Midterm 3 - Lecture 24

Question 1

Implantation/Attachment

Answer 1

joining of the extra-embryonic membranes to the uterine endometrium

Question 2

Placentation

Answer 2

organization and physical relationship of embryonic/fetal membranes to the uterine endometrium that provides a site of metabolic exchange between the dam and embryo/fetus

Question 3

Placenta

Answer 3

temporary organ of metabolic exchange btw the embryo/fetus and the dam consisting of tissues of embryonic origin and maternal origin

Question 4

4 steps in pre-attachment embryonic development

Answer 4

1. developing within the zona pellucida
2. hatching from the zona pellucida
3. maternal recognition of pregnancy
4. extra-embryonic membranes
   - preparation for placentation and attachment to endometrium

Question 5

Following hatching what happens prior to attachment?

Answer 5

“explosion” of embryonic tissue growth occurs to establish the extra-embryonic membranes

Question 6

Why is the formation of the extra-embryonic membranes necessary?

Answer 6

to allow the developing embryo to attach to the uterus

Question 7

What are the 4 extra-embryonic membranes?

Answer 7

1. yolk sac
2. chorion
3. amnion
4. allantois

Question 8

Yolk sac

Answer 8

• a transient membrane that regresses as the conceptus develops
• formed from the primitive endoderm of the embryo
• contributes primordial germ cells and early RBC

Question 9

Chorion

Answer 9

• outermost membrane that develops villi (chorionic villi) which attach to the endometrium to form fetal sites of placental attachment
• formed from the trophoblast (ectoderm), primitive endoderm and mesoderm of the embryo

Question 10

Amnion

Answer 10

• liquid filled membrane enclosing the fetus the serves to protect the embryo against mechanical damage and prevent tissue adhesions
• formed from the trophoblast (ectoderm), primitive endoderm and mesoderm of the embryo

Question 11

Allantois

Answer 11

• membrane that encloses a liquid waster storage reservoir for the developing embryo/fetus
• formed from the primitive gut of the developing embryo

Question 12

Origin of amnionic fluid

Answer 12

• maternal circulation
• secretions from fetal respiratory tract

Question 13

Functions of amnionic fluid

Answer 13

• protects fetus from mechanical damage
• prevents adhesions
• lubricates birth passage during parturition

Question 14

Origin of allantoic fluid

Answer 14

• fetal waste
• secretions of allantoic membrane

Question 15

Functions of allantoic fluid

Answer 15

• positions allantochorion in contact with endometrium during attachment
• stores fetal waste

Question 16

Allantochorion

Answer 16

the fetal contribution to the fetal/maternal interface of the placenta

Question 17

Chorionic villi

Answer 17

small, finger-like projections on the surface of the allantochorion that serve as the interface btw the embryonic/fetal and maternal systems

Question 18

How are placentas classified?

Answer 18

according to the distribution of chorionic villi on their surface AND the number of tissue layers separating maternal and fetal blood

Question 19

What are the 4 different placenta chorionic villi distributions?

Answer 19

1. diffuse
2. cotyledonary
3. zonary
4. discoid

Question 20

What are the 3 different placenta maternal-fetal layers?

Answer 20

1. epitheliochorial (6)
2. endotheliochorial (~5)
3. hemochorial (3)

Question 21

Diffuse

Answer 21

uniform distribution of chorionic villi that cover the surface of the chorion
- sows and mares

Question 22

Zonary

Answer 22

placenta has a band-like zone of chorionic microvilli
- bitch

Question 23

Discoid

Answer 23

placenta forms regionalized disc
- rodents and primates

Question 24

Cotyledonary

Answer 24

placenta has numerous discrete button-like structures referred to as cotelydons
- cows and ewes

Question 25

Epitheliochorial

Answer 25

- 6 layers btw fetal and maternal blood - sows, mares, and ruminants

Question 26

Endotheliochorial

Answer 26

- 5 layers between fetal and maternal blood - bitches and queens

Question 27

Hemochorial

Answer 27

- 3 layers between fetal and maternal blood - primate and rodents

Question 28

Pig placenta

Answer 28

diffuse; epitheliochorial

Question 29

Mare placenta

Answer 29

diffuse; epitheliochorial

Question 30

Cow, sheep, goat placenta

Answer 30

cotyledonary; epitheliochorial

Question 31

Dog, cat placenta

Answer 31

zonary; endotheliochorial

Question 32

Primates, rodents placenta

Answer 32

Discoid; endotheliochorial

Question 33

Epitheliochorial placenta

Answer 33

- both endometrial epithelium (maternal side) and epithelium of the chorionic villi (fetal side) are intact - in ruminants the endometrial epithelium periodically erodes and then re-grows allowing for occasional contact of maternal capillaries with chorionic epithelium = syndeschorial

Question 34

Binucleate giant cells

Answer 34

- large cells with 2 nuclei formed in the placental tissues of ruminants - migrate from the chorionic epithelium and invade the endometrial epithelium - roles: 1. transport complex molecules from the fetal to maternal placenta 2. secretes steroids (P4)

Question 35

Endotheliochorial placenta

Answer 35

- endometrial epithelium and interstitium are eroded - direct exposure of the maternal capillaries to the chorionic epithelium

Question 36

Hemochorial placenta

Answer 36

- chorionic epithelium is in direct contact with maternal blood - nutrients and gases are exchanged directly btw maternal and fetal blood

Question 37

3 mechanisms of placental exchange

Answer 37

1. Simple diffusion - gases and water move from high to low concentration 2. Facilitated diffusion - specific carrier proteins facilitate the diffusion of important metabolic substances such as glucose and amino acids 3. Active transport - sodium, potassium and calcium are moved across the placenta by transport pumps

Question 38

What does not cross the placenta?

Answer 38

1. Proteins - fetus uses maternal AA to synthesize proteins 2. Lipids - placenta hydrolyses triglycerides and maternal phospholipids to be used by the fetus 3. Vitamins - fat soluble vitamins do not, water soluble vitamins cross with ease 4. Hormones - large peptide hormones do not; small molecular wt hormones can

Question 39

What does cross the placenta?

Answer 39

1. glucose - major source of energy for the fetus - derived from maternal circulation - glucose consumption is very high towards the end of gestation and can drain maternal system 2. vitamins - water soluble cross 3. Hormones - small molecular wt hormones cross 4. viruses and bacteria