Reproductive and Excretory Systems

Reproductive System

The reproductive systems should be examined first because they are

ventral to many of the excretory structures.

You will be responsible for both male and female systems.

You may choose to remove the digestive tract in order to study the

reproductive and excretory systems. Do no discard any organs that have not

yet been studied.

Sharks have four reproductive strategies, depending on the species.

oviparous:

fertilized eggs are laid along reef beds, some

species leave eggs, others guard them until

hatching

viviparous:

embryos nourished by connection to

mother via placenta, live birth

ovoviviparous:

young are nourished by egg yolk

within mother, no direct connection to

mother, live birth (spiny dogfish falls

into this category)

parthenogensis:

female sharks who do not encounter a male and are unable to mate may

eventually give birth to clones of themselves via parthenogensis

It is unclear if all or some

species are capable of this.

Mating rituals vary between species. Some gather in large numbers in

specific areas.

Nearly all mating rituals are

initiated by a male biting a female.

In some species, females have skin

that is 2-3 inches thicker than male

skin in order to minimize risk of

mating injury.

Females often exhibit mating scars.

Males will compete for females and the female will ultimately choose

which male to mate with.

Fertilization is internal.

The male will insert a single

clasper into the female cloaca.

Sperm will funnel along the

clasper groove into the female’s

reproductive tract.

Eggs are fertilized and either laid

externally or incubated internally.

In some species egg yolk becomes

placenta.

Gestation range varies widely from

8-22 months (22 months in spiny

dogfish.)

Young are born as fully formed

miniature adults.

Male Reproductive System

testes

clasper

sperm sac

vas deferens

seminal vesicle

urogenital papilla

In this photo, the mesentery on the left side of the spine has been removed to expose the

structures beneath. This can be accomplished with gentle manipulation of teasing needles

and occasionally the use of dissecting scissors.

The kidney appears as a layer of tissue slightly darker than muscle. It also has a distinctly

different texture. The vas deferens is a convoluted tubule on the ventral surface of the kidney.

The seminal vesicle is enlarged and straightened caudal aspect of the vas deferens.

testeskidney

vas deferens

seminal vesicle

sperm sac

• Sperm is generated in the testes.

• It is transported to the vas deferens via the efferent ducts.

• It travels the vas deferens to the seminal vesicle.

• Secretions are added here.

• Sperm is stored in the sperm sac until release.

testes

kidney

kidney with vas deferens

on ventral surface

seminal vesicle

sperm sac

urogenital papilla

seminal vesicle

vas deferens

kidney

kidney

vas deferens

sperm sac

seminal vesicle

urogenital papilla

Sperm exits via the urogenital papillae.

It travels along the clasper, funneled by

the clasper groove.

Specialized cells release serotonin

along with the sperm. The mixture is

transferred into the female’s uterus via

the cloacal opening.

The serotonin causes uterine

contractions that help pull the sperm

further into the female’s reproductive

tract.

Female Reproductive System

egg

uterus without embryo

uterus with embryooviduct

ovary

egg

oviduct

• Multiple eggs develop in the ovaries

• An egg is released into the oviduct

• The cranial portion of the oviduct has a

shell gland that will add secretions to the

egg

• The egg will continue to travel the oviduct

The eggs then gestate in the uterus.

oviduct

uterus with embryo

uterus without embryo

Uterus opened to reveal gestating

embryo attached to yolk (candle.)

Embryos emerge directly from uterus

through cloaca for birth.

emerging embryo

emerging embryo

urinary papilla

Excretory System

Female (rectal gland removed) Male (rectal gland present)

Mesentery over

kidneys still in

place.

Female

Female

kidney: filters waste from

blood, generates urea as waste

ducts drain urea to

archinephric duct

archinephric duct drain urea to

urinary papilla for excretion

Male

• The kidneys extend from the caudal end of

the animal cranially along much of the

length of the spine.

• It is thicker and wider in the most caudal

region.

• This is true of both male and females.

• In males, the archinephric duct and the vas

deferens are the same structure, thus males

excrete both sperm and urea via the

urogenital papilla.

Rectal glad: removes excess salt from blood, concentrates it, then

releases it to the colon for excretion through cloaca

rectal gland

colon

urogenital

papilla