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Home , Anal columns, Anal sinuses, External anal sphincter, Gastric pits, Haustrum (anatomy), Internal anal sphincter

5/14/2016

Introduction

• Every cell requires a constant energy source Digestive System – Ingested food is complex • Modification is needed to utilize

Introduction

Parotid gland Mouth (oral cavity) • Sublingual gland Salivary Digestive system is a tube Tongue Submandibular glands – gland • Specialized regions – Mouth – Pharynx Pancreas (Spleen) – Esophagus Liver Gallbladder – Stomach – – Small intestine Large intestine Vermiform

Figure 23.1

Introduction Ingestion Food Mechanical digestion Pharynx • • Chewing (mouth) Esophagus Digestive processes • Churning (stomach) Propulsion • Segmentation • Swallowing 1. Ingestion (small intestine) (oropharynx) Chemical • digestion Stomach (esophagus, 2. Propulsion stomach, small intestine, 3. Mechanical digestion large intestine) Absorption 4. Chemical digestion vessel 5. Absorption Small intestine 6. Large Blood intestine vessel Mainly H 2O

Defecation Anus

Figure 23.2

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Intrinsic plexuses Introduction • Myenteric nerve plexus • Submucosal nerve plexus Glands in • Histology of the alimentary canal Mucosa – • Four basic layers (tunics) • • Tunica mucosa – innermost layer • – Protection and absorption Submucosa – Epithelium and connective tissue Muscularis • Tunica submucosa externa • Longitudinal – Connective tissue muscle – Binds tube together • Circular muscle Serosa • Nerve Tunica muscularis (externa) • Epithelium – Double layer of muscle • Connective • Tunica serosa tissue Gland in mucosa Lumen – Single layer of epithelium and connective tissue Lymphatic Duct of gland outside Mucosa-associated – Forms the visceral peritoneum Mesentery vessel alimentary canal lymphoid tissue

Figure 23.6

Introduction

• Peritoneum – Membrane that lines abdominal cavity – – remember, that means 2 layers! • Parietal peritoneum = outer layer (attached to abdominal wall) • Visceral peritoneum = inner layer (wrapped around visceral organs) • Space in between = peritoneal cavity

Introduction Introduction

• Mesentery • Omenta – Folds in the peritoneum – Folds in peritoneum – – Lesser Attached to intestinal tract Connect stomach to another organ omentum – Encapsulate blood vessels, , fat stores that • Examples: supply the intestine – Lesser omentum connects stomach to liver – Greater omentum connects stomach to colon

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Peritoneum Liver Abdominopelvic Lesser omentum cavity Pancreas Vertebra Stomach Transverse mesocolon Dorsal mesentery Duodenum Transverse colon Mesentery Parietal peritoneum Ventral Greater omentum mesentery Visceral Jejunum peritoneum Ileum Visceral peritoneum Peritoneal Alimentary Liver cavity canal organ Parietal peritoneum (a) Schematic cross sections of abdominal cavity illustrate the peritoneums and mesenteries. Rectum (d)

Figure 23.5a Figure 23.30d

Digestive System Soft palate Palatoglossal arch Uvula Hard palate • Mouth Oral cavity – Cheek, palate, Palatine tonsil tongue Tongue Oropharynx – Opens into Lingual tonsil oropharynx Epiglottis – Salivary glands Hyoid bone Laryngopharynx

Esophagus

Trachea (a) Sagittal section of the oral cavity and pharynx

Figure 23.7a

Salivary glands secrete about 1250 ml of saliva per day! Digestive System

Tongue • Teeth Teeth – Held in place by periodontal ligaments Parotid Ducts of gland sublingual – Gingiva covers bone gland Parotid duct Masseter muscle Frenulum – 2 dentitions of tongue Body of Sublingual mandible (cut) • gland Posterior belly Deciduous Mylohyoid of digastric • Permanent muscle (cut) muscle Submandibular Anterior belly of Submandibular duct digastric muscle gland Mucous Serous cells (a) cells forming demilunes (b)

Figure 23.9

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Teeth 20 deciduous 32 permanent Digestive System

Incisors Incisors Central (6–8 mo) Central (7 yr) Lateral (8 yr) • Teeth Lateral (8–10 mo) Canine (eyetooth) Canine (eyetooth) (11 yr) – Anatomy (16–20 mo) Premolars • Molars (bicuspids) Crown First molar First premolar – Covered by enamel (10–15 mo) Deciduous (11 yr) Second molar (milk) teeth Second premolar • Dentin (about 2 yr) (12–13 yr) Molars • Pulp cavity First molar (6–7 yr) • Roots Second molar (12–13 yr) – Function Third molar Permanent (wisdom tooth) • (a) teeth Break down food (17–25 yr) • Mixed with saliva to form bolus

Figure 23.10a

Enamel Digestive System Dentin Crown Dentinal tubules Pulp cavity (contains ó Esophagus blood vessels and ó Pharynx to stomach Neck nerves) ó Moves bolus to stomach Gingiva (gum) ó Peristalsis ó Cardiac (gastroesophageal) Cementum ó Heartburn Root canal ó Histology Root Periodontal ó Mucosa ligament ó Stratified squamous epithelium ó Abundant mucous glands ó Serosa Apical foramen ó Entirely connective tissue

Bone

Figure 23.11

Relaxed muscles 4 Food is moved through Circular muscles the esophagus to the stomach by peristalsis. Parotid gland contract Mouth (oral cavity) Sublingual gland Salivary Tongue Submandibular Bolus of food glands gland Longitudinal muscles contract Esophagus Pharynx Stomach Pancreas Liver (Spleen) Gallbladder Gastroesophageal sphincter closed Transverse colon Duodenum Descending colon Small Jejunum Ascending colon intestine Ileum Cecum Large Stomach Sigmoid colon intestine Rectum Vermiform appendix Anus Anal canal

Figure 23.1 Figure 23.13, step 4

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Relaxed 5 The gastroesophageal muscles sphincter opens, and food enters the stomach.

Mucosa (contains a stratified squamous epithelium)

Submucosa (areolar connective tissue)

Lumen Gastroesophageal Muscularis externa sphincter opens • Longitudinal layer • Circular layer (fibrous connective tissue) (a)

Figure 23.13, step 5 Figure 23.12a

Cardia simple columnar Fundus epithelium Esophagus Muscularis externa Serosa • Longitudinal layer • Circular layer Body • Oblique layer Lumen Mucosa Lesser (contains a stratified curvature Rugae of squamous epithelium) mucosa

Esophagus stomach junction Greater curvature Pyloric Pyloric Duodenum canal antrum Pyloric sphincter (b) (a) (valve) at

Figure 23.12b Figure 23.14a

Digestive System Falciform ligament Liver Gallbladder • Stomach Spleen – From cardiac orifice to pyloric sphincter Stomach • Rugae (flatten as stomach fills) – Greater curvature Ligamentum teres • Convex lateral surface Greater omentum • Greater omentum Small intestine – Lesser curvature • Concave medial surface Cecum • Lesser omentum

(a)

Figure 23.30a

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Digestive System Liver

Gallbladder Lesser omentum • Stomach – Stomach Four tunics Duodenum • Muscularis – Additional layer of muscle in an oblique orientation Transverse colon – Three layers of Small intestine

Cecum

Urinary bladder (b)

Figure 23.30b

Cardia Fundus Digestive System Esophagus Muscularis externa Serosa • • Longitudinal layer Stomach • Circular layer Body – Four tunics • Oblique layer • Lesser Lumen Mucosa curvature Rugae of – mucosa » Mucous cells = Mucous » Parietal cells = Intrinsic factor and HCl » Greater Zymogenic (chief) cells = Pepsinogen » curvature Enteroendocrine cells = Gastrin and cholecystokinin Pyloric Pyloric Duodenum canal antrum Pyloric sphincter (a) (valve) at pylorus

Figure 23.14a

Gastric pits Surface epithelium Surface epithelium (mucous cells)

Mucosa Gastric pit Mucous neck cells Mucosa contains gastric glands Lamina propria Chief cell Muscularis mucosae Gastric Submucosa gland (contains submucosal plexus) Oblique layer Muscularis externa Circular layer (contains myenteric Longitudinal plexus) layer Serosa Stomach wall (a) Layers of the stomach wall (l.s.) (b) Enlarged view of and gastric glands

Figure 23.15a Figure 23.15b

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Pepsinogen Digestive System HCl

• Chemical digestion in the stomach Mitochondria – Protein catabolism → polypeptides Parietal cell – Secretions HCl • Pepsinogen → pepsin • HCl – Chief (Zymogenic) cell pH 1.5–3.5 – Denatures protein in food – Kills many bacteria Enteroendocrine cell • Intrinsic factor – (c) Location of the HCl-producing parietal cells and Required for absorption of vitamin B 12 in small intestine pepsin-secreting chief cells in a gastric gland

Figure 23.15c

Digestive System Digestive System

• Chemical digestion in the stomach • Chemical digestion in the stomach – Enteroendocrine cells – • Secrete hormone-like substances • – Gastrin Product of stomach digestion » Stimulates parietal cells to release HCl – Prevention of autodigestion » Increases gastric motility, emptying • – Cholecystokinin Mucous » Primarily produced by enteroendocrine cells in the • Gastritis duodenum • Peptic ulcers » Inhibits HCl release and gastric emptying – » Stimulates pancreas to release digestive enzymes Gastric ulcers » Stimulates production and release of bile from gall bladder – Duodenal ulcers » Contributes to feelings of satiety after eating

Digestive System Digestive System

• Control of gastric secretions • Control of gastric secretions – Neural control – Hormonal control • Seeing, smelling, tasting, thinking about food stimulates • Gastrin gastric secretions via the vagus nerve – Released reflexively by enteroendocrine cells in • Enteric nervous system provides local control independently of brain and spinal cord response to stomach distension, peptides, and low acidity – Spinal cord injury will not damage! – – Ischemia can damage, but transplants have been Release stimulated by caffeine performed since 2011 • Also subject to ANS control – “Rest and digest”

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Digestive System Stimulatory events Inhibitory events 1 Cephalic Sight and thought Cerebral cortex Lack of Cerebral 1 Loss of phase of food Conditioned reflex stimulatory cortex appetite, impulses to depression 2 Stimulation of Hypothalamus Vagus parasym- taste and smell and medulla nerve pathetic receptors ó Control of gastric secretions oblongata center 1 Stomach Vagovagal Medulla Vagus Gastrin G cells 1Excessive distension reflexes nerve secretion acidity Stimulatory and inhibitory events occur in three phases activates declines (pH <2) ó stretch in stomach Gastric receptors Local Overrides Sympathetic 2 Emotional phase reflexes parasym- nervous upset 1. Cephalic pathetic system controls activation 2 Food chemicals G cells Gastrin 2. Gastric (especially peptides and release caffeine) and rising pH to blood activate chemoreceptors Stomach secretory 3. Intestinal activity Entero- Local 1 Distension gastric reflexes of duodenum; reflex presence of 1 Presence of low Intestinal pH, partially digested fatty, acidic, (enteric) Vagal hypertonic foods, fats, or gastrin nuclei chyme, and/or hypertonic solution release Brief Intestinal in medulla irritants in in duodenum when to blood effect phase stomach begins to Pyloric the duodenum empty sphincter

Release of intestinal 2 Distension; hormones (secretin, presence of cholecystokinin, vasoactive fatty, acidic, intestinal peptide) partially digested food Stimulate in the Inhibit duodenum

Figure 23.17

Digestive System Digestive System

• ó Control of gastric secretions Control of gastric secretions – ó Stimulatory and inhibitory events occur in three phases Stimulatory and inhibitory events occur in three phases 1. Cephalic ó Hearing, seeing, smelling, tasting, thinking about food 1.Cephalic ó Vagus nerve stimulated 2.Gastric » Gastric secretion starts • Arrival of food in stomach – Stomach distension, peptides, low acidity → gastrin released » Relaxes pyloric sphincter » Increases stomach motility

Digestive System Stimulatory events Inhibitory events 1 Cephalic Sight and thought Cerebral cortex Lack of Cerebral 1 Loss of phase of food Conditioned reflex stimulatory cortex appetite, impulses to depression 2 Stimulation of Hypothalamus Vagus parasym- taste and smell and medulla nerve pathetic • Control of gastric secretions receptors oblongata center 1 Stomach Vagovagal Medulla Vagus Gastrin G cells 1Excessive distension reflexes nerve secretion acidity – activates declines (pH <2) Stimulatory and inhibitory events occur in three stretch in stomach Gastric receptors Local Overrides Sympathetic 2 Emotional phases phase reflexes parasym- nervous upset pathetic system controls activation 2 Food chemicals G cells Gastrin 1.Cephalic (especially peptides and release caffeine) and rising pH to blood activate chemoreceptors Stomach secretory 2.Gastric activity Entero- Local 1 Distension gastric reflexes of duodenum; reflex presence of 3.Intestinal 1 Presence of low Intestinal pH, partially digested fatty, acidic, (enteric) Vagal hypertonic foods, fats, or gastrin nuclei chyme, and/or hypertonic solution release Brief • Chyme reaches duodenum Intestinal in medulla irritants in in duodenum when to blood effect phase stomach begins to Pyloric the duodenum – Intestinal distention → enterogastric reflex empty sphincter Release of intestinal 2 Distension; – Release of secretin, CCK, VIP hormones (secretin, presence of cholecystokinin, vasoactive fatty, acidic, intestinal peptide) partially » Inhibit stomach motility and delay emptying digested food Stimulate in the Inhibit duodenum

Figure 23.17

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Presence of fatty, hypertonic, acidic chyme in duodenum

Pyloric Pyloric Pyloric Duodenal entero- Chemoreceptors and valve valve valve endocrine cells stretch receptors closed closed slightly opened Secrete Target

Enterogastric Reflex Enterogastrones Via short Via long (secretin, reflexes reflexes cholecystokinin, vasoactive intestinal peptide) 1 Propulsion: Peristaltic 2 Grinding: The most 3 Retropulsion: The pyloric Enteric CNS centers waves move from the vigorous peristalsis and end of the stomach acts as a neurons sympathetic fundus toward the mixing action occur pump that delivers small Duodenal activity; pylorus. close to the pylorus. amounts of chyme into the stimuli parasympathetic duodenum, simultaneously decline activity forcing most of its contained material backward into the stomach. Contractile force and Initial stimulus rate of stomach Physiological response emptying decline Stimulate Result Inhibit

Figure 23.19 Figure 23.20

Digestive System Digestive System

• Small intestine • Small intestine – Major organ of digestion and absorption – Structural modifications – 2 - 4 m long; from pyloric sphincter to ileocecal • Villi (“fingers”) valve • Intestinal glands – – Subdivisions Mucosa – Submucosa • Duodenum

• Jejunum Located • within the Ileum peritoneal cavity

Vein carrying blood to Parotid gland hepatic portal vessel Mouth (oral cavity) Sublingual gland Salivary Tongue Submandibular glands gland Muscle Esophagus Pharynx Stomach layers Lumen Pancreas Circular Liver (Spleen) folds Gallbladder Villi Transverse colon Duodenum Descending colon Small Jejunum Ascending colon intestine Ileum Cecum Large Sigmoid colon intestine Rectum Vermiform appendix Anus Anal canal (a)

Figure 23.1 Figure 23.22a

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Microvilli (brush border)

Absorptive cells Microvilli

Lacteal Blood Vilus capillaries Mucosa associated lymphoid tissue Enteroendocrine Intestinal crypt cells Muscularis Venule mucosae Lymphatic vessel Absorptive Duodenal gland Submucosa cell (b) (b)

Figure 23.22b Figure 23.3b

Microvilli Digestive System (brush border)

ó Chemical digestion in the small intestine ó Food entering SI = partially digested Absorptive cells ó Intestinal juice Lacteal ó Water, mucous Goblet cell Blood Villus ó Crypt cells produce lysozyme capillaries Mucosa associated lymphoid tissue Enteroendocrine Intestinal crypt cells Muscularis Venule mucosae Lymphatic vessel Duodenal gland Submucosa (b)

Figure 23.22b

Digestive System

Stomach ó Chemical digestion in the small intestine ó Pancreatic juice ó Enzymes Pancreas ó Amylase Epithelial » Carbohydrates cells ó Lipase Membrane-bound » Fats enteropeptidase ó Trypsinogen, chymotrypsinogen, carboxypeptidase Trypsinogen Trypsin (inactive) » Notice the “-ogen” Chymotrypsinogen Chymotrypsin » These must be activated to digest protein (inactive) Procarboxypeptidase Carboxypeptidase ó Sodium bicarbonate (inactive) ó Neutralize stomach acid

Figure 23.27

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Digestive System Digestive System

• Chemical digestion in the small intestine • Accessory digestive organs – Intestinal juice – Liver • Alkaline, mucous rich watery secretion • • Lysosozymes – why are these defensive enzymes so Gallbladder important here? – Pancreas – Brush border enzymes • Enzymes for carbohydrates and proteins – Pancreatic secretions • Bicarbonate rich watery secretion • Amylases, lipases, proteases, and nucleases – Bile • Bile salts emulsify lipids

Digestive System

Sternum Bare area • Accessory digestive organs Nipple Falciform – Liver Liver ligament • Largest internal surface area of any body organ Left lobe of liver • Blood supply Right lobe of liver – Hepatic artery – oxygenated blood to the liver – Hepatic-portal vein – venous blood to the liver – Round ligament Hepatic vein – all blood exiting the liver Gallbladder (ligamentum (a) teres)

Figure 23.24a

Inferior vena cava (not part of ) Gastric Hepatic veins Spleen Inferior vena cava Liver Splenic vein Right gastroepiploic Hepatic portal vein vein Inferior mesenteric vein Superior mesenteric vein Small intestine Large intestine

Rectum (a)Lobule (b) Central vein Connective (c) The hepatic portal circulation. tissue septum

Figure 19.29c Figure 23.25a, b

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Interlobular veins Digestive System (to hepatic vein) Central vein

Sinusoids • Accessory digestive organs Plates of Bile canaliculi hepatocytes – Liver • Microscopic compartments = lobules

Bile duct (receives – Lined by hepatocytes = screen blood bile from bile canaliculi) » Store nutrients Fenestrated lining (endothelial » Manage toxins cells) of sinusoids » Produce bile

Bile duct Hepatic Portal venule Portal triad macrophages Portal arteriole in sinusoid walls Portal vein

Digestive System

Cystic, Hepatic and Bile ducts • Accessory digestive organs Right and left – Liver hepatic ducts of liver • Hepatocyte functions Cystic duct – Process blood borne nutrients Common hepatic duct » Store fat-soluble vitamins and minerals Bile duct and sphincter » Glucose is stored as glycogen Accessory pancreatic duct – Perform detoxification » Stores fat soluble toxins Mucosa – Produce ~900 ml bile per day with folds Tail of pancreas » Note: gall bladder does not MAKE bile, only stores excess Gallbladder Pancreas – Makes heparin and other plasma proteins Major duodenal Jejunum – Catabolizes nitrogenous wastes papilla Main pancreatic duct Hepatopancreatic and sphincter ampulla and sphincter Duodenum Head of pancreas

Figure 23.21

Digestive System Digestive System

• Accessory digestive organs • Accessory digestive organs – Liver – Liver • Bile • Bile – Yellow-green, alkaline solution – Bilirubin – Bile salts » Pigment formed from heme » Cholesterol derivatives that function in fat » Metabolized to form urobilinogen → stercobilin emulsification & absorption – Lack of bile = grayish stools with fatty streaks (acholic feces)

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Digestive System

• Accessory digestive organs – Liver • Gallbladder – Thin-walled muscular sac on the ventral surface of the liver – Stores and concentrates bile by absorbing its water and ions – Releases bile via the cystic duct » Flows into the bile duct

Digestive System

Parotid gland • Mouth (oral cavity) Accessory digestive organs Sublingual gland Salivary Tongue Submandibular glands – Pancreas gland • Function – Pharynx Delivers digestive fluids and NaHCO 3 to duodenum via Esophagus pancreatic duct Stomach • Tissue types Pancreas Liver (Spleen) – Endocrine Gallbladder » Islets of Langerhans → insulin and glucagon Transverse colon – Exocrine Duodenum Descending colon Small Jejunum » Acinar tissue → pancreatic juice Ascending colon intestine Ileum Cecum Large Sigmoid colon intestine Rectum Vermiform appendix Anus Anal canal

Figure 23.1

Small duct

Right and left Acinar cells hepatic ducts of liver Cystic duct Basement Common hepatic duct membrane Bile duct and sphincter Accessory pancreatic duct Zymogen granules

Mucosa with folds Tail of pancreas Rough Gallbladder Pancreas endoplasmic Jejunum Major duodenal reticulum papilla Main pancreatic duct Hepatopancreatic and sphincter ampulla and sphincter Duodenum Head of pancreas Exocrine pancreas

Figure 23.21 Figure 23.26a

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Slide 1

1 Chyme enter- 4 Bile salts and, Digestive System ing duodenum to a lesser extent, causes release of secretin cholecystokinin transported via bloodstream • Accessory digestive organs (CCK) and stimulate liver to secretin from produce bile – Pancreas duodenal more rapidly. enteroendocrine • Secretion mediated by hormones (where were these hormones cells. 5 CCK (via made?) bloodstream) – 2 CCK (red causes Secretin dots) and gallbladder to » Released in response to acid secretin (yellow contract and hepatopancreatic » dots) enter the Stimulates release of base from pancreas bloodstream. sphincter to » relax; bile enters Also stimulates release of pancreatic secretions and bile duodenum. – 3 CCK induces Cholecystokinin secretion of 6 During » Released when protein and fat enter intestine enzyme-rich cephalic and gastric phases, » Stimulates the release of pancreatic secretions and bile pancreatic juice. vagal nerve Secretin causes stimulation secretion of causes weak – HCO 3 -rich contractions of pancreatic juice. gallbladder.

Figure 23.28

Digestive System Right colic Left colic (hepatic) (splenic) flexure flexure Transverse • Large intestine Transverse mesocolon colon Epiploic – Superior appendages About 1.5 meters in length in a cadaver (SI about mesenteric 6m long) artery Descending colon • Functions Ascending Cut edge of colon – mesentery Vitamins, water, and electrolytes are reclaimed IIeum Teniae coli – Propulsion of feces toward the anus IIeocecal valve Sigmoid – Cecum Colon is not essential for life colon Vermiform appendix Rectum

Anal canal (a)

Figure 23.29a

Digestive System Digestive System

ó Regions ó Regions ó Cecum ó Cecum ó Colon ó Blind pouch ó Rectum ó Appendix attaches to this area ó Anal canal ó Bacteria ó Immune function ó Fermentation chamber in some other species ó Examples: horse, rabbit, koala

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Digestive System Greater omentum

ó Regions Transverse colon ó Colon Transverse ó Ascending mesocolon ó Retroperitoneal ó Transverse Descending colon ó Anchored via mesocolons (mesenteries) Jejunum ó Descending Mesentery Sigmoid ó Retroperitoneal mesocolon ó Sigmoid Sigmoid colon ó Anchored via mesocolons (mesenteries) Ileum

(c)

Figure 23.30c

Liver Lesser omentum Digestive System Pancreas Stomach óRegions Transverse mesocolon ó Rectum Duodenum ó Rectal valves stop feces from being passed with gas Transverse colon ó Anal canal Mesentery ó Last segment of the large intestine Greater omentum ó Jejunum ó Smooth muscle (involuntary) Ileum ó Spinal reflex arcs Visceral peritoneum ó External anal sphincter ó (voluntary) Parietal peritoneum Urinary bladder Rectum (d)

Figure 23.30d

Rectal valve Digestive System Rectum Hemorrhoidal veins muscle ó Defecation Anal canal ó Mass movements force feces into rectum External anal ó Distension initiates spinal defecation reflex sphincter ó Parasympathetic signals Internal anal ó Stimulate contraction of the sigmoid colon and rectum sphincter ó Relax the internal anal sphincter ó Conscious control allows relaxation of external anal sphincter Anus ó Valsalva’s maneuver (b)

Figure 23.29b

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Impulses from 1 Distension, or stretch, of the cerebral cortex rectal walls due to movement Digestion (conscious of feces into the rectum stimulates stretch receptors control) Sensory there. The receptors transmit signals along afferent fibers to nerve fibers • Ingested materials must be broken down for spinal cord neurons. Voluntary motor 2 A spinal reflex is initiated in absorption nerve to external which parasympathetic motor • anal sphincter Sigmoid (efferent) fibers stimulate Majority of absorption in small intestine colon contraction of the rectal walls and relaxation of the internal – Water and alcohol in stomach mucosa anal sphincter. – Stretch receptors in wall Water, some salts and water-soluble vitamins in Rectum Involuntary motor nerve large intestine External anal (parasympathetic division) • sphincter Internal anal sphincter Non-absorbable materials removed by (skeletal muscle) (smooth muscle) defecation 3 If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so that feces may pass.

Figure 23.31

Fate of Digested Materials Fate of Digested Materials

• Carbohydrates • Carbohydrates – Glucose, fructose, and galactose are directly – Cellulose absorbed • Humans lack the enzymes to digest • Glucose: metabolized by nearly all cells • Metabolized by bacteria – • Fructose: metabolized almost entirely by the liver Vitamins K and B 12 are byproducts (very small amounts) – Converted to glucose -> stored as glycogen – Converted to glycerol -> triglycerides • Galactose: metabolized to glucose, mostly in the liver

Fate of Digested Materials

Carbohydrate digestion Enzyme(s) Site of • Foodstuff and source action Path of absorption Proteins • Glucose and galactose – Starch and disaccharides are absorbed via Amino acids, dipeptides, and some tripeptides Salivary Mouth cotransport with • Absorbed by active transport amylase sodium ions. Pancreatic Small • Fructose passes via – Further metabolism in cells → free amino acids → facilitated diffusion. Oligosaccharides amylase intestine • All monosaccharides bloodstream and disaccharides leave the epithelial Brush border Small cells via facilitated Lactose Maltose Sucrose enzymes in intestine diffusion, enter the small intestine capillary blood in the (dextrinase, gluco- villi, and are amylase, lactase, transported to the liver Galactose Glucose Fructose maltase, and sucrase) via the hepatic portal vein.

Figure 23.32 (1 of 4)

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Lumen of Amino acids of protein fragments intestine Brush border enzymes Apical membrane (microvilli) Pancreatic Protein digestion proteases 1 Proteins and protein fragments Enzyme(s) Site of Na + are digested to amino acids by Foodstuff and source action Path of absorption pancreatic proteases (trypsin, chymotrypsin, and carboxy- • Amino acids are absorbed Protein Pepsin peptidase), and by brush border by cotransport with (stomach glands) + Absorptive enzymes (carboxypeptidase, Stomach sodium ions. Na in presence epithelial aminopeptidase, and dipeptidase) • Some dipeptides and of HCl cell of mucosal cells. Large polypeptides tripeptides are absorbed Pancreatic + + Small via cotransport with H enzymes and hydrolyzed to amino intestine 2 The amino acids are then (trypsin, chymotrypsin, acids within the cells. Small polypeptides, absorbed by active transport into carboxypeptidase) • Amino acids leave the small peptides the absorptive cells, and move to Brush border epithelial cells by Small their opposite side (transcytosis). enzymes facilitated diffusion, enter intestine Amino acids (aminopeptidase, the capillary blood in the Amino (some dipeptides carboxypeptidase, villi, and are transported acid and tripeptides) and dipeptidase) to the liver via the hepatic carrier portal vein.

3 The amino acids leave the villus epithelial cell by facilitated Active transport Capillary diffusion and enter the capillary Passive transport via intercellular clefts.

Figure 23.32 (2 of 4) Figure 23.33

Fate of Digested Materials Fate of Digested Materials • • Lipids Lipids – Within intestinal cells Emuslified by bile salts and digested by lipase Triglycerides are formed into monoglycerides and FFAs Combined with proteins and cholesterol in Micelles formed (lipid and bile salts) and move the cell between microvilli Chylomicrons Lipids diffuse into intestinal epithelium (bile salts later reabsorbed in ileum) Enter lymphatics through lacteal

Enter blood vascular system

Fat globule Fate of Digested Materials

1 Large fat globules are emulsified • Bile salts (physically broken up into smaller fat Lipids droplets) by bile salts in the duodenum. Plasma enzymes generate FFAs and glycerol 2 Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate Fat droplets with bile salts to form micelles which Pass thru capillary wall to serve tissues coated with “ferry” them to the intestinal mucosa. bile salts Micelles made up of fatty acids, monoglycerides, and bile salts The remaining protein-cholesterol combo returns to liver 3 Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other lipoid substances and proteins to form chylomicrons. Additional proteins added

4 Chylomicrons are extruded from the Epithelial epithelial cells by exocytosis. The cells of chylomicrons enter lacteals. They are Lacteal HDL and LDL created (carriers for lipids) small carried away from the intestine by lymph. intestine

Figure 23.34

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Fat digestion Fate of Digested Materials Enzyme(s) Site of Foodstuff and source action Path of absorption Unemulsified • Fatty acids and monoglycerides • fats enter the intestinal cells via Water Emulsification by Small diffusion. the detergent intestine • Fatty acids and monoglycerides – After digested nutrients removed, large volumes action of bile are recombined to form salts ducted triglycerides and then of salt and water remain in LI in from the liver combined with other lipids and proteins within the cells, and the resulting chylomicrons are – + - Pancreatic Small Active Na uptake → passive Cl and water uptake extruded by exocytosis. lipases intestine • The chylomicrons enter the • Undigested materials (cellulose) cause water to be lacteals of the villi and are transported to the systemic retained in LI circulation via the lymph in the Monoglycerides Glycerol thoracic duct. • Antibiotics may kill bacteria → digestion impaired and fatty acids and • Some short-chain fatty acids fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein.

Figure 23.32 (3 of 4)

Disorders of the Digestive System Disorders of the Digestive System

• Colon cancer • Colon cancer – Second most common cause of cancer death in – Contributing factors U.S. in men • Contact time with carcinogenic material in colon • 98,000 new cases annually – Diets high in animal material = slowed motility • 48,000 deaths/year • P53 (tumor suppressor gene) mutation – Diagnosis • Hereditary component • Colonoscopy – Fiberoptic endoscope – Polyps often occur before tumor

Disorders of the Digestive System Disorders of the Digestive System

• Gallstones • Celiac disease – A.K.A. cholelithiasis – Autoimmune disease – Bile salts precipitate – Immune system destroys intestinal villi in • Block bile ducts response to gluten • Jaundice due to bilirubin – No villi = no nutrient absorption – Treatment • Lithotripsy • Medications • Cholecystectomy

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