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