AP 110Fundamentals of Anatomy and Physiology

Objectives

• Describe the structure and function of blood vessels and the circulatory system

Blood Vessels

• The blood vessels (arteries, arterioles, capillaries, venules, and veins) form a closed tube that carries blood away from the heart, to the cells, and back again.

• Arteryarteriole capillary venule vein

Types of Blood Vessels

• Arteries:– Blood is pumped out of the ventricles into the

arteries– Carry blood away from the heart and toward the

lungs and capillaries in the tissues. – The smallest arteries are called arterioles. These

carry blood to the capillaries.

Types of Blood Vessels

• Veins : – Drain capillaries in the tissues and return the

blood to the heart. – The smallest veins are the venules.

Types of Blood Vessels

• Capillaries:– Tiny, thin-walled vessels– Allow for exchanges between the blood and body

cells, or between the blood and air in the lung tissue.

– The capillaries connect the arterioles and venules.

Blood Circuits

• Pulmonary circuit – Vessels carrying blood from the heart to the lungs

and back to the heart

• Systemic circuit – Vessels carrying blood from the heart to the rest of

the body and back.

Pulmonary Circuit

Convey blood from RV pulmonary artery to the lungs, alveolar capillaries, and pulmonary veins leading from the lungs to the left atrium.

Systemic Circuit

The systemic circuit includes the aorta and its branches leading to all body tissues as well as the system of veins returning blood to the right atrium.

Arteries and Arterioles

• Arteries are strong, elastic vessels adapted for carrying blood under high pressure.

• Arteries become smaller as they divide and give rise to arterioles.

• Arterioles carry blood capillaries

Vessel Structure

• The wall of an artery consists of an Endothelium Tunica media (smooth muscle) Tunica externa (connective tissue).

• Arteries are capable of vasoconstriction as directed by the sympathetic impulses; when impulses are inhibited, vasodilatation results.

Capillaries

Capillaries are the smallest vessels, consisting only of a layer of endothelium through which substances are exchanged with tissue cells.

Capillaries join arterioles and venules.

Exchanges in the Capillaries

• Blood entering capillaries contains high concentrations of oxygen and nutrients that diffuse out of the capillary wall and into the tissues.

• Plasma proteins remain in the blood due to their large size.

Exchanges in the Capillaries

• Hydrostatic pressure drives the passage of fluids and very small molecules out of the capillary at this point.

• At the venule end, osmosis, due to the osmotic pressure of the blood, causes much of the tissue fluid to return to the bloodstream

Systemic Arteries

Aorta

• The Aorta extends upward and to the right from the left ventricle. Then it curves backward and to the left. It continues down behind the heart just in front of the vertebral column, through the diaphragm, and into the abdomen.

Aorta

• This is the main trunk of the systemic arterial circulation and is composed of 4 parts:

– Ascending aorta is near the heart and inside the pericardial sac.

– Aortic arch curves from the right to the left and also extends backward.

Aorta

– Thoracic aorta lies just in front of the vertebral column behind the heart and in the space behind the pleura.

– Abdominal aorta is the longest section of the aorta, spanning the abdominal cavity

Principal Branches of the Aorta

The branches of the ascending aorta are:1. Right and Left coronary arteries

( lead to the heart muscle )2. Branches of the aortic arch include: the brachiocephalic artery Left common carotid artery Left subclavian artery

Venules and Veins

Venules lead from capillaries & merge toform veins that return blood to the heart.

Veins have the same three layers as arteries (different thicknesses) and have a flap-like valve inside to prevent backflow of blood.

Venules and Veins

Veins are thinner and less muscular than arteries; they do not carry high-pressure blood.

Veins also function as blood reservoirs.

Venous Blood Flow

• Blood flow through the venous system is only partially the result of heart action and instead also depends on: 1. skeletal muscle contraction2. breathing movements3. vasoconstriction of veins

Venous Blood Flow

Contractions of skeletal muscle squeeze blood back up veins one valve at a time.

Differences in thoracic and abdominal pressures draw blood back up the veins.

Venous System

• Veins return blood to the heart after the exchange of substances has occurred in the tissues.

Venous System

Characteristics of Venous Pathways

Larger veins parallel the courses of arteries and are named accordingly; smaller veins take irregular pathways and are unnamed.

Venous System

Veins from the head and upper torso drain into the superior vena cava.

Veins from the lower body drain into the inferior vena cava.

The vena cavae merge to join the right atrium.

The Venae Cavae and their Tributaries

• The veins of the head, neck, upper extremities, and chest all drain into the superior vena cava, which goes to the heart.

• The azygos vein drains the thorax and enters the superior vena cava before it joins the heart

The Hepatic Portal System

• A “portal system” is a kind of detour in the pathway of venous return that transports materials directly from one organ to another.– Eg. The hepatic portal system carries blood from

the abdominal organs to the liver.

The Hepatic Portal System

• Instead of emptying their blood directly into the inferior vena cava, they deliver it to this system.

• On entering the liver, the portal vein divides into a network called sinusoids.

• The purpose of this system is to transport blood from the digestive organs and the spleen to the liver, so the liver cells can carry out their function. (nutrients are processed, stored, and released as needed by the body.

Anastomoses

• A communication between two vessels is called an anastomosis. By means of arterial anastomoses, blood reaches vital organs by more than one route.

• Examples:– Circle of Willis– The palmar arch in

the hand– The mesenteric

arches in the intestines

– Arterial arches in the foot

The Dynamics of Blood Flow

• The flow of blood is carefully regulated to supply the needs of the tissues without unnecessary burden on the heart.

• The brain, liver, and kidneys require large quantities of blood, even at rest.

• Blood is affected by vasodilation, vasoconstriction.

Blood Flow

• The requirements of some tissues, such as those of skeletal muscles and digestive organs, increase greatly during periods of activity.

• The volume of blood flowing to a particular organ can be regulated by changing the size of the blood vessels supplying that organ

Blood Flow

• Vasodilation is an increase in the diameter of a blood vessel. This allows for the delivery of more blood to an area.

• Vasoconstriction is a decrease in the diameter of blood vessel, causing a decrease in blood flow.

• These vasomotor activities result from the contraction or relaxation of smooth muscle in the walls of the blood vessels, mainly the arterioles.

Pulse and Pulse Rate

• The ventricles pump blood into the arteries regularly about 70-80 times a minute (in the adult). The force of ventricular contraction starts a wave of increased pressure that begins at the heart and travels along the arteries.

• This wave, called the pulse, can be felt in any artery that is relatively close to the surface.

Pulse rate

• Various factors may influence the pulse rate:

• Pulse is faster in small people than in large people and usually is slightly faster in women.

• Muscular activity• Emotional

disturbances• Infections

Pulse and Pulse Rate• Normally, the pulse rate is the same as the

heartbeat

• If a heartbeat is abnormally weak or if the artery is obstructed, the heartbeat may not be detected as a pulse.

• In checking a pulse, it is important to gauge the strength as well as the regularity and rate.

Blood Pressure

• Blood pressure is the force of blood against the inner walls of blood vessels anywhere in the cardiovascular system, although the term "blood pressure" usually refers to arterial pressure.

Arterial Blood Pressure

• Arterial blood pressure rises and falls following a pattern established by the cardiac cycle– During ventricular contraction, arterial pressure is

at its highest (systolic pressure).– When ventricles are relaxing, arterial pressure is at

its lowest (diastolic pressure).

Arterial Blood Pressure

• The surge of blood that occurs with ventricular contraction can be felt at certain points in the body as a pulse.

Factors that Influence Arterial Blood Pressure

Arterial pressure depends on:Heart actionBlood volumeResistance to flowBlood viscosity.

Factors that Influence Arterial BP

• Heart Action– Heart action is dependent upon stroke volume

and heart rate (together called cardiac output); if cardiac output increases, so does blood pressure

• Blood Volume – Blood pressure is normally directly proportional to

the volume of blood within the cardiovascular system.• Blood volume varies with age, body size , and gender

Factors that Influence Arterial BP

• Peripheral Resistance– Friction between blood and the walls of blood

vessels is a force called peripheral resistance.

– As peripheral resistance increases, such as during sympathetic constriction of blood vessels, blood pressure increases.

Factors that Influence Arterial BP

• Blood Viscosity: = thickness of the bloodeg. Milkshake vs milk

↑ blood viscosity ↑ BP Eg. Caused by: dehydration, loss of plasma

volume, or increased # RBCs

Blood ViscosityThe greater the viscosity of blood, the greater

its resistance to flowing, and the greater the blood pressure.

Control of BP

Blood pressure is determined by cardiac output and peripheral resistance.

The body maintains normal blood pressure by adjusting cardiac output and peripheral resistance

Control of BP

Cardiac output depends on stroke volume and heart rate, and a number of factors can affect these actions.

The volume of blood that enters the right atrium is normally equal to the volume leaving the left ventricle.

Control of BP

If arterial pressure increases, the cardiac center of the medulla oblongata sends parasympathetic impulses to slow heart rate.

If arterial pressure drops, the medulla oblongata sends sympathetic impulses to increase heart rate to adjust blood pressure.

Control of BP

The vasomotor center of the medulla oblongata can adjust the sympathetic impulses to smooth muscles in arteriole walls, adjusting blood pressure.

Certain chemicals, such as carbon dioxide, oxygen, and hydrogen ions, can also affect peripheral resistance.

Control of BP

Other factors, such as emotional upset, exercise, and a rise in temperature can result in increased cardiac output and increased blood pressure.

Measurement of BP

• May prove a valuable guide

• Instrument used is called a sphygmomanometer

• Two variables:– Systolic pressure–Diastolic pressure

• Reported as a fraction

• Experience is required to ensure an accurate reading

• BP varies throughout the day.