Physiology of Animal Reproduction Exam #1

Disadvantages of sexual reproduction

Requires 2 gamete donors, only 50% of the population can reproduce. Only passing on 50% of own genetic material.

Advantages of sexual reproduction

Genetic variation from crossover during meiosis, prevents accumulation of genetic mutations (chromosomal rearrangements). Novel genotypes more rapid than asexual (asexual populations have clonal interface). Red Queen Hypothesis.

Red Queen Hypothesis

Adapt as fast as possible. Quick change in environment can change neutral or deleterious alleles to favorable

Differentiation

ability to change into more progressively specialized functions that are unique. Driving factors are water, pressure, ion concentration, gases, etc.

Hierarchical Body Plan

• macromolecules & micronutrients

• intracellular organelles

• cell (basic unit of life)

• tissues

• organs

• systems

• organism

• population

Tissue

Multicellular aggregates of specialized cell types with special form and function as a unit

• connective (tendon, ligament)

• muscular (skeletal, cardio, smooth)

• nervous (CNS/ PNS)

• epithelial (skin, airways, reproductive tract)

Organs

Structures with 2 or more tissue types that are integrated to perform certain functions

• heart is made of myocardium (cardiac muscle) and nervous, circulatory, and connective tissue

Organ Systems

2 or more organs with similar or related functions that work to perform essential processes for an organism.

• alimentary (digestive), cardiovascular (circulatory), respiratory (lungs, diaphragm), integumentary (skin, hair), immune, sensory, endocrine

Reproductive Organ System

Essential for the survival of a population or individual’s genetics.

Tubular Components of the female reproductive tract

oviducts, uterus, cervix, vagina

Layers of female reproductive tract

serosa, muscularis, submucosa, mucosa

Serosa

• outermost layer of cells

• single layer of squamous (flattened) cells

• provide support and protection to the tract

Muscularis

• double layer of smooth muscle (outer longitudinal and inner circular layer)

• allows for muscle contractions (movement of secretions, gametes, embryos, and expulsion of fetus)

Submucosa

• varying thickness depending on area of tract

• houses blood vessels, nerves, and lymphatics

• supports the mucosa

Mucosa

• secretory layer of epithelium

• each part of the tract is lined with a different type of mucosal epithelium

• oviduct has ciliated and nonciliated columnar epithelium (to move things), posterior vagina has stratified squamous epithelium (hardy, to prevent abrasion in mating)

3 components of the broad ligament

1. mesovarium

2. mesosalpinx

3. mesometrium

Mesovarium

Most cranial component of the broad ligament, supports the ovary

Mesosalpinx

• thin membrane in the broad ligament that supports the oviduct.

• Forms bursa that completely (dog) or partially (cow) surrounds the ovary.

• Orients the infundibulum to increase probability of ova entering oviduct

Mesometrium

• largest part of the broad ligament

• supports uterine horns and body

• ovary receives additional support from the utero-ovarian ligament

Ovary

• primary reproductive organ

• houses eggs

• bilaterally paired- right and left side

• shape/ form depends on species

• monovulator; 1-2 oocytes (humans, equids, cervids, ursines, ovine, bovine)

• polyovulator; >7 oocytes (canines, felids, rodentia, lagomorphs, swine)

Ovarian Hormones

progesterone, estrogen, oxytocin, relaxin, inhibin. Oxytocin, relaxin, and inhibin are in the Corpus Luteum

Progesterone

a steroid hormone produced by the corpus luteum and placenta; required for the maintenance of pregnancy

estrogen

a steroid hormone produced by follicles; causes “estrus behavior”

oxytocin

causes smooth muscle contractions; regulates luteolysis

relaxin

a polypeptide hormones; causes cervix to dilate and softens pelvic ligaments

inhibin

a glycoprotein hormone; inhibits release of FSH from anterior pituitary

4 kinds of follicles

• primordial follicles

• primary follicles

• secondary follicles

• tertiary/ antral follicles

Primordial follicles

most immature and are stored int he cortex of the ovary. Surrounded by a single layer of flattened squamous cells

Primary follicles

oocyte is surrounded by a single layer of cuboidal epithelium

Secondary follicles

Two or more layers of cuboidal epithelium surround the oocyte. Follicle has no antrum. Oocyte is surrounded by zona peliculada

Tertiary/ 3°/ Antral/ Graafian/ Dominant follicle

When antrum is present, follicular fluid filled cavity, contains 3 distinct layers

3 layers of Tertiary follicle

1. theca interna- supports follicle

2. theca externa- produce androgens under control of LH

3. Granulosa/ membrana granulosa- have FSH receptors, produce estrogen, inhibin, and follicular fluid, play role in oocyte maturation

corpus hemorrhagicum

ovulation of ovary results in protrusion of tissue (granulosa, theca, and antrum) and rupture of small blood vessels. Very short lived, only at immediate beginning of ovulation

corpus luteum

“yellow body”, produces progesterone

corpus albicans

degenerating CL; white appearance due to increasing connective tissue (tendon like) to secretory tissue

Ovulation in mare

occurs only at a specific location on the ovary called the ovulation fossa

Parts of the oviduct

• infundibulum

• fimbriae

• ampulla

• ampullary-isthmic junction (AIJ)

• isthmus

• uterotubal junction (UTJ)

• uterine horn

Infundibulum

• terminal end of the oviduct and funnel-shaped

• catches the newly ovulated oocyte

• about 6-10 cm2 in ewe and 20-30 cm2 in cow

fimbriae

fingerlike projections that allow oocyte to move toward ostium (opening of the oviduct)

Ampulla

• relatively thick portion of the oviduct, occupies at least ½ of the oviductal length

• many projections/ folds (increasing surface area for more secretions and nutrients)

• moves and supports environment favorable for oocyte towards AIJ.

ampullary-isthmic junction (AIJ)

fertilization occurs here

Isthmus

• lower region of oviduct that connects to uterine horns at the utertubular junction

• smooth muscle helps propel sperm toward oocyte and maintain them in a sugar bath (lots of secretions, high sugar to give single cell sperm energy so they can move in tract)

• has a thicker muscular wall than ampulla and less folds

Oviduct

• primary purpose is to transport ova and sperm toward each other

• following fertilization, provides a temporary environment for sustaining the zygote before transferred to the uterine body

• In cow and sow, uterotubual junction acts as a “kink” before zygote enters uterine body (dependent on E2 levels) to prevent polyspermy and stops zygote from traveling back up the tract.

Duplex Uterus

• Marsupials- single vaginal canal opening, splits into 2 vaginas and cervices, male has forked penis, deposits sperm on both sides simultaneously

• Rabbit- has two uterine horns, two cervices, can be inseminated by 2 different males, single vagina and opening

Bicornuate

• mare and sow have poorly to moderately developed uterine horns

• dog, cat, and sow have highly developed uterine horns

Simplex

• primate and human, no uterine horns

Components of uterus

• perimetrium (serosa)

• myometrium (muscularis)

• endometirum (mucosa and submucosa)

Perimetrium function

protection and structure

myometrium function

• motility for sperm (sperm and uterine mucus products)
  important for determining uterine tone (turgidity with high E2 and flaccidity with P4) (will be rigid when ready to breed)

• parturition

endometrium function

• secretions

• secrete products essential for preimplantory embryo and sperm

• prostaglandin F2a secreted- luteolysis/ cyclicity

• caruncles- give rise to the maternal portion of placenta (placenta attaches to uterus here)

Cervix

• located between uterus and vagina

• functions as a physical, chemical, and immunologic barrier for external and internal environments of the female

• secretory: cervical fluids (about 50% of the cells)

  • sperm transport, removal of debris, cervical plug, lubrication of vagina

• part of birth canal

cervical plug

in mice and pigs, prevents in and out of fluids during pregnancy, mucus becomes glue-like with P4

Cervix Differences

• cow and ewe- annular rings, barrier for sperm

• sow- cork screw, not a barrier for sperm. Penis locks into cervix before ejaculation

• mare- longitudinal folds, not a barrier for sperm

Vagina

• the female copulatory organ

• part of birth canal

• cranial portion of vagina is made up of cuboidal/ columnar cells; secretory in nature (buffer for urine)

• causal portion is made up of stratified squamous epithelium; protective armor (increases with estrogen, estrus)

• development is due to paramesonephric ducts joining urogenital sinus (caudal vagina) in developing embryo

Fornix vagina

• crypt formed by protruding cervix into anterior vagina (dog, cow, mare)

• in the bull, sperm are deposited in this location

• composed of columnar epithelium that secrete high amounts of mucus during estrus

Vestibule

• caudal vagina, both urinary and genital

  • extends from the urethral orifice to labia of vulva

  • suburethral diverticulum; blind pouch

• Gartner ducts present on the floor of vestibule

  • blind sacs

  • formed form wollfian ducts/ remnants of possible male pathway

• Houses vestibular glands

  • secrete mucus like material during estrus

Vulva

• composed of two labia

  • constrictor vulvae muscles (keep labia closed)

  • made up of fat, CT, elastin, and muscle

• form two commissures (sites of union)

  • dorsal and ventral

  • ventral commissure houses clitoral fossa or clitoris (female penis)

• AI improves up to 6% if stimulated

Male reproductive tract function

produce and deliver viable gametes to the female reproductive tract

Parts of the male reproductive tract

• spermatic cord

• scrotum

• testes

• excurrent duct system

• accessory sex glands

• penis and muscles for protrusion, erection, and ejaculation

Spermatic cord

• suspends testes within scrotum

• provides a pathway for testicular vasculature, lymphatics, and nerves

• allows for heat exchange

• houses ductus deferens, cremaster muscle, pampiniform plexus

Blood supply of spermatic cord

• spermatogenesis requires a 4-6°C lower temp than core

• testicular artery becomes highly convoluted around the testis, carries arterial blood to the testis

• Pampiniform plexus is a venous network surrounding the testicular artery

• TA and PP form countercurrent heat exchange system

TA as a pulse pressure eliminator

• difference between systolic (heart contraction) and diastolic (heart relaxation) pressure. TA pules pressure almost eliminated at the testis surface, blood entering the testis is almost pulseless

Cremaster Muscle

• supports testes extending the entire length of the spermatic cord

• striated muscle; continuous with abdominal oblique muscle

• aids in temperature regulation of testes

  • raising and lowering blood temp through pumping action on the pampiniform plexus

  • promotes venous return, increasing cooling effect

  • does not sustain contractions (temporary)

• active during fight or flight and sexual excitation

Scrotum

• 2 lobed sac that protects and supports the testis

• 4 major layers of the skin, tunica dartos (sustains during cold weather), scrotal fascia, and parietal vaginal tunic

• function: thermo sensor, evaporative heat transfer “swamp cooler”, movement of testis, protective sac

Scrotal Sweating Thermal Polypnea

• respiration rate increases when scrotal temperatures rise above 26°C

• Panting wills tart around 39°C

• Possible use of this to eliminate bulls that cannot cool their scrotum in breeding.

• Fat gain can also impact this

Tunica dartos

• smooth muscle lying just beneath scrotal skin

• can elevate the testes for sustained periods; unlike cremaster muscle

• sensory nerves responsible for changes in contraction are located in scrotal skin

• cold= contract; heat= relax

Testis

• primary male reproduction organ

• paired organ

• spermatogenesis and testosterone

• manufacturing and assembly plant for spermatozoa

• produces male hormones (androgens), spermatozoa, testosterone, inhibin, estrogens, and rets fluid

• made of testicular capsule, parenchyma, mediastinum, rete tubules

Testicular Capsule

• “suborgan”

• composed of 2 layers, visceral vaginal tunic and tunica albuginea

• Tunica albuginea sends fingerlike projections into the parenchyma, which joins the mediastinum

• interior surfaced are highly vascularized- tunica vasculosa

• tunica albuginea contains both connective tissue and smooth muscle for contractions

• moves spermatozoa to rete tubules and efferent ducts

Testicular Parenchyma major compartments

• seminiferous tubules

• interstitial cells of leydig (produce testosterone)

• capillaries

• lymphatic vessels

• connective tissue

2 parts of the testicular parenchyma

1. tubular component

   • seminiferous tubules and the materials within

   • location of spermatozoa production

2. Interstitial compartment

   • all materials outside seminiferous tubules; blood vessels, connective tissue, lymphatics, nerves, interstitial cells of leydig, mediastinum (central connective tissue core of testis), houses rete tubules (channels by which spermatozoa are moved out of the testis)

Seminiferous Tubule

Composed of:

• basement membrane

• seminiferous epithelium (germinal epithelium- basal and adluminal compartment)

Surrounded by:

• contractile peritubular muscles

• sertoli cells (fluid and host cells for spermatozoa)

Sertoli Cells

• only somatic cells in seminiferous tubule (non-reproductive)

• cellular governor of spermatogenesis

• receptors for FSH and testosterone

• produce a variety of products (ABP, SGP 1 & 2, transferrin, inhibin)

• Tight junctions

  • separates germinal epithelium to basal compartment and barrier for immunoglobins and immune cells

• Blood-testes junction

  • peritubular cells in smooth muscle prevent autoimmune cells from crossing. Immune cells and immunoglobins would recognize developing germinal cells as foreign because they are undergoing meiosis

• somatic cells undergo mitosis

Spermatozoa Sperm Types

Spermatogonia, primary spermatocyte, secondary spermatocyte, spermatid

• Completion of spermatogenesis is marked by the release of mature sperm into the lumen of the tubules, termed “spermiation”

basal compartment

spermatogonia and early primary spermatocytes

adluminal compartment

primary spermatocyte, secondary spermatocyte, and spermatids

Excurrent Duct System

• allows for final maturation, storage, and delivery of spermatozoa to pelvic urethra

Parts of the excurrent duct system

1. Efferent ducts

   • connect the rete testis to the head of the epididymis

2. Epididymal ducts

   • connect efferent ducts to ductus deferens; serves as storage, maturation site for spermatozoa

3. Ductus deferens

   • connects the tail of the epididymis to the ampulla and transports sperm to the pelvic urethra

Epididymal duct

• highly convoluted and 30-60 m in length

  • 50-70 in stallion

  • 50 in boar and ram

  • 35-40 in bull

• 3 regions

  • head (caput)

  • body (corpus)

  • tail (cauda)

• surrounded by smooth muscle. Muscle in tail is relatively quiet except during sexual excitation

Head of Epididymis

• “caput” epididymis

• 25-50 × 10^6 sperm

• 2 regions

  • proximal head and distal head

• spermatozoa characteristics

  • not motile, not fertile, proximal cytoplasmic droplet is at base of head

• low disulfide crosslinking

Disulfide crosslinking

Essential for tightly packing & stabilizing DNA in sperm during maturation. Locks DNA into a dense 3D network, makes it resistant to damage

Body of Epididymis

• “corpus” epididymis

• 8-25 × 10^9 sperm

• spermatozoa characteristics:

  • some motility, increasing fertility, cytoplasmic droplet gradually moving down tail, can bind to oocytes

Tail of Epididymis

• “cauda” epididymis

• 10-50 × 10^9 sperm

• 2 regions: proximal tail and distal tail

• Only sperm in distal tail can be ejaculated upon stimulation

• spermatozoa characteristics:

  • normal motility after dilution, fertile potential, high disulfide crosslinking, bind to oocyte

Epididymal transit time

• time required to transport spermatozoa from the proximal head to the distal tail.

• Sperm spending extended period in tail are lower quality compared to sperm from males ejaculated 1-2 times/week

• Periodic contractions of ductus deferens and epididymis results in a gradual trickle of spermatozoa to pelvic urethra (prevents pressure build up)

• Number of sperm ejaculated can be increased when male is subjected to false mounting or restrained from mounting, but transit time through the head and body are not altered by sexual excitation

• higher ejaculation frequency= fewer sperm

• frequent (within one day) sequanetial ejaculations will deplete spermatozoal reserves in the distal tail

Seminal Plasma

• produced by epididymis and accessory sex glands (ampulla, vesicular glands, prostate gland, and bulbourethral gland)

• The fluid vehicle for sperm transport; not required for fertility

• contains special coagulation properties in boar and stallion

Accessory sex glands

ampullae, vesicular glands, prostate gland, bulbourethral gland

Ampullae

• enlargement of ductus deferens; reservoir

• secrete mucosa for seminal plasma and fructose

Vesicular glands

• paired glands and empty into pelvic urethra

• reservoir for secretions for spermatic fluid in semen (do not store sperm)

• contribute a large number of ejaculate volume

Prostate gland

• secretes prostate fluid, an important part of seminal plasma (slightly alkaline, neutralized acidity of vaginal tract)

• two structural forms

  • corpus: outside urethralis muscle (stallion entirely; boar and bull partially)

  • disseminate: glandular tissue along lateral walls of pelvic urethra (ram entirely; bull and boar partially), occasionally called the urethral gland

Bulbourethral gland

• small and ovoid and are very dense

• located on either side of the pelivc urethra

• secrete a viscous fluid that’s an important gel fraction of the ejaculate; coagulates semen fluid

  • highly developed in boar, also present but small in stallion, bull, ram (under bulbospongious muscle)

Penis

• male copulatory organ

• 3 parts: base, shaft, gland

• High amount of sensory nerves and responsible for the signaling to ejaculate (homologous to clitoris of female)

Penis modifications

• cat has barbs/ spines in cat

• Boar has corkscrew

Parts of Penis

Corpus cavernosum

• majority of penile interior

• Spongy erectile tissue

• Allows for the influx of blood during erection

  Corpus spongiosum

• Surrounds urethra, extends to gland

• Very prominent in stallion- belling

Fibroelastic Penis

• found in bulls, boars, and rams

• Limited erectile tissue, instead dense connective tissue

• Sigmoid flexors

Muscles of Penis

• Retractor penis: contracted/ relaxed state

• Ischiocavernosus: inserts on crus penis, compresses crus penis, plays role in protrusion of the penis

• Bulbospongiosus: overlaps root of or

Reproduction is regulated by

1. nervous system

2. endocrine system

• the two systems act in conjunction to translate stimuli into neural signals for target tissues

Simple neural reflex

• mechanism by which external stimuli trigger a response without cognition

Components of simple neural reflex

• afferent sensory neuron: carries stimulus towards CNS

• interneuron: located in the spinal cord

• efferent neuron: leaves spinal cord and innervates the target tissue

example of simple neural reflex

ejaculation. Stimulated by temperature and sensation. Activates a motor neuron that contracts muscle to release semen

Neuroendocrine reflex

a reflex initiated by stimulation of sensory neurons that causes the release of a neurohormone from neurosecretory cells

• a hormone synthesized and secreted by neurons, released through the blood stream rather than directly to target

example of a neuroendocrine reflex

nursing, suckling stimulus carried to spinal cord, brain, hypothalamus, efferent nerve, to the mammary gland, releases oxytocin to let down milk