Chapter 2. Vertebrate Structure Relationships: in Phylum Chordata, Subphylum Vertebrata

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Chapter 2. Vertebrate Structure

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Relationships: in Phylum Chordata, Subphylum Vertebrata

– Chordate Characters

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Notochord

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Dorsal hollow nerve cord

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Muscular postanal tail

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Endostyle (mucus secreting groove – homologous to thyroid)

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Pharyngeal slits

Other Chordate characters

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Deuterostomic development

– Shared with echinoderms and hemichordates

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Triploblastic (ectoderm, mesoderm, endoderm)

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Coelomate

Nonvertebrate Chordates

„ Subphylum Urochordata (Tunicates)

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– Tadpole has all characters

Subphylum Cephalochordata (lancelets)

– Adult has all characters, plus others

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Circulatory system, embryonic induction

– “amphioxus”

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Pikaia

– Burgess Shale chordate

– Myomeres, notochord – Early Cambrian

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Haikouella

– Chengiang of China (Early Cambrian)

– Enlarged brain, eyes, pharynx with gill tissue and bars (neural crest)

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Definition of a Vertebrate

Vertebral column surrounding nerve cord

– Can be bony or cartilaginous

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Hagfishes lack

Cranium – bony, cartilaginous, fibrous

– Hagfishes have – “Craniates”

Duplication of Hox gene complex

– Directs development of segments

Neural Crest tissue – a 4 th

Tissue layer?

– Forms new head structures

Large, tripartite brain

– Forebrain, midbrain, hindbrain

Basic Vertebrate Structure

„ Embryology

– No “ontongeny recapitulates phylogeny”

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But embryology gives clues to phylogeny

– Ectoderm: epidermis, nervous system, sense organs

– Endoderm: lining of gut and glands, respiratory surfaces

– Mesoderm: everything else (muscles, skeleton, blood, connective tissue, urogenital system)

– Neural Crest: bones and muscles of head, peripheral nervous system, adrenal glands, melanocytes

Adult tissue types

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5 basic types:

– Epithelial, connective, blood, muscular, nervous

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Collagen – component of most – fibrous protein

– Forms ligaments, matrix of bone, etc. (mesodermal derivatives)

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Elastin – stretchy protein

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Keratin – protein in tetrapods – forms hair, scales, feathers, horns, beaks, baleen

– Epidermal derivatives

Integument

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External covering – skin and derivatives

– Glands, hair, scales

– Epidermis – (ectodermal)

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Boundary, sensory

– Dermis – (mesodermal and N.C.)

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Muscles and blood, melanocytes

Mineralized tissues

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Hydroxyapatite – mineral unique to vertebrates

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Major mineralized tissues:

– Bone (50%)

– Dentine (90%)

– Enamel (99%)

– Cartilage (sharks) – slightly mineralized

– Enameloid (in fishes)

– Cementum – holds teeth in sockets

Bone

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Produced by osteocytes

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Living tissue

– In amniotes – arranged in Haversion systems

– Compact bone on outside – cancellous bone inside

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2 types: Dermal (ancestral) and endochondral

(replacement)

Bone (cont.) and Teeth

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Early vertebrates (ostracoderms) had dermal bone on outside, cartilaginous internal skeleton

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Replacement bone allows growth

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Teeth

– Inner dentine outer enamel or enameloid

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Similar to shark scales

Skeletomuscular System

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Notochord – vacuolar cells

– Retained in agnathans

– Forms part of intervertebral disks

„ Cranial Skeleton

– Chondrocranium – surrounds brain

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Replaced by bone in derived vertebrates

– Splanchnocranium – pharyngeal arches

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Forms jaws and throat structures in derived

– Dermatocranium – derived from dermal bone

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Forms most of skull – lost in cartilaginous fish

Axial Skeleton and Muscles

„ Vertebrae

– Centrum (surrounds and obliterates notochord)

– Neural arch (surrounds nerve cord)

– Hemal arch (caudal vertebrae)

– Projections (apophyses) for muscle or rib attachment

– Tetrapods – zygapophyses allow interlocking to resist gravity

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Myotomes folded (W shape) across several vertebrae

– Epaxial and hypaxial muscles

Appendicular Skeleton and Muscles

„ Limbs and limb (fin) girdles

– Pectoral girdle anchors forefins (limbs)

– Pelvic anchors hind fins or limbs

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Fins

– Basal elements, radials, rays

– Lobefin fish extend basals and radials

„ Limbs

– Bony extensions (e.g. humerus, radius ulna, carpals, metacarpals, phalanges)

Locomotion

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Muscle contraction against notochord or skeleton

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Lateral trunk – fish, amphibs, limbless tetrapods

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Limb motion/lateral – amphibs reptiles

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Limb motion/vertical - mammals

Feeding and Digestion

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Mechanical and Chemical breakdown

– Muscularized gut – churns food

– Enzymes chemically digest

– Stomach present only in gnathostomes

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Site of protein digestion

– Liver and pancreas secrete enzymes into intestines

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Fat and carbohydrate digestion

– Primitively – no large and small intestine

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Empties into cloaca (common house)

Respiration and Ventilation

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Cutaneous respiration in some verts.

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Most have specialized structures

– Lungs, gills

– Large surface area for exchange

Cardiovascular System

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Blood – erythrocytes, leukocytes, thrombocytes (platelets in mammals)

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Arteries, veins, capillaries (exchange sites)

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Portal systems – between cap beds

– Hepatic portal system

Cardiovascular System (cont.)

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Heart

– Primitively, 3 chambers:

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Sinus venosus, atrium, ventricle

Gnathostomes add conus arteriosus after vent.

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Blood flows to ventral aorta, up through aortic arches in gills

– Some goes to head (carotid arteries)

– Rest goes to dorsal aorta to trunk

– Cardinal veins return blood to sinus venosus

Excretory System

„ Kidneys – remove nitrogenous waste, regulate osmotic potential of fluid

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Primitively – 3 portions along length

– Pronephros (in hagfishes)

– Mesonephros

– Metanephros

– Fishes and amphibs have meso and metanephric portions (opisthonephric)

– Amniotes have only metanephric kidney drained by ureter

Reproductive System

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Testes and ovaries produce gametes

„ Ovaries produce estrogen and ova

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Testes (seminiferous tubules) produce sperm and testosterone

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Agnathans – gametes move through coelom to pores

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Gnathostomes – gametes move through tubes

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Oviparous vertebrates vs. viviparous

– Some overlap (lecithotrophic viviparity vs. matrotrophic viviparity)

Coordination and Integration: Nervous System

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Dual system unique to vertebrates

– Somatic nervous system (voluntary)

– Visceral nervous system (involuntary)

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Autonomic (motor part of visceral)

– Sympathetic (fight/flight)

– Parasympathetic (digestion, relaxation)

Coordination and Integration

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Brain Anatomy and Evolution

– Hindbrain (rhombencephalon)

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Myelencephalon (medulla oblongota) – basic functions (respiration)

Metencephalon (cerebellum) – coordination

– Midbrain (mesencephalon) – optic input

– Forebrain (prosencephalon) – smell

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Diencephalon – pituitary and hypothalamus

– Hormonal controls

Telencephalon – cerebrum – coordinates higher activities

Sense Organs

„ Lateral line system – vibrations in water (neuromast organs)

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Smell and taste – chemoreception

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Vision – electromagnetic reception

– Retina with rods and cones

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Electroreception – primitive – aquatic

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Balance and hearing – mechanoreception

– Hair cells

– Inner ear – semicircular canals, vestibular apparatus, cochlea

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