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Alimentary canal (in order)

Oral cavity → pharynx → esophagus → stomach → small intestine → large intestine → rectum → anal canal.

Accessory digestive organs

Tongue, teeth, salivary glands, liver, gallbladder, pancreas.

Digestive system functions

Ingestion, digestion, absorption, and elimination.

Digestion

Breakdown of nutrients into absorbable molecules.

OUTSIDE THE BODY

Tongue functions

Manipulates food, assists swallowing and speech.

Tongue epithelium

Stratified squamous; keratinized anteriorly and moist posteriorly.
MUCOSA IS MODIFIED WITH PAPILLAE

Filiform papillae

Manipulate food; lack taste buds.

Fungiform papillae

Located among filiform papillae; contain some taste buds.

Circumvallate papillae

Large papillae surrounded by grooves; taste buds on lateral walls.

has von ebner glands

Von Ebner glands

Serous glands that rinse circumvallate grooves and taste buds.

Foliate papillae

Located on back of tongue; contain taste buds.

Tongue muscle

Intrinsic skeletal muscle.

Submandibular, Sublingual, and Parotid

What are the types of salivary glands in the oral cavity?

Tooth crown composition

Enamel —> dentin —> pulp.

Enamel

Acellular mineralized crown covering; produced by ameloblasts during development.

Dentin

Acellular tissue supporting enamel; produced throughout life by odontoblasts.

Pulp cavity

Contains loose connective tissue, blood vessels, and nerves.

Cementum

Covers root dentin; produced by cementoblasts.

Periodontal ligament

Attaches teeth to jaw bones.

Salivary glands

compound exocrine glands that empty into the oral cavity

Saliva contents

Water, digestive enzymes, mucus, bicarbonate, and lysosomal enzymes.

Parotid gland

Serous acinar cells; watery and rich in amylase.

Submandibular gland

Both serous and mucous acinar cells, mainly serous

Sublingual gland

Mixed serous and acinar cells, predominantly mucus.

Serous demilunes

Crescent-shaped serous cell appearances; artifact of tissue processing

Sialoliths

Mineralized deposits that can block salivary ducts.

Four alimentary canal wall layers (inside to outside)

Mucosa → submucosa → muscularis externa → adventitia/serosa.

Mucosa

surrounds lumen and divided into three layers: Epithelium, lamina propria, and muscularis mucosae.

Epithelium

Lining responsible for protection, secretion, or absorption.

Lamina propria

Loose connective tissue containing vessels and immune cells. (GLANDS)

Muscularis mucosae

Thin smooth muscle producing local mucosal movements.

Submucosa

Connective tissue containing larger vessels, nerves, and sometimes glands.

Muscularis externa

Usually inner circular and outer longitudinal smooth muscle; controls mixing and propulsion.

Adventitia

Connective tissue that anchors organs to surrounding structures. ONLY IN ESOPHAGUS

Serosa

Connective tissue and mesothelium; reduces friction. STOMACH DOWN

Esophagus

Transports food from pharynx to stomach by peristalsis.

Esophageal epithelium

Nonkeratinized stratified squamous; protects against abrasion.

Submucosal Glands

Mucus-secreting glands in submucosa and mucosa, in beginning and ends of esophagus.

MALT

Mucosa-associated lymphatic tissue; immune protection. FOUND IN LAMINA PROPRIA

Upper third of esophagus muscle type

Skeletal muscle.

Middle third of esophagus muscle type

Mixed skeletal and smooth muscle.

Lower third of esophagus muscle type

Smooth muscle.

Stomach functions

Stores, mixes, and digests food; forms chyme.

mucosal layer with rugae, pits and glands

Rugae

Longitudinal folds of mucosa and submucosa that allow stomach expansion.

Gastric pits

Invaginations of stomach mucosa leading to gastric glands.

Stomach regions (in order)

Cardia → fundus/body → pylorus.

Cardia

Receives food from esophagus. has equal parts pits and glands

Fundus/body

Major portion of stomach. has more glands than pits

Pylorus

Empties chyme into duodenum. has more pits than glands

Surface mucous cells

Secrete mucus and bicarbonate to protect stomach lining. found in stomach glands

Mucous neck cells

Secrete mucus in neck of gastric glands.

Parietal cells

Secrete hydrochloric acid. bigger with central nucleus, pink

Chief cells

Secrete pepsinogen and are smaller with a nucleus towards the side and purple

Enteroendocrine cells

Secrete hormones such as gastrin, somatostatin (hormones), and ghrelin (hunger)

Stomach muscularis externa

Three layers: inner oblique, middle circular, outer longitudinal.

Meissner’s plexus

Located in submucosa, line of random cells

Auerbach’s plexus

Between muscularis externa layers; nerve bodies

Small intestine functions

principle organ for completing digestion and absorption of nutrients

INCREASE SURFACE AREA TO INCREASE ABSORPTION

Small intestine regions (in order)

Duodenum → jejunum → ileum.

Duodenum

First section of small intestine, receives chyme and digestive secretions.

BRUNNERS GLANDS

Jejunum

Middle segment of small intestine; major nutrient absorption via PLICAE CIRCULARES

Ileum

Final part of small intestine; absorbs remaining nutrients

PEYERS PATCHES (GALT)

Plicae circulares

Folds of mucosa and submucosa that slow chyme and increase surface area.

Villi

Finger-like mucosal projections of lamina propria that increase absorption surface area.

Microvilli

brush border of each individual plasma membrane

Lacteals

Lymphatic vessels in villi that absorb products of fat digestion.

Enterocytes

Absorptive cells that take up nutrients. (simple columnar epithelium)

Goblet cells

Secrete mucus for lubrication and protection. GHOST CELLS

Paneth cells

Crypt cells that secrete antimicrobial substances. SUPER BRIGHT PINK AT BOTTOM OF PITS

Enteroendocrine cells

Release hormones regulating digestive activity.

Crypts of Lieberkühn

Intestinal glands containing secretory and renewing cells.

Brunner’s glands

Duodenal submucosal glands that secrete bicarbonate-rich mucus to neutralize acid

Peyer’s patches

Lymphatic nodules in ileum; provide immune protection.

Ileum vs. jejunum

Ileum has more goblet cells and prominent Peyer’s patches.

Large intestine function

Absorbs water and electrolytes and compacts feces. made up of colon, rectum and anal canal

Large intestine mucosa

Lacks villi; contains simple tubular glands.

Taeniae coli

Three thickened bands of longitudinal smooth muscle in colon. (bulges that come out of muscularus externa)

Haustra

Pouch-like segments of colon formed by taeniae coli contractions.

Liver functions

Produces bile, detoxifies blood, synthesizes plasma proteins, and stores glycogen and vitamins.

Hepatic portal system

Carries blood from aorta —> hepatic artery —> liver —> portal vein —> digestive organs —> heptic vein —> inferior vena cava

Hepatocytes

Main liver cells that make up epithelia. organized into heazonal lobules separated with CT

Portal triad

Bile duct, branch of hepatic portal vein, and branch of hepatic artery.

Central vein

Located in center of lobule; drains blood from liver lobule.

Hepatic sinusoids

Discontinuous capillaries in liver allowing exchange between blood and hepatocytes.

Kupffer cells

Macrophages lining sinusoids; star-shaped

Bile canaliculi

Tiny channels between hepatocytes where bile is first secreted.

Liver blood flow

Portal triads → sinusoids → central vein.

Liver bile flow

Hepatocytes → bile canaliculi → bile ducts in portal triads; opposite direction to blood.

Gallbladder function

Stores and concentrates bile produced by liver.

Gallbladder mucosa

Simple columnar epithelium with short microvilli, lamina propria (NO MUSCULARIS MUCOSA OR SUBMUCOSA)

Bile entering gallbladder

Hepatic duct → cystic duct → gallbladder.

Bile leaving gallbladder

Gallbladder → cystic duct → common bile duct → duodenum.

Pancreas functions

Exocrine digestive secretion and endocrine hormone regulation.

Exocrine pancreas structure

Compound acinar glands producing digestive secretions.

Acinar cells function

Secrete digestive enzyme precursors called zymogens.

Pancreatic duct cells function (Intercalated ducts)

Secrete bicarbonate to neutralize acidic chyme.

Exocrine pancreatic secretions pathway

Travel through pancreatic ducts into duodenum.

Islets of Langerhans

Endocrine cell clusters that release hormones into blood. (alpha, beta, delta)

Alpha (A) cells

Secrete glucagon; raises blood glucose.

Beta (B) cells

Secrete insulin; lowers blood glucose.