Reproductive System Chapter 27: Anatomy and Physiology of the Male Reproductive System

Male Reproductive System

• Gamete: specialized sex cell carrying 23 chromosomes
• Sperm: male gamete
• Oocyte: female gamete
• Testes:
  • Produce sperm and androgens to support reproduction
  • Located inside the scrotum to maintain a temperature 2-4°C lower than body temperature
  • Surrounded by dartos and cremaster muscles that contract or relax to raise or lower the testes
• Testes anatomy:
  • Paired, 2-layered male gonads
  • Tunica vaginalis: outer serous membrane
  • Tunica albuginea: tough connective tissue covering the entire testes, separating it into 300-400 lobules
  • Seminiferous tubules: where sperm develops inside the lobules, tightly coiled
• Sertoli cells: promote sperm production, create the blood-testis barrier due to tight junctions
• Spermatogonia: stem cells or germ cells of the testes
• Spermatogenesis: process of producing sperm in the seminiferous tubules, begins at puberty, takes 64 days, and one cycle starts every 16 days, producing 4 haploid daughter cells (spermatids)

Structure of Formed Sperm

• Smaller than most cells, 85,000 times less volume than female gametes
• Composed of:
  • Head: haploid nucleus and little cytoplasm, covered in lysosomal enzymes in the acrosome
  • Mid-piece: tightly packed mitochondria
  • Tail: flagellum for movement or motility
• Produce 100-300 million sperm per day

Sperm Travel

• Start in seminiferous tubules and move via fluid to epididymis, taking 12 days to move through the epididymis
• Epididymis: 6 meters long, tightly coiled, continues maturation, and stores sperm in the tail until ejaculation occurs
• Duct system: sperm exit and are pushed to ductus deferens (thick muscular tube, part of spermatic cord)
• Ampulla: where the duct ends, posterior to the bladder

Seminal Vesicles and Prostate Gland

• Seminal vesicles: contribute 60% of semen volume, producing fructose for ATP
• Prostate gland:
  • As big as a walnut, consisting of muscle and gland tissue
  • Secrete fluid to coagulate semen, which will later de-coagulate in the female
  • Size doubles at puberty and gradually grows after age 25
  • Benign prostatic hyperplasia (BPH): prostate enlargement leading to urinary issues
  • Prostate cancer: second most common cancer in men, detected by Hx, blood test, and rectal exam

Bulbourethral Glands and Penis

• Bulbourethral glands: add a thick and salty fluid to semen to lubricate the end of the urethra and vagina and clean urine residue
• Penis:
  • 3 chambers surrounding the urethra fill with blood (vasocongestion) during arousal and REM sleep
  • Nitric oxide (NO) release dilates blood vessels and rapidly increases blood volume to fill chambers

Testosterone

• Secreted by the testes from the 7th week of development to differentiate male sexual organs
• Increases at puberty, producing 6-7 mg/day, with low levels leading to infertility
• Maintains the male reproductive system, promotes muscle development, bone growth, secondary sex characteristics, and libido in men and women
• Ovaries and adrenal glands secrete a small amount of testosterone
• Controlled by the hypothalamus and pituitary gland, with GnRH stimulating the release of LH and FSH

Female Reproductive System

• Produces gametes and hormones, supports and delivers a developing fetus
• Primarily located inside the pelvic cavity
• Ovaries: female gonads
• Oocyte: gamete produced in females
• Vulva: external reproductive structures
• Labia minora: protect the reproductive tract and urethra
• Clitoris: derives from the same cells as the penis, with abundant nerve innervation
• Hymen: thin membrane that partially covers the vagina
• Vagina: muscular canal, entrance to the reproductive tract, exit for the fetus, expands for intercourse and childbirth, and has an acidic pH for self-cleaning

Ovaries

• Paired gonads, almond-sized
• Attached to the uterus by the ovarian ligament
• Superficial ovarian epithelium covers dense tunica albuginea
• Oocytes develop in the outer layer of the cortex
• Follicle: supporting cells surrounding the oocyte
• Ovarian medulla: blood vessels, lymph vessels, and nerves of the ovary

Ovarian Cycle

• 28-day cycle, not the same as the menstrual cycle
• Only occurs during reproductive years
• Consists of two interrelated processes: oogenesis and folliculogenesis
• Follicular phase: follicles mature and prepare to release an oocyte
• Ovulation: release of a mature oocyte
• Luteal phase: the dominant follicle becomes the corpus luteum and produces progesterone

Oogenesis

• Oogonia: ovarian stem cells, divide by mitosis, formed during fetal development
• Primary oocytes halt development until puberty and last until menopause
• 1-2 million oogonia in an infant, 400,000 at puberty, and 0 at menopause
• Ovulation: releasing an oocyte from the ovary
• Cells divide unequally, with only 1 cell large enough to become a mature ovum, and the other 3 becoming polar bodies

Folliculogenesis

• Normally leads to ovulation every 28 days, with the death of multiple other follicles
• Atresia: death of ovarian follicles
• A few primordial follicles respond to recruitment each day and become primary follicles
• Primary follicles increase in size and become secondary follicles
• Oocyte secretes a membrane to increase size, becoming a tertiary follicle

Uterine Tubes (Fallopian)

• Path from ovary to uterus, not connected to the ovary
• Isthmus: narrow end connected to the uterus
• Infundibulum: wide distal end with fimbriae
• Ampulla: middle section where fertilization often occurs
• Cilia propel the oocyte to the uterus, with stronger beats in the presence of estrogen

Uterus and Cervix

• Uterus: muscular organ to nourish the growing embryo
• Fundus: area superior to the uterine tubes
• Body of uterus: middle section
• Cervix: inferior section that projects into the vagina, secreting mucus that assists sperm movement
• Uterus is held in place by ligaments and consists of 3 layers (perimetrium, myometrium, endometrium)
• The stratum functionalis is the layer of the endometrium that is shed during menstruation

Menstrual Cycle

• Uterine lining is shed, rebuilt, and prepares for implantation, with three phases:
  • Menses phase: lining is shed, lasts about 5 days, with low hormone levels
  • Proliferative phase: endometrium rebuilds, with rising hormone levels
  • Secretory phase: started by progesterone from the corpus luteum, preparing the body for implantation

The Breasts

• Accessory organs that supply milk to the infant, lactation
• Mammary glands produce milk, which exits through the nipple
• Areolar glands surround the nipple and secrete lubricating fluid to prevent chaffing
• Breasts are supported by suspensory ligaments
• Changing hormone levels lead to swelling and tenderness during pregnancy, and mammary tissue develops and breasts enlarge

Hormonal Birth Control

• Manipulate the negative feedback system
• Provide constant hormones to prevent FSH and LH production
• Endometrial wall will not get as thick
• New birth control pills may result in no menses
• Missing the wrong day or two can lead to ovulation