Reproduction and Developmental Biology Flashcards
What is gastrulation?
Conversion from a bilaminar to a trilaminar embryo
Fertilization occurs in the ___________
Oviduct
What begins the process of gastrulation?
Epiblast cells invaginate inwards through the primitive streak to form three cell germ layers: ectoderm, mesoderm and endoderm —> embryo is now in the gastrula stage
Primitive streak
Forms in the epiblast layer (as it thickens)
Defines left/right and top/bottom axes of the embryo
Crucial structure in the process of gastrulation
Invagination through primitive streak creates an opening called the ___________, which further deepens to become the _________
Blastopore
Archenteron (gut tube)
What structure eventually becomes the digestive tract
The archenteron (center cavity)
The blastopore eventually develops into:
The anus (deuterostomes) or the mouth (protostomes)
What structures are formed from the ectoderm?
- CNS and PNS
- Sensory parts of ear, eye, and nose
- Epidermis layer of skin, nails, and hair
- Enamel of teeth
- Pigmentation cells
- Adrenal medulla
- Mammary and sweat glands
- neural tube
What structures are formed from the mesoderm?
- Bones
- Muscles
- circular/lymphatic system
- somites
- kidney
- dermis of skin
- Cardiovascular system
- Gonads
- Adrenal cortex
- Spleen
- Notochord
What structures are formed from the endoderm?
- epithelial living of digestive, respiratory systems
- gall bladder
- Stomach
- Pancreas
- Liver (parts of it)
- Lungs
- Bladder lining
- Thyroid and parathyroid
- Thymus
What stage comes after the gastrula stage?
Neurula stage
Neurulation
Formation of the nervous system
Beginning of organogenesis
Organogenesis
Formation of new organs
Steps in formation of the nervous system:
0) “Pre-step”: formation of the notochord
1) Notochord stimulates overlying ectoderm to thicken, forming the neural plate
2) Neural plate folds onto itself, forming the neural fold/groove
3) Neural fold/groove continues to fold until edges touch, creating a hollow tube called the neural tube
4) The neural tube becomes the CNS
What occurs during folding of the neural tube?
Some cells at the crest migrate and differentiate into neural crest cells which migrate to form the PNS, teeth, pigmented cells and craniofacial bones
What layer do neural crest cells come from?
Ectoderm (not mesoderm)
What occurs to the mesoderm during the final stages of organogenesis?
Mesoderm cells called somites form two masses alongside the notochord which go on to form the vertebrae and skeletal muscles associated with the axial skeleton
Stem cells
Undifferentiated cells with potential (potency) to become many types of cells
Totipotent cells
Stem cells that can become any cell
Single cell that can produce an entire organism
Es: zygote, blastomeres of morula
Pluripotent
Stem cells that can become any of the three germ layers
Cannot form extraembryonic tissue
Ex: ICM cells, “embryonic stem cells”
Multipotent
Stem cells that can only differentiated into a few cell types of a specific tissue type
Can only give rise to more then one germ layer of cell type, but not all
Example: hematopoietic stem cells —> many blood cells
Extraembryonic development
Development of support structures outside the fetus, which include: amnion, chorion, yolk sac and allantois
Provides protection and nourishment to fetus
Amnion
- Innermost layer, closest to developing embryo
- Secretes **amniotic fluid*: water cushion, protecting embryo
Amniotes
- tetrapods (4-limb aminals with backbones/spinal columns)
- have adapted eggs that are supported by several extraembryonic membranes
- Mammals, reptiles, birds
- do NOT include amphibians or frogs
Anamniotes
Organisms with no amnion
Fish, amphibians
Eggs get laid in water, water serves as cushion so they dont need it
Chorion
- Outermost layer, surrounds the embryo
- In placental mammals: forms the fetal half of the placenta (platform for exchange of gases, nutrients, and wastes) and forms maternal tissue
- In egg-laying mammals: membrane for gas exchange just underneath the egg shell (against the inner surface of the egg)
Allantois
- Outpouching sac off of the archenteron that encircles the embryo, just below the chorion
- Stores waste for disposal
- placental mammals: transports wastes to placenta, becomes part of the umbilical cord (which transports gases, nutrients and wastes), and eventually becomes the urinary bladder in adults
- egg-laying mammals: initially stores waste products as uric acid, later fuses with the chorion to help with gas exchange due to its rich blood supply
Yolk sac
- Contains yolk: functions to provide nutrients to the growing embryo
- Yolk sac is extraembryonic while the yolk is intraembryonic (part of the embryo)
- In placental mammals: provides nutrients to growing embryo transiently until placenta is mature and is the first location of blood cell formation for the fetus
- In egg-laying mammals: provides nutrients to growing embryo permanently
Viviparous
Gives birth to offspring that developed within mother
Most mammals
Oviparous
Produce eggs that develop and hatch once they have been expelled from the mother
Most birds, reptiles and fish