Chapter 12: Homeostasis

• Homeostasis is the maintenance of constant internal environment.

• for any homeostatic control there must be:

  • A stimulus (change).

  • A receptor (to detect a change).

  • An automatic or self-regulatory corrective mechanism which brings;

  • A negative feedback.

Examples of Homeostasis:

• Regulation of blood glucose concentration

  After a meal rich in sugar or starch:

  • An increase in blood glucose concentration (stimulus).

  • Pancreas is stimulated (receptor).

  • Pancreas will start secreting more insulin; to convert glucose to glycogen in liver (corrective mechanism).

  • Normal condition achieved.

  • The same thing happens when blood glucose level is low; but instead of insulin glucagon is released which converts glycogen to glucose.

• Regulation of blood water potential (osmotic pressure)

  Due to through profuse sweating:

  • Water potential decreases (stimulus).

  • More ADH secreted - more water reabsorbed by kidney tubules - less urine produced (corrective mechanism).

  • Normal condition achieved.

  • The same happens when water potential increases; but instead of more ADH less ADH is released and less water is reabsorbed by kidney tubules and more urine is formed.

    Note: ADH is antidiuretic hormone.

Mammalian Skin

Structure

• Epidermis

  • Cornified layer

    • Cells are dead, dry, flat and horny - deposition of keratin.

    • Water resistant and prevents uncontrolled water loss.

    • Prevents germs from entering.

  • Granular layer

    • living cells - dry.

  • Malpighian layer

    • Living cells - give skin its colour.

    • Pigment protects skin against UV.

    • Undergo cell division.

• Dermis

  • Blood vessels

    • Carry blood.

    • Bring reflex contraction (vasoconstriction) and dilation (vasodilation).

    • Vasoconstriction - reduced amount of blood flow.

    • Vasodilation - increased amount of blood low.

  • Hair

  • Sebaceous glands

    • Secretes oily substance; sebum

  • Sweat glands

    • Surrounded by blood capillaries

    • Sweat is secreted which through sweat duct

    • Sweat helps in regulation of body temperature as the sweat evaporates

  • Sense receptors

    • Nerve endings

    • Enable us to sense pain, pressure or temperature change in the external environment

• Subcutaneous fat

  • Serve as insulating layer

Responses to change in temperature