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Develop sy

  1. 1. Outlines of d evelopment of endocrine glands the central nervous system the eye the ear and skin and skin appendages
  2. 2. D evelopment of endocrine glands Endocrine system includes: - endocrine glands - hypophysis, pineal, thyroid, parathyroid, adrenal , and islets of Langerhans - endocrine component s of glands with exocrine or other function s - pancreas, gonads, placenta, and kidneys - cells with endocrine function that are scattered in nonglandular organs (as a gut, stomach, trachea, etc.) - e.g. GEP cells
  3. 3. Hypophysis
  4. 4. Epiphysis
  5. 5. Thyroid gland
  6. 7. Parathyroid gland
  7. 9. Adrenal gland
  8. 10. Development of suprarenal glands! The cortex and medulla of the suprarenal glands have different origin. The cortex develops from mesoderm and the medulla from neural crest cells. 6 th week aggregation of mesenchymal cells on each side. The cells that form the fetal cortex are derived from the mesothelial cells lining the posterior abdominal wall. The cells that form the medulla are derived from the adjacent symphatetic ganglion. The cells lie first of the medial side of the cortex and as they become surrounded they start to develop into secretory cells of the suprarenal medulla. Later more mesenchymal cells from the mesothelium enclose the cortex and they become the permanent cortex. Zona reticularis develops in the end of 3 rd year!!
  9. 11. Development of the pancreas
  10. 14. Endocrine glands- summary hypophysis: adenohypophysis - ectoderm of the stomodeum neurohypophysis - neuroectoderm of the diencephalon (base) epiphysis - neuroectoderm of the diencephalon (roof) thyroid gland - endoderm of the primitive pharynx parathyroid glands - endoderm of pharyngeal pouches (3rd, 4th) adrenal gland: cortex - coelomic mesoderm medulla - neural crest (crista neuralis) Langerhans islets - endoderm of the foregut (duodenum)
  11. 15. D evelopment the central nervous system Development of neural tube H istogenesis of neural tube Overwiev of development of the brain and spinal cord Development of cavitis in CNS
  12. 16. Development of the neural tube CNS develops from a thickened area of the embryonic ectoderm - neural plate it occurs very early on the dorsal aspect of the embryonic disc cranially to the primitive knob reaching to the oropharyngeal membrane over the notochord on about day 18, the neural plate begins to invaginate along the cranio-caudal axis and forms neural groove limited with neural folds on each side by the end of the third week, the neural folds become to move together and fuse into a neural tube the neural tube separates from the ectoderm and is then located between it and notochord
  13. 17. . a t the time when the neural folds fuse, some neuroectodermal cells separate from them and form along the dorsal aspect of the tube single cord - called the neural crest ; it soon divides in the left and right parts that migrate to the dorsolateral aspect of the neural tube n eural crest cells give rise to cells of the spinal ganglia and cells of the autonomic ganglia
  14. 18. f rom the beginning, the proximal segment of the neural tube is broadened and correspond s to future brain the narrower caudal one develop s in the spinal cord
  15. 19. Histogenesis of the neural tube t he wall of the neural tube is initially composed of a thick pseudostratified columnar epithelium , cells then rapidly proliferate in entire thickness of the wall - but later mitotic activity is reduced only on cells situated near the luminal aspect of the neural tube ; a s a result of this process, the wall of neural tube differentiates into 2 zones: the inner germinative and the outer marginal ones i n the germinative zone the cells continue in their mitotic activity and migrate peripherally finally , the wall of neural tube shows 3-layered structure: - the ependymal layer = ependyma, - the intermediate or mantle layer= gray matter - cells of mantle layer soon differentiate into primitive neurons - neuroblasts and spongioblasts (glioblasts), - the marginal layer = white matter (contains no cells)
  16. 20. DEVELOPMENT OF THE SPINAL CORD it develops from the caudal portion of the neural tube in contrast with lateral walls of the neural tube, where cells rapidly proliferate, the dorsal and ventral aspects remain thin l ongitudinal groove - sulcus limitans - divides both lateral walls in the dorsal part - alar plate and ventral part - basal plate cells of mantle layer rapidly proliferate and differentiate in the gray matter Remember: The alar plate - give s rise to dorsal horn, the basal plate - to ventral horn
  17. 22. Positional changes of the spinal cord Initially, the spinal cord extends the entire length of the vertebra l canal d uring further development, the vertebra l canal grows more rapidly than spinal cord and its caudal end gradually comes to lie at relatively higher levels i n adults, it usually terminates at the inferior border of the first lumbar vertebra
  18. 23. DEVELOPMENT OF THE BRAIN t he brain develops from the cranial part of the neural tube at the fourth week , three primary brain vesicles differentiate : - the forebrain - prosencephalon - the midbrain - mesencephalon - the hindbrain - rhombencephalon During the fifth week, the forebrain and hindbrain divides so that 5 secondary vesicles arise: TELENCEPHALON VENTRICULI LAT.CEREBRI PROSENCEPHALON DIENCEPHALON VENTRICULUS TERTIUS MESENCEPHALON MESENCEPHALON AQUAEDUCTUS CEREBRI METENCEPHALON RHOMBENCEPHALON V ENTRICULUS QUARTUS MYELENCEPHALON
  20. 29. D evelopment the eye Development of the retina Development of the external and middle layer of the eye Development of the lens
  21. 30. <ul><li>t he eye primordia appear very early (about on the 22nd day) as optic </li></ul><ul><li>grooves (optic sulci) in the neural folds at the site of forebrain </li></ul><ul><li>a s neural folds fuse, the optic grooves evaginate to form paired hollow </li></ul><ul><li>diverticula called optic vesicles </li></ul><ul><li>t he optic vesicle then grows laterally on each side and its connection with </li></ul><ul><li>the forebrain becomes to narrow and forms optic stalk </li></ul>
  22. 31. <ul><li>l ater both optic vesicles invaginate and become double-walled, cup-like structures - optic </li></ul><ul><li>c ups </li></ul><ul><li>th ey reach up to the surface ectoderm that becomes thickened and form lens placode </li></ul><ul><li>t he central region of each lens placode invaginates and sinks below the surface, forming </li></ul><ul><li>a l ens pit </li></ul><ul><li>t he edges of the lens pit gradually come together and fuse to form a spherical lens vesicle </li></ul><ul><li>Remember: the lens vesicle and optic cup derive from the ectoderm and are completely </li></ul><ul><li>surrounded with head mesenchyme </li></ul>
  23. 32. <ul><li>The retina </li></ul><ul><li>develops from the double-layered optic cup </li></ul><ul><li>th e outer layer becomes the pigment epithelium, and the inner layer differentiates into the remaining layers (rod and cone, bipolar, and ganglion cells) </li></ul><ul><li>i ntraretinal space, presented initially between the outer and inner layers gradually disappears so that the pigment epithelium and remaining retinal layers fuse </li></ul><ul><li>the junction of definitive pigment layer with the layer of rods and cones is not so firm as elsewhere so that detachment of retina may occur (after traumatic injury of the eye) </li></ul><ul><li>The edge of the optic cup gives rise to the ciliary epithelium and posterior epithelium of the iris </li></ul><ul><li>is identical with the not photosensitive portion of the retina </li></ul>
  24. 34. <ul><li>The middle and external layers </li></ul><ul><li>develop from the mesenchyma that envelops the external surface of the </li></ul><ul><li>optic cup </li></ul><ul><li>The lens is develop ed from the lens vesicle </li></ul><ul><li>the anterior wall of th e vesicle gives rise to the anterior epithelium of the </li></ul><ul><li>lens, the cells of the posterior wall gradually lengthen and form lens fibers </li></ul><ul><li>the lens capsule is produced by the epithelial cells of both aspects of the </li></ul><ul><li>lens vesicle </li></ul><ul><li>nu trition of the lens during development is provided by the hyaloid artery , </li></ul><ul><li>a branch of the ophthalmic artery </li></ul><ul><li>r ests of the hyaloid artery found in vitreous body are known as hyaloid canal </li></ul><ul><li>(Cloqueti) </li></ul><ul><li>The anterior eye chamber originates as cleft-like space that forms between </li></ul><ul><li>the lens and the surface ectoderm </li></ul><ul><li>The cornea develops from the surface ectoderm and mesenchyme adhering </li></ul><ul><li>to it after forming of the anterior eye chamber </li></ul><ul><li>the stalk of the optic cup becomes the optic nerve </li></ul>
  25. 37. D evelopment the ear Development of the external ear Development of the middle ear Development of the external ear
  26. 38. <ul><li>THE EXTERNAL EAR </li></ul><ul><li>The external acoustic meatus develops from the dorsal end of the 1st branchial groove ; ectodermal cells at the bottom of th e groove proliferate and extend inward as a solid epithelial plate - meatal plug ; in the fetal period, the central cells of this plug degenerate, forming cavity that becomes the inner part of the external acoustic meatus </li></ul>
  27. 39. <ul><li>The auricle </li></ul><ul><li>develops from 6 swellings known as auricle hillocks that surround the margin of the first branchial groove </li></ul><ul><li>3 hillocks are on the first branchial (mandibular) arch and 3 on the second (hyoid) branchial arch </li></ul><ul><li>At the end of the 2nd month all hillocks fuse to form the definitive pinna </li></ul><ul><li>The tympanic membrane (TM) </li></ul><ul><li>derives from the branchial membrane separating the 1st branchial groove and the 1st pharyngeal pouch </li></ul><ul><li>i nitially, the membrane is made up of only the ectoderm and endoderm , a s development proceeds, mesenchyme grows between both germ layers and is differentiated into the fibrous stratum of the (tm), t he ectoderm gives rise to the epidermal and the endoderm to the mucous aspect of the definitive TM . </li></ul>
  28. 40. <ul><li>THE MIDDLE EAR </li></ul><ul><li>2 different embryonic anlagen - the 1st pharyngeal pouch and </li></ul><ul><li>- cartilages of the 1 st and 2nd pharyngeal arches </li></ul><ul><li>T he tympanic cavity - 1st pharyngeal pouch - its distal end expands that then envelopes auditory ossicles </li></ul><ul><li>t he proximal unexpanded portion becomes the Eustachian tub e </li></ul>
  29. 41. <ul><li>THE INNER EAR </li></ul><ul><li>derives from the external germ layer - the ectoderm </li></ul><ul><li>an anlage occurs early in the fourth week as a thickened plate of the ectoderm </li></ul><ul><li>- otic placode - on each side of the head </li></ul><ul><li>both placode s invaginate and sink below the surface ectoderm into the underlying </li></ul><ul><li>mesenchyme to form otic pit </li></ul><ul><li>edges of the pit come together and fuse to form an otic vesicle (otocyst) that lies </li></ul><ul><li>laterally to the rhombencephalon </li></ul>
  30. 42. t he otocyst serves a primordium of future membranous labyrinth
  31. 43. two divisions are early recognizable: a dorsal or utricular portion , differentiating into the utricle, semicircular ducts and endolymphatic duct and sac and a ventral or saccular portion that gives rise to the saccule and cochlear duct
  32. 44. <ul><li>Initially, the semicircular ducts form flat-like diverticula growing out from the utricular portion; central parts of them then fuse and disappear </li></ul><ul><li>t he peripheral infused portions of the diverticula become the semicircular ducts </li></ul><ul><li>f rom the ventral saccular portion of the otocyst, the coiled cochlear diverticulum grows out </li></ul><ul><li>st arting the 4th month , differentiation of maculae, cristae begins within the utricle, saccule, and semicircular ducts as well as the organ of Corti within the cochlear duct </li></ul><ul><li>t he mesenchyme around the otic vesicle (later its parts) condenses and differentiates into the bony labyrinth </li></ul><ul><li>a space separating the membranous labyrinth from the osseous one soon fills the perilymph </li></ul>
  33. 47. D evelopment the skin and skin appendages Development of epidermis and dermis Development of eccrine sweet glands Development of hairs Development of nails
  34. 48. Epidermis i nitially, a single layer of ectodermal cells covers the embryo s tarting from the 2nd month, the ectodermal cells divide and form a superficial protective layer of flattened cells, the periderm or epitrichium at the end of 4th month, the epidermis acquires its definitive arrangement a nd 4 layers are distinguished: basal, spinous, granular and horny layer ; a ll layers of the epidermis -at birth
  35. 49. Cells that have been exfoliated during fetal life form part of the vernix caseosa , a white, cheese-like, protective substance that covers the fetal skin During the early fetal period, melanoblasts migrate from the neural crest to the dermoepidermal junction, where they differentiate into melanocytes
  36. 50. <ul><li>Dermis </li></ul><ul><li>t he dermis is derived from the mesenchyme underlying </li></ul><ul><li>the surface ectoderm </li></ul><ul><li>t he mesenchyme arises from 2 sources: </li></ul><ul><ul><li>from the somatic layer of lateral mesoderm (most of the mesenchyme), </li></ul></ul><ul><ul><li>from the dermomyotome regions of the somites (in lesser extent) </li></ul></ul><ul><li>By 11 weeks, the mesenchymal cells have begun to produce </li></ul><ul><li>collagenous and elastic connective tissue fibers </li></ul><ul><li>As the epidermal ridges form, the dermis project upward into </li></ul><ul><li>the epidermis and forms dermal papillae </li></ul>
  37. 51. Eccrine sweat glands develop as solid epidermal downgrowths that extend into the underlying dermis a s buds elongate, their ends become coiled, forming the primordia of future secretory portions of glands
  38. 54. <ul><li>Development of hairs </li></ul><ul><li>begin to develop early in the fetal period, but they do not become readily visible </li></ul><ul><li>until about twentieth week </li></ul><ul><li>first recognizable hairs occur on the eyebrows, upper lip, and chin </li></ul><ul><li>A hair follicle begins as a solid downgrowth of the stratum </li></ul><ul><li>germinativun of the epidermis and extends into the underlying </li></ul><ul><li>dermis </li></ul><ul><li>t he deepest part of the hair bud soon becomes club-shaped, forming a hair bulb. </li></ul><ul><li>t he epithelial cells of the hair bulb constitute the germinal matrix - it gives rise to hair </li></ul><ul><li>The hair bulb is then invaginated by a small mesenchymal hair papilla </li></ul><ul><li>t he peripheral cells of the developing hair follicle form the epithelial root sheath </li></ul><ul><li>t he surrounding mesenchymal cells differentiate into the dermal (connective tissue) root </li></ul><ul><li>sheath </li></ul><ul><li>first hairs are called lanugo , are fine a nd colourless </li></ul><ul><li>these hairs are replaced during the perinatal period by coarser hairs, called vellus </li></ul><ul><li>that persist over most of the body, except in the axillary and pubic regions </li></ul><ul><li>Hairs of these reagions are replaced during puberty </li></ul>
  39. 57. a pocrine sweat glands (axilla, pubic region, anal region, areolae) develop from the hair follicle similar as sebaceous glands
  40. 58. Development of mammary gland
  41. 59. <ul><li>The mammary glands develop during the sixth week as a solid downgrowth of the epidermis that extend into the underlying mesenchyme </li></ul><ul><li>t hese downgrowths occur along the mammary ridges , two thickened strips of ectoderm that extend from the axillary to the inguinal regions </li></ul><ul><li>i n human embryos, these epithelial ridges occur during the fourth week, but except the pectoral area rapidly disappear </li></ul><ul><li>e ach primary mammary bud soon gives rise to several secondary buds that develop into lactiferous ducts and their branches. The fibrous connective tissue and fat develop from the surrounding mesenchyme </li></ul>
  42. 60. <ul><li>Nails </li></ul><ul><li>Toenails and fingernails begin to develop at the distal ends of the digits at about 10 weeks , d evelopment of fingernails precedes that of the toenails </li></ul><ul><li>The nails first appear as thickened areas of the developing epidermis on the dorsal aspect of each digit </li></ul><ul><li>These nail fields are surrounded laterally and proximally by folds - nail folds </li></ul><ul><li>Cells from the proximal nail fold grow over the nail field and become keratinised to form the nail, or nail plate </li></ul><ul><li>At first, superficial layers of epidermis called the eponychium cover the developing nail. This later degenerates, except at the base of the nail, where it persists. </li></ul>