5. Secretion: release of water, acids. Enzymes, buffers by digestive tract.

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1 Digestive System CH-16 Lecture topics Functions of the digestive system: p Ingestion: Taking food in 2. Propulsion: movement of food thru alimentary canal p.490. voluntary: swalloing : skeletal muscle involuntary: peristalsis : smooth muscle 3. Mechanical processing: physical breaking of food chewing by teeth churning by stomach segmentation by intestines (= mixing food) p (Chemical ) Digestion: by enzymes (= globular proteins), secreted by digestive exocrine glands number of steps in which macromolecules break down to the buildiong blocks carbohydrates break down to sugar proteins break down to amino acids lipids break down to fatty acids + phosphoric acid DNA (nucleic acid) break down to nucleotides 5. Secretion: release of water, acids. Enzymes, buffers by digestive tract. 6. Absorption: transport of building blocks of digested macromolecules to blood & lymph( fatty acids) from the lumen of the alimentary canal. 7. Excretion: removal of waste from the body: defecation General Histology: mucus membrane: epithelium smooth muscle: ANS control serous membrane: peritoneum Aniko Szabo Hill MD, PhD 1 of 9

2 GI tract: structure and functions of organs Organs of the alimentary canal: mouth pharynx esophagus stomach small intestines large intestines Mouth and Its Accessory Organs 1. Mouth (oral cavity) Histology: stratified squamous (thick epithelium for solid food) Superior border: hard & soft palate Functions: Ingestion Mechanical digestion: Chemical digestion: sugar digestion begins here by amylase!!! 2. Teeth 3. Tongue - functions to manipulate food while chewing & swallowing 4. Salivary Glands: Types: Parotid glands Submandibular glands Sublingual glands Saliva Contents and their functions: - mucus and water - salivary amylase digests complex carbohydrates - antibacterial proteins Aniko Szabo Hill MD, PhD 2 of 9

3 Pharynx location: muscular tube posterior to nasal-, oral cavity histology: - stratified squamous (solid food) - skeletal muscle for voluntary swallowing subdivisions: nasopharynx oropharynx laryngopharynx: this is where food and air cross each other function: swallowing Esophagus Location: thoracic cavity, behind trachea, continuation of pharynx piercing thru the diaphragm joins stomach at cardia Histology: stratified squamous (thick epithelium for solid food) smooth muscle for peristalsis Function: peristalsis food to stomach at cardia cardiac sphincter pass portions of food to stomach Aniko Szabo Hill MD, PhD 3 of 9

4 Stomach Location: left hypochondric region + epigastric region from esophagus to duodenum Gross anatomy: cardiac/gastroesophageal sphincter, pyloric sphincter, rugae body Histology: simple columnar epithelium (thin epithelium for liquid food) drawing of stomach: Functions: Temporary Storage Mechanical digestion:churning Chemical digestion: HCl (acid environment) and pepsin (digests proteins) Propulsion Chyme= juice = food is not solid any more, like paste Aniko Szabo Hill MD, PhD 4 of 9

5 Small Intestine Location: all 9 regions of the abdominal cavity Gross Anatomy: duodenum + jejunum + ileum: 20 feet/ 7 m long Histology p Type of epithelium: simple columnar epithelium (thin epithelium for liquid food) 3 Levels of folding of mucus membrane increases absorption surface to 200 m2 -Plicae: folding of mucosa -Villi: finfer-like projections of mucosa -Microvilli: tiny projections of plasma membrane = brush border brush border enzymes: final stages of digestion Functions: into Blood capillaries: absorption into Lacteals: fat absorption intestinal glands watery intestinal juice mechanical digestion: segmentation (=mixing food) Chemical digestion: Brush border enzymes complete digestion of carbohydrates and proteins Propulsion Aniko Szabo Hill MD, PhD 5 of 9

6 Large Intestine Location: abdomino-pelvic cavity frames small intestines on 3 sides from ileocecal valve to anus Gross Anatomy: Five Subdivisions of the Large Intestine: Cecum- ileocecal valve Appendix Colon: ascending + transverse + descending + sigmoid Rectum pelvic floor Anal Canal (external to pelvic cavity) Histology Mucosa: simple columnar epithelium (except anus, where solid stuff passes stratified squamous) no foldings, no villi, no enzymes!!!!!!! Functions Propulsion Mass movements: 3-4 times a day Absorption: water + electrolytes Formation of feces Aniko Szabo Hill MD, PhD 6 of 9

7 Accessory organs: Structure and function: teeth tongue gall bladder exocrine glands: salivary glands + liver + pancreas Pancreas Location: in abdominal cavity b. spleen + duodenum hanging on back wall Gross Anatomy: head + body + tail main pancreatic duct duodenum Histology: Endocrine cells in pancreatic islets: insulin + glucagon Exocrine secretory cells Exocrine function: pancreatic juice secretion Produces bicarbonates (to neutralize acid) Produces pancreatic enzymes pancreatic amylase enzyme (digests complex carbohydrates) pancreatic lipase enzyme (digests fats) pancreatic proteases enzyme (digest proteins) Aniko Szabo Hill MD, PhD 7 of 9

8 Gall bladder: Location: ventral surface of liver Macroscopy: muscular sac for bile storage cyctic duct common hepatic duct Function: bile storage bile concentration bile delivery to duodenum ( by cholecytokinin hormone) Liver Location: right hypochondric region + epigastric region protected by rib-cage Gross Anatomy Right lobe Left lobe ducts are on next page!!!! Functions: Detoxification Red blood cell destruction Bile production Other metabolic functions Bile Production and Function Produced by hepatocytes Function of bile: needed for complete fat digestion Aniko Szabo Hill MD, PhD 8 of 9

9 FLOW CHART: PATHWAY OF BILE Bile from: Bile from Right Lobe Left Lobe bile canaliculi bile canaliculi small bile ducts small bile ducts right hepatic duct left hepatic duct common hepatic duct Stored Bile from Gall Bladder cystic duct common bile duct pancreatic duct duodenum Aniko Szabo Hill MD, PhD 9 of 9