Reproduction

Question 1

Gametogenesis is

Answer 1

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)

Question 2

Meiosis is

Answer 2

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

Question 3

Spermatogenesis is

Answer 3

Spermatogenesis: ‘to create spermatozoa’
Spermatozoa are produced continuously and in large numbers
Complete process varies by species, but can take weeks to months

Question 4

Where are spermatogonia located

Answer 4

Spermatogonia are large cells on the outermost part of the seminiferous tubules
Called the germinal epithelium

Question 5

Spermatogenesis first steps

Answer 5

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

Question 6

Spermatogenesis second step

Answer 6

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

Question 7

Mature sperm cell contains

Answer 7

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

Question 8

Semen evaluation is

Answer 8

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.

Question 9

What to look at during semen evaluation

Answer 9

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

Question 10

Oogenesis is

Answer 10

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.

Question 11

Steps of oogenesis

Answer 11

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

Question 12

Mating during estrus

Answer 12

Female: Estrus
Female secretes pheromones
Attracts male
Stands (or kneels) to accept mating
Male:
Achieves erection
Followed by copulatio

Question 13

Copulation is

Answer 13

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

Question 14

Transport of spermatozoa is caused by

Answer 14

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

Question 15

Capacitation is

Answer 15

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

Question 16

The sequence of mating

Answer 16

Breeding occurs (usually before ovulation)
Capacitation of sperm (within oviduct)
Ovulation
Fertilization

Question 17

Fertilization of the ovum is caused by

Answer 17

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

Question 18

Early development of a fetus is and called

Answer 18

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

Question 19

Fertilization and implantation of a zygote is and changes to

Answer 19

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

Question 20

Blastocyst is consisted of and changes to

Answer 20

Outer layer
The trophoblast
Develops into placenta
Inner cell mass which will become the embryo

Question 21

Implantation of the blastocyst is

Answer 21

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

Question 22

Embryology is

Answer 22

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)

Question 23

Teratogens are and can be

Answer 23

A teratogen is anything that causes defects in the embryo or fetus.
Can be
Genetic
Infectious
BVD, Feline panleukopenia
Environmental toxin
Alcohol

Question 24

Effect of a teratogen can be

Answer 24

Death
Early embryonic death or abortion
Malformation
Growth retardation

Question 25

What is the placenta formed form and what does it do

Answer 25

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

Question 26

Structure of the placenta

Answer 26

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

Question 27

Structure of the umbilical cord

Answer 27

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

Question 28

Diffuse attachment placenta is

Answer 28

Diffuse, loosely attached sites throughout entire surface of placenta
Detaches easily and completely
Horse, pig

Question 29

Cotyledonary Attachment placenta is

Answer 29

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

Question 30

Cotyledonary Attachment placenta is

Answer 30

May end up with incomplete detachment causing retained placenta
Can lead to life-threatening metritis
i.e. ruminants – cattle, sheep, goats

Question 31

Zonary attachment placenta is

Answer 31

Chorion forms a belt-shaped structure around middle of placenta
Usually detaches easily and completely
Dogs and cats

Question 32

Discoid attachment placenta is

Answer 32

Disc-shaped attachment site
i.e. humans, primates, rabbits, rodents

Question 33

Pregnancy is

Answer 33

Gestation period: the time from fertilization to delivery of fetus
Usually divided into 3 time periods or trimesters

Question 34

First trimester consists of

Answer 34

Fertilization→ implantation→ placenta formation→ early cellular organization
Embryo

Question 35

Second trimester consists of

Answer 35

Fetal development period: presence and differentiation of all different body tissues and organs
Fetus

Question 36

Third trimester is

Answer 36

Fetal growth period: dramatic growth, preparation for survival after delivery
Fetus

Question 37

Parturition is though to be triggered by

Answer 37

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

Question 38

What happens if dystocia occurs

Answer 38

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

Question 39

First stage of parturition

Answer 39

characterized by uterine contractions
Presses fetus against cervix
Causes dilation of the cervix
Animal behavior includes restlessness, discomfort, panting, nest-building.

Question 40

Second stage of parturition

Answer 40

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!!!

Question 41

Third stage of parturition

Answer 41

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

Question 42

Fetal changes at birth

Answer 42

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

Question 43

Fetal circulation changes

Answer 43

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

Question 44

Involution of uterus

Answer 44

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

Question 45

Mammary glands are

Answer 45

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

Question 46

Mammae consists of

Answer 46

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

Question 47

Milk sinus is

Answer 47

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

Question 48

papillae in the teat is

Answer 48

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

Question 49

Openings per teat on different species

Answer 49

Cows, sheep, goats: one
Mares: two
Queen: several
Bitch: many
Can only give intramammary medications in large animals

Question 50

Milk composition is

Answer 50

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

Question 51

Colostrum is and contains

Answer 51

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!

Question 52

How soon after birth does colostrum need to be consumed and why

Answer 52

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

Question 53

Maintenance of lactation is caused by

Answer 53

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

Question 54

Milk let down is caused by

Answer 54

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

Question 55

Lactation hormones are and what for

Answer 55

Milk production: prolactin, growth hormone, estrogen and progesterone, thyroid hormone and adrenal cortex.
Milk letdown: oxytocin

Question 56

Udder is

Answer 56

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

Question 57

Cows mammary glands differentiate by

Answer 57

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

Question 58

Canine mammary glands are

Answer 58

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)

Question 59

Feline mammary glands

Answer 59

Usually has 5 pairs (10 teats) but may also vary as per k9
Thoracic (2 pair) and abdominal (2 pair) and inguinal

Question 60

Equine Mammary gland

Answer 60

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.

Question 61

Mastitis is and can be treated by

Answer 61

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

Question 62

Mammary tumors are and can be treated by

Answer 62

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