Anatomy: Skin and Integumentary System

Chapter 6: Skin and the Integumentary System

• The skin is the largest organ, making up approximately 15% of body weight.
• The skin consists of the epidermis, dermis, and hypodermis.
• Hair follicles produce hair for UV protection and heat trapping.
• Sebaceous glands secrete sebum to moisturize skin and hair.
• Sweat glands regulate temperature by cooling the body.
• Nails protect fingertips and enhance grip.
• Sensory receptors detect touch, pressure, temperature, and pain.

Structure of the Skin

• The epidermis is the outer layer and lacks a blood supply.
• The epidermis is made up of stratified squamous epithelium.
• The layers of the epidermis from deep to superficial are stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum, remembered by the mnemonic "Come Let’s Get Sun Burned".
• The stratum basale undergoes mitosis and includes melanocytes and Merkel cells.
• The stratum spinosum is the thickest layer, with desmosomes holding cells together.
• The stratum granulosum produces keratohyalin, a precursor to keratin.
• The stratum lucidum is found only in thick skin (palms, soles).
• The stratum corneum consists of dead, keratinized cells forming a waterproof barrier.
• The dermis is the middle layer, known as "true skin," and has a blood supply.
• The papillary layer of the dermis contains dermal papillae (fingerprints) and loose connective tissue.
• The reticular layer of the dermis is made of dense connective tissue, providing strength and elasticity.
• The hypodermis is the subcutaneous layer, not technically part of the skin.
• The hypodermis is composed of adipose tissue for fat storage, insulation, and cushioning.
• Major blood vessels supplying the skin are located in the hypodermis.

Functions of the Skin

• The functions of the skin can be remembered using the mnemonic PSTEV "pastive".
• Protection: Serves as a barrier against bacteria, UV radiation, and water loss.
• Sensation: Detects pain, touch, temperature, and pressure.
• Temperature Regulation: Controls heat loss through sweat and blood flow.
• Excretion: Removes urea, salts, and excess water through sweat.
• Vitamin D Synthesis: UV rays trigger Vitamin D production, aiding calcium absorption.

Body Temperature Regulation

• In response to heat, vasodilation (blood vessels widen) and sweating occur to promote heat loss.
• In response to cold, vasoconstriction (blood vessels constrict), shivering, and goosebumps occur to promote heat retention.

Factors Determining Skin Color

• Melanin, hemoglobin, and carotene determine skin color.
• Melanin is produced by melanocytes in the stratum basale.
• More melanin results in darker skin.
• Eumelanin produces black/brown pigment, while pheomelanin produces yellow/red pigment.
• Hemoglobin is a red pigment from blood.
• Carotene is a yellow-orange pigment from diet.
• Differences in skin tone are due to genetics and UV exposure influencing melanin production.
• More active melanocytes indicate darker skin, while less active melanocytes indicate lighter skin.

Epidermis vs. Dermis

• The epidermis is made of stratified squamous epithelium and lacks a blood supply, while the dermis is made of dense connective tissue and has a blood supply.
• The epidermis is thin (except in thick skin areas), while the dermis is thick.

Merocrine vs. Apocrine Sweat Glands

• Merocrine (eccrine) glands are located all over the body, especially on palms and soles, and function in cooling.
• Apocrine glands are located in armpits and the groin of the body and function in emotional sweating.
• Merocrine glands secrete a watery, odorless substance, while apocrine glands secrete a milky, odor-causing substance.

Healing of Skin Injuries

• In shallow cuts, cells divide and fill the gap.
• In deep wounds, a blood clot forms then inflammation occurs, fibroblasts then lay down collagen, and finally scar tissue forms.

Chapter 7: The Skeletal System

• Bone development occurs through intramembranous and endochondral ossification.

Bone Development

• Intramembranous ossification forms flat bones directly from mesenchyme without a cartilage model (e.g., skull, clavicle).
• Endochondral ossification forms long bones, starting as cartilage that turns into bone (e.g., femur, humerus, tibia).

Structure of a Long Bone

• "People Don’t Make Pretty Artistic Cakes & Snacks" is a mnemonic for remembering key parts of the long bone.
• Proximal epiphysis is the top end of the long bone.
• Distal epiphysis is the bottom end of the long bone.
• The medullary cavity is hollow and contains bone marrow.
• The periosteum is the outer protective covering of the long bone.
• Articular cartilage covers joint surfaces.
• Compact bone is the dense, strong outer layer.
• Spongy bone is porous and houses marrow.

Bone Cells

• Osteoblasts build bone and deposit minerals.
• Osteocytes maintain bone structure.
• Osteoclasts break down bone and release calcium.

Factors Affecting Bone Growth

• Sunlight increases Vitamin D levels and leads to better calcium absorption.
• Nutrition: Calcium, phosphorus, and Vitamin D are needed.
• Hormones: Growth hormone and sex hormones regulate bone density.
• Exercise: Wolff’s Law states that bone strengthens with use.

Regulation of Blood Calcium Levels

• Calcitonin (from the thyroid gland) lowers blood calcium levels by stimulating osteoblasts to build bone.
• Parathyroid hormone (PTH) raises blood calcium levels by stimulating osteoclasts to break down bone.

Axial vs. Appendicular Skeleton

• The axial skeleton includes the skull, vertebrae, ribs, and sternum.
• The appendicular skeleton includes the arms, legs, pelvis, and shoulder girdle.

Major Features of the Vertebral Column

• "Can The Lads Sing Christmas Carols?" is a mnemonic for remembering the parts of the vertebral column.
• Cervical (7 vertebrae) are in the neck.
• Thoracic (12 vertebrae) have rib attachments.
• Lumbar (5 vertebrae) are in the lower back.
• Sacrum (5 fused vertebrae) attaches to the pelvis.
• Coccyx (4 fused vertebrae) is the tailbone.

True vs. False Ribs

• True ribs (1-7) attach directly to the sternum.
• False ribs (8-12) have indirect or no attachment to the sternum.