Vertebrate Circulatory Systems - Springfield Public Schools Vertebrate Circulatory Systems Mammals,...

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The Circulatory and Respiratory Systems

Chapter 49

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Invertebrate Circulatory Systems

Sponges, Cnidarians, and nematodes lack a separate circulatory system -Sponges circulate water using many incurrent pores and one excurrent pore -Hydra circulates water through a gastrovascular cavity (also for digestion) -Nematodes are thin enough that the digestive tract can also be used as a circulatory system

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Invertebrate Circulatory Systems

Larger animals require a separate circulatory system for nutrient and waste transport -Open circulatory system = No distinction between circulating and extracellular fluid -Fluid called hemolymph -Closed circulatory system = Distinct circulatory fluid enclosed in blood vessels & transported away from and back to the heart

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Vertebrate Circulatory Systems

Fishes evolved a true chamber-pump heart -Four structures are arrayed one after the other to form two pumping chambers -First chamber consists of the sinus

venosus and atrium, and the second, of the ventricle and conus arteriosus

-These contract in the order listed -Blood is pumped through the gills, and then to the rest of the body

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The advent of lungs in amphibians required a second pumping circuit, or double circulation

-Pulmonary circulation moves blood between the heart and lungs -Systemic circulation moves blood between the heart and the rest of the body

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The frog has a three-chambered heart, consisting of two atria and one ventricle -Oxygenated and deoxygenated blood mix very little

Amphibians living in water obtain additional oxygen by diffusion through their skin

Reptiles have a septum that partially subdivides the ventricle, thereby further reducing the mixing of blood in the heart

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Mammals, birds and crocodilians have a four-chambered heart with two separate atria and two separate ventricles -Right atrium receives deoxygenated blood from the body and delivers it to the right ventricle, which pumps it to the lungs -Left atrium receives oxygenated blood from the lungs and delivers it to the left ventricle, which pumps it to rest of the body

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The Cardiac Cycle

The heart has two pairs of valves: -Atrioventricular (AV) valves guard the openings between atria and ventricles -Tricuspid valve = On the right -Bicuspid, or mitral, valve = On the left -Semilunar valves guard the exits from the ventricles to the arterial system -Pulmonary valve = On the right -Aortic valve = On the left

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The Cardiac Cycle

These valves open and close as the heart goes through the cardiac cycle of rest (diastole) and contraction (systole) -“Lub-dub” sounds heard with stethoscope

Right and left pulmonary arteries deliver deoxygenated blood from the right ventricle to the right and left lungs -Pulmonary veins return oxygenated blood from the lungs to the left atrium

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The Cardiac Cycle

The aorta and all its branches are systemic arteries, carrying oxygen-rich blood from the left ventricle to all parts of the body -Coronary arteries supply the heart muscle itself

Superior vena cava drains the upper body Inferior vena cava drains the lower body These veins empty into the right atrium,

completing the systemic circulation 15

The Cardiac Cycle

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The Cardiac Cycle (Cont.)

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The Cardiac Cycle

Arterial blood pressure can be measured with a sphygmomanometer -Systolic pressure is the peak pressure at which ventricles are contracting -Diastolic pressure is the minimum pressure between heartbeats at which the ventricles are relaxed

Blood pressure is written as a ratio of systolic over diastolic pressure

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Contraction of Heart Muscle

Contraction of the heart muscle is stimulated by membrane depolarization -Triggered by the sinoatrial (SA) node, the most important of the autorhythmic fibers -Located in the right atrium, the SA node

acts as a pacemaker for rest of the heart -Produces spontaneous action

potentials faster than other cells

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Depolarization travels to the atrioventricular (AV) node -It is then conducted rapidly over both ventricles by a network of fibers called the atrioventricular bundle, or bundle of His -Relayed to the Purkinje fibers -Directly stimulate the myocardial

cells of both ventricles to contract

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The electrical activity can be recorded on an electrocardiogram (ECG or EKG) -First peak (P) is produced by depolarization of atria (atrial systole) -Second, larger peak (QRS) is produced by ventricular depolarization (ventricular systole) -Last peak (T) is produced by repolarization of ventricles (ventricular diastole)

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Characteristics of Blood Vessels

Blood leaves heart through the arteries -Arterioles are the finest, microscopic branches of the arterial tree -Blood from arterioles enters capillaries -Blood is collected into venules,

which lead to larger vessels, veins -Carry blood back to heart

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Arteries and veins are composed of four tissue layers -Endothelium, elastic fibers, smooth muscle, and connective tissue

Capillaries are composed of only a single layer of endothelial cells -Allow rapid exchange of gases and metabolites between blood and body cells

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Characteristics of Blood Vessels (Cont.)

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Arteries and arterioles -Contraction of the smooth muscle layer results in vasoconstriction, which greatly increases resistance & decreases blood flow -Chronic vasoconstriction can result in

hypertension (high blood pressure) -Relaxation of the smooth muscle layer results in vasodilation, decreasing resistance & increasing blood flow to organs 32 33


Veins and venules -Have thinner layer of smooth muscles than arteries -Return blood to the heart with the help of skeletal muscle contractions and one-way venous valves

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The Lymphatic System

The lymphatic system consists of lymphatic capillaries, lymphatic vessels, lymph nodes, and lymphatic organs -Excess fluid in the tissues drains into blind-ended lymph capillaries -Lymph passes into progressively larger vessels with one-way valves -Eventually drains into subclavian veins

Lymph nodes contain germinal centers -Site of lymphocyte activation 35

Cardiovascular Diseases

Heart attacks (myocardial infarctions) -Main cause of cardiovascular deaths in US -Insufficient supply of blood to heart

Angina pectoris (“chest pain”) -Similar to but not as severe as heart attack

Stroke -Interference with blood supply to the brain

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Cardiovascular Diseases

Atherosclerosis -Accumulation of fatty material within arteries

Arteriosclerosis -Arterial hardening due to calcium deposition

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Blood Flow and Blood Pressure

Blood flow and pressure are regulated by the autonomic nervous system

The cardiac center of the medulla oblongata modulates heart rate -Norepinephrine, from sympathetic neurons, increases heart rate -Acetylcholine, from parasympathetic neurons, decreases heart rate

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Cardiac output is the volume of blood pumped by each ventricle per minute -Increases during exertion because of an increase in both heart rate & stroke volume

Arterial blood pressure (BP) depends on the cardiac output (CO) and the resistance (R) to blood flow in the vascular system BP = CO x R

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The baroreceptor reflex is a negative feedback loop that responds to BP changes -Baroreceptors detect changes in arterial BP -If BP decreases, the number of

impulses to cardiac center is decreased -Ultimately resulting in BP increase -If BP increases, the number of

impulses to cardiac center is increased -Ultimately resulting in BP decrease

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Blood pressure increases with blood volume

Blood volume is regulated by four hormones -Antidiuretic hormone (ADH) -Aldosterone -Atrial natriuretic hormone -Nitric oxide (NO)

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The Components of Blood

Blood is a connective tissue composed of a fluid matrix, called plasma, within which are found different cells and formed elements

The functions of circulating blood are: 1. Transportation of materials 2. Regulation of body functions 3. Protection from injury and invasion

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Plasma is 92% water, but it also contains the following solutes: -Nutrients, wastes, and hormones -Ions -Proteins -Albumin, alpha (α) & beta (β) globulins

-Fibrinogen -If removed, plasma is called serum

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The formed elements of the blood include red blood cells, white blood cells and platelets

Red blood cells (erythrocytes) -About 5 million per microliter of blood -Hematocrit is the fraction of the total blood volume occupied by red blood cells -RBCs of vertebrates contain hemoglobin, a pigment that binds and transports oxygen

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White blood cells (leukocytes) -Less than 1% of blood cells -Larger than erythrocytes and have nuclei -Can also migrate out of capillaries -Granular leukocytes -Neutrophils, eosinophils, and basophils -Agranular leukocytes -Monocytes and lymphocytes

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Platelets are cell fragments that pinch off from larger cells in the bone marrow -Function in the formation of blood clots

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All of the formed elements develop from pluripotent stem cells

Hematopoiesis is blood cell production -Occurs in the bone marrow, and produces: -Lymphoid stem cell Lymphocytes -Myeloid stem cell All other blood cells

-Red blood cell production is called erythropoiesis

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Gas Exchange

The rate of diffusion between two regions is governed by Fick’s law of diffusion

R = D A Δp

d R = Rate of diffusion D = Diffusion constant A = Area over which diffusion takes places Δp = Pressure difference between two sides d = Distance over which diffusion occurs 51

Gas Exchange

Gases diffuse directly into unicellular organisms However, most multicellular animals require

system adaptations to enhance gas exchange -Amphibians respire across their skin -Echinoderms have protruding papulae -Insects have an extensive tracheal system -Fish use gills -Mammals have a large network of alveoli

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Gills

Gills are specialized extensions of tissue that project into water

External gills are not enclosed within body structures -Found in immature fish and amphibians -Two main disadvantages -Must be constantly moved to ensure

contact with oxygen-rich fresh water -Are easily damaged 56

Gills

The gills of bony fishes are located between the oral (buccal or mouth) cavity and the opercular cavities -These two sets of cavities function as pumps that alternately expand -Moving water into the mouth, through

the gills, and out of the fish through the open operculum or gill cover

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Gills

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Gills

There are four gill arches on each side of a fish’s head -Each is composed of two rows of gill filaments, which consist of lamellae -Within each lamella, blood flows

opposite to direction of water movement -Countercurrent flow -Maximizes oxygenation of blood

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Gills

Many amphibians use cutaneous respiration for gas exchange

In terrestrial arthropods, the respiratory system consists of air ducts called trachea, which branch into very small tracheoles -Spiracles (openings in the exoskeleton) can be opened or closed by valves

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Lungs

Gills were replaced in terrestrial animals because 1. Air is less supportive than water 2. Water evaporates

The lung minimizes evaporation by moving air through a branched tubular passage -A two-way flow system

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Lungs

Air exerts a pressure downward, due to gravity -A pressure of 760 mm Hg is defined as one atmosphere (1.0 atm) of pressure

Partial pressure is the pressure contributed by a gas to the total atmospheric pressure -Based on the % of the gas in dry air -PN2 = 760 x 79.02% = 600.6 mm Hg -PO2 = 760 x 20.95% = 159.2 mm Hg -PCO2 = 760 x 0.03% = 0.2 mm Hg

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Lungs

Lungs of amphibians are formed as saclike outpouchings of the gut

Frogs have positive pressure breathing -Force air into their lungs by creating a positive pressure in the buccal cavity

Reptiles have negative pressure breathing -Expand rib cages by muscular contractions, creating lower pressure inside the lungs

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Lungs

Lungs of mammals are packed with millions of alveoli (sites of gas exchange) -Inhaled air passes through the larynx, glottis and trachea -Bifurcates into the right and left

bronchi, which enter each lung and further subdivide into bronchioles

-Surrounded by an extensive capillary network

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Lungs

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Lungs

Lungs of birds channel air through very tiny air vessels called parabronchi -Unidirectional flow -Achieved through the action of anterior

and poster sacs (unique to birds) -When expanded during inhalation,

they take in air -When compressed during exhalation,

they push air in and through lungs

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Lungs

Respiration in birds occurs in two cycles -Cycle 1 = Inhaled air is drawn from the trachea into posterior air sacs, and exhaled into the lungs -Cycle 2 = Air is drawn from the lungs into anterior air sacs, and exhaled through the trachea

Blood flow runs 90o to the air flow -Crosscurrent flow

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Lungs

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Gas Exchange

Gas exchange is driven by differences in partial pressures -As a result of gas exchange in the lungs, systemic arteries carry oxygenated blood with relatively low CO2 concentration -After the oxygen is unloaded to the tissues, systemic veins carry deoxygenated blood with a high CO2 concentration

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Lung Structure and Function

The outside of each lung is covered by the visceral pleural membrane -The inner wall of the thoracic cavity is lined by the parietal pleural membrane -The space between the two membranes

is called the pleural cavity -Normally very small and filled with

fluid

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During inhalation, thoracic volume increases through contraction of two muscle sets -Contraction of the external intercostal muscles expands the rib cage -Contraction of the diaphragm expands the volume of thorax and lungs -Produces negative pressure which

draws air into the lungs

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Thorax and lungs have a degree of elasticity -Expansion during inhalation puts these structures under elastic tension -Tension is released by the relaxation of

the external intercostal muscles and diaphragm

-This produces unforced exhalation, allowing thorax and lungs to recoil

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Tidal volume = Volume of air moving in and out of lungs in a person at rest

Vital capacity = Maximum amount of air that can be expired after a forceful inspiration

Hypoventilation = Insufficient breathing -Blood has abnormally high PCO2

Hyperventilation = Excessive breathing -Blood has abnormally low PCO2

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Each breath is initiated by neurons in a respiratory control center in the medulla oblongata -Stimulate external intercostal muscles and diaphragm to contract, causing inhalation -When neurons stop producing impulses,

respiratory muscles relax, and exhalation occurs

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Neurons are sensitive to blood PCO2 changes -A rise in PCO2 causes increased production of carbonic acid (H2CO3), lowering the pH -Stimulates chemosensitive neurons in

the aortic and carotid bodies -Send impulses to control center

Brain also contains central chemoreceptors that are sensitive to changes in the pH of cerebrospinal fluid (CSF)

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Respiratory Diseases

Chronic obstructive pulmonary disease (COPD) refers to any disorder that obstructs airflow on a long-term basis -Asthma = An allergen triggers the release of histamine, causing intense constriction of the bronchi and sometimes suffocation -Emphysema = Alveolar walls break down and the lung exhibits larger but fewer alveoli -Lungs become less elastic

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Respiratory Diseases

Lung cancer follows or accompanies COPD -The number one cancer killer -Caused mainly by cigarette smoking

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Hemoglobin

Hemoglobin consists of four polypeptide chains: two α and two β -Each chain is associated with a heme group, and each heme group has a central iron atom that can bind a molecule of O2

Hemoglobin loads up with oxygen in the lungs, forming oxyhemoglobin -Some molecules lose O2 as blood passes in capillaries, forming deoxyhemoglobin

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Hemoglobin

In a person at rest, about one-fifth of the oxygen is unloaded in the tissues -Leaving four-fifths of the oxygen in the blood as a reserve -This reserve enables the blood to supply

body’s oxygen needs during exertion The oxyhemoglobin dissociation curve is a

graphic representation of these changes

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Hemoglobin

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Hemoglobin

Hemoglobin’s affinity for O2 is affected by pH and temperature -The pH effect is known as the Bohr shift -Caused by H+ binding to hemoglobin -Results in a shift of oxyhemoglobin

dissociation curve to the right -Facilitates oxygen unloading -Increasing temperature has a similar effect

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Hemoglobin

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Transportation of Carbon Dioxide

About 8% of the CO2 in blood is dissolved in plasma, and 20% is bound to hemoglobin -Remaining 72% diffuses into red blood cells -The enzyme carbonic anhydrase

combines CO2 with H2O to form H2CO3

-H2CO3 dissociates into H+ and HCO3–

-H+ binds to deoxyhemoglobin -HCO3

– moves out of the blood, and into plasma 90

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When the blood passes through pulmonary capillaries, these reactions are reversed -The result is the production of CO2 gas, which is exhaled

Other dissolved gases are also transported by hemoglobin -For example, nitric oxide (NO) and carbon monoxide (CO)

Transportation of Carbon Dioxide

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