Digestive System

Liver functions

The veins draining the intestine lead to a second set of capillary beds in the liver. Here the liver removes many of the materials that were absorbed by the intestine: -Glucose is removed and converted into glycogen. Other monosaccharides are removed and converted into glucose. Excess amino acids are removed and deaminated. The amino group is converted into urea. The residue can then enter the pathways of cellular respiration and be oxidized for energy. Many nonnutritive molecules, such as ingested drugs, are removed by the liver and, often, detoxified. The liver serves as a gatekeeper between the intestines and the general circulation. It screens blood reaching it in the hepatic portal system so that its composition when it leaves will be close to normal for the body. Furthermore, this homeostatic mechanism works both ways. When, for example, the concentration of glucose in the blood drops between meals, the liver releases more to the blood by converting its glycogen stores to glucose (glycogenolysis) converting certain amino acids into glucose (gluconeogenesis).

Alimentary Canal

These are the organs of the _________ __________: Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus

Chief (enzyme secreting) Cells

These cells aka zymogen cells are most abundant near the base of a gastric gland. -Columnar in shape like mucous cells and secrete pepsinogen which is converted by the acids in the lumen to a proteolytic enzyme, pepsin. -Newborns also produced rennin and lipase, important for milk digestion.

Submucosa

This is a: Layer of dense, irregular CT that surrounds muscularis mucosa LARGE blood vessels & lymphatics Outer margin contains network of nerve fibers (plexus of Meissner or submucosal plexus) innervates the mucosa with ps ganglia and postgang sump. fibers some submucosa regions secrete enzymes and buffer into lumen (think pancreas)

Large Intestine (Facts)

This organ: -Begins at the ileocecal valve and ends at the anus. -Often called the large bowel 3 parts: C,C,R cecum, colon, rectum

Salivary Glands

Three pairs Parotid-Parotid duct into vestibule at level of 2nd upper molar Largest of 3, produces salivary amylase (NOTE: -ase = enzyme) Sublingual-Sublingual duct along lingual frenulum Submandibular-Submandibular ducts open at sides of lingual frenulum Contributes ~70% of saliva

Esophageal Phase

Upper esophageal sphincter opens, peristalsis pushes bolus along Bolus triggers lower esophageal sphincter

Peristalsis

Waves of muscular contraction that move a bolus along the digestive tract ****Afferent/efferent fibers of glossopharyngeal, vagus, and pelvic nerves can trigger peristaltic waves (WITHIN MYENTERIC PLEXUS BETWEEN CIRC AND LONG MUSCLES IN MUSC EXTERNA) ***1-Circular muscles first contract BEHIND the bolus ***2-Longitudinal muscles AHEAD of bolus 3-Wavelike contraction of circular muscles forces bolus forward

Mouth Physiology

________ ___________: Mastication (chewing) of food Mixing masticated food with saliva Initiation of swallowing by the tongue Allows for the sense of taste Mastication = Chewing Deglutition= Swallowing

Gallbladder

a pear-shaped muscular organ. the gallbladder is a muscular sac that -stores and concentrates bile before its excretion into the small intestine. -this organ is located in a visceral fossa of the liver. (intraperitoneal) -Three regions: fundis, body, and neck -**Cystic Duct leads from the gallbladder toward the porta hepatis, where the common hepatic duct and the cystic duct unite to create the common bile duct -At the dudodenum, a muscular hepatopancreatic sphincter or sphincter of Oddi, surrounds the lumen of the common bile duct and duodenal ampulla. -The duodenal ampulla opens into the duodenum at the duodenal papilla, a small raised projection. contraction of this sphincter seals off the passageway and prevents bile from entering the si. Gallbladder functions: 1) Bile Storage 2)Bile Modification -when the sphincter of oddi is closed, bile enter cystic duct for storage , gb holds 40-70 ml -composition gradually changes -Bile ejection occurs under stimulation of CCK when it is released into the bloodstream when chyme arrives containing large amounts of lipids and partially digested proteins. ****-CCK causes relaxation of the hepatopancreatic sphincter and contraction of gallbladder = releasing bile into the small intestine Location: Fossa on visceral surface of right lobe of liver Cystic duct leaving gall bladder unites with common hepatic duct to form the common bile duct entering duodenum

chyme

a viscous, strongly acidic, soupy mixture secreted by stomach glands

transverse colon

as this part of the colon passes across the stomach, its peritoneal relationship changes, initially intraperitoneal, separated from teh abdominal wall by the greater omentum. becomes secondarily retroperitoneal as it passes below the stomach. Changes at the splenic flexure

Large Intestine

bacteria like E Coli are normal habitants within the lumen of the ____ __________, and are nourished by the surrounding mucosa . The epithelial barriers (cells, mucus, and digestive juices) and underlying lymphoid cells, protect the small intestine from bacteria migrating from this organ. Peyers patches most abundant in the terminal portion of the small intestine

Blood supply to the stomach

celiac trunk goes to: 1- left gastric artery to lesser curvature and cardia 2-splenic artery supplies the funds and greater curvature through the left ge artery. 3- Common hepatic artery supplies blood to the lesser and greater curvatures of the pylorus through the rga, r ge a, gastric and gastroepiploic veins drain blood from the stomach into the hepatic portal vein

Alimentary canal (gastrointestinal or GI tract)—

continuous coiled hollow tube These organs ingest, digest, absorb, defecate

Movement of Digestive Materials

digestive tract contains visceral smooth muscle tissue surrounded by CT (collagen fibers) contractile proteins are NOT organized into sarcomeres Pacesetter cells located in mucularis mucosae and muscularis externa (rhythmic contractions), hormones, chemicals, physical stimulation Wave-like contractions result in peristalsis and segmentation *** Plasticity: the ability to tolerate extreme stretching and adapt to its new size as in the stomach because contractile filament of smooth muscle are not organized. Afferent/efferent fibers of glossopharyngeal, vagus, and pelvic nerves Local sensory receptors in GI walls Triggering of long reflexes through the CNS

small intestine

during absorption, weak peristaltic contractions move materials slowly along the _________ ___________. Movements are controlled by neural reflexes involving the submucosal and myenteric plexuses. -Parasympathetic stimulation increases sensitivity of these reflexes and accelerates the contractions

Greater Omentum

forms a large pouch that hangs like an apron from the greater curvature of the stomach. lipids in this are thought to be an important energy reserve. this provides lots of insulation

Liver Functions

functions: Secretion of bile (important for lipid digestion) storage of nutrients, many other vital functions

Oral Cavity Functions (teeth, tongue)

functions: mechanical processing, moistening, mixing with salivary secretions, analysis, lubrication, digestion

Gallbladder functions

functions: storage and concentration of bile

Stomach

functions: Chemical breakdown of materials via acid and enzymes; mechanical processing through muscular contraction and BULK STORAGE

Large Intestine Functions

functions: Dehydration and composition of undigestible materials in preparation for elimination; also vitamin absorption and storage of feces

Esophagus

functions: Transport of materials to the stomach

Pharynx Funtions

functions: muscular propulsion of materials into the esophagus aka initation of swallowing

Salivary Glands functions

functions: secretion of lubricating fluid containing enzymes that break down carbs

Small Intestine

functions: Enzymatic digestion and absorption of water, organic substrates, vitamins, and ions

Pancreas functions

functions: Exocrine cells secrete buffers and digestive enzymes; endocrine cells secrete hormones

Ileum (histology)

here is where plicae and villi become smaller and continue to diminish in size and number to the end of the _______, this reduction coorelates to the decrease in nutrient absorption. most nutrient absorption occurs before the terminal end of this organ.

Intestinal juice

hormonal and CNS controls regulate the secretory output of the small intestine and accessory glands. small intestine secretions are called ___________ ________. -Secretory activities are triggered by vagal stimulation (parasympathetic), -sympathetic stimulation inhibits secretion. Duodenal enteroendocrine cells produce secretin and CCK, which coordinate the secretory activities of the stomach, pancreas, liver, and duodenum.

Duodenum

initial part of the small intestine; shortest and widest segment; connected to pylorus, interconnection guarded by pyloric sphincter -also called a mixing bowl; receives chyme from pylorus and digestive secretions from the pancreas and liver. *Almost all essential digestive enzymes enter the small intestine from the pancreas. (the duodenum encloses the pancreas) -Has no supporting mesentery, jejunum and the ileum are supported by a fan shaped mesentery known as the mesentery proper for blood vessels, lymphatics, and nerve endings -Blood vessels involved are intestinal arteries, branches of sup. mes. artery, and superior mes. vein ***-Parasympathetic innervation is provided by the vagus nerve ***-Sympathetic Innervation is provided by the postganglionic fibers from superior mesenteric ganglion

Lesser Omentum

is a much smaller pocket between the lesser curvature of the stomach and liver. provides an access route for blood vessels and other structures entering and leaving the stomach

jejunum (nutrient absorption)

plicae and villi remain prominent over the proximal half of the _______, where most nutrient absorption occurs.

ascending colon

retroperitoneal part of the colon, becomes transverse colon at the hepatic flexure

sigmoid colon

s-shaped segment of the large intestine -begins at the sigmoid flexure, ends at rectum -intraperitoneal -posterior to the urinary bladder

Peritoneal Cavity

serous membrane (epithelial tissue) lines abdominal cavity 2 membranes- parietal and visceral space between is filled peritoneal fluid

Pancreas (blood supply)

splenic, superior mesenteric, common hepatic arteries supply this alligator shaped organ

Stomach (cont)

the volume of this organ -increases when mealtime and -decreases when chyme leaves the _______ and enters the small intestine. In an empty __________, the mucosa is thrown into a number of prominent folds, called rugae which: -permit expansion -epithelial lining cannot stretch, it just flattens out, in a full stomach the rugae almost disappear.

Mucous cells

these cells are columnar in shape, secretes a water soluble product and functions to lubricate the stomach contents

CCK (cholecystoskinin)

this hormone, ___________ along with secretin are the two hormones released by the small intestine to stimulate secretion by the liver and pancreas. the depression of gastric activity is a secondary but complementary, effect

Duodenum (histology)

this initial part of the small intestine contains numerous mucous glands -in addition to the intestinal crypts, the submucosa contains duodenal submucosal glands (Brunner's glands) -Brunner's glands produce large quantities of mucus. -Mucus from the intestinal and submucosal glands prevent the epithelium from the chyme. -Mucus contains buffers that help elevate the pH of the chyme. -submucosal glands are most prominent in the proximal part of the duodenum and decrease as they approach the jejunum. -As this happens the pH changes from 1-2 to 7-8; making extra mucus secretion unnecessary in the jejunum. -Buffers and Enzymes from the pancreas and bile from the liver enter the duodenum roughly halfway along its length

Purpose of digestion

this is the ____________ ___ ___________: to reduce the solid, complex, chemical structures of food molecules that can be absorbed by the epithelium lining the digestive tract for transfer to the circulating blood.

Large Intestine (functions)

this organ does the following: 1) reabsorption of water and electrolytes (less than the small intestine) and compaction into feces 2) absorption of vitamins produced by bacterial action 3) storing of fecal matter before defecation this organ receives blood from tributaries of the superior mes and inferior mes. Sup and inf. mes veins collect from it

Pancreas

this organ extends laterally from the duodenum toward the spleen. -the broad head lies within the duodenum -The slender body lies transversely toward the spleen -The tail is short and bluntly rounded -secondarily retroperitoneal -Surface is lumpy and nodular, wrapped in clear, thin connective tissue

Pancreas (cont.)

this organ is primarily exocrine producing digestive enzymes and buffers, although it does serve an endocrine function. -large pancreatic duct (duct of Wirsung) delivers these secretions to the duodenal ampulla. -A small accessory pancreatic duct, or duct of santorini, may branch from the pancreatic duct before it leaves the pancreas Pancreatic Duct Produces Digestive enzymes & buffers Stimulated to release by: Gastrin, CCK, secretin

Rectum

this part of the LI is where the sigmoid colon discharges the fecal matter. -expandable for temporary storage of fecal matter -Anal canal contains small longitudinal folds, anal columns -changes from columnar to non keritanized strat. squamous epithelium of that found in the mouth. -anus(anal orifice) -Veins in the lamina propia become distended, producing hemorrhoids -Circular muscle layer of the muscularis externa forms the internal anal sphincter (non voluntary) -Ring of skeletal muscle fibers (external anal sphincter) is under voluntary control

descending colon

this part of the colon is secondarily retroperitoneal. At the iliac fossa, this becomes the sigmoid colon.

duodenal ampulla

within the duodenal wall, where the common bile duct and the pancreatic duct come together at a muscular chamber called the _____ ________ aka hepatopancreatic. -This chamber opens into the duodenal lumen at a small mound known as the (greater) duodenal papilla

enteric nervous system

*****neural network that coordinates myenteric plexus N IX NX, pelvic nerves to peristalsis -has roughly the same amount of neurons as the spinal cord -short reflexes control activities in one area of the d. tract -Long reflexes involve neurons and interneurons in CNS to move materials from one region of the digestive tract to another (large waves)

Parietal (acid secreting) Cells

****these cells aka oxyntic cells secrete intrinsic factor and HCl and are pyramid cells -proximal portions of each gastric gland ****Intrinsic factor facilitates the absorption of Vitamin B12 across the intestinal lining, which is necessary for erythropoiesis ****HCL -lowers the pH of the gastric juice, - -kills microorganisms, -breaks down cell walls and connective tissues in food -activates the secretions of the chief cells

Pooping

***-moves slowly -involves peristaltic and haustral churning -slow movement allows for fecal material to become a sludgy paste ****-Movement from the transverse colon by powerful peristaltic contractions are called "mass movements" and occur a few times a day -the stimulus is distension of the stomach and duodenum, nerve plexuses signal movement of fecal materials into the rectum to produce the conscious urge to defecate. -The rectal chamber is usually empty except when mass movements force fecal material into rectum. -Rectal distension causes defecation urge. -**Relaxation of the external anal sphincter causes defecation

small intestine roles

***90% of nutrient absorption occurs in the _____ __________ -occupies all regions except the left hypochondriac and epigastric regions -stabilized by mesenteries to dorsal body wall -restricted movement by stomach, LI, abdominal wall, and pelvic girdle. *******-bears plicae circulares, unlike stomach, these plicae do not disappear as the small intestine fills.

Colon

**Larger diameter & thinner walls (compared to SI) -Haustra: pouches in walls for distension, makes waves -Taeniae coli: 3 bands of longitudinal smooth muscle -Divided into 4 regions (ascending, transverse, descending, sigmoid) -serosa of the colon contain numerous fat sacs called omental appendices

Stomach Histology

-**a simple columnar epithelium lines all stomach regions (mucous surface cells form secretory sheet which produces mucous) -shallow depressions (gastric pits) -stem cells in the gastric pit actively divide to replace superficial cells that are shed continuously into the chyme -the continual replacement of epithelial cells provides an additional defense against the gastric contents. -If stomach acid and digestive enzymes penetrate the mucous layers, any damaged epithelial cells are quickly replaced.

Pancreatic Enzymes

-Lipases digest lipids, -carbohydrases such as amylase digest sugars and starches. -nucleases attack nucleic acids -proteolytic (proteinases break down big complexes and peptidases break down small peptide chains) enzymes break proteins apart into individual amino acids

Cecum

-Materials enter here from the Ileum into the expanded pouch called the ______. opens into the ___ at the ileal papilla. encircling muscles from the ileocecal valve. -This organ part collects and stores the arriving materials and begins the process of compaction. -The slender, hollow vermiform appendix (appendix) is attached to the cecum. -The mesoappenix connects the appendix to the ileum and _______. -The appendix is dominated by lymphoid nodules in ints mucosa and sub-mucosa.

Regulation of Pancreatic Secretion

-Secretion of Pancreatic juice occurs primarily in response to hormonal instructions from the duodenum. -chyme arrives, secretin is released -secretin triggers the production of watery pancreatic juice containing buffers, like NaHCO3 -CCK stimulates the production and secretion of pancreatic enzymes

Pancreas (cont..)

-This organ has ducts within each lobule that branch repeatedly before ending in blind pockets, pancreatic acini lined by simple cuboidal epithelium. -Acini secrete a mixture of water, ions, and pancreatic digestive enzymes. -These enzymes do most of the digestive work in the small intestine, breaking down ingested materials into molecules suitable for absorption -blood vessels and tributaries of the pancreatic duct are found within the connective tissue septa.

Liver (blood supply)

-afferent blood vessels reach the liver through connective tissue of the lesser omentum -converge at porta hepatis -two blood vessels deliver blood to liver, hepatic artery proper (1/3), and and hepatic portal vein (2/3) -CHECK CLASS NOTES

Jejunum

-duodenojejunal flexure marks the boundary between the duodenum and the jejunum -where the small intestine re-enters the peritoneal cavity becoming intraperitoneal and supporting a sheet of mesentery. -*** The bulk of chemical digestion and nutrient absorption occurs in the jejunum

Liver (facts)

-largest intraperitoneal organ, tough fibrous capsule -falciform marks the division of the r/l lobes -coronary ligament suspend liver to diaphragm -livers shape conforms to surroundings -Has four lobes -inferior vena cava splits the right lobe from the small caudate lobe. -inferior to the caudate lobe is the quadrate lobe, sandwiched between the left lobe and the gall bladder -New system divides liver into segments based on subdivisions of hepatic artery, portal vein, and hepatic ducts -boundaries cannot be determined without dissection

Regulation of the Stomach

-production of acid and enzymes by the gastric mucosa can be directly controlled by the nervous system and indirectly regulated by local hormones. -CNS regulation involves both the *(***vagus nerve (parasymp.) and branches of the ***celiac plexus (symp.) -****The sight or thought of food triggers motor output in the vagus nerve. -Postganglionic parasympathetic fibers innervate parietal, chief, and mucous cells of the stomach. -stimulation causes an increase in the production of acids, enzymes, and mucus. Sympathetic activation leads to inhibition of gastric activity. 1-Arrival of food in the stomach stimulates stretch receptors in the stomach walls and chemoreceptors in the mucosa. 2-Reflexive contractions occur in the muscularis layers of the stomach wall and gastrin is released by the enteroendocrine cells. 3-Parietal cells are sensitive to gastrin so acid is secreted

Enteroendocrine cells

-these cells are scattered among the parietal and chief cells. -these cells produce at least 7 different secretions. -G cells, for example, are these cells that are most abundant in the gastric pits in the pyloric region. -These secrete gastrin, which is released when food enters the stomach, stimulates the secretory activity of both parietal and chief cells. -Gastrin also promotes smooth muscle activity in the stomach wall, which enhances churning and mixing.

Large Intestine (histology)

-thin walls, large diameter -lacks villi unlike si -goblet cells are much more abundant than si -goblet cell dominated intestinal crypts, deeper than si -Large lymphoid nodules throughout lamina propia and into submucosa -**Muscularis externa is unique because the longitudinal layer has been reduced to muscular bands of the taeniae coli

Gallbladder (Histology)

3 layers for this bile secreting organ mucosa thrown into folds called mucosal crypts, lamina propia, and muscularis externa

Ileum

3rd segment of SI, largest/longest -Ends at ileocecal valve /sphincter -intraperitoneal Plicae & intestinal villi (density decreases) -Plicae circulares allows for huge surface area for absorption Lacteals (function)

Bile secretion and Transport

Bile is secreted into Bile canaliculi -canaliculi connect with bile ductules that carry bile to a bile duct in the nearest portal. -The r/l hepatic ducts collect bile from all of the bile ducts of the liver lobes. -ducts unite to form common hepatic duct that leaves the liver. -Bile within the common hepatic duct may either flow into the common bile duct that empties into the duodenum or enter the cystic duct that leads to the gallbladder

Liver Lobules (cont)

Blood enters the liver sinsusoids from small branches of the portal vein and hepatic artery. -Lobules are hexagonal in cross section -6 portal areas (hepatic triads) one at each corner of the hexagon -a portal area contains three structures: 1)branch of the hepatic portal vein, 2)branch of the hepatic artery proper 3)a small branch of the bile duct -These branches deliver blood to the sinusoids of adjacent lobules, -As blood flows through the sinusoids, hepatocytes absorb and secret materials into the bloodstream across their exposed surfaces. -Blood then leaves the sinusoids and enters the central vein of the lobule. -Central veins ultimately merge to form hepatic veins into the inferior vena cava.

Pharyngeal Phase:

Bolus contacts pharyngeal wall, larynx elevates, epiglottis folds, bolus moves past closed glottis

Buccal Phase (voluntary)

Compression of bolus against hard palate, tongue retracts & forces bolus into pharynx

Small Intestine Histology

Epithelium -each villus is covered by simple columnar epithelium -apical surfaces covered with microvilli -fingerlike projections intestinal villi that project into the lumen -Mucosal layer with plicae circulares (contains intestinal villi) Intestinal Crypts (crypts of Lieberkuhn) -provide the ongoing replacement of epithelium cells into the lumen. They also contain enteroendocrine cells which produce CCK and secretin and antibacterial activity. -are At base of villi, extend into lamina propia -between epithelial cells, goblet cells eject mucins onto the intestinal surface -New epithelial cells produced -Production of hormones for digestions Lamina propria -****Network of capillaries -> hepatic portal system -Occasionaly contain lymphoid nodules (Peyers patches) *******-Lacteal (transport larger nutrients lipids) -> thoracic duct -> venous circulation

Layers of Tissue in the Alimentary Canal Organs

Four layers from deep to superficial: Mucosa Submucosa Muscularis externa Serosa

Gastric Secretory Cells

In the fundus and body of the stomach, each gastric pit communicates with several gastric glands that extend deep into the underlying basil lamina. -Gastric glands are simple branched tubular glands dominated by four types of secretory cells. MCEP (Mucous, Chief, Parietal, Enteroendocrine) Chief and Parietal secrete 1.5 L of gastric juices per day

Accessory digestive organs

Includes teeth, tongue, and other large digestive organs such as glandular organs like like the liver, salivary glands, and pancreas

Digestive System Functions

Ingestion-foods enter via mouth Mechanical processing-tongue, teeth, swirling, mixing, churning, and propulsive motions of the digestive tract Digestion-chemical and enzymatic breakdown of complex breakdown of sugars (carbs), lipids, and proteins into molecules that can be absorbed Secretion- action of acids, enzymes, and buffers produced by active secretion of digestive lining and some organs Absorption- movement of organic molecules, electrolytes, vitamins, and water across dig. epithelium and into interstitial fluid of dig. tract Compaction-progressive dehydration of indigestible materials and organic wastes prior to elimination from the body. This material is called feces Excretion (Defecation): waste products are secreted into the dig. tract, primarily by accessory organs (liver) defecation is the elimination of the feces from the body.

Mouth (Oral Buccal Cavity)

Lips (labia)—protect the anterior opening Cheeks—form the lateral walls Hard palate—forms the anterior roof Soft palate—forms the posterior roof Uvula—fleshy projection of the soft palate Vestibule—space between lips externally and teeth and gums internally Oral cavity proper—area contained by the teeth Tongue—attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum to the floor of the mouth Tonsils Palatine—located at posterior end of oral cavity Lingual—located at the base of the tongue

Esophagus

Location - posterior to trachea (25 cm) Enters peritoneal cavity through hole in diaphragm esophageal hiatus C6 (cricoid cartilage) T7 No serosa, just CT lining (adventitia) Layers Mucosal: resist abrasion Submucosal: lubricates bolus Muscularis externa: Upper portion of esophagus is skeletal muscle Middle portion is combo Lower portion is smooth muscle

Segmentation

Mostly in small intestine but some of large intestine Churn and fragment digestive materials (mix contents with interstitial fluid) ***along with peristalsis, triggered by pacemaker cells, hormones, chemicals, and physical stimulation ***No net movement in any particular direction

Mucosa

Mucosal epithelium (stratified or simple) moisturized by glandular epithelium stomach, small intestine, large intestine= simple columnar lamina propia (areolar tissue) underlying contains vessels, sensory nerve endings, lymph vessels, smooth muscle fibers, lymph tissue (MALT or peyer's patches) ****Organized in folds called PLICA =Dramatically increase the surface area for absorption and are permanent or non permanent like in stomach!!! Muscularis Mucosae Layers of smooth muscle & elastic fibers arranged in circular layer and longitudinal layer; these contract to change the lumen shape and plicae

Musculature of the stomach

Muscularis Mucosae (Mucosa layer) and the Muscularis Externa contain extra layers of smooth muscle in addition to the usual circular and longitudinal layer. Muscularis Mucosae contains an additional outer, circular layer. Musc. Externa has an extra inner, oblique layer that is not well defined except in the cardia. But so what? ***These layers of smooth muscles strengthen the stomach wall and perform the mixing and churning activities essential to the formation of chyme.

Accessory (Glandular) Organs

Organs cooperating with alimentary canal for digestive functions (alimentary canal = mouth -> anus) -** These organs produce and store enzymes and buffers that are essential to normal digestive function. -** In addition to their digestive roles, sal glands, liver, and pancreas have exocrine functions. Salivary Glands Liver Gall Bladder Pancreas

Liver

Over 200 functions with a limited ability to regenerate -this is the most visceral organ. -Most versatile organ -Main categories of functions 1. Metabolic regulation -circulating levels of carbs, lipids, and aminos are regulated -blood leaving absorptive part of the digestive tract enters hepatic portal system, flows to liver where it extracts absorbed nutrients or toxins through the hepatic veins. -Hepatocytes monitor the circulating levels of metabolites and adjust them -excess nutrients are removed and stored, also stores nutrients for correction *****-fat soluble vitamins A,D,E,K are stored and absorbed by liver 2. Hematological regulation -liver is the largest blood reservoir in the body, 25% of cardiac output a) **phagocytic cells remove damaged or dead RBCs, pathogens, cell debris b)**** synthesize plasma proteins that contribute to the osmotic pressure, blood concentration, transport nutrients, establish clotting system! 3. Bile production -Bile is synthesized by the liver, stored in gallbladder, excreted into the lumen of the duodenum. -Bile consists of mostly water, minor amounts of ions, bilirubin (pigment derived from hemoglobin), an assortment of lipids known as bile salts. -Water and ions assist in the buffering and diluting of acids in chyme as it enters the small intestine -Bile salts make it possible for enzymes to break down these lipids in the chyme and make it possible for enzymes to break down these lipids into fatty acids suitable for absorption

Peritoneum

Serosa or visceral peritoneum is continuous with the parietal peritoneum that lines the inner surfaces of the body walls. Liver disease or heart failure, volume of peritoneal fluid increases markedly= dangerous amount of blood volume and distortion of organs Intraperitoneal Organs= within the cavity, covered by visceral peritoneum on all sides, (ie stomach, liver, ileum) Retroperitoneal organs are covered by the visceral peritoneum on the anterior, and the organs lie outside the cavity (i.e. kidney, ureters, abdominal aorta) Secondarily Retroperitoneal organs= organs of the dig. tract that form as intraperitoneal and become retroperitoneal (pancreas and duodenum)

Serosa

Serous membrane that covers the 'externa' ****Note: not found in oral cavity, pharynx, esophagus, & rectum instead it is wrapped by a dense network of collage fibers, a fibrous sheath called the adventitia.

Muscularis Externa

Surrounds submucosa Has smooth muscle (circular & longitudinal) Forms sphincters and valves (at specific locations): where thick circular muscles helps prevent untimely back flow of materials restricts flow ***essential role in mechanical processing and propulsion of materials Myenteric Plexus (plexus of Auerbach) lies between circ. and long. layers ps stim. increases muscle tone and digestion, and s stim promotes muscle relaxation and inhibition of contractions

Lacteal

Terminal lymphatic Transports materials that cannot enter local capillaries (lipid-protein complexes)

Digestive Lining

The ________ __________ plays a defense role by protecting surrounding tissues against 1-Corrosive effects of digestive acids and enzymes 2-mechanical stresses, such as abrasion 3-Pathogens that are either swallowed with food or reside within the digestive tract.

Liver lobule (histology)

The basic functional unit of liver lobules. Liver cells (hepatocytes) form a series of irregular plates arranged like the spokes of a wheel. -no more than 2 cells thick up to the age of seven -exposed hepatocytes surfaces are covered with short microvilli -Sinusoids between adjacent plates empty into the central vein. -Fenestrated walls of the sinusoids contian large openings that allow substances to pass out of the circulation and into the space surrounding the sinusoids. -Sinusoidal lining includes a large number of Kuppfer cells (engulf pathogens, damaged blood cells) and engulf heavy metals like tin or mercury, aka stellate reticuloendothelial cells part of monocyte-macrophage system.

Stomach (continued)

The location of this is T7 -L3 -intraperitoneal -In the shape of an "expanded J" and the size varies by person -(left hypochondriac, epigastric, umbilical, and left lumbar) 4 regions: 1-esophagus contacts the stomach at the CARDIA (cardiac orifice) 2-top left part of your stomach contacts diaphragm is the FUNDUS 3-big, central part is the BODY: largest region and functions as a mixing tank for ingested food and gastric secretions. -the curve of the J is the PYLORUS (pylorus antrum is connected to the body, pyloric canal is connected to the duodenum. Pylorus constantly changes shape during digestion, and a muscular sphincter regulates the release of chyme from the pyloric orifice into the duodenum. Function 1-Bulk storage 2-Mechanical breakdown 3-Chemical digestion through acids and enzymes ***PRIMARY absorption of caffeine and alcohol