Embryology Flashcards
Key terminology
Gamete
Mature haploid male or female germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote
Key terminology
Embryonic period
weeks 3 - 8 in humans (most critical period in terms of risk of teratogens as most major stuctures developing at this time)
Key terminology
Teratology
the study of abnormal development
Key terminology
Teratogen
cause irreversible, deleterious structural malformations in fetuses
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Mutagen
cause changes (mutations) in the genetic material of cells
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Malformations
complete or partial absence of a structure or alterations in its normal configuration can be caused by environmental and/or genetic factors
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Disruption
morphological alterations of already formed structures and are caused by destructive processes
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Deformation
Abnormal formation due to mechanical factors over a prolonged period
List the 7 Phases of embryogenesis
- Gametogenesis
- Fertilisation
- Cleavage
- Gastrulation
- Embryonic folding (morphogenesis)
- Organogenesis (3-8 week)
- Foetal period
Describe Gametogenesis
- Formation of gametes from primordial germ cells (consists of mitosis and meiosis leading to genetic variation)
- Spermatogenesis -males
- Oogenesis - females
Describe Spermatogenesis
- formation of male gametes
- Whole process 64-74 days and produces 300 million sperm cells per day
- Occurs at puberty and continues throughout life
Phases:
Spermatogonial phase - spermatogonium cells divide by mitosis to form primary spermatocytes
Spermatocyte phase - Primary spermatocytes undergo meiosis forming secondary spermatocytes and then secondary spermatocytes undergo meiosis II to form spermatids
Spermatid Phase
-spermatids differentiate into spermatozoa with specific morphology - Spermatagonium found nearer to periphery of gonads and move towards lumen as they mature to from spermatids.
Describe Oogenesis
- Formation of female gametes
- Starts in development and ends at menopause
Describe Fertilisation
Union of gametes:
* Fusion of sperm and oocyte to form a zygote (single cell embryo, diploid and sex determined)
* Takes place in the ampulla of the uterine tube
Describe Cleavage
- Period of rapid mitotic cell division with no increase in size or volume as cells are confined within the ZP the embryo will change shape (compaction)
- Daughter cell= blastomere
- Formation of morula (16+ cells) then blastocyst (200-300 cells)
- Cells maximize available space by coming into closer contact with each other
- Inner cells form cell junctions, outer cells form gap junctions
- Fluid enters through ZP producing a blurred cell mass - signals the formation of the blastocyst
Describe Gastrulation
- Formation of the germ layers - ectoderm, mesoderm, endoderm (in order from out to in)
- Body axis established
- Embryo goes from a 2 layered structure to a 3 layered structure (end of week 2- start of week 3)
Describe Embryonic folding (morphogenesis)
- Formation of the body plan
- Tube within a tube
- Cranial and lateral regions on Day 22
Caudal region on Day 23
Describe Organogenesis
- (3-8 week)
- Formation of Organs and Organ Systems
- Basis of these all in place by end of embryonic period
- Will continue to develop through foetal period
Describe the Foetal period
- From week 9 until birth
- Growth, weight gain:
- Mainly grows in length during 2nd trimester
- Most weight is added in 3rd trimester
- 14g (end of 2nd month) to 3500g (at birth)
- Tissues mature and become functional
- Overt sexual differentiation
- Bone laid down; connections made in CNS
List 6 Primary Developmental Processes
- Cell Division
- Differentiation
- Cell Attachment
- Apoptosis
- Induction
- Cell migration
What is Cell division?
increase in number of cells influences the shape and growth of embyro
What is Differentiation?
change in appearance or structure of cells allows for adoption of new functions
What is Cell attachment?
physical/functional linkages between cells formation of tissue
What is Apoptosis?
programmed cell death. creates spaces and cavities
What is Induction?
ability of one cell type to cause another to differentiate, directly or at a distance
What is Cell migration?
movement from one location to another
List the 3 Secondary processes of embryonic development
- Axis formation
- Folding/rotation
- Increase/decreases in mass or dimension
Describe the Basic Chromosome Theory of inheritance
- 23 pairs to form diploid number of 46 chromosomes
- Female XX and male XY
List Anatomy terms for feotus
- Cephalic/cranial - superior
- Caudal - inferior
- Ventral - anterior
- Dorsal - posterior
- Rostral - anterior of head
- Caudal - back of head
List anatomical planes of a feotus
- Frontal/coronal plane splits embryo in ventral and dorsal aspect
- axial/transverse plane splits embryo into cephalic/cranial aspects
- Saggital plane spits embryo into a right and left side
Describe the 4 stages of Fertilisation
- Sperm binds to zona pellucida glycoprotein
- Acrosomal enzymes released from sperm head; sperm digests its way into egg
- Egg and sperm plasma membranes fuse and sperm contents enters the egg
- Sperm entry triggers completion of meiosis 2 and release of cortical granules by oocyte (make ZP impenetrable to other sperm)
OCCURS IN AMPULLA
Name the different parts of the blastocyst and what they give rise to
- Outer cell mass (trophoblast): contacts with the endometrium of the uterus to facilitate implantation and the formation of the placenta
- Inner cell mass (embryoblast): responsible for the formation of the embryo itself
Where in the uterus does the embryo normally implant?
- Implantation (day 6-8) typically occurs in posterior wall of the uterine cavity
- Abnormal implantation site= ectopic pregnancy
Describe the changes in the trophoblast and embryoblast during implantation
- Day 7
- Trophoblast divides into cytotrophoblast (individual cells) and syncytioblast (single multinucleated cell which produces hCG)
- Embryobast divides into epiblast (dorsal surface) and hypoblast (ventral surface)
Describe day 8-9 of embryo developement
- Formation of 2 cavities = amniotic cavity (epiblast) and primitive yolk sac (hypoblast)
- Implantation complete
Describe day 10-12 of embryo developement
- Uteroplacental circulation established
- Extraembryonic mesoderm develops then degenerates, forming chorionic cavity
Describe day 13 of embryo developement
Formation of secondary yolk sac, connecting stalk, and chorionic cavity
Name the layers of the trilaminar embryo
- ectoderm
- mesoderm
- endoderm
State the major tissues derived from the Ectoderm
- Epidermis of skin, hair, nails
- Nervous system
State the major tissues derived from the Endoderm
- Lining of gut tube
- Lining of respiratory tract
- Lining of bladder and urethra
State the major tissues derived from the mesoderm (Paraxial/ Intermediate)
- Paraxial mesoderm: axial skeleton, skeletal muscle
- Intermediate mesoderm: urogenital systems
State the major tissues derived from the mesoderm (lateral plate)
- Somatic layer: dermis, lining of body wall, parts of limbs
- Visceral layer: cardiovascular system, mesothelial covering of organs, smooth muscle
What is the Notochord?
- Cellular rod
- Serves as longitudinal support
- Crucial for signalling that transforms unspecialised embryonic cells to definitive tissues and organs
- Becomes the nucleus pulposus
