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Chapter 42 Notes
Circulation and Gas
Exchange
Circulation in Animals
Diffusion alone is not enough to transport
substances over long distances in
animals
- ex. moving O2 from the lungs to the
brain
The circulatory system solves this by
making sure substances only diffuse a
short distance
Circulation in Animals
Invertebrates have a gastrovascular
cavity or circulatory system for internal
transport
- ex. the body wall of the hydra is only
2 cells thick; the body cavity can serve
for digestion and distribution
Circulation in Animals
Circulation in Animals
In animals with many cell layers,
gastrovascular cavities are not enough
because diffusion distances are too
great
They will use an open or closed
circulatory system
- contains blood, blood vessels, and a
muscular pump (heart)
Circulation in Animals
In insects blood bathes the organs
directly in an open circulatory
system
- no distinction between blood and
interstitial fluid
In a closed circulatory system, blood
is confined to vessels and is distinct
from interstitial fluid
Circulation in Animals
Circulation in Animals
Humans have a closed system called the
cardiovascular system
- the heart has 1 atria or 2 atrium
that receive blood returning to the
heart
- the heart also has 1 or 2 ventricles
that pump blood out of the heart
Circulation in Animals
- arteries, veins, and capillaries are
the three main types of blood vessels
- arteries are going to branch into
arterioles  pass blood to the
capillaries
- capillary beds infiltrate each tissue;
here gasses are exchanged by diffusion
Circulation in Animals
Metabolic rate is an important factor in
the evolution of the circulatory system
- animals with high metabolic rates
have more complex circulatory systems
and more powerful hearts
- differences are associated with gill
breathing versus lung breathing
Circulation in Animals
A fish heart has 2 main chambers (1 atria
and 1 ventricle)
- blood pumps from the ventricle to the
gills; from the gill capillaries the blood
moves through all other parts of the
body
- problem is when blood pumps through
a capillary, blood pressure will drop
Circulation in Animals
- this constrains the delivery of O2 to
body tissues and the maximum aerobic
metabolic rate of fishes
Amphibians have a 3 chambered heart (2
atrium and 1 ventricle)
- the ventricle pumps blood into a
forked artery that splits the ventricle's
output
Circulation in Animals
- the pulmocutaneous circulation
leads to capillaries for gas exchange
- systemic circulation supplies the
bodies organs with oxygenated blood
- some mixing of blood occurs
- reptiles have less mixing since they
have a partially divided ventricle
Circulation in Animals
Crocodiles, birds, and mammals have a 4
chambered heart
- the left side of the heart receives and
pumps oxygen-rich blood; the right side
handles oxygen-poor blood
- the evolution of this supported
endothermic life
- use 10X more energy than ectotherms
Circulation in Animals
Circulation in Animals
Circulation in Animals
The mammalian heart
- about the size of a closed fist
- contracts and relaxes in a rhythmic
cycle
- cardiac cycle: one complete
pumping and filling of blood
Circulation in Animals
Circulation in Animals
- systole: the contraction phase
- diastole: the relaxation phase
Cardiac output depends on the heart
rate (# of beats per min.) and stroke
volume (amt. of blood pumped)
Circulation in Animals
The heart has 4 valves that prevent
backflow of blood
- atrioventricular (AV) valve:
between atrium and ventricle
- semilunar valves: located at the 2
exits of the heart
- the “lub-dup” sound is the of the
valves closing
Circulation in Animals
Circulation in Animals
- heart murmur: a defect in the heart
valves when blood squirts backward
The sinoatrial (SA) node or
pacemaker sets the rate and timing at
which cardiac muscles contract
Circulation in Animals
Circulation in Animals
The lymphatic system returns fluid to the
blood and aids in body defense
- fluid enters the system by diffusing
into tiny lymph capillaries; the systems
drains back into the circulatory system
Along the lymph vessel are lymph
nodes: filter lymph and attack viruses
and bacteria
Circulation in Animals
Blood consists of several kinds of cells
suspended in a liquid called plasma
- blood plasma is 90% water
- in the plasma are red blood cells
(RBC), white blood cells (WBC),
and platelets
Circulation in Animals
Circulation in Animals
RBC, or erythrocytes, are the most
common blood cells
- main fcn. is to transport O2
- lack nuclei; leaves more space for
hemoglobin
- lack mitochondria; no aerobic
respiration
Circulation in Animals
Circulation in Animals
There are 5 major types of WBC’s or
leukocytes
- monocytes, neutrophils, basophils,
eosinophils, and lymphocytes
- monocytes and neutrophils are
phagocytes
Platelets are important for blood clotting
Gas Exchange in Animals
Gas exchange: the uptake of oxygen
and the release of carbon dioxide
- don’t confuse with (cellular)
respiration
Respiratory medium: source of oxygen
- air and water
Gas Exchange in Animals
Respiratory surface: part of an animal
where gases are exchanged
- movement must be from diffusion
- surfaces are thin w/ large surface
areas
- cells must be bathed in water (for
plasma membrane)
Gas Exchange in Animals
Gas Exchange in Animals
The structure of the respiratory surface
depends on the size of the animal and
whether it lives in water or on land
- also influenced by metabolic demands
ex. endotherms vs. ectotherms
Gas Exchange in Animals
In simple animals, the plasma membrane
of every cell is able to have gases
diffuse in and out
In other animals, their outer skin acts as
a respiratory organ
- animals are small and usually long and
thin or flat
Gas Exchange in Animals
For most other animals, the body doesn’t
have enough area for gas exchange
- the solution is an organ that is highly
branched and folded; enlarges the
surface area for gas exchange
- ex. lungs, gills, and tracheae
Gas Exchange in Animals
Gas Exchange in Animals
Gills are respiratory adaptations of most
aquatic animals
Gills are outfoldings of the body surface
that are suspended in the water
- total surface area of the gills is often
much greater than the surface area of
the rest of the body
Gas Exchange in Animals
As a respiratory medium, water has
advantages and disadvantages
- no problem keeping the cell
membranes moist
- low [O2] in water
Gills must be very effective to obtain
enough oxygen
Gas Exchange in Animals
Ventilation: increases the flow of the
respiratory medium over the respiratory
surface
Gas Exchange in Animals
Gas Exchange in Animals
The arrangement of capillaries in a fish
gill enhances gas exchange and reduces
the energy cost of ventilation
Countercurrent exchange: blood flows
in opposite direction to the movement
of water past the gills
Gas Exchange in Animals
- as blood moves through the capillary,
it becomes more and more loaded with
oxygen. Simultaneously, it encounters
water with even higher oxygen
concentrations.
- along the entire length of the
capillary, there is a diffusion gradient
Gas Exchange in Animals
Gas Exchange in Animals
Tracheal systems and lungs are
respiratory adaptations of terrestrial
animals
Tracheal system: made up of air tubes
that branch throughout the body
- largest tube is called the tracheae;
opens to outside
Gas Exchange in Animals
- for small insects, diffusion through the
trachea brings in enough O2 and
removes enough CO2 to support cellular
respiration
- larger insects ventilate their tracheal
systems with rhythmic body movements
Gas Exchange in Animals
Gas Exchange in Animals
Unlike the tracheal systems that branch
throughout the insect’s body, the lungs
are restricted to one location
- not in direct contact with all cells
- the circulatory system must transport
gases between the lungs and the body
- size is correlated to metabolic rate
Gas Exchange in Animals
Pathway of air to the lungs
- the nasal cavity leads to the pharynx;
when food is swallowed; the larynx
moves upward and tips the epiglottis
over the glottis; allows food to go to
the stomach
- the rest of the time the glottis is open
Gas Exchange in Animals
- from the larynx, air passes into the
trachea (windpipe)
- the trachea forks into two bronchi,
one leading to each lung
- within the lung, each bronchus
branches repeatedly into finer and finer
tubes called bronchioles
Gas Exchange in Animals
Gas Exchange in Animals
The system of air ducts looks like an
inverted tree
- the epithelium lining of the major
branches are covered by cilia and a thin
film of mucus
- traps and moves dust, and pollen
away from lungs
Gas Exchange in Animals
At the tips of the bronchioles, there is a
dead-end cluster of air sacs called
alveoli
- location of gas exchange across the
epithelium
-O2 and CO2 diffuse across the
epithelium and the capillaries
Gas Exchange in Animals
Gas Exchange in Animals
Ventilating the lungs
- needed to maintain high [O2] and low
[CO2] at the gas exchange surfaces
- breathing ventilates the lungs
- mammals ventilate the lungs by
negative pressure breathing
- pulls air instead of pushing it
Gas Exchange in Animals
Lung volume increases as a result of
contraction of the rib cage muscles and
the diaphragm
Because gas flows from high pressure to
low pressure, through the nostrils and
down the breathing tube to the alveoli
Gas Exchange in Animals

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