The Circulatory System

The circulatory system Refer Chapter 43, Internal transport, pg 919

Circulatory system in………. Unicellular organisms and Multicellular organisms

Trading with the Environment • Every organism must exchange materials with its environment – And this exchange occurs at the cellular level

• In unicellular organisms – exchanges occur directly with the environment • In multicellular organisms – by diffusion is NOT possible, WHY? – not possible for transporting substances over long distance in animal – The surface area to volume ratio of the organism is small so that diffusion of materials across the body surface cannot keep pace with demand Most complex animals have internal transport systems That circulate fluid, providing a lifeline between the aqueous environment of living cells and the exchange organs (such as lungs) that exchange chemicals with the outside environment

Unicellular organism: in contact with the environment • A single-celled protist living in water

Diffusion

– Has a sufficient surface area of plasma membrane to facilitates the direct exchange with the environment

(S.A.-to-Vol. R ↑) • Exchange with the environment occurs as substances dissolved in the aqueous medium – Nutrients and oxygen move across the plasma membrane into the cytoplasm. – Metabolic wastes (CO2) move

(a) Single cell

Contact with the environment

• The feathery gills projecting from a salmon – Are an example of a specialized exchange system found in animals

Invertebrate circulation (1) Gastrovascular cavities (2) Open and closed circulatory system L.O. Compare and contrast internal transport in animals with NO circulatory system (gastrovascular cavity) With an open circulatory system And with a closed circulatory system

Types of circulatory systems • NO circulatory system

– No specialized circulatory structures – E.g. sponges, jellyfish, comb jellies, flat worms, round worms – Cnidarians (jellyfish), gastrovascular cavity (both circulatory and digestive organs)---animal stretches and contracts—stir up the contents of the gastrovascular cavity, distribute nutrients – Flatworm, flattened body— effective gas exchange by diffusion, gastrovascular cavity —branched

Invertebrate circulation: Gastrovascular Cavities

• Simple animals/multicellular organism, (cnidarians) – body wall only two cells thick that encloses a gastrovascular cavity

Mouth

Gastrovascular cavity

Diffusion

• The fluid inside the cavity is continuous with the water outside, via a single opening.

Diffusion

• Only the cells of the inner layer have direct access to nutrients,

– but the nutrients have to diffuse only a short distance to

(b) Two cell layers

Invertebrate circulation: Open and Closed Circulatory Systems • More complex animals – Have one of two types of circulatory systems: open or closed • Both of these types of systems have three basic components – A circulatory fluid (blood> con. t) – A set of tubes (blood vessels, in which blood circulates) – A muscular pump (the heart)

Open circulatory system In insects (arthropods) and most molluscs – Blood bathes the organs directly in an open circulatory system – and Heart pumps blood intothe vessels have open Blood interstitial fluid are samethat – hemolymph. ends Spaces surrounding the organs – sinuses---make up the hemocoel (invert. blood cavity) Heart

Hemolymph in sinuses surrounding organs

Figure:

(a) An open circulatory system

Open circulatory system When the heart contracts, the heart pumps the hemolymph through vessels out into sinuses---where materials are exchanged between the hemolymph and cells. When the heart relaxes, hemolymph returns to the heart through ostia, which are equipped with valves

Heart

Hemolymph in sinuses surrounding organs

Anterior vessel

Lateral vessels

Ostia

The body movements that squeeze the sinuses help circulate the hemolymph. The rate of hemolymph Figure 42.3a circulation increases when

(a) An open circulatory system

Tubular heart

Figure 43.2: Open circulatory systems. In mollusks and arthropods, a heart pumps the blood into arteries that end in sinuses of the hemocoel. Hemolymph circulates through the hemocoel. In mollusks, Heart- 3 chambers (TWO atria, SINGLE ventricle) heart >sinuses of the hemocoel >gills >heart In arthropods, heart> sinuses of the hemocoel > heart via ostia In some molluscs and arthropods---have hemocyanin, open circulatory system cannot (copper-containingAn hemolymph pigment); when provide enoughBLOODS!! oxygen to maintain the oxygenated, blue colour----BLUE

Open circulatory system Open circulatory system show : (2) a lowered transport efficiency and (3) a slower circulatory time

Annelids, cephalopods and echinoderms

Closed circulatory system In a closed circulatory system – Blood is confined to vessels and is distinct from Chemical exchange occurs: the interstitial fluid -between the blood and the interstitial fluid, -and between interstitial fluid and body cells.

Interstitial fluid bathing the cells

Heart

Small branch vessels in each organ

Dorsal vessel (main heart)

Auxiliary hearts Ventral vessels (b) A closed circulatory system

• Earthworms, have hemoglobin – NOT contained within RBC, but dissolved in the blood plasma

• TWO main blood vessels – dorsal and ventral vessels, connected by lateral vessels

• FIVE contractile b.v. (heart) pump blood • Dorsal vessel, 5 contractile b.v. and contraction body wall muscle--> circulate the blood

What is the advantage associated with… …..? Open circulatory system – Energy expenditure ↓ –Because they lack an extensive system of blood vessels-- require less energy.

Closed circulatory system -More efficient at transporting circulatory fluids >> tissues and cells. -To meet the high metabolic demands of the tissues and cells of larger and more active animals

Vertebrate Circulation Cardiovascular system

What are the functions of the vertebrate circulatory system? (1) Transportation of nutrients, respiratory gases, wastes and hormones (2) Maintenance of fluid balance (3) Internal defense (4) Thermoregulation (5) Maintenance of pH

Vertebrate Circulation

• Humans and other vertebrates have a closed circulatory system – cardiovascular system • Blood flows in a closed cardiovascular system – Consisting of blood vessels and a two- to four-chambered heart

Evolution of the vertebrate cardiovascular system L.O. Describe the evolution of the vertebrate cardiovascular system from fish to mammal

Vertebrate circulation: Fishes • A fish heart has two main chambers Fish – One ventricle and one atriumswimming • A single circuit of blood flow – one way street!

movement aids blood circulation

• Blood pumped from the ventricle – Travels to the gills (gill circulation), where it picks up O2 , disposes of CO2 – The gill capillaries converge into a vessel that carries O2 rich blood to capillary beds, all other Note: In a fish, blood must pass through two capillary parts of the body (systemic beds during each circuit.

FISHES Gill capillaries

Artery

Gill circulation Heart: ventricle (V) Atrium (A)

Systemic Vein circulation

Systemic capillaries

Pressure low here

Vertebrate circulation: Amphibians

• Frogs and other amphibians

– Have a three-chambered heart, with two atria (singular, atrium) and one ventricle – Oxygen-rich and oxygen-poor blood— kept separated – Both atria pump into a single ventricle, oxygen-poor blood is pumped out of the ventricle before oxygen-rich blood enters – Atria separated, ventricle undivided, oxygen and de-oxygenated blood are prevented from mixing by conus arteriosus, which keeps the blood apart

• The ventricle pumps blood into a forked artery – That splits the ventricle’s output into

AMPHIBIANS

Lung and skin capillaries

Pulmocutaneous circuit A

A

V Right Left Systemic circuit

Systemic capillaries

Vertebrate circulation: Amphibians • Pulmocutaneous circuit (pulmo- lung; cutaneous-skin) – The route of circulation that directs blood to the skin and lungs.

• Systemic circuit – The branch of the circulatory system that supplies oxygen-rich blood (oxygenated blood) to all body organs and then return oxygen-poor blood (deoxygenated blood) to the right atrium via the veins.

Sinus venosus > atrium > ventricle

Conus arteriosus, an artery with fold that helps to keep blood separate

Sinus venosus receives oxygen-poor blood returning from tissues and pumps it into atrium

Vertebrate circulation: Reptiles (e.g. crocodiles, alligators) • Reptiles have double circulation – With a pulmonary circuit (lungs) and a systemic circuit

• In most reptiles (turtles, lizards, snakes)—wall separating the ventricles is incomplete, partially divided ventricle—3 chambered heart

REPTILES Lung capillaries

Pulmonary circuit

Right systemic aorta A V Right

V

Left A Systemic aorta

Left

Systemic circuit Systemic capillaries

Vertebrate circulation: Mammals and birds • In all mammals and birds

– The ventricle is completely divided into separate right and left chambers

MAMMALS AND BIRDS Lung capillaries

• The left side of the heart pumps and receives only oxygen-rich blood

– While the right side receives and pumps only oxygen-poor blood

Pulmonary circuit

A

A

V Right

V

Left Systemic circuit

Systemic capillaries

Vertebrate circulatory systems

AMPHIBIANS

REPTILES

MAMMALS AND BIRDS

Lung and skin capillaries

Lung capillaries

Lung capillaries

FISHES

Gill capillaries

Gill circulation Heart: ventricle (V) A

Atrium (A) Systemic Vein circulation

Right systemic aorta

Pulmocutaneous circuit

Artery

Pulmonary circuit

A

A

V Right

V Left Right Systemic circuit

Pulmonary circuit

Left Systemic V aorta Left A

A V Right

A V Left Systemic circuit

Systemic circuit

Systemic capillaries

Systemic capillaries Figure 42.4

Systemic capillaries

Systemic capillaries

The human heart L.O. (1) Draw the structure and describe the function of the human heart (2) Describe the events of the cardiac cycle, relate the normal heart sound to the cardiac cycle

human heart: FACTS!! Not much bigger than a FIST!! Beats about 2.5 million times in an average lifetime, vary its output from 5 to > 20 L blood

Pericardium, Epicardium, myocardium, Endocardium • Walls of the heart, – cardiac muscle—myocardium

• Inner surface of heart, endocardium • Outer surface of the heart, Epicardium • Pericardium – Connective tissue sac, encloses the heart – Between inner and outer pericardium form a small space, pericardial cavity contain pericardial fluid, reduce friction

What are the major blood vessels to and from the heart ??

Coronary arteries: arteries which supply blood to the heart muscle

Structure and functions of the four heart chamber • The heart has four chamber

– The receiving chambers: right atrium, left atrium – The discharging chambers: right ventricle, left ventricle

• The internal partition (septum) that divides the heart longitudinally is called

– Interatrial septum (between atria) – Interventricular septum (between ventricles) – Fossa ovalis is located in the interatrial septum, remnant of the fetal foramen ovale

• Bloods enters the right atrium through:

– (1) anterior vena cava: returns blood from body regions above the diaphragm (upper body) – (2) posterior vena cava: returns blood from body regions below the diaphragm (lower body)

a.k.a Brachiocephalic trunk

Head & neck

I

Right pulmonary artery

L

C

S

L

Aorta Left pulmonary artery

Anterior vena cava

Left atrium

Right atrium Right pulmonary veins

Left pulmonary veins Semilunar (aortic) valve

Semilunar (pulmonary) valve

Bicuspid valve

Tricuspid valve

Posterior vena cava

Upper limb (arm)

Right ventricle Left ventricle

Aortic arch> Innominate artery (IA), Left common carotid artery (LCCA), Left Subclavian artery (LSA)

Brachio- = arm; Cephalic- = head

Fetal Foramen ovale become Fossa ovalis

• Foramen ovale (fetal heart)

– an opening on the interatrial septum – Lets blood flow directly from right to left atrium – So very little passes to the non-functional lungs

• Fossa ovalis – Shallow depression Foramen ovale closes shortly after birth, become fossa ovalis. When an infant takes its first breath, the lung expand and blood flow to the lung increases---blood return from lung to heart---increase pressure in left atrium, pushes a valve against the interatrial

Ductus arteriosus---a vessel linking pulmonary artery and aorta Ductus arteriosus closes by vasoconstriction almost immediately after birth, becomes the ligamentum arteriosum

Heart valves • Blood flows through the heart in one direction • This one-way traffic is enforced by four heart valves:

– the paired atrioventricular (AV) and semilunar (SL) valves

• AV valves held in place by chordae tendinae (KORde TEN-di-nee), “heartstrings” – Attach valves to the papillary muscles at the wall of the ventricles, prevent from opening backward into atria, ensure the valves open in one direction.

• Both the left AV (bicuspid/mitral valve, two cusps/flaps) and the right AV (tricuspid valve, three cusps/flaps) open when the ventricles relaxes. – When the ventricles contract, the AV valves close, forcing blood to leave the heart via the two semilunar valves

• SL valves (pulmonary valve and aortic valve)

Semilunar valve and atrioventricular valve, which is which?? Where are they located? Semilun ar valve Semilun ar valve

AV valve

AV valve

AV valves located between the atria and ventricles Semilunar valves located between the ventricles and blood vessels of the heart

Superior vena cava

Right pulmonary arteries Pulmonary valve Right atrium Pulmonary veins Tricuspid valve

Aorta Left pulmonary arteries Pulmonary artery Pulmonary veins Left atrium Mitral valve Aortic valve Chordae tendineae (“heartstrings”) Papillary muscles

Right ventricle

Left ventricle

Inferior vena cava

Interventricular septum Aorta Fig. 43-9, p. 929

Mammalian Circulation: The Pathway

• Heart valves – Dictate a one-way flow of blood through the heart • Blood begins its flow – With the right ventricle pumping blood to the lungs Anterior vena cava

• In the lungs – The blood loads O2 and unloads CO2 • Oxygen-rich blood from the lungs – Enters the heart at the left atrium and is pumped to the body tissues by the left ventricle

Pulmonary artery

Pulmonary veins

Right

Posterior vena cava

Left

Pathway of blood through the heart • The heart is a double pump that serves two circulations. • The blood vessels that carry blood to and from the lungs form the pulmonary circuit, strictly serves gas exchange. • The right side of the heart (right ventricle) is the pulmonary pump, to the lung.blood Oxygen-poor ORcircuit carbon dioxide-rich

returning from the body → right atrium → right ventricle → pumps it to the lung via pulmonary artery

• The blood vessels that carry blood to and from all body tissues constitute the systemic circuit. • The left side of the heart (left ventricle) is the systemic circuit pump, that has to pump blood through the entire systemic circulation against high resistance.

Oxygenated blood leaving the lungs → return to the left atrium → left ventricle → pump through the aorta → the body tissues (gases and nutrients exchange) → right atrium through anterior and posterior vena cava

The cardiovascular system: On the right side, blood flows out to the lungs, pulmonary circulation While on the left side, blood flows into aorta and to the systemic 7 Capillaries of head and forelimbs

circulation.Anterior

vena cava Pulmonary artery

Aorta

9

6

Capillaries of right lung

2

3

4

3

11

Pulmonary vein Right atrium

Pulmonary artery

5

1

Left atrium

Capillaries of left lung Pulmonary vein

10

Left ventricle Right ventricle

Aorta

Posterior vena cava 8

Figure 42.5

Capillaries of abdominal organs and hind limbs

Anatomical differences in the right and left ventricles • Although equal volumes of blood are flowing in the pulmonary and systemic circuits, the two ventricles have very unequal work loads.

– The pulmonary circuit, served by the right ventricle is a low pressure circulation whereas – The systemic circuit, associated by the left ventricle, takes a long pathway through the entire body, has a higher blood pressure. – The pressure needed to keep the blood flowing in the pulmonary circulation (typically 4kPa) is much less than needed in the systemic circulation (typically 16kPa) – Thus, the walls of the left ventricle are thicker and more muscular than those in the right ventricle.

Cardiac cycle • The sequence of heart beat (heart contracts and relaxes) – In a rhythmic cycle called the cardiac cycle

• The contraction or pumping phase of the cycle – Is called systole (atrial systole; ventricular systole)

The cardiac cycle Cardiac cycle refers to events occurring during one heart Semilunar beat. 2 Atrial systole; For a human adult at rest, a ventricular valves diastole closed pulse of about 75 beats per min, one complete cardiac cycle takes about 0.8s. 0.1 sec

Semilunar valves open

0.3 sec 0.4 sec

AV valves open

1 Atrial and ventricular diastole

Figure 42.7

AV valves closed 3 Ventricular systole; atrial diastole

(1) During a relaxation phase, blood returning from large veins flows into the atria and ventricles. (2) Atrial systole forces all remaining blood out of the atria into the ventricles. (3) Ventricular systole pumps blood into the large arteries.

Superior vena cava Right atrium Tricuspid valve Inferior vena cava 5 Period of falling pressure. Blood flows from veins into relaxed atria.

Aorta

Pulmonary artery Semilunar valves Pulmonary vein Left atrium Mitral valve

Right Left ventricle ventricle

“lub” Heart sounds

“dup” 4 Beginning of ventricular diastole. Pressure in relaxing ventricles drops below that in arteries. Semilunar valves snap shut, causing second heart sound.

1 Atrial systole. Atria contract, pushing blood through open tricuspid and mitral valves into ventricles. Semilunar valves are closed. 2 Beginning of ventricular systole. Ventricles contract; pressure within ventricles increases and closes tricuspid and mitral valves, causing first heart sound.

3 Period of rising pressure. Semilunar valves open when pressure in ventricle exceeds that in arteries. Blood spurts into aorta and pulmonary artery. Fig. 43-11, p. 931

Heart Sound • Normal heart sounds arise from the closing of heart valves. • During each cardiac cycle, two distinguishable sounds can be heard with a stethoscope : “lub-dup” • The first sound – “lub” : created by the recoil of blood against the closed AV valves (during ventricular systole). • The second sound – “dup” : created by the recoil of blood against the semilunar valves (during ventricular diastole). • Abnormal or unusual heart sounds are called heart murmurs (a defect in one or more valves). – Some are born with heart murmurs, some damaged by infection (e.g. rheumatic fever).

“lub”

“dup”

Pulse: Think of the water hose!! During the passage of blood from ventricle into the aorta and along the entire systemic circulation, a wave of dilation (expansion) sweeps along a linear fashion followed immediately by a wave of contraction. These alternate contractions and dilations may be felt as the pulse if a finger is placed above an artery that lies close to skin. The pulse is actually a measure of the

Pulse • The elastic walls of the arteries expand when they receive the blood expelled from the ventricles. • By feeling your pulse, your heart rate can be measured. • Pulse: the rhythmic stretching of arteries caused by the pressure of blood driven by the powerful contractions of the ventricles

Cardiac output • The volume of blood that left the ventricle, pumps into the systemic circuit in 1 minute is called – Cardiac output

• Cardiac output depends on two factors: – (1) Heart rate (pulse) = no. of beats (ventricular contraction) per minute – (2) Stroke volume = the amount of blood pumped by left ventricle with each beat. Cardiac output (L/min) = HR (beats/min) X SV (ml/beat) = 70 beats/min X 75 mL/beat

Coordination of the heart

Sinoatrial node (SAN) • The heart has an innate ability to beat on their own. • The sinoatrial node (SAN), a small patch of specialized cardiac muscle, located in the wall of the right atrium near the entrance of the anterior vena cava. • It acts as the pacemaker, sets the rhythm of the heart • The pacemaker is influenced by – Nerves, hormones, body temperature (temp↑, HR ↑) and exercise.

Coordination of the heart beat • The cells of the SAN are spontaneously active or myogenic (self excitable), contract rhythmically in the absence of stimulation. • Nerve that carry impulse to the heart, influence rate and strength of contraction, do NOT initiate heartbeat • Excitation originating in the SAN spreads out across the atria, producing a uniform contraction called atrial systole, which fill ventricles with blood. • Excitation must pass to the ventricles by the way of the atrioventricular node (AVN), a

Coordination of the heart beat….continue • From the AVN, the impulse sweeps to the atrioventricular bundle (bundle of His) and through the right and left bundle branches. • The bundle branches carry signals downward to the base of the heart. • The signals are transmitted to a network of Purkinje fibers within the ventricle walls. • Thus, the contraction, called ventricular systole, starts at the bottom of the heart and spread upwards, forcing the blood out from the ventricles into the aorta and pulmonary artery.

SAN> Atrial muscle fibers (atria contract)>AVN > AV bundle “Bundle of His”> Right and Left AV bundle branches > Purkinje fibers> ventricular fibers (ventricles contract)

1. SA node or pacemaker

Left atrium

Right atrium 2.

AV node

5. Purkinje fibers Right ventricle

3. AV bundle Left ventricle Right and left branches of AV bundle

4.

Fig. 43-10a, p. 930

Electrocardiogram (ECG) • The electrical activity of a person’s heart can be detected by placing metal electrodes on the external surface of his body, usually on the legs, arms and chest. • The graphic recording of electrical changes during the heart activity, called an electrocardiogram (ECG). • Diagnosis of heart diseases: monitoring changes in heart rate (tracing electrical changes in the heart), used in conjunction with exercise machines.

Abnormalities in the ECG What does that implies? Irregular rhythm of the heart Impulse transmission is delayed, blocked at some point in the conduction of the heart What is the solution?? Artificial pacemakers

P-wave, QRS region, T-wave Each beat of the heart is characterized by five separable wave regions on the ECG. • The P-wave represents the electrical activity (atrial depolarization, loss of resting potential) and contraction of the atria as excitation spreads outwards from the SAN. • QRS region corresponds to excitation of the ventricles (ventricular depolarization; ventricular contraction). Its complicated shape reveals the different size of the two ventricles and the time required for each to depolarize. • The final T-wave signals recovery of the ventricles (ventricular repolarization) at the end of contraction, muscle relaxing, ventricles starting

Membrane potential (mV)

Spike

Depolarization

Repolarization

Threshold level

Resting state

Time (milliseconds)

(a) Action potential. Fig. 40-7a, p. 853

The control of heart rhythm 1 Pacemaker generates

wave of signals to contract.

2 Signals are delayed

at AV node.

3 Signals pass

to heart apex.

4 Signals spread

Throughout ventricles.

Bundle of His

AV node

SA node (pacemaker)

Bundle branches Heart apex

R T

P ECG

Q

S

Figure 42.8

Purkinje fibers

Systemic circulation • The pattern of circulation: – Blood is pumped through pulmonary and systemic circuits

• The pulmonary circulation oxygenates the blood • The systemic circulation delivers blood to the tissues – The carotid arteries supply the brain (head) & neck – The subclavian arteries supply the upper appendages

Systemic circulation • Veins return blood to the right side of the heart – Jugular veins return blood from the brain – Subclavian veins, from the upper appendages – Renal veins, from kidneys – Iliac veins, from lower appendages Renal, iliac and hepatic veins empty into the Posterior vena cava – Hepatic veins, from the liver Jugular and subclavian veins empty into the Anterior vena cava

Blood vessel: The blood’s highway

Blood vessels: Arteries> arterioles> capillaries> venules > veins • Arteries – Carry blood from the heart – Smaller arteries: arterioles – Branch into arterioles that convey blood to capillaries

• Capillaries – The sites of chemical exchange between the blood and interstitial fluid – Network of these vessels: capillary beds (Lies between arterioles and venules) – Capillaries converge into venules and venules converge into veins. • Veins – Return blood to the heart – Smaller veins:and venules REMEMBER: Arteries veins are distinguished by the direction in which they carry blood, NOT by the characteristic of the blood they contain.

Blood Vessel: Structure and Function

The “infrastructure” of the circulatory system –

network of blood vessels

All blood vessels

(artery, arteriole, venule, vein

except capillaries)

–

are built of three similar layers; • Outer layer: Connective tissue • Middle layer: Smooth muscle • Inner layer: Endothelium

Capillaries: lack the two outer layers, consist of endothelium and basement membrane

Vein

Artery

Basement membrane Endothelium

100 µm Valve

Endothelium

Smooth muscle Connective tissue

Endothelium

Smooth muscle

Capillary Connective tissue

Artery

Vein

Venule Arteriole

Figure 42.9: The structure of blood vessels.

Arteries • Connective tissue (tunica externa: inelastic) • Smooth muscle (tunica media: thickest layer) The functional contractions of the artery are carried out by this layer. (3) Endothelium (intima: elastic membrane)

Veins • •

Have similar 3 structure walls except that they are thinner. Rely on a series of one-way valves working

• Structural differences in arteries, veins, and capillaries – Correlate with their different functions

• Arteries have thicker walls outer layers)

(middle and

– To accommodate the high pressure of blood pumped from the heart – Their elasticity helps maintain blood pressure even when the heart relaxes between contractions.

• In the thinner-walled veins – Blood flows back to the heart mainly as a result of muscle action – Blood is convey back to the heart at low velocity and pressure Direction of blood flow in vein (toward heart) Valve (open)

Contraction of skeletal muscles helps move blood through the veins.

Skeletal muscle Valve (clos ed) Figure 42.10: Blood flow in veins

Several mechanisms assist the return of venous blood to the heart (1) Rhythmic contraction of smooth muscles in walls of venules and vein (2) Contraction of skeletal muscles during exercise (3) Change in pressure within thoracic (chest) cavity during inhalation causes vena cava and other large vein expand and filled with blood

Systolic pressure

Venae cavae

Veins

Venules

Capillaries

Diastolic pressure

Arterioles

120 100 80 60 40 20 0

Arteries

Area (cm2)

50 40 30 20 10 0

Aorta

Figure 42.11: The interrelationship of blood flow velocity, cross sectional area pf blood vessels and blood pressure

Velocity (cm/sec)

• The velocity of blood flow varies in the circulatory system – And is slowest in the capillary beds as a result of the high resistance and large total cross-sectional area

5,000 4,000 3,000 2,000 1,000 0

Pressure (mm Hg)

Blood flow velocity

Blood pressure CO increases, increase blood flow, blood pressure increases, BP greatest in the artery, very low in the vein

depends on blood flow and resistance to blood flow Peripheral resistance> friction between blood and vessel’s wall---blood viscosity, size of the blood vessel lumen, total blood vessel length

Vasoconstriction of bv raises BP, vasodilation lowers BP During hemorrhage or chronic bleeding, blood volume reduced, blood pressure drop. A high dietary in-take of salts causes water retention, increases blood volume, raises blood pressure.

Blood Pressure Blood Pressure –Is the force that blood exerts against the inner wall of a vessel –Determined by CO, blood vol. , and resistance to blood flow –Expressed as a fraction, systolic--numerator, diastolic --denominator Systolic pressure A normal blood –Is the pressure in the arteries during ventricular pressure, systole measured in the upper arm with a –Is the highest pressure in the arteries sphygmomanomet –< 120 mm Hg er—110/73 mm Hg Diastolic pressure –Is the pressure in the arteries during diastole

•

The blood pressure

Produced by two primary events

The first force: the force of the heartbeat imposed on the blood leaving the ventricle (cardiac output/blood flow) The second force: the peripheral resistance (back pressure) to that force, imposed by the arteries and, more significantly, the arterioles

For example,

When water moves through a garden hose, the pressure within the hose is determined by the head of pressure at the source and the resistance along the hose and its end. If the nozzle of the hose is constricted, the hydrostatic pressure will rise. Similarly, if the hose itself is sharply bent, the resistance to flow increases sharply and the pressure will go way up.

Blood pressure 1 A typical blood pressure reading for a 20-year-old is 120/70. The units for these numbers are mm of mercury (Hg); a blood pressure of 120 is a force that can support a column of mercury 120 mm high.

Pressure in cuff below 120

Pressure in cuff above 120

Rubber cuff inflated with air

Artery

4 The cuff is loosened further until the blood flows freely through the artery and the sounds below the cuff disappear. The pressure at this point is the diastolic pressure remaining in the artery when the heart is relaxed. Blood pressure reading: 120/70 Pressure in cuff below 70

120

120

70

Sounds audible in stethoscope

Sounds stop

Artery closed

2 A sphygmomanometer, an inflatable cuff attached to a pressure gauge, measures blood pressure in an artery. The cuff is wrapped around the upper arm and inflated until the pressure closes the artery, so that no blood flows past the cuff. When this occurs, the pressure exerted by the cuff exceeds the pressure in the artery.

3

A stethoscope is used to listen for sounds of blood flow

below the cuff. If the artery is closed, there is no pulse below the cuff. The cuff is gradually deflated until blood begins to flow into the forearm, and sounds from blood pulsing into the artery below the cuff can be heard with the stethoscope. This occurs when the blood pressure is greater than the pressure exerted by the cuff. The pressure at this point is the systolic pressure.

Figure 42.12: Measurement of blood pressure. Blood pressure is recorded as two numbers separated by a slash. First number= systolic pressure; the second number= diastolic pressure

Capillary Function • Capillaries in major organs are usually filled to capacity (brain, heart, kidney and liver) – But in many other sites, the blood supply varies – Blood is divert from one destination to another For example,

After a meal, blood supply increases in the digestive tract. During strenuous exercise, blood is diverted from the digestive tract and supplied more generously to skeletal muscles and skin.

Capillary Function • Two mechanisms regulate the distribution of blood in capillary beds – In one mechanism • Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel

– In a second mechanism • Precapillary sphincters control the flow of blood between arterioles and venules • Precapillary sphincters? -rings of smooth muscle located at the entrance to capillary beds.

Precapillary sphincters

• The critical exchange of substances between the blood and interstitial fluid – Takes place across the thin endothelial walls of the capillaries Figure 42.13 a–c

Thoroughfare channel

Arteriole

Venule Capillaries

(a) Sphincters relaxed

Arteriole

Venule

(b) Sphincters contracted

(c) Capillaries and larger vessels (SEM) 20 µm

• The difference between blood pressure and osmotic pressure – Drives fluids out of capillaries at the arteriole end and into capillaries at the venule end • Interstitial fluid: – The internal environmental in vertebrates, exchanges nutrientsTissue and cell wastes with blood carried in capillaries. INTERSTITIAL FLUID Capillary Red Blood cell

Net fluid movement in

15 µm

At the arterial end of a capillary, blood pressure is greater than osmotic pressure, and fluid flows out of the capillary into the interstitial fluid.

Direction of blood flow

Pressure

Capillary

Net fluid movement out

Blood pressure Osmotic pressure

At the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary.

Inward flow

Outward flow

Arterial end of capillary

Venule end

Figure 42.14: Fluid exchange between capillaries and the interstitial fluid

Fluid Return by the Lymphatic System • The lymphatic system functions – (1) Collects and returns interstitial fluid to the blood – (2) Aids in body defense – (3) Absorbs lipids from the digestive tract

• Fluid reenters the circulation – Directly at the venous end of the capillary bed and indirectly through the lymphatic system

Fluid Return by the Lymphatic System • Interstitial fluid diffuses into tiny lymph capillaries intermingled among capillaries of the cardiovascular system. • Once inside the lymphatic system, the fluid is called lymph. • Its composition is about the same as that of interstitial fluid. • The lymphatic system return lymph into the circulatory system, at the base of the subclavian veins

• Lymph vessels (like veins) – have valves, to prevent the backflow of fluid toward the capillaries. – depend mainly the movement of skeletal muscles, to squeeze fluid toward the heart. • Lymph nodes – Filter the lymph and attack viruses and bacteria. – This defense is carried out by specialized white blood cells that inhabit the lymph nodes. • Lymph capillaries – penetrate small intestine villi and absorb fats, thus transporting them from the digestive system to the circulatory system. of lymph tissue, Tonsils, thymus gland, and spleen—masses part of lymphatic system

The lymphatic system plays an important role in fluid homeostasis • Bloods enters a capillary network--under high pressure, plasma forced out of the capillaries into tissues • Plasma that leaves the b.v. called interstitial fluid OR tissue fluid--contain glucose, a.a., nutrients, var. of salts, oxygen • Force pushing plasma out from blood is hydrostatic pressure (blood pressure against capillary wall)

A shortage of proteins within the blood, largely albumin, would inhibit the reabsorption of fluid at the venule end of a capillary bed. The failure to reabsorb fluid will produce a generalized swelling known as edema.

Blood “Blood is a connective tissue with cells suspended in plasma.” • Blood in the circulatory systems of vertebrates – Is a specialized connective tissue

Blood: Composition and Function • Blood consists of several kinds of cells – Suspended in a liquid matrix called plasma, 55% of the blood vol.

• The cellular elements (platelets and blood cells) – Occupy about 45% of the volume of blood

Plasma

• Blood plasma is ~90-92% water • ~7-10% dissolved materials (Proteins, glucose, ions, hormones, wastes and gases) – Inorganic salts in the form of dissolved ions, referred to as electrolytes • Types of plasma proteins – E.g. Albumin, fibrinogen, globulins (α, β, γ or Immunoglobulins) – Function in lipid transport, immunity, and blood clotting • plasma proteins---albumins and globulins

When the proteins involved in blood clotting removed from plasma, liquid called serum

Plasma 55% Constituent

Major functions

Water

Solvent for carrying other substances

Ions (blood electrolytes) Sodium Potassium Calcium Magnesium Chloride Bicarbonate Plasma proteins Albumin Fibrinogen Immunoglobulins (antibodies)

Osmotic balance pH buffering, and regulation of membrane permeability

Separated blood elements

Osmotic balance, pH buffering Clotting Defense

Substances transported by blood Nutrients (such as glucose, fatty acids, vitamins) Waste products of metabolism Respiratory gases (O2 and CO2) Hormones

Figure 42.15: The composition of mammalian plasma

The composition of mammalian plasma

Cellular Elements • Suspended in blood plasma are two classes of cells – Red blood cells, which transport oxygen – White blood cells, which function in defense

• A third cellular element, platelets – Are fragments of cells that are involved in clotting (stop hemorrhage/bleeding)

The shape of the red blood cell is often described as a biconcave disc. What is the evidence from this photograph that these cells could have a biconcave shape?

Erythrocytes (RBC): “bags” of hemoglobin

• Red blood cells, or erythrocytes – Biconcave disc: • thinner in the center than at the edges – 7- 8.5µm in diameter, Lifespan: 120 days or 3-4 months – Are by far the most numerous blood cells – Produced within the red bone marrow of certain bones: RBC production, regulated by hormone, • Vertebrae, ribs, breastbone, skull bones and erythropoietin long bones

RBC • Mature red blood cells lack a nucleus, have no organelles • The bulk of the RBC is taken up by protein hemoglobin. Hemoglobin is the chief transport protein involved in carrying oxygen. • An erythrocyte contains about 250 million molecules of hemoglobin, Each hemoglobin binds up to four molecules of O2. • When blood circulates through the liver and spleen, phagocytic cells remove worn-out RBCs Anemia a deficiency of hemoglobin, or no. of RBC, or BOTH---due to fromisthe circulation bleeding, decreased production of hemoglobin or RBCs due to lack of iron, or destruction of RBCs (sickle cell anemia)

RBC: Facts!! Biconcave shape gives 30% more surface area than a sphere Easily deformed—important in passing through tiny capillaries RBCs have no mitochondria, don’t use the oxygen they carry, rely on glucose absorbed from the blood plasma Their metabolism entirely anaerobic!! (Hence, short lifespan)

Leukocytes (WBC) • Larger than erythrocytes (RBC) • Have a nucleus, lack hemoglobin • The blood contains five major types of white blood cells, or leukocytes – Basophils, eosinophils, neutrophils, monocytes, and lymphocytes, – which function in defense (by phagocytizing bacteria and debris or by producing antibodies) Leukemia is a cancer of WBC, overabundance of these immature cells, leads to impaired clotting

Leucocytes (WBC) Two main groups: • Granulocytes:

– Basophils, eosinophils, neutrophils >Have granules in their cytoplasm >Have a multilobed nucleus

• Nongranulocytes (agranulocytes) – Lymphocytes and monocytes

>Do NOT have granules and have nonlobular nuclei

– Lymphocytes (T and B cells)

>T cells: attack cells containing bacteria >B cells: produce antibodies

Cellular elements 45% Cell type

Separated blood elements

Number per µL (mm3) of blood

Functions

Erythrocytes (red blood cells)

5–6 million

Transport oxygen and help transport carbon dioxide

Leukocytes (white blood cells)

5,000–10,000

Defense and immunity

Lymphocyte

Basophil Eosinophil Neutrophil Platelets

Monocyte

250,000− 400,000

Blood clotting

The cellular elements of mammalian blood

Figure 42.15: Cellular elements of the mammalian blood

Platelets (Thrombocytes)

• Are rounded bodies (cell fragments that bud off from megakaryocytes in bone marrow) • 2-3µm in diameter, no nuclei • Essential in blood clotting, they initiate blood clotting process

Stem Cells and the Replacement of Cellular Elements • The cellular elements of blood wear out – And are replaced constantly throughout a person’s life

Erythrocytes, leukocytes, and platelets all develop from a common source

Pluripotent stem cells (in bone marrow)

–A single population of cells called pluripotent stem cells in the red marrow of bones

Lymphoid stem cells

Myeloid stem cells

Basophils

B cells

T cells

Lymphocytes Eosinophils

Neutrophils

Pluripotent: ability to develop into many different cell types of the body

Erythrocytes

Figure 42.16

Platelets

Monocytes

Blood Clotting – The clotting process is initiated by injury to blood-vessel walls. – The clot consists of a network of fibrin and blood cells

A cascade of complex reactions – Converts fibrinogen to fibrin, forming a clot 3

1 The clotting process begins when the endothelium of a vessel is damaged, exposing connective tissue in the vessel wall to blood. Platelets adhere to collagen fibers in the connective tissue and release a substance that makes nearby platelets sticky.

2 The platelets form a plug that provides emergency protection against blood loss.

Collagen fibers Platelet plug Platelet releases chemicals that make nearby platelets sticky

This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via a multistep process: Clotting factors released from the clumped platelets or damaged cells mix with clotting factors in the plasma, forming an activation cascade that converts a plasma protein called prothrombin to its active form, thrombin. Thrombin itself is an enzyme that catalyzes the final step of the clotting process, the conversion of fibrinogen to fibrin. The threads of fibrin become interwoven into a patch (see colorized SEM).

Fibrin clot Red blood cell

Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K) Prothrombin

Figure 42.17

Thrombin

Fibrinogen

Fibrin

5 µm

Cardiovascular disease

Cardiovascular disease: Atherosclerosis • atherosclerosis – Is caused by the buildup of cholesterol within arteries Connective tissue Smooth muscle

(a) Normal artery Atherosclerosis

Plaque Endothelium

50 µm (b) Partly clogged artery

250 µm

Atherosclerosis

– narrowing of the coronary arteries, inadequate supply of blood to the heart muscle, lead to angina. – angina: pain in the chest because of narrowing of the arteries supplying blood to the heart muscle)

Cardiovascular diseases: disorders of the heart and the blood vessels

• Hypertension, or high blood pressure – Promotes atherosclerosis and increases the risk of heart attack and stroke

• A heart attack – Is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries

• A stroke – Is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head

END OF LECTURE