placenta Flashcards
(29 cards)
How are placentas classified?
Based on the distribution of the chorionic villi.
What is a diffuse placenta?
Villi are around the whole surface of the chorion.
Example: Pig
What is unique about the mare’s diffuse placenta?
It has patches called micro-cotyledons and endometrial cups that produce eCG.
What is a zonary placenta?
Region of exchange similar to a band around the chorion, found in dogs and cats.
What are the three segments of significance in a zonary placenta?
- Region of exchange around the middle band
- Paraplacenta: highly pigmented hematomas for iron transport
- Distal ends: poorly vascular and transparent for absorption
What is a discoid placenta?
Two adjacent discs of villi that interface with the endometrium for metabolic exchange.
Example: Primates and rodents
What is a cotyledon?
Placental segment derived from the trophoblast, a ring of blood and connective tissue.
What are the two types of cotyledons?
- Convex: villi protrude towards the lumen
- Concave: chorionic tissue pushes inwards
How are placentas classified by microscopic appearance?
Based on the number of placental layers separating fetal and maternal blood.
What is an epitheliochorial placenta?
Both maternal and chorionic villi epitheliums are intact.
What characterizes a syndesmochorial placenta?
Endometrial epithelium periodically erodes and regrows with binucleate giant cells.
What is an endotheliochorial placenta?
Complete erosion of the endometrial epithelium and underlying interstitium.
What defines a hemochorial placenta?
Chorionic epithelium is in direct contact with maternal blood.
What is the function of the placenta?
Transient organ for metabolic interchange between conceptus and mother.
What are the mechanisms of nutrient transport across the placenta?
- Simple diffusion
- Facilitated diffusion
- Active transport
What substances do not cross the placenta?
- Large peptide hormones
- Lipids (instead hydrolyzed)
What can cross the placenta?
- Small steroidal hormones
- Immunoglobulins (only in hemochorial and endotheliochorial)
What role does the placenta play as an endocrine organ during pregnancy?
Stimulates ovarian function, maintains pregnancy, influences fetal growth, stimulates mammary function, assists in parturition.
What is the progesterone block?
Placenta produces progesterone inhibiting myometrial contraction during embryonic development.
What triggers parturition in the fetal hypothalamo-pituitary-adrenal axis?
Fetal stress triggers ACTH production from the fetal anterior pituitary.
What effect do corticoids have during parturition?
- Convert progesterone to estradiol
- Stimulate PGF2a synthesis for CL regression
What does oxytocin do during parturition?
Facilitates contractility of the cervix and promotes positive feedback loop.
What is relaxin’s role during parturition?
Softens connective tissue in the cervix and promotes pelvic ligament elasticity.
What is the role of estradiol prior to parturition?
Increases secretion in the reproductive tract to wash away the cervical seal.
