Comparative Anatomy Lecture Notes

COMPARATIVE ANATOMY LECTURE NOTES

LECTURE 1 Origin and Diversity

LECTURE 2 Diversity and Phylogeny

LECTURE 3 Diversity and Phylogeny

LECTURE 4 Biological Design

LECTURE 5 Life History

LECTURE 6 The integument

LECTURE 7 Cranial skeletons

LECTURE 8 Post-cranial skeletons

LECTURE 9 Muscles

LECTURE 10 The Respiratory System

LECTURE 11 The Circulatory System

LECTURE 12 The Digestive System

LECTURE 13 The Urogenital System

LECTURE 14 The Endocrine System

LECTURE 15 The Nervous System

LECTURE 16 Senseory organs

Introduction, Origin and Diversity

Comparative anatomy is a subject about forms, their functions, and their evolution.

function
structures / similar / different
similar / phylogeny
/convergence
/parallelism / evolution
different / independent evolution
/convergence / nothing to compare

As Mayr put it, biology is a mixture of two quite distinct realms: functional biology is reducable to the level of physical sciences; while historical biology is not reducable; it has to be considered in terms of phylogeny, and the unique evolutionary history of the group being studied.

Generally, disciplines in biology belong to only one realm. Biochemistry, physiology, and molecular biology are examples of the functional biology; examples of historical biology are topics such as systematics, genetics, and evolution.

Comparative anatomy is one of the few disiplines whose explanations are partly functional and partly historical. A state found in an organism is determined not only by the physical aspects of the design, but is determined also by the history of the lineages. Physical part is a universal phenomenon, but the history of the organism is unique.

terms and concepts

phylogeny: inheritance

evolution: modification and inheritance

convergence: found in distantly related groups; evolved independently.

parallelism: found in closely related groups; evolved independently.

independent evolution/convergence: unrelated groups

Names and events:

1. evolution

Carolus Linnaeus (1707-1778): species unchanged; used characters to group organisms

Jean Baptiste de Lamarck (1744-1829): progressive change of characters (and species) dictated by use or disuse

Alfred Russel Wallace (1823-1913): survival of the fittest

Charles Darwin (1809-1882): survival of the fittest, tree of life

2. morphology/comparative methods

Georges Cuvier (1769-1832): form and function/comparative methods/species immutable

Richard Owen (1804-1892): archetypes/homology

Morphological concepts receive information from anatomy, physiology,

receive insights from phylogeny and paleontology

Functions and Biological Role

Preadaptation: structures evolve not with a purpose, but with a 'potential'

Remodeling: evolution is not about inventing new things, it is mainly about switching/alteration

pharyngeal slits: filter-feeding; gills: gas exchange

fins: balance; limb: propulsion; fore-limbs: grasping, making gestures

Phylogeny is based on cladistic methods. Phylogeny is not a fact, but a hypothesis that is constantly being challenged.

homology can be ancestral (primitive) or evolved (derived)

only shared derived homology (synapomorphy) diagnoses a monophyletic group

Analysis of vertebrate design, three steps

1. THE QUESTION: not so easy as it sounds. Use tools to help define the questions, such as dissection, taxonomy,

2. THE FUNCTION: detect and describe performance using various recording techniques

3. BIOLOGICAL ROLE: pronghorn's high speed not for escaping predator, but to move between scattered resources.

Diversity and Phylogeny

Chordate Phylogeny

determine primitive and derived characteristics

discover monophyletic groups

understand character evolution

Phylum Chordata

Urochordata

Cephalochordata

Craniata (Vertebrata)

Synapomorphies

Chordata: notochord, pharyngeal slits, endostyle, dorsal hollow nerve cord, postanal tail

Urochordata,

Cephalochordata

Craniata (Vertebrata): vertebral column(vertebral column is a new structure), head

Back-trace our ancestor From Homo sapiens:

Homo sapiens

Primates (other monkeys and apes added)

Mammalia (other hairy beasts added)

Amniota (reptiles added)

Tetrapoda (amphibians added)

Sarcopterygia (lungfish and coelacanth added)

Osteichthyes (actinopterygians added)

Gnathostomes (chondrichthyians added)

Vertebrates (lampreys added)

Craniata (hagfish added)

Chordata (cephalochordates and urochordates added)

Agnatha: a term for hagfish and lamprey combined

Gnathostomes

Chondrichthyes

Osteichthyes

Actinopterygii

Sarcopterygii

Actinistia

Choanata

Dipnoi

Tetrapoda

(early tetrapods)

Amphibia

Amniotes

Reptilia

Testudines

Diapsida

Archosauria (Croc and birds)

Squamates

Mammalia

Monotremes

Theria

Metatheria

Eutheria

Biological Design

Size:

relationships among length, area, and volume

surface area: chewing, intestinal absorption, breathing, capillaries

volume and mass: increase in mass compared to surface area

Shape:

alter length, area, and volume as animal change in size

allometry

Biomechanics

units and derived quantities

metric units

velocity, acceleration, force, power, work, pressure

torques and levers

life on land: gravity

life in fluid:

dynamic fluids: drag, boundary layer

Reynolds number: Re = ρlU / μ

ρ: density; l: shape and size; U: velocity through fluid; μ: viscosity

strength of material

forces acting on body: compression, tension, shear

Biomaterials response to stress, failure

Other physical processes important in anatomy

diffusion and exchange: pressures /partial pressure; countercurrent exchange

optics, depth perception, accommodation

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Life History

ontogeny: from fertilization, to death of individuals

embryology: from fertilization to birth, hatching

1. fertilization: the union of sperm and egg

yolk contents differs: microlecithal, mesolecithal, macrolecithal

2. cleavage: cell division

cleavage pattern differs: holoblastic, meroblastic, discoidal

yolk contents affect cleavage patterns

3. Gastrulation and Neurulation

a. the formation of blastocoel

b. the formation of blastopore

c. the formation of gut (gastrocoel):

cell movements: epibody, involution, invagination, delamination, ingression

d. the formation of neural tube (spinal cord)

e. formation of three germ layers

f. the formation of coelom:

4. organogenesis

a. histogenesis: epithelium, connective tissue

b. organs

c. neural crest and ectodermal placodes

5. extraembryonic membranes (amniotes)

amnion, chorion(ectoderm), allantois, yolk sac (endoderm)

6. maturation and metamorphosis

heterochrony can explain many of the morphological diversity

a. peramorphosis

b. paedomorphosis

7. biogenetic law and von Baer's law

a. biogenetic law (recapitulation, Haeckel): ancestor's form reappears in the ontogeny of descedents

b. von Baer's law: the resemblance between embryos of ancestors and descendents.

The integument

the most prominent and important organ

the first defense

the most versatile organ

the most conspicuous

from ectoderm and mesoderm (dermatome)

dermal scales and unicellular glands

placoid scale, cosmoid scale, ganoid scale (only enamel), teleost scale (only lamellar bone)

epidermal scales and multicellular glands

keratinized structures

reptile scale

skin lack many glands

bird feather

uropygial gland

mammal hair and glands

glands: sebacous, wax, sweat, mammary lagnds

Teeth:

specializations of the integuments

a. nails, claws, hooves

b. horns and antlers

c. baleen

d. scales

e. dermal armor

f. mucus

g. color: melanophores, iridophores, erythrophores

Cranial skeletons

the skeletal system: exoskeleton and endoskeleton

skull (cranium): from different phylogenetic and embryonic sources

splanchnocranium (visceral skeleton)

chondrocranium: endochondral bone or cartilage

dermatocranium: dermal bones

chondrocranium: floor and lateral side of brain; mostly fused to other elements, occipital series remains

splanchnocranium: from branchial arches

arch: pharyngobranchial, epibranchial, ceratobranchial, hypobranchial, basibranchial

origin of jaws:

serial theory, from an original 7 arches, 1st becomes mandibular, 2nd becomes hyoid

composite theory: 10 or more arches, complex loss and fusion forms the jaws

types of jaw attachment: how mandible (lower jaw) is attached to the skull

paleostylic: agnathans, no attachment

euautostylic: placoderms and acanthodians; to skull

hyostylic: most groups; through hyoid arch and derivatives

caniostylic: mammals, to dermal bones

dermatocranium:

facial

orbital

temporal

vault

palatal

mandibular

Phylogeny of the Skull

Jawless vertebrates: well developed sense organs, not predaceous

Gnathostomes:

placoderms: predators, skull heavily ossified

Chondrichthyans: predators, mandible and upper jaw movement

Actinopterygians: head specialized for feeding

suspensorium: causing the jaw to protrude

Sarcopterygians

Tetrapods: internal nares, flattened skull

suction feeding, buccal pumping

Amniotes:

skull fenestra: for jaw movement and closing

skull kinesis

tongue in chameleon

mammals: turbinates, tongue, secondary palate, middle ear bones

functions of skulls

prey capture

in water: suction feeding and suspension feeding

in air: swallowing

Post-cranial skeletons

Axial skeleton: notochord and vertebral column combined to define the long axis of body; for

muscle attachment, prevent telescoping of the body, and support.

vertebrae:

general morphology: neural arch, interneural arch, centra, hemal arch

regionalization: atlas, axis, cervical, thoracic, lumbar, sacral, postsacral, caudal

Centrum: shape

an important structure for phylogenetic reconstruction

Ribs: between myoseptum

dorsal and ventral

bicipital: capitulum, to parapophysis, and tuberculum to diapophysis

sternum: endochondral

Gastralia: abdominal ribs

Phylogeny

regionalization, lateral processes

Appendicular system

Fins: pectoral, pelvic

fin rays: ceratotrichia (keratinized in elasmobranch), lepidotrichia (chondrified or bony in bony fish)

LImbs

stylopodium, zeugopodium, autopodium

Origin of paired fins

gill arch theory

fin-fold theory

Limbs and girdles

pelvic girdle: endochondral

pectoral girdle: dual origin, both endochondral and dermal

Muscles

movement, heat production, electric organs

classification of muscles

skeletal

cardiac

smooth

structures of skeletal muscles

muscle cells; muscle organ, tendons (aponeurosis, fascia)

Muscle contraction:

tension-length curve for single muscle fiber

properties of muscle fibers

1. color: myoglobin

2. tonic and twitch fibers (tab 10.1)

Whole muscle contraction: combination of passive and active tension

Graded force: by rate modulation, or selective contraction of motor units.

Maximum force proportional to cross section area of muscle

fiber orientation: parallel or pinnate muscles

velocity of shortening: long muscle fibers

distance of shortening:

Bone-msucle lever system: near point of rotation, for speed; away from point of rotation, for strength

Muscle homologies

attachment similarity

functional similarity

nervous innervation

embryology (?)

embryonic origins

1. mesenchyme: smooth muscles of blood vessel walls

2. hypomere: smooth muscle of guts, to cardiace muscles

3. paraxial mesoderm: skeletal muscles

somites: in the trunk

somitomeres: in the head

cranial musculature

jaw and pharyngeal: hypobranchial muscles fro trunk somites; and branchiomeric musculature from head somitomeres.

extrinsic eye muscles: three fomitomeres

Postcranial musculature

differentiation of epaxial and hypaxial muscles

appendicular musculature: dorsal and ventral muscles, all from myotome

tetrapod pectoral and forelimb muscles from

branchiomeric

axial musculature

dorsal muscles

ventral muscles

tetrapod pelvic muscles from dorsal and ventral muscles

Cranial musculature

branchiomeric musculature: mandibular, hyoid, and branchial arches

hypobranchial

The Respiratory System

diffusion not enough for large animals which have more oxygen demands.

The rate of diffusion depends on surface area, distance, and the resistance to diffusion by the tissue.

Also important is the partial oxygen pressure. In warm and stagnant water, the oxygen may come out of the body.

Respiratory organs:

Gills: internal gills: pharyngeal slits, interbranchial septum, operculum

external gills

Lungs: trachea, glottis, bronchi, bronchioles, dead space, tidal volume

Gas bladders: pneumatic duct

cutaneous respiration

accessory air-breathing organs:

ventilation mechanisms

cilia: not for ventilation, but for clearing tract and surface.

muscular mechanisms

1. water ventilation: dual pump

2. air ventilation: buccal pump

3. air ventilation: aspiration pump

Lamprey: ammocoete: velum ventilation; adults: in and out through gill openings

hagfish: velum movement, and then from nostril to pharynx

elasmobranchs: holobranch and hemibranch, spiracle

bony fish

The Circulatory System

cardiovascular system: from mesoderm

blood

blood vessels: arteries, veins, and capillaries

blood pessure and circulation

microcirculation

single and double circulation

heart: from mesoderm; self-contractile, promote the formation of vessels.

Phylogeny

ventral aorta, aortic arches, external carotids, dorsal aorta, internal carotids, aorta, caudal arteries (paired parietal arteries, subclavian, iliac, genital, renal

portal system: hepatic and renal

basic pattern: shark example

aortic arches

heart

venous system: systemic system: three pairs in embryos: vitelline veins, cardinals, lateral abdominals

hepatic portal system: from veins of the digestive tract

Heart:

sinus venosus, sinoatrial valve, atrium; atrioventricular valve; ventricle, conus arteriosus, semilunar valve

hagfish with heart (branchial heart) and other accessory hearts (caudal, portal, cardinal)

amphibians with spiral valves in conus

special circumstances

accessory air-breathing organs: to air bladder, gut

diving: bradycardia (decreased heart rate), anaerobic metabolism increases; microcirculation changes

embryo circulations:

umbilical vein: oxy blood away from placenta to liver, half to liver, other half to ductus venosus to hepatic vein. blood in the hepatic vain joins two cava to right atrium, not to pulmonary artery, most through ductus arteriosus to dorsal aorga; in heart, foramen ovale allows most blood to left atrium

at birth: placental circulation ceases, neonate lung expand,

rise in blood oxygen stimulate the contraction of muscle in ductus arteriosus and closing it and becomes ligamentum arteriosum.

more blood in lungs, and more blood returns to left atrium, closing of the septum of foramen ovale.

ductus venosus forms from the original umbilical vein.

heat transfer: dolphin, bear skin, sinus in ungulates and carnivores

The Digestive System

digestive tracts and digestrive glands

components

buccal cavity

palate

teeth

tongue

alimentary canal

esophagus

stomach

intestines

cloaca

specializations in the alimentary canal

glands

oral glands

liver

pancreas

functions

absorption

food processing

fermentation

The Urogenital System

Structure of the mammalian kidney

medulla, cortex, calyx, pelvis, ureter, to urinary bladder, urethra.

uriniferous tubule in cortex, loops and tubules in medulla

uriniferous tubules

nephron (nephric tubule):

glomerulus

renal capsule (Bowman's capsule)

proximal, intermediate, and distal tubules

collecting tubule:

Pronephros: transitional

mesonephros: embryos, in adult amphibians called opisthonephros

metanephros: adult kidney in amniotes, duct is the ureter.

kidney phylogeny

lampreys and hagfish: anterior aglomerular pronephros (to coelom); posterior glomerular tubules to pronephric duct (archinephric duct)

most fish: pronephros functional for some time, most fish's pronephros degenerate, adn replaced with a mesonephros and into opisthonephros

Tetrapods: opisthonephros:

amniotes: embryo kidney is the mesonephros,

only mammals and some birds have loops to produce urine with concentrations greater than blood

bird loops are independently evolved

Kidney function

removing nitrogeninous waste: uricotelism, ammonotelism, ureotelism

osmoregulation: water and salt: osmoconformer and osmoregulators

water elimination: hyperosmotic animals in freshwater: filtration kidney

water conservation: hot-dry and sea: eliminate filtration need (aglomerular kidney)

REPRODUCTIVE SYSTEM

Mammalian reproductive system

genital ridge from splanchnic mesoderm; germ cells form from extraembryonic endoderm. female in cortex, male in medulla

mesonephric duct: wolffian duct: vas deference

mullerian duct: oviduct

female reproductive system

ovary: hormone and ova, mesovarium

genital duct:

hag and lamprey: eggs into coelom and through secondary pores to cloaca or anus.

elasmobranchs: mullerian duct into funnel shell gland, isthmus, uterus; archinephric duct drains opisthonephric kidney

bony fish: most have a new ovarian duct, not from mullerian duct

amphibians: both ducts normal

amniotes: metanephric duct is the ureter; oviduct persist, arthinephric duct rudimentary

oviducts

uterus

Male reproductive system

testis, mesorchium

cyclostome: no ducts, archinephric duct only urine

elasmobranchs: rudimentary mullerian; accessory urinary duct for kieney; archinephric duct for sperm (vas deferens)