Download Male external structures

Male external structures
Skinning cuts—do
NOT cut the organs
underneath
First become familiar with the external anatomy of the rat
that is given in the diagrams. Any bold-face term is a hint that that
structure is something you will need to know. Each person is
responsible for knowing the anatomy of both genders of rat.
Following the center dotted line in the diagram cut through
the skin and muscles only and 2 cm laterally from the incision line.
There may be an incision near the neck where the circulatory
system was injected. Sometimes this is a useful starting point for
inserting the scissors for the cut and then pulls the skin away from
the body.
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If the specimens came in a bucket of preservative, the body
cavities may have excess fluid in them due to diffusion. (it isn’t
water so osmosis is out) You may have to dump the excess fluid
into the sink when you cut into the abdominal cavity.
each testis is large and housed in a pouch (scrotum) located
between the penis and anus.
Mouth Structures: You will need the bone cutter for this part and
it will make noise. This bothers some people. Cut the jaws apart at
the mandibular joint and identify the following structures: soft
palate, hard palate molars, and tongue.
Anatomical Terms for External Anatomy
Pinna (not pictured)-The flaplike, external ear that directs sound
into the ear opening (external auditory meatus).
Three groups need to do the next part, and everyone will need to
observe these structures while intact and when excised.
To easily see the trachea and esophagus, cut into the throat
area. Move the muscles to the side with the probe or
dissecting needle until you come to a structure that looks like
a white vacuum cleaner hose. There will be a large swelling
in this tube. Remove the swelling by cutting the tube ½ cm
below the swelling and directly above the swelling. You
should find the following structures:
Vibrissae-long, stiff hairs located on the face that have a sensory
(tactile0function; the “whiskers”
Nares-Paired openings leading into the nose; the nostrils.
Anus-The opening to the digestive tract, located under the base of
the tail.
Female urogenital structures-In female rats, there are two
openings, close together, in front of the anus, whereas male have
only one. The most anterior opening of the female is the urethral
orifice, and it leads to the urinary system. The vaginal orifice is the
external opening of the reproductive system, and it lies posterior to
the urethral orifice.
Mammary papillae (nipples)-Present in females only. There
generally are six on each side, three in the chest area and three in
the abdominal area.
Trachea: The white tube that looks like it has rings in it. This is
also known as the wind pipe as it carries air to the lungs.
Esophagus-A thin-walled, unsupported tube for food transport that
lies dorsal to the larynx and trachea. Its connection to the stomach
is described in abdominal section. Sometimes people inadvertently
cut this when they cut out the trachea, please make sure you are
only cutting the trachea.
Larynx-This structure is also known as the voice box and you
should see the vocal cords on the top of the large part of the trachea.
Male urogenital structures -In males, reproductive products and
urine exit the body at the tip of the penis. The penis is usually
hidden inside a fold of skin and will be described in more detail in
urinary and reproductive section. In males in breeding condition,
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Abdominal Cavity and Digestive System (Fig 8)
constriction. There are three parts to the small intestines based on
microscopic structures: the duodenum, jejunum and ileum.
Using scissors carefully open the abdominal cavity by cutting
through the abdominal muscles, along the ventral midline, from the
urogenital area to the sternum. Be sure to lift the muscles as you cut
to avoid damage to the internal organs. If necessary, cut laterally
from the sternum, along the posterior boundary of the rib cage, and
again laterally from the urogenital area, toward the backbone, in
front of the legs. This will leave you with a flap of tissue on each
side that may be pinned to the tray, allowing an unobstructed view
of the organs.
Mesenteries-Translucent membranes attaching to and holding the
internal organs in place. Fat bodies often appear within the
mesenteries and blood vessels travel along them to various organs.
Liver-Large brown organ dominating the anterior of the cavity. It
consists of four sections or lobes. The median lobe is most
superficial, and it is divided by a long notch near the ventral
midline. A small caudate lobe is hidden under the left lobe. Among
other things, the liver manufactures bile to aid fat digestion. Each
lobe is drained by tubes that eventually combine to form a bile duct
that carries bile to the small intestine. Unlike humans, a rat lacks a
storage organ (gall bladder) for bile.
Stomach-Curved baglike structure under the left side of the liver.
The greater omentum is a prominent mesentery that is attached to
the outer curve of the stomach and contains multiple fat deposits.
Three groups will cut open the stomach and look for undigested
food particles.
Small Intestines-Long coiled tube that leaves the stomach. The
junction between the stomach and small intestine has a distinct
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Colon-Is shorter and wider than the small intestine. The cecum is a
sacklike bulge near the junction with the small intestine that is near
the appendix which is a projection from the intestine that doesn’t
go anywhere.
Pancreas-Gland that is light tan and has a bumpy appearance.
Usually found near the mesentery nearest the stomach and
duodenum. Produces insulin to regulate blood sugar.
Spleen-Dark colored long gland near the left of the stomach. It is
not related to the digestive system, it is part of the immune system.
Figure 2
Thoracic Cavity: Respiratory and Circulatory Systems
Respiratory System
To observe the organs of the thoracic cavity, one needs to cut
laterally to the sternum through the cartilage of the ribs. To make
the flaps lie flat one may need to cut through the clavicle. The
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muscle and bone can then be bent back to that the rib cage can be
folded over like a book.
Bronchus- Dorsal to the heart, the trachea splits into a right and left
bronchus that travels to the lungs. Their dorsal location means that
they are not visible in the ventral view shown.
Lung- Spongy structures located in the thoracic cavity. The right
lung consists of four lobes, whereas the left has only one; what may
appear to be a second left lobe, in reality, is a lobe that extends
from the right side. The surface of the lung is covered by visceral
pleura, and the walls of the thoracic cavity are covered by parietal
pleura. The pleura are homologous to the peritoneum of the
abdominal cavity.
Diaphragm- A thin muscular sheet, seen earlier, that separates the
abdominal and thoracic cavities. Its action draws air into the lungs.
Heart and Associated Structures
Pericardium- the tough membrane forming a sac around the heart.
Cut through it to expose the structures inside.
Atria- Portions of the outer walls of the right and left atria are
extremely visible as dark flaps on top of the heart. Blood vessels
entering the right atrium are the vena cava (two anterior and one
posterior) that return oxygen-poor blood from the body.
Pulmonary veins (4) leave the lungs and enter the left atrium with
oxygen-rich blood; their dorsal location means that they are not
visible in the ventral view shown.
Ventricles-The major pumping chambers of the heart. Right and
left ventricles can be distinguished by pushing on them with the
blunt probe. Someone in the class will be responsible for cutting the
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heart so one can see the thickness of the different chambers. A
pulmonary artery exits the right ventricle from the lungs. The
aorta leaves the left ventricle, sends major branches forward, and
makes a prominent turn to the left before disappearing dorsal to the
heart.
Arteries
Our specimens are not injected with paint to differentiate the
arteries from the veins.
Aorta- The major artery leaving the dorsal part of the heart and
immediately curving to the animal’s left.
Urinary and Reproductive Structures
You will be responsible for structures on BOTH genders so make
sure you get a chance to study whatever you don't have. Also make
sure you see what the pregnant uterine horns look like. Depending
on length of gestation, that group may be able to remove a fetus
with the placenta intact.
Urinary Structures
Kidney- Located against the dorsal body wall and surrounded by
fat. You will have to move most of the intestines to the side or even
completely out of the abdominal cavity. Note its beanlike shape.
This indentation along the medial surface, where the arteries and
veins connect, is the hilus. Slice one kidney horizontally into two
halves using a scalpel. On the inside, you can readily distinguish
two regions—an outer renal cortex, where the blood is filtered, and
an inner renal medulla, where the urine is concentrated and
collected. Also embedded in fat, just anterior to the kidney, is the
smaller adrenal gland, an organ of the endocrine system; it appears
dark compared to the surrounding fat.
Ureter- A whitish tube that leaves each hilus and passes caudally to
the urinary bladder. The ureters are surrounded by fat of the same
color; use forceps to remove the fat, but go slowly to avoid tearing
the ureter.
Urinary bladder- A small sack for temporary storage of urine. It is
about the size of a pea when empty.
Female Genital Structures
Ovary-A small nodule, usually buried in fat, posterior and lateral to
each kidney, A tiny, coiled tube (oviduct) leads from the ovary to
the uterus, but it is not readily seen without magnification.
Uterus-Unlike its human counterpart, the uterus of a rat consists of
a pair of elongated structures called the uterine horns. These may
be greatly expanded in a pregnant female; if so, open one horn and
look for embryos.
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Vagina- The horns open into a single vagina that lies dorsal to the
urethra. The vagina exits the body at the vaginal orifice seen
earlier.
Male Genital Structures
Testis-Open the scrotum and associated tissues on one side, and
observe the testis.
Epididymis-A highly coiled tube attached to the surface of the
testis. It acts as a storage site for mature spermatozoa.
Penis-The intromittent organ that allows internal fertilization of the
female.
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