there are two groups of organs in the digestive system - what are they

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

what are the organs of the alimentary canal

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

what is the function of the alimentary canal

to digest and absorb food

what are the accessory digestive organs

teeth tongue gallbladder salivary glands liver and pancreas

the digestive process contain 6 activities - what are they

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

desribe peristalsis

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

describe segmentation

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

what is deglutition

swallowing

what is the Peritoneum

serous membrane of the abdominal cavity

where is the Visceral peritoneum

on external surface of most digestive organs

where is the Parietal peritoneum

lines the body wall

where is the Peritoneal cavity and what is its function

found Between the two peritoneums
the Fluid lubricates mobile organs

what is the Mesentery and what is its function

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

where are the Retroperitoneal organs found

lie posterior to the peritoneum

Intraperitoneal (peritoneal) organs are
surrounded by what

the peritoneum

what are the Arteries of the splanchinic circulation

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

What is the function of the arteries of the splanchnic circulation

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

What are the four basic layers of the alimentary canal

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

the mucosa is found where

Lines the lumen

what is the function of the mucosa

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

what are the sublayers of the mucosa

Three sublayers: epithelium, lamina propria,
and muscularis mucosae

where is Stratified squamous epithelium found

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

where is Simple columnar epithelium found, and what are some of its functions

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)

what is the Lamina propria composed of

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

what is the Muscularis mucosae composed of and what is its function

smooth muscle that produces local movements
of mucosa

what is the Submucosa composed of

• 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

what is the function of the Submucosa

Responsible for segmentation and peristalsis

Visceral peritoneum is Replaced by what in the esophagus

the fibrous adventitia

•Retroperitoneal organs have both an ___ and a ____

an adventitia and serosa

describe the enteric nervous system

•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

the mouth is also known as

Oral (buccal) cavity

the mouth is bound by what organs

•Bounded by lips, cheeks, palate, and tongue

what type of epethelium lines the mouth

•Lined with stratified squamous epithelium

what muscles are found in the area of the mouth

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

describe the Hard palate

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

describe the Soft palate

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

what is the purpose of the Tongue

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

where are the Extrinsic salivary glands located

(parotid, submandibular, and sublingual)

where are the intrinsic (buccal) salivary glands located

they are scattered in the oral mucosa

what is the function of saliva

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

from where is saliva secreted

Secreted by serous and mucous cells

what is saliva composed of

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

which glands continuously keep the mouth moist

Intrinsic glands

Extrinsic salivary glands produce secretions when

Ingested food stimulates chemoreceptors and mechanoreceptors in the mouth

•Salivatory nuclei in the brain stem send impulses where

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

Primary and permanent dentitions are formed by what age

21

some details about teeth

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

what is the function of the Incisors

•Chisel shaped for cutting

what is the function of the canines

they are Fanglike teeth that tear or pierce

describe Premolars (bicuspids) and molars

Have broad crowns with rounded cusps for grinding or crushing

describe the structure of the tooth

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

what are Dental caries

(cavities): gradual demineralization of enamel and dentin

how are cavities formed

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

how can one prevent cavities

•Prevention: daily flossing and brushing

what is Gingivitis

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

describe Periodontitis

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

what are the consequences of Periodontitis

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

what is the function of the Oropharynx and laryngopharynx

•Allow passage of food, fluids, and air

what are the Oropharynx and laryngopharynx composed of

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

describe the esophagus

•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

what is the function of the mouth (digestion)

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

describe 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

where is the cardiac region located in the Stomach

the Cardiac region (cardia)Surrounds the cardiac orifice

where is the fundus of the stomach located

Dome-shaped region beneath the diaphragm

where is the body of the stomach

Midportion

where is the Pyloric region (antrum, pyloric canal, and pylorus)

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

where is the Greater curvature of the stomach

convex lateral surface

where is the Lesser curvature of the stomach

Concave medial surface

where is the Lesser omentum

From the liver to the lesser curvature

where is the Greater omentum located

•Drapes from greater curvature
•Anterior to the small intestine

describe the ANS nerve supply

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

describe the Blood supply of the stomach

•Celiac trunk
•Veins of the hepatic portal system

how many layers (tunics) are there in the stomach

Four tunics

the muscularis externa contains 3 layers of smooth muscle, describe the function

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

the mucosa of the stomach is composed of what type of epithelium

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

what are the cell types in the gastric glands and what are thier functions

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

where is most of the gastric juice produced

Glands in the fundus and body

one of the Parietal cell secretions is HCl
what is its function

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

what is Intrinsic factor

•Glycoprotein required for absorption of vitamin B12 in small intestine

Chief cell secretions

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

•Enteroendocrine cells

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

•Pepsin is responsible for what

protein digestion

Somatostatin does what

inhibits gastric secretion

gastrin does what

increase HCl secretion

describe the Mucosal Barrier

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

what is Gastritis:

inflammation caused by anything that breaches the mucosal barrier

what are Peptic or gastric ulcers:

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

what are the Digestive Processes in the Stomach

•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

Regulation of Gastric Secretion occur through what sort of mechanisms

Neural and hormonal mechanisms

•Stimulatory and inhibitory events occur in three phases what are they

1.Cephalic
2.Gastric phase
3.Intestinal phase

describe the cephalic phase

few minutes prior to food entry

describe the Gastric phase

3–4 hours after food enters the stomach

describe the Intestinal phase

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

•Peristaltic waves move toward the pylorus at the rate of what

3 per minute

•Chyme is either Delivered in ~____spurts to the _______, or __________

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

•Carbohydrate-rich _____ moves quickly through the _________

chyme duodenum

•Fatty chyme remains in the duodenum for how long

6 hours or more

what is the Major organ of digestion and absorption

the small intestine

describe the small intestine

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

what are the 3 Subdivisions of the small intestine

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

The bile duct and main pancreatic duct join where

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

what are some of the Structural Modifications of the duodenum

•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

describe the villi of the duodenum

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

describe the Microvilli of the duodenum

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

explain the Intestinal crypt epithelium

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

describe Paneth cells

•Secrete antimicrobial agents (defensins and lysozyme)

what other cells are found in the intestinal crypts

•Stem cells

where are peyers patches found and what do they do

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

what do the Duodenal (Brunner’s) glands of the duodenum do

secrete alkaline mucus

describe intestinal juice and its functions

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

what is the largest gland in the body

the liver

describe the liver

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

what is the function of the Falciform ligament

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

what is the •Round ligament (ligamentum teres)

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

what is the function of the Lesser omentum

it anchors liver to stomach

what are the blood vessels associated with the liver

Hepatic artery and vein at the porta hepatis

what are the Bile ducts and where are they located

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

how is the Bile duct formed

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

what are teh function of the liver Hepatocyte functions

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

describe bile

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

what is the purpose of Enterohepatic circulation

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

what is the gallbladder, where is it located and what is its function

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

what is the location of the pancreas

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

what is the endocrine function of the pancreas

Pancreatic islets secrete insulin and glucagon

what is the exocrine function of the pancreas

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

describe the compostition of pancreatic juice

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

Bile secretion is stimulated by

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

•Gallbladder contraction is stimulated by

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

•CKK also causes the hepatopancreatic sphincter to do what

relax

CCK induces the secretion of what

enzyme-rich pancreatic juice by acini

•Secretin causes secretion of what

bicarbonate-rich pancreatic juice by duct cells

•Vagal stimulation also causes release of what

pancreatic juice (minor stimulus)

Chyme from stomach contains

Partially digested carbohydrates and proteins
and Undigested fats

what are the Requirements for Digestion and Absorption in the Small Intestine

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

Motility of the Small Intestine is caused by Segmentation describe

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

describe Peristalsis

•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

what are the unique features of 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

what are the Regions of the large intestine

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

Ascending colon and descending colon are (location)

retroperitoneal

Transverse colon and sigmoid colon are anchored via

mesocolons (mesenteries)

describe the Rectum

Three rectal valves stop feces from being passed with gas

the Anal canal is what

•The last segment of the large intestine

what are the Sphincters of the anal canal

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

describe the Large Intestine: Microscopic Anatomy

•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

Bacterial Flora enter from where, and do what

•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)

what is the function of the large intestine

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

is the colon essential for life

no

what are Haustral contractions

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

what is Gastrocolic reflex

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

describe defecation

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

Chemical Digestion and Absorption of Carbohydrates occurs where

the small intestine

Digestive enzymes are

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

describe Absorption

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

Chemical Digestion and Absorption of Proteins
•Enzymes:

pepsin in the stomach

•Pancreatic proteases are

•Trypsin, chymotrypsin, and carboxypeptidase

•Brush border enzymes are

•Aminopeptidases, carboxypeptidases, and dipeptidases

chemical digestion and absorption of proteins

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

Chemical Digestion and Absorption of Lipids

•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

Chemical Digestion and Absorption of Nucleic Acids

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

Vitamin Absorption In small intestine

•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 Absorption In large intestine

•Vitamin K and B

Electrolyte Absorption occurs where

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)

Water Absorption

•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

Malabsorption of Nutrients
•Causes

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

what is Gluten-sensitive enteropathy (celiac disease)

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

GERD (heartburn)

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

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.

•gastric ulcers (Helicobacter pylori)

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.

emesis

(vomiting)

•Gallstones

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

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

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

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