The Digestive System

Stages of Food Processing

IngestionTaking in of nutrients

DigestionBreakdown of complex organic molecules into smaller components by physical and chemical means

AbsorptionTaking up of digested molecules into the cells of the digestive tract

EgestionRemoval of waste food materials from the body

Appearance of the Digestive System

Humans●Digestive system is one

long tube, open at both ends

●Gastrointestinal tract/alimentary canal

Birds●One long tube that will

store, grind up, and absorb food

Perch (Fish)●One long tube similar to humans

Rat●Very similar to humans – really only size that

varies●One long tube that goes from mouth to anus

Let’s Start at the Top

Mouth●Digestion begins here●Teeth begin the physical

breakdown of food●Action of chewing

stimulates salivary glands (parotid, sublingual & submandibular)

●Saliva: water, mucus (mucin) & enzymes that breaks down carbs into maltose (amylase)

●Tongue: forms bolus out of food

Neck Area●Pharynx: double purpose

tube – bolus from mouth comes to pharynx to get to digestive tract

●Epiglottis: flap over your airway to make sure food does not go down

●Esophagus: tube that joins the mouth and the stomach. Food moves down by smooth muscle contractions “peristalsis”

Stomach●Movement in and out of the stomach is

controlled by sphincters – like drawstrings on a bag

●Stomach has 3 muscle layers – contract/relax to churn food

●Cells in stomach lining secrete gastric juice (HCl + enzymes) and mucus●HCl + enzymes break down fibrous food●HCl kills foreign invaders●Mucus protects the stomach lining

Stomach●Our stomach is super acidic – without mucus

barrier, our stomach would digest itself●Damage to the mucus – gastric ulcers●Pepsin – breaks down proteins, needs an

acidic environment●Minimal absorption (small amounts of water,

medicine, alcohol)

A Small Detour

A Small Detour – the Liver●Produces bile – emulsifying agent – digest fats●Bile contains bile salts that break large fat

globules into small ones●Bile is secreted continuously by the liver and

stored in the gallbladder●Liver stores carbs, vitamins, and is a detox

organ

A Small Detour – the Pancreas●Produces sodium bicarbonate to raise the pH

of chyme from 2.5 to 9.0 (acidic to basic)●Also secretes digestive enzymes such as

lipase (fat digesting), pancreatic amylase (carb digesting), trypsin (protein)

Small Intestine●Duodenum: receives secretions from the

pancreas and the liver●food from the stomach is called chyme –

water, food, gastric juice●UH OH! Chyme is very acidic but the small

intestine can’t handle it...what do we do?●Thankfully, the pancreas secretes sodium

bicarbonate to raise the pH●Structure contains ridges and folds as well as

villi and microvilli to increase surface area for absorption.

Small Intestine●Secretes maltase (converts maltose to

glucose)●Secretes peptidases (complete digestion of

protein – amino acids)●Once digestion is complete, the products are

ready to be removes from the digestive tube and transported

●Most absorption takes place in the small intestine – villi increase surface area, microvilli further increase surface area for absorption

●Lacteals transport materials

Large Intestine (aka Colon)●Shorter than the small

intestine but larger in diameter

●Absorbs usable materials – primarily water

●Has bacteria that produce vitamin K and some B

●Cellulose (from plants) reaches large intestine pretty much undigested

●Feces = cellulose, living/dead bacteria, water

●As waste builds up, CNS prompts to void the waste

What about the End?

Rectum and Anus●Bowel (large intestine) movements propel

waste through the rectum and anus●Allow our bodies to get rid of potentially very

toxic wastes

Where does Homeostasis fit?●Seeing, smelling, tasting, thinking about food will

stimulate glands to produce hormone secretions●Stimulation of salivary glands – saliva●Gastrin (hormone) stimulates gastric juice release●Secretin (hormone) travels to the pancreas to

initiate release of sodium bicarbonate●Large meal – more forceful stomach contractions,

faster emptying●Fatty meal – slow peristalsis – more time for fat

digestion and absorption – feel full longer after a high fat meal

What happens when things go wrong?

Case Study●Jess came to the hospital with significant

weight loss and fever. ●She was also was bleeding from the rectum

(both red and black)●She was found to be anemic●What’s wrong?

Let’s look at her symptoms:●Weight loss

● If she’s eating properly, something may be wrong with her digestive system

● Ideas?●Fever

● Infection● Inflammation (body trying to attack invader)

●Rectal bleed● Red – small intestine● Black – large intestine

●Anemia● Low iron● Nutrients may not be getting where they need to go?

How do we figure out the cause?●Blood tests – anemia●Colonoscopy – insert camera into the anus –

look for inflammation or bleeding in the large intestine

●Upper Gastrointestinal examination – look at small intestine ●patient drinks Barium solution that coats lining

of the small intestine ●shows up white on X-ray film to show

abnormalities or inflammation

Crohn’s Disease●Chronic inflammation of the intestines●Causes ulcers●Can affect anywhere in the digestive system●Kids can have stunted growth and

development●Treatment: correct nutritional deficiencies,

relieve symptoms●Treatment: drugs, nutrition supplements,

surgery, combination●NO CURE! Chronic means will act up again

and again

Other Digestive System Disorders●Appendicitis - appendix●Tape Worm – stomach/intestine●Dysentery - intestine●Gallstones – gallbladder, liver, pancreas●Gingivitis - mouth●Hiatus Hernia - stomach

Digestive System●Our digestive system is an open ended tube

that starts at the mouth and ends at the anus●It is necessary to receive nutrients to keep our

bodies running with the energy that we need●Each area of the digestive system has a

particular role to play in the big picture●The nervous and endocrine systems control

the actions of the digestive system in various ways

Fetal Pig Pictures