Reproductive & Development System

Male Reproductive Structures

Hormones

Female Reproductive Structures

Males

Females

Seminiferous tubules of the testis

Location of spermatogenesis

sustentacular cells (Sertoli Cells)

interstitial cells (Leydig Cells)

stimulated by FSH

produce testosterone, stimulated by LH

estrogen

progesterone

LH stimulates interstitial cells to produce testosterone

provide the means for sexual maturation

produce special cells for procreation

ovum derived from primordial follicles

female organs

ovary

clitoris

labia minora

labia majora

greater vestibular gland

produces gametes and sex hormones

stimulates sexual arousal and climax

contains erectile tissue

protect and cover some reproductive structures

secretes mucin for lubrication

male organs

testis

glans of penis

body of penis

scrotum

accessory glands

bulbourethral gland (Cowper's gland)

contains erectile tissue that stimulates sexual arousal and climax

produces gametes and sex hormones

contains ereticle tissue that stimulates sexual arousal and climax

protect and cove testicular structures

Spermatogenesis and Oogenesis

germinal epithelium

simple cuboidal epithelial layer surrounding ovar

tunica albuginea

deep to germinal epithelium

dense CT capsule

consists of oocyte surrounded by follicle cells

by puberty 400,000 follicles remain in ovaries

ovarian cycle: follicular, ovulation, and luteal phases

FSH stimulates sustentacular cells to produce androgen-binding protein

if low, can inhibit GnRh, FSH, and LH secretion

follicle maturation

cooperates with estrogen in breast maturation and regulation of the uterine cycle

FSH and LH

Human chorionic gonadotropin

Spermatogenesis

Oogenesis

Oogonia are diploid cells that are the origin of oocytes. Mitotic divisions of oogonia produce primary oocytes.

Production of male gametes in seminiferous tubules, begins at puberty

Fetal Development

promotes oogenesis. at puberty they stimulate the growth of the reproductive organs and the growth spurt

promote appearance of the secondary sex characteristics

Spermatogonia divide by mitosis to maintain germ cell line. some of their progeny become primary spermatocytes which undergo meisos i to produce secondary spermatocytes
Secondary spermatocytes undergo meiosis II, each producing two haploid (n) spermatids

Meiosis, basis of gamete production, consists of two consecutive nuclear divisions without DNA replication in between. Meiosis reduces the chromosomal number by half and introduces genetic variability. Synapsis and cross of homologous chromosomes.

Spermiogenesis converts spermatids to functional sperm, stripping away superfluous cytoplasm and producing an acrosome and a flagellum (tail).

Sustentocytes form the blood testis barrier, nourish spermatogenic cells, move them toward the lumen of the tubules and secrete fluid for sperm transport

9-12 weeks

13-16 weeks

21-30 weeks

liver prominent

sex readily detected

embryonic development

The three week embryo is flattened, disc-shaped structure. Embryonic disc.

week 3

primitive streak

neural tube

somites forming

heart forming

amnion nearly covers embryo

chorion well developed

week 4

internal organs forming

spinal cord and brain forming

somites present

embryo fully covered by amnion

cartilage skeleton and muscles develop

facial features and ears appear develop

week 5-8

All internal organs complete, some functioning

cartilage skeleton and muscles complete

extremities develop from limn buds

placenta and umbilical cord function

facial features and ears nearly complete

embryo assumes a human appearance

head dominant but body elongating, brain enlarging, lumbar enlargements apparent in spinal cord

skin epidermis and dermis obvious

blood cell formation

notochord degenerating

kidneys attain typical structure

cerebellum prominent

most bones are now distinct

most bones are now distinct

17-20 weeks

fetal position

vernix caseosa

quickening occurs

distal limb bones are beginning to ossify

Period of substantial increase

body is lean and well proportioned

30-40 weeks

testes reach scrotum in seventh month

skin is wrinkled and red

bone marrow becomes sole site of blood cell formation

myelination of spinal cord begins

approximate crown-to-rump length at end of interval 360 mm (14 inches)

fat laid down in subcataneous tissue (hypodermis)

skin whitish pink

testosterone facilitates the production sperm

nourish and protects developing sperm, secrete androgen-binding protein

secretes mucin for lubrication of penile urethra

prostate gland

seminal vesicles

secretes slightly milky fluid

citric acid: nutrient for sperm health

secrete fructose and prostaglandins

seminalplasmin: combats UTI in males

PSA: enzyme to help liquify semen

fructose nourishes sperm in the female reproductive tract

prostaglandins promote the widening and slight dilation of cervix

Primary oocytes start the process of meiosis but are arrested in prophase I.

Childhood

Ovaries are inactive. They house primordial follicles. Some primordial follicles break down.

Monthly, from puberty to menopause

Up to twenty primordial follicles mature into primary follicles every month. Some of the primary follicles will mature into secondary follicles. Those that don't, disintegrate.

Typically only one secondary follicle matures into a mature follicle, where the primary oocyte completes the first meiotic division to produce a polar body and a secondary oocyte.

The secondary oocyte is a haploid cell that is arrested in the second meiotic phase.

If the secondary oocyte is fertilized, it completes the second meiotic division and becomes an ovum.

If the secondary oocyte is not fertilized, it degenerates.

Events of the Menstrual Cycle

The ovarian follows three phases

Follicular phase, ovulation, and luteal phase

The hypothalamus initiates the ovarian cycle by secreting GnRH, stimulating the secretion of FSH and LH.

FSH and LH target the ovaries and stimulate follicular development.

The maturing follicles secrete inhibin and estrogen. These hormones have a negative feedback on the hypothalamus.

Inhibin helps inhibit FSH release by the anterior pituitary and low levels of estrogen inhibit the secretion of GnRH, FSH, and LH.

Estrogen also assists with the development of the mature ovarian follicle. A secondary follicle matures under the influence of estrogen.

The developed mature follicle produces a higher amount of estrogen. Higher levels of estrogen have a positive feedback effect on the hypothalamus.

The positive feedback loop results on an LH surge, inducing ovulation. Ovulation is impossible without this surge.

LH influences the remaining follicular cells in the ovary to develop into the corpus luteum.

The corpus luteum acts as an endocrine gland, secreting copious amounts of progesterone, estrogen, and inhibin. This combination of hormones inhibit the hypothalamus and anterior pituitary. Helps build the uterine lining.

The corpus luteum degenerates in 10 to 13 days if no fertilization takes place. Decrease in hormones levels ensue.

secreted by the hypothalamus to initiate the ovarian cylcle

FSH promotes the maturation of follicles

LH induces the formation of corpus luteum

heart beating

The shape transformation begins during the late third and fourth weeks of development.

Cephalocaudal folding occurs in the cephalic and caudal regions of the embryo.

Transverse folding occurs when the left and right sides of the embryo curve and migrate towards the midline.

Forms the head and buttocks region of the embryo.

Creates torso region of embryo.

Once the embryo has undergone cephalocaudal and transverse folding, organogenesis begins.

The upper and lower limbs attain their adult shapes, and the basic forms of most organs have developed by week 8.

During the embryonic period, the embryo is peculiarly sensitive to teratogens.

Teratogens are substances that can cause birth defects or the death of an embryo.

Alcohol, tobacco smoke, drugs, and some viruses.

Meiosis

Meiosis I

Prophase I

Homologous maternal and paternal replicated chromosomes pair up, and the pair forms a tetrad.

Crossing over occurs between homologous maternal and paternal chromosomes, increasing genetic diversity.

Metaphase I

Homologous replicated chromosomes line up above and below the equator of the cell, forming a double line of chromosomes.

Spindle fibers attach to the centromeres.

Anaphase I

Maternal and paternal pairs of replicated hormones are separated and pulled to the opposite ends of the cell; reduction division.

The sister chromatids remain attached in each replicated chromosome.

Telophase I

Nuclear division finishes and nuclear envelopes re-form. The cytoplasm divides and two new cells are produced, each containing 23 replicated chromosomes only.

The replicated chromosomes are still composed of sister chromatids.

Meiosis II

Prophase II

Nuclear envelope breaks down, and replicated chromosomes cluster together.

Metaphase II

Spindle fibers extend from the centrioles from the centrioles to each sister chromatid in each chromosome and align the replicated chromosomes along the equator line.

Anaphase II

Sister chromatids of each replicated chromosome are pulled apart at the centromere. They migrate to opposite ends of the cell

Telophase II

Nuclear division finishes, and the nuclear envelopes re-form. The four new daughter cells that are produced each contain 23 single chromosomes only.

inhibin

secreted by follicular cells to inhibit further FSH production

preventing excessive ovarian follicle development, allowing current primary follicles to mature.

The corpus luteum regresses and becomes a corpus albicans.

as the corpus luteum regresses, its levels of secreted progesterone and estrogen drop.

this causes the uterine lining to be shed, menstruation

the shed lining is called menses

this marks the end of the luteal phase

a female's first menstrual cycle is called menarche