Circulation and Gas Exchange
The Respiratory System


What is its function? Why is it necessary?
 GETS oxygen for the body
 Needed for cellular respiration
 GETS RID of carbon dioxide
 Produced during cellular respiration
Characteristics/Requirements of ALL Gas
Exchange Mechanisms:
 MOIST membranes
 High surface area-to-volume ratio
 An animal’s respiratory surfaces must
be large enough to provide oxygen and
expel carbon dioxide for the entire body
Respiration in Non-Mammals


Small animals (earthworms, etc.) exchange
gases by diffusion across its general body
surface
Gills are outfoldings of the body surface
specialized for gas exchange for aquatic
organisms

Blood flowing through the capillaries picks up
oxygen from the water
Countercurrent Exchange- blood &
water flow in opposite directions
Countercurrent Exchange (Aquatic Animals)

Countercurrent exchange allows for
the efficient transfer of oxygen to
the blood


As blood flows through the capillary, it
becomes more and more loaded with
oxygen
Steep concentration gradient allows for
efficient uptake of oxygen
Tracheae



The respiratory
system used by
insects
Tracheae are air
tubes that branch
throughout the
insect body
The finest branches
of the tracheae
extend to the
surface of nearly
every cell, where gas
is exchanged by
diffusion
Lungs

Lungs are found in terrestrial vertebrates


Reptiles, birds, mammals, amphibians
Lungs of mammals have a large enough
surface area to carry out gas exchange
for the entire body


How do the gases get from the lungs
throughout the rest of the body, though??
The circulatory system transports the gases
throughout the body after they’re exchanged in
the lungs
Human Respiratory System
Human Respiratory System

Air enters
the lungs by
a system of
branching
ducts







Nostrils
Pharynx
Larynx
Trachea (w/
cilia)
2 bronchi
Bronchioles
Alveoli
Alveoli

Alveoli are clusters of air sacs
at the end of bronchioles



Alveoli have thin epithelium,
which serve as the respiratory
surface
Oxygen diffuses from the alveoli
into the web of capillaries around
each alveolus
The capillaries then transfer the
oxygen throughout the body, via
the circulatory system
Why is the circulatory system necessary?



TRANSPORTATION!
Diffusion is not fast enough to
transport chemicals throughout an
animal’s body
The circulatory system transports
fluid throughout the body

This solves the problem of diffusion by
ensuring that no substance had to
diffuse far to enter or leave a cell
Open vs. Closed Circulatory Systems

In open circulatory systems,
hemolymph bathes the internal
organs directly


Insects, arthropods, mollusks
In closed circulatory systems, blood
is confined to vessels


Blood exchanges materials with the ISF
bathing the cells
Earthworms, squids, octopuses,
vertebrates
Open vs. Closed Circulatory Systems
Adaptations of the Vertebrate
Circulatory System




Fish - Heart with 2 chambers (one atrium, one
ventricle)
Amphibians (frogs)- 3-chambered heart (two atria,
one ventricle)
Reptiles – (3-chambered with partial septum)
Birds/Mammals-4-chambered heart (two atria, two
ventricles)

Vertebrate circulatory systems
AMPHIBIANS
REPTILES (EXCEPT BIRDS)
MAMMALS AND BIRDS
Lung and skin capillaries
Lung capillaries
Lung capillaries
FISHES
Gill capillaries
Artery
Pulmocutaneous
circuit
Gill
circulation
Right
systemic
aorta
Pulmonary
circuit
Heart:
ventricle (V)
A
A
Atrium (A)
V
V
Right
Vein
Systemic
circulation
Systemic capillaries
A
Left
Right
A Left
Systemic
V aorta
Left
A
V
Right
A
V
Left
Systemic
circuit
Systemic
circuit
Systemic capillaries
Pulmonary
circuit
Systemic capillaries
Systemic capillaries
Double Pump



Right side pumps to the lungs and
back to left atrium (PULMONARY
CIRCUIT)
Left side pumps to the entire body
and returns blood to right atrium
(SYSTEMIC CIRCUIT)
Oxygenated & deoxygenated blood
never mix!

The mammalian cardiovascular system
7
Capillaries of
head and
forelimbs
Anterior
vena cava
Pulmonary
artery
Aorta
Pulmonary
artery
9
6
Capillaries
of right lung
Capillaries
of left lung
2
4
3
Pulmonary
vein
5
1
Right atrium
3
11
Left atrium
Pulmonary
vein
10
Left ventricle
Right ventricle
Aorta
Posterior
vena cava
8
Figure 42.5
Capillaries of
abdominal organs
and hind limbs
The Heart



About the size of a
clenched fist
Made up of mostly
cardiac muscle
tissue: striated with
branches;
involuntary
Atria have thin
walls, ventricles
have thicker walls


Why??
Ventricles must
pump blood through
the pulmonary &
systemic circuits.
(LONG DISTANCE)
The Heart: Structure and Function

AV Valves:



Located between each atrium and
ventricle
Keep blood from flowing back into the
atria
Semilunar Valves:


Located at the exits of the heart (at the
bottom of each ventricle)
Prevent blood from flowing back into
the ventricles
The Human Heart
Blood Vessels

Arteries carry blood away from the heart to
organs throughout the body
 Arteries are thicker than veins…why??
Thick layer of smooth muscle (nonstriated;
involuntary)+ elastic tissue
Veins return blood to the heart
 Categorized by direction of flow, NOT
whether or not they contain oxygen
 Thinner layer of smooth muscle; VALVES to
prevent back flow of blood; not very elastic
Capillaries are microscopic vessels with very
thin, porous walls



.9
Vein
Artery
Basement
membrane
Endothelium
100 µm
Valve
Endothelium
Endothelium
Smooth
muscle
Smooth
muscle
Capillary
Connective
tissue
Connective
tissue
Artery
Vein
Venule
Arteriole
Venous Transport

In the thinner-walled veins

Blood flows back to the heart mainly
as a result of muscle action
Direction of blood flow
in vein (toward heart)
Valve (open)
Skeletal muscle
Valve (closed)
Capillary Exchange


The capillary wall is a single layer of
flattened cells
The transfer of substances occurs
between the capillaries and the
interstitial fluid (which bathes the
cells)


This occurs by bulk flow, the movement
of fluid due to pressure
Water, sugars, salts, oxygen, and urea
pass through the capillary walls
Capillary Exchange
Area (cm2)
5,000
4,000
3,000
2,000
1,000
0
Velocity (cm/sec)
50
40
30
20
10
0

The velocity of
blood flow varies
in the circulatory
system
Systolic
pressure
Veins
Venules
Capillaries
Arterioles
Diastolic
pressure
Arteries
120
100
80
60
40
20
0
Aorta
Pressure (mm Hg)

Venae cavae
e 42.11
Velocity, B. Pressure, & Area
And is slowest in the
capillary beds as a
result of the high
resistance and large
total cross-sectional
area
Blood Pressure

Systolic pressure



Is the pressure in the arteries during
ventricular systole
Is the highest pressure in the arteries
Diastolic pressure




Is the pressure in the arteries during diastole
Is lower than systolic pressure
Measured with sphygmomanometer
Normal pressure = 120/80 mm Hg
Control of the Heart


Cardiac muscles contract (systole)
and relax (diastole) in a rhythmic
cycle
The sinoatrial node (SA node), also
known as the pacemaker,
maintains the heart’s pumping
rhythm by setting the rate at which
all cardiac muscles contract
Control of the Heart
Cardiac Cycle
Atria
Systole
Diastole
Diastole
Ventricles
EKG
Diastole P wave
Systole QRSwave
Diastole T wave
2.7

The cardiac cycle
2 Atrial systole;
ventricular
diastole
Semilunar
valves
closed
0.1 sec
Semilunar
valves
open
0.3 sec
0.4 sec
AV valves
open
1
Atrial and
ventricular
diastole
AV valves
closed
3
Ventricular systole;
atrial diastole
The Structure of Blood


Blood is made up of plasma, red blood cells, white blood
cells, and platelets
Plasma, which makes up about 55% of blood volume, is
mostly water


Plasma also contains antibodies
Plasma also contains fibrinogens, proteins that act as
clotting factors
Fibrinogen (inactive) is a protein in blood that is
converted into fibrin (active), when needed
 Thrombin is the enzyme that activates the
fibrinogen. K & Ca are important minerals for
clotting reaction to occur.



Hemophilia is an inherited disorder, characterized by
excessive bleeding from minor cuts and bruises
People with hemophilia can die from minor cuts
The Structure of Blood

Red Blood Cells (Erythrocytes)




The human body contains 25 trillion
red blood cells
Major function is to transport oxygen
Contains hemoglobin, an ironcontaining protein that carries oxygen
Red blood cells are produced in the
bone marrow
Hemoglobin Carries Oxygen

Like all respiratory pigments
Hemoglobin must reversibly bind O2,
loading O2 in the lungs and unloading it
in other parts of the body
Heme group Iron atom

O2 loaded
in lungs
O2 unloaded
In tissues
Figure 42.28
Polypeptide chain
O2
O2
Carbon Dioxide Transport





Small amount binds to hemoglobin
to form carboxyhemoglobin.
MOST is transported as bicarbonate
ion:
CO2 + H2O H2CO3H+ + HCO3Serves as a buffer to control pH of blood.
pH = 7.4
The Structure of Blood

White blood cells (leukocytes)


Major function is to fight infection
5 major types


Monocytes, neutrophils, basophils,
eosinophils, lymphocytes
White blood cells spend most of their
time patrolling through the ISF and the
lymphatic system, where most of the
battles against pathogens are waged
The Structure of Blood

Platelets (Thrombocytes)


Platelets are fragments of cells
Platelets enter the blood and function
in the process of blood clotting
Blood: An Overview
Cardiovascular Disease


Cardiovascular disease (diseases of the
heart and blood vessels) cause more than
half of all deaths in the US
Heart attack:


Death of cardiac muscle tissue as a result of
blockage of a coronary artery
Stroke:

Death of nervous tissue in the brain, resulting
from blockage of arteries in the head
Artherosclerosis


Plaque (cholesterol and
triglycerides/fats) deposit in blood
vessels
Can lead to stroke or heart attack.