Chapter 8: Circulatory Systems

During periods of activity, when the heart rate is rapid, the mean arterial pressure in humans is

1/2 diastolic pressure and 1/2 systolic pressure.

How many hearts does an octopus have?

3

There are different types of pumping structures in animal circulatory systems. Describe the three different types. How is one-way flow ensured?

All circulatory systems have some type of pumping structure that propels fluids around the system. There are three main types of pumping structures in animal circulatory systems. a. External pump: Organs not strictly associated with the circulatory system, such as skeletal muscle, can be used to develop pressure gradients. Contraction and relaxation of skeletal muscles, such as during movements of the legs, can alternately compress and expand a blood vessel, forcing fluid along its pressure gradient. A one-way valve guarantees one-way flow. b. Peristaltic contraction: This rhythmic wave of muscle contraction along a blood vessel wall proceeds in a coordinated fashion from one end to the other, similar to squeezing toothpaste from a tube. Because the contractions usually occur in a specific direction, the flow is usually one-way even when no valves are present. c. Contractile chambers, such as the vertebrate heart: Muscular contraction of the walls of the chamber increase pressure, and when this pressure exceeds that in the rest of the circulatory system, blood will flow down the pressure gradient. Blood does not flow backwards during the contraction because a one-way valve prevents such flow.

What are angiogenic inhibitors and why are they being studied as possible treatments for cancer?

Angiogenesis is the process by which small blood vessels such as arterioles, capillaries, and venules undergo remodeling. This process is controlled by both activator and inhibitor molecules that influence the rate of growth and division. Normally, inhibitory factors predominate, and blood vessels rarely divide. However, under certain conditions, such as in wound healing, angiogenic activators will be present to promote new blood vessel growth. A number of factors, such as wounding and hypoxia, result in angiogenesis. Cancerous tumors secrete high levels of angiogenic activators, stimulating new vessel growth that is required to supply the tumor with oxygen and nutrients. Blocking angiogenesis through the action of angiogenic inhibiting drugs will slow or stop tumor growth.

TRUE/FALSE: All multicellular animals have a cardiovascular system.

FALSE

TRUE/FALSE: Capillaries can assist in the process of diffusion by contracting their muscular walls.

FALSE

TRUE/FALSE: Chambered hearts are found only in vertebrates.

FALSE

TRUE/FALSE: In a closed circulatory system, there is no need for the process of diffusion.

FALSE

TRUE/FALSE: In an open circulatory system, there is no need for the process of diffusion.

FALSE

TRUE/FALSE: In the mammalian heart, when the AV valves are open and the semilunar valves are closed, this is most likely ventricular systole.

FALSE

TRUE/FALSE: Insects have a closed circulatory system in order to support high energy activities such as flight.

FALSE

TRUE/FALSE: Overactivity of the sympathetic nervous system can cause the heart to go into tetanus.

FALSE

TRUE/FALSE: When reptiles dive underwater, they redirect blood flow from the pulmonary circuit and develop a L-R shunt.

FALSE

TRUE/FALSE: Within a species, the thickness of the arterial blood vessel wall is fixed.

FALSE

When there is more blood in the ventricle of the heart, the heart will contract more forcefully and increase stroke volume. This phenomenon is known as the __________.

Frank-Starling effect

In birds and mammals, blood pressures are different between the pulmonary and systemic circuits. Which one is greater? Why is the difference advantageous?

In birds and mammals, the pulmonary and systemic circuits are completely separated. One advantage of this complete separation is that pressures can be different in each circuit. When blood flows to the lungs, the capillaries in the lungs must be very thin to permit gas exchange. However, if blood flows too forcefully through them, fluid will leak through the capillary walls. When this fluid accumulates, it increases the diffusion distance and reduces the efficiency of gas exchange. Therefore, a low-pressure pulmonary circuit is advantageous. The systemic circuit however, can be very long, especially in very large animals. High blood pressure is required to force blood all the way through it. Having two separate pressures allows the differing demands to be met.

Arthropod hearts share some common features. Which of the following is NOT a feature of all arthropod hearts?

Myogenic action potentials lead to contraction.

Electrical signals move through the mammalian heart in a particular order. Which order is correct?

SA node; internodal pathway; AV node; bundle of His; Purkinje fibers

In open circulatory systems, the circulating fluid comes into direct contact with tissues in open spaces called __________.

Sinuses; hemocoel

TRUE/FALSE: Acetylcholine can slow the vertebrate heart rate through a signal transduction cascade that causes increased potassium conductance.

TRUE

TRUE/FALSE: An EKG is designed to measure electrical activity of the heart.

TRUE

TRUE/FALSE: Birds and mammals have completely separated pulmonary and systemic blood circuits.

TRUE

TRUE/FALSE: Cardiac pacemaker cells do not contract.

TRUE

TRUE/FALSE: Circulatory systems follow the law of bulk flow.

TRUE

TRUE/FALSE: During inhalation, the thoracic pressure drops, and this respiratory pump helps draw blood into the veins of the thoracic cavity.

TRUE

TRUE/FALSE: Erythrocytes are the most abundant cells in the blood of vertebrates.

TRUE

TRUE/FALSE: In the decapod crustacean, when the heart contracts, the ostia close.

TRUE

TRUE/FALSE: In the fish, the sinus venosus is the heart chamber that initiates the cardiac cycle.

TRUE

TRUE/FALSE: Many invertebrate animals have a circulatory system.

TRUE

TRUE/FALSE: Most open circulatory systems contain blood vessels.

TRUE

TRUE/FALSE: Norepinephrine, released during the fight-or-flight response, causes vasoconstriction of the arterioles leading to skeletal muscle.

TRUE

TRUE/FALSE: Properties of pacemaker cells can be modified by the release of norepinephrine from sympathetic neurons.

TRUE

TRUE/FALSE: Protein concentration in circulatory fluids is generally much higher than that of interstitial fluid.

TRUE

TRUE/FALSE: The elastic nature of the aorta helps to maintain stable blood pressure during ventricular diastole.

TRUE

TRUE/FALSE: The rhythmic activity of the heart of the decapod crustacean is controlled by a neural rhythm generator.

TRUE

TRUE/FALSE: When a cardiomyocyte is stretched, the strength of its contraction increases.

TRUE

__________ are positioned at points along vasculature to prevent blood from flowing backwards.

Valves

What is NOT one of the functional distinctions between arteries and veins?

Veins always carry deoxygenated blood.

Poiseuille's equation makes a variety of assumptions regarding the physics of blood flow through the circulatory system. Give Poiseuille's equation, and list the violations for each of its four variable parameters.

a. Poiseuille's equation is given as: Q = ΔΡπr4/8Lη? b. Poiseuille's equation can be thought of the same way one can think about liquid moving through a drinking straw. The resistance of liquids within the straw is a function of the length of the tube (L), the radius of the tube (r), and the viscosity of the liquid (η). This resistance is given as: R = 8Lη/ πr4. c. By substituting the resistance relationship into the law of bulk flow, Q = ΔP/R, you can derive Poiseuille's equation. Based on the terms given in the equation, we know that flow can be affected by the pressure gradient, the radius of the vessel, the length of the vessel, and the viscosity of the fluid. The radius of the vessel (changed by vasoconstriction or vasodilation) can have a huge impact on the flow of the circulating fluid throughout the system, more than some of the other factors, because it is raised to the fourth power. d. Poiseuille's equation makes a variety of assumptions regarding the physics of the circulatory system. For example, it assumes that the blood vessels are unbranched and rigid, and that the flow is steady. Violations to the equation include: i. The circulatory system is branched, in both convergent and divergent ways, which makes the length of the system complicated. This violates the simple function of length (L). ii. Vessel walls are flexible, or "compliant," in response to pressure, which makes the calculation of 'r' complicated. Moreover, there are some vessels that stretch easily when exposed to pressure (highly compliant), while others stretch less. Also, the compliance of a blood vessel is not constant, but becomes less compliant at higher pressures. Finally, blood vessels take time to stretch. Together, these factors add up to the violation of the assumption r. iii. In larger vessels, pressure of blood flow is pulsatile, increasing when the heart contracts. Also, flow can sometimes be turbulent (instead of laminar), mainly in the heart and some vessel branching points. Additionally, the velocity profile of the blood is not identical across the diameter of the vessel. Instead, flow is slower near the walls, and faster near the center. Overall, flow is complex, and these issues add up to a violation of pressure (P). iv. Finally, blood is a mixture of components with different viscosities. It acts as a non-Newtonian fluid, which means that its viscosity varies depending on the size of the tube that it flows through. The components of blood tend to separate in smaller blood vessels. That is, blood cells get swept into the high velocity flow in the center of the vessel, while it is mainly plasma at the walls, leading to "low viscosity" and "high viscosity" parts of the vessel. In even smaller vessels, blood cells take up almost the whole diameter of the vessel. Cells change shape to squeeze through, and blood vessels tend to stick to the vessel walls and to each other, leading to high viscosity in those areas. Therefore, fluid is a complex mixture, and viscosity is variable, which violates η.

What is edema?

accumulation of interstitial fluid in any tissue

The direct connection between two arteries in the circulatory system is called an __________.

anastomosis

In jawed vertebrates, the large artery leading from the heart to the body is called the __________.

aorta

When there is an immediate requirement for increased oxygen to a particular body tissue in the systemic circuit,

arterioles will dilate in that area.

The general term for blood vessels that carry blood away from the heart is

artery.

Hematopoiesis is the production of

blood cells.

In fishes and amphibians, spongy myocardium receives oxygen from

blood in the heart chambers.

Baroreceptors are important for the regulation of __________.

blood pressure

The term for a decrease in heart rate is __________.

bradycardia

In the bony fish, all heart chambers are contractile except the

bulbus arteriosus.

The rising phase of a cardiac pacemaker action potential is caused by a __________ current.

calcium

In most non-crocodilian reptiles, the ventricle is divided into three chambers. Which of the following is NOT one of the chambers?

cavum cardiacum

In the mammalian heart, the valves open and close because

changes in chamber pressure cause them to open and close.

Sponges do not have a true circulatory system, but they can propel water through their bodies using flagellated __________.

choanocytes

What differentiates a closed circulatory system from an open circulatory system?

cirect contact of circulating fluid with tissues

Excluding capillaries in the central nervous system, the least permeable type of capillary is the

continuous capillary.

Unicellular organisms rely on the process of __________ to transport substances throughout the body.

diffusion

How do substances move across capillaries?

diffusion, through pores, and transcytosis (all of the above)

What type of capillary is normally found in the kidney?

fenestrated

Fish hearts consist of __________ chambers arranged in a series.

four

How do cardiomyocytes communicate with one another?

gap junctions

What physiological or morphological characteristics prevent a giraffe from developing cerebral edema while drinking?

highly elastic blood vessels near the brain

Which of the following is FALSE? Mammalian hemocytes are involved in

hormone secretion.

Which of the following does NOT cause vasodilation?

increased nitrogen

Norepinephrine has the following effect on pacemaker cells:

increased sodium influx.

Blood volume is maintained by the

kidney.

What types of blood cells are involved in immunity?

leukocytes

What is hypoxia?

low levels of oxygen

Which of the following fluids is NOT circulated by the cardiovascular system?

lymph

The vertebrate heart muscle is known as

myocardium.

An osmotic pressure that is due to proteins is termed __________.

oncotic pressure

In the decapod crustacean, blood returns to the heart through small holes called __________.

ostia

The main function of vertebrate erythrocytes is the storage and transport of __________.

oxygen

Which of the following is NOT one of the essential components of a circulatory system?

oxygen

In the cardiac cycle of mammals and birds, the ventricles fill mostly as a result of

passive blood flow from the atrium.

How does the dorsal blood vessel of the earthworm pump blood?

peristalsis

What is hydrostatic pressure?

pressure exerted by a fluid at rest

In mammals, the __________ is the main blood vessel leading from the heart to the lungs.

pulmonary artery

Tetrapods have two circuits within their circulatory system. The one that pushes blood through the lungs is called the

pulmonary circuit.

In mammals, the __________ is the main blood vessel leading from the lungs to the heart.

pulmonary vein

In the tetrapod circulatory system, the right side of the heart is responsible for the __________ circuit, and the left side is responsible for the __________ circuit.

pulmonary; systemic

Small increases in blood vessel __________ can lead to big decreases in vessel resistance.

radius

The law of bulk flow quantifies the relationship between flow, pressure, and __________.

resistance

In tetrapods, the __________ side of the heart pushes blood through the pulmonary circuit.

right

The ridge that separates the two ventricles in the mammalian heart is called the intraventricular __________.

septum

In vertebrates other than fish, the cardiac pacemaker cells are located in an area of the right atrium called the __________.

sinoatrial node

Cardiac pacemaker cells have an unstable resting membrane potential as the result of an unusual __________ current.

sodium

The rising phase of the action potential of a cardiac cardiomyocyte is caused by a __________ current.

sodium

Cardiac output is a function of heart rate and

stroke volume.

Angiogenesis refers to

synthesis of blood vessels.

Cardiac contraction is called __________.

systole

Which of the following possibilities is incorrect? During the mammalian cardiac cycle, the right ventricle contracts less forcefully than the left because

the capillary bed offers high resistance.

The end-diastolic volume is

the maximum volume of blood in the ventricle.

Total flow in the vertebrate circulatory system can be expressed as the total pressure change divided by

total peripheral resistance.

What is believed to be the major evolutionary pressure in the development of closed circulatory systems?

transport of oxygen

Vertebrate blood vessels have complex walls. The smooth muscle of the __________ layer of the blood vessel causes vasoconstriction.

tunica media

Vasoconstriction is the result of the contraction of smooth muscle of the

tunica media.

How do veins prevent the backflow of blood?

valves

The primary pump in chambered hearts is called the __________.

ventricle

Capillaries empty into __________.

venules

Based on the law of bulk flow, what is the unit for "flow"?

volume time