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The lungs are the spongy, pyramidal-shaped organs that house the bronchial
tree and the extensive pulmonary vascular network. Each lung is surrounded
by a thin mesothelial covering, the visceral pleura, and sits on either side of
Lungs
the heart within the thoracic cavity. The vascular and respiratory passageways enter each lung on
its medial aspect at the hilum. The wide base of the lung sits on the diaphragm inferiorly and
tapers to a narrow apex superiorly. The right lung has three lobes and the left lung two lobes.
Right lung
Lateral view, anterior to the right
Right lung
Medial view, anterior to the left
Photomicrograph of lung tissue
100x
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1 Apex
2 Superior lobe
3 Middle lobe
4 Inferior lobe
5 Oblique fissure
6 Transverse fissure
7 Segmental (tertiary) bronchus
8 Pulmonary artery
9 Pulmonary vein
10 Costal impression
11 Diaphragmatic surface
12 Aortic impression
13 Cardiac notch
Left lung
Lateral view, anterior to the left
Left lung
Medial view, anterior to the right
Photomicrograph of lung tissue
100x
14 Hilum
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16 Small artery
17 Alveolar spaces
18 Blood vessels with rbcs
19 Lingula
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Cast of Trachea and Bronchial Tree
Latex cast of respiratory passageways of trachea and lungs of a dog
Anterior view at left, posterior view at right
1 Trachea
2 Right main (primary) bronchus
3 Left main (primary) bronchus
4 Lobar (secondary) bronchus
5 Segmental (tertiary) bronchus
6 Branching bronchiole network
The cast below is from a large dog’s lungs and is approximately the same size as human lungs. The casts were created by
forcing liquid latex into the respiratory passageways of the lungs and then letting the latex harden. The lungs were then
placed in a weak acid until the organic tissue of the lungs was digested away. These views of the cast allow you to visualize
the extensive nature of the bronchial tree as it branches out to the larger alveolar passageways within the lungs. The
smaller alveolar spaces did not get incorported into the casts.
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REAL ANATOMY
18 Digestive System
Th e digestive system is the extensive environmental interface that makes
it possible to transfer nutrients, water, and electrolytes
from the food we eat into the body’s internal environment. Th is is made possible by a complex lining,
which through a series of folds and a variety of small
to microscopic projections greatly increases the surface interface between the digested contents within
the gastrointestinal organs and the numerous small
capillaries beneath this lining. To better appreciate
the degree of this surface increase, realize that the
average total surface area of the skin of an adult
human is about 20 square feet, while the surface
area of the digestive system is approximately 2,500
square feet, or about the size of a tennis court. To
make the transfer across this extensive surface area
possible, the food we eat must be broken down
into small molecules that can be absorbed from the
digestive tract into the circulatory system, which
then distributes the molecular metabolites to the
cells. Th erefore, the digestive organs also function in
the mechanical and chemical breakdown of the food.
Developmentally the digestive system begins as a
simple tube called the gut tube or gut. As this simple
tube develops into the highly convoluted organs of the
adult anatomy, it undergoes structural changes that account for its various functions. Th ough these structural
changes lead to diff erences in the tube from one region to
the next, there is a basic pattern of design throughout the
length of the tube. Th is structural pattern is responsible for
the general function of the digestive system. Modifi cations of
this pattern allow for the variation in structure and function
along its length. Th is chapter will highlight the structural variation and underlying design of the digestive system.
Find more information
about the digestive
system in
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Superfi cial dissection of abdominal viscera
Anterior view
Intermediate dissection of abdominal viscera
Anterior view
The digestive system begins at the mouth, where
food and drink enter this tubular organ system to be
processed by the teeth and tongue. From the mouth
Digestive System Organs
the broken-down food moves through the transport tube called the esophagus to the storage and mixing organ called the
stomach. The stomach thoroughly mixes digestive juices and mucous with the food as it tosses it around to produce a softened substance called chyme. The chyme is slowly moved into the small intestine where powerful digestive chemicals are
added from the pancreas. As the chyme slowly moves through the long small intestine, the digestive enzymes break it into
small metabolic fuel molecules that the intestine absorbs. The material that cannot be digested and absorbed is passed into
the large intestine where the nondigested remains are held until they can be removed through the anus as feces. The photos on this and the facing page depict the digestive organs and their related mesenteries.
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Intermediate dissection of abdominal viscera
Anterior view
Deep dissection of abdominal viscera
Anterior view
1 Esophagus
2 Stomach
3 Liver
4 Gallbladder
5 Pancreas
6 Duodenum
7 Jejunum
8 Ileum
9 Cecum
10 Ascending colon
11 Transverse colon
12 Descending colon
13 Rectum
14 Greater omentum
15 Lesser omentum
16 Mesentery
17 Transverse mesocolon
18 Lungs
19 Heart
20 Diaphragm
21 Aorta
22 Spleen
23 Trachea
24 Inferior vena cava
25 Kidney
26 Bladder
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Photomicrograph of small intestine wall
40x
The wall of the digestive tract has a basic pattern of
design that is found throughout its length. This pattern
consists of three tunics or layers of anatomy. The tunica
Design of the Gut Wall
mucosa and its subdivisions, including the tela submucosa, form the inner layer of the wall and consist of an extensive
epithelial lining with an underlying vascullar connective tissue. The middle layer, or tunica muscularis, consists of smooth
muscle that provides for the varied types of movements that occur within the digestive organs. The majority of the organs
have an outer layer, the tunica serosa, comprised of a lubricated meosthelial membrane that reduces friction as the organs
move against one another. The image below, from the small intestine, illustrates the basic layers of the digestive tract wall.
Tunica mucosa
consisting of:
epithelium,
lamina propria,
and
muscularis
mucosae
Tunica serosa
Tela
submucosa
Tunica muscularis
circular layer
Tunica muscularis
longitudinal layer
1 Simple columnar epithelium
2 Lamina propria
3 Muscularis mucosae
4 Submucosal (Brunner’s) glands
5 Villi
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1 Lips
2 Teeth
3 Tongue
4 Hard palate
5 Soft palate
6 Nasopharynx
7 Oropharynx
8 Laryngopharynx
9 Parotid gland
10 Submandibular gland
11 Parotid duct
12 Serous acini
13 Mucous acini
14 Vein
15 Trabecula
16 Masseter
17 Sternocleidomastoid
18 Sphenoid sinus
19 Epiglottis
20 Vertebral column
21 Cerebrum
22 Spinal cord
Dissection of head showing salivary glands
Lateral view
Sagittal section of head and neck
Medial view
The mouth, or oral cavity, is the entryway into the digestive system.
In addition to serving as the portal to the tubular gut, the mouth
contains structures, such as the tongue, teeth, and salivary glands,
Mouth and Pharynx
that help initiate the digestive process. The boundaries of this region are defi ned by the lips and cheeks, which form the
anterior and lateral walls, the palate, which forms the roof, and numerous muscles, the most conspicuous being the muscles
of the tongue, which form the fl oor of the mouth. The pharynx is the fi rst portion of the gut tube and is divided into three
regions. Each region communicates with a different cavity — the nasopharynx with the nasal cavity, the oropharynx with the
oral cavity, and the laryngopharynx with the cavity of the larynx.
Photomicrograph of submandibular gland
240x
Photomicrograph of parotid gland
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salivary glands
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Pharynx, esophagus, and stomach
Anterior view Photomicrograph of esophageal wall
40x
Step dissection of esophagus
Anterior view
Below the laryngopharynx the gut tube branches into an anterior respiratory tube, the larynx and a posterior digestive tube, the esophagus.
The esophagus is a narrow, collapsed muscular tube coursing from the
Esophagus
laryngopharynx to the stomach. It is approximately 25 cm in length and begins near the level of the sixth
cervical vertebra, where it runs inferiorly against the anterior surface of the thoracic vertebral column.
At the level of the tenth thoracic vertebra it deviates slightly to the left passing through the esophageal
hiatus of the diaphragm to enter the stomach. It functions as a muscular tube of transmission.
1 Esophagus
2 Tunica mucosa
3 Tela submucosa
4 Tunica muscularis circular layer
5 Tunica muscularis longitudinal layer
6 Stratified squamous epithelium
7 Lamina propria
8 Muscularis mucosae
9 Tunica adventitia
10 Stomach
11 Pharynx - dorsal wall
12 Vagus nerve
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Frontal section of stomach
Anterior view Photomicrograph of stomach mucosa
with callout above
40x and 100x
1 Stomach
2 Cardia of stomach
3 Fundus of stomach
4 Body of stomach
5 Pyloric antrum
6 Pyloric canal
The stomach is a J-shaped organ of variable size and shape and has the greatest diameter of any part of the gut tube. It occupies the upper left quadrant of
the abdominal cavity, where it is anchored to the posterior abdominal wall by a
Stomach
7 Pylorus
8 Pyloric sphincter
9 Gastric rugae
10 Greater curvature
11 Lesser curvature
12 Gastric pit
mesentery. The stomach performs several functions, the most important of which is to store ingested food
until it can be emptied into the small intestine at a rate that allows for optimal digestion and absorption.
13 Surface mucous cell
14 Lamina propria
15 Mucous neck cell
16 Gastric glands
17 Liver
18 Gallbladder
19 Spleen
20 Greater omentum
Abdominal dissection revealing stomach
Anterior view
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Small intestine in situ
Anterior view
The small intestine is a highly coiled tube with a fairly consistent diameter from beginning to end. It is approximately
6 to 7 meters long in the cadaver but, because of its muscle
Small Intestine
tone only around 4 to 5 meters in the living. The small intestine occupies the greater part of the mid- to
lower abdominal cavity and consists of three regions. The retroperitoneal fi rst part is called the duodenum and is about 30 cm in length. This C-shaped region receives the secretions from the pancreas and
liver. The remaining parts of the small intestine are the jejunum and ileum, which make up the bulk of
the organ and are attached to the posterior wall of the abdomen by the mesentery. The small intestine
is the principal site of digestion and absorption.
Sectioned small intestine
revealing circular folds
Internal view
Entire small intestine sectioned to show changes in
internal surface from the duodenal end to the ileal end
Internal view
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Loop of small intestine from unembalmed cadaver, opened to show circular folds
Anterior view
Loop of small intestine
Anterior view
1 Duodenal end
2 Ileal end
3 Jejunum
4 Ileum
5 Circular folds
6 Simple columnar epithelium
7 Goblet cell
8 Lamina propria
9 Liver
10 Stomach
11 Cecum
12 Transverse colon
13 Descending colon
14 Mesentery
15 Microvillus brush border
Photomicrograph of cross-section of intestinal villus
400x
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1 Tail of pancreas
2 Body of pancreas
3 Head of pancreas
4 Uncinate process of pancreas
5 Pancreatic duct (of Wirsung)
6 Major duodenal papilla
7 Exocrine acinus
8 Pancreatic ductule
9 Pancreatic islet (endocrine cells)
10 Trabecula
11 Duodenum
12 Liver
13 Gallbladder
14 Common bile duct
15 Spleen
16 Diaphragm
The pancreas is a pinkish glandular structure situated posterior to the stomach
in the retroperitoneal space of the abdominal cavity. It arises as an outgrowth
of the duodenum during development and retains this connection via the panPancreas
creatic duct. It is a dual glandular organ consisting of both exocrine and endocrine glandular tissue. It has
four basic regions: a head, neck, body, and tail. The exocrine glands and ducts produce and deliver the
powerful digestive enzymes to the small intestine.
Photomicrograph of pancreas
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Abdominal dissection with part of liver
and peritoneal organs removed
Anterior view
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