Chapter 39: Animal Cardiovascular & Respiratory System

Voluntary and involuntary mechanisms control breathing.

Animals adjust their respiratory rate to meet their cells' changing demanding for O2. In breathing, the sensors are chemoreceptors located within the brainstem and in sensory structures called the carotid and aortic bodies. The carotid bodies sense O2 and H+ concen of blood going to brain while the aortic bodies moniter their levels in blood moving to the body. The chemoreceptors in brainstem sense O2 and H+ concen. Breathing becomes stronger or faster when CO2 levels increase or O2 levels decrease.

Gills

Aquatic animals take in O2 from water breathe through gills, delicate structures that facilitate gas exchange with the surrounding water. Fish need sufficient O2 to meet energy demands of swimming so they actively pump water through their mouth and over the gills. fish greatly reduce the energy cost of moving water by maintaining a continuous, unidirectional flow of water past their gills to overcome the density and viscosity of water. Gills have a large surface area for their size so O2 in water passing over the gill can readily diffuse into the small blood vessels.

Circulatory systems have vessels of different sizes to facilitate bulk flow and diffusion.

Arteries are large high-pressure vessels that move blood away from the heart to the tissues. Arteries branch into blood vessels of smaller diameter called arterioles that ultimately connect to capillaries. Veins are the large, low-pressure vessels that return blood to the heart. Numerous capillaries drain into vessels of larger diameter called venules which drain into a few larger veins that return blood to the heart. It is at the capillaries that gases are exchanged by diffusion with the surrounding tissues.

Why doesn't the blood plasma lose all of its water and ions over time?

As water is filtered out of the capillaries, some ions, cells, proteins, and other large compounds remain inside, increasing in concentration. As a result, there's a tendency of water to flow back into the capillaries by osmosis. At the same time, blood pressure decreases because of the flow resistance imposed by the capillaries. When the pressure is no longer high enough to counter osmosis, water moves back into the capillaries.

Cardiac muscles are muscle cells that make up the walls of the atria and ventricles and contract to pump blood through the heart.

Atrial muscle cells are activated to contract in synchrony during diastole to fill the ventricles, and the ventricular muscle cells must contract in synchrony during systole to eject the blood from the heart. For cardiac muscle cells to pump in unison, they must be depolarized in unison by an AP.

Describe two mechanisms by which the cardiac output of an animal's heart can be adjusted and indicate which is more important for increasing cardiac output in mammals and which is more important in fish.

Cardiac output can be adjusted by changing either how fast the heart pumps the blood(heart rate) or how much blood is pumped through the heart in each cardiac cycle(stroke volume). Mammals increase cardiac output mainly by increasing heart rate in response to signals from the NS, whereas fish typically increase stroke volume to increase cardiac output.

As animals evolved to be larger and more complex, they faced the challenge of obtaining an adequate supply of O2 and nutrients, at the same time, eliminating CO2 and other waste products.

Diffusion only works over short distances so these animals evolved respiratory structures at the body's surface for taking up O2 and releasing CO2 and internal circulatory systems for long-distance transport to different body regions.

Thoracic cavity

Mammals/reptiles expand their thoracic cavity to draw air inside their lungs on inhalation. The expansion of the lungs causes the air pressure inside the lungs to become lower than the air pressure outside the lungs. The resulting negative pressure draws air into the lungs. Exhalation is passively driven by elastic recoil of tissues that were previously stretched during inhalation. Elastic recoil compresses the lungs, causing the air pressure inside the lungs to become higher than the air pressure outside the lungs. The resulting positive pressure forces air out of the lungs.

Countercurrent exchange

The type of organization in which fluids with diff properties move in opp directions is an efficient way to exchange properties between the two fluids. The property could be a chemical property like O2 or a physical property like heart. As a result of this, fish gills can extract nearly all the O2 in the water that passes over them. The O2 in the oxygen-rich water moves down its concentration gradient into the oxygen-poor blood of the gills. At the same time, CO2 readily diffuses out of the blood vessels and into the water that leaves the gill chamber. A set of blood vessels carries the O2 rich blood away from the gills to supply the fish's body.

Mammalian lungs are well adapted for gas exchange.

Their lungs have a large surface area and a short diffusion distance for has exchange. The lungs supply O2 quickly enough to support high metabolic rates. 1. Air is taken in though the mouth and nasal passages and then passes through the larynx, an organ in throat made of muscle and cartilage that helps to isolate breathing and swallowing and within which the vocal cords are located. 2. Air then enters the trachea, the central airways leading to the lungs. 3. The trachea divides into two airways, called the primary bronchi, one of which supplies each lung. -The trachea and bronchi are supported by rings of cartilage that prevent them from collapsing during respiration, ensuring that airflow meets with minimal resistance. 4. The primary bronchi divide into finer bronchioles. 5. At the end of the bronchioles are alveoli where gas exchange by diffusion takes place. -Because of all this branching pattern, each lung consists of millions of alveoli, providing a large surface area. Smaller blood vessels, the pulmonary capillaries supply the alveolar wall. The diffusion distance from the alveolus into the capillary is short.

Cardiac cycle

This is the contraction of the two atria followed by the contraction of the two ventricles. This cycle is divided into two phases. 1.Systole is the contraction of ventricles. This is the phase of the cycle in which blood is pumped from the heart into the pulmonary and systematic circulations. 2. Diastole is the relaxation of the ventricles. This is the phase in which the atria contract and the ventricles fill with blood.

Most nerve cells maintain their resting membrane potential until they receive a signal from another cell but in pacemaker cells, their resting membrane gradually become less negative on its own until it reaches threshold and the cell fires an AP.

This tendency to become less negative is due to slow leakage of Na+ ions into the cell and decreased flow of K+ out of the cell. When the cell reaches threshold, voltage-gated Ca+ ion channels open, causing more rapid depolarization. After firing an AP, the pacemaker cells repolarize to reach their resting potential, keeping the heart relaxed between contractions. Pacemaker cells repolarize by opening voltage-gated K+ channels to allow K+ ions to leave the cell.

Amphibians and reptiles

Three-chambered hearts and partially divided circulations 1. Deoxygenated blood from the tissues enters the right atrium from a major vein and is pumped into the single ventricle. 2. Oxygenated blood from the lungs enters the left atrium and is pumped into the ventricle. 3. Mixed oxygenated and deoxygenated blood is pumped out of the common ventricle into separate arteries leading to the lungs and tissues.

During the ___ phase of the cardiac cycle, blood enters the ventricle. During the ____ phase, blood exits the ventricles.

diastole; systole

Partial pressure(p)

Of a gas, it's defined as its fractional concentration relative to other gases present, multiplied by the overall pressure. The sum of the partial pressures of a mixture of gases equals the total atmospheric pressure. O2 - 21%; exerts a pO2 of ~160mmHg N2 - 78%; 593 mmHg CO2 - 0.03%; 0.2 mmHg Remainder are trace gases For O2 to diffuse from air into cells, pO2 inside cell must be lower than pO2 in atm

Oxygen transport by hemoglobin

Once O2 is extracted from the environment and diffuses into the animal, it's transported to respiring cells. O2 is transported in the circulation by specialized body fluids- the blood of vertebrates or hemolymph of invertebrates.

Open Circulatory Systems

Open circulatory systems have few blood vessels and in which most of the circulating fluid is contained within the body's cavity. The circulating blood, the hemolymph is contained within the body's cavity and bathes the animal's tissues and organs They have limited control of where the fluid moves. Operate under slow pressure. Ability to control respiratory gases and metabolites to specific tissues and regions is limited

In vertebrates, excess interstitial fluid is also returned to bloodstream by means of lymphatic system, a network of vessels distributed throughout the body.

The fluid that enters the lymphatic system is called lymph.

How can the rate of diffusion through the gas exchange surface in lungs or gills keep up with the rate of O2 supplied by ventilation?

The gas exchange surface must have a large surface area and be extremely thin. The respiratory surfaces are highly folded, creating a large surface area within a small space.

Rate of diffusion...

is directly proportional to the surface area over which exchange occurs and to the concentration difference, and inversely proportional to the distance over which the molecules move(or thickness of barrier). It is increased by a large surface area for exchange and a short diffusion distance.

Sound

is produced by voluntarily adjusting the magnitude and rate of airflow over the vocal cords of mammals.

Resistance to flow

measures the difficulty of pumping the fluid through a network of chambers and vessels located within respiratory and circulatory systems. The longer and narrower the vessels are, the greater the vessels' resistance to the fluid moving through them.

The pacemaker of the mammalian heart is:

modulated by signals from the autonomic nervous system; a group of specialized cardiac muscle cells that initiate the heartbeat

Why do cells in the airways of the lungs produce mucus?

to trap pathogens and guard against infection

Fish

two chambered hearts and a single circulatory system Deoxygenated blood returning from fish's tissues enters atrium which fills and then contracts to move the blood into a thicker-walled ventricle. The muscular ventricle pumps the blood through a main artery to the gills for uptake of O2 and elimination of CO2. Oxygenated blood collected from the gills travels to the tissues through a large artery called the aorta. The small gill capillaries impose a large resistance to flow. As a result, much of the blood pressure is lost in moving blood through the gills. The loss of pressure limits the flow of oxygenated blood to body tissues. 1. Deoxygenated blood enters the atrium from a main vein and is pumped into the ventricle. 2. Deoxygenated blood is pumped from the ventricle into a main artery.

For both aquatic and terrestrial animals...

ventilation supplies O2 to gas exchange surfaces, and then O2 crosses the surface through diffusion. Diffusion is much slower over long distances than the bulk flow of ventilation.

Osmosis requires:

a semipermeable membrane separating areas of different solute concentration

Dilated pupils, inhibited digestive activity, increased respiratory rate, and release of glucose from the liver are all signs of activity of:

the sympathetic division of the autonomic system.

Tidal ventilation

A breathing technique in most land vertebrates in which air is drawn into the lungs during inhalation and moved out during exhalation. The density and viscosity of air enables animals to breathe by tidal ventilation without expending too much energy. In tidal respiration, air is drawn into the lungs during inhalation and then moved out during exhalation.

With the evolution of life on land, animals that breathe air were able to increase their uptake of O2 and achieve higher rates of metabolism. O2 uptake increased for the following reasons:

1. O2 content of air is 50x greater than that of a similar volume of water. 2. Oxygen diffuses 8000x faster in air than in water. 3. Water is 800x denser and 50x more viscous than air. Thus, it requires more energy to pump air past a gas exchange surface.

These two features of cardiac muscle cells ensure that all muscle cells in a region surrounding a heart chamber are activated and contract in unison.

1. Specialized cardiac muscle cells can generate APs on their own, independently of the NS. 2. Cardiac muscle cells are in electrical continuity with one another through gap junctions meaning that they can pass their APs to adjacent cells.

The specialized cardiac muscle cells capable of generating APs independently function as a pacemaker that causes the heart to beat with a basic rhythm. These cells stimulate neighboring cells to contract in synchrony and are found in two specialized regions of the heart, the sinoatrial(SA) and atrioventricular(AV) nodes. SA is a specialized region of the heart containing pacemaker cells where the heartbreak is initiated. AV nodes is a specialized region of the heart containing peacemaker cells that transmit APs from the SA nodes to the ventricles of the heart.

1. The pacemaker generates APs that spread through the atria. The atria contracts. 2. The signals from the pacemaker reach the AV node, which is activated and fires. 3a. The APs are transmitted through a set of modified muscle fibers. 3b. The depolarization spreads from the modified muscle fibers through the entire ventricle. The ventricles contract.

Closed Circulatory Systems

A circulatory system made up of a set of internal vessels and a heart that functions as a pump to move blood to different regions of the body. They must produce enough pressure to carry the circulating blood to all the tissues, but once the blood reaches smaller vessels that supply cells within the tissues, the blood pressure and flow rate must not be too high. High pressure would push fluid through the walls of the smaller vessels and cause blood to flow so quickly that there wouldn't be enough time to exchange gases. It delivers O2 at high rates to exercising tissues, necessary to enable their mitochondria to provide the energy needed to chase prey. Can control blood flow to specific blood flow to specific regions of body by varying the resistance to flow

The heartbeat is initiated at the SA node. Because adjacent cardiac muscles cells are in electrical contact, APs initiated at the SA node spread rapidly from one cell to the next. Thus, when the pacemaker cells in the SA node fire an AP, their depolarization spreads electrically throughout the right and left atria, causing them to contract in unison. Because there's no electrical contact between atria and ventricles, the ventricles don't contract. Instead, the depolarization in the atria reaches a second set of pacemaker cells, located in AV node.

Activation of the AV node transmits the APs to the ventricles. A modified set of cardiac muscle fibers transmits the AP from the AV node to the base of the ventricle. Here, the depolarization spreads throughout the ventricle walls, causing the ventricles to contract in unison. The delay in transmission from the AV node and through the conducting fibers ensures that the ventricles don't contract until they're fully filled with blood from the atria.

What properties of air make it possible for humans and other mammals to breathe by tidal ventilation?

Air has low density and viscosity and a high O2 content relative to that of water.

How do hormones and nerves provide homeostatic regulation of blood flow as well as allow an animal to respond to stress?

An animal that's dehydrated or has lost blood may experience a drop in blood pressure. The ADH/vasopressin will circulate and cause arteries to constrict, increasing their resistance to blood flow. The higher resistance elevates blood pressure throughout the body. Vasoconstriction is the process in which the supply of blood to the limbs is reduced by constriction of the arteries that supply the limbs. Vasodilation is the process in which resistance in the arteries is decreased and blood flow increased following the relaxation of the smooth arterial muscles.

The structure of birds allows unidirectional airflow for increased oxygen uptake.

Birds extract O2 efficiently to supply the considerable energy needed for flight. Bird lungs don't inflate/deflate so they don't use tidal breathing. They benefit from unidirectional airflow that enhances gas exchange by maintaining larger concen gradients for diffusion. Their respiratory system has two sets of air sacs: one posterior and one anterior. 1. First inhalation draws oxygen-rich air into posterior air sacs. 2. First exhalation moves fresh air into lung. 3. Second inhalation moves stale-oxygen depleted air from lung into anterior air sacs. 4. Second exhalation moves air out of anterior air sacs. Birds achieve a continuous supply of fresh air into the lung during both exhalation/inhalation.

Arteries are muscular, elastic vessels that carry blood away from the heart under high pressure.

Blood flow must be increased to their muscles and reduced to their digestive organs. Animals meet this challenge by changing vessel's radius since resistance to flow is affected by vessel radius. Collagen fibers are strong and resist the expansion of arterial wall during pressure pulses. Together with elastin fibers, the collagen provides an elastic rebound of the arterial wall once the pulse has passed, returning energy to help smooth out blood flow. If an artery wall deteriorates, the collagen and elastin can become so thin that the artery bulges outward. The bulge is called an aneurysm, that can lead to a life-threatening rupture.

Veins are thin-walled vessels that return blood to the heart under low pressure.

Blood from capillary drain in to the largest two veins, the venae cava. The venae cavae drain blood from the head and body into the heart. Because of the low pressure, blood tends to accumulate within the veins. Veins located in the limbs and in the body below the heart have one-way valves that help prevent blood form pooling owing to gravity. Most important mechanisms of returning blood to the heart is the voluntary muscle contractions that occur during walking and exercise, which exert pressure on the veins.

Which of the following animals has a heart in which oxygenated and deoxygenated blood mix?

Frog

Hemoglobin reversibly binds oxygen.

Hemoglobin consists of 4 PP units, each surrounds a heme group that contains iron, which reversibly binds 1 O2 molc. After O2 diffuses into the blood, it diffuses into the RBC and binds to the heme group in hemoglobin. Hemoglobin's binding of O2 removes O2 from solution, keeping the pO2 of RBC below that of blood plasma so O2 continues to diffuse into the cell. The removal of O2 from the plasma keeps the pO2 of the plasma below that of the lung alveolus, so O2 continues to diffuse form the lungs into the blood. When more O2 is present in blood plasma, more O2 binds to hemoglobin. As blood pO2 increases, hemoglobin saturation rises slowly at first, then more steeply, and then more slowly again until it levels up. The curve is the hemoglobin's oxygen dissociation curve.

Diaphragm

In mammals, inhalation is driven by contaction of diaphgram. Exhalation occurs passively by elastic recoil of the lungs and chest wall. During exercise, other muscles come to play to assist with inhalation and exhalation.

Those who suffer an asthma attack have difficulty breathing. From the discussion of bulk flow, what do you think happens to these individuals' airways that makes it difficult for them to breathe?

In those with asthma, resistance to airflow increases, thereby decreasing the flow of air. Resistance increases because the diameter of the airways decreases as a result of smooth muscle contraction in the airway walls.

Insects breathe air through tracheae.

Insects can use a direct pathway of air transport that gets air right to their tissues. They rely on a 2 step process of ventilation and diffusion to supply their cells with O2 and eliminate CO2. 1. Air enters through openings called spiracles along either side of its abdomen. The spiracles can be opened or closed to limit water loss and regulate O2 delivery. Inside the insect body, air is ventilated through a branching series of air tubes-tracheae and tracheoles-directly to the cells. 2. Diffusion occurs at the cell: O2 is supplied by the fine airways diffuses into the cell, and CO2 diffuses out and is eliminated through the insect's tracheae. Because O2 and CO2 diffuse rapidly in air, the tracheal system delivers O2 to cellular mitochondria at right rates. Powered by contracting abdominal muscles, the air sacs act like bellows to pump air through the tracheae, speeding the movement of air to tissues so that gas exchange is faster.

Tracheae

Instead of lungs, terrestrial insects evolved a system of air tubes called tracheae that branch from openings along their abdominal surface into smaller airways, directing O2 to and removing CO2 from respiring tissues. The smaller airways, tracheoles, supply air directly to the cells within their bodies.

Blood is composed of fluid and several types of cell.

It can be separated into a cellular fraction and a fluid fraction(blood plasma). Red blood cells that carry hemoglobin constitute most of the cellular fraction of blood. In both vertebrates and invertebrates, hemoglobin evolved as a specialized iron-containing, or heme, molecule for O2 transport. The fraction of RBC within the blood of vertebrates is defined as hematocrit. Blood with a lower hematocrit flows with less resistance(has a lower viscosity), but carries less oxygen. Humans with low hematocrits are considered to be iron deficient because their blood has fewer RBC and therefore too little hemoglobin. The smaller fraction(~1%) are WBC which help to defend body against pathogens. The remaining cells are platelets, which respond to damaged blood vessels by helping to form a clot to prevent blood loss. Hemoglobin gives the cell and their blood their red appearance.

Myoglobin stores oxygen, enhancing delivery to muscle mitochondria.

It is a specialized O2 carrier within the cells of vertebrate muscles. It is a monomer that contains only a single heme group. It has a greater affinity for O2 than hemoglobin does and binds O2 more tightly. As a result, hemoglobin releases O2 to exercising muscles. As the exercising muscles consume the available O2, the intracellular pO2 drops, and the myoglobin releases its bound O2 to the mitochondria. Red muscle cells that depend mainly on aerobic respiration to produce ATP store large amounts of myoglobin because they can release O2 quickly at the onset of activity before respiratory and circulatory systems have had time to increase the supply of O2.

Bulk flow

It is the physical movement of fluid & gases and the compounds carried by the fluid, over a given distance due to pressure differences at rates beyond those possible by diffusion across a concentration gradient. Occurs in 2 steps to meet gas exchange needs of a cell 1. Ventilation- movement of animal's respiratory medium past a specialized respiratory surface 2. Circulation- movement of a specialized body fluid that carries O2 and CO2; circulatory fluid is called hemolymph in invertebrates and blood in vertebrates; the fluid delivers O2 to cells within diff region of body and carries CO2 back to respiratory exchange surface Ventilation and circulation each require a pump to produce to produce a pressure that drives flow against the resistance to flow : Q=P/R

Heart

Pulmonary circulation - circulation of the blood to the lungs Systemic circulation - circulation of the blood to the body, excluding lungs This double circulation is made possible by the evolution of a four-chambered heart. Advantages: it increases the supply of oxygenated blood to active tissues, and it increases the uptake of O2 at the gas exchange surface.

Blood function

Role in O2 and CO2 transport Heat transport for temperature regulation and nutrient transport to metabolically active tissues Hormone transport Waste transport to excretory organs Transport of immune cells involved in fighting pathogens

Compounds and fluids move across capillary walls by diffusion, filtration, and osmosis.

Water, certain ions, and other small molecules move from capillaries into the surrounding interstitial fluid forced by blood pressure. The blood is thus filtered as it passes through the capillary wall.

Keeping the surfaces of the alveoli moist is critical because moisture helps move O2 molecules from the air into solution and thus helps them diffuse across the alveolar wall.

Some alveolar cells produce a surfactant, a compound that acts to reduce the surface tension of fluid film. -surface tension=cohesive force that holds the molecules of a liquid together, causing the surface to act like an elastic membrane. because of the surface tension, it requires greater pressure to inflate a smaller balloon than a large one. The surfactant allows the lungs to be inflated easily at low volumes when the alveoli are partially collapsed and small. It enables nearly uniform ventilation of the lung. Mucus-secreting cells line the airways of lungs to keep them moist and to trap and remove foreign participles and microorganisms that an animal may breathe in with air. Beating cilia on the surface of these cells move the mucus and foreign debris out of the lungs and into the throat, where it's swallowed and digested. Smoking can stop cilia's beating for several hours or destory them. This is one reason why smokers cough- they must clear the mucus that builds up.

Many factors affect hemoglobin-oxygen binding.

Species adapt by evolving forms of hemoglobin with higher binding affinity. Maternal and fetal blood exchange gases across the placenta. Fetal mammals produce a form of hemoglobin before birth that has a higher affinity for O2 than their mother's. At birth when the newborn begins to breathe, its RBC shift to produce adult form of hemoglobin. Tissue and blood pH have an important physiological effect on O2 affinity to hemoglobin. When H+ concen increases, the affinity of hemoglobin for O2 decreases. This is the Bohr effect. Decreases in pH occur when CO2 is released from metabolizing cells, or when an inadequate supply of O2 leads to the production lactic acid. Because hemoglobin's affinity for O2 is reduced, more O2 is released and supplied to the cells for aerobic ATP synthesis.

Lungs

Terrestrial animals have internal lungs for gas exchange. Internal respiratory exchange surfaces are adaptations that protect the lung surfaces from drying out in a terrestrial environment.

What pressure difference between the ventricle and the atrium causes the atrioventricular valve to close?

The AV closes when the pressure in the ventricle exceed the pressure in the atrium.

Tidal volume

The amount of air inhaled and exhaled in a cycle; in humans, tidal volume is 0.5L when breathing at rest. The fresh air inhaled during tidal breathing mixes with O2-depleted stale air that remains in airways after exhalation so the pO2 in lungs is lower than the pO2 of freshly inhaled air

Gas exchange in multicellular organism procedure

To deliver O2 to mitochondria in animal's cell, 1. Fresh air/water moves past respiratory exchange surface in process of ventilation(in bulk flow). Ventilation maximizes the concentration of O2 in air/water on outside of respiratory surfaces. -Breathing moves air(containing O2) into the lungs and air(containing CO2) out of lungs 2. The buildup of O2 favors the diffusion of O2 into the animal across its respiratory surface. -O2 diffuses form lung into the blood and CO2 diffuses out of blood into lungs 3. Following diffusion into the blood, O2 is transported by the circulation(in bulk flow) to the tissues. Internal circulation again serves to maximize the concentration of O2 outside cells. -O2 and CO2 are transported by the circulatory system to and from cells 4. Oxygen then diffuses from the blood across the cell membrane and into the mitochondria, where it burns fuels for ATP production. -O2 diffuses from blood into cells and CO2 diffuses out of cells into the blood

Excluding movement of blood between the lungs and the heart, which of the following carry CO2-rich (and O2 poor) back to the heart?

Venules, veins

Recall that the muscles of marine mammals contain a great deal of _____________. Oxygen binds to the one heme site in this molecule, and can be "stored" in muscles until it is required by muscle cells during a dive.

myoglobin

Which of the following affect the rate of diffusion of a substance?

temperature, concentration gradient