LIVER AND GALLBLADDER

Liver Figure 24.16a 2nd largest organ Heaviest gland Right and left lobes Falciform ligament

Liver Quadrate and caudate lobes in the right lobe Lobules

Histology of the Liver Lobules Contain: Hepatocytes Bile canaliculi Sinusoids Stellate reticuloendothelial cells Central vein

Histology of the Liver Lobules Contain: Hepatocytes / hepatic cells (80%) Major functional cells of the liver Bile canaliculi Small ducts between hepatocytes Collect bile produced by the hepatocytes Bile pathway* Sinusoids Permeable blood capillaries between rows of hepatocytes

Figure 24.18 From GI organs and spleen Vitamins, nutrients, drugs, toxins, microbes Liver Lobules Double supply of blood All leaves through hepatic vein

Histology of the Liver Lobules Contain: Figure 24.17 Histology of the Liver Lobules Contain: 4. Stellate reticuloendothelial cells Fixed phagocytes in hepatocytes Hepatic macrophages 5. Central vein

Figure 24.17 Histology of a lobule, the functional unit of the liver

Hepatic Acinus

Three models – pg. 924-925 Hepatic Lobule – functional unit Portal Lobule – exocrine (bile) function Hepatic Acinus – more recently preferred functional unit

Figure 24.16 Gallbladder Sac beneath liver Fundus, body, neck

Gallbladder Mucosa Simple columnar Rugae No submucosa Muscularis Smooth muscle Ejects bile into cystic duct Serosa Visceral peritoneum FUNCTION - Store and concentrate bile

Bile Yellow, brown, olive Water, bile salts, cholesterol, lecithin, ions, bile pigments Excretory product (worn out RBCs)  bilirubin Digestive secretion  Emulsification of triglycerides.

Bile Pigment Bilirubin

Bile pathway: produced by hepatocytes  bile canaliculi  bile ductules  bile ducts  R and L hepatic ducts  common hepatic duct  cystic duct (storage)  common bile duct  hepatopancreatic ampulla  duodenum to aid digestion

Other Liver Functions Metabolism of carbohydrates, lipids, proteins Removal of substances Drugs Hormones Excretion of bilirubin Synthesis of bile salts Vitamin and mineral storage Phagocytosis Activation of vitamin D

SMALL INTESTINE

Small Intestine Majority of digestion and absorption Figure 24.19 Small Intestine Majority of digestion and absorption Pyloric sphincter  ileocecal sphincter 3 regions: Duodenum, jejunum, ileum Same 4 layers as most of GI

Mucosa Figure 24.19b

Figure 24.20 Histology of the small intestine

Mucosa Figure 24.20 S cells CCK cells K cells

Mucosa Figure 24.21

Figure 24.21

Figure 24.21 Brush border of Absorptive cells Brush border enzymes work inside epithelial cells (surface of microvilli) Carbs, proteins, nucleic acids Some absorptive cells slough off to act in the lumen

Intestinal Juice Clear to yellow fluid Composition is highly variable Hormones, enzymes, mucus, neutralizing substances Alkaline pH Vehicle for absorption Composition of enzymes Depends on food actually eaten

Submucosa Duodenum Duodenal glands (Brunner’s) Alkaline mucous Ileum Figure 24.21 Duodenum Duodenal glands (Brunner’s) Alkaline mucous Ileum Lymphatic nodules (Peyer’s patches)

Mechanical Digestion Segmentation and Peristalsis (MMC)

Assigned Reading Digestion and Absorption in the small intestine Look at pages 931-936 in textbook Pay attention to enzymes and where they act and what they break down. Take note of when they are activated / inactivated. Focus on tables 24.4 and 24.5 (pages 936-937) Focus on understanding diagram 24.22 on page 934

Absorption End products of digestion moves into the blood or lymph. Occurs by diffusion, facilitated diffusion, osmosis and various forms of active transport. MICELLES CHYLOMICRON

Water Absorption via osmosis Fig 24 Water Absorption via osmosis Fig 24.23 Based on electrolyte and nutrient [ ]

LARGE INTESTINE

Large Intestine (colon) Completion of: absorption production of vitamins formation and expulsion of feces Terminal portion of GI tract Ileocecal sphincter  anus Cecum, colon, rectum, anal canal Colon = ascending, transverse, descending, sigmoid

Figure 24.24

Histology of the L.I Summary Mucosa Simple columnar epithelium No villi or permanent circular folds Absorptive and goblet cells in crypts Crypts of Lieberkuhn Microvilli Submucosa Areolar connective tissue

Figure 24.25

Figure 24.25b

Figure 24.25 c / d

Histology of the L.I Summary Muscularis Internal circular smooth muscle External longitudinal muscle Teniae coli Haustra Serosa Visceral peritoneum Omental appendices

Epiploic appendages or omental appendices

Rectum and Anus Figure 24.24b Rectum Anal canal Anal columns  mucous membrane  longitudinal folds Anus Internal anal sphincter  smooth muscle External anal sphincter  skeletal muscle

Mechanical Digestion Chemical Digestion Gastroileal reflex Haustral churning Peristalsis Mass peristalsis Bacterial fermentation Absorption Feces Formation Water Electrolytes Some vitamins Inorganic salts Sloughed-off epithelial cells Bacteria Indigestible and unabsorbed food

Water Absorption via osmosis Fig 24 Water Absorption via osmosis Fig 24.22 Based on electrolyte and nutrient [ ]

Defecation Reflex

Look at tables 24.6 and 24.7

PHASES OF DIGESTION

Three Phases of Digestion Cephalic Phase Gastric Phase Intestinal Phase

Cephalic Phase Cerebral cortex, hypothalamus, and brainstem Activated by sight, smell, thought, and taste of food. Brainstem activates parasympathetic nuclei: CN VII – salivation CN IX – salivation CN X – gastric juice Prepares mouth and stomach for food that is about to be eaten

Gastric Phase Begins when food reaches the stomach Promotes gastric secretion and motility Neural and Hormonal regulation

Gastric Phase – Neural Regulation Food entering stomach increases gastric juice pH and distends stomach walls. Chemoreceptors and stretch receptors in stomach Detect pH increase Detect distention Send nerve impulses to submucosal plexus Submucosal plexus stimulates: Parietal cells to secrete HCl Muscularis to contract more vigorously Causes mixing and initiates gastric emptying.

Figure 24.26 Neural Feedback Loop Food entering stomach Disrupts homeostasis by increasing CONTROLLED CONDITION pH of gastric juice Distention (stretching) of stomach walls RECEPTORS Chemoreceptors and stretch receptors in stomach detect pH increase and distension Input Nerve impulses CONTROL CENTER Return to homeostasis when response brings pH of gastric juice and distention of stomach walls back to normal (pre-eating status) Submucosal plexus Output Nerve impulses (parasympathetic) EFFECTORS Smooth muscle in stomach wall Parietal cells HCI Parietal cells secrete HCI Smooth muscle contracts more vigorously RESPONSE Increase in acidity of stomach chyme; mixing of stomach contents; emptying of stomach

Gastric Phase – Hormonal Regulation Food entering stomach increases gastric juice pH and distends stomach walls. ANS is triggered to release acetylcholine. ACh stimulates G cells in pyloric antrum and secrete gastrin hormone into blood.

Gastrin’s Actions Major Effects Promotes gastric juice secretion Increases gastric motility Promotes gastric mucosal growth Minor Effects Constricts lower esophageal sphincter Relaxes pyloric and ileocecal sphincters

Intestinal Phase Begins when food enters the small intestine. Inhibits gastric secretion and motility. Promotes intestinal and pancreatic juice secretion, bile ejection, and intestinal motility. Regulated by neural and hormonal activities.

Intestinal Phase – Neural Regulation Gastric emptying of chyme into small intestine distends duodenal walls. Stretch receptors detect distention  nerve impulses to brainstem. Brainstem ↓ parasympathetic and ↑ sympathetic nerves to stomach and pyloric sphincter. Gastric motility and emptying is inhibited.

Intestinal Phase – Hormonal Regulation Chyme containing digested proteins and fatty acids stimulates intestinal glands to secrete cholecystokinin into blood. Acidic chyme stimulates intestinal glands to secrete secretin into blood.

Secretin’s Actions Major Effects Stimulates secretion of pancreatic juice and bile rich in HCO3- Minor Effects Inhibits gastric juice secretion Promotes normal pancreatic growth and maintenance Enhances CCK’s effects

CCK’s Actions Major Effects Minor Effects Stimulate secretion of enzyme-rich pancreatic juice Ejection of bile from gallbladder Opens sphincter of hepatopancreatic ampulla (oddi) Minor Effects Inhibits gastric emptying Promotes normal pancreatic growth and maintenance Enhances secretin’s effects

Table 24.8 Major Hormones that Control Digestion There are at least 10 other hormones involved in the GI tract

Development and Aging of the Digestive System Read the last page in your notes Read pages 945-946 in your textbook Add any important information to your notes on these two topics.