BIO 202: Chapter 7 and 8 Digestive System, Metabolism, and Nutrition

oral cavity → pharynx → esophagus → stomach → small intestine → large intestine

passage of food through the main regions

accessory structures of GI tract

assist with mechanical processing and chemical digestion but do not form part of the continous food pathway

teeth

break down food into smaller pieces through chewing/mastication and increasing surface area for enzymatic action

tongue

muscular manipulator of food that positions and moves food for chewing, assists with swallowing, and contains taste receptors that initiate digestive reflexes

• body: anterior 2/3 in the oral cavity

• root: posterior 1/3 in the oropharynx 

salivary glands

exocrine glands that produce saliva containing enzymes begin the breakdown of carbohydrates and moisten food for easier swallowing 

amylase

enzyme that begins the chemical breakdown of carbohydrates in the mouth

liver

largest exocrine gland in the body

• produces 500-1000 mL/day of bile to emulsify fats for easier digestion and absorption

• nutrient storage of glycogen, vitamins, and minerals

• detoxifies toxins, drugs, and alcohol  

falciform ligament

suspends liver from diaphragm and anterior abdominal wall

• separates right and left lobes of the liver

ligamentum teres

remnant of fetal umbilical vein

coronary ligaments

attach superior liver to diaphragm and define the bare area of the liver

right and left triangular ligaments

formed by meeting of anterior and posterior coronary ligament layers

• help stabilize the liver laterally

common bile duct

transports bile from the liver and gallbladder to the duodenum

gallbladder

stores and releases bile into the small intestine when needed for fat digestion into:

• cystic duct → common bile duct → duodenum 

gallstones

hardened deposits of cholesterol, bile salts, or bilirubin

• can block ducts and cause abdominal pain, nausea, or jaundice

pancreas

endocrine glands that produces digestive enzymes and bicarbonate to neutralize stomach acid to aid chemical digestion in the small intestine 

pancreatic amylase

breaks carbohydrates/starch into maltose and smaller carbohydrates 

pancreatic lipase

breaks triglycerides into glycerol and free fatty acids 

zymogens

inactive enzyme precursors that must be activated after reaching their target site in the small intestine

• includes trypsinogen, chymotrypsinogen, and procarboxypeptidase

trypsinogen

activated by enteropeptidase in the duodenum to trypsin

• breaks proteins into smaller peptides and amino acids 

chymotrypsinogen

activated by trypsin to chymotrypsin

• breaks proteins into smaller peptides and amino acids 

procarboxypeptidase

activated by trypsin to carboxypeptidase

• breaks proteins into smaller peptides and amino acids 

main pancreatic duct

merges with the common bile duct at the h

abdominal cavity

largest hollow space in the body that houses most of the digestive organs, along with parts of the urinary and lymphatic systems

peritoneal cavity

smaller, specialized potential space within the abdominal cavity

• lies between two layers of the peritoneum

peritoneum 

thin, continuous serous membrane that protects and stabilizes the abdominal organs

• has two layers

parietal peritoneum

lines the inside of the abdominal and pelvic walls

visceral peritoneum

covers the surfaces of most abdominal organs

peritoneal space

space between the parietal and visceral peritoneum

• contains small amount of peritoneal fluid

peritoneal fluid

reduces friction and allows organs to move smoothly during digestion and breathing

ascites

excess fluid in the peritoneal space which may result from liver disease, infection, cancer, or trauma

• can be removed through paracentesis

mesentery

double layer of visceral peritoneum that folds over to suspend and anchor certain abdominal organs 

• holds organs in place during movement 

• provides pathway for blood vessels, lymphatics, and nerves

• stores fat and limits spread of infection 

greater omentum

drapes over the abdominal organs

lesser omentum

connects the liver to the stomach and duodenum

mesocolon

anchors parts of the large intestine including the transverse mesocolon and sigmoid mesocolon

intraperitoneal

organs completely enclosed by visceral peritoneum and suspended within the peritoneal cavity by mesenteries

• includes the stomach, spleen, liver, first inch of duodenum, jejunum, ileum, transverse colon, and sigmoid colon

retroperitoneal

organs located behind the peritoneal cavity with only part of their surface covered by peritoneum

• includes the remaining parts of the duodenum, cecum, ascending colon, descending colon, and pancreas

mucosa

deepest layer of the alimentary canal that contains epithelial tissue and directly contacts food and other materials entering the tract

• contains goblet cells that produce mucus

• close to layer of MALT

• surrounds the lumen

lamina propia

beneath the epithelium, layer of loose connective tissue that contains blood vessels, lymphatic vessels, and immune cells

• supports the epithelium, nourishes it, and plays role in immune defense

submucosa

second principal layer of the alimentary canal that is composed of dense connective tissue

• contains lymph vessels, blood vessels, nerves, and elastic fibers for structural support and flexibility

muscularis externa

consists of two muscle layers in the intestines and three layers in the stomach

• skeletal or smooth muscle depending on the region

• responsible for moving materials down the tract by ryhthmic contractions called peristalsis

serosa

most superficial layer of the alimentary canal

• consists of visceral peritoneum which encapsulates and protects the organs

oral cavity

region around the mouth, including the teeth, tongue, and salivary glands

cheeks and lips

keep food between teeth for chewing and are important for speech and suckling in infants

vestibule

space between the teeth and cheeks where the gingivae (gums) are located

lips

mark the transition between the skin-colored cutaneous region and the red vermilion area

frenulum

midline structures that anchor specific parts of the mouth

• superior labial frenulum: anchors the upper lip

• inferior labial frenulum: anchors the lower lip

• lingual frenulum: anchors the tongue

hard palate

roof of the oral cavity that is formed by the palatine bones and the palatine processes of the maxillae

soft palate

muscular region posterior to the hard palate

uvula

hangs from the soft palate and prevents food from entering the nasal cavity during swallowing

adult dentition

32 teeth total

• 4 incisors: cutting

• 2 canines: puncturing and shredding

• 4 premolars: crushing and grinding

• 6 molars: crushing and grinding

deciduous dentition

20 teeth total

• 4 incisors: cutting

• 2 canines: tearing

• 4 molars: grinding

bolus

food becomes this once it has been mechanically broken down by chewing, mixed with saliva, and formed into a soft mass in the mouth

filiform papillae

rough surface that aids in food breakdown and has NO taste function

circumvallate papillae

large, arranged in a V formation on the dorsal tongue, and contains taste buds

foliate papillae

located on the lateral sides of the tongue and contain taste buds

fungiform papillae

mushroom-shaped on the dorsal surface and contain taste buds

taste buds

found mainly on the papillae of the tongue but also on the soft palate, pharynx, and epiglottis and function to send signals to brain through specific cranial nerves to allow for the perception of taste

• contain gustatory cells that detect chemicals dissolved in saliva

• sweet, sour, salty, bitter, and umami

facial nerve (CN VII)

carries taste sensation from the anterior 2/3 of the tongue

glossopharyngeal nerve (CN IX)

carries taste sensations from the posterior 1/3 of the tongue

vagus nerve (CN X)

carries taste sensations from the soft palate, pharynx, and epiglottis

intrinsic salivary glands

located beneath the mucous membrane inside the mouth

• secrete saliva at a constant low rate to prevent drying of the oral mucosa 

• includes labial, buccal, palatine, and lingual glands 

labial glands

intrinsic salivary glands found in the lips

buccal glands

intrinsic salivary glands found in the cheeks

palatine glands

intrinsic salivary glands found in the palate

lingual glands

intrinsic salivary glands found in the tongue

extrinsic salivary glands

large and discrete organs located outside the oral mucosa 

• connected to the oral cavity by ducts

• includes the paired parotid, submandibular, and sublingual glands 

parotid glands

connected by the parotid ducts and located superficial to the masseter muscle

submandibular glands

connected by submandibular ducts and located below the mylohyoid muscle in the mandible

sublingual glands

connected by the sublingual ducts and located beneath the tongue and floor of the mouth 

pharynx

shared passageway for food and air

• deep and superficial layers of skeletal muscle contract to push bolus down

esophagus

straight, muscular tube that transports the bolus from the pharynx to the stomach and passes through the diaphragm at the esophageal hiatus 

• mucosa lined with non-keratinized stratified squamous epithelium 

• submucosa with esophageal glands that secrete mucus

muscularis externa

• upper 1/3: skeletal muscle

• middle 1/3: combination of skeletal and smooth muscle

• lower 1/3: smooth muscle only

stomach

J-shaped organ that receives the bolus from the esophagus and functions to mechanically and enzymatically break down food

mechanical digestion

churning motions that mix food with gastric secretions

chemical digestion

enzymes like proteases break down proteins and lipases break down fats

true

true or false: the stomach does not absorb significant nutrients but it can absorb certain substances like aspirin and lipid-soluble drugs

cardiac region

small area near the lower esophageal sphincter where food enters

• contains mucous cells that secrete protective mucus to shield the esophagus-stomach junction from acid

gastric fundus

dome-shaped area of the stomach that lies superior to the lower esophageal sphincter and contains majority of gastric glands, which include … 

• mucous neck cells, parietal cells, chief cells, and stem cells 

mucous neck cells

secrete mucus for protection and lubrication

parietal cells

secrete hydrochloric acid for protein digestions and intrinsic factor for vitamin B12 absorption in the small intestine

pernicious anemia

condition where vitamin B12 deficiency results in abnormally large, immature red blood cells 

chief cells

secrete pepsinogen and gastric lipase for protein and fat digestion

stem cells

replace damaged epithelial cells

gastric region

largest and main portion of the stomach

• shared the same cells types and functions as the gastric fundus

pyloric region

narrow, distal portion of the stomach that is lined with mucous cells for protection

• subdivided into pyloric antrum, pylorus, and pyloric sphincter 

pyloric region

funnel-like passage leading toward the pylorus

pylorus

narrow terminal portion of the stomach

pyloric sphincter

ring of smooth muscle at the end of the pylorus that regulates the flow of chyme into the duodenum 

• also called the gastroduodenal sphincter 

greater curvature

inferolateral margin of the stomach that is attached to the greater omentum

lesser curvature

superomedial margin of the stomach that is attached to the liver via the lesser omentum

gastric rugae

internal folds of the mucosa that allow the stomach to expand when filled and return to its smaller size when empty 

stomach sounds

caused by the movement of gas and fluid within the stomach and intestines during digestion but can also occur when the stomach is empty as muscles contract in anticipation of food

• often called borborygmi

mucosa of the stomach

lumen is lined with simple columnar glandular epithelium

• gastric pits: indented regions in mucosa that lead to gastric glands

• goblet cells: secrete mucus to further protect lining

muscularis externa of the stomach 

three layers of smooth muscle oriented at different angles to maximize churning efficiency to enhance mechanical breakdown of food and aid in mixing 

• longitudinal layer

• circular layer

• oblique layer 

small intestine

coiled mass that fills most of the abdominal cavity and is the primary site that maximizes surface area for digestion and nutrient absorption

• divided into duodenum, jejunum, and ileum

circular folds of small intestine

large transverse ridges in the mucosa and submucosa that slow the movement of chyme, increasing contact time for absorption

villi

finger-like projections extending from circular fold of the small intestine

• lines with enterocytes specialized for absorption

• capillary network absorbs amino acids, sugars, and water-soluble nutrients

• lacteals absorb fats and lipid-soluble vitamins 

microvilli

microscopic projections from the apical surface of enterocytes 

• further increase surface area and contain enzymes for chemical digestion

• form the intestinal brush border with enterocytes 

intestinal crypts

deep pits extending downward from base of the villi into the mucosa that contain…

• absorptive cells: take in digested nutrients

• goblet cells: produce mucus

• stem cells: replace shed epithelial cells

• paneth cells: secrete lysozyme to protect against bacterial infection

duodenum

receives stomach contents, pancreatic juice, and bile

• 10 inches long and means “twelve fingers”

• neutralizes stomach acid, emulsifies fats, inactivates pensin, activates pancreatic enzymes, and regulates stomach emptying