Reproductive System

Main purpose of the reproductive system

To ensure the survival of the species as a whole.

Is the reproductive system essential to an individual animal's life?

No, animals can be spayed or castrated without risking individual survival.

What makes the reproductive system unique among body systems?

It requires another animal to carry out its full function of reproduction.

Definition of meiosis

A unique form of cell division that produces reproductive cells.

Purpose of meiosis

To ensure the genetic makeup of each new animal is unique.

Definition of chromosomes

The body's genetic material contained in coiled masses of DNA.

Normal number of chromosomes in a somatic cell

An even number occurring in paired sets.

Diploid chromosome number

The total number of chromosomes in the nucleus of each somatic cell.

Haploid chromosome number

The reduced number of chromosomes found in reproductive cells.

Definition of sex chromosomes

The pair of chromosomes responsible for determining the fetus's gender.

Two types of sex chromosomes

X and Y.

Sex chromosome combination for a female

XX.

Sex chromosome combination for a male

XY.

Origin of fetal chromosomes

One chromosome from each parent.

Definition of spermatogenesis

The production of spermatozoa (sperm).

Location of sperm production

In the seminiferous tubules of the testes.

Storage site for mature sperm

The epididymis.

Percentage of sperm carrying an X chromosome

Approximately 50%.

Percentage of sperm carrying a Y chromosome

Approximately 50%.

Definition of oogenesis

The production of ova (eggs).

Location of ova production

In the follicles of the ovaries.

Are ova produced continuously like sperm?

No.

Timing of oocyte production in females

Females are born with a fixed number of oocytes for life.

Two main functions of the male reproductive system

Production of sperm and deposition of sperm into the female.

Primary site of sperm production

Seminiferous tubules of the testes.

Storage location for produced sperm

The epididymis.

Is sperm production continuous in males?

Yes.

Definition of testes

The organs where male reproductive cells are formed.

Location of the testes

In the inguinal region outside the abdomen, housed inside the scrotum.

Two major functions of the testes

Spermatogenesis and hormone production.

Product of spermatogenesis

Spermatozoa.

Location of hormone production in the testes

In the interstitial cells.

Primary male androgen

Testosterone.

Functions of testosterone

Develops secondary sex characteristics, affects libido, and enhances muscle and bone.

Function of Sertoli cells

Nurse cells that support developing spermatozoa.

Function of Leydig cells

Interstitial cells that produce male sex hormones (androgens).

Definition of tunica albuginea

A heavy fibrous connective tissue capsule protecting the testis.

Three main parts of a sperm cell

Head, midpiece, and tail.

Structures inside the head of a sperm cell

The nucleus and acrosome.

Definition and function of the acrosome

A cap with digestive enzymes that helps sperm penetrate the egg.

Function of the sperm midpiece

Connects the head of the sperm to the tail.

Function of the sperm tail

Helps propel the sperm through the female reproductive tract.

Location of testicular development prior to birth

In the abdominal cavity near the kidneys.

Structure that guides the testes into the scrotum

The gubernaculum.

Definition of cryptorchidism

Failure of one or both testicles to descend into the scrotum.

Function of the scrotum

Houses the testes and regulates their temperature.

Why must testes be kept cooler than body temperature?

To successfully produce viable spermatozoa.

Definition and function of the tunica dartos

Smooth muscle in the scrotum that contracts in cold weather.

Function of the cremaster muscle

Adjusts testicular position relative to the body based on temperature.

Response of the cremaster muscle to warm temperatures

It relaxes, allowing the testes to hang farther from the body.

Response of the cremaster muscle to cold temperatures

It contracts, pulling the testes closer to the body.

Contents of the spermatic cord

Blood vessels, nerves, lymphatic vessels, and the vas deferens.

Definition of the pampiniform plexus

An intricate meshwork of veins surrounding the testicular artery.

Function of the pampiniform plexus

Acts as a heat-exchange mechanism to cool arterial blood entering the testes.

Function of the vas deferens

Carries sperm from the epididymis to the urethra.

What is the vaginal tunic?

A sheath-like layer surrounding the testes in the scrotum and the spermatic cord.

What are the two layers of the vaginal tunic?

Visceral vaginal tunic and parietal vaginal tunic.

Which vaginal tunic layer is thin?

Visceral vaginal tunic.

Which vaginal tunic layer is thick?

Parietal vaginal tunic.

What is the tunica albuginea?

The heavy fibrous connective tissue capsule enclosing each testis.

Where does spermatogenesis occur?

In the seminiferous tubules.

What is the function of Sertoli cells in the seminiferous tubules?

They help developing sperm transform and help shield sperm from the immune system.

What is the epididymis?

The main storage site for spermatozoa where they mature before ejaculation.

What are the three regions of the epididymis?

Head, body, and tail.

What happens in the head of the epididymis?

Sperm enter the epididymis.

What happens in the body of the epididymis?

It is the main portion lying along the surface of the testis.

What does the tail of the epididymis connect to?

The vas deferens.

How long must sperm mature in the epididymis before they can fertilize ova?

A week or more.

What does the vas deferens do?

Moves sperm from the epididymis to the urethra during ejaculation.

What type of muscle makes up the vas deferens?

Smooth muscle.

What is the ampulla?

An enlargement of the vas deferens just before it joins the urethra.

What is the function of the ampulla?

Helps propel sperm and seminal fluid quickly from the epididymis to the urethra.

Which domestic animal does NOT have an ampulla?

The boar.

What are the two functions of the male urethra?

Urinary and reproductive.

What happens to urine flow during ejaculation?

It is temporarily blocked.

What are the two portions of the male urethra?

Pelvic portion and penile portion.

What makes up most of the volume of semen?

Secretions from the accessory reproductive glands.

What do accessory reproductive glands produce?

Alkaline fluids containing electrolytes, fructose, and prostaglandins.

Why is the semen alkaline?

To counteract the acidity of the female reproductive tract.

What is the function of fructose in semen?

It provides an energy source.

What is the function of prostaglandins?

They stimulate contractions in the female reproductive tract to help move sperm.

Are seminal vesicles present in dogs and cats?

No. They are present in all domestic animals except dogs and cats.

What is unique about the prostate gland?

It is a single structure that completely surrounds the urethra.

Which domestic animal has a particularly large prostate?

The dog.

Why is the dog's prostate larger?

It is the only accessory reproductive organ the dog has.

What do the bulbourethral glands secrete?

Mucinous fluid just before ejaculation that cleans and lubricates the urethra.

What is the penis?

The male breeding organ.

What are the three main parts of the penis?

Root, body, and glans.

What does the root of the penis do?

Attaches the penis to the brim of the pelvis.

What is the largest part of the penis?

The body.

What is the corpus spongiosum?

A smaller body of erectile tissue that forms a sleeve around the urethra.

What is the corpus cavernosum?

The larger body of erectile tissue located dorsal to the urethra.

What is the glans?

The free end of the penis.

What is the prepuce?

The sheath of skin covering the penis when it is not erect.

What is the os penis?

A bone found in the dog's penis.

What is the bulb of the glans?

An erectile structure that becomes engorged with blood during breeding and causes the dog to remain locked with the female.

What is a "tie" in dogs?

The period when the male and female remain physically locked together after breeding.

How long does a dog tie usually last?

About 15-20 minutes.

Should you try to pull dogs apart during a tie?

No. They can be injured.

What is the sigmoid flexure?

An S-shaped bend in the non-erect penis of the bull, ram, and boar.