Male and Female Reproductive System

Reproductive System Overview

• Gonads are the primary sex organs
• Testes are present in males
• Ovaries are present in females
• Gonads produce gametes: sex cells
• Gonads secrete horomones
• Sperm are male gametes
• Ova or eggs are female gametes

Male Reproductive System Components

• The testes are the primary male reproductive organ
• The duct system includes the epididymis, ductus deferens, and urethra
• Accessory organs include the seminal vesicle, prostate gland, and bulbourethral gland
• The external genitalia consists of the penis and scrotum

Testes

• Coverings of the testes include the tunica albuginea which encapsulates each testis
• Septa are extensions of the capsule; they extend into the testis and divide it into lobules
• Each lobule contains one to four seminiferous tubules: tightly coiled sperm-forming structures
• Sperm are emptied into the rete testis
• Sperm travel through the rete testis into the epididymis
• Interstitial cells produce androgens, such as testosterone

Epididymis

• Comma-shaped, tightly coiled tube
• Located on the superior part of the testis and along the posterior lateral side
• Functions to mature and store sperm cells for at least 20 days
• Sperm are expelled with the contraction of muscles in the walls to the vas deferens

Ductus Deferens (Vas Deferens)

• Carries sperm from the epididymis to the ejaculatory duct
• Passes through the inguinal canal and over the bladder
• Moves the sperm by peristalsis
• The spermatic cord contains the ductus deferens, blood vessels, and nerves within a connective tissue sheath
• Ends in the ejaculatory duct and then unites with the urethra
• Vasectomy: cutting the ductus deferens at the level of the testes; this prevents the transportation of sperm

Urethra

• Extends from the base of the urinary bladder to the tip of the penis
• Carries both urine and sperm
• Sperm enters the ejaculatory duct to urethra
• Regions of the urethra include:
  • Prostatic urethra: surrounded by prostate
  • Membranous urethra: from the prostatic urethra to the penis
  • Spongy (penile) urethra: runs the length of the penis

Seminal Vesicles

• Located at the base of the bladder
• Produces a thick, yellowish secretion accounting for 60% of semen
• This secretion includes fructose (sugar), vitamin C, prostaglandins, and other substances that nourish/activate sperm

Prostate Gland

• Encircles the upper part of the urethra
• Secretes a milky fluid to help activate sperm
• Enters the urethra through several small ducts

Bulbourethral Glands

• Pea-sized glands inferior to the prostate
• Produces a thick, clear mucus which:
  • Cleanses the urethra of acidic urine
  • Serves as a lubricant during sexual intercourse
  • Is secreted into the penile urethra

Semen

• Is a mixture of sperm and accessory gland secretions
• Accessory gland secretions have many advantages:
  • Fructose provides energy for sperm cells
  • The alkalinity in semen helps neutralize the acidic environment of the vagina
  • Semen inhibits bacterial multiplication
  • Elements of semen enhance sperm motility

External Genitalia: Scrotum

• The scrotum is a divided sac of skin outside of the abdomen.
• It maintains the testes at 3°C lower than normal body temperature to protect sperm viability.

External Genitalia: Penis

• Delivers sperm into the female reproductive tract
• Regions of the penis:
  • Shaft
  • Glans penis (enlarged tip)
  • Prepuce (foreskin): the skin that is folded around the proximal end and is often removed by circumcision
• The penis has three areas of spongy erectile tissue around the urethra

Spermatogenesis

• Production of sperm cells which begins at puberty and continues throughout life
• Occurs in the seminiferous tubules
• Spermatogonia (stem cells) undergo rapid mitosis to produce more stem cells before puberty
• Follicle Stimulating Hormone (FSH) modifies spermatogonia division
  • Results in one stem cell
  • The other cell produced becomes a primary spermatocyte
• Primary spermatocytes undergo meiosis and haploid spermatids are produced
• Spermiogenesis: late spermatids are produced with distinct regions
  • Head contains DNA covered by the acrosome
  • Midpiece
  • Tall
• Sperm cells are produced after the maturing of spermatids
• Spermatogenesis takes 64 to 72 days

Female Reproductive System

• Includes the ovaries and duct system
• The duct system consists of the uterine (fallopian) tubes, uterus, and vagina
• The external genitalia is included

Ovaries

• Composed of ovarian follicles (sac-like structures)
• Structure of an ovarian follicle includes:
  • Oocyte
  • Follicular cells

Ovarian Follicle Stages

• Primary follicle contains an immature oocyte
• Graafian (vesicular) follicle is a growing follicle with a maturing oocyte
• Ovulation occurs when the mature egg ruptures; this occurs about every 28 days
• The ruptured follicle is then transformed into a corpus luteum

Support for Ovaries

• Suspensory ligaments secure the ovary to the lateral walls of the pelvis
• Ovarian ligaments attach it to the uterus
• A broad ligament, a fold of the peritoneum, encloses the suspensory ligament

Uterine (Fallopian) Tubes

• Receives the ovulated oocyte
• Provides a site for fertilization and attaches to the uterus
• Does not physically attach to the ovary, but is supported by the broad ligament
• Fimbriae are finger-like projections at the distal end that receive the oocyte
• Cilia inside the uterine tube slowly move the oocyte towards the uterus (takes three to four days)
• Fertilization occurs inside of the uterine tube

Uterus

• Located between the urinary bladder and rectum
• Hollow organ with several functions:
  • Receives a fertilized egg
  • Retains the fertilized egg
  • Nourishes the fertilized egg
• Support includes:
  • Broad ligament attached to the pelvis
  • Round ligament anchored interiorly
  • Uterosacral ligaments anchored posteriorly
• Regions of the uterus:
  • Body: main protion
  • Fundus: area where uterine tube enters
  • Cervix: narrow outlet that protrudes into the vagina
• Walls include:
  • Endometrium: inner layer that allows for implantation of a fertilized egg and sloughs off when pregnancy does not occur (menses)
  • Myometrium: middle layer of smooth muscle
  • Serous layer: outer visceral peritoneum

Vagina

• Extends from the cervix to the exterior of body
• Behind the bladder and in front of the rectum
• Serves as the birth canal
• Receives the penis during sexual intercourse
• The hymen partially closes the vagina until it is ruptured

External Genitalia (Vulva)

• Mons pubis: fatty area overlying the pubic symphysis that is covered with pubic hair Labia skin folds:
  • Labia majora
  • Labia minora
• Vestibule: enclosed by the labia majora that contains the opening of the urethra and the greater vestibular glands (produce mucus)
• Clitoris: contains erectile tissue and corresponds to the male penis

Oogenesis

• Total supply of eggs are present at birth
• The ability to release eggs begins at puberty
• Reproductive ability ends at menopause
• Oocytes are matured in developing the ovarian follicles
• Oogonia are female stem cells found in a developing fetus
• Undergo mitosis to produce primary oocytes
• Are surrounded by cells to form primary follicles in the ovary
• No longer exists by the time of birth
• Primary oocytes are inactive until puberty
• Follicle Stimulating Horomone (FSH) causes some primary follicles to mature
• Meiosis starts inside a maturing follicle and produces a secondary oocyte and the first polar body
• Meiosis is completed after ovulation only if sperm penetrates and two additional polar bodies are produced

Menstrual (Uterine) Cycle

• Cyclic changes of the endometrium are regulated by the cyclic production of estrogens and progesterone
• Stages include:
  • Menses: functional layer of the endometrium is being sloughed.
  • Proliferative stage: regeneration of the functional layer
  • Secretory stage: endometrium will increase in size and will ready for implantations for fertilized eggs

Hormone Production in Ovaries

• Estrogen is produced by follicle cells and cause secondary sex characteristics to develop
• These include the enlargement of the accessory organs, development of breasts, appearance of pubic air, an increased fat beneath the skin, widening and lightning of the pelvis, and the onset of menses
• Progesterone is produced by the corupus luteum and production of it contains until Luteinizing Horomone (LH) diminishes in the blood
• Progesterone helps maintain pregnancy

Mammary Glands

• Present in both sexes, but only function in females
• Modified sweat glands
• Functions is to produce milk
• Stimulated by sex hormones (mostly estrogens) to increase in size

Stages of Pregnancy and Development

• Fertilization precedes embryonic development and then fetal development and finally childbirth

Fertilization

• The oocyte is viable for 12-24 hours after ovulation.
• Sperm is viable for 12-48 hours after ejaculation.
• Sperm cells must make their way to the uterine tube for fertilization to be possible
• Membrane receptors on an oocyte pull in the head of the first sperm cell to make contact; then the oocyte undergoes its second meiotic division
• Fertilization occurs when the genetic material of a sperm combines with that of an oocyte to form a zygote

The Zygote

• Is the first cell of new individual
• The result of a fusion of DNA from sperm and egg
• Begins rapid mitotic cell divisions and is in the uterine tube, moving towards the uterus

The Embryo

• Developmental stage from the start of cleavage until the ninth week
• Undergoes division without growth.
• Enters the uterus at the 16-cell state
• Floats free in the uterus temporarily
• Has uterine secretions that are used for nourishments

The Blastocyst

• Ball-like circle of cells which begins at about the 100 cell stage
• Secretes human chorionic gonadotropin (hCG)to produce the corpus luteum and continue producing hormones
• Implants in the wall of the uterus by day 14

Development After Implantation

• Chorionic villi: projections of the blastocyst that develop and cooperate with cells of the uterus to form the placenta
• Embryo is surrounded by the amnion (a fluid filled sac)
• An umbilical cord forms to attach the embryo to the placenta

Functions of the Placenta

• Forms a barrier between mother and embryo (blood is not exchanged)
• Delivers nutrients and oxygen
• Removes waste from embryonic blood
• Becomes an endocrine organ (produces horomones) and takes over for the corpus luteum:
  • Estrogen -Progesterone
  • Other horomones that maintain pregnancy

The Fetus

• By the end of the eighth week all organ systems are formed
• Activities include growth and organ specialization
• Stage of tremendous growth and change in appearance

The Effects of Pregnancy on the Mother

• Pregnancy is the period from conception until birth
• Anatomical changes include:
  • Enlargements of the uterus
  • Accentuated lumbar curvature
  • Relaxation of the pelvic ligaments and public symphysis due to productions of relaxin
• Physiological changes
  • Gastrointestinal system: morning sickness due to elevated progesterone; heartburn due to organ crowding; and constipation due to declining motility of the digestive tract
  • Urinary system: kidneys have additional burden and produce more urine; the uterus compresses the bladder
  • Respiratory system: nasal mucosa becomes congested and swollen; vital capacity and respiratory rate increase
  • Cardiovascular system: body water rises; blood volume increase by 25 to 40%; blood pressure and pulse increase; varicose veins are common

Childbirth (Partition)

• Labor is the series of events that expel the infant from the uterus
• Initiation of labor is enacted by estrogen levels rising, uterine contractions beginning, the placenta releases prostaglandins, oxytocin is released by the pituitary, and the combination of these hormones produces contractions
• Stages of labor:
  • Dilation: cervix becomes dilated; uterine contractions begin and increase; the amnion ruptures
  • Expulsion: infant passes through the cervix and vagina; normal delivery is head first
  • Placental stage: delivery of the placenta

Developmental Aspects of the Reproductive System

• Gender is determined at fertilization: males have XY sex chromosomes and females have XX sex chromosomes
• Gonads do not begin to form until the eighth week
• Testes form in the abdominal cavity and descend to the scrotum one month before birth
• The determining factor for gonad differentiation is testosterone
• Reproductive system organs do not function until puberty, which occurs usually between the ages of 10-15
• The first menses usually occurs about two years after the start of puberty
• Most women reach peak reproductive ability in their late 20s
• Menopause occurs when ovulation and menses cease entirely; the ovaries stop functioning as endocrine organs
• There is no equivalent of menopause in males, but there is a steady decline in testosterone

Test your knowledge of the male and female reproductive systems. Questions cover gamete production, accessory organs, and the functions of various structures. Explore the roles of testes, ovaries, uterine tubes, and associated ligaments.