What Is Splachnology ? | Gross Anatomy | Anjani Mishra

                                                Written by- Anjani Mishra

Splanchnology

Definition: Splanchnology is the division of systematic Anatomy which deals with the form and structure of visceral organs(digestive system, Respiratory system, Uro-genital system and Endocrine system). In broad sense, splanchnology comprises the organs of vascular system(heart, spleen).

Viscera- means the soft internal organs.

BODY CAVITIES

The body as a whole is built around the bony frame work or skeleton and consists of a number of different parts like the head, neck and the trunk. The trunk further can be divided into the chest or thorax, abdomen and pelvis. For descriptive purpose, the body cavities means the thoracic cavity, abdominal cavity and pelvic cavity.

Fig: Projection of viscera of bull on body wall; Left view

Fig: Projection of viscera of bull on body wall; Right view

i) Thoracic cavity: The thoracic cavity is formed dorsally by the thoracic vertebrae, ligament and muscles connected with them, ventrally by the sternum, cartilages of the sternal ribs and muscles connected with them, laterally by ribs and intercostal muscles, anteriorly by thoracic inlet and posteriorly by the diaphragm/thoracic outlet.                                                                                       

Contents:

Ø  The heart

Ø  The lungs

Ø  The trachea(thoracic part)

Ø  Oesophagus(thoracic part)

Ø  Bronchi

Ø  Brachiocephalic trunk

Ø  Arch of aorta

Ø  Cranial venacava

Ø  Caudal venacava

Ø  Lymph vessels

Ø  Lymphnodes

Ø  Blood vessels

Ø  Nerves etc.

What is thoracic inlet ?

The thoracic inlet or anterior aperture is an anterior bony boundry of thoracic cavity which is somewhat oval in outline.

The thoracic inlet is formed dorsally by the 1st thoracic vertebra, laterally by the 1st pair of ribs and cartilages and ventrally by the pre-sternum (manubrium sterni).

What are the structures passing through thoracic inlet ?

Structures passing through thoracic inlet are as follows;

Ø  Oesophagus

Ø  Trachea

Ø  Carotid artery

Ø  Jugular vein

Ø  Vagosympathetic trunk

Ø  Recurrent laryngeal nerve

Ø  Longus coli muscle

Ø  Phrenic nerve

Ø  Lymph trunk etc

         
What is thoracic outlet ?

The thoracic outlet or posterior aperture is formed dorsally by the last thoracic vertebra, laterally by the last few ribs along the line of attachment of the diaphragm and ventrally by the xiphoid cartilage of the sternum.

What are the structures passing through thoracic outlet ?

Structures passing through thoracic outlet are as follows;

Hiatus aorticus- Descending aorta, Thoracic duct, Left vena azygos(cisterna chyli and right vena azygos in horse instead of thoracic duct and left vena azygos)

Hiatus oesophageus- Esophagus, Esophageal vessels, Dorsal and ventral vagal trunk

Foramen vanae cavae- Posterior venacava

What is foramen ?

Foramen is a natural opening for the perforation of vessels, nerves and muscles through a bone or membranous structure. It is usually round in shape.

What is hiatus ?

Hiatus is the aggregation of several foramen found in diaphragm.

What is thoracic duct ?

Thoracic duct is the main lymphatic duct which receives lymph from all parts of the body except the right side of the head, neck, thorax and right forelimb.

What is vena azygos ?

Single vein that drains the blood from the dorsal wall of the left side of the thoracic and abdominal cavity and opens independently to the right atrium of the heart ventral to the caudal venacava.

Fig: Thoracic cavity of ox showing hiatus and foramen of diaphragm(from left side)

                 Fig: Thoracic cavity of ox showing hiatus and foramen of diaphragm(from right side)

ii) Abdominal cavity: The abdominal cavity is formed dorsally by lumbar vertebrae, lumbar muscles and lumbar part of the diphragm, ventrally by the two recti, the aponeurosis of oblique and transverse muscle and xyphoid cartilage, the lateral wall is formed by the oblique and transverse abdominal muscles, the anterior wall is formed by the diaphragm and posteriorly by an imaginary line, the pelvic inlet.

Contents:

Ø  The stomach

Ø  The small intestine(major parts)

Ø  Most of the large intestine

Ø  The liver

Ø  The gall bladder

Ø  The bile duct

Ø  The pancreas

Ø  The spleen

Ø  Ureter (cranial/upper part)

Ø  The adrenal glands

Ø  Blood and lymph vessels

Ø  Lymph nodes

Ø  Nerves etc.

In female:

Ø  Horn of uterus

Ø  Body of uterus(partly)

iii) Pelvic cavity: The pelvic cavity is formed dorsally by sacrum and first few coccygeal vertebrae, ventrally by the pubic and ischial bones, laterally by the parts of the ilium and sacrosciatic ligament and acetabular part of the ischia.

Contents:

Ø  Some loops of small intestine

Ø  The lower/posterior part of large intestine like rectum and anus

Ø  The urinary bladder

Ø  The caudal/lower part of ureter

In male:

Ø  Seminal vesicles,

Ø  Prostate gland,

Ø  Bulbo urethral glands,

Ø  Spermatic cord,

Ø  Ductus deferens(upper part)

Ø  Ejaculatory ducts

Ø  Urethra(pelvic part)

In female:

Ø  Ovaries

Ø  Fallopian tubes/uterine tubes

Ø  Uterus(neck/cervix/os-uteri and body partly)

Ø  Vagina etc

Ø  Urethra

What is Pelvic inlet ?

The pelvic inlet or anterior aperture is an anterior bony boundry of pelvic cavity which is somewhat round in shape.

The pelvic inlet or cranial aperture is formed dorsally by the anterior part of sacrum base(sacral promontory), laterally by the arcuate line(iliopectinal line) and ventrally by the pubic bone(pectin ossis pubis). It has two principal diameter. The conjugate or sacro-pubic diameter is measured from the sacral promontory to the cranial end of of the pubic symphysis. The transverse diameter is measured at the greatest width i.e. Just dorsal to the psoas tubercle.

What is Pelvic outlet ?

The pelvic outlet or caudal aperture is formed dorsally by the 3rd caudal vertebra, ventrally by the ischiatic arch and laterally by the broad sacrotuberal ligament and the semimembranosus muscle, thus enclosing the perineum.

What are the structures located outside the pelvic cavity ?

Structures outside the pelvic cavity are as follows;

In male:

Ø                         Ø  The caudal part of anus

Ø                          Ø  The testes

Ø                           Ø  Epididymis

Ø                           Ø  Ductus deferens(lower part)

Ø                            Ø  Spermatic cord

Ø                             Ø  Penis

Ø                              Ø  Urethra(extra-pelvic/penile part)

In female:

Ø                               Ø  The caudal part of anus

Ø                                Ø  The vulva

               Ø The mammary gland

                                                 Diaphragm

Fig: Diaphragm of horse; Abdominal surface

It is a broad, unpaired muscle of thorax which forms a partition between the thoracic and abdominal cavities. It is arch shaped. The thoracic surface is strongly convex where as the abdominal surface is concave. It has fleshy periphery and tendinous center. The fleshy part may be divided into costal and sternal part. The lumbar part present two well developed crura or muscular pillars.

Fig: Dissection of floor of thorax of horse

1. Eighth rib; 2,3. cartilages of ninth and tenth ribs; 4. Xyphoid cartilage; 5. Apex of pericardium

Sternal part: It is attached to the abdominal surface of the xiphoid cartilage.

Costal part: It is attached to the ribs and the 8th costal cartilage. The dorsal limit extends almost in a straight line from the last rib, about a hand's breadth ventral to its vertebral end, to the junction of the 8th rib with its cartilage.

Lumbar part: It is formed by two muscular pillars, the left and right crura, which originate on either side from the ventral surface of the bodies of the lumbar vertebra. The right crus atttaches to the first four lumbar vertebrae by means of ventral longitudinal ligament. The left crus, which is smaller attaches to the ventral longitudinal ligament of the first and second lumbar vertebrae.

        The right crus divides into two branches which circumscribe the esophageal hiatus to unite ventrally and then spread out in the tendinous center.

Opening of diaphragm

1)     Aortic hiatus: is ventral to the last thoracic vertebra and between the crura. 

2)     Esophageal hiatus: situated about a hand's breadth ventral to the 8th thoracic vertebra, a little   to the left of the median plane

3)     Foramen venaecavae: is slightly more ventral and almost in the median plane.

      Peritoneum

Peritoneum is the thin serous membrane which lines the abdominal cavity and the pelvic cavity (in part) and covers, to a greater or lesser extent, the viscera contained there in. In the male it is completely closed sac, but in the female it has two small openings; these are the abdominal orifices of the uterine or fallopian tubes, which at their other ends communicates with the uterus.

         It has two layers; parietal layer and visceral layer. The space between these two layers is known as peritoneal cavity. The cavity is only potential, since its opposing walls are normally separates only by thin film of serous fluid (secreted by the membrane), which acts as a lubricant.

          The free surface of the membrane has a glistening appearance and is very smooth. This is due to the fact that this surface is formed by the layer of flat mesothelial cells and is moistened by the peritoneal fluid. Friction is thus reduced to a minimum during the movements of the viscera. The outer surface of the peritoneum is related to the subserous tissue, which attaches it to the abdominal wall or the viscera.

     Fig: Diagram of general arrangement of peritoneum(female pelvis) in sagittal tracing

   a. Sacro-rectal pouch/para-rectal pouch; b. Recto-genital pouch; c. Vesico-genital pouch; d. Vesico-pubic pouch; f. Lesser omentum

According to the disposition of the peritoneum, there are three major connecting folds of visceral peritoneum, namely:

(A) Omentum

(B) Mesentery

(C) Ligaments

(A)  Omentum:

An omentum is a fold attached to the stomach. There are two of these;

Ø  Greater omentum and

Ø  Lesser omentum

Greater omentum: which pass from the dorsal abdominal wall to the greater curvature of the stomach and spleen.

Lesser omentum: which passes from the lesser curvature of the stomach to the liver.

  (B)  Mesentery:

The mesentery is a fold attached to the intestine. Specific names are applied to the peritoneal folds attached to various portions of the digestive tubes.

Great mesentery: is a fold which attaches the greater part of small intestine (jejunum and ileum) to the dorsal abdominal wall.

Ø  Mesocolon: Attaches the colon to the dorsal abdominal wall.

Ø  Mesoduodenum: Attaches the duodenum to the dorsal abdominal wall.

Ø  Mesorectum: Attaches the rectum to the dorsal abdominal wall.

 Fig: Diagram of sagittal section of male pelvis to show disposition of peritoneum

a. Sacro-rectal pouch/para-rectal pouch; b. Recto-genital pouch; c. Vesico-genital pouch; d. Vesico-pubic pouch

(C)  Ligaments:

Ligaments are fold which pass between viscera other than parts of digestive tube, or connect them with the abdominal wall. The term is also applied to fold which attach parts of the digestive tract to the abdominal wall but do not contain their blood vessels and nerves.

Eg; The lateral and coronary ligaments of liver are strengthened by fibrous tissue, broad ligament of the uterus also contain smooth muscular tissue.

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