Reproductive Biology (one)

Reproduction is an interesting topic throughout history.
Castration of animals prevents reproduction and alters behavior.
There's a link between reproduction/fertility and metabolism/energy balance.
Early anatomical sketches were done by Vesalis in the 1500s.
Van Leeuwenhoek discovered sperm (animacules) with the invention of the microscope.
De Graaf described ovarian follicles.
Pre-formationism: the idea that a fully formed individual exists in the oocyte or sperm.
Discovery of the oocyte and identification of sperm as single cells containing half the genetic material.
Discovery of steroid hormones (estrogen, progesterone, testosterone) in the 20th century.
In vitro fertilization was discovered in the 1980s, and cloning in 1997.

Learning Objectives:
- Use correct anatomical terminology to describe the main structures.
- Relate structure to function.
- Explain the importance of the anatomical position of the testis.
- Describe the mechanism of penile erection.
Order of Structures:
- Testis -> Epididymis -> Ductus Deferens (Vas Deferens) -> Seminal Vesicle, Prostate Gland, Bulbar Urethra Gland -> Urethra -> Penis

Located in the scrotum, external to the body.
Develop inside the abdomen during fetal development and descend around 28 weeks, guided by the gubernaculum.
Undescended testes (cryptorchidism) cause infertility because spermatogenesis is temperature-sensitive.

Spermatogenesis requires a temperature 2-3 degrees cooler than the body's internal temperature.
Structures for temperature regulation:
- Cremaster muscle: surrounds the spermatic cord, contracts when cold, relaxes when warm.
- Dartos muscle: surrounds the testis, contracts when cold, relaxes when warm.
- Sweat glands on the scrotum skin.
- Pampiniform plexus: a network of arteries and veins facilitating heat exchange.
  - The commingling of vessels facilitates heat exchange, cooling the blood entering the testis.
  - Blood entering from the pelvic cavity into the testis is cooled by the venous blood coming back up into the body.

Outer layer: Tunica Albuginea (thick connective tissue).
Seminiferous tubules: where sperm are produced.
Sperm transport: Seminiferous tubules -> Rete Testis -> Efferent Ductiles -> Epididymis -> Vas Deferens.
Two Major Roles:
- Gamete production (inside seminiferous tubules).
- Androgen secretion (outside tubules, in interstitial cells/Leydig cells).

Gamate production within the seminiferous tubule and androgen production outside.
Leydig cells (interstitial cells) produce testosterone.
Germ cells (spermatogonia) along the basement membrane initiate sperm production.
Sertoli cells (nurse cells) guide, support, and protect developing sperm.
Blood-Testis Barrier: Sertoli cells protect developing sperm from the male immune response.
- Anything sperm cells need has to go through the Sertoli cell.

A single, highly coiled tube.
Sperm undergo maturation (gain motility, metabolic changes, cell membrane changes) during transport (2-6 days).
Can store sperm for a period of time.
Stereocilia: tight folds at the end of cells to facilitate an increase in surface area
- Stereocilia function: Absorbing excess fluid to concentrate sperm.
- All maturation changes are androgen/testosterone-dependent.

A long tube (35 cm) that transports sperm from the external to internal environment.
Has a thick muscular wall with longitudinal and circular smooth muscle layers.
Functions for sperm storage and transport.
Sperm can be stored for up to two months.
Vasectomy: cutting the vas deferens for semi-permanent sterilization; requires using other contraceptive methods for two months post-surgery.
The thick muscular wall facilitates effective ejaculation by responding to pressure changes.

Contribute to seminal fluid.
Three important accessory glands:
- Bulbar Urethra Glands: paired glands that contribute less than 5% of the seminal fluid; neutralize the acidic environment of the urethra.
- Seminal Vesicle: paired glands that produce about 65% of the seminal fluid; alkaline to neutralize the acidic environment of the female reproductive tract; contains prostaglandins, clotting proteins, and fructose.
- Prostate: a single gland that provides about 30% of the seminal fluid; contains liquefying enzymes that counteract clotting proteins; high clinical significance due to hypertrophy and cancer risk in males.