Early Development And Basic Principles (embryology) Flashcards
Hypertrophy
Increase the size of cells
Hyperplasia
Increase in number of cells
What leads to neoplasia?
Abnormal hyperplasia
What are the different morphological processes?
- Localized growth
- Cell movement
- Apparent movement
- Aggregation of cells
- Folding
- Fusion
- Splitting
- Induction
Example of localized growth
Cells aggregate to form glands , teeth buds, hair follicles, etc.
Yolk sac endodermal cell movement
Cells migrate to the genital ridge and differentiate into germ cells
Neural crest cell movement
Cells migrate to form ganglia, odontoblasts in teeth, chromaffin cells in the adrenal medulla
Apparent movement
Cells/ organs change relative positions “without movement” - adjacent tissues move
Aggregation of cells
Cells with similar characteristics tend to clump together
Example: formation of glands
Folding
Inward folding: invagination
Outward folding: evagination
Example: formation of neural tube that developed into nervous system
Fusion
Fusion of cells to form ridges, tubes
Examples: formation neural tube; formation of palate from fusion of palatine process maxilla
Splitting
Cells split and form another layer of detachment from the parent mass (delamination)
Example: formation of hypoblast coelom
Induction
A population of cells (inductor) acts upon another population to change the behavior of second population (induced)
Examples of induction
- Notochord (inductor) —> overlying neural ectoderm induced to form neural tube
- Neural tube (inductor) —> overlying ectoderm induced to form lens of the eye
- Epithelial - mesenchyme interaction: mesenchyme (inductor) induces the overlying epithelial to form glands
Morphogenesis
Formation of an organ with a definite morphology (size, shape, structure)
Ex: development of a gland from epithelium
Development of a gland from epithelium
- Epithelium
- Thickening of epithelium
- Invagination of CT
- Proliferation of cells
- Branching of cells
- Arrangement of epithelial cells in acini
- Canalization to form lumen and duct system
- Disappearance of duct cells in endocrine glands
Teratogens
An agent which causes abnormal development
Teratogenic effects can differ depending on…
Developmental state
Dose
Genotype
Developmental state
- Pre-differentiation (usually causes death)
- Differentiation and organogenesis (causes structural malformations)
- Advanced morphogenesis (causes functional disorders)
Dose
Higher the dose, greater the teratogenic effect
Each developmental stage has a threshold dose
Genotype
Effects can vary among species between organs within the same species
Giving different species cortisone and thalidomide causes different effects
Cortisone
Given at a certain stage will cause cleft palate in mice but not other species
Thalidomide (sedative)
Given at 20-35 days and will cause hypoplasia of limbs in humans but not other mammals
Causes abnormal coiling of colon in pigs if given from 2-6 weeks
Incomplete growth
Common anomaly
Aphasia or hypoplasia
Dwarfism, gonadal hypoplasia
Failure to fuse
Common Anomaly
Cleft plate, septal defect in the heart and diaphragm
Incomplete migration
Common Anomaly
Cryptorchidism, ectopic cordis
Persistence of embryonic structures
Common Anomaly
Persistent pupillary membrane, persistent anal membrane
Mal-positioning of embryonic structures
Dextrocardia (heart formed on right side)
Transportation of viscera (situs inversus)
Apoptosis
Programmed cell death
Ex: Paramesonephric duct degenerates on males (mullerian inhibiting syndrome)
Mesonephric duct degenerates in females (lack of testosterone)
Why are the causative agents of teratogenic effect?
Abnormal gene
Abnormal chromosomes
Radiation
Hormone imbalance
Chemical agent
Infectious agent
Nutritional deficiencies
Spermatogenesis
All cellular stages involved in the production of sperm (mitosis and meiosis)
Spermatogonia —> sperm
Spermiogenesis
Metamorphosis of spermatid to sperm (no division)
Spermiation
Release of sperm into the lumen of seminiferous tubules
Which cells undergo mitosis?
Somatic cells
Produces genetically identical cells
What is the significance of meiosis?
Achieving haploid chromos
Segregation of genes
Genetic exchange
Recombination of chromatids
Which cells undergo meiosis?
Specific germ cells
Prophase 1 of meiosis 1
- Leptotene: chromos visible
- Zygotene: homologous chromo pair up gene by gene (synapse), synaptonemal complex develops
- Pachytene: gene exchange, sister chromatids evident
- Diplotene: sites of crossing over
- Diakinesis: chromos separate and held by centromeres
Metaphase 1 of meiosis 1
Alignment of homologous pairs at cell equator
Anaphase 1 of of meiosis 1
Homologous chromosomes separate
Non-disjunction of chromos can occur here resulting in monosomy/ trisomy
Telophase 1 of meiosis 1
Chromos reach the respective poles, cytokinesis
Meiosis II
No DNA duplication
Prophase II (similar to mitosis)
Metaphase II
Anaphase II: sister chromatids become chromos
Telophase II`
Euploidy
Abnormalities in chromo number involving whole sets of chromos
Ex: triploid, tetraploid
Aneuploidy
Abnormalities in chromo number
Cause: nondisjunction chromos
Ex: monosomy, trisomy
Deletion
Loss of a part of a chromo
Inversion
Change in the gene sequence on the same chromo
Translocation
Transfer of a part of a chromo to another non homologous chromo
Cause: radiation
Fusion
Whole chromosome may fuse with another chromo
Chimera
Mixture of genotypes among cells of an individual
Cause: fusion between zygotes
Klinefelter Syndrome
Trisomy, XXY, rare in domestic animals
EX: Male tricolor cat
Turner
Monosomy, XO, phenotypic females, sterile
Reported in horse, sheep, pig and cat
Free Martin
XX/XY mosaics, caused by mixing of blood supply of two fetuses
Common in cattle
