The Anatomy Of Dog: The Urinary & Genital Systems

In dog and bitch, the urinary system consists of a pair of kidneys and ureters, the bladder, and the urethra. Urine is manufactured in the kidneys, passes through the ureters to the bladder and is eventually evacuated through the urethra. Each kidney is a bean-shaped organ. Dark reddish-blue in colour and situated on the roof of the abdomen either side of the aorta. It consists of millions of pinpoint-sized filtering units through which the circulating blood passes. Waste products and excess salts and water in the blood pass through these into long, microscopically narrow tubules which convey the fluid to the point on the kidney where the ureter arises. During its passage the fluid is altered until it enters the ureters as urine, the production of which is a continuous process. The ureters are muscular tubes which convey the urine into the dorsal surface of the bladder, a highly distensible. muscular, balloon-shaped sac which narrows to a neck in the pelvis and is continued as the urethra. In the male dog, the urethra is narrow and curves round the near edge of the pelvic floor, passing forward into the penis. The urethra of the bitch is short and wider and opens into the floor of the vagina. The kidneys play a large part in the regulation of water and salts in the blood and in the body tissues, rapidly altering, for example, the concentration and volume of urine in response to body requirements. Another major function of the kidneys is the removal from the blood of soluble nitrogenous waste products derived from the digestion of protein. The kidneys can also eliminate from the blood many foreign chemicals such as drugs.

The female reproductive system

The reproductive organs of the bitch consist of the paired ovaries and oviducts, the uterus, vagina, vestibule and vulva. The right and left ovaries, suspended by ligaments from the roof of the abdomen, produce ova and the female hormone, oestrogen. During pregnancy they produce another hormone, progesterone. Ova are released during oestrus and pass via the oviducts or fallopian tubes into the uterus. When a bitch is spayed, the ovaries and oviducts up to the cervix are removed. The uterus, consisting of two long, muscular horns, terminates at the cervix as a thick muscular ring which closes completely in pregnancy; the foetuses are arranged in a row in both horns. The vagina passes through the pelvis. its caudal continuation being the vestibule, which is directed downwards to the vulva, the external opening of the genital passage.

The male reproductive system

This consists of the testicles, spermatic cord, vas deferens, prostate, urethra and penis, the former three being paired. The testicles, in the scrotum, produce spermatozoa as well as the male hormone testosterone. The thick spermatic cord, running from each testicle into the abdomen, is made up of a large artery, vein, and nerve, a slip of muscle, and the vas deferens. The latter conveys spermatozoa from the testicle to the urethra which acts as a common channel for urine and semen. The bi-lobed prostrate gland, encircling the urethra, produces the bulk of the seminal fluid in which the spermatozoa are carried. The penis is formed of spongy erectile tissue with the urethra running through the centre. The free part of the penis has a bulbous portion. During erection and mating, this portion enlarges, locking it in the vagina of the bitch, in the so-called tie. Animals risk injury if they are pulled apart when tied.

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