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Body Systems – Levels of organization
Specialized cells function together in tissues, organs,
organ systems, and the whole organism.
• Specialized cells perform specific tasks.
• Tissues are groups of similar cells working together.
– epithelial tissue
– connective tissue
– muscle tissue
– nervous tissue
cell
tissue
Body Systems – Levels of organization
• Organs are different tissues working together.
• Organ systems are two or more organs working together.
• Organism is all organ systems working together.
ORGANS
ORGAN SYSTEM
ORGANISM
Body Systems – Levels of organization
• There are 11 major organ systems in the human body.
The Nervous System and Endocrine Systems
KEY CONCEPT
The nervous system and the endocrine system provide the
means by which organ systems communicate.
Homeostasis
The body’s communication systems help maintain
homeostasis.
• A stimulus causes a response.
– Responses can be chemical, cellular, or behavioral.
– The nervous and endocrine systems respond to stimuli.
• The nervous system controls
thoughts, movement, and
emotion.
• The endocrine system controls
growth, development, and
digestion.
The nervous and endocrine systems have different
methods and rates of communication.
• The nervous system works quickly, using chemical and
electrical signals.
– interconnected network of
cells
– signals move through cells
– divided into central nervous
system (CNS) and peripheral
nervous system (PNS)
nerv
es
spin
al
chor
d
28.1 Levels of Organization
• The endocrine system works more slowly.
– only chemical signals
– signals move through bloodstream
– physically unconnected organs
hormone
target cell
bloodstr
eam
receptor
not a target
cell
28.1 Levels of Organization
Conditions within the body must remain within a narrow
range.
• Homeostasis involves keeping the internal environment
within set ranges.
pore
• Control systems help
maintain homeostasis.
– sensors gather data
– control center receives
data, sends messages
– communication system
delivers messages to
target organs, tissues
– targets respond to change
sweat
glands
hair
follicle
muscle
goose
bump
Homeostatsis involves Feedback Loops
Negative feedback loops are necessary for homeostasis.
• Feedback compares current conditions to set ranges.
• Negative feedback counteracts change.
Negative Feedback Loop
Holding breath, CO2
levels rise,
O2 / CO2 level returns to
normal
Control system forces
exhale, inhale
Homeostatsis involves Feedback Loops
Positive feedback loops are necessary for homeostasis.
• Positive feedback increases change.
– Torn vessel stimulates release of clotting factors
platelets
blood vessel
fibrin
clot
white blood cell
red blood cell
– growth hormones stimulate cell division
BODY SYSTEMS OVERVIEW
Circulatory System
Blood Composition
Plasma (55%): Fluid portion of blood
Red blood cells (44%): Carry oxygen
White blood cells: Defend against pathogens
Platelets: Cell fragments, form blood clots
Red Blood Cells




Hemoglobin: Iron-containing molecule
Loosely binds O2 in lungs (high concentration)
Releases O2 in body tissue (low concentration)
Shape of RBC’s allows them to travel through narrow
capillaries more easily
Red Blood Cell Lifespan




Produced in the marrow
Only type of body cell without a nucleus
Old RBC destroyed in liver, spleen
Average lifespan 120 days
Blood Types
RBC Marker Proteins
A- A protein
B- B protein
AB- both A and B proteins
O – neither A nor B proteins
Another marker protein is Rh factor.
Rh +: has Rh factor; Rh - : no Rh factor
Immune system produces antibodies against foreign antigens
(any protein etc. not produced in the body)
AB + is the universal receipient
O – is the universal donor
Blood Vessels
Arteries  Arterioles (thinner arteries) 
Capillaries  Venules (thinner veins)  Veins
Arteries
• Carry blood away from the heart
• Most arteries contain oxygenated blood
• Blood is under greater pressure (most arteries protected
deeper within body)
• Thick walled vessels
• Muscular walls expand/ contract to help move blood
•
•
•
•
Capillaries: Site of
Gas/Nutrient Exchange
Microscopic blood vessels
Lining is 1 cell thick
Allows oxygen and nutrients to diffuse into body cells
Waste from cells diffuses into blood
Veins
• Carry blood back to the heart
• Most veins carry deoxygenated blood
• Since many veins travel against gravity,
equipped with one-way valves to prevent back-ups
Artery: Thicker layer of
smooth muscle
Vein: One way valves
Heart
• Mainly cardiac muscle
• Cells have numerous mitochondria
• Mammalian hearts have 4 chambers
• 2 Upper Chambers: Atria
oReceiving chambers
• 2 Lower Chambers: Ventricles
oPump blood out of heart
•
Left and right sides separated by solid wall to create two
pumps
Pathway of Blood
Oxygen poor blood returning from body
enters right atrium
Right atrium  right ventricle 
pulmonary artery  lungs 
pulmonary vein  left atrium 
left ventricle aorta  arteries
 capillaries  veins  vena cavae
28.1 Levels of Organization
Respiratory System
Respiration is the process of bringing oxygen
(O2) to the cells and removing waste carbon
dioxide (CO2).
Cellular respiration
 Occurs in aerobic cells
 Uses O2 and food molecules (esp. glucose)
to make ATP, the cell’s energy currency
 Carbon dioxide and water are by-products
Overall: C6H12O6 + 6 O2  6 CO2 + 6 H2O
The Mechanics of
Breathing
 The diaphragm (a muscle located at the base of the rib
cage) pulls downward.
 Muscles in the rib cage pull outwards.
The Mechanics of Breathing
Continued…
 These actions increase the volume of the chest cavity,
decreasing the air pressure.
 This difference in pressure causes inhalation, as higher
pressure air outside moves into the lungs.
28.1 Levels of Organization
Air Pathway
Nose or Mouth
Pharynx
Trachea: starts below larynx (voicebox)
Bronchi: 2 branching tubes
}
Bronchioles: smaller branches
Alveoli: air sacs in lungs
Lungs
Epiglottis separates the pharynx from the trachea. This
flap of tissue covers the trachea when swallowing.
Exchange of Gases
Alveoli have thin walls and are surrounded by a network of
capillaries (thin blood vessels).
O2 from the alveoli diffuses into the blood stream and CO2 in the
returning blood enters the alveoli.
Keeping the Lungs Clean
Nose hairs filter dirt particles.
The trachea is lined with cilia (tiny hairs) and mucus.
• The sticky mucus traps dirt particles.
• The cilia wave upwards to expel dirt.
• Smoking tobacco products PARALYZES CILIA!
Control of Respiration
Brain region called the medulla oblongata regulates breathing
to maintain homeostasis.
If CO2 levels in blood stream are high, the medulla oblongata
signals an increase in the breathing rate.
Digestive System
Mouth
Mechanical Digestion:
Chewing increases the surface area of the food.
Chemical Digestion:
The enzyme salivary amylase begins breaking starches into
disaccharides.
Esophagus
Tube that connects mouth to stomach.
Peristalsis:
Involuntary contractions of smooth muscle.
Epiglottis: Flap that covers
the larynx (upper windpipe)
when you swallow.
Stomach
Mechanical digestion:
muscular churning
Chemical digestion:
Enzyme pepsin digests proteins into amino acids. Pepsin
functional at low pH (acidic).
Gastric juices (stomach fluid):
Contains hydrochloric acid (HCl) in addition to pepsin.
Mucus layer protects stomach from acid.
Pancreas, Liver and Gall Bladder
Food does not pass through these organs.
Pancreas secretes digestive enzymes and hormones.
Pancreatic juice: Enzymes and a base
Trypsin: digests proteins
Lipase: digests lipids
Pancreatic amylase: digests starch
Nucleases: digest nucleic acids
Sodium hydrogen carbonate: creates alkaline
conditions
Liver:
Produces bile (among many important functions)
Bile breaks fat into droplets. This process is mechanical
digestion rather than chemical.
Gall Bladder:
Stores bile
Small Intestine
• Small diameter (2.5 cm)
• 6 meters long (provides a large surface)
• Complete the digestion of food
 Mechanical digestion
 Chemical digestion
Enzymes from pancreas and duodenum
(first section of small intestine)
• Digested foods (sugars, amino acids etc.) absorbed into the
blood stream for transport throughout the body.
Small Intestine Villi
Villi (singular: villus) are small projections in the small intestine,
that greatly increase its surface area.
Each villus has a network of blood vessels and lymph ducts.
Digested food is absorbed for transport.
Large Intestine
(Colon)
•
•
•
•
•
6.5 cm wide
1.5 meters long
Indigestible materials pass into large intestine
Water is absorbed
Anaerobic bacteria that reside in colon synthesize vitamin K
and some B vitamins
28.1 Levels of Organization
Healthy Bodies - What are 4 things that you can do that
will help your bones, digestive system, nervous,
endocrine, respiratory and circulatory systems healthy?
• Exercising regularly – promotes strong bones and muscles,
helps remove waste and increases circulation. It also
promotes brain health.
• Eating nutritious food – provides the nutrients (enzyme
cofactors a.k.a. vitamins) and minerals (like iron that carries
oxygen in hemoglobin or calcium that helps build bone
tissue) you need for good health.
• Getting adequate sleep – promotes a healthy immune and
nervous system, and maintenance of healthy weight.
• Avoiding tobacco and smoking – smoking tobacco paralyzes
lung cilia, and tobacco products are linked with increased
rates of cancer, heart disease, birth defects, and premature
death.