Exam 2 Study Guide

These four chapters are the body's cover and its frame. You start with the skin, which is the largest organ you have. Then you learn bone as living tissue that rebuilds itself and banks your calcium. Then you name the eighty bones along the midline. Then you name the hundred and twenty-six that let you reach and walk. This set rewards counting and ordering more than any other. Say each list out loud, write it from memory, then check it. The cram sheet at the end holds every count and value in one place.

Chapter 5The Integumentary System

What to know

The integumentary system is the skin plus everything that grows out of it. That means hair, nails and glands. The skin is the largest organ in the body, both by weight and by surface area. Spread flat it would cover about two square meters.

Read the skin from the top down and you pass three named layers. The epidermis is epithelium with no blood vessels. The dermis is connective tissue, and it holds the vessels, nerves, follicles and glands. The hypodermis below is fat and loose tissue, and it is not skin at all.

The dermis has two parts. The thin papillary layer sits on top, and its bumps make your fingerprints. The thick reticular layer below holds most of the collagen.

Thick skin covers the palms and the soles. It has all five layers of epidermis. Thin skin covers the rest, has four layers, and is the only skin that grows hair. Those names describe the epidermis only.

The main cell of the epidermis is the keratinocyte. It is born at the bottom, fills with keratin as it is pushed up, dies, and flakes off the top. The whole trip takes about four weeks, or roughly 25 to 45 days. That slow climb is keratinization.

Three pigments mix to give skin color. Melanin is the main one. Carotene is a yellow-orange pigment from food. Hemoglobin is the red pigment in blood. Melanocytes make melanin in the stratum basale, then hand it off in small sacs to the keratinocytes around them. Inside a keratinocyte the melanin caps the nucleus and soaks up ultraviolet light before it can harm DNA. Everyone has about the same number of melanocytes. Color differences come from the amount and type of melanin.

Hair, nails and glands are the accessory structures. They grow from the epidermis but sit down in the dermis, where the blood supply is. Hair is dead keratin, and only the matrix at its base is alive. Nails grow from the nail matrix under the pale half-moon.

The skin does five jobs: protection, thermoregulation, sensation, making vitamin D, and excretion with storage. Protection works three ways at once. Keratin is the physical barrier. The slightly acidic acid mantle is the chemical barrier. Immune dendritic cells are the biological barrier.

Burns are graded by depth first. A deep burn may not hurt at all, because the nerves are gone. The two big dangers of a serious burn are fluid loss and infection. Skin cancer is the most common cancer of all, and its leading cause is years of ultraviolet exposure.

Worth memorizing

The five strata are the single most tested list in this chapter. Read them from the base up and use the sentence "Bad Students Get Lousy Classes."

Check a suspicious mole with the ABCDE letters. A is asymmetry, so one half does not match the other. B is border, so the edges are ragged or blurred. C is color, so the shade is uneven. D is diameter, so it is wider than about 6 mm, the size of a pencil eraser. E is evolving, so it changes in size, shape or color over time.

How to reason through it

Chapter 6Bone Tissue & the Skeletal System

What to know

Bone is living tissue. Every bone is an organ built from several tissue types, and a fresh bone bleeds when it snaps. The skeletal system is all the bones, cartilages and joints together.

The skeleton does five jobs: support, protection, movement, storing minerals and fat, and making blood cells. That last one is hematopoiesis, and it happens in red marrow. About 99% of the body's calcium is stored in bone.

An adult has 206 bones. The axial skeleton has about 80 and runs down the midline. The appendicular skeleton has about 126 and hangs off that line.

Bones come in five shape classes, and the shape is a clue to the job. The label "long" is about proportion, not size, so the small finger bones count as long bones.

A long bone has a shaft called the diaphysis, which is compact bone around a hollow medullary cavity. Each wide end is an epiphysis, filled with spongy bone and red marrow, and capped with articular cartilage. Between them is the metaphysis, which holds the growth plate in a child and a thin growth line in an adult.

Two thin layers keep a bone alive. The periosteum wraps the outside and carries vessels, nerves and bone-making cells. The endosteum lines the marrow cavity and the spaces in spongy bone.

Under a microscope, compact bone is a bundle of tiny weight-bearing pillars called osteons. Each osteon is rings of matrix, the lamellae, around a central canal holding a vessel and a nerve. Osteocytes sit in small pockets called lacunae, linked by hair-thin canaliculi.

Bone matrix mixes two opposite qualities. Collagen gives it the strength to resist being pulled, so bone bends a little instead of snapping. Hydroxyapatite crystals of calcium and phosphate give it the strength to resist being squeezed. Take the mineral away and bone turns rubbery. Take the collagen away and it turns brittle like chalk.

Four cells run the crew. Remodeling is the lifelong tug-of-war between them, and it replaces about 10% of the skeleton every year. Load tunes it, which is Wolff's law, and hormones tune it too. If breakdown wins for years, the result is osteoporosis.

Blood calcium must stay near 9 to 10 mg/dL, because muscles, nerves and clotting all depend on it. Two hormones work as a push-pull pair. Parathyroid hormone raises calcium. Calcitonin lowers it.

A fracture is a broken bone, and the first question is whether the skin stayed whole. A closed break leaves the skin unbroken. An open break goes through the skin and risks infection. Healing runs in four stages and can take months.

Worth memorizing

Low calcium makes nerves jumpy, which causes the muscle spasms called tetany. High calcium makes nerves and muscles sluggish.

Treatment has two steps. Reduction lines the ends back up, either from the outside or by surgery. Immobilization holds the bone still in a cast or with metal hardware, which keeps the fragile callus safe.

How to reason through it

Chapter 7The Axial Skeleton

What to know

The axial skeleton is the 80 bones on the body's center line. Its job is protection and support. The appendicular skeleton is the 126 bones of the limbs and girdles, and its job is movement. A quick test works well. If a bone sits on the midline or wraps an organ, it is axial. If it helps you reach, walk or grip, it is appendicular.

The 80 axial bones fall into three groups, and each group matches the organ it guards. The skull wraps the brain. The vertebrae wrap the spinal cord. The rib cage wraps the heart and lungs.

The skull has 22 bones, split into 8 cranial and 14 facial. Four cranial bones are single and sit on the midline. Two come in pairs. The occipital bone carries a large hole, the foramen magnum, where the spinal cord leaves the skull. The sphenoid spans the floor of the skull and locks the others together like the keystone of an arch. The mandible is the only skull bone that moves freely.

Cranial bones meet at jagged seams called sutures, and sutures cannot move. In a newborn these seams are still open, and the gaps are the fontanelles, or soft spots. Some skull bones hold air pockets, the paranasal sinuses, which make the skull lighter and help the voice carry.

The backbone is a stack of 26 bones in five regions. Remember 7, then 12, then 5, like breakfast at 7, lunch at 12 and dinner at 5. A child starts with 33 separate vertebrae. Five fuse into the sacrum and four into the coccyx, so the adult total is 26. The bones get larger as you go down, because each one carries the weight of everything above it.

From the second neck bone down, a pad called an intervertebral disc sits between each pair. It has a tough outer ring and a soft, jelly-like center. Think of a jelly donut, and there are 23 of them. The discs soften every step and let the spine bend. When the soft center pushes out through a weak spot, the result is a herniated disc, which can press a spinal nerve and send pain down an arm or a leg.

Every vertebra shares one plan. The body in front carries weight. The arch behind shields the cord. Seven processes stick out as handles and joints.

The rib cage is the three-part sternum plus 12 pairs of ribs. The sternal angle, where the top piece meets the middle, lines up with the second rib, so it is the landmark for counting ribs. The cage is not a box. It lifts out with each breath and drops back down.

Seen from the side, a healthy spine makes a gentle S with four curves. Two are there at birth and two form later. The curves balance your weight over your hips and act like a spring.

Worth memorizing

Four sutures are worth naming. The coronal suture runs between the frontal and the parietal bones. The sagittal suture runs front to back between the two parietal bones. The lambdoid suture runs between the parietal bones and the occipital bone. The squamous suture runs along the top of each temporal bone.

The atlas holds up the skull and lets your head nod yes. The axis has a peg pointing up and lets your head turn to say no.

Pairs 8 through 12 are all false ribs, because none of them reaches the sternum directly. The last two pairs are also called floating, because they have no front attachment at all. The sternum itself has three parts. The wide manubrium sits on top and joins the collarbones. The long body forms the middle. The small xiphoid process is the pointed tip, and it starts out as cartilage.

Three problem curves have names. Kyphosis is a thoracic curve that is too deep, so the upper back looks hunched. It is common in older adults with osteoporosis. Lordosis is a lumbar curve that is too deep, so the lower back sways inward too much. Scoliosis is different from both, because it is a sideways curve. Seen from behind, the spine bends into a C or an S.

How to reason through it

Chapter 8The Appendicular Skeleton

What to know

The appendicular skeleton has 126 bones. These are the two limb girdles plus the arms and legs that hang from them. Almost every one is a lever built for movement. One theme runs through the whole chapter. The shoulder is built for freedom and the hip is built for strength.

The pectoral girdle is the shoulder girdle, and it has only two bones on each side. The clavicle sits in front and the scapula sits in back. The whole arm hangs from the axial skeleton at one small joint, the sternoclavicular joint. The scapula has no bony link to the ribs or spine at all, so only muscles hold it on. That loose setup trades steadiness for a huge range of motion, and the price is that the shoulder dislocates easily.

The clavicle is an S-shaped brace that holds the shoulder out from the chest. It is thin and sits right under the skin, so it is the bone broken most often in the body, usually in its middle third. The scapula is a flat triangle covered with landmarks. The one that matters most is the glenoid cavity, a shallow socket that holds the head of the arm bone. Picture a ball resting on a saucer instead of sitting in a cup.

Each upper limb has 30 bones, and three long ones do the heavy work. The humerus is the upper arm. The radius and the ulna are the forearm. Read them from the anatomical position, with palms forward. Then the radius is on the thumb side and the ulna is on the little-finger side.

The ulna leads at the elbow, where its olecranon makes the bony point. The radius leads at the wrist, and it is the bone that turns. Turning the palm up is supination. Turning it down is pronation, and then the radius crosses over the ulna.

The hand has 27 bones in three groups: 8 carpals, 5 metacarpals and 14 phalanges. The thumb's own metacarpal meets a carpal at a saddle joint, which lets the thumb swing across the palm and touch the other fingers.

The pelvic girdle is built for the opposite of the shoulder. Its jobs are strength and bearing weight. It attaches firmly at the sacroiliac joints, which barely move. Each hip bone starts as three separate bones that fuse during adolescence, and they meet at a deep socket called the acetabulum. That deep socket grips the thigh bone firmly, so the hip almost never dislocates.

The pelvis is the part of the skeleton that differs most clearly between males and females, because the female pelvis is shaped to let a baby pass through.

Each lower limb also has 30 bones, and four big ones hold it up. The femur is the longest, heaviest and strongest bone in the body. The patella is the largest sesamoid bone. In the leg, unlike the forearm, the two bones do not share the load. The tibia carries almost all the weight and is the only one that reaches the knee. The fibula carries almost none and mainly steadies the ankle.

The foot has 26 bones in the same three-group plan: 7 tarsals, 5 metatarsals and 14 phalanges. What sets it apart from the hand is its three arches, which make it a natural spring and shock absorber.

Worth memorizing

Account for all 126 bones before you learn anything else. There are four divisions.

1. Pectoral girdles — clavicle and scapula on each side, so 4 bones.
2. Upper limbs — 30 bones each, so 60.
3. Pelvic girdle — one hip bone on each side, so 2 bones.
4. Lower limbs — 30 bones each, so 60.

Three landmarks on the humerus are worth naming. The surgical neck sits just below the head and breaks often, close to a nerve. The deltoid tuberosity is a rough bump where the deltoid muscle attaches. At the elbow, the capitulum meets the radius and the pulley-shaped trochlea grips the ulna. The ulnar nerve runs in a groove behind the inner epicondyle with no muscle to cover it, which is why bumping that spot sends a jolt down your forearm.

Learn the eight carpals in order with the sentence "Sally Left The Party To Take Cathy Home." Start on the thumb side of the row nearest the forearm, then move to the row nearest the fingers. That gives scaphoid, lunate, triquetrum, pisiform, then trapezium, trapezoid, capitate, hamate. The scaphoid deserves extra care. Its blood supply enters from only one end, so a break can cut off blood and part of the bone can die.

Each hip bone has three named parts. The ilium is the large fan-shaped upper part, and its rim is the crest where you rest your hands. The ischium is the lower back part, and its rough tuberosity is the bone you sit on. The pubis is the front part, and the two pubic bones meet at the pubic symphysis.

The foot's three arches are the medial longitudinal arch along the inside, the lateral longitudinal arch along the outside, and the transverse arch across the foot. They flatten a little to soak up each step, then spring back to push you off. When they drop, the result is flat feet, and the legs tire because the shock absorber is gone.

How to reason through it

One pageCram sheet