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Homeostasis
Homeostasis definitions 2021 revision
| Term | Definition |
|---|---|
| Homeostasis | the maintenance of the ‘steady state’ in response to changes, in both the external and the internal environment. |
| Homeostasis is achieved through a range of mechanisms including | structural, physiological, behavioral |
| Factors for which organisms have tolerance limits include | body temperature, water availability, blood glucose level, carbon dioxide concentration in the blood and tissues |
| Stimulus | Variable factor in internal/external environment that is able to be detected by the organism. |
| Receptor | Cells/ tissues that are able to detect a change in the internal/external environment as a stimulus which results in generation of nerve impulses. |
| Transmission | Relay of information via nerves and/or hormones to an effector. |
| Effector | A gland or muscle that bring about a response after receiving the information. |
| Response | An action which occurs due to the initial stimulus. |
| Negative feedback | When a response diminishes or reverses the original stimulus, response inhibits the original stimulus. e.g. fall in body temperature |
| Positive feedback | When the response reinforces or brings about an increase in the initial stimulus. e.g. newborn baby suckles on mother's nipple |
| Central nervous system (CNS) | It detects changes in the brain, receives stimuli from peripheral nerves, processes information and sends nerve impulses to relevant tissues and organs to bring about response |
| Peripheral nervous system (PNS) | Its role is to connect the CNS to all parts of the body |
| Neuron consists of | cell body, an axon, dendrites |
| Nerve impulses can only travel in one direction | From dendrite end to the axon terminal |
| At the synapse... | a chemical called neurotransmitter, crosses the gap and transfers the impulse to the next neuron in the pathway |
| Sensory neurons | Detects stimuli and carries nerve impulses towards interneurons in the CNS |
| Interneurons | Receive signals from sensory neurons and transmit them to motor neurons |
| Motor neurons | Carry nerve impulses from CNS to effectors (muscles and glands) which results in movement/ secretion |
| Reflex response | Automatic response to stimulus |
| Types of hormones | Peptides, Proteins, Steroids |
| A hormone will only produce an effect when | it reaches the target cells |
| Hormones can alter metabolism of | target cells, tissues, organs |
| Thyroid stimulating hormone (TSH) is produced | by the anterior gland |
| TSH will only produce an effect there (anterior gland) although | it will be present in the blood in all parts of the body |
| What is the role of TSH | acts on thyroid gland causing it to release thyroxine which signals cells to increase their metabolic rate and increases body temperature. |
| What does ADH do | acts on walls of collecting ducts in the kidneys to increase water reabsorption -> reduces urine |
| Fight or flight | If the body receives fright, brain sends a signal via the sympathetic nervous system to adrenal glands which secretes adrenaline |
| TSH controls | production of thyroxine |
| Osmoregulation | the maintenance of water and solute balance in the body. The kidneys are the main organs involved in osmoregulation. |
| Role of ADH | makes the collecting ducts wall more permeable to water by increasing the number of aquaporins present in the cell membrane on the filtrate side of collecting ducts |
Created by:
biology2021
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