Surface Anatomy of Visceral Organs of Thoracic, Abdominal, and Pelvic Cavities | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Thoracic Cavity

• The thoracic cavity is the second largest cavity in the body, shaped like a cone with its top cut off at an angle, pointing backward.
• It has a roof, floor, two side walls, a back wall, and a front opening.
• The roof is made up of thoracic vertebrae, the side walls by ribs and muscles, the floor by the diaphragm, and the back wall by the diaphragm's curved surface.
• The entrance is small and narrow.

Lungs:

• Lungs come in pairs, one on each side of the chest, and they fill most of the thoracic cavity.
• They are soft, spongy, and stretchy, making a crackling sound when pressed and floating in water.
• Their color varies but is usually pink due to blood flow, and they weigh around 3 to 3.5 kilograms.
• In fetuses, lungs are smaller, firmer, pale grey, and sink in water.

Lung Structure:

• Each lung has two surfaces, two edges, a base, and a tip.
• The base is oval and concave to fit snugly against the diaphragm.

Thyroid Gland:

• The thyroid gland sits in front of the windpipe (trachea).
• It's a red, soft gland without ducts, weighing about 14 to 15 grams.

Parathyroid Glands:

• These are tiny glands, four in total, two on each side of the thyroid gland.

Thymus:

• The thymus is an organ involved in the immune system.
• It's well-developed before birth and shrinks afterward.
• In young animals like calves, it's pale, lobulated, and weighs around 425 to 500 grams.

Abdominal Cavity 

• The abdominal cavity is the largest cavity in the body, separated from the chest cavity by the diaphragm and connected to the pelvic cavity.
• It's lined by a slippery membrane called the peritoneum.
• Inside, there are organs like the digestive system, parts of the reproductive system, urinary system, blood vessels, nerves, lymph nodes, ductless glands, and some fetal remains.

Peritoneum:

• The peritoneum is a thin membrane lining the abdominal and pelvic cavities and their organs.
• In males, it's a closed sac, but in females, there are two openings for the oviducts.
• It forms a potential space with two layers, parietal and visceral, normally touching each other with a lubricating fluid between them.
• The parietal layer lines the cavity walls and folds over to cover organs, creating a pathway for vessels and nerves.

Omentum:

• Omentum is a double-fold of peritoneum that connects organs or attaches them to the abdominal wall.
• The Greater Omentum covers most of the intestines on the right side and stores fat.

Types of Omentum:

• Greater Omentum: Covers intestines on the right side, storing fat.
• Lesser Omentum: Connects the liver to the stomach's surface, the first part of the small intestine (duodenum), and the omasum and pyloric part of the abomasum.

Pelvic Cavity

• The pelvic cavity is a small space within the body located at the bottom of the abdomen.
• It is connected to the abdominal cavity and is surrounded by bones and ligaments.
• The roof of the pelvic cavity is formed by the sacrum and the first three coccygeal vertebrae.
• The floor is mainly composed of the pubic bones and ischial bones.
• It contains organs such as the rectum, parts of the internal reproductive organs, blood vessels, nerves, muscles, and some fetal remnants.
• In males, it also contains the root of the penis, while in females, it includes the vulva.

Stomach:

• In animals like cows, the stomach is quite large and occupies a significant portion of the abdominal cavity.
• It consists of four compartments:
  • Rumen (Paunch): This is the largest compartment, where food is initially stored and partially fermented.
  • Reticulum (Honeycomb): A smaller compartment connected to the rumen, aiding in the breakdown of ingested material.
  • Omasum (Many folds): Functions in further processing and absorption of nutrients.
  • Abomasum (Rennet or true stomach): Resembles the stomach in other mammals and is involved in the final stages of digestion.
• The capacity of the stomach varies depending on factors like age, size, and breed of the animal.

Intestines:

• Divided into the small intestine and the large intestine.
• Small Intestine:
  • Measures about 40 meters in length in cows.
  • Consists of the duodenum, jejunum, and ileum.
  • Main site for nutrient absorption.
• Large Intestine:
  • Extends from the end of the small intestine to the anus.
  • Consists of the cecum, colon, and rectum.
  • Absorbs water and electrolytes, and forms feces.

Liver:

• The liver is the largest gland in the body.
• Located in the abdominal cavity, primarily on the right side.
• It plays a crucial role in metabolism, detoxification, and synthesis of various substances.
• The liver has two main lobes and is highly vascularized.

Pancreas:

• A glandular organ located near the stomach and small intestine.
• Produces digestive enzymes and hormones like insulin and glucagon.
• Consists of a head, body, and tail, and is involved in the digestion of carbohydrates, proteins, and fats.

Spleen:

• A lymphoid organ located on the left side of the abdomen.
• Involved in filtering blood, removing old or damaged red blood cells, and producing immune cells.
• Plays a role in storing blood and regulating its flow.

Urinary System:

• Consists of the kidneys, ureters, bladder, and urethra.
• Responsible for removing waste products from the body and maintaining fluid and electrolyte balance.
• Kidneys filter blood to produce urine, which is then transported to the bladder for storage and eventual excretion through the urethra.

Adrenal Glands:

• Located above each kidney.
• Produce hormones such as adrenaline and cortisol, which are involved in the body's stress response, metabolism, and regulation of blood pressure.

Fig: Position of the organs in the Thoracic, Abdominal and Pelvic Cavities (Left Side)

Fig: Course of the Thoracic part of the Oesophagus

Fig: Genital and Part of Urinary Organs (Cost Left lateral wall of the abdomen änd pelvis removed)