Reproductive System and Development

Male Reproductive Structures

Female Reproductive Structures

Meiosis, Spermatogenesis, Oogenesis

Hormones of Reproductive System

Male

Female

Menstrual Cycle Events (AKA uterine cycle)

Embryonic Development

Fetal Development

Testes

enclosed in scrotum

Scrotum

pouch of skin designed to regulate temperature of testes

contains seminiferous tubules

Seminiferous Tubules

produces sperm cells (spermatozoa)

contain interstitial cells between tubules that secrete testosterone

Epididymis

comma-shaped structure composed of internal duct and external covering of connective tissue

stores sperm until fully mature and capable of being motile

releases its sperm into vas deferens during sexual intercourse

Vas Deferens (AKA ductus deferens)

receives sperm from epididymis during sexual intercourse

transports sperm outward by means of rapid peristalsis

passes above a ureter behind bladder

Seminal Vesicle

Ejaculatory Duct

Prostate

Bulbourethral Glands (Cowper's glands)

lie posterior to and at base of urinary bladder

donut-shaped organ located at base of bladder and encloses the proximal part of urethra

provides fructose for nourishment

Ovary

Fallopian Tube

Fimbrae

Uterus

Vagina

Follicle

pseudostratified ciliated columnar epithelium

mucus coats and lubricates urethra for passage of sperm during sexual intercourse

raises semen pH

produces sperm and androgens (male sex hormones), especiallly testosterone

produces oocytes that carry maternal chromosomes

finger-like projections

generate a current that moves any oocyte released by ovary into fallopian tube

site of fertilization

protects and nourishes developing baby by forming a vascular connection that later develops into the placenta

implantation occurs in endometrium (innermost layer of uterus)

connects to vagina

serves as receptacle for penis during sexual intercourse

birth canal

serves as passageway for menstruation

Menstrual Phase

Proliferative Phase

Secretory Phase

Meiosis

Spermatogenesis

Oogenesis

Day 1-5 of cycle

Day 6-13

Day 15-28

phase marked by shedding of functional layer of endometrium and lasts through period of menstrual bleeding

development of new functional layer of endometrium overlaps the time of follicle growth and estrogen secretion by ovary

increased vascularization and development of uterine glands occurs primarily in response to progesterone secretion from corpus luteum

FSH and LH stimulated to be secreted

some ovarian follicles develop and produce estrogen

estrogen and inhibin inhibit the hypothalamus and anterior pituitary which causes a drop in FSH

corpus luteum forms and secretes large amounts of estrogen, progesterone, and inhibin

progesterone stimulates uterine lining growth

if oocyte is not fertilized, the corpus luteum regresses and hormone levels drop

estrogen level is higher than progesterone

estrogen level increases, progesterone remains the same, FSH level is higher then decreases below LH

estrogen level starts off higher than progesterone, then progesterone increases and exceeds estrogen

follicle goes into secondary follicle stage

secondary follicle continues into mature follicle

sex cell division that starts off with a diploid parent cell in gonad (each containing 23 chromosomes) and produces haploid daughter cells called gametes

produces four daughter cells that are genetically different from parent cell

includes process of crossing over- genetic material is exchanged between homologous chromosomes

Meiosis I

homologous pairs of replicated chromosomes are separated when the cell divides

result is 2 cells, each containing 23 chromosomes (not pairs) that consists of replicated sister chromatids

AKA reduction division because it results in reduction of number of chromosomes in daughter cells

4 phases and cytokinesis

Prophase I

Metaphase I

Anaphase I

Telophase I

homologous replicated chromosomes in parent cell pair up to from a tetrad (synapsis)

crossing over occurs as chromosomes come together; ensures continued genetic diversity in new organisms

ends with breakdown of nuclear envelope

pairs of each tetrad line up at midline, forming double line of chromosomes according to independent assortment (maternal and paternal chromosomes can be on either side of midline)

spindle fibers extend from centrioles at opposite ends of the cell and attach to centromere of each homologous replicated chromosome

pairs of chromosomes are pulled to opposite ends of the cell (process of maternal and paternal pairs moving to opposite sides is called reduction division)

pairs of chromosomes are no longer together, but each replicated chromosome still consists of two sister chromatids

replicated chromosomes arrive at opposite ends of cell, then nuclear membrane may re-form around these chromosomes

Cytokinesis

cleavage furrow forms in cell, then cell cytoplasm divides to produce 2 new cells

each daughter cell contains 23 replicated chromosomes only, but each chromosome is composed of 2 sister chromatids bound together

cells formed then must undergo another round of cell division (meiosis II) to separate sister chromatids

Meiosis II

AKA second meiotic division

sister chromatids separate and become single chromosomes in haploid cells

Prophase II

resembles prophase stage of mitosis

in each of 2 new cells, nuclear envelope breaks down and chromosomes collect together

crossing over does not occur

Metaphase II

spindle fibers extend from centroles to centromere of each chromatid

replicated chromosomes (sister chromatids) align to from a single line along equator in middle of cell

Anaphase II

sister chromatids of each replicated chromosome are pulled apart at centromere and are now separated

sister chromatid is now called single chromosome and is pulled to opposite pole of cell

Telophase II

nuclear membranes re-form

Cytokinesis

cleavage furrow forms

cytoplasm in both cells divide

daughter cells mature into secondary oocytes in females; mature into sperm in males

process of sperm development that occurs in seminiferous tubule of the testis

starts at puberty when significant levels of FSH and LH stimulate the testis to begin gamete development

Step 1

spermatogonia are diploid cells so they have 23 pairs of chromosomes; total of 46 chromosomes

sperm develop from primordial germ (stem) cells called spermatogonia

mitotic divisions of these cells produce a new germ cell and a committed cell (primary spermatocyte)

Step 2

haploid cells (containing 23 chromosomes) produced during meiosis I are called secondary spermatocytes

meiosis I begins in the diploid primary spermatocytes

Step 3

meiosis II originates with the secondary spermatocytes and produces spermatids

Step 4

process of spermiogenesis begins with spermatids and results in morphologic changes needed to form sperm

spermatid sheds excess cytoplasm and its nucleus elongates

acrosome cap forms over the nucleus; contains digestive enzymes that help penetrate the secondary oocyte for fertilization

sperm tail (AKA flagellum) forms

tail attached to midpiece, which contains mitochondria and a centriole (mitochondria used to provide energy to move tail)

the maturation of a primary oocyte to a secondary oocyte

Before birth

embryonic and fetal period

oogonia are diploid cells (contain 23 pairs of chromosomes; total of 46) that are origin of oocytes

mitotic divisions of oogonia produce primary oocytes (diploid cells)

primary oocytes start process of meiosis but are arrested in prophase I

Childhood

ovary is inactive

houses primordial follicles

some deterioration of primordial follicles occur

meiosis I is arrested

Monthly, from puberty to menopause

about 20 primordial follicles mature into primary follicles every month

some primary follicles mature into secondary follicles

primary follicles that do not mature deteriorate

only one secondary follicle matures into a mature follicle

primary oocyte completes the first meiotic division to produce a polar body and a secondary oocyte

secondary oocyte is a haploid cell (23 chromosomes) that is arrested in the second meiotic metaphase

if second oocyte is fertilized, it completes the second meiotic division and becomes an ovum; if not fertilized, it degenerates

without significant levels of progesterone, functional layer lining slacks off

located in pelvic cavity lateral to uterus

consists of an oocyte surrounded by follicle cells which supports the oocyte

6 types of follicles

primordial follicle

earliest type of ovarian follicle

consists of a primary oocyte surrounded by a single layer of flattened follicle cells

primary oocyte is an oocyte that is arrested in the first meiotic prophase

primary follicle

consists of primary oocyte surrounded by one or more layers of cuboidal follicular cells (AKA granulosa cells)

secretes estrogen which stimulates changes in the uterine lining

secondary follicle

contains a primary oocyte, many layers of granulosa cells, and fluid-filled space called antrum

oocyte forced toward one side of follicle, where it is surrounded by a cluster of follicle cells termed cumulus oophorus

primary oocyte surrounded by two protective stuctures- zona pellucida and corona radiata

zona pellucida: allows passage of light, contains glycoproteins

corona radiata; external to zona pellucida, innermost layer of cumulus oophorus cells

mature follicle

AKA vesicular follicle or Graafian follicle

becomes large, contains a secondary oocyte, layers of granulosa cells, and a large, fluid-filled, crescent-shaped antrum

seondary oocyte has completed meiosis I and is arrested in second meiotic metaphase

only one mature follicle forms each month

corpus luteum

mature follicle ruptures and expels oocyte (ovulation) and remaining of follicle in ovary turns yellowish

secretes sex hormones progesterone and estrogen

stimulate and support the continuing buildup of uterine lining and prepare uterus for possible implantation of a fertilized oocyte

corpus albican

corpus luteum undergoes break down, turns into a white connective tissue scar

most are completely resorbed, only a few remain in ovary

AKA uterine tubes

extends laterally from both sides of uterus towards the ovaries

function to transport ovulated oocyte to uterus

composed of infundibulum (contain fimbriae), ampulla (fertilization of oocyte usually occurs here), and isthmus (extends from ampulla toward lateral wall of uterus), uterine part (extends from isthmus and penetrates wall of uterus)

during birth, oxytocin levels increase to initiate uterine contractions of labor

if no oocyte is fertilized, the muscular wall of uterus contracts and sheds its inner lining as menstruation

receives blood supply from the uterine arteries

Regions

Fundus: curved, superior region extending between the lateral attachments of the uterine tubes

Body: middle region, major part of organ, composed of thick wall of smooth muscle

Cervix: narrow, inferiormost portion of uterus that projects into vagina

mucus plug; suspected to be a barrier that prevents pathogens from invading the uterus from the vagina

3 tunics

perimetrium

myometrium

endometrium

outer layer

thick, middle tunic of uterine wall

innermost tunic

composed of simple columnar epithelium and an underlying lamina propria

lamina propria is filled with uterine glands, which enlarge during the uterine cycle

2 distinct layers

basal layer: deepest layer, permanent layer that undergoes few changes during each uterine cycle

functional layer: superficial layer, this layer grows from the basal layer under the influence of estrogen and progesterone secreted from ovarian follicles

if not fertilized and implanted, this layer sheds as menses

new functional layer grows from basal layer after the end of each menses

3 tunics

inner mucosa

middle muscularis

outer adventitia

nonkeratinized stratified squamous epithelium, highly vascularized lamina propria

vaginal epithelial cells produce acidic secretion that helps prevent bacterial and other pathogenic infection

inferior region has folds (rugae); near external opening there is the hymen which is typically perforated during the first instance of sexual intercourse

both outer and inner layers of smooth muscle

contains some inner elastic fibers and an outer layer of areolar connective tissue

between thighs

homologous to labia majora in female

contain 2 types of cells

sustentacular cells; AKA Sertoli cells or nurse cells

population of dividing germ cells that continuously produce sperm beginning at puberty

provide protective environment for developing sperm, their cytoplasm helps nourish developing sperm

release hormone inhibin when sperm count is high (inhibits FSH secretion)

bound by tight junctions, which form blood-testis barrier- helps protect developing sperm from materials in the blood, protects sperm from leukocytes (which may perceive sperm as foreign because of different chromosome numbers and proteins

conducts sperm and a component of seminal fluid toward the urethra

each duct opens into the prostatic urethra

Urethra

transports semen from both ejaculatory ducts to the outside of the body

subdivided into prostatic urethra (extends from bladder through prostate gland), membranous urethra (continues through urogenital diaphragm), and a spongy urethra (extends through penis)

medial portion merges with a ductus deferens to form ejaculatory duct

secrete a viscous, whitish-yellow, alkaline fluid containing fructose and prostaglandins

fructose nourishes sperm as they travel through female reproductive tract

prostaglandins are hormonelike substances that promote widening and slight dilation of external os of cervix, which facilitates sperm entry into uterus

includes submucosal glands that produce mucin

secretes a slightly milky fluid that is weakly acidic and rich in citric acid, seminalplasmin, and prostate-specific antigen (PSA)

citric acid is a nutrient for sperm health

seminalplasmin is an antibiotic that combats urinary tract infections in male

PSA acts as enzyme to help liquefy semen following ejaculation

alkaline and functions to neutralize acidity of vagina

secretory product is a clear, viscous mucin that forms mucus

Male/ Female

Gonadotropin-Releasing Hormone (GnRH)

Follicle-Simulating Hormone (FSH)

Luteinizing Hormone (LH)

acts on specific endocrine cells in the anterior pituitary and stimulates them to release gonadotropins

prior to puberty, virtually nonexistent in girls and boys

prior to puberty, virtually nonexistent in girls and boys

as levels increase, gonads produce significant levels of sex hormones and start of process of gamete and sexual maturation

as levels increase, gonads produce significant levels of sex hormones and start of process of gamete and sexual maturation

FSH and LH cause maturation of follicles

FSH and LH affect ovarian follicle's secretion of other hormones

Inhibin

helps inhibit FSH release by anterior pituitary to prevent excessive follicular development

estrogen

low levels inhibit production of GnRH, FSH, and LH

assists with development of mature ovarian follicle

high levels have a stimulatory effect on hypothalamus and anterior pituitary, which initiates positive feedback loop, which induces ovulation

LH

after ovulation, induces remaining follicular cells in ovary to develop into corpus luteum which secretes large amounts of progesterone, estrogen, and inhibin

human chorionic gonadotropin (hCG)

secreted when secondary oocyte is fertilized

enters mother's blood and acts on corpus luteum

mimics effects of LH so it continues to stimulate corpus luteum

initiates and maintains growth of functional layer of endometrium

progesterone

primary hormone responsible for functional layer growth after ovulation

causes increase in blood vessel distribution, uterine gland size, and nutrition production

prolactin

produced in anterior pituitary

responsible for milk production

when amount increases, mammary gland grows

oxytocin

produced by hypothalamus

released from posterior pituitary

responsible for milk ejection

inhibin

inhibits FSH secretion which regulates sperm production

testosterone

high levels facilitate spermatogenesis

acts on brain so there is increased desire for and sensitivity to sexual stimulation

stimulates development of secondary sex characteristics (hair in pubic and axillary regions, deeper voice, growth of facial hair)

3rd week

gastrulation occurs after implantation

neurulation begins

somites

becomes bones and muscles

neural fold

becomes fold

neural tube

becomes spinal cord

measures about 2.5mm

forms 3 primary germ layers

mesoderm

endoderm

ectoderm

cells from which body tissues develop

develops into nervous system, sense organs, skin, and skin derivatives

middle layer of cells

inferior layer

superior layer

made up of cells that line the archenteron

develops into digestive system

forms the circulatory system, excretory system, most of reproductive system, skeletal system, and muscles

ectodermal cells invaginate to form first neural groove which deepens into neural fold and then forms the neural tube (which forms brain and spinal cord)

heart formed late in third week

4th week

most of internal organs are formed

cartilage skeleton begins to develop

muscles appear

has an obvious tail

5th week

arm and leg buds appear along cartilaginous vertebral column

placenta and umbilical cord have become connected via blood vessels and are functioning in food, oxygen, and waste exchange between developing embryo and mother

blood cell production has begun in liver and spleen

between 6th and 8th week

head and facial features become more refined

nose,eyes, and ears appear

upper and lower jaw formed, producing mouth

limb buds develop projections that will be fingers and toes

reproductive organs begin developing

heart starts beating

surrounded by amnion fluid and amnion for protection

surrounded by chorion which will become placenta

weeks 9-12

primary ossification centers appear in most bones

reproductive organs begin to develop

coordination between nerves and muscles for movement of limbs occurs

brain enlarges

body elongates

permanent kidneys develop

epidermis and dermis of skin become more fully developed

palate develops

weeks 13-16

body grows rapidly

ossification in skeleton continues

brain and skull continue to enlarge

limbs become more proportionate in length to body

weeks 17-20

muscle movements become stronger and more frequent

lanugo covers skin (fine, downy hair)

vernix caseosa covers skin; mixture of sebum from sebaceous glands and dead epidermal cells

limbs near final proportions

brain and skull continue to enlarge

weeks 21-38

body gains major amount of weight

eyebrows and eyelashes appear

eyelids open

blood cells from in marrow only

testes descend into scrotum (month 9)

Corpus Cavernosa

Corpus Spongiosum

terminates in shaft of the penis

continues within the glans

keeps penis erected

keeps urethra open so sperm can exit