Comprehensive Study Guide for Domestic Animal Anatomy

General Anatomical Concepts and Definitions

An anastomosis is defined as the communication between adjacent arteries that serves for the irrigation of an organ. This communication can take a transverse form or an arterial arch form. This mechanism ensures redundant blood supply to various tissues and organs.

Omentos (omenta) are folds of the peritoneum that connect the stomach with other viscera. These structures contain connective tissue and significant amounts of fat, as well as blood vessels, lymph nodes, and nerves that travel toward the organs they support.

The liver is characterized as the most voluminous gland in the organism. Its primary physiological function is to maintain the levels of nutrients within the blood, acting as a central hub for metabolic regulation.

The Digestive System: Oral Cavity and Salivary Glands

The mandibular gland (glándula mandibular) does not receive its arterial irrigation through the occipital, carotid, and external maxillary arteries. This statement is considered false in anatomical examinations. Similarly, the arterial irrigation of the parotid gland is not provided via the occipital and common carotid arteries.

The parotid gland is the most voluminous salivary gland. It is situated adjacent to the ear within a space formed by the ramus of the mandible. It possesses an elongated, roughly triangular shape.

In domestic poultry, specifically the chicken (gallina), the mouth is not divided into a vestibule (vestíbulo de la boca) and a buccal cavity (cavidad bucal) in the same manner as other domestic mammals. This distinction marks a significant anatomical difference between avian species and domestic mammalian species.

The dental formula for the pig (cerdo) is expressed as $(3+1+4+3) \times 2 = 44$ teeth. This includes incisors, canines, premolars, and molars in both the upper and lower arcades.

The tongue receives its arterial irrigation primarily through the lingual artery, but it does not receive supply through internal incisive branches. For anatomical purposes, the stomach-colon junction is not referred to as the pylorus; the pylorus specifically refers to the sphincter-guarded opening between the stomach and the duodenum.

The Digestive System: Stomach and Accessory Organs

In monogastric animals, the venous irrigation of the stomach is facilitated by the branches of the portal vein. Arterially, the stomach receives irrigation from three main arteries stemming from the celiac trunk: the left gastric artery (gástrica izquierda), the hepatic artery (hepática), and the splenic artery (esplénica).

Ruminant stomachs consist of four compartments. The reticulum (retículo) is the most cranial and leftmost compartment, situated at the level of the seventh rib. The omasum (omaso) and the abomasum (abomaso) are the other compartments, with the abomasum being the true glandular stomach of ruminants, which is elongated and applied to the floor of the abdominal cavity on the right side. In bovine species, the stomach is massive, occupying nearly three-quarters of the left side of the abdominal cavity and extending from the ninth intercostal space to the pelvic inlet.

Birds possess two stomachs: the proventriculus (proventrículo), which is the glandular stomach, and the gizzard (molleja). These are essential for the chemical and mechanical breakdown of food.

The pancreas in the equine is situated transversally in the dorsal wall of the abdominal cavity, beneath the seventeenth or eighteenth thoracic vertebrae. It lies to the right of the median line in the first curve of the sigmoid flexure of the duodenum.

The spleen (bazo) is located in the cranial part of the abdominal cavity, positioned between the stomach and the small intestine, behind the diaphragm and the liver, and to the left of the median line.

The gallbladder (vesícula biliar) is notably absent in the horse (equino). It is false to state that it is located in the dorsal part of the quadrate lobe in the horse. In other species, such as those with a multi-lobed liver viewed from the diaphragmatic surface, the lobes are identified as: right lateral lobe (1), caudate lobe (2), left medial lobe (3), left lateral lobe (4), caudate process (5), and the gallbladder (6).

The Digestive System: Intestines by Species

The small intestine of the pig (cerdo) measures approximately $16\,m$ in length and $6\,cm$ in diameter. It forms numerous flexures supported by the cranial mesenteric artery. The bile duct ($conductobiliar$) and pancreatic duct ($pancreático$) discharge separately. The mesentery in pigs typically contains a significant amount of fat and numerous lymph nodes.

The small intestine of the bovine (bovino) is found to the right of the median plane, measuring $40\,m$ in length and $7\,cm$ in diameter. The bile and pancreatic ducts discharge separately at a distance of $30\,cm$. The aggregated lymph nodules (Peyer's patches) are larger than those found in the horse.

The small intestine of the dog (perro) measures approximately $4\,m$ in length and $6\,cm$ in diameter. It occupies the majority of the abdominal cavity with a high number of mesenteric loops. The bile and pancreatic ducts discharge separately near the pylorus, and the duodenum contains relatively few duodenal glands.

In avian species, the intestine consists of the duodenum, jejunum, ileum, two cecal sacs (sacos ciegos), and the rectum. The glands of the small intestine across species are generally divided into two types: duodenal glands and intestinal glands.

The Urinary System

The kidneys are retroperitoneal organs. In the equine, the right kidney is located between the thoracic vertebrae $T15 - T17$, while the left kidney is located between $T17 - L3$. In the bovine, the kidneys are unique among domestic species because they lack a renal pelvis ($pelvis renal$).

Internal renal structures include the renal pelvis (the dilated origin of the ureter found in the renal sinus), the renal hilus ($hilio renal$), the cortex ($corteza$), and the medulla ($médula$). Lymphatic vessels within the kidney are distributed specifically in the cortex and the renal sinus.

The arterial irrigation of the ureters is provided by the renal and spermatic arteries. The urinary bladder (vejiga urinaria) is irrigated by the internal pudendal ($pudenda interna$) and umbilical arteries. The urogenital anatomy of a cat, viewed ventrally, reveals structures such as the left ovary ($A$), uterine horns ($B$), ureteral orifices ($C$), body of the bladder ($D$), neck of the bladder ($E$), vertex of the bladder ($F$), uterus ($G$), and ureters ($H$).

The Reproductive System

In the male, parts of the reproductive apparatus include the bulbospongiosus muscle of the penis ($músculo bulboesponjoso del pene$), the bulbourethral gland ($glándula bulbouretral$), and the prostate. The testis contains seminiferous tubules ($túbulos seminíferos$), efferent ducts ($conducto eferente$), and the ductus deferens ($conducto deferente$). Within the seminiferous tubules, germinal cells and Sertoli cells are responsible for favoring nutrition and support.

The male intrapelvic urethra receives arterial irrigation from the internal pudendal, external pudendal, and obturator arteries ($arteria pudenda interna, externa y obturatriz$).

In the female, the reproductive apparatus consists of the ovary, infundibulum, and cervix ($cuello uterino$). Other components include the oviduct and the proper ligament of the ovary ($ligamento propio del ovario$). The uterus does not receive its arterial irrigation through the internal pudendal arteries; however, the oviducts do receive arterial irrigation through branches of the ovarian arteries. Ovaries can be identified by species: the cow ($vaca$), the sow ($cerda$), the bitch ($perra$), and the mare ($yegua$) each have distinct morphologies.

In avian reproduction, the female reproductive tract includes the infundibulum, magnum, isthmus, uterus, and vagina. In birds, the function of the magnum is not to secrete the shell membrane (which is a false statement); rather, it secretes egg white (albumin). In many avian species, specifically certain birds, the right ovary and oviduct atrophy, leaving only the left side functional. Additionally, it is false that avian lymph nodes are categorized as mandibular and parotid.

Vascular and Endocrine Structures

The azygos vein ($vena ácigos$) is responsible for returning blood to the heart from the dorsal and lateral portions of the thoracic wall. The cranial vena cava ($vena cava craneal$) returns blood from the head and thoracic limbs, while the caudal vena cava ($vena cava caudal$) returns blood from the abdomen, pelvis, and pelvic limbs.

The adrenal glands ($glándulas suprarrenales$) are two retroperitoneal glands situated above the kidneys. In specific anatomical imaging, the right adrenal gland ($glándula adrenal derecha$) and the abdominal aorta may be identified as critical vascular and endocrine landmarks.

Questions & Discussion

Q: Is it true that the mandibular gland is irrigated by the occipital, carotid, and external maxillary arteries? A: False.

Q: Does the chicken's mouth have a vestibule and buccal cavity like other domestic species? A: False.

Q: Is the union of the stomach that narrows to join the colon called the pylorus? A: False.

Q: Do avian species have two stomachs called the proventriculus and gizzard? A: True.

Q: In horses, is the gallbladder located in the dorsal part of the quadrate lobe? A: False.

Q: Do the kidneys of bovines lack a renal pelvis? A: True.

Q: In birds, does the magnum secrete the shell membrane? A: False.

Q: Are the mandibular and parotid lymph nodes present in birds? A: False.