Human Digestion

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Transcript Human Digestion

Human Digestion
Nutrition
Process by which organisms obtain and utilize their food.
There are two parts to Nutrition:
1. Ingestion- process of taking food into the
digestive system so that it may be
hydrolized or digested.
2. Digestion- the breakdown of food (either
chemically or mechanically) in order to
utilize nutrients
Types of Nutrients
• Micronutrients- vitamins, minerals, & water
• Macronutrients- proteins, lipids,
carbohydrates, etc…
Human digestive
system
GI (gastrointestinal) tract = alimentary canal
Ingestion
• Mouth
– mechanical digestion
• teeth
– breaking up food
– chemical digestion
• saliva
– amylase
» enzyme digests starch
– mucin
» slippery protein (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
mouth
break up food
digest starch
kill germs
moisten food
Mouth
• Chemical and
mechanical
digestion.
• Food is chewed
(masticated)
mechanically.
• A bolus (lump) is
formed with saliva
and the tongue.
Swallowing (& not choking)
• Epiglottis
– flap of cartilage
– closes trachea (windpipe) when swallowing
– food travels down esophagus
• Peristalsis
– involuntary muscle contractions to move food along
Which type of digestion is the
following?
1. Chewing a saltine? 2. Saliva breaking the saltine down into molecules of
glucose? 3. Your tongue breaking pieces of a hamburger apart?
4. Pepsin (an enzyme) in your stomach breaking the
hamburger into amino acids?
Pharynx
• The back of the
throat.
• Larynxpassage for air,
closes when we
swallow.
• Is approximately
15cm long.
Digestive Glands
• Groups of
specialized
secretory
cells.
• Found in the
lining of the
alimentary
canal or
accessory
organs.
Peristalsis
• series of involuntary
wave-like muscle
contractions which
move food along the
digestive tract
Stomach
• Food is temporarily
stored here.
• Gastric juices are
secreted.
• Has layers of
muscle that line the
inside.
• Mechanically and
chemically breaks
down food.
Stomach
• Functions
– food storage
• can stretch to fit ~2L food
– disinfect food
• HCl = pH 2
– kills bacteria
– chemical digestion
• pepsin
– enzyme breaks down proteins
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
Gastric Juices
• Secreted by the
stomach.
• Acidic (pH 1.5-2.5)
(HCl).
• Pepsin- an enzyme that
breaks down large
proteins into amino
acids.
• Food is further broken
down into a thin liquid
called chyme.
Accessory Organs
• Pancreas
• Gall Bladder
• Spleen
Gall bladder
• Pouch structure located near the liver
which concentrates and stores bile
• Bile duct – a long tube that carries BILE.
The top half of the common bile duct is
associated with the liver, while the bottom
half of the common bile duct is associated
with the pancreas, through which it passes
on its way to the intestine.
BILE
• Bile emulsifies lipids (physically breaks
apart FATS)
• Bile is a bitter, greenish-yellow alkaline
fluid, stored in the gallbladder between
meals and upon eating is discharged into
the duodenum where it aids the process of
digestion.
Pancreas
• An organ which secretes both digestive
enzymes (exocrine) and hormones (endocrine)
• ** Pancreatic juice digests all major nutrient
types.
• Nearly all digestion occurs in the small intestine
& all digestion is completed in the SI.
Pancreas
• Digestive enzymes
– digest proteins
• trypsin, chymotrypsin
– digest starch
• amylase
• Buffers
– neutralizes
acid from
stomach
Liver
• Function
– produces bile
• bile stored in gallbladder until needed
• breaks up fats
– act like detergents to breakup fats
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
Small Intestine
• Most chemical
digestion takes place
here.
• Simple sugars and
proteins are absorbed
into the inner lining.
• Fatty acids and
glycerol go to lymphatic
system.
• Lined with villi, which
increase surface area for
absorption, one cell
thick.
Small intestine
• Function
– chemical digestion
• major organ of digestion & absorption
– absorption through lining
• over 6 meters!
• small intestine has huge surface area = 300m2
(~size of tennis court)
• Structure
– 3 sections
• duodenum = most digestion
• jejunum = absorption of nutrients & water
• ileum = absorption of nutrients & water
Duodenum
• 1st section of small intestines
– acid food from stomach
– mixes with digestive juices from:
 pancreas
 liver
 gall
bladder
mouth
break up food
digest starch
kill germs
moisten food
pancreas
produces enzymes to
digest proteins & starch
stomach
kills germs
break up food
digest proteins
store food
Absorption in the SI
•
Much absorption is thought to occur directly through the wall
without the need for special adaptations
•
Almost 90% of our daily fluid intake is absorbed in the small
intestine.
•
Villi - increase the surface area of the small intestines, thus
providing better absorption of materials
Absorption by Small Intestines
• Absorption through villi & microvilli
– finger-like projections
– increase surface area for absorption
VILLI
Large intestines
(colon)
• Function
– re-absorb water
• use ~9 liters of water every
day in digestive juices
• > 90% of water reabsorbed
– not enough water absorbed
» diarrhea
– too much water absorbed
» constipation
Large Intestine
• Solid materials pass
through the large
intestine.
• These are undigestible
solids (fibers).
• Water is absorbed.
• Vitamins K and B are
reabsorbed with the
water.
• Rectum- solid wastes
exit the body.
You’ve got company!
• Living in the large intestine is a
community of helpful bacteria
– Escherichia coli (E. coli)
• produce vitamins
– vitamin K; B vitamins
• generate gases
– by-product of bacterial metabolism
– methane, hydrogen sulfide
Vestigial organ
Appendix
Rectum
• Last section of colon
(large intestines)
– eliminate feces
• undigested materials
– extracellular waste
» mainly cellulose
from plants
» roughage or fiber
– masses of bacteria
Digestive Homeostasis Disorders
• ULCERS – erosion of the surface of the
alimentary canal generally associated
with some kind of irritant
Digestive Homeostasis Disorders
• CONSTIPATION – a
condition in which the
large intestine is emptied
with difficulty.
• Too much water is
reabsorbed
• and the solid waste
hardens
Digestive Homeostasis
Disorders
• DIARRHEA – a gastrointestinal
disturbance characterized by
decreased water absorption and
increased peristaltic activity of
the large intestine.
• This results in increased,
multiple, watery feces.
• This condition may result in
severe dehydration, especially in
infants
Digestive Homeostasis
Disorders
• APPENDICITIS – an inflammation of
the appendix due to infection
• Common treatment is removal of the
appendix via surgery
Digestive Homeostasis
Disorders
• GALLSTONES – an accumulation of
hardened cholesterol and/or calcium
deposits in the gallbladder
• Can either be “passed” (OUCH!!) or
surgically removed
Digestive Homeostasis
Disorders
•
•
•
ANOREXIA NERVOSA - a psychological
condition where an individual thinks they
appear overweight and refuses to eat.
Weighs 85% or less than what is
developmentally expected for age and
height
Young girls do not begin to menstruate at
the appropriate age.
Digestive Homeostasis
Disorders
• HEART BURN – ACID from the
stomach backs up into the esophagus.
Overview of Digestive System
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Histological Organization
• Same basic
arrangement of
tissues from
esophagus to anal
canal
• Four layers (from
innermost to
outermost)
–
–
–
–
Mucosa
Submucosa
Muscularis
Serosa
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Movement and Mixing of Digestive
Materials
• Peristalsis
– Coordinated motion
of two muscular
layers
– Circular muscles
contract, then
longitudinal
muscles
• Segmentation
– Mixing of food
– Circular muscles in
two areas contract
– Longitudinal
muscles alternately
contract & relax
Human Anatomy, 3rd edition
Prentice Hall, © 2001
External Anatomy of the Stomach
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Stomach
• Same 4 basic layers
• When the stomach
is empty, the
mucosa lies in large
folds
– Rugae
• Pyloric sphincter
separates stomach
from small intestine
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Histology of the Stomach
• Mucosa is simple
columnar epithelium
with goblet cells
• Mucosa is folded to
form gastric pits
– Gastric glands
secrete gastric
juice
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Gastric Gland
• Several kinds of
cells produce
substances that
form gastric juice
–
–
–
–
Mucus cells
Chief cells
Parietal cells
Enteroendocri
ne cells
Human Anatomy, 3rd edition
Prentice Hall, © 2001
• Mechanical
digestion
Functions
of the
Stomach
– Food reaches pylorus
• Chemical digestion
– Digestion of proteins
• Absorption
–
–
–
–
No food
Water, electrolytes
Some drugs
Alcohol
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Small Intestine
• About 18 feet long
• The duodenum
– About 8 inches long
– Common bile duct &
pancreatic duct empty
here
• The jejunum
– About 8 feet long
– Most digestion occurs here
• The ileum
– About 9.5 feet long
– Most absorption occurs
here
Human Anatomy, 3rd edition
– Ends in the ileocecalPrentice Hall, © 2001
Histology of the Small Intestine
• The lining is folded
into circular pleats
– Plicae circulares
• The mucosal
surface is folded into
villi
• The epithelial cell
membranes are
highly folded into
microvilli
• Intestinal glands are
found in the crypts
at the base of villi Human Anatomy, 3rd edition
– Secrete intestinal
Prentice Hall, © 2001
A Villus
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Functions
the Small
• Chyme
is furtherof
broken
down
Intestine
– Proteins
– Carbohydrates
– Fats
• Most absorption is in the small intestine
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Large Intestine (Colon)
•
•
•
•
•
•
•
•
•
About 4.5 feet long
Mesocolon supports
Begins with the cecum
Appendix is attached
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Colon connects to
rectum
• Rectum connects to anal
canal
• Empties to the exterior
Human Anatomy, 3rd edition
through the anus
Prentice Hall, © 2001
Histology and Functions of the Large
Intestine
• Mucosa - simple
columnar epithelium
– Completion of
absorption
– Formation of feces
• Lots of mucus
glands
• Expulsion of feces
from the body
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Liver
• Performs many lifesustaining functions
• Location – under the
diaphragm on the
right
– Connected to the
diaphragm by the
falciform ligament
• Divided into lobes
–
–
–
–
Right lobe
Left lobe
Caudate lobe
Quadrate lobe
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Histology of the Liver
• Outside is a
capsule
• Composed of tiny
lobules
• Each lobule is
surrounded by liver
cells and sinusoids
– Hepatocytes
– Kupffer cells
• Bile ducts run
between liver cells
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Gallbladder
• Location –
underside of right
lobe of liver
• Function –
concentrate and
store bile
– Collected from liver
• Hepatic ducts
– Adds bile to
duodenum
• Cystic duct
• Common bile
duct
• Gallstones
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Pancreas
• Location – in the
curvature of the
duodenum
• Connected to the
duodenum by the
pancreatic duct
• Produces
pancreatic juice
• Functions
– Exocrine digestion of all
nutrient groups
– Endocrine –
control blood
glucose level
Human Anatomy, 3rd edition
Prentice Hall, © 2001