The Heart: Regulation of Heart RateThe Heart: Regulation of Heart Rate

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Stroke volume usually remains relatively constant

Starling’s law of the heart – the more that the cardiac muscle is stretched, the stronger the contraction

Changing heart rate is the most common way to change cardiac output

The Heart: Regulation of Heart RateThe Heart: Regulation of Heart Rate

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Increased heart rate Sympathetic nervous system

Crisis Low blood pressure

Hormones Epinephrine Thyroxine

Exercise Decreased blood volume

The Heart: Regulation of Heart RateThe Heart: Regulation of Heart Rate

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Decreased heart rate

Parasympathetic nervous system

High blood pressure or blood volume

Decreased venous return

Blood Vessels: The Vascular Blood Vessels: The Vascular SystemSystem

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Taking blood to the tissues and back Arteries

Arterioles

Capillaries

Venules

Veins

The Vascular SystemThe Vascular System

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Figure 11.8b

Blood Vessels: AnatomyBlood Vessels: Anatomy

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Three layers (tunicas) Tunica interna

Endothelium

Tunica media

Smooth muscle (smaller in veins)

Controlled by sympathetic nervous system

Tunica externa

Mostly fibrous connective tissue

Differences Between Blood Vessel Differences Between Blood Vessel TypesTypes

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Walls of arteries are the thickest

Lumens of veins are larger

Walls of capillaries are only one cell layer thick to allow for exchanges between blood and tissue

Movement of Blood Through Movement of Blood Through VesselsVessels

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Most arterial blood is pumped by the heart

Veins use the milking action of muscles to help move blood

Figure 11.9

Capillary BedsCapillary Beds

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Capillary beds consist of two types of vessels

Vascular shunt – directly connects an arteriole to a venule

Figure 11.10

Capillary BedsCapillary Beds

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True capillaries – exchange vessels

Oxygen and nutrients cross to cells

Carbon dioxide and metabolic waste products cross into blood

Figure 11.10

Circulation to the FetusCirculation to the Fetus

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Figure 11.15

PulsePulse

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Pulse – pressure wave of blood

Monitored at “pressure points” where pulse is easily palpated

Figure 11.16

Blood PressureBlood Pressure

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Measurements by health professionals are made on the pressure in large arteries

Systolic – pressure at the peak of ventricular contraction

Diastolic – pressure when ventricles relax

Pressure in blood vessels decreases as the distance away from the heart increases

Measuring Arterial Blood PressureMeasuring Arterial Blood Pressure

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Figure 11.18

Comparison of Blood Pressures in Different Comparison of Blood Pressures in Different VesselsVessels

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Figure 11.17

Blood Pressure: Effects of FactorsBlood Pressure: Effects of Factors

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Neural factors Autonomic nervous system adjustments

(sympathetic division)

Renal factors

Regulation by altering blood volume

Renin – hormonal control

Blood Pressure: Effects of FactorsBlood Pressure: Effects of Factors

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Temperature

Heat has a vasodilation effect

Cold has a vasoconstricting effect

Chemicals

Various substances can cause increases or decreases

Diet

Factors Determining Blood PressureFactors Determining Blood Pressure

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Figure 11.19

Variations in Blood PressureVariations in Blood Pressure

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Human normal range is variable Normal

140–110 mm Hg systolic 80–75 mm Hg diastolic

Hypotension Low systolic (below 110 mm HG) Often associated with illness

Hypertension High systolic (above 140 mm HG) Can be dangerous if it is chronic

Capillary ExchangeCapillary Exchange

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Substances exchanged due to concentration gradients

Oxygen and nutrients leave the blood

Carbon dioxide and other wastes leave the cells

Capillary Exchange: MechanismsCapillary Exchange: Mechanisms

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Direct diffusion across plasma membranes

Endocytosis or exocytosis

Some capillaries have gaps (intercellular clefts) Plasma membrane not joined by tight

junctions

Fenestrations of some capillaries Fenestrations = pores

Diffusion at Capillary BedsDiffusion at Capillary Beds

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Figure 11.20

Homeostatic Imbalances of the Homeostatic Imbalances of the Cardiovascular SystemCardiovascular System

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CHF (congestive heart failure)—progressive condition reflects coronary atherosclerosis, persistent high BP, or multiple myocardial infarcts

Varicose Veins—pooling of blood in feet and legs, inefficient venous return

Hypertension—high BP

Hypotension—low BP

Homeostatic Imbalances of the Homeostatic Imbalances of the Cardiovascular SystemCardiovascular System

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Atherosclerosis—small, fatty mounds of muscle protrude into vessel wall

Arteriosclerosis—end stage of atherosclerosis, hardening of plaques, increased rigidity of vessels

Coronary artery disease—filling of blood vessels with fatty, calcified deposits

Developmental Aspects of the Developmental Aspects of the Cardiovascular SystemCardiovascular System

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A simple “tube heart” develops in the embryo and pumps by the fourth week

The heart becomes a four-chambered organ by the end of seven weeks

Few structural changes occur after the seventh week