Chapter 3

Saliva

A mixture of water, mucus, enzymes, and other chemicals that moistens the mouth and food, binds food particles together, and begins the digestion of carbohydrates.

Esophagus

A muscular tube of the GI tract connecting the back of the mouth to the stomach

Peptic ulcer

An area of the GI tract that has been eroded away by the acidic gastric juice of the stomach. The 2 main causes of peptic ulcers are helicobacter pylori infection and the use of nonsteroidal anti-inflammatory drugs.

Haustration

Involuntary sluggish contraction of the haustra of the proximal colon, which moves wastes toward the sigmoid colon.

constipation

a condition characterized by the absence of bowel movements for a period of time that is significantly longer than normal for the individual.

Celiac disease

a disorder characterized by an immune reaction that damages the lining of the small intestine when the individual is exposed to a component of a protein called gluten.

Irritable bowel syndrome (IBS)

a stress-related disorder that interferes with normal functions of the colon. Symptoms are abdominal cramps, bloating, and constipation of diarrhea.

Facilitated diffusion

a transport process in which ions and molecules are shuttled across the cell membrane with the help of a carrier protein.

Active transport

a transport process that requires the use of energy to shuttle ions and molecules across the cell membrane in combination with a carrier protein.

enteric nervous system (ENS)

the autonomic nerves in the walls of the GI tract.

vomiting

the involuntary expulsion of the contents of the stomach and duodenum from the mouth.

digestion

the process by which foods are broken down into their component molecules, either mechanically or chemically.

Hormone

A chemical messenger that is secreted into the bloodstream by one of the many endocrine glands of the body. hormones act as regulators of physiologic processes at sites remote from the glands that secreted them.

Hydrolysis

A chemical reaction that breaks down substances by the addition of water.

Ulcerative colitis

A chronic disease of the colon, indicated by inflammation and ulceration of the mucosa, or innermost lining, of the colon.

crohn's disease

A chronic disease that causes inflammation in the small intestine, leading to diarrhea, abdominal pain, rectal bleeding, weight loss, and fever.

Diarrhea

A condition characterized by the frequent passage of loose, watery stools.

Pancreas

A gland located behind the stomach that secretes digestive enzymes.

Salivary glands

A group of glands found under and behind the tongue and beneath the jaw that releases saliva continually as well as in response to the thought, sight, smell, or presence of food

Stomach

A j-shaped organ where food is partially digested, churned, and stored until released into the small intestine.

Gastrointestinal (GI) tract

A long, muscular tube consisting of several organs: the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.

Bolus

A mass of food that has been chewed and moistened in the mouth

Gastroesophageal reflux disease (GERD)

A painful type of heartburn that occurs more than twice per week.

Gallbladder

A pear-shaped organ beneath the liver that stores bile and secretes it into the small intestine

Hunger

A physiologic sensation that prompts us to eat.

Appetite

A psychological desire to consume specific foods

Hypothalamus

A region of the brain below (hypo-) the thalamus and cerebral hemispheres and above the pituitary gland and brain stem where visceral sensations such as hunger and thirst are regulated.

Chyme

A semifluid mass consisting of partially digested food, water and gastric juices.

Lacteal

A small lymphatic vessel located inside the villi of the small intestine.

Portal venous system

A system of blood vessels that drains blood and various products of digestion from the digestive organs and spleen and delivers them to the liver.

Sphincter

A tight ring of muscle separating some of the organs of the GI tract and opening in response to nerve signals indicating that food is ready to pass into the next section.

Endocytosis

A transport process in which ions and molecules are engulfed by the cell membrane, which folds inwardly and is released in the cell interior ( also called pinocytosis)

Passive diffusion

A transport process in which ions and molecules, following their concentration gradient, cross the cell membrane without the use of a carrier protein or the requirement of energy.

Gastric juice

Acidic liquid secreted within the stomach; it contains hydrochloric acid, pepsin, and other compounds.

Bile

Fluid produced by the liver and stored in the gallbladder; it emulsifies lipids in the small intestine.

Food intolerance

Gastrointestinal discomfort caused by certain foods that is not a result of an immune system reaction.

Probiotics

Microorganisms, typically bacteria, theorized to benefit human health.

Segmentation

Rhythmic contraction of the circular muscles of the small intestine, which squeezes chyme, mixes it, and enhances the digestion and absorption of nutrients from the chyme.

Enzymes

Small chemicals, usually proteins, that act on other chemicals to speed up bodily processes but are not changed during those processes.

Enterocytes

Specialized absorptive cells in the villi of the small intestine.

Gastrointestinal (GI) system

The body system responsible for digestion, absorption, and elimination. It includes the organs of the GI tract and the accessory organs.

Cephalic phase

The earliest phase of digestion, in which the brain thinks about and prepares the digestive organs for the consumption of food.

Large intestine

The final organ of the GI tract, consisting of the cecum, colon, rectum, and anal canal and in which most water is absorbed and feces are formed.

Ghrelin and cholecystokinin

The hormone ghrelin is produced by the stomach. immediately after a meal, ghrelin levels plummet. As time since our last meal elapses, ghrelin levels begin to rise. a fast-acting hormone, ghrelin triggers the hypothalamus to strongly induce us to eat. As you might suppose, when we dramatically restrict our food intake, ghrelin levels surge. Opposite in action to ghrelin is the hormone cholecystokinin (CCK) Which is produced in the small intestine in response to food entry. CCK causes stimulation of the satiety center.

Leptin

The hormones we've discussed so far act in short-term regulation of food intake. But our body produces other hormones that regulate food intake over time. one of the most important of these is leptin, a protein produced by our adipose cells ( fat cells). When we consume more calories than we burn, the extra calories are converted to fat and stored in adipose tissue. The more adipose tissue our body carries, the more leptin we produce. Leptin acts on the hypothalamus to suppress hunger. Unfortunately, obese people appear to be leptin-resistant.

Liver

The largest accessory organ of the GI tract and one of the most important organs of the body. Its functions include the production of bile and processing of nutrient-rich blood from the small intestine.

Small intestine

The longest portion of the GI tract, where most digestion and absorption takes place.

Brush border

The microvilli of the small intestine's lining. These microvilli tremendously increase the small intestine's absorptive capacity.

HEartburn

The painful sensation that occurs over the sternum when gastric juice backs up into the lower esophagus.

Absorption

The process by which molecules of food are taken from the gastrointestinal tract into the circulation.

Elimination

The process by which the undigested portions of food and waste products are removed from the body.

Accessory organs of digestion

The salivary glands, liver, pancreas, and gallbladder, which contribute to GI function but are not anatomically part of the GI tract.

Insulin and glucagon

These hormones are produced in the pancreas and are responsible for maintaining blood glucose levels. GLUCOSE, a simple sugar, is the body's most readily available fuel supply. its not surprising, then, that its level in our blood is an important signal regulating hunger. when we have not eaten for a while, our blood glucose levels fall, prompting a decrease in the level of insulin and an increase in glucagon. This chemical message is relayed to the hypothalamus, which then prompts us to eat in order to supply our bodies with more glucose. after we eat, the hypothalamus picks up the sensation of distention in the stomach and intestine and the rise in blood glucose levels as our body begins to absorb nutrients from our meal. these signals trigger an increase in insulin secretion and a decrease in glucagon, and the feeling of satiety.

Peristalsis

Waves of squeezing and pushing contractions that move food, chime, and feces in one direction through the length of the GI tract.

food allergy

an allergic reaction to food, caused by a reaction of the immune system.

Mass movement

involuntary, sustained, forceful contraction of the colon that occurs 2 or more times a day to push wastes toward the rectum.