a. Ingestion-receiving
food
b. Digestion-breakdown
of food particles into particles small enough to pass through cell membranes
c. Transfer of food into circulation
2. Functional units
a. Oral Cavity
1). Teeth
a). incisors and canines: cutting and tearing
b). premolars and molars: mastication
2).
Tongue--pushes food around for mastication
3). Salivary glands
2). esophagus: transports food to the stomach
c. Stomach
a). helps to lubricate the stomach
wall and facilitate food movement
b). helps to protect the wall of
the stomach from the acid produced by other cells
2).
The exocrine glands of the stomach contain two (2) types of secreting cells
a). chief: secrete pepsinogen
(a protein) which is quickly converted into an
enzyme, pepsin,
by the acid of the stomach. Pepsin is an
enzyme that breaks down proteins. Proteins are the only nutrients
degraded in the stomach.
b). parietal: secrete HCl
. The primary function of the acid is to
convert pepsinogen to pepsin. Acid, also, helps break down the food
in the stomach into very small particles.
d. Small Intestine: where
most of the enzymatic activity and absorption occurs.
1). Duodenum
a). Pancreatic enzymes
and bile from the liver
enter the small
intestine, initiating digestion.
b). villi: microscopic hair-like projections--increase amount of surface area for absorption
c). cells that line the small intestine produce enzymes of several types,
and actively
transport sugars and amino acids across membranes.
d). the small intestine enzmyes work with enzymes from the pancreas to
break
down carbohydrates, proteins, fats
into sugars, amino acids, &
fatty acids
e). these smaller molecules pass through the epithelial wall of the small
intestine
into the bloodstream
2). Jejunum - 2nd portion of small intestine and helps digest proteins and fats
3). Ileum - last portion of the small intestine
e. Accessory organs associated with the Duodenum
b). components of bile combine to render
fat soluble
emulsification: breakdown of large
fat droplets into
very small droplets that can be digested more efficiently by enzymes.
2). Pancreas: large gland
situated near the junction of the stomach and the small intestine.
The pancreas has two (2) types of exocrine cells.
a). secretes digestive enzymes - produces enzymes that act in the duodenum
break down carbohydrates, proteins, and fats.
b). secretes a base, bicarbonate ion. This base neutralizes
the acid
solution (chyme) from the stomach, permitting digestive enzymes to
function. Without this neutralizatoin, the acid would
destroy
the pancreatic enzymes. Secretion of bicarbonate is controlled by
secretin (a hormone).
f. Large Intestine: serves to compact the solids remaining after digestion.
1). water and a few ions (e.g. sodium) are absorbed through the walls of the large intestine.
2).
undigested material then passes into the rectum
and is finally eliminated through
the anus.
B. Digestion and Absorption in the stomach
1. HCl
+ churning action (mechanical or physical breakdown of food) results in
food broken down into small particles.
2. breakdown results in numerous small particles that have much more exposed surface area than would few, large particles. This allows the enzymes to more efficiently attack and breakdown food.
3. chyme: mixture
of small food particles + acid + mucous
4. Little absorption occurs through the walls of
the stomach. Only very small molecules such
as water can pass
through the walls and into the blood.
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