exam 3 pt 2: digestive system

what are the two groups of organs that compose the digestive system?

• gastrointestinal (GI) tract: mouth, most of pharynx, esophagus, stomach, small intestine, and large intestine

• accessory digestive organs: teeth, tongue, salivary glands, liver, gallbladder, and pancreas

functions of the digestive system

1. ingestion

2. secretion of water, acid, buffers, and enzymes into lumen

3. mixing and propulsion

4. digestion

• mechanical digestion churns food

• chemical digestion through hydrolysis

5. absorption (passing into blood or lymph)

6. defecation (elimination of feces)

what are the layers of the GI tract?

muscularis and serosa

what consists of the muscularis?

• voluntary skeletal muscle found in mouth, pharynx, upper 2/3 of esophagus, and anal sphincter

• involuntary smooth muscle elsewhere

• arranged in inner circular fibers and outer longitudinal fibers

• myenteric plexus between muscle layers

what consists of the serosa?

• outermost covering of organs suspended in abdominopelvic cavity

• also called visceral peritoneum

• consists of areolar connective tissue and epithelium

what lacks serosa?

the esophagus lacks serosa. it has adventitia; it attaches to surroundings

characterize the enteric nervous system (ENS)

• “brain of gut”

• neurons extend from esophagus to anus

what are the two plexuses of the enteric nervous system (ENS)

• myenteric plexus - GI tract motility

• submucosal plexus - controlling secretions

role of autonomic nervous system in digestive system

• parasympathetic stimulation increases secretion and activity by stimulating ENS

• sympathetic stimulation decreases secretions and activity by inhibiting ENS

what is the largest serous membrane of the body? what is it divided into?

• peritoneum

divided into:

• parietal peritoneum – lines wall of cavity

• visceral peritoneum – covers some organs (also called called serosa)

• space between is peritoneal cavity

what are the five major peritoneal folds? function?

• greater omentum, falciform ligament, lesser omentum, mesentery, and mesocolon

• weave between viscera binding organs together

what is the mouth called? what is it formed by?

• oral or buccal cavity

• formed by cheeks, hard and soft palates, and tongue

what is the oral cavity proper?

space that extends from gums and teeth to fauces (opening between oral cavity and oropharynx)

what are the three pairs of major salivary glands that secrete most of the saliva?

• parotid

• submandibular

• sublingual

characterize saliva

• mostly water (99.5%)

• 0.5% solutes such as lysozyme, salivary amylase, and immunoglobulin

• not all salivary gland produce the same saliva

what controls salivation?

• the autonomic nervous system

• parasympathetic promotes secretion of moderate amount of saliva

• sympathetic decreases salivation

what is the tongue considered to be? what covers it? its function? its glands function?

• an accessory digestive organ

• mucous membrane covers skeletal muscle

• maneuvers food for chewing, shapes mass, and forces food back for swallowing

• lingual glands secret salivary lipase

what is the tongue considered to be? what are the major structures?

• an accessory digestive organ

• three major regions include crown, root, and neck

• dentin of crown covered by enamel

• two dentitions include deciduous and permanent teeth

what does mechanical digestion in the mouth involve?

• chewing or mastication

• food manipulated by tongue, ground by teeth, and mixed with saliva

• forms bolus

what does chemical digestion in the mouth involve?

• secreted salivary amylase acts on starches

• only monosaccharides can be absorbed

• salivary amylase acts until inactivated by stomach acid

what acts on triglycerides? how does it become activated?

• lingual lipase secreted by lingual glands

• activated in acidic environment of stomach

• triglycerides are digested into fatty acids and diglycerides

what are the three parts of the pharynx? what are their functions?

• nasopharynx = respiration

• oropharynx = digestive and respiratory functions

• laryngopharynx = digestive and respiratory functions

function of the esophagus

secretes mucous and transports food

function of mucosa

protect against wear and tear

what is the muscularis of the esophagus divided into?

divided into thirds

• superior 1/3 skeletal muscle

• middle 1/3 skeletal and smooth muscle

• inferior 1/3 smooth muscle

what are the two sphincters of the esophagus and their function?

• upper esophageal sphincter (UES) - regulates movement into esophagus

• lower esophageal sphincter (LES) - regulates movement into stomach

what epithelium lines the esophagus?

non-keratinized stratified squamous epithelium

what are the three stages of deglutition (swallowing)? describe them

• voluntary - bolus passed to oropharynx

• pharyngeal – involuntary passage through pharynx into esophagus

• esophageal – involuntary passage through esophagus to stomach

what pushes bolus foward?

peristalsis (wave like muscular contraction and relaxation)

function of the stomach

serves as mixing chamber and holding reservoir

what are the four main regions of the stomach

• cardia

• fundus

• body

• pylorus

what are the three types of exocrine gland cells of the stomach?

• mucous neck cells (mucus)

• parietal cells (intrinsic factoe and HCl)

• chief cells (pepsinogen and gastric lipase)

what is the G cell of the stomach? its function?

• endocrine cell

• secretes gastrin

what is chyme? what creates creates it?

• partly digested food mixed with gastric juices

• gentle, rippling peristaltic movements

what do parietal cells secrete?

• H+ and Cl- separately which form HCl

• kill many microbes and denature proteins

what is pepsin secreted by? what is it secreted as?

• chief cells that digest proteins

• secreted by pepsinogen

function of gastric lipase

split triglycerides into fatty acids and monoglycerides

where is pancreatic juice secreted?

into pancreatic duct, accessory duct, and small intestine

what does the pancreatic duct join?

joins common bile duct and enters duodenum at hepatopancreatic ampulla

describe pancreatic cells and their function

99% are acini (exocrine)

• secrete pancreatic juice which is a mixture of fluid and digestive enzymes

1% are pancreatic islets (islets of Langerhans) and are endocrine

• secrete hormones such as insulin and glucagon

how much pancreatic juice is produced daily? what is pancreatic juice made of?

• 1200-1500ml daily

• mostly water followed by sodium bicarbonate that buffers acidic stomach enzyme, and pancreatic enzymes (amylase, lipase, etc.)

what is the heaviest gland of the body?

the liver

what are the major functional cells of the liver? their function?

• hepatocytes

• secrete bile and do a wide variety of metabolic, secretory, and endocrine functions

what are bile canaliculi? what does it form?

• ducts between hepatocytes that collect bile

• exists liver as common hepatic duct then forms common bile duct by joining cystic duct from gallbladder

what are hepatic sinusoids?

highly permeable blood capillaries receiving oxygenated blood from hepatic artery and deoxygenated nutrient-rich blood from hepatic portal vein

what is the hepatic acinus?

the functional, diamond-shaped unit of the liver that models blood flow, oxygen gradients, and metabolism

what causes the gallbladder to eject its contents?

the contraction of smooth muscle fibers eject gallbladder contents into cystic duct

function of gallbladder

• store and concentrate bile produced by liver until need by small intestine

• absorb water and ions to concentrate bile

hepatic blood flow

liver receives blood from hepatic artery and hepatic vein

• hepatic artery carrying oxygenated blood

• hepatic portal vein carrying deoxygenated blood with newly absorbed nutrients and possibly drugs, microbes or toxins from GI tract

how much bile do hepatocytes secrete daily?

800-1000mL of bile consisting of water, bile salts, cholesterol, and other substances

what is bilirubin?

• principle bile pigment

• derived from heme of recycled red blood cells

what gives feces brown color?

the breakdown product of bilirubin called stercobilin

role of bile salts

• emulsification

• absorption of lipids following digestion

what are the three regions of the small intestine?

• duodenum

• jejunum

• ileum

what is in the mucosa of the small intestine?

• absorptive cells (digest and absorb)

• goblet cells (mucus)

• intestinal glands (intestinal juice)

• Paneth cells (lysozyme)

• enteroendocrine cells

what is in the submucosa of the small intestine?

duodenal glands secrete alkaline mucus

what is MALT and where can it be found

• Mucosa-Associated Lymphoid Tissue (MALT) is in small intestine

• primarily as part of the body's immune defense system

what does the serosa in the small intestine NOT cover?

major portion of duodenum

what are circular folds? their function?

• permanent ridges of mucosa and submucosa

• cause chyme to spiral

what are villi? what do they contain?

• fingerlike projections of mucosa

• contains arteriole, venule, blood capillary, and lacteal

what are microvilli? what are their function?

• projects of apical membrane of absorptive cells

• brush border with brush border enzymes

how much intestinal juice is produced daily? what does it contain? what is its function?