• Some cells live just a day, liver 1 month etc. variable time • 2 copies in genome (us) crossing over occurs in gametes. Following s phase: 4 copies of every chrom. Duplication to get 2 daughter cells.
• G1- GROWING IN VOLUME. Most variable time in life. Check point: division of cell okay? Screening: bad: won’t copy genome, stops uncontrolled cell replication • G0: leaves cell cycle that cant divide again. E.g. Satellite cells (transiently there) • S Phase: (before mitosis) duplication of genome. Check point 2: copy of chromosome okay? No= stops cell dividing. If checkpoint goes bad: cancer e.g. p53. • G2: gets cell ready to divide (mitosis entry: so stock up on ATP) In mitosis no gene expression! Cant make new energy. (short prd of time) • 5 stages of mitosis: prophase, prometa, meta, ana, tela (defined by nucleus underlying mitosis) 2. Disassemble cytoskeleton. Microtubules form spindle only during mitosis: transport vesicles, nucleus) NO ROADWAY: so no exocytosis, endosytosis • Cytokinesis: division of cytoplasm. Overlaps with telophase. Microfilament (actin filaments) acts as belt, cuts into 2. • Meiosis diff to Mitosis : does it twice: but no duplication again: so get haploid. Crossing over. No duplication. Recombination occurs. Only 1 copy of every chromosome. Only in germ cells. Recomb : prophase 1. Indep assortment of chromosomes in meiosis 1. Progeny diff not identical.
• Female gametogenesis occurs in embryo. Oogenesis. Normally puberty: 12-13. All arrested at meiosis 1. Only complete meiosis 1 once oocyte released. (grafted follicle only, other follicles don’t complete it). Ovulated oocyte doesn’t complete meiosis 2 unless its fertilised. When it does, get a second polar body. Possible: 1st polar body also undergoes meiosis 2 then get 3 polar body. No point. • Meiosis 1 = major cause of Down’s. 1 chromosome gets left behind on spindle apparatus = 3 chrom 21’s. Instance increase with age. Aneuploidy= abnormal number of chrom. Meiosis safest when it occurs quickest, age increase, resources decrease. More env. exposure. • Male: diploid spermatogonia in testes. Around periphery of seminiferous tubule. Undergo mitosis before meiosis ( to replace itself coz it’s a stem cell). Setoli cells: support to spermatozoa. Its junctions form blood-testes barrier. • Primary spermatocyte : meiosis 1. Secondary spermatocute: meisos 2 ( cant see it coz it does it so quickly) Spermatid: round, haploid cell that’s completed meiosis, but hasn’t completed everything yet in development? Cytokinesis not completed! All progeny joing by cyto bridges? UNLIKE FEMALE 2 with x chromosomes, 2 with y. • Oocyte takes years, male takes 44 days? • Cortex thicker in infant (only primordial follicles), than older. Get germinal epithelium then cortex then medulla? Stromal cells (tiny dots?) • Medulla: large maternal blood vessels. Not many primordial oocyes here. • HUGEEE variability in number of NGF’S (oocytes) lose it by apoptosis (atresia) • Ovary lies within peritoneal cavity. Oocyte increases in volume, 4 hormones released.
• hcG synthesised by syn/blsat. Local secretion. Taken up by maternal blood through lacunae. Preserves the corpus luteum- makes progesterone which maintains uterus in secretory phase. • Placenta takes over (after placentation, get the endocrine role of placenta function) e.g. estrogen and progesterone. • Extravillous syto.blast. mixed in with maternal stroma and surround ? • Epiblast and hypoblast = week 2. Presence of endometrial to dissidual cells = indicates pregnancy. • Endometrial glands secrete onto surface, empty into lacunae (has maternal blood and endometrial glands) • Chorionic cavity= largest space. Forms placenta (chorion frondosum- week 3), few villi. Other side has a lot of villus(mothers vessels) • Conceptus: embryo and extraembryonic apparatus. • Decidua b. maternal contribution. • Decidualisation occurs over entire uterus.
• Muscle: striated mm. aren’t smooth mm., as there aren’t sarcomeres within them. However, include actin, myosin etc. • Ex/for Intramembranous ossification (in embryo have endochondral ossification-cartilage) • Ist skeleton= cartilage./ degenerates and replaced by bone. (ex/for joint cartilage of bone) • Sk. Mm. forms by same process for all types of skeletal mm. • All sk/mm originated from somites (mesoderm) which migrate into anatomical location • Somites form r/c (head to tail) • Differentiates dorsolaterally (sclerotome- receives signals from spinal cord). Dermomyotome closer to ectoderm. • Somite disperses and spreads/ 2 sclerotomes together contribute half of skel. • Vertebra= cartilage/ ossifies (primary oss.) 1st element = centre. • Dorsal portion forms dermis. (dermatome) ventral migration of dermis around body wall into limb bud. Maintains segmental pattern. Forms connective tissue/not bone or cartilage. • Myotome are precursor cells to muscle cells. NONE of these cells are mm cells. Spreads dorsally like dermatome. • Epaxial mm are from dorsally migrating myotome. • Hypaxial mm. form 3 mm layers of body walls. (interc.) Migrates into limb bud • Form flexors (ventral) and extensors (dorsal) • MM. Position themselves adjacent to cartilage • Diff to form myoblasts. (precursor) then proliferate at mm site. Under effect of growth factors. • Critical mass= depleting growth factor levels. Therefore, plasma membrane of adjacent myoblasts fuse together (unique) = multinucleated/ but no contractility. = Myotube • Don’t extend laterally but end to end • 1st = primary myotubes (not all myoblasts fuse/ they’re in the surrounding) • Differentiates/ get sarcomeres = myofibres • (not complete) quantity is not maximal. • Primary fibres , motor neurons attract to its growth factors.. (motor neuron will branch out) • Secondary myof/ adjacent fibres • Form motor unit collectively. • Mm fibres differentially/ postnatally • Pattern of innervation determines quantity.
• Meso diff into cartilage = chondro. Centre. • Overt diff. = tissue you want. • Primary ossif. Centre = bands of bone formation (cartilage) dying chondroblast releases VEGF = stimulates BV growth. To this region. Brings osteoblasts to this site. Bone is highly vascular. • Head region = second ossification centre. Also brings osteoblasts • Ongoing process = postnatally. • Notochord may form part of nucleuspulposis. • Remodelling of bone by osteoclasts/ from Haemopoeitic stem cells lying on fibrous layers covering bone. • Intramem. Ossification. Base of skull forms by endochondral ossification. (base initially is cartilaginous ossification) not completed coz brains needs to grow. Therefore there needs to be a reserve of cartilage for growth. • Ventral portion of cartilage remains as cartilage e.g. nasal septum. • Cranial vault = intramemb. Except sutures / mesenchyme which don’t ossify (to expland/pass through birth canal)
|Uploading Images in 5 Easy Steps|
|First Read the help page Images and Copyright Tutorial.
Students cannot delete images once uploaded. You will need to email me with the full image name and request deletion, that I am happy to do with no penalty if done before I assess.