Chapter 19 Reproductive System Flashcards
Why Sex?
Survival of the species
*All other body systems are about the survival of the individual animal
Economic system for agricultural species
* Dairy
*Beef
*Equine (horse racing)
*Pork
Asexual vs. Sexual Reproduction
Asexual reproduction – massive numbers of
“offspring” in short period of time, all organisms with same DNA
*Bacteria, protozoans, cloning
Sexual reproduction – fewer numbers of offspring, all organisms with different DNA
*Increased genetic diversity (larger gene pool)
*Increased survival of the species
* Most multicellular organisms
Animal Reproductive System Physiology
Works to ensure survival of the species of the animal
Interacts with other body systems
*Purely reproductive structures are not essential to the life of an animal
Requires a second animal (of the opposite sex) tocfully carry out its function
Process begins with fertilization
* Head of spermatozoon must penetratecinto the cytoplasm of ovum
— S + E= Z
Chromosomes
Coiled masses of DNA in the nuclei of cells
Each cell in an animal’s body (except spermatozoa or ova) contains paired, identical chromosomes
Diploid chromosome number = 2n
* Total number of chromosomes in the nucleus of each body cell is the same (except for reproductive cells)
* Always an even number – chromosomes occur in pairs.
Sex Chromosomes
Designated as either “X” chromosomes or “Y” chromosomes
If both of the sex chromosomes are X chromosomes (XX), the individual is genetically female
If one is an X and the other is a Y (XY), the individual is genetically male
Mitosis vs. Meiosis
Mitosis – diploid chromosome number (2n)
*Production of all cells in body except gametes
Meiosis – haploid chromosome number (n)
*Production of gametes (sex cells)
Fertilization
*Sperm (n) + ovum (n) = =
zygote (2n)
Cell Division Mitosis vs Meiosis
Mitosis = 2n
* Each chromosome produces a duplicate copy of itself
* Half of chromosomes go to one daughter cell, and half go to the other
* Genetic makeup exactly the same as each other and as the parent cell
Meiosis = n
* Chromosomes do not produce duplicate copies before daughter cells pull apart
* Random half of total chromosomes go to each daughter cell
Mitosis
Most body cells divide after the cell first makes a duplicate copy of its chromosomes
Half the chromosomes go to one daughter cell and half go to the other
Genetic makeup of the two daughter cells is exactly the same as each other and as the parent cell
Meiosis
Cell division that produces basic reproductive cells
* Ova
*Spermatozoa
Process ensures that the genetic makeup
of each new animal is unique
Creation of reproductive cells (gametes)
*Sperm & egg
* Occurs in gonads (sex organs)
Diploid (2n) number haploid (n) number
Meiosis I (where genetic diversity happens)
* Tetrads
* Crossing over
Meiosis II
* Like mitosis
Haploid Chromosome Number (meiosis)
The reduced number of chromosomes in the gamete
Results from a reduction division (meiosis)
* Cell divides
* Total number of chromosomes in each daughter cell is reduced to ½ number of the parent cell
Ensures that fertilized ovum from union of ova and
spermatozoa has the diploid number
Meiosis – Gamete Formation
Diploid number to haploid number of chromosomes
Spermatogenesis in male animal
* 1 spermatogonium produces 4 mature sperm
Oogenesis in female animal
* 1 oogonium produces 1 mature egg (ovum) + 3 polar bodies
Spermatogenesis
The process where spermatozoa (male gametes) are produced in large numbers in the seminiferous tubules of the testes
Primary spermatocyte divides by meiosis into secondary spermatocytes – haploid number
The secondary spermatocytes divide by mitosis into four spermatids
Spermatids grow tails and undergo other physical changes that convert them to spermatozoa.
When the spermatozoa are fully developed, they detach and are carried to the epididymis for storage before ejaculation
Half of the spermatozoa produced have an “X” sex
chromosome, and half have a “Y” sex chromosome
*The male sperm determines the sex of the
offspring!
Oogenesis
*The process where ova (female gametes) are produced (a few at a time) in the follicles of the ovaries
*Female has fixed number of primary oocytes at or soon after birth
Primary oocyte divides by meiosis into a large secondary oocyte and a small “polar body”
Each has the haploid chromosome number
Secondary oocyte and the first polar body divide by mitosis into an ovum and three polar bodies
The Male Reproductive System
*The testes are the male gonads
*The male reproductive cells are formed in the testes Testes located outside body in the scrotum
Male Reproductive System Physiology
Produces male sex hormones
Develops spermatozoa
Deliver the spermatozoa to the female system at the appropriate time
Male Reproductive System Anatomy
Scrotum
* Cremaster muscle
* Tunica albuginea
Testicles (testes)
Epididymis
Spermatic cord
* Ductus deferens (vas deferens)
* Testicular vessels
Scrotum
Sac of skin that houses the testes
Helps regulate temperature of testes
* Testes must be kept slightly cooler than body temperature
Cremaster muscle passes down through the inguinal ring and attaches to the scrotum.
*Adjusts the position of the testes relative to the body depending on temperature
Tunica Albuginea
Fibrous connective tissue capsule that encloses each testis
Septa divide each testis into tiny lobules that contain the seminiferous tubules
Produce sperm and hormones
Located outside the abdomen in the inguinal region
Housed in a sac of skin – the scrotum
Histology of Testicle
Seminiferous tubules
*Produce sperm (spermatogenesis)
Interstitial cells (Cells of Leydig)
*Produce testosterone
Seminiferous Tubules
Site of spermatogenesis
*takes place in U-shaped tube =
Long, convoluted U-shaped tube attached at both ends to system of ducts (rete testis)
Interstitial cells – endocrine cells between the seminiferous tubules -produce androgens
*produce androgens (testosterone)
Sertoli cells – Support developing spermatids
*and shield from body’s immune system
Testicle Development
Develop just posterior to kidneys
Descends into scrotum by passing through inguinal canal
Gubernaculum (cordlike structure containing muscle) extends from the testicle to the inner lining of scrotum
*It shortens, and guides the testicle to the scrotum
Functions of the Testes
Spermatogenesis
*Spermatozoa are produced in seminiferous tubules of the testes
Hormone production
*Androgens (male sex hormones) produced in interstitial cells of the seminiferous tubules
*Principal androgen = testosterone
Spermatozoa
Long, thin cells
3 main parts
* Head - made up of nuclear material and is covered by a cap-like structure called the acrosome
– Acrosome contains digestive enzyme that are released once the sperm is inside the female reproductive tract – helps penetrate through the ovum)
* Midpiece - the “power plant” of the cell; contains a large
concentration of energy-producing mitochondria
* Tail - – resembles the flagellum that many single-celled organisms use for propulsion;
Head of sperm
Contains nucleus
Covered by acrosome
* Contains digestive enzymes that help spermatozoon reach and penetrate ovum
Midpiece of sperm
Large concentration of mitochondria arranged in a
spiral pattern
Tail of sperm
Contains muscle-like contractile fibrils
* Produces a whip-like movement of tail and propel sperm cell forward
Duct System
After detaching from Sertoli cells, spermatozoa enter the rete testis
Then flow through the efferent ducts to the epididymis
*Single, long, convoluted tube that connects the efferent ducts of the testis with the vas deferens
*Storage and maturation of spermatozoa
Then flow into the vas deferens of the spermatic cord
The Epididymis of sperm
Storage site for spermatozoa and a place for them to mature
Flat ribbon-like structure that lies along the surface of
the testis
Vas Deferens
Ductus deferens; part of the spermatic cord
Passes through inguinal ring then separates from spermatic cord and connects with urethra
Ampulla – enlargement of the vas deferens just before it joins the urethra found in some species
* contain glands that contribute material to semen
Spermatic Cord
Blood and lymphatic vessels, nerves, and the vas deferens.
Pampiniform plexus – meshwork of veins that surrounds testicular artery
* Maintains testes at a temperature slightly lower than body temperature
* Warms blood back to body temperature before it returns to the abdomen.
Vas Deferens Physiology
*moves the spermatozoa from the epididymis up to the urethra when ejaculation occurs
*spermatozoa mixed with secretions from accessory glands = semen
Urethra anatomy
Pelvic portion - entry point of vas deferens and accessory reproductive glands
Penile portion - runs down the length of the penis
Spermatozoa from vas deferens and secretions from accessory reproductive glands enter urethra and are pumped out as semen
Carries urine from the urinary bladder outside the body.
* Urine flow temporarily blocked when ejaculation occurs
Accessory Reproductive Glands
*Ducts of glands enter pelvic portion of the urethra
*Different species have different combinations of glands
Produce alkaline fluid to help counteract acidity of female reproductive tract
*Electrolytes
* Fructose
*Prostaglandins
Seminal vesicles
Prostate gland
Bulbourethral glands = Cowper’s glands
The Penis
The roots
* 2 bands of crura attach penis to brim of pelvis
The body
* 2 bundles of erectile tissue
*Sinuses engorge with blood = erection
–Corpus cavernosum urethrae = corpus spongiosum
–Corpus cavernosum penis
The Penis Glans
The glans
* Distal end of penis with numerous sensory nerves
*Prepuce = sheath of skin that encloses the penis when it is not erect
Penis Comparative Anatomy
*Canine
Urethra runs through groove on os penis
Bulb of the glans remains swollen after ejaculation . . .the tie
*Equine
Contains large component of erectile tissue
Glans flares into distinctive mushroom shape
– Corona glandis
Urethral process extends from central depression called the fossa glandis
*Bovine
Sigmoid Flexure Erection results from straightening the S shape of non-erect penis
Penis protrudes from prepuce for breeding
Retractor penis muscle pull penis back to non-erect, S shape
Orchidectomy
Castration, “neutering”, OE
Definition – surgical removal of testicles
Medical vs. behavioral reasons
Male Physiology
- Major sex hormone is testosterone
- Produced in the interstitial cells in the testicle
Female Reproductive System complexity and functions
More complex than male reproductive system
Functions:
*Produces sex hormones
* Develops gametes
* Receives male gametes
* Furnishes a site for gametes to fertilize the ovum
*Provides environment for embryo to grow and develop
* Carries embryo for entire pregnancy
*Pushes offspring out when fully developed
Canine Female Reproductive System Anatomy
Ligaments
Ovaries
Oviducts
Uterus
Cervix
Vagina
Vulva
Broad and Round Female Reproductive Ligaments
Broad ligament:
*Suspend ovaries, oviducts, and uterus
* Contain blood
vessels and
nerves
Round ligament of
the uterus
Suspensory Ligament of Ovary
Ovarian end of broad ligament attached to body wall in area of last rib
Must be broken during OHE
Ovaries
In dorsal abdomen just posterior to kidneys
Species variation in appearance
Site of oogenesis
2 functions
* Ova (eggs)
* Female hormones
– Estrogen - prepares for pregnancy
—progesterone - hormones of pregnancy
* Follicles & corpus luteum
Ovarian artery
Palpated rectally in cows, mares
* Determines when to breed
Oogenesis
*During fetal development meiosis begins but stops in prophase 1
*After puberty, primary oocytes complete meiosis 1
–produces a secondary oocyte and a first polar body
—- first polar body may or may not divide again
*Secondary oocyte begins meiosis 2 but stops in metaphase
* Secondary oocyte and first polar body are ovulated
(Meiosis 2)
* After fertilization meiosis 2 resumes.
– The oocyte splits into an ovum and second polar body
* The nuclei of sperm cell and the ovum unite forming a diploid zygote
Trace Sperm through reproductive tract
1) Sperm starts in testicle
2) Stored in epididymis
3) Vas Deferens (ejaculation)
4) Prostrate gland
5) Urethra
Ovarian Cycle physiology
Development of ovum, ovulation, formation of corpus luteum, and degeneration of immature follicles and corpus luteum
Influenced by follicle stimulating hormone (FSH) and luteinizing hormone (LH)
Ova are not constantly produced in ovaries
Cyclical sequence of events under influence of FSH and LH
The Ovarian Cycle in different species
Uniparous species
* Ovaries produce one mature ovum per cycle
* Horses, cattle, humans
Multiparous species (litter species)
* Ovaries produce multiple ova per cycle
* Cats, dogs, and sows give birth to a litter
Primary Follicle
*Immature oocyte surrounded by single layer of flattened follicular cells
*Follicular activation
Growing Follicle
*Occurs once primary (primordial) follicle has become activated
*Oocyte starts to grow in size
* Glycoprotein zona pellucida layer forms
* Granulosa cells multiply
*Antrum is formed
Comparative Anatomy Male Accessory Reproductive Glands
Boar- -Seminal Vesicles: Yes, Bulbourethral: Yes
Bull-Seminal Vesicles: Yes, Bulbourethral: Yes
Cat-Seminal Vesicles: No, Bulbourethral: Yes
Dog: Seminal Vesicles: No, Bulbourethral: No
Human: Seminal Vesicles: Yes, Bulbourethral: Yes
Ram: Seminal Vesicles: Yes, Bulbourethral: Yes
Stallion: Seminal Vesicles: Yes, Bulbourethral: Yes
Prostrate Gland, all species
Mature Follicle
*Oocyte sits in mound of cumulus oophorus
*Zona pellucida is surrounded by corona radiata
*Estrogen is at peak level
Ovulation
*Mature follicle ruptures
* Gamete released into oviduct – now called an ovum
*Empty follicle fills with blood to form corpus hemorrhagicum
Ovulation Stages
Primary Follicle
Growing Follicle
Mature Follicle
Ovulation
Corpus Luteum
Corpus Luteum
*Formed from cells lining corpus hemorrhagicum
*Produces the progestins needed to maintain pregnancy if ovum is fertilized
Corpus Luteum
If pregnancy occurs, remains for entire pregnancy
If pregnancy does not occur, degenerates after a short period
False pregnancy (pseudocyesis)
* Common in dogs
Ovulation occurs
Occurs spontaneously in most species
* Result of rising levels of LH
Induced ovulators
* Ovulation occurs after breeding
* Cats, camels, rabbits, ferrets
Oviducts
= Fallopian Tubes = Uterine Tubes
Guide ova from ovary to uterus
Serve as usual site for fertilization of ova by spermatozoa
Extend from tips of uterine horns
Fimbriae “catch” ova in infundibulum
— Infundibulum: enlarged opening at the ovarian end of each oviduct
—-muscular projections form margin of infundibulum; help properly position infundibulum
Linings covered with many cilia
Move ova down toward uterus
Uterus
Also called the womb
Where zygote implants and grows
“Litter species” have more horn than body
* Dogs, cats, pigs
3 layers
*Endometrium – site of zygote implantation
* Myometrium – thickest layer
*Perimetrium
Hollow muscular organ, usually Y-shaped
Forms part of placenta and afterbirth
Comparative Female Reproductive Anatomy
All species have the same part
Uterine horn in litter species is smaller than in non-litter species
3 Layers of Uterine Wall
Endometrium: lining composed of simple columnar epithelium and simple tubular glands
*Secrete mucus and other substances
Myometrium: thick layers of smooth muscle
Perimetrium: outermost layer covered by the visceral layer of peritoneum
The Cervix
Smooth muscle sphincter between body of the uterus and the vagina
Normally tightly closed/Naturally open on only 2 occasions
*Estrus (true heat)
—Sperm in
*Parturition (birthing)
—Newborns out
Muscular valve that seals off uterus
The Vagina and the Vulva
Vagina
* Muscular tube that receives penis during breeding time
*Acts as birth canal at parturition
Vulva (External Genitalia)
*Vestibule – urethra opens on floor of vestibule
* Clitoris
* Labia
Female Reproductive Physiology
Puberty – age at which reproductive organs become functional
Males
* Quite often mature later than female
*Always ready for breeding
Females
* Usually mature first
*Are only fertile and receptive for a brief time
Estrous Cycle
= Heat Period = Estrus
Definite period in each reproductive cycle when
breeding can take place
Time from the beginning of one heat period to the
beginning of the next
Controlled by 2 anterior pituitary hormones
* Follicle stimulating hormone (FSH) (from pituitary)
—- Oogenesis
* Luteinizing hormone (LH) (from pituitary)
—- Ovulation, corpus luteum production
3 female tracks exit caudally
Dorsal to ventral
Digestive
Reproductive
Urinary
Proestrus
The “building up” phase (7 days)
Blood spotting starts (Day 1)
Follicles begin developing
Estrogen output increases
Blood supply to ovaries increases
Estrus
“True heat” (7 days)
2nd stage of Estrous after proestrous
Estrogen level production peaks
Female sexually receptive
Bloody discharge lighter (straw colored?)
Ovulation! (one or multiple ova)
* Ovulation occurs near end of estrus in some species
Induced ovulator species (e.g., cat, rabbit) remain in a prolonged state of estrus if not bred
Trace an egg Cell
- Ovary
- Oviduct
- Uterine horn (zygotes)
4.body of uterus - cervix
- vagina
Metestrus
7 days
Time when corpus luteum develops
Lining of uterus thickens for implantation
Progesterone produced by corpus luteum temporarily inhibits follicular development in the ovary
Cornified epithelial lining that developed in the vagina during proestrus and estrus is lost
Diestrus
Corpus luteum at maximum size and exerting maximum effect
If fertilized ovum implants, corpus luteum is retained well into the pregnancy
If no pregnancy occurs, corpus luteum degenerates at the end of diestrus
— sometimes Pseudocyesis, or pseudopregnancy (common in dogs)
*Animal then either goes back into proestrus or ovary shuts down and animal goes into anestrus
Seen in seasonally polyestrus animals (cat, horse, cattle, swine)
Anestrus
Period of temporary ovarian inactivity
Seen in seasonally polyestrus, diestrous, and monoestrous animals
Ovary temporarily shuts down
Ovarian inactivity (5+ months in dogs)
Period between breeding cycles
Types of Estrous Cycles
Polyestrous: animals that cycle continuously throughout the year if they are not pregnant (cattle and swine)
Seasonally polyestrous: animals with seasonal variations in estrous cycles (horse, sheep, cat)
Diestrous: animals with two cycles per year, usually spring and fall (dog)
Monoestrous: animals with one cycle per year (fox and mink)
cats/rabbits fertility
Seasonally polyestrus
(10 months)
Anestrus (2 months)
Induced ovulators
* Need 2 stimuli
Post-partum estrus
* Can have 3 litters per year
Species specific Estrus
Time Intervals
*Polyestrous
–Cattle, swine
*Seasonally polyestrous
–Horses, sheep, cats
* Diestrous
—Dogs
* Monoestrous
—Foxes, minks
Breeding dogs
Breed twice when ovulation is occurring
Eggs only in oviduct 72 hours
Sperm only live for 72 hours
Best time to breed?c
Day 10 – Day 12
Vaginal cytology
*Best way to detect ovulation
Glycoprotein zona pellucida
Forms around the growing follicle
Thick extracellular matrix composed of glycoproteins to which sperm attach
antrum
Fluid-filled space within an ovarian follicle
Vaginal tunics and Testis capsule
▪ Tunics are derived from the abdominal peritoneum
– The parietal vaginal tunic forms a grossly visible fibrous sac around each testis and spermatic cord
– The visceral vaginal tunic tightly adheres to the testes – it is not grossly visible
▪ testis capsule:
➢ Is located beneath the vaginal tunics
➢ It is also known as the tunica albuginea
➢ Is composed of dense fibrous connective tissue
➢ Provides support and protection for the testis
➢ Sends branches into the testis that divide it into microscopic lobules, each containing seminiferous tubules and interstitial cells
Prostrate Gland
▪ Single structure that more or less surrounds the urethra
▪ Multiple ducts carry its secretions into the urethra
▪ It is present in all common domestic animals
▪ In dogs, it is particularly large because it is the only accessory reproductive gland they have
Seminal vesicle
▪ Ducts from the two seminal vesicles (also known as vesicular glands) enter the pelvic urethra in the same area as the vas deferens
▪ They are present in all common domestic animals except for cats and dogs
Bulbourethral glands
▪ The paired (two) bulbourethral glands are also known as Cowper’s glands
▪ They are located further caudally than the other accessory reproductive glands
▪ Their ducts enter the urethra back near the caudal border of the pelvis
▪ They secrete a mucinous (mucus-containing) fluid just before ejaculation that clears and lubricates the urethra for the passage of semen
▪ They are not found in dogs
How does the reproductive system differ from other body systems?
*Not about survival of the species
*Involves a second animal
