Our system involves…the
intake and digestion of food, absorption of
nutrients, and elimination of solid waste.
What is our system?
S
Gastro-Intestinal System
Alexandra Ford, Jenna Volpe, Alexa
Mastriano and Alexis Tomaszewski
S
Functions of the GI System
S Digestion
S Produces various chemicals to break
down food molecules
S Filters out harmful substances
S Removes solid waste
What is Digestion?
S The chemical breakdown of complex
biological molecules into their
component parts
S The breakdown involves…
S Lipids – Fatty Acids
S Proteins – Amino Acids
S Carbohydrates- Simple Sugars
5 Stages of Digestion
1. Ingestion
2. Movement
3. Mechanical and Chemical Digestion
4. Absorption
5. Elimination
Two Different Types of
Digestion….
S Mechanical Digestion
S Chemical Digestion
What do you think the difference is?
Mechanical Digestion
S Changes the physical form of food
EXAMPLES
S Chewing
S Tearing
S Grinding
S Mashing
S Mixing
Chemical Digestion
S Changes the chemical composition of
food with the aid of digestive enzymes
EXAMPLES
S Carbohydrates
S Proteins
S Lipids
GI Tract
Parts of the GI Tract
– Tube within a tube
– Direct link/path between organs
Structures
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Pharynx
Esophagus
Stomach
Small intestine
Large Intestine
Rectum
Pharynx
S Connects the nasal and oral cavities with the
larynx and esophagus
S There are 3 parts to the pharynx:
nasopharynx
o oropharynx
o laryngopharynx
o
Parts of the Pharynx
Nasopharynx
o
provides a passageway for air when breathing
Oropharynx
o
passageway for food to move from the mouth, and
for air to move to and from the nasal cavity
Laryngopharynx
o
provides a passageway to the esophagus
Esophagus
S Approximately 10” long
S Functions include:
1. Secrete mucus
2. Moves food from the throat to the
stomach using muscle movement
called peristalsis
S If acid from the stomach gets in here
that’s heartburn.
Stomach
S J-shaped muscular bag that stores
the food you eat, breaks it down
into tiny pieces.
S Mixes food with digestive juices
that contain enzymes to break
down proteins and lipids.
S Acid in the stomach kills
bacteria.
S Food found in the stomach is
called chyme.
Stomach
S The stomach is divided into the fundus (upper, rounded part), body
(main portion), and antrum (lower part).
Rugae- the folds in the mucosa lining the stomach.
Gastric Secretions: Thick mucus membrane forms the inner lining of stomach , studded with
small openings (gastric pits) that are at the ends of gastric glands
-Gastric glands have 3 types of secretory cells; mucous, chief, and parietal cells
o
Chief secrete digestive enzymes
o
Parietal release hydrochloric acid
o
The digestive enzymes and the hydrochloric acid forms gastric juice.
Small Intestine
S Small intestines are roughly
7 meters long
S Lining of intestine walls has
finger-like projections called
villi, to increase surface area.
S The villi are covered in
microvilli which further
increases surface area for
absorption.
Small Intestine
Digestion in Small Intestine Produces:
1) disaccharides
2) fatty acids
3) peptidesmonoglycerides
Portions of the Small Intestine:
1) duodenum
2) jejunum
3) ileum
Small Intestine
S Nutrients from the food pass into the
bloodstream through the small intestine walls.
S Absorbs:
S 80% ingested water
S Vitamins
S Minerals
S Carbohydrates
S Proteins
S Lipids
• Secretes digestive enzymes
Large Intestine
S About 5 feet long
S Accepts what small
intestines don’t absorb
S Rectum (short term
storage which holds feces
before it is expelled).
Large Intestine
Functions
S Bacterial digestion
S Ferment carbohydrates
S Protein breakdown
S Absorbs more water
S Concentrate wastes
Large Intestine
Movement
• Slower than in the small intestine. Peristaltic
waves happen 2-3 times a day. Intestinal wall
constricts vigorously and forces the intestinal
contents toward the rectum.
• Defecation reflex: holding a deep breath and
contracting the abdominal wall muscles
increases internal abdominal pressure and
forces feces into the rectum.
Feces from the Large Intestine
Feces
• Materials that were not absorbed or digested,
and water (75%), electrolytes, mucus, and
bacteria.
• Odor is from a variety of compounds that
bacteria produces.
• Color is from pigments now altered by
bacterialß action.
Accessory Organs
S Include: Liver, gall bladder, and pancreas
S Not part of the path of food, but play a critical role.
Liver
S Directly affects
digestion by
producing bile
S Bile helps digest fat
S filters out toxins and
waste including drugs
and alcohol
Liver Functions
Carbohydrate metabolism- helps maintain
concentration of blood glucose
Lipid metabolism-oxidizes fatty acids at a high rate,
synthesizing lipoproteins, phospholipids, and
cholesterol, and converting portions of
carbohydrate and protein molecules into fat
molecules
Protein metabolism-deaminated amino acids,
synthesizing plasma proteins, and converting
certain amino acids to other amino acids
Gall Bladder
S Stores bile from the
liver, releases it into
the small intestine.
S Fatty diets can cause
gallstones
Gall Bladder Functions
S Stores bile between meals, reabsorbs water to
concentrate bile, and contracts to release bile into small
intestine
S Functions of Bile Salts
-Aid digestive enzymes
-Break down fat globules into smaller droplets
(emulsification)
-Then they mix with water so the fat molecules
can be digested more effectively
Pancreas
S Produces digestive
enzymes to digest fats,
carbohydrates and
proteins
S Regulates blood sugar by
producing insulin
Pancreas
S Pancreatic Juice- Contains enzymes that digest
carbohydrates, fats, nucleic acids, and proteins
S Pancreatic amylase -splits molecules of starch or glycogen
into double sugars
S Pancreatic lipase- breaks triglyceride molecules to fatty
acids and glycerol
-Two nucleases, which are enzymes, break down
nucleic acid molecules into nucleotides
-Trypsin, chymotrypsin, and carboxypeptidase (protein
splitting enzymes) split the bonds between certain
amino acids in proteins
Oral Cavity
Mouth
S Teeth mechanically
break down food
into small pieces.
Tongue mixes food
with saliva
(contains amylase,
which helps break
down starch).
S Epiglottis is a
flap-like structure
at the back of the
throat that closes
over the trachea
preventing food
from entering it.
Salivary Glands
2 types of secretory cells:
o serous cells: produce a watery fluid that is rich in
proteins and glycoproteins as well as amylase (split
starch and glycogen molecules into disaccharides)
o mucous cells: secrete a thick mucus which lubricates
the food before it is swallowed
Salivation: occurs when one prepares to eat, and nerve
signals activate salivary glands to moisten the mouth
The amount of saliva secreted depends on how appealing
the particular food is to the individual
Three Types of Salivary Glands
Salivary Glands
partoids
 large
 secrete 25% of saliva (watery)
 front of ears extending to jaw bone (1 on each side)
 drains into mouth near upper teeth
submandibular
 secrete 70% of saliva (mucus)
 drains into mouth from under tongue
sublingual
 smallest
 secrete 5% of saliva (mucus)
 drains into floor of mouth
Lips and Cheeks
S LIPS
S sensory receptors and provide information
about food before its in the mouth
S few differences between lips and skin on body
o
o
no sebaceous glands- keep moisturized with saliva
no hair follicles
Cheeks
S Does anyone remember the scientific name for cheeks?
-stratified squamous epithelium
-inside of cheek is lined by mucous membrane
Tongue
S guides and molds food in the mouth
S composed of skeletal muscle fibers (willingly controlled)
S mucous membrane protects it from microbes and pathogens
S lingual frenulum connects tongue to floor of mouth
S perceives taste and texture
S over 10,000 taste buds (change with age)
Palate
o
forms the roof of the oral cavity and consists of a
bony anterior part and a muscular posterior part
o
palatine tonsils- two lymphatic tissue masses, located
on either side of the pharynx
o
help protect the body against infection (respiratory)
Fun Facts
S HOW LONG ARE YOUR INTESTINES? At least 25
feet in an adult. Be glad you're not a full-grown horse -their coiled-up intestines are 89 feet long!
S Food drying up and hanging out in the large intestine
can last 18 hours to 2 days!
S In your lifetime, your digestive system may handle
about 50 tons!!
On a sheet of paper, write the name
of each colored organ:
S Green:
S Red:
S Pink:
S Brown:
S Purple:
S Green:
S Yellow:
How’d you do?
S Green: Esophagus
S Red: Stomach
S Pink: Small Intestine
S Brown: Large Intestine
S Purple: Liver
S Green: Gall Bladder
S Yellow: Pancreas