digestive system Flashcards

the alimnetary canal (GI tract) and the accessory digestive organs

mouth, pharynx,esophagus, stomach, small intestine, and large intestine

to digest and absorb food

teeth tongue gallbladder salivary glands liver and pancreas

1. ingestion
2. propulsion
a.deglutition
b.peristalsis
c.mass movements
3. mechanical digestion
a.mastication
b. churning
c. segmentation
4. chemical digestion
5. absorption
6. defecation

Adjacent segments of alimentary tract organs alternately contract and relax, which moves food along the tract distally.

Nonadjacent segments of alimentary tract organs alternately contract and relax, moving the food forward then backward. Food mixing and slow food propulsion occurs.

swallowing

serous membrane of the abdominal cavity

on external surface of most digestive organs

lines the body wall

found Between the two peritoneums
the Fluid lubricates mobile organs

a double layer of peritoneum, Routes for blood vessels, lymphatics, and nerves
it also Holds organs in place and stores fat

lie posterior to the peritoneum

the peritoneum

• Hepatic, splenic, and left gastric
• Inferior and superior mesenteric
• Hepatic portal circulation

• Drains nutrient-rich blood from digestive organs
• Delivers it to the liver for processing

Four basic layers (tunics)
• Mucosa
• Submucosa
• Muscularis externa
• Serosa

Lines the lumen

Secretes mucus, digestive enzymes and
hormones, Absorbs end products of digestion, and Protects against infectious disease

Three sublayers: epithelium, lamina propria,
and muscularis mucosae

the oral cavity, oropharynx, nasopharynx,
esophagus, and anal canal

in the stomach, small intestine, large intestine,and rectum
• Goblet cells – secrete mucus
• Protects digestive organs from enzymes
• Eases food passage
• May secrete enzymes and hormones (e.g., in stomach and small intestine)

Loose areolar connective tissue
• Capillaries for nourishment and absorption
• Lymphoid follicles (part of MALT)

smooth muscle that produces local movements
of mucosa

• Dense connective tissue, Blood and lymphatic vessels, lymphoid, follicles, and submucosal nerve plexus, Muscularis externa, Inner circular and outer longitudinal layers, Myenteric nerve plexus and Sphincters in some regions

Responsible for segmentation and peristalsis

the fibrous adventitia

an adventitia and serosa

•Intrinsic nerve supply of the alimentary canal
•Submucosal nerve plexus
•Regulates glands and smooth muscle in the mucosa
•Myenteric nerve plexus
•Controls GI tract motility
•Long ANS fibers synapse with enteric plexuses
•Sympathetic impulses inhibit secretion and motility
•Parasympathetic impulses stimulate secretion and motility

Oral (buccal) cavity

•Bounded by lips, cheeks, palate, and tongue

•Lined with stratified squamous epithelium

Contain orbicularis oris (lips) and buccinator muscles (cheeks)

formed by the palatine bones and palatine processes of the maxillae,Slightly corrugated to help create friction against the tongue

fold formed mostly of skeletal muscle
Closes off the nasopharynx during swallowing
Uvula projects downward from its free edge

Repositioning and mixing food during chewing
Formation of the bolus
Initiation of swallowing, speech, and taste
Surface bears papillae- gustatory receptor cells

(parotid, submandibular, and sublingual)

they are scattered in the oral mucosa

Cleanses the mouth,Moistens and dissolves food chemicals, Aids in bolus formation,Contains enzymes that begin the breakdown of starch

Secreted by serous and mucous cells

97–99.5% water, slightly acidic solution containing
•Electrolytes—Na+, K+, Cl–, PO4 2–, HCO3–
•Salivary amylase
•Mucin
•Metabolic wastes—urea and uric acid
•Lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms

Intrinsic glands

Ingested food stimulates chemoreceptors and mechanoreceptors in the mouth

along parasympathetic fibers in cranial nerves VII and IX, Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia)

21

20 deciduous teeth erupt (6–24 months of age)
•Roots are resorbed, teeth fall out (6–12 years of age) as permanent teeth develop
•32 permanent teeth
•All except third molars erupt by the end of adolescence

•Chisel shaped for cutting

they are Fanglike teeth that tear or pierce

Have broad crowns with rounded cusps for grinding or crushing

Crown: the exposed part above the gingiva (gum)
•Covered by enamel—the hardest substance in the body (calcium salts and hydroxyapatite crystals)
•Root: portion embedded in the jawbone
•Connected to crown by neck
Cementum: calcified connective tissue
•Covers root and attaches it to the periodontal ligament
•Periodontal ligament
•Forms fibrous joint called a gomphosis
•Gingival sulcus: groove where gingiva borders the tooth
Dentin: bonelike material under enamel
•Maintained by odontoblasts of pulp cavity
•Pulp: connective tissue, blood vessels, and nerves
•Root canal: extends from pulp cavity to the apical foramen of the root

(cavities): gradual demineralization of enamel and dentin

caused when Dental plaque (sugar, bacteria, and debris) adheres to teeth Acid from bacteria dissolves calcium salts Proteolytic enzymes digest organic matter

•Prevention: daily flossing and brushing

Plaque calcifies to form calculus (tartar), Calculus disrupts the seal between the gingivae and the teeth, Anaerobic bacteria infect gums, Infection reversible if calculus removed

Immune cells attack intruders and body tissues, Destroy periodontal ligament, Activate osteoclasts

Possible tooth loss, promotion of atherosclerosis and clot formation in coronary and cerebral arteries

•Allow passage of food, fluids, and air

•Stratified squamous epithelium lining
•Skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors

•Flat muscular tube from laryngopharynx to stomach
•Pierces diaphragm at esophageal hiatus
•Joins stomach at the cardiac orifice
•Stratified squamous epithelium lining
•Esophageal glands in submucosa secrete mucus to aid in bolus movement
•Muscularis: skeletal superiorly; smooth inferiorly
•Adventitia instead of serosa

•Ingestion
•Mechanical digestion
•Mastication is partly voluntary, partly reflexive
•Chemical digestion (salivary amylase)
•Propulsion
•Deglutition (swallowing)

Involves the tongue, soft palate, pharynx, esophagus, and 22 muscle groups
•Buccal phase
•Voluntary contraction of the tongue
•Pharyngeal-esophageal phase
•Involuntary
•Control center in the medulla and lower pons

the Cardiac region (cardia)Surrounds the cardiac orifice

Dome-shaped region beneath the diaphragm

Midportion

Pylorus is continuous with the duodenum through the pyloric valve (sphincter)

convex lateral surface

Concave medial surface

From the liver to the lesser curvature

•Drapes from greater curvature
•Anterior to the small intestine

•Sympathetic via splanchnic nerves and celiac plexus
•Parasympathetic via vagus nerve

•Celiac trunk
•Veins of the hepatic portal system

Four tunics

the Inner oblique layer allows stomach to churn, mix, move, physically break down food

Simple columnar epithelium composed of mucous cells, the Layer of mucus traps bicarbonate-rich fluid beneath it and Gastric pits lead into gastric glands

*Mucous neck cells (secrete thin, acidic mucus)
•Parietal cells (HCl and intrinsic factor)
•Chief cells (pepsinogen)
•Enteroendocrine cells

Glands in the fundus and body

pH 1.5–3.5 denatures protein in food, activates pepsin, and kills many bacteria

•Glycoprotein required for absorption of vitamin B12 in small intestine

•Inactive enzyme pepsinogen
•Activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism)

•Secrete chemical messengers into the lamina propria
•Paracrines
•Serotonin (increase stomach contractions) and histamine (increase HCl secretion)
•Hormones

protein digestion

inhibits gastric secretion

increase HCl secretion

•Layer of bicarbonate-rich mucus
•Tight junctions between epithelial cells
•Damaged epithelial cells are quickly replaced by division of stem cells

inflammation caused by anything that breaches the mucosal barrier

erosion of the stomach wall
•Most are caused by Helicobacter pylori bacteria

•Physical digestion
•Denaturation of proteins
•Enzymatic digestion of proteins by pepsin (and rennin in infants)
•Secretes intrinsic factor required for absorption of vitamin B12
•Lack of intrinsic factor  pernicious anemia
•Delivers chyme to the small intestine

Neural and hormonal mechanisms

1.Cephalic
2.Gastric phase
3.Intestinal phase

few minutes prior to food entry

3–4 hours after food enters the stomach

brief stimulatory effect as partially digested food enters the duodenum, followed by inhibitory effects (enterogastric reflex and enterogastrones)

3 per minute

3 ml spurts to the duodenum, or
•Forced backward into the stomach

chyme duodenum

6 hours or more

the small intestine

•2–4 m long; from pyloric sphincter to ileocecal valve with three subdivisions
)

1.Duodenum (retroperitoneal)
2.Jejunum (attached posteriorly by mesentery)
3.Ileum (attached posteriorly by mesentery

at the hepatopancreatic ampulla - Enter the duodenum at the major duodenal papilla
and Are controlled by the hepato- pancreatic sphincter

•Increase surface area of proximal part for nutrient absorption
•Circular folds (plicae circulares)which are Permanent (~1 cm deep)and force chyme to slowly spiral through lumen
•Villi
•Microvilli

Motile fingerlike extensions (~1 mm high) of the mucosa
•Villus epithelium
•Simple columnar absorptive cells (enterocytes)
•Goblet cells

•Projections (brush border) of absorptive cells
•Bear brush border enzymes

•Secretory cells that produce intestinal juice
•Enteroendocrine cells
•Intraepithelial lymphocytes (IELs)
•Release cytokines that kill infected cells

•Secrete antimicrobial agents (defensins and lysozyme)

•Stem cells

in ileum protect distal part against bacteria
•Duodenal (Brunner’s) glands of the duodenum secrete alkaline mucus

secrete alkaline mucus

Secreted in response to distension or irritation of the mucosa
•Slightly alkaline and isotonic with blood plasma
•Largely water, enzyme-poor, but contains mucus
•Facilitates transport and absorption of nutrients

the liver

has Four lobes—right, left, caudate, and quadrate

•Separates the (larger) right and (smaller) left lobes
•Suspends liver from the diaphragm and anterior abdominal wall

•Remnant of fetal umbilical vein along free edge of falciform ligamen

it anchors liver to stomach

Hepatic artery and vein at the porta hepatis

•Common hepatic duct leaves the liver
•Cystic duct connects to gallbladder

by the union of the common hepatic duct and the cystic duct

•Process bloodborne nutrients
•Store fat-soluble vitamins
•Perform detoxification
•Produce ~900 ml bile per day

Yellow-green, alkaline solution containing
•Bile salts: cholesterol derivatives that function in fat emulsification and absorption
•Bilirubin: pigment formed from heme
•Cholesterol, neutral fats, phospholipids, and electrolytes

•Recycles bile salts
•Bile salts -> duodenum -> reabsorbed from ileum-> hepatic portal blood -> liver -> secreted into bile

Thin-walled muscular sac on the ventral surface of the liver
•Stores and concentrates bile by absorbing its water and ions
•Releases bile via the cystic duct, which flows into the bile duct

•Mostly retroperitoneal, deep to the greater curvature of the stomach
•Head is encircled by the duodenum; tail abuts the spleen

Pancreatic islets secrete insulin and glucagon

•Acini (clusters of secretory cells) secrete pancreatic juice
•Zymogen granules of secretory cells contain digestive enzymes

Watery alkaline solution (pH 8) neutralizes chyme
•Electrolytes (primarily HCO3–)
•Enzymes
•Amylase
•Lipases
•Nucleases (ribonuclease, deoxyribonuclease)
•Proteases (peptidases, trypsin, chymotrypsin)

•Bile salts in enterohepatic circulation
•Secretin from intestinal cells exposed to HCl and fatty chyme

•Cholecystokinin (CCK) from intestinal cells exposed to proteins and fat in chyme
•Vagal stimulation (minor stimulus)

relax

enzyme-rich pancreatic juice by acini

bicarbonate-rich pancreatic juice by duct cells

pancreatic juice (minor stimulus)

Partially digested carbohydrates and proteins
and Undigested fats

•Slow delivery of hypertonic chyme
•Delivery of bile, enzymes, and bicarbonate from the liver and pancreas
•Mixing

Initiated by intrinsic pacemaker cells
•Mixes and moves contents slowly and steadily toward the ileocecal valve
•Intensity is altered by long and short reflexes
• Wanes in the late intestinal (fasting) phase

•Initiated by motilin in the late intestinal phase
•Each wave starts distal to the previous (the migrating motility complex)
•Meal remnants, bacteria, and debris are moved to the large intestine

Unique features
•Teniae coli
•Three bands of longitudinal smooth muscle in the muscularis
•Haustra
•Pocketlike sacs caused by the tone of the teniae coli
•Epiploic appendages
•Fat-filled pouches of visceral peritoneum

•Cecum (pouch with attached vermiform appendix)
•Colon
•Rectum
•Anal canal

retroperitoneal

mesocolons (mesenteries)

Three rectal valves stop feces from being passed with gas

•The last segment of the large intestine

•Internal anal sphincter— smooth muscle
•External anal sphincter—skeletal muscle

•Mucosa of simple columnar epithelium except in the anal canal (stratified squamous)
•Abundant deep crypts with goblet cells
•Superficial venous plexuses of the anal canal form hemorrhoids if inflamed

•Enter from the small intestine or anus
•Colonize the colon
•Ferment indigestible carbohydrates
•Release irritating acids and gases
•Synthesize B complex vitamins (for cellular respiration) and vitamin K (for production of clotting proteins)

Vitamins, water, and electrolytes are reclaimed
•Compaction of feces occurs
•Major function is propulsion of feces toward the anus

no

•Slow segmenting movements
•Haustra sequentially contract in response to distension

•Initiated by presence of food in the stomach
•Activates three to four slow powerful peristaltic waves per day in the colon (mass movements)

Mass movements force feces into rectum
•Distension initiates spinal defecation reflex
•Parasympathetic signals
•Stimulate contraction of the sigmoid colon and rectum
•Relax the internal anal sphincter
•Conscious control allows relaxation of external anal sphincter

the small intestine

Salivary amylase, pancreatic amylase, and brush border enzymes of microvilli

•Enter the capillary beds in the villi
•Transported to the liver via the hepatic portal vein

pepsin in the stomach

•Trypsin, chymotrypsin, and carboxypeptidase

•Aminopeptidases, carboxypeptidases, and dipeptidases

•Enter the capillary beds in the villi
•Transported to the liver via the hepatic portal vein

•Pre-treatment—emulsification by bile salts
•Enzymes—pancreatic lipase
•Absorption of glycerol and short chain fatty acids
•Absorbed into the capillary blood in villi
•Transported via the hepatic portal vein
•Absorption of monoglycerides and fatty acids
•Cluster with bile salts and lecithin to form micelles
•Released by micelles to diffuse into epithelial cells
•Combine with proteins to form chylomicrons
•Enter lacteals and are transported to systemic circulation

•Enzymes
•Pancreatic ribonuclease and deoxyribonuclease
•Absorption
•Enter the capillary beds in the villi
•Transported to the liver via the hepatic portal vein

•Fat-soluble vitamins (A, D, E, and K) are carried by micelles and then diffuse into absorptive cells
•Water-soluble vitamins (vitamin C and B vitamins) are absorbed by diffusion or by passive or active transporters.
•Vitamin B12 binds with intrinsic factor, and is absorbed by endocytosis

•Vitamin K and B

Mostly along the length of small intestine
•Iron and calcium are absorbed in duodenum
•Na+ is coupled with absorption of glucose and amino acids
•Ionic iron is stored in mucosal cells with ferritin
•K+ diffuses in response to osmotic gradients
•Ca2+ absorption is regulated by vitamin D and parathyroid hormone (PTH)

•95% is absorbed in the small intestine by osmosis
•Net osmosis occurs whenever a concentration gradient is established by active transport of solutes
•Water uptake is coupled with solute uptake

•Anything that interferes with delivery of bile or pancreatic juice
•Damaged intestinal mucosa (e.g., bacterial infection)

•Gluten damages the intestinal villi and brush border
•Treated by eliminating gluten from the diet (all grains but rice and corn)

Gastroesophageal reflux disease (GERD) is a condition in which the stomach contents (food or liquid) leak backwards from the stomach into the esophagus (the tube from the mouth to the stomach). This action can irritate the esophagus, causing heartburn and other symptoms.

Hiatal hernia is a condition in which part of the stomach sticks upward into the chest, through an opening in the diaphragm. The diaphragm is the sheet of muscle that separates the chest from the abdomen.

A hiatal hernia occurs when a portion of the stomach prolapses through the diaphragmatic esophageal hiatus. Although the existence of hiatal hernia has been described in earlier medical literature, it has come under scrutiny only in the last century or so because of its association with gastroesophageal reflux disease (GERD) and its complications. There is also an association between obesity and the presence of hiatal hernia. By far, most hiatal hernias are asymptomatic and are discovered incidentally. On rare occasion, a life-threatening complication, such as gastric volvulus or strangulation, may present acutely.

(vomiting)

A gallstone is a crystalline concretion formed within the gallbladder by accretion of bile components. These calculi are formed in the gallbladder, but may pass distally into other parts of the biliary tract such as the cystic duct, common bile duct, pancreatic duct, or the ampulla of Vater.

Hepatitis is swelling and inflammation of the liver. It is not a condition, but is often used to refer to a viral infection of the liver.

Diverticulitis is small, bulging sacs or pouches of the inner lining of the intestine (diverticulosis) that become inflamed or infected. Most often, these pouches are in the large intestine (colon).

Irritable bowel syndrome (IBS) is a disorder that leads to abdominal pain and cramping, changes in bowel movements, and other symptoms.

IBS is not the same as inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis. In IBS, the structure of the bowel is not abnormal