The Reproductive System Pages 744-752, 755-767, 769-772 25 PART 1 The Reproductive System Pages 744-752, 755-767, 769-772

The Reproductive System Primary sex organs Testes Ovaries Accessory sex organs Glands External genitalia

The Male Reproductive System Testes are located within the scrotum The scrotum—Skin and superficial fascia surrounding the testes Positioning provides an environment 3˚ cooler than body temperature Dartos muscle—layer of smooth muscle Cremaster muscle—bands of skeletal muscle surrounding the testes Elevates the testes

The Male Reproductive System Ureter Peritoneum Urinary bladder Seminal vesicle Ampulla of ductus deferens Prostatic urethra Pubis Ejaculatory duct Membranous urethra Rectum Urogenital diaphragm Prostate Corpus cavernosum Bulbourethral gland Corpus spongiosum Anus Spongy urethra Bulb of penis Ductus (vas) deferens Epididymis Glans penis Testis Prepuce Scrotum External urethral orifice Figure 25.1

Relationship of the Testes to the Scrotum Urinary bladder Superficial inguinal ring (end of inguinal canal) Testicular artery Spermatic cord Ductus (vas) deferens Penis Autonomic nerve fibers Middle septum of scrotum Pampiniform venous plexus Cremaster muscle Epididymis External spermatic fascia Tunica vaginalis (from peritoneum) Superficial fascia containing dartos muscle Tunica albuginea of testis Scrotum Internal spermatic fascia Skin Figure 25.2

Are enclosed in a serous sac—the tunica vaginalis The Testes Are enclosed in a serous sac—the tunica vaginalis Tunica albuginea—fibrous capsule of the testes Divides each testis into 250–300 lobules Lobules contain 1–4 coiled seminiferous tubules Epididymis Comma-shaped structure on posterior testis

The Testes Figure 25.3a, b Spermatic cord Spermatic cord Blood vessels Head of epididymis Body of epididymis Tail of epididymis Efferent ductule Rete testis Straight tubule Duct of epididymis Ductus (vas) deferens Lobule Testis Septum Tunica albuginea Tunica vaginalis Cavity of tunica vaginalis Spermatic cord Seminiferous tubule Blood vessels and nerves (a) Spermatic cord Epididymis Testis (b) Figure 25.3a, b

The Testes Seminiferous tubule Spermatogenic cells Areolar connective tissue Sustentocyte and nucleus Interstitial cells Sperm Myoid cells (c) Figure 25.3c

Epithelium consists of Microscopic Anatomy Seminiferous tubules Separated by areolar connective tissue Epithelium consists of Spermatogenic cells—sperm-forming cells Columnar sustentacular cells (Sertoli)—support cells

Microscopic Anatomy Spermatogenic cells produce sperm Sperm formation 400 million sperm formed per day Begins at puberty Process takes 75 days Cells differentiate and move toward the lumen Spermatogonia—stem cells Primary spermatocytes Secondary spermatocytes Spermatids Sperm

Sustenocytes (Sertoli cells) Microscopic Anatomy Sustenocytes (Sertoli cells) Surround spermatogenic cells Extend from basal lamina to the lumen Assist sperm production Secrete testicular fluid

The Testes Seminiferous tubule Spermatogenic cells Areolar connective tissue Sustentocyte and nucleus Interstitial cells Sperm Myoid cells (c) Figure 25.3c

Myoid cells—surround seminiferous tubules Microscopic Anatomy Myoid cells—surround seminiferous tubules Contract rhythmically Interstitial cells (Leydig cells) Secrete testosterone Secretion regulated by luteinizing hormone (LH)

Duct of the epididymis is 6m long (when uncoiled) Dominated by pseudostratified columnar epithelium Bears tufts of stereocilia—immotile, long microvilli 20-day journey for sperm to move through Gain the ability to swim and to fertilize an egg through the acrosomal reaction

The Epididymis Spermatic cord Blood vessels and nerves Ductus (vas) deferens Testis Head of epididymis Seminiferous tubule Efferent ductule Rete testis Lobule Straight tubule Septum Tunica albuginea Body of epididymis Tunica vaginalis Duct of epididymis Cavity of tunica vaginalis Tail of epididymis (a) Figure 25.3a

The Epididymis Smooth muscle around the duct of the epididymis Loose connective tissue outside the duct Stereocilia Duct of the epididymis Sperm in the lumen Pseudostratified columnar epithelium (a) Duct of the epididymis (110) Lumen Mucosa Smooth muscle Pseudostratified columnar epithelium Internal longitudinal layer Middle circular layer Lamina propria External longitudinal layer Adventitia (connective tissue) (b) Ductus deferens (7) Figure 25.4

Stores and transports sperm Histology of the ductus deferens Epithelium—pseudostratified columnar Thick muscularis Adventitia

The Epididymis Smooth muscle around the duct of the epididymis Loose connective tissue outside the duct Stereocilia Duct of the epididymis Sperm in the lumen Pseudostratified columnar epithelium (a) Duct of the epididymis (110) Lumen Mucosa Smooth muscle Pseudostratified columnar epithelium Internal longitudinal layer Middle circular layer Lamina propria External longitudinal layer Adventitia (connective tissue) (b) Ductus deferens (7) Figure 25.4

The Ductus Deferens Figure 25.1 Ureter Peritoneum Urinary bladder Seminal vesicle Ampulla of ductus deferens Prostatic urethra Pubis Ejaculatory duct Membranous urethra Rectum Urogenital diaphragm Prostate Corpus cavernosum Bulbourethral gland Corpus spongiosum Anus Spongy urethra Bulb of penis Ductus (vas) deferens Epididymis Glans penis Testis Prepuce Scrotum External urethral orifice Figure 25.1

Superior portion of ductus deferens The Spermatic Cord Contains Ductus deferens Testicular blood vessels Nerves Superior portion of ductus deferens Runs through inguinal canal

The Spermatic Cord Urinary bladder Superficial inguinal ring (end of inguinal canal) Testicular artery Spermatic cord Ductus (vas) deferens Penis Autonomic nerve fibers Middle septum of scrotum Pampiniform venous plexus Cremaster muscle Epididymis External spermatic fascia Tunica vaginalis (from peritoneum) Superficial fascia containing dartos muscle Tunica albuginea of testis Scrotum Internal spermatic fascia Skin Figure 25.2

The Ductus Deferens Figure 25.1 Ureter Peritoneum Urinary bladder Seminal vesicle Ampulla of ductus deferens Prostatic urethra Pubis Ejaculatory duct Membranous urethra Rectum Urogenital diaphragm Prostate Corpus cavernosum Bulbourethral gland Corpus spongiosum Anus Spongy urethra Bulb of penis Ductus (vas) deferens Epididymis Glans penis Testis Prepuce Scrotum External urethral orifice Figure 25.1

Carries sperm from ejaculatory ducts to “outside” The Urethra Carries sperm from ejaculatory ducts to “outside” Three parts of male urethra Prostatic Membranous Spongy

The Urethra Figure 25.6 Ureter Ampulla of ductus deferens Seminal vesicle Urinary bladder Ejaculatory duct Prostate Prostatic urethra Orifices of prostatic ducts Bulbourethral gland and duct Membranous urethra Urogenital diaphragm Bulb of penis Root of penis Crus of penis Bulbourethral duct opening Ductus deferens Corpora cavernosa Epididymis Corpus spongiosum Shaft (body) of penis Testis Section of (b) Spongy urethra Glans penis Prepuce (foreskin) External urethral orifice (a) Figure 25.6

Accessory Glands The seminal vesicles Lie on the posterior surface of the urinary bladder Secretes about 60% of the volume of semen Fluid contains Fructose to nourish sperm Substances to enhance sperm motility Prostaglandins Substances that suppress immune response against semen Enzymes that clot and then liquefy semen

The Urethra Figure 25.6 Ureter Ampulla of ductus deferens Seminal vesicle Urinary bladder Ejaculatory duct Prostate Prostatic urethra Orifices of prostatic ducts Bulbourethral gland and duct Membranous urethra Urogenital diaphragm Bulb of penis Root of penis Crus of penis Bulbourethral duct opening Ductus deferens Corpora cavernosa Epididymis Corpus spongiosum Shaft (body) of penis Testis Section of (b) Spongy urethra Glans penis Prepuce (foreskin) External urethral orifice (a) Figure 25.6

Accessory Glands The prostate gland Encircles the prostatic urethra Secretes about 25—30% of seminal fluid Contains substances that Enhance sperm motility Enzymes that clot and then liquefy semen

Accessory Glands Bladder Pubic symphysis Rectum Prostate Anterior Submucosal glands Mucosal glands Main glands Urethra Connective tissue capsule Fibromuscular stroma Figure 25.7

The bulbourethral glands Accessory Glands The bulbourethral glands Pea-sized glands inferior to the prostate gland Produce a mucus Mucus enters spongy urethra prior to ejaculation Neutralizes traces of acidic urine Lubricates urethra

The Urethra Figure 25.6 Ureter Ampulla of ductus deferens Seminal vesicle Urinary bladder Ejaculatory duct Prostate Prostatic urethra Orifices of prostatic ducts Bulbourethral gland and duct Membranous urethra Urogenital diaphragm Bulb of penis Root of penis Crus of penis Bulbourethral duct opening Ductus deferens Corpora cavernosa Epididymis Corpus spongiosum Shaft (body) of penis Testis Section of (b) Spongy urethra Glans penis Prepuce (foreskin) External urethral orifice (a) Figure 25.6

The Penis External anatomy Shaft—body Glans penis—distal expanded end Prepuce—foreskin Removed during circumcision

The Penis Internal anatomy Three erectile bodies One corpus spongiosum Surrounds spongy urethra Two corpora cavernosa make up most of the penis

The Penis Figure 25.6 Ureter Ampulla of ductus deferens Urinary bladder (a) Bulbourethral gland and duct Urogenital diaphragm Bulb of penis Corpora cavernosa Corpus spongiosum Section of (b) Spongy urethra Prepuce (foreskin) External urethral orifice Crus of penis duct opening Ductus deferens Ampulla of ductus deferens Prostatic urethra Orifices of prostatic ducts Prostate Membranous urethra Root of penis Glans penis Shaft (body) of penis Ejaculatory duct Seminal vesicle Epididymis Testis Ureter Figure 25.6

The Female Reproductive System Produces gametes (ova) Prepares to support a developing embryo Undergoes changes according to the menstrual cycle Menstrual cycle is the monthly cycle as it affects all female reproductive organs Includes Ovaries Uterine tubes, uterus, and vagina

Female Internal Reproductive Organs Suspensory ligament of ovary Infundibulum Uterine tube Ovary Peritoneum Fimbriae Uterosacral ligament Uterus Round ligament Perimetrium Vesicouterine pouch Rectouterine pouch Urinary bladder Pubic symphysis Rectum Mons pubis Posterior fornix Cervix Urethra Clitoris Anterior fornix Vagina External urethral orifice Anus Hymen Urogenital diaphragm Labium minus Greater vestibular (Bartholin’s) gland Labium majus Figure 25.11

The Female Reproductive System Suspensory ligament of ovary Uterine (fallopian) tube Uterine tube Ovarian blood vessels Fundus of uterus Lumen (cavity) of uterus Ampulla Ovary Mesosalpinx Isthmus Mesovarium Infundibulum Broad ligament Fimbriae Mesometrium Round ligament of uterus Ovarian ligament Endometrium Body of uterus Myometrium Wall of uterus Ureter Perimetrium Uterine blood vessels Internal os Isthmus Cervical canal Uterosacral ligament External os Lateral cervical (cardinal) ligament Lateral fornix Cervix Vagina Figure 25.12

Small, almond-shaped organs The Ovaries Small, almond-shaped organs Produce ova Held in place by ligaments and mesenteries Broad ligament Suspensory ligament Ovarian ligament

Internal Structure of the Ovaries Tunica albuginea Fibrous capsule of the ovary Covered in simple columnar epithelium Ovarian cortex—houses developing oocytes Follicles—multicellular sacs housing oocytes Ovarian medulla—loose connective tissue Contains blood vessels, lymph vessels, and nerves

Structure of the Ovary Tunica albuginea Granulosa cells Cortex Antral follicle Degenerating corpus luteum (corpus albicans) Oocyte Mesovarium and blood vessels Germinal epithelium Mature ovarian (Graafian) follicle Primary follicles Antrum Oocyte Ovarian ligament Zona pellucida Theca folliculi Medulla Ovulated oocyte Corpus luteum Corona radiata Developing corpus luteum Figure 25.13

Figure 25.13 Photomicrograph of a mammalian ovary. Germinal epithelium Tunica albuginea Cortex Medulla Primary follicles Secondary follicle Antrum of a mature ovarian follicle

Receive ovulated oocyte Parts of the uterine tube The Uterine Tubes Receive ovulated oocyte Parts of the uterine tube Infundibulum—distal end of uterine tube Surrounded by fimbriae Ampulla—half the length of uterine tube Usual site of fertilization Isthmus—medial third of uterine tube

The Female Reproductive System Suspensory ligament of ovary Uterine (fallopian) tube Uterine tube Ovarian blood vessels Fundus of uterus Lumen (cavity) of uterus Ampulla Ovary Mesosalpinx Isthmus Mesovarium Infundibulum Broad ligament Fimbriae Mesometrium Round ligament of uterus Ovarian ligament Endometrium Body of uterus Myometrium Wall of uterus Ureter Perimetrium Uterine blood vessels Internal os Isthmus Cervical canal Uterosacral ligament External os Lateral cervical (cardinal) ligament Lateral fornix Cervix Vagina Figure 25.12

The Uterine Tubes Muscularis Mucosa Ciliated columnar epithelium Nonciliated epithelium Lamina propria (a) Cross section through the ampulla (10) (b) Enlargement of the mucosa (180) Figure 25.14

The Uterine Tubes Figure 25.12 Suspensory ligament of ovary Uterine (fallopian) tube Uterine tube Ovarian blood vessels Fundus of uterus Lumen (cavity) of uterus Ampulla Ovary Mesosalpinx Isthmus Mesovarium Infundibulum Broad ligament Fimbriae Mesometrium Round ligament of uterus Ovarian ligament Endometrium Body of uterus Myometrium Wall of uterus Ureter Perimetrium Uterine blood vessels Internal os Isthmus Cervical canal Uterosacral ligament External os Lateral cervical (cardinal) ligament Lateral fornix Cervix Vagina Figure 25.12

The Uterus Lies anterior to rectum—posterior to bladder Anteverted (anteflexed) usual position of uterus Parts of the uterus Fundus—rounded superior portion Cervix—“neck” of uterus Cervical canal—communicates with vagina inferiorly Internal os—opening connecting with uterine cavity External os—inferior opening of cervix

The Uterus Suspensory ligament of ovary Infundibulum Uterine tube Peritoneum Fimbriae Uterosacral ligament Uterus Round ligament Perimetrium Vesicouterine pouch Rectouterine pouch Urinary bladder Pubic symphysis Rectum Mons pubis Posterior fornix Cervix Urethra Clitoris Anterior fornix Vagina External urethral orifice Anus Hymen Urogenital diaphragm Labium minus Greater vestibular (Bartholin’s) gland Labium majus Figure 25.11

The Female Reproductive System Suspensory ligament of ovary Uterine (fallopian) tube Uterine tube Ovarian blood vessels Fundus of uterus Lumen (cavity) of uterus Ampulla Ovary Mesosalpinx Isthmus Mesovarium Infundibulum Broad ligament Fimbriae Mesometrium Round ligament of uterus Ovarian ligament Endometrium Body of uterus Myometrium Wall of uterus Ureter Perimetrium Uterine blood vessels Internal os Isthmus Cervical canal Uterosacral ligament External os Lateral cervical (cardinal) ligament Lateral fornix Cervix Vagina Figure 25.12

Wall of the uterus composed of Uterine Wall Wall of the uterus composed of Perimetrium, myometrium, and endometrium Embryo burrows into endometrium Endometrium has two layers Functional layer Basal layer

Figure 25.16 The endometrium of the uterus and its blood supply. Lumen of uterus Epithelium Capillaries Uterine glands Functional layer of the endometrium Venous sinusoids Lamina propria of connective tissue Spiral artery Straight artery Basal layer of the endometrium Endometrial vein Radial artery Portion of the myometrium Smooth muscle fibers Arcuate artery Uterine artery

The Female Menstrual Cycle and Oogenesis Monthly menstrual cycle Due to hormonal fluctuations in ovaries and uterus Ovarian cycle—stimulates production of ovarian follicles and oocytes Uterine cycle—prepares uterine wall for implantation

Has three successive phases The Ovarian Cycle Has three successive phases Follicular phase Ovulation Luteal phase

The Ovarian Cycle Follicular phase First half of the ovarian cycle 6–12 primordial follicles stimulated to develop Growth stimulated by FSH from anterior pituitary Primordial follicle becomes a primary follicle Zona pellucida—glycoprotein coat surrounding oocyte Theca folliculi—internal layer secretes hormones

Figure 25.18 The ovarian cycle. Primordial follicles 2 Primary follicle 3 Secondary follicle Granulosa cells Theca folliculi 3 4 4 Antral follicle 2 Forming antrum Theca folliculi 1 Primary oocyte 8 Zona pellucida Antrum Secondary oocyte 5 7 6 Secondary oocyte 7 Corona radiata Zona pellucida Antrum 7 Corpus luteum (forms from ruptured follicle) 6 Follicle ruptures; secondary oocyte ovulated 5 Mature ovarian follicle carries out meiosis I; ready to be ovulated

Follicular phase (continued) Antrum forms The Ovarian Cycle Follicular phase (continued) Antrum forms A fluid filled cavity between granulosa cells Primary follicles become a secondary follicle Corona radiata—coat of granulosa cells surrounding oocyte Secondary follicle enlarges and becomes Vesicular (Graafian) follicle—ready to be ovulated

The Ovarian Cycle Ovulation Occurs about halfway through each ovarian cycle (Day 14) One mature oocyte exits from one ovary Enters peritoneal cavity Swept into uterine tube Sudden increase in LH is signal for ovulation

The Ovarian Cycle Luteal phase Occurs after ovulation in last half of the ovarian cycle Remaining follicle becomes a corpus luteum Secretes progesterone Acts to prepare for implantation of an embryo If no implantation Corpus luteum dies and becomes a corpus albicans

Figure 25.18 The ovarian cycle. Primordial follicles 2 Primary follicle 3 Secondary follicle Granulosa cells Theca folliculi 3 4 4 Antral follicle 2 Forming antrum Theca folliculi 1 Primary oocyte 8 Zona pellucida Antrum Secondary oocyte 5 7 6 Secondary oocyte 7 Corona radiata Zona pellucida Antrum 7 Corpus luteum (forms from ruptured follicle) 6 Follicle ruptures; secondary oocyte ovulated 5 Mature ovarian follicle carries out meiosis I; ready to be ovulated

Figure 25.19 The menstrual cycle: structural and hormonal changes. Fluctuation of gonadotropin levels: Fluctuating levels of pituitary gonadotropins (follicle-stimulating hormone and luteinizing hormone) in the blood regulate the events of the ovarian cycle. LH Plasma hormone level FSH Ovarian cycle: Structural changes in the ovarian follicles during the ovarian cycle are correlated with (d) changes in the endometrium of the uterus during the uterine cycle. Mature ovarian follicle Primary follicle Secondary follicle Ovulation Corpus luteum Degenerating corpus luteum Follicular phase Ovulation (Day 14) Luteal phase Fluctuation of ovarian hormone levels: Fluctuating levels of ovarian hormones (estrogens and progesterone) cause the endometrial changes of the uterine cycle. The high estrogen levels are also responsible for the LH/FSH surge in (a). Plasma hormone level Estrogens Progesterone Endometrial glands Blood vessels The three phases of the uterine cycle Menstrual: Shedding of the functional layer of the endometrium. Proliferative: Rebuilding of the functional layer of the endometrium. Secretory: Begins immediately after ovulation. Enrichment of the blood supply and glandular secretion of nutrients prepare the endometrium to receive an embryo. Menstrual flow Functional layer Basal layer Both the menstrual and proliferative phases occur before ovulation, and together they correspond to the follicular phase of the ovarian cycle. The secretory phase corresponds in time to the luteal phase of the ovarian cycle. Days 1 5 10 15 20 25 28 Menstrual phase Proliferative phase Secretory phase

Series of cyclic phases of the endometrium The Uterine Cycle Series of cyclic phases of the endometrium Phases coordinate with the ovarian cycle Endometrial phases directed by FSH and LH Phases of uterine cycle Menstrual phase—days 1–5 Stratum functionalis is shed Proliferative phase—days 6–14 Secretory phase—days 15–28

Figure 25.19 The menstrual cycle: structural and hormonal changes. Fluctuation of gonadotropin levels: Fluctuating levels of pituitary gonadotropins (follicle-stimulating hormone and luteinizing hormone) in the blood regulate the events of the ovarian cycle. LH Plasma hormone level FSH Ovarian cycle: Structural changes in the ovarian follicles during the ovarian cycle are correlated with (d) changes in the endometrium of the uterus during the uterine cycle. Mature ovarian follicle Primary follicle Secondary follicle Ovulation Corpus luteum Degenerating corpus luteum Follicular phase Ovulation (Day 14) Luteal phase Fluctuation of ovarian hormone levels: Fluctuating levels of ovarian hormones (estrogens and progesterone) cause the endometrial changes of the uterine cycle. The high estrogen levels are also responsible for the LH/FSH surge in (a). Plasma hormone level Estrogens Progesterone Endometrial glands Blood vessels The three phases of the uterine cycle Menstrual: Shedding of the functional layer of the endometrium. Proliferative: Rebuilding of the functional layer of the endometrium. Secretory: Begins immediately after ovulation. Enrichment of the blood supply and glandular secretion of nutrients prepare the endometrium to receive an embryo. Menstrual flow Functional layer Basal layer Both the menstrual and proliferative phases occur before ovulation, and together they correspond to the follicular phase of the ovarian cycle. The secretory phase corresponds in time to the luteal phase of the ovarian cycle. Days 1 5 10 15 20 25 28 Menstrual phase Proliferative phase Secretory phase

Consists of three coats The Vagina Consists of three coats Adventitia—fibrous connective tissue Muscularis—smooth muscle Mucosa—marked by transverse folds Consists of lamina propria and stratified squamous epithelium Hymen—an incomplete diaphragm Fornix—recess formed at the superior part of the vagina

The Vagina Suspensory ligament of ovary Infundibulum Uterine tube Peritoneum Fimbriae Uterosacral ligament Uterus Round ligament Perimetrium Vesicouterine pouch Rectouterine pouch Urinary bladder Pubic symphysis Rectum Mons pubis Posterior fornix Cervix Urethra Clitoris Anterior fornix Vagina External urethral orifice Anus Hymen Urogenital diaphragm Labium minus Greater vestibular (Bartholin’s) gland Labium majus Figure 25.11

The Vagina Figure 25.12 Suspensory ligament of ovary Uterine (fallopian) tube Uterine tube Ovarian blood vessels Fundus of uterus Lumen (cavity) of uterus Ampulla Ovary Mesosalpinx Isthmus Mesovarium Infundibulum Broad ligament Fimbriae Mesometrium Round ligament of uterus Ovarian ligament Endometrium Body of uterus Myometrium Wall of uterus Ureter Perimetrium Uterine blood vessels Internal os Isthmus Cervical canal Uterosacral ligament External os Lateral cervical (cardinal) ligament Lateral fornix Cervix Vagina Figure 25.12

The External Genitalia Mons pubis Labia majora Prepuce of clitoris Labia minora Clitoris (glans) Urethral orifice Vestibule Hymen (ruptured) Vaginal orifice Anus Opening of the duct of the greater vestibular gland (a) Figure 25.20a

Pregnancy Events leading to fertilization Sperm binds to the zona pellucida Undergoes the acrosomal reaction Release of enzymes to form a slit in the zona pellucida Fusion of oocyte and sperm plasma membranes Cortical reaction Enzymes prevent any other sperm from binding to the egg Fertilization—chromosomes of male and female gametes join

Events Leading to Fertilization Fusion of oocyte and sperm plasma membranes Cortical reaction Sperm nucleus engulfed by oocyte cytoplasm (a) (b) Oocyte cytoplasm Cortical granule Oocyte plasma membrane Extracellular space Zona pellucida Sperm nucleus Granulosa cells of corona radiata Acrosomal Acrosome Oocyte in second meiotic division First polar body Corona radiata Sperm Figure 25.22

Implantation Blastocyst begins implantation Blastocyst consists of About 6 days after conception Blastocyst consists of An inner cell mass and outer trophoblast Trophoblast forms two layers Cytotrophoblast—inner layer Syncytiotrophoblast—outer layer

Implantation Figure 25.25 Maternal blood vessels Endometrium Amnion Yolk sac Extraembryonic mesoderm Chorion being formed Lumen of uterus Proliferating syncytiotrophoblast Cytotrophoblast Amniotic cavity Bilayered embryonic disc (b) 12-day blastocyst. Implantation is complete. Extraembryonic mesoderm is forming a discrete layer beneath the cytotrophoblast. Maternal blood vessels Proliferating syncytiotrophoblast Cytotrophoblast Amniotic cavity Bilayered embryonic disc Endometrial epithelium Implanting 71/2-day blastocyst. The syncytiotrophoblast is eroding the endometrium. (a) Lacuna (intervillous space) containing maternal blood Amniotic cavity Primary germ layers Ectoderm Chorionic villus Chorion Amnion Yolk sac Extraembryonic mesoderm Lumen of uterus (c) 16-day embryo. Cytotrophoblast and associated mesoderm have become the chorion, and chorionic villi are elaborating. The body stalk forms the basis of the umbilical cord. Mesoderm Endoderm Forming body stalk Allantois coelom Figure 25.25

Implantation Decidua basalis Maternal blood Chorionic villus Umbilical blood vessels in umbilical cord Amnion Amniotic cavity Yolk sac Extraembryonic coelom Chorion Lumen of uterus Decidua capsularis (d) 41/2 -week embryo. The decidua capsularis, decidua basalis, are well formed. The chorionic villi lie in blood-filled intervillous spaces within the endometrium. The embryo is now receiving its nutrition via the umbilical vessels that connect it (through the umbilical cord) to the placenta. Figure 25.25d

Embryonic and maternal tissues contribute to the placenta Decidua basalis Chorionic villi Yolk sac Amnion Amniotic cavity Umbilical cord Uterus Decidua capsularis Lumen of uterus Extraembryonic coelom (e) 13-week fetus Figure 25.25e

Anatomy of the Placenta Exchanges across the chorionic villi between maternal and fetal blood Provide fetus with nutrients and oxygen Dispose of its wastes Allow hormonal signals to be sent to the mother By Week 13 the placenta is fully formed

Anatomy of the Placenta Decidua basalis Maternal arteries Maternal veins Chorionic villi Myometrium Umbilical cord Stratum basalis of endometrium Uterus Lumen of uterus Decidua capsularis Maternal portion of placenta (decidua basalis) Chorionic villus containing fetal capillaries Fetal portion of placenta (chorion) Maternal blood in lacuna (intervillous space) Fetal arteriole Umbilical arteries Fetal venule Umbilical vein Amnion Connection to yolk sac Umbilical cord Figure 25.26