The Reproductive System - College of the Canyons

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Transcript The Reproductive System - College of the Canyons

The Reproductive System

Reproduction

Sexual determination and differentiation

Gross anatomy

Functions

Gametogenesis

Prenatal Hormones and Sex Differentiation

• Fetus is sexually undifferentiated as to which sex it will become • Gonads begin to develop at 5 or 6 weeks as gonadal ridges • Two sets of ducts adjacent to each gonadal ridge – mesonephric ducts develop into male reproductive system • paramesonephric ducts degenerate – paramesonephric ducts (müllerian ducts) develop into female reproductive tract • mesonephric ducts degenerate • SRY gene (sex-determining region of Y chromosome) – in males, codes for a protein, testes-determining factor (TDF), that initiates development of testes • begin to secrete testosterone 8 to 9 weeks • stimulates mesonephric ducts to develop into the male anatomy • secrete müllerian-inhibiting factor = degeneration of the paramesonephric ducts • Female development occurs in absence of androgen hormones – Estrogen levels always high during pregnancy

Development of Reproductive Tracts

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Mesonephros Gonadal ridge Kidney Mesonephric duct Paramesonephric (müllerian) duct Cloaca Testes Efferent ductules Epididymis Paramesonephric duct (degenerating) Mesonephric duct forming the ductus deferens Urinary bladder Seminal vesicle Urogenital sinus forming the urethra Male 7 to 8 weeks 5- to 6-week embryo; sexually indifferent stage Female Ovaries Paramesonephric duct forming the uterine tube Mesonephric duct (degenerating) Fused paramesonephric ducts forming the uterus Urinary bladder (moved aside) Urogenital sinus forming the urethra and lower vagina 8 to 9 weeks

Figure 27.3

Urinary bladder Seminal vesicle Prostate gland Bulbourethral gland Ductus deferens Epididymis Testis Urethra Penis Uterine tube Ovary Uterus Urinary bladder (moved aside) Vagina Urethra Hymen Vestibule At birth At birth

Development of External Genitalia

• Similarity of external genitalia of both sexes : – genital tubercle becomes the head (glans) of the penis or glans clitoris – pair of urogenital folds encloses urethra of male forming the penis or forms the labia minora – pair of labioscrotal folds becomes either scrotum or labia majora • Distinct male or female genitalia developed by week 12 • Homologous organs - male and female organs that develop from same embryonic structure – penis is homologous to the clitoris – scrotum is homologous to the labia majora

Development of External Genitalia

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Genital tubercle Urogenital fold Labioscrotal fold Tail 6 weeks

Figure 27.4

Phallus: Developing glans of penis Urethral groove Male Anus Urethral orifice Glans of penis Prepuce Scrotum Perineal raphe Anus 10 weeks 12 weeks

27-6

8 weeks Developing glans of clitoris Labia minora Urethral groove Labia majora Anus Female 10 weeks Prepuce Glans of clitoris Urethral orifice Vaginal orifice Perineal raphe Anus 12 weeks

Functions

Production of haploid gametes

Endocrine functions

Copulatory organs

Nurture and develop embryos

Male Reproductive System

• Primary sex organs – Testis • Accessory organs – Duct system • Epididymis • • Vas deferens Urethra – Glands • Seminal vesiscle • Prostate • Bulbourethral – Penis

Sperm production Testes

Secretion of testosterone

– Interstitial cells

Histology of Testis

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Interstitial cells Blood vessel Germ cells Sustentacular cell Tails of spermatozoa (a) Blood vessel Seminiferous tubule Spermatids Sustentacular cell nuclei Tubule lumen Germ cells Connective tissue wall of tubule Interstitial cells (b) 50 µm

a: Copyright by R.G. Kessel and R.H. Kardon,

Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy

, 1979, W.H. Freeman, All rights reserved; b: © Ed Reschke Figure 27.10 a-b

The Scrotum and Spermatic Cord

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External inguinal ring Spermatic cord: Cremaster muscle Testicular artery Ductus deferens Pampiniform plexus Epididymis Tunica vaginalis Testis Fascia of spermatic cord Superficial fascia of penis Deep fascia of penis Prepuce (foreskin) Glans Median septum of scrotum Cremaster muscle Dartos muscle Scrotal skin

Figure 27.7

Countercurrent Heat Exchanger

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Pelvic cavity 37 ° C Testicular artery Blood flow Pampiniform plexus Blood flow

Figure 27.8

Arterial blood cools as it descends Heat transfer Venous blood carries away heat as it ascends 35 ° C Testis Key Warmest blood Coolest blood

Spermatogenesis

Spermiogenesis

Spermiogenesis changes that transform spermatids into spermatozoa

– discarding excess cytoplasm and growing tails Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Golgi complex Acrosomal vesicle Nucleus Bridge to adjacent spermatid Acrosome 1 Basal body Flagellum Appearance of acrosomal vesicle and flagellum in spermatid 2 Excess cytoplasm Growth of acrosome and flagellum Head Axoneme Mitochondria Midpiece of tail 3 Shedding of excess cytoplasm 4 Mature sperm

Figure 27.16

• •

Spermatozoon

Spermatozoon two parts: head and tail – head is pear-shaped • • • • 4 to 5 microns long structure containing the nucleus, acrosome and basal body of the tail flagella nucleus contains haploid set of chromosomes acrosome – enzyme cap over the apical half of the nucleus that contains enzymes that penetrate the egg basal body – indentation in the basal end of the nucleus where flagellum attaches Tail is divided into 3 regions: – midpiece contains mitochondria around axoneme of the flagella, produces ATP for flagellar movement – principal piece is axoneme surrounded by sheath of supporting fibers • constitutes most of tail – endpiece is very narrow tip of flagella

Spermatozoon

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Acrosome Nucleus Head Basal body Mitochondrion Axoneme Midpiece of tail

Figure 27.17 a-b

Principal piece of tail Endpiece of tail (a) 2 µm

a: Visuals Unlimited

(b)

Duct System

• Epididymis – Stores sperm until ejaculation – Mature and gain motility • Vas deferens – Peristaltic contractions propel sperm toward urethra – Terminates at ejaculatory duct (seminal vesicle) • Urethra – Used in urinary system as well – Three regions • Prostatic • Membranous • spongy Copyright © The McGraw-Hill Companies

Glands

• Seminal Vesicles (seminal fluid) – Alkaline fluid • Fructose, prostaglandins, vesiculase • Prostate – Citrate – Sperm activating enzyme • Bulbourethrals – Neutralizing and cleansing mucus • Sperm + glandular secretions = semen – 2 – 5 ml, 110 million sperm per ml Copyright © The McGraw-Hill Companies

Penis

Copulatory organ in males

Erectile tissue

– Corpora spongiosum – Corpora cavernosa

(a)

Anatomy of Penis

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Dorsal vein Dorsal artery Dorsal nerve Corpus spongiosum Corpus cavernosum Deep fascia Superficial fascia Skin Urethra Corpus spongiosum Prepuce Glans of penis (b) External urethral orifice

Figure 27.12 a-b

Dorsal Ventral Deep artery Tunica albuginea Lacunae Median septum

Male Sexual Response

Excitement marked by erection

Orgasm marked by ejaculation

Resolution

Hormonal Regulation

GnRH

LH and FSH

Testosterone

– Sperm production – Male secondary sexual characteristics

Aging and Sexual Function

Decline in testosterone secretion – – peak secretion at 7 mg/day at age 20 declines to 1/5 of that by age 80 • decline in the number and activity of interstitial cells (testosterone) and sustentacular cells (inhibin) • Rise in FSH and LH secretion after age 50 produces male climacteric (andropause) – little or no effect to mood changes, hot flashes and “illusions of suffocation” • Erectile dysfunction (impotence)– the inability to produce or maintain an erection sufficient for intercourse – 20% of men in 60s to 50% of those in 80s

Functions

Same as in male

– Gametogenesis – Hormone production – Copulatory organs •

Nurture and develop embryo

Sexual Differentiation

Female reproductive tract develops from the paramesonephric ducts – – not because of the positive action of any hormone Due to absence of testosterone and müllerian-inhibiting factor (MIF) • Absence of testosterone: • causes mesonephric ducts to degenerate • genital tubercle becomes the glans clitoris • urogenital folds become the labia minora • labioscrotal folds develop into the labia majora • Absence of MIF: • paramesonephric ducts develop into the uterine tubes, uterus, and vagina

Female Reproductive System

• Primary Sex organ – Ovaries • Accessory Organs – Duct system • Uterine tubes • Uterus • Vagina – External genitalia • Mons pubis • Labia • vestibule • Greater vestibular gland • clitoris tutorvista.com

Duct System

• Uterine tubes – Receives oocytes – Site for fertilization • Uterus – Receive, nourish fertilized ovum – Site of embryological and fetal development • Vagina – Copulatory organ – Birth canal

Uterine Wall

Perimetrium - external serosa layer • Myometrium - middle muscular layer – constitutes most of the uterine wall – composed mainly of smooth muscle • sweep downward from fundus and spiral around the body • less muscular and more fibrous near cervix • produces labor contractions, expels fetus • Endometrium – inner mucosa – simple columnar epithelium, compound tubular glands, and a stroma populated with leukocytes, macrophages, and other cells.

• stratum functionalis – superficial half, shed each menstrual period • stratum basalis - deep layer, stays behind and regenerates a new stratum functionalis with each menstrual cycle – during pregnancy, the endometrium is the site of attachment of the embryo and forms the maternal part of the placenta from which the fetus is nourished

Histology of Endometrium

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Surface epithelium Endometrial gland Lamina propria

Figure 28.6 (1) © Ed Reschke

0.1 mm

Aorta

Vessels of Reproductive Tract

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Suspensory ligament Ovarian branch of uterine artery Arcuate artery Mesosalpinx Common iliac artery Ovarian artery Ovary Vaginal artery Uterine artery Internal iliac artery Spiral arteries

Figure 28.7

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Ligaments

• Uterus supported by the muscular floor of the pelvic outlet and folds of peritoneum that form ligaments around the organ – Broad ligament has two parts • mesosalpinx • mesometrium on each side of the uterus – Cardinal (lateral cervical) ligaments – supports the cervix and superior part of the vagina extending to the pelvic wall – Uterosacral ligaments – paired and attach posterior side of the uterus to the sacrum – Round ligaments – paired and arise from the anterior surface of the uterus, pass through inguinal canals, and terminate in the labia majoris • much like the gubernaculum terminating in the male scrotum

(a)

Uterus

Infundibulum Ampulla

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Isthmus Fundus Body Ovarian ligament Mesosalpinx Uterine tube Fimbriae Myometrium Endometrium Internal os Cervical canal Lateral fornix Cervix External os Ovarian artery Ovarian vein Suspensory ligament Vagina Uterosacral ligament Round ligament Cardinal ligament Ovary Mesometrium

Figure 28.3a

28-32

Vagina

Vagina (birth canal) – 8 -10 cm distensible muscular tube – allows for discharge of menstrual fluid, receipt of penis and semen, and birth of baby – – – outer adventitia, middle muscularis, and inner mucosa tilted posteriorly between rectum and urethra vagina has no glands • transudation lubricates vagina – “vaginal sweating” – serous fluid through its walls and by mucus from the cervical gland above it – fornices – blind-ended spaces formed from the vagina extends slightly beyond the cervix – – transverse friction ridges (vaginal rugae) at lower end mucosal folds form hymen across vaginal opening • Vaginal epithelium – childhood - simple cuboidal – puberty - estrogens transform to stratified squamous • bacteria ferment glycogen rich cells producing acidic pH in vagina – an example of metaplasia – the transformation of one tissue type to another – antigen-presenting dendritic cells – route by which HIV from infected semen invades the female body

The External Genitalia

• External genitalia are collectively called the vulva or pudendum – mons pubis - mound of fat over pubic symphysis bearing most of the pubic hair – labia majora – pair of thick folds of skin and adipose tissue inferior to the mons • pudendal cleft – slit between labia majora – labia minora – medial to labia majora are thin hairless folds • space between forms vestibule which contains urethral and vaginal openings • anterior margins of labia minora join to form hood-like prepuce over clitoris – clitoris - erectile, sensory organ with no urinary role • • primary center for erotic stimulation glans, body, and crura – vestibular bulbs - erectile tissue deep to the labia majora • cause the vagina to tighten around the penis, enhancing sexual stimulation – greater and lesser vestibular and paraurethral glands open into vestibule for lubrication

Ova production

Secretions

– Estrogens – Progesterone

Ovaries

med.saisayan.com

Oogenesis

Ovarian Cycle

Follicular phase

– Maturation of primordial follicle – Production of secondary oocyte •

Ovulation

Luteal phase

– Corpus luteum – Progesterone secretion med.saisayan.com

The Uterine Cycle

• Cyclic changes to endometrium • Days 1-5, menstrual phase – Shedding of stratum functionalis – Bleeding 3-5 days • Days 6-14, proliferative phase – Proliferation of endometrium – Prep for implantation • Days 15-28, secretory phase – Secretion of glycoproteins – Thickening of cervical mucus

Hormonal regulation of ovarian and uterine cycles

Breasts and Mammary Glands

• Breast – mound of tissue overlying the pectoralis major – – enlarges at puberty most of time contains very little mammary gland • Mammary gland – develops within the breast during pregnancy – remains active in the lactating breast – atrophies when a woman ceases to nurse • Principal regions of the breast: – body – conical to pendulous, with the nipple at its apex – axillary tail – extension toward the armpit • lymphatics in axillary tail are important as a route for breast cancer metastasis

Breasts and Mammary Glands

• Nipple surrounded by circular colored zone the areola – sensory nerve fibers of areola trigger a milk ejection reflex when an infant nurses – areolar glands – intermediate between sweat glands and mammary glands • secretions protect the nipple from chapping and cracking during nursing – smooth muscle fibers in dermis of areola that contract in response to cold, touch, and sexual arousal wrinkling the skin and erecting the nipple

Anatomy of Lactating Breast

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Rib Intercostal muscles Pectoralis minor Pectoralis major Fascia Suspensory ligament Lobules Lobe Adipose tissue Nipple Lactiferous sinus Lactiferous duct

Figure 28.9c

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(c) Sagittal section

• • •

Climacteric and Menopause

Climacteric -midlife change in hormone secretion – accompanied by menopause – cessation of menstruation Female born with about 2 million eggs, climacteric begins when there are about 1000 follicles left – follicles less responsive to gonadotropins – – less estrogen and progesterone secretion uterus, vagina, and breast atrophy – intercourse becomes uncomfortable as vagina becomes thinner, less distensible, and drier – vaginal infections more common – – skin becomes thinner cholesterol levels rise increasing the risk of cardiovascular disease – bone mass declines producing increased risk for osteoporosis – – blood vessels constrict and dilate in response to shifting hormone balances hot flashes – spreading sense of heat from the abdomen to the thorax, neck, and face Hormone replacement therapy (HRT) – low doses of estrogen and progesterone to relieve some of these symptoms – risks and benefits are still being debated

Female Sexual Response

Excitement

Orgasm

– Not marked by ejaculation – Rhythmic muscular contractions •

No refractory period