Cardiovascular System

Heart and blood vessels

Heart

• The heart pumps blood through blood vessels to all body tissues.

• Heart beats about 100,000 times every day

• Heart

Left

Right

Right Atrium

Left Atrium（心室）

Right Ventricle

Left Ventricle（心房）

Myocardial Thickness and Function

• The thickness of the myocardium of the four chambers varies according to each chamber’s function. The thin-walled atria deliver blood under less pressure into the adjacent ventricles.

• Because the ventricles pump blood under higher pressure over greater distances, their walls are thicker

CARDIAC OUTPUT • Cardiac output (CO) is the volume of blood ejected from

the left ventricle (or the right ventricle) into the aorta (or pulmonary trunk) each minute. Cardiac output equals the stroke volume (SV), the volume of blood ejected by the ventricle during each contraction, multiplied by the heart rate (HR), the number of heartbeats per minute: CO = SV X HR (mL/min) (mL/beat) (beats/min)

• In a typical resting adult male, stroke volume averages 70 mL/beat, and heart rate is about 75 beats/min. Thus, average cardiac output is CO = 70 mL/beat X 75 beats/min= 5250 mL/min= 5.25 L/min

• This volume is close to the total blood volume, which is about 5 liters in a typical adult male.

Autonomic Regulation of Heart Rate

• Nervous system regulation of the heart originates in the cardiovascular center in the medulla oblongata.

• This region of the brain stem receives input from a variety of sensory receptors and from higher brain centers.

• The cardiovascular center then directs appropriate output by increasing or decreasing the frequency of nerve impulses in both the sympathetic and parasympathetic branches of the ANS

• Sympathetic neurons extend from the medulla oblongata into the spinal cord. From the thoracic region of the spinal cord, sympathetic cardiac accelerator nerves extend out to the SA node, AV node, and most portions of the myocardium.

• Parasympathetic nerve impulses reach the heart via the right and left vagus (X) nerves. Vagal axons terminate in the SA node, AV node, and atrial myocardium. They release ACH (acetylcholine), which decreases heart rate.

Chemical Regulation of Heart Rate

1. Hormones. E (Epinephrine) and NE (norepinephrine) (from the adrenal medullae) enhance the heart’s pumping effectiveness.

2. Cations. K, Ca, and Na—have a large effect on cardiac function. – Elevated blood levels of K or Na decrease heart

rate and contractility. – A moderate increase intracellular Ca level

speeds heart rate and strengthens the heartbeat.

+ +

++

Other Factors in Heart Rate Regulation

• Age, gender, physical fitness, and body temperature also influence resting heart rate.

• A newborn baby is likely to have a resting heart rate over 120 beats/min; the rate then gradually declines throughout life.

• Adult females often have slightly higher resting heart rates than adult males

• Regular exercise tends to bring resting heart rate down in both sexes.

The coronary circulation

Blood vessels

• The five main types of blood vessels are : – Arteries: carry blood away from the heart to other organs.

– Arterioles: smaller arteries – Capillaries: numerous tiny vessels in tissue – Venules: small veins – Veins: convey blood from the tissues back to the heart.

CAPILLARY EXCHANGE

Capillary exchange: the movement of substances between blood and interstitial fluid.

• Diffusion-- The most important method of capillary exchange is simple diffusion. Many substances, such as oxygen (O2), carbon dioxide (CO2), glucose, amino acids, and hormones, enter and leave capillaries by simple diffusion.

• Transcytosis（转胞作用） • A small quantity of material crosses capillary

walls by transcytosis. • In this process, substances in blood plasma

become enclosed within tiny pinocytic vesicles吞饮小泡

that first enter endothelial cells by endocytosis, then move across the cell and exit on the other side by exocytosis胞吐. This method of transport is important mainly for large, lipid-insoluble molecules that cannot cross capillary walls in any other way.

• For example, the hormone insulin (a small protein) enters the bloodstream by transcytosis, and certain antibodies (also proteins) pass from the maternal circulation into the fetal circulation by transcytosis.

FACTORS AFFECTING BLOOD FLOW

• Blood Pressure • Vascular Resistance • Venous Return

CONTROL OF BLOOD PRESSURE AND BLOOD FLOW

Cardiovascular System

• The Blood Vessels

Arteries —Carry blood away from the heart

Veins – Bring blood back toward the heart

The Hepatic Portal Circulation

Lymphatic System

• Lymph Organs: – Lymph nodes – Tonsils – Thymus – Spleen

• lymph-vessel – Lymphatic capillary – Lymphatic vessel – Lymphatic trunk – Lymphatic duct – Thoracic duct or Right Lymphatic Duct

Functions of the Lymphatic System

The lymphatic system has three primary functions: 1. Drains excess interstitial fluid.

Lymphatic vessels drain excess interstitial fluid from tissue spaces and return it to the blood.

2. Transports dietary lipids. Lymphatic vessels transport lipids and lipid-soluble vitamins (A, D, E, and K) absorbed by the gastrointestinal tract.

3. Carries out immune responses. Protects against invasion through immune responses.