Lecture 20 - Skin Flashcards
Skin is a barrier… what barriers does it include?
Chemical barriers- skin secretions low in pH, or inhibit bacterial growth, and melanin that protects skin from UV damage
Physical or mechanical barriers- provided by continuity of the skin and hardness of the keratinized cells.
Biological barriers- the dendritic cells and macrophages of dermis.
Why is skin important for temp. regulation and sensation?
manufactures sweat to cool body and causes constriction of dermal capillaries to prevent heat loss.
Cutaneous sensation happens through cutaneous sensory receptors (part of the nervous system) in the layers of the skin
Skin and metabolism
The skin provides metabolic function of making a vitamin D precursor, cholecalciferol, when exposed to sunlight. Cholecalciferol is activated into vitamin D (calciferol) in the liver and kidneys, goes to the intestines and stimulates the absorption of calcium ions.
skin may act as blood reservoir by holding up to 5% of the body’s blood supply, may be diverted to other areas of body if needed.
Core temp. vs. shell
core includes organs within the skull, thoracic, and abdominal cavities, have the highest body temperature
the shell (mostly the skin) has the lowest temperature.
Core temperature is closely regulated: blood is an agent of exchange between core and shell, allowing heat to be lost through increased flow to skin, or retained by bypassing vessels in the skin.
Mechanisms of heat exchange
Heat exchange between our skin and external environment occurs through
radiant flow of heat
conductive flow of warmth from warmer to cooler objects
convective movement of warm air away from the body
And heat loss due to evaporation of fluids from the lungs, oral mucosa, and the skin.
Insensible heat loss
accompanies insensible water loss from lungs, oral mucosa, and skin and accounts for about 10% of basal heat production.
SO SETTLE YOU CAN NOT SENSE IT
Sensible heat loss
occurs when the body temperature rises and sweating increases water vaporization.
HEAT LOSS YOU CAN FEEL
Heat promoting mechanisms
maintain or increase body core temperature and include constriction of cutaneous blood vessels, shivering, increase in metabolic rate, and increased release of thyroxine (only in infants).
Heat loss mechanisms
protect the body from excessively high temperatures and include dilation of cutaneous blood vessels, sweating and behaviors that promote heat loss or reduce heat gain.
Hypothalamus
Regulates body temp.
Frostbite
occurs when blood flow to skin is restricted due to extreme cold, causing skin cells to be deprived of oxygen and nutrients. Skin cells begin to die, leading to tissue damage.
Hypothermia
is a low core body temperature from cold exposure, leading to a decrease in vital signs. Shivering stops at core temperature of 30– 32°C.
Hyperthermia
is an elevated body temperature that overwhelms the body’s ability to cool down.
Heat exhaustion
heat-associated collapse after vigorous exercise due to dehydration and low blood pressure. The heat-loss mechanisms are still functional but it can progress to heat stroke.
Heat stroke
positive-feedback loop begins at 41°C core temperature. Elevated temperatures increase metabolic rates, which further increase body temperatures and can be fatal.
Fever
Fever is a controlled increase in body temperature that results when macrophages and other cells release cytokines that act as pyrogens, causing the hypothalamus to reset to a higher than normal temperature.
Once the disease has passed, cryogens (example: vasopressin) reset the thermostat to lower (normal) level, activating heat-loss mechanisms, so temperature falls.
Cancer
occurs when the DNA of a cell is damaged or mutated and the cell begins to grow uncontrollably. The cell divides through mitosis, spreading exponentially through the body.
Carcinoma
cancer that develops from epithelial tissue.
Adenocarcinoma is a cancer specifically from glandular epithelium.
Sarcoma
cancer of connective tissues other than blood.
Leukemia and lymphoma are
cancers from blood-forming cells.
Benign tumour
mass of cells that is not classified as cancerous or malignant, they lack ability to invade neighbouring tissues or metastasize (spread throughout the body).
Most skin tumours are benign but some can become malignant, called tumour progression.
Risk factors include overexposure to UV radiation and frequent irritation of the skin.
Basal cell carcinoma
Least malignant and the most common skin cancer.
Stratum basale cells proliferate and slowly invade dermis and hypodermis.
It is cured by surgical excision in 99% of cases.
Squamous cell carcinoma
Squamous cell carcinoma are second-most common type of skin cancer and can metastasize.
derive from the keratinocytes of the stratum spinosum.
usually present as a scaly reddened papule on scalp, ears, lower lip, or hands.
tends to grow rapidly and metastasize if not removed. Good prognosis if treated by radiation therapy or removed surgically.
Melanoma
cancer of melanocytes
It is the most dangerous type of skin cancer, highly metastatic and resistant to chemotherapy.
Treated by wide surgical excision accompanied by immunotherapy.
Signs of melanoma
Asymmetry: the two sides of the pigmented area do not match.
Border irregularity: the edges are not smooth.
Colour: contains several colours (black, brown, tan,
sometimes red or blue)
Diameter: larger than 6 mm (size of pencil eraser).
Evolution: does it grow and change over time?
