The Digestive System

The Digestive System

• It is necessary to coordinate breathing, eating, and drinking through the mouth so that air goes to the lungs, and food goes to the stomach

• The throat is arranged to prevent interference between swallowing and breathing

• The diaphragm is a dome of muscle below the lungs that separates the upper and lower torso

• The body requires a passageway for food to move from the mouth, through the diaphragm, to the stomach

• The contents of the digestive tract must move forward slowly and steadily to allow reactions to complete

• Food needs lubrication from fluids for movement through the system, but the amount of fluids must be regulated

• Too much fluid will cause contents to flow too rapidly, while too little will form a dry, compact paste

• Digestive enzymes require food to be broken down into small, suspended particles

• After digestion and nutrient absorption, the remaining waste is excreted, and some water is withdrawn to create a solid waste product

• Digestive enzymes are designed to digest carbohydrate, fat, and protein

• The cells of the GI tract, made of carbohydrate, fat, and protein, need protection from the digestive juices they secrete

• Waste matter that reaches the end of the GI tract must be excreted periodically

Digestive System Definition

• The digestive system includes all organs and glands associated with food ingestion and digestion

Digestive System Function

• Ingestion entails taking food into the body
• Mechanical breakdown involves the physical breaking down of food
• Digestion includes the chemical breakdown of food
• Secretion is the release of enzymes and other substances
• Absorption consists of taking nutrients into the body
• Excretion is the removal of waste

Anatomy of the Digestive Tract

• The digestive tract is a flexible muscular tube from the mouth to the anus
• It includes the esophagus, stomach, small intestine, large intestine, and rectum
• The human body surrounds the GI tract
• The lumen is the inner space within the GI tract and it is continuous
• Nutrients or other substances must pass through the GI tract's wall to enter the body

Mouth

• Digestion initiates in the mouth
• Teeth crush food into smaller pieces during chewing, and fluids blend with these pieces to ease swallowing
• Fluids dissolve food so the tongue can taste it, and only particles in solution react with taste buds

Pharynx

• The pharynx is a short tube shared by the digestive and respiratory systems
• The epiglottis closes off the airway to prevent choking when swallowing
• A bolus is a mouthful of food that has been chewed and swallowed

Esophagus

• The esophagus is a hollow muscular tube, approximately 25 cm long and 2 cm wide
• It moves food to the stomach through peristalsis and it is not involved in absorption
• It has a sphincter muscle at each end
• During swallowing, the upper esophageal sphincter opens, and the bolus slides down the esophagus, which passes through the diaphragm
• The lower esophageal sphincter closes behind the bolus at the entrance to the stomach, which allows it to proceed forward

Stomach

• The stomach is a muscular, elastic, saclike part of the digestive tract that grinds and churns food
• It mixes it with acid and enzymes to form chyme
• The stomach retains the bolus in its upper portion before transferring it to the lower portion
• A semiliquid mass called chyme is formed as the stomach churns the bolus and adds digestive juices
• The stomach releases the chyme through the pyloric sphincter into the small intestine, and then closes behind the chyme

Small Intestine

• At the beginning of the small intestine, the chyme bypasses the common bile duct opening, which drips fluids from the gallbladder and the pancreas
• The chyme travels through the duodenum, the jejunum, and the ileum (almost 10 feet of tubing)
• The small intestine's three segments are coiled within the abdomen

Large Intestine (Colon)

• The large intestine absorbs water and minerals, and it passes waste (fiber, bacteria, and unabsorbed nutrients) along with water to the rectum

• After traveling the length of the small intestine, contents reach the ileocecal valve, at the start of the large intestine in the lower right abdomen

• Upon entering the colon, the contents pass another opening. Should they enter this opening, they would end up in the appendix: a blind sac about the size of your little finger

• Normally, the contents travel up the right side of the abdomen, across the front to the left side, and down to the lower left side of the large intestine

• As intestinal contents pass to the rectum, the colon withdraws water, which leaves semisolid waste

• The rectum and anal canal muscles hold back waste until defecation

• Then the rectal muscles relax, and the anal sphincters open to allow waste passage