takes in food, breaks it down into nutrient molecules, absorbs these molecules into the bloodstream, and then rids the body of the indigestible remains.
also called the gastrointestinal (GI) tract or gut, is the continuous, muscular digestive tube that winds through the body.
breaks it down into smaller fragments
organs are the teeth, tongue, gallbladder, and a number of large digestive glands, salivary glands, liver, and pancreas. Ingestion is simply taking food into the digestive tract, usually via the mouth.
which moves food through the alimentary canal, includes swallowing, which is initiated voluntarily, and peristalsis an involuntary process. Peristalsis (peri = around; stalsis = constriction), the major means of propulsion, involves alternate waves of contraction and relaxation of muscles in the organ walls. Its main effect is to squeeze food along the tract, but some mixing occurs as well. In fact, peristaltic waves are so powerful that, once swallowed, food and fluids will reach your stomach even if you stand on your head.
physically prepares food for chemical digestion by enzymes. Mechanical processes include chewing, mixing of food with saliva by the tongue, churning food in the stomach, and segmentation, or rhythmic local constrictions of the small intestine (Figure 23.3b).
mixes food with digestive juices and increases the efficiency of absorption by repeatedly moving different parts of the food mass over the intestinal wall.
is a series of catabolic steps in which complex food molecules are broken down to their chemical building blocks by enzymes secreted into the lumen of the alimentary canal. Chemical digestion of foodstuffs begins in the mouth and is essentially complete in the small intestine.
is the passage of digested end products (plus vitamins, minerals, and water) from the lumen of the GI tract through the mucosal cells by active or passive transport into the blood or lymph. The small intestine is the major absorptive site.
eliminates indigestible substances from the body via the anus in the form of feces.
of the abdominopelvic cavity is the most extensive of these membranes
covers the external surfaces of most digestive organs
lines the body wall.
a slitlike potential space containing a slippery fluid secreted by the serous membranes.
is a double layer of peritoneum, a sheet of two serous membranes fused back to back—that extends to the digestive organs from the body wall. Mesenteries provide routes for blood vessels, lymphatics, and nerves to reach the digestive viscera; hold organs in place; and store fat.
organs not suspended by a mesentery. include most of the pancreas and parts of the small and large intestine.
Intraperitoneal or Peritoneal organs – with mesentery
inflammation of the peritoneum. It can arise from a piercing abdominal wound, from a perforating ulcer that leaks stomach juices into the peritoneal cavity, or from poor sterile technique during abdominal surgery, but most commonly it results from a burst appendix (that sprays bacteriacontaining feces all over the peritoneum).
includes those arteries that branch off the abdominal aorta to serve the digestive organs and the hepatic portal circulation
mucous membrane—the innermost layer—is a moist epithelial membrane that lines the alimentary canal lumen from mouth to anus. Its major functions are
(1) to secrete mucus, digestive enzymes, and hormones,
(2) to absorb the end products of digestion into the blood, and
(3) to protect against infectious disease.
Simple Columnar epithelium
the typical tissue of the digestive mucosa, rich in mucus-secreting cells.
(proprius = one’s own), which underlies the epithelium, is loose areolar connective tissue. Its capillaries nourish the epithelium and absorb digested nutrients.
a scant layer of smooth muscle cells that produces local movements of the mucosa.
just external to the mucosa, is areolar connective tissue containing a rich supply of blood and lymphatic vessels, lymphoid follicles, and nerve fibers.
Surrounding the submucosa, this layer is responsible for segmentation and peristalsis.
the protective outermost layer of the intraperitoneal organs
The adventitia is ordinary fibrous connective tissue that binds the esophagus to surrounding structures.
(enter = gut), which communicate widely with one another to regulate digestive system activity.
Submucosal Nerve Plexus
occupies the submucosa. It includes sensory as well as motor neurons, and it chiefly regulates the activity of glands and smooth muscle in the mucosa.
Myenteric Nerve Plexus
(“intestinal muscle”) lies between the circular and longitudinal muscle layers of the muscularis externa. Enteric neurons of this plexus provide the major nerve supply to the GI tract wall and control GI tract motility.
mouth, a mucosa-lined cavity
lips (labia) and cheeks
help keep food between the teeth when we chew, are composed of a core of skeletal muscle covered externally by skin.
forming the roof of the mouth
underlain by the palatine bones and the palatine processes of the maxillae, and it forms a rigid surface against which the tongue forces food during chewing.
a mobile fold formed mostly of skeletal muscle that rises reflexively to close off the nasopharynx when we swallow.
(fauc = throat), the arched area of the oropharynx that contains the palatine tonsils.
fingerlike, Projecting downward from the free edge of the soft palate
occupies the floor of the mouth and fills most of the oral cavity when the mouth is closed
a compact mass of food mixed with saliva by the tongue
are confined in the tongue and are not attached to bone.
extend to the tongue from their points of origin on bones of the skull or the soft palate
secures the tongue to the floor of the mouth and limits posterior movements of the tongue.
give the tongue surface a roughness that aids in licking semisolid foods (such as ice cream) and provide friction for manipulating foods in the mouth
are scattered widely over the tongue surface. Each has a vascular core that gives it a reddish hue.
are located on the lateral aspects of the posterior tongue.
a groove that distinguishes the portion of the tongue that lies in the oral cavity (its body) from its posterior portion in the oropharynx (its root)
a common children’s disease, is an inflammation of the parotid glands caused by the mumps virus (myxovirus), which spreads from person to person in saliva.
lies along the medial aspect of the mandibular body. Its duct runs beneath the mucosa of the oral cavity floor and opens at the base of the lingual frenulum
lies anterior to the submandibular gland under the tongue and opens via 10–12 ducts into the floor of the mouth
produce a watery secretion containing enzymes, ions, and a tiny bit of mucin
a stringy, viscous solution
in the brain stem triggers salivation
lie in sockets (alveoli) in the gum-covered margins of the mandible and maxilla.
called milk or baby teeth. The first teeth to appear
enlarge and develop, the roots of the milk teeth are resorbed from below, causing them to loosen and fall out between the ages of 6 and 12 years.
adapted for cutting or nipping off pieces of food.
premolars (bicuspids) and molars
have broad crowns with rounded cusps (tips) and are best suited for grinding or crushing.
(cuspids or eyeteeth) tear and pierce.
shorthand way of indicating the numbers and relative positions of the different types of teeth in the mouth. This formula is written as a ratio, uppers over lowers, for one half of the mouth. Since the other side is a mirror image, the total dentition is obtained by multiplying the dental formula by 2.
the exposed part of the tooth
gum, which surrounds the tooth like a tight collar.
brittle ceramiclike material thick as a dime, directly bears the force of chewing. The hardest substance in the body, it is heavily mineralized with calcium salts, and its densely packed hydroxyapatite (mineral) crystals are oriented in force-resisting columns perpendicular to the tooth’s surface.
The portion of the tooth embedded in the jawbone
The crown and root are connected by a constricted tooth region
“around the tooth” This ligament anchors the tooth in the bony alveolus of the jaw, forming a fibrous joint called a gomphosis
a protein-rich bonelike material, underlies the enamel cap and forms the bulk of a tooth
supplies nutrients to the tooth tissues and provides for tooth sensation
where the pulp cavity extends into the root
“tooth former”, the cell type that secretes and maintains the dentin.
“rottenness” or cavities, result from gradual demineralization of enamel and underlying dentin by bacterial action.
film of sugar, bacteria, and other mouth debris adheres to the teeth.
dental plaque accumulates, it calcifies, forming calculus “stone”
the gums are red, sore, swollen, and may bleed.
or periodontitis, affects up to 95% of all people over the age of 35 and accounts for 80–90% of tooth loss in adults
“carry food” a muscular tube about 25 cm (10 inches) long, is collapsed when not involved in food propulsion
“gap” to enter the abdomen.
which is a physiological sphincter , it acts as a valve, but the only structural evidence of this sphincter is a slight thickening of the circular smooth muscle at that point.
the first symptom of gastroesophageal reflux disease (GERD), is the burning, radiating substernal pain that occurs when the acidic gastric juice regurgitates into the esophagus.
a structural abnormality (most often due to an abnormal relaxation or weakening of the gastroesophageal sphincter) in which the superior part of the stomach protrudes slightly above the diaphragm.
swallowing, is a complicated process that involves coordinated activity of over 22 separate muscle groups.
occurs in the mouth and is voluntary. In the buccal phase, we place the tip of the tongue against the hard palate, and then contract the tongue to force the bolus into the oropharynx
esophageal phase - The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus.
temporary “storage tank” where chemical breakdown of proteins begins and food is converted to a creamy paste called chime
When empty, the stomach collapses inward, throwing its mucosa (and submucosa) into large, longitudinal folds
(“near the heart”), surrounds the cardiac orifice through which food enters the stomach from the esophagus.
dome-shaped part, tucked beneath the diaphragm, that bulges superolaterally to the cardia.
funnel-shaped region of the stomach
more superior part of the pyloric region
where the stomach meets the duodenum
pyloric valve or sphincter
which controls stomach emptying (pylorus = gatekeeper).
The convex lateral surface of the stomach
concave medial surface of the stomach
runs from the liver to the lesser curvature of the stomach, where it becomes continuous with the visceral peritoneum covering the stomach
drapes inferiorly from the greater curvature of the stomach to cover the coils of the small intestine.
in the lining of the duodenum which lead into the tubular gastric glands
produce the stomach secretion called gastric juice
Mucous neck cells
found in the upper, or “neck,” regions of the glands, produce a thin, soluble mucus
found mainly in the middle region of the glands, simultaneously secrete hydrochloric acid (HCl) and intrinsic factor. Although the parietal cells appear spherical when viewed with a light microscope, they actually have three prongs that bear dense microvilli (they look like fuzzy pitchforks!). This structure provides a huge surface area for secreting H and Cl into the stomach lumen. HCl makes the stomach contents extremely acidic (pH 1.5–3.5), a condition necessary for activation and optimal activity of pepsin. The acidity also helps in food digestion by denaturing proteins and breaking down cell walls of plant foods, and is harsh enough to kill many of the bacteria ingested with foods. Intrinsic factor is a glycoprotein required for vitamin B12 absorption in the small intestine.
occur mainly in the basal regions of the gastric glands. The chief cells produce pepsinogen, the inactive form of the protein-digesting enzyme pepsin. Chief cells also secrete insignificant amounts of lipases (fat-digesting enzymes).
(“gut endocrine”), typically located deep in the gastric glands, release a variety of chemical messengers directly into the interstitial fluid of the lamina propria.
the stomachs aggressive counterattack to protect itself
1. A thick coating of bicarbonate-rich mucus is built up on the stomach wall.
2. The epithelial cells of the mucosa are joined together by tight junctions that prevent gastric juice from leaking into the underlying tissue layers.
3. Damaged epithelial mucosal cells are shed and quickly replaced by division of undifferentiated stem cells that reside where the gastric pits join the gastric glands. The stomach surface epithelium of mucous cells is completely renewed every three to six days, because these cells can survive only a few days in the stomach’s harsh environment.
specifically called gastric ulcers when they are erosions of the stomach wall
an enzyme that acts on milk protein (casein), converting it to a curdy substance that looks like soured milk.
required for intestinal absorption of vitamin B12, needed to produce mature erythrocytes.
Reflex phase (cephalic)
few minutes prior to food entry: smell/taste
3–4 hours after food enters the stomach
brief stimulatory effect as chyme enters the duodenum, followed by inhibitory effects (enterogastric reflex and enterogastrones): not too much now!
a collection of hormones that inhibit gastric secretion when the stomach is very active. They include secretin, cholecystokinin (CCK), and vasoactive intestinal peptide (VIP)
of smooth muscle in the stomach fundus and body occurs both in anticipation of and in response to food movement through the esophagus and into the stomach
an example of smooth muscle plasticity, is the intrinsic ability of visceral smooth muscle to exhibit the stress-relaxation response
CCK mediates a number of physiological processes, including digestion and satiety. It is released by I cells located in the mucosal epithelium of the small intestine (mostly in the duodenum and jejunum), neurons of the enteric nervous system and neurons in the brain.
Release of CCK is stimulated by monitor peptide released by pancreatic acinar cells as well as CCK-releasing protein, a paracrine factor secreted by enterocytes in the gastrointestinal mucosa. In addition, release of acetylcholine by the parasympathetic nerve fibers of the vagus nerve also stimulate its secretion. The presence of fatty acids and/or certain amino acids in the chyme entering the duodenum is the greatest stimulator of CCK release.
CCK mediates digestion in the small intestine by inhibiting gastric emptying and gastric acid secretion. It stimulates the acinar cells of the pancreas to release digestive enzymes and stimulates the secretion of a juice rich in pancreatic digestive enzymes, hence the old name pancreozymin. Together these enzymes catalyze the digestion of fat, protein, and carbohydrates. Thus, as the levels of the substances that stimulated the release of CCK drop, the concentration of the hormone drops as well. The release of CCK is also inhibited by somatostatin. Trypsin, a protease released by pancreatic acinar cells hydrolyzes CCK-releasing peptide and monitor peptide effectively turning off the additional signals to secrete CCK.
CCK also causes the increased production of hepatic bile, and stimulates the contraction of the gall bladder and the relaxation of the Sphincter of Oddi (Glisson's sphincter), resulting in the delivery of bile into the duodenal part of the small intestine. Bile salts form amphipathic micelles that emulsify fats, aiding in their digestion and absorption.
Gastric inhibitory peptide (GIP)
It is now believed that the function of GIP is to induce insulin secretion, which is stimulated primarily by hyperosmolarity of glucose in the duodenum. After this discovery, some researchers prefer the new name of glucose-dependent insulinotropic peptide, while retaining the acronym "GIP." The amount of insulin secreted is greater when glucose is administered orally than intravenously.
a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility.
Activates parietal cells to release HCl
Stimulates gastric glands and motility
Stimulates migrating motility complex
hormone that both controls the environment in the duodenum by regulating secretions of the stomach and pancreas, and regulates water homeostasis throughout the body.
Causes contraction of stomach muscle
(also known as growth hormone-inhibiting hormone (GHIH) or somatotropin release-inhibiting factor (SRIF)) or somatotropin release-inhibiting hormone is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones.
Vasoactive intestinal peptide
VIP stimulates contractility in the heart, causes vasodilation, increases glycogenolysis, lowers arterial blood pressure and relaxes the smooth muscle of trachea, stomach and gall bladder. In humans, the vasoactive intestinal peptide is encoded by the VIP gene.
the body’s major digestive organ.Within its twisted passageways, digestion is completed and virtually all absorption occurs.
in the right iliac region where sm intestines join the large intestine.
“twelve finger widths long”, which curves around the head of the pancreas, is about 25 cm (10 inches) long Although it is the shortest intestinal subdivision, the duodenum has the most features of interest.
The bile duct, delivering bile from the liver, and the main pancreatic duct, carrying pancreatic juice from the pancreas, unite at the wall of the duodenum in a bulblike point
major duodenal papilla volcano
shaped region where the ampulla opens into the duodenum via.
smooth muscle valve that control the entry of bile and pancreatic juice
“empty”, about 2.5 m (8 ft) long, extends from the duodenum to the ileum.
“twisted”, approximately 3.6 m (12 ft) in length, joins the large intestine at the ileocecal valve.
or plicae circulares , are deep, permanent folds of the mucosa and submucosa
“tufts of hair” are fingerlike projections of the mucosa, over 1 mm high, that give it a velvety texture, much like the soft nap of a towel
of the absorptive cells of the mucosa give the mucosal surface a fuzzy appearance called the brush border
brush border enzymes
which complete the digestion of carbohydrates and proteins in the small intestine.
crypts of Lieberkühn Crypt epithelial cells are primarily secretory cells that secrete intestinal juice, a watery mixture containing mucus that serves as a carrier fluid for absorbing nutrients from chyme.
(also called Brunner’s glands) are found in the submucosa of the duodenum only. These glands produce an alkaline (bicarbonate-rich) mucus that helps neutralize the acidic chyme moving in from the stomach.
separates the right and left lobes anteriorly and suspends the liver from the diaphragm and anterior abdominal wall
ligamentum teres “round”, a fibrous remnant of the fetal umbilical vein.
It transmits the hepatic portal vein (entering), hepatic artery proper (entering), Common hepatic duct (leaving)
common hepatic duct
Bile leaves the liver through several bile ducts that ultimately fuse to form the large common hepatic duct
draining the gallbladder
The liver is composed of sesame seed–sized structural and functional units.
running in the longitudinal axis of the lobule
region at six corners of a lobule
leaky capillaries Between the hepatocyte plates are enlarged
called Kupffer cells remove debris such as bacteria and worn-out blood cells from the blood as it flows past.
tiny canals Secreted bile flows through
inflammation of the liver, is most often due to viral infection.
“orange colored” is a progressive chronic inflammation of the liver that typically results from chronic alcoholism or severe chronic hepatitis
obstructed blood flow throughout the hepatic portal system
a yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, triglycerides, phospholipids (lecithin and others), and a variety of electrolytes. Of these, only bile salts and phospholipids aid the digestive process.
primarily cholic and chenodeoxycholic acids, are cholesterol derivatives. Their role is to emulsify fats
recycling mechanism in which bile salts are conserved
a waste product of the heme of hemoglobin formed during the breakdown of worn-out erythrocytes
thin-walled green muscular sac about 10 cm (4 inches) long. The gallbladder stores bile that is not immediately needed for digestion and concentrates it by absorbing some of its water and ions.
biliary calculi which obstruct the flow of bile from the gallbladder
An accessory digestive organ, the pancreas is important to the digestive process because it produces enzymes that break down all categories of foodstuffs, which the pancreas then delivers to the duodenum.
drains from the pancreas
Main pancreatic duct
duct which pancreatic juice drains from the pancreas
“fermenting” containing the digestive enzymes
migrating motility complex
waves of activity that sweep through the intestines in a regular cycle during fasting state.
a long reflex that enhances the force of segmentation in the ileum.
three bands of smooth muscle
pocketlike sacs of the large intestines
“membrane covered”, small fat-filled pouches of visceral peritoneum that hang from ithe surface of the large intestine
“blind pouch”, which lies below the ileocecal valve in the right iliac fossa, is the first part of the large intestine
The appendix contains masses of lymphoid tissue, and as part of MALT it plays an important role in body immunity.
results from a blockage (often by feces) that traps infectious bacteria in its lumen.
travels up the right side of the abdominal cavity to the level of the right kidney.
right colic flexure
hepatic, flexure the region the ascending colon makes a right angle turn into the transverse colon
colon travels across the abdominal cavity.
left colic (splenic) flexure
the colon, Directly anterior to the spleen, it bends acutely into the descending colon.
descends down the left side of the posterior abdominal wall
Sigmoid colon – colon enters the pelvis, where it becomes the S
runs posteroinferiorly just in front of the sacrum.
three lateral curves or bends in the rectum
the last segment of the large intestine, lies in the perineum, entirely external to the abdominopelvic cavity.
region anal canal opens to the exterior
internal anal sphincter
involuntary sphincters of the anal canal composed of smooth muscle
external anal sphincter
voluntary sphincters of the anal canal composed of skeletal muscle
number of vertical folds, produced by an infolding of the mucous membrane and some of the muscular tissue in the upper half of the lumen of the anal canal.
recesses between the anal columns, exude mucus when compressed by feces, which aids in emptying the anal canal
community of bacteria that exists on or in the body
slow segmenting movements lasting about one minute that occur every 30 minutes
(mass peristalsis) are long, slow-moving, but powerful contractile waves that move over large areas of the colon three or four times daily and force the contents toward the rectum.
small herniations of the mucosa through the colon walls.
in which the diverticula become inflamed and may rupture, leaking feces into the peritoneal cavity
Irritable bowel syndrome
(IBS) is a functional GI disorder not explained by anatomical or biochemical abnormalities.Affected individuals have recurring (or persistent) abdominal pain that is relieved by defecation, changes in the consistency
initiated by stretching of the rectal wall
result from any condition that rushes food residue through the large intestine before that organ has had sufficient time to absorb the remaining water
when food remains in the colon for extended periods, too much water is absorbed and the stool becomes hard and difficult to pass
is a catabolic process in which large food molecules are broken down to monomers
The enzymatic breakdown of any type of food molecule
•Amino acids are absorbed by cotransport with sodium ions.
•Some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolyzed to amino acids within the cells.
•Amino acids leave the epithelial cells by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.
•Fatty acids and monoglycerides enter the intestinal cells via diffusion.
•Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells, and the resulting chylomicrons are extruded by exocytosis.
•The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct.
•Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein.
•Monosaccharides (simple sugars), the monomers of carbohydrates, are absorbed immediately
•Glucose and galactose are absorbed via cotransport with sodium ions.
•Fructose passes via facilitated diffusion.
•All monosaccharides leave the epithelial cells via facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.
•Units enter intestinal cells by active transport via membrane carriers.
•Units are absorbed into capillary blood in the villi and transported to the liver via the hepatic portal vein.
present in saliva, splits starch into oligosaccharides, smaller fragments of two to eight linked glucose molecules. Salivary amylase works best in the slightly acid to neutral environment
are collections of fatty elements clustered together with bile salts in such a way that the polar (hydrophilic) ends of the molecules face the water and the nonpolar portions form the core
triglycerides are combined with lecithin and other phospholipids and cholesterol, and coated with a “skin” of proteins to form water-soluble lipoprotein droplets
an enzyme associated with the capillary endothelium of liver and adipose tissue
protein that stores iron and releases it in a controlled fashion.
impaired nutrient absorption
The epithelial lining of the developing alimentary canal