Reproductive systems
Page 3: Reproduction, Development and Aging
The continuation of life is important to all species, human and non-human
The male and female reproductive organs are perfectly adapted for the purpose of sexual reproduction
The development of the fetus into a healthy baby is dependent upon both environmental and genetic factors
From the moment of birth, human beings begin to experience continuous aging
Everyone develops and ages at different rates
The various tissues and organs of the body also develop and age at different rates
Page 4: The Reproductive System: Overview
Sexual Reproduction is the process in which organisms produce offspring by means of uniting gametes
Gametes (spermatozoa ♂, ova ♀) are produced by gonads
Gonads are the primary sex organs: Testes ♂, Ovaries ♀
Gametes are haploid (1n) - contain one set of chromosomes (23 chromosomes)
Union of male and female gametes creates a diploid zygote (2n, 46 chromosomes)
All somatic cells are diploid (2n) - contain two sets of chromosomes, one maternal, one paternal
Page 6: The Reproductive System: Overview
Sex hormones: ♂ androgens, ♀ estrogens & progesterone
They play roles in:
Development and function of the reproductive organs
Sexual behavior and drives
Growth and development of many other organs and tissues
Cause secondary sex characteristics
♂ Deepening of voice, appearance of axillary, facial and pubic hair, enlargement of skeletal muscles and bones
♀ Development of breasts, appearance of axillary and pubic hair, increase in fat beneath the skin, part, widening and lightening of the pelvis, onset of menses (menstrual cycle)
Page 7: Reproductive Anatomy
The genitals are all the structures of reproduction and include:
The gonads
Various ducts which store and transport gametes
Accessory sex glands which produce secretions to protect and support the gametes
Supporting structures that facilitate fertilization and, in females, sustain the growth of the conceptus
Page 8: Male Reproductive System
Testes: Produce spermatozoa and testosterone
Duct system: Deliver sperm to the exterior
Epididymis, ductus (vas) deferens, urethra
Accessory organs: Glands that empty secretions to protect and support sperm into the ducts during ejaculation; produce the bulk of the semen
Seminal vesicles, prostate, bulbourethral glands
External genitalia
Penis (♂ copulatory organ), scrotum (sac of skin and superficial fascia surrounding the testes)
Page 10: Testes
Each testis is approx 4cm X 2.5 cm
Divided into lobules
Each lobule contains 1-4 seminiferous tubules where sperm are produced
Empty sperm into the rete testis
Sperm travels through the rete testis to the epididymis
Interstitial (Leydig) cells surrounding the seminiferous tubules produce androgens such as testosterone
Page 12: The Male Duct System: Epididymis
Tightly coiled tube (6m) found on the superior part of the testis and along the posterior lateral side
Functions to mature and store sperm cells
Sperm takes at least 20 days to mature while they move along the epididymis
Expels sperm during ejaculation with the contraction of muscles in the epididymis walls to the ductus deferens
Sperm can be stored for several months after which time they are phagocytosed
Page 13: The Male Duct System: Ductus (Vas) Deferens & Ejaculatory Duct
The ductus deferens
Carries sperm from the epididymis to the ejaculatory duct by rapid peristalsis during ejaculation
Is carried in the spermatic cord (along with blood vessels, and nerves) from each testis to the deep inguinal ring
Passes through the inguinal canal and over the bladder
Vasectomy = the surgical cutting and sealing of part of each vas deferens, as a means of sterilization
The ejaculatory duct
passes through the prostate gland to merge with the urethra
Page 14: The Male Duct System: Urethra
Extends from the base of the urinary bladder to the tip of the penis
Carries urine or semen (containing sperm)
Regions of the urethra
Prostatic: surrounded by prostate
Membranous: from prostatic urethra to penis
Spongy (penile): runs the length of the penis
Page 16: Accessory Organs
Seminal Vesicles
Located at the base of the bladder
Produces a thick, yellowish alkaline secretion (60% of semen) which contains: Fructose (sugar), Vitamin C, Prostaglandins, other substances that nourish and activate sperm
Prostate
Encircles the upper part of the urethra just below the bladder
Secretes a milky fluid which helps to activate sperm
Enters the urethra through several small ducts
Page 17: Bulbourethral Glands
Pea-sized gland inferior to the prostate
Produces a thick, clear alkaline mucus which is secreted into the penile urethra
The secretion is the first to pass down the urethra during sexual excitation (pre-cum)
Cleanses the urethra of acidic urine
Serves as a lubricant during sexual intercourse
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Semen is a mixture of sperm and accessory gland secretions
Fructose in semen provides energy for sperm cells
The alkalinity of semen helps neutralize the acidic environment of the vagina
Semen has antimicrobial properties
Elements in semen enhance sperm motility
A typical ejaculation contains 2-5 mL of semen, which contains 50-150 million sperm
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The scrotum is a sac of loose skin that contains the testes and maintains them at a lower temperature than the rest of the body
The penis is the copulatory organ that delivers sperm into the female reproductive tract
It has regions such as the shaft, glans penis, and prepuce
Internally, there are three areas of spongy erectile tissue
Erections occur when this erectile tissue fills with blood during sexual excitement
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Spermatogenesis is the production of spermatozoa in the seminiferous tubules of the testes
It begins at puberty and continues throughout life
FSH and LH, secreted by the anterior pituitary, play a role in spermatogenesis
FSH stimulates Sertoli cells and increases the rate of spermatogenesis
LH stimulates Leydig cells to secrete testosterone
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Spermatogenesis takes 64-72 days to complete
FSH stimulates spermatogonia to divide mitotically
The primary spermatocyte divides into two secondary spermatocytes during Meiosis I
Each secondary spermatocyte divides into two spermatids during Meiosis II
Each spermatid loses excess cytoplasm and forms a tail to become a spermatozoan via spermiogenesis
One primary spermatocyte produces four haploid spermatozoa
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The anatomy of a mature sperm cell includes a head, midpiece, and tail
The head contains DNA in a nucleus covered by the acrosome, which helps the sperm penetrate a secondary oocyte
The midpiece is wrapped by mitochondria for ATP generation
The tail, or flagellum, provides motility
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Diagram of the different stages of spermatogenesis
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Role of Sertoli cells in spermatogenesis
Provide nutrients and signals to dividing cells
Dispose of excess cytoplasm sloughed off during spermiogenesis
Secrete testicular fluid for transport of sperm
Tight junctions between Sertoli cells form a blood-testis barrier, preventing sperm antigens from escaping into the blood
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Diagram of the structure of a sperm cell
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Diagram of the different cells involved in spermatogenesis
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Diagram of the different cells involved in spermatogenesis
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The Hypothalamic-Pituitary-Gonadal (HPG) Axis is responsible for hormonal regulation of male reproductive function
The hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to secrete FSH and LH
FSH causes Sertoli cells to release androgen-binding protein (ABP), which makes spermatogenic cells receptive to testosterone
LH stimulates Leydig cells to release testosterone, which triggers spermatogenesis
Rising levels of testosterone result in feedback inhibition on the hypothalamus and pituitary
Inhibin, released by Sertoli cells when sperm count is high, inhibits FSH secretion
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Diagram of the hormonal regulation of male reproductive function
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The sexual response of males requires the parasympathetic and sympathetic nervous systems to work together
Parasympathetic fibers initiate and maintain an erection upon sexual stimulation
Sympathetic stimulation is necessary for the rest of the sexual response, including ejaculation
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Introduction to the female reproductive system
Ovaries produce gametes and sex hormones
Duct system includes uterine tubes, uterus, and vagina
External genitalia are called the vulva or pudendum
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Diagram of the female reproductive system
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Ovaries are paired female reproductive organs that produce oocytes and secrete female hormones
They are composed of ovarian follicles embedded in a highly vascular connective tissue
The ovarian medulla contains blood vessels, lymphatic vessels, and nerves
The ovaries are held in place by several ligaments
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Suspensory Uterine (fallopian) tube ligament of ovary
Fundus Ovarian blood Lumen (cavity) Uterine of uterus of uterus vessels tube Ovary Infundib- ulum Broad ligament Fimbriae Ovarian ligament Round ligament of uterus Body of uterus Endometrium Myometrium Wall of Ureter Perimetrium uterus Cervical canal Uterine blood vessels Uterosacral ligament Cervix Vagina
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Follicles
Each follicle contains an immature egg (oocyte) surrounded by cells called follicle cells if only one layer or Granulosa cells when more than one layer is present
Several stages of development
Primodial/early primary follicle: one layer of follicle cells surrounding a primary oocyte
Late primary follicle/early secondary follicle: two or more layers of granulosa cells form; Meiosis I occurs and a secondary oocyte forms
Late secondary follicle: fluid-filled space between appears between the granulosa cells
Graafian follicle (also called vesicular or tertiary follicle): fluid coalesces to form a central antrum
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Degenerating corpus luteum
Primary follicle
Corpus luteum
Blood vessels
Growing follicles
Corona radiata
Mature vesicular
Secondary oocyte (Graafian) follicle
Germinal
Ovulation
Epithelium
Ruptured follicle
Antrum
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Oogenesis
The primary role of the ovaries are to produce mature secondary oocytes (female gametes) and release one (ovulation) during each monthly ovarian cycle
The total supply of ooctyes are present at birth and the ability to release secondary oocytes begins at puberty
Oocytes are matured in developing ovarian follicles
During reproductive years, non-pregnant females normally exhibit cyclical changes
Reproductive ability ends at menopause
Each cycle takes about a month and involves both oogenesis (ovarian cycle) and preparation of the uterus to receive a fertilized ovum (uterine cycle)
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Oogenesis
During early foetal development, primordial germ cells migrate to the ovaries where they differentiate into oogonia
Oogonia (2n) undergo mitosis to produce primary oocytes
Primary oocytes are surrounded by cells that form primary follicles in the ovary
Oogonia no longer exist by the time of birth
Primary oocytes are inactive until puberty
Follicle stimulating hormone (FSH) causes a primary follicle to mature each month
Cyclic monthly changes constitute the ovarian cycle
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Oogenesis and Ovulation
Each month meiosis I is completed inside a maturing follicle
Produces a secondary oocyte and the first polar body (both 1n)
Follicle development to the stage of a Graafian follicle takes about 14 days
When the secondary oocyte is mature, the follicle ruptures; occurs about every 28 days
Ovulation of a secondary oocyte occurs with the release of luteinizing hormone (LH)
Secondary oocyte is released and surrounded by a corona radiata
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Oogenesis and Ovulation
In the ovary, what remains of the ruptured Graafian follicle becomes the corpus luteum
Essential for establishing and maintaining pregnancy
Secretes progesterone which is responsible for the thickening of the endometrium and its development and maintenance
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Oogenesis and Fertilisation
Meiosis II is completed after ovulation only if sperm penetrates resulting in an ovum and two additional polar bodies
Once the ovum is formed, the 23 chromosomes can be combined with those of the sperm to form the fertilized egg (zygote)
The corpus luteum is “rescued” from degeneration by an LH-like hormone called human chorionic gonadotrophin (hCG) produced by the developing embryo
The corpus luteum goes on to produce hormones well into the 1st trimester until the placenta can take over
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If the secondary oocyte is not penetrated by a sperm, it dies and does not complete meiosis to form an ovum
After approx. 14 days the corpus luteum stops secreting progesterone and degenerates into a corpus albicans (just a mass of fibrous scar tissue)
Without oestrogen (from the follicle) and progesterone (from the corpus luteum) the uterine lining cannot be maintained and it sloughs (menses) = menstruation Oogenesis and Fertilisation
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Male and Female Differences in Gamete Production
Meiosis
Males: produces four functional sperm
Females: produces one functional ovum and three polar bodies
Sex cell size and structure
Sperm are tiny, motile, and get their nutrients from the seminal fluid
Egg is large, non-motile, and contains nutrient reserves to nourish the embryo until implantation
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Meiotic Events Follicle Development in Ovary
Before birth Childhood Primary oocyte Primary oocyte (still arrested in prophase I) Mature vesicular (Graafian) follicle Primary follicle Primary follicle Primary follicle Oocyte Ovulated secondary oocyte Growing follicle Primary oocyte (arrested in prophase I; present at birth) Oogonium (stem cell) Each month from puberty to menopause Meiosis I (completed by one primary oocyte each month) First polar body Mitosis Growth Meiosis II of polar body (may or may not occur) Polar bodies (all polar bodies degenerate) Ovum Second polar body Meiosis II completed (only if sperm penetration occurs) Sperm Ovulation Secondary oocyte (arrested in metaphase II) Follicle cells (ovary inactive)
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Ovary Secondary oocyte LM 30x (c) Ovulation of a secondary oocyte
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Ovarian Cycle
As puberty nears, GnRH is released from the hypothalamus stimulating FSH and LH release by the pituitary
Monthly series of events occurs in two consecutive phases (approx. a 28-day cycle)
Follicular phase: period of follicle growth (days 1–14)
There is a rise in FSH secretion resulting in follicular growth
High levels of estrogens from almost mature follicle stimulate release of more GnRH, FSH and LH.
LH induces ovulation mid-cycle
Luteal phase: period of corpus luteum activity (days 14–28)
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The Hypothalamic-Pituitary-Gonadal (HPG) Axis Responsible for hormonal regulation of reproductive function
Hypothalamus releases GnRH which stimulates the anterior pituitary to secrete FSH and LH
FSH causes the growth of the follicle in the ovary - cells of the developing follicle produce more and more oestrogen stimulating a surge in LH and FSH
LH surge stimulates ovulation
After ovulation the ruptured follicle forms a corpus luteum that produces high levels of progesterone which inhibits FSH
Towards the end of the cycle the corpus luteum breaks down, progesterone production decreases and the next menstrual cycle begins when FSH starts to rise again
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High levels of estrogens from almost mature follicle stimulate release of more GnRH and LH
Hypothalamus, anterior pituitary, ovary, corpus hemorrhagicum (ruptured follicle), almost mature (graafian) follicle
LH surge brings about ovulation
Ovulated secondary oocyte
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Female Duct System: Uterine (Fallopian) Tubes
Approx. 10 cm long supported by part of the broad ligament called the mesosalpinx
Attach to the uterus via the isthmus
Receive the ovulated secondary oocyte and provide a site for fertilization
Cilia create currents to move oocyte into and along the uterine tube towards the uterus
Non-ciliated cells nourish the oocyte and the sperm
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Female Duct System: Uterus
Hollow, muscular organ located between the urinary bladder and rectum
Serves as part of the pathway for sperm deposited in the vagina to reach the uterine tubes
Site of implantation of a fertilized ovum, development of the fetus during pregnancy, and labor
The source of menstrual flow during reproductive cycles when implantation does not occur
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Female Duct System: Uterus
Regions of the uterus: body, fundus, cervix
Cervical glands secrete acidic mucus that blocks sperm entry except during mid-cycle
Layers of the uterus wall: endometrium, myometrium, perimetrium (visceral peritoneum)
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Fundus of uterus
Body of uterus
Cervix of uterus
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Suspensory Uterine (fallopian) tube ligament of ovary
Fundus
Ovarian blood vessels
Lumen (cavity) of uterus
Uterine tube
Ovary
Infundibulum
Broad ligament
Fimbriae
Ovarian ligament
Round ligament of uterus
Body of uterus
Endometrium
Myometrium
Wall of uterus
Perimetrium
Cervical canal
Uterine blood vessels
Uterosacral ligament
Cervix
Vagina
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Endometrium
Two layers: stratum functionalis (functional layer) and stratum basalis (basal layer)
Stratum functionalis changes in response to ovarian hormone cycles and is shed during menstruation
Stratum basalis forms new functionalis after menstruation and is unresponsive to ovarian hormones
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Uterine Vascular Supply
Uterine arteries arise from internal iliacs
Arcuate arteries in the myometrium
Radial branches in the endometrium branch into spiral arteries (stratum functionalis) and straight arteries (stratum basalis)
Constriction of spiral arteries leads to shedding of stratum functionalis resulting in menses
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Perimetrium
Myometrium
Endometrium
Uterine cavity
Radial artery
Endometrial gland
Arcuate artery
Endometrium: Stratum functionalis, Stratum basalis
Uterine artery
Straight arteriole
Radial artery
Spiral arteriole
Cervix
Vagina
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Uterine (Menstrual) Cycle
Cyclic changes of the endometrium regulated by cyclic production of estrogens and progesterone due to the ovarian cycle
Stages of the menstrual cycle: menstrual phase, proliferative stage, secretory stage
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Uterine (Menstrual) Cycle
Menstrual phase: functional layer of the endometrium is sloughed, bleeding occurs for 3-5 days, growing ovarian follicles are producing more estrogen
Proliferative stage: estrogen levels rise and regeneration of functional layer of the endometrium occurs, ovulation occurs at the end of this stage
Secretory stage: levels of progesterone rise and increase the blood supply to the endometrium, which increases in size and readies for implantation
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Uterine (Menstrual) Cycle
If fertilization occurs, the embryo produces hCG which rescues the corpus luteum
If fertilization does not occur, the corpus luteum degenerates and levels of progesterone decline, prostaglandins are released by the "unsupported" endometrium causing constriction of supply arteries and a reduction in blood flow, bloody endometrial tissue eventually sloughs (menses) and exits the body via the vagina
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Hypothalamus, GnRH, anterior pituitary, follicular phase, FSH, luteal phase, LH, mature corpus, primordial, primary, secondary (graafian), ovulation, corpus hemorrhagicum, corpus luteum, corpus albicans, ovarian cycle, progesterone and estrogens, secretory phase, uterine (menstrual) cycle, stratum functionalis, stratum basalis
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Female Duct System: Vagina
A fibromuscular canal lined with mucous membrane that extends from cervix to exterior of body and located between bladder and rectum
Organ of copulation, forms lower birth canal, serves as a passageway for menstrual flow, hymen partially closes the vagina until it is ruptured
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External Genitalia (Vulva or Pudendum)
Mons pubis
Labia
Clitoris
Urethral orifice
Vaginal orifice
Greater vestibular glands
Perineum
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Mons pubis
Labia majora
Prepuce of clitoris
Clitoris
Vestibule
Urethral orifice
Vaginal orifice
Orifice of greater vestibular gland
Labia minora
Perineum
Anus