Lecture#16

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)

• 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 = interstitial fluid + respiratory pigments for carrying O2

– bathes the body cells for exchange

– open system does have a heart (or hearts) and can have short circulatory vessels leading from and into this heart

– BUT no capillary beds for exchange – done in the sinuses

(a) An open circulatory system

Heart

Hemolymph in sinusessurrounding 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

– 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

– large arteries à smaller arteries à arterioles àcapillary beds à venules à smaller veins à larger veins

Dorsalvessel

(main heart)

Auxiliaryhearts

Small branchvessels ineach organ

Ventral vessels

Blood

Interstitial fluid

Heart

(b) A closed circulatory system

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– 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

Artery

Heart:

Atrium (A)

Ventricle (V)

Vein

Gillcapillaries

Bodycapillaries

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 arteriosus ventral aorta– gills are supplied by five afferent vessels forming branchial arches off of the

ventral aorta– gas exchange within the gill capillaries– blood is returned to a dorsal aorta via efferent vessels– moves to the body where gas is exchanged in body capillaries

• fish circulation: single circulation– some fish will have lungs – lungfishes

• allows the fish to be able to breathe air• 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• blood enters the right atrium via the sinus venosus – but now can

travel to the lung via a pulmonary artery • blood from the lung then returns to the left atrium via the

pulmonary veins

The Heart• double circulation: amphibians,

reptiles, birds and mammals– comprised of two circuits: pulmonary

and systemic– heart is actually two pumps:

• right side of heart: pulmonary pump/circuit – to the lungs and other gas exchange structures and back to the left side of the heart

• left side of the heart: systemic pump/circuit – to the body and back to the right side of the heart

– provides a vigorous flow of blood to the brain, muscles and other organs

(b) Double circulation

Systemic circuit

Systemiccapillaries

Right Left

A A

VV

Lungcapillaries

Pulmonary circuit

Key

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– ridge of tissue in the conus arteriosus vessel leaving the ventricle= spiral valve

- directs oxygen poor blood toward the pulmocutaneous circuit and oxygen rich blood to the body

– 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

Lungand skincapillaries

Atrium(A)

Atrium(A)

LeftRight

Ventricle (V)

Systemiccapillaries

Systemic circuit

Key

Oxygen-rich bloodOxygen-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)– 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• 2. two systemic aortas for transport of oxygenated blood

• left systemic aorta à body • right systemic aorta à “shunts” blood toward the systemic ventral aorta

when the animal is underwater (purple blood)• blood returns to the left atrium via pulmonary veins

Reptiles (Except Birds)

Pulmonary circuit

Systemic circuit

Systemiccapillaries

Incompleteseptum

Leftsystemicaorta

LeftRight

Rightsystemicaorta

A

V

Lungcapillaries

Atrium(A)

Ventricle(V)

Key

Oxygen-rich bloodOxygen-poor 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

• blood travels to body via a single aorta

Systemic circuit

Lungcapillaries

Pulmonary circuit

AV

LeftRight

Systemiccapillaries

Mammals and Birds

Atrium(A)

Ventricle(V)

Key

Oxygen-rich bloodOxygen-poor blood

Mammalian Heart

• blood flow through the heart: deoxygenated blood arrives at right atrium à right ventricle à lungs à left atrium à left ventricle à body

Pulmonary artery

Rightatrium

Semilunarvalve

Atrioventricularvalve

Rightventricle

Leftventricle

Atrioventricularvalve

Semilunarvalve

Leftatrium

Pulmonaryartery

Aorta

Superior vena cava

Pulmonaryartery

Capillariesof right lung

Pulmonaryvein

Aorta

Inferiorvena cava

Right ventricle

Capillaries ofabdominal organsand hind limbs

Right atrium

Aorta

Left ventricle

Left atrium

Pulmonary vein

Pulmonaryartery

Capillariesof left lung

Capillaries ofhead and forelimbs

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 à atrial contractile cells & AV node à bundle branches à bundles of His à Purkinje fibers à ventricular contractile cells

• electrical impulses can be picked up by electrodes placed on the skin surface = EKG

SA node(pacemaker)

AVnode Bundle

branches Heartapex

Purkinjefibers

ECG

1 2 3 4

20-15

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

– time for ventricular contraction and emptying

• QT interval– time from the start of ventricular

depolarization to the end of its repolarization

• T wave– ventricular repolarization/relaxation

20-16

Cardiac Cycle

Atrial and

ventricular diastole

Atrial systole and ventricular

diastole

Ventricular systole and atrial

diastole

0.1sec

0.4sec

0.3 sec

2

1

3

• diastole – rest period– chambers are filling with blood

• systole – pumping period– cardiac muscle contraction forces

blood out under pressure• 1. Atrial and ventricular diastole

– atria and ventricles are filling with blood

– muscle is relaxed• 2. Atrial systole/ventricular

diastole– contraction of atria forces blood into

ventricles• 3. Ventricular systole/atrial

diastole– ventricular contraction forces blood

out of lungs and body– atria start to fill again

Organization of the Mammalian Circulatory System

– large arteries à smaller arteries à arterioles àcapillary beds à venules à smaller veins à 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: 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– increase in diameter of an artery

= vasodilation– decrease in diameter of an artery

= vasoconstriction

Artery

Red blood cells

Endothelium

Artery

Smoothmuscle

Connectivetissue

Capillary

Valve

Vein

Vein

Basal lamina

Endothelium

Smoothmuscle

Connectivetissue

100 mm

LM

Venule

15

mm

LM

Arteriole

Red blood cell

Capillary

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– endothelium – lining of the blood

vessel– capillaries – comprised of basal

lamina and endothelium only

Artery

Red blood cells

Endothelium

Artery

Smoothmuscle

Connectivetissue

Capillary

Valve

Vein

Vein

Basal lamina

Endothelium

Smoothmuscle

Connectivetissue

100 mm

LM

Venule

15

mm

LM

Arteriole

Red blood cell

Capillary

Arteries & Veins• veins have a couple of

modifications vs. arteries– 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

Artery

Red blood cells

Endothelium

Artery

Smoothmuscle

Connectivetissue

Capillary

Valve

Vein

Vein

Basal lamina

Endothelium

Smoothmuscle

Connectivetissue

100 mm

LM

Venule

15

mm

LM

Arteriole

Red blood cell

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

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 = venous return

Veins• venous return is enhanced by 4

extrinsic factors:– 1. sympathetic activity –

venoconstriction can happen in some veins

– 2. respiratory activity– a pressure difference found between the veins in the limbs and in the chest 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 BloodPlasma 55%

Constituent Major functions

Water

Ions (bloodelectrolytes)SodiumPotassiumCalciumMagnesiumChlorideBicarbonate

Solvent forcarrying othersubstances

Osmotic balance,pH buffering,and regulationof membranepermeability

Plasma proteinsOsmotic balance,pH buffering

Albumin

Fibrinogen

Immunoglobulins(antibodies)

Clotting

Defense

Substances transported by blood

NutrientsWaste productsRespiratory gasesHormones

Separatedbloodelements

Basophils

Neutrophils Monocytes

Lymphocytes

Eosinophils

Platelets

Erythrocytes (red blood cells) 5–6 million

250,000–400,000 Bloodclotting

Transportof O2 and

some CO2

Defense andimmunity

FunctionsNumber per mL(mm3) of blood

Cell type

Cellular elements 45%

Leukocytes (white blood cells) 5,000–10,000

Mammalian Blood• Blood is 55% plasma and 45%

cellular elements– 1. erythrocytes – 99% of these cells– 2. thrombocytes– 3. leukocytes

• 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

– Various plasma proteins function in lipid transport, immunity, and blood clotting

Plasma 55%

Constituent Major functions

Water

Ions (bloodelectrolytes)

SodiumPotassiumCalciumMagnesiumChlorideBicarbonate

Solvent forcarrying othersubstances

Osmotic balance,pH buffering,and regulationof membranepermeablity

Plasma proteins

Osmotic balance, pH bufferingAlbumin

Fibrinogen

Immunoglobulins (antibodies)

Clotting

Defense

Substances transported by blood

NutrientsWaste products

Respiratory gasesHormones

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: – 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– 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

Precapillarysphincters

Thoroughfarechannel

Arteriole

Capillaries

Venule

(a) Sphincters relaxed

Arteriole Venule

(b) Sphincters contracted

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

– osmotic pressure of the blood/OP – determined by the solutes within the blood plasma

• inward driving force – from interstitial fluid to plasma

INTERSTITIALFLUID Net fluid movement out

Bloodpressure

Osmoticpressure

Arterial endof capillary Direction of blood flow

Venous endof capillary

Body cell

Ultrafiltration Reabsorption

PC decreases with blood flowOP remains the same

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

INTERSTITIALFLUID Net fluid movement out

Bloodpressure

Osmoticpressure

Arterial endof capillary Direction of blood flow

Venous endof capillary

Body cell

Ultrafiltration Reabsorption

PC decreases with blood flowOP remains the same

Bulk Flow = Ultrafiltration – ReabsorptionUltrafiltration is driven by PcReabsorption is driven by OP