Human Biology

• Organ system


  Cells make up body tissues, tissues make up an organ, organs are part of an organ system
• Major human body systems

  • 11 major human body systems
• Integumentary system

  • Involves the skin, the largest human organ
  • Critical for homeostasis as it maintains internal body temperature and fluid balance
  • Protects internal structures and organs from damage, along with the invasion of pathogens
  • Where Vitamin D is produced
  • Has sensory functions
• Epidermis


  The outermost layer of the skin
• Keratinocytes


  Cells that can be found in different locations in the epidermis, make keratin, a protein that helps cells become water resistant and tough
• Keratinocyte development

  Produced at the bottom layer of the epidermis and get pushed upward to the or superficial layer of the epidermis where they are considered cornified
• Cornified cells


  Hardened, flattened, tough, and dead due to the loss of organelles (thus, it is just full of keratin)
• Layers of the Epidermis

  • Corneum
  • Lucidum
  • Granulosum
  • Spinosum
  • Basale
• Corneum


  Consists of cornified cells (dead cells), continuously shed off with replacement cells coming from layers below
• Lucidum


  Not in all skin areas and are generally just in thick skin areas (ex. the bottom of your feet or on one's palms), also consists of cornified cells, contain a type of protein that gives them a transparent kind of appearance called lucid ghost cells
• Granulosum


  Where keratinocytes have been pushed from the lower layer and will develop a flatter structure, contains granules that have a variety of functions, the keratinocytes from this area will eventually lose their organelles and becomes the cornified cells of the layers above
• Spinosum


  Have many layers of keratinocytes, has a type of cell that will consume worn out cells or bacteria, acting like a macrophage, its name is related on how it looks under the microscope when it's stained - it looks spiky
• Basale


  Consists of one layer of cells called basal cells whom are the ones constantly doing mitosis and give rise to the keratinocytes in the layers above, where callus are formed when this layer is trying to respond to frequent abrasion by making more cells, which mature and result in a thicker stratum corneum, has other types of cells like melanocytes and Merkel cells
• Dermis


  • Where you will find blood vessels, a type of connective tissues, also where you will find sweat glands, hair follicles, and nerves, have fibers or two types of proteins, collagen (provides support) and elastin (gives elasticity)
• Layers of the Dermis

  • Papillary Layer
  • Reticular Layer
• Papillary Layer


  Has connective tissue that is more loose
• Reticular Layer


  Deeper and is where connective tissue is more tightly packed
• Scarring


  • If a cut makes it to the dermis, it can often scar, tend to look different from the rest of the skin as they are not put together exactly like the original skin, when fibroblasts are generating collagen to fix the damage, they tend to not arrange it in the pattern that had originally been there before and accessory structures (like sweat glands or hair) won't be re-created, also tends to have less elasticity, large scars from large wounds can affect range of movement, the collagen production keeps on going even after everything is healed, resulting in a raise scar or a keloid which is from the excessive producing of collagen
• Hypodermis


  Also called subcutaneous tissues, a vascular layer like the dermis that has blood vessels, connects the skin to bone and muscle tissue, contains adipose tissue, which is stored body fat and has important functions such as insulation
• Accessory structures of the integumentary system

  • Sweat Glands
  • Sebaceous Glands
  • Hair
  • Nails
• Sweat Glands


  Control and regulate body temperature
• Sebaceous Glands

  Produce oil and help keep the skin and hair waterproof, also help lubricate all the dead keratinocytes
• Hair


  Hair follicles are found in the dermis, there are cells that are found here are doing mitosis rapidly, causing them to get pushes outward as the hair root grows, the hair shaft (hair itself) is made of keratin and is non-living
• Nails


  The base of these are part of the epidermis, the nail body (the portion that protects the ends of fingers and toes) is made of dead keratinocytes, the nail root has cells that are doing mitosis frequently and as those get pushes outward, they help the nail grow
• Types of skin cancer

  • Basal cell carcinoma
  • Melanoma
  • Merkel cell carcinoma
• Burns


  First degree burns are isolated to the epidermis, second degree burns affects the epidermis and part of the dermis, third degree burns affects the epidermis and all of the dermis, fourth degree burns go beyond all the layers, even affecting bones and muscles, in this degree, along with the third degree, often involves nerve damages, making it feel less painful despite being more severe, can be dangerous as the functions of the skin, such as maintaining fluids and protecting all the internal structures, can be compromised with a significant burn, the skin is now more vulnerable to getting infected
• Skeletal system


  • Includes not just bones but also connective tissue like ligaments, tendons, and cartilage, has an important job of supporting the body and protecting the organs inside, also provides storage of important minerals, involves the making of red and white blood cells, and, along with the help of muscles, movement
• Divisions of the skeletal system

  • Axial skeleton
  • Appendicular skeleton
• Axial skeleton


  Includes the bones in the skull, in your ears (called ossicles), in your throat (called the hyoid), vertebral column, and the ribcage
• Appendicular skeleton


  All the bones in the arms and hands and the should girdle where they attach (essential for the function of arms and hands) and all the bones of legs and feet and the pelvic girdle where they attach (essential for movement)
• Classifications of bones by shape

  • Long bones
  • Short bones
  • Sesamoid bones
  • Flat bones
  • Irregular bones
• Long bones


  Have a cylinder shape and are longer than wide, tend to be moved in muscle contraction
• Short bones


  More like a cube as their length and width are close to equal, also moved using muscle contractions and can offer stability
• Sesamoid bones


  Like sesame seeds, they are roundish, great about handling pressure
• Flat bones


  Often curves and thin
• Irregular bones


  Has no specific shape description, can be protective from an assortment of forces
• Types of bone tissue

  • Compact bone tissue
  • Spongy tissue
• Compact bone tissue


  An outer layer that is hard
• Spongy tissue


  A layer where you will find bone marrow, some is yellow marrow that stores fat, which is important for long term energy storage, some is red marrow where blood cells can be made
• Bone cells

  • Osteoblasts
  • Osteocytes
  • Osteoclasts