Digestive System

Alimentary canal (gastrointestinal tract)

one long continuous tube from the mouth to the anus

Accessory digestive organs

provide chewing, enzymes and buffers that assist in mechanical and chemical breakdown of food

Ingestion

taking in food and water via the mouth

Propulsion

movement of food/water by swallowing or peristalsis

Mechanical Breakdown

increases surface area of food, preparing for chemical digestion by enzymes

Digestion

enzymes secreted into lumen break food into chemical building blocks

Absorption

movement of nutrients from lumen to blood or lymph

Defecation

elimination of solid waste; indigestible substances and metabolic wastes

Motility

moves food in an aboral direction and facilitates mixing

Aboral

Peristalsis

mostly proposive (forward) movement

Segmentation

mostly for mixing and mechanical breakdown

Peritoneum (parietal and visceral layers)

serous membrane of the abdominal cavity; visceral lines the organs (inner layer), parietal lines the abdominal wall

Intraperitoneal

organs are surrounded or suspended by peritoneum; can move freely for the most part

Retroperitoneal

lies posterior to the peritoneum; glued to the wall, cannot move

Peritoneal cavity

fluid filled potential space between the peritoneal layers (sterile space)

Mesentery

folds of peritoneum that suspend organs in the abdomen

Greater and lesser omentum

mesentery sheets that attach to the stomach

Serosa

only visceral peritoneum; areolar connective tissue with mesothelium

Adventitia

if no peritoneum; dense connective tissue

Enteric nervous system

consists of neurons in the wall of the gut involved in local reflexes; respond to stimuli within the GI tract and mediate short reflexes that regulate digestive system activity

Myenteric nerve plexus

between layers in muscularis externa

Submucosal nerve plexus

in the submucosa layer

Enteroendocrine cells

hormone producing cells within the gut wall; hormones released into interstitial fluid and then enter the blood and enter target cells within organs

Oral Cavity

performs ingestion, mechanical breakdown, digestion and propulsion

Tonsils

palatine and lingual tonsils provide immune defenses

Palate : hard and soft

hard palate towards the front of the mouth, soft more posterior and into the throat

Uvula

continuation of the most midline part of the soft palate

Bolus

mixed food and saliva

Papillae with taste buds

elevated tissue that contain indentations into the epithelium where taste buds are found; when food mixes with saliva it flows into these crevices and can be sensed with the taste buds

Oropharynx

portion of the pharynx behind the oral cavity; stratified squamous epithelium

Laryngopharynx

portion of the pharynx behind the larynx; stratified squamous epithelium

Esophagus

tube that carries food from the pharynx to the stomach; nonkeratinized stratified squamous epithelium; muscularis externa is pretty thick to move big chunks of food

Upper Esophageal sphincter

skeletal muscle, prevents passage of air into the esophagus while breathing

Lower Esophageal sphincter

smooth muscle, prevents reflux of stomach contents into the esophagus, thickening of smooth muscle that is reinforced by the diaphragm

GERD

acid reflex from stomach inflames epithelium and esophagus wall

Achalasia

difficulty opening LES sphincter, or weakening of peristalsis

Deglutition

process of swallowing

Dysphasia

difficulty swallowing; can be due to nervous system or muscular system tissue

Stomach

j shaped temporary storage tank that aids in chemical and mechanical digestion and propulsion of food; holds roughly 1 gallon of food

Rugae

longitudinal folds in the wall that allow for expansion

Pyloric sphincter

controls entry of chyme into the small intestine

Chyme

food that’s been broken down mechanically (churning) and chemically (acid/enzymes) in the stomach

Mucous cell

secrete mucous and bicarbonate; act as a protective barrier

Parietal cell

secretes intrinsic factor and produce HCl creating the acidic environment

Intrinsic factor

allows vit B12 absorption in small intestines

Hydrochloric acid

denatures proteins, breaks down cell walls of plant foods, kill bacteria and microorganisms, activation of pepsinogen to pepsin

Chief cells

secrete pepsinogen and gastric lipase

Pepsinogen

inactive form of protease pepsin (digests proteins)

Enteroendocrine cell

secretes hormones into the blood; senses food in the lumen, secrete chemical messengers into interstitial fluid where they act as paracrine or hormone signals

G cells

secrete gastrin into bloodstream

Gastrin

stimulates HCl production and motility

Gastric Ulcer

caused by the disruption of mucous barriers in the stomach, can damage organ wall and lead to perforation, peritonitis or hemorrhage; most caused by H. pylori bacteria

Gastric motility

includes propulsion and mechanical breakdown;

Liver lobule

structural and functional unit of the liver

Hepatocytes

produce and secrete bile, process nutrients, store fat soluble vitamins, detoxify blood, store glucose as glycogen, build amino acids into proteins

Portal triad

contains hepatic artery, hepatic vein, and bile duct

Portal Vein

delivers low oxygen but nutrient rich blood to the liver from the digestive organs; blood leaving the liver through the portal vein flows to the inferior vena cava

Bile Duct

bile flows from the liver through this to the intestines and excess bile backs up into the gall bladder

Bile

contains bile salts, bilirubin, phospholipids, and cholesterol; produced in the liver, stored in the gallbladder, used in the small intestine to emulsify fats

Gallbladder

stores and concentrates bile that is produced in the liver

Exocrine pancreas

composed of pancreatic acini and ducts that secrete digestive enzymes and pancreatic juice

Acini

clusters of secretory acinar cells that secrete digestive enzymes into ducts

Zymogen

inactive forms of digestive enzymes that are typically activated in the small intestine

Protease

digests proteins

Amylase

digests starch

Lipase

digests fat

Nuclease

digests nucleic acids

Pancreatic duct

provide transport for acinar cell secretions

Hepatopancreatic sphincter

valve opening at the small intestine that allows contents from the liver, gallbladder and pancreas into the duodenum

Cholecystokinin (CCK)

release is stimulated by proteins and fats in chyme; causes acinar cells to secrete enzymes into pancreatic ducts, causes smooth muscle contraction in the gallbladder wall, causes relaxation of the sphincter allowing materials to enter the small intestine

Secretin

release is stimulated by acidic chyme; causes pancreatic duct cells to secrete bicarbonate buffer into ducts, weak stimulus for bile production and release from the liver

Gallstones

formed from precipitates of bile solutes as bile is concentrated in the gallbladder; pain in URQ or referred to shoulder, can block common bile duct/cystic duct/pancreatic duct causing pancreatitis

Enteropeptidase

an enzyme attached to the apical surface of the small intestine epithelial cells that activates trypsinogen

Trypsin

activated trypsinogen that can then activate of zymogens

Duodenum

first 12 inches of small intestine, most digestion occurs here, secretions neutralize the acidic chyme

Jejunum

middle section 8 ft long, lots of absorption occurs here

Ileum

final portion 12 ft long, absorption of vit B12 and bile salts,

Circular folds

extensions of mucosa and submucosa into the lumen to increase surface area for absorption, visible to the naked eye

Villi

finger like projections of the mucosa into the lumen to increase surface area, contain blood and lymph capillaries that collect the absorbed material

Lacteals

lymph capillaries

Microvilli

apical surface extensions off of individual absorptive cells containing transport proteins and brush border enzymes that complete carb and proteins digestion

Brush border

microvilli make the apical surface of enterocytes appear fuzzy

Enterocytes

absorptive cells of the small intestine; form the bulk of the epithelium, simple columnar cells with microvilli bound by tight junctions

Goblets cells

mucous secreting cells

Enteroendocrine cells

secrete hormones like CCK and secretin, sense food in the lumen

Paneth cells

release antimicrobial agents determining which bacteria can colonize the intestines

Stem cells

continuously divide with daughter cells differentiating into 4 other cells

Cecum

first part of the large intestine in the RLQ

Ascending colon

part of the intestine that travels up into the RUQ

Transverse colon

the horizontal portion that travels from RUQ to LUQ

Descending colon

the descending portion that travels to the LLQ

Sigmoid colon

travels over the pelvis and attaches to the rectum and anal canal

Rectum

last section of large intestine before the anal canal

Anal canal and anus

about 3 cm long, lined by stratified squamous epithelium that merges with surrounding skin

Teniae coli

longitudinal layer of muscularis reduced to 3 strips

Haustra

pockets in the wall due to smooth muscle tone

Appendix

worm like appendage that contains immune cells and stores bacteria to recolonize gut

Appendicitis

inflammation of appendix; risk of rupture and bacterial spread throughout peritoneal cavity

Ileocecal valve

prevents the backflow of chyme into the small intestine