Albia Dugger • Miami Dade College

Chapter 36CirculationSections 1-7

36.2 The Nature of Blood Circulation

• A circulatory system distributes materials throughout the vertebrate body (and some invertebrates)

• It includes one or more hearts (muscular pumps) that propel fluid through vessels extending through the body

Open and Closed Circulatory Systems

• Open circulatory system (arthropods, mollusks)• A heart pumps hemolymph into open-ended vessels• Hemolymph leaves the vessels and mixes with interstitial

fluid

• Closed circulatory system (annelids, vertebrates)• A heart pumps blood through a continuous series of

vessels• Materials diffuse across the walls of the smallest-diameter

blood vessels

Figure 36-2a p628

spaces orcavitiesin bodytissues

pumpaorta heart

pump

capillary bed (many small vesselsthat serve as a diffusion zone)

large-diameterblood vessels(rapid flow)

large-diameterblood vessels(rapid flow)

dorsal blood vessel

two of fivehearts

ventral bloodvessels

gut cavity

ANIMATED FIGURE: Types of circulatory systems

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Evolution of Vertebrate Circulation

• Fishes• Heart with two chambers• Single circuit of circulation

• Amphibians• Heart with three chambers• Two partially separated circuits

• Birds and mammals• Heart with four chambers• Two fully separate circuits

Figure 36-3a p629

atrium

gill capillaries

capillaries of body

heart:ventricle

Figure 36-3b p629

Sys

tem

icC

ircu

it

lungs

rightatrium

leftatrium

rest of bodyPu

lmo

nar

yC

ircu

it

ventricle

Figure 36-3c p629

Sys

tem

icC

ircu

it

lungs

rightatrium

leftatrium

rest of body

left ventricleright ventricle

Pu

lmo

nar

yC

ircu

it

Circulation in Birds and Mammals

• The four-chambered heart has two separate halves, each with an atrium and a ventricle

• Each half pumps blood in a separate circuit• Pulmonary circuit: Blood flows from right half of heart, to

lungs (gains oxygen), to left half of heart • Systemic circuit: Blood flows from left half of heart, to

body (loses oxygen), to right half of heart

Take-Home Message: How do animals distribute substances to body cells?

• Most animals have a circulatory system that speeds the distribution of substances through the body.

• Some invertebrates have an open circulatory system, other invertebrates and all vertebrates have a closed circulatory system, in which blood always remains enclosed within the heart or blood vessels.

Take-Home Message: (cont.)

• Fish have a one-circuit circulatory system. All other vertebrates have a short pulmonary circuit that carries blood to and from the lungs, and a longer systemic circuit that moves blood to and from the body’s other tissues.

• A four-chambered heart evolved independently in birds and mammals. Such a heart allows strong contraction of one ventricle to speed blood through the systemic circuit, while a weaker contraction of the other ventricle

36.3 Human Cardiovascular System

• The term “cardiovascular” comes from the Greek kardia (for heart) and Latin vasculum (vessel)

• Each circuit includes a network of blood vessels that carries blood from the heart to small vessels where exchanges occur and then back to the heart

Blood Vessels

• The ventricles force blood through a series of vessels:• Arteries carry blood from ventricles to arterioles• Arterioles control blood distribution to capillaries• Capillaries exchange substances• Venules collect blood from capillaries• Veins deliver blood back to heart

Figure 36-4 p630

Hepatic Veins

Jugular Veins

Superior Vena Cava

Pulmonary Veins

Renal Veins

Inferior Vena Cava

Iliac Veins

Femoral Veins

Carotid Arteries

Ascending Aorta

Pulmonary Arteries

Coronary Arteries

Brachial Arteries

Renal Arteries

Abdominal Aorta

Iliac Arteries

Femoral Arteries

The Pulmonary Circuit

• The pulmonary circuit carries blood to and from the lungs

• Oxygen-poor blood is pumped from the right ventricle into pulmonary arteries

• As blood flows through pulmonary capillaries, it picks up oxygen and gives up carbon dioxide.

• Oxygen-rich blood returns through pulmonary veins to the left atrium

The Pulmonary Circuit

right pulmonary artery left pulmonary artery

fromsystemiccircuit pulmonary

veins

to systemiccircuit

capillary bedof left lung

capillary bedof right lung

pulmonarytrunk

capillariesof rightlung

capillariesof leftlung

heart

a Pulmonary Circuit

The Systemic Circuit

• The systemic circuit carries blood to and from the body

• The left ventricle pumps blood into the aorta

• Arteries and arterioles carry blood to various body parts

• Blood gives up oxygen and picks up carbon dioxide as it flows through capillaries

• Oxygen-poor blood returns through venules and veins to the right atrium

Hepatic Blood Flow

• Most blood moving through the systemic circuit flows through only one capillary bed

• Blood that passes through capillaries in the small intestine flows through the hepatic portal vein to capillaries in the liver

• The liver stores some absorbed glucose as glycogen, and breaks down some absorbed toxins, including alcohol

Figure 36-5b p631

heart

B Systemic Circuitcapillaries of other abdominalorgans, lower trunk, legs

capillaries ofthe intestines

capillariesof the liver

capillaries of head,neck, upper trunk, arms

frompulmonarycircuit

capillaries of organsin the thoracic cavity

to pulmonarycircuit

aorta

Take-Home Message: What are the two circuits of the human cardiovascular system?

• The pulmonary circuit carries oxygen-poor blood from the heart through the pulmonary arteries to arterioles and then capillaries in the lungs. Pulmonary veins return oxygenated blood to the heart.

• The systemic circuit carries oxygenated blood from the heart out the aorta, through branching arteries and to capillaries throughout the body. It returns oxygen-poor blood to the heart by way of venules and veins.

• Most blood in the systemic circuit passes through one capillary bed, but blood that flows through capillaries in the intestines also flows through capillaries in the liver.

36.4 Components and Functions of Blood

• Vertebrate blood carries oxygen, nutrients, and other solutes to cells, and carries away their metabolic wastes and secretions, including hormones

• Blood also carries cells and proteins that protect and repair tissues

• In birds and mammals, shifts in the distribution of blood flow help maintain a constant body temperature

Blood Volume and Composition

• An average adult human has about 5 liters (10 pints) of blood

• Blood’s fluid portion is plasma

• Blood cells and platelets form in bone marrow and are transported in plasma

Plasma

• Plasma is mostly water with hundreds of different plasma proteins dissolved in it

• Some plasma proteins transport lipids and fat-soluble vitamins; others have a role in blood clotting or immunity

• Some gases and nutrients such as sugars, amino acids, and vitamins are dissolved in plasma

Blood Cells

• Red blood cells (erythrocytes)• Contain hemoglobin that carries oxygen from lungs to

tissues• Quantified in a cell count

• White blood cells (leukocytes)• Defend the body from pathogens• Neutrophils, basophils, eosinophils, monocytes, and

lymphocytes (B and T cells)

Platelets

• Platelets are fragments of megakaryocytes

• After a platelet forms, it lasts five to nine days

• When activated, it releases substances needed for blood clotting

Components of Human Blood

Cellular Components of Mammalian Blood

hematopoietic stem cellsin red bone marrow

myeloid stem cell lymphoid stem cell

red blood cellprecursor

granulocyteprecursor

monocyteprecursor

T lymphocytes(mature inthymus)

B lymphocytes(mature in

bone marrow)

megakaryocytes

basophilsred blood cells(erythrocytes)

neutrophils eosinophils monocytes(immature

phagocytes)

platelets

Take-Home Message: What are the components and functions of human blood?

• Blood consists mainly of plasma, a protein-rich fluid that carries wastes, gases, and nutrients.

• Blood cells and platelets form in bone marrow and are transported in plasma. Red blood cells contain hemoglobin that carries oxygen from lungs to tissues. White cells help defend the body from pathogens. Platelets are cell fragments involved in clotting.

36.5 Hemostasis

• Hemostasis is a three-phase process that stops blood loss, constructs a framework for repairs:• Damaged vessel constricts• Platelets accumulate• Cascading enzyme reactions involving plasma proteins

cause clot formation

Three-Phase Process of Hemostasis

Take-Home Message: How does the body halt bleeding?

• The vessel constricts, platelets accumulate, and cascading enzyme reactions involving protein components of plasma cause clot formation.

36.6 Blood Typing

• Blood type• Genetically determined differences in molecules on the

surface of red blood cells

• Agglutination• Clumping of foreign cells by plasma proteins• When blood of incompatible types mixes, the immune

system attacks the unfamiliar molecules

ABO Blood Typing

• ABO blood typing analyzes variations in one type of glycolipid on the surface of red blood cells

• Blood type O has neither A nor B – the immune system treats both type A and type B cells as foreign

• Blood type O is a universal donor

• Blood type AB can receive blood from any donor

ABO Blood Types

Mixing ABO Blood Types

Rh Blood Typing

• Rh blood typing is based on the presence or absence of the Rh protein

• An Rh- mother may develop Rh+ antibodies if blood from an Rh+ child enters her bloodstream during childbirth

• These antibodies may attack the red blood cells of the next Rh+ fetus

Figure 36-10a p635

Rh+

Rh+

markerson the redblood cellsof a fetus

fetus

Rh–

Figure 36-10b p635

anti-Rh+

antibodymolecules

anysubsequentRh+ fetus

Take-Home Message:

What is a blood type?

• Blood type refers to the kind of surface molecules on red blood cells. Genes determine which form of these molecules an individual has.

• When blood of incompatible types mixes, the immune system attacks the unfamiliar molecules, with results that can be fatal.

36.7 The Human Heart

• The heart is a durable, muscular pump that contracts in response to its own spontaneous action potentials

• A sac of connective tissue (pericardium) surrounds the heart muscle (myocardium)

• Endothelium lines heart chambers and blood vessels

The Human Heart

• Each side of the human heart contains two chambers:• An atrium that receives blood from veins• A ventricle that pumps blood into arteries

• Heart valves keep blood moving in one direction:• AV valves separate atria and ventricles• Semilunar valves separate ventricles and arteries

Major Blood Vessels

• Two veins deliver deoxygenated blood to the right atrium:• The superior vena cava from upper regions • The inferior vena cava from lower regions

• The right ventricle pumps blood into two pulmonary arteries, each leading to one lung

• Oxygenated blood returns to the left atrium via pulmonary veins, and is pumped out of the left ventricle into the aorta

Figure 36-11 p636

right lung

diaphragm

pericardium

left lung

Right Ventricle

superior vena cava(flow from head, arms)

pulmonary valve(closed)

right pulmonaryveins (from lungs)

right AV valve(open)

inferior vena cava(from trunk, legs)

Right Atrium

septum

trunk of pulmonaryarteries (to lungs)

left pulmonaryveins (from lungs)

left AV valve(open)

aortic valve (closed)

aorta (to body)

cardiac muscle

Left Atrium

Left Ventricle

C Cutaway view, showing the heart’s internal organization. Arrows indicate the path taken by oxygenated (red) and oxygen-poor (blue) blood.

septum

cardiac muscle

pulmonary valve (closed)

right AV valve (open)

right pulmonary veins (from lungs)

left AV valve(open)

aortic valve (closed)

Left Ventricle

Left Atrium

Right Ventricle

Right Atrium

inferior vena cava (from trunk, legs)

superior vena cava (flow from head, arms)

left pulmonary veins (from lungs)

trunk of pulmonary arteries (to lungs)

aorta (to body)

Stepped Art

Figure 36-11 p636

The Cardiac Cycle

• In the cardiac cycle, heart muscle alternates between diastole (relaxation) and systole (contraction)• Blood collects in atria• AV valves open, blood flows into ventricles• Contraction of ventricles drives blood circulation• Ventricles contract with a wringing motion from bottom to

top

Stepped Art

Relaxed atria fill. Fluid pressure opens AV valves and blood flows into the relaxed ventricles.

1

As blood flows into the arteries, pressure in the ventriclesdeclines and the aortic and pulmonaryvalves close.

4 Ventricles start contracting and rising pressure pushes AV valves shut. A further rise in pressure opens aortic and pulmonary valves.

3

Contracting atrial squeeze more blood into the still-relaxed ventricles.

2

Figure 36-12a p637

Setting the Pace for Contraction

• The sinoatrial (SA) node in the wall of the right atrium, is the cardiac pacemaker – it generates about 70 action potentials per minute

• Gap junctions between adjacent cells allow action potentials generated by the SA node to spread across the atria

• The signal spreads from the SA node to the atrioventricular (AV) node, then to junctional fibers in the septum, so the heart contracts from the bottom up

Figure 36-13 p637

SA node(cardiacpacemaker)

AV node

conductingfibers

Take-Home Message: How does heart structure relate to its function?

• The four-chambered heart is a muscular pump partitioned into two halves, each with an atrium and a ventricle. Forceful contraction of the ventricles provides the driving force for blood circulation.

• The SA node is the cardiac pacemaker. Its spontaneous, rhythmic signals make cardiac muscle cells of the heart wall contract in a coordinated fashion.

36.8 Blood Vessel Structure and Function

• Contracting ventricles put pressure on the blood, forcing it through a series of vessels that vary in their structure.

• Arteries have thick walls containing smooth muscle reinforced with elastic connective tissue

• When a ventricle contracts, artery walls to bulge and spring back, creating a pulse

Blood Vessel Structure and Function

• Blood flows from arteries into arterioles

• In the systemic circuit, the distribution of blood to particular body parts is adjusted by altering the diameter of arterioles

• Smooth muscle that rings each arteriole responds to signals from the autonomic nervous system, and to chemical signals

• Sympathetic stimulation causes vasodilation of arterioles in the extremities and vasoconstriction of arterioles of the gut

Blood Vessel Structure and Function

• A capillary is a cylinder of endothelial cells, one cell thick, wrapped in basement membrane – its narrow diameter facilitate exchanges between blood and interstitial fluid

• Blood flows from capillaries into venules, which empty Into veins

• Veins are large-diameter, low-resistance vessels that convey blood to the heart – many veins have flaplike valves that help prevent backflow

Figure 36-14 p638

valve

fromthe heart

tothe heart

endotheliumsmooth muscle

connective tissue

capillary network

C CapillaryA Artery E Vein

ArterioleB

VenuleD

endothelium

Take-Home Message: How do blood vessels differ in structure and function?

• Arteries are thick-walled, large-diameter vessels. Stretching and recoil of arteries helps keep blood moving.

• Smooth muscle in the wall of arterioles allows adjustments to blood flow in the systemic circuit.

• Capillaries are narrow tubes of epithelial cells. They are the site of exchanges with interstitial fluid.

• Veins have valves that prevent backflow.

36.9 Blood Pressure

• Blood pressure is the pressure exerted by blood on the walls of blood vessels

• Blood pressure is highest in arteries, then declines throughout a cardiovascular circuit

Change in Blood Pressure through the Systemic Circuit.

Systolic and Diastolic Pressure

• Systolic pressure, the highest pressure of a cardiac cycle, occurs as contracting ventricles force blood into arteries

• Diastolic pressure, the lowest blood pressure of a cardiac cycle, occurs when ventricles are relaxed

• Blood pressure is measured in millimeters of mercury (mm Hg), and is written as systolic /diastolic

• Normal blood pressure is about 120/80 mm Hg

Controlling Blood Pressure

• Blood pressure depends on total blood volume, how much blood the ventricles pump (cardiac output), and whether arterioles are constricted or dilated

• Receptors in the aorta and carotid arteries monitor blood pressure and send signals to the medulla, which regulates cardiac output and arteriole diameter

• Inability to regulate blood pressure can result in hypertension, in which resting blood pressure remains above 140/90

Take-Home Message: How is blood pressure recorded and regulated?

• Blood pressure is the fluid pressure exerted against a vessel wall. It is recorded as systolic/diastolic pressure.

• Adjustments to arteriole diameter, cardiac output, and blood volume regulate blood pressure.

36.10 Mechanisms of Capillary Exchange

• Capillary beds are diffusion zones, where blood exchanges substances with interstitial fluid

• As blood flows through a circuit, it moves fastest through arteries, and slowest in capillaries

• Slow flow through capillaries enhances the rate of exchanges between the blood and interstitial fluid

Substance Exchange

• To move between the blood and interstitial fluid, a substance must cross a capillary wall

• Oxygen, CO2 , and small lipid-soluble molecules diffuse across endothelial cells of a capillary

• Some larger molecules enter endothelial cells by endocytosis, diffuse through, then enter interstitial fluid by exocytosis

Fluid Exchange

• Higher blood pressure at the arterial end of a capillary bed forces fluid out between cells

• At the venous end of the capillary, interstitial fluid enters the capillaries by osmotic pressure

• Normally, there is a small net outward flow of fluid

• The lymphatic system returns fluid to the blood

Fluid Movement at a Capillary Bed

blood tovenule

bloodfromarteriole

high pressure causesoutward flow

cells oftissue

inward-directedosmotic movement

Take-Home Message: How do blood and interstitial fluid exchange materials?

• Small molecules cross cells of a capillary by diffusion and larger ones move across by exocytosis.

• Fluid rich in oxygen and nutrients also leaks out between cells of the capillary wall.

36.11 Venous Function

• Veins are the body’s largest blood reservoir

• Skeletal muscle activity helps move blood at low pressure through veins and back to the heart

• Valves in veins help prevent backflow

• Contractions of smooth muscle inside vein walls helps force blood toward the heart

Figure 36-18 p641

venous valve

Figure 36-19a p641

valveclosed

valveopen

blood flow to heart

valveclosed

valveclosed

Take-Home Message:What are the functions of veins?

• Veins are the body’s main blood reservoir. The amount of blood in the veins changes depending on activity level.

• Blood pressure in veins is low. One-way valves, activity of skeletal muscle, and respiratory muscle action all help move the blood toward the heart.

Take-Home Message:

What factors impair circulatory function?

• Altered blood cell number or quality can alter blood’s ability to carry out its functions.

• Atherosclerosis and hypertension raise the risk of heart attack and stroke.

• Problems with the cardiac pacemaker cause arrhythmias.

Take-Home Message: What are the functions of the lymphatic system?

• The lymph vascular system consists of tubes that collect and deliver excess water and solutes from interstitial fluid to blood. It also carries absorbed fats to the blood, and delivers disease agents to lymph nodes.

• The system’s lymphoid organs, including lymph nodes, have specific roles in body defenses.