Spinal Nerves Reflexes Quiz: The Autonomic Nervous System. The Somatic Senses Vision Quiz: Vision Hearing Sensory Receptors Quiz: Antagonistic Hormones Hormones Quiz: Hormones The Hypothalamus and Pituitary Glands. The Blood Blood Formation Quiz: Blood Formation Hemostasis Quiz: Blood Groups Circulatory Pathways Quiz: Circulatory Pathways The Heart Quiz: Lymphatic Vessels Lymphoid Cells Quiz: Lymphatic System Components Quiz: Lymphatic Tissues and Organs.
Nonspecific Barriers Nonspecific Defenses Quiz: Major Histocompatibility Complex Lymphocytes Quiz: Supplements to the Immune Response. Structure of the Respiratory System Lungs Quiz: Lungs Mechanics of Breathing Quiz: Gas Exchange Gas Transport Quiz: Epithelial tissue is composed of closely packed cells, bound to each other by cell adhesion molecules , with little intercellular space.
Epithelial cells can be squamous flat , cuboidal or columnar and rest on a basal lamina , the upper layer of the basement membrane ,  the lower layer is the reticular lamina lying next to the connective tissue in the extracellular matrix secreted by the epithelial cells.
In the respiratory tract there is a type of ciliated epithelial lining; in the small intestine there are microvilli on the epithelial lining and in the large intestine there are intestinal villi.
Skin consists of an outer layer of keratinized stratified squamous epithelium that covers the exterior of the vertebrate body. In simple animals this may just be a coat of glycoproteins.
Muscle cells myocytes form the active contractile tissue of the body. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle is formed of contractile filaments and is separated into three main types; smooth muscle , skeletal muscle and cardiac muscle.
Smooth muscle has no striations when examined microscopically. It contracts slowly but maintains contractibility over a wide range of stretch lengths.
It is found in such organs as sea anemone tentacles and the body wall of sea cucumbers. Skeletal muscle contracts rapidly but has a limited range of extension. It is found in the movement of appendages and jaws. Obliquely striated muscle is intermediate between the other two.
The filaments are staggered and this is the type of muscle found in earthworms that can extend slowly or make rapid contractions. Smooth muscle is found in the walls of the uterus , bladder , intestines , stomach , o esophagus , respiratory airways , and blood vessels. Cardiac muscle is found only in the heart , allowing it to contract and pump blood round the body. Nervous tissue is composed of many nerve cells known as neurons which transmit information.
In some slow-moving radially symmetrical marine animals such as ctenophores and cnidarians including sea anemones and jellyfish , the nerves form a nerve net , but in most animals they are organized longitudinally into bundles.
In simple animals, receptor neurons in the body wall cause a local reaction to a stimulus. In more complex animals, specialized receptor cells such as chemoreceptors and photoreceptors are found in groups and send messages along neural networks to other parts of the organism. Neurons can be connected together in ganglia. The latter consists of sensory nerves that transmit information from sense organs and motor nerves that influence target organs.
All vertebrates have a similar basic body plan and at some point in their lives, mostly in the embryonic stage, share the major chordate characteristics; a stiffening rod, the notochord ; a dorsal hollow tube of nervous material, the neural tube ; pharyngeal arches ; and a tail posterior to the anus.
The spinal cord is protected by the vertebral column and is above the notochord and the gastrointestinal tract is below it. At the posterior end is a tail which continues the spinal cord and vertebrae but not the gut.
The mouth is found at the anterior end of the animal, and the anus at the base of the tail. In most vertebrates the notochord becomes the nucleus pulposus of the intervertebral discs. However, a few vertebrates, such as the sturgeon and the coelacanth retain the notochord into adulthood. The limbs of vertebrates are considered to be homologous because the same underlying skeletal structure was inherited from their last common ancestor.
This is one of the arguments put forward by Charles Darwin to support his theory of evolution. The body of a fish is divided into a head, trunk and tail, although the divisions between the three are not always externally visible.
The skeleton, which forms the support structure inside the fish, is either made of cartilage, in cartilaginous fish , or bone in bony fish. The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles.
The main external features of the fish, the fins , are composed of either bony or soft spines called rays, which with the exception of the caudal fins , have no direct connection with the spine. They are supported by the muscles which compose the main part of the trunk. There is an inner ear but no external or middle ear. Low frequency vibrations are detected by the lateral line system of sense organs that run along the length of the sides of fish, and these respond to nearby movements and to changes in water pressure.
Sharks and rays are basal fish with numerous primitive anatomical features similar to those of ancient fish, including skeletons composed of cartilage. Their bodies tend to be dorso-ventrally flattened, they usually have five pairs of gill slits and a large mouth set on the underside of the head. The dermis is covered with separate dermal placoid scales. They have a cloaca into which the urinary and genital passages open, but not a swim bladder. Cartilaginous fish produce a small number of large, yolky eggs.
Some species are ovoviviparous and the young develop internally but others are oviparous and the larvae develop externally in egg cases. The bony fish lineage shows more derived anatomical traits, often with major evolutionary changes from the features of ancient fish. They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an operculum , and a mouth at or near the tip of the snout.
The dermis is covered with overlapping scales. Bony fish have a swim bladder which helps them maintain a constant depth in the water column, but not a cloaca. They mostly spawn a large number of small eggs with little yolk which they broadcast into the water column.
Amphibians are a class of animals comprising frogs , salamanders and caecilians. They are tetrapods , but the caecilians and a few species of salamander have either no limbs or their limbs are much reduced in size. Their main bones are hollow and lightweight and are fully ossified and the vertebrae interlock with each other and have articular processes.
Their ribs are usually short and may be fused to the vertebrae. Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little keratin and lacks scales, but contains many mucous glands and in some species, poison glands. The hearts of amphibians have three chambers, two atria and one ventricle. They have a urinary bladder and nitrogenous waste products are excreted primarily as urea.
Amphibians breathe by means of buccal pumping , a pump action in which air is first drawn into the buccopharyngeal region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat.
In frogs the pelvic girdle is robust and the hind legs are much longer and stronger than the forelimbs. The feet have four or five digits and the toes are often webbed for swimming or have suction pads for climbing. Frogs have large eyes and no tail. Salamanders resemble lizards in appearance; their short legs project sideways, the belly is close to or in contact with the ground and they have a long tail.
Caecilians superficially resemble earthworms and are limbless. They burrow by means of zones of muscle contractions which move along the body and they swim by undulating their body from side to side. Reptiles are a class of animals comprising turtles , tuataras , lizards , snakes and crocodiles. They are tetrapods , but the snakes and a few species of lizard either have no limbs or their limbs are much reduced in size.
Their bones are better ossified and their skeletons stronger than those of amphibians. The teeth are conical and mostly uniform in size.
The surface cells of the epidermis are modified into horny scales which create a waterproof layer. Reptiles are unable to use their skin for respiration as do amphibians and have a more efficient respiratory system drawing air into their lungs by expanding their chest walls. The heart resembles that of the amphibian but there is a septum which more completely separates the oxygenated and deoxygenated bloodstreams.
The reproductive system has evolved for internal fertilization, with a copulatory organ present in most species. The eggs are surrounded by amniotic membranes which prevents them from drying out and are laid on land, or develop internally in some species. The bladder is small as nitrogenous waste is excreted as uric acid. Turtles are notable for their protective shells. They have an inflexible trunk encased in a horny carapace above and a plastron below.
These are formed from bony plates embedded in the dermis which are overlain by horny ones and are partially fused with the ribs and spine. The neck is long and flexible and the head and the legs can be drawn back inside the shell. Turtles are vegetarians and the typical reptile teeth have been replaced by sharp, horny plates.
In aquatic species, the front legs are modified into flippers. Tuataras superficially resemble lizards but the lineages diverged in the Triassic period. There is one living species, Sphenodon punctatus. The skull has two openings fenestrae on either side and the jaw is rigidly attached to the skull. There is one row of teeth in the lower jaw and this fits between the two rows in the upper jaw when the animal chews. The teeth are merely projections of bony material from the jaw and eventually wear down.
The brain and heart are more primitive than those of other reptiles, and the lungs have a single chamber and lack bronchi. The tuatara has a well-developed parietal eye on its forehead. Lizards have skulls with only one fenestra on each side, the lower bar of bone below the second fenestra having been lost. This results in the jaws being less rigidly attached which allows the mouth to open wider.
Lizards are mostly quadrupeds, with the trunk held off the ground by short, sideways-facing legs, but a few species have no limbs and resemble snakes. Lizards have moveable eyelids, eardrums are present and some species have a central parietal eye. Snakes are closely related to lizards, having branched off from a common ancestral lineage during the Cretaceous period, and they share many of the same features.
The skeleton consists of a skull, a hyoid bone, spine and ribs though a few species retain a vestige of the pelvis and rear limbs in the form of pelvic spurs. The bar under the second fenestra has also been lost and the jaws have extreme flexibility allowing the snake to swallow its prey whole. Snakes lack moveable eyelids, the eyes being covered by transparent "spectacle" scales. They do not have eardrums but can detect ground vibrations through the bones of their skull.
Their forked tongues are used as organs of taste and smell and some species have sensory pits on their heads enabling them to locate warm-blooded prey. Crocodilians are large, low-slung aquatic reptiles with long snouts and large numbers of teeth. The head and trunk are dorso-ventrally flattened and the tail is laterally compressed. It undulates from side to side to force the animal through the water when swimming. The tough keratinized scales provide body armour and some are fused to the skull.
The nostrils, eyes and ears are elevated above the top of the flat head enabling them to remain above the surface of the water when the animal is floating. Valves seal the nostrils and ears when it is submerged. Unlike other reptiles, crocodilians have hearts with four chambers allowing complete separation of oxygenated and deoxygenated blood. Birds are tetrapods but though their hind limbs are used for walking or hopping, their front limbs are wings covered with feathers and adapted for flight.
Birds are endothermic , have a high metabolic rate , a light skeletal system and powerful muscles. The long bones are thin, hollow and very light. Air sac extensions from the lungs occupy the centre of some bones. The sternum is wide and usually has a keel and the caudal vertebrae are fused. Help select the Caption Contest winner! I am taking a 12 week summer course over Anatomy and Physiology 1.
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