Reproduction Flashcards
Gametogenesis is
Gametes: the reproductive cell of an animal or plant. A very broad definition.
Female gamete = ova
Male gamete = sperm
Oogenesis = creation of the ova
Spermatogenesis = creation of spermatozoa (=sperm)
Meiosis is
This is the unique type of cell division that spermatozoa and ova undergo
Also called ‘reduction division’ because the total number of chromosomes in the cell is halved.
At fertilization the spermatozoa and ova each provide half of the genetic information necessary for the new individual
Spermatogenesis is
Spermatogenesis: ‘to create spermatozoa’
Spermatozoa are produced continuously and in large numbers
Complete process varies by species, but can take weeks to months
Where are spermatogonia located
Spermatogonia are large cells on the outermost part of the seminiferous tubules
Called the germinal epithelium
Spermatogenesis first steps
Diploid chromosome numbers
Divides by mitosis first
Produces 2 spermatogonia, each with diploid numbers
One spermatogonium remains a spermatogonium at the margins of the tubule
Continue to divide by mitosis to continue creating cells that become spermatozoa
One spermatogonium moves inwards towards the lumen of the tubule → becomes a primary spermatocyte
Primary spermatocyte divides by undergoing meiosis twice. This results in 4 cells, called spermatids.
Each spermatid has HALF the genetic material, so 1 chromosome instead of 2
Spermatogenesis second step
During spermatogenesis, the cells move closer toward the lumen of the seminiferous tubule
Spermatids are held by supporting cells mature, where they will lose their excess cytoplasm and develop a flagellum
At this point they are free in the lumen
Transported to the epididymis to mature
If they are not ejaculated, they die and are absorbed by the lining of the epididymis
Mature sperm cell contains
Head
Nucleus with chromosomes
Covered by a cap-like structure called the acrosome
Contains an enzyme to help penetrate the ova
Body (midpiece)
Contains mitochondria
Makes ATP to power the flagellum
Flagellum
Contains contractile proteins (like muscles)
Enables movement
Semen evaluation is
Semen evaluation is a common procedure in large animal practice to determine fertility
Examine stained sperm to determine % alive/dead, and to evaluate morphology.
Some abnormal sperm is normal. We look at the total number of healthy sperm to determine fertility.
What to look at during semen evaluation
Volume produced
Concentration of sperm in the semen
Motility of sperm
Live/dead sperm ratio
Morphology (shape) of sperm – can have deformities or defects affecting fertility
Oogenesis is
Oogenesis: ‘to create oocytes’
Not a continuous process
Development of primary oocytes occurs before birth
Many degenerate before and after birth to leave the female with a final fixed number that she will have for her lifetime
Unlike people, domestic animals do not usually run out of eggs
Oogenesis involves a diploid primary oocyte undergoing meiosis to produce a haploid ovum, just like spermatogenesis.
The process starts when the follicle, under influence of FSH, starts to grow.
Steps of oogenesis
The primary oocyte divides, to make a single secondary oocyte that contains ½ the chromosomes and most of the cytoplasm.
The other set of chromosomes are in a polar body, a small cell containing the chromosomes and not much else. The polar body will divide, then degenerate.
The secondary oocytes then divide again to make a single ovum and another polar body.
Therefore, 1 primary oocyte will divide to make 1 mature ovum that is ready to be fertilized, and 3 polar bodies that will degenerate
Mating during estrus
Female: Estrus
Female secretes pheromones
Attracts male
Stands (or kneels) to accept mating
Male:
Achieves erection
Followed by copulatio
Copulation is
Physical act of breeding
Only allowed by the female during estrus
Mounting → intromission →thrusting →ejaculation
Ejaculation occurs into vagina
Except horses and pigs – into uterus
Transport of spermatozoa is caused by
Sperm move by
Active swimming
Propulsive contractions of the uterus and oviducts
Stimulated by oxytocin released in response to copulation (climax)
Prostaglandins in semen
Ciliary action in the oviducts
Sperm often reach the upper parts of the oviducts within an hour
Can survive in the reproductive tract for 72 hours in humans and possibly up to a week in some species
Capacitation is
Spermatozoa undergo changes to prepare them to fertilize the ovum
Occurs in the female reproductive tract
Includes exposure of enzymes on the acrosome which assist the spermatozoa to penetrate the oocyte
Capacitation requires the sperm to be in the oviduct for some time
So, most species ovulate near the end of the heat cycle
Eggs released when sperm are fully capacitated
The sequence of mating
Breeding occurs (usually before ovulation)
Capacitation of sperm (within oviduct)
Ovulation
Fertilization
Fertilization of the ovum is caused by
Spermatozoa are attracted to large round cells
Many spermatozoa are required because many fail to reach the oocyte
Each tries to penetrate the layers around the ovum helped by the acrosome enzymes.
The more sperm, the greater the chances of one getting through
Once one spermatozoa penetrates the oocyte, the cell membrane changes and no more are allowed through
The secondary oocyte completes its division to become an ovum
The (pro) nuclei of the male and female sex cells (spermatozoa and ovum) join.
Each contributes a haploid number of chromosomes
Create a diploid cell: a fertilized ovum or zygote
Early development of a fetus is and called
Zygote begins rapid cell division (mitosis), called cleavage
After few days
Ball of very tiny cells that is about the same size as the original single-celled zygote
Called a morula
Fertilization and implantation of a zygote is and changes to
At the same time, the zygote is moving down the oviduct aided by muscular contractions and ciliary waves
Morula is solid mass of cells
Develops into a hollow ball
Called a blastocyst
Blastocyst is consisted of and changes to
Outer layer
The trophoblast
Develops into placenta
Inner cell mass which will become the embryo
Implantation of the blastocyst is
Blastocyst attaches to the endometrium
Creates a small pit by secreting enzymes that dissolve a small piece of uterine lining
Attaches into that small pit
Multiparous species have multiple implantation sites along the horns and body of the uterus
Embryology is
The period of the ‘embryo’ terminates when the various organs and organ systems have been formed
The embryo becomes a fetus when it resembles an adult
The fetus becomes a neonate (newborn) at parturition (birth)
Teratogens are and can be
A teratogen is anything that causes defects in the embryo or fetus.
Can be
Genetic
Infectious
BVD, Feline panleukopenia
Environmental toxin
Alcohol
Effect of a teratogen can be
Death
Early embryonic death or abortion
Malformation
Growth retardation
What is the placenta formed form and what does it do
At implantation, the blastocyst is becoming too big for adequate nutrition through diffusion
Development of a placenta allows increased nutrient and waste exchange from the mother
Becomes the life support for the fetus and provides from the dam all the nutrients and substances needed for growth and development
Structure of the placenta
Multilayered, fluid-filled, membranous sac
Forms around embryo
Connected to embryo by umbilical cord
Connects to mother by outer placental attachments to the uterus
Site for nutrient and waste exchange
Note that fetal and maternal blood don’t mix!!!
Come very close to each other, allowing for diffusion and exchange of nutrients and waste
Two fluid-filled sacs around the fetus
Amniotic sac – surrounds the fetus
fetus floats in amniotic fluid
Allantoic sac – surrounds the amniotic sac
The allantoic sac is covered by chorion
Attaches to uterine lining in a variety of patterns, depending on species (see below)
The “chorioallantois” is the combined allantois and chorion that forms the fetal part of the placenta
Linked to fetus by umbilical cord
Structure of the umbilical cord
The umbilical cord contains blood vessels (umbilical arteries and vein) and the urachus (drains waste from the fetal bladder)
Umbilical arteries: Two arteries that carry waste to the placenta from the fetus
Umbilical vein: single vein that carries oxygen and nutrients from the placenta to the fetus
Urachus: Tube draining fetal bladder into the allantoic sac
Not true urine, but the product of developing kidneys
Diffuse attachment placenta is
Diffuse, loosely attached sites throughout entire surface of placenta
Detaches easily and completely
Horse, pig
Cotyledonary Attachment placenta is
Many small, button-like sites called placentomes
Placental half called a cotyledon
Maternal (uterine) half called a caruncle
Strong attachment formed by interdigitation of cotyledon and caruncle
Cotyledonary Attachment placenta is
May end up with incomplete detachment causing retained placenta
Can lead to life-threatening metritis
i.e. ruminants – cattle, sheep, goats
Zonary attachment placenta is
Chorion forms a belt-shaped structure around middle of placenta
Usually detaches easily and completely
Dogs and cats
Discoid attachment placenta is
Disc-shaped attachment site
i.e. humans, primates, rabbits, rodents
Pregnancy is
Gestation period: the time from fertilization to delivery of fetus
Usually divided into 3 time periods or trimesters
First trimester consists of
Fertilization→ implantation→ placenta formation→ early cellular organization
Embryo
Second trimester consists of
Fetal development period: presence and differentiation of all different body tissues and organs
Fetus
Third trimester is
Fetal growth period: dramatic growth, preparation for survival after delivery
Fetus
Parturition is though to be triggered by
Size and weight of uterus
Hormonal changes in fetus
Increased glucocorticoid hormones
Hormonal changes in mother
Rising fetal cortisol levels increase uterine/placental estrogen and PGF2a
Cause luteolysis
Sensitize uterine muscle to oxytocin
Decreasing progesterone levels allow uterine contractions
Oxytocin release stimulates myometrial contractions and onset of labor
What happens if dystocia occurs
A problem in delivery (due to size of fetus or position in the birth canal) is called dystocia
May require manual repositioning or C- section (cesarean section)
If dead, may require fetotomy
First stage of parturition
characterized by uterine contractions
Presses fetus against cervix
Causes dilation of the cervix
Animal behavior includes restlessness, discomfort, panting, nest-building.
Second stage of parturition
characterized by delivery of newborn
Strong uterine and abdominal contractions (‘pushing’)
Pushing increases in frequency and strength
‘Water breaking’ is rupture of the allantoic (and amniotic) sacs and release of the fluid
Outward sign of second stage labor
Delivery of newborn then usually occurs
Often still has amniotic membrane over face and body
Remove immediately if mother doesn’t!!!
Third stage of parturition
delivery of placenta (afterbirth)
Attachments of the placenta separate, and placenta is delivered through milder uterine contractions
May be eaten by mother!
In multiparous sp. alternates with neonates
Fetal changes at birth
Lungs must start breathing air and delivering oxygen
Urachus must close to prevent urine leakage from umbilicus
Cardiovascular: must start delivering blood to lungs and not to the placenta
Fetal circulation changes
Foramen ovale is a fetal opening between the right and left atria.
Shunts blood away from the non-functioning lungs
Closes after birth
Ductus arteriosus connects the fetal aorta with the pulmonary trunk
Shunts blood away from the lungs
Shrinks and becomes a ligament after birth
Both changes are aided by the neonates first deep breaths – expand the lungs and make it easier for blood to flow
Ductus venosus
In the fetus takes oxygenated blood from the umbilical vein to the caudal vena cava for circulation to the body of the fetus
Constricts to become a ligament after birth
Involution of uterus
Involution is gradual return of uterus to non-pregnant size
Sloughing of placental attachment sites
Myometrial contractions
Prevent bleeding from placental attachment sites
Expel sloughed material and blood
Seen as discharge for up to a week or more after delivery
Initially bloody, then darker
Mammary glands are
Specialized skin glands which produce colostrum and milk
Undeveloped at birth in both male and female but develops in the female as a secondary sex characteristic
Note: males usually have same number and position of teats as females
Grow during pregnancy
During the first lactation, the mammary glands attain full size and function
After weaning, milk production ceases and gland regresses
In older animals the mammary glands regress and are replaced by connective tissue and function is lost
Mammae consists of
Consist of the teat and mammae
The parenchyma (epithelial tissue) of the mammary gland
Consists of:
Alveoli: milk-secreting cells
Arranged like clusters of grapes around the alveolar ducts which join to form larger and larger ducts
Eventually empty into a milk storage cavity known as the milk sinus
Milk sinus is
Milk Sinus: within the mammae it is called the gland sinus (or cistern)
In the teat it is called the teat sinus
Is the area where milk accumulates when milk letdown occurs
papillae in the teat is
Protruding duct of mammary gland
Contains teat sinus
Streak (teat) canal –
A passageway leading from the teat sinus to exterior teat opening
Sphincter muscle surrounds the streak canal at the end of the teat
Prevents milk flow except during sucking or milking
Openings per teat on different species
Cows, sheep, goats: one
Mares: two
Queen: several
Bitch: many
Can only give intramammary medications in large animals
Milk composition is
Lipid (fat): mostly triglycerides
Carbohydrates: mostly lactose (milk sugar)
Lactose is a disaccharide formed by combining galactose with a glucose molecule
Proteins: mostly caseins
Also lactalbumin and lactoglobulins
Colostrum is and contains
The “First Milk”
Contains large amounts of essential nutrients for the newborn, including:
More proteins, lipids, and amino acids than regular milk
Essential vitamins
Laxative to help newborn clear the meconium
Antibodies, or immunoglobulins, to transfer immunity – this is the most important!
How soon after birth does colostrum need to be consumed and why
Note that colostrum must be consumed within the first few hours to 24 hours after birth
Antibody absorption starts decreasing 6 hours after birth!
The newborn’s GIT only absorbs intact proteins during this period. Rapidly, it becomes impermeable to immunoglobulin absorption and immunity will NOT be transferred!!!
Very important in all common domestic species
Maintenance of lactation is caused by
Lactation tends to continue for as long as nursing (or milking) continues
Requires physical stimulation of teat AND regular removal of milk from the gland.
Mammary gland involution (“drying up”) occurs when milking stops
Increased pressure within the gland in combination with cessation of hormones
Milk let down is caused by
Milk is produced and stored high up in mammary gland
Needs appropriate stimulus to be ‘let down’ into the teat
Stimulus is usually the physical act of nursing – rapidly releases oxytocin from the posterior pituitary
Causes contraction of cells around the storage area of the mammary gland
Forces milk into large ducts/sinuses for nursing
Lactation hormones are and what for
Milk production: prolactin, growth hormone, estrogen and progesterone, thyroid hormone and adrenal cortex.
Milk letdown: oxytocin
Udder is
term used for all mammae of ruminants and horses (can also be used for sows)
More teats than usual which may or may not be connected to mammary tissue are known as supernumerary teats
Cows mammary glands differentiate by
Four quarters, each is an individual mammary gland
Intermammary groove - separates the 2 halves of the udder
Each half consists of a cranial (front) quarter and caudal (hind) quarter
All the milk from one teat is produced by the glandular tissue of that respective quarter
Milk vein - caudal superficial epigastric vein runs along ventral abdomen, draining the udder
Huge!
Suspensory ligaments hold up the udder which can weigh more than 50 kgs
Canine mammary glands are
Usually has 5 pairs (10 teats) but varies with breed (smaller k9’s have less) and individual
May also vary on the two sides
Divided into thoracic (2 pairs), abdominal (2 pairs) and inguinal (1 pair)
Feline mammary glands
Usually has 5 pairs (10 teats) but may also vary as per k9
Thoracic (2 pair) and abdominal (2 pair) and inguinal
Equine Mammary gland
One pair (2 teats), one teat on each half of udder
Each teat has 2 streak canals and 2 teat cisterns which have separate milk sinuses so looks like a cow internally
The udder and teats are also covered with numerous sebaceous (oil) glands and sweat glands.
Mastitis is and can be treated by
Inflammation of mammary gland
Bovine: each quarter is separate so can get it in only one or all four quarters
Treated by milking out - complete emptying of quarter
Infusion of medications through streak canal
Usually associated with bacterial infections
Mammary tumors are and can be treated by
K9 most frequently affected
Treatment:
Lumpectomy - removal of tumour only
Mastectomy - whole gland removed
Chain mastectomy – All glands on 1 side of the body.
Ovariohysterectomy – removes hormones that tumor cells may require
