IVRI Anatomy
A free veterinary anatomy learning platform for B.V.Sc., M.V.Sc., DVM and veterinary medicine students worldwide, developed at the Veterinary Anatomy Section, ICAR-Indian Veterinary Research Institute, Bareilly—covering VCI/MSVE and international university curricula through regional anatomy, histology, embryology, comparative biomechanics, clinical notes, quizzes and revision.
Each adrenal gland is a small flattened organ (~5 cm × 2 cm in cattle) lying retroperitoneally on the cranio-medial pole of its kidney. They are made of two embryologically and functionally distinct parts:
Cortex (mesodermal origin) — produces steroid hormones in three concentric zones:
• Zona glomerulosa (outer) → aldosterone (regulates Na+/K+, blood pressure).
• Zona fasciculata (middle, thickest) → cortisol (glucocorticoid; stress response).
• Zona reticularis (inner) → adrenal androgens.
Medulla (neural-crest derived and functionally comparable to a modified sympathetic ganglion) — chromaffin cells secrete epinephrine/adrenaline and norepinephrine/noradrenaline. Their relative proportions vary by species and physiological state; a fixed 80:20 ratio is not a universal veterinary rule.
Vasculature: The glands receive multiple arterial branches from adjacent major vessels. Venous drainage is asymmetric and species-dependent; the right adrenal vein commonly has a short connection to the caudal vena cava, while left-sided drainage commonly joins the renal or adjacent venous system.
| OX | Right gland heart-shaped, left bean-shaped. Cortex pale yellow; medulla reddish-brown. |
| HORSE | Larger and more elongated. Strong cortisol response to stress (laminitis link). |
| DOG | Small, bean-shaped. Common diseases: hyperadrenocorticism (Cushing's) and hypoadrenocorticism (Addison's). |
Explore the hidden mechanics of why structures are present, absent or modified across domestic and wildlife species—and how each anatomical design supports movement, function and clinical practice.
Explanation goes here.