alt="Photo depicts vaginal and cervical lumen."/>
Figure 22.8 Vaginal and cervical lumen. V, Vagina; C, cervix; U, body uterus; Uh, uterine horn; Ov, ovary.
The arrangement of the cervical musculature and mucosa is responsible for this characteristic architecture (Figure 22.9). The superficial mucosa is arranged in longitudinal folds punctuated by circular folds that interdigitate to form a series of ridges and interlocking notches when the cervix is closed [4]. This arrangement effectively seals the external environment from the internal uterine environment.
Figure 22.9 Close‐up of vaginal and cervical lumen allowing visualization of the external cervical os. V, Vagina; C, cervix; U, uterus; Cf, circular folds; Lf, longitudinal folds.
Vagina
The vagina is positioned between the caudal extent of the cervix and border of the vestibule at the external urethral orifice. The cervix projects into the lumen of the vagina caudoventrally, causing the dorsal vaginal fornix to form a deeper recess than the ventral fornix [4].
Vestibule
The vestibule is a small area in the cow that originates at the urethral opening and ends caudally to blend with the labia of the vulva.
Vulva
The labia of the vulva are located on either side of the labial fissure [3] (Figure 22.10). The labia meet dorsally, forming the dorsal commissure, and again ventrally to form the ventral commissure. The clitoris is found just cranial to the ventral commissure [3].
Figure 22.10 External view of perineum. A, Anus; Vs, vestibule; Uo, urethral orifice; V, vulva.
Blood Supply
The arterial supply to the reproductive system of the cow is provided by the ovarian, umbilical, vaginal, and internal pudendal arteries with their associated branches (Figure 22.11). The ovarian artery leaves the abdominal aorta, passing within the mesovarium to perfuse the ovary. The ovarian artery gives off branches to the uterine tube and the uterine horn [4]. The umbilical artery arises from the internal iliac artery near the pelvic inlet and sends out a uterine branch that supplies the cervix, body, and horns of the uterus. The vaginal artery arises directly from the internal iliac artery. The vaginal artery gives off a uterine branch that anastomoses with the uterine branch of the umbilical artery. The uterine artery formed by this anastomosis in turn anastomoses with the uterine branch of the ovarian artery, completing an arterial loop that supplies all the internal components of the reproductive system [4]. The internal pudendal artery is a direct continuation of the internal iliac artery. It courses caudally after the vaginal artery branches off within the ischiorectal fossa. The internal pudendal artery terminates as ventral perineal and dorsal labial branches [4].
Figure 22.11 Arterial blood supply to the reproductive tract. Aa, Abdominal aorta; Ov, ovarian artery; Um, umbilical artery; Ii, internal iliac artery; V, vaginal artery; Uv, uterine branch of vaginal artery; Uu, uterine branch of the umbilical artery; Uo, uterine branch of ovarian artery.
The innervation of the external genitalia of the cow consists of the pudendal nerve and its branches. The pudendal nerve carries motor, sensory, and parasympathetic nerve fibers [2]. The pudendal nerve passes through the pelvic cavity medial to the sacrosciatic ligament and divides as it approaches the lesser ischiatic notch of the pelvis into proximal and distal cutaneous branches that supply the skin of the caudal hip and thigh [2, 3]. The pudendal nerve continues through the ischiorectal fossa and terminates as the dorsal nerve of the clitoris and a mammary branch [3]. Parasympathetic components of the pudendal nerve come by way of the pelvic nerve, which originates as a coalescence of branches of the sacral spinal nerves at the sacral plexus [4]. Sympathetic components of the pudendal nerve arise from the paired hypogastric nerves, which contribute sympathetic fibers from the caudal mesenteric plexus to the genital system [4].
Placenta
The cotyledonary bovine placenta is composed of the fetal cotyledons and the maternal caruncles that fuse and form the placentomes [4]. The placentomes are the sites for the transfer of maternal nutrients to the fetal circulation. The fetal membranes consist of two fluid‐filled sacs. The innermost sac is the amnion, which surrounds the developing embryo; the outermost sac is the chorioallantois, which encircles the amnion and is composed of two separate tissues that fuse as the embryo develops. The outer layer is the chorion that develops from the trophoblast layer, which is the outer layer of the blastocyst of the embryo. As the embryo develops, the allantois, a sac that arises from the embryo hindgut, expands and eventually fuses with the chorion to form the chorioallantois.
References
1 1 Ross, M., Kaye, G., and Pawlina, W. (2003). Histology: A Text and Atlas, 4e, 875. Philadelphia: Lippincott Williams & Wilkins.
2 2 Schaller, O. and Constantinescu, G. (1992). Illustrated Veterinary Anatomical Nomenclature, 614. Stuttgart: F. Enke Verlag.
3 3 Budras, K.‐D. (2003). Bovine Anatomy: An Illustrated Text, 138. Hannover: Schlütersche.
4 4 Nickel, R., Schummer, A., Seiferle, E., and Sack, W. (1973). The Viscera of the Domestic Mammals, 401. Berlin: Verlag Paul Parey; New York: Springer‐Verlag.
5 5 Pineda, M. and Dooley, M. (2003). McDonald's Veterinary Endocrinology and Reproduction, 5e, 597. Ames, IA: Iowa State Press.
6 6 Mullins, K. and Saacke, R. (2003). Illustrated Anatomy of the Bovine Male and Female Reproductive Tracts: From Gross to Microscopic, 79. Blacksburg, VA: Germinal Dimensions.
23 Initiation of Puberty in Heifers
Charles T. Estill
Department of Clinical Sciences, Carlson College of Veterinary Medicine, Oregon State University, Corvallis, OR, USA
Introduction
Puberty is a critical physiological milestone in a heifer's reproductive life. In general terms, puberty can be defined as the process whereby animals become capable of reproducing themselves [1]. At the onset of puberty, a rise in plasma progesterone concentrations indicates cyclic ovarian activity before the first observed estrus [2].
