Anatomy and Physiology Cheat
Sheet Science Olympiad 2021
Anatomy
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Skeletal System:
Skeletal Cartilage: Cartilage is mainly composed of water. It is not vascularized (having veins) or innervated (having nerves). Cartilage is strong, resilient, and heals poorly. Cartilage is found in the epiphyseal plate, as well as in joints to provide shock absorption. It is also found in a newborn’s body. Cartilage is replaced later on by bones that form at the site and fuse
together. Chondroblasts are mesenchymal progenitor cells that develop into chondrocytes through endochondral ossification. Chondrocytes secrete extracellular m atrix to maintain the cartilage. Cartilage is surrounded by the perichondrium, a layer of dense irregular connective tissue. When the cartilage is com pressed, the perichondrium prevents it from expanding
outward. The extracellular matrix is a network of m acromolecules that provides structural support to the cells surrounding it. Within the extracellular matrix are sm all cavities called lacunae, with each one housing a chondrocyte. Lacunae are connected to each other by canaliculi, which are essentially canals. Cartilage gro ws through appositional and interstitial
growth. Appositional growth is a process that occurs when a new bone m atrix is secreted at the bone surface, causing its diameter to increase. Interstitial growth occurs when chondrocytes within the extracellular matrix divide and secrete ne w matrix. This causes the cartilage to expand from within itself. Hyaline cartilage is the m ost abundant type of cartilage. It
has a glass-like appearance and has a pearl-gray color. Hyaline cartilage is flexible and resilient. It can be divided into several subtypes—articular, costal, respiratory, and nasal cartilage—depending on its location. Elastic cartilage is similar to hyaline cartilage, the main exception being that it has more elastic fibers. This allows it to stand up better to repeated bending.
Elastic cartilage can be found in the external ear and epiglottis. Fibrocartilage resembles fibrous tissue, with the exception that it has chondrocytes. It is very strong and highly compressible. Fibrocartilage can be found in the menisci of the knee, the intervertebral disks, and the pubic symphysis.
Bone Classification: Long bones are the most fam iliar type of bones, being longer than they are wide. They are com posed of a shaft, or diaphysis, and two ends, or epiphyses. All lim b bones—except for the patella, wrist, and ankle bones—are long bones. The outer layer of long bones is com posed of com pact bone, while the inner layer is com posed of spongy bone.
The surfaces that articulate with other bones contain hyaline cartilage. Short bones are roughly cube shaped. Exam ples include the carpals of your wrist and the tarsals of your ankle. Sesamoid bones are a special type of short bones that are located inside of tendons. Examples include the patella and pisiform, though numbers vary between individuals. Flat bones are
thin, flat, and slightly curved. Examples include the ribs and cranial bones. Their function is to protect internal organs. Irregular bones are any bones that do not fit under the preceding categories. Examples include hip bones, vertebrae, and more.
Bone Functions: You may recognize that the skeleton is essentially just a framework of bones. This framework serves to support the body.This framework also serves to protect vital structures including the brain, spinal cord, and thoracic organs. Bones, muscles, cartilage, tendons, ligaments, joints, and other connective tissue compose the skeletomuscular system.
They work together to make movement possible. Bones are also responsible for the storage of triglycerides inside of yellow bone marrow. They also serve as a reservoir for minerals. Bones produce hormones such as osteocalcin and some growth factors.
Bone Structure: All bones are m ade up of an outer layer of compact bone, which looks sm ooth and solid. The inside is com posed of spongy bone (referred to as diploë in flat bones). Spongy bone contains many bands or colum ns of connective tissue called trabeculae, which help the bone resist stress. Spongy bone contains many pores, which are filled with bone
marrow. The long axis of the bone is the diaphysis, or the shaft. It is constructed of com pact bone that surrounds the medullary cavity, which contains bone m arrow. This bone marrow can be in the form of red bone marrow, which produces blood cells, or yellow bone marrow, which stores fat. Red bone m arrow is replaced by yellow bone m arrow as you age. In
cases of extreme blood loss, the body may willingly revert yellow bone marrow back to red bone marrow, increasing the production of blood cells. The ends of the bone are called the epiphyses. The exterior is composed of com pact bone, while the interior is composed of spongy bone. The joint surface of each epiphysis is covered by a thin layer of articular cartilage.
The metaphysis is located where the diaphysis and the epiphysis meet. The epiphyseal line is a disc of hyaline cartilage that is located in the metaphysis of adult long bones. The periosteum is a white membrane that covers the external surface of bones. The outer layer of the periosteum is the fibrous layer, made up of dense irregular connective tissue. The inner layer
is known as the osteogenic layer, made up of osteogenic cells. The periosteum is secured to the bone by collagen fibers known as Sharpey’s fibers. The endosteum is a membrane made up of delicate connective tissue that covers the internal surface of bones, along the medullary cavity. This membrane is made up of osteogenic cells. Osteons, the structural units of
long bones, are long cylinders parallel to the long axis of bones. They function as small, weight-bearing pillars. A Haversian canal runs through the center of each osteon, while perforating canals, also called Volkmann's canals, run perpendicular to these. These enable vessels and nerves to enter the bone to supply nutrients.
Bone Markings: Bone markings are surface features on bones that serve various functions. These include enabling joint motion, locking bones in place, providing structural support, providing stabilization, and providing protection. Several bone markings serve as sites of muscle and ligament attachment. A tuberosity is a lange, rounded projection that is often
roughene d. A good exam ple is the ischial tuberosity. A crest is a narrow, prom inent ridge of bone. A good exam ple is the iliac crest. A trochanter is a very large, blunt, irregularly shaped process. The only trochanters are the greater and lesser trochanters of the fem ur. A line is a narrow ridge of bone that is less prominent than a crest. A good exam ple of a line is the
intertrochanteric line of the fem ur. A tubercle is a small, rounded projection or process. A good exam ple is the adductor tubercle of the fem ur. An epicondyle is a raised area located on or above a condyle. A good example is the medial epicondyle of the fem ur, which is located above the medial condyle of the fem ur. A spine is a sharp, slender, pointed projection. A
great example of a spine is the ischial spine. A process is a bony prominence. These are abundant markings and an example is the spinous processes of the vertebrae. Other bone markings serve to help form joints. A head is the expanded articular end of an epiphysis, separated from the diaphysis or shaft by a neck. A good example is the head of the humerus. A neck is a
narro w connection between the epiphysis and diaphysis. A good exam ple is the neck of the humerus. A facet is a sm ooth, nearly flat articular surface. A good exam ple is the costal facet located on each rib. A condyle is a smooth, rounded articular process. A good exam ple is the medial condyle of the femur. A ramus is an armlike or branchlike bar of bone. An exam ple
of a ram us is the ram us of the mandible. A trochlea is a sm ooth, grooved articular process shaped like a pulley. An exam ple is the trochlea of the fem ur. Some bone m arkings are depressions and openings. A groove, or sulcus, is a furro w in a bone. An exam ple is the mylohyoid groove, or sulcus of the mandible. A fissure is a narrow, slitlike opening. A great exam ple is
the inferior orbital fissure. A foramen is a round opening through a bone that serves as a passageway for structures to pass through. Most foramina are found in the skull, an example being the foramen magnum. A meatus is a canal-like passageway through a bone. An example is the internal acoustic meatus. A sinus is a cavity within a bone, filled with air and lined with
mucous membrane. An example is the paranasal sinus. A fossa is a shallow, basinlike depression in a bone. Good examples include the posterior, middle, and anterior cranial fossa.
Bone Cells: Osteoblasts are bone form ing cells. They can be found in areas of high metabolism within the bone. Osteocytes are mature bone cells; they develop from osteoblasts. Osteocytes help maintain healthy bone tissue by secreting enzymes and controlling calcium released from bone tissue into the bloodstream . Osteogenic cells respond to traum a by giving rise
to bone forming cells, or osteoblasts, and bone destroying cells, or osteoclasts. Bone-lining cells develop from osteoblasts. They are located along the surface of m ost adult bones. Bone-lining cells regulate the movement of calcium and phosphate into and out of the bones. Osteoclasts develop from hem atopoietic stem cells. They are large, m ultinucleate cells that are
located at sites of bone resorption. Osteoclasts break down bone tissue and are im portant to bone growth, healing, and remodeling.
Bone Development: Ossification is the process by which bones form in em bryos. In adults, however, ossification is the process of bone remodeling and repair. Endochondral ossification is the replacement of hyaline cartilage with endochondral bone. Intramembranous ossification is the development of fibrous mem branes into membrane bones.
Bone Homeostasis: Every day, up to half a gram of calcium leaves the adult skeleton. Every week, we recycle five to seven percent of our bone mass. Every three to four years, all of our spongy bone is replaced. Every ten years, all of our compact bone is replaced. The aforementioned things occur due to bone remodeling, which is made up of two processes: bone
deposit and bone resorption. Bone deposit is the process by which osteoblasts deposit hydroxyapatite crystals into the bone matrix. Bone resorption is the process by which osteoclasts secrete lysosomal enzymes that break down bone tissue, transferring calcium into the blood. Calcitriol, the active form of vitamin D, inhibits the release of calcitonin. Calcitonin
inhibits the release of calcium from bone, reducing blood levels of calcium ions. When blood levels of calcium ions decline, parathyroid hormone is released. This stimulates bone resorption, which once again increases blood levels of calcium ions. Leptin is a hormone released by adipose tissue to regulate bone density. Serotonin, when produced outside of the brain,
inhibits bone formation.
Muscular System:
The three types of muscle tissue are skeletal muscle, cardiac muscle, and smooth muscle. Both skeletal and smooth muscle cells are elongated. For this reason, they are called muscle fibers. Skeletal muscles attach to the skeleton and cover it. Skeletal muscle fibers are the longest muscle fibers and they are striated. Skeletal muscles are called voluntary muscles because they
are the only type of muscle subject to conscious control. Their function is mainly to give the body its mobility. Cardiac muscles are only found in the heart, where it constitutes the walls of the heart. Cardiac muscle cells (not fibers, cells) are also striated, but not elongated. Cardiac muscle can contract without stimulation, but it is involuntary because we do not have
conscious control over our hearts. The nervous system is responsible for changes in the heartbeat. Smooth muscles can be found in the walls of hollow visceral organs. These organs include the stomach, bladder, and respiratory passages. It functions to force substances, especially fluids, throughout channels in the body. Smooth muscle fibers are elongated, but not striated.
It is involuntary as you have no conscious control over its actions.
Muscle tissues have four special characteristics that distinguish them from other tissues. One characteristic that muscles have is excitability, or responsiveness, which is the ability to receive stimuli and respond to them. When muscles are stimulated by neurotransmitters, they respond by generating electrical impulses that cause their cells to contract. This leads to the next
characteristic, contractility. Contractility is the ability for a cell to shorten in response to stim uli. This characteristic is com pletely unique to m uscle tissues. Another characteristic that m uscle tissues have is extensibility. This is the ability to extend or stretch. When muscles are relaxed, they can stretch beyond resting length. When muscles stretch beyond their resting
length, they m ust be able to recoil in order to resume its resting length. The ability to do so is called elasticity. Muscles serve many purposes in the body, though they have four main functions. Muscles are responsible for producing m ovements. Skeletal m uscles are responsible for locomotion and manipulation. Cardiac m uscles pump blood throughout your body.
Smooth muscles help squeeze substances through tracts in the body. Muscles give the body the ability to maintain posture. Our muscles are constantly making tiny movements one after another to counteract the forces being applied to your body; for example, gravity. Muscles assist bones, ligaments, and tendons in stabilizing joints. Muscles are also responsible for
generating heat. Skeletal muscles account for at least 40% of the body’s mass, making them responsible for generating heat. This helps maintain normal body temperature, which is vital to survival. Skeletal muscles provide protection by enclosing internal organs that are vital to survival. Smooth muscles form valves to regulate the passage of substances through tracts in
the body. They dilate and constrict the pupils of your eyes. They form the arrector pili muscles found attached to hair follicles. Muscles have so many functions.
Gross Anatomy: Each of our roughly 650 skeletal m uscles is a discrete organ, made of several tissues. The main tissues in skeletal muscles are m uscle fibers; however, blood vessels, nerve fibers, and connective tissue are all present in skeletal m uscles. Each m uscle is innervated by a nerve and supplied by blood vessels. The nerve is responsible for stim ulating the muscle,
producing contractions. Blood supply is vital to m uscles; they use huge am ounts of energy, requiring constant delivery of oxy gen and nutrients via arteries; they produce m any metabolic wastes that are removed via veins; tiny capillaries actually help accommodate for changes in m uscle length during contraction. Connective tissue sheaths help support cells and hold the
muscle together as a whole. On the outside, the epimysium is composed of dense irregular connective tissue that surrounds the muscle. Inside of each muscle is an abundance of fascicles, which are basically bundles of sticks (except the sticks are muscle fibers). Each fascicle is surrounded by a layer of fibrous connective tissue, the perimysium. Inside of each fascicle is an
abundance of individual m uscle fibers, each of which is surrounded by a sheath of fine areolar connective tissue, the endomysium. Skeletal m uscles work together with bones, ligaments, tendons, and other connective tissues to produce movement (it’s in the name, after all). Most skeletal m uscles attach to bones in at least two places, an insertion and an origin. During
muscle contraction, the insertion moves towards the origin (the origin stays in place, just like on a coordinate plane). Muscles may be attached directly or indirectly, the latter of which is much m ore com mon.
Microscopic Anatomy: Let’s examine a single skeletal muscle fiber. It is essentially just a long, cylindrical cell. Each muscle fiber has multiple oval-shaped nuclei underneath its sarcolemma (the plasma membrane of skeletal muscle fibers). Their diameter is quite large, ranging from ten to a hundred
micrometers. Their length is astounding, some up to thirty centimeters long. This is only the case because each m uscle fiber is produced by the fusing of hundreds of em bryonic cells. Each muscle cell has a sarcoplasm, which is similar to the cytoplasm ; the exception is that sarcoplasm has large numbers
of glycosomes and myoglobin. It has all the organelles that you would expect to find in any given cell. In addition to this, it has m yofibrils, a sarcoplasmic reticulum , and T-tubules. These structures are vital to m uscle contraction. Hundreds to thousands of myofibrils can be found in a single m uscle fiber.
These m yofibrils, which run in the same direction as m uscle fibers, are very tightly packed; they take up 80% of the cell’s volume. Myofibrils contain sarcomeres, which are responsible for contraction. These sarcomeres contain three types of myofilaments. The thick filaments, which are found primarily
in the center, contain myosin. The thin filaments, which are found primarily towards the sides, contain action. These also contain tropom yosin, which blocks myosin-binding sites on actin, and troponin, which binds to actin, tropom yosin, and calcium ions. The elastic filaments, which are
composed of titin. Titin is a giant protein that holds the thick filaments in place. Myosin, actin, tropomyosin, troponin, and titin all play a role in the cross-bridge cycle, in which proteins slide past each other to generate movement. You may also find proteins such as dystrophin, nebulin, myomesin,
and C proteins that also play roles in this cycle. The sarcoplasmic reticulum is a smooth endoplasmic reticulum whose tubules surround myofibrils. Most SR tubules run along the long axis of the myofibril; others, called terminal cisterns, run perpendicularly and occur in pairs. The function of the
sarcoplasmic reticulum is to regulate the levels of calcium ions within cells. It stores calcium ions, or Ca2+, and releases them when the muscle fiber is stimulated; this gives the final go signal for contraction. T-tubules are elongated tubes that run between paired terminal cisterns, forming triads—groups
composed of a pair of terminal cisterns as well as a T-tubule. T-tubules are essentially just continuations of the sarcolemma. This means that when electrical impulses travel along the sarcolemma, T-tubules conduct the impulses to every single sarcomere, releasing calcium ions. The sliding filament
model of contraction describes the process in which m yosin heads latch onto m yosin-binding sites on actin, form ing cross-bridges. These cross bridges form and break several times during a single m uscle contraction, generating tension at sliding thin filaments to ward the center of the sarcomere. As
this occurs in sarcomeres throughout a cell, it shortens. When thin filaments slide towards the center of the sarcomere, Z discs are pulled to ward the M line. Overall, the I bands shorten, Z discs become closer together, H zones disappear, and A bands m ove closer together.
Physiology
Skeletal muscle fibers are activated by somatic motor neurons, whose axons extend to muscle cells. Each axon ending forms several short, curling branches that form a neuromuscular junction with a single muscle fiber. The axon terminal is very close to the muscle fiber, but they are separated by the
synaptic cleft; this space is filled with a gel-like substance. Small mem branous sacs, called synaptic vesicles, are located within the axon term inal. These sacs contain acetylcholine, a neurotransm itter (pictured to the right). Where the sarcolemm a folds to form the neurom uscular joint, junctional
folds provide a surface area for acetylcholine receptors. When an action potential reaches an axon term inal, the axon terminal releases acetylcholine into the synaptic cleft. The acetylcholine diffuses across the cleft, attaching to acetylcholine receptors on the sarcolemm a. The effects of acetylcholine
are quickly term inated by acetylcholinesterase, an enzyme that breaks down acetylcholine to acetic acid and choline; this prevents m uscle fibers from contracting without s tim ulation. The binding of acetylcholine to acetylcholine receptors opens ligand -gated ion channels, increasing the num ber of
sodium ions diffusing in and decreasing the num ber of potassium ions diffusing out. This causes a change in mem brane potential called depolarization. The endplate potential (localized depolarization) spreads to adjacent mem branes and opens voltage-gated sodium channels, allowing sodium ions to
enter. Once the threshold potential is reached, an action potential is generated. The action potential moves along the sarcolemma, its depolarization wave opening voltage-gated sodium channels in more areas and allowing sodium ions to enter. The repolarization wave causes voltage-gated sodium
channels to close and voltage-gated potassium channels to open, causing another change in membrane potential called repolarization. During repolarization, muscle fibers are in a refractory period; they are incapable of being stimulated again until repolarization is complete. Skeletal muscle fibers
can be classified as slow fibers and fast fibers on the basis of the velocity at which they shorten. They can also be classified as oxidative fibers or glycolytic fibers on the basis of the pathways they use for forming ATP. Slow oxidative fibers contract slowly because their myosin ATPases are slow.
They are dependent on oxygen delivery and aerobic pathways. They have high levels of m yoglobin (m aking them red), low stores of glycogen, small fiber diameters, m any m itochondria, and many capillaries. All of these qualities m ake SO fibers best suited for endurance activities. Fast oxidative fibers contract quickly because their m yosin ATPases are fast. They are
dependent on aerobic pathways, though they also use glycolytic reserves. They have high levels of m yoglobin (making them red to pink), m oderate stores of glycogen, moderate fiber diameters, m any m itochondria, and m any capillaries. This m akes FO fibers best suited for activities such as sprinting and walking. Fast glycolytic fibers contract rapidly because their
myosin ATPases are fast. They are independent of oxygen and use glycolytic reserves for fuel. They have lo w levels of myoglobin (m aking them white), low stores of glycogen, large fiber diameters, few mitochondria, and few capillaries. All of these qualities make FG fibers best suited for short, rapid, intense m ovements. The force exerted by a m uscle on an object is
called muscle tension. The force exerted on the m uscle by the weight of the object is called the load. If force is exerted by the m uscle but the load does not m ove, m uscle fibers do not change lengths; hence, the contraction i s an isometric contraction. If the force overcomes the load, m uscle fibers change lengths; hence, the contraction is an isotonic contraction.
Concentric contractions are isotonic contractions in which the force overcomes the load and the m uscle fiber shortens. Eccentric contractions are isotonic contractions in which the force overcomes the load and the m uscle fiber lengthens. All m uscles, even while relaxed, are almost always slightly contracted. This phenomenon is called muscle tone. Muscle tone
does not produce active movements but instead keeps the muscles firm, healthy, and ready to respond to stimuli. It also assists in joint stabilization and posture maintenance.
Metabolism: Muscle contraction requires energy, which is supplied by ATP. Muscles can only store four to six seconds’ worth of ATP. This means that, since ATP is the only energy source directly used for muscle contraction, ATP must be regenerated as quickly as it is broken do wn. After ATP is hydrolyzed to ADP and inorganic phosphate, there are three pathways
that may regenerate it. Direct phosphorylation occurs when creatine phosphate, a high-energy m olecule stored in m uscles, is used to regenerate ATP. When CP couples with ADP, a phosphate group —plus energy—is transferred from CP to ADP to form ATP alm ost instantly. This reaction is catalyzed by the enzyme creatine kinase. Muscle cells store about two to
three times more CP than ATP, together accounting for about 15 seconds of power for rigorous activity. CP is replenished during rest or inactivity. Anaerobic glycolysis is used when stored ATP and CP are exhausted. In this process, ATP is generated by catabolizing glucose from the blood or glycogen from the m uscle. This process does not require oxy gen, though
it can still occur in the presence of oxygen. During glycolysis, glucose is broken down into two pyruvic acid molecules. During less rigorous activities, this pyruvic acid undergoes aerobic respiration; however, it is converted into lactic acid during vigorous activity. This harvests five percent as much ATP from each glucose m olecule as aerobic respiration but
produces it two and a half times faster. This m akes it m ost useful for thirty to forty seconds of strenuous activity. Aerobic respiration produces ninety-five percent of the ATP used during rest, light exercise, and m oderate exercise. This process requires oxy gen which, when com bined with glucose, produces carbon dioxide, water, and ATP. Glycogen is the m ain source
of energy at first, which becomes pyruvic acid, and then fatty acids. It produces a large quantity of ATP but is very slow. Sm ooth m uscle occupies the walls of almost all of the body’s hollow organs, the exception being the heart and other organs. Its m uscle fibers are spindle-shaped cells with varying sizes, each with a centralized nucleus. They are only a tenth the width
of skeletal m uscle fibers and are thousands of times shorter. Smooth m uscles lack coarse connective tissue sheaths; instead, they have fine connective tissue—endomysium —between its cells. Typically, sm ooth muscles are organized into two sheets. The longitudinal layer, the outer layer, contains m uscle fibers that run parallel to the long axis of the organ. When these
muscle fibers contract, it causes the organ to dilate or shorten. The circular layer, the inner layer, contains m uscle fibers that run around the circumference of the organ. When these muscle fibers contract, it causes the organ to constrict or elongate. These two layers are continuously contracting and relaxing involuntarily, propelling substances and mixing them
together throughout pathways in organs. This action is called peristalsis. This occurs in areas such as the rectum, bladder, and uterus to help the organs expel their contents. Smooth muscles are innervated by nerve fibers that belong to the autonomic (involuntary) nervous system. Instead of forming neuromuscular junctions, these nerve fibers have bulbous
swellings—
called varicosities—that form diffuse junctions. In these areas, the varicosities release neurotransmitters into the synaptic cleft. Smooth muscles have sarcoplasmic reticulum, though they are much less developed than that of skeletal muscles. T-tubules are absent in these; instead, the sarcolemma has multiple caveolae—pouchlike infoldings that sequester bits of
extracellular fluid containing calcium ions. Rather than the sarcoplasmic reticulum being responsible for releasing calcium for contraction, extracellular calcium ions are m ostly responsible for excitation-contraction coupling. Sm ooth m uscles, as their name indicates, are not striated. This means that they do not contain sarcomeres. They have m yosin and actin filaments,
though the ratio of them in sm ooth m uscles is one to thirteen as com pared with one to two in skeletal muscles. Sm ooth m uscles com pensate for this lack in numbers with their surplus of m yosin heads that are situated along the entire length of the muscle, making them just as strong as skeletal m uscles. They also lack troponin complexes in actin filaments; rather, a
protein called calm odulin is the calcium -binding site. When smooth m uscles contract, they twist like corkscrews; this is because their m yosin and actin filaments are arranged diagonally. When smooth muscles contract, the whole sheet contracts slowly and synchronously. This is because gap junctions, special connections between cells, allo w for action potentials to be
transm itted from each m uscle fiber to the next. Pacemaker cells in some smooth m uscle fibers set the pace of contraction for the entire m uscle sheet. The sliding filament m odel still applies to sm ooth m uscle contraction, as does the utilization of ATP. Sm ooth muscle contractions are also triggered by rises in intracellular levels of calcium ions. Calcium activates myosin
in smooth muscles by interacting with calmodulin, a calcium-binding protein. Calmodulin interacts with an enzyme called myosin kinase or myosin light chain kinase, which phosphorylates the myosin; this activates the myosin. In the process of smooth muscle contraction, calcium ions first enter the cytosol from extracellular fluid via voltage-dependent channels
or through the SR. Next, the calcium ions bind to calmodulin, activating it. This allows for calmodulin to activate myosin light chain kinase enzymes. These enzymes transfer phosphate to myosin, activating myosin ATPases. The now activated myosin forms cross bridges with actin, shortening smooth muscle fibers. Smooth muscles contract about thirty times slower
than skeletal m uscles, but they can maintain the same contractile tension for longer periods of time using less than a percent of the energy cost. In this way, skeletal m uscles are like super fast sports cars that run out of gas quickly while smooth m uscles are like slower trucks that run out of gas slo wly. Just like skeletal m uscles, smooth m uscles have muscle tone; they
maintain a m oderate degree of contraction without fatiguing. Smooth m uscles only need to produce ATP via aerobic pathways due to their low energy consumption. Sm ooth m uscle contraction is regulated by neural stim uli, hormones, and localized chem ical changes. Neural stim uli activate smooth m uscles in the same way that they activate skeletal m uscles.
Neurotransmitter binding generates an action potential, resulting in an increase in calcium ion levels in cytosol. However, some smooth muscles only respond to localized signals. Nerve endings in smooth muscles don’t only release acetylcholine; instead, they release a variety of neurotransmitters that may stimulate different smooth muscle fibers. The way that the body
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determines which sm ooth muscle fibers are stim ulated is through the type of receptor molecules on the cell’s sarcolemm a. Acetylcholine binds to acetylcholine receptors, norepinephrine binds to norepinephrine receptors, etc. Some smooth m uscles are not innervated by nerves at all. These m uscles contract through spontaneous depolarization or in response to chem ical
stimuli that bind to G protein-linked receptors. Certain hormones, histamine, excess carbon dioxide, low pH, and lack of oxygen all may cause smooth muscles to contract or relax. Besides smooth muscle tone, slow prolonged contractions, and low energy requirements, smooth muscles have a variety of special features.When skeletal muscles are stretched, they respond
by contracting vigorously. When smooth m uscles are stretched, they also respond by contracting. However, sm ooth m uscles adapt to stretching very quickly, allowing them to relax while still being able to contract when needed. In other words, sm ooth m uscles allow hollow organs to contract and relax slowly without expelling all of their contents. If this weren’t the
case, very strange things would occur; your stomach and intestines would expel undigested food and you would not absorb many nutrients from it; your bladder would not be able to hold any urine. Smooth muscle stretching generates m ore tension than skeletal m uscle stretching. The way that smooth muscle filaments overlack, in addition to their lack of sarcomeres,
allows for them to generate m ore force. Skeletal m uscles can only undergo shortening or lengthening of 30% its length while still functioning efficiently, while sm ooth m uscles can shorten to half their length and lengthen to twice their length. All m uscle fibers can hypertrophy, causing them to increase in size. Some sm ooth muscle fibers also undergo hyperplasia,
causing them to divide; this increases the num ber of smooth m uscle fibers rather than just their size. A great example is the gro wing of the uterus in girls during puberty and pregnancy. Sm ooth muscles have two m ajor categories: unitary sm ooth m uscle and m ulti-unit sm ooth m uscle. Unitary smooth muscle is found in the walls of all hollo w organs except the heart.
This is what gives it the nickname visceral muscle. All of the characteristics listed above apply to unitary smooth muscle. Multi-unit smooth muscle is found in various forms, such as the arrector pili muscles attached to hair follicles and the internal eye muscles. In these muscles, gap junctions and spontaneous depolarization are possible but rare. These are more similar
to skeletal muscles in that their muscle fibers are structurally independent of one another and they have neuromuscular junctions. However, multi-unit smooth muscles are still served by the autonomic (involuntary) nervous system and they can respond to hormones. Cardiac muscles can only be found in the walls of the heart. They appear to be striated, just like skeletal
muscles. Cardiac muscle is involuntary, as you have no conscious control over the beating of your own heart. Seeing as your entire heart (hopefully) beats at the same time, you could probably guess that cardiac muscle has pacemaker cells that set the tempo for the entire muscle sheet to contract. ATP is produced in cardiac muscles via aerobic pathways, the oxygen
being provided by blood vessels in the pulmonary circuit. Cardiac muscle cells are branched, giving the appearance of chains. Cardiac muscle cells typically have a single nucleus, though they may have two during late fetal development and around birth. Similar to smooth muscles, cardiac muscles have an endomysium which is attached to the fibrous skeleton of the
heart. Their sarcoplasmic reticulums are very similar to those of smooth muscles. Calcium ions for contraction are taken from both the sarcoplasmic reticulum and extracellular fluid, just like in smooth muscles. Cardiac muscle contraction is slower than skeletal muscles but faster than smooth muscles. Cardiac muscles are unique in that they have myofibrils, like skeletal
muscles, but they are of irregular thickness. Gap junctions are present at intercalated discs and neuromuscular junctions are absent. Troponin complexes are present, similar to skeletal muscle. They contain one large T-tubule, rather than two smaller T-tubules, in each sarcomere. Most, if not all, of muscle tissues develop from embryonic mesoderm cells called myoblasts.
In order to form skeletal muscle tissues, several myoblasts must fuse together to form multinucleated myotubes. This process is guided by integrins, a class of cell adhesion proteins. Skeletal muscle tissues start contracting by week seven of embryonic development. Nerve endings release the growth factor agrin as they begin to invade skeletal muscle tissues, activating
the enzyme muscle kinase. Satellite cells are myoblast-like cells that help repair injured skeletal muscle fibers, allowing for limited regeneration of dead skeletal muscles. In order to form cardiac and smooth muscle tissues, myoblasts develop gap junctions instead of fusing. Cardiac muscle is pumping blood only three weeks after fertilization. It was previously thought
that cardiac muscles were incapable of regenerating, though studies have shown that cardiac muscle cells divide modestly. Still, injured cardiac muscle is almost always replaced by scar tissue. Smooth muscles fibers, on the other hand, divide regularly and allow for smooth muscle to regenerate relatively well. Approximately thirty-six percent of an average woman’s body
mass is made up of skeletal muscles, whereas forty-two percent of an average man’s body mass is made up of skeletal muscles. This is primarily due to the effect of testosterone on skeletal muscles rather than the effects of exercise. Due to their amazing resistance to infection, skeletal muscles are rarely affected by homeostatic imbalances, the main exception being a genetic
disorder called muscular dystrophy. On a side note, some athletes take doses of steroids, which are essentially synthetic male sex hormones, to increase muscle mass; not only is this illegal, but it is very physiologically dangerous.
Integumentary System: In an average adult, the integumentary system has a surface area of 1.5-2.0 square meters and weighs 4 to 5 kilogram s. It varies in thickness from 0.5 mm on the covering of the eyelids to 4 mm on the palm s and soles. The integumentary system serves m any functions, the m ain of wh ich are listed below. Protection: The integumentary system's
main function is to protect your body from injury and pathogens. For exam ple, the stratum germ inativum repairs m inor injuries. Additionally, the skin acts as a barrier to protect from pathogens. Keratin and glycolipids in the skin help waterproof it and the continuity of the skin protects from bacterial invasion. There are also chem ical barriers such as skin secretions of
sebum , human defensins, and cathelicidins. The acid m antle of the skin causes the skin to have a low pH which slows bacterial growth on the skin's surface. Melanin protects the body from UV damage. Ad ditionally, Langerhans' cells and derm al m acrophages are located in the skin and activate the imm une system . The structure of DNA in the skin allows its electrons to
absorb UV radiation and convert it into heat. Temperature maintenance: The integumentary system also regulates heat exchange with the environment and keeps the body at an average of 98.6 °F or 36.0 °C. S weat, secreted by sudoriferous glands, helps cool the body. Dilation and constriction of blood vessels in the skin also helps to regulate the body temperature.
Synthesis and storage: The integumentary system synthesizes Vitamin D3 and stores lipids in adipose (fat) tissue. Sensory reception: There are touch, pressure, pain, and temperature sensory receptors in the skin which interact with the nervous system. Meissner's corpuscles and Merkel disks sense light touch while Pacinian receptors, located deeper in the dermis,
detect deep pressure. Hair follicle receptors sense movement of hairs. Nociceptors and bare nerve endings sense pain. Thermoreceptors sense heat and cold. Excretion and secretion: The skin excretes salt water and organic wastes. In post pubescent females, modified glands called mam mary glands secrete milk. Sudoriferous (sweat) glands are identified into t wo typesapocrine and eccrine. Eccrine sweat glands secrete cooling sweat and apocrine sweat glands secrete during emotional stress or excitement. Cerum inous glands are modified sweat glands that produce ear wax. Hydration: The integumentary system protects the body from dehydration. 3 Major Layers of the Skin: The epidermis is the outer, thinner layer that consists of
epithelial tissue.: The dermis is the inner, thicker layer that consists of connective tissue.: The hypodermis—also known as the subcutaneous or subQ layer—is located underneath the derm is; it is not necessarily part of the integument but shares some functions. It is composed of areolar/adipose connective tissues that anchor skin to the underlying structures—m ostly
muscles—and insulates/absorbs shock Epidermis: The epidermis is composed primarily of keratinized stratified squamous epithelium. The epidermis contains four major types of cells Keratinocytes produce keratin, a tough insoluble fibrous protein that provides protection and contributes to the strength and water resistance displayed by the epidermis, hair and nails.
Melanocytes produce melanin, a pigment that determines skin color. Langerhans cells, or dendritic cells, are macrophages that originate in the red bone marrow. They are involved in the immune response. Merkel cells function in the sensation of touch along with the other adjacent tactile discs (receptors). Skin can be classified as thin (hairy) or thick
(hairless/glabrous skin). Thin skin, or hairy skin, covers all body regions except for the palms, fingertips, and soles. It is usually 1-2 millimeters thick. Thin skin has fewer skin receptors and sudoriferous glands and more sebaceous glands than thick skin. Thick skin, also known as hairless or glabrous skin, covers the palms, fingertips, and soles. Thick skin has more
skin receptors and sudoriferous glands and fewer sebaceous glands. Skin ridges (e.g. fingerprints) are found due to well-developed dermal papillae. Skin ridges aid in grip and object manipulation.
Epidermal Layers: The epiderm is is com posed of four layers in thin skin, and five layers in thick skin. The layers are as follows, starting from the
deepest to the shallowest. The basal layer, stratum basale, or stratum germinativum. The stratum basale is the deepest epidermal layer. It is the "growing
layer of the skin" or the "base of it" (hence its other name, stratum basale). It is connected by hemidesmosomes, which are special disc-shaped proteins,
to the basement membrane, which is a network of protein fibers separating the epiderm is from the dermis below. The stratum basale, as pictured above, descends
into the derm is in what are called epidermal ridges. The areas where the dermis projects upward are called dermal papillae. These are required
because there are no blood vessels in the epidermis, so all nutrients m ust be obtained through diffusion from the derm is. These ridges are what cause the
elaborate patterns in the epiderm is of areas with thick skin, such as fingertips. There are several cells populating the stra tum basale. Basal cells, or
germinating cells, are large stem cells that undergo continuous m itosis to produce keratinocytes that are being constantly pushed up wards. These keratinocytes
replace the skin cells that we shed off every day. Melanocytes are the cells that produce melanin, a pigment whose coloration varies from brown to
yellow. These melanocytes have processes which extend throughout this layer in order to distribute the melanin. Nervous receptors provide inform ation about
external stimuli to the brain. The spiny layer or stratum spinosum. The stratum spinosum is com posed of 8 to 10 layers of keratinocytes connected
together by desmosomes. Many melanosomes and dendritic cells can be found here. In this layer, keratinocytes produced in the stratum basale divide rapidly.
The granular layer or stratum granulosum. This is where the process of keratinization begins, helping produce keratin that can be found in upper
layers. Keratinization begins and helps form keratin in upper layers As keratinocytes reach the stratum granulosum , they are too far from the dermal capillaries to
receive enough nutrients. As a result, they begin to die: The clear layer or stratum lucidum. The stratum lucidum is only present in thick skin, which
can be found at the fingertips, palm s, and soles. It is a thin, translucent band superficial to the stratum granulosum . The corny layer or stratum corneum. The
stratum corneum is the outerm ost layer; it is com posed of 20 to 30 layers of dead, flattened ker atinocytes (essentially just mem branous sacs filled with
keratin). They are continuously shed and replaced by cells from deeper strata. The keratinocytes in this layer are called keratinized cells or cornified cells.
They are primarily composed of keratin, which serves to protect the deeper and more vulnerable dermis. These cells are very tightly attached to each
other by desmosomes, which are special proteins that join two cells and are very difficult to break. These desmosomes are why one's skin peels off in sheets after
a bad sunburn instead of in individual cells.
The Dermis: The dermis, located beneath the epidermis, consists of two layers. About 70% of the dermis is composed of collagen fibers, which
give structural toughness and strength. The most superficial layer is the papillary layer while the deepest layer is the reticular layer. The papillary layer. The
papillary layer is named after the dermal papillae. It is composed of loose connective tissue whose purpose is to supply the epidermis with
nutrients. It is supplied with capillaries and innervated by nerves. The reticular layer. The reticular layer is composed of dense irregular connective tissue. It is
filled with densely packed elastin fibers, which give the skin its elasticity. This layer is also filled with collagen fibers, which resist that elasticity, in
order to keep the skin rigid. One of the major causes of wrinkles is the degradation of collagen fibers due to UV light.
Skin Color: There are three major pigments that influence skin color: carotene —a yellow-orange pigment found in carrots and
that gives the skin its red tint. Carotene can be synthesized into Vitam in A, which is needed for the maintenance of epithelial cells. Eating large
squashes—melanin—a pigment whose color varies from yellow to brown and is produced by melanocytes—and hem oglobin—a red pigment found in the blood
amounts of carotene can also cause the skin of light-skinned individuals to turn orange. Melanin is transferred into the stratum basale and stratum spinosum by
intracellular vesicles arising from melanocytes. The two m ain types of melanin are eumelanin and pheomelanin. Eumelanin is bro wnish-black
and pheomelanin is reddish-yellow. The num ber of melanocytes is about the same for all races, and there is about one melanocyte in every 10 keratinocytes. In
albinism , melanocytes are present but experience interference with melanin production. When exposed to sunlight, melanocytes will gradually
increase their production of melanin, peaking at about 10 days after the initial exposure. Freckles appear due to increased melanocyte activity in an area. They
occur mostly on surfaces exposed to the sun, such as the face. Hemoglobin, when oxygenated, is called oxyhem oglobin and is bright red. When
deoxy genated, it is called deoxyhem oglobin and is blue-purple. When blood vessels constrict, such as they do in response to fear, the skin turns pale and
sometimes blue. When the former happens, the condition is called pallor, or paling. When the latter happens, the condition is called cyanosis.
When blood vessels dilate, such as they do in response to em barrassment, the skin turns red. This condition is called erythema, erythematosus, or blushing.
Vitiligo is a condition in which an individual loses their skin color because their melanocytes stop producing melanin or their melano cytes die.
This condition is only cosmetic. UV radiation, while beneficial in small amounts, can cause serious damage in large dose s. Melanin protects the body by
absorbing the UV rays, and it clusters around the nuclei of epidermal cells to protect the DNA. Unfortunately, melanin cannot protect us from all
UV radiation as it is not perfect. Long periods of exposure can cause prem ature wrinkling and skin cancer even in dark-skinned individuals. A minimum of 15
SPF is recom mended in sunscreen, and for fair-skinned individuals, it is better to have a 20 -30 SPF sunscreen. Lentigos, or liver spots, are sm all
brown or black spots on the body and are com mon in older people. They contain abnormal melanocytes and are sim ilar to freckles. They usually occur on
sun-exposed skin. One of the main functions of the integumentary system is the synthesis of Vitamin D3 from a cholesterol-based steroid, which
is required for the uptake of calcium into our bones. This function is carried out by the stratum basale and stratum spinosum . A low am ount of UV radiation is
required for this process.
Hair: Hair is m ade of keratin, and hair follicles develop before birth. If the hair shaft is flat and ribbonlike in cross-section, the hair is kinky; if it is oval, the hair is silky and wavy; if it is round, the hair is straight and coarse. The three main types of body hair are term inal hair, lanugo, and vellus hair. Terminal hairs are thick, coarse hairs that gro w during puberty. Vellus
hairs are short, fine downy hairs found all over the body except for the palms of the hands and soles of the feet. It is thinner than lanugo. This is the body hair of children and adult fem ales. The lanugo coat is a coat of very fine, soft hairs often found on infants. If lanugo grows on the body of an adult, it is typically a sign of anorexia nervosa. The hair follicle folds down
from the surface of the epidermis into the dermis, and sometimes the hypodermis. The deep end of the hair follicle expands to form the hair bulb. A hair follicle receptor or root hair plexus wraps around the hair bulb of each follicle. When the hair is bent, these receptors are stimulated. A hair papilla is a small bit of dermal tissue that protrudes into the hair bulb,
containing capillaries that supply nutrients to the hair follicle. The outer wall of the hair follicle is composed of a peripheral connective tissue sheath, or fibrous sheath. In the middle is the glassy membrane, a thickened basal lamina. On the inside is the epithelial root sheath, which is composed of an external and internal part. The region of the hair bulb that
produces new hair is the hair matrix. The cells in the hair matrix originate from the hair bulge, slightly above the hair bulb. When chemical signals reach the hair bulge, cells migrate toward the papilla and begin to divide; this is how hair cells are produced. A bundle of smooth muscle called an arrector pilu s is attached to each hair follicle. When it contracts, the hair
follicle is pulled upright and the skin is dimpled, producing goosebumps. Hair grows roughly 2.5 mm every week. Each follicle goes through its own growth cycle. The active growth phase, anagen, lasts for weeks to years. Following this is the regressive phase, catagen, in which blood supply is cut off from each hair follicle for about 2 weeks. Next is the resting phase,
telogen, in which the hair follicle rests for 1 to 3 m onths. Some people consider there to be an extension of the resting phase, exogen, in which dead hairs are shed and new hairs begin to grow again. The hair follicles on the scalp have anagen phases lasting several years, while the hair follicles on the eyebrows have anagen phases lasting only three to four m onths at a
time; this explains why scalp hairs are significantly longer than the eyebrows.
Nails: Nails are made of tightly packed keratin. The nails help us grip things with our fingers. Each nail has a free edge, also known as a nail plate, as well as a proximal root. The deeper layers of the epidermis extend beneath the nail to form the nail bed. The thickened portion of the nail bed is the nail matrix, which is responsible for nail growth. As nail cells are
produced in the matrix, they are keratinized and slide distally over the nail bed. Nails are mostly pink because of the capil laries supplying the nail bed. The white crescent that lies over the nail matrix
is the lunula. The borders of the nails are overlapped by skin folds, called nail folds. The
eponychium, or cuticle, is the projection of the proximal nail fold onto the nail body. Below the free edge is the hyponychium, which is where dirt and debris accumulate.
Glands: The two main types of glands in the integumentary system are sebaceous glands, which produce oil, and sudoriferous glands, which produce sweat. There are m ore sebaceous glands and less
sudoriferous glands in thin skin. In thick skin, there are more sudoriferous glands and less sebaceous
glands. Sebaceous glands secrete sebum, an oily substance that lubricates hair and skin. Sebaceous glands are present everywhere except for areas with thick skin, i.e. the palm s of the hands and soles
of the feet. Sebaceous glands are located in the derm is layer and are generally connected to hair
follicles, except for in hairless areas such as the eyelids. Acne is caused by the inflammation of sebaceous gland ducts. Sudoriferous glands secrete sweat. Sudoriferous glands are found mostly on
areas of thick skin. There are two types of sudoriferous glands: apocrine and eccrine. Apocrine
sweat glands develop during puberty. These glands are located in the ear canal, around the eyes and nose, under the arm s, on the areola of the breasts, and in the pubic regions. Mammary glands
are one type of modified apocrine gland. Earwax, or cerumen, is secreted by ceruminous glands,
the other type of m odified apocrine gland. The appearance of cerumen can differ depending on genetic factors. Typical apocrin e glands secrete sweat. Eccrine sweat glands are found everywhere
except thick skin. Eccrine glands are present at birth and continue to secrete sweat from then on.
The sweat secretion produced by eccrine glands is m ade of water and sodium chloride.
Membranes: Serous membranes line body cavities that have no opening to the outside. They secrete a watery fluid called serous fluid that lubricates surfaces. Mucous membranes line cavities and
tubes that open to the outside. Synovial membranes form the inner lining of joint cavities. They
secretes a thick fluid called synovial fluid. The cutaneous membrane is the skin.
Homeostatic Imbalances: Burns are disorders of the integument caused by exposure to intense heat, radiation, electricity, or friction. Burn appearance and treatment varies greatly depending on how deeply the skin was burned. Burns are classified as first, second, and third-degree burns depending on the damage inflicted by the burn. The surface area affected by a burn
is calculated using the rule of nines in a typical adult. When the patient is obese, the rule of fives is used. When the patient is an infant, the rule of eights is used. First-degree burns are the most superficial. First degree burns affect the epidermis to the papillary layer of the dermis. First degree burns give the skin a dry red appearance, sometimes with small white
blisters. Second-degree burns destroy m ost or all of the epiderm is, and involve all layers of the derm is. Second-degree burns are pink or red, and cause the involved skin to look shiny and wet. The sensation in tissue with a second-degree burn is weakened. Third-degree burns involve all of the layers of the skin. Third-degree burns permanently dam age tissue. These
burns have a charred black or brown appearance. The tissue involved in a third-degree burn often m ust be replaced using skin grafting. An allergen is an antigen that produces a rapid response from the im mune system when introduced to the skin. An infection is an invasion of derm al tissue by disease-causing agents. Dermatitis is an inflammation of the skin due to a
variety of factors. Eczema refers to any condition in which the skin becomes itchy or inflamed, but it is m ost often used to refer to atopic dermatitis. This condition typically begins in infancy or childhood and the skin becomes dry, flaky, and irritated near creases in the skin. Areas include the elbows, the knees, and at the back of the neck. The disorder is likely
hereditary. Hot, cold, or dry conditions, as well as stress and certain allergens, can exacerbate eczema symptoms. Treatment involves preventing infection and soothing itching or discomfort. Contact dermatitis produces red, burning, itching, or stinging rashes in response to allergens or other topical irritants. Common causes include poison ivy or heavy metals.
Seborrheic dermatitis (known as cradle cap in infants) produces scaly patches, dandruff, and incessant itching. Psoriasis is a condition resulting in red, flaky patches on the skin. There are five primary types: plaque, guttate, inverse, pustular, and erythroderm ic. Psoriatic arthritis can also be considered a variation of this disorder. Many cases of psoriasis are hereditary,
but other risk factors include weight or obesity, sm oking, medications, infections, alcohol consum ption, vitam in D deficiency, and stress. The most comm on type of psoriasis, plaque psoriasis appears as raised, red, scaly patches on the skin. These scales have well-defined edges and are m ost often found on the outsides of knees and elbows, the scalp, the lower back, the
face, and the palm s of the hands and soles of the feet. Topical cream s and ointments with and without steroids (i.e. calcipotriene) are the m ain method of treatment for plaque psoriasis, but it can also be treated by medications or ultraviolet phototherapy. Rather than large scales, guttate psoriasis manifests as tiny lesions or teardrops on the skin. They mainly appear on
the abdomen and upper extremities, and they do not appear on the palm s or soles like other form s of the disorder. This form of psoriasis is most common in young adults or children, and less than a third of psoriasis patients have it. Dry air is a catalyst in flare ups, especially in winter. Severity is determ ined by the amount of coverage: m ild is approxim ately 3 percent,
moderate is 3 to 10 percent, and severe is more than 10 percent coverage or adversely impacts the patient's livelihood and appearance. Also known as flexural or intertriginous psoriasis, intertriginous psoriasis manifests on "flexor surfaces" or in skin folds. Common sites of inverse psoriasis include the navel, groin folds or genitalia, the lips, the ears, the axillae (armpit
region), under the breasts (inframammary folds), and between the buttocks (intergluteal cleft). Because these red patches occur in sensitive areas, patients may experience bleeding, pain, or irritation at the sites. They may also experience discomfort and fungal or bacterial infections. Many inverse psoriasis patients have another comorbid form of psoriasis. As the name
suggests, raised bumps filled with pus (pustules) accompany the telltale psoriatic scales. Pustular psoriasis is uncommon and can have acute flare ups associated with fever or manifest chronically. Other skin disorders can be considered variations of pustular psoriasis, such as pregnancy-associated impetigo herpetiformis. Erythrodermic psoriasis is described as aggressive
and is considered the most severe form of psoriasis. It involves a full body rash that can spread quickly from the initial site of inflammation. The rash peels and itches or burns intensely. Arthritis is an inflam mation of the joints, and psoriatic arthritis involves scaly rashes along with joint stiffness and pain. Sometimes joint problem s can start before the first rash appears.
Skin cancer is the m ost comm on type of cancer in the US. The three major types of skin cancer are basal cell carcinom a, squamous cell carcinoma, and melanoma. Skin cancer occurs when the DNA of epithelial cells is damaged, causing the cells to grow out of control. The m ost comm on cause of skin cancer is excessive exposure to sunlight. Basal cell carcinoma is
the most com mon type of skin cancer. It is curable if found early, especially because it rarely metastasizes (spreads to other organs). BCCs look like smooth, pearly bumps which are m ostly found on the face, neck, and back.Squamous cell carcinoma occurs on parts exposed to the sun. SCC often develops on areas with actinic keratoses, which are crusty red sores caused
by UV exposure. SCC looks like firm red bum ps susceptible to bleeding and crusting. Melanoma is deadly if not found early because it metastasizes quickly. It is m ost com mon in the southern hem isphere where the ozone layer is thin. Melanoma looks like irregular dark spots with a different appearance than a patient's moles.
ABCD Test: Asymmetry the area is not symmetrical Borders the borders are not even Color different shades and varieties can signal skin cancer Diameter if the diameter is larger than 1/4 inch or 6 mm, it is likely it is melanoma.
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