the digestive system consists of this canal which extends from the mouth to the anus, and several organs release secreations into the canal.

it includes: the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anal canal.  the accessory organs are salivary glands, liver, gallbladder, and pancreas.

the wall consists of 4 layers developed to different degrees from region to region

mucosa membrane

submucosa

muscular layer

serosa layer

this layer is formed of surface epithelium, underlying connective tissue and a small amount of smooth mucle. in some regions, the muscosa is folded with tiny projections that extend into passageway or lumen of digestive tube.

the mucosa also has glands that are tubular invaginations which the lining cells secrete mucus and digestive enzymes.

epithelium, connective tissue, smooth muscle-protection, secreation, absorption

mucosea protects the tissues beneath it and carries on secreation and absorbtion.

contains considerable loose connective tissue as well as glands, blood vessels, lymphatic vessels, and nerves. its vessels nourish the surrounding tissues and carry away absorbed material.

loose connective tissue, blood vessels, lymphatic vessels, nerves-noursies surrounding tissues, transports absorbed materials

provides movements of the tube, consits of two coats of smooth muscle  tissue. The fibers of the inner coat encircle the tube. when the circular fibers contract, the diameter of the tube decreases.

the fibers of the outer muscular coat run lengthwise. when theses longitudinal fibers contract the tube shortens.

smooth muscle fibers in circular and longitudinal groups-movements of the tube and its contents

outer covering of the tube, is composed of viceral peritoneum, formed of epithelium on the outside of connective tissue benath.

protect underlying tissue and secreate serous fluid, which moistens and lubricates the tubes outer surface so that the organs in the abdominal cavity slide freely against one another.

epitelium, connective tissue- protection, lubrication

mixing movements and proelling movements

mizing ocurs when smooth muscle is small segments of the tube contract rhymically. ex- when stomach is full waves of muscular contraction move along its wall from one end to the other. these waves occur every 20 seconds or so, andmix food with digestive juices that mucosa secreates. Segmentation occurs

propeliing includes wavelike motion called peristalis,

a network of nerve plexus within the wall of the canal. the submucosal plexus is important in controlling secreations by the gastrointestinal tract.

the myentric plexus of the muscular layer controls gastrointestinal motility. the plexuses also include sensory neurons

the activities of the digestive system . some of these impulses originate in the brain and are conducted through branches of the vagus nerve to the seophags, stomach, pancreas,gallbladder, small intestine, and proximal half of large intestine.

other parasympathetic impulses arise in sacral region of the spinal cord and supply the distal half of the large intestine.

the first portion of the alimentary canal, receives food and begins digestion by mechanically breaking up solid particles into smaller pieces and mixing them with saliva. This action is called mastication.

the mouth also functions as an organ of speech and sensory reception. it is surrounded by lips, cheeks, tongues calle oral cavity, as well as anarrow space between the teeth cheeks and lips called vestibule.

thick muscular organ that occupies the floor of mouth and filles oral cavity. mucous membrane covers the tongue, and a membranous fold called lingual frenulu connects themidline of the dtongue to the floor of the mouth.

body of the tongue is composed of skeletal muscle fibers that run in several directions. These musles mix food with saliva during chewing. Helps move food underneath the teeth for chewing

forms the roof of the oral cavity andconsists of a hard anterior part and a soft posterior part.

hard palate isformed by the palatine processes of the maxillary bones in front and the horizontal portions of the palatine bones in back

the soft palate forms a muscular arch, which extends posteriorlly and downward as a cone shaed projection called uvula.

primary teeth or decidous teeth usually erupt through the gums at regular intervals bewtween 6 months and two to four years.

the ten primary teeth are anchored in each jaw from the midline toward the sides in sequence: central incisor, lateral insior, canine, first molar, and second molar.

primary teeth usually shed in same order they erupted

set consists of thirty two teeth, sixteen in each jaw and are arranged as: central incisor, lateral insisor, canine, first premolar, second premolar, first molar, second molar, third molar. secondary teeth erupt around age 6.

set may not be completed until the third molars emerge between age 17 and 25 years. Wisdom teeth are the third molars.

incisors-chissel shaped andsharp edges bite off large pieces of food.

canines are cone shaped and grasp and tear food

premolars and molars have flatened surfaces and specialiezed for grinding food particles.

the crown which projects beyond the gum

and

root anchored to the alveolar process of the jaw

the regions where these protions meet is cvalled the neck of the tooth.

living cellular tissue called dentin, a substance musch like bone, but somewhat harder.

dentin surrounds the tooths central cavity which contains a combination of blood vessels, nerves, and connective tissue, collectively called pulp.

blood vessels and nerves reach this cavity through tubular root canals, extending into the root.

serous cells and mucous cells. Serous cells produce a watery fluid that containsthe digestive enzyme salivary amylase. This enzyme splits starch and glycogen molecules into disaccrides-the first step in chcemical digestion off carbs.

Mucus cells secrete a thick liquid called mucus which binds food particles and acts as a lubricant during swallowing.

sympathetic and parasympathetic nerves. impulses arriving on sympathetic fibers tiumulate the gland cells to secrete a small volume of viscous saliva.

Parasympathetic impulses elict the secretion of a large volume of watery saliva. such parassympathetic impulses are activated reflexly when a erson sees, smells tastes, or thinks about foods.

If food looks smells or tastes unpleasant parasympathetic is inhibited so less saliva is produced making swallowing difficult.

Parotid glands

submandibular

sublingual glands

largest of the maor salivary glands. Each gland lies anterior to and somewhat inferior to each ear, between theskin of the cheek and masseter muscle.

A partodid duct passes from the gland inward through the buccinator muscle, entering the mouth just opposite of the upper second molar on either side of the jaw.

The parotdid glands secrete a clear watery fluid rich in salivary amylase

connects the nasal and oral cavities with the larynx and esophagus it can be divided into the following parts

1. nasopharynx

2. oroharynx

3. larngopharynx

form inner circular and outer longitudinal groupls. the circular muscles called constrictor muscles pull the walls inward during swalloing.

the supeior constrictor muscles attached to the bony processes of the skull and mandible curve around the upper art of the pharynx.

the middle constrictor muscles araise from projections on the hyoid bone andfan around the middle of the pharynx.

the inferior constrictor muscles originate from cartilage of the larynx and pass around the lower portion of the pharyngeal cavity. some of the lower inferior constrictor muscle fibers contract most of the time, which prevents air from entering the esopphagus during breathing.

first stage is voluntary, food is chewed and mixed with saliva, then the tongue rolls the mixture into a mass or bolus and forces it into the pharynx.

second stage begins as food reaces the pharyx and stimulates sensory recepors around the pharygeal opening. this triggers the swalloinw reflex.

third stage- the swallowing reflex inhibits breathing but third stage is peristalisis transports the food in the esophagus and stomach.

1. soft palate and uvula raises, preventing food from entering the nasal cavity.

2. the hyoid bone and larynx are elevated. a flaplike structure attached to the laryx called the epiglottis closes off the top of the trachea so that food is less likely to enter the trachea.

3. the tongue is pressed against the soft palate and uvulla sealing off the oral vavity from the nasal cavity.

4. the longitudinal muscles in the pharyngeal wall contract, pulling the pharyx upward toward the food.

5. the lower portion of the inferior constrictor muscles relaxes opening the esophagus.

5. the superior constrictor muscles contract stimulated peristalic waves to veher pharngeal muscles. this wave forces the food into the esophagus.

part of the stomach protrudes through a weakened ara of the diaphragm, through the esopogeal hiatus and into the thorax. 

regurgation of gastric jucice into the esophagus may inflame the esophogeal mucosa, causing heartbearn, difficulty in swallowing, or ulceration, and blood loss.

destrucive action of gastic juice columnar epithelium may replace sqamous epithelium that normally lines the esophagus. this is called baretts esophagus which develop the risk of esophogeal cancer

mucous glands . their secretions moisten and lubricate the inner lining of the tube.

just superior to the point where the esophagus joins the stomach, some of the circular muscle fibers have increased sympathetic muscle tone, forming the lower esophageal sphincter, or cardiac sphincter. these fibers usually remain conracted and they close the entrance to the stomach. This will help revent regurgation of the stomach into the esophagus. when peristalic waves reach the stomach muscle fiers relax and swallowed food enteres.

is a j-shaped pouchlike organ, about 25-30 centimeters long, which hangs inferior to the diaphragm in the upper left portion of the abdominal cavity.  The stomach has a capacity of about one liter or more. Its inner lining has thick gastric fols of the mucosal and submucosal layers that disappear when the wall is distended.

the stomach revieves food from the esophagus, mixes it with gastric juice, initiates the digestion of proteins, carries on limited absorption, and moves food into the small intestine.

cardia, fundus, body, and pylorus.

cardia-is a small area near the esophageal opening

fundus-balloons superior to the cardia is temorary storage area and sometimes fills with swallowed air.

this produces a gastiric air bubble which cann be found in radiograph of abdomen.

Body- the main part of the stomachis between the fundus and pylorus.

pyloric antrum-funnel shaped portion that narrows and becomes pyloric canal as it approaches the small intestine. At the end of the canal circulur layer of fibers in its muscular wall thickens, forming a powerful muscle, the pyloric sphincter. This muscle is a valve that controls gastric emptying.

pepsin is by far most important digestive enzyme. the cheif cells secrete pepsin aas an inactive nonerosive enzyme precursor ccalled pepsinogen. when esiongen contracts hydrocholoric acid from parietal cells, it breaks down rapidly forming pepsin. pepsin in turn can break down pepsinogen to release more pepsin.

pepsin begins the digestion of nearly all types of dietary proteins into polypeptides. this enzyme is most active in an acididc enviornment, which is provided by the hydrocholoric acid in gastric juice.

1. pepsinogen- chief cells of gastric glands- inactive form of pepsin

2. pepsin-formed from pepsinogen in the presense of hydrocholoric acid-protein splitting enzyme that digests nearly all types of dietary protein

3. hydrocholoric acid-parietal cells of the gastric glands-provides the acid enviorment needed for production and action of pepsin

4. mucus-mucous cells-provides a viscoups alkaline protective layer on the stomachs inner surface

5. intrinsic factor- parietal cells of the gastirc glands-aids in Vitamin b12 absorption

the cephalic

gastric

and intestinal phase

cephalic- beings before food reaches the stomach and even before eating. parasympathetic relfexes operating through the vagus nerves stimulate gastric secreation at the taste, smell, sight, or thought of food. the greater the hunger the greater the gastric secreation.  accounts for 30-50% of secretory response to a meal.

accounts for 40-50 percent of secretory activity. starts when food enters the stomach. the presense of food and the distention of the stomach wall trigger the stomach to release gastrin, which stimulates production of more gastric juice.

when food enters the stomach and mixes with gastric juice the ph of the contesnts rises which enhances gastrin secreation, as esults the ph of the stomach contents drops.  when ph is around 3 secreation of gastrin is inhibited. at 1.5 gastrin stops.

alkaline tide occurs- hydrogen ions are removed from the blood to secrete hclacid, and an equal nnumber of alkaline bicarbonate  ions are released into the blood. after a meal, the blood concentration of bicarbonate ions increases, and urine excretes excess bicarbonate ions.

5% of total secretory response to a meal. begins when food leaves the stomach and enters the small intestine. when food first enters intestinal wall, it stimulates intestinal cells to realease a hormone called intestinal gastrin, that enhances gastric gland secreationn.

as food moves into small intestine a sympathetic reflex tirggered by acid in the uper part of small intestine inhbitis secreation of gatric juices from stomach the intestine stimulates the release of peptide homrone cholecystokinin, from intestinal wall, which decreases gastric motility. overall these actions decrease gastric secreation and motility as the small intestine fills with food.

Cephalic phase- the sight,taste, smell or thought of food triggers parasympathetic refleexes, gastric juice is secreted in response

gastric phase- food in stomach chemically and mechanically stimulates releases of gastrin, which in trun, stimulates secreation of gastric juice, reflex responses also stimulate gastric juice secretion

intestinal phase- as food enters the small intestine, it stimulates intestinal cells to release intestinal gastrin, which in turn promotes the secretion of gastric juice from the stomach wall.

results from a complex reflex that empties the stomach in the reverse of the normal direction. irritation or distension in the stomach can trigger vomiting.

sensory impulses travel from the site of stimulation to the vomitting enter in the medulla oblongata and motor responses follow. these include taking a deep breath, raising the soft palate, and closing the nasal cavity, closing the opening to the trachea, relaxing the circular muscle fibers at the base of the esophagus, contracting the diaphragm so it presses down over stomach and contracting the abdominal wall muscles to increase pressure inside the abdominal cavity. As a result the stomach is squezed from all sides forcing its contents upward and out through the esophagus pharynx and outh.

drugs, toxins in contaminated foods, rapid changes in body motion stimulate activity in the vomiting center. with changes in motion sensory impulses from the labyrinths of the inner ear each the vomiting center cn also be activated by stimulation of higher brain centers through sights sound sodors, tastes, emtoions, or mechanical stimulation.

Nausea emantes from activity in the v omiting center or in nerve centers near it. During nausea, stomach movements usually are diminished or absent, and duodenal contents may move back into the stomach.

pancreatic acinar cells- make up a bulk of the pancreaas. the cells form clusters of acini around tiny tubes into which they release their secretions. the smaller tubes unite to form larger ones which give rise to pancreatic duct extending the length of the pancreas and ransporting pancreatic juice to the smalll intestine. the pancreatic duct usuall connects with the duodenum at the same place where the bile duct from the liver and gallbladder joins the duodenum.

pancreatic and bile ducts jin at a short tube called hepatopancreatic ampulla. a band of smooth muscle called hepatopancreatic sphinctersurrounds this ampulla.

carbohydrates, fats, proteins, and nucleic acids. The carbohydrate digesting enxyme, pancreatic amylae, splits molecules of starch or glycogen into disaccarides.

fat digesting enzyme-panccreatic lipase breaks tirglyceride molecules into fatty acids and monoglycerides.

protein splittling enzymes are trypsin, chymotrypsin, carboxypetidase.

largest internal organ located upper right quad of abdoinal cavity inferior to the diaphragm.

a fibrous casule encloses the liver and connective tissue divides the organ into a largeright lobe and smaller left lobe.

liver carries on many important  metabolic functions.it maintains concentration of blood glucose within normal range. responds to horones such as insulin and glucagon lower the blood glucose level , effects on lipid metablolism include oxidizing fatty acids at hight rate, syntehsizing lipporoteins, phospholipids, and cholesterol, and converting portions of carboydrates and protein moelcuesinto fat molecules.

the blood transports fats synthesized in the liver to adipose tissue for storage.

most vital is amino acids, forming urea, synthesizing plasma proteins for clotting, sotres gycogen, iron, vitamins a, d, and b12 . extra iron from blood combines with protein in liver cells forming ferritin.

liver cells destryog damaged red blood cells and phagocitize foreign antigens.

removes toxic substances.

blood reserver storing 200 to 400 millilters of blood.

role in digestion is to serete bile.

yellow green liquid that hepatic cells secrete. in addition to water it containes bile salts bile pigments, cholesterol and electroyltes.

jaundice results in excess depostion of bile pigements.

pear shaped sac in a depression on the inferior surface of the liver. it is connected to the cystic duct. 

capacity of 20-50 ml and lined with columnar epitheila cells.  it stores bile between meals, concentrates bile by reaabosorbing water and contracts to release bile into the duodenum when stimulated by cholescystokinin from small intestine

gastrin- gastric cells, in response to food-increases secretory activity of gastric glands

intestinal gastrin- cells of small intestine in response to chyme-increase secretory activity of gastric glands

somatostatin-gastric cells-inhibits secreation of acid by pareital cells

intestinal somatostatin-intestinal wall cells in response to fats-inhigibts secreation of acid by parietal cells

cholecytokinin-intestinal wall cells in response to proteins and fats in the small intestine-decreases secretory activity of gastric glands and inhbits gastric motality, stimulates pancreas to secrete fluid with high digestinve enxyme concentration, stimulates gallbladder to contract and release bile

secretin- cells in the duodenal wall in resopnose to acidic chyme entering the small intestine-stimulates pancreas to secrete fluid with a high bicarbonate ion concetnration

tubular organ that extends from the pylori csphincter to the begging of large intestine.. many loops and coiles fills most of abdominal cavity.

recieves secretions from pancreas and liver and comletes digestion of nutrients in chyme , absorbes the products in digestion, and transports the remaining residue to the large intestine.

three portions: duodenum, jejunum,,  ileum

2/5 of small intestine, and remainder is ileum.

no distinct separation of the two. but diamter of jujunum is greater and its wall is thicker.

pancreatic amlyase-pancreas-breaks down starch and glycogen into disaccharides

pancreatic lipase-pancreas-breaks down fats into fatty acids and glycerol

trypsin, chymotrypisin-pancreas-breaks down proteins or partially digested proteins into peptieds

carboxypeptidase-pancreas-breaks down peptides into amino acids

nucleases-pancreas-breaks down nucleic acids into nucleoties

peptidase-mucosal cells-breaks down peptides into amino acids

sucrase, maltase, lactase-mucosal cells-breaks down disaccarides into monosaccarides

intestinal lipase-mucosal cells-breaks down fats into fatty acids and glycerol

enterokinase-mucosal cells-shortens trypsinogen into trypsin

monosaccarides-facilitated diffusion and active transport-blood in capillaries

amino acids- active transport- blood in capillaries

fatty acids and gycerol-facilitated diffusion of glycerol, diffusion of fatty acids into cells.

a. most fatty acids are resynthesized into fats and incoporated in chylomicrons for transort- lymph in lacteals

b. some fatty acids with relaviely short carbon chains are transorted wiout being canged back into fats- blood in capilarries

electrolytes- diffusion and active transport-blood in capillaries

water-osmosis-blood in capillaries.

diagmer is greater than small intestine. 1.4 meters long. lower right side of abdominal cavity where ileum joins the cecum. 

absorbs ingested water and elctryolytes remainting in alemintary canal. reabsorbs and recycles water and remants of digestive secretions. forms and stores feces.

consists of cemcum, colon, rectum, and anal canal .

cecum-beiging of large intested and dialed, appendix projects downward from it and is a narrow tube with a closed end. the appendix has no digestive function. but contains lymp tissue.

colon- divided into four parts-ascending, transverse, decending, sigmoid colon

rectum-lies next to the sacrum and follows curvatue.

anal canal- formed by last 2.5-4.0 centimeters of large intestine.

anus- distal end canal opens to the ouside as an anus which has two sphincter muscles- internal anal and external anal sphincter .

little to no giesive function