Digestive System Flashcards
1
Q
Lateral Surface Features-Cell Junctions
which bind epithelial cells together
A
• ADHESION PROTEINS link plasma
membranes of adjacent cells
• CONTOURS of adjacent cell membranes
• SPECIAL CELL JUNCTIONS
2
Q
Cell Junctions of epithelial cells
A
• Tight junctions (zona occludens) • Adhesive belt junctions (zonula adherens) • Desmosomes • Gap junctions
3
Q
Lateral Surface Features-Cell Junctions Tight junctions (zona occludens)
A
• Close off intercellular space
• Found at apical region of most epithelial
tissues types
• Belt-like junction extends around the
periphery of each cell
• Some proteins in plasma membrane of
adjacent cells are fused which forms a seal
that closes off the intercellular space
4
Q
Lateral Surface Features-Cell Junctions Tight junctions (zona occludens)
A
• Tight junctions prevent certain molecules
from passing between cells of epithelial tissue
• Some tight junctions may be partially leaky
and selectively allow certain types of ions and
molecules through
• Other tight junctions are tighter, such as
those in the epithelial lining of the intestinal
tract which keep digestive enzymes and
intestinal microbes from seeping into the
blood stream
5
Q
Lateral Surface Features-Cell Junctions
Adhesive belt junctions
(zonula adherens)
A
Located just below the tight junctions in epithelial
tissues
• Transmembrane linker proteins attach to actin
microfilaments of the cytoskeleton and bind
adjacent cells
• This junction reinforces the tight junctions,
particularly when the tissues are stretched
• Together with tight junctions, these linker proteins
form the tight junctional complex around apical
lateral borders of epithelial tissues
6
Q
Lateral Surface Features-Cell Junctions
Desmosomes
A
-Anchoring junctions which bind adjacent cells together and help form an internal tension-reducing network of fibers
-Scattered along abutting sides of adjacent cells
-Cytoplasmic side of each plasma membrane has a plaque
-Plaques of adjacent cells are joined by intercellular linker glycoproteins (cadherins)
• Intermediate filaments extend across the
cytoplasm and anchor at desmosomes on
opposite side of the cell
• Are common in cardiac muscle and
epithelial tissue
7
Q
Lateral Surface Features-Cell Junctions
Gap junctions
A
Channel between cells (connexon)
• Passageway between two adjacent cells
• Hollow cylinders of protein which
connect cells
• Allow ions and small molecules to move
directly between neighboring cells
• Function in intercellular communication
8
Q
Cytoskeleton “cell skeleton”
network made of three types of rods
A
• Microtubules—cylindrical structures made
of proteins
• Microfilaments—filaments of contractile
protein actin
• Intermediate filaments—protein fibers
9
Q
Microvilli
A
• Fingerlike extensions of the plasma membrane of
apical epithelial cells.
• Each microvillus contains a core of actin filaments
that extend into the actin microfilaments of the
cytoskeleton and function to stiffen the microvillus
to resist abrasion.
• Maximize surface area across which small
molecules can be secreted and/or absorbed.
• Occur in almost every moist epithelium of the body.
• Most abundant and longest microvilli in epithelia of
small intestine (for nutrient digestion & absorption)
and kidney (for ion transport).
10
Q
Cilia
A
Whiplike, highly motile extensions of apical
surface membranes of certain cells
• Cilia contain a core of nine pairs (doublets)
of microtubules encircling one middle pair
• Doublets have attached motor proteins
(dynein arms)
11
Q
Cilia
A
• Each cilium produces a propulsive power stroke followed by a nonpropulsive recovery stroke • This sequence of strokes assures that liquid (e.g., mucus) in the respiratory tract is moved in one direction • Air pollution and cigarette smoke can damage cilia
12
Q
Kartagener’s Syndrome
A
An inherited disease which is a type of immotile cilia syndrome because the dynein arms within the cilia fail to form. • This condition leads to frequent respiratory infections because the nonfunctional cilia can not sweep inhaled pathogens and excess mucus out of the respiratory tubes.
13
Q
Endocrine Glands
A
Ductless glands that produce and secrete hormones (messenger molecules) into blood
14
Q
Exocrine Glands
A
• Ducts carry products of exocrine glands to epithelial surface • Include the following diverse glands – Mucus-secreting glands – Sweat and oil glands – Salivary glands – Liver and pancreas
15
Q
Unicellular Exocrine Glands
The Goblet Cell
A
• Goblet cells are a unicellular exocrine gland which produces mucin • Mucin + water mucus • Mucus protects and lubricates many internal body surfaces
16
Q
Multicellular Exocrine Glands:
two basic parts
A
Epithelium-walled duct
• Secretory unit
17
Q
Multicellular Exocrine Glands
A
Classified by structure of duct – Simple – Compound (compound branching) • Categorized by secretory unit – Tubular (form tubular sacs) – Alveolar (form spherical sacs) – Tubuloalveolar
18
Q
The Basal Lamina
A
• Non-cellular supporting sheet between the
epithelium and the underlying connective
tissue
• Consists of proteins secreted by epithelial
cells
• Acts as a selective filter, determining which
molecules from connective tissue capillaries
enter the epithelium
• Acts as scaffolding along which regenerating
epithelial cells can populate
19
Q
The Basement Membrane
A
• Basal lamina and reticular layers of the
connective tissue deep to it form the
basement membrane
• In people with diabetes mellitus, the
basement membranes may thicken and
become dysfunctional in kidneys and/or
retinas resulting in kidney failure (diabetic
nephropathy) and/or blindness (diabetic
retinopathy)
20
Q
Digestive System organs & structures
A
Alimentary canal
• Accessory digestive structures & organs
21
Q
Alimentary canal
A
• mouth • pharynx • esophagus • stomach • small intestine • large intestine includes rectum and anal canal
22
Q
Accessory digestive
structures & organs
A
• Teeth, tongue
• Salivary glands, pancreas, liver, and
gallbladder which are connected to the
alimentary canal by ducts
23
Q
Digestive Processes
A
• Ingestion: taking food into mouth
• Propulsion: swallowing and peristalsis moves food
• Mechanical digestion: chewing food in mouth, churning
food in stomach, and segmentation of food in small
intestine
• Chemical digestion: complex molecules
(carbohydrates, proteins, and lipids) broken down to
chemical components in the mouth, stomach, and small
intestine
• Absorption: transport of digested nutrients from the
lumen of the alimentary tract into blood and lacteals
• Defecation: elimination of indigestible substances as
feces
24
Q
Peristalsis
A
Major means of propulsion • Adjacent segments of the alimentary canal relax and contract which propels food forward
25
Segmentation
```
Nonadjacent
segments of small
intestine alternately
contract and relax
which moves food
forward and then
backward
• Food is mixed with
digestive juices and
slowly propelled
```
26
Four Abdominal Quadrants
Right upper quadrant
• Left upper quadrant
• Right lower quadrant
• Left lower quadrant
27
The Peritoneal Cavity & Peritoneum
• Peritoneum—serous membrane that lines
the abdominal-pelvic cavity, surrounds the
digestive organs and line the body wall
– Visceral peritoneum surrounds digestive
organs
– Parietal peritoneum lines the body wall
• Peritoneal cavity—a slit-like space in
between the visceral peritoneum and the
parietal peritoneum, the two membranes
which separate the organs in the abdominal
cavity from the abdominal wall
28
Mesentery 1
• A double layer of peritoneum which is a sheet
of two fused layers of serous membranes that
extends from the body wall (either dorsal wall
or ventral wall) to the digestive organs
• Holds organs in place
• Sites of fat storage
• Provides a route for circulatory vessels and
nerves
29
Dorsal Mesenteries 1
```
Greater omentum—
a “fatty apron” of
peritoneum attaches
greater curvature of
stomach
• Mesentery proper
(jejunal & duodenal
mesentery)
• Transverse
mesocolon
• Sigmoid
mesocolon
```
30
Dorsal Mesenteries 2
• Dorsal mesenteries extend from the alimentary tract
to the posterior abdominal wall.
• The greater omentum is rich in fat and connects
the greater curvature of the stomach to the posterior
abdominal wall.
• Mesentary proper supports the jejunum and ileum.
• Transverse mesocolon supports the transverse
colon.
• Sigmoid megacolon connects sigmoid colon to
posterior pelvic wall.
31
Mesenteries 2
```
Sagittal section
through the
abdominopelvic
cavity
• Mesenteries attach
to abdominal wall
```
32
Ventral mesentery: lesser omentum
• Lesser omentum attaches to lesser
| curvature of stomach
33
Ventral Mesenteries
| falciform ligament and lesser omentum
• The two ventral mesentaries are in the superior
abdomen and extend ventrally to the anterior
abdominal wall.
• The falciform ligament binds the anterior aspect of
the liver to anterior abdominal wall and diaphragm
(mesenteries may be called “ligaments” even
though they are peritoneal sheets)
• The lesser omentum runs from the liver to lesser
curvature of stomach and the beginning of the
duodenum.
34
Intraperitoneal organs and
| their mesenteries
* Liver (lesser omentum & falciform ligament)
* Stomach (lesser & greater omentums)
* Ileum & jejunum (mesentery proper)
* Transverse colon (transverse mesocolon)
* Sigmoid colon (sigmoid mesocolon)
35
Retroperitoneal organs: organs behind
peritoneum which lack mesenteries and
fuse directly to posterior abdominal wall
* Pancreas (except the tail)
* Duodenum (except the proximal part)
* Ascending colon
* Descending colon
* Rectum (except proximal part)
* Adrenal glands, kidneys, ureters, bladder
* Aorta, inferior vena cava
36
Four layers of alimentary tract
from esophagus to anal canal
from inside to outside
```
• Mucosa
• Submucosa
• Muscularis externa
• Serosa layer (or adventitia layer in
retroperitoneal organs)
```
37
Mucosa the innermost layer of
| alimentary tract
• Epithelium
• Lamina propria: loose areolar and/or
reticular connective tissue whose capillaries
nourish the epithelium and absorb digested
nutrients
• Muscularis mucosae: this layer of smooth
muscle that produces local movements of
the mucosa.
38
Submucosa layer of alimentary tract
Layer of connective tissue external to the
mucosa
• Moderately dense connective tissue rich in
elastic fibers and is intermediate between
loose areolar and dense irregular; enables
alimentary canal to stretch and return to its
shape as food passes through it.
• Rich supply of blood vessels, lymphatic
vessels, nerve fibers, and glands.
39
Muscularis externa is
external to submucosa and is made
of two layers of smooth muscle
• Circular muscularis—inner layer which
orients around the circumference of the
canal
• Longitudinal muscularis—outer layer
which orient along the length of the canal
• These two layers are responsible for
peristalsis and segmentation
40
Serosa: outer most layer
• The serosa layer is visceral peritoneum
which is outermost layer external to the
muscularis externa
• Serosa layer is made of simple squamous
epithelium (mesothelium) underlain by a
layer of areolar connective tissue
41
Adventitia:
outer most layer in organs
not associated with peritoneal cavity
Parts of the alimentary tract which are not
associated with peritoneal cavity (e.g.
esophagus and retroperitoneal organs)
lack a serosa and instead have an
adventitia consisting of fibrous connective
tissue as their outer laye
42
Nerve Plexuses innervating
| Alimentary Tract
```
• Myenteric nerve plexus
• Lies between circular and longitudinal
muscularis
• Controls peristalsis
• Submucosal nerve plexus
– Lies in submucosa
– Signals glands to secrete
• Innervation
– Sympathetic and parasympathetic motor fibers
– Visceral sensory fibers
```
43
Smooth muscle 1
Myofilaments in smooth muscle interact with
cytoskeleton
• Tension-resisting intermediate filaments
extend through the cell in a lattice-like
arrangement
• Dense bodies anchor thin filaments to
sarcolemma
• Through this anchoring attachment, the
sliding myofilaments shorten the muscle cell
by pulling on the cytoskeleton during muscle
contraction
44
Smooth muscle 2
```
Entry of Ca2+ into sarcoplasma
stimulates smooth muscle to contract
• Some Ca2+ enters from extracellular
fluid through calveolae
• Calveolae are spherical infoldings of
sarcolemma
• Ca2+ is also stored and released by
intracellular sarcoplasmic reticulum
```
45
Epithelia of mucous lining of
| alimentary tract
Oral cavity: stratified squamous epithelium
• Pharynx: stratified squamous epithelium
• Esophagus: stratified squamous epithelium
• Stomach: simple columnar epithelium
• Small intestine villi: simple columnar
epithelium
• Large intestine: simple columnar epithelium
• Anal canal: stratified squamous epithelium
46
Anatomy of the Mouth
```
The labial frenulum connects
lips to gum
• The lingual frenulum connects
tongue to mouth floor
• The palate forms the roof of the
mouth
• The teeth chew food
• The tongue dorsum has
conical, pointed, and keratinized
filiform papillae which enable it
to grasp and move food and mix
it with saliva during chewing and
form it into a bolus that is
swallowed
• During swallowing, tongue
moves posteriorly to push the
bolus into the pharynx
```
47
The Teeth 1
• Deciduous teeth—20 teeth
– First appear at 6 months of age
• Permanent teeth—32 teeth
– Start emerging by 6 years of age and all are
usually in by the end of adolescence except for
3rd molars (wisdom teeth) which may not erupt
until the early 20s
– 8 incisors, 4 canines, 8 premolars, 12 molars
48
The Teeth 2
```
Incisors Central (6–8 mo) (deciduous)
Incisors Central (7 yr) (permanent)
```
Canine (eyetooth) (deciduous)
(16–20 mo)
Canine (permanent)
(eyetooth)
(11 yr)
Premolars
(bicuspids)
First premolar
(11 yr)
Molars
```
First molar (deciduous)
(10–15 mo)
```
```
First molar (perm)
(6–7 yr)
```
Lateral (8–10 mo) (decid)
Lateral (8 yr) (perm
Second molar
(about 2 yr) (decid)
Second molar (perm)
(12–13 yr)
```
Third molar (perm)
(wisdom tooth)
(17–25 yr)
```
49
Tooth Structure
```
Longitudinal
section of tooth in
bone alveolus
• Enamel
• Dentin
• Pulp cavity
• Root canal
• Cementum
• Apical foramen
• Periodontal
ligament
```
50
Anatomy of the Mouth
• Openings of
sublingual duct &
submandibular
duct
51
Salivary Glands: compound tubuloalveolar
| glands that produce saliva
-- Parotid glands
• Lies anterior to ear & is largest extrinsic gland
• Parotid duct—parallel to zygomatic arch and opens
into mouth lateral to 2nd upper molar to release watery
serous fluid from serous cells
• Infected with mumps virus
– Submandibular glands
• Lies along medial surface of mandibular body
• Opens lateral to tongue’s lingua frenulum and
contains serous and mucous cells
– Sublingual glands
• Lies in floor of oral cavity inferior to tongue
• Contains primarily mucous cells
52
Saliva contents
```
Water, ions, and mucus
• Bicarbonate buffer that neutralizes
acids produced by oral bacteria
• Enzymes including amylase, which
begins the digestion of complex
carbohydrates
```
53
Oropharynx & laryngopharynx
• Passages for air and food
• Lined with stratified squamous
epithelium
54
The Esophagus
```
Begins as a continuation of the pharynx
• Joins the stomach inferior to the
diaphragm
• Cardiac (gastro-espophageal)
sphincter—closes to prevent stomach
acid from entering esophagus
```
55
Esophagus microscopic anatomy
• Epithelium is stratified squamous epithelium
• When empty, mucosa and submucosa are in
longitudinal folds; when bolus passes through,
the folds flatten out
• Mucous glands: primarily compound
tubuloalveolar glands
• Muscularis externa: Skeletal muscle in
superior third of length, mixed skeletal and
smooth muscle in middle third of length, and
smooth muscle in lower third of length
• Adventitia—most external layer consisting of
connective tissue
56
Transition of esophageal to
| gastric epithelium
Esophagus: stratified squamous epithelium
| • Stomach: simple columnar epithelium
57
Regions of the Stomach
* Cardiac region next to esophagus
* Fundus
* Body
* Pyloric region next to duodenum
* Pyloric sphincter
* Lesser curvature of stomach
* Greater curvature of stomach
58
Microscopic Anatomy of Stomach
```
Epithelium is simple columnar epithelium
• Internal surface of stomach contains
longitudinal folds called rugae which can
flatten when stomach fills
• Muscularis externa has three layers
– circular
– longitudinal layers
– oblique layer
```
59
Gastric pits and gastric glands
| of stomach mucosa
Mucosa dotted with gastric pits
• Simple branched tubular gastric glands are
deep to gastric pits
60
Cells lining gastric glands
| of gastric fundus & body
Mucous neck cells: secrete mucus
• Enteroendocrine cells: hormone (e.g.
gastrin) secreting cells; gastrin signals parietal
cells to produce HCl acid when food enters
the stomach
• Parietal (oxyntic) cells: Secrete hydrochloric
acid and gastric intrinsic factor
• Chief (zymogenic) cells: Secrete
pepsinogen which is activated to pepsin when
it encounters acid in the gastric glands
61
The Stomach
- Site where food is churned into a paste-like substance called chyme
- Secretion of hydrochloric acid creates acidic condition
- Pepsin begins protein digestion
- Minor absorption can occur in stomach including water, electrolytes, and some drugs
62
Peptic Ulcers
Erosions of the mucosa
• Gastric ulcers occur in pyloric region of the
stomach
• Duodenal ulcers occur in duodenum of the small
intestine
• Caused by Helicobacter pylori
• Helicobacter pylori
– Acid-resistant
– Binds to gastric epithelium
• Induces oversecretion of acid & inflammation
63
Small & Large Intestine Length
Small intestine: 6 meters long
| • Large intestine: 1.5 meters long
64
Small Intestine
• Longest portion of the alimentary canal
• Site of most digestion by enzymes and
absorption
• Foods moves through by segmentation
and peristalsis in 3-6 hours
• Three subdivisions
– Duodenum (0.3 meters)
– Jejunum (2.4 meters)
– Ileum (3.5 meters)
• Innervation
– Parasympathetic fibers from vagus nerve
– Sympathetic from thoracic splanchnic nerves 111
65
```
Digestive enzymes produced by
pancreas and released into duodenum
to digest (break down) foods
```
```
• Proteases and peptidases split
proteins into amino acids
• Lipases split fat into fatty acids and
glycerol
• Carbohydrases split carbohydrates
e.g., starch into sugars
• Nucleases split nucleic acids into
nucleotides
```
66
The Duodenum
Digestion (break down) of foods in duodenum by
pancreatic enzymes
• Duodenum receives pancreatic digestive enzymes
from main pancreatic duct and bile from common
bile duct
• The hepatopancreatic ampulla is a bulb which
contains the pancreatic sphincter that controls
entry of pancreatic juice enzymes and the bile
sphincter that controls entry of pancreatic bile
• The ampulla opens into the duodenal lumen via the
major duodenal papilla
67
Histology of small intestine wall
* Enteroendocrine cells
* Goblet cells: secrete mucin
* Absorptive cells
* Intestinal crypts (crypts of Lieberkuhn)
68
Enteroendocrine cells in
| duodenum release cholecytokinin
```
• cholecytokinin is released in response
to fatty chyme and causes gallbladder’s
muscular wall to contract and ducts to
relax to release bile into duodenum
which emulsifies fats
• signal the pancreas to secrete digestive
enzymes and bicarbonate-rich juice to
neutralize acidic chyme which enters
duodenum
```
69
Compound tubular
| duodenal glands
Secrete alkaline bicarbonate mucus into
duodenum lumen to help neutralize the
acidic chyme from the stomach
70
Goblet cells of small intestine
• Secrete mucus that lubricates chyme and
protects intestinal wall from enzymatic
digestion
71
```
Intestinal crypts (crypts of
Lieberkuhn) in small intestine
```
• Epithelial cells secrete watery intestinal juice
which mixes with chyme
• Undifferentiated epithelial cells lining the
intestinal crypts renew the mucosal
epithelium by dividing rapidly and moving
onto the villi with complete renewal of inner
epithelium of the small intestine every 3-6
days
72
Absorptive cells in small intestine
• Uptake digested nutrients which are then
absorbed by blood capillaries and lacteal
capillaries in the lamina propria
73
The small intestine
| modifications for absorption
```
Circular folds (plicae circulares):
transverse ridges of mucosa and
submucosa increase absorptive surface
area
• Villi
• Microvilli
```
74
Villi for absorption
• Villi (finger-like projections) of the mucosa increase
surface area for absorption
• Smooth muscle in the muscularis mucosae allows
villi to move during digestion which enhances
absorptive efficiency and squeezes lymph through
lacteals
• Covered with simple columnar epithelium
• Made up primarily of absorptive cells
• The villi/microvilli system provides 200
square
meters of absorptive surface within small intestine
75
Absorption of nutrients in
| jejunum and ileum
Apical surfaces of the absorptive cells have many
microvilli which are long and densely packed and
contain brush border enzymes that complete the
final stages of digestion (breakdown) of nutrient
molecules
• Villi absorb amino acids, sugars, fatty acid particles,
vitamins, minerals, electrolytes and water across the
villi
• Ileum villi absorb bile salts and other products of
digestion
• intrinsic factor produced by stomach enables ileum
villi to absorb vitamin B12
76
Villi lamina propria capillaries for absorption
Within core of lamina propria of each villi is a network
of blood capillaries and lymphatic capillaries
(lacteals)
• Blood capillaries absorb products of digestion of
carbohydrates and protein
• Lacteals (lymphatic capillaries) absorb products of
digestion of fat
• Blood vessels that drain the small intestine carry
absorbed carbohydrates and protein to liver via
hepatic portal system
• Newly absorbed lipids are assembled into lipid-protein
complexes called chylomicrons and enter the lacteal
capillaries
77
Ileocecal valve
ileocecal valve connects ileum (end of
small intestine) with cecum (beginning
of large intestine)
78
Ileocecal valve to anus
* Ileocecal valve
* Cecum: beginning of large intestine
* Vermiform appendix
* Ascending colon
* Right colic (hepatic) flexure
* Transverse colon
* Left colic (splenic) flexure
* Descending colon
* Sigmoid colon
* Rectum
* Anal canal
79
Microscopic Anatomy of Large
| Intestine
• Villi are absent
• Contains numerous goblet cells
• Intestinal crypts are simple tubular glands
containing many goblet cells
• Undifferentiated stem cells occur at the bases of
intestinal crypts and epithelial cells are fully
replaced every 7 days
• Lined with simple columnar epithelial tissue
• Epithelium changes at anal canal to become
stratified squamous epithelium
80
The Large Intestine
```
• Digested residue contains few nutrients
• Small amount of digestion by bacteria
• Main functions
– Absorb water, electrolytes, and
vitamins produced by bacteria
• Mass peristaltic movements and
haustral churning move feces toward
the rectum
```
81
Special Features of Large Intestine
Teniae coli: Thickening of longitudinal
muscularis with three longitudinal strips
placed at equal intervals around colon and
cecum
• Haustra: Puckering sacs in large intestine
created by teniae coli; haustral churning is
the sequential movements of contents from
one haustra to the next
• Epiploic (omental) appendages: Fat-filled
pouches of visceral peritoneum attached to
intestine
82
Rectum & Anal Canal
Rectum
– Sigmoid colon joins the rectum in the pelvis
– Descends along the inferior half of the
sacrum
– Has no teniae coli but instead has well
developed longitudinal muscle layer that can
generate strong contractions for defecation
• Anal canal
– The last subdivision of the large intestine
– Lined with stratified squamous epithelium
83
Defecation reflex
As feces moves into the rectum, the walls distend
which stimulates sensory stretch receptors that
transmit signals along afferent fibers to spinal cord
• Spinal reflex is triggered causing parasympathetic
efferent fibers to stimulate contraction of the
smooth muscle in rectal walls and relaxation of the
internal anal sphincter (smooth muscle)
• If it is convenient to defecate, the voluntary motor
neurons are inhibited, allowing the external anal
sphincter (skeletal muscle) to relax and allow the
feces to pass out the anus
84
The Liver
* Largest gland in the body
* Performs many metabolic functions
* Digestive function includes bile production
85
Microscopic Anatomy of the Liver
• Hepatocyte—functional cells of the liver
• Portal triad is a component of the hepatic lobule
and is composed of
– Bile duct tributary
– Portal venule: branch of hepatic portal vein
– Portal arteriole: branch of hepatic portal artery
• Kupffer cells are specialized macrophages
which line the sinusoids and destroy bacteria
86
The gallbladder
```
Gall bladder: gall stones may develop
in this bladder
• Cystic duct
• Bile duct
• Bile sphincter
• Gallbladder stores and concentrates bile
• Bile duct expels bile into duodenum
– bile emulsifies fats
```
87
The Pancreas
• Exocrine function
– Acinar cells make, store, and secrete at
pancreatic enzymes into duodenum
– Zymogen granules in acinar cells: enzymes
are stored in inactive precursor form in these
intracellular granules
• Endocrine function
– Alpha cells (α cells)—secrete glucagon
– Beta cells (β cells)—secrete insulin
– Delta cells (∂ cells) —secrete somatatostatin
– Regulate blood sugar
88
Layers of alimentary tract from inside to outside
Epithelium of mucosa:
• Lamina propria of mucosa: loose areolar and/or reticular
connective tissue (CT) rich with capillaries which nourish the
epithelium and absorb digested nutrients
• Muscularis mucosae of mucosa: this layer of smooth muscle that
produces local movements of the mucosa.
• Submucosa: moderately dense CT rich in elastic fibers allows
alimentary tract to stretch as food moves through
• Circular muscularis of muscularis externa: orients around the
circumference of the canal
• Longitudinal muscularis of muscularis externa: orients along
the length the canal
• Muscularis externa: responsible for peristalsis and segmentation
• Serosa layer: loose areolar CT with outer layer of squamous
epithelium (mesothelium) or adventitia layer on retroperitoneal
organs or surfaces
89
Mouth & associated accessory
| organs
```
• Ingestion into mouth
• Mechanical digestion: mastication by
teeth and movement by tongue
• Chemical digestion: starch breakdown
begins in mouth with salivary amylase
• Propulsion: swallowing of food with
tongue
```
90
Pharynx & esophagus
• Propulsion: Peristalic waves move
| food bolus to stomach
91
Stomach
Mechanical digestion and propulsion:
peristaltic waves mix food and propel it to
duodenum
• Chemical digestion: digestion of protein
started by pepsin
• Absorption: of a few fat soluble substances
92
Small intestine and accessory
| organs (liver, gall bladder, pancreas)
Mechanical digestion and propulsion:
segmentation by smooth muscle mixes contents
and peristalsis moves food toward large intestine
• Chemical digestion: digestive enzymes from
pancreas, brush border enzymes attached to
microvilli, and bile from the gall bladder digest food
• Absorption: absorb breakdown products of fat,
carbohydrates, protein, and nucleic acids as well as
vitamins, electrolytes and water
93
Large intestine
Chemical digestion: some remaining food
residues are digested by enteric bacteria
• Absorption: absorbs most remaining water,
electrolytes, and vitamins produced by
bacteria
• Propulsion: propels feces toward rectum
by peristalsis and haustral churning
• Defecation: reflex triggered by rectal
distension and feces is eliminated from body
