Living organisms need food.
All food contains nutrients.
Nutrients are substances
that provide the energy and
materials needed for growth,
repair and maintenance of
cells and regulation.
Nutrition is the process by
which organisms get food and
break it down so it can be
Water and minerals are inorganic nutrients which
must be obtained from the environment.
Minerals are chemical elements that organisms
need for normal functioning.
Energy is provided by the chemical breakdown of
CHO, fats and proteins.
The calorie is the unit used to measure energy
content of food.
Calorie is defined as the amount of heat needed
to raise the temperature of 1 gram of water 1oC.
Humans need the 6 basic nutrients
These nutrients are obtained by eating a healthy
diet from the 4 major food groups:
Grains and grain products (G & GP)
Dairy and dairy products (D & DP)
Fruits and vegetables (F & V)
Meats and alternates (M & A)
Along with the 6 nutrients, humans need fibre.
Fibre is made of cellulose and other indigestible
materials found in the cell walls of fruits, vegetables
Fibre stimulates the muscles of the digestive system
to keep foods moving through it.
The life process of nutrition
consists of two parts
– Ingestion: Taking food
into the body (eating).
– Digestion: Breaking
down food into smaller
particles and absorbing
them into the body.
Food is broken down into smaller pieces.
Proteins, starches, and fats, are too big to diffuse
through cell membrane.
Amino acids, simple sugars, glycerol, and fatty
acids are absorbed by the body and transported
Mechanical digestion: Physical breakdown of food.
Chewing, grinding and mixing food with mouth, tongue
Chemical digestion: Chemical breakdown of food
using enzymes, bile, and hydrochloric acid (HCl).
system is a group of
organs that takes in
Digestive system is made up of the following
Accessory Organs: Important in digestion, but
food does not pass through these organs.
Mouth Pharynx Epiglottis Esophagus
Tracing a piece of
toast through the
The mouth is also called the oral cavity.
Food is taken into the mouth and chewed with the
assistance of the cheek muscles.
Tongue and teeth function in mechanical
digestion (chewing of food).
Process of chewing is called mastication.
Various tooth types (molars, incisors) make
chewing more efficient.
Tongue helps mix food with saliva.
Manipulates material inside mouth
Base of tongue extends to pharynx
Mechanical processing by
compression, abrasion, distortion.
Manipulation to assist in chewing and to prepare
material for swallowing.
Sensory analysis by touch, temperature, taste
– Breaks down starch so it can be absorbed by
Submandibular and sublingual glands
Secretion contains less enzymes but more
buffers and mucus.
All 3 release saliva during eating
Saliva increases pH
– Goes from 6.7 to 7.5
Compression of bolus against hard palate
• Forces bolus into pharynx
• Elevates hard palate
Only phPrevents bolus from entering nasopharynx.
– Bolus in contact with sensory receptors
• Initiates swallowing reflex
• Larynx elevates, epiglottis folds (protects glottis)
• Contraction of pharyngeal muscles forces into
Muscular tube about 5 inches long in adults
Also known as the throat
Transmits food into the esophagus
The epiglottis (a flap of tissue) covers the trachea
to prevent food from entering the larynx during
swallowing which causes choking.
Bolus enters esophagus
Approach to stomach opens lower esophageal
9 seconds from oral cavity to stomach
Muscular tube about 9 to 10 inches long in the
adult that contracts rhythmically (peristalsis)
to propel food toward the stomach.
Contains a group of muscles called the lower
esophageal sphincter that closes off the
entrance to the stomach to prevent reflux of
food, emesis or regurgitation (vomiting).
The stomach is a thick-walled, muscular sac where
food is stored temporarily.
The mechanical breakdown of food and partial
digestion of proteins occur here.
Food is broken down mechanically by contractions
of the muscular stomach walls.
Food is churned and mixed with acidic gastric
juice secreted by glands in the stomach wall.
Four primary functions
– Temporary storage of ingested food
– Mechanical breakdown of resistant materials
– Breaking chemical bonds in food materials
• Acids and enzymes
– Production of intrinsic factor
• Necessary for absorption of vitamin B12
Ingested materials mix with secretions of glands
– Product is highly acidic soupy mixture
– Product called chyme (pyloric sphincter
regulates flow into small intestines)
The lining of the stomach contains 2 types of
– Pyloric glands- secrete mucus which covers the
stomach lining and protects it from being digested
– Gastric glands- secrete gastric juice which has a pH of
1.5 – 2.5 (due to its high [HCl])
• HCl kills most of the bacteria swallowed in food
• Gastric juice also contains pepsin, a digestive
enzyme, that breaks down proteins into short
chains of amino acids call polypeptides
The salivary amylase, released in the
mouth, continues to digest starches in the
Eventually, the low pH of the acid in the stomach
inactivates the enzyme and starch breakdown
When the stomach is empty, there is little gastric
When food is eaten, the flow of gastric juice
Liquids pass through the stomach in 20 minutes or
Solids must be turned into chyme, a thin, soupy
The chyme passes in small amounts at a time
through the pyloric sphincter, the ring of muscle
that connects the stomach to the small intestine.
The stomach will empty 2-6 hours after a meal.
Hunger is felt when an empty stomach is churning.
About 6.5 meters long; 2.5 cm in diameter
Food leaves the stomach through the pyloric
Small Intestine consists of 3 parts:
– Duodenum (shortest of the 3 sections- 25 cm)
Most chemical digestions takes place in the S.I.
Following digestion, simple sugars, amino
acids, vitamins, minerals and other substances
Absorption takes place through the wall of the small
intestine into the blood vessels of the circulatory
Fatty acids and glycerol are absorbed into the
lacteals, vessels of the lymphatic system.
Many factors allow the Small intestine to be well
suited for absorption:-
1. Very long
2. Lining has many folds
3. Lining is covered with millions of finger-like
projections called villi.
4. Epithelial cells that make up the intestinal lining have
The S.I. is in constant motion when food is
These peristaltic movements have four main
1. They squeeze chyme through the intestine.
2. They mix the chyme with the digestive enzymes
present in the small intestine.
3. They break down food particles mechanically.
4. They speed up absorption of digestive end
products by bringing the intestinal contents into
contact with them intestinal wall.
Undigested and unabsorbed materials pass from
the Small Intestine through a sphincter into
the Large Intestine.
The Large Intestine is about 1.5 meters long and
6 cm in diameter.
Digestion does not occur here, but most of the
water reabsorption from food mass does
Water is mixed with food as it moves through the
Normally, ¾ of the water is reabsorbed.
Reabsorption in the Large Intestine allows the
body to conserve water.
L.I. also absorbs vitamins produced by intestinal
bacteria living in the L.I.
The vitamins are absorbed with the water from the
The L.I. is important in the removal or undigested
and indigestible material from the digestive tract.
Ex. Cellulose, large quantities of bacteria, bile,
mucus, worn-out cells from the digestive tract.
This material becomes feces or stool.
“Poo” is stored in the last part of the L.I., rectum
and passed through the anus.
Located in the right quadrant of the abdominal cavity .
Divided into right and left lobes.
Converts food nutrients into usable substances.
Secretes a yellowish-brown to greenish substance called
bile which is stored in the gall bladder.
Stores glucose in the form of glycogen.
Secretes bilirubin, a bile pigment that is combined with
bile and excreted into the duodenum.