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