Hepatocytes’ functions include: Liver Functions: Hepatocytes’ functions include: Production of bile (not an enzyme): Emulsification of fat Facilitates fat & cholesterol absorption Processing bloodborne nutrients : Glucose to glycogen Amino acids to plasma proteins Storage of fat-soluble vitamins Detoxification: Convert ammonia to urea

Yellow-green, alkaline solution Contains: Composition of Bile Yellow-green, alkaline solution Contains: Bile salts (emulsification agents) Bile pigments Cholesterol Phospholipids Other substances

Pancreas Location Lies deep to the greater curvature of the stomach Three regions: Head, body and tail The head: Encircled by the duodenum Body: Between head & tail Tail: Close to the spleen

Pancreas Exocrine function Endocrine function Production of enzyme-rich pancreatic juice: Contains enzymes for breakdown of all classes of food Acini (clusters of secretory cells): Contain zymogen granules with digestive enzymes Endocrine function Production of hormones: Glucagon (Alpha cells) Insulin (Beta cells) Other hormones ex. somatostatin, pancreatic Polypeptide “pp”

Acinus of the Pancreas Figure 23.26a

Pancreatic Juice Composition & Function Exocrine product of pancreas & consists mainly of: Water Electrolytes (mainly HCO3–): Released by epithelial cells of smallest pancreatic ducts Neutralizes acid chyme Provides optimal environment for pancreatic enzymes Enzymes: Produced by the acinar cells in active & inactive forms Proteases are produced in an inactive form Activation takes place in the duodenum

Composition and Function of Pancreatic Juice Active pancreatic enzymes: Produced in the active form Require ions or bile for optimal activity Include: Amylase: Breakdown of starch (carbohydrates) Lipases: Breakdown of fat (lipids) Nucleases: Breakdown of nucleic acids

Composition and Function of Pancreatic Juice Inactive enzymes (proteases): Trypsinogen: Activated to trypsin by dudenal enteropeptidase Enteropeptidase is a brush boarder protease Trypsin activates more trypsinogrn (+feedback) Chymotrypsinogen: Activated to chymotrypsin by trypsin Procarboxypeptidase : Activated to carboxypeptidase by trypsin

Pancreatic Enzyme Activation: Figure 23.27

Digestion in the Small Intestine As chyme enters the duodenum: Only carbohydrates & proteins were partially digested No fat digestion has taken place Chyme (hypertonic & hi H+) is slowly released into duodenum Mixing is required for proper digestion The liver & the pancreas supply required digestive substances (name them?) Virtually all nutrient absorption occurs in the small intestine

Motility in the Small Intestine Most common motion of the small intestine: Segmentation: Initiated by intrinsic pacemaker cells Forward and backward (mixing) movement of food Moves contents steadily toward the ileocecal valve Following nutrient absorption: Peristalsis dominates (each wave is distal to the previous) Unidirectional (distal) movement of food Meal remnants, (bacteria, mucosal cells, and debris) are moved into the large intestine

Has three unique features: Large Intestine Has three unique features: Teniae coli: Three longitudinal smooth muscle bands Reduced bands of the longitudinal muscle layer of the muscularis Haustra: Pocket-like sacs Caused by the tone of teniae coli Epiploic appendages: Fat-filled pouches of visceral peritoneum

Large Intestine Subdivided into: The saclike cecum: Cecum Appendix Colon Rectum Anal canal The saclike cecum: Lies below the ileocecal valve Contains a wormlike (vermiform) appendix

Large Intestine Figure 23.29a

Colon Has distinct regions: Ascending colon Hepatic flexure Transverse colon Splenic flexure Descending colon Sigmoid colon

Colon The mesocolons: The sigmoid colon: The anal canal: Mesentery sheets Anchor transverse & sigmoid colons to the posterior abdominal wall The sigmoid colon: S-shaped part of the colon that joins the rectum The anal canal: Last segment of the large intestine Lies in the perineum (external to abdominopelvic cavity) Opens to the exterior at the anus

Valves & Sphincters of the Rectum & Anus Three valves of the rectum: Stop feces from being passed with gas Two anal sphincters: Internal: Composed of smooth muscle External: Composed of skeletal muscle Sphincters are closed except during defecation

Large Intestine: Microscopic Anatomy Colon mucosa: Simple columnar epithelium Has numerous deep crypts lined with goblet cells Anal canal mucosa: Stratified squamous epithelium Anal columns: Hanging long ridges or folds of mucosa

Large Intestine: Microscopic Anatomy (cont’d) Anal sinuses: Recesses between anal columns Exude mucus Compress feces Two superficial venous plexuses associated with anal canal: One is associated with anal column The other is associated with the anus itself Inflammation of these veins causes hemorrhoids (itchy varicosities)

Structure of the Anal Canal Figure 23.29b

Two sources of large intestine bacterial flora: Surviving flora entering the cecum from the S.I. Flora entering via the anus These bacteria: Colonize the colon Ferment indigestible carbohydrates Release irritating acids and gases (flatus) Synthesize vitamins: B complex vitamins Vitamin K

Functions of the Large Intestine Propulsion of fecal material toward the anus (major function) Reabsorption of Vitamins, water, and electrolytes Except for enteric bacterial digestion, no further digestion takes place in large intestine Though essential for comfort, the colon is not essential for life

Chemical Digestion: Carbohydrates Forms of carbohydrates in food: Monosaccharides : Glucose Galactose Fructose Disaccharides: Sucrose (table sugar) Maltose (grain sugar) Lactose (milk sugar) Polysaccharides : Starch (main), glycogen, & cellulose (indigestible)

Chemical Digestion: Carbohydrates Enzymes used: Salivary amylase (mouth): Hydrolyze starch & glycogen to oligosaccharides (2-8 chain) Pancreatic amylase (small intestine): Hydrolyze escaped carbs. to oligosaccharides (mostly maltose) Brush border enzymes: Dextrinase, glucoamylase: Hydrolyze oligosaccharides (> 3 sugars) to monosach. Maltase, sucrase and lactase: Hydrolyze disaccharides (maltose, sucrose, &lactose) to their respective monosaccharides

Chemical Digestion: Carbohydrates Absorption glucose & galactose: Into epithelial cell : By 2ndary active transport (co-transport with Na+), & Carrier proteins Out of epithelial cell: By facilitated diffusion Into capillary bed via intercellular clefts To the liver (for metabolic processing): Via the hepatic portal vein (hepatci portal circulation) Absorption of fructose: Entirely by facilitated diffusion

Chemical Digestion: Proteins Enzymes used in Stomach: Pepsin Enzymes acting in the small intestine: Pancreatic enzymes: Trypsin, chymotrypsin, and carboxypeptidases Brush border enzymes: Aminopeptidases, dipeptidases, and carboxypeptidases Absorption: Similar to carbohydrates : Active co-transport with Na+ via carrier proteins H+ dependant co-transport ( dipeptides & tripeptides) Resulting amino acids enter capillary blood by diffusion

Figure 23.34

Chemical Digestion: Fats Enzymes & chemicals used: Pancreatic lipases: Produce H2O-insolubale free fatty acids & monoglycerides Bile salts: Combine with lipases end products forming micelles Absorption: Micelles come in contact with luminal cell surface Content crosses cell membrane (simple diffusion) Inside intestinal cells: Triglycerides are re-synthesized Combined with cholesterol & phospholipids All coated with protein forming the chylomicrons

Chemical Digestion: Fats Absorption (cont’d): Chylomicrons (soluble lipoprotein): Enter lacteals Transported in lymphatic stream Emptied into the venous blood via the thoracic duct Glycerol & short chain fatty acids are: Absorbed into the capillary blood of the villi Transported via the hepatic portal vein

Chemical Digestion: Fats Figure 23.35

Fatty Acid Absorption Figure 23.36 Fatty acids and Lumen of monoglycerides associated with micelles in lumen of intestine Lumen of intestine Absorptive epithelial cell cytoplasm ER Golgi apparatus Lacteal Figure 23.36

Fatty Acid Absorption Figure 23.36 Fatty acids and Lumen of monoglycerides associated with micelles in lumen of intestine Lumen of intestine 1 Fatty acids and monoglycerides resulting from fat digestion leave micelles and enter epithelial cell by diffusion. Absorptive epithelial cell cytoplasm ER Golgi apparatus Lacteal Figure 23.36

Fatty Acid Absorption Figure 23.36 Fatty acids and monoglycerides associated with micelles in lumen of intestine Lumen of intestine 1 Fatty acids and monoglycerides resulting from fat digestion leave micelles and enter epithelial cell by diffusion. Absorptive epithelial cell cytoplasm 2 Fatty acids are used to synthesize triglycerides in smooth endo- plasmic reticulum. ER Golgi apparatus Lacteal Figure 23.36

Fatty Acid Absorption Figure 23.36 Fatty acids and monoglycerides associated with micelles in lumen of intestine Lumen of intestine 1 Fatty acids and monoglycerides resulting from fat digestion leave micelles and enter epithelial cell by diffusion. Absorptive epithelial cell cytoplasm 2 Fatty acids are used to synthesize triglycerides in smooth endo- plasmic reticulum. ER Golgi apparatus 3 Fatty globules are combined with proteins to form chylomicrons (within Golgi apparatus). Lacteal Figure 23.36

Fatty Acid Absorption Figure 23.36 Fatty acids and monoglycerides associated with micelles in lumen of intestine Lumen of intestine 1 Fatty acids and monoglycerides resulting from fat digestion leave micelles and enter epithelial cell by diffusion. Absorptive epithelial cell cytoplasm 2 Fatty acids are used to synthesize triglycerides in smooth endo- plasmic reticulum. ER Golgi apparatus 3 Fatty globules are combined with proteins to form chylomicrons (within Golgi apparatus). 4 Vesicles containing chylomicrons migrate to the basal membrane, are extruded from the epithelial cell, and enter a lacteal (lymphatic capillary). Chylomicron Lacteal Figure 23.36

Fatty Acid Absorption Figure 23.36 Fatty acids and monoglycerides associated with micelles in lumen of intestine Lumen of intestine 1 Fatty acids and monoglycerides resulting from fat digestion leave micelles and enter epithelial cell by diffusion. Absorptive epithelial cell cytoplasm 2 Fatty acids are used to synthesize triglycerides in smooth endo- plasmic reticulum. ER Golgi apparatus 3 Fatty globules are combined with proteins to form chylomicrons (within Golgi apparatus). 4 Vesicles containing chylomicrons migrate to the basal membrane, are extruded from the epithelial cell, and enter a lacteal (lymphatic capillary). 5 Lymph in the lacteal transports chylomicrons away from intestine. Chylomicron Lacteal Figure 23.36