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Cardiovascular System
Simplest Circulatory System: The
Gastrovascular Cavity
• found in animals that lack a true
circulatory system
• can function in the distribution of
materials throughout the body
• fluid bathes the outside of the animal
(ectodermal origin) and bathes the inside
(gastrodermis/endodermis)
– facilitates exchange via diffusion
• hydra – GV cavity found in the stalk + thin
branches that run into the tentacles
• other cnidarians – more complex
branching pattern possible
• in planarians and other flatworms – thin,
flattened body + GV cavity – very efficient
exchange system
Circulatory System Properties
• three basic components
– 1. circulating fluid
– 2. interconnecting vessels for fluid movement
– 3. heart for pumping
• circulation of fluid allows for the exchange of
gases, the absorption of nutrients and the
removal of wastes
• circulatory fluid is propelled by the muscular
contractions of the heat
Open and Closed Circulatory Systems
• arthropods and most molluscs: open
system
– circulatory fluid bathes the organs
directly in sinuses
– circulatory fluid is called hemolymph
– hemolymph = cells + interstitial
fluid + respiratory pigments for
carrying O2
– bathes the body cells for exchange
– open system does have a heart (or
hearts) and can have circulatory vessels
(e.g. dorsal aorta) leading from and into
this heart
– BUT no capillary beds for exchange –
done in the sinuses
(a) An open circulatory system
Heart
Hemolymph in sinuses
surrounding organs
Pores
Tubular heart
Open and Closed Circulatory Systems
• vertebrates, cephalopods and many
worms: closed system
– circulatory fluid is called blood
– is confined at all times to a series
of vessels
– blood is distinct from interstitial fluid
– exchange takes place between the
blood in the vessels and the interstitial
fluid in the tissues
– in capillary beds in many animals
– closed system does have a heart (or
hearts)
– heart can pump the blood at higher
pressures than seen in open systems –
better and faster delivery of oxygen
– closed systems also allow for selective
distribution of blood to tissues
– large arteries  smaller arteries 
arterioles capillary beds  venules
 smaller veins  larger veins
(b) A closed circulatory system
Heart
Interstitial fluid
Blood
Small branch
vessels in
each organ
Dorsal Auxiliary
vessel
hearts
(main heart)
Ventral vessels
The Heart
• all vertebrates have a heart with at
least one atrium for receiving blood
and one ventricle for pumping blood
• single circulation: bony fishes, sharks
and rays
– single circuit of blood flow
– blood passes through two capillary
beds before returning to the heart
• gill capillaries and then body capillaries
– heart is two chambered: one atrium,
one ventricle
– contraction of ventricle pumps blood to
gills for gas exchange
– blood then travels onto the body
capillaries for the delivery of the
oxygenated blood
(a) Single circulation
Gill
capillaries
Artery
Heart:
Atrium (A)
Ventricle (V)
Vein
Body
capillaries
Key
Oxygen-rich blood
Oxygen-poor blood
• fish circulation: single circulation
– blood enters the single atrium via a sinus venosus
– flows out of the single ventricle via the conus/bulbus arteriosus  ventral
aorta  gills
– gills are supplied by five afferent vessels forming branchial arteries off of the
ventral aorta
– numbered II through VI (anterior to posterior)
– gas exchange within the gill capillaries
– blood is returned to a dorsal aorta via efferent vessels
– dorsal aorta supplies the body
Ventral
aorta
• fish circulation: single circulation
– some fish will have lungs – lungfishes
• allows the fish to be able to breathe air and supplement gill blood
• circulation to the gills is still present
• the heart now has a right and left atrium and a single ventricle
divided partially by a septum to prevent mixing of blood
• deoxygenated blood from body enters the right atrium via the
sinus venosus
• meets with oxygenated blood from the lungs
• “mixed” blood  heart  gills  body
Australian lungfish
Lungfishes can drown!
• Most lungfish are obligate lung breathers!
• most lungfish have gills that have degenerated and do not oxygenate well
• have a heart with a semi-divided ventricle
• deoxygenated blood from body is pumped by the “right” ventricle to the
non-functional gills  lungs for oxygenation
• oxygenated blood from lungs is pumped by the “left” ventricle to the
body – passes through non-functional gills on the way
The Heart
• double circulation: amphibians,
reptiles, birds and mammals
(b) Double circulation
Pulmonary circuit
– comprised of two circuits: pulmonary
and systemic
– heart is actually two pumps:
Lung
capillaries
• right side of heart: pulmonary
pump/circuit – to the lungs and other
gas exchange structures and back to
the left side of the heart
A
– for the exchange of CO2 with O2 from
the air
V
Right
A
V
Left
• left side of the heart: systemic
pump/circuit – to the body and back
to the right side of the heart
Systemic
capillaries
– for the delivery of oxygenated blood
– provides a vigorous flow of blood to
the brain, muscles and other organs
Key
Systemic circuit
Oxygen-rich blood
Oxygen-poor blood
• amphibian circulation:
– heart with two atria and one ventricle
– blood is pumped not only to the lungs but also to the skin for gas exchange =
pulmocutaneous circuit
– most gas exchange is done through the skin
– when submerged in water – can shut off blood flow to its lungs
Amphibians
Pulmocutaneous circuit
Lung
and skin
capillaries
Atrium
(A)
Atrium
(A)
Right
dO2 blood  RA  “RV”  lungs/ skin  LA 
“LV”  body
Left
Ventricle (V)
Systemic
capillaries
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood
• amphibian circulation:
– ridge of tissue in the conus arteriosus vessel leaving the ventricle= spiral valve or fold
- directs oxygen poor blood toward the pulmocutaneous circuit (i.e. “RV”) and
oxygen rich blood to the body (i.e. “LV)
– after leaving the conus arteriosus – the blood may enter:
• the carotid artery to the head
• the systemic artery for transport to the body
• the pulmonary artery for transport to the lungs
Amphibians
Pulmocutaneous circuit
Lung
and skin
capillaries
Atrium
(A)
Atrium
(A)
Right
Left
Ventricle (V)
Systemic
capillaries
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood
• reptile circulation and gas exchange:
– larger size means more blood pressure required to move the blood
– development of a patch of cardiac muscle that functions as a pacemaker (except for
the turtles)
– ventricle is more divided then the ventricle of amphibians
Reptiles (Except Birds)
Pulmonary circuit
Lung
capillaries
Right
systemic
aorta
Left
systemic
aorta
A
Atrium
(A)
V
Ventricle
(V)
Right
Incomplete
septum
Left
Systemic
capillaries
Systemic circuit
dO2 blood  RA  “RV”  lungs  LA  “LV” 
body
Key
Oxygen-rich blood
Oxygen-poor blood
• reptile circulation and gas exchange:
– two atria and one ventricle
• ventricle has an incomplete septum - there is a muscular ridge to help directly
blood flow into:
• 1. pulmonary artery – for exit of deoxygenated blood to lungs
• blood returns to the left atrium via pulmonary veins
• dO2 blood flows to pulmonary artery due to a build up of pressure in the
ventricle
• 2. two systemic aortas for transport of oxygenated blood
• oxygenated blood moves into the aorta when the V actually contracts
• left systemic aorta  body
• right systemic aorta  “shunts” blood toward the systemic ventral aorta
when the animal is underwater (purple blood)
Mammalian Circulation
•
heart - four chambered pump: right side pulmonary pump + left side
systemic pump
• two circuits like amphibians
• pulmonary
• systemic
• blood travels to lung via the pulmonary arteries – back to the left atrium via the
pulmonary veins
– evolution of the conus arteriosus into a pulmonary trunk  pulmonary arteries
• blood travels to body via a single aorta
– loss of multiple aortas to only one
Mammals and Birds
Pulmonary circuit
Lung
capillaries
Atrium
(A)
Ventricle
(V)
Right
A
V
Left
Systemic
capillaries
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood
Mammalian Heart
• blood flow through the heart:
deoxygenated blood arrives at
right atrium  right ventricle 
lungs  left atrium  left
ventricle  body
Capillaries of
head and forelimbs
Superior vena cava
Pulmonary
artery
Capillaries
of right lung
Pulmonary
vein
Right atrium
Right ventricle
Pulmonary
artery
Aorta
Capillaries
of left lung
Pulmonary vein
Left atrium
Left ventricle
Aorta
Inferior
vena cava
Capillaries of
abdominal organs
and hind limbs
Aorta
Pulmonary artery
Pulmonary
artery
Right
atrium
Left
atrium
Semilunar
valve
Semilunar
valve
Atrioventricular
valve
Atrioventricular
valve
Right
ventricle
Left
ventricle
Conduction system of the Mammalian Heart
•
two kinds of heart muscle cells
– 1. contractile – 99% of heart muscle
– 2. autorhythmic
•
•
•
•
autorhythmic cells are non-contractile and produce electrical impulses in a regular,
rhythmic manner
electrical impulse leaves these cells to travel into the contractile cells and induce
their contraction
pathway: SA node  atrial contractile cells & AV node  bundle branches 
bundles of His  Purkinje fibers  ventricular contractile cells
electrical impulses can be picked up by electrodes placed on the skin surface = EKG
1
2
SA node
(pacemaker)
AV
node
ECG
3
Bundle
branches
4
Heart
apex
Purkinje
fibers
Electrocardiogram---ECG or EKG
• P wave
– atrial depolarization & contraction
• PR interval (PQ interval)
– conduction time from atrial to
ventricular excitation
• QRS complex
– ventricular
depolarization/contraction
• ST interval
2 Atrial systole and ventricular
diastole
– time for ventricular contraction and
emptying
• QT interval
1 Atrial and
ventricular diastole
0.1
sec
0.4
sec
0.3 sec
3 Ventricular systole and atrial
diastole
– time from the start of ventricular
depolarization to the end of its
repolarization
• T wave
– ventricular
repolarization/relaxation
20-18
Cardiac Cycle
2 Atrial systole and ventricular
diastole
– chambers are filling with blood
• systole – pumping period
– cardiac muscle contraction forces
blood out under pressure
• 1. Atrial and ventricular diastole
1 Atrial and
ventricular diastole
– atria and ventricles are filling with
blood
– muscle is relaxed
0.1
sec
0.4
sec
• diastole – rest period
0.3 sec
• 2. Atrial systole/ventricular
diastole
– contraction of atria forces blood into
ventricles
3 Ventricular systole and atrial
diastole
• 3. Ventricular systole/atrial
diastole
– ventricular contraction forces blood
out of lungs and body
– atria start to fill again
20-19
Organization of the Mammalian
Circulatory System
• large arteries  smaller arteries  arterioles 
capillary beds  venules  smaller veins  larger
veins
• arteries carry blood away from the heart
• veins carry blood toward the heart
• capillaries – one cell thick, for material exchange
– O2, CO2, individual solutes by diffusion
– multiple solutes “in bulk” by bulk flow
Arteries & Veins
• arteries and veins have the same
histologic construction
• made of three tunics or coats:
• 1. tunica externa/adventitia: made
of collagen and elastic fibers for
protection and elasticity
• 2. tunica media: contains a circular
layer of smooth muscle for change
in vessel diameter
LM
Vein
Red blood cells
100 mm
Valve
Basal lamina
Endothelium
Smooth
muscle
Connective Capillary
tissue
Endothelium
Smooth
muscle
Connective
tissue
Artery
Vein
Red blood cell
Venule
15 mm
Arteriole
Capillary
LM
– increase in diameter of an artery =
vasodilation
– decrease in diameter of an artery =
vasoconstriction
Artery
Arteries & Veins
• 3. tunica interna/intima: comprised
of a basement membrane called the
basal lamina (no cells - proteins and
sugars) + a single layer of epithelial
cells called the endothelium
Vein
LM
Artery
Red blood cells
– endothelium – lining of the blood vessel
– capillaries – comprised of basal lamina
and endothelium only
100 mm
Valve
Basal lamina
Endothelium
Smooth
muscle
Connective Capillary
tissue
Endothelium
Smooth
muscle
Connective
tissue
Artery
Vein
Red blood cell
Venule
15 mm
Arteriole
LM
Capillary
Arteries & Veins
• veins have a couple of
modifications vs. arteries
Artery
LM
– virtually no smooth muscle in
their tunica media
– presence of valves – projections
off of the endothelium to
prevent back flow of blood
during inactivity of the lower
limbs
Vein
Red blood cells
100 mm
Valve
Basal lamina
Endothelium
Smooth
muscle
Connective Capillary
tissue
Endothelium
Smooth
muscle
Connective
tissue
Artery
Vein
Red blood cell
Venule
15 mm
Arteriole
LM
Capillary
Blood Flow and Blood Pressure
• the blood leaving the left ventricle is at its
highest pressure and velocity
• as it moves through arteries and then into
smaller arterioles – blood velocity and
pressure drops
• arteries help propel blood along at high speeds
and pressure because they can distend and
recoil
• arterioles slow blood down and decrease its
pressure because they can control their
diameter
– arterioles are the major resistance vessels in
the body
– through vasoconstriction – velocity drops
– through distance from the heart – pressure
drops
– the job of the arteriole is to slow blood flow
down and to decrease blood pressure so that it
is at their lowest levels in the capillary beds
Veins
• veins are incapable of increasing blood pressure
– BP averages 17 mm Hg in the veins
– the lowest pressure is in the vena cava = 0 mmHg pressure
• problem for the return of blood to the right atrium
• Volume of blood returning to the right atrium = venous return
• Venous return determines how much blood the heart will pump to
the body (cardiac output)
Venous Return
• venous return is enhanced by 4 extrinsic factors:
– 1. sympathetic activity – some
venoconstriction can happen in some veins
– 2. respiratory activity– there is a pressure
difference between the veins in the limbs and
in the chest (lower) – drives more blood into
the thoracic veins and back to the heart =
respiratory pump
– 3. skeletal muscle activity –
contraction of skeletal muscles can
push on the vein walls, decreasing their
size and decreasing their capacity
– 4. venous valves – can shut off sections of
veins to prevent back-flow towards the feet
when standing
Measuring Blood
Pressure
• the blood leaving the left
ventricle is at its highest
pressure and velocity
• the pulsatile nature of blood
moving through an artery can be
measured using a
sphygmomanometer or BP cuff
Mammalian Blood
Cellular elements 45%
Plasma 55%
Constituent
Water
Solvent for
carrying other
substances
Ions (blood
electrolytes)
Sodium
Potassium
Calcium
Magnesium
Chloride
Bicarbonate
Osmotic balance,
pH buffering,
and regulation
of membrane
permeability
Plasma proteins
Albumin
Fibrinogen
Leukocytes (white blood cells)
Separated
blood
elements
5,000–10,000
Functions
Defense and
immunity
Lymphocytes
Basophils
Eosinophils
Neutrophils
Osmotic balance,
pH buffering
Monocytes
Platelets
250,000–400,000
Clotting
Immunoglobulins Defense
(antibodies)
Substances transported by blood
Nutrients
Waste products
Respiratory gases
Hormones
Number per mL
(mm3) of blood
Cell type
Major functions
Erythrocytes (red blood cells)
5–6 million
Blood
clotting
Transport
of O2 and
some CO2
Mammalian Blood
Plasma 55%
Constituent
• Blood is 55% plasma and 45%
cellular elements
– 1. erythrocytes – 99% of these
cells
– 2. thrombocytes
– 3. leukocytes
Major functions
Water
Solvent for
carrying other
substances
Ions (blood
electrolytes)
Osmotic balance,
pH buffering,
and regulation
of membrane
permeablity
Sodium
Potassium
Calcium
Magnesium
Chloride
Bicarbonate
Plasma proteins
Albumin
Osmotic balance, pH buffering
Fibrinogen
Clotting
Immunoglobulins (antibodies)Defense
Substances transported by blood
Nutrients
Respiratory gases
Waste products Hormones
Mammalian Blood
• Blood plasma:
– Blood plasma is about 90% water
– Among its solutes are inorganic
salts in the form of dissolved ions,
sometimes called electrolytes
– Another important class of solutes
is the plasma proteins, which
influence blood pH, osmotic
pressure, and viscosity
• plasma protein concentration
determines the bloods osmotic
pressure
– Various plasma proteins function
in lipid transport, immunity, and
blood clotting
Plasma 55%
Constituent
Major functions
Water
Solvent for
carrying other
substances
Ions (blood
electrolytes)
Osmotic balance,
pH buffering,
and regulation
of membrane
permeablity
Sodium
Potassium
Calcium
Magnesium
Chloride
Bicarbonate
Plasma proteins
Albumin
Osmotic balance, pH buffering
Fibrinogen
Clotting
Immunoglobulins (antibodies)Defense
Substances transported by blood
Nutrients
Respiratory gases
Waste products Hormones
Capillaries & Exchange
• capillaries are the site of exchange from blood plasma to the
tissue cell
• materials move out of the blood plasma into the interstitial fluid
first – then move from the IF into the cell based on gradients
• endothelial cells are not held tightly together – except for in the
brain
–
–
–
–
so materials can move from the blood plasma to a cell using several ways:
1. through the cell itself/transcytosis– O2, CO2 and small and lipid soluble
2. in between the endothelial cells/paracytosis – small & water-soluble
3. vesicular transport
Capillaries & Exchange
• capillary exchange is via diffusion and bulk-flow
• diffusion: the movement of a single solute from the
plasma from high concentration to low concentration
– for the exchange of O2 and CO2 via transcytosis
– for the movement of single solutes – e.g. glucose molecules
via paracytosis
Capillaries
• rate and efficiency of diffusion
depends on several factors:
Precapillary
sphincters
Thoroughfare
channel
– 1. the solute’s concentration gradient
• the steeper the gradient the faster the
diffusion
– 2. the permeability of the capillary
• the more permeable the faster the
diffusion
– 3. the surface area for diffusion
• the more capillaries open to blood flow the
more efficient the diffusion
• pre-capillary sphincters
Arteriole
Capillaries
Venule
(a) Sphincters relaxed
– 4. the size of the solute
• the smaller the solute the faster the
diffusion
– 5. the distance between the capillary and
the cell
• the closer the distance the more efficient
the diffusion
Arteriole
(b) Sphincters contracted
Venule
Capillaries
• bulk flow: movement of plasma into the interstitial fluid
• determines the composition of interstitial fluid of your tissues
• determined by two major components
– blood pressure/Pc
• outward driving force – from plasma to interstitial fluid = ULTRAFILTRATION
– osmotic pressure of the blood/OP – determined by the solutes within the
blood plasma
• mostly determined by plasma proteins that cannot move out of the plasma due
to their size
• inward driving force – from interstitial fluid to plasma = REABSORPTION
INTERSTITIAL
FLUID
Net fluid movement out
Blood
pressure
Body cell
PC decreases with blood flow
OP remains the same
Osmotic
pressure
Reabsorption
Ultrafiltration
Arterial end
of capillary
Direction of blood flow
Venous end
of capillary
Bulk Flow at Capillaries
• as blood flows into the capillary – the blood pressure/Pc is greater than osmotic
pressure/OP and more blood plasma moves out into the IF then moves back in
• as blood continues to move along the capillary – Pc drops
• at the end of the capillary – Pc has dropped enough so that OP is now greater
than it and more blood moves back into the plasma than is pushed out
Bulk Flow = Ultrafiltration – Reabsorption
Ultrafiltration is driven by Pc
Reabsorption is driven by OP