Unit 5: Digestive System

Major Salivary Glands: Discuss 5 functions of saliva

**Saliva has both protective and digestive roles:* 1. moisten oral mucosa 2. moisten dry foods 3. provide medium for food materials to dissolve so they can chemically stimulate taste buds (tastes can only sense dissolved materials) 4. buffer contents of oral cavity (via bicarbonate and phosphate ions) 5. contains amylase that partially breaks down starch (a polysaccharide)

Pharynx: Describe the 3 different parts of the pharynx

*3 PARTS OF PHARYNX:* (superior to inferior) 1. Nasopharynx: -air passageway ONLY -superior to soft palate; when swallowing, the soft palate and uvula move superiorly to close off nasopharynx (so food does not go to nasal cavity) 2. Oropharynx: -air AND food passageway -posterior to oral cavity; b/w level of soft palate and epiglottis 3. Laryngopharynx: -air AND food passageway -laryngopharynx is continuous with both the esophagus and larynx inferiorly; extends from an upright epiglottis to larynx; but when swallow, epiglottis flaps down and covers larynx

Large Intestine: 5 Functions?

*FUNCTIONS OF LARGE INTESTINE:* 1. a little reabsorption of electrolytes and water- not enough water reabsorbed = diarrhea; and too much water reabsorbed = constipation 2. formation and elimination of feces (undigested food/wastes) >>bacteria in large intestine have 3 jobs: >3. ferment remaining carbs and release methane, hydrogen, and CO2 gases >4. breakdown any remaining aa >5. synthesize some vitamins which are absorbed (B and K)

Small Intestine: 4 Main Functions

*Main Functions of Small Intestine:* 1. mix chyme with digestive juices and bring food into contact with mucosa for absorption 2. move chyme further through digestive tract via peristalsis 3.complete digestion of carbs, proteins, and lipids; begin and complete digestion of nucleic acids 4. absorption of material; 90% of all absorption in GI occurs here

Pancreas: Functions?

*both an endocrine and exocrine gland:* 1. 99% exocrine: (digestive system) -makes and secretes enzymes to duodenum for chemical digestion -secretes pancreatic juice (fluid and dig. enzymes to digest 4 macromolecules), also serves to buffer acidic gastric juices as chyme moves to duodenum 2. 1% endocrine: (endocrine system) -makes at pancreatic islets and secretes hormones (glucagon and insulin) into blood

Trace the pathway of food through the digestive system

*food passing through alimentary canal: 1. oral cavity ↓ (accessory: teeth and 3 salivary glands) 2. P: oropharynx ↓ 3. P: laryngopharynx ↓ 4. esophagus ↓ 5. stomach ↓(accessory: pancreas, gallbladder, and liver) 6. SI: duodenum ↓ 7. SI: jejunum ↓ 8. SI: ileum ↓ 9. LI: cecum ↓ 10. LI: ascending colon ↓ 11. LI: transverse colon ↓ 12. LI: descending colon ↓ 13. LI: sigmoid colon ↓ 14. rectum ↓ 15. anal canal ↓ 16. anus ↓ POOP

Differentiate between the 2 types of digestion by stating where they take place

-2 types of digestion: mechanical v. chemical -mechanical digestion: occurs when chew food with teeth or churning of smooth muscle of stomach -chemical digestion: occurs via enzymes of salivary glands, pancreas, stomach, and tongue

Liver: location? 4 lobes?

-2nd largest organ of body, largest internal -located just inferior to diaphragm (RUQ) -4 Lobes of Liver: 1. right lobe: large 2. left lobe: large *R and L separated via falciform ligament 3. quadrate lobe: small 4.caudate lobe: small * 3 and 4 = seen posteriorly

Briefly list the 3 major salivary glands

-Major salivary glands: secrete saliva into oral cavity; there are 3 pairs (R and L); stimulated to secrete via parasym. system; secretion inhibited via symp. system -3 Pairs: 1. parotid gland 2. submandibular gland 3. sublingual gland

Describe the serosa OR adventitia layer of GI tract

-OUTERMOST layer of GI tract -serosa: the serous membrane which is the outermost part of GI tract in abdominpelvic cavity; this serosa is known as visceral peritoneum -adventitia: in esophagus, ascending colon, descending colon, and most of the duodenum (which all lack serosa); adventitia is CT (where tube is fixed)

Peritoneum: discuss retroperitoneal?

-Retroperitoneal organs: organs lying behind peritoneum; organs which do not need to move to func = not surrounded by peritoneum; lie in permanent position on post. abdominal wall; only have peritoneum on ant. surfaces -organs? kidneys, adrenal glands, pancreas, ascending colon, descending colon, aorta, and most of duodenum

Gallbladder: structure and function?

-Structure: >pear-shaped sac located in depression on posterior surface of right lobe of liver >composed of broad fundus, body, and neck -Function: >to store and concentrate bile produced by liver until it's needed in small intestine >bile released via smooth muscle contractions into cystic duct

Stomach: 4 gross anatomical subdivisions?

-What are the 4 gross anatomical subdivisions? 1. cardia: area that surrounds the superior opening of the stomach (just distal to esophagus' opening to stomach) 2. fundus: superior and to the left of the cardia (gas collects for burps lol) 3.body: large central portion of stomach inferior to fundus 4. pylorus: connects the stomach to the duodenum; starts to narrow as it approaches the pyloric sphincter >>2 parts of pylorus: a. pyloric antrum: next to body of stomach; proximal portion b. pyloric canal: leads into duodenum; most distal part of stomach

Describe the structure and function of the esophagus.

-collapsible muscular tube (10 inch) which connects laryngopharynx to the stomach -found posterior to the trachea -goes through the diaphragm at the esophageal hiatus at level of T-10 -an exception: muscularis externa of superior 1/3 = skeletal muscle, lower 1/3 = smooth, intermediate 1/3 = mixed -deglutition is the act of swallowing (4-8 sec from mouth to stomach for solid foods and 1 sec for liquids) -no digestive enzymes are produced by esophagus and no absorption occurs -2 FUNCTIONS: 1) secrete mucous and 2) transport food to stomach

Describe the process of absorption performed by the digestive system: location and what forms of molecules can be absorbed

-digestion leads to changes in food, so they can pass through the epithelial cells lining the GI tract and pass into either BV or lymphatic vessels -90% of absorption occurs in small intestine, 10% occurs in stomach and large intestine -Forms of Broken down molecules which can be absorbed: 1. carbs → monosaccharides 2. proteins → amino acids, dipeptides, and tripeptides 3. fats/triglycerides → fatty acids and monoglycerides 4. RNA and DNA → pentoses, phosphates, and nitrogenous bases

Pancreas: Structure? and path of pancreatic juices?

-elongated gland found posterior to the greater curvature of stomach = on left side -has a head, body, and tail -mostly retroperitoneal -path of pancreatic juices: secreted by exocrine cells into small ducts > ducts unit to form pancreatic duct > joins with bile duct to form hepatopancreatic ampulla > dumps into duodenum

Small Intestine: Structure? 3 divisions?

-large SA for digestion and absorption = due to long length, circular folds (plicae circulares), villi, and microvilli -small intestine begins at pyloric sphincter and opens into large intestine at the cecum -3 Divisions: (proximal to distal) 1. duodenum: 10 in (short); begins at pyloric sphincter of stomach 2. jejunum: 3 ft long 3. ileum: 6 ft long; joins large intestine at ileocecal sphincter

3 Major Salivary Glands: Parotid Gland

-largest of 3 major salivary glands -lies b/w skin and masseter muscle just anterior to the ear -relatively long excretory duct called the parotid duct, which opens into the mouth at the parotid papilla -the parotid papilla is found on the cheek opposite to the second upper molar -gland located outside oral cavity

Describe the submucosa layer of GI tract.

-layer of loose CT that binds to mucosa to muscularis externa; may contain glands, vessels, lymphatic tissue, and nerves; contains submucosal plexus, which provides secretory cells (aka plexus of Meissner)

3 Major Salivary Glands: Submandibular Gland

-lies in/under floor of mouth along the medial surfaces of the mandible -relatively long excretory duct called the submandibular duct, which empties on either side of the lingual frenulum -gland is located outside of the oral cavity (because it beneath the oral cavity)

Liver: blood supply and drainage

-liver receives blood from 2 sources: 1) hepatic a.: oxygenated and 2) hepatic portal vein (deoxygenated blood with nutrients/toxins from GI tract) Path: (blood enters, then exits) hep a. and hep portal v. → liver sinusoids (filters blood here via hepatocytes) →central vein → hepatic vein → IVC → RA of heart

Liver: hepatocytes and bile?

-livers cells called hepatocytes secrete bile -bile: partially an excretory product and partially a digestion secretion -composition of bile: 1. water, 2. bile salts (for emulsifying for dig and absorp. of lipids into smaller pieces), 3. bilirubin (detoxified by liver), and 4) electrocytes

Describe the anatomy of the oral cavity.

-mouth, aka oral or buccal cavity, is formed by the cheeks, hard and soft palates, and tongue -lips or labia are fleshy folds that surround the opening of mouth and contain the orbicularis oris muscle -opens posteriorly into the oropharynx through an opening called the fauces -2 Parts of the Oral Cavity: 1. Vestibule: b/w lips and teeth and b/w cheeks and teeth 2. Oral Cavity Proper: superior border is hard and soft palates; inferior border is tongue and floor of the mouth; posterior border is entrance to oropharynx; all other borders are the teeth

Peritoneum: what's the lining of the abdominopelvic cavity/its viscera?

-parietal peritoneum/visceral peritoneum: serous lining the abdominopelvic cavity and its viscera, respectively -serous fluid: secreted by these membranes; located b/w 2 layers in peritoneal cavity (b/w 2 peritoneum) to reduce friction as viscera move and prevent viscera fusing together

Stomach: Functions?

-part of GI tract which connects esophagus to duodenum -stomach receives bolus from esophagus and passes the now chyme onto the small intestine for further digestion and absorption -mixing (mechanical digestion) and holding area for food, continues chem. digestion of carbs, begins chem. digestion of proteins and triglycerides, converts bolus to chyme. Can absorb some substances. SO**mech. dig., chem. dig., and absorp.

Peritoneum: mesentery?

-peritoneum contains large folds that are double layered and fused = mesenteries -these mesenteries bind organs to one another and to the walls of abdominal cavity -also contain BV, lymphatic vessels, and nerves which supply abdominal organs

Describe the anatomy and 3 functions of the pharynx.

-pharynx begins at internal nares and continues inferiorly -connects nasal cavity and oral cavity (found superiorly) to the larynx and esophagus (found inferiorly) -entrance from pharynx to larynx will be anterior = resp. portion; while entrance from pharynx to esophagus will be posterior = digestive portion -contraction of muscles in oropharynx and laryngopharynx help propel food into esophagus -3 Functions: 1. passageway for air and food 2. resonate sounds 3. house tonsils (for immunity)

3 Major Salivary Glands: Sublingual Gland

-smallest of 3 major salivary glands -beneath tongue and superior to the submandibular glands -lesser sublingual ducts open into the floor of the mouth -gland located within the oral cavity

Stomach: How is its muscular externa an exception to the rest of the GI tract's?

-stomach's muscular externa has 3 layers of smooth muscle, not the usual 2 = increased mechanical breakdown -outer longitudinal layer, middle circular layer, and inner oblique layer

Large Intestine: Structure-describe the different sections of the large intestine in order as they occur

-terminal portion of the GI tract -no villi or plicae circulares on mucosa of large intestine -Sections in Order: 1. cecum: entered into from the small intestine via ileocecal valve 2. from the cecum you enter the colon, which is divided (proximal to distal) into ascending, transverse, descending, and sigmoid portions 3. once leave the sigmoid portion of the colon, enter the rectum 4. from rectum, you enter the anal canal 5. the opening of the anal canal to the exterior is called the anus

Describe the mucosa layer of GI tract.

-the inner lining of GI tract; composed of a lining epithelium with underlying CT; the 3 principle function of the mucosa are: protection, absorption, and secretion

Briefly list the structural organization GI tract's wall

-the structural organization of alimentary canal's wall from the esophagus to the anal canal is the same, although some specializations for functional needs will occur -From the lumen outward: (lumen (inner opening where food moves through) -> outside) 1. mucosa 2. submucosa 3. muscularis externa 4. serosa OR adventitia (depends on section of GI tract)

Describe the muscularis externa layer of GI tract.

-this layer contains smooth muscle; helps to mechanically break down food, mix it with digestive secretions, and move it through the GI tract; generally found in 2 sheets: 1) inner circular fibers (help squeeze and mechanical digestion) and 2) outer longitudinal fibers (propels food) -a number of sphincters or valves are created along the GI tract by the thickening of the circular muscle layer (open/close) (ex: pyloric sphincter) -NOTE: in the STOMACH, there is a THIRD, innermost layer of smooth muscle, which is oblique = allows for more breakdown -NOTE: in wall of proximal esophagus, the muscular externa is SKELETAL muscle. There's also skeletal muscle outside around the anal canal wall, creating the external anal sphincter.

Pathway of bile delivery to small intestine

1. bile produced in liver ↓ (emptied to hep. ducts) 2. R and L hepatic ducts ↓ (empty into common hepatic duct) 3. common hepatic duct from liver ↓ (cystic duct from gallbladder empties its contents into common hepatic = so liver and gallbladder empty into common bile duct) 4. common bile duct ↓(pancreatic duct empties its pancreatic juices into common bile duct before small intestine) 5. duodenum of small intestine

site of chemical digestion for 4 macromolecules

1. carbohydrates: starts in mouth via saliva; continues in stomach; finishes in small intestine 2. proteins: starts in stomach; finishes in small intestine 3. fats: starts in stomach; finishes in small intestine 4. nucleic acids: starts and finishes in small intestine

Peritoneum: 6 examples of mesenteries in body?

1. mesentery (proper): attaches small intestine to posterior abdominal wall 2. mesocolon: attaches colon to post. abdominal wall 3. coronary ligament: attaches liver to inferior diaphragm 4. falciform ligament: attached liver to ant abdominal wall and diaphragm 5. lesser omentum: attaches lesser curvature and liver 6. greater omenutm: largest of fold; hangs off greater curvature of stomach; drapes over transverse colon and small intestine; total of 4 layers bc it's double-layered and it folds back on itself

Liver: porta hepatis? ligamentum teres hepatis?

1. porta hepatis: fissure on inferior side of liver where neurovascular structures run/enter/leave (not veins) 2. ligamentum teres hepatis: aka round ligament of liver; was umbilical vein in embryo

Stomach: more anatomical features- rugae? lesser curvature? greater curvature? pyloric sphincter?

1. rugae: longitudinal folds where the mucosa lies when stomach is empty; these folds do not alter SA for absorption, rather they accommodate overall expansion of stomach with food 2. lesser curvature: concave medial border of stomach; @ curv, visceral peritoneum becomes the lesser omentum 3. greater curvature: convex lateral border of stomach; @ curv, visceral peritoneum becomes the greater omentum 4. pyloric sphincter: lies b/w stomach and duodenum; created by thickening of circular layer of muscular externa; regulates movement of chyme into the duodenum

Large Intestine: Associated Structures with the tube of intestine- vermiform appendix, hepatic flexure, splenic flexure, teniae coli, haustra, and omental appendices (i.e. epiploic appendages)?

1. vermiform appendix: attached to the cecum 2. hepatic flexure: how the ascending colon is connected to the transverse colon 3. splenic flexure: how the transverse colon is connected to the descending colon 4. teniae coli: 3 thickened bands seen on the cecum's and colon's outer longitudinal layer of muscular externa 5. haustra: sacs/pouches on cecum and colon 6. omental appendices: visible fatty projections of serosa on outer surface on large intestine

What are the 8 Major Processes of the Digestive System?

1.) Ingestion: taking food into the body 2.) Secretion: body produces 7 L of secretions per day for chemical breakdown of food 3.) Mixing and Propulsion (Motility Capability): moving broken down food throughout body; via alternating contraction and relaxation of smooth muscle; "peristalsis" = mix food with secretions + propel to distal end 4.) Digestion: breakdown of food a. Mechanical Digestion: physical breakdown of food to smaller pieces b. Chemical Digestion: large carb, lipids, and proteins are split into smaller molecules so they can be absorbed 5.) Absorption: moving molecules across barrier so can be used in body; primarily occurs in small intestine (material will go into blood or lymph) 6.) Defecation (of Feces): indigestible materials that exit the body 7.) Barrier: mucosal tissue lining of GI tract prevents entry of noxious substances 8.) Immunologic Protection: lymphatic tissue in GI tract's mucosa = 1st line of defense

What are the 2 divisions of the digestive system?

The digestive system consists of: 1. Alimentary Canal: 30 ft in living; (aka GI tract) organs of GI tract include mouth, most of pharynx, esophagus, stomach, small intestine, and large intestine 2. Associated or Accessory Digestive Organs: tongue (PB), teeth (PB), salivary glands (S), pancreas (S), liver (S), and gallbladder (S) >PB = physical break down and S = secretions (don't directly come into contact with food)