1. EMBRYOLOGY & TISSUES Sonya Schuh-Huerta, Ph.D. Human Anatomy Human Fetus, 12 weeks

2. Basic Embryology, Ch 3

3. (Physiology, Silverthorn, 2000) Fertilization & the Early Embryo

4. Embryology Embryology – study of the origin & development of a single individual Prenatal period –Embryonic period  first 8 weeks –Fetal period  remaining 30+ weeks

5. The Prenatal Period Fertilization 1-week conceptus 3-week embryo (3 mm) Embryo Duration: Weeks 9–38 (or birth) Major events: Organs grow in size and complexity. Embryonic period Fetal period 12-week fetus (90 mm) 8-week embryo (22 mm) 5-week embryo (10 mm) 38 weeks Duration: First 8 weeks post-fertilization Major events: Organs form from 3 primary germ layers. The basic body plan emerges.

6. The Basic Body Plan Skin  dermis and epidermis Outer body wall  trunk muscles, ribs, vertebrae Body cavity & digestive tube (inner tube) Kidneys & gonads  deep to body wall Limbs

7. The Embryonic Period Week 1  from zygote to blastocyst –Fertilization – in lateral 3 rd of uterine tube –Zygote (fertilized oocyte) – moves toward uterus –Cleavage – daughter cells formed from zygote –Morula – solid cluster of 12–16 blastomeres –Blastocyst – fluid-filled ball of cells Inner cell mass  forms embryo Trophoblast  forms placenta

8. (d)Early blastocyst (morula hollows out and fills with fluid). 4 days Blastocyst cavity Inner cell mass Blastocyst cavity Trophoblast (e)Implanting Blastocyst (consists of a sphere of trophoblast cells and an eccentric cell cluster called the inner cell mass). 7 days Cavity of uterus Uterus Endometrium (a)Zygote (fertilized egg) (b)4-cell stage 2 days Ovulation Ovary Fertilization (sperm meets and enters egg) Uterine tube Oocyte (egg) Sperm Week 1: Early Embryonic Development

9. hESCs d3.5 d3.0 A Closer Look at Week 1 of Human Embryo Development Reijo Pera R, et al. 1999

10. Embryo Development in Action Wong C, et al. 2010

11. (a)Day 5: Blastocyst floating in uterine cavity. (b)Day 6: Blastocyst adheres to uterine wall. (c)Day 7: Implantation begins as trophoblast invades into uterine wall. Trophoblast Inner cell mass Trophoblast Wall of uterus Cavity of uterus Inner cell mass (d)Day 9: Implantation continues; inner cell mass forms bilaminar disc. (e)Day 11: Implantation complete; amniotic sac and yolk sac form. Trophoblast Amniotic sac cavity Hypoblast Amniotic sac cavity Layers from trophoblast Amnion Bilaminar embryonic disc Yolk sac Epiblast Hypoblast Epiblast Implantation of the Embryo

12. Week 2: The 2-Layered Embryo Bilaminar embryonic disc  inner cell mass divided into 2 sheets –Epiblast & hypoblast Together they make up the bilaminar embryonic disc Amniotic sac  formed by an extension of epiblast Filled with amniotic fluid Surrounds developing embryo/fetus

13. Week 2: The 2-Layered Embryo Yolk sac – formed by an extension of hypoblast –Digestive tube forms from yolk sac –NOT a major source of nutrients for mammalian embryo –Tissues around yolk sac Give rise to earliest blood cells and blood vessels

14. Week 3: The 3-Layered Embryo Primitive streak = raised groove on the dorsal surface of the epiblast Gastrulation = a process of invagination of epiblast cells & gives rise to the germ layers –Begins at the primitive streak –Forms the 3 primary germ layers!

15. Week 3: The 3-Layered Embryo Three Germ Layers* –Endoderm – formed from migrating cells that replace the hypoblast –Mesoderm – formed between epiblast and endoderm –Ectoderm – formed from epiblast cells that stay on dorsal surface *All layers derived from epiblast cells

16. Yolk sac (cut edge) Cut edge of amnion Primitive node Left Right Primitive streak Head end Tail end (e) Bilayered embryonic disc, superior view The Primitive Streak Stage

17. Primitive streak Notochord Amnion Amniotic sac Plane of section Head Ectoderm Mesoderm Embryonic disc Endoderm Yolk sac Sections (b) and (c) Amnion Ectoderm Right Left Invaginating mesodermal cells Notochord Mesoderm Endoderm Yolk sac (a) (b) Section through primitive streak(c) Section anterior to primitive streak Tail Yolk sac Epiblast cells that migrate through the primitive node form the notochord. Epiblast cells that migrate through primitive streak form the mesoderm layer. Primitive node Formation of the 3-Layered Embryo

18. The Notochord Primitive node = a swelling at one end of primitive streak –Notochord forms from primitive node & endoderm Notochord – defines the body axis –Is the site of the future vertebral column –Appears on Day 16

19. Neurulation Neurulation  formation of the brain & spinal cord from ectoderm –Neural plate = ectoderm in the dorsal midline thickens –Neural groove = ectoderm folds inward Somite Intermediate mesoderm Lateral plate mesoderm Coelom Neural crest Neural groove Neural fold Somite (covered by ectoderm) Neural groove Neural fold Splanchnic mesoderm Somatic mesoderm (b)20 days. The neural folds form by folding of the neural plate and then deepen, producing the neural groove. Neural fold cells migrate to form the neural crest. Three mesodermal aggregates form on each side of the notochord (somite, intermediate mesoderm, and lateral plate mesoderm). Lateral plate mesoderm splits. Coelom forms between the two layers. Primitive streak

20. Neurulation Neural tube – hollow tube pinches off into the body Cranial part of the neural tube becomes  brain Maternal folic acid deficiency causes neural tube defects! Neural fold Somite Neural crest Somite Surface ectoderm Neural tube Notochord (c)22 days. The neural folds have closed, forming the neural tube which has detached from the surface ectoderm and lies between the surface ectoderm and the notochord. Embryonic body is beginning to undercut. Cut edge of amnion Head Tail

21. Neurulation Neural crest –Cells originate from ectodermal cells –Forms sensory nerve cells Induction –Ability of one group of cells to influence developmental direction (differentiation) of other cells

22. Week 4: The Body Takes Shape The embryo folds laterally & at the head & tail –Embryonic disc bulges; growing faster than yolk sac –“Tadpole shape” by Day 24 after conception –Primitive gut – encloses tubular part of the yolk sac Site of future digestive tube & respiratory structures

23. Tail Amnion Head Yolk sac Lateral fold Future gut (digestive tube) Somites (seen through ectoderm) Cut edge of amnion Cut edge of amnion Primitive gut Foregut Hindgut Neural tube Notochord Yolk sac Yolk sac Ectoderm Mesoderm Endoderm Trilaminar embryonic disc Head fold Tail fold (a) (b) (c) (d) Folding of the Embryo

24. Week 4: The Body Takes Shape Derivatives of the germ layers –Ectoderm forms: Brain, spinal cord, & epidermis –Endoderm forms: Inner epithelial lining of the gut tube Respiratory tubes, digestive organs, & bladder - Mesoderm differentiates further and is more complex than the other 2 layers –Somites & intermediate mesoderm –Somatic & splanchnic mesoderm

25. The Mesoderm Begins to Differentiate Somites – our first body segments; 40 pairs –Paraxial mesoderm Intermediate mesoderm – begins as a continuous strip of tissue just lateral to the paraxial mesoderm –Each segment attached to a somite Lateral plate – most lateral part of the mesoderm –Coelom – becomes serous body cavities Somatic mesoderm – next to the ectoderm Splanchnic mesoderm – next to the endoderm

26. Mesoderm –Somites divide into: Sclerotome Dermatome Myotome –Intermediate mesoderm forms: Kidneys & gonads –Splanchnic mesoderm forms: Musculature, connective tissues, & serosa of the digestive & respiratory structures Heart & most blood vessels –Somatic mesoderm forms: Dermis of skin, bones, & ligaments

27. (a) Embryo, day 24 Future gut (digestive tube) Somatic mesoderm Splanchnic mesoderm Lateral fold Yolk sac Coelom Somite Tail Intermediate mesoderm Notochord Ectoderm Mesoderm Endoderm Head The Germ Layers in Week 4

28. (b) Embryo, day 28 Kidney & gonads (intermediate mesoderm) Gut lining (endoderm) Parietal serosa Limb bud Somatic mesoderm Dermis Visceral serosa Splanchnic mesoderm Smooth muscle of gut Epidermis (ectoderm) Dermatome Myotome Sclerotome Peritoneal cavity (coelom) Neural tube (ectoderm) Somite Ectoderm Mesoderm Endoderm The Germ Layers End of Week 4

29. (c) Adult Skin Epidermis Dermis Lining of digestive tube Muscle of digestive tube Visceral serosa Peritoneal cavity Spinal cord Vertebral column Rib Kidney Trunk muscles Parietal serosa Outer body wall Inner tube Ectoderm Mesoderm Endoderm Trunk Germ Layers & Their Adult Derivatives

30. Major Derivatives of Germ Layers

31. Ear Pharyngeal arches Eye Heart Upper limb bud Tail Lower limb bud Somites (soon to give rise to myotomes) (b)(a) A 4-Week Embryo

32. Developing Fetus

33. Developmental Events of Fetal Period

36. THE TISSUES, Ch 4

37. Tissues Cells work together in functionally-related groups called tissues Tissue –A group of closely associated cells that perform related functions & are similar in structure

38. 4 Basic Tissue Types & Their Functions Epithelial tissue  covering (Chs 4 & 5) Connective tissue  support (Chs 4, 5, 6, & 9) Muscle tissue  movement (Chs 10 & 11) Nervous tissue  control (Chs 12–16 & 25)

39. Epithelial Tissue Covers a body surface or lines a body cavity Forms parts of most glands Functions of epithelia: –Protection –Diffusion –Absorption, secretion, & ion transport –Filtration –Forms slippery surfaces

40. Special Characteristics of Epithelia Cellularity –Cells separated by minimal extracellular material Specialized contacts –Cells joined by special junctions Polarity –Cell regions of the apical surface differ from the basal surface

41. Special Characteristics of Epithelia Support by connective tissue Avascular, but innervated –Epithelia receive nutrients from underlying connective tissue Regeneration –Lost cells are quickly replaced by rapidly dividing cells; many stem cells

42. Special Characteristics of Epithelia Epithelium Connective tissue Apical region of an epithelial cell Basal region Tight junction Adhesive belt Gap junction Desmosome Basal lamina Reticular fibers Basement membrane Nerve ending Capillary Cilia Narrow extracellular space Microvilli Cell junctions

43. Classifications of Epithelia First name of tissue indicates number of cell layers –Simple  one layer of cells –Stratified  more than one layer of cells

44. Classifications of Epithelia Last name of tissue describes shape of cells –Squamous = cells are wider than tall (plate-like) ‘squashed’ = squamous –Cuboidal = cells are as wide as tall (like cubes) –Columnar = cells are taller than they are wide (like columns)

45. Classifications of Epithelia Squamous Cuboidal Columnar (b) Classification based on cell shape Stratified Simple Apical surface Basal surface Apical surface Basal surface (a)Classification based on number of cell layers

46. Simple Squamous Epithelium Description: single layer; flat cells with disc- shaped nuclei Function: –Passage of materials by passive diffusion & filtration –Secretes lubricating substances in serosae Location: –Renal corpuscles –Alveoli of lungs –Lining of heart, blood, & lymphatic vessels –Lining of ventral body cavity (serosae)

47. Simple Squamous Epithelium (a) Simple squamous epithelium Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia. Function: Allows passage of materials by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae. Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae). Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (200  ). Air sacs of lung tissue Nuclei of squamous epithelial cells

48. Simple Cuboidal Epithelium Description: –Single layer of cube-like cells with large, spherical central nuclei Function: –Secretion & absorption Location: –Kidney tubules, secretory portions of small glands, ovary surface

49. Simple Cuboidal Epithelium (b) Simple cuboidal epithelium Description: Single layer of cubelike cells with large, spherical central nuclei. Function: Secretion and absorption. Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface. Photomicrograph: Simple cuboidal epithelium in kidney tubules (430  ). Basement membrane Connective tissue Simple cuboidal epithelial cells

50. Simple Columnar Epithelium Description: single layer of column-shaped (rectangular) cells with oval nuclei –Some have cilia at their apical surface –May contain goblet cells Function: –Absorption; secretion of mucus, enzymes, & other substances –Ciliated type propels mucus or reproductive cells by ciliary action

51. Simple Columnar Epithelium Location: –Non-ciliated form Lines digestive tract, gallbladder, ducts of some glands –Ciliated form Lines small bronchi, uterine tubes, & uterus

52. Simple Columnar Epithelium (c) Simple columnar epithelium Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus- secreting unicellular glands (goblet cells). Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action. Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus. Photomicrograph: Simple columnar epithelium of the stomach mucosa (1150  ). Simple columnar epithelial cell Basement membrane

53. Pseudostratified Columnar Epithelium Description: –All cells originate at basement membrane –Only tall cells reach the apical surface –May contain goblet cells & cilia –Nuclei lie at varying heights within cells Gives false impression of stratification!

54. Pseudostratified Columnar Epithelium Function: secretion of mucus; propulsion of mucus by cilia Locations: –Non-ciliated type Ducts of male reproductive tubes Ducts of large glands –Ciliated type Lines trachea and most of upper respiratory tract

55. (d) Pseudostratified columnar epithelium Description: Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus-secreting goblet cells and bear cilia. Function: Secretion, particularly of mucus; propulsion of mucus by ciliary action. Location: Nonciliated type in male’s sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract. Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (780  ). Trachea Cilia Pseudo- stratified epithelial layer Basement membrane Mucus of goblet cell Pseudostratified Ciliated Columnar Epithelium

56. Stratified Epithelia Properties –Contain 2 or more layers of cells –Regenerate from below (basal layer) –Major role is protection –Named according to shape of cells at apical layer

57. Stratified Squamous Epithelium Description: –Many layers of cells are squamous in shape –Deeper layers of cells appear cuboidal or columnar –Thickest epithelial tissue Adapted for protection from abrasion

58. Stratified Squamous Epithelium 2 types  keratinized & non-keratinized Keratinized –Location: epidermis –Contains the protective protein keratin –Waterproof –Surface cells are dead and full of keratin Non-keratinized –Forms moist lining of body openings

59. Stratified Squamous Epithelium Function: Protects underlying tissues in areas subject to abrasion Location: –Keratinized – forms epidermis –Non-keratinized – forms lining of mucous membranes Esophagus Mouth Anus Vagina Urethra

60. Stratified Squamous Epithelium (e) Stratified squamous epithelium Description: Thick membrane composed of several cell layers; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous); in the keratinized type, the surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers. Function: Protects underlying tissues in areas subjected to abrasion. Location: Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane. Photomicrograph: Stratified squamous epithelium lining the esophagus (430  ). Stratified squamous epithelium Nuclei Basement membrane Connective tissue

61. Stratified Cuboidal Epithelium Description: generally 2 layers of cube-shaped cells Function: protection Location: –Ducts of: Mammary glands Salivary glands Largest sweat glands

62. Stratified Cuboidal Epithelium (f) Stratified cuboidal epithelium Description: Generally two layers of cubelike cells. Function: Protection Location: Largest ducts of sweat glands, mammary glands, and salivary glands. Photomicrograph: Stratified cuboidal epithelium forming a salivary gland duct (285  ). Cuboidal epithelial cells Basement membrane Duct lumen

63. Stratified Columnar Epithelium Description: several layers; basal cells usually cuboidal; superficial cells elongated Function: protection & secretion Location: –Rare tissue type –Found in male urethra & large ducts of some glands

64. Stratified Columnar Epithelium (g) Stratified columnar epithelium Location: Rare in the body; small amounts in male urethra and in large ducts of some glands. Function: Protection; secretion. Description: Several cell layers; basal cells usually cuboidal; superficial cells elongated and columnar. Urethra Stratified columnar epithelium Underlying connective tissue Basement membrane Photomicrograph: Stratified columnar epithelium lining of the male urethra (315  ).

65. Transitional Epithelium Description: –Has characteristics of stratified cuboidal & stratified squamous –Superficial cells dome-shaped when bladder is relaxed, squamous when full Function: permits distension of urinary organs by contained urine and also expansion of uterus Location: epithelium of urinary bladder, ureters, proximal urethra, uterus

66. Transitional Epithelium (h) Transitional epithelium Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamous-like, depending on degree of organ stretch. Function: Stretches readily and permits distension of urinary organ by contained urine. Location: Lines the ureters, bladder, and part of the urethra. Photomicrograph: Transitional epithelium lining the bladder, relaxed state (390  ); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine. Basement membrane Connective tissue Transitional epithelium

67. Questions? What’s Next? Lab: Embryos and Tissues Mon Lecture: Tissues cont.; Skin Mon Lab: Tissues & Skin Rhythm of Life Dave Henniker