The Digestive System

• The digestive system performs ingestion, digestion, absorption, and egestion.
• Ingestion is taking nutrients into the body.
• Digestion is the physical and chemical breakdown of food into smaller sub-units.
• Absorption is absorbing nutrients into the blood stream.
• Egestion is removing the undigested food waste from the body.

Human Digestive Tract

• The digestive tract includes the liver, gallbladder, pancreas, stomach, splenic flexura of transverse colon, transverse colon, ascending colon, ileum, cecum, appendix, rectum, jejunum, descending colon, sigmoid colon, sigmoid flexure, and anus.

Digestion

• Digestion involves two basic processes: physical and chemical.
• Physical digestion increases the surface area of food through physical means.
• Examples of physical digestion organs are teeth, tongue, and stomach.
• Chemical digestion uses chemicals and enzymes to break chemical bonds in foods.
• Chemical digestion occurs in the mouth, stomach, and small intestine.

The Mouth

• Salivary glands produce a watery fluid containing amylase, a starch-digesting enzyme, which breaks down starches into simple carbohydrates.
• Saliva lubricates food for swallowing.
• Teeth grind food into smaller pieces, increasing the surface area for digestion.
• The tongue rolls food into a bolus and helps force it into the pharynx and enables taste perception.
• The epiglottis, a cartilaginous flap, blocks the trachea during swallowing.
• The esophagus, a muscular tube, transports the bolus from the mouth to the stomach.

Ingestion Summary

• The tongue forces food into the pharynx.
• The epiglottis covers the trachea to allow food entry into the esophagus.
• Peristalsis, a rhythmic and wave-like contraction, moves food into the stomach.

Peristalsis

• Peristalsis involves rhythmic, wave-like contractions of muscle that move food through the digestive tract.

The Stomach

• A large, muscular structure stores and churns food, it is also the initial site of protein digestion.
• The stomach is flanked by the lower esophageal and pyloric sphincters.
• The lower esophageal sphincter prevents food and acid from regurgitating up into the esophagus.
• Heartburn happens when stomach acid enters the esophagus.
• The pyloric sphincter regulates the movement of food and stomach acids into the small intestine.
• The stomach can absorb water, vitamins, medicine, and alcohol.
• The cells lining the stomach secrete gastric juice, which contains hydrochloric acid, enzymes, and mucous.
• Hydrochloric acid kills any bacteria in the food.
• Enzymes initiate protein breakdown.
• Mucous, containing NaOH, protects the stomach walls from the acid.
• The watery mixture of food and secretions is now known as chyme.

Stomach Enzymes

• Pepsin is a protein-digesting enzyme found in the stomach that breaks down large amino acid chains into smaller polypeptides.
• Pepsin is stored as pepsinogen in cells in an inactivated form.
• In the presence of HCl, pepsinogen is converted into pepsin and is an active form.

The Small Intestine

• This is the longest portion of the digestive tract.

Small Intestine Sections

• It is divided into 3 major parts: duodenum, jejunum, and ileum.
• The duodenum is the first 12" of the small intestine and is the site of most digestion.
• The jejunum is the middle 2.5m of the small intestinte.
• The ileum is the last 2-4m of the small intestinte.

Small Intestine: Villi

• The interior of the small intestine is lined by finger-like projections called villi, and each villus has microvilli.
• Villi increases the surface area available for absorption.
• Villi is also the site of most macromolecule breakdown/chemical digestion and sub-unit absorption.
• Examples of these are monosaccharides, amino acids, and fatty acids.
• Each villus contains a capillary network and a lacteal/lymph vessel.
• Monosaccharides and amino acids are absorbed into the bloodstream through the capillary network.
• Lipids are absorbed by the lacteal and transported to the circulatory system.

Large Intestine

• It is responsible for the absorption of water, salt, vitamins, and minerals.
• Chemical digestion and macromolecule absorption are complete by the time the chyme reaches the large intestine.
• The large intestine is shorter and wider than the small intestine.
• It houses symbiotic bacteria that feed on the waste products of our digestive system.
• Feces are toxic and must be removed.
• Feces are stored in the rectum until a bowel movement sweepts them out, through the anal sphincter (anus).
• Complex materials like cellulose and fiber are not digested and add bulk to the remnants.

Accessory Organs

• Accessory organs secrete chemicals and enzymes that aid in the digestion of food.
• The 4 major accessory organs of the digestive tract are:
  • Salivary Glands
  • Liver
  • Gall Bladder
  • Pancreas

Salivary Glands

• The major secretion of the salivary glands is the enzyme amylase, which digests starch.
• Salivary glands functions to break down polysaccharides into disaccharides.

The Liver

• It has multiple functions within the human body.
• The liver produces bile, manufactures blood proteins, and breaks down toxic nitrogenous compounds.
• The liver also breaks down alcohol into less harmful products, breaks down old hemoglobin giving feces their brown color.
• It stores glycogen and various vitamins (A, B12, and D), and regulates blood glucose levels.

Gall Bladder

• This stores bile produced by the liver.
• Bile is made up of bile salts, secreted from the gall bladder into the duodenum when fats are detected.
• Bile performs emulsification

Emulisification

• Emulsification is the breaking down of large fat globules into small fat droplets.
• It is part of the physical digestion process and increases the surface area of fats.

Liver/Gall Bladder Bile

• Emulsification of fat globules

Pancreas

• Pancreatic secretions into the small intestine contain various types of enzymes and bicarbonate ions (HCO3-).
• The function of bicarbonate is to neutralize the acidic contents of the stomach.
• Pancreatic secretions are controlled by 3 major steps:
  • HCl enters the duodenum
  • HCl converts prosecretin into secretin
  • Secretin stimulates the release of pancreatic fluids
• Pancreatic fluids contain enzymes that break down proteins, carbohydrates, lipids, and nucleic acids:

Pancreatic Fluid

• Trypsinogen is a protein digesting enzymes

Digestive Track Secretions

• Trypsinogen is an inactive enzyme that is converted into the active enzyme trypsin by the action of enterokinase.
• Trypsin will then break down large polypeptides into small polypeptides.
• Pancreatic amylase digests Starch/Carbohydrates - It breaks down small polysaccharides into disaccharides.
• Pancreatic Lipase digests Lipids - Breaks down fats into fatty acids and glycerol
• Nuclease digests Nucleotide. - This enzyme break downs nucleic acids into nucleotides.

Other Secretions In Digestive Track: Stomach

• Gastrin (hormone) is secreted in response to the stretching of the stomach, with the presence of protein - Controls the release of HCI
• Secretes HCl which activates pepsinogen into pepsin - HCl also acts as a way to kill bacteria.
• Secretes pepsinogen that digests enzymes - Upon activation into pepsin (protein digesting enzyme), it will digest the large polypeptides into smaller ones.
• Secretes mucus which contains NaOH to protect the cells lining the stomach. -Protects from pH levels and activated pepsin

Other Secretions in Small Intestine

• Secretes protein digesting enzyme called petidase.
• Secretes sugar digesting enzymes called disacchariades
• Digests disaccharides into monosaccharides -Eg. maltase, sucrase, and lactase

Absorption

• Absorption is the process to absorbing nutrients across the intestinal wall
• Occurs for all macromolecule of sub-units

Absorption: Carbohydrates

• Monosaccharides are absorbed through the intestinal wall directly into the bloodstream by the process of active transport.
• Glucose/monosaccharides are then transparted to the liver where it has 3 fates - Converted to glycogen - Circulated throught the body and used for energy - Converted to Fat

Absorption: Proteins

• Amino acids are absorbed through the intestinal wall directly into the bloodstream through the process of active transport.
• Amino acids then travel directly to the liver where 3 fates will occur:
  • Will be converted into sugars to be used by the body
  • Can excreted into urea and excreted by the body
  • Used to make proteins in body cells: enzymes and cell structures

Absorption: Lipids

• Glycerol and fatty acids are absorbed through the intestinal wall directly into the lacteal(lymphactic system) through a diffusion process.
• Sub-Units are then reassembled and brought to the bloodstream where 3 events happen -Converted into sugars -Converted into cholesterols -Stored as fat into fat deposits

###Nucleic Acids

• Nucleotides and absorbed through the intestinal walls directly into the bloodstream

Disorders

• Peptic Ulcers: The lining of the stomach is destroyed leading to lesions and irrigation.
• Caused by stomach acid, also due to stress - Dr. Barry Marshall proved otherwise, that ulcers are caused by a specific barium, Heliobacter pylori -Ulcers were treated with antibiotics

Diarrhea

• Watery stool as results of bacterial/viral infection. -Infection disrupts the normal bacteria in large intestine. -Leads to less water absorbed: life-threatening for severe cases

Inflammatory Bowel Disease

• This is a disorder characterizied by infammation of the tissues in the digestive tract -Chron's Disease is when the immune system attacks normal body cells and the symptoms are only treated for this disease

Lactose Intolerance

• The disacchriade known as lactase, which us responsible for digesting lactose,is not produced
• The bacteria that metabolizes the large intestine occurs due to the lactose produced -This leads to gass and severe abdominal pain -Individuals can avoid it by consuming milk products with tactase enzymes

Colon Cancer

• The cells lining the colon is cancerous and divides out of control. -The cell mass can grow to block body fluids and disrupt normal bodily functions. -Cancerous cells spread to other bodily tissues and become malignant tissues. -Hepatitis is when there's inflammation in the live caused by a virus.

Three Types of Hepatitis

• Hep A: contaminated from waters
• Hep B: spread through sexual content
• Hep C: contracted from contact with injected blood
• Cirrhosis is when the liver tissue becomes scarred and damaged, preventing regular functionality. - Due to chronic alcoholism

Gall Stones

• When there is a small hard mess of cystallized cholesterol in the gall bladder, - Due to obesity, alcohol intake.and heredity -Medications and ultrasound can treat gallstones. -The small stones are eventually passed through urine but the gallbladder is removed should it become too aggressive. -Hepatis Is when the inflammation of the liveris cuased by a virus

Learn about the digestive system involving ingestion, digestion, absorption, and egestion. Understand the processes of physical and chemical digestion. Explore the organs involved in the human digestive tract and their functions.