mod 7

• Anatomy


  The biological form of an organism
• Physiology


  The biological functions an organism performs
• Homeostasis


  Used to maintain a "steady state" or internal balance regardless of external environment
• In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level
• Mechanisms of homeostasis

  1. Control changes in the internal environment

  2. Fluctuations above or below a set point serve as a stimulus; these are detected by a sensor and trigger a response

  3. The response returns the variable to the set point
• Homeostasis in animals


  • Relies largely on negative feedback, which helps to return a variable to a normal range
• Positive feedback


  • Amplifies a stimulus and does not usually contribute to homeostasis in animals
• Set points and normal ranges can change with age or show cyclic variation
• In animals and plants, a circadian rhythm governs physiological changes that occur roughly every 24 hours
• Thermoregulation


  The process by which animals maintain an internal temperature within a tolerable range
• Endothermic animals


  Generate heat by metabolism; birds and mammals are endotherms
• Ectothermic animals


  Gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and nonavian reptiles
• Homeostatic processes for thermoregulation


  Involve form, function, and behavior
• Acclimatization


  A process by which homeostasis can adjust to changes in external environment
• Birds and mammals can vary their insulation to acclimatize to seasonal temperature changes
• When temperatures are subzero, some ectotherms produce "antifreeze" compounds to prevent ice formation in their cells
• Integumentary system


  The outer covering of the body, including the skin and all structures derived from or associated with skin
• Many invertebrate have a single-layered epidermis covering the body. Others have added secreted non-cellular cuticle over the epidermis
• Molluscs have a delicate epidermis that is why it needs a shell for protection
• Skin


  • Chemical factors: Sebum, sweat, and melanin provide protection
  • Physical factors: Stratified squamous epithelium and keratinized cells provide a barrier
  • Biological factor: White blood cells destroy invaded bacteria and foreign substances
• Skin

  • Excretion of waste materials
  • Body temperature regulation through sweating and vasoconstriction/vasodilation
  • Cutaneous sensation through nerve receptors
  • Vitamin D synthesis
• Single-celled protozoa have only a plasma membrane for an external covering
• Most invertebrates have an integument consisting of a single layer of columnar epithelial cells called an epidermis
• Specializations outside of this epithelial layer may be in the form of cuticles, shells, or teguments
• Vertebrate integument


  Skin, which has two main layers: the epidermis and the dermis
• A hypodermis consists of loose connective tissue, adipose tissue, and nerve endings, and separates the skin from the deeper tissues
• Accessory organs of the skin

  • Hair (hair root and hair shaft)
  • Hair follicle
  • Pili arrector muscle
  • Sebaceous gland
  • Sudoriferous gland
  • Nails
  • Mammary gland
• The skin of jawless fishes, such as lampreys and hagfishes, have relatively thick skin
• The skin of cartilaginous fishes (e.g., sharks) is multilayered and contains mucous and sensory cells
• The skin of bony fishes (teleosts) contains scales
• The skin of amphibians consists of a stratified epidermis and a dermis containing mucous and serous glands plus pigmentation cells
• Epidermis


  Made of stratified squamous epithelium, avascular (no blood vessels), nutrients diffuse upward from the dermis
• Stratum basale (stratum germinativum)


  Cuboidal cells that reproduce rapidly using mitosis, new cells pushed upward and flattened
• Keratinization


  Process where cells in stratum granulosum and stratum corneum produce the protein keratin, making them tough and waterproof
• Layers of the epidermis

  • Stratum basale or germinativum
  • Stratum spinosum
  • Stratum granulosum
  • Stratum corneum
  • Stratum lucidum (in palms and soles)
• Melanocytes


  Specialized cells in the stratum basale layer that produce the skin pigment, melanin
• Dermis


  Rich supply of nerves and vessels, made of fibrous connective tissue, contains two layers: papillary and reticular
• Pili arrector muscles wrinkle the skin and erect the hairs
• Nerves and nerve receptors in the dermis detect the sensations of heat, cold, pressure, touch, and pain
• The hypodermis is made of adipose tissue and loose connective tissue, serves as a heat insulator and allows the skin to be bound with underlying muscles