Placentation and Puberty

What is the yolk sac?

Early entodermal layer; early nutrient supply for early embryo, picks up uterine secretions from endometrium to stimulate early embryonic development

What is the amnion?

Cavitation from inner cell mass; encloses fetus in a fluid-filled cavity

Protects fetus from injury, provides lubrication for parturition, and reservoir for urine and wastes

What is the allantois?

Diverticulum of hindgut; blood vessels connect fetal with placental circulation

Fuses with chorion to form the chorioallantoic placenta

What is the chorion?

Trophoblastic capsule of blastocysts; encloses embryo and other fetal membranes

Attaches to uterus, absorbs nutrients from uterus, allows maternal/fetal gas exchange, and produces hormones

What is the umbilical cord?

Amnion wraps about the yolk stock; encloses allantoic vessels and acts as the vascular link between mother and fetus

What is the chorio-allantois?

Vascular, extra-embryonic membrane formed by the fusion of the chorion and allantois

Functions as primary organ for gas exchange, nutrient transfer, and wast removal

What is the caruncle?

On mom’s side (mom drive the car)

What is the cotyledon?

On baby’s side (baby sleeps on cot)

Has button-like structures distributed across the surface

What is the placentome?

Where fetal and maternal tissues connect to transfer nutrients, oxygen, and waste products

Formed by the interlocking of maternal caruncles and fetal cotyledons

What are the 4 placental membranes?

Chorion, yolk sac, amnion, and allantois

What are the days of gestation when the placenta attaches to the uterus for the cow, sow, ewe, and mare?

Cow- 30-35

Sow- 12-20

Ewe- 18-20

Mare- 50-60

What are the 2 types of implantation?

Superficial- chorion fuses to endometrium (cow, sow, ewe)

Interstitial- embryo invades endometrium and develops in the endometrium

What are the fetal membranes of farm animals?

Yolk sac, allantois, chorion, and umbilical cord

How does the fetal membrane grow, regress, change, and develop in the early embryo?

What are the placental classifications?

Epitheliochorial (pigs, horses, and ruminants) (6 parts)

Endotheliochorial (dogs and cats) (5 parts)

Hemochorial (primates and rodents) (3 parts)

What are the characteristics of fetal nutrition in farm animals?

Blood gas exchange at chorion-endometrium attachment

Placenta tightly permeable to water and electrolytes stored in and exchanged between allantoic and amniotic fluids

Placenta converts glucose to fructose

What is the approximate route of blood flow in fetal circulation?

Placenta → liver → left atrium, lungs, or right atrium

Left atrium → heart, head, aorta → tissues, umbilical arteries, back to placenta

Right atrium → aorta → tissues, umbilical arteries, back to placenta

What is puberty?

Acquisition of reproductive competence

Occurs over time

Based on development of hypothalamic GnRH neurons

What is the final “step” of development that is necessary for puberty to occur?

Increase in the pulse frequency and amplitude of GnRH release from hypothalamus

What is the difference between male and female hypothalamus, how is the brain masculinized/defeminized?

Male- testosterone → estradiol → defeminizes hypothalamus

Conversion occurs in brain

Tonic center

Female- alpha-fetoprotein binds fetal estradiol and doesn’t allow access across BBB

Surge and tonic center

What are the factors that influence puberty and how do they influence internal and external puberty?

What are the different events/characteristics that are used to measure attainment of puberty for females?

Fully functioning tonic and surge center

Pubertal transition, negative feedback of estradiol is decreased and more GnRH produced

• More GnRH → increased LH → increased estradiol from ovary → positive feedback and massive release GnRH → ovulation

What are the different events/characteristics that are used to measure attainment of puberty for males?

Decreased hypothalamic sensitivity to negative feedback by T/E2 causes onset of puberty

• More and more T/E2 required to inhibit GnRH

• More inhibition required → more GnRH produced → more LH/FSH → puberty

What is the relative age at puberty for the species and breeds discussed in class?

Cattle- 8.5-19 months

Swine- 3-7 months

Sheep- 8.6-9.2 months

*all depend on breed within species*

How does positive and negative feedback change leading up to puberty for both females and males?

Decrease in sensitivity of the hypothalamus and pituitary gland to negative feedback by hormones in both males and females

Positive feedback (causes the preovulatory surge of LH in females) only develops in females

How does GnRH pulsatility change in both females and males?

Prepubertal period- minimal GnRH release

Puberty period- increase in the pulse frequency and amplitude of GnRH release

What is silent ovulation and why does it often happen the first time a female ovulates?

Release of an egg (ovulation) that occurs without the typical external behavioral or physical signs of being in "heat" or estrus

Silent ovulation often happens the first time a female ovulates due to the lack of sufficient progesterone

How does feed intake, body size, fatness, and metabolism affect puberty?

Females must attain a certain body size prior to onset of puberty and growth requires increased energy consumption