Chapter 4: Human Digestion, Absorption, and Transport
Lumen
A hollow space through which food and fluids pass
GI tract
A hollow, muscular tube that extends approximately over 16 feet in length
Enzyme
A protein that speeds up the rate of chemical reaction without being altered in the process
Bile
A substance produced by the liver that breaks up fat particles.
Pepsin
An enzyme present in gastric juice that begins the hydrolysis of proteins
Accessory Organs
Assists the functioning of the GI tract (teeth, tongue, salivary glands, liver, gallbladder, and pancreas
Facilitated diffusion
Enterocytes absorb some nutrients by facilitated diffusion, a process that also does not require energy
Two parts to the digestive system
GI tract and accessory organs
Gastroesophageal reflux
Heartburn or acid reflux
Innermost layer of the GI tract
Mucosa
Simple diffusion
Occurs when the concentration of a particular nutrient is higher in the lumen of the small intestine that in an enterocyte
Mechanical Digestion
Physical treatments that food undergoes while it is in the intestinal tract (being chewed into smaller pieces and mixed with various secretions)
Hydrolytic
Requiring water
Pharynx
Section of the alimentary canal that connects the nasal cavity with the top of the esophagus
Active Transport
Some nutrients move from the lumen of the intestine and into an enterocyte against the concentration gradient
HCI
Strong acid that contributes to the low pH of gastric juice
Prebiotics
Substances in food that are poorly digested by humans but support and promote the growth of probiotics in the colon
Mucosa
Surronds the lumen of the digestive tract
Chemical digestion
The breakdown of large nutrient molecules in food into smaller components, primarily by the action of stomach acid and various enzymes
Digestion
The process of breaking down large food molecules into nutrients that the body can use
Absorption
The uptake and removal of nutrients from the digestive tract, alimentary canal, or gut
Sphincters
Thickened regions of circular muscle that function like valves to control the flow of contents at various points in the GI tract
Saliva
Watery fluid that contains mucus and few enzymes
Hemorrhoids
cluster of small veins in the anal canal
Small intestine
coiled, hollow tube that extends from the stomach to the large intestine
Ulcerative colitis
develop ulcers in the mucosa of the colon and rectum
Duodenum
first part of the small intestine, the acidic stomach contents mix with alkaline fluids secreted by the pancreas and gallbladder
Probiotics
live, beneficial microbes that have been grown under laboratory conditions
Gut microbiota
metabolize certain phytochemicals into forms that can be absorbed and used by the body
Villi
mucosa of the small intestine is highly folded and covered by tiny, fingerlike projections
Bilirubin
orange-yellow pigment in bile; formed by the breakdown of hemoglobin when red blood cells are destroyed
Hepatic
pertaining to the liver
Mastication
physical activity that prepares solid foods for swallowing and chemical digestion
jejunum
second part of the small intestine, most digestion and nutrient absorption occurs in the upper part of the small intestine
Enterocytes
specialized absorptive cells in the villi of the small intestine
Bioavailability
the extent to which the digestive tract absorbs a nutrient and how well the body uses it
Peristalsis
the process of wave-like muscle contractions of the alimentary tract that moves food along
When the pH is lower than 4.5
the salivary amylase does not function
ileum
third part of the small intestine
