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Anatomy of Digestive system
By- Dureti Godanna 1
1/9/2024

Objectives
At the end of this session you are expected to
?List organs of digestive system
? Locate all organs of digestive system anatomically.
?Understand the anatomy of digestive organs in relation to other organ
s
?Understand the Vasculatures and innervation of digestive organs
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Digestive system
Functional activities
Ingestion
Mastication
Deglutition
Digestion
Peristalsis
Absorption
Defecation
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Organs of digestive system
Two groups of organs
? The gastrointestinal (GI) tract
?Accessory digestive organs
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GI tract and Accessory digestive organs
GI tract
?Approximately 9m long
?Extends from the mouth to the anus.
Oral cavity Stomach
Pharynx Small intestine,
Esophagus Large intestine.
.
? Accessory organs
Teeth
Liver
Tongue
Gallbladder
Salivary glands
Pancreas
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Layers of the GI Tract
? The wall of the GI tract from the lower esophagus to the anal canal
has the same basic, four-layered arrangement of tissues.
? The four layers of the tract from deep to superficial.
? Mucosa
? Sub mucosa
? Muscularis
? Serosa/adventitia
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Mouth
? It also known as the oral or buccal cavity .
? It is formed by the cheeks, lips, hard and soft palates, tongue.
The oral cavity is divided into
? Vestibule And Mouth proper.
The vestibule
? is the area b/n the cheeks and lips externally and the gums and
teeth internally.
The mouth proper
? is the space bounded by the teeth.
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Tongue
? Occupies the floor of the mouth and fills the oral cavity when
mouth is closed
Functions
? Mixing food with saliva and forming the bolus
? Initiation of swallowing, and speech
Note: Lingual frenulum secures the tongue to the floor of the
mouth
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Lingual papillae
Superior surface bears three types of papillae
? Filiform - give the tongue roughness and provide friction
? Fungiform - scattered widely over the tongue and give it a
reddish hue
? Circumvallate - V-shaped row in back of tongue
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Teeth
?Humans as other mammals have hetrodont dentition.
i.e. the teeth vary structurally and are adapted to handle food in
different ways.
?An adult human has four types of teeth:
? Incisors
? Canines (cupids)
? Premolars (bicuspids)
? Molars (six pairs)
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Teeth
? The teeth, are accessory digestive organs located in sockets of the al
veolar processes of the mandible and maxillae.
? The alveolar processes are covered by the gingivae ( gums).
? Which extend slightly into each socket.
? The sockets are lined by the periodontal ligament (periodontal mem
brane)
? Which consists of dense fibrous connective tissue that anchors the te
eth to the socket walls and acts as a shock absorber during chewing.
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Dentitions
Humans have two dentitions
i.e., two sets of teeth develop in a person��s life time.
Deciduous (milk) teeth
?Begin to develop in each jaw before birth.
?The first teeth usually erupt at 6 to 8 monthly after birth
beginning with the incisor.
?Eruption of these teeth have completed by 2 ? years.
?20 in number
?Formula for deciduous dentition of humans
?I-2/2, C -1/1 , DM -2/2 = 10 x 2 = 20 (DM = deciduous molar)
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Permanent teeth
? Replace the deciduous teeth at predictable sequence from age 6
to 17.
? The third molars, or wisdom teeth, are the last to erupt between
the ages of 17 to 25.
? 32 in number
? Formula for permanent dentition
? I- 2/2, C- 1/1, P- 2/2, m-3/3 = 16x2 = 32
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Parts of teeth
? A tooth consists of a crown and one or more roots.
? The crown Functional part that is visible above the gum.
? The root is the unseen portion that supports and fastens the tooth in
the jawbone.
? The root - attached to the tooth-bearing bone the alveolar processes
of the jaws by a fibrous ligament called the periodontal ligament.
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Salivary Glands
?Secret saliva.
Saliva has various functions:
? Serves as a solvent
? Cleansing the teeth
? Dissolving food chemicals so that they can be tasted
? Contains enzymes which digest starch
? Contains mucous which lubricates the pharynx to facilitate
swallowing
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Salivary Glands��..
? It is a gland that releases a secretion called saliva into the oral cavity
.
? The mucous membrane of the mouth and tongue contains many sma
ll salivary glands.
? Open directly or indirectly via short ducts to the oral cavity.
? These glands include labial, buccal and palatal glands in the lips, ch
eeks, and palate, respectively.
? Lingual glands in the tongue, all of which make a small contributio
n to saliva.
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Salivary Glands
? Most saliva is secreted by the major salivary glands.
? Lie beyond the oral mucosa, into ducts that lead to the oral cavity.
The parotid gland
? Largest salivary glands
? Found between the skin and the masseter muscle.
? Located anterior and inferior to the auricle.
? The parotid duct, which is about 5cm long drains into the oral
cavity opposite the 2nd upper molar.
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Parotid gland ��
? Each secretes saliva into the oral ca
vity via a parotid duct
? Pierces the Buccinator muscle to op
en into the vestibule opposite the se
cond maxillary (upper) molar tooth.
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The pharynx
? It is funnel-shaped tube that extends fro
m the internal nares to the esophagus p
osteriorly and to the larynx anteriorly.
? The pharynx consists of external and
internal muscles.
? The external include the superior,
middle inferior muscles
? Which constrict the pharynx during
swallowing.
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Pharynx��
? These muscles elevate the larynx and pharynx in swallowing and
during speaking.
? The inferior constrictor muscle prevents air from entering the
esophagus during breathing
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Esophagus
? This is a collapsible muscular
tube (25cm).
? Connects the pharynx to the
stomach.
? Located posterior to the trachea.
? It passes through the diaphragm
is an opening called esophageal
hiatus.
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Esophagus
? The upper third of the esophagus contains
skeletal muscle.
? The middle third contains both skeletal and
smooth muscle, and the terminal portion
contains only smooth muscle.
? The terminal portion of the esophagus is
slightly narrowed due to the presence of the
lower esophageal (gastro esophageal)
sphincter.
? This prevents regurgitation of stomach
contents into the esophagus. 34
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Peritoneum
? The peritoneum is the largest serous membrane of the body.
? It consists of a layer of simple squamous epithelium with an underlyi
ng supporting layer of areolar connective tissue.
? The peritoneum is divided into the parietal and visceral peritoneu
m
? Parietal peritoneum lines the wall of the abdominal cavity.
? Visceral peritoneum covers some of the organs in the cavity and is
their serosa
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Peritoneal cavity
? The slim space containing lubricating s
erous fluid.
? Found between the parietal and viscer
al portions of the peritoneum.
? In certain diseases, the peritoneal cavit
y may become distended by the accum
ulation of several liters of fluid, a cond
ition called ascites
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Stomach
? The stomach is a J-shaped pouch and is the most distensible part
of the GIT.
? Found directly inferior to the diaphragm in the abdomen.
? The stomach connects the esophagus to the duodenum (the first
part of the small intestine)
? The functions of the stomach are:
? Store food as it is mechanically churned with gastric
secretions
? Initiate the digestion of proteins
?Move food into the small intestine as a chyme (pasty material)
?Secretion of gastric juice
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Anatomy of the Stomach
? The stomach has four main regions:
1. Cardia: surrounds the opening of th
e esophagus into the stomach.
2. Fundus: Rounded portion superior t
o and to the left of the Cardia
3. Body: Inferior to the fundus is the la
rge central portion of the stomach.
4. Pyloric part
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Pyloric part
It is divided in to three regions
?The first region is pyloric antrum,
connects to the body of the stomach.
?The second region is pyloric canal
?The pylorus which in turn connect
s to the duodenum.
?When the stomach is empty, the m
ucosa lies in large folds or rugae.
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Anatomy of the Stomach��..
? The concave medial border of the stomach is called the lesser curv
ature.
? The convex lateral border is called the greater curvature.
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Histology of the Stomach
? The gastric glands contain three types of
exocrine gland cells
? Secrete their products into the stomach lu
men:
? Mucous neck cells , Chief cells and Parie
tal cells
? mucous neck cells secrete mucus
? Parietal cells produce intrinsic factor (ne
eded for absorption of vitamin B12) and
hydrochloric acid.
? The chief cells secrete pepsinogen and ga
stric lipase. 48
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Vasculature of the stomach
? The right and left gastric
arteries run along the lesser
curvature while the right and
left gastro-omental arteries
run along the greater
curvature.
? The fundus and upper body of
stomach receive blood from the
short and posterior gastric
arteries branches of the splenic
artery. 49
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Small intestine
? Most digestion and absorption of nutrients
occur in a long tube called the small intest
ine.
? Its length alone provides a large surface ar
ea for digestion and absorption.
? The area is further increased by circular fo
lds, villi, and microvilli.
? The small intestine begins at the pyloric sp
hincter of the stomach.
? Opens into the large intestine.
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Small intestine
? It is the portion of the GIT b/n
the pyloric sphincter of the
stomach and the ileocecal valve
opening into the large intestine.
? It is the site where digestion is
completed and nutrients are
absorbed.
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Functions of small intestine
? Reception of the secretions from the liver and pancreas
? Chemically breakdown of chyme
? Absorption of nutrients
? Transportation of the remaining undigested material to the large
intestine.
The small intestine is divided into three regions
? Duodenum
? Jejunum
? Ileum
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The duodenum
? It is a relatively fixed C- shaped tube (25cm long)
? Extend from the pyloric sphincter to the duodeno jejunal flexure.
? Its left concave surface receives bile secretions through the
common bile duct from the liver and gallbladder, and pancreatic
secretions through the duct of the pancreas.
? Both ducts unite to form a common entry into the duodenum
called the hepatopancreatic ampulla (or ampulla of Vater).
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The blood supply to the duodenum
It comes from two sources.
?The first and second part are supplied by the gastro duodenal arte
ry.
?The third and fourth parts are supplied by SMA.
?Duodenal veins, follow the arteries and drain into the portal vein.
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? The jejunum
? (1m long) extends from the duodenum to the ileum.
? It has a slightly larger lumen and more internal folds than the
ileum.
? The ileum
? (2m long) makes up the remaining part of the small intestine.
?The terminal portion of the ileum empties into the medial side of
the cecum through the ileocecal valve.
?The walls of the ileum have an abundance of lymphatic tissue
aggregated into nodules called mesenteric (payer��s) patches
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Characteristics of Jejunum &
ileum
Characteristics Jejunum ileum
color Deeper red Paler pink
caliber 2-4cm 2-3cm
wall Thick and heavy Thin and light
Vascularity Greater Lesser
Fat in mesentery less more
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Blood supplies
The jejunum and ileum have:
?Arterial supply from the (superior mesenteric artery) SMA.
?The SMA runs between the layers of the mesentery and sends many
branches to the jejunum and ileum..
?Venous drainage from the (superior mesenteric vein) SMV .
?The SMV lies anterior and to the right of the SMA in the root of the
mesentery.
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Large Intestine
? The large intestine is the terminal portion of the GI tract.
? It is about 1.5m long begins at the terminal end of the ileum and te
rminates at the anus
? Has 6.5 cm in diameter in living humans
? The large intestine has little or no digestive functions.
It functions
? Absorb water and electrolytes from the remaining chyme
? Forms stores
? Expels feces from the body.
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Large Intestine
? The large intestine is structurally divided into
o Cecum
o Colon
o Rectum
o Anal canal.
? The cecum, the first part of the large intestine that is continuous with
the ascending colon, has a blind intestinal pouch(appendix) in the
right lower quadrant.
? The transverse colon, the largest and most mobile part of the large
intestine
? Crosses the abdomen from the right colic flexure to the left colic fle
ure.
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Large Intestine
? Ascending colon ascends on the right side of the abdomen.
? Reaches the inferior surface of the liver.
? Turns abruptly to the left to form the right colic (hepatic) flexure.
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The rectum
? It is about 15 cm in length
? Lies anterior to the sacrum and coccyx.
? The terminal 2�C3 cm of the large intestine is called the anal canal.
? The opening of the anal canal to the exterior called the anus.
? It is guarded by an internal anal sphincter of smooth muscle (involu
ntary) and an external anal sphincter of skeletal muscle (voluntary).
? Normally these sphincters keep the anus closed except during the eli
mination of feces.
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Accessory digestive organs
? These organs aid in the chemical break down of food.
These are
? Liver
? Gallbladder
? pancreas
? The liver and pancreas function as exocrine glands .
? Because their secretions are transported to the lumen of the GIT
via ducts.
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Liver
? The liver is the largest internal
organ of the body
? Weighing about 1.3 kg in an
adult.
? It is reddish-brown in color
because of its great vascularity.
? The liver has two major lobes
1. The right lobe
2. The left lobe
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The liver carries out numerous functions:
osynthesis, storage, and release of glycogen
osynthesis of blood proteins
oPhagocytosis of old red blood cells
oDetoxify toxic substances
oproduction of bile.
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Liver��.
? The liver is inferior to the diaphragm
? Occupies most of the right hypochondriac and part of the epigastric
regions of the abdominopelvic cavity
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Gallbladder
? This is a pear-shaped sac that is located in a depression of the posteri
or surface of the liver.
? It is 7�C10 cm long and typically hangs from the postero inferior mar
gin of the liver.
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Gall bladder
? It is a sac like organ attached to the inferior surface of the liver.
? It stores and concentrates bile, which drains to it from the liver
? Bile is a yellowish-green fluid
? Bile is continuously produced by the liver and drains through the
hepatic and common bile ducts to the duodenum for the
emulsification and absorption of fats.
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Plain abdominal X-ray abdomen
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