HISTOLOGY (TISSUES) & INTEGUMENTARY SYSTEM

What is a tissue?

a group of similar cells that work together to perform a specific function

what are the four main tissue types?

epithelial tissue, connective tissue, muscle tissue, nervous tissue

epithelial tissue

covers and lines

connective tissue

supports, connects, protects

muscle tissue

contracts and produces movement

nervous tissue

communicates using electrical signals

Major layers of the skin

epidermis and dermis

epidermis

outer layer, made primarily of epithelial tissue, provides protection, contains keratinocytes and melanocytes, no blood vessels

dermis

located underneath the epidermis, made primarily of connective tissue, contains: blood vessels, nerves, hair follicles, sweat glands, sebaceous glands, arrector pili muscles

hypodermis

Under the skin/below the dermis. It contains lots of adipose and areolar connective tissue

keratinocytes

most common cells in the epidermis, produce keratin, keratin helps make skin tough and waterproof, and helps protect against physical and environmental damage

melanocytes

Melanin, located primarily in the deepest part of the epidermis, absorbs UV radiation and helps protect DNA in skin cells from UV damage

Major Structures of the skin

hair, hair follicle, arrector pili muscle, sebaceous gland, sweat gland, sweat duct, blood vessels, sensory receptors/nerves

hair

made primarily of keratin, provides protection and helps with sensation

hair follicle

structure surrounding the hair root, produces and anchors hair

arrector pili muscle

tiny smooth muscle attached to hair follicles, contracts and makes hair stand up (goosebumps)

sebaceous gland

produces sebum/oil, usually empties into hair follicles, lubricates and helps protect skin and hair

sweat gland

produces sweat, important for temperature regulation, also helps remove small amounts of waste

sweat duct

carries sweat to the skin surface

blood vessels

located mainly in the dermis, deliver oxygen/nutrients and help regulate temperature

sensory receptors/nerve

detect touch, pressure, pain, and temperature

Ella’s disease in the case study

epidermolysis bullosa or butterfly disease

What is epidermolysis bullosa

a group of genetic disorders that cause the skin to be very fragile and blister easily, often from minor friction or trauma

What type of tissue does epidermolysis bullosa affect

epithelial tissue, specifically the epidermis of the skin

What cells are affected by epidermolysis bullosa

keratinocytes are involved because they make important proteins that help give the epidermis strength and structure

What type of fibers/proteins does epidermolysis bullosa affect

mutations can affect keratin proteins or proteins that help anchor the epidermis to the underlying basement membrane/dermis

why isn’t skin cancer the main selective pressure for dark skin in areas with high UV

skin cancer occurs later in life, often after people have already reached reproductive age

what is the more likely selective pressure for dark skin in areas with high UV

protection of folate

protection of folate

high UV radiation can break down folate (vitamin 89) in the body, higher melanin levels provide protection against UV radiation and help reduce folate breakdown

Why is folate important

DNA synthesis, cell division, embryonic development, reproduction

selective pressure for light skin in areas with low UV

vitamin D production

Vitamin D production

In areas with low UV radiation, having less melanin allows more UV radiation to penetrate the skin, helping the body produce vitamin D

Vitamin D is important for…

calcium absorption, bone development, normal body function

hemostasis for injury repair in the bloodstream and skin

blood vessels constrict, platelets gather at the injury, platelets form a temporary plug, clotting proteins create a stronger fibrin clot

inflammation for injury repair in the bloodstream and skin

blood vessels become more permeable, white blood cells enter the damaged area, immune cells attack pathogens and remove damaged/dead cells, the area may become red, warm, swollen, and painful

proliferative phase for injury repair in the bloodstream and skin

fibroblasts produce collagen, new blood vessels form (angiogenesis), new connective tissue develops, skin cells begin covering the wound, granulation tissues forms

remodeling for injury repair in the bloodstream and skin

collagen fibers are reorganized, excess tissue is removed, the scar becomes stronger over time the repaired tissue gradually becomes more organized