Histogenesis

151Course 5: Cells and tissue

development

Course 5: Development• 137 Case report: Thalidomide• 138 Basic morphogenetic processes• 139 Regeneration and reparation• 140 Female reproductive system• 142 Gametogenesis and fertilization• 144 Genetic determination of the sex• 145 Signalization in development• 146 Blastogenesis, notogenesis• 149 Notogenesis, neurulation• 150 Embryonic period• 151 Histogenesis• 152 Human reproductive genetics• 153 Developmental toxicology• 154 Ageing

• 141 Female reproductive system• 143 Male reproductive system• 147 Extraembryonic organs• 148 Early embryonic development, chick

Aim

• histogenesis – the origin and development of specialised tissues and organs – the derivates of:

• ectoderm• mesoderm• endoderm

blastogenesis

embryonic period

fetal period

Histogenesis, organogenesis

Ontogenesis

• mechanisms operate…at different levels

• cells - differentiation• cell populations - morphogenesis - structure development• cell populations set - morphogenetic system – realizes

structure and function programme in organ or part of the body – basic morphogenetic processes

1. Cell level – differentiation – mesenchymal cell

mesenchymal cell

chondroblast lipoblast fibroblast osteoblast myoblast

cartilage fat

connective tissue, ligaments, tendons

bone muscle

endothelium blood cells

hemocytoblast

Cell level – differentiation – neuroepithelim

2. Cell populations level

• development of structures/ organs - morphogenesis• 1. induction – one cell population induces the change of the

fate in another cell population • epithelial-mesenchymal interactions examples: limbs, lens, nephrons, teethcross-talk• 2. cell-signalling, signalising cell x target cell (must be

sensitive to this signal) paracrine interactions, contact interactions

• induction neuroectoderm / surface ectoderm – lens placode

Induction in gonad – indifferent stageinduction – primordial germ cells/ testes, ovaryinduction – coelomic epithelium / mesenchyme

3. Morphogenetic systems level= group of cell populations relize the developmental

programme

• basic morphogenetic processes - 4 processes play out at the cell population level to essentially create the final organism

• proliferation

• migration

• asociation

• programmed cell death - apoptosis

Morphogenetic system level neural tube differentiation in CNS development

Histogenesis

• EPIBLAST is the maternal of 3 germ layers• ectoderm and endoderm are epithelia• Expression CAM +• mesoderm is connective tissue – primary

mesenchyme• No Expression CAM -

Origin of 3 germ layers

Germ layers derivates

• nervous systeme• senses connectives• skin circulatory s. hematopoesis, immune s. endocrine s.

Epiblast

ectoderm mesoderm endoderm

urogenital sytem

mesenchyme digestive s.respiratory s

Ectoderm and its differentiation1.neuroectoderm (neural tube a neural crest)

2. surface ectoderm

1.neuroectoderm

2. surface ectoderm

neuroectoderm:NT, neural crest placodessurface ectoderm:epidermis

Neural tube – region of the future brain (segmentation- neuromers- brain vesicles)

induction neuroectoderm / surface ectodermplacodes - otic placodes and lens placodes

Neuroectoderm - neural crest – definitive derivates

connectives, cartilage, bone, dermis of the head

cranial nerves ganglia

odontoblasts, Schwann cells melanocytes, C-cells of thyroidautonomic ganglia

adrenal medulla

Ectoderm derivates mediate the contact between body and outer environment

• CNS• PNS• sensory epithelium of the ear, nose, eye• epidermis and its derivates – hairs, nails• glands of the skin, mammary gland• hypophysis• enamel

Endoderm and its differentiation yolk sac roof and wall,

primitive gut

Endoderm-lined cavity and its position during cephalo-caudal folding

sagittal midline section

Endoderm and its derivates

• gastrointestinal tract – epithelium• respiratory sytem – epithelium• parenchyme of the liver, pancreas, thyroid• reticular stroma of tonsils and thymus• epithelium of salivary glands • epithelium of urinary bladder, urethra• epitel of middle ear and Eustachian tube

Mesoderm and its early differentiationaxial, paraxial, intermediate, lateral

Mesoderm – mesenchyme – embryonic connective tissue

Somite differentiationsclerotome, dermatome, myotome

epiteloid arrangement of somitesclerotome – connectives coating spinal cord

dorsolateral cells migrate to the limb bud - muscles

Dorsomedial cells – myotome –trunk muscles

dorsally - dermatom – beneath ectoderm – dermis in the skin

Somites, 42 – 44 pairs . 1.pair in occipital region, 20EDMaterial: paraxial mesodermSegmentation: Notch, WNT, segmentation genesRetinoic acid, FGF8, cranio-caudal gradient

S

Intermediate mesoderm – derivatesurogenital sytem

in cervical, and thoracal region – segmented in nephrotomesabdominal – nefrogenic blastema

Excretory units of kidney and gonad primordium

Lateral mesoderm – splanchnic/ splanchnopleura and somatic/ somatopleura

splanchnopleura – wall of gut (CT, muscle)somatopleura – serous membrane – inner

lining of coelomtransversal section

3week 4week

Mesoderm and its derivates

• connectives (connective tissue proper, cartilage, bone)

• blood• mesothel and endothel– the only epithelia• kidneys• gonads

• mesothel – simple squamous epithel of the visceral peritoneum /splanchnopleura in peritoneal cavity

Tissues family tree