Biology Chapter 6: Integumentary System

The Integumentary System

• The integumentary system consists of skin and its accessory structures, including hair, nails, and glands.
• Functions of the skin:
  • Protection
  • Regulation of body temperature
  • Sensation
  • Excretion
  • Immune function

Epidermis

• The epidermis is the outermost layer of the skin.
• Five types of epidermal cells:
  • Stem cells: undifferentiated cells that give rise to keratinocytes.
  • Keratinocytes: majority of epidermal cells, synthesize keratin.
  • Melanocytes: produce melanin, shields DNA from ultraviolet radiation.
  • Tactile cells: touch receptor cells associated with dermal nerve fibers.
  • Dendritic cells: macrophages that guard against pathogens.

Layers of the Epidermis

• Thin skin contains four layers, while thick skin contains five.
• Stratum corneum: outermost layer, several layers of dead, scaly, keratinized cells.
• Stratum lucidum: found only in thick skin, pale layer with eleidin protein.
• Stratum granulosum: three to five layers of flat keratinocytes with keratohyalin granules.
• Stratum spinosum: several layers of keratinocytes joined by desmosomes and tight junctions.
• Stratum basale: deepest layer, single layer of stem cells and keratinocytes.

The Life History of a Keratinocyte

• Keratinocytes are produced by mitosis in the stratum basale.
• New keratinocytes push older ones towards the surface.
• Cells undergo differentiation, keratinization, and eventually die.

Dermis

• The dermis is the layer beneath the epidermis.
• Ranges in thickness from 0.2 mm to 4 mm.
• Composed mainly of collagen, well supplied with blood vessels, sweat glands, sebaceous glands, and nerve endings.
• Houses hair follicles and nail roots.
• Muscles of facial expression attach to the dermis.

Hypodermis

• The hypodermis is the subcutaneous tissue.
• Contains more areolar and adipose tissue than the dermis.
• Pads the body and binds skin to underlying tissues.
• Common site of drug injection due to many blood vessels.

Skin Color

• Dark and light-skinned individuals have the same number of melanocytes, but different types of melanin.
• Eumelanin: brown/black pigment, more prevalent in dark skin.
• Pheomelanin: red and blond pigment, more prevalent in light skin.
• UV light exposure stimulates melanin secretion and darkens skin.
• Other pigments that influence skin color:
  • Hemoglobin: adds reddish to pinkish hue.
  • Carotene: yellow pigment acquired from diet.

Hair

• Three types of hair:
  • Lanugo: fine, downy hair that appears on the fetus.
  • Vellus: fine, pale hair that replaces lanugo by birth.
  • Terminal: longer, coarser, and more heavily pigmented.
• Structure of hair:
  • Medulla: core of loosely arranged cells and air spaces.
  • Cortex: constitutes bulk of the hair, consists of several layers of elongated keratinized cells.
  • Cuticle: composed of multiple layers of very thin, scaly cells.

Nails

• Anatomy of a fingernail:
  • Nail plate: visible portion of the nail.
  • Nail fold: area of skin surrounding the nail plate.
  • Nail groove: groove on the underside of the nail plate.
  • Nail bed: area beneath the nail plate.
  • Nail matrix: area beneath the cuticle, where nail growth occurs.
• Hyponychium: area between the nail plate and the nail bed.

Glands

• Three modes of exocrine secretion:
  • Merocrine: sweat glands and pancreas.
  • Apocrine: apocrine sweat glands.
  • Holocrine: sebaceous glands.
• Types of glands:
  • Sweat glands: apocrine and eccrine.
  • Sebaceous glands: holocrine, produce sebum.
  • Ceruminous glands: apocrine, produce cerumen (earwax).
  • Mammary glands: modified apocrine glands, produce milk.

Functions of Hair

• Depends on body region and type of hair.
• Alerts us to parasites crawling on the skin.
• Hair on the scalp, trunk, and limbs provides warmth and protection.
• Eyelashes and eyebrows protect the eyes.

Skin Markings

• Colors of diagnostic value:
  • Cyanosis: blueness due to oxygen deficiency.
  • Erythema: redness due to increased blood flow.
  • Pallor: paleness due to decreased blood flow.
  • Albinism: white skin due to genetic lack of melanin.
  • Jaundice: yellowing due to bilirubin in the blood.
  • Hematoma: bruising.

Cancer and Skin

• Types of skin cancer:
  • Basal cell carcinoma: least dangerous, seldom metastasizes.
  • Squamous cell carcinoma: more aggressive, can metastasize.
  • Melanoma: most aggressive, can be fatal if not treated early.

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Please let me know if you need any further assistance.### Joints and Their Classification

• A joint is any point where two bones meet, whether or not the bones are movable at that interface.
• Joint names are typically derived from the names of the bones involved (e.g., radioulnar joint).
• Joints can be classified according to the manner in which the bones are bound to each other (structure) or the degree of movement.

Classification of Joints by Structure

• Bony joints (synostosis): immobile joint formed when the gap between two bones ossifies, and the bones become, in effect, a single bone.
• Fibrous joints: join bones using fibrous connective tissue.
  • Sutures: immobile or slightly mobile fibrous joints in which short collagen fibers bind the bones of the skull to each other.
  • Gomphoses: attachment of a tooth to its socket, held in place by a fibrous periodontal ligament.
  • Syndesmoses: fibrous joints at which two bones are bound by long collagen fibers.
• Cartilaginous joints: join bones using cartilage.
  • Synchondroses: bones joined by hyaline cartilage, temporary joints in the epiphysial plates in children.
  • Symphyses: two bones joined by fibrocartilage, allowing for slight movements.

Classification of Joints by Degree of Movement

• Synarthrosis: immobile joints.
• Amphiarthrosis: partially moveable joints.
• Diarthrosis: freely moveable joints.

Synovial Joints

• General anatomy: consisting of a joint capsule, articular cartilage, and synovial fluid.
• In a few synovial joints, fibrocartilage grows inward from the joint capsule.
• Examples of synovial joints include the temporomandibular joint, knee joint, and shoulder joint.

Lever Systems

• Long bones act as levers to enhance the speed or power of limb movements.
• Types of levers:
  • First-class lever: has the fulcrum in the middle between effort and resistance.
  • Second-class lever: has the resistance between the fulcrum and effort.
  • Third-class lever: has the effort between the resistance and the fulcrum.

Range of Motion

• Range of motion (ROM): the degrees through which a joint can move.
• An aspect of joint performance and physical assessment of a patient's joint flexibility.

Axes of Rotation

• A moving bone has a relatively stationary axis of rotation that passes through the bone in a direction perpendicular to the plane of movement.
• Multiaxial joint: has three degrees of freedom or axes of rotation.

Muscular System

• Muscles are classified as skeletal, cardiac, or smooth.
• Skeletal muscles are voluntary, striated, and under conscious control.
• Functions of muscles:
  • Movement
  • Stability
  • Control of openings and passageways
  • Heat production
  • Glucose storage

Muscle Compartment

• Intermuscular septa: thick fascia that separate one compartment from another.
• Muscle compartment contains nerves, blood vessels, and stretch receptors.

Fascia

• Fibrous connective tissue that is found below the skin.
• Classified as superficial, deep, visceral, or parietal.

Strength of a Muscle

• Determined partly by the orientation of its fascicles.
• Muscles come in different shapes, such as pennate, circular, and parallel.

Types of Muscle Arrangements

• Pennate: feather-shaped, with fascicles approaching the tendon from one side.
• Unipennate: fascicles approaching the tendon from both sides.
• Bipennate: fascicles approaching the tendon from one side and then dividing into two parts.
• Multipennate: bunches of feathers converging to a single point.

Muscle Attachment

• Direct manner: muscle attaches to bone directly.
• Indirect manner: muscle attaches to bone using a tendon or aponeurosis.

Muscle Movement

• Muscles work in antagonistic pairs to produce movement.
• Agonist: the muscle that provides the major force to complete the movement.
• Antagonist: the muscle that opposes the action of the prime mover.

Characteristics of Muscle

• Excitability: ability to respond to a stimulus.
• Contractility: ability to shorten when stimulated.
• Conductivity: ability to transmit electrical signals.
• Extensibility: ability to be stretched.
• Elasticity: ability to return to its original rest length after being stretched.

Muscle Fiber

• Multinucleated: formed from the fusion of embryonic myoblasts.
• Has a sarcolemma, sarcoplasm, and myofibrils.
• Myofibrils are composed of contractile proteins, such as actin and myosin.

Neuromuscular Junction

• Site where a motor neuron terminates and forms a synapse with a muscle fiber.
• Responsible for transmitting electrical signals from the neuron to the muscle fiber.### Muscle Striations and Their Molecular Basis
• Muscle striations result from the precise organization of myosin and actin in cardiac and skeletal muscle cells
• Striations are alternating A-bands (dark) and I-bands (light)

Sarcomere Structure

• A sarcomere is the functional contractile unit of a muscle fiber
• It is the segment from one Z disc to the next Z disc
• Contains thick filaments (myosin) and thin filaments (actin)

Thick Filaments (Myosin)

• Have a double globular head with a shaft-like tail
• Each head has an active site that can bind to actin subunits
• Have a bare zone with no heads in the middle

Thin Filaments (Actin)

• Consist of two intertwined strands (F-actin)
• Have tropomyosin molecules that block 6-7 active sites on each actin subunit
• Ca-binding protein on each tropomyosin molecule

Titin (Elastic Filament)

• A giant, springy protein that interconnects thick filaments with the Z-line
• Helps stabilize and position thick filaments, preventing overstretching and providing recoil

Muscle Diseases

• Muscular dystrophy: a number of diseases that cause progressive loss of muscle mass, resulting in weakness and sometimes loss of mobility
• Genetic defects in dystrophin produce disabling disease muscular dystrophy

Muscle Functions

• Different muscle groups have specific functions, such as blinking, closing lips, elevating the mandible, flexing the forearm, and rotating the arm

Muscle Terminology

• Study aid to help with learning muscle names
• Includes muscles such as orbicularis oculi, obicularis oris, masseter, sternocleidomastoid, temporalis, and many others