Human AnatomyBio 22

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Human Anatomy-Bio 22 Lecture 25 The Digestive
System Presented by Tealia Davis, MSc
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Digestive System An Overview

• The alimentary canal or gastrointestinal (GI)
  tract digests and absorbs food
• mouth, pharynx, esophagus, stomach, small
  intestine, and large intestine
• teeth, tongue, gallbladder, salivary glands,
  liver, and pancreas

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Digestive System An Overview
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Peritoneum and Peritoneal Cavity
serous membrane of the abdominal cavity
covers external surface of most digestive
organs lines the body wall Peritoneal
cavity Lubricates digestive organs Allows
them to slide across one another
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Mouth

• Oral or buccal cavity
• Is bounded by
• Has the oral orifice as its anterior opening
• Is continuous with the posteriorly
• To withstand abrasions
• The mouth is lined with stratified squamous
  epithelium
• The gums, hard palate, and dorsum of the tongue
  are

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Anatomy of the Mouth
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Anatomy of the Mouth
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Palates
underlain by palatine bones and palatine
processes of the maxillae Assists the tongue in
chewing Slightly corrugated on either side of
the raphe (midline ridge) mobile fold
formed mostly of skeletal muscle Closes off the
during swallowing Uvula projects downward
from its free edge Palatoglossal and
palatopharyngeal arches form the borders of the
fauces
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Tongue
Functions include Gripping and repositioning
food during chewing Mixing food with saliva and
forming the bolus Initiation of swallowing, and
speech change the shape of the tongue alter
the tongues position secures the tongue to the
floor of the mouth
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Esophagus
Muscular tube going from the to the Travels
through the and pierces the Joins the
stomach at the
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Stomach
Chemical breakdown of proteins begins and food is
converted to surrounds the cardiac
orifice dome-shaped region beneath the
diaphragm midportion of the stomach
made up of the antrum and canal which terminates
at the pylorus The pylorus is continuous with
the duodenum through the
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Stomach
entire extent of the convex lateral
surface concave medial surface runs
from the liver to the lesser curvature
drapes inferiorly from the greater curvature to
the small intestine
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Stomach
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Microscopic Anatomy of the Stomach
has an additional oblique layer that
Allows the stomach to churn, mix, and pummel
food physically Breaks down food into smaller
fragments Epithelial lining is composed
of Goblet cells that produce a coat of The
mucous surface layer traps a bicarbonate-rich
fluid beneath it Gastric pits contain gastric
glands that secrete
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Microscopic Anatomy of the Stomach
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Glands of the Stomach Fundus and Body
Gastric glands of the fundus and body have a
variety of secretory cells Mucous neck cells
secrete Parietal cells secrete Chief cells
produce
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Gross Anatomy of the Small Intestine
Runs from to the Has three subdivisions The
bile duct and main pancreatic duct Join the
duodenum at the Are controlled by the The
extends from the duodenum to the ileum The
ileum joins the large intestine at the
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Microscopic Anatomy of the Small Intestine
Structural modifications of the small intestine
wall increase surface area deep circular
folds of the mucosa and submucosa
fingerlike extensions of the mucosa tiny
projections of absorptive mucosal cells plasma
membranes
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Microscopic Anatomy of the Small Intestine
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Histology of the Small Intestine Wall
The epithelium of the mucosa is made up
of Absorptive cells and goblet cells
Enteroendocrine cells Interspersed T cells
called intraepithelial lymphocytes (IELs) IELs
immediately release cytokines upon encountering
Ag Cells of intestinal crypts secrete intestinal
juice are found in the submucosa in the
duodenum secrete alkaline mucus
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Liver

• The largest gland in the body
• Superficially has four lobes
• The falciform ligament
• Separates the lobes anteriorly
• Suspends the liver from the diaphragm and
  anterior abdominal wall
• The ligamentum teres
• Is a remnant of the fetal
• Runs along the free edge of the falciform
  ligament

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Associated Structures of the Liver
The lesser omentum anchors the liver to the
stomach The hepatic blood vessels enter the
liver at the The rests in a recess on the
inferior surface of the right lobe Bile leaves
the liver via Bile ducts, which fuse into
the The common hepatic duct, which fuses with
the These two ducts form the
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Associated Structures of the Liver
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Microscopic Anatomy of the Liver
Hexagonal-shaped liver lobules are the structural
and functional units of the liver Composed of
hepatocyte (liver cell) plates radiating outward
from a central vein Portal triads are found at
each of the six corners of each liver
lobule Portal triads consist of a and
supplies oxygen-rich blood to the liver
carries venous blood with nutrients from
digestive viscera enlarged, leaky
capillaries located between hepatic plates
hepatic macrophages found in liver sinusoids
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Microscopic Anatomy of the Liver
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The Gallbladder
Thin-walled, green muscular sac on the ventral
surface of the liver by absorbing its water
and ions Releases bile via the , which flows
into the
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The Pancreas

• Lies deep to the greater curvature of the stomach
• The head is encircled by the and the tail
  abuts the
• Exocrine function
• Secretes pancreatic juice which breaks down all
  categories of foodstuff
• Acini (clusters of secretory cells) contain
  zymogen granules with digestive enzymes
• The pancreas also has an endocrine function
  release of

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The Large Intestine
Has three unique features three bands of
longitudinal smooth muscle in its
muscularis pocketlike sacs caused by the
tone of the teniae coli fat-filled pouches
of visceral peritoneum Is subdivided into the
The saclike cecum Lies below the ileocecal
valve in the right iliac fossa Contains a
wormlike vermiform appendix
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The Large Intestine
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Colon
Has distinct regions ascending colon, hepatic
flexure, transverse colon, splenic flexure,
descending colon, and sigmoid colon The
transverse and sigmoid portions are anchored via
mesenteries called mesocolons The joins The
anal canal, the last segment of the large
intestine, opens to the exterior at the anus
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Microscopic Anatomy of the Large Intestine

• Colon mucosa is simple columnar epithelium except
  in the anal canal
• Has numerous deep crypts lined with
• Anal canal mucosa is stratified squamous
  epithelium
• Anal sinuses exude mucus and compress feces
• Superficial venous plexuses are associated with
  the anal canal
• Inflammation of these veins results in itchy
  varicosities called hemorrhoids

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Structure of the Anal Canal