Lymphatic system
Lymphatic system
• Plays important role
in fluid distribution
• Important part of the
immune system
Lymphatic system
Edema
Pulmonary edema
Peripheral edema
Skeletal muscle pump
Moving Blood Back to the Heart
Blood in veins is under
low pressure
Two major pumps assist
in moving blood back
to the heart
• Skeletal muscle
• Respiratory pumps
• Inhalation: pressure in
thoracic cage drops and
draws blood into veins
• Exhalation: pressure
increases in the thoracic
cage and pushes the
blood towards the heart;
blood does not move
backwards because of
valves
Figure 9.38
Veins – volume reservoir
• Veins have thinner and more compliant walls
• Small increases in blood pressure lead to large changes in volume
• In mammals veins hold more than 60% of the blood
Regulation of circulatory systems
Law of Bulk flow
Q = DP/R
For circulatory system
CO = MAP/ TPR
HR x SV = MAP/ TPR
Regulation of circulatory systems
Regulation of circulatory systems
Baroreceptor reflex
• Important
mechanism for
regulating blood
pressure
• “Pressure” (stretch)
receptors located in
carotid and aortic
bodies
Baroreceptor reflex
• Baroreceptors are stretchsensitive mechanoreceptors
located in the walls of many
major blood vessels
• Most important of these are
located in the carotid artery
and aorta
• Baroreceptor reflex
regulates MAP
Rapid changes in blood pressure are
possible through sympathetic changes
in cardiac output & arteriolar tone
Baroreceptor discharges
• Most sensitive in physiological range
• More sensitive to pulsatile pressures
Arterial Pressure and blood volume
Blood volume regulation via kidneys
1. Simple filtration
2. Humoral controls
Renin-angiotensin system (RAS)
Antidiuretic hormone (ADH)
Effects of gravity on blood pressure
• Measured blood
pressure when
standing includes a
hydrostatic (gravity)
component
• What happens
when we change
body positions?
Effects of gravity
How Does Gravity Affect Blood Circulation?
How Does Gravity Affect Blood Circulation?
• Very tall animals
(e.g. giraffe) must
be able to pump
blood up to the
head
• They could also
have difficulty
with blood
pooling in the
feet, and
peripheral edema
Differences in central arterial blood pressures
systole/diastole
Trout
45/33
gill
ventral
aorta
systole/diastole
Human
120/80
Elephant 120/70
Pigeon
135/100
systole/diastole
Turtle
31/25
pulmonary
artery
lung
pulmonary
artery
aorta
dorsal
aorta
lung
aorta
Composition of Blood
• Primarily water containing ions and
organic solutes
• Blood cells
• Proteins
Blood Proteins
• Invertebrates: primarily respiratory
pigments
• Vertebrates: carrier proteins such as
albumin and globulins, and proteins
involved in blood clotting
Blood Cells or Hemocytes
Functions: oxygen transport or storage, nutrient
transport or storage, phagocytosis, immune
defense, blood clotting
Figure 9.44
Erythrocytes
• Red blood cells are the most abundant
cells in the blood of vertebrates
• Contain high concentrations of respiratory
pigments such as hemoglobin
• Major function is the storage and transport
of oxygen
• Have evolved independently several times
Vertebrate Blood
Separates into three
main components
when centrifuged
• Plasma
• Erythrocytes
• Other blood cells and
clotting cells
Hematocrit – fraction of
blood made up of
erythrocytes
Figure 9.45
Erythrocytes
Round or oval in shape
Mammalian erythrocytes are biconcave
disks
• This shape increases surface area, facilitating
oxygen transfer
Leukocytes
• White blood cells
• Function in the
immune response
• All are nucleated
• Found both in the
blood and the
interstitial fluid
• Some are able to
move across
capillary walls
• Five major types
Figure 9.46
Thrombocytes
Play a key role in blood clotting
Spindle-shaped cells in nonmammals and
classified as leukocytes
Anucleated cell fragments in mammals
called platelets
Three steps in blood clotting
• Vasoconstriction
• Platelet plug formation
• Clot formation through coagulation cascade
Blood Cell Formation
Process is called hematopoiesis
Location of stem cells
• Adult mammals: only in bone marrow
• Fishes: kidney
• Amphibians, reptiles, birds: spleen, liver,
kidney, bone marrow
Specific signaling factors are involved, e.g.,
erythropoietin is a hormone released by
the kidney in response to low blood
oxygen
Blood flow distribution & circulatory patterns
Evolution of air breathing: Plumbing & pressures
• Separation of respiratory & systemic circulations
Air-breathing fishes
Lungfishes
Amphibians
Reptiles
• Mammalian fetal circulation
In-series circuits
1 atrium + 1 ventricle
Single pump
In-parallel circuits
2 atria + 1 ventricle
Single pump or a
functional double pump
In-series circuits
2 atria + 2 ventricles
Double pump
Fish
Heart has four chambers arranged in series
Air-Breathing Fishes
• Air-breathing evolved several times in fishes
• Air-breathing organs are arranged in parallel; oxygenated and
deoxygenated blood mix
• Lungfish are the most specialized air-breathing fishes and have only
limited mixing of the oxygenated and deoxygenated blood
Various organs serve as ABOs in fish
• Can use: Swimbladder, mouth, gut, gills, skin, etc.
• Common problems:
O2 blood enters venous system  mixed venous blood
Single atrium receives mixed venous blood
Lungfish
Lungfish: true lung (developmentally)
• Largely solved the problem of mixed venous blood
• Atrium has a partial septum: oxygenated on one side; deoxygenated on the other
• Ventricle has partial septum: separation maintained
• Outflow vessel has a partial septum: separation is maintained
Amphibians and Reptiles
• Like lungfish, the heart is only partially divided; two atria
and one ventricle
• Oxygenated and deoxygenated blood can mix
• Two streams of blood are kept fairly separate although
the mechanism is not completely understood
• Crocodilians have a completely divided ventricle
Amphibians
Anatomically undivided heart, in-parallel circulations
pulmonary capillaries
heart
systemic capillaries
Two atria
Single ventricle
• Separate pulmonary
& systemic venous return
• Blood mixing
• Single outflow vessel
• High lung pressure
The beauty
vagal vasoconstriction can close
off lung circulation
during breath-hold or diving
Solutions
• Trabecular heart
• Spiral valve
• Lymph hearts
Amphibian heart
• Spongy myocardium & spiral valve in conus help separate
oxygenated & deoxygenated blood within the single ventricle
• Three chambered heart: two atria and one ventricle
• Trabeculae within the ventricle and a spiral fold within the conus
arteriosus help to keep oxygenated and deoxygenated blood
separate
Reptilian hearts: 3 major strategies
1. Anatomically undivided heart, in-parallel circulations
Squamate lizards, turtles, tortoises & most snakes
• Spongy myocardium & ventricular septa (creating cava) helps separate
oxygenated & deoxygenated blood within the single ventricle
• Right atrium largely to cavum pulmonale
• Two outflow vessels: pulmonary & systemic arteries
• Blood pressures in cavum venosum,
cavum pulmonale & cavum arteriosum
are identical during ventricular contraction
• Pulmonary capillaries protected by
outflow resistance site (vagal constriction)
Reptilian hearts: 3 major strategies
2. Functionally divided heart, in-parallel circulations
Varanid lizards & pythons
• Highly developed ventricular muscular ridge
• Systolic pressure in cavum pulmonale is lower than cavum arteriosum,
but no difference during diastole: low pulmonary pressure
• = functional, but not anatomical separation
Crocodilian heart: best of both worlds:
3. Anatomically divided heart, double circulation with a by-pass
heart  pulmonary capillaries  heart  systemic capillaries
Right ventricle has pulmonary artery
& a right systemic aorta
Left ventricle has a “left” systemic aorta
Foramen of Panizza provides a pressure
connection between “left” & “right” aortae
Cog valve
Can close off lung circulation
(vagal vasoconstriction)
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2 atria & 2 ventricles with same wall thickness
Reptiles
Can shunt blood to bypass
either the pulmonary or
systemic circuit
• Right-to-left shunt:
deoxygenated blood
bypasses the pulmonary
circuit and reenters the
systemic circuit
• Left-to-right shunt: some
pulmonary blood reenters the
pulmonary circuit
Figure 9.16a
Mammalian fetal circulation
• No air ventilation of lungs
• O2 comes from placenta
placenta
In-series circuits
2 atria + 2 ventricles
Double pump
Low pulmonary pressure