Download Human Digestive System

Human Digestive System

Digestion is the process by which
organisms break large molecules into
smaller ones
 For
example, breaking down carbs, fats,
proteins
 Digestion
must take place so that
molecules will be small enough to pass
through cell membranes
Mouth
• Food enters here
• Mechanical breakdown occurs
•Teeth bite and grind food
•Tongue moves and shapes food
•The digestive juice called
saliva is added
•Wets the food
•Sticks food together into a bolus
•Contains a digestive enzyme called salivary
amylase
•Salivary amylase breaks down starch (a
polysaccharide) into maltose (a disaccharide)
•Food is pushed into the throat
•Food is kept from entering the larynx and
trachea by a flap of tissue called the epiglottis
Esophagus
•No mechanical or chemical
breakdown occurs here
•Food is pushed to the stomach by
the muscular walls of the food
tube ~ peristalsis
•Food enters the stomach when a
ring of muscle – the cardiac
sphincter lets it through
•Reverse peristalsis – cardiac
sphincter opens and stomach
contents are forced out – vomiting
Esophagus
•Heartburn – when the cardiac
sphincter relaxes causing stomach
juices containing hydrochloric acid
to come into contact with the
esophagus
Stomach
• a thick-walled muscular sac
•Mechanical breakdown is completed
here
•Solid food is reduced to a
thin soupy liquid called chyme
(2-6 h)
•Liquids pass through in 20
min. or less
•Stomach has pyloric glands
•Secrete mucus to protect the
stomach from being “digested”
Stomach
• Stomach has gastric glands
•Secrete gastric juices
•Gastric juices contain hydrochloric acid and the
digestive enzyme called pepsin
•Pepsin can only break down proteins in an
acidic environment
•When acid is present it changes the
proteins into shorter chains of amino acids
called polypeptides
•When stomach is empty only small amount of
juice is present
Stomach
•
All
stimulate
gastric
juices
When food is eaten gastric juice
increases
1. Thought, sight, smell, taste of food
2. Food touching the stomach lining
3. Food mass stretching stomach walls
• Food exits through the pyloric sphincter
into the small intestine
Stomach
• Ulcers can occur when the mucous layer
breaks down and part of the stomach is
“digested”
Small intestine
• About 6.5 m long, 2.5 cm in diameter
• Coiled tube
• Three sections:
a. duodenum (25 cm)
b. jejunum (several metres)
c. ileum (largest section)
• Chemical digestion is completed here
• Absorption of nutrients is completed here
Small intestine
• When food is present the small intestine is in
constant motion (peristalsis)
• Four main effects:
1. Squeezes chyme through
2. Mixes chyme with digestive enzymes
3. Breaks down food
4. Speeds up absorption
• Small intestine fluids are alkaline (pH > 7)
Small intestine
• Three juices mix with the chyme
1. Bile
• Made by liver
• Stored by gallbladder
• Emulsifies fats (breaks them into smaller
drops to make it easier to break them
down later)
• Contains no enzymes
• Neutralizes the acids from the stomach
2. Pancreatic juice
•
when acidic chyme enters the small
intestine it stimulates hormones which signal
the pancreas to release juice and enzymes
into the upper part of the small intestine
• Contains several enzymes:
• Amylase ~ continues to breakdown starch to
maltose)
• Trypsin (protease) ~ breaks down the
polypeptides called peptones and proteoses,
into peptides
• Lipase ~ breaks down fats and oils into fatty
acids and glycerol
3. Intestinal juice
•
contains the enzymes
• Peptidase ~ breaks down peptides into
amino acids
• Maltase ~ finishes carbohydrate
digestion by breaking down maltose into
glucose
• Now all nutrients have been broken down:
• carbohydrates
• fats
• proteins
glucose (monosaccharides)
fatty acids and glycerol
amino acids
Small intestine (cont’d)
•Absorption of these nutrients takes place
through finger-like projections called villi
that line the intestinal walls
•Each villus has a network of capillaries and a
lacteal
•Through diffusion and active transport the
nutrients are absorbed
•Monosaccharides, amino acids, vitamins,
minerals are all absorbed into the capillaries
•Fatty acids and glycerol are absorbed into
the lacteal and into the lymphatic system
Large intestine
•No digestion here
•About 1.5 m long and 6 cm diameter
•Small pouch called appendix situated where
the small intestine joins the large intestine
•Has no function but can cause problems
Large intestine (3 main functions):
1. Re-absorption of water (about ¾ of it)
• Too much water absorbed = constipation
• Too little absorbed = diarrhea
2. Absorption of vitamin K and some B
vitamins that are produced by bacteria
that live in the large intestine
3. Elimination of undigested and indigestible
materials like plant cell walls, bacteria, bile,
mucus, worn-out cells
Large intestine
•As the material travels through it becomes
feces or stool
•Feces stored in the rectum (last part of
colon) before being eliminated through the
anus
Label diagram of respiratory
system in resource booklet!!!