Difficulty: Introductory to Intermediate | Prerequisites: Chapter 4 (tissue types, especially epithelial and connective tissue)
Chapter 5 covers the skin, the body's largest organ, and the structures embedded in it (hair, nails, glands). Chapter 6 moves to bone tissue itself: how it is classified, how compact and trabecular bone differ at the microscopic level, and the anatomy of a long bone. Chapters 7 and 8 are the identification chapters, requiring you to know the names and locations of every bone in the axial and appendicular skeleton. If your tissue foundations from Chapter 4 are shaky, review epithelial and connective tissue types first, because both chapters lean on them heavily.
Skin is an organ made of two true layers (epidermis and dermis) sitting on a hypodermis that is technically not part of the skin. Bones are classified by shape, built from either compact or trabecular bone, and wrapped in periosteum on the outside and endosteum on the inside. You need to know every bone of the body by name and general location for Chapters 7-8.
Epidermis
The outermost layer of the skin. Composed of keratinised stratified squamous epithelium. Avascular (no blood supply of its own).
Dermis
The layer beneath the epidermis. Composed mostly of dense connective tissue. This is where blood vessels, nerve endings, hair follicles, and glands reside. It is vascularised.
Hypodermis (subcutaneous layer)
The layer deep to the dermis, composed mainly of adipose tissue (fat). It is not technically part of the skin, though it anchors the skin to underlying structures.
Keratinocytes
The dominant cell type of the epidermis. They produce keratin, a tough protective protein. Hair and nails are also composed of keratinised cells (dead keratinocytes).
Sebaceous glands
Oil-producing glands usually associated with hair follicles. They secrete sebum, which lubricates the skin and hair.
Sudoriferous (sweat) glands
Glands that produce sweat. Eccrine glands are found over most of the body and produce watery sweat for thermoregulation. Apocrine glands are found mainly in the axillae and groin and produce a thicker secretion.
Compact bone
Dense, solid-looking bone tissue found on the outer surfaces of bones. Organised into osteons (Haversian systems), with concentric lamellae surrounding a central canal.
Trabecular (spongy/cancellous) bone
Bone tissue with an open, lattice-like structure. Found in the interior of bones, especially in the epiphyses of long bones. Contains red bone marrow in its spaces.
Periosteum
A tough, fibrous membrane covering the outer surface of a bone (everywhere except joint surfaces). Serves as an attachment point for tendons and ligaments and supplies blood to the bone's surface.
Endosteum
A thin membrane lining the internal surfaces of bone, including the medullary cavity and the trabeculae of spongy bone.
Epiphyseal plate
A disc of hyaline cartilage at the ends of long bones in growing individuals. The site of longitudinal bone growth. In simple terms, this is the "growth plate."
Epiphyseal line
The remnant of the epiphyseal plate after growth has ceased. A thin line of bone marking where the plate once was. Its presence indicates the bone has stopped growing in length.
Diaphysis
The shaft (long central portion) of a long bone. Composed primarily of compact bone surrounding the medullary cavity.
Epiphysis
The expanded ends of a long bone. Composed of a thin shell of compact bone over trabecular bone. The articular surfaces are covered in hyaline cartilage, not periosteum.
Medullary cavity
The hollow interior of the diaphysis. In adults, it contains yellow bone marrow (fat storage).
Why skin is considered an organ
It is composed of multiple tissue types (epithelial, connective, nervous, muscle) working together
An organ is defined as a structure made of two or more tissue types that performs a specific function; skin meets that definition
Layers of the skin
Epidermis (superficial): keratinised stratified squamous epithelium, avascular
Dermis (deep): mostly dense irregular connective tissue, vascularised
Hypodermis is deep to the dermis but is not part of the skin itself; composed of areolar and adipose connective tissue
Tissue associations
Epidermis: epithelial tissue
Dermis: connective tissue (with nerve endings, blood vessels, glands)
Hypodermis: connective tissue (primarily adipose)
Vascularisation
The dermis is vascularised. The epidermis is avascular.
The hypodermis is also vascularised, but again, it is not part of the skin proper.
Hair and nails
Both are made of dead, keratinised cells (hard keratin)
Hair anatomy: the hair shaft projects above the skin surface; the hair root is embedded in the follicle; the hair bulb at the base contains the matrix (growth zone); the arrector pili muscle is a tiny smooth muscle attached to each follicle that causes "goosebumps"
Glands
Sebaceous glands: secrete sebum (oily substance) into hair follicles; lubricate skin and hair
Eccrine sweat glands: most numerous, found nearly everywhere on the body, open onto the skin surface via pores, primary role is thermoregulation
Apocrine sweat glands: found in axillary (armpit) and anogenital regions, open into hair follicles, become active at puberty
Organs of the skeletal system
Bones, cartilage, ligaments, and other connective tissues that stabilise or connect bones
Classification of bones by shape
Long bones: longer than they are wide (e.g. femur, humerus)
Short bones: roughly cube-shaped (e.g. carpals, tarsals)
Flat bones: thin, flattened, often curved (e.g. sternum, skull bones, scapula)
Irregular bones: complex shapes that do not fit other categories (e.g. vertebrae, hip bones)
Sesamoid bones: small, round bones embedded in tendons (e.g. patella)
Compact versus trabecular bone
Compact bone: dense, found on external surfaces; microscopic structure features osteons (concentric rings of lamellae around a central Haversian canal carrying blood vessels and nerves); provides strength and rigidity
Trabecular bone: open lattice of bony struts (trabeculae); found internally, especially in epiphyses; spaces filled with bone marrow; lighter than compact bone, resists stress from many directions
Gross anatomy of a long bone
Diaphysis (shaft): thick collar of compact bone, medullary cavity inside
Epiphyses (ends): thin shell of compact bone, interior of trabecular bone; articular surfaces coated with hyaline cartilage
Metaphysis: the region between the diaphysis and each epiphysis; location of the epiphyseal plate or line
Periosteum wraps the outside of the diaphysis and metaphysis (not the articular surfaces)
Endosteum lines the medullary cavity and internal bone surfaces
Periosteum versus endosteum
Periosteum: outer covering, fibrous and vascular, anchors tendons/ligaments, involved in appositional (width) growth and fracture repair
Endosteum: inner lining, thinner, lines the medullary cavity and trabeculae, active during bone remodelling and repair
Epiphyseal plate versus line
Plate: present in children and adolescents, made of hyaline cartilage, responsible for bone lengthening
Line: present in adults, the plate has been replaced by bone, growth in length is complete
What you need to know
Names and locations of all bones of the body (axial skeleton: skull, vertebral column, thoracic cage; appendicular skeleton: pectoral girdle, upper limbs, pelvic girdle, lower limbs)
Major bony landmarks are useful for the exam; while you do not need every marking from lab, familiarity with landmarks such as the medial malleolus, lateral malleolus, olecranon process, acromion, and greater trochanter is expected
The best way to study this material is with labelled diagrams, models, or flashcards. Rote memorisation is unavoidable here.
Axial skeleton highlights
Skull: frontal, parietal (2), temporal (2), occipital, sphenoid, ethmoid, plus facial bones (maxilla, mandible, zygomatic, nasal, lacrimal, palatine, vomer, inferior nasal conchae)
Vertebral column: 7 cervical, 12 thoracic, 5 lumbar, sacrum (5 fused), coccyx (3-5 fused)
Thoracic cage: sternum (manubrium, body, xiphoid process), 12 pairs of ribs
Appendicular skeleton highlights
Pectoral girdle: clavicle and scapula on each side
Upper limb: humerus, radius, ulna, carpals (8), metacarpals (5), phalanges (14)
Pelvic girdle: each hip bone (os coxae) composed of the fused ilium, ischium, and pubis
Lower limb: femur, patella, tibia, fibula, tarsals (7), metatarsals (5), phalanges (14)
Students often think the hypodermis is a layer of skin. It is not. The skin has two layers: epidermis and dermis. The hypodermis lies beneath the skin.
"Spongy bone" does not mean the bone is soft or weak. Trabecular bone is strong, lightweight, and resists multidirectional stress; the name refers to its appearance, not its structural quality.
The epiphyseal plate and the epiphyseal line are not the same thing. The plate is active cartilage in a growing bone; the line is the bony remnant after growth stops.
Students sometimes assume the periosteum covers the entire bone. It does not cover articular surfaces (the joint ends), which are covered by hyaline cartilage instead.
⚠️ Know which layers are vascularised (dermis, hypodermis) versus avascular (epidermis). This is a frequently tested distinction.
⚠️ Be able to associate each skin layer with its tissue type: epidermis = epithelial, dermis = connective, hypodermis = connective (adipose).
⚠️ Compact versus trabecular bone: know both the microscopic differences (osteons vs. trabeculae) and where each is found in a long bone.
⚠️ Periosteum versus endosteum is a common comparison question. Remember: periosteum = outside, endosteum = inside.
⚠️ Chapters 7-8 are heavily identification-based. Practise with diagrams until you can label bones from memory.
True or false: The hypodermis is part of the skin.
Fill in the blank: Hair and nails are composed of dead __________ cells.
True or false: Compact bone is found primarily in the interior of the epiphyses.
Fill in the blank: The __________ lines the medullary cavity and internal surfaces of bone.
True or false: An epiphyseal line indicates the bone is still growing.
Answers: 1. False. 2. Keratinised (or keratinocyte). 3. False (that describes trabecular bone; compact bone is on the outer surface). 4. Endosteum. 5. False (the line means growth has stopped; the plate indicates active growth).
Q: Why is skin classified as an organ rather than just a tissue?
A: Skin contains multiple tissue types (epithelial, connective, nervous, and small amounts of muscle tissue) working together, which meets the definition of an organ.
Q: Which parts of the integumentary system receive a blood supply?
A: The dermis and the hypodermis are vascularised. The epidermis is avascular and receives nutrients by diffusion from the dermis.
Q: Compare compact and trabecular bone in terms of structure and location.
A: Compact bone is dense, organised into osteons, and found on the outer surfaces of bones (especially the diaphysis of long bones). Trabecular bone has an open lattice of trabeculae, is found in the interior of bones (especially the epiphyses), and contains bone marrow in its spaces.
Q: Distinguish between periosteum and endosteum.
A: The periosteum is a fibrous membrane on the outer surface of bone (excluding articular surfaces); it anchors tendons and ligaments and is involved in appositional growth. The endosteum is a thinner membrane lining internal bone surfaces, including the medullary cavity.
Q: What is the difference between an epiphyseal plate and an epiphyseal line?
A: The epiphyseal plate is a disc of hyaline cartilage where bone growth in length occurs; it is present in children and adolescents. The epiphyseal line is the bony remnant left after the plate ossifies, indicating that longitudinal growth is complete.
The keratinised stratified squamous epithelium of the epidermis (Ch. 5) connects directly to the epithelial tissue types covered in Chapter 4. Understanding tissue classification makes skin histology much easier.
Bone landmarks from Chapters 7-8 are the attachment points for muscles in Chapters 10-11 and the contact surfaces for joints in Chapter 9.
The concept of vascularisation in the integumentary system (Ch. 5) foreshadows the distinction between arteries, veins, and capillaries in Chapter 20.
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