Digestive SystemDigestive System

What goes in, must come out.What goes in, must come out.

Major Activities of Digestive Major Activities of Digestive SystemSystem

IngestionIngestion Mechanical Mechanical

ProcessingProcessing DigestionDigestion SecretionSecretion AbsorptionAbsorption DefecationDefecation DefenseDefense PeristalsisPeristalsis

Organs of the Digestive Organs of the Digestive TractTract

Digestive Tract consists of Digestive Tract consists of two parts:two parts:

Alimentary CanalAlimentary Canal – actual – actual digestive tract organsdigestive tract organs

Accessory OrgansAccessory Organs – organs that – organs that help in digestion but no food ever help in digestion but no food ever entersenters

Alimentary Canal Accessory Organsmouth salivary glandspharynx teethesophagus pancreasstomach liversmall intestine gall bladderlarge intestineanus

Oral CavityOral Cavity Food enters the digestive Food enters the digestive

system heresystem here Teeth tear, cut and grind Teeth tear, cut and grind

food into small pieces food into small pieces (mechanical digestion)(mechanical digestion)

Saliva from salivary Saliva from salivary glands moistens foodglands moistens food

Saliva also contains Saliva also contains amylase that break down amylase that break down large carbohydrateslarge carbohydrates

SalivarySalivary GlandsGlands Parotid, Parotid,

submandibular and submandibular and sublingual glands sublingual glands located in the oral located in the oral cavity produce the cavity produce the majority of the majority of the salivasaliva

Saliva is mostly Saliva is mostly water with mucouswater with mucous

What’s a bolus?What’s a bolus? The The bolusbolus is a small mass of chewed is a small mass of chewed

food mixed with saliva. food mixed with saliva. EpiglottisEpiglottis, flap , flap of cartilage, covers the opening of the of cartilage, covers the opening of the larynx to prevent food from going to larynx to prevent food from going to lungs. lungs. Soft palateSoft palate raises to prevent raises to prevent bolus from entering into nasal cavitybolus from entering into nasal cavity

PeristalsisPeristalsis PeristalsisPeristalsis is the rhythmic contraction of is the rhythmic contraction of

smooth muscles to move contents through smooth muscles to move contents through the digestive tract. the digestive tract.

PeristalsisPeristalsis starts in the esophagus where starts in the esophagus where the bolus is propelled down towards the the bolus is propelled down towards the stomach.stomach.

Lower esophageal (cardiac) sphincterLower esophageal (cardiac) sphincter is is the opening of the stomach and relaxes the opening of the stomach and relaxes allowing bolus to enterallowing bolus to enter

Peristalsis in Action

StomachStomach

Stores ingested food until it is released into Stores ingested food until it is released into the small intestinethe small intestine

Secretes hydrochloric acid (HCl) and enzymes Secretes hydrochloric acid (HCl) and enzymes (pepsin) that begins protein digestion = (pepsin) that begins protein digestion = chymechyme

High acidic levels (low pH) kill most bacteria High acidic levels (low pH) kill most bacteria and other pathogens found in the food we eatand other pathogens found in the food we eat

Absorbs vitamin B12, alcohol, aspirin, water, Absorbs vitamin B12, alcohol, aspirin, water, and caffeineand caffeine

Facts about the StomachFacts about the Stomach muscular, elastic, pear-shapedmuscular, elastic, pear-shaped can change size … 12” x 6” and can can change size … 12” x 6” and can

hold about 2-4 liters of foodhold about 2-4 liters of food Cardiac sphincterCardiac sphincter prevents food from prevents food from

passing back to the esophagus passing back to the esophagus (heartburn)(heartburn)

Stomach empties into the Stomach empties into the duodenumduodenum and is separated by and is separated by pyloric sphincterpyloric sphincter

You re-grow a new stomach lining You re-grow a new stomach lining every 3 daysevery 3 days

Layers of the StomachLayers of the Stomach Starting from inside…Starting from inside…

MucosaMucosa – acid and digestive juices – acid and digestive juices secretedsecreted

SubmucosaSubmucosa – connective tissue – connective tissue MuscularisMuscularis – layer of muscle that – layer of muscle that

moves and mixes stomach contentmoves and mixes stomach content SubserosaSubserosa and and serosaserosa – wrapping for – wrapping for

the stomachthe stomach

Inside of Stomach Outside of Stomach

The journey….The journey….

After 1 to 3 hours in the stomach, After 1 to 3 hours in the stomach, chymechyme moves into the small moves into the small intestineintestine

Strong peristaltic waves propel Strong peristaltic waves propel chymechyme through through pyloric canalpyloric canal toward toward pyloric orificepyloric orifice (the opening between (the opening between stomach and small intestine)stomach and small intestine)

Phyloric sphincterPhyloric sphincter controls the rate controls the rate and amount of chyme entering and amount of chyme entering intestineintestine

Small IntestineSmall Intestine

Divided into three sectionsDivided into three sections duodenumduodenum jejunumjejunum ileumileum

DuodenumDuodenum First section of small intestineFirst section of small intestine C-shaped and ~ 10 inches longC-shaped and ~ 10 inches long Complete digestion of food molecules Complete digestion of food molecules

occurs in the duodenumoccurs in the duodenum Presence of acidic chyme stimulates Presence of acidic chyme stimulates

the release of pancreatic secretionsthe release of pancreatic secretions these secretions are clear, basic, and these secretions are clear, basic, and

contain mostly water and some contain mostly water and some enzymes.enzymes.

secretions help neutralize stomach acidsecretions help neutralize stomach acid

Pancreas makes insulin and digestive enzymes which are ‘dumped’ into the duodenum

Insulin regulates glucose levels and is related to Diabetes

Pancreas

MicrovilliMicrovilli

Increase surface area of intestine

so more absorption can

occur

Jejunum and IleumJejunum and Ileum Most absorption of the Most absorption of the

digested food occurs in digested food occurs in the the jejunumjejunum

JejunumJejunum is the middle is the middle part of the small intestinepart of the small intestine

IleumIleum is the last part of is the last part of small intestine and is small intestine and is primarily responsible for primarily responsible for absorbing salts and absorbing salts and vitamin B12vitamin B12

LiverLiver the liver is an the liver is an accessory organaccessory organ

produces bile that is produces bile that is dumped into dumped into duodenum. duodenum.

Bile is basic, contains Bile is basic, contains water, bile salts, bile water, bile salts, bile pigments, cholesterol pigments, cholesterol and enzymesand enzymes

Absorbs alcoholAbsorbs alcoholBileBile breaks down large fat droplets breaks down large fat droplets into smaller ones so enzymes can into smaller ones so enzymes can digest the fatdigest the fat

Excess bile is stored in the Excess bile is stored in the gall gall bladderbladder

Large IntestineLarge Intestine

Large IntestineLarge Intestine a.k.a. “a.k.a. “large bowellarge bowel” – part of the ” – part of the

digestive system where waste digestive system where waste products from food are collected and products from food are collected and processed into feces.processed into feces.

Large Intestine’s FunctionsLarge Intestine’s Functions:: reabsorbs water; maintains fluid balancereabsorbs water; maintains fluid balance absorbs certain vitaminsabsorbs certain vitamins processes undigested material (fiber)processes undigested material (fiber) stores waste before it is eliminatedstores waste before it is eliminated

CecumCecum first part of the large intestinefirst part of the large intestine shaped like a small pouch and is shaped like a small pouch and is

located in the right lower abdomenlocated in the right lower abdomen it connects the small and large it connects the small and large

intestinesintestines the the cecumcecum accepts and stores accepts and stores

processed material from small intestine processed material from small intestine and moves it towards the colonand moves it towards the colon

ileocecal valveileocecal valve is the sphincter is the sphincter between the two intestinesbetween the two intestines

the the appendixappendix extends from the cecum extends from the cecum

Vermiform AppendixVermiform Appendix A blind ended tube connected to the A blind ended tube connected to the cecumcecum Vermiform in Latin means “worm-like”Vermiform in Latin means “worm-like” The biological purpose of the appendix has The biological purpose of the appendix has

mystified scientists for some time mystified scientists for some time The most common explanation is that the The most common explanation is that the

appendix is a vestigial structure with no appendix is a vestigial structure with no absolute purpose absolute purpose

Some people are born without an appendixSome people are born without an appendix Sometimes bacteria and indigestible Sometimes bacteria and indigestible

material become trapped in the appendix material become trapped in the appendix causing it to swell and rupturecausing it to swell and rupture

ColonColon Shaped like an inverted Shaped like an inverted

“U”“U” Largest part of the large Largest part of the large

intestineintestine Colon has four sections:Colon has four sections:

Ascending colonAscending colon Transverse colonTransverse colon Descending colonDescending colon Sigmoid colonSigmoid colon

What does the colon do?What does the colon do? Fiber, small amounts of water, vitamins, etc. Fiber, small amounts of water, vitamins, etc.

mix with mucus and bacteria and start to mix with mucus and bacteria and start to form fecesform feces

The lining of the colon absorbs most of the The lining of the colon absorbs most of the water along with vitamins and mineralswater along with vitamins and minerals

Bacteria chemically break down some fiber Bacteria chemically break down some fiber for their own nourishmentfor their own nourishment

Through muscular movement, feces is Through muscular movement, feces is pushed along until the sigmoid colon pushed along until the sigmoid colon contracts, and then the feces is moved into contracts, and then the feces is moved into the rectum.the rectum.

The rectum is the final part of the large The rectum is the final part of the large intestine. Stool is stored here before being intestine. Stool is stored here before being passed as a bowel motion.passed as a bowel motion.