Development and Life History 1 PDF

Development and life history 1 BI2CV1 Comparative Vertebrate Biology Dr Manabu Sakamoto [email protected] Overview Early embryology Development of tissues and organs Body cavities Development of body regions Early embryology Early embryology S...

Development and life history 1 BI2CV1 Comparative Vertebrate Biology Dr Manabu Sakamoto [email protected] Overview Early embryology Development of tissues and organs Body cavities Development of body regions Early embryology Early embryology Stages of early embryology Zygote (fertilized egg) Morula Blastula Gastrula Neurula Embryonic area Blastula Gastrula Extraembryonic area Supports the embryo, e.g., yolk Neurula Zygote (fertilized egg) Union of two mature sex cells (gametes) forms a fertilized egg, or zygote. Zygotes are the earliest developmental stage. Yolk delivered into the egg from the mother and accumulates. Quantity of yolk varies with species. Yolk content in eggs Microlecithal Slight amount of yolk Mesolecithal Moderate amount of yolk Macrolecithal Enormous amount of yolk Distribution of yolk in the egg Isolecithal Yolk evenly distributed Telolecithal Yolk concentrated at one pole of the egg Vegetal pole Pole of egg where most of the yolk resides. Animal pole Pole opposite the yolk where the embryonic area is. Oviparity Laying eggs encapsulated in shells or other tertiary egg envelopes (exterior wrapping around the egg). Parents may incubate eggs by nestling over the eggs to add warmth. Viviparity Giving birth to embryos without shells or other tertiary egg envelopes. Embryos develops (gestated) within the female. Viviparity independently evolved over 100 times in vertebrates! Cleavage In all vertebrate groups, cleavage converts a single-celled zygote into a multicellular, hollow blastula. Cleavage Blastoderm Inner cell mass Zygote Morula Trophoblast Blastula Blastoderm Blastocoel Blastocoel Morula Blastula Cleavage Zygote Morula Blastula Blastoderm Blastocoel Gastrulation and neurulation Gastrulation Forming the endodermal tube “Gut formation” Neurulation Forming the ectodermal tube, the neural tube. “Nerve formation” Gastrulation and neurulation Three embryonic germ layers Ectoderm Endoderm Mesoderm Each germ layer develops into distinct tissues or body regions. Coelom forms within the mesoderm. Neurula Neural crest cells Key features of neural crest cells are their migratory ability and multipotency. They move to distant sites and differentiate into many different cell types. Neural crest cells only occur in vertebrates. Development of tissues and organs Tissue categories Epithelial tissue Connective tissue Muscle tissue Nervous tissue Epithelial tissue Epithelia fall into one of two groups: Membranes that line or cover cavities Glands that secrete products that act elsewhere in the body. Connective tissue Cartilage Bone Fibrous connective tissue Adipose tissue Blood Cartilage There are three types of cartilage: Hard but pliant material - mainly Hyaline cartilage polysaccharide called chondroitin Fibrocartilage sulphates, which bind with ground Elastic cartilage substance proteins to form proteoglycans Specialized cells called chondrocytes produce a large amount of extracellular chondroitin sulphate matrix interspersed with collagenous or elastic protein fibres Appearance and functional roles dependent on the number and type of the protein fibres Hyaline Cartilage Most common type of Found in cartilage in the body. Embryonic bones Consists of short and Nose dispersed collagen fibres Tips of ribs and contains large amounts Tracheal rings of proteoglycans. Articular ends of long bones No fibres are visible when viewed under light microscopy. A plate of hyaline cartilage at the ends of bone allows continued growth until adulthood. Fibrocartilage Collagen fibres are Found in abundant giving Intervertebral disks mechanical resistance to Pubic symphysis tensile forces Found under conditions where tensile or warping loads applied Elastic cartilage Predominate protein fibre Found in is elastin, which makes Internal support for ear the cartilage springy and Epiglottis flexible. Elastic cartilage gives rigid support as well as elasticity.  Bone Bone has a soft framework made of the protein collagen, impregnated with calcium phosphate, which adds strength and hardens the framework. This combination of collagen and calcium makes bone strong but flexible enough to withstand stress. Layers of bone matrix Osteo n of concentric rings Series of bone cells and layers of bone matrix around a central canal that houses blood vessels, lymph vessels and nerves Zimmerman et al. 2016. Sci Rep 6: 210 Bone cells Bone cells are classified according to their role: Osteoblasts – osteogenesis (producing new bone) Osteoclasts – remove existing bone Osteocytes – maintain equilibrium in fully formed bone Types of bone Compact Spongy or bone (dense) cancellous bone Trabecul formed of consists of bony ae osteons traberculae and bone marrow Growth and development of bones Contains epiphyseal plate, or the growth Filled with plate, a layer of yellow hyaline cartilage in marrow a growing bone Growth and development of bones Endochondral bone development Develops from cartilage – “replacement” bone Intramembranous bone development Direct development from mesenchyme tissue without cartilage precursor Endochondral ossification a) Mesenchymal cells differentiate to chondrocytes that form the cartilaginous skeletal precursors of bone. b) Hyaline cartilage is surrounded by perichondrium. c) Hyaline cartilage in core of diaphysis ossified by accumulation of inorganic salts. Entombed chondrocytes die and blood vessels invade and erode calcified cartilage to form initial spaces of marrow Endochondral ossification c) Osteoblasts appear in the core of the bone and primary centre of ossification appears. Old cartilage replaced by bone. Trabeculae form. Cartilage replacement moves to the metaphysis. d) Epiphyseal plate is last region of cartilage proliferation. Fishes, amphibians and reptiles have indeterminate growth – they can continue to grow through life. Birds & mammals have determinate growth and stop growing at maturity Endochondral ossification e) Mammals, some lizards and birds secondary centres of ossification arise in the epiphysis. f) At sexual maturity in mammals the epiphyses ossify completely. Cartilage remains at joint surface as articular cartilage Intramembranous ossification Direct development from mesenchyme tissue without cartilage precursor Dermal bone – skull, pectoral girdle and integument Sesamoid bone – associated with tendons Perichondral bone – develops early and retain ability to form bone in the adult Intramembranous ossification a) Mesenchymal cells group into clusters and ossification centres form. b) Secreted osteoid traps osteoblasts, which then become osteocytes. c) Trabecular matrix and periosteum form. d) Compact bone develops superficial to the trabecular bone and crowded blood vessels condense into red marrow. The coelom and body cavities Coelom In vertebrates, the coelom develops into body cavities. Develops within the mesoderm. Filled with coelomic fluid. Neurula Body cavities Pericardial cavity Pleuroperitoneal cavity Separated by the transverse septum Amniotes In amniotes, anterior portion of pleuroperitoneal cavity forms paired pleural cavities around each lung. Mammals In mammals, pleuroperitoneal membrane separates the pleural cavities from the peritoneal cavity. Mammals have four cavities: pericardial cavity, paired pleural cavity, peritoneal cavity. Pleuroperitoneal membrane + transverse septum = diaphragm. Development of body regions Development of the vertebral column Vertebrates replace the notochord with a vertebral column. Sclerotomes, segmented clusters of cells, gather around notochord. Differentiate into segmentally arranged vertebrae. Vertebral column protects nerve cord and provide attachment sites for muscles. Notochord persists only as a small core of the intervertebral disks. Pharyngeal region Pharyngeal arches are the segmental structures of the pharynx. Derivatives of the pharyngeal arches are phylogenetically conserved. Mandibular arch develops into the jaws. Hyoid arch supports the jaws. Five gill-bearing arches.