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Chapter 19 Lecture 1 (Microbiome of the Skin (Yeast, and bacteria …
Chapter 19 Lecture 1
Microbiome of the Skin
Yeast, and bacteria tolerate and even thrive in the cavities of hair follicles and the interiors of the sweat glands
These are normal residents of the body and they make up the microbiome
They compete with potential pathogens for nutrients and space and produce chemicals that interfere with the growth of other microbes (those that give defense to fight off infection
You can scrub and scrub which may reduce the number on your skin
It will not eliminate all of them because some microbes live deep in the hair follicles and sweat ducts and recolonize the skin’s surface
Grow in small clusters and in ares of the armpits and between the legs where it is moister
Their waste products produce body odor
Epidermis
Epidermis is bloodless and has 4 to 5 layers
Each layers is made up of tightly packed cells
Basal cells- adjoin the dermis, divide continuously, pushing their offspring towards the surface. They absorb melanin
Epidermal cells also fill with a waterproofing protein called keratin
A hardened form of keratin forms nails and hairs (accessory organs)
Defensive cells called dendritic cells phagocytize microbes that penetrate the deeper levels of the epidermis and then deliver microbial antigens to defensive lymphocytes
Malassezia
A member of the microbiome
It is a lipophilic yeast and they digest sebum
Rarely pathogenic although can cause disease in immunosuppressed patients
Gram-positive bacteria (Staphylococcus & Micrococcus) also grow on the skin and can tolerate salt concentrations
Most common species on the skin would be staphylococcus epidermidis
Surface of the Skin
Inhospitable environment covered with salt and sebum
Sebum is an oily lipid secreted by the sebaceous glands in the dermis
Between these two you get a barrier that acts as an antimicrobial
In addition the skin sloughs off microbes attached
Dermis
Dermis is a tough leathery structure
Made up loosely packed cells, connecting protein fibers, small muscles, sweat glands, and sebaceous gland, blood vessels, nerve endings, and hair follicles.
Provides strength and flexibility and supports the growth of the covering epidermis
Hypodermis
Layer of fat cells and fibers beneath the dermis
Technically not part of the skin because it is subcutaneous .
It is stored fat-
Provides energy
Cushioning
Insulation
Fibers in the hypodermis anchor the skin to underlying tissues
Diphtheroid
Gram-positive bacteria living on the skin
Pleomorphic bacilli are named for their appearance that is like Corynebacterium diphtheriae and are usually nonpathogenic
A common troublesome diphtheroid is Propionibacterium acnes – causes acne
It resides (lives) in hair follicles where they ferment carbohydrates to form propionic acid
Lowers pH of the skin which in turn is further defense against additional infection
Structures of the Skin
Also called the cutaneous membrane and does more than just keep the internal organs together
Functions of the skins:
Prevents water loss
Regulates body temperature ( sweat, dilation & constriction of blood vessels)
Helps make Vitamin D
Involved in sensory phenomena
Barriers against microbial invaders
Limits infection and diseases unless it has been damaged by burns, broken, and cuts
Two Main Layers
2 meters (about 6 feet) of skin makes this one of the larger organs of the body
Made up of two main, distinct layers:
Epidermis
Dermis