ESOPHAGUS

Hiatal (diaphragmatic) Hernia

Histology of the Esophagus Wall has 3 layers: Mucosa  stratified squamous Normal 3 layers. Submucosa  large mucous glands Muscularis  Upper 1/3 is skeletal Middle is mixed Lower 1/3 is smooth Upper & lower esophageal sphincters are prominent circular muscle Skeletal and smooth Figure 24.9

Histology of the Esophagus Adventitia Outermost layer of esophagus Connective tissue Blends with surrounding connective tissue No peritoneum Differences from serosa Serosa  lubrication  secretions Adventitia  binds structures  no secretions Figure 24.9

Physiology of the Esophagus - Deglutition Figure 24.10 Physiology of the Esophagus - Deglutition Moves bolus from the mouth to the stomach. Facilitated by saliva and mucus. Involves the mouth, tongue, pharynx, and esophagus. It consists of 3 stages: Voluntary stage Pharyngeal stage Esophageal stage

Physiology of the Esophagus - Deglutition Figure 24.10 Physiology of the Esophagus - Deglutition Voluntary stage Food: Tongue  back of oral cavity  oropharynx Pharyngeal stage Moves food from pharynx to esophagus Receptors in oropharynx stimulate deglutition center in M.O. Breathing stops and airways are closed Uvula and soft palate lift to close off nasopharynx Vocal cords close Epiglottis closes over larynx Upper esophageal sphincter relaxes

Figure 24.10ab Deglutition (swallowing)

Physiology of the Esophagus - Deglutition Figure 24.10 Physiology of the Esophagus - Deglutition 3. Esophageal stage Bolus enters esophagus. Upper sphincter relaxes when larynx is lifted Peristalsis begins Circular fibers contract behind bolus Longitudinal fibers shorten the distance Lower sphincter relaxes as food approaches Travel time: Solids: 4-8 seconds Liquids: 1 second

Deglutition Summary Swallowed food Mouth Oropharynx Laryngopharynx Upper esophageal sphincter Esophagus Peristalsis Lower esophageal sphincter Stomach

STOMACH

Stomach J shaped enlargement of GI tract Figure 24.11a Stomach J shaped enlargement of GI tract Mixing chamber and holding reservoir Some absorption Does very little “digestion” Starts digestion of proteins Continues lipid and starch digestion Semisolid bolus converted to chyme Size of your fist. Expands. 2 curves

Stomach Four Main Regions: Cardia Fundus Body Pyloris Three regions: Figure 24.11b Stomach Four Main Regions: Cardia Fundus Body Pyloris Three regions: Pyloric antrum Pyloric canal Pylorus Communicates with duodenum via pyloric sphincter Rugae – folds in mucosa when stomach empty

Histology of the Stomach Figure 24.12a Histology of the Stomach Same layers as rest of GI with some modifications: Surface of mucosa – simple columnar cells called surface mucous cells

Histology of the Stomach Figure 24.12b Histology of the Stomach Epithelial cells extend into the lamina propria forming gastric pits and 3 types of exocrine gastric glands. Mucous neck cells Zymogenic (chief) cells Parietal (oxyntic) cells

Histology of the Stomach Figure 24.12b Histology of the Stomach Gastric glands also contain entero-endocrine cells (G cells) Gastrin Stimulate gastric activity

Figure 24.12c Histology of the stomach

Histology of the Stomach Figure 24.12a Histology of the Stomach Muscularis has 3 layers of smooth muscle instead of 2 longitudinal, circular, and an inner oblique layer.

Histology of the Stomach The serosa is a part of the visceral peritoneum. At lesser curvature, visceral peritoneum = lesser omentum. At greater curvature, visceral peritoneum = greater omentum.

Digestion in the Stomach Mechanical Chemical Peristalsis Propulsion Retropulsion https://www.youtube.com/watch?v=hpS5kMn_B0I Gastric emptying* 2-6 hours after ingestion 1st carbs, 2nd protein, last fats Salivary amylase Lingual lipase Parietal cells – HCl H+ Cl- Proton pumps Carbonic anhydrase Antiporters HCO3- Pepsinogen  pepsin Gastric lipase

Figure 24.13 Secretion of HCl (hydrochloric acid) by parietal cells in the stomach

Protection of the Stomach Figure 24.12b Protection of the Stomach Zymogenic cells Pepsinogen  pepsin pH of 2 activates Prevents digestion of protein in organ Protection Surface and neck cells 1-3 mm alkaline mucous Limited absorption Certain drugs (aspirin, alcohol), electrolytes, some water

PANCREAS

Pancreas Retroperitoneal gland Head, body and tail Figure 24.14a Pancreas Retroperitoneal gland Head, body and tail Connects to duodenum via 2 ducts Secretes pancreatic juices Hepatopancreatic ampulla

Figures 24.14b and c

Histology of the Pancreas Small clusters of glandular epithelial cells Exocrine  Acini – 99% of clusters Secrete pancreatic juice Endocrine  Pancreatic islets – 1% of clusters Secrete hormones

Pancreatic Juice Clear liquid: Water, salt, sodium bicarbonate, and enzymes Starch – pancreatic amylase Proteins – trypsin, chymotrypsin, carboxypeptidase Fats – pancreatic lipase Nucleic acids – ribonuclease, deoxyribonuclease Sodium bicarbonate – brings pH to 7.1-8.2 Inactivates pepsin Stimulates pancreatic enzymes

LIVER AND GALLBLADDER

Liver Right and left lobes Falciform ligament 2nd largest organ Figure 24.15a Liver Right and left lobes Falciform ligament Quadrate and caudate lobes Lobules 2nd largest organ Heaviest gland

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

Histology of the Liver Lobules Contain: Hepatocytes (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 24.16 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 24.16b Histology of the Liver Lobules Contain: 4. Stellate reticuloendothelial cells Fixed phagocytes in hepatocytes Hepatic macrophages 5. Central vein

Figure 24.16d Histology of a lobule, the functional unit of the liver

Three models – pg. 911 Hepatic Lobule – functional unit Portal Lobule – exocrine (bile) function Hepatic Acinus – more recently preferred functional unit

Bile Gallbladder Sac located beneath liver Figure 24.15 Gallbladder Bile Sac located beneath liver Fundus, body and neck Mucosa - simple columnar arranged in rugae No submucosa Muscularis ejects bile into cystic duct Serosa - visceral peritoneum Store and concentrate bile Water, bile salts, cholesterol, lecithin, ions, bile pigments Excretory product (worn out RBCs)  bilirubin Emulsification of triglycerides.

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

Assignment for the weekend Read through all the notes we have currently done. Come to class Monday with any questions or required clarification. Read through pages of notes on Digestion and Absorption in the small intestine Look at pages 918-922 in textbook Focus on understanding diagram 24.21 on page 921