Circulation — The Heart and Blood Vessels

Chapter 9

Circulatory System

• Accepts oxygen, nutrients, and other substances from the respiratory and digestive systems and delivers them to cells

• Accepts carbon dioxide and wastes from cells and delivers them to respiratory and urinary systems for disposal

Functional Connections

food, water intake oxygen intake

DIGESTIVESYSTEM

RESPIRATORYSYSTEM

eliminationof carbondioxide

nutrients,water,salts

oxygen carbondioxide

CIRCULATORYSYSTEM

URINARYSYSTEM

water,solutes

eliminationof foodresidues

rapid transportto and from allliving cells

elimination ofexcess water,salts, wastes

Cardiovascular

System• Heart• Blood vessels

– Arteries– Arterioles– Capillaries– Venules– Veins

Location of the Heart

• Heart is about size of a fist

• Lies in thoracic cavity between the lungs

• Enclosed in the pericardium

Layers of Heart Wall

• Inner layer of the pericardium is the outer layer of the heart wall

• Beneath that is the myocardium, the thick cardiac muscle tissue

• Thin endocardium lines the chambers of the heart and blood vessels

Heart Structure

• Each side has two chambers

– Upper atrium

– Lower ventricle

• Valves between atria and ventricles

Heart Valvesthree cusps two cusps

right AV valve (tricuspid)

right semilunar valve

Heart from above with atria removed

left semilunar valve

left AV valve (bicuspid or mitral valve)

Cardiac Cycle

• Contraction phase is systole

• Relaxation phase is diastole

Mid to late diastole.

Early diastole Ventricular

systole

Direction of Blood Flow

• Superior and inferior vena cava • Right atrium• Right ventricle• Pulmonary artery • Pulmonary veins• Left atrium• Left ventricle• Aorta

Pulmonary Circuit

Short loop that oxygenates blood

right pulmonary artery left pulmonary artery

capillarybed ofrightlung

pulmonarytrunk

capillary bedof left lung

(to systemic circuit)

pulmonary veins

lungs

(fromsystemiccircuit)

heart

Systemic Circuit

Longer loop that carries blood to and from body tissues

capillary beds of headand upper extremities

(to pulmonarycircuit)

aorta

(frompulmonarycircuit)

heart

capillary beds of otherorgans in thoracic cavity

capillary bed of liver

capillary beds of intestines

Hepatic Portal System

• Carries blood from capillaries in digestive organs to capillaries in the liver

• Enables liver to detoxify substances from digestive tract before they are carried to the body

Statins: Heart-Saving Drugs

• Interrupt the metabolic pathway in the liver that creates cholesterol

• Increase receptor proteins that bind with and remove LDL cholesterol

• Raise blood level of “good” cholesterol (HDLs)

• Lower blood levels of triglycerides

Conduction and Contraction

• SA node in right atrium is pacemaker

• Electrical signals cause contraction of atria

• Signal flows to AV node and down septum to ventricles

SA node

Nervous System

• Triggers the contraction of skeletal muscle

• Can only adjust the rate and strength of cardiac muscle contraction

• Centers for neural control of heart functions are in the spinal cord and parts of the brain

Blood Pressure

• Highest in arteries, lowest in veins

• Systolic pressure is peak pressure (ventricular contraction)

• Diastolic pressure is

the lowest • Greatest pressure drop is in arterioles

Arteries, Arterioles, Capillaries

• Arteries: main transporters of oxygenated blood

• Arterioles: diameter is adjusted to regulate blood flow

• Capillaries: diffusion occurs across thin walls

Venous System

• Blood flows from capillaries into venules, then on to veins

• Veins are large-diameter vessels with some smooth muscle in wall

• Valves in some veins prevent blood from flowing backward

Controlling Blood Pressure

• Cardiac output adjusted by controls over rate and strength of heartbeat

• Total resistance is controlled by vasoconstriction of arterioles

• Baroreceptor response is main short-term control of blood pressure

Velocity of Flow Varies

• Volume of blood flowing through vessels always has to equal heart’s output

• Flow velocity is highest in large-diameter transport vessels

• Flow velocity is slowest in capillary beds; blood spreads out into many vessels with greater total cross-sectional area

Diffusion Zone

• Capillary beds are the site of exchange between blood and interstitial fluid

• Capillary is a single sheet of epithelial cells

• Flow is slow; enables gases to diffuse across membranes of blood cells and across endothelium

Bulk Flow

• Movement of water and solutes in response to fluid pressure

to venule

inward-directedosmotic movement

cells oftissue

outward-directedbulk flow

from arteriole

Net Bulk Flow

• Normally, ultrafiltration only slightly exceeds reabsorption

• Fluid enters interstitial fluid and eventually returns to blood by way of lymphatic system

• High blood pressure causes excessive ultrafiltration and results in edema

Risk Factors for Cardiovascular Disease

• Smoking • Gender (maleness)• Genetic factors• Old age• High cholesterol• Obesity• Lack of exercise• Diabetes mellitus

Hypertension

• Blood pressure above 140/90

• Tends to be genetic

• May also be influenced by diet

• Contributes to atherosclerosis

• “Silent killer” - few outward signs

Atherosclerosis

• Arteries thicken, lose elasticity, and fill up with cholesterol and lipids

• High LDL level increases risk

Arrhythmias

• Bradycardia - slow heart rate

• Tachycardia - 100+ beats/minute

• Atrial fibrillation - irregular heartbeat

• Ventricular fibrillation - uncontrolled contraction of ventricles; quickly fatal

Lymphatic System

• The circulatory system is leaky

• Some fluid is forced out of the smallest vessels and into the interstitial fluid

• Vessels of the lymphatic system pick up this fluid, filter it, and return it to the circulatory system

Lymph Vascular System

• Fluid enters lymph capillaries

• Capillaries merge into lymph vessels

• Lymph vessels converge into ducts that funnel fluid

into veins in the lower neck

Lymph Nodes

• Located at intervals

along lymph vessels

• Act as a filter for lymph

• Contain lymphocytes

that can recognize a

foreign invader

Lymphoid Organs

• Central to the body’s defense

• Tonsils

• Spleen

• Thymus gland