Integumentary system

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Last Updated: Thursday, 10 October 2024 01:29
Published: Monday, 07 October 2024 00:05
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Integumentary System:

Integumentary system consists of skin and appendages as hair, nail. It also includes glands that generate sweat. The cells on top layer of skin as well as nail, hair, etc are dead cells.

Khan academy => https://www.youtube.com/watch?v=4zKjzl0futI&list=PLBWKfzsMAETxjVs5C_-vdYhZGIvQzIzfO

 

Skin:

Skin is impermeable, meaning it can't allow water to get in the body via the skin. Skin has multiple layers.

  1. Epidermis => The first 5 layers of skin. and are called strata or stratum. They are all keratinocytes or cells with keratin. The top 2 layers re dead, while next 3 are alive. These layers don't have any blood vessels as our nutrients and oxygen come from below, and hence it's harder and harder to get to the top cells. Hence top cells starting going dead.
    1. corneum: These are 15-20 layers of these cells which are flat cells. Word comes from "coroner's office" or where dead bodies go. This is the layer that gets shed from our body. Reptiles shed this layer in one piece, but for humans, this layer is in very small pieces that fall off our body w/o us seeing them.
    2. lucidum: These are dead cells. They lose their nuclei and other organelles.
    3. granulosum: They are keratin handling cells. These releases lamellar bodies, which provides the lipid layer that makes our skin impermeable. These cells work very hard, and so they are dead by the time they move to the upper layer or lucidum.
    4. spinosum: This is a spiny layer. The cells here are keratinocytes. The cells here overlap with each other, and the overlapping area is called desmosome. When we have less moisture or water in our body, these cells lose water and become shriveled. This causes them to become spiny (in star shape). There are also langerhans cells here, which provides immunity as it eats external invaders.
    5. basale: It's called basale, as it's the basal layer or the bottom layer. The cells here are keratinocytes (cytes mean cells). Rapid cell division happens here. Skin color comes from here. These cells are called melanocytes. This cells make special pigment called melanin. People with any skin color have same number of melanocytes, but the amount of melanin produced differs. Darker skin ppl have more melanin pigment in this layer.
  2. Dermis => The next 2 layers of skin are called dermis. Both the layers have connective tissues (CT), i.e kind of tissues that hold bones to muscles etc.
    1. Papillary dermis => It has loose CT, It's the 1st layer that has blood vessels. It has arterioles coming in, branching to become capillaries to transfer oxygen, nutrients to cells via diffusion to cells surrounding it. They finally join back tobecome veins, which carry deoxygenated blood back to heart, This layer also has nerve endings to feel touch/pain etc. The cell body for this nerve starts somewhere depper in Hypodermis layer. The nerve ending passes thru the Reticular dermis and ends in this layer.
    2. Reticular dermis => This has thicker, dense CT. It has tons of glands to secrete our sweat. It also has hair follicles from where the hair grows, and protrudes out from our top layer of skin. A muscle, arrector pilli muscle is attached to the follicle, which alows our hair to stand up )giving us goosebumps). This is involuntary muscle, so we have no control. It's more important for animals, where these muscles make hair stand up in cold weather. That allows warm insulating air layer embedded in the hair that gives warmth. This muscle is a vestigial organ, as it's there but is just a left over from our evolution. There are 3 types of sweat glands in this region:
      1. Holocrine glands => These are in the face, chest an back. They release sebum, an oily substance. They lubricate skin,which slows bacterial growth.
      2. Apocrine glands => These are in nipples, armpits, groins, etc. They are also called emotional glands, as they are released when are in stress, etc. They develop around puberty. These are used in animals to attract mates. Not so much in humans.
      3. Merocrine glands => They are found in rest of the body and are most common sweat glands. It's mainly water and salt that comes out from these glands.
  3. Hypodermis => Hypo means below, so this surface is just below the skin. It's also called subcutaneous layer. This layer has mostly fat. It's not part of skin. Muscles and bones sits below this layer.

In a hot environment, blood arteries relax. Relaxing blood vessels allow more blood to flow. They have RBC, WBC etc which bounce against the walls and transfer the energy to the walls of skin so that internals of the body gets cooler. Reverse happens when the it's colder outside, where arteries contract.

Burns: 1st, 2nd or 3rd degree burns are characterized by what layer of skin cells have burned. Buring of epidermis layer is 1st degree. Causes reddening of skin and lot of pain. 2nd degree burn is n=burning of Dermis layer and doesn't cause any pain as nerve cells themselves get burned. 3rd degree burn is burning of hypodermis and muscles/bones below it.

 

Hair and nails:

Hair and nail are comprised of cells. But they are not living cells, but dead cells. The only living cells in nails/hair are the cells at the root of these. As the cells die, they are pushed up by new living cells being formed.

Hair and Nail structure => https://www.youtube.com/watch?v=9zh-7hIiP3Q

Nails => nails are found in epidermis layer, with Nail root originating from there. Nail is actually part of epidermis. Nails are made of thick keratin, which are dead cells packed with keratin. Basale layer starts the growth process, with keratonocytes moving up and getting dead. Some of these move to the top of skin, while move sideways giving rise to nails.

Hairs => Hair is over all of our body, though the hears in some part as head grow lot more.Hair grows from the dermis (2nd layer of skin) and not from Epidermis. Hair follicle or hair root is in Reticular dermis as mentioned above. Hair grow about 1.25 cm/month (about 1/2 inch). That's why you need haircut every 3 months !! Hair shaft is the long pointy part of hair that goes thru the dermis, the epidermis and then protrudes out. HAir shaft is also all deead cells filled of keratine.