The heart circulates blood to every tissue and organ, sustaining all bodily strength

Functions of the Circulatory System

• Transportation:– Respiratory:

• Transport 02 and C02.

– Nutritive:• Carry absorbed digestion products to liver and

to tissues.

– Excretory:• Carry metabolic wastes to kidneys to be

excreted.

Functions of the Circulatory System (continued)

• Regulation:– Hormonal:

• Carry hormones to target tissues to produce their effects.

– Temperature: • Divert blood to cool or warm the body.

– Protection:• Blood clotting.

– Immune: • Leukocytes, cytokines and complement act against

pathogens.

Components of Circulatory System

• Components of Cardiovascular system (CV):– Heart:

• Pumping action creates pressure head needed to push blood through vessels.

– Blood vessels:• Permits blood flow from heart to cells and back to the

heart.– Arteries, arterioles, capillaries, venules, veins.

• Lymphatic System:– Lymphatic vessels transport interstitial fluid.

• Lymph nodes cleanse lymph prior to return in venous blood.

Components of Whole Blood

Figure 17.1

Composition of Blood

• Composition of blood• Plasma:

– Straw-colored liquid.• Consists of H20 and dissolved solutes.

– Ions, metabolites, hormones, antibodies.» Na+ is the major solute of the plasma.

• Plasma proteins:– Constitute 7-9% of plasma.

• Albumin: – Accounts for 60-80% of plasma proteins.– Provides the colloid osmotic pressure needed to draw H20

from interstitial fluid to capillaries.» Maintains blood pressure.

• Composition of blood:• Plasma proteins (continued):

– Globulins:globulin:

– Transport lipids and fat soluble vitamins.globulin:

– Transport lipids and fat soluble vitamins.globulin:

– Antibodies that function in immunity.

• Fibrinogen:– Constitutes 4% of plasma proteins.– Important clotting factor.

• Converted into fibrin during the clotting process.

Composition of the Blood (continued)

• Composition of blood

• Serum:– Fluid from clotted blood.

• Does not contain fibrinogen.

• Plasma volume:– Number of regulatory mechanisms in the

body maintain homeostasis of plasma volume.

• Osmoreceptors.• ADH.• Renin-angiotensin-aldosterone system.

Composition of the Blood (continued)

Blood Cells and Platelets

Erythrocytes• Erythrocytes– Flattened biconcave discs.– Provide increased surface area through which

gas can diffuse.– Lack nuclei and mitochondria.

• Half-life ~ 120 days.

– Each RBC contains 280 million hemoglobin with 4 heme chains (contain iron).

– Removed from circulation by phagocytic cells in liver, spleen, and bone marrow.

Leukocytes• Leukocytes:– Contain nuclei and mitochondria. – Move in amoeboid fashion.

• Can squeeze through capillary walls (diapedesis).

– Almost invisible, so named after their staining properties.

• Granular leukocytes:– Help detoxify foreign substances.

» Release heparin.

• Agranular leukocytes:– Phagocytic.

» Produce antibodies.

Platelets (thrombocytes)• Platelets (thrombocytes)– Smallest of formed elements.

• Are fragments of megakaryocytes.• Lack nuclei.

– Capable of amoeboid movement.– Important in blood clotting:

• Constitute most of the mass of the clot.• Release serotonin to vasoconstrict and reduce

blood flow to area.

– Secrete growth factors:• Maintain the integrity of blood vessel wall.

– Survive 5-9 days.

Hematopoiesis

• Hematopoiesus– Undifferentiated cells gradually differentiate to

become stem cells, that form blood cells.– Occurs in myeloid tissue (bone marrow of long

bones) and lymphoid tissue.– 2 types of hematopoiesis:

• Erythropoiesis:– Formation of RBCs.

• Leukopoiesis:– Formation of WBCs.

Figure 23.1 The human heart

Figure 23.14 The circulatory plan in gill-breathing fish (Part 2)

Figure 23.22 Circulation through the body of a crayfish or lobster (Part 1)

Figure 23.18 Blood flow in heart ventricles and systemic and pulmonary arteries of crocodilians

Pulmonary and Systemic Circulations

• Pulmonary circulation:– Path of blood from right

ventricle through the lungs and back to the heart.

• Systemic circulation:– Oxygen-rich blood

pumped to all organ systems to supply nutrients.

• Rate of blood flow through systemic circulation = flow rate through pulmonary circulation.

Figure 23.10 The circulatory plan in mammals and birds (Part 1)

Figure 23.10 The circulatory plan in mammals and birds (Part 2)

Figure 23.14 The circulatory plan in gill-breathing fish (Part 1)

Figure 23.15 The circulatory plans of some air-breathing fish (Part 1)

Figure 23.15 The circulatory plans of some air-breathing fish (Part 2)

Figure 23.16 The branchial vascular arches of a lungfish

Figure 23.19 The circulatory plan of squids and octopuses (Part 1)

Figure 23.22 Circulation through the body of a crayfish or lobster (Part 2)

Box 23.3 Blood flow through the tissues of an insect is principally through lacunae and sinuses

Conducting Tissues of the Heart

• Contracting tissues of the heart:– APs spread through myocardial cells through gap

junctions.– Impulses cannot spread to ventricles directly because

of fibrous tissue.– Conduction pathway:

• SA node.• AV node.• Bundle of His.• Purkinje fibers.

– Stimulation of Purkinje fibers cause both ventricles to contract simultaneously.

Conducting Tissues of the Heart (continued)

Conduction of Impulse

• Conduction of impulse– APs from SA node spread quickly at rate of

0.8 - 1.0 m/sec.– Time delay occurs as impulses pass

through AV node. • Slow conduction of 0.03 – 0.05 m/sec.

– Impulse conduction increases as spread to Purkinje fibers at a velocity of 5.0 m/sec.

• Ventricular contraction begins 0.1–0.2 sec. after contraction of the atria.

Refractory Periods

• Refractory periods:• Heart contracts as

syncytium.• Contraction lasts

almost 300 msec. • Refractory periods

last almost as long as contraction.

• Myocardial muscle cannot be stimulated to contract again until it has relaxed.– Summation cannot

occur.

Electrocardiogram (ECG/EKG)

• EKG (ECG)• The body is a good conductor of electricity.

– Tissue fluids have a high [ions] that move in response to potential differences.

• Electrocardiogram:– Measure of the electrical activity of the heart per

unit time.• Potential differences generated by heart are conducted

to body surface where they can be recorded on electrodes on the skin.

• Does NOT measure the flow of blood through the heart.

ECG Leads

• ECG leads• Bipolar leads:

– Record voltage between electrodes placed on wrists and legs.

– Right leg is ground.

• Unipolar leads:– Voltage is recorded between

a single “exploratory electrode” placed on body and an electrode built into the electrocardiograph.

– Placed on right arm, left arm, left leg, and chest.

• Allow to view the changing pattern of electrical activity from different perspectives.

Figure 23.4 The conducting system and the process of conduction in the mammalian heart (Part 1)

Figure 23.4 The conducting system and the process of conduction in the mammalian heart (Part 2)

Figure 23.4 The conducting system and the process of conduction in the mammalian heart (Part 3)

Figure 23.6 Electrocardiography (Part 1)

ECG

• P wave:– Atrial

depolarization.

• QRS complex: – Ventricular

depolarization.– Atrial

repolarization.

• T wave:– Ventricular

repolarization.

Figure 23.6 Electrocardiography (Part 2)

Figure 23.6 Electrocardiography (Part 3)

Figure 23.2 The heart as a pump: The dynamics of the left side of the human heart

Figure 23.2 The heart as a pump: The dynamics of the left side of the human heart (Part 1)

Cardiac Cycle (continued)

• Step 1: Isovolumetric contraction:– QRS just occurred.– Contraction of the ventricle causes ventricular pressure to

rise above atrial pressure.• AV valves close.

– Ventricular pressure is less than aortic pressure.• Semilunar valves are closed.

– Volume of blood in ventricle is EDV.

• Step 2: Ejection:– Contraction of the ventricle causes ventricular pressure to

rise above aortic pressure.• Semilunar valves open.

– Ventricular pressure is greater than atrial pressure.• AV valves are closed.

– Volume of blood ejected: SV.

Cardiac Cycle (continued)

• Step 3: T wave occurs:– Ventricular pressure drops below aortic pressure.

• Step 4: Isovolumetric relaxation:– Back pressure causes semilunar valves to close.

• AV valves are still closed.– Volume of blood in the ventricle: ESV.

• Step 5: Rapid filling of ventricles:– Ventricular pressure decreases below atrial pressure.

• AV valves open.– Rapid ventricular filling occurs.

Figure 23.2 The heart as a pump: The dynamics of the left side of the human heart (Part 2)

Figure 23.3 Four systems evolved by animals to supply O2 to the myocardium (Part 1)

Figure 23.3 Four systems evolved by animals to supply O2 to the myocardium (Part 2)

Figure 23.7 Fluid-column effects on blood pressure in the arterial vascular system

Figure 23.8 Total fluid energy: The true driving force for blood flow

Figure 23.9 The physics of flow through tubes

Figure 23.11 A microcirculatory bed

Figure 23.12 Blood flow in the human systemic vasculature (Part 1)

Figure 23.12 Blood flow in the human systemic vasculature (Part 2)

Figure 23.13 Fluid exchange across mammalian systemic capillary walls

Maintaining Blood Pressure

• Maintaining blood pressure requires:– Cooperation of the heart, blood vessels, and

kidneys– Supervision of the brain

Maintaining Blood Pressure

• The main factors influencing blood pressure are:– Cardiac output (CO)– Peripheral resistance (PR)– Blood volume

• Blood pressure = CO x PR

• Blood pressure varies directly with CO, PR, and blood volume

Cardiac Output (CO)

• Cardiac output is determined by venous return and neural and hormonal controls

• Resting heart rate is controlled by the cardioinhibitory center via the vagus nerves– Stroke volume is controlled by venous return

(end diastolic volume, or EDV)

• Under stress, the cardioacceleratory center increases heart rate and stroke volume– The end systolic volume (ESV) decreases and

MAP increases

Frank-Starling Law

Cardiac Output (CO)

Figure 19.7

Controls of Blood Pressure

• Short-term controls: – Are mediated by the nervous system and

bloodborne chemicals– Counteract moment-to-moment fluctuations in

blood pressure by altering peripheral resistance

• Long-term controls regulate blood volume

Short-Term Mechanisms: Neural Controls

• Neural controls of peripheral resistance:– Alter blood distribution in response to demands– Maintain MAP by altering blood vessel diameter

• Neural controls operate via reflex arcs involving:– Baroreceptors– Vasomotor centers and vasomotor fibers– Vascular smooth muscle

Short-Term Mechanisms: Vasomotor Activity

• Sympathetic activity causes:– Vasoconstriction and a rise in BP if increased– BP to decline to basal levels if decreased

• Vasomotor activity is modified by:– Baroreceptors (pressure-sensitive),

chemoreceptors (O2, CO2, and H+ sensitive), higher brain centers, bloodborne chemicals, and hormones

Short-Term Mechanisms: Baroreceptor-Initiated Reflexes

• Increased blood pressure stimulates the cardioinhibitory center to:– Increase vessel diameter– Decrease heart rate, cardiac output,

peripheral resistance, and blood pressure

Short-Term Mechanisms: Baroreceptor-Initiated Reflexes

• Declining blood pressure stimulates the cardioacceleratory center to:– Increase cardiac output and peripheral

resistance

• Low blood pressure also stimulates the vasomotor center to constrict blood vessels

Baroreceptor Reflex (continued)

Regulation by ADH

• Released by posterior pituitary when osmoreceptors detect an increase in plasma osmolality.

• Dehydration or excess salt intake:– Produces sensation

of thirst.

– Stimulates H20 reabsorption from urine.

Chemicals that Decrease Blood Pressure

• Atrial natriuretic peptide (ANP) – causes blood volume and pressure to decline

• Nitric oxide (NO) – is a brief but potent vasodilator

• Inflammatory chemicals – histamine, prostacyclin, and kinins are potent vasodilators

• Alcohol – causes BP to drop by inhibiting ADH

Long-Term Mechanisms: Renal Regulation

• Long-term mechanisms control BP by altering blood volume

• Baroreceptors adapt to chronic high or low BP– Increased BP stimulates the kidneys to

eliminate water, thus reducing BP– Decreased BP stimulates the kidneys to

increase blood volume and BP

Kidney Action and Blood Pressure

• Kidneys act directly and indirectly to maintain long-term blood pressure– Direct renal mechanism alters blood volume– Indirect renal mechanism involves the renin-

angiotensin mechanism

Kidney Action and Blood Pressure

– Declining BP causes the release of renin, which triggers the release of angiotensin II

– Angiotensin II is a potent vasoconstrictor that stimulates aldosterone secretion

– Aldosterone enhances renal reabsorption and stimulates ADH release

Renin-Angiotension-Aldosterone System (continued)

Diving physiology part 1

• The oxygen store of divers– Adjustment of circulatory function

• CNS and heart dependent on aerobic catabolism for ATP production

• Skeletal muscle tolerant of O2 deprivation

• Blood flow to skin, gut, kidneys is curtailed by vasoconstriction

• Oxygen deprived tissue will turn to anaerobic catabolism

– Lactic acid accumulates

Diving physiology part 2

• The amount of O2 stored in blood depends on:– O2 carrying capacity of the blood

– Volume of blood

– Degree of saturation of blood with O2 at the time of submergence

Diving physiology

• Thoracic cavity and lungs-- compressible

• High myoglobin concentrations– In skeletal muscle – Large myoglobin-bound O2 stores– O2 remains bound to the myoglobin until the

O2 partial pressure in the muscles falls to a low level

Circulatory adjustment during dives

• Bradycardia – Drop in cardiac output– Weddell seals show an 86% drop in cardiac work and

an 85% reduction in blood flow to their ventricular heart muscle

• Regional vasoconstriction– Becomes a “heart-lung-brain” machine– Large concentration of rbcs in their blood when they

are diving– Rbcs stored in their spleen- release during dive

Metabolism during dives

• 3 factors determine the limits of endurance of the O2 –dependent tissues – Magnitude of O2 store available– Rate of use of the O2 store– Extent to which P02 can fall before impairing the

function of O2-dependent tissues

• MR during dive is the most important factor in determining metabolic limits on dive duration– low MR, slow O2 depletion, and slow lactic acid

accumulation

The aerobic dive limit

• Prolong dive has major behavioral consequences– Requires time for ridding body of lactic acid– Must stay at the water’s surface where it can

breathe– Lactic acid burdens of successive dives

• Additive • Example- a seal that accumulates 80 ml lactic

acid/ 100 ml of blood has to remain at the surface over an hour to return its lactic acid to resting level

Decompression sickness (DS)

• Caused by N2 absorption from a compressed-air source– Start of dive– tissue contains a [N2]

• DS occur after a long deep dive and then surfaces suddenly– PN2 pressure falls in the lungs to its ordinary value

– N2-charged blood and other tissues start to lose N2 in the lung air

– Bubbles of blood may form within the blood and tissues

Decompression sickness (DS) 2

• Breath-hold dives must be repeated many times to cause DS in humans

• Marine animals avoid DS during deep dives by alveolar collapse– Special features of lungs and thorax

• Keep pulmonary N2 within lungs

• Avoid build up in blood and tissues• Lung air moves to conducting airways