Cell

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• Zygote: fertilized cell
(egg + sperm)
• >200 types of human
cells
• Embryonic stem cells
– Created during
earliest divisions
– Potential to become
any type of cell
Determination
• Determination
– Stem cells
commit to a
specific type
– Few weeks into
development
– Irreversible
Stem cell programmed to become a muscle cell
ON
ON
ON
Genes (switches) exist in both cells, but are activated
in one type and deactivated in the other.
Stem cell programmed to become a nerve cell
ON
ON
ON
Differentiation
• Differentiation
– Cells acquire the
structures &
functions of a
specialized cell
– Specific genes
activated
Programmed
cell death
(apoptosis)
between the
fingers
Webbed Toes
• Cell: Basic unit
• Tissue: Group of cells
– 4 types
• Organ: Groups of tissue
– Ex: lung contains each
tissue
• Organ System: Group of
organs working together
– Digestive System
• Organism: all organ
systems working
together
• Muscle: contracting cells
– Skeletal, cardiac cells
• Connective Tissue: Support the body
– Bone, fat, tendons
• Epithelial: protection sheet of cells
– skin, stomach lining
• Nerve Tissue: Transmit electric signals
– Brain & Spinal Cord
Homeostasis
• Process where the
body maintains a
constant internal
environment
• Reactions & enzymes
work best in specific
conditions
• Control systems
adjust to
internal/external
changes
– pH, temp, fluids
Control Systems
• Sensors (aka: receptors)
– Gather information about the body
and environment
– Ex: skin senses pressure
• Communication Center
– Messages sent throughout the body to
respond
– Ex: Impulse travel through your nerves
• Control Center
– Receives information from the sensors
– Ex: Brain interprets the impulse
• Targets
– Body part that changes its activity
– Ex: Muscles in foot stretch/contract
abruptly
!*%!?%&#
Negative Feedback Loops
• Regulates most of
the body
• Counters changes
in the body that
move conditions
away from a set
point
– Reverses the
change
• Keeps internal
environment
stable
• Ex:
Thermoregulation
Negative Feedback Loop
Holding breath, CO2 levels rise
O2 / CO2 level
returns to normal
Control system
forces exhale
and inhale
Positive Feedback Loop
• Increases the changes
away from set points
• Important when rapid
changes needed
• Ex: Oxytocin released
– When uterus
contractions begin,
oxytocin released to
speed up the
contractions (not
stop them)
Positive Feedback Loop
– Ex:
– Torn vessel stimulates release of clotting factors
platelets
blood vessel
fibrin
clot
red blood cell
white blood cell
– growth hormones stimulate cell division
Homeostasis disruption
• Sensors fail
• Wrong messages sent
• Message doesn’t reach
target
• Serious injury
• Microorganism infection
• Short Term
– Temporary discomfort
(usually)
– Ex: cold or flu
Long Term: Diabetes
• Normal
– Insulin controls glucose level
– High: cells intake more glucose
– Low: pancreas creates more
glucose
• Type 1
– Immune system destroys cells
to produce insulin
– Pancreas fails
– Blood pH decreases (more
acidic)
• Type 2
– Insulin production decreases
– Glucose level in blood rises
– Cells starve
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