The integument is the external body covering. In invertebrates it may include cuticle, epidermis, shell, or other protective surfaces.

The integument is the external body covering. In invertebrates it may include cuticle, epidermis, shell, or other protective surfaces.

The integument is the external body covering. In invertebrates it may include cuticle, epidermis, shell, or other protective surfaces.

The arthropod cuticle is secreted by the epidermis and provides protection, support, and attachment for muscles.

The arthropod cuticle is secreted by the epidermis and provides protection, support, and attachment for muscles.

The arthropod cuticle is secreted by the epidermis and provides protection, support, and attachment for muscles.

Chitin strengthens the cuticle of many arthropods and also occurs in fungal cell walls.

Chitin strengthens the cuticle of many arthropods and also occurs in fungal cell walls.

Chitin strengthens the cuticle of many arthropods and also occurs in fungal cell walls.

The exoskeleton is outside the body. In arthropods it supports movement because muscles attach to its inner surface.

The exoskeleton is outside the body. In arthropods it supports movement because muscles attach to its inner surface.

The exoskeleton is outside the body. In arthropods it supports movement because muscles attach to its inner surface.

Because a rigid exoskeleton cannot expand continuously, many arthropods grow by molting.

Because a rigid exoskeleton cannot expand continuously, many arthropods grow by molting.

Because a rigid exoskeleton cannot expand continuously, many arthropods grow by molting.

In many molluscs the mantle secretes calcium carbonate layers that make the shell.

In many molluscs the mantle secretes calcium carbonate layers that make the shell.

In many molluscs the mantle secretes calcium carbonate layers that make the shell.

Fish scales protect the body and, with mucus, make movement through water smoother.

Fish scales protect the body and, with mucus, make movement through water smoother.

Fish scales protect the body and, with mucus, make movement through water smoother.

Amphibian skin is thin, moist, and vascular, which makes cutaneous respiration possible in many species.

Amphibian skin is thin, moist, and vascular, which makes cutaneous respiration possible in many species.

Amphibian skin is thin, moist, and vascular, which makes cutaneous respiration possible in many species.

Reptilian scales are dry and keratinized, helping reptiles live in drier environments.

Reptilian scales are dry and keratinized, helping reptiles live in drier environments.

Reptilian scales are dry and keratinized, helping reptiles live in drier environments.

Feathers are specialized epidermal structures. Their functions vary among contour, down, flight, and display feathers.

Feathers are specialized epidermal structures. Their functions vary among contour, down, flight, and display feathers.

Feathers are specialized epidermal structures. Their functions vary among contour, down, flight, and display feathers.

Mammalian skin protects the body, regulates temperature, senses stimuli, and supports hair and gland functions.

Mammalian skin protects the body, regulates temperature, senses stimuli, and supports hair and gland functions.

Mammalian skin protects the body, regulates temperature, senses stimuli, and supports hair and gland functions.

Many soft-bodied animals use fluid pressure and muscle contraction for support and movement.

Many soft-bodied animals use fluid pressure and muscle contraction for support and movement.

Many soft-bodied animals use fluid pressure and muscle contraction for support and movement.

Vertebrates have an endoskeleton that grows with the body and supports muscles and organs.

Vertebrates have an endoskeleton that grows with the body and supports muscles and organs.

Vertebrates have an endoskeleton that grows with the body and supports muscles and organs.

Cartilage is strong but flexible and is common in joints, nose, ear, and some skeletal parts.

Cartilage is strong but flexible and is common in joints, nose, ear, and some skeletal parts.

Cartilage is strong but flexible and is common in joints, nose, ear, and some skeletal parts.

Bone is living tissue with mineral salts, collagen, blood vessels, and cells.

Bone is living tissue with mineral salts, collagen, blood vessels, and cells.

Bone is living tissue with mineral salts, collagen, blood vessels, and cells.

Joints range from immovable to freely movable and are important for locomotion.

Joints range from immovable to freely movable and are important for locomotion.

Joints range from immovable to freely movable and are important for locomotion.

Skeletal muscles contract to pull on bones and produce movement.

Skeletal muscles contract to pull on bones and produce movement.

Skeletal muscles contract to pull on bones and produce movement.

Smooth muscle moves food, regulates vessel diameter, and controls many internal body functions.

Smooth muscle moves food, regulates vessel diameter, and controls many internal body functions.

Smooth muscle moves food, regulates vessel diameter, and controls many internal body functions.

Cardiac muscle cells are interconnected and contract rhythmically to pump blood.

Cardiac muscle cells are interconnected and contract rhythmically to pump blood.

Cardiac muscle cells are interconnected and contract rhythmically to pump blood.

Because muscles pull rather than push, opposite muscle groups are needed for controlled movement.

Because muscles pull rather than push, opposite muscle groups are needed for controlled movement.

Because muscles pull rather than push, opposite muscle groups are needed for controlled movement.

Neurons are the basic functional units of nervous systems.

Neurons are the basic functional units of nervous systems.

Neurons are the basic functional units of nervous systems.

Dendrites increase the receiving surface of a neuron.

Dendrites increase the receiving surface of a neuron.

Dendrites increase the receiving surface of a neuron.

The axon carries action potentials to synaptic terminals or effector cells.

The axon carries action potentials to synaptic terminals or effector cells.

The axon carries action potentials to synaptic terminals or effector cells.

Myelin allows faster saltatory conduction along axons.

Myelin allows faster saltatory conduction along axons.

Myelin allows faster saltatory conduction along axons.

Impulses jump from node to node in myelinated fibers.

Impulses jump from node to node in myelinated fibers.

Impulses jump from node to node in myelinated fibers.

Synapses allow directed communication between excitable cells.

Synapses allow directed communication between excitable cells.

Synapses allow directed communication between excitable cells.

Neurotransmitters bind to receptors on the postsynaptic cell and change its activity.

Neurotransmitters bind to receptors on the postsynaptic cell and change its activity.

Neurotransmitters bind to receptors on the postsynaptic cell and change its activity.

Action potentials are the main electrical signals of neurons and muscle cells.

Action potentials are the main electrical signals of neurons and muscle cells.

Action potentials are the main electrical signals of neurons and muscle cells.

Resting potential results from ion gradients and membrane permeability.

Resting potential results from ion gradients and membrane permeability.

Resting potential results from ion gradients and membrane permeability.

Sensory neurons connect receptors to processing centers.

Sensory neurons connect receptors to processing centers.

Sensory neurons connect receptors to processing centers.

Motor neurons activate effectors such as skeletal muscles.

Motor neurons activate effectors such as skeletal muscles.

Motor neurons activate effectors such as skeletal muscles.

Interneurons integrate sensory input and help produce suitable responses.

Interneurons integrate sensory input and help produce suitable responses.

Interneurons integrate sensory input and help produce suitable responses.

A reflex arc usually includes receptor, sensory neuron, integration center, motor neuron, and effector.

A reflex arc usually includes receptor, sensory neuron, integration center, motor neuron, and effector.

A reflex arc usually includes receptor, sensory neuron, integration center, motor neuron, and effector.

Ganglia act as local processing centers in many animals.

Ganglia act as local processing centers in many animals.

Ganglia act as local processing centers in many animals.

A nerve net allows simple coordination without a centralized brain.

A nerve net allows simple coordination without a centralized brain.

A nerve net allows simple coordination without a centralized brain.

Cephalization is associated with directional movement and head formation.

Cephalization is associated with directional movement and head formation.

Cephalization is associated with directional movement and head formation.

The central nervous system integrates information and coordinates responses.

The central nervous system integrates information and coordinates responses.

The central nervous system integrates information and coordinates responses.

The peripheral nervous system carries sensory and motor information.

The peripheral nervous system carries sensory and motor information.

The peripheral nervous system carries sensory and motor information.

The autonomic system controls functions such as heart rate, digestion, and vessel diameter.

The autonomic system controls functions such as heart rate, digestion, and vessel diameter.

The autonomic system controls functions such as heart rate, digestion, and vessel diameter.

At chemical synapses, neurotransmitters cross the synaptic cleft to affect the next cell.

At chemical synapses, neurotransmitters cross the synaptic cleft to affect the next cell.

At chemical synapses, neurotransmitters cross the synaptic cleft to affect the next cell.

Sensory receptors convert environmental or internal stimuli into signals the nervous system can use.

Sensory receptors convert environmental or internal stimuli into signals the nervous system can use.

Sensory receptors convert environmental or internal stimuli into signals the nervous system can use.

Baroreceptors help monitor pressure and contribute to circulatory regulation.

Baroreceptors help monitor pressure and contribute to circulatory regulation.

Baroreceptors help monitor pressure and contribute to circulatory regulation.

Chemoreceptors are involved in smell, taste, and internal monitoring of gases or pH.

Chemoreceptors are involved in smell, taste, and internal monitoring of gases or pH.

Chemoreceptors are involved in smell, taste, and internal monitoring of gases or pH.

Statocysts are common balance organs in many invertebrates.

Statocysts are common balance organs in many invertebrates.

Statocysts are common balance organs in many invertebrates.

Hygroreceptors are important for animals that must manage water balance.

Hygroreceptors are important for animals that must manage water balance.

Hygroreceptors are important for animals that must manage water balance.

Phonoreceptors support hearing or vibration detection in many animals.

Phonoreceptors support hearing or vibration detection in many animals.

Phonoreceptors support hearing or vibration detection in many animals.

Photoreceptors may occur in simple eyes, compound eyes, or vertebrate retinas.

Photoreceptors may occur in simple eyes, compound eyes, or vertebrate retinas.

Photoreceptors may occur in simple eyes, compound eyes, or vertebrate retinas.

Proprioceptors help animals coordinate posture and movement.

Proprioceptors help animals coordinate posture and movement.

Proprioceptors help animals coordinate posture and movement.

Tactile receptors contribute to touch, pressure, and texture perception.

Tactile receptors contribute to touch, pressure, and texture perception.

Tactile receptors contribute to touch, pressure, and texture perception.

Thermoreceptors allow animals to sense warmth or cold and help regulate behavior.

Thermoreceptors allow animals to sense warmth or cold and help regulate behavior.

Thermoreceptors allow animals to sense warmth or cold and help regulate behavior.

The lateral line helps aquatic animals detect currents, prey, predators, and nearby objects.

The lateral line helps aquatic animals detect currents, prey, predators, and nearby objects.

The lateral line helps aquatic animals detect currents, prey, predators, and nearby objects.

Some fishes use electroreception for prey detection, navigation, and communication.

Some fishes use electroreception for prey detection, navigation, and communication.

Some fishes use electroreception for prey detection, navigation, and communication.

The vestibular apparatus helps maintain balance and spatial orientation in vertebrates.

The vestibular apparatus helps maintain balance and spatial orientation in vertebrates.

The vestibular apparatus helps maintain balance and spatial orientation in vertebrates.

Hearing depends on converting vibrations into nerve impulses.

Hearing depends on converting vibrations into nerve impulses.

Hearing depends on converting vibrations into nerve impulses.

Compound eyes provide a wide field of view and are well developed in many insects and crustaceans.

Compound eyes provide a wide field of view and are well developed in many insects and crustaceans.

Compound eyes provide a wide field of view and are well developed in many insects and crustaceans.

Ocelli help many animals respond to light direction or intensity.

Ocelli help many animals respond to light direction or intensity.

Ocelli help many animals respond to light direction or intensity.

Rods are sensitive to low light but do not provide detailed color vision.

Rods are sensitive to low light but do not provide detailed color vision.

Rods are sensitive to low light but do not provide detailed color vision.

Cones are important for color discrimination and visual acuity.

Cones are important for color discrimination and visual acuity.

Cones are important for color discrimination and visual acuity.

Olfaction is a chemical sense used in feeding, mating, navigation, and danger detection.

Olfaction is a chemical sense used in feeding, mating, navigation, and danger detection.

Olfaction is a chemical sense used in feeding, mating, navigation, and danger detection.

Gustation helps animals evaluate food quality and avoid harmful substances.

Gustation helps animals evaluate food quality and avoid harmful substances.

Gustation helps animals evaluate food quality and avoid harmful substances.

The endocrine system coordinates slower, longer-lasting responses through hormones.

The endocrine system coordinates slower, longer-lasting responses through hormones.

The endocrine system coordinates slower, longer-lasting responses through hormones.

Hormones act on target cells that have suitable receptors.

Hormones act on target cells that have suitable receptors.

Hormones act on target cells that have suitable receptors.

Hormone specificity depends on receptor presence in the target cell.

Hormone specificity depends on receptor presence in the target cell.

Hormone specificity depends on receptor presence in the target cell.

Endocrine glands differ from exocrine glands because they do not use ducts.

Endocrine glands differ from exocrine glands because they do not use ducts.

Endocrine glands differ from exocrine glands because they do not use ducts.

Neurosecretory cells link nervous and endocrine regulation, especially in many invertebrates.

Neurosecretory cells link nervous and endocrine regulation, especially in many invertebrates.

Neurosecretory cells link nervous and endocrine regulation, especially in many invertebrates.

Peptide hormones are water-soluble and commonly act through membrane receptors and second messengers.

Peptide hormones are water-soluble and commonly act through membrane receptors and second messengers.

Peptide hormones are water-soluble and commonly act through membrane receptors and second messengers.

Steroid hormones include many adrenal and reproductive hormones.

Steroid hormones include many adrenal and reproductive hormones.

Steroid hormones include many adrenal and reproductive hormones.

Negative feedback helps maintain stable internal conditions and hormone levels.

Negative feedback helps maintain stable internal conditions and hormone levels.

Negative feedback helps maintain stable internal conditions and hormone levels.

The hypothalamus regulates many pituitary functions through releasing and inhibiting signals.

The hypothalamus regulates many pituitary functions through releasing and inhibiting signals.

The hypothalamus regulates many pituitary functions through releasing and inhibiting signals.

The pituitary is often called a master gland because it influences several other endocrine glands.

The pituitary is often called a master gland because it influences several other endocrine glands.

The pituitary is often called a master gland because it influences several other endocrine glands.

Thyroid hormones are important for metabolism and normal development.

Thyroid hormones are important for metabolism and normal development.

Thyroid hormones are important for metabolism and normal development.

Adrenal hormones include catecholamines and corticosteroids with important regulatory effects.

Adrenal hormones include catecholamines and corticosteroids with important regulatory effects.

Adrenal hormones include catecholamines and corticosteroids with important regulatory effects.

Insulin is central to glucose homeostasis in vertebrates.

Insulin is central to glucose homeostasis in vertebrates.

Insulin is central to glucose homeostasis in vertebrates.

Glucagon acts opposite to insulin in blood glucose regulation.

Glucagon acts opposite to insulin in blood glucose regulation.

Glucagon acts opposite to insulin in blood glucose regulation.

Ecdysone is important in insect and arthropod development and molting.

Ecdysone is important in insect and arthropod development and molting.

Ecdysone is important in insect and arthropod development and molting.

The balance between juvenile hormone and ecdysone influences insect metamorphosis.

The balance between juvenile hormone and ecdysone influences insect metamorphosis.

The balance between juvenile hormone and ecdysone influences insect metamorphosis.

Pheromones are important in communication such as mating, alarm, and trail marking.

Pheromones are important in communication such as mating, alarm, and trail marking.

Pheromones are important in communication such as mating, alarm, and trail marking.

Paracrine messengers act over short distances, unlike many classic endocrine hormones.

Paracrine messengers act over short distances, unlike many classic endocrine hormones.

Paracrine messengers act over short distances, unlike many classic endocrine hormones.

Hyperthyroidism commonly produces signs linked to elevated metabolism.

Hyperthyroidism commonly produces signs linked to elevated metabolism.

Hyperthyroidism commonly produces signs linked to elevated metabolism.

Adrenal disorders disturb stress response, blood pressure, salt-water balance, or metabolism.

Adrenal disorders disturb stress response, blood pressure, salt-water balance, or metabolism.

Adrenal disorders disturb stress response, blood pressure, salt-water balance, or metabolism.

Circulatory systems support internal transport, especially in larger and more active animals.

Circulatory systems support internal transport, especially in larger and more active animals.

Circulatory systems support internal transport, especially in larger and more active animals.

Many arthropods and most molluscs have open circulation with hemolymph.

Many arthropods and most molluscs have open circulation with hemolymph.

Many arthropods and most molluscs have open circulation with hemolymph.

Closed circulation is found in annelids, cephalopods, and vertebrates and supports efficient transport.

Closed circulation is found in annelids, cephalopods, and vertebrates and supports efficient transport.

Closed circulation is found in annelids, cephalopods, and vertebrates and supports efficient transport.

Hemolymph functions in transport and defense in animals such as arthropods.

Hemolymph functions in transport and defense in animals such as arthropods.

Hemolymph functions in transport and defense in animals such as arthropods.

In some invertebrates, coelomic fluid helps move materials and may contribute to hydrostatic support.

In some invertebrates, coelomic fluid helps move materials and may contribute to hydrostatic support.

In some invertebrates, coelomic fluid helps move materials and may contribute to hydrostatic support.

Vertebrate blood contains plasma, red cells, white cells, and platelets or thrombocytes.

Vertebrate blood contains plasma, red cells, white cells, and platelets or thrombocytes.

Vertebrate blood contains plasma, red cells, white cells, and platelets or thrombocytes.

Arteries have strong elastic walls suited to high-pressure flow.

Arteries have strong elastic walls suited to high-pressure flow.

Arteries have strong elastic walls suited to high-pressure flow.

Veins usually operate at lower pressure and may have valves to prevent backflow.

Veins usually operate at lower pressure and may have valves to prevent backflow.

Veins usually operate at lower pressure and may have valves to prevent backflow.

Capillaries allow diffusion of gases, nutrients, wastes, and fluids.

Capillaries allow diffusion of gases, nutrients, wastes, and fluids.

Capillaries allow diffusion of gases, nutrients, wastes, and fluids.

Fish generally have one atrium and one ventricle and a single circuit.

Fish generally have one atrium and one ventricle and a single circuit.

Fish generally have one atrium and one ventricle and a single circuit.

Amphibians have double circulation with some mixing in the single ventricle.

Amphibians have double circulation with some mixing in the single ventricle.

Amphibians have double circulation with some mixing in the single ventricle.

Most reptiles have incomplete separation, while crocodilians have a four-chambered heart.

Most reptiles have incomplete separation, while crocodilians have a four-chambered heart.

Most reptiles have incomplete separation, while crocodilians have a four-chambered heart.

Complete separation supports high metabolic rates in birds and mammals.

Complete separation supports high metabolic rates in birds and mammals.

Complete separation supports high metabolic rates in birds and mammals.

Blood pressure is influenced by heart pumping, vessel resistance, and blood volume.

Blood pressure is influenced by heart pumping, vessel resistance, and blood volume.

Blood pressure is influenced by heart pumping, vessel resistance, and blood volume.

The lymphatic system transports lymph, absorbs fats, and houses immune cells.

The lymphatic system transports lymph, absorbs fats, and houses immune cells.

The lymphatic system transports lymph, absorbs fats, and houses immune cells.

Innate immunity includes barriers, inflammation, phagocytes, and antimicrobial substances.

Innate immunity includes barriers, inflammation, phagocytes, and antimicrobial substances.

Innate immunity includes barriers, inflammation, phagocytes, and antimicrobial substances.

Inflammation helps recruit defensive cells and molecules to damaged or infected tissues.

Inflammation helps recruit defensive cells and molecules to damaged or infected tissues.

Inflammation helps recruit defensive cells and molecules to damaged or infected tissues.

Macrophages and neutrophils are examples of phagocytic cells in immune defense.

Macrophages and neutrophils are examples of phagocytic cells in immune defense.

Macrophages and neutrophils are examples of phagocytic cells in immune defense.

Antibodies are produced by B cell-derived plasma cells and help neutralize or mark targets.

Antibodies are produced by B cell-derived plasma cells and help neutralize or mark targets.

Antibodies are produced by B cell-derived plasma cells and help neutralize or mark targets.

Adaptive immunity is slower at first exposure but can respond faster after memory develops.

Adaptive immunity is slower at first exposure but can respond faster after memory develops.

Adaptive immunity is slower at first exposure but can respond faster after memory develops.