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Reproductive and development System (Meiosis, Spermatogenesis, and…
Reproductive and development System
Hormones and Menstrual Cycle
Hypothalamus
Secretes GnRH at a constant rate and as a result FSH and LH release from the pituitary in males is constant through life
Luteinizing hormone
Targets interstitial cells of the testes to produce testosterone
Testosterone effects
CNS; stimulates bone and muscle growth; establishes secondary male characteristics such as hair and adipose distribution and muscle mass
Follicle stimulating hormone
Targets primarily the nurse cells of seminiferous tubules to promote spermatogenesis and spermiogenesis
Testosterone
Produced primarily by interstitial cells of the testes
What is dihydrotestosterone?
It is converted from arriving testosterone in many target tissues
Dihydrotestosterone effects
Makes its way into bloodstream where it stimulates DHT receptors (notably external genitalia and prostate gland)
Female: Functions of Female Reproductive System
-Oogenesis
-Produce female sex hormones
female reproductive system purposes
Produces and delivers gametes
-Provides nutrition and safe harbor for fetal development
-Gives birth
-Nourishes infant
internal genitalia
ovaries, uterine tubes, uterus, & vagina
estradiol
-Stimulates growth of ovaries and secondary sex organs
-Stimulates growth hormone secretion
estrogens
are feminizing hormones with widespread effects on the body
estrogens & progesterone
suppress FSH and LH secretion through
negative feedback
menstrual cycle
parallel changes in uterus, consists of a buildup of the
endometrium during most of the sexual cycle,
followed by its breakdown and vaginal discharge
Divided into four phases: proliferative phase,
secretory phase,premenstrual phase, and menstrual
phase
First day of noticeable vaginal discharge is defined as
day 1 of the sexual cycle
•Average: 5 days
Male Reproductive
Reproductive structures
accessory glands and organs
Secrete fluids into ducts of the reproductive system or into excretory ducts
Gonads
Reproductive organs that produce gametes and hormones
perineal structures
On pelvic floor, collectively known as external genitalia
Spermatozoa
Produced by the testes mature and travel along the male reproductive tract mixed with secretions of accessory glands to form semen as they proceed
undergo capacitation to become motile
Testes
Paired oval shaped glands (gonads) in the scrotum; contain seminiferous tubules that create sperm cells
Male reproductive structures sperm travels through
Testes, epididymis, external genitalia
Fetal development of testes
Develop adjacent to kidneys on embyro's posterior abdominal wall; as fetus grows, the connective tissue around testes do not grow
late in fetal life, hormones cause connective tissue to contract, pulling testes through abdominal musculature into scrotum
Epididymis
Comma shaped organ that lies along the posterior border of testis
site of maturation (capable of and storage; sperm may remain in storage for at least 2 weeks, where they are either expelled or degenerated and reabsorbed
transports sperm out of testis through this
Sperm pathway from testes to urethra
Out of the testes through epididymis
ductus deferens
ejaculatory duct
urethra
seminal glands, prostate, bulbourethral glands add various fluids into ejaculatory duct and urethra
Spermatogenesis
Process by which the seminiferous tubules of the testes produce haploid sperm; involves mitosis, meiosis, spermiogenesis
External genitalia
Include the scrotum (encloses the testes) and the penis (erectile organ)
Spermatic cord
Consists of ductus deferens, testicular artery, nerves, veins, lymphatic vessels and cremaster muscle (elevates testes toward the body - ^ temperature) and the dartos (contracts and causes wrinkling of (scrotal surface)
Sperm pathway through epididymis
Seminiferous tubule > rete testis > efferent ductules > ductus deferens
Ductus deferens anatomy
Part of the spermatic cord, ascends through inguinal canal, enters abdominal cavity, and passes posteriorly to to the prostate, connects epididymis to the ejaculatory duct
Ductus deferens physiology
stores sperm and propels them toward the urethra during ejaculation
Embryonic and Fetal Development
Fertilization & implantation
Fertilization - union of egg & sperm to form a zygote (fertilized egg)
Fertilization take place in the Fallopian Tube
A woman's most fertile time is 3-4 days before ovulation to 1 day after
Implantation - implants in the endometrium of the uterus about
7
days after fertilization
Formation of Extraembryonic Membranes
Function: Surround, protect & nourish the embryo & fetus
Amnion - Thin, protective membrane that surrounds embryo
Amniocentesis - Some of the amniotic fluid is withdrawn & analyzed for genetic abnormalities
Chorion - Surround amnion; become part of the placenta; protects embryo/fetus from mother's immune responses; produces hCG
Amniotic fluid - Absorbs shock; regulates body temperature inside amnion
Placenta
Forms during 3rd month; part of it is formed by mother & part by fetus
Placenta Functions
Exchanges nutrients, wastes, & gasses between maternal & fetal blood
Transmission (passage) of antibodies to fetus
Produces estrogen & progesterone to maintain pregnancy
Stores nutrients
Attaches to fetus at the umbilical cord
Umbilical vein brings blood
TO
fetus; two umbilical arteries take blood
AWAY
from fetus
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Pregnancy Division
Pregnancy is divided into 3 trimesters
2nd Trimester - Organs grow & develop; maternal tissues expand
3rd Trimester - Weight gain & final maturation of fetus; mother's body prepares for labor & delivery
1st Trimester - Organs start forming; most vulnerable to birth defects & miscarriage at this time
Prematurity
Infant is born before 38 week; weights less than 5.5 lbs
Caused by:
a) Preterm labor
b) Preeclampsia/eclampsia
c) Multiples
d) Lack of/poor prenatal care
e) Drug abuse
f) Smoking
Parturition (labor)
Physical expulsion/delivery of fetus & placenta
Labor begins when:
a) Progesterone levels decrease
b) Oxytocin & prostagladins cause uterine contractions via positive feedback
Stages of Labor & Delivery
Dilation stage - Time from onset of labor to complete dilation of cervix
a) Regular uterine contractions that intensify
b) Amniotic sac ruptures
c) Cervix dilates & effaces (thins)
Expulsion stage - Delivery of the baby
Placental stage - Placenta is expelled
ectopic pregnancy
development of an embryo or fetus outside uterine cavity
Meiosis, Spermatogenesis, and oogenesis
Meiosis
Production of haploid cells that contain only 23 chromosomes; has haploid
Mitosis
Part of the process, somatic cell division, producing two daughter cells each containing identical 23 pairs of chromosomes; has diploid
Spermatogensis
Process by which the seminiferous tubules of the testes produce haploid sperm; involves mitosis, meiosis, spermiogenesis;
Haploid
Cell with only one chromosome from each pair (n); gametes; finishes Meiosis I
Meiosis I
Two chromatids of each pair of chromosomes pair off, an event called synapsis; resulting in four chromatids that form a tetrad
Meiosis II
Phases are similar to those in mitosis, but result in four haploid cells
Spermatogonia
Stem cells in seminiferous tubules that divide (mitosis) to produce spermatozoa in a process called spermatogenesis
mitosis of spermatogonium
Each division of diploid spermatogonium produces two daughter cells. One remains a spermatogonium and the other becomes a primary spermatocyte
Process of Meiosis I
Each primary spermatocyte contains 46 chromosomes. At the end of meiosis I, the daughter cells are called secondary spermatocytes and they contain 23 chromosomes (now haploid)
Process of Meiosis II
Secondary spermatocytes soon enter meiosis II, yielding four haploid spermatids, each containing 23 chromosomes
Spermiogensis
(physical maturation - takes 5 weeks) Each spermatid matures into a single spermatozoon (sperm)
Components of Spermatogensis
Diploid spermatogonium, diploid primary spermatocyte, haploid secondary spermatocyte, haploid spermatid
Diploid Spermatogonium
(one) Stem cells; undergo mitosis to reserve future stem cells
Diploid primary spermatocyte
(one) for sperm production; undergo mitosis I
Haploid secondary spermatocyte
(two) undergo mitosis II
Haploid spermatid
(four) mature into (spermiogenesis)
sperm (spermatozoon)
Components of mature sperm
Acrosomal cap (digestive enzymes), head (DNA), neck, midpeice (mitochondria), tail (flagellum)