1. Pre-differentiation (usually causes death) 2. Differentiation and organogenesis (causes structural malformations) 3. Advanced morphogenesis (causes functional disorders)

Early Development And Basic Principles (embryology) Flashcards by Trenni Jefferson

Hypertrophy

Increase the size of cells

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Hyperplasia

Increase in number of cells

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What leads to neoplasia?

Abnormal hyperplasia

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What are the different morphological processes?

Localized growth
Cell movement
Apparent movement
Aggregation of cells
Folding
Fusion
Splitting
Induction

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Example of localized growth

Cells aggregate to form glands , teeth buds, hair follicles, etc.

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Yolk sac endodermal cell movement

Cells migrate to the genital ridge and differentiate into germ cells

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Neural crest cell movement

Cells migrate to form ganglia, odontoblasts in teeth, chromaffin cells in the adrenal medulla

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Apparent movement

Cells/ organs change relative positions “without movement” - adjacent tissues move

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Aggregation of cells

Cells with similar characteristics tend to clump together
Example: formation of glands

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Folding

Inward folding: invagination
Outward folding: evagination
Example: formation of neural tube that developed into nervous system

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Fusion

Fusion of cells to form ridges, tubes
Examples: formation neural tube; formation of palate from fusion of palatine process maxilla

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Splitting

Cells split and form another layer of detachment from the parent mass (delamination)
Example: formation of hypoblast coelom

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Induction

A population of cells (inductor) acts upon another population to change the behavior of second population (induced)

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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

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Morphogenesis

Formation of an organ with a definite morphology (size, shape, structure)
Ex: development of a gland from epithelium

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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

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Teratogens

An agent which causes abnormal development

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Teratogenic effects can differ depending on…

Developmental state
Dose
Genotype

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Developmental state

Pre-differentiation (usually causes death)
Differentiation and organogenesis (causes structural malformations)
Advanced morphogenesis (causes functional disorders)

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Dose

Higher the dose, greater the teratogenic effect
Each developmental stage has a threshold dose

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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

1. Leptotene: chromos visible 2. Zygotene: homologous chromo pair up gene by gene (synapse), synaptonemal complex develops 3. Pachytene: gene exchange, sister chromatids evident 4. Diplotene: sites of crossing over 5. 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