Anatomy Notes Week 3 PDF

Development of the embryo A) Germinal (pre-embyonic) period – first 2 weeks Zygote (single cell) pronuclei ~ 4 to 5 rapid cleavage (mitotic) cell divisions Morula – solid ball of 16–32 cells (blastomeres) formed within ~72 hr of fertilization Blastocyst formed by ~5 days embryoblast (inner cell ma...

Development of the embryo A) Germinal (pre-embyonic) period – first 2 weeks Zygote (single cell) pronuclei ~ 4 to 5 rapid cleavage (mitotic) cell divisions Morula – solid ball of 16–32 cells (blastomeres) formed within ~72 hr of fertilization Blastocyst formed by ~5 days embryoblast (inner cell mass) – future embryro blastocoel – fluid filled cavity trophoblast – single layer of trophoblast cells  will form chorion; provides nutrients to embryo Implantation 5 to 7 days following fertilization, the blastocyst enters the uterus and attaches to the endometrium Days 7-13: Following implantation, a bilaminar (two-layered) embryonic disk forms from the embryoblast trophoblast epiblast a) epiblast  cells of this layer will later develop into the three germ layers of the embryo b) hypoblast hypoblast Extraembryonic membranes also begin to form, via mitosis and cell differentiation, from trophoblast, epiblast, and hypoblast cells during the pre-embryonic period Extraembryonic membranes 1. Amnion – derived from epiblast cells  forming a fluid-filled amniotic cavity amnion amniotic cavity chorion  will later develop to surround the embryo/fetus, where it functions as a ‘shock absorber’/temperature regulator 2. Chorion – largely derived from trophoblast cells  surrounds all other extraembryonic membranes will later form the fetal part of the placenta which develops chorionic villi (site of maternal/fetal nutrient, waste, and O2/CO2 transfer) chorion  embryo amnion Extraembryonic membranes 3. Yolk sac – develops from migrating hypoblast cells  future yolk sac source of primordial germ (reproductive) cells  also will develop to form part of the gut and produce embryonic blood cells 4. Allantois – an out-pocket of the yolk sac  later develops into the umbilical cord and the urinary bladder embryo yolk sac allantois Development of the embryo B) Embryonic period – weeks 3 to 8 Epiblast cells within the bilaminar embryonic disk multiply, thus displacing hypoblast cells, and differentiate to form a trilaminar embryo composed of: i) ectoderm – develops into the nervous system and the epidermis of the skin ii) mesoderm – develops into tissues such as muscle, bone, dermis, and blood vessels iii) endoderm – develops into the epithelial lining of the urinary, digestive, respiratory, and reproductive systems and associated glands Development of the embryo Weeks 4 to 8: General human characteristics and major organ systems become almost fully developed  i.e. heart begins to beat, brain begins to develop, and limb buds differentiate C) Fetal period – weeks 9 to 40 Growth and maturation of organs continues Genetics – the study of heredity or inheritance Transfer of genetically determined characteristics (encoded by genes) from one generation to the next Recall: XX homologous pair; XY not homologous 23 chromosome → 22 autosomal pairs → pairs (somatic characteristics) 1 sex pair (Y♂/♀X) alleles – matched genes at the same location (locus) on homologous chromosomes genotype – catalogue of a person’s genetic makeup  whether gene alleles encode the same (homozygous; BB or bb) or different (heterozygous; Bb) traits phenotype – the observable expression of the genotype  e.g. curly hair, blue eyes Genetics homozygous alleles – the same allele of a particular gene on homologous chromosomes  both alleles express the same version of a given trait e.g. blond hair (bb) ♂ b or black hair (BB) ♂ B ♀ ♀ B b heterozygous alleles – different versions of the same gene on homologous chromosomes (each encodes slightly different traits)  same gene, but each allele encodes a protein with a different amino acid composition (and different phenotype) ♂ B ♂ ♀ b ♀ b B Genetics dominant allele – the allele (gene) expressed in the phenotype, regardless of any conflicting instructions from the other allele e.g. curly hair allele = C, straight hair allele = c  people with CC ♂ ♀ or Cc will have curly hair C C c c C c C c Curly hair Straight hair recessive allele – allele whose expression is hidden by the dominant allele (i.e. c in above example)  both recessive alleles must be present for the trait to be seen in the phenotype*  e.g. need cc (homozygous recessive) to get straight hair Predicting Inheritance – Punnett Square  determines the probability of inheritance  predicts characteristics of the offspring Autosomal inheritance – genes on autosomes C = curly hair (dominant); c = straight hair (recessive) ♂ gametes c c  ____% C C ♀ gametes ♀ gametes C ♂ gametes c C c of offspring heterozygous  ____% of offspring will (will have curly hair) have curly hair and ____% straight hair Sex-linked inheritance – ‘X-linked’ inheritance Inheritance determined solely by genes on the X chromosome colour blindness, hemophilia, Duchenne’s muscular dystrophy (all caused by recessive genes)  e.g. Colour blindness – ‘N’ = not colour blind, ‘n’ = colour blind Genotype Phenotype XNXN ♀ not colour blind homozygous dominant XNXn ♀ not colour blind heterozygous dominant (carrier) Xn Xn ♀ colour blind homozygous recessive XNY ♂ not colour blind Xn Y ♂ colour blind no gene on Y chromosome to mask effect of recessive allele Tissues – group of cells with similar structure/function Histology – the study of tissues Recall, there are four basic tissue types: A) epithelium  lining tissue B) muscle  contractile tissue C) connective  connecting/supporting tissue D) nervous  sensory and signaling tissue Cell connections (junctions) Points of contact between membrane proteins of adjacent cells  seen in epithelial and some nervous and muscle tissues i) tight junctions – hold epithelial cells together with tight seals  formed by the partial fusion of integral proteins on the lateral surfaces of adjacent cell membranes  prevents materials (e.g. bacteria, proteins, fluids, and ions) from passing between cells, though some tight junctions are ‘leaky’ to some substances tight junctions  stops integral membrane proteins from moving between the apical (lumen exposed) and basolateral surfaces of the cell Cell connections (junctions) ii) desmosomes (anchoring junctions) – Velcro-like protein links between cells  form ‘rivets’ that adds strength to sheets of cells (e.g. skin and cardiac tissue) and decreases the chance of tears iii) gap junctions – small ‘communication’ channels between cells formed of hollow transmembrane proteins  lets ions/small molecules to freely pass between the cytoplasm of neighbouring cells  important for cardiac and smooth muscle function (allows for synchronization of contractions) A. Epithelial Tissue Form ‘boundaries’ between the body and the environment, and between different tissues Characteristics: Covers the body surface and lines the body cavities  has a free (apical) surface Little extracellular space between cells Avascular – contains no blood vessels* Possess an extracellular layer (basement membrane/basal lamina) on the basal surface  attaches epithelium to underlying connective tissue layer; is formed by cells of both tissues A. Epithelial Tissue Functions: 1. Protects underlying tissues from injury/bacteria  e.g. stratified epithelium 2. Secretion of products  e.g. glandular epithelium 3. Allows selective passage of materials across body surfaces simple epithelium (lines digestive tract and blood vessels)  e.g. Classification of Epithelium Each epithelial subtype is given a two-part name, based on: 1. Number of cell layers simple stratified 2. Shape of cells squamous cuboidal E.g. simple squamous epithelium stratified columnar epithelium columnar Classification of Epithelium 1. Number of cell layers a) simple epithelium – single cell layer thick  important for gas, nutrient, and ion exchange  e.g. cells that line the lungs, glomeruli, and blood vessels b) stratified epithelium – more than one layer thick  physical, chemical, and biological protection  e.g. epidermis of skin c) pseudostratified epithelium – looks stratified, but isn’t  cells reach different heights, nuclei at  however,  e.g. different levels all cells sit on the basement membrane cells that line the respiratory tract (are ciliated) Classification of Epithelium 2. Shape of cells a) squamous – flat, fish-scale-like cells  for rapid diffusion or filtration of substances, or for resisting abrasion  nucleus flattened and disk-like b) cuboidal – cube shaped cells  for secretion and absorption (e.g. in kidneys)  spherical nucleus c) columnar – column shaped cells (tall and thin)  for secretion and absorption of mucous, enzymes, and other substances (e.g. in digestive tract)  nucleus elongated and near the base of the cell 2. Shape of cells d) transitional – ‘shape-changer’ cells  always stratified; basal cells cuboidal or columnar  appearance of  e.g. surface cells vary with stretching urinary bladder empty surface cells appear cuboidal full surface cells appear squamous Classification of Epithelium Glandular epithelium – ‘functional classification’  epithelial cells that function for secretion a) exocrine glands  secrete products onto body surface or into the body cavity, either directly or via a duct i) unicellular – ductless goblet cells – secrete mucous directly into digestive, urinary, reproductive, and respiratory tracts  e.g. Glandular Epithelium ii) multicellular  structurally more complex; have secretory cells and a defined duct  mucous, sweat, oil, digestive, and mammary glands b) endocrine glands  ductless glands that secrete products (hormones) directly into the extracellular (interstitial) fluid  products then enter blood or lymphatic system (for transport to target tissue/organ)  e.g. thyroid hormones thyroid gland cells B. Connective Tissue (CT) Characteristics:  cells widely separated and surrounded by an extracellular matrix  generally highly  mainly vascular (except cartilage) supports and connects other tissue types CT cell types: i) blasts – create matrix  e.g. osteoblasts, chondroblasts, fibroblasts ii) cytes – maintain matrix  e.g. osteocytes, chondrocytes, fibrocytes iii) clasts – break down matrix  e.g. osteoclasts B. Connective Tissue (CT) proteoglycans collagen Extracellular matrix: Gives most CTs their characteristics i.e. how you recognize them plasma membrane i) protein fibres  collagen (for cytoplasm strength)  elastin (stretch and  reticular (short, recoil) fine collagenous fibres; form networks) ii) ground substance (gs)  unstructured material between cells (e.g. proteoglycans) iii) water – interstitial fluid (ISF) CT Classification: 1. Connective tissue proper e.g. lamina propria a) loose CT i) areolar – binds organs together  loose arrangement of protein fibres  cells: fibrocytes, fibroblasts matrix: collagen, elastin, and a little ground substance ii) adipose – fat tissue  cells: adipocytes (can get very large; store triglycerides) matrix: very scanty, highly vascular CT classification b) dense (fibrous) CT – many fibres (mostly collagen), little ground substance i) dense regular – fibres arranged in same direction  gives strength; e.g. tendons, ligaments ii) dense irregular – fibres arranged irregularly  e.g. dermis of skin Fascia – connective tissue layers and wrappings that surround and support many body structures i) superficial fascia = layer of loose areolar and adipose CT underlying the skin ii) deep fascia = dense fibrous CT surrounding organs, muscles, bones, nerves, and blood vessels CT classification lacunae 2. Cartilage – avascular tissue (heals slowly) E.g. the hyaline cartilage of trachea, ribs, and the ends of long bones  cells: chondroblasts/chondrocytes  matrix: H2O located in lacunae (80% of matrix) Collagen and elastin fibres Ground substance contains chondroitin sulphate and hyaluronic acid CT classification spongy 3. Bone – highly vascular  cells: osteocytes/blasts/clasts in lacunae  matrix: collagen, gs, H2O  *formed of hydroxyapatite (Ca2+-phosphate salts) and proteoglycans compact i) spongy – cancellous bone  contains lattice of thin threads of bone called trabeculae ii) compact – hard bone WBC 4. Blood  cells: red platelets and white blood cells, platelets* matrix (plasma): H2O, ions, and protein molecules (e.g. fibrin – important for blood clotting)  fluid RBC C. Muscle Tissue  contractile tissue i) skeletal (striated) ii) cardiac (striated) iii) smooth (non-striated) D. Nervous Tissue  conducts electrical impulses (neurons) or supports and protects neurons (glial cells) Organs The simplest organs are epithelial membranes  formed of continuous multicellular ‘sheets’ containing both epithelial and connective tissue a) cutaneous membranes – skin  stratified squamous epithelial layer (the epidermis) epidermis basal lamina dermis  underlying layer of dense irregular CT (the dermis) Epithelial membranes b) mucous membranes – mucosa epithelium basal lamina lamina propria Line cavities that open directly to the body exterior E.g. digestive, respiratory, urinary, and reproductive systems i) epithelial layer – varies from stratified squamous to simple columnar epithelium  avascular; often contains goblet cells  apical surface in contact with the luminal space ii) underlying vascular loose CT layer  termed the lamina propria Epithelial membranes c) serous membranes – serosa Double-layered membranes that line the abdominal and thoracic body cavities and their organs  each layer is composed of a serous fluid secreting simple squamous epithelium fused to thin areolar CT areolar CT parietal layer { organ wall } visceral layer squamous epithelium serous fluid body cavity wall visceral pleura i) visceral layer (fused to organ wall) parietal pleura ii) parietal layer (fused to cavity wall) c) serous membranes – serosa Three subtypes named for their location: i) pericardium (heart) ii) pleura (lungs) iii) peritoneum (alimentary tract and abdominal organs) Synovial membranes – located within some joints  formed of synovial fluid secreting areolar CT; no epithelium