Download Human Digestion

Human Digestion -Ch. 21.1
Section Objectives:
Interpret the different functions of the digestive
system organs.
Outline the pathway food follows through the
digestive tract.
Identify the role of enzymes in chemical digestion.
Human Digestion
• This part of the life process of NUTRITION-> process
by which an organism obtains and utilizes food
Overview: Food processing occurs in four
stages
1. Ingestion: taking in food
2. Digestion: mechanical and chemical breakdown of
food so that it can be absorbed by the cells
3. Absorption: cells lining the digestive tract take up
(absorb) small nutrient molecules
4. Elimination: undigested material passes out of the
digestive tract
Human Digestion~ a 2 part process that changes
food into a form useable by the body cells
• 1. Mechanical digestion – physical breakdown of
large pieces of food into smaller ones
• 2. Chemical digestion – hydrolysis – the splitting of
large insoluble molecules in small, soluble molecules
with the use of water and enzymes ( in other words;
breaking complex molecules into simple ones)
The process of chemical digestion ( hydrolysis) is
regulated by enzymes
Examples of chemical Digestion:
• 1. Carbohydrates+ water -> simple sugars
(glucose for instance)
• 2. Proteins+ water -> amino acids
• 3. Lipids+ water -> 3 fatty acids +gylcerol
HUMAN DIGESTIVE SYSTEM
• Human digestive
tract = GI
(gastrointestinal)
Consists of a
continuous one way
food tube (mouth to
anus)
HUMAN DIGESTIVE SYSTEM
• 1. Mouth: (oral cavity)
ingests food
• 2. Teeth: function in
mechanical breakdown of
food, increases surface area
of food for enzyme action
• 3.Tongue: acts as a plunger
to push food back into the
throat (pharynx) taste buds
are located on the surface
of the tongue
Mouth
• Functions
– mechanical digestion
• teeth
– break up food
– chemical digestion (saliva)
• amylase enzyme
– digests starch
• mucus
– protects soft lining of digestive system
– lubricates food for easier swallowing
• buffers
– neutralizes acid to prevent tooth decay
• anti-bacterial chemicals
– kill bacteria that enter mouth with food
All that
in spit!
Yeast Infection of the Mouth!!
mouth
break up food
digest starch
kill germs
moisten food
HUMAN DIGESTIVE SYSTEM
• 4. Pharynx: food is pushed by tongue to back of throat,
initiates swallowing – food is now in the form of a bolus
– Epiglottis: flap that prevents choking
• 5. Esophagus: muscular tube that moves food from mouth to
the stomach by process of peristalsis: wave of muscular
contractions that moves chewed food to stomach
Swallowing (& not choking)
• Epiglottis
– flap of cartilage
– closes trachea (windpipe) when swallowing
– food travels down esophagus
• Peristalsis
– involuntary muscle contractions to move food along
Stomach
• Functions
–disinfect food
• hydrochloric acid = pH 2
– kills bacteria
–food storage
• can stretch to fit ~2L food
–digests protein
• pepsin enzyme
But the stomach is made out of protein!
What stops the stomach from digesting itself?
mucus secreted by stomach cells protects
stomach lining
mouth
break up food
digest starch
kill germs
moisten food
stomach
kills germs
break up food
digest proteins
store food
sphincter
sphincter
Small intestine
• Functions
– digestion
• digest carbohydrates
– amylase from pancreas
• digest proteins
– trypsin & chymotrypsin from pancreas
• digest lipids (fats)
– bile from liver & lipase from pancreas
– absorption
• nutrients move into body cells by:
– diffusion
– active transport
This is
where all the
work is done!
Absorption in Small Intestines
• Absorption through villi & microvilli
– finger-like projections
– increases surface area for absorption
SMALL INTESTINES
6 meters long,
but can stretch
to cover a
tennis court
mouth
break up food
digest starch
kill germs
moisten food
liver
produces bile
- stored in gall bladder
break up fats
pancreas
produces enzymes to
digest proteins & starch
stomach
kills germs
break up food
digest proteins
store food
small intestines
breakdown food
- proteins
- starch
- fats
absorb nutrients
Pancreas ~ accessory organ
• Produces digestive enzymes
– digest proteins
• trypsin, chymotrypsin
– digest starch
• amylase
– digest lipids
• lipase
• Buffers
– neutralizes
acid from
stomach
small
intestine
pancreas
mouth
break up food
digest starch
kill germs
moisten food
pancreas
produces enzymes to
digest all foods
stomach
kills germs
break up food
digest proteins
store food
Liver & Gall Bladder ~accessory organs
• Produces bile
– breaks up fats
– gallbladder only stores bile
• that’s why you can have your gall bladder removed
bile contains colors
from old red blood cells
collected in liver =
iron in RBC rusts &
makes feces brown
mouth
break up food
digest starch
kill germs
moisten food
liver
produces bile
- stored in gall bladder
break up fats
pancreas
produces enzymes to
digest proteins & starch
stomach
kills germs
break up food
digest proteins
store food
Large intestines (colon)
• Function
– re-absorbs water
• use ~9 liters of water every day in
digestive juices
– if don’t reabsorb water
would die of dehydration
• > 90% of water re-absorbed
– not enough water re-absorbed
» diarrhea
» can be fatal!
– too much water re-absorbed
» constipation
• reabsorb by diffusion
You’ve got company!
• Living in the large intestine is a community
of helpful bacteria
– Escherichia coli: E. coli
• digest cellulose
– digests fruits & vegetables
• produce vitamins
PEE-YOO!
– vitamin K & B vitamins
• BUT generate gases
– by-product of bacterial metabolism
– methane, hydrogen sulfide
– STINKY!
mouth
break up food
digest starch
kill germs
moisten food
liver
produces bile
- stored in gall bladder
break up fats
pancreas
produces enzymes to
digest proteins & carbs
stomach
kills germs
break up food
digest proteins
store food
small intestines
breakdown food
- proteins
- starch
- fats
absorb nutrients
large intestines
absorb water
Rectum
• Last section of large intestines
– eliminate feces through anus
– what’s left over?
• undigested materials
– mainly cellulose from plants
– called roughage or fiber
– keeps everything moving & cleans out intestines
• masses of bacteria
So don’t forget
to wash
your hands!
Appendix
Vestigial organ
Some Digestive Homeostasis Disorders
• 1.Constipation– person has uncomfortable or infrequent
bowel movements results from sluggish peristalsis that allows
excess water to be removed from feces (fecal matter
hardens)- may result from insufficient fiber in diet
• 2. Diarrhea– opposite of constipation– associated with
intestinal disturbances caused by infections or stress–
prolonged diarrhea may result in severe dehydration
• 3. Gall stones– small hard particles made of cholesterol which
form & collect in gall bladder- may block the bile duct and
cause pain
• 4. acid reflux -backflow of stomach contents upward into
esophagus
• 5. appendicitis- inflammation of appendix
Ulcers
Colonized by
H. pylori
• Used to think ulcers
were caused by
stress
inflammation of
stomach
– tried to control with
antacids
• Now know ulcers
caused by bacterial
infection of
stomach
– H. pylori bacteria
– now cure with
antibiotics
Free of
H. pylori
inflammation of
esophagus
H. pylori
inflammatory
proteins
(CagA)
cell damaging
proteins
(VacA)
 
cytokines
helper T cells
neutrophil cells
white blood cells