EXSC%223:%Week%of%10/31%Notes%from%textbook%Ch%23.1-23.2%23.1%What%major%processes%occur%during%digestive%system%activity?%1. Ingestion%a. Taking%food%into%the%digestive%tract%2. Propulsion%a. Moves%food%through%the%alimentary%canal%b. Includes%swallowing%and%peristalsis%i. Swallowing%1. Voluntary%ii. Peristalsis%1. Involuntary%2. Alternating%waves%of%contraction%and%relaxation%in%the%muscles%of%the%organ%walls%%3. Squeezes%food%along%the%tract%3. Mechanical%breakdown%a. Increases%the%surface%area%of%ingested%food%b. Physically%preparing%it%for%digestion%by%enzymes%c. Chewing%and%mixing%of%food%with%saliva%by%the%tongue%d. Churning%food%in%the%stomach%e. Segmentation%i. Rhythmic%local%constrictions%of%the%small%intestine%ii. Mixes%food%with%digestive%juices%4. Digestion%a. Series%of%catabolic%steps%b. Enzymes%secreted%into%the%lumen%of%the%alimentary%canal%break%down%food%molecules%to%their%chemical%building%blocks%5. Absorption%a. Passage%of%digested%end%products%from%the%lumen%of%the%GI%tract%through%the%mucosal%cells%into%the%blood%or%lymph%b. Active%or%passive%transport%6. Defecation%a. Eliminates%indigestible%substances%from%the%body%via%the%anus%%23.2%The%GI%tract%has%four%layers%and%is%usually%surrounded%by%peritoneum%• Relationship%of%the%digestive%organs%to%the%peritoneum%o Most%digestive%system%organs%are%in%the%abdominopelvic%cavity%o Remember:%all%ventral%cavities%have%serous%membranes%o Peritoneum%is%the%serous%membrane%of%the%abdominopelvic%cavity%§ Has%2%regions%• Visceral%peritoneum:%covers%the%external%surfaces%of%most%digestive%organs%• Parietal%peritoneum:%lines%the%body%wall%• ***they%are%not%separate.%They%are%just%two%regions%of%the%same%membrane***%§ peritoneal%cavity%• space%between%the%2%regions%of%the%peritoneum%• contains%a%slippery%fluid%secreted%by%the%serous%membrane%• reduces%friction%• allows%digestive%organs%to%easily%slide%past%one%another%and%along%the%body%wall%§ mesentery%• double%layer%of%peritoneum%• sheet%of%two%serous%membranes%fused%together%• functions%o provide%routes%for%blood%vessels,%lymphatics,%and%nerves%to%reach%the%digestive%viscera%o holds%organs%in%places%o stores%fat%• most%mesentery%is%dorsal%(attaches%to%posterior%abdominal%wall)%• all%the%organs%of%the%alimentary%canal%have%the%same%4%basic%layers%1. mucosa%a. mucous%membrane%b. moist%epithelial%membrane%c. functions%i. secrete%mucus,%digestive%enzymes,%and%hormones%ii. absorb%the%end%products%of%digestion%into%the%blood%iii. protect%against%infectious%disease%d. 3%sublayers%i. lining%epithelium%1. simple%columnar%epithelium%a. except%in%the%mouth,%esophagus,%and%anus%which%are%stratified%squamous%2. rich%in%mucus-secreting%cells%a. mucus%produced%protects%digestive%organs%ii. lamina%propria%1. loose%areolar%connective%tissue%2. capillaries%nourish%epithelium%and%absorb%digested%nutrients%iii. muscularis%mucosae%1. layer%of%smooth%muscle%cells%2. produce%local%movements%of%the%mucosa%3. enhance%absorption%and%secretion%2. submucosa%a. areolar%connective%tissue%b. rich%supply%of%blood%and%lymphatic%vessels,%and%nerve%fibers%c. abundant%elastic%fibers%3. muscularis%externa%a. responsible%for%segmentation%and%peristalsis%b. 2%layers%of%smooth%muscle%i. inner%circular%layer%1. thickens%at%certain%points%to%form%sphincters%(valves%that%control%food%passage%from%one%organ%to%the%next%and%prevent%backflow)%ii. outer%longitudinal%layer%4. serosa%a. outermost%layer%of%intraperitoneal%organs%b. visceral%peritoneum%c. areolar%connective%tissue%covered%with%mesothelium%%Lecture%10/31%notes%Ch%23:%The%Digestive%System%Digestive%system%is%made%up%of%the%alimentary%canal%and%accessory%structures%• Alimentary%canal%o Includes%§ Mouth%§ Esophagus%§ Small%intestine%§ Large%intestine%o Anything%in%the%alimentary%canal%is%outside%the%body%o Substances%are%only%in%the%body%if%they%are%absorbed%(i.e.%nutrients)%o Indigestible%material%is%never%absorbed%• Accessory%structures%o Tongue%o Pancreas%§ Endocrine%and%exocrine%gland%§ Secretes%insulin%and%glucagon%§ Secretes%enzymes%into%the%small%intestine%o Salivary%glands%o Liver%§ detoxify%o Gall%bladder%§ Stores%bile%§ Breakdown%fat%Digestion%• Digestion%proper:%only%includes%an%enzymatic%reaction%• Common%to%refer%to%digestion%to%include%mechanical%oprocesses%too%1. Ingestion%a. Normally%through%the%mouth%2. Propulsion%a. Swallowing%b. Peristalsis%i. Movement%of%food%through%the%esophagusm%stomach,%small%intestine,%and%large%intestine%3. Mechanical%digestion%a. Chewing%(mouth)%b. Churning%(stomach)%i. Not%the%same%as%peristalsis%ii. Mixes%food%with%enzymes%c. Segmentation%(small%intestine)%4. Chemical%digestion%5. Absorption%a. Most%is%absorbed%in%the%small%intestine%b. Small%amount%can%be%absorbed%in%the%mouth%c. Some%absorbed%in%the%large%intestine%i. Mostly%water%ii. Some%vitamins%6. Defecation%a. Eliminate%the%waste%i. Whatever%isn’t%absorbed%b. Most%of%what%is%defecated%is%bacteria%i. A%lot%is%E.coli%ii. Need%E.coli%to%live,%but%if%you%ingest%it%you%die%Peritoneum%• Serous%membrane%o Sac-like%membrane%o Self-contained%o Hollow,%fluid-filled%• Fluid%filled%core,%the%fluid%acts%as%a%lubricant%• 2%regions%o parietal:%associated%with%the%outer%abdominal%wall%but%also%part%of%the%dorsal%side%o visceral:%always%adjacent%to%the%organ%%• protects%from%bacteria%and%infection%• allows%for%alimentary%canal%to%expand%and%contract%• also%called%omentium%• wraps%around%portions%of%the%digestive%system,%not%all%of%it%o not%liver%o not%some%parts%of%the%intestines%• holds%things%in%place%• mesentery:%2%regions%of%the%peritoneum%that%come%together%and%fuse%4%basic%layers%of%the%alimentary%canal%• lumen%o hollow%center%o anything%in%it%is%outside%the%body%• mucosa%o lines%any%structure%open%to%the%outside%o membrane%o may%or%may%not%have%mucous%o is%wet%o associated%with%simple%columnar%epithelia%o stratified%squamous%epithelia%at%the%mouth%and%anus%o 2%primary%tissue%types%§ epithelium%§ lamina%propria%• like%a%basement%membrane%• loose%areolar%connective%tissue%o muscularis%mucosae%§ not%involved%with%peristalsis%§ helps%excrete%substances%from%glands%• submucosa%o lots%of%elastic%fibers%present%so%it%can%recoil%o dense%irregular%connective%tissue%o lots%of%blood%vessels,%nerves,%and%lymphatic%vessels%o
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