Circulation

What does a circulatory system consist of?

Muscular pump (the heart)

Fluid (blood)

Series of conduits (blood vessels)

What is the function of bulk flow of blood?

Transporting O2 rapidly throughout the body

Transport of nutrient molecules, hormones, heat, and metabolic wastes

What is a closed circulator system?

A heart pumps blood into arteries, which branch into smaller arterioles, and eventually into capillaries of microscopic size

As blood leaves tissues and organs, it flows into larger and larger vessels, the veins, back to the heart

Arterioles, capillaries, and venules comprise the microcirculation

Which animals have a closed circulatory system?

Vertebrates

What do capillary walls consist of?

Vascular endothelium, <1 micron thick

Small blood cells must pass through one at a time

Where are capillaries found?

Near every tissue cell

What happens in capillaries

Primary sites where O2, CO2, and other materials are exchanged between blood and cells

What is an open circulatory system?

Blood exits vessels as it flows through the body

No distinction between blood and interstitial fluids

Which animals have an open circulatory system?

Arthropods and most mollusks

What is the fluid in open circulatory systems referred to as?

Hemolymph instead of blood

What does blood consist of?

Plasma and cells

What is blood plasma?

Water and solutes such as glucose, ions, wastes, hormones, clotting proteins, and O2

What are red blood cells?

Erythrocytes

Contain hemoglobin

What are white blood cells?

Leukocytes

Participate in immune responses

What are platelets?

Cell fragments

Involved in blood clotting

What is the function of respiratory pigments?

Greatly increase the amount of O2 that can be carried in blood

What is oxygenation?

When a pigment combines with O2 (picks up O2) in the lungs

What is deoxygenation?

When a pigment releases O2 in the tissues

What does an oxygen equilibrium curve demonstrate?

Loading and offloading of O2

How does human hemoglobin interact with oxygen (O2)?

Hemoglobin in humans combines reversibly with O2 (oxygenation and deoxygenation)

How does the partial pressure of oxygen (PO2) control the reversible loading and unloading of O2 by hemoglobin?

Hemoglobin combines reversibly with O2 based on local partial pressure differences:

High PO2 (lungs) - promotes oxygenation, where hemoglobin binds tightly to O2

Low PO2 (active tissues) - promotes deoxygenation, causing hemoglobin to release O2, where it is needed for cellular respiration

What is myocardium?

The muscle tissue of a heart

What is cardiac output?

Volume of blood pumped per minute, affected by heart rate and stroke volume

What is stroke volume?

Volume of blood pumped per heartbeat

What happens to stroke volume and heart rate during exercise?

Both increase

How many chambers do fish, amphibians, mammals, and bird hearts have?

Fish have 2

Amphibians have 3

Mammals and birds have 4

How many ventricles and atria are in mammal and bird hearts?

2 ventricles and 2 atria

What is the purpose of one-way valves?

Ensure that blood flows through the chambers in the correct direction

What are the steps of circulation?

O2 depleted blood from systemic tissues enters the right atrium

Then flows into the right ventricle

Right ventricle contracts blood pumped to pulmonary arteries to the lungs

O2-rich blood from the lungs enter the left atrium

Passes into the left ventricle

Left ventricle contracts, pumping O2-rich blood is pumped through the aorta to the systemic tissues

What is the cardiac cycle?

Cycle of contraction and relaxation of the heart

What is systole?

When ventricles contract (max pressure)

What is diastole?

When ventricles relax (min pressure)

How is heartbeat initiated?

By pacemaker cells in the sinoatrial (S - A) node in the right atrial wall

Modified muscle cells generate pacemaker potentials (myogenic)

Electrical depolarization and contraction spread rapidly throughout the muscle

Depolarization reaches the atrioventricular (A-V) node, then spreads throughout the ventricles

Results in ventricular contraction

What is an electrocardiogram?

ECG or EKG

Record of heart-related voltage differences on the surface of the body over time

Provides a readout of electrical changes across the heart

What is the function of coronary circulation?

Providing blood flow and O2 to heart tissues

Necessary for healthy heart function

What is coronary artery disease?

Common

Arteries can become blocked leading to heart attack

What is extrinsic control in the heart?

Adrenal glands secrete a rush of epinephrine in response to fright or stress, which increases heart rate and stroke volume

What is the autonomic nervous system?

Sympathetic stimulation (high stress/energy) - increases heart rate and stroke volume

Parasympathetic stimulation (relaxed) - decreases heart rate

What is the structure of arteries leaving the heart?

Thick walls of elastic fibers and smooth muscles, so that they can withstand high pressure

What is the structure function of small arteries and arterioles?

Have smooth muscle

Exercise vasomotor control over blood flow to capillary beds

On an ECG, if the P wave is normal, but there is not a QRS complex, what could this mean?

There is a problem with electrical conduction between the pacemaker and ventricles

How is the blood pressure in veins?

Much lower blood pressure

Walls are thinner and expand more easily

Contraction of skeletal muscles help proper blood through the veins

One-way valves prevent backflow

What is the blood-brain barrier?

Many types of solutes can’t cross the capillary walls in the brain and spinal cord because the walls have no pores

Protects neurons from toxins and allows tight control of solute exchange

What is the role of kidneys in circulation?

Capillaries in the glomerulus have many pores and allow many types of solutes to pass

Blood pressure drives fluid and solutes into kidneys

Kidney helps to regulate blood pressure

How do blood pressure levels change during blood flow?

It stays high in the arteries, because of their large diameter, but drops when blood reaches the arterioles, capillaries, then veins

How does blood move in and out of the capillaries?

Capillaries are so permeable that fluid is squeezed out by blood pressure

When blood reaches the end of the capillary, blood osmotic pressure (due to dissolved proteins) exceeds blood pressure, and some water move back in

What is the net effect of circulation each day?

Some loss of fluid from the blood

2-4 liters of fluid in a person’s systemic interstitial fluids each day

What is the function of the lymphatic system?

Returns interstitial fluid to the blood

Lymphatic capillaries continually take up excess fluid

They merge into larger and larger vessels that ultimately empty into veins in the neck

What does the countercurrent heat exchange depend on?

Parallel arrays of arteries and veins

How do tuna use a countercurrent system?

Keep swimming muscles warm

Numerous arteries and veins going to and from the red swimming muscles are closely juxtaposed

Red swimming muscle produces a lot of heat

Blood returning from periphery picks up heat and returns it to swimming muscles