Chapter 42 (1)

The resources that animal cells requrie, like nutrients and oxygen, enter the cytoplasm by crossing the plasma membrane. Metabolic byproducts, like __, exit the cell by crossing the same membrane. In unicell organisns, exchange occurs directlly with the external environment. For most multi cell orgaisms, however, direct exchange between every cell and the environment is not possible. Instead, tehse organisms rely on specialized systems that carry out exchange witht eh environment and that transport materials between sites of exchange and the rest of the body.

The molecular trade that animals carry out with their environment- gaining O2 and nutrients while shedding CO2 and other waste products- must ultimately involve every cell in the body.
- What is the relationship between the time it takes for a substance to diffuse from one place to another?

How does each cell of an animal participate in exchange?
-Natural selection resulted in two general solutions. What are they?
o Each cell, due to the first solution, can exchange directly witht he surrounding meddium.

In hydras and other cnidarians, a central __ functions both in digestion and in the distribution of substances throughout the system. A signel opening maintains continuity between the fluid inside the cavity and the water outside. As a result, both the inner and outer tissue layers are bathed by fluid. Only hte cells of the inner layer have direct access to nutrients, but since the body wall is a mere two cells thick, the nutrients must diffuse only a short distance to reach the cells of the outer layer. Thin branches of a hydra's __ extend into the animal's tentacles. Some cnidarians, have __ with a much more elaborate branching pattern.

Planarians and other flatworms survive without a __. Their combo of a __ and a flt body is well suited for exchange.

For animals with many cell layers, ___ distances are too great for adequate echange of nutrients and wastes by a __. In these organisms, a circulatory system mininmizes the distances that substances must diffuse to enter or leave a cell.

By transporting fluid throughout the body, the __ functionally connects the aqueous environment of the body cells to the organs that exchange gases, absorb nutrients and dispose of wastes.

In mammals, O2 from inhaled air diffuses acrossonly two layers of cells in lungs before reaching hte blood. The __, poered by the heart, then carries the oxygen-rich blood to all parts of the body. As the blood streams throughout the body tissues in tiny blood vessels, O2 in the blood again diffuses only a short distance befre entering the ___ that directly bathes the cells.

A circulatory system has three basic components: __, __, __.
o The __ powers circulation by using metabolic energy to elevate the hydrostatic pressure of the circulatory fluid, which then flows through a circuit of vessels and back to the heart.

Arthropods and most mollusks have a n __, in whicht eh circulatory fluid bathes the organs directly. In these animas, the circulatory fluid, calle __, is also the interstitial fluid. contraction of one or more hearts pumps the __ through the circulatory vessels into interconnected __, spaces surrouding the organs. Within the __, chemical exchange occurs between the __ and the ody cells.

Relaxation of the heart draws __ back in through pores, and body movements help circulate the __ by periodically squeezing the sinuses. The __ of larger crustaceean includes a more extensive sytstem of vessels as well as an accessory pump.

In a __, blood is confined to vessels and is distinct fromt he __. One or more hearts pump blood into large vessels that branch into smaller ones coursing through the organs. Materials are exchanged between the smallest vessels and the interstitial fluid bathing the cells.

The fact that both open and closed circulatory systems are widespread among animals suggests that there are advantages to each system. The lower hydrostatic pressures associated with __ makes them less costly than __ in terms of energy expenditure. In some invertebrates, __ serve additional funcitions, like the force for extension of the animal's leg.

The benefits of __ include relatively high blood pressures, which enable the effective delivery of O2 and nutrients to the cells of larger and more active animals. They are also particularly well suited to regulating hte distribution of blood to different organs.

The closed circulatory system of humans and other vertebrates is often called the __. Blood circulates to and from the heart through an amazingly extensive network of vessels.

__, __, and __ are the three main types of blood vessels. W/in each type, blood flows in only one idrection. __ carry blood away from the heart to organs throughout the body. Within organs, __ branch into __, small vessels that convey blood to the capillaries.

__ are microscopic vessels with very thin, porous walls. Networks of tehse vessels, called __, infiltrate each tissue, passing within a few cell idametsers of every cell in thebody. Across the thin walls of __, chemicals, including dissolved gases, are exchanged by diffusion between the blood and the interstitial fluid around the tissue cells.

At their "downstreeam" end, __ converge into __, and __ converge into __, teh vessels that carry blood back to the heart.

Arteries and veins are distinguished by the __ in which they carry blood, not by the O2 content or other characteristscs of the blood they contain.
- __ carry blood from the heart toward capillaries, and __ return blood to the heart from capillaries.
o There is one exeption: __.

The __ carries blood from capillary beds in the digestive system to capillary beds i the liver. From the liver, blood passes into the __, which conduct blood toward the heart.

natural selection has modified hte __ of dif vertebrates in accordance with their level of activities.

The hearts of all vertebrates contain two or muscular chambers. The chambers that receive blood entering the heart are called __. The chambers responsible for pumping blood out of the heart are called __.
- The # of chambers and the extent to which they are separated from one another differ substantially among groups of vertebrates. These important differences reflect the close fit of __ to __.

In fishes, rays, sharks- teh heart consists of two chambers: an __ and a __. The blood passes through the heart oce in each complete circuit, called __. Blood entering the heart collectis int he __ befor etransfer to the __. Contraction of the __ pumps blood to the gillls, where there is a net diffusion of O2 into the blood and of CO2 out of the blood. As blood leaves the gills the capillaries converge into a vessel that carries oxygen-rich blood to capillary beds throughout the body. Blood then returns to the heart.

In __, blood that leaves the heart passses through two __ before returning to the heart. When blood flos through a __, blood pressure drops substantially. The drop in blood pressure in gills of bony fish, ray or shark limits the rate of blood flow in the rest of the animal's body. As the animal swins, the contraction and relaxation of its muscles help accelerate the relatively sluggish pace of circulation

The circulatory system of amphibians, reptiles, and mammals have two distinct circuits, an arrangement called __. The pumps for the two circuits serve different tissues but are combined into a single organ, the __. Having both pumps within a single heat simplifies coordination of the pumping cycles.

One pump, the right side of the heart, dilivers oxygen-poor blood to the capilarry beds of the gas exchange tissues, where there is anet movement of O2 into the blood and of CO2 out of the blood. This part of the circulation is called a __ if the capilllary beds involved are all in the lungs, as in reptiles and mammals. It is called a __ if it includes capillaries in both the lungs and the skin, as in many amphibians.

After the oxygen-enriched blood leaves the gas exchange tissues, it enters the other pump, the left side of the heart. Contraction of the heartt propels this blood to capillary beds in organs and tissue throughout the body. Following the exchange of O2 and CO2, as well as nutrients and waste products the now ocygen poor blood returns to the heart, completing the __.

__ provides a vigorous flow of blood to the brain, muscles and other organs because the heart repressurizes the blood ddestined for these tissues after it passes through the capillary beds of the lungs or skin. Indedd, blood pressure is often much higher in the __ than in the _. This contrasts sharply with __, in which blood flows directly fromt he repiraatory organs to other organs, under reduced pressure.

Frogs and amphibians have a heart with three chambers: two __ and one __. A ridge within hte __ diverts most (abt 90%) of the oxygenpoor blood from teh right atrium into the __ and most of the oxygen-rich blood from the left atriuminto the __. When underwater,a frog adjusts ints circulation, for the most part shutting off blood flow to its temporarily ineffective lungs. Blood flow continues to the skin, which acts as the sole site of __ while the frog is submerged.

Reptiles have a three chambered heart, with a __ partially dividing the __ into separate right and left chambers. In alligantors, etc. the __ is complete, but the __ and __ circuits are connected where the arteries exit the heart. When a crocodilian in underwater, __ divert most of the blood flow fro the pulmonary circuit to the systemic circuit through this connection.

In all mammals and birds, the __ is completely divided, such that there are two __ and two __. The left side of the heart receives and pumps only oxygen rich blood, while the right side receives and pumps only oxygen poor blood.

A powerful four-chambered heart is a key adaptation that supports the __ way of life characteristic of mammals and birds. __ use about ten times as much energy as equal-sized ectotherms; therefore, their circulatory systems need to deliver about 10 x as much fuel and O2 to their tissues) and removes 10 x as much CO2 and other wastes.) This large traffic of substances is made possible by separate and independently powered systemic and pulmonary circuits and by large hearts that pump the necessary volume of blood.