The Reproductive System and Pregnancy Physiology
Male and female reproductive anatomy, the menstrual cycle in brief, and the physiological changes of pregnancy that change how a patient presents, including the blood volume increase and the effect of the uterus on venous return.
9 min read · Updated September 10, 2026
Why This One Is on the List
Reproductive anatomy earns its place for two reasons. Obstetric calls happen, and the physiology of pregnancy changes how a patient presents so substantially that reading her vital signs against non pregnant expectations will mislead you.
Male Reproductive Anatomy
Testes. Two, held outside the body in the scrotum, which keeps them slightly below core temperature because sperm production requires it. They produce sperm and testosterone.
Epididymis. A coiled tube on the back of each testis where sperm mature and are stored.
Vas deferens. The tube carrying sperm from the epididymis up into the pelvis toward the urethra.
Prostate. A gland surrounding the urethra just below the bladder. It contributes fluid to semen. It enlarges with age in most men, which narrows the urethra and produces difficulty urinating and incomplete emptying.
Seminal vesicles and bulbourethral glands. Additional glands adding fluid to semen.
Penis. Contains erectile tissue and carries the urethra, which serves both urinary and reproductive functions in males.
Two conditions worth knowing. Testicular torsion is a twisting of the testis on its own blood supply, producing sudden severe scrotal pain, often in adolescents, and it is time critical because the testis loses its circulation. Priapism, a prolonged erection unrelated to arousal, can accompany sickle cell disease, certain medications, and spinal cord injury.
Quick check
The prostate surrounds which structure?
Frequently asked questions
How does blood volume change in pregnancy?
Circulating volume rises by roughly 40 to 50 percent by the third trimester, and plasma rises more than red cells do, which is why the hematocrit reads low. A pregnant patient can lose a significant amount of blood before her vital signs change, so a normal pressure is not reassurance.
Why is supine positioning a problem late in pregnancy?
The weight of the uterus presses the inferior vena cava against the spine when the patient lies flat, which cuts the blood returning to the heart and drops cardiac output. Positioning her on her left side, or displacing the uterus to the left, takes the weight off the vessel and restores the return.
What is the placenta and what does it do?
A temporary organ that forms on the uterine wall and connects to the fetus through the umbilical cord. It exchanges oxygen, nutrients and waste between two circulations that never actually mix, and it produces the hormones that maintain the pregnancy.
Now go use it
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