An Overview of Digestion
→ Anatomy Overview
** know this in order
● Alimentary tract: mouth to ya
anus
● Gastro tract: stomach to anus
Food enters mouth → food mixed
with saliva (3 pairs: parotid,
submandibular, sublingual)
→glands secrete saliva into
stomach → saliva helps with
chemical breakdown → food goes
to back of mouth (pharynx) →
esophagus → stomach → small
intestine: duodenum (most VIP
part of alimentary tract)
● Liver (produces bile - helps with
breakdown of fat - stored in
gallbladder)
● Pancreas: produces enzymes that break down 3 food groups
○ Release contents in duodenum (breaks down food, helps with absorbtion)
partly digested food goes down the rest of the small intestine (jejunum, ileum) →
leaves ileum and empties into colon / large intestine→ ascending: food / fecal matter
goes up → transverse colon: goes from right to left → descending colon → sigmoid
colon (so it turns) → rectus → anus
● Cecum: first part of ascending colon
● Appendix: end of cecum
→ Functions (of the alimentary tract)
1. Ingestion
a. Mouth
2. Motility
a. Move food from point a to point b
● Maintain muscle tone
○ stomach stretches after meal→ needs to contract to get food
down into the SI→ stomach contracts even when empty so it can
, return to its original size (which is why you can hear your
stomach when you’re hungry - you have gas in your stomach
and constantly contracting to maintain muscle tone and
elasticity of the wall )
a. Propulsive movement: unidirectional
i. Peristalsis: wave like muscle contractions that moves food downward
ii. Esophagus, surrounded by smooth muscle (also happens in the colon but
it doesn’t look like that)
1. Wave of contraction starts in the esophagus
b. Mixing movement: bidirectional
i. Stomach, small intestine
3. Secretion
a. Secretion must occur so digestion can occur
i. Secrete enzymes / other substances into alimentary tract for digestion to occur
b. Mouth (saliva) , stomach, liver, pancreas → goes into small intestine (which
also secretes substances) and help break down foods
4. Digestion
1. Mechanical
a. Mouth (chewing), stomach (churning), small intestine (segmentation)
b. Physical break down
2. Chemical
a. Need break down because too complicated molecules to need to break down for
passage across plasma membrane
i. In order to absorb you need to absorb it across the cells of the SI to get it
into the blood (get molecule across plasma membrane)
b. Carbs: tri / disaccharides → monosaccharides
c. Proteins: into amino acids
d. Fats: monoglycerides and fatty acids
5. Absorption
a. 80% in the duodenum, rest in small and large intestine
i. Smallest part / but most VIP
6. Elimination of wastes
● Get rid of what you can’t absorb
→ Small Intestine Anatomy
● Absorption is from the inside out
○ Lumen → blood vessels
Number 1: Mucosa
, 1. Simple epithelium
a. Makes up inner portion of mucous
b. Single layer → absorbs nutrients
2. Lamina propria
a. Made up of connective tissue
b. Capillaries are found here, as well as lacteal (lymphatic vessels) and nerve fibers
c. Middle portion of mucosa
3. Muscularis mucosae
a. Smooth muscle: contracts
b. Last layer of mucosae
Number 2
4. Submucosa
a. Connective tissue
b. Made up of nerve fibers
c. Cross section: arteries / veins are found inside
Number 3: Muscularis externa (Externa : external to muscularis mucosa )
5. Circular muscle
a. On the inside, muscle cells located in circular shape
b. When contrats diameter decreases
6. Longitudinal muscle
a. On the outside, along the long axis of the tube
b. Muscle contracts along long axis
** how you get motility **
Number 4: Serosa
7. Epithelial
8. Connective tissue
**Holding everything
together **
, → Absorption
● Vili's made up of a collection of cells
○ Cells that line the villis do not have a flat
apical membrane, instead they have
microvilli
● Inside single layer of epithelium: lamina propria
○ Layer of muscle: muscularis mucosae
● Microvilli: tiny hairs on epithelial cell
○ Increase surface area to aid in absorption
of food/ nutrients
→ Absorption Through Villi
1. Esophagus : flat - not going to absorb
anything
2. Apical surface of stomach: flat -
a. Purple dots: nucleus of cells (each
long structure is an individual cell in
the stomach)
b. Stomach only absorbs alcohol
3. Small intestine
● Long structures: villi - absorb stuff
4. Colon: flat - notmuch
absorption going on
→ Anatomy Overview
** know this in order
● Alimentary tract: mouth to ya
anus
● Gastro tract: stomach to anus
Food enters mouth → food mixed
with saliva (3 pairs: parotid,
submandibular, sublingual)
→glands secrete saliva into
stomach → saliva helps with
chemical breakdown → food goes
to back of mouth (pharynx) →
esophagus → stomach → small
intestine: duodenum (most VIP
part of alimentary tract)
● Liver (produces bile - helps with
breakdown of fat - stored in
gallbladder)
● Pancreas: produces enzymes that break down 3 food groups
○ Release contents in duodenum (breaks down food, helps with absorbtion)
partly digested food goes down the rest of the small intestine (jejunum, ileum) →
leaves ileum and empties into colon / large intestine→ ascending: food / fecal matter
goes up → transverse colon: goes from right to left → descending colon → sigmoid
colon (so it turns) → rectus → anus
● Cecum: first part of ascending colon
● Appendix: end of cecum
→ Functions (of the alimentary tract)
1. Ingestion
a. Mouth
2. Motility
a. Move food from point a to point b
● Maintain muscle tone
○ stomach stretches after meal→ needs to contract to get food
down into the SI→ stomach contracts even when empty so it can
, return to its original size (which is why you can hear your
stomach when you’re hungry - you have gas in your stomach
and constantly contracting to maintain muscle tone and
elasticity of the wall )
a. Propulsive movement: unidirectional
i. Peristalsis: wave like muscle contractions that moves food downward
ii. Esophagus, surrounded by smooth muscle (also happens in the colon but
it doesn’t look like that)
1. Wave of contraction starts in the esophagus
b. Mixing movement: bidirectional
i. Stomach, small intestine
3. Secretion
a. Secretion must occur so digestion can occur
i. Secrete enzymes / other substances into alimentary tract for digestion to occur
b. Mouth (saliva) , stomach, liver, pancreas → goes into small intestine (which
also secretes substances) and help break down foods
4. Digestion
1. Mechanical
a. Mouth (chewing), stomach (churning), small intestine (segmentation)
b. Physical break down
2. Chemical
a. Need break down because too complicated molecules to need to break down for
passage across plasma membrane
i. In order to absorb you need to absorb it across the cells of the SI to get it
into the blood (get molecule across plasma membrane)
b. Carbs: tri / disaccharides → monosaccharides
c. Proteins: into amino acids
d. Fats: monoglycerides and fatty acids
5. Absorption
a. 80% in the duodenum, rest in small and large intestine
i. Smallest part / but most VIP
6. Elimination of wastes
● Get rid of what you can’t absorb
→ Small Intestine Anatomy
● Absorption is from the inside out
○ Lumen → blood vessels
Number 1: Mucosa
, 1. Simple epithelium
a. Makes up inner portion of mucous
b. Single layer → absorbs nutrients
2. Lamina propria
a. Made up of connective tissue
b. Capillaries are found here, as well as lacteal (lymphatic vessels) and nerve fibers
c. Middle portion of mucosa
3. Muscularis mucosae
a. Smooth muscle: contracts
b. Last layer of mucosae
Number 2
4. Submucosa
a. Connective tissue
b. Made up of nerve fibers
c. Cross section: arteries / veins are found inside
Number 3: Muscularis externa (Externa : external to muscularis mucosa )
5. Circular muscle
a. On the inside, muscle cells located in circular shape
b. When contrats diameter decreases
6. Longitudinal muscle
a. On the outside, along the long axis of the tube
b. Muscle contracts along long axis
** how you get motility **
Number 4: Serosa
7. Epithelial
8. Connective tissue
**Holding everything
together **
, → Absorption
● Vili's made up of a collection of cells
○ Cells that line the villis do not have a flat
apical membrane, instead they have
microvilli
● Inside single layer of epithelium: lamina propria
○ Layer of muscle: muscularis mucosae
● Microvilli: tiny hairs on epithelial cell
○ Increase surface area to aid in absorption
of food/ nutrients
→ Absorption Through Villi
1. Esophagus : flat - not going to absorb
anything
2. Apical surface of stomach: flat -
a. Purple dots: nucleus of cells (each
long structure is an individual cell in
the stomach)
b. Stomach only absorbs alcohol
3. Small intestine
● Long structures: villi - absorb stuff
4. Colon: flat - notmuch
absorption going on
