The integument is derived from:

Correct Answer: B

Rationale: During embryonic development, the integumentary system, which includes the skin and its derivatives like hair and nails, originates from specific germ layers. The epidermis, the outermost layer of skin, arises from the ectoderm, which is the outermost embryonic layer responsible for forming external structures. The dermis, the underlying layer of skin, develops from the mesoderm, the middle germ layer that gives rise to connective tissues, muscles, and blood vessels. The endoderm, which forms internal structures like the digestive tract, does not contribute to the integument. Therefore, the correct developmental origin involves only the ectoderm and mesoderm. This dual origin explains the skin's diverse functions: the ectoderm-derived epidermis provides a protective barrier, while the mesoderm-derived dermis supports it with blood vessels, nerves, and connective tissue. Misincluding the endoderm or excluding one of the correct layers would misrepresent the embryological process, making the combination of ectoderm and mesoderm the accurate description of integumentary development.

Correct Answer: C

Rationale: Alopecia, or hair loss, has multiple potential causes, but one predominates. Protein deficiencies can weaken hair, as keratin requires amino acids, but this is rare in well-nourished populations and not the leading cause. Dermal viral infections might cause localized hair loss (e.g., fungal infections like ringworm), but they are not primary alopecia triggers. Stress can induce temporary hair loss (telogen effluvium), where hair follicles enter a resting phase, but it's reversible and less common as a chronic cause. Genetic inheritance, particularly androgenetic alopecia (male or female pattern baldness), is the most probable and widespread cause, affecting millions globally. Driven by hormones (androgens) and genetics, it leads to progressive follicle miniaturization. Studies show its prevalence up to 50% of men and 25% of women by age 50 outstrips other causes. Its permanence and familial patterns distinguish it as the dominant etiology, aligning with clinical observations and epidemiological data.

Correct Answer: C

Rationale: The arrector pili are small muscles attached to hair follicles, controlled by the sympathetic nervous system. When stimulated (e.g., by cold or fear), they contract, pulling the hair upright and causing the skin to pucker, resulting in goose bumps (piloerection). They are not glands, so they don't secrete anything like sebum (which comes from sebaceous glands) or sweat (from sweat glands). Excessive sweating is linked to eccrine glands, not arrector pili. Their role in creating goose bumps is a well-known physiological response to sympathetic activation, conserved from animals raising fur for warmth or defense, making this the correct function.

Correct Answer: A

Rationale: The stratum corneum, the outermost epidermal layer, is composed of dead, keratinized cells that form a waterproof barrier, preventing water loss and keeping the body from drying out. The stratum basale generates new cells but doesn't block water loss. The stratum spinosum provides strength, not a moisture barrier. The stratum granulosum begins keratinization, but the corneum completes it, acting as the skin's primary shield against dehydration. This layer's lipid-rich, tough structure is why humans don't shrivel like the fish, making it the key protective layer.

Correct Answer: C

Rationale: Adipose tissue, a type of connective tissue rich in fat cells, is found in the hypodermis, the deepest layer of the integumentary system. The hypodermis, also called the subcutaneous layer, lies beneath the dermis and serves as an energy reserve, insulator, and cushion for underlying structures like muscles and bones. The dermis, above the hypodermis, contains dense connective tissue with collagen and elastic fibers, blood vessels, and glands, but not significant adipose tissue. The epidermis, the outermost layer, is composed of stratified squamous epithelium, a keratinized tissue focused on protection, not fat storage. 'Stratified Squamous' as an option likely refers to the epidermis's tissue type, not a distinct layer, and lacks adipose tissue. The hypodermis's fat content varies by body region and individual, but its role in lipid storage is consistent, distinguishing it from the dermis's structural support and the epidermis's barrier function. This anatomical arrangement ensures the skin's protective and metabolic roles are compartmentalized effectively.