Tissues, organs, and organ
systems
Which of the following are never
multicellular?
1.
2.
3.
4.
5.
Fungi
Animals
Plants
Bacteria
All can be multicellular
Outline
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Introduction-Stem cells
Kinds of Tissues
Organs
Organ systems
The skin
Disorders of the skin
Homeostasis
All human life begins with a single cell
After 3 mitotic divisions, the
individual has 8 identical cells
After many divisions, a solid
morula becomes a hollow blastula
Morula
Blastula
During gastrulation, cells begin to
differentiate
Gastrula
Gastrula invagination
Frog eggs develop similarly
In vertebrates, 3 kinds of tissue layers
(“germ layers”):
-Ectoderm: becomes skin, nervous system
-Mesoderm: bones, muscles, sex cells, etc.
-Endoderm: digestive sys, liver, glands, etc.
All the cells of your body come from
that original single cell
• The process by which
one cell becomes many
kinds of cells is called
differentiation
• There are
approximately 200 cell
types in the human
body
• And 100 trillion cells
Cell differentiation becomes more and
more specific during development
• Cells which can
differentiate into any
kind of cell are called
totipotent
• Cells which can
differentiate into more
than one cell are called
pluripotent
Cells differentiate according to signals
from their neighbors
• One of the major
promises of stem cells
comes from this fact
• Stem cells can thus be
used to heal damaged
tissue, such as nervous
tissue, cardiac tissue, or
bone marrow
Adults have some stem cells left
• In places where
continual growth and
differentiation is
necessary
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Blood
Hair follicles
Breast tissue
Skin
Tissues
Groups of similar cells working
toward a common task
There are four major types of human
tissue
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Epithelial
Connective
Muscle
Nervous
Epithelial tissue forms body surfaces
and lines body cavities
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Squamous tissue- flat, easily passed
Cuboidal- cube-shaped, often secretory
Columnar- Oblong, often formed in glands
Ciliated- featuring cilia
Epithelial tissue is bound to connective
tissues by a basement membrane
• Basement membrane- acellular surface made of
proteins and polysaccharides
• Usually connects epithelia to loose connective tissue
Epithelial cells can form glands
• A gland- a
collection of cells
which secrete a
product
• Exocrine- release
substances through
ducts or tubes
Endocrine glands secrete hormones
directly into the body
• Hormone- a signalling
chemical which is
released in one part of
the body and affects
another part of the
body
• Examples- Insulin,
Follicle stimulating
hormone, testosterone
Connective tissues are diverse in
structure
• They include bone,
cartilage, adipose tissue
(fat cells), blood, etc.
• Most connective tissue
exists in an extracellular
matrix
• Fibers add flexibility,
durability, and strength
Collagen adds tensile strength, elastin
flexibility
The extracellular matrix often determines
the properties of connective tissues
• Fibrous connective
tissues
• Loose• Dense
• Elastic
Adipocytes have
very little
extracellular
matrix
• Sits beneath skin
• Provides insulation,
energy storage
• Also protects organs
Bone is a kind of connective tissue
• Osteocytes are
surrouned by a matrix
rich in collagen and
calcium
• Chondrocytes of
cartilage
• Blood is also a tissue
Muscle tissue
• Contractile tissue
• For movement of
body, blood,
organs
• Three major kinds
– Smooth
– Skeletal
– Cardiac
• All contain actin
and myosin fibers
for contraction
Skeletal, cardiac muscle striations
are bands of actin and myosin
Neurons carry messages
• Neurons are the basic
unit of the nervous
system
• Many connections are
the cause of brain’s
complexity
• Length increases speed
and fidelity of
communication
• Neurons communicate
with electrochemical
signals
Generalized neuron structure
Glial cells provide support
• Schwann cells provide
protection, electric
insulation
• Astrocytes provide
nutrition
The cells in tissues are held together with
transmembrane proteins
• Tight junctions- ensures
passage of substances
through cells
• Adhering junctions
allow stretching
• Gap junctions- allow
cell-to-cell
communication
between adjacent cells
in a tissues
Protein junctions bind membrane
layers to a basement membrane
• Tight junctions usually sit
higher- prevent leakage
• Adherens band form a ring
around epidermal cells in
membrane
• Hemidesmosomes bind
epithelial cells to basement
membrane
• Gap junctions allow
communication between
cells
Membranes cover and protect
organs and other surfaces
• Two major kinds of
membranes:
– Epithelial
– Connective tissue
• Two major kinds of
epithelial membranes:
– Mucous: contain glands
to secrete substances
– Serous: secrete only
serous fluid
Organs
• Collections of tissue
which form functions
together
• Heart, kidney, etc.
• Contained in body
cavities– Cranial/spinal
– Thoracic
– Abdominal/pelvic
The heart is an organ
• Main tissue: the tissue
forming the greatest
mass of the organ
• Heart: cardiac muscle
• Sporadic tissues: tissues
comprising a minority
of the mass of the
organ
• Nervous tissue,
connective tissue
(blood vessels, etc.)
SUPERIOR (of two body parts, the one closer to head)
distal (farthest from trunk or
from point of origin of a body
part)
frontal plane
(aqua)
midsagittal
plane
(green)
proximal (closest to
trunk or to point of
origin of a body part)
ANTERIOR
(at or near front of body)
POSTERIOR
(at or near back of body)
Fig. 4.8b, p. 76
INFERIOR
(of two body parts,
the one farthest from head)
transverse
plane
(yellow)
Organ Systems work together
toward collections of general tasks
Lymphatic
System
Respiratory
System
Digestive
System
Urinary
System
Reproductive
System
The Skin
The integumentary system includes
the body’s largest organ, the skin
• All 4 kinds of
tissue, each
comprised of many
kinds of cells
• Smooth muscle- for
contraction
• Adipose cellsconnective tissue
• Sweat/sebaceous
glands (endocrine
or exocrine?)
Functions of the skin
• Protect body from
foreign invaders
• Protect against impact,
abrasions
• Detect environmental
information
• Regulate temperature
• Synthesize vitamin D
There are 3 basic layers to the skin
• Epidermis, dermis, and
hypodermis
• Epidermis- source of
structures such as hair
follicles,
sweat/sebaceous glands
• Made mostly of
keratinocytes,
• Melanocytes give skin
its color
The epidermis is made primarily of
epithelial cells
• New Cells are formed from the
basal layer
• Stratum Basale- source of
“Epidermal stem cells”
• Cells die and become keratinized
(filled with keratin) on the way
up
• Spinosum- cells are keratinized
Keratin
• A tough, fibrous protein
• Found in hair, nails,
reptile scales, bird
beaks, whale baleen
• Holds out water
• As hair, skin & nail cells
die, they become
keratinized- filled with
keratin
There are 3 basic layers to the skin
• Dermis
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mostly loose connective tissue
Provides flexibility
Vascularized
Nerve endings terminate
Separation of dermis from
epidermis causes a blister
• Hypodermis/subcutis:
– Fatty tissue (50% of body)
– Connects skin to bone or
muscle
One cm2 has:
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200 nerve endings
100 sweat glands
10 hairs with muscles
15 oil glands
12 heat receptors
25 pressure receptors
2 cold receptors
3 blood vessels
Disorders of the skin
• Acne
• Albinism and Vitiligo
• Melanoma
Acne is caused by infection in follicles
Albinisim and vitiligo
Figure 4.12
Melanoma is the deadliest form of
skin cancer
Identifying melanoma
• Rember your ABCD
• Look out for “ugly
ducklings”
• Fair skinned people- be
vigilant for light
melanoma
• Better yet, avoid it
altogether
– Wear a hat
– Skip the tanning salon
– Wear sunscreen?
Epidermal/dermal layers in closeup
Which of the following statements is false
concerning the outermost layer of the
epidermis?
1.
2.
3.
4.
5.
It is the first to experience any abrasion.
Keratin provides waterproofing.
Millions of cells are worn off daily.
Its cells are undergoing rapid cell division.
It is called the stratum corneum.
Homeostasis & Skeletal System
Lecture Outline
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Homeostasis
Midterm review
Begin Chapter 9- Senses
Cow eye dissection lab
Homeostasis
Homeostasis means “staying the
same”
• Recall: Living
things do not exist
at equilibrium
• Living things do
exist at “steady
state”
• Living things work
to maintain a
stable internal
environment
A closed system
eventually reaches
equilibrium
G < 0
A closed hydroelectric system
G = 0
The body works to maintain a constant,
stable internal environment
• This requires changes to
account for an unstable
external environment
• Homeostatic
mechanisms exist
throughout the body
• Temperature, blood pH,
dO2, [glucose], etc. are
all regulated by
negative feedback
A thermostat operates by negative
feedback
• The classic homeostatic
mechanism analogy
• How does it work?
• What mechanisms must
it contain in order to
function properly?
• What is its cost?
Cycle of Homeostasis- a receptor, a control
center, and an effector
Figure 4.13
Homeostasis
• Then, a control center, such as the brain,
integrates the information coming from all
receptors and sends out an appropriate
response
• The effector carries out the response
returning the system to homeostasis again
Homeostasis
• The thermostat for the body is located in the
hypothalamus
• Hyperthermia, abnormally elevated body
temperature, and hypothermia, abnormally
low body temperature, are both lifethreatening conditions that result when this
mechanism fails
In the human body, the brain controls most
Homeostasis mechanisms
Figure 4.14 (1 of 2)
The hypothalamus receives information about
changes in the envoronment and responds
Figure 4.14 (2 of 2)
The price of minimizing entropy is the
constant expenditure of free energy
Why do you think homeostasis
with respect to temperature and
pH might be important?
Think of mechanisms and structures
which might depend on a stable
internal environment.
Insulin & Glucagon work together
to regulate blood sugar levels
A few human body mechanisms
operate on positive feedback
• Some are regulated by
positive feedback
Other Positive feedback
mechanisms in real life
More positive feeback loops
A large increase in the body’s core temperature
will cause what change in proteins?
1.
2.
3.
4.
5.
Denaturation
an increase in function
Replication
doubling of the rate of a reaction
a small reduction in the rate of reaction
Which of the following involves a
positive feedback mechanism?
1.
2.
3.
4.
5.
temperature control
childbirth
glucose concentration
absorption of toxins
muscle concentration