Homeostasis

homeostasis

maintaining a constant environment within tolerance limits despite the changes in the internal and external environment

Stages of homeostatic regulation

\-detection of stimulus (change from stable)

\-response to stimulus (counteracting change)

biochemical pathway

linked series of chemical reactions in living organisms

metabolism

sum of all chemical reactions in biochemical pathways in organisms

enzymes

reusable, biological catalyst (protein) - ↓ the activation energy a chemical reaction

Internal receptors

receive signals from within the body about external environment

\-Examples:

\-chemoreceptors (in carotid and aortic arteries) detect oxygen, carbon dioxide and pH ion levels in interstitial fluid

\-osmoreceptors (in hypothalamus) detect change in osmotic pressure (change in blood water conc)

External receptors

detect changes in external environment

Examples:

\-Photoreceptors (light sensitive cells on retina or skin of some invertebrates) detect light

\-Thermoreceptor detect temperature variation in internal (hypothalamus) and external (skin) environment

Nervous system consist of

Central nervous system (brain and spinal cord)

Peripheral nervous system (sensory and motor neuron)

Types of neuron

Sensory neuron - transmit messages from sense organ to brain via spinal cord

Motor neurone - transmit message to effector organs from brain as response to counteract changes

Interconnecting neurone - relay electrical impulses from sensory neuron to motor neuron

Myelin sheath

fatty material that surrounds the axon

\-provides insulation

\-speeds up transmission along length of nerve

\-prevent messages from crossing over adjacent neurons

Endocrine system

\-made up of many endocrine glands that produce hormones

Examples:

\-Pituitary gland (master endocrine gland), parathyroid gland, thyroid gland

Comparison between endocrine and nervous system

Nervous system

• fast response

• travel through neurone in form of electrical impulses

Endocrine system

• response takes time

• travel through the bloodstream

Why pituitary gland known as master gland

produces many hormones that affect hormone production by other endocrine glands

hormones

\-substance secreted by ductless glands into bloodstream

\-target and activate particular cells and organs

Negative feedback model/loop

\-homeostastic process that changes direction of stimulus as stimulus initially deviates from normal

\-always ↓ stimulus

\-modelled as a flow diagram

Positive feedback model/loop

\-reinforces original stimulus

\-↑ output of system enhancing deviation from optimal value

\-rare but necessary in some cases e.g. blood clotting, childbirth