Transcript Passage of Food cont.

Digestion
Topic 6.1
Functions
*Provides fuel for cellular respiration.
*Provides raw materials need for the body to grow and
maintain itself.
1. Carbs
2. Amino acids (needed for building what?)
--Body can synthesize most
--8 must be obtained by the diet
*Most meat products
*Few plants provide all of these, but
combining various plants usually will
provide them all
Note: A vegetarian diet should be carefully monitored
to assure all amino acids are being obtained.
Especially since the body is unable to store them
for very long.
Functions cont.
3. Fatty acids (needed for synthesizing membranes
and hormones.
4. Vitamins organic molecules needed in small amts.
--niacin: component of NAD+
--riboflavin: component of FAD
--Vitamin A: component of pigments of the eye
5. Minerals inorganic molecules (ions) needed in small
amounts
--Sodium, potassium: needed for nerve function
--Calcium: needed for bones, muscle, and nerve
function
--Iron: found in hemoglobin
Processes
1. Mechanical Digestion: food is broken into small pieces
2. Chemical Digestion: enzymes break polymers into
monomers by adding water (process?)
*Amylases: break down sugars (poly to mono)
* Lipases: break down lipids (to glycerol and F.A.)
* Proteases: break down proteins (to A.A.)
Anatomy
*Passage of Food
Note that almost all the structures are smooth
muscle and therefore propel the food through.
*Accessory Organs
Aid in digestion, but food doesn’t pass through them.
Passage of Food
We basically have a 20-something foot hollow tube
running through our bodies, leading from our mouth to
our anus. Food passes through this. Our waste never
actually enters our bodies at all—it just moves
through this hollow tube. SO, what happens during
this passage? (I know your dying to know!)
*Mouth: teeth mechanically break down food
--incisors: biting
--canines: tearing meat (carnivores)
--molars: grinding vegetation (herbivores)
*Saliva released by salivary glands.
--Contains salivary amylase (poly to mono)
--Kills bacteria and moistens food for
swallowing.
Passage of Food cont.
*Food passes through pharynx (epiglottis blocks trachea)
*Esophagus: tube leading to stomach
*Anterior is skeletal to allow control of
swallowing; the rest is smooth muscle.
*Peristalsis: involuntary wave of contractions
that moves through digestive tract
* Stomach: stores food
*Accordian-like walls that can expand .
*Food stays here 2-6 hours.
Passage of Food cont.
Movement of Food
*Cardiac Sphincter regulates entry of food into stomach
--Sphincter is simply a circular muscle.
*Smooth muscle of stomach wall mechanically break down
food.
*Glands in the stomach lining secrete substances.
1. Chief cells: pepsinogen
2. Parietal cells:
--HCl (denatures proteins for easier digestion)
--Pepsinogen (inactive precursor of pepsin)
Pepsin is an enzyme (one of very few that
don’t end in ase)
3. Epithelium: mucous protecting stomach lining from acid
Passage of Food cont.
*Pyloric Sphincter: regulates exit of food to small intestine
*Exit of acid from stomach can cause problems
1. Exit via cardiac sphincter esophagusheartburn
2. Exit via pyloric sphincter sm. Intestine ulcer
Hormonal Control of stomach
*Proteins in food release of gastrin from stomach wall 
release of pepsin and HCl
*Small Intestine: site of most digestion and absorption
--About 17 feet long, food stays here 3-6 hours
1. Duodenum: digestion; first 25cm, or so, receives
enzymes from accessory organs
Passage of Food cont.
*2 accessory organs:
1. Pancreas: secretes proteases, lipases, amylase
into the small intestine
2. Liver: produces bile; (gallbladder stores/releases
bile)
Bile: helps dissolve fats in water
--One end is hydrophilic other is hydrophobic
Hormonal Control of duodenum**
*Failure of secretin to neutralize the acid ulcers in
small intestine.
--Due to stress or bacterial infection
*We feel full after a fatty meal due to GIP.
**See chart on chapter outline
Small Intestine cont. (first section = duodenum)
2. Illeum & Jejunum absorption
*Absorption relies on active transport and diffusion
*Brush border: epithelial cells lining sm. Intestine
--Villi and Microvilli create a high surface area to
volume ratio to facilitate lots of absorption.
--Associated with capillaries to facilitate absorption
*Tight junctions prevent food from slipping between
cells.
*Anything that continues past these sites of absorption
can be considered waste.
*Large intestine: reabsorbs water from waste; about 4
feet; food stays here up to two days
--Diarrhea not enough water reabsorbed
--Constipation too much water reabsorbed
--Bacteria feed on undigested food (cellulose)
*Produces gas (beans contain lots of cellulose)
*Rectum stores feces until they can be eliminated
*Anus opening that allows the exit of waste
--So far, all the muscles of the digestive system have
been smooth; fortunately, a skeletal muscle sphincter
before the anus gives us control over when to eliminate
waste.
Review:
Mouth pharynx esophagus stomach duodenum
large intestine rectum
anus
GOT IT?
Ileum jejunum 