Vertebrate Relationships and Structure

Chapter 2

What is a vertebrate

• Classification– Kingdom: Animalia– Phylum: Chordata– Subphyla

• Vertebrata• Urochordata• Cephalochordata

What is a vertebrate?

• Is a chordate• Chordates have shared derived and

primitive characters seen in all members of the phylum

• multicellular

Shared Derived Characters of Chordates:

• Notochord– Long and dorsal, flexible rod which runs the length of

the back in some kinds – In vertebrates, the notochord appears in the embryo and

then later develops into part of the backbone. – Made from cartilage– The notochord serves as the skeletal structure and

support of all chordates, and it is from the notochord that chordates derive their name

Shared Derived Characters of Chordates

• Dorsal Hollow Nerve Cord– A bundle of nerve fibers which runs down the

back . – The dorsal nerve cord lies directly above the

notochord : supported by the notochord– Connects brain and with lateral muscles and

other organs

• Muscular Post-anal tail– Represents posterior elongation of body beyond anus.

– A postanal tail (post = behind, after; anal refers to the anus) is present and extends behind the anus in many taxa, thus the anus isn’t at posterior tip of body. In humans, the tail is present during embryonic development, but is subsequently resorbed.

• Endostyle– A groove below the pharynx or throat.– Secretes mucus for trapping food during filter

feeding– Present in tunicates and cephalochordates– Homologous to the thyroid gland in vertebrates

• Pharyngeal slits– are openings through which water is taken into the

pharynx, or throat. – In primitive chordates the pharyngeal slits are

used to strain water and filter out food particles; – in fishes they are modified for respiration- gills.– Most terrestrial vertebrates have pharyngeal slits

only in the embryonic stage. – Seen in hemichordates: sister taxon

• pharyngeal slits are only present in the human fetus

Shared Primitive Characters

• Bilateral symmetry• Coelomate body plan• Segmentation• Deutrostome developments

– Chordates are deutrostomates– In deutrostomes the anus comes from an early opening

called a blastopore. Initial opening of the digestive tract is the anus

– Mouth develops later

Sister Taxon to Chordates: next of Kin

• Closest non-chordate relatives– Hemichordates and– Echinoderms

• Shared Primitive Characters include– Bilateral symmetry– Coelomate body form– Segmentation– Deutrostome development– Pharyngeal slits only seen in Hemichordates

Sister Taxon to Chordates: next of Kin

• Modern Echinoderms lack the pharyngeal slits

• May have existed in extinct individuals, hence further away from the chordates compared to hemi-chordates

• See figure 2.1

Non-vertebrate Chordates: Subphylum: Urochordate

• Relative of vertebrates in phylum chordata• Represented by tunicates (or sea squits)• Sessile marine animals (invertebrates):

attach to the sea-bed• Filter feed food particles: have an endostyle

and pharyngeal slits for filter feeding.• Have a notochord, dorsal hollow nerve cord

and post-anal tail

Urochordate

• In general little resemblance to vertebrates• Start off as tad-pole like larva with a notochord.• Several authors have argued for the urochordata to

be the sister taxon of vertebrates. Early verts. Possibly originated from a tunicate-like larva that became sexually mature without metamophorphosis to the adult body plan thru a process called paedomorphosis.

Non-vertebrate Chordates: Subphylum: Cephalochordate

• ~ 22 speciec• Small, fishlike marine animals (,5 cm)• Lancelets are common bottom-dwelling forms that

possess all four chordate characteristics (a notochord, dorsal tail, etc)

• Commonly called amphioxus or Brachiostoma• No distinct head or tail; both ends sharp or pointed• Sedentary as adults; pharyngeal slits for filter

feeding• See figure 2.2 (a, b)

Cephalochordate

• Contain myomeres (muscle fiber blocks)• Body divided by myomeres• Notochord extend the whole body• Gas exchange is by diffusion• Coelom- internal body cavity• External boy cavity called atrium which opens

outside thru an atriopore• Atrium lost in vertebrates: primitive trait

Why are sister taxon to vertebrates

• Shared derived characters– Muscle segments– Circulatory system with a heartlike structure– Excretory tissue is formed from cells called

podocytes: – No kidneys in amphioxus

Subphylum Vertebrata

• Define a vertebrate– Members of Phylum chordata– Show major chordate features

• A. Vertebral column/backbone– Typical feature– Surround and protects main nerve cord– Replaces original notochord after embryonic

development– Fishes: vertebrae is made up of cartilage or bone.

Vertebral Column: Centrum

• The centrum is the main bony disk-shaped or spool-shaped portion of the vertebra; it forms around, and usually replaces, the notochord. On the dorsal side of the centrum is the neural arch, through which the nerve cord or spinal cord passes. It is the main body of a vertebrae

• In jawed fishes, it is the bony portion of the vertebrae that surrounds the notochord; Jawed fishes retain a notochord into adultwood

• Seen in jawed fishes (Gnathostomes)

Cranium

• Skull, surround the brain• Hagfishes (jawless vertebrate: agnatha) have

remnants of cranium but no vertebrae• Lampreys (jawless vert, agnatha) have a

rudimentary cartilaginous vertebrae• Craniata

– Name proposed to replace vertebrata since Hagfishes have no vertebrae but are in the subphylum

– However, loss of vertebral elements maybe derived, hence hagfishes included with hagfishes.

Hox gene complex duplication

• Belong to the homeobox gene family.  • The homeobox gene family encodes a

cluster of genes that encode a specific body part. Thus regulate other genes that code for the shape of the body

• Thus control regional differentiation during embryonic development

Neural Crest tissue

• Believed to be a 4th embroyonic germ tissue (besides, endoderm, ectoderm, mesoderm)

• Vertebrates are quadroblastic with 4 germ layers• N. tissue gives rise to

– Head tissues– Peripheral nervous system– Adrenal glands– Pigment cells in the skin (melanocytes)– Secretory cells of the gut– Smooth muscle tissue lining the aorta

3-part Brain

• Forebrain, midbrain, hindbrain• Brain of cephalochordates is undivided• Telencephalon

– Portion of the forebrain that bears the cerebral cortex• Area of higher processing in vertebrate

Summarize Definition of a vertebrate

• A chordate with a cartilaginous or bony endoskeleton. Shared derived characters are– Serially arranged vertebrae– Cranium– 3-part brain– Duplication of hox gene complex– Presence of neural crest.

Structure of Vertebrates

• See table 2.1 and figure 2.4

Embryology

• Study of embryonic development helpful in determining phylogeny of various organisms

• Need to be familiar with beginning of embryonic development.

Embryology: germ layers

• Three are first seen during gastrulation• This is the embryonic stage when first

primitive germ layers form

Embryology: germ layers:

• ECTODERM– Forms the epidermis (skin ), lining of the anterior &

posterior ends of the gut and the nervous system• ENDODERM

– Innermost layer- – Lining of gut and glands of the gut– Lining of respiratory structures– Liver, pancreas

Embryology: germ layers

• Mesoderm– Middele layer; last to appear– Forms muscle, notochord and skeleton,

connective tissue, circulatory system, urogenital system

– Splits to form a coelom– Coelom contains internal organs– Divided into 2 cavities

Embryology: germ layers Mesoderm

• Pleuroperitoneal cavity (Lungs and abdomen)– Around the internal organs (Viscera)– Lined by a thin sheet of mesoderm called

peritoneum• Pericardial cavity

– Around the heart– Lined by pericardium

Embryology: germ layers

• Neural Crest– 4th germ layer characteristic of vertebrates

Vertebrate Embryo: Figure 2.5

• Chordate features shown are:– Pharyngeal pouches and clefts– Pharyngeal grooves- will later become gills in fish but

dissappear in land vertebrates– Pharyngeal tissue (lining) develops into glandular

structures of the lymphatic systems• Thymus gland, parathyroid glands, carotid bodies and tonsils

– Dorsal hollow nerve cord– Notochord

Embryonic Mesoderm: 3 regions

• Dorsal mesoderm next to the nerve cord• Forms the somites (epimere). Form segmented

body parts• Somites form along both sides of the notochord.

– Segmented portion that forms • Dermis of skin• Striated muscles of the body for mvnt• Dorsal segmented muscles (epaxial)• Some epaxial muscles form the hypaxial muscles on the

ventral side of the body• Part of the vertebral column and skull

Embryonic Mesoderm: 3 regions

• Lateral Plate– Ventral embryonic mesoderm – Called hypomere– Forms all internal and non-segmented portions of the

body• Connective tissue• Blood vessels• Mesentries• Peritoneum (peritoneal and pericardial• Reproductive system• Smooth muscles of the gut• Heart muscles, smooth muscles, girdles

Embryonic Mesoderm: 3 regions

• Nephrotomes– Middle part of the mesoderm– Segmented– Links somites & lateral plate– Forms the kidneys (segmented)– Kidney drainage ducts (archinephric ducts)– Gonads (testes and ovaries)

Adult Tissue Types

• 5 kinds of tissues– Epithelial– Connective– Vascular– Muscular– Nervous

• Form larger organs

Adult Tissue Types

• Collagen– Fibrous protein in all tissues– Mesodermal protein– Part of bone, tendons, ligaments– Soft, non stretching.

• Elastin– Flexible protein, stretches, recoils and recoil. – Function s in connective tissue together with collagen. – Provides elasticity, collagen provides rigidity to

connective tissue.

Adult Tissue Types

• Keratin– is a highly fibrous protein that is the primary

material in the cells of the skin, hair and nails, horns, feathers, claws, beaks,

– the outer covering of the body

Basic Organ Systems: The Integument

• The outer covering of the body :– Skin and it derivatives

• Single organ: makes 15-20% of body • Divided into 3 parts

– Epidermis– Dermis

• Deep layer, support the epidermis, contains vascular tissue and nervous tissues

– Hypodermis• Deepest layer, stores fat (subcutaneous)• Also striated muscles

Functions of the integument

• Protection from pathogens• Exchange of materials with env• Sensation (input to NS)• Contain melanocytes: house pigment cells

– Cells contain melanin

• Prevents water loss• Secretes (mucus, poison and , sweat glands)• Stores subcutaneous fat in hypodermis

Skeleton system: made of Mineralized tissue

• Made of collagen fibers and Hydroxyapatite– Ca and P deposits– Hardy mineral resistant to acids – Resists lactic acid

Types of Mineralized tissuea. enamel

• 99% mineralized (entirely Ca and P)• In teeth of vertebrates (hardest)

– Teeth long lived, fossil records• In dermal skeleton of some fishes

– Mineralized exoskeleton– dermal bone elements are usually present in the head

region – early vertebrates (ostracoderms) had so much dermal

bone they were called 'armored fishes' • Ectodermal

b. Dentine

• Inner layer of teeth• Forms the root and inner core of the tooth

crwon• Contains cells called odontoblasts• 90% mineralized• In teeth and dermal armor of primitive

fishes• Mesodermal( formed from neural crest)

C. Cartilage

• Mineralized in sharks but not in other vertes• Forms internal skeleton in sharks and other

cartilagenous fishes• Mesodermal• Formed by cells called chondrocytes• Calcified cartilage has no blood vessels,

cannot remodel itself.

d. Enameloid

• Resembles enamel• Seen in most fishes• It’s a primitive vertebrate condition• Formed from mesodermal cells

e. Cementum

• Bone like substance that fastens the teeth in their sockets• Outer covering of a tooth’s root• Hard but thin• _____________________________• Primitive teeth of veetebrates - odontodes

– Vertebrate teeth have Outer layer: enamel or enameloid– Inner layer: dentine– Central part: pulp cavity

• Shark scales : dermal denticles: similar structure to teeth.

d. BONE

• Made of collagen fibers, protein secreting cells, hydroxyapatite

• Bone cells (osteocytes) are called osteoblasts, form bone

• 50 % mineralized• Formed by mesodermal cells• Highly vascularised, can self remodel• Osteoclasts cells that remove old bone

Types of Bone: Dermal Bone

• Develops in the skin• First type of bone to evolve in vertebrates• Formed external armor in early fishes

(ostracoderms)• Gave rise to many bones: skull, pectoral

girdle• Thus vertebrates do not only possess

endoskeleton

b. Endochondral bone

• Form inside cartilage• Becomes internal skeleton in bony fishes

and descendants• Formed in and replaces cartilage

– Cartilage destroyed by the process of calcification.

– Cartilage is then reabsorbed.

Body systems

Skeletomuscular System

• Notochord: – basic endoskeleton: a dorsal stiffening rod

along the lengths of the body

• Cranial skeleton– Cranium surroundd and protects brain– Formed by 3 compartments

Skeletomuscular System: cranium parts

• Chondrocranium– Surround brain; Formed by neural crest– Either cartilage (primitive or endochodral)

• Splanchocranium– Made from neural crest tissue– Either cartilage or endochondral

• Dermatocranium– Contain dermal bone– Cartilaginous in some fishes

Skeletomuscular System: Cranial Muscles

• Striated muscles in the head region– Transverse stripes on muscles– Connected on either or both ends to a bone and

so move parts of the skeleton• 2 types of striated muscles

– Branchiomeric• Assoc. with splanchocranium, gills, jaws• Function in feeds and feeding• Innervated by dorsal nerves from brain

Skeletomuscular System: Cranial Muscles

• Extrinsic muscles– Eye muscles: 6 in each eye– Rotate the eye ball in all vertebrates– Not seen in hagfishes– Controlled by somatic motor nerves

AXIAL SKELETON

• Includes: vertebral column, ribs, limbs, girdles, cranium parts

• Axial muscles– Myomeres (segmented muscles)– Have a V-shape in non-vertebrates (amphioxus)– W-shaped in other vertebrates (see figure 2.10)

• Lamprey (jawless) shark (jawed)

– Segmention most visible in fishes . Muscle blocks which are myomeres

Locomation

• Vertebrates characterized by mvnt• Aquatic larval forms use cilia• Larger chordates: serial contractions of

segmented muscles in truck and tail• Segmented muscles attach to notochord

Feeding & Digestion systems

• Feeding is – Process of taking food items into oral chamber– Processing (if any) e.g. chewing– Swallowing

• Digestion– Process of breaking down food into smaller

units for absorption

Digestive System

• Non-vertebrates chordates (amphioxus)– Filter feed– Digest feed in gut cells

• Primitive vertebrates: Lampreys– Filter feeding using pharyngeal slits– No stomach– No division of intestine; no rectum– Intestines open into a cloaca

• Common opening for digestive, urtinary and reproductive systems in many vertebrates

Digestive System

• Divided into – Esophagus, stomach, intestines, cecum, large

intestine, anus– Herbivores have large and digestive system– Enzymes produced by pancreas, liver, intestinal

walls, stomach lining etc.–

Respiratory System

• Allows exchange of gases between the body and the environment.

• Occurs in various ways– Aquatic: gills– Aquatic (amphioxus) cutaneous (skin)– Aquatic and terrestrial : lungs

Cardiovascular system

• Function– Transports gases, nutrients, heat throughout the body– Immunological response cells (WBC)

• Closed: blood enclosed in within vessels– Arteries: carry blood away from heart– Veins: carry blood to heart– Capillaries are sites of exchange between blood and

tissues: form capillary beds

Cardiovascular system

• Heart– Muscular heart– Pumps blood– Primitively: 3 major compartments

• Sinus venous– Mostly seen in amniotes & reptiles– Most posterior chamber– Receives blood from systemic veins

Cardiovascular system: heart

• Atrium– With valves to prevent backflow

• Ventricle – Primary pumping chamber

• Study the basic plan of the circulatory system (fig 2.11 a) for general (primitive) scheme of blood flow

Cardiovascular system: Blood Flow

• Heart ventral aortagills (for oxygen)• Gills dorsal aorta(has O2)• Dorsal aorta divides into Carotid arteries that

supply the head and mesenteric arteries that supply the gut

• From tissues blood returns to heart via cardinal veins– Anterior cardinal veins(Jugular):from head– Posterior cardinal vein: from body

Cardiovascular system:terminology

• Plasma: liquid part of blood• Hemoglobin: iron rich proteins that carry oxygen• Erythrocytes: RBC• Leukocytes: WBC• Thrombocytes: Clotting cells: Platelets• Arteriovenous anastomosis: direct connection

between arterioles and venules that bypass the capillary system. Blood by passes the capillaries

Cardiovascular system:terminology

• Presphincter muscles: muscles that regulate blood flow through the capilllaries

• Portal veins: Blood vessels that begin and end in a capillary bed. Transport substances from site of production to site of action

• Hepatic Portal veins:– Veins between GIT and lungs

• Renal portal vein: between body and kidneys

Excretory system

• Kidney is the primary organ• 2 primary functions

– Dispose nitrogen wastes: by products of pn metabolism– Regulate salt, water balance (osmoregulation)

• Development– From the nephrotome (mesomere)– Embryonic tissue between the epimere and hypomere

Excretory system: Kidney structure

• 3 regions seen at embryonic stage– 1. Pronephros

• Anterior most segment• Tubules called pronephric tubules• They form the archinephric duct• Develops early in all vertebrate embryos• Regresses in most vertebrates• Functional in embryos and hagfishes and

Excretory system: Kidney structure

• 2. Opisthonephros– Replaces the pronephros– Formed by 2 regions mesonephros (middle) and

metanephros (posterior)– Seen in fishes and amphioxus– Kidney of fishes tend to be long and segmented

Excretory system: Kidney structure

• 3. Metanephric Kidney– Includes only the metanephros– Drained by ureters– Bean shaped– Kidney of amniotes (synapomorphy)

Reproductive system

• Gonads: unsegmented, paired, posterior to body wall, lie behind the peritoneum– Ovaries:

• contains follicles (primary cells) – produce ovum• Produce estrogens, • Ovulation (Oviducts-Passageway for eggs)

– Testes• Seminiferous tubules (functional)• Produce testosterone

Reproductive system: Sertoli cells

• Sertoli cells are the somatic cells of the testis that are essential for testis formation and spermatogenesis. Sertoli cells facilitate the progression of germ cells to spermatozoa via direct contact and by controlling the environment milieu within the seminiferous tubules.

• The regulation of spermatogenesis by FSH and testosterone occurs by the action of these hormones on the Sertoli cells.

• While the action of testosterone is necessary for spermatogenesis, the action of FSH minimally serves to promote spermatogenic output by increasing the number of Sertoli cells.

Coordination and Integration: Nervous system

• Neuron= basic structural unit– Have axons, dendrites,cell bodies (have nucleus)– Axons encased in myelin sheaths– Collection of axons =

• Nerves in PNS• Tracts in CNS

• Nerve cord= spinal code– Gray matter: cell bodies– White matter: myelin covered axons– Connects brain with body, controls swimming in fish, hand reflexs

before impulse reach the brain.

Nervous system:Peripheral Nervous System

• Nerves exit from spinal cord between vertebrae

• Divided into two– Somatic nervous system– Visceral nervous system

Peripheral Nervous System: Somatic nervous system

• Voluntary system– Innervates the striated muscles of the limb– Responds to pain and temperature receptors

• Somatic motor fibers carry impulses from CNS to body muscles

• Somatic sensory fibers relay information to the CNS from muscles

Peripheral Nervous System: Visceral nervous system

• Consists of sensory neurons and motor neurons that run between the central nervous system (especially the hypothalamus and medulla oblongata) and various internal organs such as the: – heart , lungs,viscera,glands

• The actions of the system are largely involuntary • Forms the autonomic nervous system• Divided into two

– Sympathetic nervous system– Parasympathetic nervous system

Sympathetic Nervous System

• sympathetic branch of the autonomic nervous system prepares the body for emergencies: for "fight or flight".

• Stimulates heart beat • Raises blood pressure • dilates the pupils • dilates the trachea and bronchi • stimulates the conversion of liver glycogen into glucose • shunts blood away from the skin and viscera to the skeletal

muscles, brain, and heart • inhibits peristalsis in the gastrointestinal (GI) tract • inhibits contraction of the bladder and rectum

Parasympathetic Nervous System

• Parasympathetic stimulation causes – slowing down of the heartbeat – lowering of blood pressure – constriction of the pupils – increased blood flow to the skin and viscera – peristalsis of the GI tract

• In short, the parasympathetic system returns the body functions to normal after they have been altered by sympathetic stimulation.

• In times of danger, the sympathetic system prepares the body for violent activity. The parasympathetic system reverses these changes when the danger is over.

Cranial Nerves

• Nerves of the somatic nervous system• Emerge from the brain• 10 pairs in primitive vertebrates• 12 pairs in amniotes• Numbered by roman numerals• Vagus nerve (Cranial nerve 10)

– Main nerve of parasympathetic nervous system– Has mixed sensory and motor neurons

Brain Anatomy

• Forebrain– Has two parts– Diencephalon: posterior region associated with

• Pituitary gland: endocrine gland: outgrowth from the diencephalon

• Hypothalamus (the floor of diencephalon)• Pineal gland: dorsal outgrowth of the diencephalon

– Telencephalon• Is the cerebrum (cerebral hemisheres)• Associated with learning and language devt in humans• Very large in tetrapods• Tetrapods develop a neocortex: center for nervous control and

sensory integration• The of the brain, and is the most

Brain Anatomy: Midbrain

• Associated with vision• Receives input from optic nerves• In mammals forebrain has taken over

functions of the midbrain

Brain Anatomy: Hindbrain

• Two parts• Myelencephalon (medulla oblongata):

– most posterior section of hindbrain– Controls respiration, balance and hearing

• Metencephalon– Anterior portion– Develops the cerebellum

• Coordinates motor activities• Maintenance of posture

Sense Organs

• The major sensory modalities are o mechanoreception (touch and body position) o chemoreception (taste and smell) o vision (detection of light) o electroreception (detection of electrical/magnetic

fields) : mostly seen in fisheso electric discharges from fish for communication and for

sensing predators. Receptors detect electrical currentso acousticolateralis (hearing and motion)

Sense Organs

• Sense of vision– Retina light receptor center– Two photoreceptor cells

• Rods: function effectively under conditions of dim light

• Cones: differentially sensitive to light of varying wavelengths. Perceive color

Sense Organs: hearing

• Sense of hearing– Inner ear for detection of sound waves in

tetrapods and some fishes– Hair cell: basic sensory cell in inner ear- detects

fluid movement– Neuromast organs

• Clusters of hair cells and associated structures on the surface of the head and body of aquatic vertebrates.

• Detect movement of water across the body

Sense Organs: hearing

• Vestibular apparatus (membranous labyrinth)– Part of the inner ear that contain organs of balance and

cochlea (organ of hearing in tetrapods)– Found in the optic capsule of the skull and contains

tubules and sacs with fluid called endolymph– Contains the vestibular cells that are similar to hair

cells• Semicircular canals

– Jawed vertebrates have three canals.. They are structures of the inner ear containing fluid that moves through them when the head moves, signaling rotational or angular movement to the brain

– inform the brain about tilts of the head and body.

Endocrine system

The regulation and control of various functions are performed through chemicals. The chemical messengers are hormones and they are released by endocrine glands.

Made up of small organs or scattered cells in fishes but larger well defined organs in amniotes.