Female Reproductive Organs 7 Male Reproductive Organs 10 Gametogenesis 10
Meiosis 10
Spermatogenesis 11 Oogenesis 14
Comparison of Male and Female Gametes 14
Female Reproductive Cycles 14 Ovarian Cycle 14
Menstrual Cycle 18
Transportation of Gametes 19 Oocyte Transport 19
Sperm Transport 19 Maturation of Sperms 20
Viability of Oocytes and Sperms 20 Clinically Oriented Questions 20
uberty begins when secondary sex characteristics appear, usually between the ages of 10 to 13 years in females and 12 to 14 years in males. Menarche (first menstrual period) may occur as early as 8 years. Puberty in females is largely completed by age 16.
Puberty in males is also largely completed by age 16; it ends when the first mature sperms are formed.
REPRODUCTIVE ORGANS
Reproductive organs produce and transport germ cells (gametes) from the gonads (testes or ovaries) to the site of fertilization in the uterine tube (Fig. 2-1).
Female Reproductive Organs
Vagina
The vagina serves as the excretory passage for menstrual fluid, receives the penis during sexual intercourse, and forms the inferior part of the birth canal—the cavity of the uterus and vagina through which the fetus passes (see Fig. 2-1A and B).
Uterus
The uterus (womb) is a thick-walled, pear-shaped organ (Fig. 2-2A and B) that consists of two main parts:
•
The body, the expanded superior two thirds•
The cervix, the cylindrical inferior thirdP
1
8 BEFORE WE ARE BORN ESSENTIALS OF EMBRYOLOGY AND BIRTH DEFECTS
Figure 2–1 Schematic sagittal sections of the pelvic regions of a woman (A) and a man (B).
Urinary bladder
Perimetrium Uterine tube Ovary
Sacrum
Cervix
Rectum
Vagina
Anus Labium minora Myometrium
Endometrium
Urinary bladder
Pubic bone
Clitoris Labium majora
A
Pubic bone
Urethra Penis
Ureter
Rectum Sacrum
Ductus deferens Seminal gland
Ejaculatory duct
Prostate
Anus
Bulbourethral gland Ductus deferens
Scrotum
Tail of epididymis Glans penis
Prepuce (foreskin) Seminiferous tubules of testis Erectile tissue of penis
B
The fundus of the uterus is the rounded part of the uterine body that lies superior to the orifices of the uterine tubes. The body of the uterus narrows from the fundus to the isthmus, the constricted region between the body and the cervix (see Fig. 2-2A). The lumen of the cervix, the cervical canal, has a constricted opening, the os (ostium), at each end. The internal os communicates with
the cavity of the body of the uterus, whereas the external os communicates with the vagina. The walls of the body consist of three layers:
•
Perimetrium, a thin external peritoneal layer•
Myometrium, a thick smooth muscle layer•
Endometrium, a thin internal layerC H A P T E R 2 HuMAN REPRODuCTION 9
Figure 2–2 Female reproductive organs. A, Parts of the uterus. B, Diagrammatic frontal (coronal) section of the uterus, uterine tubes, and vagina. The ovaries are also shown.
C, Enlargement of the area outlined in B. The functional layer of the endometrium is sloughed off during menstruation.
Uterine cavity Horn Fundus
Uterine tube
Vagina
Uterine cavity Internal os (opening) Cervical canal External os (opening) Body
Isthmus Cervix
Fornix of vagina
Endometrium Ovary
Cervix
External os Vagina
Isthmus Uterine part
Infundibulum
Fimbria Ampulla
Myometrium Perimetrium
A
B
C
Functional layer
Uterine lumen Epithelium
Uterine gland
Spiral artery
Straight artery Radial branch
Arcuate artery
Uterine artery
Capillary
Lacunae (venous spaces)
Basal layer
Endometrium approx. 5 mm Myometrium
At the peak of its development, the endometrium is 4 to 5 mm thick. During the luteal (secretory) phase of the menstrual cycle (see Fig. 2-8), three layers of the endo- metrium can be distinguished microscopically (see Fig.
2-2C) into the following:
•
A compact layer, consisting of densely packed connec- tive tissue around the neck of the uterine glands•
A spongy layer, composed of edematous connective tissue containing the dilated, tortuous bodies of the uterine glands10 BEFORE WE ARE BORN ESSENTIALS OF EMBRYOLOGY AND BIRTH DEFECTS
•
A basal layer, containing the blind ends of the uterine glandsThe compact and spongy layers—the functional layer—disintegrate and are shed at menstruation and after parturition (childbirth). The basal layer has its own blood supply and is not cast off during menstruation.
Uterine Tubes
The uterine tubes, measuring 10 cm long and 1 cm in diameter, extend laterally from the horns of the uterus (see Fig. 2-2A). Each tube opens into a horn at its proxi- mal end and into the peritoneal cavity at its distal end.
The uterine tube is divided into the following parts:
infundibulum, ampulla, isthmus, and uterine part. The tubes carry oocytes from the ovaries and sperms to the fertilization site in the ampulla (see Fig. 2-2B). The uterine tube also conveys the dividing zygote to the uterine cavity.
Ovaries
The ovaries are almond-shaped reproductive glands that are located close to the lateral wall of the pelvis on each side of the uterus. The ovaries produce oocytes (see Fig.
2-5). When released from the ovary at ovulation, the secondary oocyte passes into one of the uterine tubes.
These tubes open into the uterus, which protects and nourishes the embryo and fetus until birth. The ovaries also produce estrogen and progesterone, the hormones responsible for the development of secondary sex charac- teristics and regulation of pregnancy.
Female External Sex Organs
The female external sex organs are known collectively as the vulva (Fig. 2-3). The labia majora, fatty external folds of skin, conceal the vaginal orifice, the opening of the vagina. Inside these labia are two smaller folds of mucous membrane, the labia minora. The clitoris, a small erectile
organ, is situated at the superior junction of these folds.
The vagina and urethra open into a cavity, the vestibule (cleft between the labia minora). The vaginal orifice varies with the condition of the hymen, a fold of mucous mem- brane that surrounds the orifice (see Fig. 2-3).
Male Reproductive Organs
The male reproductive organs (see Fig. 2-1B) include the penis, testes, epididymis, ductus deferens (vas deferens), prostate, seminal glands, bulbourethral glands, ejacula- tory ducts, and urethra. The oval testes (testicles) are located in the cavity of the scrotum. Each testis consists of many highly coiled seminiferous tubules that produce sperms. Immature sperms pass from the testis into a single, complexly coiled tube, the epididymis, where they are stored. From the epididymis, the ductus deferens carries the sperms to the ejaculatory duct. This duct descends into the pelvis, where it fuses with the ducts of the seminal glands to form the ejaculatory duct, which enters the urethra.
The urethra is a tube that leads from the urinary bladder through the penis to the outside of the body.
Within the penis, erectile tissue surrounds the urethra.
During sexual excitement, this tissue fills with blood, causing the penis to erect. Semen (penile ejaculate) con- sists of sperms mixed with seminal fluid produced by the seminal glands, bulbourethral glands, and prostate.