Transcript Animal Form and Function Chapter 40 Fate of Embryonic Cell Layers What is a Tissue? • The human body is composed of trillions of.

Animal Form
and
Function
Chapter 40
Fate of Embryonic Cell Layers
What is a Tissue?
• The human body is composed of trillions of cells
• There are approximately 200 cell types that
make up the trillions of cells
• These 200 cell types can be further grouped into
4 categories according to their roles – these 4
categories are called tissues
• Tissues are groups of cells that function together
to keep a body alive
• These cells are held together by a sticky
extracellular matrix that either coats them or
weaves them together.
Types of Tissues
• Epithelial Tissue (endoderm and ectoderm
derived)
• Connective Tissue (mesoderm derived)
• Muscle Tissue (mesoderm derived)
• Neural Tissue (ectoderm derived)
Epithelial Tissue
Consist of 2 sub-categories:
1. Epithelium
2. Glandular
Epithelia are layers of epithelial cells that cover the
internal or external surfaces of various organs,
ducts, vessels, etc.
Glands are structures whose cells produce fluid
secretions. They are either attached to epithelia
or made from epithelia
Specialized Epithelial Tissue
• Endothelium (the inner lining of blood vessels,
the heart, and lymphatic vessels) is a
specialized form of epithelium.
• Another type, Mesothelium, forms the walls of
the
– pericardium (cavity that holds the heart),
– pleurae (cavity that holds the lungs), and
– peritoneum (cavity that holds the organs below the
diaphragm).
Characteristics of Epithelia
• Cellularity – made up entirely of cells that are closely
bound by tight junctions, gap junctions and desmosomes
• Polarity – One end of the tissue usually faces an
internal or external area of an organ (apical surface) and
the other end is either attached to other tissues or a
basement membrane called a basal lamina (basolateral
surface)
• Avascularity – Epithelia do not contain blood vessels
– they get their oxygen and nutrients from adjacent cells.
• Regeneration – Epithelial cells are constantly lost on
the exposed surface – so they are constantly replaced
by cell division of stem cells
Polarity of Epithelial Cells
What are the Functions of Epithelial Tissue?
• Provide Physical Protection – against
abrasion, dehydration and destruction from
chemical or biological agents
• Control Permeability – some allow substances
to enter / leave or pass through, other epithelial
cells are quite impermeable
• Provide Sensation – large sensory nerve
supply
• Produce Specialized Secretions – These
epithelial cells are called gland cells (Cells of the
thyroid, salivary glands, etc.) They use blood
and interstitial fluid as carriers of the chemicals
they release
Even more about epithelia
I. Epithelial cells attach each
other with tight junctions, gap
junctions and desmosomes
II. Attachment to the Basal
Lamina
Epidermal cells hold each other
as well as the basal lamina or
basement membrane
Yet more about epithelia
III. Epithelial Maintenance and Repair
Stem cells or germinative cells within the
epithelial tissue divide continually, to give
rise to new epithelial cells to replace those
that have died out due to exposure to toxic
chemicals, pathogenic bacteria, abrasions,
etc.
Types of
Epithelial Tissue
(Epithelia)
Simple Squamous
• Thin, single layer of flat cells attached to
basal membrane (lamina)
• Substances pass through very easily
• Forms walls of capillaries, lines other
blood and lymph vessels, lines insides of
certain organs (called endothelium in this
case)
• Lines alveoli of lungs
• Easily damaged!
(Mesothelium)
Simple Cuboidal
• Single layer of cube-shaped cells attached
to basal membrane
• Covers ovaries, lines tubes and ducts of
kidneys, certain glands such as pancreas,
salivary glands and liver
• Can be used to secrete glandular products
or reabsorb materials such as water (in
kidneys)
Simple Columnar
• Single layer of elongated cells, attached to basal
membrane
• Cells may or may not be ciliated on their apical
surface
• Nonciliated simple columnar epithelia lines the uterus,
parts of the GI tract and
• Can secrete digestive juices
• Because of thickness, they protect underlying tissues
• Ciliated simple columnar epithelia lines the fallopian
tubes, to move eggs
• Some line intestines and have villi and microvilli to
increase surface are for absorption
Pseudostratified Ciliated Columnar
•Appears stratified,
but is not
•Apical surface of
cells have cilia
•Line respiratory
tract
•Contain special
cells called goblet
cells that secrete
mucous to trap dust
and microorganisms
•Mucociliary
exhalator
Stratified Squamous Epithelium
Stratified Squamous
• Many layers of squamous cells, so relatively
thick
• Cells at apical surface are flattened and buildup
a protein called keratin, which protects them
from water damage, microorganisms, etc. Cell
division occurs in deeper layers where cells are
cuboidal or columnar
• Upper layer of skin (keratinized)- tough, dead
• Oral cavities, throat, esophagus, vagina, anal
canal – all non-keratinized; upper layer cells are
soft, alive.
Stratified Columnar
• Cells at apical end
tend to be columnar
(elongated) whereas
cells at the basal level
are cuboidal in shape
• Line the vas deferens,
male urethra and
areas of the pharynx
Extracellular Matrix (ECM)
• The extracellular matrix is basically connective tissue that
– provides structural support and anchorage to the cells in addition to
– performs various other important functions.
• Extracellular matrix includes the
– interstitial matrix and the
– basement membrane. Basement membranes are a sheet-like layer on
which various epithelial cells rest.
• Interstitial matrix is present between various cells (i.e., in the intercellular
spaces).
• Fibroblasts are cells found in the ECM. They make,
glycosaminoglycans, collagen, reticular and elastic fibers, and
glycoproteins found in the extracellular matrix.
Extracellular Matrix
Integrins
• Integrins are cell surface receptors that interact
with the extracellular matrix (ECM) and mediate
various intracellular signals.
• These are integral membrane proteins –
comprised of a single alpha helix.
• Integrin plays a role in the attachment of cells to
other cells, and also plays a role in the
attachment of a cell to the extracellular matrix.
• Integrin also plays a role in signal transduction,
a process by which a cell transforms one kind of
signal or stimulus into another.
Fibroblasts – the cells in found in connective tissue
• Fibroblast synthesize
several different types of
fibers :
1.Collagen - connecting
and supporting fibers,
which is a major
component of skin,
tendons, ligaments, and
bones
2.elastic fibers, which are
found, for example, in the
walls of large blood
vessels
3.reticular fibers, which
form networks inside
solid organs, such as the
liver.
Interstitial Fluid
• This is a fluid that fills all the spaces
between cells of all tissues
• It is needed for the exchange of nutrients
and wastes from capillaries and cells (It is
a good vehicle for the transport of all these
chemicals)
Connective Tissue
• Connective tissue binds together, supports, and
protects the other three kinds of tissue.
• Unlike epithelial tissue cells, the cells of
connective tissue are widely separated from
one another by large amounts of intercellular
material, the matrix, which anchors and
supports the tissue.
• The matrix comprises a :
– ground substance, which is more or less fluid and
amorphous (formless), and
– fibers synthesized by the tissue cells.
Connective Tissue
Categories
1.
2.
3.
4.
5.
6.
Loose connective tissue
Dense connective tissue (fibrous connective)
Adipose tissue
Cartilage
Bone
Blood
Connective Tissue, cont’d.
Loose Connective Tissue
Found between
muscles, under skin,
under epithelial
tissue
CONTAINS MANY
BLOOD VESSELS –
which supplies blood
to epithelial cells
• Forms thin membranes throughout body,
• Cells are mainly fibroblasts separated by a a gel-like
substance made up of loosely packed collagen and elastin
fibers which the fibroblasts secrete
Dense Connective Tissue
•
•
•
Closely packed fibers of elastin and collagen fibers,
arranged in parallel bundles
Only a few cells inside; mainly fibroblasts
Found in tendons (attach muscle to bone), ligaments
(attach bone to bone)
Adipose Tissue
•Two types of adipose cells are found in fat tissues, white and brown
adipocytes. These adipose cell types vary in their ability to mobilize energy from
stored fat. Brown fat cells are smaller and produce heat rather than ATP. Brown fat
is more typical in infants, being replaced gradually by white fat as we age. In both
cell types fat droplets enlarge to push nuclei and cytoplasm to the periphery.
Cartilage
• Rigid, structural model for
developing bones – as children
mature into adults, more and
more cartilage gets replaced by
bone
• The matrix is mainly collagen
fibers embedded in a gel-like
ground substance which is
made of protein-carbohydrates
like chondroitin sulfate and
water
• Chondrocytes (collagen and
condroitin secreting cells) lie in
the matrix in small cavities
called lacunae
Cartilage, cont’d.
• Cartilage lacks blood supply
• Cartilage heals slowly and chondrocytes do not
often divide (lack of blood supply)
• 3 Types:
– Hyaline - Most common
• Glass-like
• Found on ends of bones
» End of nose
» Rings in respiratory passages (trachea)
» Embryonic skeleton – template for bone development
– Elastic –
• Very flexible, found in the epiglottis and “skeleton” of external
ear
– Fibrocartilage – intervertebral discs, pubic symphysis
Bone (Osseous Tissue)
• Most rigid connective tissue
• Rigidity due to mineral salts such as
calcium phosphate and calcium carbonate
in its matrix
• Bone also contains collagen
• Contains red and yellow marrow which
forms blood cells, stores and releases
inorganic salts
Bone Tissue – active, living tissue!
• Consists of concentric layers called
lamellae, around central canals or
Haversian canals
• Each bone unit around a central
canal is called an osteon or
Haversian system
• Each central canal contains blood
vessels
• Chambers called lacunae (lacuna)
contain osteocytes which used to be
bone-making osteoblasts that have
become entrapped in their own
secretions.
• Osteocytes extend their cellular
extensions into the bone matrix
through fine tubes called canaliculi
• The cell extensions form gap
junctions with each other - this way
nutrients can pass from the blood
vessels to all bone cells quickly
Blood
• Various cell types found in a liquid matrix called
plasma
– Erythrocytes (RBCs)
• Transport O2, CO2
• Stay within blood vessels
– Leukocytes (WBCs)
• Fight infection (immune system)
• Can move from blood vessels to connective tissues
– Platelets (Cell fragments)
• Help with clotting
• Most blood cells are produced in hematopoietic
tissue like red marrow
White Blood Cell
Platelets
Red Blood Cells
Muscle Tissue
• Skeletal Muscle (voluntary muscles striated)
• Smooth Muscle (involuntary muscles –
non-striated)
• Cardiac Muscle
Skeletal Muscle
– Attach bones
– Movement can be controlled by us
– Long and narrow cells (Muscle fiber) containing
myofibrils made of actin and myosin filaments
– The myofibrils have alternating light and dark
striations
– Cells are multinucleated and have many
mitochondria
– Actin and myosin protein filaments in cells slide past
each other in response to nerve impulses and
cause muscle to contract and resume its original
shape.
Skeletal Muscle Dissected
(Plasma membrane of a muscle cell)
(Cytoplasm of a muscle cell)
(Group of Filaments)
(Muscle Cell)
(A bundle of muscle cells)
(Threads of
Myosin and
actin proteins)
Smooth Muscle
•
•
•
•
•
Called smooth because it lacks striations
Cells shorter than skeletal muscle cells
Spindle-shaped
Single, central nucleus
Forms muscles of the digestive tract,
uterus, urinary bladder, blood vessels, etc.
• Cannot be controlled – involuntary
contractions called peristalsis
Smooth Muscle Fibers cells)
Muscle Tissue, cont’d.
• Alternating contractions
of circular and
longitudinal muscles
move food along the
digestive tract, a process
known as peristalsis.
• Similar arrangements of
muscles are involved in
many other animal
functions, including, for
example, the locomotion
of the earthworm.
Cardiac Muscle
•
•
•
•
•
Found in heart only
Cells striated and joined end-to-end
Cells form branches
Single-nucleated
Special intercellular junctions between cells
is called an intercalated disc – found only in
cardiac muscle cells
• Involuntary – can even continue to function
without nerve stimulus
Cardiac Muscle
Branching
Nervous Tissue
• Found in brain, spinal cord (CNS) and peripheral
nervous system (PNS)
• Main nerve cells are called neurons
• Highly specialized
• Send impulses to each other, muscles and
glands
• Other supporting nervous tissue is made up of
cells called Neuroglial cells, which support
neurons, provide them with nutrients and help
with cell-to-cell communication
Membranes and Organs
• Two or more types of tissues working
together form an organ or membrane
• Epithelial membranes are composed of
epithelial tissue and its underlying
connective tissue
• Epithelial membranes are considered
organs!
Neurons may reach astonishing lengths. For example, the axon of a single
motor neuron may extend from the spinal cord down the whole length of the
leg to the toe. Or a sensory neuron may send a dendrite down to the toe and
an axon up the entire length of the spinal cord to terminate in the lower part
of the brain. In an adult human, such a cell might be close to 2 meters long
(5 meters in a giraffe).
Nervous Tissue
1. cell body, which contains the nucleus and
much of the metabolic machinery of the cell;
the
2. dendrites, usually numerous, short, threadlike
cytoplasmic extensions--processes--that
receive stimuli from other cells; and the
3. axon, a single long process that carries the
nerve impulse away from the cell body to other
cells or organs.
– A special junction called a synapse helps
transmit a nerve impulse from one neuron to
the next.
– Both dendrites and axons are also called nerve
fibers.
Metabolic Rate
• The amount of energy an animal uses in a given
amount of time is its metabolic rate.
• If one compared animals gram-per-gram,
smaller animals require more energy to maintain
their body weight.
– For example, a gram of mouse requires more energy
than a gram of elephant – even though, overall, the
elephant requires more total energy to maintain itself
because it is much larger.
What do we all spend our energy on?
Smaller animals use more energy
to maintain their body mass
WHY THIS INVERSE
RELATIONSHIP OF BMR
PER KG BODY MASS
TO BODY SIZE FOR
THE SAME ANIMALS?
Smaller animals lose heat more
easily so:
They use more energy to
maintain body temperature
this in turn requires them to have
a higher metabolic rate, which in
turn requires more calories, more
O2, more eating, faster breathing,
faster heart rate and so on.
Heat and Energy are always Lost
• Heat is lost (as
mechanical energy) by
the body due to all body
activities such as
digestion, cellular
respiration, reproduction,
protein synthesis, growth,
etc.
• Energy is lost (chemical
energy) in chemicals that
the body loses in urine,
sweat, feces, etc.
Temperature Regulation – Endotherms and
Homeotherms
• Mammals and Birds* are endotherms (warm-blooded).
This means they generate their own body heat by using
the heat produced by their metabolic activities
• In addition to this, most endotherms are homeotherms.
This means they maintain a fairly constant body
temperature.
• They do this mainly by adjusting the rate of cellular
respiration and by using organs such as the skin to warm
up and cool down (vasoconstriction, vasodilation and,
sweating and shivering)
*some fish, some reptiles and several insect species are “endotherms”,
believe it or not, they keep warm by moving.
Thermoregulation – Ectotherms
and Poikilotherms
• Most invertebrates are ectotherms – they
maintain their body temperature by using
the environment – basking in the sun or
going into the shade.
• They also tend to be Poikilotherms, which
means that their internal temperatures
tend to vary widely
Homeotherm, Poikilotherm
Regulators and Conformers
• A Regulator is an animal that can maintain
constant internal conditions, even if the external
environment fluctuates.
– Example – endotherms/homeotherms such as mammals
and birds
• A Conformer is an animal that allows its internal
conditions to fluctuate in response to its external
environment.
– Example – certain fish (large mouth bass) allow their
body temperature to increase or decrease with the
outside water temperature. (different from
ectotherms/poikilotherms)
– Example – certain marine arthropods are able to change
their internal solute (salinity) levels to match that of the
ocean around them
Acclimatization (a.ka. Acclimation)
• The process by which an animal adjusts to
changes in its environment such as temperature,
moisture, food, altitude, daylight changes, etc.
• Animals do this by growing/shedding fur,
increasing or decreasing level of activity, etc.
• Human examples:
– Humans need time to adjust to higher elevations by
producing more RBCs to carry more O2
– A move to a different time zone will cause the feeling
of “jet lag” or desynchronosis until the body resumes
its normal 24 hour circadian rhythm.
BMR and SMR
• BMR or Basal Metabolic Rate is the
metabolic rate of a resting, non-growing,
non-reproducing, non-stressed endotherm
with an empty stomach (fasting) at a
particular temperature.
• SMR or Standard Metabolic Rate is the
metabolic rate of a resting, non-growing,
non-reproducing, non-stressed ectotherm
with an empty stomach (fasting) at a
particular temperature
Saving Energy
• Hibernation allows animals to
conserve energy during the
winter when food is short.
• During hibernation, animals
drastically lower their
metabolism so their stored
body fat is used up at a slower
rate.
• Torpor – a shorter period of
reduced activity and
metabolism (temporary
hibernation)
Homeostasis –keeping the body’s
environment stable
(Greek - Unchanging/standing)
Pathway of Homeostatic Regulation
• Receptor – receives environmental
stimulus (Thermoreceptors in skin)
• Control center or integration center
(Hypothalamus of the Brain)
• Effector – responds to command from
control center (Eccrine sweat glands
in skin)
Example of Homeostatic Regulation
Positive Feedback
Operates for short periods of time
Example: Blood Clotting
1.
2.
3.
Receptors may or may not trigger
control center
Control center sends message to
effectors
Effectors create conditions
different from the norm
Positive feedback mechanisms
produce unstable conditions
and therefore are short lived –
such as uterine contractions, milk
and clot productions
Negative Feedback
Most feedback mechanisms in the body are negative
Example: The Control of Body Temperature
(e.g. By perspiration by skin or
shivering by muscles)
1.
2.
3.
4.
Receptor senses change or deviation from
norm
Message sent to Control center which
sends message to effectors
Effectors return condition back to normal
As conditions return to normal, effectors are
shut off
Negative feedback mechanisms bring unstable
conditions back to normal – they restore stability
I’m
so
Hot!
Cooling Down
• Radiation – heat from body radiates to cooler
surroundings (Passive and active)
• Conduction – heat from body transfers
directly to a cooler surface (your rear end
warms your seat, so it feels warm to the
touch) (Passive)
• Convection – heat from the body escapes to
cooler air around the body (Passive and
active)
• Evaporation – when sweat evaporates, it
takes body heat away with it, cooling the
body. (Active effort by body)
Heat Loss, cont’d.
In cold weather, blood vessels
constrict, so that heat is
retained in the body.
In hot weather, blood vessels
dilate, so heat is lost by
convection and radiation
Evaporative cooling
As water molecules evaporate,
they carry some of the heat with
them, thus cooling the surface
they leave behind
Warming up
• Increased Cellular Respiration rates – more heat
• Brown Fat – when brown fat is metabolized by
the mitochondria, more heat than ATP is
generated – babies and many cold-weather
mammals store brown fat
• Shivering – produces heat in many mammals
and even some insects – prior to flight in the
cold, their flight muscles shiver. Some reptiles
shiver too.
Insulation
• Reduces the flow of heat
between an animal and its
environment
– Feathers
• In winter, bird feathers are
raised - it creates a thicker
blanket of trapped air around
the bird.
– Hair
• Mammals also raise their fur in
response to the cold
– Layers of fat (adipose
tissue)
• Mammals that lack thick fur
rely on fat insulation
When we are cold, the “goose bumps”
that form are an evolutionary souvenir
of our furry ancestors and their hairraising abilities.
THE END