Digestive System Part 2

Anatomy and Physiology of the Digestive System  Small intestine  Major organ of digestion and absorption  2–4 m long; from pyloric sphincter to ileocecal valve  Subdivisions Duodenum  Jejunum  Ileum 

Anatomy and Physiology of the Digestive System  Small intestine  Structural modifications  Villi  Intestinal glands

Mucosa  Submucosa 

Mouth (oral cavity) Tongue

Esophagus

Liver Gallbladder Duodenum Jejunum Small intestine Ileum

Anus

Parotid gland Sublingual gland Salivary Submandibular glands gland Pharynx Stomach Pancreas (Spleen) Transverse colon Descending colon Ascending colon Large Cecum intestine Sigmoid colon Rectum Vermiform appendix Anal canal Figure 23.1

Vein carrying blood to hepatic portal vessel

Muscle layers Circular folds Villi

Lumen

(a) Figure 23.22a

Microvilli (brush border)

Absorptive cells

Lacteal Goblet cell Blood capillaries Mucosa associated lymphoid tissue Intestinal crypt Muscularis mucosae Duodenal gland (b)

Vilus

Enteroendocrine cells Venule Lymphatic vessel Submucosa Figure 23.22b

Microvilli

(b)

Absorptive cell Figure 23.3b

Anatomy and Physiology of the Digestive System  Chemical digestion in the small intestine  Food entering SI = partially digested  Intestinal juice  Water, mucous

 Crypt cells produce lysozyme

Microvilli (brush border)

Absorptive cells

Lacteal Goblet cell Blood capillaries Mucosa associated lymphoid tissue Intestinal crypt Muscularis mucosae Duodenal gland (b)

Villus

Enteroendocrine cells Venule Lymphatic vessel Submucosa Figure 23.22b

Anatomy and Physiology of the Digestive System  Chemical digestion in the small intestine  Pancreatic juice  Enzymes

Amylase o Carbohydates  Lipase o Fats  Trypsinogen, chymotrypsinogen, carboxypeptidase o Activated to digest protein  Sodium bicarbonate  Neutralize stomach acid 

Stomach

Pancreas Epithelial cells Membrane-bound enteropeptidase Trypsinogen Trypsin (inactive) Chymotrypsin Chymotrypsinogen (inactive) Carboxypeptidase Procarboxypeptidase (inactive)

Figure 23.27

Anatomy and Physiology of the Digestive System  Chemical digestion in the small intestine  Bile  Emilsify lipids

 Disaccharides and peptidases

 Protective mucous secreted as well

Right and left hepatic ducts of liver Cystic duct Common hepatic duct Bile duct and sphincter Accessory pancreatic duct

Mucosa with folds Gallbladder Major duodenal papilla Hepatopancreatic ampulla and sphincter

Tail of pancreas Pancreas Jejunum

Duodenum

Main pancreatic duct and sphincter Head of pancreas Figure 23.21

Anatomy and Physiology of the Digestive System  Accessory digestive organs  Liver  Pancreas  Gallbladder

Anatomy and Physiology of the Digestive System  Accessory digestive organs  Liver  Largest internal surface area of any body organ  Blood supply   

Hepatic artery Hepatic-portal vein Hepatic vein

Inferior vena cava (not part of hepatic portal system) Hepatic veins

Liver Hepatic portal vein

Small intestine

Gastric veins Spleen Inferior vena cava Splenic vein Right gastroepiploic vein Inferior mesenteric vein Superior mesenteric vein Large intestine

Rectum

(c) The hepatic portal circulation. Copyright © 2010 Pearson Education, Inc.

Figure 19.29c

Interlobular veins (to hepatic vein)

Central vein

Sinusoids Bile canaliculi

Plates of hepatocytes

Bile duct (receives bile from bile canaliculi) Fenestrated lining (endothelial cells) of sinusoids

Portal vein

Hepatic macrophages in sinusoid walls

Bile duct Portal venule Portal arteriole

Portal triad

(c) Copyright © 2010 Pearson Education, Inc.

Figure 23.25c

Anatomy and Physiology of the Digestive System  Accessory digestive organs  Liver  Microscopic compartments = lobules 

Lined by hepatocytes = screen blood o Store nutrients o Manage toxins

Sternum Nipple Liver

Bare area Falciform ligament Left lobe of liver

Right lobe of liver

Gallbladder

(a)

Round ligament (ligamentum teres)

Figure 23.24a

(a)

Lobule

Copyright © 2010 Pearson Education, Inc.

(b)

Central vein

Connective tissue septum Figure 23.25a, b

Anatomy and Physiology of the Digestive System  Accessory digestive organs  Liver  Hepatocyte functions  Process blood borne nutrients  Store fat-soluble vitamins  Perform detoxification  Produce ~900 ml bile per day  Glucose is stored as glycogen

Cystic, Hepatic and Bile ducts

Right and left hepatic ducts of liver Cystic duct

Common hepatic duct Bile duct and sphincter Accessory pancreatic duct

Mucosa with folds Gallbladder Major duodenal papilla Hepatopancreatic ampulla and sphincter Copyright © 2010 Pearson Education, Inc.

Tail of pancreas Pancreas Jejunum

Duodenum

Main pancreatic duct and sphincter Head of pancreas Figure 23.21

Anatomy and Physiology of the Digestive System  Accessory digestive organs  Liver  Bile  Yellow-green, alkaline solution  Bile salts o Cholesterol derivatives that function in fat emulsification and absorption  Bilirubin o Pigment formed from heme  Metabolized to form urobilinogen → stercobilin  Lack of bile = grayish stools with fatty streaks (Acholic feces)

Anatomy and Physiology of the Digestive System  Accessory digestive organs  Liver  Other functions 

  

Makes heparin and other plasma proteins Stores vitamins, minerals and lipid soluble toxins Stores nutrients Catabolizes nitrogenous wastes

Anatomy and Physiology of the 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 o Flows into the bile duct

Anatomy and Physiology of the Digestive System  Accessory digestive organs  Pancreas  Function  Delivers digestive fluids and NaHCO3 to duodenum via pancreatic duct

 Tissue types  Endocrine o Islets of Langerhans → insulin and glucagon  Exocrine o Acinar tissue → pancreatic juice

Mouth (oral cavity) Tongue

Esophagus

Liver Gallbladder Duodenum Jejunum Small intestine Ileum

Anus

Parotid gland Sublingual gland Salivary Submandibular glands gland Pharynx Stomach Pancreas (Spleen) Transverse colon Descending colon Ascending colon Large Cecum intestine Sigmoid colon Rectum Vermiform appendix Anal canal Figure 23.1

Anatomy and Physiology of the Digestive System  Accessory digestive organs  Pancreas  Secretion mediated by hormones  Secretin o Released in response to acid o Stimulates release of base  Cholecystokinin o Released when protein and fat enter intestine o Stimulates the release of bile and pancreatic juice

Right and left hepatic ducts of liver Cystic duct Common hepatic duct Bile duct and sphincter Accessory pancreatic duct

Mucosa with folds Gallbladder Major duodenal papilla Hepatopancreatic ampulla and sphincter

Tail of pancreas Pancreas Jejunum

Duodenum

Main pancreatic duct and sphincter Head of pancreas Figure 23.21

Small duct

Acinar cells Basement membrane Zymogen granules Rough endoplasmic reticulum (a) Figure 23.26a

Slide 1

1

Chyme entering duodenum causes release of cholecystokinin (CCK) and secretin from duodenal enteroendocrine cells. 2

CCK (red dots) and secretin (yellow dots) enter the bloodstream. 3

CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO3–-rich pancreatic juice.

4

Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate liver to produce bile more rapidly. 5

CCK (via bloodstream) causes gallbladder to contract and hepatopancreatic sphincter to relax; bile enters duodenum. 6 During cephalic and gastric phases, vagal nerve stimulation causes weak contractions of gallbladder. Figure 23.28

Anatomy and Physiology of the Digestive System  Large intestine  About 1.5 meters in length in a cadaver (SI about 6m long)  Functions  Vitamins, water, and electrolytes are reclaimed  Propulsion of feces toward the anus  Colon is not essential for life

Left colic (splenic) flexure Transverse mesocolon Epiploic appendages

Right colic (hepatic) flexure Transverse colon Superior mesenteric artery Haustrum

Descending colon

Ascending colon IIeum

Cut edge of mesentery Teniae coli

IIeocecal valve Cecum Vermiform appendix

Sigmoid colon Rectum

Anal canal (a)

External anal sphincter Figure 23.29a

Anatomy and Physiology of the Digestive System  Regions  Cecum  Colon  Rectum  Anal canal

Anatomy and Physiology of the Digestive System  Regions  Cecum  Blind pouch  Appendix attaches to this area  Bacteria  Immune function

Anatomy and Physiology of the Digestive System  Regions  Colon  Ascending  Retroperitoneal  Transverse  Anchored via mesocolons (mesenteries)  Descending  Retroperitoneal  Sigmoid  Anchored via mesocolons (mesenteries)

Greater omentum Transverse colon Transverse mesocolon Descending colon Jejunum Mesentery

Sigmoid mesocolon Sigmoid colon Ileum (c) Figure 23.30c

Liver Lesser omentum Pancreas Stomach Transverse mesocolon Duodenum Transverse colon Mesentery Greater omentum Jejunum Ileum Visceral peritoneum Parietal peritoneum

(d)

Urinary bladder Rectum Figure 23.30d

Anatomy and Physiology of the Digestive System  Regions  Rectum  Rectal valves stop feces from being passed with gas  Anal canal  Last segment of the large intestine  Internal anal sphincter  Smooth muscle (involuntary)  Spinal reflex arcs  External anal sphincter  Skeletal muscle (voluntary)

Rectal valve Rectum Hemorrhoidal veins Levator ani muscle Anal canal

External anal sphincter Internal anal sphincter Anal columns Pectinate line Anal sinuses Anus (b) Figure 23.29b

Anatomy and Physiology of the Digestive System  Defectation  Mass movements force feces into rectum  Distension initiates spinal defecation reflex  Parasympathetic signals  Stimulate contraction of the sigmoid colon and rectum  Relax the internal anal sphincter  Conscious control allows relaxation of external anal sphincter  Valsalva’s maneuver

Impulses from cerebral cortex (conscious control)

1

Sensory nerve fibers

Distension, or stretch, of the rectal walls due to movement of feces into the rectum stimulates stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons. 2

Voluntary motor nerve to external anal sphincter

Sigmoid colon

A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectal walls and relaxation of the internal anal sphincter.

Stretch receptors in wall

Rectum External anal sphincter (skeletal muscle)

Involuntary motor nerve (parasympathetic division) Internal anal sphincter (smooth muscle)

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

Questions?