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Transcript
Ingegneria delle tecnologie
per la salute
Fondamenti di
anatomia e istologia
aa. 2016-17
Digestive
System
(b)
Salivary Glands
= many small salivary glands housed within
mucous membranes of mouth and tongue,
constantly secreting saliva, either directly into
oral cavity or indirectly through ducts (1-1.5
lts/day): usually just enough saliva is present to
moisten mouth and teeth, but increases when
eating, because it is essential to moisten food
and initiate chemical digestion of
carbohydrates
Major Salivary Glands
=outside oral mucosa 3 pairs of glands,
secreting majority of saliva into ducts opening
into mouth:
• submandibular glands = in floor of mouth,
secreting through submandibular ducts.
• sublingual glands = below tongue, using lesser
sublingual ducts to secrete into oral cavity.
• parotid glands = between skin and masseter
muscle (near ears), secreting through parotid
duct (located near second upper molar tooth).
Salivary
Glands
Salivary
Glands
Salivary
Glands
Salivary
Glands
Salivary Glands
Salivary Glands
Salivary Glands
Saliva
= essentially (95.5 %) water + 4.5 % [=complex mixture of ions, glycoproteins,
enzymes, growth factors, and waste products]
salivary amylase = perhaps most important ingredient in saliva initiating
breakdown of carbohydrates (not enough time in mouth to allow all carbohydrates
break down, but salivary amylase continues acting until inactivated by stomach
acids)
Bicarbonate + phosphate ions = chemical buffers, maintaining saliva at a pH
6.35-6.85.
Salivary mucus = lubricate food, facilitating movement in mouth, bolus formation,
and swallowing.
immunoglobulin A + lysozyme = antimicrobial
Regulation of Salivation
• autonomic nervous system regulates salivation (secretion of saliva):
parasympathetic stimulate - sympathetic reduce salivation
• chemicals stimulating taste receptors on tongue  impulses to sup and inf
salivatory nuclei in brain stem  parasympathetic impulses through fibers in
glossopharyngeal and facial nerves, stimulating salivation
Teeth
= organs similar to bones used to
tear, grind, and otherwise
mechanically break down food.
Types of Teeth
2 sets of teeth (= dentition): 20
deciduous teeth, or baby teeth,
first appearing at about 6 mos of
age; between approximately age
6 and 12, replaced by 32
permanent teeth, moving from
center of mouth toward side:
• 8 incisors, 4 top + 4 bottom
• 4 canines
• 8 premolars (or bicuspids)
• 12 molars
Teeth:
Anatomy of a Tooth
= secured in alveolar processes
(sockets) of maxilla and mandible by
connective tissue called periodontal
ligament
gingivae (gums) = soft tissues that line
alveolar processes and surround necks
of teeth.
2 main parts of a tooth: 1. crown (=
portion projecting above gum line, 2.
root (embedded in maxilla+mandible),
both containing inner pulp cavity with
loose connective tissue inside through
which run nerves and blood vessels
[root canal = pulp cavity that runs
through root of tooth]; surrounding
pulp cavity is dentin (=bone-like tissue)
covered in root by an even harder
bone-like layer called cementum and in
crown by an outer layer of enamel
(hardest substance in body)
Teeth
Pharynx
= (involved in both digestion and respiration, when food
enters pharynx, involuntary muscle contractions close off air
passageways) short tube of skeletal muscle lined with
mucous membrane, running from posterior oral and nasal
cavities to opening of esophagus and larynx; 3 subdivisions:
sup, nasopharynx, involved only in breathing and speech,
other 2 subdivisions, oropharynx and laryngopharynx, used
for both breathing and digestion: oropharynx begins inf to
nasopharynx and continue below with laryngopharynx,
connecting to esophagus, whereas ant portion connects to
larynx, allowing air to flow into bronchial tree; histologically,
wall of oropharynx is similar to that of oral cavity, with
mucosa of stratified squamous epithelium endowing with
mucus-producing glands. During swallowing, elevator skeletal
muscles of pharynx contract, raising and expanding pharynx
to receive bolus of food, then relax and constrictor muscles
of pharynx contract, forcing bolus into esophagus and
initiating peristalsis, meanwhile soft palate and uvula rise
reflexively to close off entrance to nasopharynx and larynx
is pulled superiorly with cartilaginous epiglottis folding
inferiorly to cover glottis
Esophagus
= muscular tube connecting
pharynx to stomach (running a
mainly straight route through
mediastinum of thorax, but to
enter abdomen penetrates
diaphragm through an opening
= esophageal hiatus),
approximately 25 cm in
length, located post to
trachea, and remaining
collapsed when not engaged in
swallowing
Esophagus
Passage of Food through Esophagus
 upper esophageal sphincter (continuous with
inferior pharyngeal constrictor) = controls
movement of food from pharynx into
esophagus.
 upper two-thirds of esophagus = both
smooth and skeletal muscle fibers, with the
latter fading out in the bottom third of
esophagus
 rhythmic waves of peristalsis, which begin in
upper esophagus, propel bolus of food toward
stomach, meanwhile, secretions from
esophageal mucosa lubricate esophagus and
food, that passes from esophagus into
stomach at lower esophageal sphincter (also
called gastroesophageal or cardiac sphincter),
relaxing to let food pass into stomach, then
contracting to prevent stomach acids from
backing up into esophagus.
Esophagus
Histology of the Esophagus
mucosa with non-keratinized,
stratified squamous
epithelium, with a layer of
basal and parabasal cells,
protecting against erosion
from food particles + lamina
propria containing mucussecreting glands + muscularis
layer changing according to
location: in upper third
muscularis = skeletal muscle,
in middle third = skeletal and
smooth muscle and in lower
third = smooth muscle +
adventitia, most superficial
layer of esophagus not
covered by a fold of visceral
peritoneum.
Esophagus
Esophagus
Esophagus
Esophagus
Esophagus
Esophagus
Esophagus Digestive functions
Stomach
[FUNCTION] =
 temporary holding chamber = meal can
be ingested far more quickly than it
can be digested and absorbed by small
intestine: stomach holds food and
parses only small amounts into small
intestine at a time; foods not
processed in order are eaten, but
mixed together with digestive juices
in stomach (= chyme), released into
small intestine.
 plays several important roles in
chemical digestion, including continued
digestion of carbohydrates and initial
digestion of proteins and triglycerides
 little if any nutrient absorption occurs
in stomach, with exception of
negligible amount of nutrients in
alcohol
Stomach: structure
 4 main regions in stomach:
1. cardia (or cardiac region) =
point where esophagus
connects to stomach and
through which food passes
into stomach
2. Fundus = dome-shaped and
located inf to diaphragm,
above and left of cardia
3. Body = below fundus, main
part of stomach
4. Pylorus = funnel-shaped,
connecting stomach (pyloric
antrum) to duodenum
(=narrower end, called
pyloric canal, with smooth
muscle pyloric sphincter
located at latter point of
connection and controls
stomach emptying)
Stomach: structure
 In absence of food, stomach deflates inward, and mucosa and
submucosa fall into a large fold (=ruga).
 greater curvature = convex lateral surface
 lesser curvature = concave medial border
 held in place by lesser omentum (extending from liver to lesser
curvature) and greater omentum (running from greater curvature to
posterior abdominal wall)
Stomach:
structure
Stomach: histology
wall made of same 4 layers as
rest of alimentary canal, but
with adaptations for unique
functions of this organ to:
a) Muscularis = in addition to
typical circular and
longitudinal smooth muscle
layers, muscularis has an
inner oblique (= in addition to
moving food through canal,
stomach can vigorously churn
food, mechanically breaking it
down into smaller particles)
Stomach: histology
b) mucosa
Stomach: histology
b) Mucosa = epithelial lining consists only of surface mucus cells, secreting a
protective coat of alkaline mucus + vast number of gastric pits dot surface of
epithelium, marking entry to each gastric gland, secreting complex digestive fluid
referred to as gastric juice;
Stomach: histology
walls of gastric pits made up primarily of mucus cells, but gastric glands made up
of different types of cells:
 glands of cardia and pylorus = primarily mucus-secreting cells
 pyloric antrum = mucus and a number of hormones, including majority of
stimulatory hormone, gastrin
 fundus and body = (much larger glands) site of most chemical digestion,
producing most of gastric secretions, due to a variety of secretory cells:
Stomach:
histology
Stomach: histology
1. Parietal cells—located primarily in middle region of
gastric glands (among the most highly differentiated of
the body‘s epithelial cells) producing both hydrochloric
acid (HCl, responsible for high acidity [pH 1.5 to 3.5]
needed to activate protein-digesting enzyme, pepsin,
and also killing much of bacteria ingested with food and
helping to denature proteins, making them more
available for enzymatic digestion) and intrinsic factor
(glycoprotein necessary for absorption of vitamin B12 in
small intestine).
2. Chief cells—located primarily in basal regions of gastric
glands, secreting pepsinogen (inactive proenzyme form
of pepsin, with HCl necessary for its conversion from
pepsinogen)
3. Mucous neck cells— (gastric glands in upper part of
stomach) secreting thin, acidic mucus that is much
different from the mucus secreted by the goblet cells
of the surface epithelium (role not currently known)
4. Enteroendocrine cells— secreting various hormones into
interstitial fluid of lamina propria (including gastrin
released mainly by enteroendocrine G cells)
Stomach:
histology
Stomach:
histology
Stomach:
histology
Stomach:
histology
Stomach: histology
Stomach:
histology
Stomach: histology
Small Intestine: generality
Chyme released from stomach enters small intestine =
primary digestive organ in body.
Not only where most digestion occurs, also where
practically all absorption occurs.
longest part of alimentary canal: about 3 mts long in a
living person (twice as long in a cadaver due to loss of
muscle tone).
smaller diameter of only about 2.5 cm, compared with 7.5
cm for the large intestine.
in addition to its length, folds and projections of lining of
small intestine work to give it an enormous surface area,
which is approximately 200 m2 , more than 100 times
surface area of your skin: necessary for complex
processes of digestion and absorption
Small Intestine: structure
coiled tube of small intestine is subdivided into 3
regions: duodenum, jejunum, and ileum
Small Intestine: structure
 Duodenum = shortest region ( 25cm), beginning
at pyloric sphincter, bends posteriorly behind
peritoneum, becoming retroperitoneal, and then
makes a C-shaped curve around the head of
pancreas before ascending anteriorly again to
return to peritoneal cavity and join jejunum,
therefore being subdivided into 4 segments:
sup, descending, horizontal, ascending
 hepatopancreatic ampulla (ampulla of Vater) =
located in duodenal wall, marks transition from
ant portion of alimentary canal to mid-region,
where bile duct (through which bile passes
from liver) and main pancreatic duct (through
which pancreatic juice passes from pancreas)
join, opening into duodenum at a tiny volcanoshaped structure called the major duodenal
papilla (where hepatopancreatic sphincter,
sphincter of Oddi, regulates flow of bilepancreatic juice from ampulla into duodenum).
Small Intestine: structure
Small Intestine: structure
 jejunum = about 1 mt long (in life), [means
―empty‖ in Latin], without clear
demarcation between it and ileum.
 ileum = longest part of small intestine,
measuring about 2 mts: thicker, more
vascular, more developed mucosal folds
than jejunum, joins cecum, at ileocecal
sphincter (or valve); both tethered to post
abd wall by mesentery;
 large intestine frames these 3 parts of SI.
 Parasympathetic nerve fibers from vagus
nerve and sympathetic nerve fibers from
thoracic splanchnic nerve = extrinsic
innervation to small intestine
 sup mesenteric artery = main arterial
supply
 veins running parallel to arteries, drain into
sup mesenteric vein = nutrient-rich blood
from small intestine is then carried to liver
via hepatic portal vein.
Small Intestine: Histology
wall composed of same 4 layers typically present in alimentary system, but 3
features of mucosa and submucosa are unique, increasing absorptive surface area
more than 600-fold, include circular folds, villi, and microvilli (these adaptations
most abundant in proximal 2/3 of SI, where majority of absorption occurs)
(a) The absorptive
surface of the small
intestine is vastly
enlarged by the
presence of circular
folds, villi, and microvilli.
(b) Micrograph of the
circular folds. (c)
Micrograph of the villi.
(d) Electron micrograph
of the microvilli.
Small Intestine: Histology
Circular folds = (also called plica circulare), deep ridge in mucosa and submucosa,
beginning near proximal part of duodenum and ending near middle of ileum,
facilitating absorption, because their shape causes chyme to spiral, rather than
move in a straight line, through SI, slowing movement of chyme and providing time
needed for nutrients to be fully absorbed.
Villi = within circular folds, small (0.5–1 mm long) hairlike vascularized projections
called villi (singular = villus), giving mucosa a furry texture, being about 20 to 40
villi mm2, increasing surface area tremendously; mucosal epithelium, primarily
composed of absorptive cells, covering villi, that (in addition to muscle and
connective tissue to support its structure) contains a capillary bed composed of 1
arteriole and 1 venule, as well as a lymphatic capillary called lacteal: breakdown
products of carbohydrates and proteins (sugars and amino acids) enter
bloodstream directly, but lipid breakdown products absorbed by lacteals and
transported to bloodstream via lymphatic system.
Microvilli = much smaller (1 µm) than villi, being cylindrical apical surface
extensions of plasma membrane of mucosa‘s epithelial cells, supported by
microfilaments, combined microscopic appearance suggests a mass of bristles
(brush border), containing at surface enzymes that finish digesting carbohydrates
and proteins, estimating 200 million microvilli per mm2, greatly expanding surface
area of the plasma membrane and thus greatly enhancing absorption.
Small Intestine: Histology
Intestinal Glands = mucosa between villi is dotted with deep crevices that each
lead into a tubular intestinal gland (crypt of Lieberkühn), formed by cells lining
crevices, producing intestinal juice, a slightly alkaline (pH 7.4 to 7.8) mixture of
water and mucus (daily about 1-2 lts secreted in response to distention of small
intestine or irritating effects of chyme on intestinal mucosa).
duodenal glands (Brunner’s glands) = submucosa of duodenum, only site of
complex mucus-secreting, producing a bicarbonate-rich alkaline mucus buffering
acidic chyme as it enters from stomach.
roles of cells in small intestinal mucosa:
Small Intestine: Histology
Intestinal MALT
= lamina propria of small intestine mucosa is studded with quite a bit of MALT: in
addition to solitary lymphatic nodules, aggregations of intestinal MALT (=
typically referred to as Peyer’s patches, concentrated in distal ileum, most
prominent in young people and becoming less distinct in elders, coinciding with
general activity of our immune system) serving to keep bacteria from entering
bloodstream.
Small Intestine
(and Large
Intestine…):
Histology
Small Intestine: Histology
Small Intestine: Histology
Small
Intestine:
Histology
Small Intestine: Histology
Small Intestine: Histology
Small Intestine: Histology
Small Intestine: Histology
Small Intestine: Histology
Large Intestine
= terminal part of alimentary
canal, with function:
 finish absorption of
nutrients and water,
 synthesize certain vitamins,
 form feces,
 eliminate feces
running from appendix to anus,
and framing small intestine on 3
sides small intestine (large =
more than twice  of small
intestine, about 3 inches)
Subdivisions = 4 main regions:
cecum, colon, rectum, anus
(ileocecal valve = located at
opening between ileum and
large intestine, controling flow
of chyme)
CECUM = sac-like structure, suspended
inferior to ileocecal valve, about 6 cm long,
receiving contents of ileum, and continuing
absorption of water and salts (VERMIFORM
APPENDIX = winding tube attached to cecum,
8-cm long containing lymphoid tissue,
suggesting an immunologic function, generally
considered vestigial, but postulated a survival
advantage in diarrheal illness, where may
serve as bacterial reservoir to repopulate
enteric bacteria for those surviving the initial
phases of illness; mesoappendix = mesentery
of appendix, tethering to mesentery of ileum)
COLON = follows cecum: ascending colon,
right colic flexure (hepatic flexure),
transverse colon (with last third of this
begins region defined as hindgut), left colic
flexure (splenic flexure), descending colon,
sigmoid colon (=entering pelvis inf, s-shaped,
extending medially to midline ); ascending and
descending colon, and rectum located
retroperitoneally, meanwhile transverse and
sigmoid colon tethered to post abd wall by
mesocolon
Large
Intestine
Large Intestine
Foregut,
midgut,
hindgut…
Large Intestine
Rectum
= in pelvis, near third sacral
vertebra, final 20 cm of
alimentary canal, extending ant to
sacrum and coccyx, with 3 lateral
bends creating a trio of internal
transverse folds called rectal
valves (helping separate feces
from gas to prevent simultaneous
passage of feces and gas).
Anal Canal
= located in perineum, completely
outside of abdominopelvic cavity,
4–5 cm long, opening to exterior
at anus (2 sphincters: internal anal
sphincter made of smooth muscle,
with involuntary contractions and
external anal sphincter made of
skeletal muscle, under voluntary
control)
Large Intestine
3 features unique to large intestine:
1. Teniae coli = three bands of smooth
muscle that make up longitudinal
muscle layer of muscularis of large
intestine, except at its terminal end
(tonic contractions bunch up colon
into a succession of pouches =
2. Haustra (singular = hostrum) =
responsible for wrinkled appearance
of colon
3. epiploic appendages = small, fat-filled
sacs of visceral peritoneum, attached
to teniae coli, purpose unknown.
Although rectum and anal canal have
neither teniae coli nor haustra, they do
have well-developed layers of muscularis
that create the strong contractions
needed for defecation.
Large Intestine: Histology
several notable differences between
walls of large and small intestines:
 few enzyme-secreting cells found
in large intestine, and no circular
folds or villi.
 other than in anal canal, mucosa of
colon is simple columnar epithelium
made mostly of enterocytes
(absorptive cells) and goblet cells.
 wall of large intestine far more
intestinal glands, containing a vast
population of enterocytes
(absorbing water and salts as well
as vitamins produced by intestinal
bacteria) and goblet cells
(secreting mucus, easing movement
of feces, protecting intestine from
effects of acids and gases
produced by enteric bacteria).
Large Intestine: Histology
Large Intestine: Histology
Large Intestine: Histology
Large Intestine: Histology
Large Intestine: Histology
Large Intestine: Histology
2. Accessory Organs in Digestion
Chemical digestion in small
intestine relies on activities
of 3 accessory digestive
organs:
1. liver = to produce bile and
export it to duodenum.
2. gallbladder = primarily
stores, concentrates, and
releases bile.
3. pancreas = produces
pancreatic juice, which
contains digestive
enzymes and bicarbonate
ions, and delivers it to
duodenum.
Liver
= largest gland in body, weighing about 1,5 kg in an adult, also one of most important,
being an accessory digestive organ and playing number of roles in metabolism and
regulation.
 lies inf to diaphragm in right upper quadrant of abd cavity, receiving protection from
surrounding ribs.
 divided in 2 primary lobes (large right + much smaller left), in right lobe, some
anatomists also identify inf quadrate + post caudate lobe, defined by internal
features
 connected to abd wall and diaphragm by 5 peritoneal folds referred to as ligaments:
1. falciform ligament, 2. ligamentum teres hepatis (both actually remnants of
umbilical vein, separating right and left lobes anteriorly), 3-4. lateral ligaments, and 5
coronary ligament. + lesser omentum tethers liver to lesser curvature of stomach.
Liver
human
liver
is
divided
by
the
falciform ligament
into an anatomical
right lobe and left
lobe.
also has a functional right and left side, divided by Cantlie's line: a
hypothetical line from the gallbladder fossa to the middle hepatic vein.
Each functional hemi-liver is composed of 2 sections: on right, an ant
section (segments 5 + 8) and a post section (segments 6 + 7) separated
by right hepatic vein; and on left, a lat section (segments 2 + 3) and a
medial section (segment 4) separated by left hepatic vein and the
falciform ligament (not shown). Each segment can be individually
resected. Black dashed lines show demarcations between sections.
Liver
Liver
Liver
Diaphragmatic surface
1 - coronary ligament of liver;
2 - aperture;
3 - triangular ligament of the liver;
4 - sickle ligament of the liver;
5 - the right lobe of the liver;
6 - Left lobe of the liver;
7 - Round ligament of liver;
8 - a sharp lower edge;
9 - gall bladder
Liver
Lower surface
1 - Left lobe of the liver;
2 - the triangular ligament of
the liver;
3 - Rear (tailed) fraction of the
liver;
4 - adrenal indentation;
5 - kidney indentation;
6 - proper hepatic artery;
7 - Vienna gate;
8 - the common bile duct;
9 - common hepatic duct;
10 - cystic duct;
11 - the right lobe of the liver;
12 - duodenal-intestinal
indentation;
13 - Round ligament of liver;
14 - colon-intestinal
indentation;
15 - Front (square) share;
16 - gall bladder
Liver
Liver: biliary tree
Liver
•
•
•
porta hepatis = (―gate to the liver‖)
where hepatic artery and hepatic portal
vein enter liver (running along with
common hepatic duct behind lateral
border of lesser omentum on way to
their destinations)
hepatic artery delivers oxygenated
blood from heart to liver, hepatic portal
vein delivers partially deoxygenated
blood containing nutrients (+ drugs and
toxins) absorbed from the SI and
actually supplies more oxygen to liver
than do much smaller hepatic arteries;
after processing bloodborne nutrients
and toxins, liver releases nutrients
needed by other cells back into the
blood, which drains into central vein and
then through hepatic vein to inferior
vena cava.
hepatic portal circulation = all blood
from alimentary canal passes through
liver (explaining liver most common site
for alimentary canal cancers metastasis)
Liver: Histology
= 3 main components:
1. hepatocytes [liver‘s main cell type, accounting for around 80% of liver's volume,
playing a role in a wide variety of secretory, metabolic, and endocrine functions;
plates of hepatocytes called hepatic laminae radiate outward from portal vein in
each hepatic lobule] = from their central position, hepatocytes process nutrients, toxins,
and waste materials carried by blood: materials such as bilirubin processed and excreted
into bile canaliculi, other materials including proteins, lipids, and carbohydrates processed
and secreted into sinusoids or just stored in cells until needed
2. bile canaliculi [grooves in cell membranes between adjacent hepatocytes
accumulating bile produced by hepatocytes: from here, bile flows first into bile
ductules and then into bile ducts, uniting to form larger right and left hepatic
ducts, which themselves merge and exit liver as common hepatic duct, that joins
with cystic duct from gallbladder, forming common bile duct through which bile
flows into small intestine]
3. hepatic sinusoids [open, porous blood space formed by fenestrated capillaries from
nutrient-rich hepatic portal veins and oxygen-rich hepatic arteries, where
hepatocytes are tightly packed around, giving them easy access to the blood] =
combine and send blood to a central vein and then through hepatic vein into inf vena cava
(this means that blood and bile flow in opposite directions); also contain star-shaped
reticuloendothelial cells (Kupffer cells), phagocytes removing dead red and white blood
cells, bacteria, and other foreign material that enter sinusoids
Liver: Histology
Liver: Histology
Liver: Histology
Liver: Histology
portal triad = distinctive arrangement around perimeter of hepatic lobules,
consisting of 3 basic structures: a bile duct, a hepatic artery branch, and a hepatic
portal vein branch.
Liver: Histology
Liver: Histology
Liver: Histology
Liver: Histology
Liver: Histology
Liver: Histology
Liver: Histology
Liver: Histology
Liver: Histology
Liver: Histology
Liver: Histology
Liver: Bile
• lipids are hydrophobic (= do not dissolve in
water), before they can be digested in watery
environment of SI, large lipid globules must be
broken down into smaller lipid globules (=
emulsification)
• Bile = yellow-brown or yellow-green alkaline
solution (pH 7.6 to 8.6) mixture of water, bile
salts, bile pigments, phospholipids (such as
lecithin), electrolytes, cholesterol, and
triglycerides secreted (about lt/day) by liver to
accomplish emulsification of lipids in SI.
• bile salts and phospholipids = components most
critical to emulsification having a nonpolar
(hydrophobic) region as well as a polar
(hydrophilic) region [hydrophobic region
interacts with large lipid molecules, whereas
hydrophilic region interacts with watery chyme
in intestine: large lipid globules being pulled
apart into many tiny lipid fragments of about 1
μm , dramatically increasing surface area
available for lipid-digesting enzyme activity]
Liver: Bile
•
•
•
While most constituents of bile are eliminated in
feces, bile salts are reclaimed by enterohepatic
circulation: once bile salts reach ileum, they are
absorbed and returned to liver in hepatic portal
blood; hepatocytes then excrete bile salts into
newly formed bile.
bilirubin = main bile pigment [waste product
produced when spleen removes old or damaged red
blood cells from circulation, including proteins, iron,
and toxic bilirubin, transported to liver via splenic
vein of hepatic portal system]: proteins and iron
recycled, whereas bilirubin excreted in bile,
accounting for green color of bile, and transformed
by intestinal bacteria into stercobilin [=brown
pigment giving stool its characteristic color: in some
disease states, bile does not enter intestine,
resulting in white (‗acholic‘) stool with a high fat
content, since virtually no fats are broken down or
absorbed]
Hepatocytes work non-stop, but bile production
increases when fatty chyme enters duodenum and
stimulates secretion of gut hormone secretin.
Between meals, bile is produced but conserved:
valve-like hepatopancreatic ampulla closes, allowing
bile to divert to gallbladder, where it is
concentrated and stored until next meal.
Liver &
Pancreas
PANCREAS ANATOMY
=
soft,
oblong,
glandular organ lying
transversely
in
retroperitoneum behind
stomach: head nestled
into
“c-shaped”
curvature of duodenum
with body extending to
left about 15 cm and
ending as a tapering
tail in hilum of spleen
[curious
mix
of
exocrine
(secreting
digestive enzymes) and
endocrine
(releasing
hormones into blood)
functions]
esophagus
stomach
ductus choledocus
pancreas
duodenum
duct of
Santorini
duct of
Wirsung
Pancreas
•
exocrine part = arises as little grape-like cell clusters, each called an acinus (plural =
acini), located at terminal ends of pancreatic ducts, secreting enzyme-rich pancreatic
juice into tiny merging ducts that form 2 dominant ducts [larger duct, Wirsung, fuses
with common bile duct (carrying bile from liver and gallbladder) just before entering the
duodenum via a common opening (hepatopancreatic ampulla)]; smooth muscle sphincter of
hepatopancreatic ampulla controls release of pancreatic juice and bile into small
intestine; second and smaller pancreatic duct, the accessory duct (duct of Santorini),
runs from pancreas directly into duodenum, approximately 1 inch above hepatopancreatic
ampulla.
Pancreas
• Scattered through sea of
exocrine acini are small
islands of endocrine cells,
islets of Langerhans,
producing
hormones
pancreatic polypeptide,
insulin,
glucagon,
and
somatostatin
PANCREATIC SECRETIONS
1. PROTEASES (70%)
Endopeptidases (trypsin, chymotrypsin, elastases)
Exopeptidases (carboxypeptidases)
trypsinogen
trypsin
activates all other precursors
enterokinase
(duct walls)
2. NUCLEASES (DNAase, RNAase)
3. PANCREATIC AMYLASE (hydrolyse starch and glycogen)
4. PANCREATIC LIPASE (triglycerides
fatty acids and glycerol)
REGULATION OF SECRETION
1. SECRETIN
food in
stomach
release of
stomach acid
into duodenum
release of secretin
into blood by
duodenal cells
secretion of
bicarbonate
by duct cells
alkaline pH
(ideal for
pancreatic enzymes)
2. PANCREOZYMIN (cholecystokinen)
amino acids and
fats in intestine
release of pancreozymin
by intestinal mucosa
into blood
relase of pancreatic enzymes
into the intestine
3. GASTRIN
food in stomach
gastrin secretion
by stomach mucosa
4. AUTONOMIC INNERVATION (vagus nerve)
release of pancreatic enzymes
into the intestine
Pancreas: Histology
Pancreas: Histology
islet of
Langerhans
pancreatic acini
islet of
Langerhans
pancreatic lobe
BV
Pancreas: Histology
LARGE SECRETORY DUCT
INTERLOBULAR DUCT
PANCREATIC SECRETORY DUCTS
simple
cuboidal
epithelium
acinus
simple
columnar
epithelium
Exocrine Pancreas: Histology
pyramidal
secretory
basal basophilia
cell
(rough ER)
acinus
merocrine secretion
(exocytosis)
zymogen
granules
centroacinar
cells
blood
vessel
condensing
vacuoles
golgi
vesicles
intercalated
duct
rough
endoplasmic
reticulum
nerve
interlobular
duct
zymogen
granules
golgi
apparatus
Pancreas: Histology
INTERCALARY DUCTS AND CENTROACINAR CELLS
intercalary duct
centroacinar
cell
intercalary
duct
PANCREATIC EXOCRINE SECRETORY CELL
zymogen
granules
centroacinar
cell
CELL BIOLOGY OF PANCREATIC SECRETION
1. SYNTHESIS
2. SEGREGATION
14
C -leucine + tRNA
mRNA for
chymotrysinogen
14
C-amino-acyl tRNA
ribosomes
mRNA
ribosomes
polypeptide
chymotrysinogen
RER cisterna
6. DISCHARGE
3. INTRACELLULAR TRANSPORT
exocytosis
RER
transitional
elements
5. INTRACELLULAR
STORAGE
zymogen
granules
4. CONCENTRATION
golgi
apparatus
H2O
H2O
condensing vacuoles
golgi vesicles
ISLET OF LANGERHANS
alpha cell
(glucagon)
vascular pole
(secretion by exocytosis)
acinus
beta cell
beta
cell
(insulin)
fenestrated
capillary
blood
capillary
INSULIN- increases membrane
permeability to glucose
GLUCAGON - promotes glycogenolysis
promotes glycogenesis
decrease blood glucose levels
increases blood glucose levels
“ ANTAGONISTIC HORMONES”
alpha
cell
Pancreas: Histology
Pancreas: Histology
ISLET OF LANGERHANS
Pancreas: Histology
ISLET OF LANGERHANS - TEM
STAINED ALPHA AND BETA CELLS
ALPHA CELLS
BETA CELLS
Pancreas: Histology
INTERCALARY DUCTS AND CENTROACINAR CELLS
intercalary duct
centroacinar
cell
intercalary
duct
Pancreas: Histology
Gallbladder
= 8–10 cm (~3–4 in) long, nested in a shallow area on posterior aspect of
right liver lobe , muscular sac storing, concentrating, and, when stimulated,
propelling bile into duodenum via common bile duct, divided into 3 regions:
1.fundus = widest portion, tapering medially into 2.body, which in turn
narrows to become 3.neck, angling slightly superiorly as it approaches
hepatic duct;
 cystic duct = 1–2 cm (less than 1 in) long,
turning inferiorly as it bridges neck and
hepatic duct.
 simple columnar epithelium organized in
rugae, similar to those of stomach,
absorbing water and ions from bile and
concentrating it by up to 10-fold: no
submucosa in gallbladder wall and wall‘s
middle, muscular coat is made of smooth
muscle fibers [when contracting,
gallbladder‘s contents ejected through
cystic duct and into bile duct]
 visceral peritoneum reflected from liver
capsule holds gallbladder against liver and
forms outer coat of the gallbladder.
Gallbladder: Histology
Liver, Pancreas, and Gallbladder
Anatomy-Histology Correlate
• The liver and gallbladder play important roles in
digestion via the production and storage of bile.
The liver is also the major organ for metabolism
and detoxification. The pancreas also produces
digestive enzymes to break down proteins, sugars,
and fats.
• The processes described above are the exocrine
functions of the liver and gallbladder. But they
also have endocrine roles, secreting compounds
into the bloodstream. The hepatocytes produce
albumin, fibrinogen, and thrombin, for example.
The pancreatic islets produce insulin, glucagon, and
somatostatin.
Liver, Pancreas, and
Gallbladder
Anatomy-Histology
Correlate
 The liver, gallbladder, and pancreas receive
blood supply from the celiac trunk. One
main branch is the common hepatic artery,
leading to the hepatic artery proper that
branches into left and right hepatic
arteries to supply the liver. The right
hepatic artery gives off the cystic artery
to supply the gallbladder.
 The pancreas is supplied by multiple
vessels. The body and tail are supplied by
the dorsal, inferior, and great pancreatic
arteries, which all branch off the splenic
artery (another main branch of the celiac
trunk). The head, neck, and uncinate process
are supplied by anastomoses of arteries
branching off the celiac trunk and sup
mesenteric artery. The gastroduodenal
artery, from the common hepatic artery,
divides into the anterior and posterior
superior pancreaticoduodenal arteries.
They anastomose with inferior branches of
the inferior pancreatico-duodenal artery
from the superior mesenteric artery. The
same arteries supply the duodenum.
Liver, Pancreas,
and Gallbladder
AnatomyHistology
Correlate
-The liver has diaphragmatic and visceral surfaces which contact the diaphragm and abdominal viscera, respectively. Note
the right triangular, left triangular, and coronary ligaments that attach to the diaphragm. Note also the bare area not
covered by peritoneum. Anteriorly, there is a fold of peritoneum connecting the liver to the umbilicus called the falciform
ligament, which contains the round ligament or ligamentum teres. It is the remnant of the umbilical vein that brought
oxygenated blood from the placenta to the fetus heart. The ligamentum venosum is the remnant of the fetal ductus venosus
that shunted blood from the umbilical vein to the inferior vena cava to bypass the liver. In the adult liver, the porta hepatis
includes the hepatic arteries from the hepatic artery proper, the hepatic portal vein, and the hepatic and cystic ducts
joining to form the common bile duct.
- The portal vein brings nutrients and other compounds absorbed by the GI tract to be stored and/or processed.
- Anatomical lobes: Note how the inferior vena cava, gallbladder, ligamentum teres, ligamentum venosum, and porta hepatis
form an ―H‖ shape on the visceral surface. It divides the liver into 4 anatomical lobes based on outer appearance – the right,
left, caudate, and quadrate lobes.
- Functional lobes: These are based on the distribution of the hepatic arteries, portal vein, and hepatic bile duct. The
inferior vena cava and the gallbladder serve as the dividing line between the functional right and left lobes.
Liver, Pancreas,
and Gallbladder
Anatomy-Histology
Correlate
- The liver is divided into many hepatic lobules. Inflow to the liver
involves hepatic arteries, which bring oxygenated blood to hepatic
tissue, and portal veins, which bring nutrients and other compounds
absorbed by the GI tract to be processed and/or stored in the liver.
Outflow also involves two routes – hepatic veins which drain into the
inferior vena cava and the common hepatic duct which joins the cystic
duct and empties bile into the duodenum.
- Major characteristics of the liver are portal triads (labeled ―portal‖
in bottom left and shown in the middle) and central veins (labeled in
bottom left and shown in the right). Red arrows indicate direction of
blood flow within blood sinusoids flanking cords of liver cells.
- Note the portal triad contains 1) the portal vein, 2) the hepatic
artery, and 3) the bile duct. Each has its typical appearance. The
central vein is lined with endothelial cells, with perforations into which
the sinusoids empty.
Liver, Pancreas, and Gallbladder
Anatomy-Histology Correlate
•
The central veins lead to sublobular veins, which reach collecting veins, hepatic veins,
and finally the inferior vena cava. The venous outflow of the liver has no regard to
the organization of the lobules.
•
The liver sinusoids are shown in higher magnification in the bottom left. They are
dilated, capillary-like vessels lined by fenestrated, discontinuous epithelium (labeled
―e‖). Interspersed among the endothelial cells are Kupffer cells (labeled ―k‖), which are
fixed macrophages within the hepatic tissue. They have distinct cytoplasm that may
enter the sinusoidal lumen and function like other macrophages within the body. They
also break down damaged red blood cell hemoglobin.
•
In the bottom middle panel, there are many spaces between the hepatocytes and
sinusoidal epithelial cells marked by arrowheads. They are referred to the space of
Disse where exchange between hepatocytes and blood flow takes place.
•
Once again, in the bottom right, we review the Kupffer cell, endothelial cell of the liver
sinusoid, and the space of Disse.
- The liver lobules can be defined in 3 ways:
- 1) Classic lobule – centered around the central vein with the portal
triads at each corner. Shown below on the left, the classic lobule may not
always be hexagonal in shape.
- 2) Portal lobule (not shown) – centered on the portal triad, based on bile
secretion, and approximately triangular in shape.
- As mentioned earlier, the
liver has both endocrine and
exocrine functions. The
various proteins that
hepatocytes secrete enter the
bloodstream via the liver
sinusoids. The liver also
secretes bile in the
conventional exocrine fashion.
- The hepatocytes secrete
bile into sealed extracellular
spaces called bile canaliculi.
The typical ―chicken-wire‖
appearance is more easily
visualized with silver stain.
- 3) Liver acinus of Rappaport – this is the most functionally important
classification. Shown below on the right, the acinus is roughly oval in shape
with 2 central veins and 2 portal triads on opposite ends. Based on the
blood flow within hepatic tissue, the acinus is divided into 3 zones. Cells in
different zones are specialized for different activity. Zone 1 cells, being
closest to the portal triads and hence most oxygenated blood, have the
most drug-metabolizing enzymatic activity. Following that same reasoning,
zone 3 hepatocytes near the central veins are most susceptible to
ischemia.
- Once again, inflow to the liver involves
oxygenated blood via hepatic arteries and
absorbed nutrients and compounds from
the GI tract via the hepatic portal veins.
- All venous drainage from the GI tract
and abdominal visceral organs enters the
portal system back to the liver. The
overall order is as following: arteries →
capillaries → veins → portal vein →
hepatic sinusoids → veins → vena cava →
heart.
- In contrast, the caval system is as
following: arteries → capillaries → veins
→ vena cava → heart. Obviously, this is
the circulatory system within the rest of
the body.
- The portal and caval system are not
exclusive from each other. There are 4
sites of portocaval anastomoses:
- 1) esophageal veins
- 2) paraumbilical veins
- 3) rectal veins
- 4) retroperitoneal veins
- If there is liver damage or cirrhosis –
accumulation of fibrous tissue that
constricts the sinusoids – there may be
portal hypertension. This may lead to
varicose veins at the 4 sites of
anastomoses.
- The gallbladder is found under the right lobe of the liver. Its
function is to store bile produced by the liver, which leaves via the
cystic duct. It also enters the gallbladder in the cystic duct,
traveling retrograde when the bile is not needed for digestion. Note
the fundus, body, neck, and infundibulum of the gallbladder.
- Note the right and left hepatic ducts coming together as the
common hepatic duct, joining the cystic duct to form the common
bile duct. This descends to the 2nd part of the duodenum, is joined
by the pancreatic duct, and empties its contents into the duodenal
lumen via the major duodenal papilla.
- The gallbladder is supplied by the cystic artery, which is
extremely important to find during a cholecystectomy. In most
people it branches off the right hepatic artery, but could also come
off the left hepatic, proper hepatic, or gastroduodenal arteries.
- Note the extensive folds of mucosa extending into the lumen,
consisting of tall, simple columnar epithelium. The underlying
connective tissue is comprised of lamina propria, with no distinctly
defined submucosa. There are scattered bundles of smooth muscle
in the muscularis. The adventitia has rather dense connective tissue
connecting the gallbladder to the liver.
- Finally, we will look at the pancreas. To review:
The head of the pancreas and duodenum are
supplied from both the celiac trunk and the
superior mesenteric artery.
- The body and tail of the pancreas are mostly
supplied by branches of the splenic artery,
namely the dorsal, greater, and inferior
pancreatic arteries.
- Piece of advice: It can be very confusing when
identifying these arteries. First orient yourself,
note whether the duodenum is in anatomical
position or reflected (as it is on the bottom
left), and identify where the arteries branch
from and where they lead.
- The pancreas contains multiple ducts, but the main pancreatic
duct runs from the tail to the head of the pancreas. There may be a
smaller accessory pancreatic duct. They join the common bile duct
to empty into the duodenum. The pancreas is retroperitoneal.
- Histologically, we can see the septa (S) between pancreatic lobules
with interlobular ducts (D). As mentioned above, the pancreas also
has both exocrine and endocrine functions. Most of the bottom left
panel is filled with exocrine pancreatic tissue. Secretory portions
are called acini. The scattered endocrine islets of Langerhans (I)
are paler staining.
- An islet is magnified in the bottom right. It is a compact mass of
epithelial cells that receive rich vascular supply (arrows). It is
typically very difficult to identify the different cell types in the
islets. Briefly, the alpha cells secrete glucagon, the beta cells
secrete insulin, and the delta cells secrete somatostatin.
-Once again, most of the pancreas contains exocrine acini. Pancreatic enzymes are very diverse, including extremely
efficient proteases, lipases, and amylases.
- Separate acini are shown in the left. The pancreatic acinar or secretory cells are polarized, meaning the basal
portions are filled with basophilic rough ER. The apical regions are filled with zymogen granules that contain many
stored pro-enzymes.
- Centroacinar cells, with paler staining, can be seen in the middle of some acini and mark the beginning of the duct
system (marked ―A‖ in the middle panel). They converge at ―B‖ to form intercalated ducts, marked as ―C‖. The
intercalated duct cells may be hard to identify, but they actively pump water and bicarbonate into the duct lumen.
Intercalated ducts empty into interlobular ducts, marked as ―small duct‖ in the bottom right, which lead to the main
pancreatic duct.
luca.ansaloni@unibg.it
lansaloni@asst-pg23.it