Chapter 23 Digestive System

ailmentary canal

the digestive tract, the gastrointestinal tract

ingestion

intake of food; eating

peritoneum

membrane that lines the abdominal cavity

peritoneal cavity

space between the parietal and visceral peritoneum

parietal peritoneum

serous membrane; the outer layer of the peritoneum that lines the body wall

visceral peritoneum

serous membrane; the inner layer of the peritoneum that surrounds the organs of the abdominal cavity

peritoneal fluid

watery serous fluid that fills the spaces between the organs and allows them to slide past each other during the movements of digestion

serous fluid

A clear, watery fluid secreted by the cells of a serous membrane.

ascites

accumulation of fluid in the peritoneal cavity

peritonitis

inflammation of the peritoneum

serosa

visceral peritoneum

mucosa

The innermost layer of the human digestive tract; in some parts of the digestive system, it contains mucus-secreting cells and glands that secrete digestive enzymes. It consists of 2 layers (epithelium + lamina propria areolar tissue)

submucosa

The layer of dense irregular connective tissue directly under the mucosa of an open body cavity. This layer of the human digestive system that contains nerves, blood vessels, and lymph nodes

submucosal plexus

consists of sensory neurons as well as PSNS and SNS neurons; controls secretions

muscularis mucosae

thin layer of smooth muscle that produces local movements of mucosa; alter shape of lumen

enteric nervous system

The nervous system of the gastrointestinal tract. It consists of sensory and motor nerves (predominantly PSNS and SNS nerves). It controls secretion and motility within the GI tract, and is linked to the central nervous system.

myenteric plexus

nerve supply between the two layers of the muscularis externa; provides smooth, coordinated contraction for peristalsis

muscularis externa

smooth muscle, inner circular layer, outer longitudinal layer; responsible for segmentation and peristalsis

pacesetter cells

Located in muscularis mucosae and muscularis externa
Surrounding lumen of digestive tract. Spontaneously trigger the contraction of entire muscular sheets.

mesenteries

parts of the peritoneum that hold the abdominal organs in place and provide a passageway for blood vessels and nerves to the organs. A double sheet of peritoneum with an areolar tissue in the middle providing a rout for blood vessels nerves, and lymphatic vessels. There are 5 mesenteries: greater omentum, lesser omentum, falciform ligament, mesentery proper, and mesocolon.

greater omentum

part of the peritoneum attached to the stomach and to the colon and covering the intestines; a fatty sheet that hangs like an apron over the abdominal viscera

lesser omentum

part of the peritoneum that attaches stomach to liver

falciform ligament

attaches liver to anterior abdominal wall and diaphragm

mesentery proper

attaches the small intestine to the posterior abdominal wall

mesocolon

extension of the mesentery that anchors the colon to the posterior abdominal wall

retroperitoneal

located behind the peritoneum

retroperitoneal organs

kidneys, pancreas, duodenum, ascending & descending colon, and rectum

Goblet cells

a column-shaped cell found in the respiratory and intestinal tracts, which secretes the main component of mucus.

mucin

a glycoprotein constituent of mucus

enteroendocrine cells

secrete hormones (e.g. gastrin)

paracrine cells

secrete products that affect adjacent cells (e.g. histamine secreting cells in GI tract)

G cells

secrete gastrin

parietal cells

secrete HCl and intrinsic factor

chief cells

secrete pepsinogen and gastric lipase

peristalsis

Involuntary waves of muscle contraction that keep food moving along in one direction through the digestive system.

intrinsic factor

A substance produced by the mucosa of the stomach and intestines that is essential for the absorption of vitamin B12.

pepsin

An enzyme present in gastric juice that begins the hydrolysis of proteins

lipase

enzyme that breaks down lipid

triglyceride

storage form of fat; a lipid made of three fatty acid molecules and one glycerol molecule

polysaccharide

large macromolecule formed from monosaccharides

mastication

chewing

enamel

hard, outermost layer of a tooth; 96% CaPO4; no cells

dentin

Primary material found in teeth. It is covered by the enamel in the crown and a protective layer of cementum in the root. 70% CaPO4; no cells

pulp

soft tissue within a tooth, containing nerves and blood vessels

gomphosis

a synarthrosis that binds the teeth to bony sockets in the maxillae and mandible

cementum

Specialized, calcified connective tissue that covers the anatomic root of a tooth.

gingiva

gum tissue

gingivitis

inflammation of the gums

tartar

hard deposit on the teeth near the gum line formed by plaque buildup and dead bacteria

deciduous teeth

The 20 baby teeth that begin to erupt around the age of 6 months. Eventually pushed out by the permanent teeth.

tongue muscles (intrinsic and extrinsic)

change shape of tongue; assist in mastication; and are required for articulation of speech

salivary amylase

enzyme that begins starch digestion in the mouth

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. Parotid, Pharyngeal and Palatine

esophageal hiatus

opening in diaphragm where esophagus passes through

deglutition

swallowing food

rugae

the folds in the mucosa lining the stomach

cardia of the stomach

area in the stomach around the opening of the esophagus

fundus of stomach

The top portion of the stomach; has no acid producing cells

pyloric antrum and pyloric canal

Narrowed bottom part of stomach
Function: prevent intestinal contents from reentering the stomach when the small intestine contracts and to limit the passage of large food particles or undigested material into the intestine

pyloric sphincter (pylorus)

ring of muscle that guards the opening between the stomach and the duodenum

pyloric orifice

opening between stomach and small intestine

cephalic phase of digestion

The secretory phase of digestion initiated by the CNS in response to the thought or smell of food.

Gastric phase of digestion

neural and hormonal mechanisms promote gastric secretion and motility in the presence of food

Intestinal phase of digestion

slows exit of chyme from stomach stimulates flow of bile and pancreatic juice and intestinal mucus production as well as the enterogastric reflex (reducing gastric secretions and motility)

bolus

A term used to describe food after it has been chewed and mixed with saliva and packed into a small rounded mass

chyme

Partially digested, semiliquid food mixed with digestive enzymes and acids in the stomach.

enterogastric reflex

Stretch and Chemoreceptors in the duodenum inhibits acid secretion in stomach and gastric motility by:
Enteric nervous system short reflexes. This is reinforced by the release of GIP, CCK, Secretin, and VIP.

gastroenteric reflex

Distension in the stomach is sensed by stretch receptors that then stimulate motility and secretion along the entire small intestine

gastroileal reflex

Distension in the stomach is sensed by stretch receptors that then triggers relaxation of ileocecal valve allowing movement of material from ileum (small intestine) into cecum (large intestine)

pancreatic juice

Alkaline mixture of water, enzymes, sodium bicarbonate and other electrolytes

trypsinogen

inactive form of trypsin produced by the pancreas; converted to trypsin by enterokinases in the small intestine where it digests polypeptides into smaller amino acids

chymotrypsinogen

produced by the pancreas and converted to chymotrypsin by trypsin in the small intestine where it digests polypeptides into smaller amino acids

procarboxypeptidase

produced by the pancreas and converted to carboxypeptidase by trypsin in the small intestine where it digests polypeptides into smaller amino acids

acinar cells

enzyme-secreting cells of the pancreas

pancreatic islets (islets of Langerhans)

contain endocrine cells

insulin

A protein hormone secreted by the pancreas that is essential for the metabolism of carbohydrates and the regulation of glucose levels in the blood.

nuclease

An enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides.

protease

enzyme that breaks down proteins

peptidase

a digestive enzyme that hydrolyzes peptide bonds

hepatocytes

liver cells

hepatopancreatic ampulla

Connection of the common bile duct (brings in bile) and the pancreatic duct (brings enzymes & juices) to the duodenum

hepatopancreatic sphincter

controls entry of bile and pancreatic juice into duodenum

portal vein

large vein bringing blood to the liver from the intestines

Kupffer cells

macrophages of the liver; also store iron, lipids, and heavy metals (tin, mercury)

bile

a bitter greenish-brown alkaline fluid that aids digestion and is secreted by the liver and stored in the gallbladder.

bile salts

compounds in bile that aid in emulsification

emulsification

physical process of breaking up large fat globules into smaller globules, thereby increasing the surface area that enzymes can use to digest the fat

micelles

tiny spherical complexes of emulsified fat that arise during digestion; most contain bile salts and the products of lipid digestion, including fatty acids, monoglycerides, and cholesterol

gallbladder

a muscular sac attached to the liver that secretes bile and stores it until needed for digestion

duodenum

first part of the small intestine

jejunum

second part of the small intestine

ileum

third part of the small intestine

plicae circulares

circular folds in small intestine

lacteal

a lymph tubule located in the villus that absorbs digested fats

chylomicron

A lipid transport globule composed of fats mixed with cholesterol and coated with proteins.

large intestine (colon)

cecum, ascending colon, transverse colon, descending colon, sigmoid colon

rectum

A short tube at the end of the large intestine where waste material is compressed into a solid form before being eliminated

appendix

A small, fingerlike extension of the vertebrate cecum; contains a mass of white blood cells that contribute to immunity.

Normal flora of the intestinal tract

Complex and important interactions with the host.
The large intestine (cecum and colon) and the rectum contain huge population of microbes

Feces

approximately 75% water + 5% bacteria + 20% indigestible material