Week 5

Question 1

There are four levels of organization​

Answer 1

Cells​

Tissues​

Organs​

Organ systems

Question 2

Tissues

Answer 2

Groups of cells that are similar in structure and function​

3 fundamental embryonic tissues are called germ layers​

Endoderm, mesoderm, and ectoderm​

In adult vertebrates, there are four primary tissues​

Epithelial, connective, muscle, and nerve

Question 3

Organs and Organ Systems

Answer 3

Organs​

Combinations of different tissues that form a structural and functional unit​

Organ systems​

Groups of organs that cooperate to perform the major activities of the body

Question 4

Epithelial Tissue

Answer 4

An epithelial membrane, or epithelium, covers every surface of the vertebrate body​

Can come from any of the 3 germ layers​

Some epithelia change into glands​

Cells of epithelia are tightly bound together​

Provide a protective barrier

Question 5

Epithelial Characteristics

Answer 5

Epithelia possess remarkable regenerative powers replacing cells throughout life​

Epithelial tissues attach to underlying connective tissues by a fibrous membrane

Question 6

Classification of Epithelia

Answer 6

Two general classes​

Simple – one layer thick​

Stratified – two or more layers thick​

Each class subdivided into​

Squamous cells – flat​

Cuboidal cells – about as wide as tall​

Columnar cells – taller than they are wide

Question 7

Simple Epithelium

Answer 7

Simple squamous epithelium​

Lines lungs and blood capillaries​

Delicate nature permits diffusion​

Simple cuboidal epithelium​

Lines kidney tubules and several glands​

Simple columnar epithelium​

Lines airways of respiratory tract and most of the gastrointestinal tract​

Contains goblet cells – secrete mucus

Question 8

Stratified Epithelium

Answer 8

Two to several layers thick​

Epidermis is a stratified squamous epithelium​

Many vertebrates have a keratin in the outer layers of the epidermis

Question 9

Glands

Answer 9

Glands made from epithelial tissues that produce metabolic products​

Exocrine glands​

Connected to epithelium by a duct​

Sweat, sebaceous, and salivary glands​

Endocrine glands​

Secretions (hormones) enter blood​

Thyroid, pituitary, liver, pancreas, adrenal glands

Question 10

Connective Tissues

Answer 10

Arise from mesoderm​

Divided into two major classes​

Connective tissue proper​

Loose or dense​

Special connective tissue​

Cartilage, bone, and blood​

All have abundant extracellular material called the matrix​

Protein fibers plus ground substance

Question 11

Fibroblasts produce and secrete

Answer 11

Fibroblasts produce and secrete extracellular matrix

Question 12

Loose connective tissue

Answer 12

Loose connective tissue​

Cells scattered within a matrix that contains a large amount of ground substance​

Strengthened by protein fibers​

Collagen – supports tissue​

Elastin – makes tissue elastic​

Reticulin – helps support the network of collagen

Question 13

Adipose Tissue

Answer 13

Adipose cells (fat cells) also occur in loose connective tissue​

Develop in large groups in certain areas, forming adipose tissue

Question 14

Dense Connective Tissue

Answer 14

Contains less ground substance than loose connective tissue​

Dense regular connective tissue​

Collagen fibers line up in parallel​

Makes up tendons and ligaments​

Dense irregular connective tissue​

Collagen fibers have different orientations​

Covers kidney, muscles, nerves, and bone

Question 15

Cartilage

Answer 15

Ground substance made from characteristic glycoprotein (chondroitin) and collagen fibers in long, parallel arrays​

Firm and flexible tissue that does not stretch​

Great tensile strength​

Found in joint surfaces and other locations​

Chondrocytes (cartilage cells) live within lacunae (spaces) in the ground substance

Question 16

Bone and Blood

Answer 16

Bone​

Osteocytes (bone cells) remain alive in a matrix hardened with calcium phosphate​

Communicate through canaliculi​

Blood​

Extracellular material is the fluid plasma​

Erythrocytes – red blood cells​

Leukocytes – white blood cells​

Thrombocytes – platelets

Question 17

Muscle Tissue

Answer 17

Muscles are the motors of vertebrate bodies​

Three kinds: smooth, skeletal, and cardiac​

Skeletal and cardiac muscles are also known as striated muscles​

Skeletal muscle is under voluntary control, whereas contraction of the other two is involuntary

Question 18

Smooth Muscle and Skeletal Muscle

Answer 18

Smooth muscle​

Found in walls of blood vessels and visceral organs ​

Contain a single nucleus​

Skeletal muscle​

Usually attached to bone by tendons, so muscle contraction causes bones to move​

Muscle fibers (cells) are multinucleated​

Contract by means of myofibrils, which contain ordered actin and myosin filaments

Question 19

Cardiac Muscle

Answer 19

Cardiac muscle​

Composed of smaller, interconnected cells​

Each with a single nucleus​

Interconnections appear as dark lines called intercalated disks​

Gap junctions link adjacent cells​

Enable cardiac muscle cells to form a single functioning unit

Question 20

Nerve Tissue

Answer 20

Cells include neurons and their supporting cells (neuroglia)​

Most neurons consist of three parts​

Cell body – contains the nucleus​

Dendrites – highly branched extensions​

Conduct electrical impulses toward the cell body​

Axon – single cytoplasmic extension​

Conducts impulses away from cell body

Question 21

Neuroglia

Answer 21

Do not conduct electrical impulses​

Support, nourish, and protect neurons

Question 22

Overview of Organ Systems

Answer 22

Communication and integration​

Two organ systems detect external stimuli and coordinate the body’s responses​

Nervous and sensory systems​

Endocrine system issues chemical signals​

Support and movement​

Musculoskeletal system consists of two interrelated organ systems​

Muscles and skeletal system

Question 23

Regulation and Maintenance and Defense

Answer 23

Regulation and maintenance​

Four organ systems regulate and maintain the body’s chemistry​

Digestive, circulatory, respiratory, and urinary systems​

Defense​

The body defends itself​

Integumentary and immune systems

Question 24

Reproduction and Development

Answer 24

The biological continuity of vertebrates​

In females, the system also nurtures the developing embryo and fetus

Question 25

Homeostasis

Answer 25

For cells to function efficiently and interact properly, internal body conditions must be relatively constant​

Temperature, pH, concentrations of glucose and oxygen

Question 26

Negative Feedback

Answer 26

Mechanisms​

Changing conditions are detected by sensors (cells or membrane receptors)​

Information is fed to an integrating center (brain, spinal cord, or endocrine gland)​

Compares conditions to a set point​

If conditions deviate too far from a set point, biochemical reactions are initiated to change conditions back toward the set point

Question 27

Components of Negative Feedback

Answer 27

Humans have set points for body temperature, blood glucose concentrations, electrolyte (ion) concentration, tendon tension, etc.​

Integrating center is often a particular region of the brain or spinal cord​

Effectors (muscles or glands) change the value of the condition in question back toward the set point value

Question 28

Mammals and Birds

Answer 28

Mammals and birds are endothermic​

Maintain a relatively constant body temperature independent of the environmental temperature​

Humans 37°C or 98.6°F​

Changes in body temperature are detected by the hypothalamus in the brain

Question 29

Opposition of Negative Feedback Mechanisms

Answer 29

Negative feedback mechanisms often oppose each other to produce finer degree of control​

Many internal factors are controlled by antagonistic effectors​

Have “push–pull” action​

Increasing activity of one effector is accompanied by decrease in the other

Question 30

Antagonistic Effectors

Answer 30

Antagonistic effectors are involved in the control of body temperature​

If hypothalamus detects high temperature​

Promotes heat dissipation via sweating and dilation of blood vessels in skin​

If hypothalamus detects low temperature​

Promotes heat conservation via shivering and constriction of blood vessels in skin

Question 31

Positive Feedback

Answer 31

Mechanisms​

Enhance a change – not common​

These do not in themselves maintain homeostasis​

Important components of some physiological mechanisms.​

Blood clotting​

Contraction of uterus during childbirth

Question 32

Regulating Body Temperature

Answer 32

Temperature is one of the most important aspects of the environment​

Some organisms have a body temperature that conforms to the environment​

Other organisms regulate their body temperature​

Q(10) is a measure of temperature sensitivity​

The rate of any chemical reaction is affected by temperature​

The rate increases with increasing temperature​

Every 10°C increase in temperature doubles the reaction rate

Q(10)=R(t+10)/R(T) (root)

Question 33

Temperature Determination

Answer 33

Temperature determined by internal and external factors​

Overall metabolic rate and body temperature are interrelated​

Organisms must deal with external and internal factors that relate body heat, metabolism, and the environment​

body heat = heat produced + heat transferred

Question 34

Mechanisms of heat transfer

Answer 34

Radiation- transfer of heat by electromagnetic radiation​

Conduction- direct transfer of heat from hotter object to a colder one​

Convection- transfer of heat brought about by the movement of a gas or liquid​

Evaporation- heat of vaporization or the amount of energy needed to change them from a liquid to a gas phase

Question 35

Ectotherms

Answer 35

Ectotherms regulate temperature using behavior​

Low metabolic rates​

Regulate their temperature using behavior

Question 36

Endotherms

Answer 36

Endotherms create internal metabolic heat​

Conservation or dissipation​

Heat transfer is controlled by amount of blood flow to the surface of the animal​

Countercurrent exchange​

Allows sustained high-energy activity​

Tradeoff is the high metabolic rate

Question 37

Body Size and Insulation

Answer 37

Changes in body mass have a large effect on metabolic rate​

Smaller animals consume much more energy per unit of body mass than larger animals​

Summarized in the “mouse to elephant” curve

Question 38

Mammalian Thermoregulation

Answer 38

Mammalian thermoregulation is controlled by the hypothalamus​

Neurons in the hypothalamus detect the temperature change​

Stimulation of the heat-losing center​

Peripheral blood vessel dilation​

Sweating​

Stimulation of heat-promoting center​

Thermogenesis​

Constriction of blood peripheral blood vessels​

Epinephrine production by adrenal glands​

Anterior pituitary produces T S H

Question 39

Nervous System Organization

Answer 39

All animals must be able to respond to environmental stimuli​

In most invertebrate phyla and in all vertebrate classes, animals use:​

Sensory receptors – detect stimulus​

Motor effectors – respond to it​

Nervous system links the two​

Consists of neurons and supporting cells

Question 40

CNS consists of:

Answer 40

The brain ​

Spinal cord

Question 41

Types of Neurons

Answer 41

Vertebrates have three types of neurons​

Sensory neurons (afferent neurons) carry impulses to central nervous system (C N S)​

Motor neurons (efferent neurons) carry impulses from C N S to effectors (muscles and glands)​

Interneurons (association neurons) provide more complex reflexes and associative functions (learning and memory)

Question 42

Peripheral Nervous System

Answer 42

P N S consists of:​

Sensory and motor neurons​

Somatic N S stimulates skeletal muscles​

Autonomic N S stimulates smooth and cardiac muscles, as well as glands​

Sympathetic and parasympathetic N S​

Counterbalance each other

Question 43

Components of a Neuron

Answer 43

Neurons have the same basic structure​

Cell body​

Enlarged part containing nucleus​

Dendrites​

Short, cytoplasmic extensions that receive stimuli​

Axon​

Single, long extension that conducts impulses away from cell body

Question 44

Supportive Cells

Answer 44

Neuroglia​

Support neurons both structurally and functionally​

Schwann cells and oligodendrocytes produce myelin sheaths surrounding axons​

In the C N S, myelinated axons form white matter​

Dendrites/cell bodies form gray matter​

In the P N S, myelinated axons are bundled to form nerves

Question 45

Electrical Difference Across the Plasma Membrane

Answer 45

A potential difference exists across every cell’s plasma membrane​

Negative pole − cytoplasmic side​

Positive pole − extracellular fluid side​

When a neuron is not being stimulated, it maintains a resting potential​

Ranges from −40 to −90 millivolts (mV)​

Average about −70 mV

Question 46

Interior of the Cell

Answer 46

The inside of the cell is more negatively charged than the outside​

Sodium-Potassium Pump - 2 K+ in, three Na in

Ion Leakage Channels - More K+ out than Na+ in

Differential distribution of other ions and molecules across the pm​

Especially negatively charged proteins

Question 47

Nerve Impulse Transmission

Answer 47

Sodium–potassium pump creates significant concentration gradient

K+ concentration much higher in the cell

Membrane not permeable to negative ions​

Leads to buildup of positive charges outside and negative charges inside cell​

Attractive force to bring​ K+ back inside cell

Equilibrium potential – balance between diffusional force and electrical force​

Question 48

Uniqueness of Neurons

Answer 48

Uniqueness of neurons compared with other cells is not the production and maintenance of the resting membrane potential​

Rather the sudden temporary disruptions to the resting membrane potential that occur in response to stimuli​

2 types of changes​

Graded potentials​

Action potentials.

Question 49

Overview of Potentials

Answer 49

Graded potentials​

Small consistent changes in membrane potential due to activation of gated ion channels​

Action potentials​

Transient disruptions triggered by a threshold change in potential​

The actual signals that move along an axon​

Question 50

Gated Channels

Answer 50

Chemically-gated or ligand-gated channels​

Ligands are chemical signals​

hormones or neurotransmitters​

Induce opening and cause changes in cell membrane permeability

Question 51

Depolarization

Answer 51

Depolarization makes the membrane potential more positive​

Hyperpolarization makes it more negative​

These small changes result in graded potentials​

Size depends on either the strength of the stimulus or the amount of ligand available to bind with their receptors​

Can reinforce or negate each other​

Summation is the ability of graded potentials to combine

Question 52

Action Potentials

Answer 52

Result when depolarization reaches the threshold potential (−55 mV) Voltage-gated​

Depolarizations bring a neuron closer to the threshold​

Hyperpolarizations move the neuron further from the threshold​

Question 53

Caused by voltage-gated ion channels

Answer 53

Voltage-Gated Na+ and K+ Channels

Question 54

Phases of an Action Potential

Answer 54

The action potential has three phases​

Rising, falling, and undershoot​

Action potentials are always separate, all-or-none events with the same amplitude​

Do not add up or interfere with each other​

Intensity of a stimulus is coded by the frequency, not amplitude, of action potentials

Question 55

Nerve Impulse Propagation

Answer 55

Propagation of action potentials​

Each action potential, in its rising phase, reflects a reversal in membrane polarity​

Positive charges due to influx of​ Na+ can depolarize the adjacent region to threshold​

And so, the next region produces its own action potential​

Meanwhile, the previous region repolarizes back to the resting membrane potential​

Signal does not go back toward cell body

Question 56

Two ways to increase velocity of conduction

Answer 56

Two ways to increase velocity of conduction​

Axon has a large diameter.​

Less resistance to current flow.​

Found primarily in invertebrates​

Axon is myelinated​

Action potential is only produced at the nodes of Ranvier​

Impulse jumps from node to node​

Saltatory conduction

Question 57

Synapses

Answer 57

Specialized intercellular junctions with the other neurons, with muscle cells, or with gland cells​

Presynaptic cell transmits action potential​

Postsynaptic cell receives it​

Two basic types: electrical and chemical

Question 58

Electrical and Chemical Synapses

Answer 58

Electrical synapses​

Involve direct cytoplasmic connections between the two cells formed by gap junctions​

Relatively rare in vertebrates​

Chemical synapses​

Have a synaptic cleft between the two cells​

End of presynaptic cell contains synaptic vesicles packed with neurotransmitters

Question 59

Chemical Synapses

Answer 59

Action potential triggers influx of ​Ca^2+

Synaptic vesicles fuse with cell membrane​

Neurotransmitter is released by exocytosis​

Diffuses to other side of cleft and binds to chemical- or ligand-gated receptor proteins​

Produces graded potentials in the postsynaptic membrane​

Neurotransmitter action is terminated by enzymatic digestion or cellular uptake

Question 60

Neurotransmitters: Acetylcholine

Answer 60

Acetylcholine (ACh)​

Crosses the synapse between a motor neuron and a muscle fiber​

Neuromuscular junction

Binds to receptor in the postsynaptic membrane​

Causes ligand-gated ion channels to open​

Produces a depolarization called an excitatory postsynaptic potential (E P S P) ​

Stimulates muscle contraction​

Acetylcholinesterase (AChE) degrades ACh​

Causes muscle relaxation

Question 61

Neurotransmitters: Amino Acids

Answer 61

Glutamate​

Major excitatory neurotransmitter in the vertebrate C N S​

Glycine and G A B A (γ-aminobutyric acid) are inhibitory neurotransmitters​

Open ligand-gated channels for​ Cl-

Produce a hyperpolarization called an inhibitory postsynaptic potential (I P S P)​

Question 62

Neurotransmitters: Biogenic Amines

Answer 62

Epinephrine (adrenaline) and norepinephrine are responsible for the “fight or flight” response​

Dopamine is used in some areas of the brain that control body movements​

Serotonin is involved in the regulation of sleep

Question 63

Neurotransmitters: Neuropeptides

Answer 63

Neuropeptides​

Substance P is released from sensory neurons activated by painful stimuli​

Intensity of pain perception depends on enkephalins and endorphins​

Nitric oxide (NO).​

A gas – produced as needed from arginine​

Causes smooth muscle relaxation

Question 64

Synaptic Integration

Answer 64

Integration of E P S Ps (depolarization) and I S P Ss (hyperpolarization) occurs on the neuronal cell body​

Small E P S Ps add together to bring the membrane potential closer to the threshold​

I P S Ps subtract from the depolarizing effect of E P S Ps​

Deter the membrane potential from reaching threshold

Question 65

There are two ways that the membrane can reach the threshold voltage

Answer 65

Spatial summation​

Many different dendrites produce E P S Ps​

Temporal summation​

One dendrite produces repeated E P S Ps

Question 66

Habituation

Answer 66

Prolonged exposure to a stimulus may cause cells to lose the ability to respond to it​

Cell decreases the number of receptors because there is an abundance of neurotransmitters​

In long-term drug use, means that more of the drug is needed to obtain the same effect

Question 67

Cocaine

Answer 67

Affects neurons in the brain’s “pleasure pathways” (limbic system)​

Binds dopamine transporters and prevents the reuptake of dopamine​

Dopamine survives longer in the synapse and fires pleasure pathways more and more

Question 68

Nicotine

Answer 68

Binds directly to a specific receptor on postsynaptic neurons of the brain​

Binds to a receptor for acetylcholine​

Brain adjusts to prolonged exposure by “turning down the volume” by​

Making fewer receptors to which nicotine binds​

Altering the pattern of activation of the nicotine receptors

Question 69

Evolution of the Central Nervous System

Answer 69

Sponges are only major phylum without nerves​

Cnidarians have the simplest nervous system​

Neurons linked to each other in a nerve net​

No associative activity​

Free-living flatworms (phylum Platyhelminthes) are simplest animals with associative activity​

Two nerve cords run down the body​

Permit complex muscle control​

All of the subsequent evolutionary changes in nervous systems can be viewed as a series of elaborations on the characteristics already present in flatworms​

Question 70

Vertebrate Brains​/All vertebrate brains have three basic divisions:​

Answer 70

All vertebrate brains have three basic divisions:​

Hindbrain or rhombencephalon​

Midbrain or mesencephalon​

Forebrain or prosencephalon​

In fishes,​

Hindbrain – largest portion​

Midbrain – processes visual information​

Forebrain – processes olfactory information

Question 71

Forebrain is composed of two elements

Answer 71

Forebrain is composed of two elements​

Diencephalon​

Thalamus – integration and relay center​

Hypothalamus – participates in basic drives and emotions, controls pituitary gland​

Telencephalon (“end brain”)​

Devoted largely to associative activity​

Called the cerebrum in mammals

Question 72

Cerebrum

Answer 72

The increase in brain size in mammals reflects the great enlargement of the cerebrum​

Split into right and left cerebral hemispheres, which are connected by a tract called the corpus callosum​

Each hemisphere receives sensory input from the opposite side​

Hemispheres are divided into: frontal, parietal, temporal, and occipital lobes

Question 73

Cerebrum: Cerebral Cortex

Answer 73

Cerebral cortex​

Outer layer of the cerebrum​

Contains about 10% of all neurons in brain​

Highly convoluted surface​

Increases threefold the surface area of the human brain​

Activities are motor, sensory, or associative

Question 74

Cerebral Cortex

Answer 74

Primary motor cortex – movement control​

Primary somatosensory cortex – sensory control ​

Association cortex – higher mental functions ​

Basal nuclei​

Aggregates of neuron cell bodies – gray matter​

Participate in the control of body movements

Question 75

Thalamus

Answer 75

Integrates visual, auditory, and somatosensory information

Question 76

Hypothalamus

Answer 76

Integrates visceral activities​

Controls pituitary gland​

Question 77

Limbic system

Answer 77

Hypothalamus, hippocampus, and amygdala​

Responsible for emotional responses

Question 78

Complex Functions of the Brain

Answer 78

Sleep and arousal​

One section of reticular formation is the reticular-activating system​

Controls consciousness and alertness​

Brain state can be monitored by means of an electroencephalogram (E E G)​

Records electrical activity

Question 79

Complex Functions of the Brain: Language

Answer 79

Language​

Left hemisphere is “dominant” hemisphere​

Different regions control various language activities​

Adept at sequential reasoning​

Right hemisphere is adept at spatial reasoning​

Primarily involved in musical ability​

Nondominant hemisphere is also important for the consolidation of memories of nonverbal experiences

Question 80

Complex Functions of the Brain: Memory

Answer 80

Appears dispersed across the brain​

Short-term memory is stored in the form of transient neural excitations​

Long-term memory appears to involve structural changes in neural connections​

Two parts of the temporal lobes, the hippocampus and the amygdala, are involved in both short-term memory and its consolidation into long-term memory

Question 81

Synaptic Plasticity

Answer 81

Cellular basis of learning and memory​

Long-term changes in the strength of synaptic connection​

Two examples of synaptic plasticity​

Long-term potentiation (L T P)​

Long-term depression (L T D)

Question 82

Alzheimer Disease

Answer 82

Condition where memory and thought become dysfunctional​

Two causes have been proposed​

Nerve cells are killed from the outside in​

External protein: β-amyloid​

Nerve cells are killed from the inside out​

Internal proteins: tau (τ)

Question 83

Spinal Cord

Answer 83

Cable of neurons extending from the brain down through the backbone​

Enclosed and protected by the vertebral column and the meninges

Question 84

Composition of the Spinal Cord

Answer 84

Two zones​

Inner zone is gray matter​

Primarily consists of the cell bodies of interneurons, motor neurons, and neuroglia​

Outer zone is white matter​

Contains cables of sensory axons in the dorsal columns and motor axons in the ventral columns

Question 85

Role of the Spinal Cord

Answer 85

It serves as the body’s “information highway”​

Relays messages between the body and the brain​

It also functions in reflexes​

The knee-jerk reflex is monosynaptic.​

However, most reflexes in vertebrates involve a single interneuron

Question 86

Composition of the Peripheral Nervous System

Answer 86

Consists of nerves and ganglia​

Nerves are bundles of axons bound by connective tissue​

Ganglia are aggregates of neuron cell bodies​

Function is to receive info from the environment, convey it to the C N S, and to carry responses to effectors such as muscle cells

Question 87

Neurons of the Peripheral Nervous System

Answer 87

Sensory neurons​

Axons enter the dorsal surface of the spinal cord and form dorsal root of spinal nerve​

Cell bodies are grouped outside the spinal cord in dorsal root ganglia​

Motor neurons​

Axons leave from the ventral surface and form ventral root of spinal nerve​

Cell bodies are located in the spinal cord

Question 88

The Somatic Nervous System

Answer 88

Somatic motor neurons stimulate the skeletal muscles to contract​

In response to conscious command or reflex actions​

Antagonist of the muscle is inhibited by hyperpolarization (I P S Ps) of spinal motor neurons

Question 89

The Autonomic Nervous System

Answer 89

Composed of the sympathetic and parasympathetic divisions, plus the medulla oblongata ​

In both, efferent motor pathway has two neurons​

Preganglionic neuron – exits the C N S and synapses at an autonomic ganglion​

Postganglionic neuron – exits the ganglion and regulates visceral effectors​

Smooth or cardiac muscle or glands

Question 90

Divisions of the Autonomic Nervous System

Answer 90

Sympathetic division​

Preganglionic neurons originate in the thoracic and lumbar regions of spinal cord​

Most axons synapse in two parallel chains of ganglia right outside the spinal cord​

Parasympathetic division​

Preganglionic neurons originate in the brain and sacral regions of spinal cord​

Axons terminate in ganglia near or even within internal organs​

Question 91

Cranial Nerves

Answer 91

Twelve pairs of cranial nerves arise from the underside of the brain​

They carry sensory neurons for the special and general senses as well as somatic and autonomic motor neurons

Question 92

Sensory receptors give an organism the senses of:

Answer 92

Vision​

Hearing​

Taste​

Smell​

Touch

Question 93

Overview of Sensory Receptors

Answer 93

Sensory receptors provide information from our internal and external environments that is crucial for survival and success​

Exteroceptors sense external stimuli​

Interoceptors sense internal stimuli

Question 94

Sensory information is conveyed to the C N S and perceived in a four-step process

Answer 94

Stimulation​

Transduction​

Transmission​

Interpretation

Question 95

Response to Stimuli

Answer 95

Sensory cells respond to stimuli via stimulus-gated ion channels in their membranes​

Open or close depending on the sensory system involved​

In most cases, a depolarization of the receptor cell occurs​

Analogous to the excitatory postsynaptic potential (E P S P)​

Referred to as receptor potential

Question 96

Receptor Potential

Answer 96

Receptor potential like a graded potential​

The larger the sensory stimulus, the greater the degree of depolarization​

The greater the sensory stimulus, the greater the depolarization of the receptor potential and the higher the frequency of action potentials

Question 97

Overview of Mechanoreceptors

Answer 97

Mechanoreceptors are stimulated by physical or mechanical forces​

pressure that results from “pushing” or “pulling”​

or from vibrations through water or air​

Give rise to the senses of touch and hearing​

Provide input for balance and body position

Question 98

Mechanoreceptors in Skin

Answer 98

Several types of mechanoreceptors in the skin detect the sense of touch​

Contain sensory cells with ion channels that open in response to membrane distortions​

Two types​

Phasic – intermittently activated​

Hair follicle receptors, Meissner corpuscles, Pacinian corpuscles​

Tonic – continuously activated​

Ruffini corpuscles, Merkel’s disks

Question 99

Proprioceptors

Answer 99

Monitor muscle length and tension​

Provide information about the relative position or movement of animal’s body parts​

Examples​

Muscle spindles – monitor stretch on muscle – receptors that lie in parallel with muscle fibers – knee jerk reflex​

Golgi tendon organs – monitor tension on tendons – reflex inhibits motor neurons – prevents damage to tendons

Question 100

Baroreceptors

Answer 100

Monitor blood pressure​

Located at carotid sinus and aortic arch​

Detect tension or stretch in the walls of these blood vessels​

When blood pressure decreases, the frequency of impulses produced by baroreceptors decreases​

Results in increased heart rate and vasoconstriction

Question 101

Mechanoreceptor in Hearing, Vibration, and Balance​

Answer 101

These receptors are also stimulated by physical or mechanical forces detecting: ​

Vibrations through water or air—hearing and lateral line system​

Gravity and acceleration—balance and body position

Question 102

Hearing

Answer 102

Detection of sound waves​

Sound is the result of vibration, or waves, traveling through a medium​

Detection of sound waves is possible through the action of specialized mechanoreceptors that first evolved in aquatic organisms

Question 103

Lateral Line System in Fish

Answer 103

Sense objects that reflect pressure waves and low-frequency vibrations​

Supplements hearing​

Consists of hair cells within a longitudinal canal in the fish’s skin that extends along each side of the body and within several canals in the head​

Hair cells’ surface processes project into a gelatinous membrane called a cupula​

Hair cells are innervated by sensory neurons that transmit impulses to the brain

Question 104

Hearing Structures in Fish

Answer 104

Hearing structures in fish​

Called otoliths- composed of calcium carbonate crystals.​

Contained in the otolith organs of the membranous labyrinth​

Otoliths vibrate against stereocilia projecting from hair cells​

Produces action potentials

Question 105

Ear Structure of Terrestrial Vertebrates

Answer 105

Air vibrations are channeled through the ear canal of the outer ear​

Vibrations reach the tympanic membrane causing movement of three small bones (ossicles) in the middle ear​

Malleus (hammer), incus (anvil), and stapes (stirrup)​

The stapes vibrates against the oval window, which leads into the inner ear

Question 106

Inner Ear Structure of Land Vertebrates

Answer 106

The inner ear consists of the cochlea​

Bony structure containing part of the cochlear duct​

The vestibular canal lies above this duct, while the tympanic canal lies below it​

All three chambers are filled with fluid​

Pressure waves travel down the tympanic canal to the round window, which is another flexible membrane​

Transmits pressure back to middle ear

Question 107

Pressure Waves in the Ear

Answer 107

As pressure waves are transmitted through the cochlea to the round window, they cause the cochlear duct to vibrate​

Organ of Corti​

Basilar membrane contains sensory hair cells​

Stereocilia from hair cells project into tectorial membrane​

Bending of stereocilia depolarizes hair cells​

Hair cells send action potentials to the brain

Question 108

Ear Structure of Land Vertebrates

Answer 108

Basilar membrane of the cochlea consists of elastic fibers that respond to different frequencies, or pitch, of sound​

Hair cell depolarization is greatest in region that responds to a particular frequency​

Afferent axons from that region stimulated more​

Brain interprets that as representing sound of a particular frequency or pitch

Question 109

Navigation by Sound

Answer 109

A few mammals have the ability to perceive presence and distance of objects by sound​

Bats, shrews, whales, dolphins​

They emit sounds and then determine the time it takes these sounds to return​

This process is called echolocation​

The invention of sonar and radar are based on the same principles

Question 110

Detection of Body Position

Answer 110

Most invertebrates can orient themselves with respect to gravity using a statocyst​

Consists of ciliated hair cells embedded in a membrane with calcium carbonate stones (statoliths)​

In vertebrates, the gravity receptors consist of two chambers in the membranous labyrinth​

Utricle and saccule

Question 111

Utricle and Saccule

Answer 111

Within the utricle and saccule are hair cells with stereocilia and a kinocilium​

Processes embedded in the calcium carbonate-rich otolith membrane​

Utricle more sensitive to horizontal acceleration​

Saccule more sensitive to vertical acceleration​

Both types of accelerations cause cilia to bend, thus producing an action potential in an associated sensory neuron

Question 112

Semicircular Canals

Answer 112

The utricle and saccule are continuous with three semicircular canals that detect angular acceleration in any direction​

At the ends of the canals are swollen chambers called ampullae​

Groups of cilia protrude into them​

Tips of cilia are embedded within a gelatinous cupula that protrudes into the endolymph fluid of each canal

Question 113

Vestibular Apparatus

Answer 113

When the head rotates, the semicircular canal fluid pushes against the cupula, causing the cilia to bend​

Bending in the direction of the kinocilium causes a receptor potential​

Stimulates an action potential in the associated sensory neuron​

Saccule, utricle, and semicircular canals are collectively called the vestibular apparatus

Question 114

Chemoreceptors

Answer 114

Bind to particular chemicals in the extracellular fluid​

Membrane of sensory neuron becomes depolarized and produces action potentials​

Chemoreceptors are used in the senses of taste and smell​

Also important in monitoring the chemical composition of blood

Question 115

Taste (gustation)

Answer 115

Mixture of physical and psychological factors​

Broken down into five categories​

Sweet, sour, salty, bitter, and umami (hearty)​

Taste buds are collections of chemosensitive cells associated with afferent neurons

Question 116

Taste

Answer 116

In fish, taste buds are scattered all over the body surface​

In land vertebrates, taste buds are located in the epithelium of the tongue and oral cavity within raised areas called papillae​

Salty and sour tastes act directly through ion channels​

Other tastes act indirectly by binding to specific G protein–coupled receptors

Question 117

Taste in Arthropods

Answer 117

Many arthropods have taste chemoreceptors​

Flies have them in sensory hairs located on their feet

Question 118

Smell (olfaction)

Answer 118

In land vertebrates, involves neurons located in the upper portion of the nasal passages​

Receptors project into the nasal mucosa, and their axons project directly into the cerebral cortex​

Particles must first dissolve in extracellular fluid before they can activate the olfactory receptors​

Humans can detect thousands of different smells

Question 119

pH/Peripheral chemoreceptors​/Central chemoreceptors​/Increased CO2 in blood lowers pH​

Answer 119

Peripheral chemoreceptors​

Found in the aortic and carotid bodies​

Sensitive primarily to the pH of plasma​

Central chemoreceptors​

Found in the medulla oblongata of the brain​

Sensitive to the pH of cerebrospinal fluid​

Increased CO2 in blood lowers pH​

Stimulates respiratory control center

Question 120

Thermoreceptors

Answer 120

Nonspecialized sensory receptors that are sensitive to changes in temperature​

Warm and cold receptors​

Vertebrates have most of their thermoreceptors in the dermis layer of the skin

Question 121

Sensing infrared radiation

Answer 121

Some snakes use thermoreception for detection of prey​

Pit vipers​

Have a pair of heat-detecting pit organs on either side of the head between the eye and nostril​

Locate heat sources in the environment, including prey in darkness​

Paired pits appear to be stereoscopic​

To some extent can form a thermal image

Question 122

Nociceptors

Answer 122

Transmit impulses perceived as pain​

Sensitive to tissue damage​

Most consist of free nerve endings located throughout the body, especially near surfaces​

Vertebrate nociceptors use neurotransmitters, substance P, and glutamate​

Endorphins and enkephalins block the release of substance P

Question 123

Electroreceptors and Magnetoreceptors

Answer 123

Detect electrical currents​

Elasmobranchs (sharks, rays, and skates) have electroreceptors called the ampullae of Lorenzini ​

Can sense electrical currents generated by the muscle contractions of their prey​

Detect magnetic fields​

Eels, sharks, bees, and many birds appear to navigate along the magnetic field lines of the Earth

Question 124

Vision

Answer 124

Begins with the capture of light energy by photoreceptors​

Can be used to determine both the direction and distance of an object​

Invertebrates have simple visual systems with photoreceptors clustered in an eyespot​

Flatworms can perceive the direction of light but cannot construct a visual image

Question 125

Animals with Well-Developed Eyes

Answer 125

Members of four phyla have evolved well-developed, image-forming eyes​

Annelids, mollusks, arthropods, and chordates​

Although these eyes are similar in structure, they have evolved independently​

Example of convergent evolution

Question 126

Structure of the Vertebrate Eye

Answer 126

Sclera​

White portion of the eye, formed of tough connective tissue​

Cornea​

Transparent portion through which light enters; begins to focus light​

Iris​

Colored portion of the eye​

Contraction of iris muscles in bright light decreases the size of its opening, the pupil​

Lens​

Transparent structure that completes focusing of light onto the retina​

Question 127

Near versus Distance Vision

Answer 127

The lens is attached to the ciliary muscles by the suspensory ligament​

Changes shape of lens​

In near vision, ciliary muscles contract​

Lens becomes more rounded and bends light more strongly​

In distance vision, ciliary muscles relax​

Lens becomes more flattened and bends light less

Question 128

The Retina

Answer 128

Vertebrate retina contains two types of photoreceptors​

Rods​

Responsible for black-and-white vision when illumination is dim​

Cones​

Responsible for color vision and high visual acuity (sharpness)​

Most are located in the central region of the retina known as the fovea​

Sharpest image is formed

Question 129

Rods and Cones

Answer 129

Rods and cones have same basic structure​

Both have inner segment rich in mitochondria and vesicles filled with neurotransmitter molecules​

Connected by narrow stalk to the outer segment​

Packed with hundreds of flattened disks which contain photopigments

Question 130

Photopigments

Answer 130

Photopigment in rods is rhodopsin​

Photopigments of cones are photopsins​

Humans have three kinds of cones​

Each possesses a photopsin consisting of a cis-retinal bound to a protein with a slightly different amino acid sequence​

These shift the absorption maximum, the region of the electromagnetic spectrum that the pigment best absorbs

Question 131

Cell Layers in the Retina

Answer 131

The retina consists of three layers of cells​

External layer contains the rods and cones​

Middle layer contain bipolar cells​

Layer closest to eye cavity contains ganglion cell​

Once photoreceptors are activated, they stimulate bipolar cells, which in turn stimulate ganglion cells​

Ganglion cells transmit impulses to brain via optic nerve

Question 132

Sensory Transduction

Answer 132

In the dark​

Photoreceptor cells release an inhibitory neurotransmitter that hyperpolarizes the bipolar neurons​

Prevents the bipolar neurons from releasing excitatory neurotransmitter to the ganglion cells that signal to the brain​

In the presence of light​

Photoreceptor cells stop releasing their inhibitory neurotransmitter, in effect, stimulating bipolar cells​

Bipolar cells in turn stimulate the ganglion cells, which transmit action potentials to the brain​

Question 133

Visual Processing

Answer 133

Action potentials in the optic nerves are relayed from the retina to the lateral geniculate nuclei of the thalamus​

They are then projected to the occipital lobes of the cerebral cortex​

Each hemisphere of the cerebrum receives input from both eyes

Question 134

Visual Acuity

Answer 134

Relationship between receptors, bipolar cells, and ganglion cells varies in different parts of the retina​

Fovea – one-to-one connections = high acuity​

Outside of fovea, many rods converge on a single bipolar cell and many bipolar cells converge on a single ganglion cell​

More sensitive to dim light​

At the expense of acuity and color vision

Question 135

Color Vision

Answer 135

Color blindness is due to an inherited lack of one or more types of cones​

People with normal vision are trichromats​

Have all three cones​

Color blind individuals are dichromats​

Sex-linked recessive trait​

More common in men

Question 136

Binocular vision

Answer 136

Primates and most predators have two eyes, one located on each side of the face​

Two fields of vision overlap​

Parallax permits binocular vision​

Ability to perceive 3-D images and depth.​

In contrast, prey animals generally have eyes located to the sides of the head​

Prevents binocular vision, but enlarges the overall receptive field

Question 137

Evolution of Eyes

Answer 137

Explaining complicated structures was one of Darwin’s greatest challenges​

Incremental improvements in function could build a complex structure through natural selection​

Morphologists concluded that eyes are an example of convergent evolution

Question 138

Pax6 in eye development

Answer 138

Genes discovered that code for transcription factor important in lens development​

Pax6 in mice, eyeless in flies​

Sequence of genes highly similar – homologues​

Walter Gehring inserted mouse Pax6 into genome of a fruit fly​

Created transgenic fly​

Pax6 gene turned on by regulatory factors in the fly’s leg​

Eye formed on leg of fly

Replacement of fly Pax6 with mouse Pax6 results completely unexpected​

Insects and vertebrates diverged more than 500 M Y A​

Large differences in eye structure​

Expected eye development to be controlled by completely different genes​

Pax6 and eyeless cave fish​

Pax6 gene expression reduced​

Eyes start to develop, then degenerate​

Question 139

Pax6 in worms

Answer 139

Ribbon worms, Lineus sanguineus, also rely on Pax6 for eyespot development​

Pax6 homologue has been cloned and has been shown to express at the sites where eyespots develop​

In contrast, planarian worms do not rely on Pax6 for eyespot development

Question 140

Pax genes in cnidarians

Answer 140

Pax genes involved in eye development much earlier in evolutionary history than imagined​

Jellyfish PaxA gene can make a compound eye on a fly leg​

Different Pax genes have been recruited by different animal lineages for eye development after early gene duplications

Question 141

Several possible explanations for Pa

Answer 141

Eyes in different types of animals evolved truly independently, as originally believed​

Possible Pax6 had role in forehead development and this role has been co-opted time and time again for eye development​

Many think this unlikely since gene sequences and functional roles so similar​

Suggests to many that Pax6 acquired its eye development role only a single time in the ancestor to all organisms using Pax6 for eye development

Question 142

Four mechanisms of cell communication​

Answer 142

Four mechanisms of cell communication​

Direct contact​

Synaptic signaling​

Endocrine signaling​

Paracrine signaling

Question 143

Types of Chemical Messengers

Answer 143

Hormone​

Regulatory chemical that is secreted into extracellular fluid and carried by the blood​

Can act at a distance from source​

Endocrine system​

Organs and tissues that produce hormones​

Only targets with receptor can respond

Question 144

Paracrine Regulators and Pheromones

Answer 144

Paracrine regulators do not travel in blood​

Allow cells of organ to regulate each other​

Pheromones are chemicals released into the environment to communicate among individuals of a single species​

Not involved in normal metabolic regulation within an animal

Question 145

Neurotransmitters and Neurohormones​

Answer 145

Some neurotransmitters are distributed by the blood and act as a hormone​

Norepinephrine coordinates the activity of heart, liver, and blood vessels during stress​

Neurons can also secrete a class of hormones called neurohormones that are carried by blood​

Antidiuretic hormone is secreted by neurons of the brain

Question 146

Endocrine System Components

Answer 146

The endocrine system includes all the organs that secrete hormones​

Endocrine – product secreted into extracellular fluid and carried in blood​

Exocrine – secrete product into a duct​

Two basic hormone characteristics​

Must be sufficiently complex to convey regulatory information to their target cells​

Must be adequately stable to resist destruction before reaching their target cells

Question 147

3 Classes of Hormones

Answer 147

Peptides and proteins​

Glycoproteins​

Amino acid derivatives​

Catecholamines​

Thyroid hormones​

Melatonin​

Steroids​

Sex steroids​

Corticosteroids

Question 148

Classification of Hormones

Answer 148

Hormones may be categorized as:​

Lipophilic (nonpolar) – fat-soluble​

Steroid hormones and thyroid hormones​

Travel on transport proteins in blood​

Bind to intracellular receptors​

Tend to act over brief time period​

Hydrophilic (polar) – water-soluble​

All other hormones​

Freely soluble in blood​

Bind to extracellular receptors​

Tend to have much longer active period

Question 149

Paracrine Regulators

Answer 149

Paracrine regulation occurs in most organs​

Growth factors​

Proteins that promote growth and cell division in specific organs​

Epidermal growth factor​

Activates mitosis in skin​

Nerve growth factor​

Stimulates growth and survival of neurons​

Insulin-like growth factor​

Stimulates cell division in developing bone​

Cytokines​

Specialize in control of cell division and differentiation in immune system

Question 150

Paracrine Regulation of Blood Vessels

Answer 150

Nitric oxide (N O)​

Function as neurotransmitter​

Produced by endothelium of blood vessels​

Dilates arteries to control blood pressure.​

Endothelin stimulates vasoconstriction​

Bradykinin promotes vasodilation​

Paracrine regulation supplements autonomic nervous system

Question 151

Prostaglandins

Answer 151

Diverse group of fatty acids that are produced in almost every organ​

Regulate a variety of functions​

Smooth muscle contraction, lung function, labor, and inflammation​

Synthesis is inhibited by nonsteroidal anti-inflammatory drugs (N S A I Ds) such as aspirin and ibuprofen

Question 152

Lipophilic Hormones

Answer 152

Lipophilic hormones include the steroid hormones and the thyroid hormones​

Also retinoids, or vitamin A​

Can enter cells through plasma membrane

Question 153

Characteristics of Lipophilic Hormones

Answer 153

Circulate in the blood bound to transport proteins​

Dissociate from carrier at target cells​

Pass through the cell membrane​

Bind to an intracellular receptor, either in the cytoplasm or the nucleus​

Hormone-receptor complex binds to hormone response elements in D N A​

Regulate gene expression

Question 154

Characteristics of Hydrophilic Hormones

Answer 154

Peptide, protein, glycoprotein, and catecholamine hormones​

Too large or polar to cross cell membrane​

Bind to receptors on plasma membrane​

Initiate signal transduction pathways​

Activation of protein kinases​

Activate or deactivate intracellular proteins by phosphorylation​

Production of second messengers

Question 155

Receptor Kinases

Answer 155

For some peptide hormones (like insulin) the receptor itself is a kinase​

Can directly phosphorylate intracellular proteins that alter cellular activity​

For other peptide hormones (like growth hormone) the receptor itself is not a kinase​

Rather, it activates intracellular kinases

Question 156

Hydrophilic Hormones

Answer 156

Second-messenger systems​

Many hydrophilic hormones work through second messenger systems​

Two have been described​

One involving cyclic adenosine monophosphate (cAMP)​

One that generates 2 lipid messengers: inositol triphosphate (IP3) and diacyl glycerol (D A G)

Question 157

G Protein-Coupled Receptors

Answer 157

Second-messenger systems​

Receptors are linked to a second-messenger-generating enzyme via membrane proteins called G proteins​

G protein–coupled receptors (G P C Rs)​

When the G protein activates the enzyme, the second-messenger molecules increase​

Cellular response depends on the type of G protein activated​

Some activate while others inhibit their second-messenger-generating system​

Single hormone can have distinct actions in two different cells

Question 158

The Pituitary Gland

Answer 158

Also known as the hypophysis​

Hangs by a stalk from the hypothalamus​

Consists of two parts​

Anterior pituitary (adenohypophysis)​

Appears glandular​

Posterior pituitary (neurohypophysis)​

Appears fibrous​

Different embryonic origins​

Different hormones

Question 159

The Posterior Pituitary

Answer 159

Appears fibrous because it contains axons that originate in cell bodies within the hypothalamus and that extend along the stalk of the pituitary as a tract of fibers​

Develops from outgrowth of the brain​

Stores and releases two hormones​

Both are produced by neuron cell bodies in the hypothalamus​

Neuroendocrine reflex

Question 160

Antidiuretic Hormone and Oxytocin

Answer 160

Antidiuretic hormone (A D H)​

Peptide hormone that stimulates water reabsorption by the kidney, and thus inhibits diuresis (urine production)​

Oxytocin​

Like A D H, composed of 9 amino acids​

In mammals, it stimulates the milk ejection reflex and uterine contractions during labor, and it regulates reproductive behavior

Question 161

The Anterior Pituitary

Answer 161

Develops from a pouch of epithelial tissue of the embryo’s mouth​

Not part of the nervous system​

Produces at least 7 essential hormones​

Tropic hormones or tropins​

Act on other endocrine glands.​

Can be categorized into three families​

Peptide hormones, protein hormones, and glycoprotein hormones.

Question 162

Anterior Pituitary Peptide and Protein Hormones

Answer 162

Peptide hormones​

Cleaved from a single precursor protein​

Fewer than 40 amino acids in size​

Adrenocorticotropic hormone (A C T H)​

Melanocyte-stimulating hormone (M S H)​

Protein hormones​

A single chain of about 200 amino acids​

Growth hormone (G H)​

Prolactin (P R L)

Question 163

Glycoprotein Hormones of the Anterior Pituitary

Answer 163

Glycoprotein hormones​

Dimers, containing alpha (α) and beta (β) subunits, each around 100 amino acids​

Thyroid-stimulating hormone (T S H)​

Luteinizing hormone (L H)​

Follicle-stimulating hormone (F S H)​

F S H and L H​

Function in both men and women​

Referred to as gonadotropins

Question 164

Regulation of the Anterior Pituitary

Answer 164

Anterior pituitary is controlled by hormones from hypothalamus​

Neurons secrete releasing hormones and inhibiting hormones, which diffuse into blood capillaries at the hypothalamus’ base​

Each hormone delivered by the hypothalamo-hypophyseal portal system regulates a specific anterior pituitary hormone​

Portal system has 2 capillary beds (not 1)

Question 165

Feedback

Answer 165

The hypothalamus and the anterior pituitary are partially controlled by the very hormones whose secretion they stimulate​

Negative feedback or feedback inhibition​

Acts to maintain relatively constant levels of the target cell hormone​

Positive feedback not as common​

Causes deviations from homeostasis​

Control of ovulation

Question 166

The Master Gland

Answer 166

Pituitary gland was referred to as the “master gland”​

Hypophysectomy caused a number of deficits​

Effects may be direct or indirect​

Direct: activation of nonendocrine targets​

Growth hormone, prolactin, and M S H.​

Indirect: activation of other endocrine glands​

Tropic hormones A C T H, T S H, L H, and F S H

Question 167

Anterior Pituitary Disorders

Answer 167

Growth Hormone​

Stimulates protein synthesis and growth of muscles and connective tissues​

Stimulates production of insulin-like growth factors that stimulate cell division in epiphyseal growth plates – elongation of bone​

Gigantism versus pituitary dwarfism​

Also functions in adults to regulate protein, lipid, and carbohydrate metabolism​

Acromegaly

Question 168

Other Anterior Pituitary Hormones

Answer 168

Prolactin​

Acts on glands that are not endocrine glands​

Actions appear diverse​

Milk production in mammals, “crop milk” and brood patch in birds, electrolyte balance in kidneys​

T S H stimulates thyroid​

A C T H stimulates only adrenal cortex​

F S H and L H act only on the gonads​

M S H regulates melanophores or melanocytes that contain melanin

Question 169

The Thyroid Gland

Answer 169

In humans, the thyroid gland is shaped like a bow tie, and lies just below the Adam’s apple in the front of the neck​

Secretes​

Thyroid hormones​

Thyroxine​

Triiodothyronine​

Calcitonin

Question 170

Thyroid Hormones

Answer 170

Thyroid hormones bind to nuclear receptors​

Regulates enzymes controlling carbohydrate and lipid metabolism​

Hypothyroidism vs hyperthyroidism in adults​

Often functions synergistically with other hormones​

Trigger metamorphosis in tadpoles

Question 171

Calcitonin

Answer 171

Peptide hormone​

Stimulates the uptake of calcium​ (Ca^2+) into bones - lowering blood Ca^2+ levels

Appears less important in day-to-day regulation of Ca^2+ levels in adult humans

Question 172

The Parathyroid Glands

Answer 172

Four small glands attached to the thyroid​

Produce parathyroid hormone (P T H) ​

Raises blood​ Ca^2+ levels

Stimulates osteoclasts to dissolve calcium phosphate crystals in the bone matrix and release​ Ca^2+ into blood

Stimulates the kidneys to reabsorb​ Ca^2+ from urine

Vitamin D activated by a P T H controlled enzyme​

Stimulates the intestinal absorption of​

Question 173

The Adrenal Glands

Answer 173

Medulla (inner portion)​

Stimulated by the sympathetic division of the autonomic nervous system​

Secretes the catecholamines epinephrine and norepinephrine​

Cortex (outer portion)​

Stimulated by anterior pituitary hormone A C T H​

Corticosteroids​

Glucocorticoids (like cortisol) act on various cells to maintain glucose homeostasis​

Aldosterone (mineralocorticoid) helps regulate mineral balance

Question 174

The Pancreas

Answer 174

Exocrine and endocrine glands​

Connected to the duodenum of the small intestine by the pancreatic duct​

Islets of Langerhans are scattered clusters of cells throughout the pancreas​

These govern blood glucose levels through two hormones with antagonistic functions

Question 175

Insulin and Glucagon

Answer 175

Insulin​

Secreted by beta (β) cells of the islets​

Stimulates cellular uptake of blood glucose and its storage as glycogen in the liver and muscle cells, or as fat in fat cells​

Glucagon ​

Secreted by alpha () cells of the islets​

Promotes the hydrolysis of glycogen in the liver and fat in adipose tissue

Question 176

Diabetes Mellitus

Answer 176

Diabetics cannot take up glucose from blood​

Type 1 (insulin-dependent diabetes)​

Individuals lack insulin-secreting b cells​

Treated by daily injections of insulin​

Type 2 (noninsulin-dependent diabetes)​

Most patients have this form​

Very low number of insulin receptors​

Treated by diet and exercise

Question 177

The Gonads

Answer 177

Ovaries and testes in vertebrates​

Produce sex steroids that regulate reproductive development​

Estrogen and progesterone​

“Female” hormones​

Androgens​

“Male” hormones​

Testosterone and its derivatives

Question 178

The Pineal Gland

Answer 178

Located in the roof of the third ventricle of the brain​

Secretes hormone melatonin​

Functions of melatonin​

Reduces dispersal of melanin granules​

Synchronizes various body processes to a circadian rhythm​

Secretion of melatonin activated in the dark

Question 179

Other Hormones

Answer 179

Some hormones are secreted by organs that are not exclusively endocrine glands​

Atrial natriuretic hormone is secreted by the right atrium of the heart​

Promotes salt and water excretion​

Erythropoietin is secreted by the kidney​

Stimulates the bone marrow to produce red blood cells

Question 180

Insect Hormones

Answer 180

Insects undergo two types of transformations during post-embryonic development​

Molting​

Shedding of old exoskeleton and secretion of a new larger one​

Metamorphosis​

Radical transformation from the larval to the adult form

Question 181

Influences of Insect Hormones

Answer 181

Hormonal secretions influence both molting and metamorphosis​

Brain hormone stimulates prothoracic gland to produce ecdysone, or molting hormone​

High levels cause molting​

Corpora allata produces juvenile hormone​

Low levels result in metamorphosis