Lesson 4- Part I - Histology (study of the structure and composition of a tissue) Flashcards
Define tissue
It is a collection of similar cells which act together to perform a particular function. I.e. muscle tissue for movement, epithelial tissue for protection.
List the fundamental tissues of the body
- epithelial
- connective
- muscle
- nervous
Describe epithelial tissue [covering]
- Mucus membrane, skin
- Cells are closely packed together
- Protection is the general function of this tissue
- Secretion and absorption are other functions of this tissue i.e. secretion of mucus
- It lines the body surface both inside and out
- It consists of one or more layers of cells which are held together by matrix [outer cellular material]
- it acts as a protection against bacteria and a buffer against mechanical injury
Describe connective tissue
- Most abundant form of tissue
- Also provide support and protection
- The connective tissue is the supportive, protective and binding tissue. Fats, ligaments and tendons, bones, cartilage and blood are all connective tissue two structures
Complex connective tissue has a job of carrying. For example blood and lymph.
Describe muscle tissue
- Cells here form skeletal, smooth and cardiac muscle tissue.
- It’s main function is that of movement through contraction and relaxation.
- Each cell [skeletal, smooth, and cardiac muscle tissue] looks different they have the same function in common
- The involuntary muscles are smooth muscle tissue in the heart has its own special muscle tissue [cardiac]
Skeletal – the muscles that use the bones as levers to move the body
Smooth – the involuntary muscles
Cardiac – the heart has its own special muscle tissue
Describe nervous tissue
- Carries messages from the brain to other parts of the body
- This specialized tissue makes up the nervous system.
- The neuron receives and conducts electrochemical impulses from one part of the body to another
- It’s function is to control and coordinate all of the complicated activities of the body
Describe cells variety of one part of the body
One part of the body has several types of tissue and cells: bones, cartilage, blood, loose connective tissue, fibrous connective tissue, adipose tissue
What are organs
- Once we have a group of tissues designed to perform a specific function that’s when we have organs.
- are structures composed of specialized tissues designed to perform their specific functions in plants and animals
- some important body organs include:
1. Brain: controls the body
2. Eyes: controls vision
3. Heart: circulates the blood
4. Kidneys: excretes water and waste products
5. Lungs: supplies oxygen to the blood
6. Liver: removes toxic products from digestion
7. Skin: forms external protection for the body
8.  stomach and intestines: digest food
What are body systems
These are groups of organs which cooperate for a common purpose
How many major systems does the human body consist of
11
Name the 11 major systems of the human body consist of
1 Integumentary [the skin]
- Respiratory system
- Digestive system
- Urinary system
- Reproductive system
- Skeletal system
- Muscular system
- Nervous system
- Cardiovascular system
- Lymphatic system
- Endocrine system
What is Skin Science [integumentary system]
The science of skin histology and physiology includes the functions, layers and anatomy of the skin.
Skin histology is the study of the structure and composition of the tissue.
Physiology is the study of the function of living organisms
Skin facts – list them
- Largest organ in the body
- Our skin is a cell making factory with miles of blood vessels, millions of sweat glands, and an array of nerves within a network of fibres
- The skin of an average adult weighs 8 to 10 pounds and averages an area of about 22 ft.²
- It contains 1/2 to 2/3 of the blood in the body and 1/2 of the primary immune cells
- It is a strong barrier designed to protect us from the outside elements
- Skin layers, nervous, cellular functions, hair follicles and glands all work together harmoniously to regulate the body and protect the body
- healthy skin is slightly moist, soft, smooth, and somewhat acidic
- The thickness of our skin varies according to body part, age, race
- our skin contains millions of skin cells, which are linked to nerves, blood vessels and pores, which provide the opening for hair follicles, sweat glands and sebaceous oil glands
- skin is flexible
- skin is waterproof
- The skins most amazing feature is its ability to heal itself through hyper production of cells and blood clotting ability
Each square inch of skin contains approximately…
-Millions of cells
-8 feet of blood vessels
-32 feet of nerves
-650 sweat glands
-100 oil glands
-65 hairs
-1300 nerve endings
-155 pressure receptors
-12 cold and heat receptors
How many functions does the skin perform
Six
List the six functions of the skin
- Protection
- Sensation
- Heat regulation
- Excretion
- Secretion
- Absorption
Describe the protective function of skin
- The skin is the protective barrier to outside elements in micro organisms
- The skin has many defence mechanisms to protect the body from injury and invasion such as…
- Sebum oil on the epidermidis gives protection from external factors such as invasion by certain bacteria
- The acid mantle: made from sebum, lipids, sweat, and water. These components form a Hydrolipidic film to protect the skin from drying out and from exposure to external factors
- The acid mantle is part of the skin barriers function. The barrier function helps to protect the skin from irritation and the water loss caused by evaporation on the skin surface. Damage to our barrier layer is the cause of many skin problems including sensitivities, aging, and dehydration
- The skin barriers function is the mechanism that protects us from irritation as well as trans epidermal water loss [TEWL]
- Skins most amazing features the ability to heal itself. Skin can repair itself when injured thus protecting the body from infections and damage from injury. Fibroblast cells are activated to help rejuvenate and quickly repair the skin
- Other protective components of the skin include cells in the immune system
- melanin is another form of protection that the skin produces to protect us from the sun i.e. UV rays.
Describe the sensation function of the skin
- Refers to the nerve conduction of the skin as these nerve endings make us aware of our environment
- When the body senses touch it affects our bodies function
- Millions of nerve-end fibres on the surface of the skin detect stimuli. The Sunsations send messages that something is stimulating the surface
- Sensory fibres are most abundant in the fingertips and less are designed to be one of the most sensitive parts of the body
- Sensory nerve endings in the dermis respond to touch, pain, cold, heat and pressure
- sensory nerve endings can become dull over time
List sensory nerves and their function
- Free nerve endings – pain, Itch, temperature
- Ruffini ending – touch, pressure (light)
- Merkel’s disc – touch
- Meissner’s corpuscle – sensitive touch
- Pacinian corpuscle - pressure (deep)
Organization of skin structures [picture]
Describe heat regulation
- The average body thermostat is set at 98.6°F [37°C] In order to prevent the evaporation of fluids
- When the outside temperature changes, the skin adjusts to warm or cool the body
- We cool ourselves by evaporation through the sweat glands. Blood vessel dilation also assists in cooling the body [vasodilation]
- We protect ourselves from cold by constriction of blood vessels and decreasing blood flow
Vasodilation
- an increase in diameter of blood vessels
- skin will be pink and warm
- it is caused by relaxation of the smooth muscles in the vessel wall
- blood in the skin moves more freely
- surface heat is lost and body temperature is reduced = perspiration
Vasoconstriction
- Hair follicles also help regulate body temperature and protect us from heat loss
- Arrector pili muscle contracts and causes goosebumps to warm the skin
- contraction of the smooth muscle layers of vessels
- decrease in the diameter of blood vessels
- passage of blood slows, skin pills, a blueish cast can be noticed (loss of oxygen)
- arrector pili muscle causes the hairs to rise closing the surface of the skin, keeping body heat inside
Define excretion
- The sudoriferous or sweat glands excrete perspiration and detoxify the body by excreting salt and unwanted chemicals through pores
- pores are opening for sweat glands
Define secretion
- sebum– Is an oily substance that protects the surface of the skin and lubricate both skin and hair
- Sebaceous glands – are responsible for producing sebum which also helps slow down the evaporation of water. These oils also keep the skin soft and protected from outside elements
- emotional stress and hormone imbalances can stimulate oil glands to increase the flow of sebum, which can lead to skin problems
Organization of skin structures [picture]
What are the three main layers of the skin?
[From exterior to interior]  1. Epidermidis 2. Dermis [Intermediate layer] 3. Hypo dermis
The epidermidis is composed of stratified epithelial tissue, the dermis of connective tissue and the hypo dermis of connective adipose tissue.

The skin forms a protective covering over the entire surface of the body. Its colour will vary according to pigmentation, season and location on the body.
How many skin layers are there in the epidermis [List them all]
Five (from the bottom of the epidermidis upwards)
- Basil membrane / Germanitive layer [Stratum germinativum] also known as the basil layer (germinate means grow)
- Prickle cell layer [stratum Spinosum] or spiny layer
- Granular layer [stratum granulosum]
- Clear layer [stratum lucidum]
- Horny layer [stratum corneum]
How many different types of cells is the epidermidis composed of [list them]
Five
- Stem cells – replacement cells
- Keratinocytes – majority of the epidermidis is composed of these
- Melanocytes – produce melanin
- Tactile sells – Merkel cells
5. dendritic [immune cells/Langerhans cell]
The soldiers that guard the epidermis.
Describe the Germanative layer [Stratum germinativum] also known as the basale layer (The bottom layer of the epidermis)
- The live layer of the epidermis located just above the dermis at the Basale membrane
- it is composed of a single layer of cells which is constantly dividing and giving birth to new cells [keratinocytes]. These cells migrate towards the skin surface becoming older new cells are born in the Germanative layer
- This is the most active layer of the epidermidis because mitosis takes place here. Mitosis occurs mostly at night in the skin.
- stem cells are basically mother cells that divide to produce daughter cells
- Specialized melanocytes are distributed through the layers, which are responsible for production of melanin
- Tactile cells, relatively few in number, our receptors for the sense of touch. They are found in the basil layer of the epidermis. The tactile cell and its nerve fibre are collectively called a tactile [Merkel] disc
- Melanin is a black protein pigment responsible for skin coloration. It also protects skin from UV rays
-  damage to DNA triggers melanocyte stimulating hormones to produce melanin
- Melanosomes carry in produce the protein called melanin [pigment granules that provide the skin color]
- People of all races have approximately equal numbers of melanocytes
- difference in skin colour result from the differences in the rate of melanin synthesis and how clumped or spread out the melanin is. Differences in genetic skin colour are due to the amount of melanin activated in the skin and the way it is distributed. Individuals with darker skin and melanin have more activity in their melanocytes
- Hey melanin production is stimulated by exposure to sunlight and protects the cell is below by absorbing and blocking UV radiation
-  Tyrosinase is the enzyme that stimulated melanocytes and that produces melanin
- Enzyme is a protein that is involved as a catalyst in a chemical reaction
- it takes 3 to 4 weeks for cells to migrate from the germinated layer to the skin surface depending on the age and health of an individual
Describe melanocytes
- The stratum germinativum also contains melanocytes which are cells that produce pigment granules in the basil layer
- About 5 to 10% of basil cells are melanocytes
- The pigment carrying granules, called melanosomes, then produce a complex protein, melanin, which determines skin, eye and hair colour
Describe Melanogenesis / The melanin pathway
- The highly complex process of melanin production
- It is initiated/triggered by three or more factors
- Melanocyte – stimulating hormone [MSH]
- Adrenal cortisotropic hormone
- Exposure to ultraviolet light and inflammation
- Melanin production, when stimulated by exposure to sunlight and protects the cell is below by absorbing and blocking UV radiation
- Can also be triggered by chemicals and hormones. These signals affect the pituitary gland to produce a peptide hormone [melanin stimulating hormone Dash MFH] which signals the melanocytes to start the production of melanin
- melanin is a protein and to make a protein, the body needs an amino acid and an enzyme. Tyrosine is the amino acid and tyrosinase is the enzyme necessary for the production of melanin
- as soon as Tyrosinase reacts to tyrosine, a copper is added and this will then initiate a series of oxidation reactions
- Once the protein (melanin) is formed, it is packaged into melanosomes (package parcel of melanin)
- Then these packaged melanosomes are transferred into Keratinocytes [skin cells] through the melanocyte dendrites [arms, or cellular projections, that branch out to interact with other cells]
- melanin containing melanosomes will cluster over the nucleus of the Keratinocyte cells to protect the DNA of the cell [prime purpose of melanin]
- The keratinocyte will now start its journey moving upwards through the epidermis and undergo keratinization, until it eventually reaches the skin surface where it will be soft off/shed off
Teachers cake analogy for melanogenesis and melanin
The production of melanin is compared to baking a cake analogy by our teacher in the lecture for one hour two minutes and 23 seconds.
She describes giving a recipe for a cake and you go home and try to make the cake and realize that you don’t have the necessary ingredients so you substitute the ingredients. The result is not the same cake as the original recipe. The reason she gave this example is because when she’s talking about Melanogenesis there are certain things that have to be in place in order for us to build this protein. She is referring to needing a protein and an enzyme as discussed on the previous slide.
She compares the ingredients of the cake to the protein and the baker of the cake to the enzyme
Melanosomes picture and chart reference
-You can see in this picture the melanosomes which were referred to as the packaging process in the previous slide, are the little dots that the melanin is actually inside of [almost like a vehicle]
-Once the melanin is in the melanosomes they have to go through what is referred to as highways in the analogy which are called dendrites [the Greene of the picture]
-in the second picture you can see the melanocytes hover over the nucleus and protect from further damage of the cells
The second picture also shows how the melanocytes are deposited into keratinocyte cells and once inside that is when they hover over the nucleus to protect it.
Melanogenesis steps summary picture
What are dendrites
- Dendrites are the arms, or cellular projections, that branch out to interact with other cells in the matrix between the cells.
- dendrites receive information from other neurons
- this process is how pigment darkening occurs
Melanocytes and melanosomes picture chart from online lecture
What are the benefits of melanin
-Melanin protect the cells below by absorbing and blocking UV radiation
- Melanin is transferred into the cells through dendrites that move up to the skin surface
- It is stimulated by exposure to sunlight- as well as the other factors listed in previous slides
- tyrosinase is the enzyme that stimulates melanocytes and thus produces melanin
What are the different types of melanin [this is not in your manual Dash the teacher just wanted you to be familiar with it in case you come across it in your future career]
- Pheomelanin - red to yellow in colour
2. Eumelanin - dark brown to black
Describe the prickle cell layer [stratum Spinosum] Or spiny layer.
- also known as spiny layer
- Just above the germinativum
-  Cells continue to divide and change shape here and the enzymes are creating lipids and proteins
- Consists of several layers of keratinocytes
- Layers closest to the germinative layer are small as they are still growing
- Cell appendages, which resemble prickly spines, become desmosomes, the structures that assist in strengthening and holding the cells together
- Langerhans cells also found in this layer, which protect the body from infections by identifying foreign invaders
- This Spinosum is the largest layer of the epidermidis
What are Langerhans cells?
-Immune cells or guard cells of the immune system that sense unrecognized foreign invaders, such as bacteria, and then process these antigens for removal through the lymphatic system
-they are present in all layers of the epidermidis, but are most prominent in the stratum spinosum. They also occur in the papillary dermis, particularly around blood vessels, as well as the mucosa of the mouth, foreskin, and vagina
-Langerhans immune cells, which protect the body from infections by identifying foreign material [antigens]. They stand on guard and alert the immune system
Langerhans immune cells pictures and charts from online lecture
What are desmosomes
Desmosomes are keratin filaments – the Pro Tien bonds that creates the junction between cells. They are the structures that assist in strengthening and holding the cells together. Can also be referred to as the “glue“ that holds cells together.
Describe the granular layer [stratum granulosum] of the epidermidis layers
- The cells that resemble granules and are filled with keratin
- The production of keratin and intercellular Lipids also take place here
- In this layer, enzymes dissolve the structures [desmosomes] that hold the cells together
- It is composed of 3 to 5 layers of flattening granular cells
- Keratinocytes in this layer contain course, dark staining Keratohyalin granule that gives this layer its name
- Natural moisturizing substances such as triglycerides, ceramides, waxes, fatty acids and other intracellular lipids are made here and are excreted from cells to form components of the skins waterproofing barrier function of the top layer
- These water soluuable compounds are referred to as natural moisturizing factors (NMF’s] and hydrate the lipids layer surrounding cells, absorb water, and prevent water loss
- cells start to die here because enzymes are released which destroy the nucleus
Granular layer picture that highlights Langerhans cell
Describe the clear layer [stratum lucidum] of the epidermal layers
-Is a thin, clear layer of dead skin cells under the stratum corneum and on top of the stratum granulosum
-One layer of flat transparent cells that let the light pass through
-The keratinocytes in this layer contains clear keratin
-The cells here release lipid forming bilayers of oils and water
-This layer is thickest on the palms of the hands and soles of the feet. The thicker skin on the palm and souls is composed of epidermal ridges that provide better grip while walking and using our hands
-This layer also forms are unique fingerprints and footprints
-The keratinocytes are densely packed with elidin which Produced by keratohyaline and will eventually form keratin
-The cells have no nuclei or other organelles. Because organelles are absent and eleidin does not stain well, this zone has a pale, featureless appearance with distinct cell boundaries
-contrary to popular belief, the stratum lucidum is found all over the body, not just on the palms and soles, where it is most apparent. But also present in areas of thick skin mostly.

Describe the horny layer [stratum corneum]/the outer most layer of the Epidermidis layers
-The top layer of the epidermis
-30 layers of dead, scaly, keratinized cells form a durable surface layer
-especially resistant to abrasion, penetration and water loss
-It is called horny Layer because of these scale like cells or horns
-Keratin acts as a water repellent and prevents the loss of moisture of the lower skin and body layers
-acid mantle
-Keratinocytes on the surface have hardened into corneocytes, the waterproof, protective cells. These “dead” proteins cells have dried out and lack nuclei
-Keratinocytes are continually shed from the skin in process called desquamation. The cells are replaced by new cells coming to the surface from the lower stratum
-It is very thin but waterproof, permeable, regenerative [Regenerates itself], detoxifies the body, and response to stimuli
-Cells will be pushed out of their layer in approximately two weeks upon entrance to the horny layer
-The keratinocytes on the surface of the skin are also called squamous layer:
— Squamous [flat and scaly] keratinized are consistently being brushed, washed or rubbed off
— this peeling off process is called exfoliation
— The surface cells are both flat and hardened
-The purpose of the stratum corneum is to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress such as abrasion.
Describe the squamous layer
-in anatomy, squamous epithelium is an epithelium characterized by its most superficial layer consisting of flat and scale like cells called squamous epithelial cells. Epithelium may be composed of one layer of the cells, in which case it is referred to as simple squamous epithelium, or it may possess multiple layers were referred to then as stratified squamous epithelium. Both types perform different functions, ranging from nutrient exchange to protection
- Squamous cells are very flat, thin and often have an angular view from above
- squams are consistently being brushed, washed or rubbed off and exfoliation
- it is the visible layer of skin that we can see feel in touch
Epidermidis layers picture chart
