• Study Guide, Skin - Chapter 4
• NEGATIVE FEEDBACK HOMEOSTASIS

Study Guide, Skin - Chapter 5, Marieb

Human Anatomy and Physiology text, p. 151.

Many organs make up an organ system. The integumentary system is composed of the
skin and derivatives like the hair, nails and teeth.

Skin Physiology - Functions - See p. 163.

1. Regulation of body temperature - when the core temperature exceeds 37 degrees C,
the blood vessels of the skin dilate allowing for more blood flow and the skin reddens in
lighter skinned people. Heat is moved from the blood to the air. Sweat glands assist. In
cold weather, the core temperature may drop below 37 degree C and the blood vessels
of the skin will constrict, thereby reducing blood flow and heat loss. In lighter skinned
people, the skin will get pale.
2. Protection against infection and ultraviolet radiation.
3. Senses of touch, pain, temperature and pressure.
4. Excretion of salts and a little urea. Why does Poweraid have salts (electrolytes) and
glucose in it?
5. Blood reservoir in the cases of heavy exercise and compensated shock -
the skin pales in both cases as blood is moved from it to internal organs.
6. Synthesis of Vitamin D calciferol from cholesterol-like precursors

Negative feedback homeostasis produces a response or output opposite to the stimulus
(or stress) or input. Notice that in negative feedback homeostasis,
the sign, positive or negative, is opposite for the input and output.

Explain sweating as negative feedback.

NEGATIVE FEEDBACK HOMEOSTASIS

Skin Structure

Skin has three layers. See page 153.

1. Epidermis is avascular and composed of a cornified, stratified squamous epithelium.

Sub layers include the stratum basale where melanocytes make the skin pigment
melanin that serves to convert ultraviolet rays into heat, thereby protecting the skin
and the stratum lucidum which is glassy and the area where dead cells move into
the stratum corneum as they are pushed upwards from new cells forming in the
stratum germinativum. Free nerve endings, sweat gland ducts and hair follicles
are also present. In a first degree burn the epidermis is reddened and the top of
the dermis, described below, may be inflamed and swollen also. See pg. 164-165.
2. Dermis is highly vascular and filled with loose and dense irregular connective tissues,

nervous sensory receptors such as Meissner's and Pacinian corpuscles, the bases of hair
follicles with associated sebaceous glands, and sweat glands. In a second degree burn
blisters form between the dermis and the epidermis and the epidermis is destroyed.
3. Hypodermis or subcutaneous layer is composed mostly of fibrous irregular connective

tissues and calorie-storing fat. In a third degree burn all three layers are charred.
The nerves are dead so there is no feeling there, electrolytes leak
out and infection sets in. Fifty per cent of all body fat is in the hypodermis. Fat serves
Eskimos well as an insulator.

In adults, the whole head = 9%; each arm is 9%; the trunk anterior = 18% and posterior = 18%;
each anterior thigh, leg and feet  = 18%; each posterior thigh, leg and feet  = 18%; and the
perineum = 1%.

How are babies different?

Compute the surface area of the anterior, right side of the face and neck.

Skin Color is due to melanin. Black people have larger amounts of melanin (they also have
lower levels of skin cancer than other races). Italians generally have more melanin than
Scandinavians or Irish. Asians and American Indians have a relative of vitamin A, carotenes
(yellow), in addition to melanin. Melanin serves to degrade the mutagenic ultraviolet radiation
to hear (infrared) waves. Albinism, a genetic mutation, prevents the formation of melanin
from the amino acid tyrosine in skin and hair. The enzyme tyrosinase is absent in oculocutaneous
albinism. Hair is white, skin is very light in color and the eyes will appear pink - The laclk of
melanin in the iris allows blood vessels to show through. See pg. 157.

Hair is genetically programmed to be kinky (dominant over all types), curly, wavy or
straight. Hair color is due to eumelanin (dark brown) and phaeomelanin (red-blonde).
Male pattern baldness (hair today, gone tomorrow!) is a genetic predisposition in which
dihydrotestosterone inhibits hair follicle growth. Normal hair follicles have cycles of activity
and dormancy. See pg. 159.

Sebaceous glands are joined into the shaft of the hair follicle. They are called holocrine
glands because the cell with its oil vacuoles becomes the secretion. The oily secretion protects
against infections, makes the skin water repellant and protects against ultraviolet radiation
(poorly). When these hair follicles become plugged up with bacteria growing in the oily
secretions, "zits" or acne results. Dr. Aliff is rumored to have terminal acne.

Sweat glands - merocrine or eccrine glands secrete a watery sweat that also contains
salts and urea. When perspiration evaporates from the skin surface, it carries heat with it.
When a liquid turns into a gas, the gas cools by taking heat with it.

Ceruminous glands are found in the ears and make ear wax that protects against infection.

Nails are hardened cornified tissue derived from the epidermal nail bed. See page 163.

Label the epidermal nail bed.

Deep Wound Healing - see pg. 144.

1. Inflammatory phase - white blood cells migrate to the swollen area and clean up
damaged cells and bacteria.


2. Maturation or resolution phase - collagen fibers are made by fibroblasts
that make a scar in the dermis. A scab forms from old blood and cells at the surface
of the wound. Epidermis fills the wound from the sides.

Diseases

1. Boils - abscesses caused by Staph infection.

2. Warts - caused by human papilloma virus.

3. Basal cell carcinoma and squamous cell carcinomas - slow growing epithelial cell
cancers caused by exposure to large amounts of ultraviolet radiation.

4. Malignant melanoma - Caused by ultraviolet radiation, melanocytes mutate
and spread quickly into underlying connective tissues, blood vessels and lymphatic
ducts of the dermis. Red moles with phaeomelanin are a major risk factor.
Use the ABCDE rule to diagnose: A= asymmetry, B = border irregularity,
C = color varied, D = diameter 6mm or greater, and E = elevation frtom surrounding surface..

5. "Ringworm" fungus, "jock itch," "athletes foot," and "nail fungus" are
common enough to have large over-the-counter sales of anti fungal medications.
Look for inflammation accompanied by a dry, flaky lesion.

Study Questions
1. If one arm, one side of the face and one anterior surface of one arm received 3rd degree burns,
how much surface area in % of the body would be burned?
2. What is the ABCD rule of melanoma?
3. Explain albinism.

 Email:jaliff @ gpc.edu