CH48: Circulatory System

What are the three main components of a circulatory system?

A muscular pump (heart), a fluid (blood), and a series of conduits (blood vessels).

What is another name for a circulatory system?

A cardiovascular system.

What functions does the circulatory system serve in transporting substances around the body?

It transports heat, hormones, respiratory gases, blood cells, platelets, immune components, nutrients, and waste products.

Why do very small animals not require a circulatory system?

All their cells are close enough to the environment to allow for direct exchange of materials.

In an open circulatory system, fluid called _____ leaves the vessels and moves between the cells.

hemolymph

In a _____ circulatory system, the fluid is contained within a continuous system of vessels.

closed

In closed systems, what two components make up the extracellular fluid?

The blood plasma (fluid in the circulatory system) and the interstitial fluid (fluid around the cells).

Which two major invertebrate phyla are examples of organisms with open circulatory systems?

Arthropods and mollusks.

In arthropods, how does hemolymph return to the heart?

It reenters the heart through openings called ostia, which have one-way valves.

Which two major groups of animals have closed circulatory systems?

Vertebrates and annelids (like earthworms).

What is a key feature of closed circulatory systems regarding blood components?

Blood is kept separate from the interstitial fluid, and its cellular and macromolecular components never leave the vessels.

What is a primary advantage of closed circulatory systems concerning transport speed?

They allow for faster transport of materials through vessels compared to open systems.

How can closed systems regulate blood flow to specific tissues?

By varying the resistance (diameter) of the blood vessels.

In the vertebrate circulatory system, what is the path of blood vessels starting from the heart and returning to it?

Arteries branch into arterioles, which feed into capillaries, drained by venules that join to form veins.

Where does the exchange of materials between blood and interstitial fluid occur in vertebrates?

In the capillaries, which are tiny, thin-walled vessels.

What major evolutionary trend occurred in vertebrate circulatory systems?

They evolved from a single circuit to a double circuit, with increasing separation of blood for gas exchange and blood for the body.

Describe the circulatory pathway in fish.

The heart pumps blood to the gills and then to the rest of the body in a single circuit.

In birds and mammals, the _____ circuit pumps blood from the heart to the lungs and back.

pulmonary

In birds and mammals, the _____ circuit pumps blood from the heart to the rest of the body.

systemic

What are the four chambers of a fish heart, in order of blood flow?

The sinus venosus, atrium, ventricle, and bulbus arteriosus.

In a fish's single-circuit system, where does blood go immediately after leaving the bulbus arteriosus?

It moves through the gills for oxygenation.

Which animal group shows the evolutionary transition from water-breathing to air-breathing with a modified circulatory system?

Lungfish.

In lungfish, the atrium is partially divided. What type of blood does the left side receive and from where?

The left side receives oxygenated blood from the lung.

In lungfish, what type of blood does the right side of the partially divided atrium receive and from where?

The right side receives deoxygenated blood from the body.

How many chambers does an adult amphibian heart have?

Three chambers: two atria and one ventricle.

In the amphibian heart, the right atrium receives _____ blood from the _____, while the left atrium receives _____ blood from the _____.

deoxygenated; body; oxygenated; lungs

What is an advantage of the partial separation of pulmonary and systemic circuits seen in amphibians?

It allows blood going to the tissues to maintain high pressure by sidestepping the pressure drop in the gas exchange organ.

Besides lungs, how can amphibians pick up oxygen from the environment?

They can absorb oxygen through small blood vessels in their skin.

What adaptation allows ectothermic reptiles to bypass the pulmonary circuit when inactive and not breathing?

They can shunt blood away from the lungs, as their metabolic rate and oxygen needs are very low during inactivity.

In the 3-chambered reptilian heart (turtles, snakes, lizards), how is the ventricle structured?

The ventricle is partly divided by a septum.

In a breathing reptile, why does blood from the right side of the ventricle flow into the pulmonary artery?

Because resistance in the pulmonary circuit is lower than in the systemic circuit.

When a reptile is not breathing, pulmonary vessels constrict, causing blood from the right side of the ventricle to flow into the _____.

right aorta

How does a crocodilian heart differ structurally from that of other ectothermic reptiles?

Crocodilians have a four-chambered heart with completely divided ventricles.

Despite having a four-chambered heart, how can crocodilians shunt blood between circuits?

They can selectively shunt blood through a connection between the two aortas.

What is a major advantage of the four-chambered heart in birds and mammals regarding blood oxygenation?

The systemic circuit always receives blood with higher oxygen content, maximizing gas exchange.

What is another advantage of the completely separate circuits in birds and mammals?

The pulmonary and systemic circuits can operate at different pressures.

Which chamber of the human heart pumps deoxygenated blood into the pulmonary circuit?

The right ventricle.

Which chamber of the human heart pumps oxygenated blood into the systemic circuit?

The left ventricle.

What is the function of the atrioventricular (AV) valves?

They prevent backflow of blood into the atria when the ventricles contract.

The right AV valve is called the _____ valve, and the left AV valve is called the _____ or _____ valve.

tricuspid; bicuspid; mitral

What is the function of the pulmonary and aortic valves?

They prevent backflow of blood into the ventricles when the ventricles relax.

The right atrium receives deoxygenated blood from the body through which two large veins?

The superior vena cava and the inferior vena cava.

Oxygenated blood returns from the lungs to the left atrium via the _____.

pulmonary veins

Trace the path of deoxygenated blood starting from the vena cavae to the lungs.

Vena cavae -> right atrium -> tricuspid valve -> right ventricle -> pulmonary valve -> pulmonary artery -> lungs.

Trace the path of oxygenated blood starting from the pulmonary veins to the body.

Pulmonary veins -> left atrium -> bicuspid (mitral) valve -> left ventricle -> aortic valve -> aorta -> body.

Why is the wall of the left ventricle thicker than the wall of the right ventricle?

It must pump blood through the entire systemic circuit, which has much higher resistance than the pulmonary circuit.

The cardiac cycle phase when ventricles contract is called _____.

systole

The cardiac cycle phase when ventricles relax is called _____.

diastole

What event creates the first heart sound, "lub"?

The closing of the atrioventricular (AV) valves at the beginning of systole.

What event creates the second heart sound, "dup"?

The closing of the aortic and pulmonary valves at the end of systole.

What is a heart murmur?

An abnormal sound caused by a defective heart valve that does not close properly.

In a blood pressure reading of 120/70, what does the 120 represent?

The systolic pressure, which is the peak pressure in the artery during ventricular contraction.

In a blood pressure reading of 120/70, what does the 70 represent?

The diastolic pressure, which is the pressure in the artery when the ventricles are relaxed.

Cardiac muscle cells are in electrical contact with each other through structures called _____.

gap junctions

What is the primary pacemaker of the heart?

The sinoatrial (SA) node.

Why do pacemaker cells spontaneously generate action potentials without nervous system input?

Their resting membrane potential is unstable and gradually drifts upward to reach threshold.

The action potential in pacemaker cells is primarily generated by the opening of voltage-gated _____ channels.

Ca2+

In pacemaker cells, a slow influx of Na+ and Ca2+ through T-type channels causes a gradual _____ of the cell membrane.

depolarization

Once threshold is reached in a pacemaker cell, the opening of _____-type Ca2+ channels generates the main action potential.

L-type (long-lasting)

How does norepinephrine from the sympathetic nervous system affect heart rate?

It increases the permeability of Na+ and Ca2+ channels, causing the resting potential to rise faster and increasing heart rate.

How does acetylcholine from the parasympathetic nervous system affect heart rate?

It increases K+ permeability and decreases Ca2+ permeability, causing the resting potential to rise more slowly and decreasing heart rate.

What is the role of the atrioventricular (AV) node in the heart's conduction system?

It receives the action potential from the atria and, after a slight delay, transmits it to the ventricles.

What is the purpose of the delay at the AV node?

It ensures that the atria finish contracting and emptying blood into the ventricles before the ventricles contract.

After the AV node, the action potential travels down the _____ and then spreads throughout the ventricles via the _____.

bundle of His; Purkinje fibers

What type of instrument is used to record the electrical events of the cardiac cycle from the body surface?

An electrocardiogram (ECG or EKG).

Blood is a type of connective tissue composed of cells in an extracellular fluid matrix called _____.

blood plasma

What is hematocrit?

The percentage of total blood volume that is composed of red blood cells (RBCs).

What are mature erythrocytes (RBCs) packed with, and what major organelle do they lack?

They are packed with hemoglobin and lack a nucleus.

How does the biconcave shape of red blood cells aid their function?

It provides a large surface area for gas exchange and flexibility to squeeze through narrow capillaries.

What hormone controls red blood cell production, and where is it released?

Erythropoietin (EPO), which is released by the kidney.

What condition stimulates the release of erythropoietin (EPO)?

Hypoxia (low oxygen levels).

What is the average lifespan of a circulating red blood cell?

About 120 days.

What are platelets, and from what type of cell do they originate?

Platelets are cell fragments that originate from large bone marrow cells called megakaryocytes.

What is the initial trigger for platelet activation in the blood clotting process?

Exposure to collagen fibers in a damaged blood vessel wall.

In the clotting cascade, the enzyme _____ converts the inactive prothrombin into its active form, thrombin.

clotting factors (from platelets and tissue)

What is the role of the enzyme thrombin in blood clotting?

Thrombin cleaves the soluble plasma protein fibrinogen to form insoluble fibrin.

What is the final step in forming a blood clot?

Fibrin threads form a mesh that binds platelets and blood cells, sealing the vessel.

Why do the walls of large arteries contain many collagen and elastin fibers?

To allow them to withstand high blood pressure and elastically recoil, pushing blood forward.

What type of blood vessels are known as 'resistance vessels' because their diameter can be varied to control blood flow to specific tissues?

Arterioles.

Why do blood pressure and flow rate drop significantly in the capillaries?

The total cross-sectional area of all capillaries combined is much greater than that of the arteries feeding them.

What are the two opposing Starling's forces that maintain water balance in capillaries?

Blood pressure (hydrostatic pressure), which forces fluid out, and osmotic pressure, which pulls fluid in.

At the arterial end of a capillary, fluid is forced out because blood pressure is _____ than osmotic pressure.

higher

At the venous end of a capillary, fluid is drawn back in because blood pressure is _____ than osmotic pressure.

lower

What are veins known as 'capacitance vessels'?

Because their walls are expandable, allowing them to stretch and store a large volume of blood.

How does the skeletal muscle pump aid venous return from below the heart?

Contractions of skeletal muscles squeeze the veins, pushing blood toward the heart, with one-way valves preventing backflow.

What is the primary function of the lymphatic system?

It returns interstitial fluid (lymph) that has leaked from the capillaries back to the blood.

What is atherosclerosis?

A condition known as "hardening of the arteries," where plaque builds up on the endothelial lining.

A blood clot that forms on an atherosclerotic plaque is called a _____.

thrombus

What is it called when a thrombus blocks a coronary artery, and what is the medical consequence?

It is called a coronary thrombosis, which can lead to a heart attack (myocardial infarction).

What is an embolus?

A piece of a thrombus or other material that breaks loose and travels through the bloodstream.

A stroke is often caused by an _____ that lodges in an artery in the _____.

embolism (blockage by an embolus); brain

What is the formula for Mean Arterial Pressure (MAP) using cardiac output and total peripheral resistance?

MAP = Cardiac Output (CO) × Total Peripheral Resistance (TPR).

How is cardiac output (CO) calculated?

Cardiac Output = Heart Rate (HR) × Stroke Volume (SV).

What is the expanded formula for Mean Arterial Pressure (MAP) including heart rate and stroke volume?

MAP = Heart Rate (HR) × Stroke Volume (SV) × Total Peripheral Resistance (TPR).

What is autoregulation in the context of blood flow?

It is the local control of blood flow in a capillary bed, managed by smooth muscles in arterioles responding to local chemical changes.

What is hyperemia, and what conditions cause it?

Hyperemia is an increase in blood flow to a capillary bed, caused by low oxygen, high carbon dioxide, or exercise by-products like lactic acid.

How does the sympathetic nervous system cause arterioles in non-essential tissues to constrict during a 'fight-or-flight' response?

It releases norepinephrine, which acts on the smooth muscle of the arterioles.

What hormone, produced when blood pressure in the kidneys drops, reduces flow to peripheral tissues?

Angiotensin.

Where is the cardiovascular control center located in the brain?

In the medulla.

What are baroreceptors, and what do they detect?

Baroreceptors are stretch receptors in the aorta and carotid arteries that detect changes in blood pressure.