Animal Diversity and the
Body Plan
•  Much of the diversity of animal life centers
around the divergence of the body plan.
•  What are some of the important events that
shape the evolution of animal body plans?
•  These body plans have formed the framework
for subsequent natural selection as form and
function coevolve.
•  The basic animal body plan centers around
fundamental levels of organization.
Animal Diversity and the
Body Plan
•  Levels of Organization:
•  Cells organized into tissues which are organized into
organs.
•  What is this increase in complexity with increasing
levels of organization known as?
•  It is the subtle (and not-so-subtle) modifications of
basic tissues and organ systems that permit form to
match function via the process of natural selection.
Animal Diversity and the
Body Plan
• 
Tissues and types of tissues
1. 
2. 
3. 
4. 
• 
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue
Organized into organ systems
1
TISSUES
•  Sheets of cells with
similar structure and
a common function
•  Cell structure
studied by
histology
–  the study of the
microscopic anatomy
of cells and tissues
TISSUES
• 
1. 
2. 
3. 
4. 
Four basic types of
tissues:
Epithelial
Connective
Muscle
Nervous
Epithelial Tissue
•  Where?
•  Covers the outside
of body and lines
organs and cavities
within body
•  What will be
epithelial tissue
then?
2
Epithelial Tissue
•  What?
•  A protective barrier
of closely packed
cells that functions
in absorption,
secretion, sensation
detection, and
selective
permeability.
Epithelial Tissue
•  All epithelial cells are polar
•  Apical surface
–  Free service exposed to air or
liquid
–  Often covered with
specialized projections (e.g.
microvilli, cilia)
•  Basal surface
–  Attached to basal lamina
•  Layer of extracellular matrix
on which epithelium sits and
which is secreted by the
epithelial cells
•  In turn attached to reticular
lamina of underlying
connective tissue to form
basement membrane
Epithelial Tissue
•  Classified based on number of cell layers or
stratification AND shape of cells on apical
surface
3
Epithelial tissue: Stratification
•  Single layer: simple epithelium
•  Multiple layers: stratified epithelium
•  Pseudostratified epithelium is a single layer, but cells vary in
length and appear stratified.
Epithelial tissue: Shape
• 
• 
• 
• 
Squamous: Smooth, flat and very thin, as well as typically soft
Cuboidal: Shape similar to a cube
Columnar: Taller than they are wide like a cylindrical structure
Transitional: Specialized type of epithelium found lining organs that can stretch.
Because cells slide over each other, appearance can depend on whether organ is
distended or contracted.
Epithelial tissue
•  Therefore, combining by layers and shape:
•  Simple squamous
–  Thin and leaky
–  Functions in exchange of materials by diffusion
–  Where?
4
Epithelial tissue
•  Stratified squamous
–  Regenerates rapidly by cell division
–  Found on surfaces subject to abrasion
–  Where?
Epithelial tissue
•  Simple columnar
–  Involved in secretion and absorption
–  Where?
Epithelial tissue
•  Simple cuboidal
–  Specialized for secretion
–  Where?
5
Epithelial tissue
•  Pseudostratified columnar
–  When numerous functions are present
–  E.g. mucus secretion, cilia movement, absorption
–  Where?
Epithelial tissue
•  Transitional
–  Lines organs that can stretch.
–  Where?
Connective tissue
•  Binds and supports
other tissues in the
body
•  Comprised of cells
separated by nonliving material, which is
called extracellular
matrix
•  Ability to stretch and
contract passively
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Connective tissue
•  Extracellular matrix: Nonliving
web of fibers embedded in
homogeneous ground
substance (liquid, jelly-like,
solid)
•  Fibers:
•  Collagen
–  Combines strength with
flexibility
•  Elastic
–  Easily stretched but also
resilient
•  Reticular
–  Fine network of fibers, forms
soft fabric that binds connective
tissue to adjacent tissues
Types of Connective Tissue
• 
• 
• 
• 
• 
• 
• 
Loose or areolar connective tissue
Adipose connective tissue
Dense or fibrous connective tissue
Elastic connective tissue
Cartilage
Bone
Blood
Loose or areolar connective
tissue
•  Binds epithelium to
underlying tissues
•  Holds organs in place
•  Most widespread
connective tissue in
vertebrates
•  All three fiber types
present
•  Fibroblasts: secrete
protein ingredients
•  Macrophages: roaming,
amoeboid, cleanup among
the fibers
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Adipose connective tissue
•  Specialized tissue
•  Used for cushioning,
thermal insulation,
lubrication (primarily
in the pericardium)
•  Energy storage
•  Specialized cells:
adipocytes
Dense or fibrous connective
tissue
•  Forms ligaments and
tendons.
–  Tendons: Muscle to bone
–  Ligaments: Bone to bone
•  Densely packed collagen
fibers have great tensile
strength.
•  Most cells are fibroblasts
Elastic connective tissue
•  Primarily composed of
elastic fibers
•  Very elastic
•  Found in the walls of the
aorta
•  Helps to make the wall
easily distensible and
helps maintain a constant
blood flow
8
Cartilage
•  Collagen fibers embedded
in rubbery chondroitin
matrix (proteincarbohydrate complex)
secreted by
chondrocytes
•  Strong, flexible support
material
•  Chondrichthyes skeleton,
general Gnathostome
embryonic skeleton
•  Nose, ears, trachea,
intervertebral discs, joints
Bone
•  Hard, mineralized (Calcium,
magnesium, phosphate)
connective tissue in a matrix
of collagen.
•  Combination is stronger than
cartilage without being brittle
•  Secreted by osteoblasts
Bone
•  Hard, mineralized (Calcium,
magnesium, phosphate)
connective tissue in a matrix
of collagen.
•  Combination is stronger than
cartilage without being brittle
•  Secreted by osteoblasts
•  Repeating units (osteons) laid
down in concentric Haversian
system surrounding a central
canal containing blood
vessels and nerves.
•  Replaces cartilage in skeleton
in Osteichthyes
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Blood
•  Functions in transport
•  Liquid extracellular matrix is
blood plasma, which transports
dissolved nutrients, hormones,
and carbon dioxide in the form
of bicarbonate
•  Red blood cells (main
component)
–  Carry oxygen
•  White blood cells
–  Function in defense
•  Platelets
–  Function in clotting
Muscle tissue
•  Most abundant
tissue in most
vertebrates
•  Long, excitable
cells
•  Contraction via
microfilaments of
contractile
proteins: actin and
myosin
Skeletal muscle
•  Attached to bones by
tendons
•  Voluntary movement
•  Quick to contract and
fatigue
•  Striated appearance
from arrangement of
sarcomeres (contractile
units)
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Smooth muscle
•  Walls of digestive tract, urinary bladder, arteries, other
internal organs
•  Involuntary movement (e.g. churning of digestive
system)
•  Slow to contract and fatigue
•  Cells spindle-shaped
Cardiac muscle
•  Forms contractile wall of heart
•  Striated and branched
•  Relays impulses via intercalated disks:
synchronizes heartbeat
Nervous Tissue
•  Receives stimuli AND transmits
impulses
•  Basic cell is neuron
•  Dendrites conduct impulses
received from other neural cells
to the cell body of the neuron
•  Axons conduct electrical
impulses away from the neuron
–  Bundled into nerves
•  Glial cells provide support,
nutrition, and protection to
neurons
•  Concentration of neurons in
cephalic region forms brain
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Organ System I: Digestion
Digestion
•  The function of the digestive system is to
prepare food (by mechanical and chemical
breakdown) for absorption into the blood or
lymphatic system.
•  The resulting nutrients provide the energy
that animals need for growth, reproduction,
activity and life.
Digestion
•  Many different signals cause reactions
within the digestive tract.
•  Can you think of any?
•  Sight, smell, taste or even thought of
food can cause (cephalic trigger):
Salivation, gastric juice production and
gastric contraction
These all prepare the digestive tract for
food.
12
Digestion
•  Once food is in the stomach (gastric
trigger)…
•  The contents and volume initiate
reflexes that cause production of more
gastric secretions and more gastric
motility.
Digestion
•  And the food moves into the intestines
(intestinal trigger)…
•  Results in secretion of bicarbonate,
enzymes, bile, and increases
contractions to mix food with all of these
substances.
Digestion
Sensory system- used to locate food
(chemosensory, visual, electrosensory, thermosensory,
etc.)
Physical structures used to
mechanically break up food
Chemical processes that break food
into forms that can be transported in
the body and metabolized into other
molecules. (enzymatic breakdown)
Undigested material is expelled from
the animal
The inner surface of the
gastrointestinal tract is contiguous
with the external environment!
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Digestion
Basic dietary strategies:
Carnivory
Herbivory
Omnivory
Feeding structures: specialized mouthparts that assist feeding
Very diverse! Mouthparts may manipulate, suck, crush, shred,
etc.
Let s go on a tour of some interesting mouthparts…..
Snail Radula- rasping mouthparts
Cone snail: harpoon-like mouthpart
Venomous cone snails use a highly developed projectile apparatus to
deliver their cocktail of toxic conotoxins into their prey.
In fish-eating species such as Conus magus the snail detects the presence
of the fish using chemosensors in its siphon and when close enough
extends its proboscis and fires a hollow harpoon-like tooth containing venom
into the fish.
This immobilizes the fish and enables the cone snail to wind it into its mouth
via an attached filament. The fish is then digested.
cone snail hunting
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Moths and Butterflies- sucking mouthparts
Darwin s orchid:
- Nectar at end of 30cm long
spur
- Charles Darwin theorized that a
pollinator
must exist with
a tongue at least that long.
- Was not believed at the time
After Darwin's death, the predicted pollinator was discovered, a
hawk moth now named Xanthopan morganii praedicta (praedicta
meaning predicted).
Specializations in bird beaks
15
Mammal teeth
Shape of mammalian
teeth reflects the nature
of the diet.
Mouth
Mechanical breakdown
Saliva moistens and lubricates food
Enzymes in saliva (amylase) does minimal
starch breakdown
Lysozymes in saliva are also antibacterial.
Esophagus- transport food to stomach
Stomach
Reservoir for food (2-3 hours)
Food is churned into chyme (liquid food) by
mixing with gastric juices
Protein digestion begins
Usually acidic (acid needed to activate
enzymes)
16
Liver
Produces bile salts (stored in gall bladder)
to emulsify fats so they can be digested and
absorbed. (also plays many other important
roles)
Pancreas
Exocrine gland: secretes enzymes into
small intestines to digest fats, carbohydrates
and proteins.
Endocrine gland: secretes…what?
Insulin and glucagon which regulate glucose
metabolism.
Small intestines
Where the bulk of chemical digestion occurs
Where most nutrient and water absorption
occurs
With so much absorption happening, what might
characterize the small intestines?
Large surface area! Due to length, folds, villi,
microvilli and brush border
Food remains here ~3-10 hours
17
Large intestine
Some water and salts reabsorption
Bacterial fermentation of undigested food
Rectum stores waste (undigestible materials)
that exit the anus.
Surface Area!
Surface area can be increased in the gut by: increasing the
length of the gut and increasing the surface undulations.
In general, the relative length
of the gut reflects the
digestibility of the diet.
Animals with diets that are
difficult to digest often have
longer guts to increase
digestion efficiency (and
absorption of nutrients).
Carnivores generally have
shorter guts than herbivores
Like other vertebrates, ruminant Artiodactyla (including deer, cows, and their
relatives) are unable to digest plant material directly, because they lack
enzymes to break down cellulose in plant cell walls.
Digestion in ruminants occurs sequentially in a four-chambered stomach.
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Plant material is initially taken into the Rumen, where it is processed
mechanically and exposed to bacteria than can break down cellulose (foregut
fermentation).
The Reticulum allows the animal to regurgitate and reprocess particulate
matter ("chew its cud").
More finely-divided food is then passed to the Omasum, for further
mechanical processing.
The mass is finally passed to the true stomach, the Abomassum, where the
digestive enzymes break down the bacteria so as to release nutrients.
Movement through the digestive tract
•  Food moves through by involuntary
muscular contractions of the smooth
muscle tissue found in the walls of the
digestive tract.
•  Peristalsis is waves of contractions of
the longitudinal and circular muscles of
the gut.
19
Stomach
structure
•  Epithelial cells (mucosa) are linked by
tight junctions to ensure that stomach
fluids cannot leak into the tissue.
•  Gastric pits increase the surface
area.
•  Acid and mucous are secreted from
within the pits.
•  Acid is necessary for activation of
some enzymes and also protective
because it kills bacteria.
•  Peptic ulcers are caused by
Helicobacter pylori which can survive
at low pH.
Serosa
Stomach
structure
•  Submucosa is composed of
connective tissue with larger blood
and lymph vessels.
•  It senses changes in the gut lumen
(stretch and contents) and regulates
blood flow and epithelial cell
function.
•  Communicates with nervous
system.
•  Fight or flight:
•  Sympathetic signalsà inhibitory
signals that slow down digestion
•  Parasympathetic signalsà stimulate
digestive activity
Serosa
Not ALL vertebrate stomachs are acidic!
Gastric Brooding Frog, Rheobatrachus silus in southeast Queensland. In
1974 it was reported to be unique in the animal kingdom in swallowing its
eggs, incubating its young in its stomach, and giving birth to baby frogs
through its mouth. This news attracted worldwide attention, but one winter
the total population disappeared. It has not been seen for 25 years.
http://www.environment.gov.au/soe/2006/publications/emerging/frogs/index.html
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Intestinal Anatomy
Enterocytesabsorptive cells with
abundant microvilli
(brush border)
Intestinal Anatomy
Goblet cells- secret mucus
Enteroendocrine cellssecrete hormones to
regulate digestion and
nutrient assimilation
Crypt- secretes
antimicrobial substances,
also contains stem cells
that replenish the other cell
types
Intestinal Anatomy
Blood supply to each villus
ensures absorption.
Lymphatic supply to each
villus too: lacteal.
Fats are absorbed into the
lacteal.
21
Digestive Enzymes
•  Break down complex macromolecules into
forms that can be absorbed and used by
tissues.
•  Lipases- break down fats
•  Proteases- break down proteins (we ll talk
about these in a bit more detail)
•  Amylases- break down polysaccharides
(carbohydrates)
•  Nucleases- break down DNA.
•  Many animals cannot digest EVERYTHING
and rely on symbiotic bacteria in their guts.
Protein digestion
•  In order to be absorbed, proteins must
be broken down into amino acids, di- or
tri-peptides.
•  Proteases break down proteins into
shorter polypeptides.
•  Endopeptidase: breaks bonds well
within proteins- still considered
polypeptides.
Protein digestion
•  In order to be absorbed, proteins must
be broken down into amino acids, di- or
tri-peptides.
•  Proteases break down proteins into
shorter polypeptides.
•  Endopeptidase: breaks bonds well
within proteins- still considered
polypeptides.
22
Protein digestion
•  Exopeptidase: attack bonds near the
ends of proteins to produce free amino
acids or di- or tri- peptides (that can
then be absorbed).
Protein digestion
•  In mammals, protein digestion begins in
the stomach.
•  Pepsinogen is a pro-enzyme secreted in
the stomach.
•  In acidic environments, pepsinogen
unfolds and cleaves itself in an
autocatalytic fashion to create pepsin.
•  Pepsin can then cleave more
pepsinogen to create more pepsin.
Protein digestion
•  Pepsin is most active at low pH and it
preferentially breaks bonds between aromatic
amino acids.
•  Pepsin will not break bonds between ALL
amino acids.
•  Why do you think pepsin is stored as a
proenzyme?
•  Pepsin is stored as a proenzyme so that it can
be stored safely (will not digest the secretory
cell) and then released only when needed.
23
Protein digestion
•  The pancreas is also an
important exocrine gland for
protein digestion.
•  Secretes inactive proteases
through the pancreatic duct
into the small intestine.
•  Become activated in
intestine.
•  The pancreas also secretes
enzymes that break down
glycogen, triglycerides and
nucleic acids.
Lipid break down
•  Bile is produced in the
liver (contains digestive
chemicals and waste
products).
•  Bile is stored in the gall
bladder then secreted into
the small intestine through
the bile duct.
•  Bile salts emulsify fatsdisperse fats into small
droplets that can be
attacked by pancreatic
lipases.
•  How are fats transported
away from the digestive
tract?
What happens in your large intestines?
•  Recovery of water and salts.
•  Formation of feces- remains of food is
dehydrated, mixed with bacteria and mucus.
•  Bacteria ferment undigested carbohydrates…
may produce socially embarrassing gases!
•  Bacteria also synthesize vitamins; e.g. vitamin K
is essential for normal blood clotting.
•  Normal feces: 75% water, 25% food waste and
bacteria
•  Color is due to compounds from bile that are not
absorbed.
•  Smell is produced by bacteria.
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Water Balance
•  In the process of producing and secreting
various digestive juices, the GI tract passes a
large quantity of water into the gut lumen.
•  In humans, this volume is usually ~8L/day (1.5 X
blood volume)
•  Clearly you do not lose this much through your
digestive system (à dehydration)
•  Nearly all is recovered by the intestines- most
occurs by solute uptake with water following by
osmosis. Note we cannot directly pump water!
Fluid Entering GI
Lumen
1500 ml (food and beverage)
1500 ml
2500 ml
500 ml
1500 ml
1500 ml
1000 ml
10,000 ml
Fluid Absorbed
Hormones act to
enhance or inhibit
water absorption (by
altering solute uptake).
9,000 ml
850 ml
150 ml
10,000 ml
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