Reproductive Strategies
+ Male Reproductive System
Reproductive Strategies
• In order for fertilization and development to
occur, the gametes and developing organism
require a high moisture environment
• There are two main reproductive strategies
determined by this necessity:
– External Fertilization
– Internal Fertilization
• Not only is fertilization case by case, but so is
development.
• Examples:
Vertebrate
Fertilization
Development
Fish
External
External
Amphibians
External
External
Reptiles
Internal
External
Birds
Internal
External
Mammals
Internal
Internal
External Fertilization
• occurs outside the female’s body.
• many eggs are necessary.
– because of the low rate of fertilization success.
• The eggs and sperm are both released into the
environment, where fertilization occurs
• The eggs are exposed to the environment and
also predators.
• occurs mainly in aquatic animals like fish and
amphibians.
Internal Fertilization
• occurs inside the female’s body.
– many fewer eggs are needed.
– much higher rate of fertilization success.
• requires a special delivery organ to deposit
the sperm (penis)
• used mainly by land animals (terrestrial) like
reptiles, birds, and mammals in environments
where moisture is low
Human Reproductive Systems
• The main function of the reproductive system
is to produce sex cells (sperm and egg).
• Gonads – primary sex organs
– Testes in males
– Ovaries in females
• Gonads produce gametes (sex cells) and
secrete hormones
– Sperm – male gametes
– Ova (eggs) – female gametes
• Testes
• Duct system
– Epididymis
– Vas deferens
– Urethra
• Accessory organs
– Seminal vesicle
– Prostate gland
– Bulbourethral gland
• External genitalia
– Penis
– Scrotum
• Production of sperm cells in males
• divided it into lobules
• Each lobule contains one
to four seminiferous tubules
– Tightly coiled structures
– Function as sperm-forming
factories- site of spermatogenesis
– Empty sperm into the
rete testis
• Sperm travels through the
rete testis to the epididymis
– Tubes that store the sperm
– Epididymis stores and matures sperm
for up to 20 days
• Interstitial cells in the testes
produce androgens such as
testosterone
• Vas Deferens- Carries sperm from the epididymis to
the ejaculatory duct.
– Vasectomy – cutting of the ductus deferens at
the level of the testes to prevent transportation
of sperm.
• Urethra- extends from the base of the urinary
bladder to the tip of the penis
– Carries both urine and sperm
– Sperm enters from the Vas Deferens
• Mixture of sperm and accessory gland
secretions
• Advantages of accessory gland secretions
– Fructose provides energy for sperm cells
– Alkalinity of semen helps neutralize the acidic
environment of vagina
– Semen inhibits bacterial multiplication
– Elements of semen enhance sperm motility
• Seminal Vesicles- glands located at the base
of the bladder
• Produces a thick, yellowish secretion (60% of
semen)
–
–
–
–
Fructose (sugar)
Vitamin C
Prostaglandins
Other substances that nourish and activate sperm
• Encircles the upper part of the urethra
• Secretes a milky fluid
– Helps to activate sperm
– Enters the urethra through several small ducts
• Pea-sized gland inferior to the prostate
• Produces a thick, clear mucus
– Cleanses the urethra of acidic urine
– Serves as a lubricant during sexual intercourse
– Secreted into the penile urethra
• Scrotum
– Divided sac of skin outside the abdomen
– Maintains testes at 3°C lower than normal body
temperature to protect sperm viability
• Penis
– Delivers sperm into the female reproductive tract
• The only human
flagellated cell
• DNA is found in
the head
• The acrosome
region helps to
dissolve the
outer layer of
the egg, so the
sperm can
enter.
Figure 16.5b
Hormones in Males
• Testosterone:
– The most important hormone of the testes
– Produced in interstitial cells
– Functions of testosterone
• Stimulates reproductive organ development
• Underlies sex drive
• Causes secondary sex characteristics
– Deepening of voice
– Increased hair growth
– Enlargement of skeletal muscles
– Thickening of bones
• Follicle Stimulating Hormone (FSH),
Luteinizing Hormone:
– Stimulate the production of testosterone and
sperm cells