Extraembryonic Membranes and Comparative Placentation PDF

Developmental Anatomy Exercise 4 Krysta Riza Jacalan Pontillas, DVM EXTRAEMBRYONIC MEMBRANES AND COMPARATIVE PLACENTATION Animal Reproductive Strategies Oviparous: Animals that lay eggs. The eggs develop and hatch outside the mother’s body. Viviparous: Animals that give...

Developmental Anatomy Exercise 4 Krysta Riza Jacalan Pontillas, DVM EXTRAEMBRYONIC MEMBRANES AND COMPARATIVE PLACENTATION Animal Reproductive Strategies Oviparous: Animals that lay eggs. The eggs develop and hatch outside the mother’s body. Viviparous: Animals that give birth to live young. The embryos develop inside the mother's body and are nourished directly by the mother, typically through a placenta or similar structure. Oviviparous: Oviviparous animals produce eggs that hatch inside the mother's body. This means that while the eggs are retained within the mother, the young are born live. EXTRAEMBRYONIC MEMBRANES EXTRAEMBRYONIC MEMBRANES Yolk Sac nutrient supply for developing embryo disappears at later stages of development EXTRAEMBRYONIC MEMBRANES Allantois a ventral outgrowth of the embryos of reptiles, birds, and mammals vestigial in humans & some species blood vessels in its wall umbilical arteries & vein, chorionic villi fuses with chorion (chorioallantoic/allantochorion) functions: collect liquid waste from embryo & exchange gases used by embryo EXTRAEMBRYONIC MEMBRANES Amnion/ extraembryonic membrane of birds, reptiles, amniotic sac and mammals contains fetus + amniotic fluid protects fetus from injury allows for fetal movement prevents adherence of fetus maintains body temperature of fetus/embryo EXTRAEMBRYONIC MEMBRANES Chorion outer layer: trophoblast  Embryo FETAL MEMBRANES chorionic epithelium chorioallantoic connective tissue allantoic endothelium Extraembryonic membranes EXTRAEMBRYONIC MEMBRANES Chorion outer layer: trophoblast inner layer: extraembryonic mesoderm attaches to the uterus; absorbs nutrients allows fetal-maternal gas exchange produce hormones forms fetal part of placenta directs the formation of the decidua in deciduate placentation Decidua (maternal part) - rich in blood vessels that provide oxygen and nutrients to the embryo; expelled with fetus at birth EXTRAEMBRYONIC MEMBRANES Umbilical fibrous remnant of allantois connecting cord from the developing cord/urachus embryo/fetus to the placenta supplies the fetus with oxygenated, nutrient- rich blood from the placenta Anatomy of an Incubating Egg  Anatomy of Balut Air space Eggshell Shell membrane Embryo Amniotic fluid Yolk Albumen Implantation  Implantation (Mammals) Ovulation Fertilization Implantation Implantation the phase of mammalian embryonic development during which the blastocyst hatches, adheres, attaches, and invades the female uterus' endometrium. Endometrium inner lining/wall of the uterus Types of Implantation Types of Implantation Interstitial implantation- Blastocyst implants itself interstitially by passing through the uterine epithelium and becoming completely cut off from the uterine lumen; Primates and guinea pigs Types of Implantation Centric/superficial implantation- Blastocyst elongates and enlarges until it fills a good part of the uterine cavity; Ungulates and carnivores Types of Implantation Eccentric implantation- Blastocyst remains small and becomes lodged in a fold of the uterine lumen, where it implants itself; Rodents Early Nutrition The embryo is nourished with embryotroph which is composed of: a. HISTOTROPH (Uterine milk) - responsible for early nourishment while the placenta is not yet well established; absorbed by imbibition of trophoblast cells. b. HEMOTROPH – nutritive material from maternal blood; absorbed through the allantochorion or vitellochorion COMPARATIVE PLACENTATION Placentation formation, type, and structure, or arrangement of placentas Mammalian embryo derives its nutrients directly from the mother (not on restored yolk) Placentation Most mammals that give birth to live offspring has placenta except monotremes (eg: duckbilled platypus and the echidna) which lay eggs; and marsupials (eg: opossums and kangaroos) which give birth to fetuses that are incompletely developed, the placenta is short-lived.  Placenta vascular organ that develops inside the uterus of most pregnant mammals provides oxygen and nutrients to the fetus, while removing carbon dioxide and other waste products expelled after birth joint fetal and maternal membranes FETAL MEMBRANES MATERNAL MEMBRANES chorionic epithelium endometrial epithelial cells chorioallantoic connective tissue maternal connective tissue allantoic endothelium maternal endothelial cells PLACENTA - BASED ON APPEARANCE DIFFUSE: Almost the entire surface of the allantochorion is involved in formation of the placenta. COTYLEDONARY: Multiple, discrete areas of attachment called cotyledons are formed by interaction of patches of allantochorion with endometrium. Cotyledons -the fetal portions of this type of placenta Caruncles - the maternal contact sites Placentome - the cotyledon-caruncle complex ZONARY: The placenta takes the form of a complete or incomplete band of tissue surrounding the fetus. DISCOID: A single placenta is formed and is discoid in shape  Types of Placenta Based on Morphology Diffuse placenta Cotyledonary placenta Zonary placenta Discoid placenta (Pig, Horse) (Ruminants) (Cat, Dog) (Human, Mouse) Number of Layers  LUMEN ENDOMETRIUM LUMEN FETAL LAYER MATERNAL LAYER ENDOMETRIUM  FETAL LAYER MATERNAL LAYER  (FETAL LAYER) Fetal endothelial cells Fetal connective tissue Chorionic epithelial cells Endometrial epithelial cells Maternal connective tissue Maternal endothelial cells (MATERNAL LAYER) Types of Placenta EPITHELIOCHORIAL All 6 layers are intact Fetal endothelial cells 3 fetal 3 maternal Fetal connective tissue Adecious or No loss of Chorionic Epithelial cells maternal tissue or any layer Maternal Epithelial cells horse, pig and cow Maternal connective tissue Maternal endothelial cells Types of Placenta SYNEPITHELIOCHORIAL (SYNDESMOCHORIAL) Fetal endothelial cells Only 5 layers are intact 3 fetal Fetal connective tissue 2 maternal Chorionic Epithelial cells sheep and goat Maternal connective tissue Maternal endothelial cells Types of Placenta ENDOTHELIOCHORIAL Only 4 layers are intact Fetal endothelial cells 3 fetal 1 maternal Fetal connective tissue carnivores (cats and dogs) Chorionic Epithelial cells Maternal endothelial cells Types of Placenta HEMOCHORIAL Only 3 fetal layers are intact Fetal endothelial cells rodent, primate, and human Fetal connective tissue Chorionic Epithelial cells Uterine blood vessels References: Hyttel, P. (2010). Essentials of domestic animal embryology. Saunders/Elsevier.