subphylum vertebrata the vertebrates are a large and diverse group including the fishes and...

Subphylum VertebrataSubphylum Vertebrata

The vertebrates are a large and diverse group The vertebrates are a large and diverse group including the fishes and tetrapods (animals with 4 including the fishes and tetrapods (animals with 4 limbs).limbs).

Vertebrates possess the basic chordate Vertebrates possess the basic chordate characteristics, but also a number of novel characteristics, but also a number of novel homologous structures.homologous structures.

An alternative name for the group An alternative name for the group CraniataCraniata is is actually a better descriptor for the entire group actually a better descriptor for the entire group because all members possess a cranium, but some because all members possess a cranium, but some jawless fishes lack vertebrae.jawless fishes lack vertebrae.

Important developments of the Important developments of the VertebratesVertebrates

Musculoskeletal systemMusculoskeletal system. Vertebrates possess . Vertebrates possess an endoskeleton, which is much more an endoskeleton, which is much more economical in materials than the exoskeleton of economical in materials than the exoskeleton of invertebrates.invertebrates.

It forms a jointed scaffolding for the attachment It forms a jointed scaffolding for the attachment of muscles. Initially the endoskeleton probably of muscles. Initially the endoskeleton probably was cartilaginous (it still is in jawless fishes and was cartilaginous (it still is in jawless fishes and sharks) and later became bony in many groups.sharks) and later became bony in many groups.

VertebraeVertebrae

The term vertebrate is derived from the vertebrae, which The term vertebrate is derived from the vertebrae, which are arranged in series to from the vertebral column or are arranged in series to from the vertebral column or backbone.backbone.

During embryonic development the vertebrae develop During embryonic development the vertebrae develop around the notochord, which degenerates to form part of around the notochord, which degenerates to form part of the intervertebral disks. The vertebrae also enclose the the intervertebral disks. The vertebrae also enclose the hollow dorsal nerve cord, protecting it from damage.hollow dorsal nerve cord, protecting it from damage.

The vertebrae, ribs and skull form the The vertebrae, ribs and skull form the axial skeletonaxial skeleton, , while the limbs, pelvic and pectoral girdles form what is while the limbs, pelvic and pectoral girdles form what is referred to as the referred to as the appendicular skeletonappendicular skeleton..

Important developments of the Important developments of the Vertebrates: BoneVertebrates: Bone

Bone is a uniquely vertebrate characteristic. Bone is a uniquely vertebrate characteristic.

Bone is stronger than cartilage, which makes it a Bone is stronger than cartilage, which makes it a better material to use for muscle attachment in better material to use for muscle attachment in places where mechanical stress may be high.places where mechanical stress may be high.

Bone may have evolved initially as a means of Bone may have evolved initially as a means of storing minerals and was later adapted for use in storing minerals and was later adapted for use in the skeleton. In many early vertebrates bone the skeleton. In many early vertebrates bone also provided protection against predators.also provided protection against predators.

Connective tissueConnective tissue

Cartilage and bone are mineralized Cartilage and bone are mineralized connective tissues (blood is also a connective tissues (blood is also a connective tissue).connective tissue).

Connective tissues are generally Connective tissues are generally characterized by a distinctive cell type characterized by a distinctive cell type surrounded or embedded in a surrounded or embedded in a comparatively abundant extracellular comparatively abundant extracellular matrix.matrix.

CartilageCartilage

Cartilage has lots of collagen (a type of Cartilage has lots of collagen (a type of protein) fibers embedded in a rubbery protein) fibers embedded in a rubbery matrix of chondroitin sulfate.matrix of chondroitin sulfate.

The chondroitin sulfate and collagen are The chondroitin sulfate and collagen are secreted by chondrocytes (cartilage cells) secreted by chondrocytes (cartilage cells) that are scattered in spaces throughout that are scattered in spaces throughout the matrix. the matrix.

CartilageCartilage

Collagen fibers have high tensile strength Collagen fibers have high tensile strength so they do not easily tear when stretched.so they do not easily tear when stretched.

Together the composite of collagen fibers Together the composite of collagen fibers and chondroitin sulfate makes cartilage a and chondroitin sulfate makes cartilage a strong, but somewhat flexible material.strong, but somewhat flexible material.

CartilageCartilage

There are several different types of There are several different types of cartilage that differ in structure depending cartilage that differ in structure depending on their function. on their function.

The more tensile strength required the The more tensile strength required the more collagen fibers are present. If the more collagen fibers are present. If the cartilage must be springy and flexible cartilage must be springy and flexible more elastic fibers are present.more elastic fibers are present.

Hyaline cartilageHyaline cartilage

Hyaline cartilage is the most widespread. In Hyaline cartilage is the most widespread. In embryos the skeleton is made of hyaline embryos the skeleton is made of hyaline cartilage before bone formation occurs.cartilage before bone formation occurs.

In adults hyaline cartilage occurs at the In adults hyaline cartilage occurs at the articulating surfaces of bones. It is smooth in articulating surfaces of bones. It is smooth in appearance because the matrix contains appearance because the matrix contains relatively few collagen fibers. The smooth matrix relatively few collagen fibers. The smooth matrix however is very good at resisting compression. however is very good at resisting compression.

Fibrocartilage and elastic cartilageFibrocartilage and elastic cartilage

Fibrocartilage contains lots of collagen fibers, Fibrocartilage contains lots of collagen fibers, which gives it the ability to better resist tensile which gives it the ability to better resist tensile forces. It’s found where stretching is likely to forces. It’s found where stretching is likely to occur and so occurs in the intervertebral disks occur and so occurs in the intervertebral disks and the pubic symphysis.and the pubic symphysis.

Elastic cartilage contains lots of elastic fibers Elastic cartilage contains lots of elastic fibers and is springy. Your epiglottis and ear are good and is springy. Your epiglottis and ear are good examples.examples.

CartilageCartilage

Cartilage, unlike bone, does not have a Cartilage, unlike bone, does not have a blood supply that penetrates into it to blood supply that penetrates into it to supply the chondrocytes.supply the chondrocytes.

Instead the chondrocytes are supplied by Instead the chondrocytes are supplied by long-range diffusion of nutrients and gases long-range diffusion of nutrients and gases through the matrix.through the matrix.

BoneBone

The skeleton of sharks is made of The skeleton of sharks is made of cartilage.cartilage.

Other vertebrates have an embryonic Other vertebrates have an embryonic skeleton that is made of cartilage, but skeleton that is made of cartilage, but most of the cartilage is replaced by bone most of the cartilage is replaced by bone as embryonic development proceeds.as embryonic development proceeds.

BoneBone

Bone, like cartilage, is a mineralized Bone, like cartilage, is a mineralized connective tissue. connective tissue.

Bone differs from cartilage in cell type Bone differs from cartilage in cell type (osteocytes), the composition of the matrix (osteocytes), the composition of the matrix (calcium phosphate in the form of (calcium phosphate in the form of hydroxyapatite) and in that it is hydroxyapatite) and in that it is vascularized. vascularized.

Bone is also generally much more highly Bone is also generally much more highly organized than cartilage. organized than cartilage.

BoneBone

In embryonic development hyaline cartilage is In embryonic development hyaline cartilage is replaced by bone.replaced by bone.

During this process of During this process of ossificationossification calcium salts calcium salts are deposited that seal off the chondrocytes, are deposited that seal off the chondrocytes, which then die. which then die.

Next blood vessels invade the calcified matrix Next blood vessels invade the calcified matrix producing channels and ultimately the marrow producing channels and ultimately the marrow cavity.cavity.

BoneBone

Finally osteoblasts (bone cells) are Finally osteoblasts (bone cells) are introduced and these lay down the calcium introduced and these lay down the calcium phosphate matrix that finishes the phosphate matrix that finishes the conversion of cartilage to bone.conversion of cartilage to bone.

Intramembranous bone Intramembranous bone development development

Not all bone develops via a cartilage Not all bone develops via a cartilage precursor. precursor.

Many bones are formed directly from Many bones are formed directly from mesenchyme (a tissue which consists of mesenchyme (a tissue which consists of loosely organized cells derived from the loosely organized cells derived from the mesoderm).mesoderm).

Intramembranous bone Intramembranous bone developmentdevelopment

As mesenchyme cells condense they are As mesenchyme cells condense they are supplied with a dense supply of blood supplied with a dense supply of blood vessels and produce a gel-like matrix into vessels and produce a gel-like matrix into which bars of bone matrix are deposited which bars of bone matrix are deposited as osteoblasts are introduced. as osteoblasts are introduced.

Over time the bars of bone matrix are Over time the bars of bone matrix are enlarged as new layers are laid down and enlarged as new layers are laid down and eventually the gel matrix is entirely eventually the gel matrix is entirely replaced.replaced.

Intramembranous bone Intramembranous bone developmentdevelopment

Among the intramembranous bones are dermal Among the intramembranous bones are dermal bones and sesamoid bones.bones and sesamoid bones.

Dermal bones develop within the dermis of the Dermal bones develop within the dermis of the skin. Many bones of the skull, pectoral girdle and skin. Many bones of the skull, pectoral girdle and integument are formed in this way.integument are formed in this way.

Sesamoid bones form within tendons. Examples Sesamoid bones form within tendons. Examples include the patella and the pisiform bone of the include the patella and the pisiform bone of the wrist.wrist.

Pisiform bone (D)

From http://en.wikipedia.org/wiki/File:Carpus.png

Structure of boneStructure of bone

Human bone is characterized by structures Human bone is characterized by structures called osteons. These are concentric rings of called osteons. These are concentric rings of osteocytes and the matrix laid down by them.osteocytes and the matrix laid down by them.

Nerves and blood vessels pass through a central Nerves and blood vessels pass through a central canal in each osteon and there are also diagonal canal in each osteon and there are also diagonal connections between osteons (Volkmann’s connections between osteons (Volkmann’s canals) which allow blood vessels to canals) which allow blood vessels to interconnect.interconnect.


Bone made up of osteons is found in many Bone made up of osteons is found in many different vertebrates, but it is not the only pattern different vertebrates, but it is not the only pattern of bone structure.of bone structure.

In many teleost fishes bone is acellular (there In many teleost fishes bone is acellular (there are no osteocytes within the calcium phosphate are no osteocytes within the calcium phosphate matrix). Bone in these fish is laid down by matrix). Bone in these fish is laid down by osteocytes on the surface of the bone that do osteocytes on the surface of the bone that do not become encased in their own secretionsnot become encased in their own secretions


In amphibians and reptiles bone is often laid In amphibians and reptiles bone is often laid down seasonally so that growth rings may be down seasonally so that growth rings may be apparent.apparent.

It is important to remember that bones are It is important to remember that bones are dynamic, not static. Thus, they respond to the dynamic, not static. Thus, they respond to the daily stresses imposed on them and to other daily stresses imposed on them and to other changes in the body. Forensic anthropologists changes in the body. Forensic anthropologists can infer a lot about an individual’s life and can infer a lot about an individual’s life and experiences simply by examining bones.experiences simply by examining bones.

Evolution of boneEvolution of bone

Bone occurs only in vertebrates and it has Bone occurs only in vertebrates and it has been suggested that it may have been suggested that it may have originated as a way of storing calcium or originated as a way of storing calcium or phosphate. phosphate.

Vertebrates evolved in the oceans and Vertebrates evolved in the oceans and would naturally have tended to accumulate would naturally have tended to accumulate calcium and phosphate because of their calcium and phosphate because of their high concentration in seawater.high concentration in seawater.


Calcium and phosphate are important in Calcium and phosphate are important in cellular metabolic pathways so selection cellular metabolic pathways so selection could have favored storing them. could have favored storing them.

Large stores in the skin would have Large stores in the skin would have produced a protective hard surface that produced a protective hard surface that provided protection against predators and provided protection against predators and selection could have then led to the armor selection could have then led to the armor found in early fishes.found in early fishes.

15.10

Figure 23.14

Ostracoderms


Only later did a bony endoskeleton Only later did a bony endoskeleton develop presumably under selection for develop presumably under selection for increased mechanical support.increased mechanical support.

The hard inorganic component of bone is The hard inorganic component of bone is calcium phosphate (in the form of calcium phosphate (in the form of hydroxyapatite) rather than the calcium hydroxyapatite) rather than the calcium carbonate found in invertebrates.carbonate found in invertebrates.


This difference in the form of calcium used This difference in the form of calcium used is believed to be due to the fact that is believed to be due to the fact that vertebrates have always engaged in vertebrates have always engaged in intense bursts of anaerobic activity.intense bursts of anaerobic activity.

Anaerobic metabolism produces lactic acid Anaerobic metabolism produces lactic acid which lowers blood pH. Under acid which lowers blood pH. Under acid conditions calcium carbonate dissolves, conditions calcium carbonate dissolves, which is not a desirable trait for a skeleton. which is not a desirable trait for a skeleton.


By using a skeleton of calcium phosphate By using a skeleton of calcium phosphate rather than calcium carbonate vertebrates rather than calcium carbonate vertebrates gained mechanical protection while gained mechanical protection while avoiding the problem of bone dissolution.avoiding the problem of bone dissolution.

Other mineralized tissuesOther mineralized tissues

These include These include enamelenamel and and dentinedentine which are the hard which are the hard components of teeth. Enamel forms the grinding surface components of teeth. Enamel forms the grinding surface and dentine is below. and dentine is below.

Enamel is about 99% and dentine 90% mineralized. Enamel is about 99% and dentine 90% mineralized. Bone and cartilage in contrast are both only about 70% Bone and cartilage in contrast are both only about 70% mineralized. Because enamel is so hard, teeth are the mineralized. Because enamel is so hard, teeth are the most common fossils.most common fossils.

A third important mineralized tissue is A third important mineralized tissue is cementumcementum. This . This is a bone-like substance that holds teeth in their sockets is a bone-like substance that holds teeth in their sockets e.g. in mammals.e.g. in mammals.

Important developments of the Important developments of the Vertebrates: gas exchangeVertebrates: gas exchange

Various aspects of vertebrate physiology have been Various aspects of vertebrate physiology have been upgraded to meet increased metabolic demands.upgraded to meet increased metabolic demands.

For example the pharynx, which was used for filter For example the pharynx, which was used for filter feeding in primitive chordates has had muscles feeding in primitive chordates has had muscles added that make it a powerful water pumping organ. added that make it a powerful water pumping organ.

With the conversion of the pharyngeal slits to highly With the conversion of the pharyngeal slits to highly vascularized gills the pharynx has become vascularized gills the pharynx has become specialized for gas exchange.specialized for gas exchange.

Gas exchangeGas exchange

Ancestral chordates probably depended Ancestral chordates probably depended on diffusion for gas exchange (as does on diffusion for gas exchange (as does Amphioxus). Amphioxus).

Vertebrates being more active need Vertebrates being more active need specialized gas exchange structures and specialized gas exchange structures and gills and lungs evolved to satisfy the need.gills and lungs evolved to satisfy the need.

Salmon Gills


Both gills and lungs have very large Both gills and lungs have very large surface areas to increase the area surface areas to increase the area available for diffusion of gases.available for diffusion of gases.

Gills are not self supporting and so are Gills are not self supporting and so are ineffective out of water. The conquest of ineffective out of water. The conquest of the land required the elaboration of lungs the land required the elaboration of lungs from simple vascularized sacs to much from simple vascularized sacs to much more complex structures.more complex structures.


Elaborations of the lungs include selection Elaborations of the lungs include selection for increased surface area to maximize the for increased surface area to maximize the rate of gas exchange and in birds a one-rate of gas exchange and in birds a one-way flow of air through the lung (facilitated way flow of air through the lung (facilitated by a series of air sacs) that increases the by a series of air sacs) that increases the efficiency of oxygen extraction from the efficiency of oxygen extraction from the air.air.

Cardiovascular systemCardiovascular system

Vertebrates possess a Vertebrates possess a closed circulatory closed circulatory systemsystem and this enables higher pressures to be and this enables higher pressures to be maintained in the system than is possible in the maintained in the system than is possible in the open circulatory system of non vertebrates open circulatory system of non vertebrates chordates and invertebrates.chordates and invertebrates.

Blood carries oxygen and nutrients to all of the Blood carries oxygen and nutrients to all of the body’s tissues and removes carbon dioxide and body’s tissues and removes carbon dioxide and other wastes.other wastes.


Blood vessels consist of arteries, veins Blood vessels consist of arteries, veins and capillaries.and capillaries.

Arteries have thick muscular walls to Arteries have thick muscular walls to enable them to withstand the pressure enable them to withstand the pressure generated by the heart. Arteries carry generated by the heart. Arteries carry oxygenated blood to the tissues.oxygenated blood to the tissues.


Capillaries are thin-walled (one cell thick) Capillaries are thin-walled (one cell thick) vessels where gases are exchanged with vessels where gases are exchanged with the tissues. the tissues.

They are very narrow but very numerous They are very narrow but very numerous and blood pressure drops as the blood and blood pressure drops as the blood passes through the capillary beds because passes through the capillary beds because of the overall increased diameter of the of the overall increased diameter of the tubes.tubes.


Veins have thinner, elastic walls and Veins have thinner, elastic walls and possess valves to prevent the backflow of possess valves to prevent the backflow of blood.blood.

They return deoxygenated blood from the They return deoxygenated blood from the tissues.tissues.


Circulatory systems vary among Circulatory systems vary among vertebrates from single circulation systems vertebrates from single circulation systems (as in fish) where a single heart beat is (as in fish) where a single heart beat is used to propel blood around the entire used to propel blood around the entire circuit to the double circulatory system in circuit to the double circulatory system in mammals in which blood goes to the heart mammals in which blood goes to the heart twice once to be pumped to the lungs and twice once to be pumped to the lungs and once to the tissues. once to the tissues.


Double circulatory systems have much Double circulatory systems have much higher pressure and are more efficient. higher pressure and are more efficient.

In addition, they keep oxygenated and In addition, they keep oxygenated and deoxygenated blood from mixing.deoxygenated blood from mixing.

Circulatory systems of different groups will Circulatory systems of different groups will be discussed in detail later. be discussed in detail later.

FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS

Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries

Lung capillaries Lung capillariesLung and skin capillariesGill capillaries

Right Left Right Left Right Left Systemic

circuitSystemic

circuit

Pulmocutaneouscircuit

Pulmonarycircuit

Pulmonarycircuit

SystemiccirculationVein

Atrium (A)

Heart:ventricle (V)

Artery Gillcirculation

A

V VV VV

A A A AALeft Systemicaorta

Right systemicaorta

Vertebrate circulatory systemsVertebrate circulatory systems

subphylum vertebrata the vertebrates are a large and diverse group including the fishes and...

Documents

cartilage cartilage

cartilage collagen fibers

bone bone

connective tissue cartilage

adults hyaline cartilage

chondrocytes cartilage

different types of cartilage

early vertebrates bone