DIGESTIVE SYSTEM     CHAPTER 24

I. Introduction

          A. Alimentary canal (GI tract)

                    1. mouth

                    2. pharynx                                                                                                                  

                    3. esophagus

                    4. stomach

                    5. small intestine

                    6. large intestine

                    7. anus

          B. Accessory organs

                    1. tongue

                    2. salivary glands

                    3. teeth

                    4. liver

                    5. gallbladder

                    6. pancreas

          C. Processes

1.     ingestion                                                                                                               

          a. take in food

                    2. mechanical breakdown

                              a. decrease size of particles

                              b. churning in stomach

                    3. chemical digestion

                              a. enzyme action to degrade to smaller units

                    4. absorption

                              a. simple units from digestion taken into blood or lymph from lumen of GI tract 

                    5. propulsion

                              a. to move contents of lumen

                              b. occurs entire length of GI tract

                              c. tongue pushes food into esophague

                              d. perstalsis

                                        (1)waves of contraction/relaxation

                    6.defecation

                              a. excretion of indigestables

 

II. ANATOMY

          A.peritoneum

                    1.membrane of abdominal cavity

                              a. visceral over surface of organs

                              b. parietal near wall of cavity

                    2. peritoneal cavity

                              a. serous fluid

                    3. mesentery

                              a. double membrane of peritoneum

                              b. contains:

                                        (1)blood vessels

                                        (2)lymphatics

                                        (3)nerves

                              c. positions organs in abdominal cavity

 

          B. circulation

                    1. arterial:

                              a.abdominal aorta

                              b.splanchnic circulation

                                        (1)celiac trunk

                                        (2)hepatic

                                        (3)splenic

                                        (4)gastric

                                        (5)mesenteric

                              c.hepatic portal circulation

                                        (1)venous blood from GI to liver -first pass

                             

          C. Histology

                    1. mucosa

                              a.columar epithelial membrane lining the lumen

                              b. functions:

                                        (1)absorption

                                        (2)secretion

                                                  (a)mucus

                                                  (b)hormones

                                                  (c)digestive enzymes and HCl

                                        (3)protection

                              c. specialized for specific sites in GI

                              d. contains underlying lamina propria of loose

                                 connective tissue and blood vessels

                              e. muscularis mucosae

                                       

                    2. submucosa

                              a. dense CT

                              b. vascular network

                              c. submucosal plexus

                                        (1) intrinsic nerve supply (autonomics)

                                                  (a)glands

                                                  (b)smooth muscle of mucosa

                             

                    3. Muscularis Externa

                              a. circular layer of smooth muscle

                              b. longitudinal layer of smooth muscle

                              c. myenteric plexus (autonomic) to control motility of GI tract

 

                    How do sympathetic and parasympathetic fibers differ

                    in regulation of GI motility?

 

                    4. Serosa

                              a. areolar connective tissue

                              b. mesothelium

                                        (1)simple squamous epithelium

                              c. certain areas may contain adventitia in place of serosa      

                                        (1)esophagus

                                        (2)rectum

          D. Organs of the alimentary canal

                    1.Mouth

                              a.oral or buccal cavity

                              b.oropharynx

                              c. lips(labia)

                              d.labial frenulum

                              e.palate(roof)

                                        (1)hard

                                                  (a)palatine and palatine process of maxillae

                                        (2)soft

                                                  (a)skeletal muscle

                                                  (b)uvula

                                                  (c)fauces

                                                            i)contain platine tonsils

                                                            ii)opening to pharynx

                                        (3)tongue

                                                  (a)taste buds

                                                  (b)moves food

                                                  (c)forms bolus

                                                  (d)muscles

                                                            i)intrinsic

                                                                      a)unattached to bone

                                                            ii)extrinsic

                                                                      a)from bones of skull or soft palate

                                                  (e)lingual frenulum

                              f.salivary glands

                                        (1)serous fluid

                                        (2)salivary amylase

                                        (3)3 pairs

                                                  (a)parotid

                                                            i)anterior to ear

                                                            ii)superficial to masseter

                                                            iii)mumps - viral infection

                                                  (b)submandibular gland

                                                  (c)sublingual

                                                            i)under tongue

                                        (4)parasympathetic control

                              g.teeth (dentitions)

                                        (1)deciduous teeth

                                                  (a)primary or baby teeth

                                                  (b)20

                                        (2)permanent teeth

                                                  (a)32 including wisdom teeth (3rd molars)

                                                  (b)impacted if remains in jaw

                                        (3)types

                                                  (a)incisors

                                                            i)cutting

                                                            ii)central and lateral

                                                  (b)canines

                                                            i)tearing

                                                  (c)premolars

                                                            i)1st and 2nd set- grind/crush

                                                  (d)molars

                                                            i)1st,2nd, and 3rd -grind/crush

                                        (4)structure

                                                  (a)crown

                                                            i)enamel - calcium salts

                                                  (b)gingiva

                                                            i)gums

                                                  (c)root

                                                            i)within jaw

                                                            ii)outer portion covered in cementum

                                                                      a)calcified CT

                                                  (d)periodontal ligament

                                                  (e)dentin

                                                            i)under enamel

                                                            ii)bonelike

                                                            iii)surrounds pulp cavity

                                                            iv)pulp cavity in root is root canal

                                                            v)odontoblasts

                                                                      a)cells secreting dentin

                                        (5)dental diseases

                                                  (a)dental caries

                                                            i)dental plaque

                                                                      a)sugar, bacteria

                                                                      b)calculus

                                                                                (i)calcified plaque

                                                  (b)gingivitis

                                                            i)inflammation of gums

                                                  (c)peridontal disease

                                                            i)tooth loss

                                        (6)functions in digestion

                                                  (a)mastication

                                                            i)chewing

                                                            ii)mechanical breakdown of food

                                                  (b)lubrication of food

                                                  (c)deglutition

                                                            i)swallowing

                                                  (d)CHO breakdown by salivary amylase

                    2.Pharynx

                              a.oropharynx and laryngopharynx

                              b.stratified squanous epithelium

                                        (1)friction

                              c.skeletal muscle in outer layer

                    3.Esophagus

                              a.carries food to stomach

                              b.located in mediastinum

                              c.esophageal hiatus

                                        (1)where esophagus passes through diaphragm

                                        (2)enters stomach at cardiac orifice

                              d.skeletal muscle in superior portions of muscularis externa

                              e.hiatal hernia

                                        (1)portion of stomach or SI enters thoracic cavity at esophageal hiatus

                              f.esophagus and pharynx function in deglutition

                    4.Stomach

                              a.empty 50ml volume

                              b.stretch to 4L

                              c. rugae

                                        (1)folds of mucosa and submucosa when empty

                              d.regions

                                        (1)cardiac

                                        (2)fundus

                                        (3)body

                                        (4)pylorus

                                                  (a)joins duodenum at pyloric sphincter

                              e.layers

                                        (1)muscularis externa

                                                  (a)has additional oblique layer

                                                  (b)churning function as well as movement

                                                            i)creates CHYME

                                                                      a)semi-liquid

                              f.simple columar epithelium

                                        (1)goblet cells

                                                  (a)secrete mucus

                              g.gastric pits

                                        (1)lead to gastric glands

                                                  (a)secrete gastric juice

                              h.cells

                                        (1)parietal cells

                                                  (a)HCl

                                                  (b)intrinsic factor

                                                            i)vitamin B12 absorption in SI

                                        (2)chief cells

                                                  (a)pepsinogen

                                        (3)enteroendocrine cells

                                                  (a)hormones of digestion

                                                            i)gastrin

                                                                      a)stimulated by proteins

                                                                      b)stimulates gastric gland secretions

                                                                      c)stimulates movement of food through GI

                                                            ii)serotonin

                                                                      a)stimulated by food

                                                                      b)stimulates contraction of Smooth muscle

                                                            iii)histamine

                                                                      a)stimulated by food

                                                                      b)stimulates secretion of HCl

                                                            iv)somatostatin

                                                                      a)stimulated by food

                                                                      b)inhibits secretion of stomach and pancreas

                   

                              i.digestive functions of the stomach

                                        (1)protein digestion

                                        (2)pepsinogen converted to pepsin

                                        (3)Phases of gastric secretion

                                                  (a)Cephalic phase

                                                            i)triggered by senses

                                                            ii) increase secretions

                                                  (b)Gastric phase

                                                            i)presence of food in stomach

                                                            ii)stimuli for secretions

                                                                      a)stretch

                                                                      b)peptides or other foodstuffs

                                                                      c)pH- proteins act as buffers

                                                                      and tie up H ions to increase pH

                                                                      d)histamine stimulates HCl

e)Cloride ions in HCl come from plasma and H ions from carbonic acid in parietal cell.. bicarobonate ions are returned to capillaries and makes blood from stomach more alkaline -  ALKALINE TIDE

                                                  (c)intestinal phase

                                                            i)excitatory

                                                            ii)inhibitory

                                                            iii)movement of food through tract

                                        (4)Motility

                                                  (a)peristalsis

                                                  (b)relaxing, contraction of valves

                                        (5)Vomiting reflex

                                                  (a)reverse emptying of stomach

                                                  (b)irritants, toxins

                                                  (c)extreme stretch

                    5.Small Intestines

                              a.most digestion and absorption occurs here

                              b.pyloric sphincter to ileocecal valve

                              c.1 inch diameter and 20 feet long (cadaver)

                              d. divisions

                                        (1)duodenum

                                                  (a)around pancreas, 10 inches

                                                  (b)hepatopancreatic ampulla

                                                            i)bile and pancreatic juice enters

                                                            ii)regulated by sphincter of Oddi

                                        (2)jejunum

                                                  (a)8 feet      

                                        (3)ileum

                                                  (a)12 feet

                                                  (b)suspended by mesentery

                              e.modified for absorption

                                        (1)plicae circulares

                                                  (a)circular folds of mucosa and submucosa

                                                  (b)mixing of chyme -spiral

                                        (2)villi

                                                  (a)fingerlike projections of mucosa

                                                  (b)absorptive columnar cells

                                        (3)microvilli

                                                  (a)projections from each epithelial cell

                                                  (b)increases surface area

                                                  (c)brush border

                                                  (d)brush border enzymes

                                                            i)to complete SI digestion of

                                                            carbohydrates and proteins

                                        (4)pits to intestinal glands

                                                  (a)intestinal crypts (glands)

                                                            i)secrete intestinal juice

                                                                      a)watery, mucous

                                                            ii)Paneth cells

                                                                      a)lysozyme

                                        (5)submucosa

                                                  (a)Peyer's Patches

                                                            i)lymphoid tissue

                                                            ii)more in LI

                                                  (b)Duodenal glands

                                                            i)alkaline mucus to increase pH

                                        (6)intestinal juice

                                                  (a)1 to 2 liters/day

                                                  (b)6.5 -7.8 pH

                              f.digestive processes

                                        (1)bile and pancreatic enzymes act on food in

                                        duodenum (3-6 hrs transit)

                                        (2)peristalsis

                                                  (a)moves food through

                                                  (b)segmentation

                                                            i)slow, waves

                    6.Large Intestine

                              a.ileocecal valve to anus

                              b.functions to absorb water

                              c.elimination of feces

                              d.regions

                                        (1)cecum

                                                  (a)first saclike section

                                                  (b)vermiform appendix

                                                  (c)appendicitis

                                        (2)colon

                                                  (a)ascending (up right side)

                                                  (b)transverse colon

                                                  (c)descending colon (down left)

                                                  (d)sigmoidal(s-shaped)

                                                  (e)mesentery sheets

                                                            i) anchor Transverse and sigmoid

                                                            ii)called mesocolons

                                        (3)rectum

                                                  (a)at 3rd sacral vertebra

                                        (4)anal canal

                                                  (a)external anal sphincter

                                                  (b)internal anal sphincter

                                                  (c)open with defecation

                                        (5)teniae coli

                                                  (a)muscularis muscle layer is three bands of smooth muscle

                                                  (b)allow for pockets

                                                            i)HAUSTRA

                                                            ii)but not in rectum

                              e.Bacteria

                                        (1)dead and alive

                                        (2)normal

                                                  (a)bacterial flora

                                                  (b)Escherichia coli

                                                            i)makes Vitamin K

                                                  (c)some produce gas

                              f.transit time

                                        (1)motility through GI

                                        (2)12 to 24 hours through the LI

                                        (3)dietary fiber decreases time

                                        (4)haustral contractions

                                                  (a)slow movement

                                        (5)mass movement

                                                  (a)specialized peristalsis

                                                  (b)forces contents to rectum

                              g.diverticulitis

                                        (1)formation of outpockets in LI

                                        (2)left sided appendicitis

                              h.defecation

                                        (1)parasympathetic reflex

                                        (2)close epiglottis

                                        (3)contract diaphragm and agdominal muscles

                                        (4)this increases intraabdominal pressure

                                        (5)Valsava's Manuever

                              i.diarrhea

                                        (1)water stools - rushes through GI

                                        (2)constipation- too much water absorbed

          B. Accessory Organs

                    1.Liver

                              a.3 pounds - largest organ

                              b.four lobes

                                        (1)right (largest

                                        (2)left

                                        (3)caudate lobe (posterior)

                                        (4)quadrate lobe

                              c.falciform ligament

                                        (1)separates right and left lobes

                                        (2)attaches to diaphragm

                              d.ligamentum terez

                                        (1)remnant of umbilical vein

                              e.hepatic artery

                              f.hepatic portal vein

                              g.hepatic duct

                                        (1)bile leaves liver

                                        (2)fuses with cystic duct from gallbladder

                                        (3)forms common bile duct

                              h.hepatocytes

                                        (1)functional liver cells

                                        (2)functional units called liver lobules

                              i.Kupffer cells

                                        (1)hepatic macrophages    

                              j.hepatitis

                                        (1)inflammation of liver by virus

                              k.cirrhosis

                                        (1)chronic inflammation of liver

                                        (2)liver becomes fibrotic and small

                              l. production of bile

                                        (1)yellow-green solution

                                        (2)bile salts

                                                  (a)function to emulsify dietary fats

                                                  (b)chendeoxycholic and cholic acids

                                                            i)made from cholesterol

                                                            ii)recycled

                                                                      a) enterohepatic circulation

                                                                      b)reabsorbed in blood via

                                                                      ileum

                                                                      c)back to liver via hepatic portal vein

                                        (3)bile pigments

                                                  (a)bilirubin

                                                            i)waste product of heme

                                                            ii)urobilinogen metabolite that

                                                            gives feces brown color

                    2. Gallbladder

                              a.in fossa on ventral surface of liver

                              b.stores bile

                              c.contraction empties bile into SI

                              d.cholecystokinin (CCK)

                                        (1)hormone that stimulates bile release

                                        (2)made in duodenum

                              e.gallstones

                                        (1)crystallizing ofcholesterol

                                        (2)obstruct bile flow

                                        (3)may be associated with high fat diets

                    3.Pancreas

                              a.Functions in production of digestive enzymes

                               as an exocrine function

                              b.pancreatic juice drains form pancreatic duct

                              c.fuses to common bile duct form liver and gallbladder and enters duodenum at hepatopancreatic ampulla

                              d.acini

                                        (1)clusters of secretory cells

                                        (2)zymogen granules

                                                  (a)contain digestive enzymes

                              e.pancreatic juice

                                        (1)1200 ml/day

                                        (2)pH 8 by pancreatic duct epithelial cell secretion of bicarbonate ions

                                                  (a)neutralizes chyme

                                        (3)enzymes secreted

                                                  (a)trypsinogen (trypsin)

                                                  (b)chymotrypsinogen (chymotrypsin)

                                                  (c)procarboxypeptidase(carboxypeptidase)

                                                  (d)pancreatic amylase

                                                  (e)pancreatic lipases

                                        (4) regulation by

                                                  (a)CCK

                                                  (b)Secretin

III. Chemical Digestion and Absorption

          A.Carbohydrates

                    1.hydrolysis to simple units

                                                      

CARBOHYDRATES TO GLUCOSE        BY      SALIVARY AMYLASE

 SUCROSE                FRUCTOSE                   PANCREATIC AMYLASE             LACTOSE                 GALACTOSE                    BRUSH BORDER ENZYMES:                MALTOSE                                                      MALTASE

STARCH                                          SUCRASE

GLYCOGEN                           LACTASE

                                                                                         

                             

                    2. absorbed

                              a.facilitated diffusion by carriers on microvilli

                              b.in SI

                              c. may be coupled to active transport of glucose

          B.Proteins

                    1.hydrolysis to amino acids

                    2. pepsin in stomach

                    3. pancreatic enzymes

                    4. brush border enzymes

                    5. most in SI - digestion and absorption

                    6. active with sodium, glucose

          C.Lipids

                    1.need bile for emulsification

                              a.form micells in water

                             

                    2.digestion in SI

                    3.pancreatic lipase

                    4.hydrolyze to glycerol and fatty acids

                    5.absorbed via lacteals

                    6.inside epithelial cells of intestinal villi

                              a.reorganize into triglycerides

                              b.combine with phospholipids and cholesterol to form CHYLOMICRONS

                                        (1)processed by golgi and released to lacteals (lymphatic vessels in villi)

                                        (2)into thoracic duct to venous blood

                                        (3)fasting before blood drawn

          D. Water

                    1.95% SI by osmosis

                    2. water and electrolytes in LI

          E.Vitamins

                    1.diffusion

                    2.fat soluble with lipids

          F.electrolytes

                    1.from GI secretions and foodstuff

                    2.Sodium

                              a.active with glucose and amino acids

                              b. Cl follows sodium

                              c. Cl actively reabsorbed when bicarbonate is

                                secreted in ileum

                    3.Potassium

                              a.diffusion

                    4.Iron

                              a.actively transported into mucosal cells

                                        (1)binds to ferritin (carrier)

                                        (2)carried in blood on transferrin

                    5.Calcium

                              a.absorption from SI regulated by Vitamin D

                              b.balanced with phosphorus

                              c.PTH stimulates Vit D activation

          G. Nucleac acids

                    1. nucleases break down to components

                    2. pancreatic nucleases

                    3. brush border nucleases

IV. Disorders

          A.malabsorption

                    1.various causes

                              a.adult celiac disease

                                        (1)gluten protein in grains damages villi

                                        (2)diarrhea

          B.Cancers

          C.Diarrhea

          D.Colitis

          E.Enteritis

          F.Pyloric Stenosis

                    1.narrowed pyloric sphenic (birth)