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Integumentary System

Integumentary System

  1. Skin
  2. Appendages
    1. Nails
    2. Hairs
    3. Sweat Glands

Skin

  1. Largest organ in our body
  2. 21 pounds
  3. Skin is impermeable to water
  4. Has Structural Barrier
  5. has an immunologic function
  6. can secret things like antibodies
  7. can secret enzymes like lysozymes
  8. langerhan cells eats bacteria
  9. Sweats – Thermoregulation
    1. helps us to cool off by a process known as evaporative cooling
  10. Perceive things – conducts sensation – Able to tell when there is a stimulus
    1. Pain
    2. Temperature

Differentiate touch

Nails

  1. Nail root is attached to epidermis
  2. Keratin in your nail keeps it stiff

Hair

  1. Grows from the dermis
  2. A follicle that originates in your reticular dermis is your hair follicle
  3. Hair itself is a whole bunch of flattened or stratified squamous epithelial cells that are filled with keratin

Hair grows at a rate of 0.5 inches or 1.25 cm a month

Temperature

What we perceive as temperature is really just the motion of the molecules of something. Higher temperature means that they are moving around more. Lower temperature means that they are moving around less. Average kinetic, we perceive it as temperatureH20 the molecules that have a high kinetic energy are the most likely to evaporate. When it evaporates the average kinetic energy will go down. This is why when you  sweat you perceive it as a decrease in body temperature.

H2o molecule Movements can be

  1. Translational
  2. Vibrating
  3. Rotating

(Kinetic) energy proportional to temperature level

Sweat

  1. Our glands are situated in the rectivular dermis
  2. 3 types of gland that exists in our skin
    1. Holocrine Gland
      1. Holocrine gland (Sebaceous Gland)releases it secretions by disintegrating the whole cell. Entire cells breaks down to release whats called sebum.
      2. Holocrine sweat glands are found on the face, chest, back
      3. This oily or lipid rich sebum is meant to lubricate the skin, in doing so it slows down the bacterial growth. Making it difficult for bacteria to move around and divide. Slows bacteria growth.
    2. Apocrine Gland
      1. Apocrine gland release secretions from the apex of the cell or the top of the cell breaks off to release a mixture of proteins, lipids, and steroids
      2. Apocrine glands are found on the armpit, the groin, and around the nipples. They release their contents into the hair follicle
      3. They wont release secretions until after puberty
      4. Apocrine glands in animal release pheromones and warning signals and even territorial marking signs that we dont really practice as human beings
      5. Involved in emotional sweating
      6. Most active during times of great anxiety, stress, fear, and pain
    3. Merocrine Gland
      1. Release watery sweat by a process called exocytosis. Thats the budding off of the cell membrane with contents from inside the cell(watery salty contents)
      2. Merocrine glands are found everywhere else in the body but mostly concentrated on palms of our hands, souls of our feet,
      3. Help us cool down with our sweat through evaporative cooling
      4. Help us eliminate waste products(extra nitrogenous waste or water or electrolytes we dont need)
      5. Also release things like lysozymes(Enzymes which will lyse bacteria and even antobodies)

Gland name is a reflection how it release its secretions

Sensation

Mechanoreceptors help us perceive our external environment. Structure of mechano receptors actually determines their functions

Meissner’s Corpuscle(body)

  1. has layers of epithelial or laminar disk(Sepcialized Epithelial Cells)
  2. stimulus from external environment(Touch) cause these disks to leak sodium and other ions to the disks below. And these ions propagate through all the cells until they get to the bottom of meissner’s corpuscle, which actually ends in an afferent nerve fiber.
  3. If a bunch of sodium ions is present within a nerve it will fire an Action Potential
  4. An action potential is generated and it sends a signal on to the central nervous system

Function of Meisnner’s corpuscle is to perceive light touch(Ex. putting on a smooth cotton TShirt) specifically in non hairy skin(Glabrous Skin)

  1. In order to fire requires constantly changing stimuliand tha

Sits in the papillary dermis

Pacinian Corpuscle(Lamellar Corpuscle) Lamella means Layer

  1. Also known as onion layered machanoreceptor
  2. Perceives Deep Touch of hairy, non hairy skin(Ex. Poke)
  3. In order to fire requires constantly changing stimuli
  4. Sit deep in the hypo dermis

It also has an afferent nerve fiber that sits in the center

Merkel’s Disk

  1. Merkel’s Disk is actually just a specialized keratinocyte or an epithelial cell
  2. Sits in epidermis
  3. It also connects to an afferent nerve fiber
  4. Merkel’s Disk holds a whole bunch of vesicles(Pockets that have membrane around them). These pockets hold a neuropeptide(np receptor)
  5. Peptide is string of amino acids that talks to the nervous system
  6. When the force is transmitted, it causes the vesicles to open up and allows the neuropeptide to be released Which allows ion channels to open which allows sodium to enter Merkel’s Disk and eventually makes it way into this afferent nerve fiber and that generates the action potential and that will communicate with our central nervous system
  7. Its found in, between the stratum basale or it can be even lower in papillary dermis

Its responsible for perceiving sustained light touch on both hairy and non hairy skin

Ruffini’s corpuscle (Ruffini’s Ending)

  1. It has a beta afferent nerve fiber
  2. It has collagen(Structural Protein)
  3. Stimulus cause the collagen to shift and perturbed . Collagen is intimately connected to the nerve fibre branches here and as the collagen shifts it opens up ion channels on these nerve branches that allow sodium to reach afferent nerve fiber to generate an action potential and move on to the central nervous system.
  4. Stimulus is sustained deep touch

The part of the skin that has collagen is the dermis. But the dermis has 2 layers. The part of the dermis that has most collagen is the recticular dermis

Hair Follicle Receptor

  1. Hair deflection is the impetus for this signal to occur
  2. Perceives light touch. Hairs are being deflected as we perceive the stimulus
  3. Sits anchored in the reticular dermis

Requires constantly changing stimuli in order to have a signal be generated

Afferent Nerve Fibres

  1. Take stimulus from external environment and create a signal and pass it to the central nervous system
  2. If a bunch of sodium ions is present within a nerve it will fire an Action Potential

An action potential is generated and it sends a signal on to the central nervous system

Stimulus -> Afferent Nerve Fibres -> Central Nervous System

Afferent Fibres

There are 2 types we talk about

  1. A Beta Fibres
    1. Used to perceive everything else
  2. A Delta Fibres

Used to perceive pain, temperature

Efferent Nerve Fibre

Central Nervous System -> Efferent Nerve Fibre -> Muscle

Reverse flow of afferent nerve fibres

To sense Pain = nociception

To sense Temperature = Thermoception

  1. We rely on a receptor known as the TrpV1 receptor. This also able to sense pain.
  2. When a cell gets broken up by a touch, it releases all kinds of different molecules. These molecules will travel around and bind to one of the little TrpV1 receptor. This will activate it and sends a signal to the brain.
  3. These nerves contains 3 different types of fibers
    1. A Beta Fibers – Fast – Fast fibers are really really fat in diameters. They have a lot of myelin. They are covered in Myelin. Myelin is an insulatore that allows the cell to conduct an action potential very quickly(Signal Travels Quickly). If the cell has a big diameter, it lowers the resistance. You have less resistance, Greater conductance because of myelin. Ex. First reaction of Touching a hot stove with hand
    2. A Delta Fibers – Medium – Medium Fibers are small in diameter.They have little bit less myelin. They dont conduct the signal as quickly as the fast fibers. Ex. Second reaction of touching a hot stove.i.e, feeling pain
    3. C Fibers – Slow – Its small in diameter and its unmyelinated. This sends a signal very very slowly. It does go to brain but it takes a lot longer for the signal to get to your brain. Ex. lingering sense of pain after the incident(Burning sensation)

Capsaicin – Cells contain a molecule called capsaicin. It will be released when you bite a chilli pepper.

This will binds to TripV1 receptor in your tongue . Triggers a similar response as that of touching a hot stove.

Trv1 Receptors are found within various sensory cells located throughout our body.Trv1 receptors are activated by change in temperature and by molecules such as capsaicin or by molecules within a dying cell and send a signal to your brain, letting your brain know that there are painful stimulus

Thermoregulation by muscles

  1. Anterior(Front) Hypothalamus (to process excess Heat)
  2. Posterior Hypothalamus (to process excess cold)

More the blood flow —> More the heat flow through the body

When we are in a hot environment

  1. Smooth muscles that lines our arterioles(Arterioles are just smaller version of arteries)
  2. Smooth muscle is going to relax
  3. In doing so the arterioles then are going to become wider or larger. This process is called vasodilation. Your arterioles are dilating. They become wider.
  4. Lot more blood flow will happen in the skin due to the above process.
  5. Energy can disipate and leave
  6. This will help you lose heat.

When we are in a cold environment

  1. Smooth muscles are going to contract. This process in arteriole is called vasoconstriction. Narrowing of arterioles.
  2. In the skin you are going to have less energy due to the above process

Skeletal muscles that is in biceps, triceps contracts. Its going to take ATP – Adenosine Tri Phosphate and break that into Adenosine Di Phosphate  ADP+ Phospate + Energy. This is called Exothermic Reaction. Where Exo means – leaving. Thermic – Heat. This energy produces more heat in the muscle groups. Contraction of Skeletal Muscle is called Shivering

What is Skin (Epidermis)?

Skin comprises of 3 different sets of Layers

  1. Epidermis – First 5 layers
  2. Dermis – Next 2 Layers
  3. Subcutaneous Tissue(Hypodermis)

Epidermis

  1. Has epithelial tissue
  2. Epithelial Tissue involves
    1. simple squamous epithelial cells
    2. Columnar epithelial cells
  1. transitional epithelial cells(seen in bladder)
  2. Top most layer of the skin. It comprises of 5 layers
    1. Stratum Corneum
    2. Stratus Lucidum
    3. Stratum Granulosum
    4. Stratum Spinosum

Bottom most layer – Stratum basale or the basal layer. Sits right above the dermis

Stratus Basale

  1. Generates keratinocytes
  2. It helps give our skins a tough outer layer
  3. In other animals keratin is the main ingredient things like horn, hooves
  4. It has very rapid cell division
  5. We get skin color from stratus basale

Melanocyte

  1. Determines the skin color
  2. Melano – Special Pigment that made in these cells determine our skin color
  3. This pigment is called melanin
  4. Its not the number of melanocytes that determine how dark our skin is
  5. People of dark skin, light skin have the same number of melanocytes
  6. Amount of melanin that we have determine how dark your skin color is

Darker Skin – People have more melanin

keratinocyteis a protein or an intermediate filament (cytokeratin or keratin)

Desmosome

Stratum Spinosum

  1. Desmosome connects cells(Keratinocyte)
  2. Langerhans cells – Part of our immune system

Stratum Granulosum

  1. Keratinocyte with granules called kerato, keratohyalin granules
  2. These granules make proteins(Keratin Handling Proteins)
  3. Releases lamellar bodies
  4. Lamellar bodies contain whole bunch of lipids, thus form lipid layer.

This lipid layer is impermeable – It provides water tight capabilities that prevent foreign pathogens from making their way

Stratus Lucidum

  1. This is our lucid(clear) layer
  2. Dead Keratinocytes. Zombie Keratinocytes because they lost their nuclei or other organelles that usually gave them the color

Stratum Corneum

  1. Top most layer of the epidermis
  2. Stacked layer of keratinocytes
  3. We have upto 15 to 20 such layers of flat, simple, squamous epithelial cells Keratinocytes(Dead). They died in stratus lucidum
  4. randomly continuously slough off or leave or fall off and that makes way for newer cells underneath or newer keratinocytes to make their way upto the top

Reptiles shed this layer off in one piece like snake skin that comes off.

Dermis

  1. Has connective tissue(CT)
  2. Sits right below the epidermis
    1. Papillary Dermis
      1. has very thin loose connective tissue
      2. has blood vessels through which oxygen and nutrients are delivered
        1. an ateriole from an artery branch off into a capillary
        2. an venule, a venule which goes off to a vein
      3. has nerve endings allow us to perceive things like touch and pain. These nerves send signals to a cell body
    2. Reticular Dermis
      1. Thicker, more denser connective tissue
      2. has tons of sweat glands, exocrine glands of other varities anchored and held down here but extend out with a duct to secrete their contents to the epidermis and to the outside world
      3. has follicle will have from it emerging a hair. Hair follicle is anchored here. Hair is allowed to flow and extend out to the top and protrude from your epidermis
      4. Has slab of muscle(Arrector pilli muscle) – involved in hair standing straight up when you are cold or when you are scared.
  3. These cells are alive and have vessels in them to nourish them

In contrast we dont have vessels any where in epidermis because our nutrients and oxygen comes from below and make their way upwards.

Connective Tissue hold things together and does not involve cells and contains a litany of proteins

  1. Actin
  2. collagen(Structural Protein)
  3. laminin
  4. elastin

desmin

Hypodermis(Subcutaneous fat) – Hypo means below

  1. Cutaneous is just another name for skin
  2. We have tons of layers of fat that varies from person to person.
    1. Fat absorbs shock

insulates our tissue

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