Biology 5.1.1- Communication and Homeostasis

Why do multicellular organisms need communication systems?

• To respond to changes in their internal and external environments (and keep the internal conditions within regular set limits through homeostasis)

• To coordinate the activities of different organs and specialised cells

What are some internal and external factors that need to be responded to during homeostasis?

Internal:

• pH

• Water potential

• Blood glucose concentration

• Internal temperature

External:

• Light

• Sound

• Temperature

• Humidity

How does cell-cell signalling work on different levels?

Between adjacent cells:

• Various chemicals can be produced by a cell, which diffuse towards the target cell and are recognised by receptors on the cell surface membrane (though some are small and non-polar enough to diffuse through) which trigger a response

• Eg. Neurotransmitters transmit signals short distances across the synapses between nerve cells

Between distant cells:

• The chemicals used are hormones, which are transported through the blood to reach the target cells

What are endotherms and ectotherms?

• Endotherms

  • Animals that possess physiological mechanisms for the maintenance of internal body temperature

  • E.g. mammals and birds

• Ectotherms

  • Animals that rely on behavioural mechanisms to maintain internal body temperature, for example by moving into or out of the sun, or huddling together for warmth

  • E.g. reptiles, amphibians and fish

  • Ectotherms that live in water, such as fish, don’t actually thermoregulate however as the temperature of water bodies are not very variable

How do endotherms cool down by thermoregulation?

• They detect external temperature changes using peripheral receptors (thermoreceptors found in the skin and mucous membranes)- these send impulses to the hypothalamus

• There are also receptors in the hypothalamus monitoring the temperature of the blood

The hypothalamus initiates homeostatic responses, such as:

• Vasodilation- the smooth muscle in arteriole walls near the skin relaxes, allowing more heat to be lost by radiation

• Sweating- sweat evaporates off the skin, removing latent heat and cooling the body

• Flattening skin hairs- the erector muscles in the skin relax, allowing air to circulate over the skin freely

How do endotherms heat up by thermoregulation?

• They detect external temperature changes using peripheral receptors (thermoreceptors found in the skin and mucous membranes)- these send impulses to the hypothalamus

• There are also receptors in the hypothalamus monitoring the temperature of the blood

The hypothalamus initiates homeostatic responses, such as:

• Vasoconstriction- the smooth muscle in arteriole walls near the skin contracts, allowing less heat to be lost by radiation

• Raising skin hairs- the erector muscles in the skin contract, forming an insulating layer of air

• Shivering- the muscles rapidly contract and relax to release heat energy from respiration

How do ectotherms conduct thermoregulation?

To cool down, they:

• Seek shade

• Move into water

• Dig burrows

To heat up, they:

• Bask in the sun/on warm surfaces

• Huddle together