reproductive system. cell cycle produces gametes by meiosis

Reproductive SystemReproductive System

Cell CycleCell Cycle

• Produces gametes by meiosis


• Meiosis reduces the number of chromosomes in half


• Gametes have only 23 chromosomes

Homologous ChromosomesHomologous Chromosomes

• 2 chromosomes that make up a chromosome pair in cells


• Contain similar genes


• The exception is the sex chromosomes


• The female contains two X chromosomes


• The male has an X and a Y chromosome


• The other 22 pairs of chromosomes are called autosomes

Diploid CellDiploid Cell

• A cell with a full set of chromosomes

Haploid CellHaploid Cell

• One with only one chromosome from each pair


• Gametes are the only haploid cells


• Eggs and spermatoza

Male Reproductive SystemMale Reproductive System

• Testes• A system of ducts• Several supporting structures• Penis

ScrotumScrotum

• Cutaneous outpouching of the abdomen that supports the testes

ScrotumScrotum

• Internally a vertical septum divides it into two sacs, each containing a single testis

TestesTestes

• Paired oval-shaped glands in the scrotum

TestesTestes

• Contain seminiferous tubules ( in which sperm cells are made)

TestesTestes

• Sertoli Cells - Embedded among the spermatogenic cells in the tubules

Sertoli CellsSertoli Cells

• Nourish spermatocytes, spermatids, and spermatozoa


• Control movements of spermatogenic cells


• Controls the release of spermatozoa into the lumen of the seminiferous tubule


• Secretes fluid for sperm transport and the hormone inhibin


• Inhibin decreases FSH when the rate of spermatogenesis is too high

TestesTestes

• Leydig cells – found in the spaces between adjacent seminiferous tubules secrete testosterone

SpermatogenesisSpermatogenesis

• Process by which seminiferous tubules of the testes produce sperm


• Spermatogonia – stem cells


• Spermatogonia undergo mitosis to produce future stem cells and primary spermatocytes


• Diploid primary spermatocytes undergo meiosis I forming haploid secondary spermatocytes


• Meiosis II results in haploid spermatids


• Spermiogenesis – maturation of the spermatids into spermatozoa

Mature SpermMature Sperm

• Consist of a head, midpiece, and tail


• The head contains a specialized lysosome called an acrosome


• The acrosome has an enzyme that helps penetrate the egg


• The midpiece is rich in mitochondria for ATP production


• ATP is essential for the motility of flagellum


• They are produced at the rate of about 100-300 million per day


• Have a life expectancy of 48 hours within the female reproductive tract

Hormonal Control of Hormonal Control of SpermatogenesisSpermatogenesis

• At puberty Gonadotropin releasing hormone increases, which stimulates the A.P. secretion of FSH and LH


• FSH initiates spermatogenesis


• LH assists spermatogenesis and stimulates the production of testosterone by the Leydig cells

TestosteroneTestosterone

• Controls the growth, development, functioning, and maintenance of sex organs


• Stimulates bone growth, protein anabolism, increases in muscle size, and sperm maturation


• It increases libido and stimulates the development of secondary sex characteristics


• It reduces LH secretion, which decreases testosterone production

Secondary Male Sex Secondary Male Sex CharacteristicsCharacteristics

• Wide shoulders


• Narrow hips


• Male hair patters


• Thick and oily skin


• Enlarged larynx with a deeper voice

DuctsDucts

• The duct system of the testes includes the 1. Seminiferous tubules2. Straight tubules3. Rete Testis4. Epididymis5. Ductus Deferens6. Ejaculatory Duct7. Urethra

EpididymisEpididymis

• Comma-shaped organ that lies along the posterior border of the testis

EpididymisEpididymis

• Sperm are transported out of the testes through the ductus epididymis

Ductus EpididymisDuctus Epididymis

• Lined by stereocilia


• Site of sperm maturation and storage


• Sperm may remain in storage here for at least a month

Vas DeferensVas Deferens

• Stores sperm and propels them toward the urethra during ejaculation

Ejaculatory DuctsEjaculatory Ducts

• Formed by the union of the ducts from the seminal vesicles and ducti deferens

Ejaculatory DuctsEjaculatory Ducts

• Function to eject spermatozoa into the prostatic urethra

Male urethraMale urethra

• Serves as a passageway for semen and urine

Seminal VesiclesSeminal Vesicles

• Secretes a viscous alkaline fluid that contains fructose that nourish and promote the fertilizing capability of sperm


• The alkaline fluid helps neutralize acid in the male urethra and female reproductive tract


• The fructose is for ATP production by sperm

Prostate GlandProstate Gland

• Secretes a milky, slightly acidic fluid

Bulbourethral GlandsBulbourethral Glands

• Secretes mucus for lubrication and an alkaline substance that neutralizes acid

SemenSemen

• Average volume 2.75 ml

SemenSemen

• Contains 50-150 million spermatozoa/ml

SemenSemen

• The average sperm count has declined from 113 million/ml to 66 million/ml over the past 44 years

SemenSemen

• May be due to estrogens in meat, marijuana, environmental toxins, alcohol, and lead exposure

PenisPenis

• Male organ of copulation that consists of a

1. Root2. Body3. Glans penis4. foreskin

PenisPenis

• Spongy tissue in shaft composed of 1. Two dorsal corpora cavernosa2. Ventral corpos spongiosum

PenisPenis

• Arterioles (which are normally constricted) supply blood to blood sinuses

PenisPenis

• The blood sinuses become filled with blood during erection

ErectionErection

• Mediated by a parasympathetic reflex

ErectionErection

• Neurons and vascular endothelial cells release nitric oxide which leads to arteriolar smooth muscle relaxation

ErectionErection

• This vasodilation increases blood flow into the penis

EjaculationEjaculation

• Propulsion of semen from the urethra to the exterior is a sympathetic reflex

Female Reproductive SystemFemale Reproductive System

• Ovaries• Uterine tubes• Uterus• Vagina• Vulva• Mammary Glands

OvariesOvaries

• Paired glands that are homologous to the testes

OvariesOvaries

• Located in the upper pelvic cavity on either side of the uterus

Ovarian CortexOvarian Cortex

• Contain ovarian follicles and consists of oocytes in various stages of development

Primordial folliclesPrimordial follicles

• Contain the primary oocyte surrounded by a single layer of flattened epithelial cells


• Contain 46 chromosomes stuck in prophase of meiosis 1


• A woman is born with 2 million primordial follicles


• During childhood, most undergo atresia


• By puberty, only 400,000 are left


• Each month, about 20 primordial follicles mature into primary follicles

Primary folliclesPrimary follicles

• Primary oocyte surrounded by one to several layers of cuboidal epithelial cells that make estrogen


• These epithelial cells are called granulosa cells


• In between the oocyte and granulosa cells is a glycoprotein called the zona pelucida


• Outside the granulosa cells are two layers of connective tissue called

1. Theca externa2. Theca interna


• Many primaries undergo atresia


• Some become secondary follicles

Secondary FolliclesSecondary Follicles

• Have a fluid filled antrum

Secondary folliclesSecondary follicles

• As the menstrual cycle progresses toward midcycle all of the secondaries undergo atresia except one

Secondary folliclesSecondary follicles

• One follicle will become the dominant follicle- the Graafian follicle

Graafian FollicleGraafian Follicle

• The primary oocyte will complete meiosis I and go through part of meiosis II, but pause at metaphase II


• It’s now called the secondary oocyte


• The follicle expel the secondary oocyte by a process called ovulation

Immature ovumImmature ovum

• Surrounding it is the zona pelucida and a layer of follicular cells called the corona radiata

Corpus luteumCorpus luteum

• Contains the remnants of an ovulated follicle and produces

1. Progesterone2. Estrogen3. Relaxin4. Inhibin

Corpus luteumCorpus luteum

• It eventually degenerates into a corpus albicans

OogenesisOogenesis

• Occurs in the ovaries

OogenesisOogenesis

• It results in the formation of a single haploid secondary oocyte

OogenesisOogenesis

• Meisosis II is not complete until fertilization

Ovarian MedullaOvarian Medulla

• Contains1. Blood vessels2. Lymphatics3. Nerves

Uterine TubeUterine Tube

• Transport ova from the ovaries to the uterus


• Normal sites of fertilizaiton


• Fimbriae – are projections of the tubes that help capture the ovulated immature ovum


• The fallopian tube is the usually the site of fertilization


• Ciliated cells and peristaltic contractions help move a secondary oocyte toward the uterus

UterusUterus

• An organ the size and shape of an inverted pear

UterusUterus

• Functions in the transport of spermatozoa, menstruation, implantation of a fertilized ovum, development of a fetus during pregnancy, and labor

UterusUterus

• Cervix – connects the vaginal cavity to the uterine cavity

UterusUterus

• Cervix – firm unless it is softened by relaxin during labor and delivery

Histology of the UterusHistology of the Uterus

1. Perimetrium2. Myometrium3. Endometrium

PerimetriumPerimetrium

• Part of the visceral peritoneum

MyometriumMyometrium

• Consists of three muscle layers and has oxytocin receptors

EndometriumEndometrium

• Divided into the 1. Stratum Functionalis2. Stratum Basalis

EndometriumEndometrium

• Spiral arteries supply the endometrium

CervixCervix

• Secretory cells of the cervix produce a cervical mucus

CervixCervix

• At mid cycle the mucus is thin and receptive to sperm

CervixCervix

• During most of the menstrual cycle the mucus is thick

VaginaVagina

• 10 cm in the adult

VaginaVagina

• Functions as a passageway for spermatozoa and the menstrual flow

VaginaVagina

• It is acidic in order to inhibit microorganisms and sperm

VaginaVagina

• The vaginal orifice in virgins is partially covered by the hymen

VulvaVulva

• External genitalia of the female

VulvaVulva

• It consists of 1. Mons pubs – rounded fatty eminence

overlying the pubic symphysis

VulvaVulva

2. Labia majora – covered with hair

VulvaVulva

3. Labia minora – thinner folds that are devoid of hair, they atrophy after menopause

VulvaVulva

4. Clitoris – homologous to the penis

VulvaVulva

5. Vestibule – cleft between labia minora where vaginal orifice opens to the outside

VulvaVulva

6. Vaginal orifice

VulvaVulva

7. Urethral orifices – between the clitoris and the vaginal orifice

VulvaVulva

8. Hymen

Mammary GlandsMammary Glands

• Milk producing glands that lie over the pectoralis major and serratus anterior muscle


• Milk secreting cells (alveoli) are clustered in small compartments (lobules) within the breasts


1. Alveoli2. Mammary ducts3. Lactiferous ducts4. Lactiferous sinuses5. Nipple


• Function to synthesize milk and secretion and ejection of milk (lactation)


• Areola is the pigmented skin that surrounds the nipple


• Develop at puberty under the stimulation of rising estrogen and progesterone levels

Phases of the Female Phases of the Female Reproductive CycleReproductive Cycle

1. Menstrual cycle2. Preovulatory phase3. Ovulation4. Postovulatory phase

Menstrual CycleMenstrual Cycle

• First five days of cycle


• About 20 small follicles in each ovary begin to develop


• Stratum functionalis layer of the endometrium is shed discharging blood, tissue fluid, mucus, and epithelial cells


• It is shed due to declining progesterone at the end of the previous cycle

Preovulatory phasePreovulatory phase

• Between menstruation and ovulation


• Lasting from days 6-13 in a 28 day cycle


• Primary follicles develop into secondary follicles


• A single secondary follicle develops into a Graafian or mature follicle


• Maturing follicles secrete estrogen


• The mature follicle continues to increase its estrogen production due to increasing levels of LH


• Estrogen stimulates endometrial repair; a new stratum functionalis is formed

OvulationOvulation

• Rupture of the Graafian or mature follicle with release of the secondary oocyte into the pelvic cavity

OvulatationOvulatation

• LH transforms the ruptured follicle into the corpus luteum

OvulationOvulation

• Occurs on day 14

OvulationOvulation

• The high levels of estrogen during the last part of the preovulatory phase exerts a positive feedback on LH and GnRH to cause ovulation

OvulationOvulation

• GnRH promotes release of FSH and LH

OvulationOvulation

• LH surge brings about the ovulation

OvulationOvulation

• Increased body temperature due to progesterone, which increases just prior to ovulation

OvulationOvulation

• Clear cervical mucus due to high estrogen

OvulationOvulation

• Corpus luteum secretes estrogens and progesterone due to LH

Postovulatory phasePostovulatory phase

• Days 15-28


• Time between ovulation and the onset of the next menstrual period


• Estrogen and progesterone are secreted in large quantities by the corpus luteum


• If fertilization and implantatin do not occur, estrogen and progesterone secreted by the corpus luteum inhibit LH


• So Corpus luteum loses its support


• The copus luteum degenerates and becomes the corpus albicans


• The decreased levels of estrogen and progesterone initiatates another menstrual phase


• Because estrogen and progesterone levels drop, there is less negative feedback on the Hyp. and A.P.


• FSH and LH begin to rise a bit at the end of the cycle, causing another round of follicular development (about 20)


• If fertilization and implantation do occur, the corpus luteum is maintained until the placenta takes over


• Corpus luteum is maintained by human chorionic gonadotropin (hCG) from the developing placenta


• The corpus luteum secretes estrogens and progesterones to support pregnancy and breast development for lactation


• Once the placenta begins secreting estrogen and progesterone, the role of corpus luteum becomes minor


• Endometrium thickens in anticipation of implantation

reproductive system. cell cycle produces gametes by meiosis

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