Lecture 3: Tissues and Integument

Epithelial tissue function

Covers body surfaces, lines body cavities and organs, forms glands

Muscle tissue function

Movement (smooth, cardiac, skeletal)

Nervous tissue function

Control/communication

Connective tissue function

Binding and support

Protection against infection

Tissue repair

Insulation

Protection/cushioning

Why is epithelial tissue avascular?

Because it has a protective barrier role; it contained blood vessels, there would be constant bleeding and easy open pathways for bacteria/viruses to enter the body.

Instead, it is avascular (no blood cells), so it receives nutrient/oxygen via diffusing from underlying connective tissue.

Apical surface

Faces outside the body/lumen (exposed to open space, facing away from connective tissue).

Basal surface

Attached to underlying basement membrane, facing toward connective tissue (separates the epithelium from underlying connective tissue).

Extracellular matrix (ECM) in connective tissue is composed of ground substance and which three types of protein fibers?

1. Collagen (strong; resists stretching)

2. Elastic (stretches/recoils)

3. Reticular (forms supporting network)

Connective tissue: Function and types of connective tissue proper

Holds, supports, and links body parts (ex: tendons, ligaments)

1. Loose connective tissue (has lots of space between fibers and cells) → areolar, reticular, adipose.

2. Dense connective tissue (has lots of collagen fibers) → dense regular, dense irrgular, elastic

Connective tissue: Main cells and state of ground substance of connective tissue proper

Fibroblasts, adipocytes

Semifluid ground substance

Connective tissue: Function of cartilage

Support and cushioning; shock-absorber

Connective tissue: Main cells and state of ground substance of cartilage

Chrondrocytes

Stiff, gelatinous ground substance

Connective tissue: Function of bone

Support, protection, framework for body

Connective tissue: Main cells and state of ground substance of bone

Osteocytes

Calcified ground substance (makes bones strong)

Connective tissue: Function of blood and lymph

Fluid connective tissues (fluid ground substance) that circulate through the body to transport materials, maintain fluid balance, and defend against disease.

Lymph helps transport WBCs to various tissues of the body

What is the integumentary system?

The body’s outer covering (skin + accessory organs like hair, nails, glands).

Blue skin indicates?

Cyanosis indicates hypoxemia (inadequate oxygen in blood)

Yellow skin indicates?

Jaundice/icterus indicates liver dysfunction

What is erythema?

Red skin, caused by heat, inflammation from injury/infection, allergic reaction, vasodilation, etc.

What is pallor caused by?

White/pale skin can occur with shock, amenia, or peripheral vasoconstriction (reduced blood flow.

In darker skin tones → assess palms, nail beds, mucous membranes (inside cheeks, gums).

What is the epidermis?

Outer layer of skin

Psoriasis

Abnormally rapid skin cell growth (complete cell turnover in 7-10 days instead of 4-6 weeks)

What does the epidermis contain (i.e: major four major cell types)?

Keratinocytes, melanocytes, Langerhan’s cells, Merkel cells

What is the function of keratinocytes?

Produce keratin → protects against heat, abrasion, microbes, chemicals, water loss.

What is the function of melanocytes?

Produce melanin → hair/skin colour, protect cells from UV radiation, protects DNA of actively cells in basal layer.

Where are melanocytes found?

Stratum basale (deepest layer of epidermis)

What is the function of Langerhan’s cells?

Intraepidermal macrophages involved in immune defense by performing phagocytosis on pathgens.

Where are Langerhan’s cells found?

Stratum spinosum (thickest layer of epidermis)

What is the function of Merkel cells?

Detech touch by releasing NTs to sensory neurons to convey touch info to the nervous sytem.

Outermost layer of the epidermis

Stratum corneum

Layer of epidermis present only in thick skin

Stratum lucidum (palms of hands, soles of feet)

Epidermal layer that is the transition between living and dead cells

Stratum granulosum

“Spiny,” thickest epidermal layer

Stratum spinosum

Deepest layer of the epidermis

Stratum basale, containing actively dividing cells, melanocytes, and Merkel cells.

What is the purpose of epidermal ridges (epidermal pegs + dermal papillae)?

Increase surface area of contact between epidermis and dermis → improves grip/friction, helps withstand mechanical stress (too much pressure can cause blisters).

Two major forms of melanin

1. Eumelanin (brown/black)

2. Pheomelanin (yellow/red)

Skin colour is the expression of which three pigments?

1. Melanin (brown-black or yellow-red)

2. Carotene (yellow-orange)

3. Hemoglobin (red)

What is the purpose of melanin?

Protects DNA by absorbing UV radiation (people near equator have higher melanin pigmentation).

Where do malignant melanomas arise from?

Malignant transformation of melanocytes that develop from nevi (moles).

What is the ABCDE rule?

Asymmetry

Border (irregular)

Colour (multiple/uneven)

Diameter (>6 mm)

Evolving/elevation

Where is the dermis located?

Underneath the epidermis and above the hypodermis/subcutaneous later.

Two regions of the derims

1. Papillary region: thin, superficial top layer

2. Reticular region: thick, deep bottom layer

What does the dermis contain?

Collagen + elastic fibers, blood vessels, nerves, sensory receptors, hair follicles, glands.

What are the four types of skin glands and what do they produce?

Sebaceous glands → sebum, which has antimicrobial defensins (absent from palms/soles)

Apocrine glands → thicker, protein-rich sweat (body odour; puberty; SNS)

Eccrine glands → watery sweat (thermoregulation; SNS)

Ceruminous glands → earwax

What are the five functions of the skin?

1. Thermoregulation (vasodilation when hot and vasoconstriction when cold)

2. Blood reservoir

3. Protection from environment (chemical, physical, biological)

4. Cutaneous sensation

5. Metabolism (through vitamin D production)

Too much UV radiation causes

Uncontrolled melanocyte growth → possible melanoma