BSC 120 Lecture Notes - Lecture 46: Ejaculatory Duct, Semen, Bulbourethral Gland
29 Apr 2018
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Chapter 46 and 47 – Human Reproduction
I. Human Reproduction
a. Background
i. Each of us began life as a single cell
1. Called a zygote
ii. A human embryo at about 6-8 weeks after conception shows development
of distinctive features
1. The 4 parts of a vertebrate: tails, gills, etc.
iii. Human reproduction- fusion of haloid egg and haploid sperm
b. Males
i. Everything is in the abdominal cavity below the diaphragm
ii. Production of Sperms
1. Highly specialized as carrier of genetic information
2. Produced by meiosis in testes (23 chromosomes)
a. 4 sperm per cell
3. Constantly diving
4. Mature in epididymis (sits atop testes)
a. Takes 18 hours to become motile
b. 6-meter-long coiled tubes
c. 3 weeks of travel time
5. Does not complete formation at body temperature
a. Testes thus are in the scrotum (sac outside of body)
6. Testes contain cells that secrete the male sex hormone testosterone
a. Testosterone responsible for triggering sperm production
i. Activated as humans go through puberty
1. Secondary features: hair produced,
beginning of sperm
2. Girls mature faster than boys
iii. Structure of the sperm
1. 10 micrometers
2. Head
a. Nucleus (haploid as a result of meiosis)
b. Acrosome
i. Enzymes that aid in penetration of protective layers
surrounding the egg
ii. Sac that penetrates through the mucus coating of the
egg and gets plasma membrane of the sperm into
contact with the plasma membrane of the egg
1. Thick mass around the egg protects the egg
a. Difficult to penetrate (sperm would
only end up at the coating)
iii. Fertilization- first sperm that makes plasma
membrane contact with the egg
1. First contact drives other suitors away
3. Body
a. Mitochondrion
i. ATP
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Chapter 46 and 47 – Human Reproduction
ii. Does not go into the egg
4. Tail (Epistocom)
a. Flagellum
i. Uses ATP for energy
iv. Delivery of the sperms through the penis
1. During intercourse sperms move through the vas deferens (tube
around pelvic bone) to the urethra
2. Sperms mixed with secretions from seminal vesicle and prostate
gland
a. Semen
i. Fluid in which to swim
ii. Has energy (fructose)
b. Accessory glands prepare fluid for sperm to continue route
for ejaculation and preparing it to survive in the vagina
(vagina is set up to destroy non-vaginal cells)
3. Sperm is released in viscous fluid
a. Viscosity decreased through bulb because it would be
difficult for the sperm to make it through the egg
4. Bulbourethral gland
a. Secretes slippery fluid that neutralizes acidity of any
residual urine and lubricates the head of the penis
i. Adjusts pH of seminal fluid to make it more
alkaline (great acidity of vagina, so it needs some
sort of buffer to survive)
5. Sperm goes to the ejector duct
a. Urine and sperm come through the same duct
i. Muscle pushes semen along ejaculatory duct and
closes off the urethra (keeps semen from backing
into the excretory system)
6. 300 million sperms ejaculated
a. Series of neurological hormonal responses
b. Stimulation of tactal tissue (vascular dilation)
i. Stimulation of penis starts dilation and blood
flushes into the penis to harden and erect
c. Number of triggers help with ejaculation
d. Pleasure encourages sexual reproduction
i. Endorphins and hormones released
ii. With age, the response is harder and harder
iii. Drugs cause vasodilation to occur
1. Side effect: heart attack
iv. If sperm are not released, they will die
c. Females
i. Production of egg
1. Only one female gamete is mature each month
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Chapter 46 and 47 – Human Reproduction
2. At birth, a female’s ovaries contain around 2 million primary
oocytes, all of which have begun the first meiotic division (arrested
at meiosis I)
a. Thus, all the oocytes needed for a lifetime are already
present at birth (usually about 500 are used)
3. In a holding pattern until receiving a hormonal signal out of the
pituitary gland to mature
a. Eggs mature in the ovary
b. Hormonal signals produce estrogen that produce menstrual
cycle
i. Release of epithelial lining in preparation for
impregnation
1. A lot of fluid because it is a blood-type
lining
4. During the reproductive cycle, one of the oocytes is initiated to
continue their development in a process called ovulation typically
with one egg ultimately produced
5. Menopause- protects from having too old of eggs for reproduction
ii. Ovulation
1. An ovary contains follicles which contain a single primary oocyte
surrounded by cells that nourish and protect the egg
2. During ovulation a single secondary oocyte is ejected from a
follicle (arrested at metaphase)
a. Moves into the oviduct where fertilization typically
happens
3. Follicle produces female sex hormone, estrogen
4. Happens periodically but not always compared to men being able
to reproduce constantly
5. Hairs and constrictions move egg through the oviduct (fallopian
tube)
iii. Fertilization
1. Bartholin gland has evolved to provide lubricant so that when the
vagina is stimulated it will secrete fluid to lubricate and help penis
enter
2. Fertilization brings the haploid nuclei of a sperm and an egg
together, forming a diploid zygote
a. Takes place in the oviduct
b. If blastocyst that develops from the zygote does not
successfully leave the oviduct, there is tubular pregnancy
i. We have a system that self-aborts
ii. Sometimes this does not happen and requires
surgery
3. Occurs in the oviducts (fallopian tubes)
a. Egg transported from ovaries to the uterus via oviducts
i. Slow: 5-7 days
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