Digestive Physiology
We need food for cellular utilization:
nutrients as building blocks for synthesis
sugars, etc to break down for energy
most food that we eat cannot be directly used by the body
too large and complex to be absorbed
chemical composition must be modified to be useable by cells
digestive system functions to altered the chemical and physical composition of
food so that it can be absorbed and used by the body; ie
physical and chemical digestion
absorption
collect & eliminate nonuseable components
lumen of GI tract is continuous with outside of body
food being digested must be isolated from body cells since it’s
the same composition as rest of body
digestion occurs OUTSIDE the internal environment of cells
and tissues
protects internal cells
Movement of Materials
as materials are being processed they are moved through alimentary canal by:
swallowing
reflex controlled by medulla
pharynx to esophagus
peristalsis
sequential smooth muscle contractions in adjacent segments
pushes food forward
esophagus, stomach, small intestine, large intestine
segmentation
alternating contractions and relaxations of adjoining
portions of intestine
food is moved backward and foreward
helps to physically break up and mix contents
for better digestion & absorption
Digestion
digestion = all food changes that occur in the alimentary canal
Anatomy & Physiology: Digestive System, Ziser, 2003 1
, need to convert food into a form that can be absorbed and used by body cells
two types of digestion:
physical digestion
breaking large pieces down into smaller pieces
chemical digestion
breaking large molecules (proteins, fats, starches, etc)
into small molecules (amino acids, fatty acids, sugars, etc)
1. Mouth
food entering mouth is physically broken down teeth
mixed with saliva
lubricant
enzyme = amylase
begins carbohydrate digestion
most (60%) of starch digestion by amylase from saliva occurs in stomach
after swallowing bolus
at end of digestion in mouth food = bolus
2. Stomach
physical digestion involves muscular contractions to separate and mix
food particles
in stomach bolus is mixed with gastric juices
gastric juices low pH ~2
hydrochloric acid
pepsin
ideal for breaking proteins into smaller fragments
body must be protected from harsh pH of gastric juices:
a. thick coating of bicarbonate rich mucous
b. tight junctions join epithelial cells to help prevent leakage
c. stomach lining is rapidly replaced
renewed every 3-6 days
d. pepsin and HCl are secreted in inactive forms
vomiting = medullary reflex:
triggered by irritants in stomach
closing nose and glottis
relaxes cardiac sphincter
spasm of diaphragm
gastric ulcers: Helicobacter pylori
part of normal flora of stomach
can neutralize stomach acids
excessive growth can irritate stomach lining to produce ulcers
Anatomy & Physiology: Digestive System, Ziser, 2003 2
We need food for cellular utilization:
nutrients as building blocks for synthesis
sugars, etc to break down for energy
most food that we eat cannot be directly used by the body
too large and complex to be absorbed
chemical composition must be modified to be useable by cells
digestive system functions to altered the chemical and physical composition of
food so that it can be absorbed and used by the body; ie
physical and chemical digestion
absorption
collect & eliminate nonuseable components
lumen of GI tract is continuous with outside of body
food being digested must be isolated from body cells since it’s
the same composition as rest of body
digestion occurs OUTSIDE the internal environment of cells
and tissues
protects internal cells
Movement of Materials
as materials are being processed they are moved through alimentary canal by:
swallowing
reflex controlled by medulla
pharynx to esophagus
peristalsis
sequential smooth muscle contractions in adjacent segments
pushes food forward
esophagus, stomach, small intestine, large intestine
segmentation
alternating contractions and relaxations of adjoining
portions of intestine
food is moved backward and foreward
helps to physically break up and mix contents
for better digestion & absorption
Digestion
digestion = all food changes that occur in the alimentary canal
Anatomy & Physiology: Digestive System, Ziser, 2003 1
, need to convert food into a form that can be absorbed and used by body cells
two types of digestion:
physical digestion
breaking large pieces down into smaller pieces
chemical digestion
breaking large molecules (proteins, fats, starches, etc)
into small molecules (amino acids, fatty acids, sugars, etc)
1. Mouth
food entering mouth is physically broken down teeth
mixed with saliva
lubricant
enzyme = amylase
begins carbohydrate digestion
most (60%) of starch digestion by amylase from saliva occurs in stomach
after swallowing bolus
at end of digestion in mouth food = bolus
2. Stomach
physical digestion involves muscular contractions to separate and mix
food particles
in stomach bolus is mixed with gastric juices
gastric juices low pH ~2
hydrochloric acid
pepsin
ideal for breaking proteins into smaller fragments
body must be protected from harsh pH of gastric juices:
a. thick coating of bicarbonate rich mucous
b. tight junctions join epithelial cells to help prevent leakage
c. stomach lining is rapidly replaced
renewed every 3-6 days
d. pepsin and HCl are secreted in inactive forms
vomiting = medullary reflex:
triggered by irritants in stomach
closing nose and glottis
relaxes cardiac sphincter
spasm of diaphragm
gastric ulcers: Helicobacter pylori
part of normal flora of stomach
can neutralize stomach acids
excessive growth can irritate stomach lining to produce ulcers
Anatomy & Physiology: Digestive System, Ziser, 2003 2
