Function of male reproductive system

• Produce and Deliver viable gametes to the female tract.
• Produce hormones (ex: testosterone

Male Reproductive Tract Parts (7)

• Scrotum
• Testes
• Epididimys
• Muscle
• Penis
• Accessory sex glands
• Spermatic Cord

Scrotum

• Two lobed pouch that houses the testes and functions to...
• Physical barrier to the environment
• Regulate temperature
• Move testes closer or further from body

Scrotum Parts (5)

• Skin containing sebaceous glands and thermosensory neurons.
• Tunica dartos muscle
• Scrotal fascia (connective tissue)
• Parietal tunic
• Visceral tunic

Spermatic Cord

• Functions primarily to suspend the testes.
• Extends from the inguinal ring to its attachement on the dorsal pole of the testis.

Spermatic Cord Parts (3)

• Vas deferens
• Cremaster muscle
• Pampiniform plexus

Vas Deferens (ductus deferens)

Ducts that connect the rete testis to the head of the epididimys.

Cremaster Muscle

A striated muscle that raises the testis for short periods of time during "fight or flight" moments (NOT to regulate temperature)

Pampiniform plexus

A vascular network that plays an essential role in thermoregulation of the testis. It is a specialized venus plexus consisting of the testicular vein that elaborately intertwines around the testicular artery in order to provide a countercurrent heat exchange mechanism.

Testes

• Male gonads that function to...
• Produce male gametes (spermatozoa)
• Produce male hormones (androgens / testosterone)

Testes Parts (4)

• Testicular capsule
• Parenchyma
• Mediastinum 
• Rete tubules

Testicular Capsule

Consists of the two outer layers

• Visceral vaginal tunic 
• Tunica Albuginia

Parenchyma

Region of the testes containing the seminiferous tubules and interstitial tissue and therefore divided into the....

• Tubular compartment 
• Interstitial compartment

Tubular Compartment

Testicular compartment that houses the seminiferous tubules

Seminiferous Tubules

Highly totuous tubules within the testes that produce spermatozoa; consists of only two cell types, gametes and Sertioli cells.

Sertioli Cells

Somatic cells that respond to the hormone FSH that function to govern spermatogenesis and produce a variety of hormones and materials. ("Nurse cells")

Interstitial Compartment

Compartment of the testes that immediately surrounds the seminiferous tubules; consists of connective tissue, blood vessels, lymphatics, nerves, and Leydig cells.

Leydig Cells

Respond to the hormone LH (Luteinizing Hormone) to produce testosterone

Blood Testis Barrier

Keeps blood out of seminiferous tubules. The white blood cells in blood recognize spermatozoa as foreign bodies as they are haploid cells.

Mediastinum

Connective tissue core of the testes that houses the rete tubules.

Rete Tubules

Tubules that transport spermatozoa and fluid from the seminiferous tubules to the efferent ducts.

Testicular Decent

From the abdominal cavity to the scrotum. Occurs during late gestation and is essential for the proper thermoregulation of the testes and development of spermatozoa.

Gubernaculum

Ligamentous tissue at the base of testes that is responsible for pulling the testis from the abdominal cavity, through the inguinal ring and into the scrotum.

Cryptorchid (unilateral¹ or bilateral²)

Failure of one or both of the testes to descend.

1) Unilateral: One testis does not descend into scrotum. The testis that descends into the scrotum is fertile, however reduced sperm concentrations usually result

2) Bilateral: when neither testis descends into the scrotum. Results in sterility due to elevated temperature of testis. Still produce hormones and may be used as gomers.

Thermoregulation

Essential for spermatogenesis. Testes must be 4° - 6° C cooler than the body temperature for spermatogenesis to occur.

Tunica Dartos

A layer of smooth muscle that controls contraction and relaxation of the scrotum. Contracts during periods of cold temperature to bring testes closer to abdominal cavity. Relaxes during periods of hot temperatures to increase surface area for heat exchange.

Sebaceous (sweat) glands

Secrete an oily substance onto the scrotum for an evaporative cooling system

Thermosensory Neurons

Govern both the degree of scrotal sweating and the respiratory rate of the animal. An increase in scrotal temperature will result in increased respiration.

Spermatogenesis

Process whereby spermatozoa are formed; occurs in the seminiferous tubules.

• Most immature gamete = spermatogonia
• Most mature gamete = spermatids

Spermiation

The release of spermatids from the Sertioli cells into the lumen of the seminiferous tubules.

Vas Efferens (efferent ducts)

Ducts that connect the rete testis to the head of the epididymis.

Epididymis

The duct connecting the vas efferens to the vas deferens and serves as a concentration, transport, maturation, ad storage site for spermatozoa

• Head (caput)
• Body (corpus)
• Tail (cauda)

Caput (head)

Site of fluid reabsorption (concentration of spermatozoa)

Corpus (body)

Site of spermatozoa maturation.

Cauda (tail)

Serves as storing place for spermatozoa.

Vas deferens (ductus deferens) 

Ducts that connects the tail of the epididymis to the ampulla and transpors sperm into the pelvic urethra.

Vasectomy

Ligation of the vas deferens to prevent spermatozoa from entering the pelvic urethra  (a simple surgical method of contraception for males)

Accessory sex glands

The glands of the male reproductive system that surround the pelvic urethra and function to produce seminal plasma. 

Ampullae

Enlargements in the vas deferens that open directly into the pelvic urethra (absent in boars)

Vesicular glands (seminal vesicles)

Function to secrete a large portion of the ejaculate in bulls and rams and a smaller portion of the ejaculate in boars and stallions. 

Prostate

Secretes an alkaline fluid into the seminal plasma.

Bulbourethral Glands (Cowper's Glands)

Produces the gel fraction of boar and stallion seminal plasma (very prominant in the boar)

Penis

Organ of copulation in the male that is comprised of three sections:

• Root (crus penis)
• Body or shaft (corpus)
• Glans penis

Corpus cavernosum

A cavernous erectile tissue making up a majority of the interior penile shaft that allows for an influx of blood during erection.

Corpus spongiosum 

The spongy tissue directly surrounding the urethra and extends to the glans penis. (very prominent in stallions for belling of the glans penis)

Fibroelastic

Composed of a fibrous elastic type tissue that exends in length to create an erection rather than in diameter. (Bull, ram, boar)

Vascular

Engorges the corpus cavernosum and corpus spongiosum with blood to cause the penis to grow in diameter when becoming erect. (Stallion)

Retractor penis muscle

Is in a contracted state when an erection is not occurring and is in a relaxed state during erection to allow for extension of the sigmoid flexure (in the bull, ram, and boar)

Ischiocavernosus

Inserts on crus penis and is important in erection as it compresses crus penis

Bulbospongiosus

Overlaps root of penis and covers bulbourethral glands.

Urethralis

Encloses pelvic urethra and covers bulborethral glands.

Bull Testicles 

• Pendulous
• Epididymis is vertically and normally oriented 
• Fibroelastic penis
• Sigmoid flexure

Ram testicles

• Pendulous testicles
• Epididymis is vertically and normally oriented
• Fibroelastic penis
• Filiform appendage located on the glans penis
• Sigmoid flexure is present

Boar testicles

• Non-pendelous testicles
• Epididymis is vertically oriented but inverted (tail of epididymis is located on top) 
• Fibroelastic penis
• Glans penis is corkscrew shaped
• Sigmoid flexure is present
• Lacks ampullae but has prominent bulbourethral glands

Stallion testicles

• non-pendulous testicles
• epididymis is horizontally oriented
• vascular penis
• no sigmoid flexure present

Mucosa

An epithelial lining or coating of a structure.

Submucosa

A general region of tissue laying just beneath the mucosal lalyer housting the vasculature, nerve supply, and lymphatics.

Muscularis

The smooth muscle layer covering a tubular or hollow organ; comprised of circular and longitudinal smooth muscle layers (help with movement)

Serosa

A serous membrane making up the outermost covering of an organ or serving as the lining of a cavity; usually a single layer of squamous cells.

Broad Ligament (3)

Ligament that supports and suspends reproductive tract as well houses the vascular, lymphatic, and nerve supply.

Mesometrium

Broad ligament that supports the uterine body.

Mesosalpinx

Broad ligament that supports the oviduct.

Mesovarium

Broad ligament that supports the ovary.

Ovary

Female gonads that function to...

• Produce female gametes (ova)
• Produce estrogen and progesterone

Shape depends on species (round = sheep; almond = cattle; bean = horse)

Cortex

Outer portion of ovary that contains developing and atretic follicles, as well as functional and regresssing corpora lutea.

Medulla

Inner portion of ovary that houses blood vessels, lymphatics and nerves.

Hilus

Region housing blood and lymphatic vessels and nerves that enter and leave an organ. 

Tunica Albuginea

Outer connective tissue surface of the ovary.

Ovulation fossa (mare)

A conspicuous depression in the ovarian surface that is the site of each ovulation in the mare (the cortex is located on the inside of the ovary and the medulla surrounds it on the outside)

Follicle

A spherical structures within the ovary that contain an oocyte.

Primordial Follicle

The most primitive stage of the ovarian follicle, surrounded by a single layer of squamous granulosa cells. (present at birth and decrease in number as a female matures)

Primary Follicle

Characterized as having a single layer of cuboidal shaped cells surrounding the oocyte. The nucleus of the oocyte is arrested in the dictyate stage. (Follicles remain at this stage until puberty; most primary follicles never ovulate and undergo atresia)

Secondary Follicle

Characterized by two or more layers of cells surrounding the oocyte (zona pellucida is formed around the oocyte)

Tertiary (Antral) Follicle

Characterized by an antrum filled with follicular fluid, layers of both granulosal and thecal cells.

Graafian Follicle

Large, dominant pre-ovulatory follicle that is characteristically similar to a tertiary follicle but contains more cell layers and a much larger antrum. Capable of ovulation following a surge of luteinizing hormone (LH)

Atretic Follicle

A follicle that is undergoing degeneration and resorption before ovulation; can occur at any follicular stage.

Corpus hemorrhagium (CH)

Small, blood clot that results from rupture of blood vessels during ovulation.

Corpus Luteum (CL)

An orange to yellow colored transcient endocrine structure formed after ovulaton from granulosal and thecal cells of the ovarian follicle. (responsible for the production of progesterone and oxytocin)

Corpus Albicans (CA)

A white, scar-like, fibrous structure that represents advanced regression of the corpus luteum.

Folliculogenesis

Process whereby ovarian follicles deveop from their initial stage as a primordial follicle through their final stage as a Graafian follicle. (each follicle houses one oocyte)

Luteogenesis

formation of the corpus luteum (brought on by the LH surge)

Luteolysis

Regression of the corpus luteum (induced by the hormone prostaglandin F2α)

Cystic follicles

The failure of the Graafian follicle to ovulate. It persists on the ovary and contiues to grow. The follicle still produces high amounts of estradiol and can cause the animal to show a continued estrus behavior.

Luteal Cysts

Occur when theca interna cells do not fill the cavity that is created upon ovulation (the rupturing of the follicle). They can cause abnormal estrous cycles and early embryonic mortality.

Persistant Corpus Luteum

The failure of the CL to regress. It causes a suppression of the estrous cycle due to its resemblance to pregnancy (progesterone is still produced and the body falsely identifies this state as a pregnancy)

Oviduct

Small, usually convoluted duct that fuctions to:

• Transport oocytes and sperm
• Storage and capacitation of sperm
• Site of fertilization (ampullary-isthmic junction; AIJ)
• Site of early embryonic development

Infundibulum

Funnel-shaped opening or "catcher's mitt"; the surface is coated with numerous velvety, finger-like projections called fimbriae. Near the time of ovulation, the fimbriae incres in surface area and cause the infundibulum to glide over the entire surface of the ovary which maximizes the chance that it will "catch" the oocyte.

Ampulla

Comprises half or more of the oviduct directly connected to the uterus; characterized by a large diameter and many mucosal folds

Isthmus

The portion of the oviduct directly connected to the uterus; characterized by a smaller diameter than the ampulla

Uterus

Hollow, tubular organ surrounded by smooth muscle and lined with epithelium that functions to:

• Transport sperm
• Induce luteolysis through the production of PG F2α
• Emryonic and subsequent fetal environment
• Formation of the maternal portion of the placenta
• Expulsion of the fetus and fetal portion of the placenta
• Consists of two uterine horns (bicornuate)

Bicornuate Ligament

Ligament that holds the uterine horns together.

Endometrium

Layer of uterus comprised of the mucosa and submucosa.

Myometrium

Layer of the uterus that is analogous to the muscularis (smooth muscle layer).

Perimetrium

Layer of the uterus that is analogous to the serosa (layer covering an organ; single layer of squamous cells)

Cervix

Structure consisting of dense connective tissue with varying degrees of folding and protursion of the mucosal epithelium that functions to:

• Provide lubrication
• Serve as a flushing system
• Serve as a barrier during pregnancy

Shapes vary among species 

• Cow and ewe - annular rings
• Sow - corkscrew shape
• Mare - longitudinal folds

Vagina

Connects the cervix to the external genitalia and serves as the female copulatory organ

Vulva

External tissue of the female reproductive tract that receives the penis during copulation.

Reproductive Cyclicity

Provides females with repeated opportunities to become pregnant.

Estrous Cycle

Consists of the physiological events that occur between periods of sexual receptivity (heat) and/or ovulations

• Lasts 21 days in the cow, sow, and mare
• Lasts 17 days in the ewe
• Two phases: Follicular and Luteal Phase
• Four stages: Estrus, Menestrus, Diestrus, and Proestrus

Estrus

The period of sexual receptivity (heat).

Anestrus

A condition when females do not exhibit regular periods of estrus (may be due to pregnancy, lactation, presence of offspring, season, stress, or pathology [6])

Polyestrus

Uniform distribution of estrous cycles occuring regularly throughout the year (cow and sow)

Seasonal Polyestrus

"Periods" of estrous cycles occurring only during certain seasons of the year (sheep [SD], goats [SD], horses [LD], and deer [SD])

• Short day breeder: cycle due to an increase in melatonin secretion when there are shorter periods of daylight
• Long day breeders: cycle during warmer temperatures and longer days of spring

Monoestrus

Only one estrous cycle occurs per year with estrus often lasting several days (dogs, wolves, foxes, and bears)

Melatonin

Horomone secreated from the pineal gland that stimulates the release of GnRH from the hypothalamus (Is synthesized and secreated at night)

Luteal Phase

Begins immediately after ovulation ad ends with luteolysis (Proestrus +Estrus)

• Immediate formation of the corpus hemmorhagicum following ovulation 
• Increasing production of progesterone as the CL forms; corresponding decrease in estrogen
• Conversion from a corpus hemmorhagicum to a fully functional CL with maximum progesterone production
• Prostaglandin F2α induced luteolsis terminates the luteal phase with the formation of a corpus albican

Follicular Phase

Begins immediately following luteolysis and ends with ovulation (Metestrus + Diestrus)

• Luteolysis induces a rapid decrease in progesterone production which allows an increase in estrogen production.
• Formation of the corpus albican occurs from the regressed corpus luteum
• Formation of new developing follicles ends with ovulation of a dominant Graafian follicle

Metestrus 

Begins following ovulation and consists of the corpus hemmorhagicum transitioning to a corpus luteum and rising levels of progesterone (6-8 days)

• Rapid growth of the CL
• Slight postestrual bleeding may occur

Diestrus

Consists of a fully functional corpus luteum and maximum progesterone production and is terminated by luteolysis (9 days; longest)

• mature corpus luteum
• thick uterine endometrium
• scant and sticky vaginal mucus
• corpus luteum regresses late

Proestrus

Begins following luteolysis and is a period of ovulatory follicle formatio with rising levels of estrogen production (3 days)

• Growth of follicle
• Increased vascularity in uterine mucosa

Estrus

The period of sexual receptivity with maximum estrogen production that terminates with the ovulation of a Graafian follicle (12-18 hours; shortest)

• ovulatio 12-14 hours after the end of estrus, 3 hours earlier in heifers
• increased blood supply to uterus
• sexual desire and acceptance of the male
• clear mucus on vulva

Follicular Dynamics

The sum of the intraovarian process involved in follicular development and degeneration

Recruitment (emergence)

A cohort of small tertiary follicles begin to grow (emerge) and secrete estrogen [most of the follicles will undergo atresia]

Selection

A group of growing follicles that were recruited and have not undergone atresia are "selected" to continue growth

Dominance

Of the follicles that undergo selection, certain ones will continue growing until they become a Graafian follicle and ovulate

• number varies in litter bearing species
• In species that only produce one offspring, only one follicle will become dominant and ovulate

Atresia

Degeneration of a follicle