea is when bowel movements are frequent and watery, caused by too little water being removed
• Colon Cancer is when cells divide uncontrollably, forming a tumor in the large intestine/colon
• Gastric ulcers are open sores in the stomach lining
• High-fat diets, smoking, caffeine, and alcohol can make gastric ulcers worse
• Some cases can be treated with antibiotics, antacids or other medicines