Small Intestine The small intestine is a tubular organ that extends from the ___________________________ to the beginning of the __________________________________ It _______________ digestion of the nutrients in chyme, absorbs products of digestion, and transports the remaining residue to the large intestine It consists of three parts that include: __________________________________ The jejunum and ileum are suspended by the mesentery The greater omentum drapes over the large intestine

Parts of the Small Intestine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stomach Duodenum Jejunum Ascending colon Cecum Mesentery Appendix Ileum

Liver Stomach Gallbladder Transverse colon underneath Greater omentum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Liver Stomach Gallbladder Transverse colon underneath Greater omentum

Structure of the Small Intestinal Wall Tiny projections of the mucosa (intestinal ______________) greatly increase the __________________________ Each villus consists of simple columnar epithelium with a core of blood vessels, a lacteal (lymph capillary), and nerve fibers Columnar cells’ free surfaces have microvilli Intestinal glands/crypts of Lieberkühn are located between bases of villi Plicae circulares are circular folds of mucosa

Structure of the Small Intestinal Wall Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lumen Simple columnar epithelium Villus Lacteal Intestinal gland Villus Blood capillary network Goblet cells Intestinal gland © The McGraw-Hill Companies, Inc./Al Telser, photographer Arteriole Venule Lymph vessel

b: © The McGraw-Hill Companies, Inc./Al Telser, photographer Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cytoplasm of epithelial cell Microvilli Lumen Microvilli Cell membrane Mitochondrion Golgi apparatus Nucleolus Rough endoplasmic reticulum Nucleus (a) (b) b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

Gross Anatomy of Small Intestine

(a) Plicae circulares Villi Submucosa Circular muscle Muscular layer Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Plicae circulares Villi Submucosa Circular muscle Muscular layer Longitudinal muscle Serosa (b)

Secretions of the Small Intestine In addition to mucous-secreting goblet cells, there are many specialized mucous-secreting glands (________________________) that secrete a thick, alkaline mucus in response to certain stimuli Enzymes in the membranes of the microvilli include: ___________________ – breaks down peptides into amino acids Sucrase, maltase, lactase – break down disaccharides into monosaccharides ________________ – breaks down fats into fatty acids and glycerol Hormones secreted by small intestine (covered in previous slides) Enterokinase – converts trypsinogen to trypsin ______________ – hormone that inhibits acid secretion by stomach _____________________________________ – hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, and stimulates the gallbladder to release bile Secretin – stimulates the pancreas to release bicarbonate ions in pancreatic juice

Regulation of Small Intestinal Secretions Regulation of small intestine secretion occurs by: _________________ secretion is stimulated by the presence of chyme in the small intestine Distension of the intestinal wall activates nerve plexuses in the wall of the small intestine Parasympathetic reflexes triggering the release of intestinal _____________________________

Absorption of the Small Intestine Villi increase the ___________________ for absorption Small intestine absorption is so effective that very little absorbable material reaches the organ’s distal end, noting that: ______________________ and amino acids absorb: Through facilitated diffusion and active transport Absorbed into blood ______________________ and glycerol absorb by: Several steps involved as noted Absorbed into lymph and blood Electrolytes and _________________________ absorb: Through diffusion, osmosis, and active transport

Fats collect in clusters encased in protein to form chylomicrons Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3 Fats collect in clusters encased in protein to form chylomicrons Nucleus 4 Chylomicrons leave epithelial cell and enter lacteal 2 Fatty acids are used to synthesize fats in endoplasmic reticulum Chylomicrons 5 Lymph in lacteal transports chylomicrons away from intestine 1 Fatty acids resulting from fat digestion enter epithelial cell Fatty acids Endoplasmic reticulum Lymph Epithelial cell Lacteal Lumen of intestine To blood

Movements of the Small Intestine The small intestine carries on mixing movements that include: ____________________________ – pushing movements that propel chyme ____________________________ – ring-like contractions that can move chyme back and forth If small intestine becomes over distended or irritated, a strong peristaltic rush may sweep contents quickly into large intestine, resulting in ______________________________ Ileocecal sphincter joins small intestine to large intestine

Large Intestine The large intestine is named because of its ______________

Parts of the Large Intestine It has five parts that include: Cecum ____________________________ Ascending, transverse, descending and sigmoid Rectum Anal canal _______________________ – surrounded by internal and external anal sphincters _________________________ is attached to cecum and contains lymphatic tissue

Parts of the Large Intestine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Muscular layer Mucous membrane Serous layer Transverse colon Hepatic flexure Splenic flexure Ascending colon Tenia coli Epiploic appendage Descending colon Ileum Ileocecal sphincter Orifice of appendix Haustra Cecum Appendix Rectum Sigmoid colon Anal canal

Structure of the Large Intestinal Wall Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lumen Mucosa Submucosa Muscular layer Serosa © Ed Reschke/Peter Arnold

Functions of the Large Intestine Has little or no ________________ function _______________ water and electrolytes Secretes ______________ – many tubular mucous glands in mucosa Houses intestinal flora Forms _____________ Carries out defecation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lumen of large intestine Goblet cells © Ed Reschke

Movements of the Large Intestine Movements of the large intestine are __________________ to those of the small intestine It is slower and less frequent than that of the small intestine Movements include: Mixing movements Peristalsis ______________________________ usually follow meals The defecation reflex relaxes the internal anal sphincter and then the external anal sphincter

Animation: Reflexes in the Colon Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 22 22

Feces ________________________ are composed of materials not digested or absorbed, and include: Water Electrolytes Mucus Bacteria Bile pigments altered by bacteria provide the color The pungent __________________ is produced by bacterial compounds including: Phenol Hydrogen sulfide Indole Skatole Ammonia

Generalities Food usually leaves the stomach in ______________ hours _________________________ – a nutrient that the body cannot synthesize but must be obtained from a balanced diet

Lifespan Changes Changes to the digestive system are slow and slight, and eventually include: ____________________________ may become sensitive ____________________________ may recede Teeth may loosen, break or fall out ________________________ may become more frequent Nutrient absorption __________________________ Accessory organs age but typically not necessarily in ways that effect health