Chapter 15 A&P2
The "Tube" Cont.
*Adventitia/Serosa - outer layer -ADVENTITIA is fibrous connective tissue in head, neck and thoracic cavity and rectum that attaches digestive tract to surrounding structures -SEROSA is a smooth slick serous membrane in the abdominal cavity also called the visceral peritoneum, surrounds the digestive tract, forms a membrane (the mesentery) that suspends the digestive tract in the abdominal cavity, then lines the abdominal cavity (parietal peritoneum). -The visceral and parietal peritoneum secrete peritoneal fluid as a lubricant
Large Intestine
*An area of recovery where water (8-9 liters/day into digestive tract, liters/day out with feces), minerals, and some vitamins are recovered from the mostly indigestible material and feces is formed and expelled. *Symbiotic bacteria are maintained and feed on what we cannot digest - the waste contains some important substances like vitamin K and biotin (B-7). *Divided into several major regions - about 1.5 m total - cecum, colon and rectum and anal canal. *The colon is supported by mesocolon. *Cecum connects to the ileum separated by the ileocecal valve; a short section that receives chyme from the small intestine. *The vermiform appendix is a blind pouch that connects to the cecum.
Specialized Regions of the Digestive Tract- Mouth (Oral Cavity & Vestibule)
*Area where food is ingested; mechanical breakdown begins (mastication); food is lubricated by mucus and saliva; some chemical digestion begins (carbohydrates); *Analysis of food occurs (taste, texture, temperature). *Bounded by cheeks, lips, hard palate, soft palate with uvula, tongue. *Prominent tooth bearing ridges covered with gingivae partially divide cavity. *Tongue forms most of floor; used to manipulate food and sense details of food. *Lymphatic nodules beneath surface help remove bacteria, etc. that enter mouth: -lingual, palatine, pharyngeal tonsils *Salivary glands (accessory glands) 3 pairs - parotid, sublingual, submandibular - 1.0-1.5 liter saliva /day - water dissolves food - mucus lubricates food (mucous glands common around mouth) - lysozyme and antibodies are antibacterial agents to kill bacteria - salivary amylase is digestive enzyme to digest starches - pH buffers reduce acidity
Regulation of Digestion: Movements and Secretions within the Digestive System!
*Cephalic phase: taste, smell, sight, thought of food stimulates (via parasympathetic nerves) salivary glands to secrete saliva, gastric glands to secrete gastric juices and the muscularis of stomach to begin churning. *Gastric phase: when food enters the stomach the wall is distended, triggering stretch receptors. This reinforces the cephalic phase - gastric glands are stimulated, stomach churning is stimulated and the hormone gastrin (produced in gastric glands) stimulates the lower esophageal sphincter (aka cardiac sphincter) to contract. Gastrin also stimulates the gastric glands and muscularis of stomach and it inhibits (so they relax and open) the pyloric sphincter and the ileocecal sphincter (this allows food to be moved along the digestive tract). *Intestinal phase: when acid chyme enters duodenum the acid stimulates sympathetic nerves that block stimulation of parasympathetic nerve stimulation of stomach, inhibiting gastric glands and the stomach muscularis churning.
Regulation of Digestion Cont.
*Distention of the duodenum stimulates parasympathetic nerves that stimulate segmentation and peristalsis. *The acid chyme stimulates the production of the hormone secretin which stimulates the pancreas to produce pH buffer. *The proteins and fats in the chyme stimulate the production of the hormone cholecystokinin (aka CCK) which stimulates the pancreas to secrete digestive enzymes, the gall bladder to contract forcing bile into the duodenum, the pyloric sphincter to contract. CCK also inhibits the gastric glands and stomach churning. *Why do things have to be so complicated!!!!
Small Intestine: Major Region of Chemical Digestion and Absorption
*Duodenum (20-30 cm), separated from the stomach by the pyloric sphincter *Jejunum (2.5 meters), most chemical digestion and absorption occurs here *Ileum (3.6 meters), an area of some absorption *The ileocecal valve is a sphincter that closes the distal end of the small intestine *The mucosa is made of simple columnar epithelium. *Has a series of permanent folds (plicae circulares), finger-like projections (villi) and each cell has folds (microvilli) - increase surface area 600 times *Each villi contains a capillary bed and a large lymph capillary, a lacteal.
Structure and Function
*FUNCTION: Digestive system processes the food used as fuel and nutrients for the body *STRUCTURE: Composed of a tube through the body (digestive tract, gastrointestinal tract or alimentary canal) and accessory organs (salivary glands, liver, gall bladder and pancreas). *Tube has specialized regions to perform specialized functions
More Accessory Glands
*LIVER - large organ involved in many metabolic functions. *Composed of cells called hepatocytes arranged into functional units, lobules *Each lobule contains a sinusoid, a large permeable capillary, that empties into a central vein. Hepatocytes are arranged as plates along the sinusoid. *Each lobule receives blood from two sources, the hepatic portal vein carrying absorbed food from the intestine and the hepatic artery carrying oxygenated blood. *Each lobule also contains bile canaliculi that collect the bile produced by hepatocytes - the canaliculi merge to larger ducts to common bile duct to duodenum or cystic duct to gall bladder. *Bile is a break down product of hemoglobin from the destruction of old red blood cells. It contains bile salts is used to emulsify fats in the intestines. *The gall bladder stores excess bile until needed
Chemical Digestion
*Large organic molecules (polymers) must be broken into small subunits (monomers) in order to pass through cell membrane of mucosa (absorption) *Digestive enzymes break chemical bonds to form smaller molecules *Bile emulsifies lipids (fats) *Know the following enzymes, where they are produced and what they digest: ***Salivary glands - salivary amylase (carbohydrates) ***Gastric glands - pepsin (proteins) ***Liver - bile (emulsifies fats) ***Pancreas - amylase (carbohydrates) nuclease (nucleic acids) lipase (fats) trypsin, chemotrypsin, carboxypeptidase (proteins)
MORE of the Poop Shoot
*Muscularis is of circular and longitudinal smooth muscle *Three thin bands of longitudinal muscle run along either side of the cecum and colon, called the taenia coli. *Muscle tone in the taenia coli pull the colon into pouches called haustra *Mass peristalsis (mass movement) moves food from haustra to haustra *The last portion of the circular muscle of the anal canal forms the internal anal sphincter - this is smooth muscle under unconscious control. *Skeletal muscle of the abdominal floor forms the external anal sphincter - this is muscle that is under conscious control.
Pharynx: Connects Mouth & Esophagus
*Oropharynx and laryngopharynx (nasopharynx is above soft palate and is not part of digestive tract) *Mucosa and muscularis same as oral cavity (stratified squamous epithelial cells and skeletal muscle).
Accessory Digestive Glands: (Salivary Glands, Pancreas, Liver)
*PANCREAS - a gland that is part endocrine (1%) and part exocrine (99%) *The exocrine portion (glands with ducts that deliver its secretions) produces an alkaline pH buffer (sodium bicarbonate) and several very effective digestive enzymes for all types of molecules. (pancreatic juices 1-1.5 liters/day) *The enzymes are secreted in inactive form and are activated in the intestine *Exocrine secretions enter small ducts that merge to larger ducts - pancreatic duct joins with common bile duct just before entering the duodenum.
Mouth Cont.
*Teeth - hard structures used to masticate food - root (in socket by periodontal ligament), neck and crown (above gingivae) - enamel covers crown; dentin forms bulk of tooth; pulp cavity is central area that contains blood vessels and nerves; cementum around root - incisors (8) clipping or cutting, cuspids (4), bicuspids (8) shearing and chopping , molars (12) crushing and grinding *Mucosa made of stratified squamous epithelium (resist abrasion) *Muscularis made of skeletal muscle
Stomach: Located in upper left of abdominal cavity
*Temporary storage of ingested food, gradual release (3-4 hour processing) *Some mechanical breakdown of food by churning, some chemical digestion (food at this point is a thick liquid called chyme) *Production of intrinsic factor necessary for some vitamin absorption *Several regions can be distinguished: - cardiac, an area around the connection with the esophagus (this forms the cardiac sphincter, which is the same as the lower esophageal sphincter) - fundic, an area that extends above the cardiac region for temporary storage - body, large main part of the stomach - pylorus, narrow lower portion that connects to small intestine - pyloric sphincter, valve that closes to regulate chyme passing into intestine
More Small Intestine
*The blood capillaries merge into hepatic portal system to the liver *The lacteals pick up materials, especially fats, and transport them into blood. *Intestinal glands form at bottom of folds between villi -secrete intestinal juices which contain mucus and water (1.8 liters/day). *Duodenal glands secrete thick alkaline mucus *Duodenal endocrine cells secrete several hormones important in regulation of the digestive process. *Cells in mucosa secrete some digestive enzymes *The muscularis is composed of longitudinal and circular smooth muscle *Peristalsis moves food slowly along small intestine *Segmentation is a type movement that mixes chyme.
Large Intestine Cont.
*The colon is divided into the ascending, transverse, descending and sigmoid colon *The rectum is the last 20 cm and fills just prior to defecation *Anal canal is the last portion of the rectum that ends at the anus *The mucosa is made of simple columnar epithelium *Mucous glands are common but no digestive glands and no villi *Beginning in the anal canal the mucosa is made of stratified squamous epithelium (for abrasion resistance).
Stomach Cont.
*The mucosa is made of simple columnar epithelium (cells specialized for secretion and absorption - in the stomach little absorption occurs) *Large accordion - like fold, the rugae, allow the stomach to expand (1 -1.5 liters) *Mucus glands produce thick alkaline mucus which protects epithelium from acids and digestive enzymes *Folds in epithelium form gastric pits and gastric glands; secrete gastric juice (2-3 liters/day) - parietal cells secrete hydrochloric acid (HCl) and intrinsic factor (helps absorb vitamin B12) - chief cells secrete pepsinogen, which is activated by acid to pepsin to begin the chemical digestion of proteins - other cells secrete a hormone called gastrin (more on this later)
More on Stomach...
*The muscularis is composed of circular, longitudinal and oblique layers of smooth muscle - this extra muscle layer improves mixing. *The serosa (visceral peritoneum) forms two mesenteries: - the lesser omentum suspends the stomach from the liver - the greater omentum hangs down over the abdominal viscera
The "Tube"
*The tube is composed of four layers "from mouth to anus", modifications in each region. *LUMEN- the opening in the center of the tube where the food is located *MUCOSA- inner lining; mucous membrane made of epithelial tissue with supporting connective tissue and smooth muscle, numerous mucus glands. -Type of epithelium and contour specialize by region *MUSCULARIS- two layers of muscle, an inner circular layer and an outer longitudinal layer and an oblique layer in the stomach -Composed of smooth muscle (skeletal muscle in the mouth, pharynx, upper esophagus, anal canal) -Causes movement of food along tract and other mixing movements
Peristalsis: Food moving along the Tube
1. Bands of circular muscle contract as waves behind bolus, decreasing diameter of tube and pushing bolus forward 2. Longitudinal muscles in front of bolus contract, making tube shorter and wider so that bolus moves easily forward 3. Sphincters relax ahead of bolus
Swallowing (deglutition): Moving food from mouth to esophagus
1. Food is mixed with saliva and pressed into bolus by tongue 2. The bolus is pushed up and back by the tongue 3. This voluntary action pushes the bolus into the oropharynx, triggering the involuntary reflex described below. 4. The soft palate is pushed up to close the nasopharynx 5. The larynx is pulled up and the epiglottis folds over the glottis - this opens the esophagus and closes the larynx. Pulmonary ventilation is stopped. 6. The bolus is moved into and along the esophagus by peristalsis.
Esophagus: Tube that Carries Food from Pharynx to Stomach
1. Through mediastinun and diaphragm into abdominal cavity 2. Mucosa is made of stratified squamous epithelium 3. Muscularis is skeletal muscle in upper portion and smooth muscle in lower. 4. Adventitia - connective tissue that anchor esophagus to surrounding 5. Circular muscle bands form sphincter at each end - upper and lower esophageal (cardiac) sphincter - prevent food from moving backwards 6. Deglutition (swallowing) moves food into esophagus from oral cavity 7. Food moved through esophagus by peristalsis
Digestive Tract Processes
Ingestion- taking food into the mouth. Mechanical processing - *mixing movements (mastication, segmentation) produce mechanical digestion. *propelling movements (swallowing, peristalsis) moving food along the tract. Chemical digestion- breaking down food by breaking chemical bonds. Secretion- production and release of substances into the Lumen. Absorption- movement of small molecules into cells. Excretion (defecation)- removal of waste, undigestible material.