Unit 3: Digestion, Absorption And Transport Flashcards
How long is the gastrointestinal (GI) tract
26 feet long from mouth to anus
What are the 2 principal organs in the GI tract?
Stomach (gastrus) and Intestines
Where does mechanical and chemical digestion begin?
The mouth
Define Digestion
The breakdown of food into absorbable forms through mechanical and chemical means.
Explain Mechanical Digestion
- Produces physical changes in food
- Chewing/mixing of food with saliva; prepares the bolus for swallowing
- Bolus enters stomach and further mixing by muscle wall produces chyme
- Peristalsis and Segmentation continue mechanical digestion
Explain Chemical Digestion
-Chemical breakdown of nutrients into basic absorbable units by the digestive enzymes secreted by specialized glands in the mouth, stomach, pancreas and epithelial cells of the small intestine.
Define Gastrointestinal (GI) tract
A flexible muscular tube that extends from the mouth, through the esophagus, stomach, small intestine, large intestine, and rectum to the anus.
Only when a nutrient or other substance finally penetrates the GI tract’s wall does it enter the body proper (digestion); many materials pass through the GI tract without being digested or absorbed. TRUE OR FALSE?
TRUE
Explain the function of the mouth
- Process of digestion begins
- Process of mastication, blends food with saliva
- Taste buds detect 1 or more of the 4 basic taste sensations (Sweet, sour, bitter, salty)
- The tongue provides sensation and moves the food around the mouth
- Food is swallowed and passes through the pharynx (short tube shared by digestive and respiratory system)
- Epiglottis closes the air way
- Once swallowed food is called a bolus
Explain Esophagus
- has a sphincter muscle at each end
- during swallowing the upper esophageal sphincter opens
- bolus slides down esophagus, which passes through a hole in the diaphragm to the stomach
- The lower esophageal sphincter at the entrance to the stomach closes behind the bolus to prevent it from reentering the esophagus
Explain the Stomach
- Retains the bolus in its upper portion for a while
- Little by little the stomach transfers food to its lower portion
- Adds juices and grinds it to a semi-liquid mass called chyme
- Then bit by bit the stomach releases chyme through the pyloric sphincter, which opens to the small intestine then closes behind the chyme.
Explain the Small Intestine
- At beginning of small intestine, chyme bypasses the opening from the common bile duct, which is dripping fluids from the gallbladder and pancreas.
- Chyme travels through the duodenum, jejunum and the ileum (3 meters of coiled tubing)
Explain the Large Intestine (Colon)
- At the end of the small intestine (distal ileum), the remaining contents arrive at another sphincter (Ileocecal sphincter) located at the beginning (Cecum) of the large intestine in the lower right side of the abdomen
- Upon entering the colon contents pass another opening (should they enter they would end up in the appendix)
- As intestinal contents pass through the large intestine the colon withdraws water, leaving semi-solid waste
- The muscles of the rectum and anal canal hold back this waste until deification
- The rectal muscles relax and the 2 sphincter of the anus open
Explain the flow of the Large intestine
Entrance to lower right side of abdomen Up right side of abdomen Across the front to the left side Down the left side Under the other intestines To the back
Define Peristalsis
The entire inside wall of the GI tract is ringed with circular muscles. Surrounding these rings are longitudinal muscles. When the rings tighten the long muscles relax–the tube is constricted–when the rings relax the long muscles contract–the tube bulges. This occurs continuously and propels the intestinal contents along. The waves of contraction ripple along the GI tract
- 3/min in stomach
- 10/min when chyme reaches Small Intestine
- After a meal: slow and continuous
- GI tract empty: quiet except for periodic bursts
- *Small intestine is 2.5 times shorter alive than at death because of muscle relaxation**
Explain the stomach Action
- thickest and strongest walls of the GI tract
- 3 layers of muscles (Longitudinal, circular, diagonal)
- Chyme is completed liquified with gastric juices
- Pyloric sphincter opens briefly, about 3 times/minute to allow small portions of chyme to pass through
Define Segmentation
The circular muscles of the intestines rhythmically contract and squeeze their contents. These contractions, called segmentation, further break apart food particles in producing chyme and promoting close contact with the digestive juice and the absorbing cells of the intestinal walls.
Explain the importance of sphincter contractions
- Movement of GI tract at a controlled pace
- Act as safety device
List in order the parts of the GI tract
- Lumen
- Mouth
- Pharynx
- Epiglottis
- Esophagus
- Esophageal sphincter
- Stomach
- Pyloric sphincter
- Small intestine
- Gallbladder
- Pancreas
- Duodenum
- Jejunum
- Ileum
- Ileocecal sphincter
- Large intestine
- Ascending colon
- Transverse colon
- Descending colon
- Sigmoid colon
- Appendix
- Rectum
- Anus
Review picture that shows Digestive tract
Computer
Define Lumen
The space within a vessel, such as the intestine
Define Mouth
The oral cavity containing the tongue and teeth
Define Pharynx
The passageway leading from the nose and mouth to the larynx and esophagus, respectively
Define Epiglottis
Cartilage in the throat that guards the entrance to the trachea and prevents fluid or food from entering it when swallowing
Define Esophagus
The food pipe; the muscular conduit from the mouth to the stomach
Define Sphincter
A circular muscle surrounding, and able to close, a body opening. Sphincters are found at specific points along the GI tract and regulate the flow of food particles
Define Esophageal Sphincter
A sphincter muscle at the upper and lower end of the esophagus. The lower esophageal sphincter is also called the cardiac sphincter because of its proximity to the heart
Define Stomach
A muscular, elastic, saclike portion of the digestive tract that grinds and churns swallowed food, mixing it with acid and enzymes to form chyme
Define Pyloric Sphincter
The circular muscle that separates the stomach from the small intestine and regulates the flow of partially digested food into the small intestine; also called Pyloric or pyloric valve
Define Small Intestine
3-metre length of small-diameter intestine that extends from the pyloric sphincter to the Ileocecal sphincter and is the major site of digestion of food and absorption of nutrients. It’s segments are the duodenum, jejunum, and ileum
Define Gallbladder
The organ that stores and concentrates bile. When it receives the signal that fat is present in the duodenum, the gallbladder contracts and squirts bile through the bile duct into the duodenum
Define Pancreas
A gland that secretes digestive enzymes and juices into the duodenum. Also secretes hormones into the blood that help maintain glucose homeostasis.
Define Duodenum
The top portion of the small intestine (about 12-fingers breadth long)
Define Jejunum
The first 2/5 of the small intestine beyond the duodenum
Define Ileum
The last segment of the small intestine, accounting for about 1/2 the length of the small intestine
Define Ileocecal Sphincter
The sphincter separating the small and large intestines
Define Large Intestine (Colon)
About 1.5 meters of large-diameter intestine; the lower portion of the intestine that completes the digestive process. It’s segments are the ascending colon, transverse colon, the defending colon, and the sigmoid colon.
Define Appendix
A narrow blind sac extending from the beginning of the colon that contains lymph cells
Define Rectum
The muscular terminal part of the intestine, extending from the sigmoid colon to the anus
Define Anus
The terminal outlet of the GI tract
Define Monosaccharide
A single-sugar molecule (glucose, fructose)
Define Disaccharide
A pair of monosaccharides linked together (maltose)
Define Polysaccharide
Numerous (up to thousands) monosaccharides linked together (starch)
Define Disaccharidase
Enzyme involved in hydrolysis (breaking down) a specific disaccharide into its monosaccharide components