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