The Circulatory and Respiratory Systems Chapter 49

The Circulatory andRespiratory Systems

Chapter 49

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Invertebrate Circulatory SystemsSponges, 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 SystemsLarger 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

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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Later-Evolved Vertebrate Circulatory Systems

-Oxygenated and deoxygenated blood don’t mix in heart

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Heart Valves

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 CycleThese valves open and close as the heart

goes through the cardiac cycle of rest (diastole) and contraction (systole)

-“Lub-dub” sounds heard with stethoscope

-Systolic pressure is the peak pressure at which ventricles are contracting AV valves close (to prevent backwash)= “lub”

-Diastolic pressure is the minimum pressure between heartbeats at which the ventricles are relaxed, semilunar valves close = (to prevent backwash)“dub”

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

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Contraction of Heart Muscle

Electrocardiogram (ECG or EKG)

Autorhythmic SA node

Initiates

depolarization

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Characteristics of Blood Vessels

*Arteries and veins are composed of four tissue layers

*Capillaries are composed of only a single layer of

endothelial cells...They allow for rapid exchange of

gases and metabolites between blood and body cells

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Arteries and Arterioles Regulate Heat Loss

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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

...and vice versa.

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Veins and Venules

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

What is Blood?

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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The Components of Blood

Plasma is 92% water, but it also contains the following solutes:

-Nutrients, wastes, and hormones

-Ions

-Proteins

-Albumin, alpha () & beta () 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

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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4. Threads of fibrin trap erythrocytes and form a clot.

1. Vessel is damaged, exposing surrounding tissue to blood.

5. Once tissue damage is healed, the clot is dissolved.

3. Cascade of enzymatic reactions is triggered by platelets, plasma factors, and damaged tissue.

2. Platelets adhere and become sticky, forming a plug.

Prothrombin

Thrombin

Thrombin

Fibrinogen

Fibrin


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 of (medullary bone),

and produces:

-Lymphoid stem cell...Lymphocytes

-Myeloid stem cell...All other blood cells

Red blood cell production

is called erythropoiesis

Making Blood “Formed Elements”

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LungsGills 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

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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

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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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Gas Exchange

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

R =D A p

dR = Rate of diffusion

D = Diffusion constant

A = Area over which diffusion takes places

p = Pressure difference between two sides

d = Distance over which diffusion occurs

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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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LungsAir 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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Lung Structure and Function

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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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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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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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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-Each breath is initiated by neurons in a respiratory control center in the medulla oblongata

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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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RBCs of vertebrates contain Hemoglobin,

a pigment that binds and transports oxygen

Hemoglobin consists of four polypeptide chains: two and two -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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-Mitochondria release CO2 after pyruvate oxidation and the Krebs Cycle

Mitochondria also reduce oxygen to H20 (water) at the end of the electron transport chain.

C02 leaves tissue cells

Gas Exchange BiochemistryIn Tissue Cells

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-The enzyme carbonic anhydrase combines CO2 with H2O to form H2CO3

-H2CO3 dissociates into H+ and HCO3

–

-H+ binds to deoxyhemoglobinmaking O2 get into tissue

-HCO3– moves out of the

blood, and into plasmaacts as buffer

72% of the CO2 in blood is“hidden” in HCO3

Gas Exchange BiochemistryIn Red Blood Cells & Plasma

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-CO2 goes into Alveoli...HCO3– moves INTO red blood cells

-H+ and HCO3– associate

into H2CO3

-H2CO3 changes into CO2

with H2O

-CO2 leaves Red Blood Cellsand goes into the alveoli

THEN YOU EXHALE IT...Bronchioles, bronchi,trachea, pharynx, mouth,atmosphere!!

Gas Exchange BiochemistryInto Alveoli

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When 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)...so these molecules compete with, oxygen, the terminal electron acceptor in the electron transport chain...can be deadly

Transportation of Carbon Dioxide

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The Circulatory and Respiratory Systems Chapter 49