Chapter 32

Circulatory System

Invertebrates w/o a Circulatory System

If an organism has a sac body plan, circulatory systems are

not necessary.

Sac body plans mean cells are capable of gas and nutrient exchange

individually

Simple diffusion and osmosis principles are all that is necessary

Single-celled organisms or members of the cnidarian phyla (sea

anemones, jellyfish, etc)

For other organisms, cells do not always have direct access to

nutrients and gasses.

These organisms need a circulatory system, or a system of

transporting water, gasses, and nutrients throughout an organism

from specified entry and exit points.

Open Circulatory System

In open circulatory systems the circulatory fluid itself makes

contact with the environment.

Most mollusks and arthropods have open circulatory systems

with hemolymph (a mixture of blood and interstitial fluid)

instead of pure blood

The hearts of these organisms pump hemolymph into body cavities

called hemocoels.

The hemolymph contains nutrients, but no oxygen. Eventually, the

hemolymph releases its nutrients then makes it’s way back to the heart

for circulation.

For oxygen, organisms have special air tubes called trachea.

Trachea flow all throughout the body, providing gas exchange for

individual cells that is independent from the blood and heart.

Closed Circulatory System

A few members of the mollusk and arthropod classes have a

closed circulatory system.

Blood (a mixture of cells and plasma) is pumped by the

heart into a system of branching blood vessels.

Some organisms, like earthworms, even contain multiple hearts

Red blood cells contains a pigment called hemoglobin, which

turns the blood of closed circulatory systems red.

Blood is capable of carrying both nutrients and oxygen to the

cells of the organism.

Some gas exchange always occurs through the body wall or epidermis

in organisms. For humans, hardly any. For earthworms, it’s a much

higher percentage.

Cardiovascular System All vertebrates have a closed circulatory system called a

cardiovascular system.

The cardiovascular system uses an organ called a heart for

pumping substances, and contains 3 types of vascular tissue

called blood vessels (vascular=transport)

Arteries: carry blood away from the heart

Capillaries: exchange materials with tissue fluid

Veins: return blood to the heart

Arteries have thick walls that are able to expand and aid in

pumping blood.

Arterioles are smaller arteries that branch into capillaries

Capillary beds allow for exchange of nutrients and waste for the cells

Veinules carry deoxygenated blood and waste materials into veins

Heartarteryarteriolecapillariescapillary bedscellscapillary

bedscapillariesveinulesveinsheart

Circulatory System Pathways

Vertebrates show three separate circulatory pathways

1) One-circuit (single-loop) system (Fishes)

The heart has a single atrium and a single ventricle.

Blood is oxygenated at gills then carried throughout the body.

2) Two-circuit (double-loop), single ventricle system (Amphibians and most reptiles)

The heart pumps blood to the tissues (the systemic circuit) and also to the lungs (the pulmonary circuit)

This is an evolutionary trait of air-breathing organisms

3) Two-circuit, double ventricle system (Crocodiles, birds and mammals)

A separate atrium and ventricle for each circuit.

Helps to ensure the blood pressure is adjustable for both the systemic and pulmonary circuit)

The Human Heart

The human heart is located between the two lungs and is tilted

toward the left side of the organism (all directions are from the

perspective of the organism the heart belongs to)

The major portion of the heart is the myocardium, which

contains the cardiac muscle that pumps the blood

The heart lies within the pericardium, a membranous sac that

secretes lubricating fluid (like engine oil).

The inner heart itself is separated by a septum, a wall dividing

the heart into the right and left sides.

The two upper chambers of the heart are the atria, while the

lower chambers are the ventricles

The Human Heart

The heart has four valves which direct the flow of blood and prevent

its backward movement.

Between the atria and ventricles the valves are called the atrioventricular

valves.

Between the ventricles and their attached vessels, the valves are called the

semilunar valves

They look like half-moons.

The vein carrying blood from the body to the heart is the Vena Cava

(Inferior/Superior)

The vein carrying blood from to lungs to heart is the Pulmonary Vein

The artery carrying blood from heart to lungs is the Pulmonary

Artery

The artery carrying blood from the heart to the rest of the body is

the Aorta

The Human Heart

The two Vena Cava veins carry

O2-poor and CO2-rich blood

from the body where it enters

the right atrium.

The tricuspid valve opens and

allows a specific amount of

blood to enter the right

ventricle

The right ventricle pushes the

blood through the pulmonary

valve into the pulmonary artery,

where it will travel to the lungs

for oxygenation

The Human Heart

Four pulmonary veins bring O2-

rich blood back from the lungs

to the left atrium

The bicuspid valve opens and

lets blood flow into the left

ventricle

The left ventricle pushes blood

through the aortic valve into the

aorta, where it takes blood

throughout the body

Heartbeat

Each heartbeat lasts around .85 seconds, for 70 beats per minute

Systole refers to when the heart chambers contract, while

diastole refers to when the chambers relax.

The heartbeat’s familiar “lub dub” sound is the valves opening

and closing

“lub”—the atrioventricular valves closing

“dub”—the semilunar valves closing

“pause”—while the atria fill with blood

The rhythmic contraction of the heart is due to the cardiac

conduction system, run by nodal tissue

SA node (sinoatrial): pacemaker

AV node (atrioventricular): opens the ventricle valves

Blood Pressure

As blood is pushed out of the ventricles, blood pressure

rises.

As blood flows from the aorta into the arteries and

arterioles, blood pressure falls.

Veins, however, have too low of blood pressure to push

blood back toward the heart. Instead, skeletal muscles aid

the veins

Veins also have tiny valves which prevent blood from

flowing backwards

Blood pressure is measured with a sphygmomanometer and

recorded in mm HG (millimeters of mercury)

Cardiovascular Disorders

Hypertension

Hypertension is high blood pressure

Hypertension is usually not detected until a stroke or heart attack

occurs

Atherosclerosis

Accumulation of soft masses of fatty materials such as cholesterol

The plaque causes clots to form, which can either remain stationary

(thrombus) or move with the blood (embolus)

Stroke

An embolus blocks the cranial artery, preventing oxygen from getting

to the brain

Heart attack

When a portion of heart muscle dies due to blockage

Blood

Blood consists of

1) transport substances for the capillaries,

2) immune agents for fighting off foreign invaders and transporting

combative agents,

3) body temperature regulators

4) clotting factors

Formed Elements

The red and white blood cells (discussed in ch 33)

Plasma

Water, proteins, salts, gases, nutrients, wastes and

hormones

Red Blood Cells

There are 6 million blood cells for every cubic mm of blood.

Each blood cell contains 250 million hemoglobin molecules

Hemoglobin, a combination of protein and iron, is able to

electrically hold 4 oxygen molecules/molecule of hemoglobin.

RBC’s are manufactured in the marrow of the skull, ribs,

vertebrae and long bones.

RBC’s contain no nucleus. They live for 120 days and then are

swallowed by the liver or spleen for recycling

The iron is returned to marrow for reuse; the heme of the

blood is released as waste

Hence, the reddish-brown hue of feces

Platelets

Platelets are small factors that are involved in the 12 steps of

blood clotting.

When a blood vessel is damaged, platelets clump at the site and

partially seal the leak.

Cell tissues release prothrombin, which activates the production

of thrombin.

Thrombin then activates fibrins, which will thread around a

platelet until the injury is sealed.

The process is complicated because formation of clots (scabs) can be

deadly if it happens at the wrong time.

The complicated process virtually ensures clotting only occurs when

necessary, never by accident.

Extra Credit Question

This question is worth an extra 5% on your essay

exam

You may check your answers with me ahead of

time for a yes or no response as many times as you

like.

•Acetomenaphin is a common drug for pain relief. It works by reducing areas of inflammation, and is powerful enough to survive gastric acid in the stomach. Yet, even a slight overdose can be fatal to a cell. How does acetomenaphin know how to target only “sick” cells and not overdose “healthy” cells?