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blood coming from the lungs mixes with oxygen-poor blood returning from the body because the wall dividing the ventricle into two chambers is not complete. In birds, the wall dividing the ventricle is complete, and the two blood circulations do not mix, so flight muscles receive fully oxygenated blood. In comparison w...
les on their snouts. Evolution of fur and the ability to regulate body temperature enabled mammals to invade colder climates that ectothermic reptiles could not inhabit, and the insulation fur provided may have ensured the survival of mammals when the dinosaurs perished. Unlike feathers, which evolved from modified rep...
the time of the dinosaurs, although they were never common until the dinosaurs disappeared. We have learned a lot about the evolutionary history of mammals from their fossils. Origin of Mammals The first mammals arose from therapsids in the mid-Triassic about 220 million years ago, just as the first dinosaurs evolved ...
remes—the duckbill platypus and the echidnas, or spiny anteaters. The other major mammalian group is the subclass Theria. All of the mammals you are familiar with, including humans, are therians. Therians are viviparous (that is, their young are born alive). The two major living therian groups are marsupials, or pouche...
away. Teeth. Reptiles have homodont dentition: their teeth are all the same. However, mammals have heterodont dentition, with different types of teeth that are highly specialized to match particular eating habits (figure 48.39). It is usually possible to determine a mammal’s diet simply by examining its teeth. Compare...
inding teeth Ripping teeth Chiseling teeth Incisors Canine Premolars and molars Dog Deer Beaver Elephant Human Chapter 48 Vertebrates 977 Digesting Plants. Most mammals are herbivores, eating mostly or only plants. Cellulose, the major component of plant cell walls, forms the bulk of a plant’s body and is a major sourc...
hairlike fibers of keratin compacted into a very hard structure. Deer antlers are made not of keratin but of bone. Male deer grow and shed a set of antlers each year. While growing during the summer, antlers are covered by a thin layer of skin known as velvet. A third type of horn, the rhinoceros horn, is composed onl...
placental. The other two are the primitive monotremes and the marsupials. Monotremes: Egg-laying Mammals. The duck-billed platypus and two species of echidna, or spiny anteater, are the only living monotremes (figure 48.41a). Among living mammals, only monotremes lay shelled eggs. The structure of their shoulder and p...
upials live in Australia and South America, areas that have been historically isolated. Marsupials in Australia and New Guinea have diversified to fill ecological positions occupied by placental mammals elsewhere in the world. For example, kangaroos are the Australian grazers, playing the role antelope, horses, and buf...
in development, of a notochord, pharyngeal slits, and a postanal tail. In vertebrates, a bony endoskeleton provides attachment sites for skeletal muscle. 1. What are the four primary characteristics of the chordates? • Chordates 48.2 Nonvertebrate chordates have a notochord but no backbone. • Tunicates and the lancele...
function? 7. The successful invasion of land by amphibians involved five major innovations. What were they, and why was each important? 8. How does the embryo obtain nutrients and excrete wastes while contained within the egg? 9. From what reptilian structure are feathers derived? 10. How do amphibian, reptile, and ma...
to expand. Do you see the problem? A running lizard cannot contract its chest muscles on both sides simultaneously for effective breathing at the same time that it is contracting the same chest muscles alternatively for running. This apparent conflict has led to a controversial hypothesis about how running lizards bre...
ular cavity compresses, forcing this air into the lungs. Like an afterburner on a jet, this added air increases the efficiency of breathing, making up for the lost contribution of the intercostal chest muscles. 981 No axial constraint VE max VE max Axial constraint ) 1000 800 600 400 200 0 Gular pumping allowed Gular p...
conducted on monitor lizards with and without gular pumping: 1. Gular pumping allowed. When the gular pumping mechanism was not obstructed, the VE increased to a maximum at a speed of 2 km/hr and decreased during the recovery period (see blue line in graph b above). This result is predicted under conditions where ther...
helial tissue forms membranes and glands. Characteristics of Epithelial Tissue. Epithelial membranes cover all body surfaces, and thus can serve for protection or for transport of materials. Glands are also epithelial tissue. Epithelial membranes may be composed of one layer or many. 49.3 Connective tissues contain abu...
the coelom. In fishes, amphibians, and most reptiles, the coelom is subdivided into two cavities, one housing the heart and the other the liver stomach, and intestines. In mammals and some reptiles, a sheet of muscle, the diaphragm, separates the peritoneal cavity, which contains the stomach, intestines, and liver, fr...
voluntary muscles Cardiac muscle in heart FIGURE 49.3 Vertebrate tissue types. Epithelial tissues are indicated by blue arrows, connective tissues by green arrows, muscle tissues by red arrows, and nerve tissue by a yellow arrow. Loose connective tissue 984 Part XIII Animal Form and Function Organs and Organ Systems O...
movement Nervous Receives stimuli, integrates information, and directs the body Reproductive Carries out reproduction Respiratory Skeletal Urinary Captures oxygen and exchanges gases Protects the body and provides support for locomotion and movement Removes metabolic wastes from the bloodstream Skeletal muscle, cardia...
leave the body. Epithelial membranes thus provide a barrier that can impede the passage of some substances while facilitating the passage of others. For land-dwelling vertebrates, the relative impermeability of the surface epithelium (the epidermis) to water offers essential protection from dehydration and from airbor...
columnar epithelial cells are numerous goblet cells, specialized to secrete mucus. The columnar epithelial cells of the respiratory airways contain cilia on their apical surface (the surface facing the lumen, or cavity), which move mucus toward the throat. In the small intestine, the apical surface of the columnar epi...
asm Columnar epithelial cells Nucleus Goblet cell Nuclei Cilia Pseudo– stratified columnar cell Goblet cell Simple squamous epithelial cell Nucleus Table 49.2 Epithelial Tissue Simple Epithelium SQUAMOUS Typical Location Lining of lungs, capillary walls, and blood vessels Function Cells very thin; provides thin layer a...
by forming a collagenous meshwork. The flavored gelatin we eat for dessert consists of the extracellular material from loose connective tissues. The cells that secrete collagen and other fibrous proteins are known as fibroblasts. Loose connective tissue contains other cells as well, including mast cells that produce h...
. Table 49.3 Connective Tissue LOOSE CONNECTIVE TISSUE Typical Location Beneath skin; between organs Function Provides support, insulation, food storage, and nourishment for epithelium Characteristic Cell Types Fibroblasts, macrophages, mast cells, fat cells DENSE CONNECTIVE TISSUE Typical Location Tendons; sheath arou...
matrix, because they receive oxygen and nutrients by diffusion through the cartilage ground substance from surrounding blood vessels. This diffusion can only occur because the cartilage matrix is not calcified, as is bone. Bone In the course of fetal development, the bones of vertebrate fins, arms, and legs, among oth...
a result, mammalian erythrocytes are relatively inactive metabolically. Each erythrocyte contains about 300 million molecules of the iron-containing protein hemoglobin, the principal carrier of oxygen in vertebrates and in many other groups of animals. There are several types of leukocytes, but together they are only ...
Though the bone matrix is calcified, the osteocytes remain alive because they can be nourished by blood vessels in the central cavity. Nourishment is carried between the osteocytes through a network of cytoplasmic processes extending through tiny canals, or canaliculi. FIGURE 49.10 White and red blood cells (500×). Wh...
to move at their joints. A skeletal muscle is made up of numerous, very long muscle cells, called muscle fibers, which lie parallel to each other within the muscle and insert into the tendons on the ends of the muscle. Each skeletal muscle fiber is stimulated to contract by a nerve fiber; therefore, a stronger muscle ...
cells appear under the microscope as dark lines called intercalated discs. In reality, these lines are regions where adjacent cells are linked by gap junctions. As we noted in chapter 7, gap junctions have openings that permit the movement of small substances and electric charges from one cell to another. These interc...
system (PNS), which includes nerves and ganglia. Nerves consist of axons in the PNS that are bundled together in much the same way as wires are bundled together in a cable. Ganglia are collections of neuron cell bodies. There are different types of neurons, but all are specialized to receive, produce, and conduct elec...
What is a tissue? What is an organ? What is an organ system? • Art Activity: Mammalian body cavities • The vertebrate body is organized into cells, tissues, organs, and organ systems, which are specialized for different functions. • The four primary tissues of the vertebrate adult body—epithelial, connective, muscle, ...
organs of the internal environment and in the walls of blood vessels. • Skeletal and cardiac muscles are striated; skeletal muscles, however, are under voluntary control whereas cardiac muscle is involuntary. • Neurons consist of a cell body with one or more dendrites and one axon. Neuron cell bodies form ganglia, and...
. Muscles generate power for movement, and also act as springs, brakes, struts, and shock absorbers. FIGURE 50.1 On the move. The movements made by this sidewinder rattlesnake are the result of strong muscle contractions acting on the bones of the skeleton. Without muscles and some type of skeletal system, complex loco...
because its old exoskeleton has been shed. Having an exoskeleton also limits the size of the animal. An animal with an exoskeleton cannot get too large because its exoskeleton would have to become thicker and heavier, in order to prevent collapse, as the animal grew larger. If an insect were the size of a human being,...
letons. The axial skeleton is shown in the peach shade, the appendicular skeleton in the yellow shade. Some of the major bones are labeled. There are three types of animal skeletons: hydrostatic skeleton, exoskeleton, and endoskeleton. The endoskeletons found in vertebrates are composed of bone or cartilage and are org...
of bone structure, called a Haversian system. Bone formation occurs in two ways. In flat bones, such as those of the skull, osteoblasts located in a web of dense connective tissue produce bone within that tissue. In long bones, the bone is first “modeled” in cartilage. Calcification then occurs, and bone is formed as ...
bones of the spine are separated by pads of cartilage called intervertebral discs (figure 50.5b). These cartilaginous joints allow some movement while acting as efficient shock absorbers. 3. Freely movable joints include many types of joints and are also called synovial joints, because the articulating ends of the bon...
muscle) to move toward the shoulder (the origin of the muscle). Muscles that cause the same action at a joint are synergists. For example, the various muscles of the quadriceps group in humans are synergists: they all act to extend the knee joint. Muscles that produce opposing actions are antagonists. For example, mus...
oskeleton. In humans, the hamstrings, a group of three muscles, produce flexion of the knee joint, whereas the quadriceps, a group of four muscles, produce extension. Synergistic muscles have the same action, whereas antagonistic muscles have opposite actions. Both muscle groups are involved in locomotion. Isotonic con...
a result, the center of an A band (called an H band) is lighter than each side, with its interdigitating thick and thin filaments. This appearance of the sarcomeres changes when the muscle contracts. A muscle contracts and shortens because its myofibrils contract and shorten. When this occurs, the myofilaments do not ...
examine the thick and thin filaments at a molecular level. Biochemical studies show that each thick filament is composed of many myosin proteins packed together, and every myosin molecule has a “head” region that protrudes from the thick filaments (figure 50.10). These myosin heads form the cross-bridges seen in elect...
(actin) (a) Thick filament (myosin) ATP Cross-bridge (d) (b) (c) FIGURE 50.13 The cross-bridge cycle in muscle contraction. (a) With ADP and Pi attached to the myosin head, (b) the head is in a conformation that can bind to actin and form a crossbridge. (c) Binding causes the myosin head to assume a more bent conforma...
Ca++ concentration is raised, Ca++ binds to troponin. This causes the troponin-tropomyosin complex to be shifted away from the attachment sites for the myosin heads on the actin. Cross-bridges can thus form, undergo power strokes, and produce muscle contraction. Where does the Ca++ come from? Muscle fibers store Ca++ ...
stimulated to contract by motor neurons. The particular motor neurons that stimulate skeletal muscles, as opposed to cardiac and smooth muscles, are called somatic motor neurons. The axon (see figure 49.12) of a somatic motor neuron extends from the neuron cell body and branches to make functional connections, or syna...
fibers in that motor unit contract together. The division of the muscle into motor units allows the muscle’s strength of contraction to be finely graded, a requirement Motor unit Muscle fiber (a) Tapping toe (b) Running FIGURE 50.16 The number and size of motor units. (a) Weak, precise muscle contractions use smaller ...
set to deliver an increasing frequency of electric shocks automatically, the relaxation time between successive twitches will get shorter and shorter, as the strength of contraction increases. Finally, at a particular frequency of stimulation, there is no visible relaxation between successive twitches. Contraction is ...
that are fast-twitch but also have a high oxidative capacity, and so are more resistant to fatigue. Endurance training increases the proportion of these fibers in muscles Incomplete tetanus Complete tetanus Summation Twitches Stimuli • • • • • • Time FIGURE 50.17 Muscle twitches summate to produce a sustained, tetaniz...
a result of anaerobic respiration. For average, healthy people, for example, a significant amount of blood lactate appears when exercise is performed at about 50 to 70% of the maximal oxygen uptake. Muscle Fatigue and Physical Training Muscle fatigue refers to the use-dependant decrease in the ability of a muscle to g...
muscle does contain actin and myosin filaments, but they are arranged less regularly within the cell. Cardiac Muscle Intercalated disks FIGURE 50.19 Cardiac muscle. Cells are organized into long branching chains that interconnect, forming a lattice; neighboring cells are linked by structures called intercalated discs....
between contraction and relaxation that is necessary for pumping. Smooth Muscle Smooth muscle surrounds hollow internal organs, including the stomach, intestines, bladder, and uterus, as well as all blood vessels except capillaries. Smooth muscle cells are long and spindle-shaped, and each contains a single nucleus. T...
The quantity, quality, and position of contractions are initiated and coordinated by the nervous system. In large animals, active locomotion is almost always produced by appendages that oscillate—appendicular locomotion—or by bodies that undulate, pulse, or undergo peristaltic waves—axial locomotion. While animal loco...
Reactive force Lateral force (b) Thrust 90˚ Push FIGURE 50.20 Movements of swimming fishes. (a) An eel pushes against the water with its whole body, (b) a trout only with its posterior half. Whales also swim using undulating body waves, but unlike any of the fishes, the waves pass from top to bottom and not from side ...
they do, the animal loses its balance and falls. It is the necessity to maintain stability that determines the sequence of leg movements, which are similar in vertebrates and arthropods. The apparent differences in the walking gaits of these two groups reflects the differences in leg number. Vertebrates are tetrapods ...
movement. Because of this, thrust tends to occur at the anterior (outside) end of the inwardcurving side of the loop of the snake’s body. Eastern bluebird Pterosaur (extinct) Samoan flying fox (fruitbat) FIGURE 50.22 Flight has evolved three times among the vertebrates. These three very different vertebrates all have ...
terosaurs disappeared with the dinosaurs, are night fliers. By flying at night bats are able to shop in a store with few other customers and a wealth of food: nightflying insects. It has proven to be a very successful approach. One-quarter of all mammal species are bats. Locomotion in larger animals is almost always pr...
nerves; the contractions are automatically produced in cardiac muscle and some smooth muscles. • Animals have adapted modes of locomotion to three different environments: water, land, and air. 1016 Part XIII Animal Form and Function 2. What are the three types of joints in a vertebrate skeleton? Give an example of whe...
The Small Intestine. The small intestine has mucosal folds called villi and smaller folds called microvilli that absorb glucose, amino acids, and fatty acids into the blood. The Large Intestine. The large intestine absorbs water, ions, and vitamin K, and excretes what remains as feces. Variations in Vertebrate Digesti...
, as are pigs, bears, and crows. Single-celled organisms (as well as sponges) digest their food intracellularly. Other animals digest their food extracellularly, within a digestive cavity. In this case, the digestive enzymes are released into a cavity that is continuous with the animal’s external environment. In coelen...
ander Stomach Intestine Cloaca Pharynx Mouth Intestine Anus Gastrovascular cavity Mouth Esophagus Liver Pancreas Anus FIGURE 51.2 The gastrovascular cavity of Hydra, a coelenterate. Because there is only one opening, the mouth is also the anus, and no specialization is possible in the different regions that participate...
a green solution that emulsifies fat), the gallbladder, which stores and concentrates the bile, and the pancreas. The pancreas produces pancreatic juice, which contains digestive enzymes and bicarbonate. Both bile and pancreatic juice are secreted into the first region of the small intestine and aid digestion. The tubu...
teeth (figure 51.6), and chewing (mastication) breaks up food into small particles and mixes it with fluid secretions. Birds, which lack teeth, break up food in their twochambered stomachs (figure 51.7). In one of these chambers, the gizzard, small pebbles ingested by the bird are churned together with the food by mus...
food very long. The secretions of the salivary glands are controlled by the nervous system, which in humans maintains a constant 1020 Part XIII Animal Form and Function Canines Incisors Molars Premolars FIGURE 51.6 Diagram of generalized vertebrate dentition. Different vertebrates will have specific variations from th...
the gizzard. Food mixed with saliva is swallowed and enters the esophagus. (a) Cusp Enamel Gingiva Dentin Pulp cavity with nerves and vessels Periodontal ligaments Root canal Cementum Bone (b) FIGURE 51.8 Human teeth. (a) The front six teeth on the upper and lower jaws are cuspids and incisors. The remaining teeth, ru...
a true sphincter and so are able to regurgitate. Normally, however, the human esophagus is closed off except during swallowing. Structure and Function of the Stomach The stomach (figure 51.11) is a saclike portion of the digestive tract. Its inner surface is highly convoluted, enabling it to fold up when empty and ope...
and keeps pepsin maximally active. Active pepsin hydrolyzes food proteins into shorter chains of polypeptides that are not fully digested until the mixture enters the small intestine. The mixture of partially digested food and gastric juice is called chyme. Esophagus Stomach Mucosa Pyloric sphincter Epithelium Villi G...
Indeed, modern antibiotic treatments of this infection can reduce symptoms and often even cure the ulcer. In addition to producing HCl, the parietal cells of the stomach also secrete intrinsic factor, a polypeptide needed for the intestinal absorption of vitamin B12. Because this vitamin is required for the production...
, villus; figure 51.12). In turn, each of the epithelial cells lining the villi is covered on its apical surface (the side facing the lumen) by many foldings of the plasma membrane that form cytoplasmic extensions called microvilli. These are quite tiny and can be seen clearly only with an electron microscope (figure 5...
ylase Pepsin Peptidases Nucleases Pancreas Lipase Lactase, maltase, sucrase Trypsin, chymotrypsin DNase RNase Substrates Starch, glycogen Proteins Short peptides DNA, RNA Disaccharides Triglycerides Proteins DNA RNA Digestion Products Disaccharides Short peptides Amino acids Sugars, nucleic acid bases Monosaccharides F...
8.5 liters are absorbed in the small intestine and an additional 350 milliliters in the large intestine. Only about 50 grams of solid and 100 milliliters of liquid leave the body as feces. The normal fluid absorption efficiency of the human digestive tract thus approaches 99%, which is very high indeed. Digestion occu...
large intestine, and the excess bacteria are incorporated into the refuse material, called feces. Bacterial fermentation produces gas within the colon at a rate of about 500 milliliters per day. This rate increases greatly after the consumption of beans or other vegetable matter because the passage of undigested plant...
other kinds of animals, including insects like termites and cockroaches, and a few groups of herbivorous mammals. The relationships between these microorganisms and their animal hosts are mutually beneficial and provide an excellent example of symbiosis. Cows, deer, and other ruminants have large, divided stomachs (fi...
Four-chambered stomach of a ruminant. The grass and other plants that a ruminant, such as a cow, eats enter the rumen, where they are partially digested. Before moving into a second chamber, the reticulum, the food may be regurgitated and rechewed. The food is then transferred to the rear two chambers: the omasum and ...
Fueling Body Activities: Digestion 1029 51.4 Accessory organs, neural stimulation, and endocrine secretions assist in digestion. Accessory Organs Secretions of the Pancreas The pancreas (figure 51.19), a large gland situated near the junction of the stomach and the small intestine, is one of the accessory organs that ...
.5 kilograms and is the size of a football. The main exocrine secretion of the liver is bile, a fluid mixture consisting of bile pigments and bile salts that is delivered into the duodenum during the digestion of a meal. The bile pigments do not participate in digestion; they are waste products resulting from the liver...
blood from the stomach and intestine directly to the liver, the liver is in a position to chemically modify the substances absorbed in the gastrointestinal tract before they reach the rest of the body. For example, ingested alcohol and other drugs are taken into liver cells and metabolized; this is why the liver is of...
, and free glucose is secreted into the blood. Skeletal muscles lack the enzyme needed to remove the phosphate group, and so, even though they have glycogen stores, they cannot secrete glucose into the blood. The breakdown of liver glycogen is stimulated by another hormone, glucagon, which is secreted by the α (alpha) ...
GIP), released by the duodenum, was named for this function but may not be the only, or even the major, enterogastrone. The secretion of enterogastrone is stimulated most strongly by the presence of fat in the chyme. Fatty meals therefore remain in the stomach longer than meals low in fat. The duodenum secretes two add...
cells + + Duodenum CCK Secretin FIGURE 51.21 Hormonal control of the gastrointestinal tract. Gastrin is secreted by the mucosa of the stomach and stimulates the secretion of pepsinogen (which is converted into pepsin) and HCl. The duodenum secretes three hormones: cholecystokinin (CCK), which stimulates contraction of...
ious to health, a condition called obesity. In the United States, about 30% of middle-aged women and 15% of middle-aged men are classified as obese, which means they weigh at least 20% more than the average weight for their height. Regulation of Food Intake Scientists have for years suspected that adipose tissue secret...
weight stays constant. Ninety to 95% of those suffering from these disorders are female; researchers estimate that 2 to 5% of the adolescent girls and young women in the United States have eating disorders. The amount of caloric energy expended by the body depends on the basal metabolic rate and the additional calorie...
(pantothenic acid) B6 (pyridoxine) B12 (cyanocobalamin) Biotin Folic acid Vitamin C Vitamin D (calciferol) Vitamin E (tocopherol) Vitamin K Table 51.3 Major Vitamins Function Source Deficiency Symptoms Used in making visual pigments, maintenance of epithelial tissues Green vegetables, milk products, liver Night blindn...
ores • The esophagus contracts in peristaltic waves to drive the swallowed food to the stomach. • Cells of the gastric mucosa secrete hydrochloric acid, which activates pepsin, an enzyme that promotes the partial hydrolysis of ingested proteins. 2. How does tooth structure vary among carnivores, herbivores, and omnivor...
) is the lowest level of energy consumption of the body. • Vitamins, minerals, and the essential amino acids and fatty acids must be supplied in the diet. 10. What is a vitamin? What is the difference between an essential amino acid and any other amino acid? • Nutrition 1036 Part XIII Animal Form and Function 52 Circul...
needs for living from other molecules in food. Like residents of a city whose food is imported from farms in the countryside, cells in the body need trucks to carry the food, highways for the trucks to travel on, and a way to cook the food when it arrives. In animals, the circulatory system provides blood and blood ve...
which also function as pumps, to a ventral vessel, which transports the blood posteriorly until it eventually reenters the dorsal vessel. Smaller vessels branch from each artery to supply the tissues of the earthworm with oxygen and nutrients and to transport waste products (figure 52.2c). The Functions of Vertebrate ...
be recirculated. (c) In the closed circulation of the earthworm, blood pumped from the hearts remains within a system of vessels that returns it to the hearts. All vertebrates also have closed circulatory systems. 1038 Part XIII Animal Form and Function the lungs or gills, oxygen attaches to hemoglobin molecules withi...
surface, so that this blood is no longer cold when it reaches the interior of the body. 3. Protection. The circulatory system protects against injury and foreign microbes or toxins introduced into the body. a. Blood clotting. The clotting mechanism protects against blood loss when vessels are damaged. This clotting me...
because free carbon dioxide would decrease blood pH. 2. Ions. Like the water of the seas in which life arose, blood plasma is a dilute salt solution. The predominant plasma ions are sodium, chloride, and bicarbonate ions. In addition, there are trace amounts of other ions such as calcium, magnesium, copper, potassium,...
volume that is occupied by erythrocytes is called the blood’s hematocrit; in humans, it is typically around 45%. A disc with a central depression, each erythrocyte resembles a doughnut with a hole that does not go all the way through. As we’ve already seen, the erythrocytes of vertebrates contain hemoglobin, a pigment...
ot Megakaryocytes are large cells present in bone marrow. Pieces of cytoplasm are pinched off of the megakaryocytes and become platelets. Platelets play an important role in Collagen fibers Red blood cell Platelet Blood vessel Platelet plug Vessel is damaged, exposing surrounding tissue to blood. Platelets adhere and b...
structure (figure 52.7). The innermost layer is an epithelial sheet called the endothelium. Covering the endothelium is a thin layer of elastic fibers, a smooth muscle layer, and a connective tissue layer. The walls of these vessels are thus too thick to permit any exchange of materials between the blood and the tissu...
µm of a capillary. On the average, capillaries are about 1 mm long and 8 µm in diameter, only slightly larger than a red blood cell (5 to 7 µm in diameter). Despite the close fit, red blood cells can squeeze through capillaries without difficulty. Although each capillary is very narrow, there are so many of them that ...
is needed because the pressure in the veins is only about one-tenth that in the arteries. Most of the blood in the cardiovascular system is contained within veins, which can expand when needed to hold additional amounts of blood. You can see the expanded veins in your feet when you stand for a long time. When the bloo...
osis of water into the capillaries (figure 52.10). Because interstitial fluid is produced because of the blood pressure, high capillary blood pressure could cause too much interstitial fluid to be produced. A common example of this occurs in pregnant women, when the fetus compresses veins and thereby increases the capi...
fluid is drained into open-ended lymphatic capillaries, which ultimately return the fluid to the cardiovascular system. FIGURE 52.11 A lymphatic vessel valve (25×). Valves allow lymph to flow in one direction (from left to right in this figure) but not in the reverse direction. As the lymph moves through lymph nodes a...
their equivalent of the sinus venosus. The fish heart is remarkably well suited to the gill respiratory apparatus and represents one of the major evolutionary innovations in the vertebrates. Perhaps its greatest advantage is that the blood that moves through the gills is fully oxygenated when it moves into the tissues...
atrium; LA = left atrium; V = ventricle. Systemic capillaries Amphibian and Reptile Circulation The advent of lungs involved a major change in the pattern of circulation. After blood is pumped by the heart through the pulmonary arteries to the lungs, it does not go directly to the tissues of the body but is instead re...
Another change in the circulation of reptiles is that the conus arteriosus has become incorporated into the trunks of the large arteries leaving the heart. Amphibians and reptiles have two circulations, pulmonary and systemic, that deliver blood to the lungs and rest of the body, respectively. The oxygenated blood fro...
the overall circulatory system is closed, the same volume of blood must move through the pulmonary circulation as through the much larger systemic circulation with each heartbeat. Therefore, the right and left ventricles must pump the same amount of blood each time they contract. If the output of one ventricle did not...
les to the arterial system; the pulmonary valve is located at the exit of the right ventricle, and the aortic valve is located at the exit of the left ventricle. These valves open and close as the heart goes through its cardiac cycle of rest (diastole) and contraction (systole). The sound of these valves closing produc...
which drains the upper body, and the inferior vena cava, which drains the lower body. These veins empty into the right atrium and thereby complete the systemic circulation. 1048 Part XIII Animal Form and Function Blood pressure gauge 100 150 50 200 0 250 Cuff Stethoscope 100 50 150 200 0 250 100 150 50 200 0 250 Cuff ...

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