Biology 212 Anatomy & Physiology I Digestive System

Functions:

Organs Two functional groups: 1. Alimentary Canal or Gastrointestinal tract Organs which ingest, propel, digest, absorb, & eliminate Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, anus 2. Accessory Digestive Organs Assist with digestion Teeth, tongue, salivary glands, liver, gall bladder, pancreas

Organs:

Oral Cavity: Includes: teeth tongue Opens posteriorly into oropharynx which leads to laryngopharynx Which opens inferiorly into esophagus

Paired Salivary Glands: Parotid Submandibular Sublingual

Saliva: 97% - 99% water Solutes: Ions (electrolytes) Antibodies Lysozyme (antibacterial) Amylase (enzyme – digests carbohydrates) Mucous Lubricates Cleans mouth and teeth Immune surveillance Begins carbohydrate digestion

Swallowing

From esophagus to anus: 4 concentric layers or tunics Alimentary Canal: From esophagus to anus: 4 concentric layers or tunics Serosa or Adventitia Muscularis Externa Submucosa Mucosa Epithelium Lamina propria Muscularis mucosa

Esophagus: Propels food from pharynx to stomach Posterior to trachea & heart

Esophagus: Propels food from pharynx to stomach Posterior to trachea & heart Mucosa: Nonkeratinized stratified squamous epithelium Many mucous-secreting cells Thin lamina propria Thin muscularis mucosa Submucosa: Thick layer of dense irregular CT Muscularis Externa: Upper third = skeletal muscle Middle third = mixed Lower third = smooth muscle Adventitia: Thin layer of connective tisssue

Esophagus: Passes from thorax to abdomen through diaphragm, enters stomach (left of midline).

Stomach: Storage: Highly distensible Delivers chyme slowly to duodenum Secretion of mucous, hydrochloric acid Secretion of enzyme pepsin - Digestion of proteins Secretion of gastric lipase – Digestion of lipids Secretion of intrinsic factor – Absorption of B12

Stomach: Fundus Cardiac Region Pyloris Body

Stomach: Lesser Curvature Greater Curvature

Stomach:

Stomach: Mucosa thrown into folds called rugae

Stomach: Pyloric sphincter releases chyme slowly into duodenum

Small Intestine: Total length: 6 to 7 meters Diameter: 2.5 to 3 centimeters Duodenum Jejunum Ileum

Small Intestine: DUODENUM: ~ 25 cm long Receives secretions of liver (bile) pancreas (enzymes) Secretes mucous digestive enzymes bicarbonate – neutralize HCl JEJUNUM: ~ 2.5 m long Specialized for absorption ILEUM: ~ 3.5 m long

Small Intestine: Serosa or Adventitia Muscularis Externa Submucosa Epithelium Lamina propria Muscularis mucosa

Mucosa specialized three ways to increase surface area for absorption Small Intestine: Mucosa specialized three ways to increase surface area for absorption 3. 1. All layers of mucosa thrown into folds called plicae circulares

Mucosa specialized three ways to increase surface area for absorption Small Intestine: Mucosa specialized three ways to increase surface area for absorption 2. Epithelium and lamina propria form finger-like villi 3.

Mucosa specialized three ways to increase surface area for absorption Small Intestine: Mucosa specialized three ways to increase surface area for absorption 3. Plasma membranes of epithelial cells form finger-like microvilli 3.

Mucosa specialized three ways to increase surface area for absorption Small Intestine: Mucosa specialized three ways to increase surface area for absorption 3. Nutrients, ions, etc. are absorbed through these plasma membranes and pass through the cells to the deeper lamina propria, where they are absorbed into capillaries & lymphatic vessels.

Large Intestine (colon): From ileocecal junction to anus ~ 2 meters long ~ 5 to 8 cm diameter Most digestion has already occurred (small intestine) Colon primarily absorbs water and electrolytes forms feces for elimination

Transverse colon Ascending colon Descending colon Sigmoid colon Cecum Rectum

Right colic (hepatic) flexure Left colic (splenic) flexure Sigmoid flexure

Abdominal Accessory Organs: Liver, Gall bladder, Pancreas, & associated ducts

Liver Most superior organ in abdomen Immediately inferior to diaphragm Partially protected by ribs Develops from embryonic intestine Mass ~ 1.5 kg Four lobes Blood supply: Hepatic artery from celiac trunk Hepatic portal vein from stomach intestine pancreas spleen

Liver Digestive functions: Regulate metabolism Store excess carbohydrate protein lipid Secrete bile: Produced from cholesterol Stored in gall bladder via cystic duct Transported to duodenum through common bile duct Emulsifies fats

Liver: Hepatic artery Hepatic portal vein Common bile duct Enter / exit together on inferior surface

Pancreas: Inferior & posterior to stomach Fits into concavity of duodenum Both endocrine (Insulin, glucagon) exocrine (digestive enzymes) Enzymes transported to duodenum by pancreatic duct (shares opening with common bile duct)

Pancreas: Produces many different digestive enzymes: Amylases: starches & monosaccharides glycogen & disaccharides Proteases: proteins amino acids Lipases: diglycerides & fatty acids triglycerides & glycerol Nucleases: nucleic acids nucleotides

The abdominal cavity is lined by a double-layered serous membrane called the peritoneum. Visceral layer – surrounds and is firmly attached to abdominal organs Parietal layer – attached to inner surface of body wall Between these = Peritoneal cavity

Mesentary – fold of peritoneum connecting visceral & parietal layers

More terminology: Intraperitoneal organs Retroperitoneal organs connected to body wall posterior to peritoneal by mesentaries cavity

Intraperitoneal organs have a serosa which includes the visceral layer of the peritoneum. Retroperitoneal organs are not covered by the visceral layer of the peritoneum, so the connective tissue on their external surface is an adventitia. Mesentery In reality, many retroperitoneal organs (no mesentery) have a serosa (visceral peritoneum) covering part of their wall and an adventitia (no visceral peritoneum) covering part of their wall.

Intraperitoneal Retroperitoneal Stomach Duodenum Jejunum Ilium Cecum & Appendix Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Liver Gall bladder Pancreas

Intestinal Motility: Moves liquid distally by peristalsis Mixes chyme from stomach with - Intestinal enzymes - Pancreatic enzymes - Bile from liver Increases contact of liquid with intestinal mucosa for absorption

Digestion: Breakdown of food into molecules small enough to be absorbed from the lumen of the intestine into its blood vessels. Four types of molecules = more than 95% of total: Water Sugars (carbohydrates) Amino acids Fatty acids Also: Nucleic acids Ions (electrolytes, minerals) Vitamins ? Others ?

Mechanical digestion In mouth (teeth) Chemical digestion Begins in mouth Continues through intestine Absorption of nutrients Primarily in electrolytes small intestine vitamins Absorption of water Both small intestine & large intestine Salivary glands produce amylases Stomach secretes proteases Small intestine secretes proteases Liver secretes bile Pancreas secretes amylases, proteases, lipases, nucleases

All absorbed molecules must pass through epithelial cells of intestinal mucosa. Tight junctions prevent anything from passing between cells.

Alimentary Canal: Since contents include many foreign substances, including microorganisms, your immune system considers it “outside” so Lined by many lymphatic and immune tissues in lamina propria and submucosa