animal reproduction exam 1

how do animals reproduce?

asexual and sexual reproduction

asexual reproduction

mitotic division “cloning”

* generates offspring genetically identical to each other and the parent
* in vertebrates: parthenogenesis
* germ cells differentiate w/o sperm into a genetically identical organism to the female

sexual reproduction

germ cells produce gametes

* sperm and oocyte
* 1/2 the genetic material of each parent
* result: increased genetic variation

benefits of sexual reproduction

* increased genetic variation
* genetic improvement
* perpetuation of the species

importance of controlling reproduction with HIGH reproductive efficiency

food animals → more food, more profit for the producer

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overpopulation

* animal damage control problems
* resource depletion

importance of controlling reproduction with LOW reproductive efficiency

* low population growth, resources conserved
* suboptimal production of animal products, less food, profits

advances in modern reproductive physiology

* in vitro fertilization (IVF)
* embryo transfer
* pregnancy detection
* contraception
* estrous synchronization
* frozen semen
* artificial insemination
* father of AI → Rutgers
* sex selection

how does a rabbit test human pregnancy?

* 1920s


* human chorionic gonadotropin (hCG) is detectable in blood & urine in early pregnancy
* rabbits are induced ovulators
* thus, hCG will induce rabbit ovulation
* rabbit test:
* female rabbit is injected with this urine, after 2-3 days, rabbit is killed and ovaries are observed
* ovulation → pregnancy
* no ovulation → no pregnancy

how do home pregnancy tests work?

* mid 1970s


* monoclonal antibodies developed to detect hCG in urine
* hCG: antibody complex generates a color reaction
* color change indicates a positive pregnancy test

asexual reproduction: cloning mammals

dolly the sheep → feb. 1997

* 1st mammal cloned from an adult cell
* transferred nucleus from adult cell to an egg whose DNA had been removed
* dolly was the first animal to show that clones can breed normally & produce healthy offspring

theriogenology

branch of veterinary medicine which deals with reproductive medicine (male and female) including clinical practice of obstetrics, gynecology, and andrology

obstetrics

field of study concentrated on pregnancy, childbirth, and the postpartum period

gynecology

medical practice dealing with health of the female reproductive system

anatomy of the female reproductive tract

* ovaries
* oviduct
* uterus
* cervix
* vagina
* external genitalia

human female reproductive anatomy

reproductive tract of the sow

reproductive tract: non ruminant (dorsal view sow)

pulvini

mounds that interdigitate with each other to close the cervix

reproductive tract: ruminant (lateral view cow)

caruncles

ruminants, button-like area of endometrium forms maternal side of placenta

peritoneum

connective tissue lining the abdominal cavity

* with embryonic growth, the tract becomes surrounded by peritoneum
* forms the broad ligament
* suspensory tissue
* houses vascular supply, lymphatics, and nerves

broad ligament development

1) UH and rectum develop dorsal to peritoneum

2) as development advances, UH and R push into body cavity and eventually become completely surrounded by peritoneum

3) broad ligament = 2 layers of peritoneum that sandwich the tract between them. each layer is continuous with the peritoneal lining of body cavity

components of broad ligament

mesovarium

* connective tissue (CT) covering ovary

mesosalpinx

* CT covering oviduct
* helps to orient infundibulum

mesometrium

* CT covering uterus
* largest part of broad ligament
* supports uterine horns and body

tubular portion of the tract

mucosa → submucosa → muscular → serosa

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mucosa

* surrounds the lumen
* secretes mucus that lubricates tract
* cell type varies depending upon region
* oviduct: ciliated cells (movement)
* vagina: squamous cells (protection)

submucosa

* beneath muscularis
* varies in thickness depending upon region
* houses blood vessels, nerves, and lymphatics
* supports mucosa

muscularis

* double layer of smooth muscle
* outer longitudal layer
* inner circular layer
* this allows for contraction of the tract

serosa

* outer layer
* squamous (flattened cells)

ovaries

* located near kidneys
* function: to produce
* gametes → ova
* hormones
* steroid - androgens, estrogens, progestins
* protein - inhibin and relaxin

ovarian anatomy

outer covering

* germinal epithelium: location of ovarian cancer
* tunica albuginea: holds everything in place

cortex (outer portion)

* follicles
* corpora lutea, corpora albicans

medulla (center)

* vasculature, nerves, lymphatics, and CT

why is the equine (horse) ovary unusual?

* medulla and cortex are reversed
* ovulation occurs at 1 location: the ovulation fossa, corpus luteum forms here
* follicles but not CL can be palpated by rectal exam

folliculogenesis

process whereby immature follicles develop into more advanced follicles and become candidates for ovulation

follicle cell types

granulosa cells (GC)

* direct oocyte development (nurse cells), steroidogenesis, and follicular fluid secretion; avascular

theca cells

* externa: outermost layer of antral follicle; provides structural integrity and support (contains CT)
* interna: flattened spindle-shaped cells along basement membrane of antral follicle and produce androgens

types of follicles

primordial

* most immature and smallest
* non-growing pool of follicles
* females are born with a set number of follicles
* oocyte w/ single layer of squamous cells

primary

* growing pool
* oocyte w/ single layer of cuboidal cells
* either (1) develop further; or (2) degenerate (atresia)

secondary

* 2 or more layers of granulosa cells
* no antrum
* contains zona pellucida (thick translucent layer surrounding oocyte)

tertiary or antral

* follicular fluid-filled antrum
* multiple granulosa cell layers
* theca externa and interna

corpus luteum

following follicle rupture…

* corpus hemorrhagicum forms (bloody body)
* granulosa and theca cells differentiate into luteal cells (CL)
* produce progesterone
* corpus albicans (scar like)

atretic follicles

degenerating follicles

* only 0.1% of ovarian follicles ovulate the rest 99.9% die (atresia)

ovulation

* follicle ruptures
* ovum released
* corpus hemorrhagicum forms

polycystic ovarian syndrome (PCOS)

* multiple small cysts > enraptured follicles
* high androgens
* infertility
* insulin resistance

ovarian cancer - causes

leading cause of death from gynecologic cancers

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theory 1: ovarian surface epithelium (OSE)


1. repeated ovulation - wound and repair of the OSE triggers mutations leading to cancer
2. gonadotropin stimulation - FSH/LH action on OSE induces tumor formation


1. most ovarian cancers occur in postmenopausal (PM) women
2. gonadotropin are elevated in PM women

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theory 2: fallopian tube epithelial (FTE) cells that have lost functional p53 from serous tube intraepithelial cancers (STIC)

* over time (6-8 yrs) these cancerous cells seed the ovary and distance metastases

new treatment for ovarian cancer

* FTE vs OSE
* clinical trials are underway to test whether salpingectomy without ovariectomy reduces the incidence of ovarian cancer

“plan ahead” test

* jan 2006
* test developed in England to predict how many eggs women have in their ovaries

how are eggs measured

blood levels of 3 hormones

1) inhibin B - a protein derived from egg follicles

2) anti-mullerian hormone - generated by the cells that surround eggs that have not yet matured

3) follicle stimulated hormone - which prompts development of the eggs

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\*Inhibin B & AMH decline as ovaries age

\*FSH increases with age

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* not a fertility test
* can be used to decide how long to delay conception
* cost: \~ $300-$400

ovarian volume & antral follicle count (AFC)

* ideal AFC is 15-20 ovaries
* if AFC is

corpus luteum (CL)

* transient endocrine organ
* formed by cells of the ruptured follicle
* theca interna & granulosa cells “luteinize” or differentiate to form the CL

CL function

* secretes progesterone
* function: maintain pregnancy; regulate the cycle
* clinical significance: 25-55% of early embryonic loss is due to insufficient luteal function

corpus albicans

* as the CL regresses
* corpus albicans is formed
* white
* “scar” from the former CL
* present at the end of cycle

avian reproductive system

* functional LEFT ovary and oviduct
* right ovary and oviduct are rudimentary
* adapted to reduce weight for flight
* flightless birds have same arrangement
* no corpus luteum

hen’s ovary

* comparable to mammalian oocyte
* called “the yolk” but consists of:
* germinal disc- location sperm enters that will form embryo
* yolk- energy + nourishment for embryo
* vitelline membrane- zona pellucida in mammals
* avian follicles- no antrum or follicular fluid
* each contains a large, yolk-filled ovum

importance of the germinal disc

* lies on the surface of the yolk
* 3 mm white spot
* contains female haploid pro nucleus
* site of fertilization

avian tract

* infundibulum - receives the egg with yolk
* magnum - secretes albumen
* isthmus - adds the shell membrane
* shell gland or uterus - secretes the shell
* vagina - receives sperm
* cloaca- common opening for the GI and reproductive tracts

mammalian oviduct

* fallopian tube or salpinx
* paired muscular tubes
* infundibulum
* fimbriae: beat to propel egg into oviduct
* ampulla
* isthmus

oviduct function

* transport of gametes, embryo
* muscosa produces secretions to maintain:
* oocyte, sperm
* fertilized egg
* site of fertilization (ampulla)

uterus

basic structure

* uterine horns (2)
* body
* cervix (neck)

duplex uterus (2 cervices)

type 1: marsupials

* 2 cervices
* 2 separate uterine horns
* 2 vaginas
* no uterine body

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type 2: rabbits

* 2 cervices
* 2 uterine horns
* 1 vagina

bicornuate uterus

* 2 uterine horns
* small uterine
* 1 cervix

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* poorly to moderately developed uterine horns (mare & cow)

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* highly developed uterine horns (bitch, queen, sow)

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simplex uterus (no uterine horns)

large uterine body

structure of the uterine wall

* perimetrium - outer layer (serosa)
* myometrium - muscle (muscular)
* circular and longitudal
* endometrium - inner layer
* mucosa and submucosa
* secretory → sperm + embryo survival
* contains uterine glands

uterine functions

* sperm transport - contractions
* regulation of CL function
* uterine signal which causes CL regression or luteolysis - PGF2alpha
* Implantation/placentation - vascularization
* Parturition - contractions

structure of cervix

* sphincter-like
* cartilage, CT, and smooth muscle
* thick walled
* canal lined with mucous membrane

function of cervix

* flushing system/lubrication
* outflow of mucus: eliminate microorganisms
* sperm reservoir
* cervical crypts
* barrier during pregnancy

cervix during pregnancy

* thick cervical mucous
* barrier to sperm transport
* prevents uterine infection
* at time of birth
* cervical plug liquifies
* cervical canal opens

cervical mucous

viscosity is hormone-dependent

* high estrogen (E2) → watery mucous
* during estrus and at ovulation
* facilitates sperm entry
* high progesterone (P4) → thick mucous
* during pregnancy
* inhibits sperm entry

vagina functions

* copulatory organ
* semen deposition
* excretory duct
* reproductive secretions
* urine
* birth canal

vagina

anterior portion - near cervix

* columnar epithelium
* highly secretory

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posterior portion = vestibule

* stratified squamous epithelium
* vestibular glands (Bartholin’s glands) secrete mucous
* portion common to the urinary and reproductive systems

external genitalia of female

vulva - external part of the tract

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* labia major and minor
* outer and inner folds of skin
* contains fat, smooth muscle
* forms a commissure
* closes entry to the vagina

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* clitoris
* homolog of the penis
* erectile tissue, sensory nerves, epithelium
* erect during estrus
* function - sensory

primary functions of the male reproductive tract

* **gamete production** and maturation
* **hormone production**
* gamete delivery
* seminal fluid production and sperm delivery

primary parts of the male reproductive tract

* testis and support tissues
* excurrent ducts
* accessory sex glands
* excretory tissues

tissues of the male reproductive tract

testis

site of gamete and hormone production (where gametes and androgens are born)

* testicular capsule → tunica albuginea

testis parenchyma

seminiferous tubules house developing gametes

a mammalian gamete needs:

* immune privilege
* correct hormone signaling
* temperature homeostasis

immune privilege

the blood testis barrier (BTB) saves sperm from self

* loss of tubule immune privilege (BTB) results in loss of meiotic and post meiotic germ cells
* the BTB is generated primarily by Sertoli cells

hormone signaling

* loss of hormone signaling (testosterone) results in loss of post-meiotic germ cells

testosterone

* made by Leydig cells
* required for normal physiology in and out of the testis

temperature homeostasis

* loss of temperature homeostasis results in loss of all germ cells

summary → what a gamete needs

* immune privilege - BTB (mostly Sertoli cells)
* hormones (testosterone) - Leydig cells
* steady temperature (cool relative to the body)

how does the testis cool itself?

testis support tissues → the SCROTUM supports and controls temperature of the testis

* via evaporation

spermatic cords

connect the testis to the body

* cremaster muscle
* supports testis
* testicular artery
* ductus deferens
* pampiniform plexus
* T return to body
* testis heat exchange
* these cords transfer hormones and heat to and from the testis

excurrent ducts

move and modify gametes

efferent ducts

moving and concentrating gametes

* mixed epithelium
* move spermatozoa (smooth muscle and ciliated cells)
* concentrate spermatozoa through water resorption (short cells)

epididymis

moving, modifying, and storing mature gametes

* single long tubule
* surrounded by smooth muscle to move sperm
* multiple segments with different cell types to generate different environments
* different segments (caput, corpus, and caudal) have different epithelial morphologies and functions

sequence of events

* Millieu changes from segment to segment
* epididymis secretes a part of the seminal fluid
* spermatozoa mature as they transit the epididymis

sperm proteins change dramatically as they transit the epididymis

caput:

* removal of abnormal spermatozoa
* membrane modification

corpus:

* sperm gain motility

cauda:

* gain fertilization (capacitation ability)
* long term storage

\*cauda → primary site for sperm reserves

ductus deferens (vas deferens)

moving and moving gametes

* narrow epithelium surrounded by smooth muscle
* moves spermatozoa from caudal epididymis to accessory sex glands
* target tissue for permanent sterilization in men (2.4% worldwide)
* cause of sterility in men with cystic fibrosis

primary functions of the excurrent ducts

* maturation
* gamete delivery
* seminal fluid production and delivery

accessory sex glands generate seminal plasma

* ampulla
* vesicular gland
* prostate gland
* bulbourethral gland

ampulla

widening of vas deferens

* moves fluid and sperm from vas to urethra (smooth muscle)
* secretes seminal fluid (mucosa)

vesicular glands (seminal vesicles)

similar morphology to ampulla

* not a contiguous portion of the reproductive tract
* generates and stores seminal fluid - majority of ejaculate

prostate

species specific morphology

* generates prostate fluid
* protects sperm after ejaculation
* PSA (prostate specific antigen) - reduces semen viscosity

bulbourethral gland

* species specific morphology

primary functions of accessory sex glands

seminal fluid production and delivery

male excretory tissues

penis and urethra

urethra

contractile muscle around a duct designed for delivery

primary functions of excretory tissues

gamete delivery and seminal fluid production & delivery

fertilization

* mammalian fertilization combines the chromosomes of the egg and the sperm
* the inherited sex chromosomes will determine sex

female → 2 X’s (XX)

male → 1 X and 1 Y (XY)

* mother (diploid XX)
* egg (haploid X)
* father (diploid XY)
* sperm (haploid X or haploid Y)

x vs Y chromosome

* X chromosome is abt 3x larger than y chromosome
* sex determining region of the Y chromosome = SRY gene
* directs development of male phenotypes

embryogenesis

fertilized egg divides

1) blastocyst

* ICM
* blastocoele

2) inner cell mass → embryo

3) trophoblast → placenta

differentiation

* during early embryogenesis, the inner cell mass (ICM) differentiates to form the 3 germ layers of the embryo:
* ectoderm
* mesoderm
* endoderm

germ layers of embryo

endoderm

* digestive system
* lungs
* endocrine system

mesoderm

* muscle
* skeleton
* cardiovascular
* reproductive system

ectoderm

* nervous sytem
* skin
* hair

the reproductive system is derived from:

* mesoderm
* ectoderm (hypothalamus and pituitary)

germ layers of the embryo

* endoderm (inside skin)
* mesoderm (middle skin)
* reproductive system
* gonads
* uterus, cervix, vagina
* epididymis, ductus deferens, accessory sex glands
* ectoderm (outer skin)
* reproductive tract
* vagina and vestibule
* penis and clitoris
* nervous system
* hypothalamus and pituitary

pituitary (hormone center)

* hypophysis: Greek for “lying underneath”
* posterior hypophysis - neurohypophyisis
* derived from neural tissue of brain floor
* anterior hypophysis - adenohypophysis
* derived from ectoderm in the roof of the embryonic mouth

mouth + brain = pituitary

* posterior pituitary (neurohypophysis)
* infundibulum of brain (neural tissue) pinches off and grows down towards the mouth
* becomes the posterior pituitary
* stores and secretes hormones OXYTOCIN and ADH
* anterior pituitary (adenohypophysis)
* rathke’s pouch diverts from roof of mouth and joins up with posterior pituitary
* becomes the anterior pituitary
* synthesizes and secretes LH, FSH, PRL, GH, TSH, ACTH

diverticulum

a sac/pouch diverting from a main tube/cavity