BYA7 SECTION 16.12Senescence Is A Characteristic Feature Of The Human Life-Span |
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The Decline of Physiological Effectiveness |
- Rate of cell division and number of cells reduce
- All cells are capable to divide during embryological development
- Cells lose ability to divide after birth or have a lower growth rate
- Born with a fixed number of neurones → cannot divide/be replaced
- Decline in functional effectiveness of cells and organ systems
- Deterioration in cells / slower responds to stimuli / slows homeostatic mechanism / increases change of dysfunction and death
- Ageing is controlled by genes but can be slowed down by
- Regular (and adequate) sleep, (well balanced) meals, exercise
- Refrain from smoking and alcohol
- Keep body mass close to desirable mass for your height
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Effect of Age on |
- BMR
- Number of cells decreases during ageing → lowers BMR
- BMR decreases by ≈ 5% every 10 years above the age of 55
- 10-20 years - rapid decrease associated with adolescent growth spurt
- 20-35 - no change as body same size / same level of activity
- 30-70 - slow decrease associated with loss of muscles / gain of fat / reduced activity
- CARDIAC OUTPUT = STROKE VOLUME x HEART RATE
- Cardiac output decreases even though heart rate does not decline
- Due to cardiac muscle fibres weaken (mainly left ventricle)
- Decreases stroke volume of ventricles/volume of blood pumped per beat/cycle
- NERVE CONDUCTION VELOCITY
- Cells in peripheral nervous system and brain get less
- Neurones (nerve cells) are lost and cannot divide
- Effect of cell loss depends on cells location
- Brain loses ≈25% of cells that control muscular movement but hardly any that control speech → changes muscle coordination but not ability to speak
- LOSS OF MYELIN: no saltatory conduction / impulses cannot jump from node to node / impulses must pass through greater amount of membrane
- INCREASED WIDTH OF SYNAPSES: longer needed for diffusion/movement/greater distance to receptors/further to stimulate post-synaptic membrane/further diffusion distance of transmitter (across synapse)
- SLOWER SYNAPTIC TRANSMISSION: presynaptic neurones produce less neurotransmitter
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Reproductive Function in the Human Female and the Consequent Decline in Fertility |
| Effect of Ageing on Female Fertility → MENOPAUSE (45-55 year old women) |
- Ovaries gradually become insensitive to FSH / secretion of oestrogen becomes less / ovulation becomes less / menstrual cycle becomes less / vagina walls become thinner / woman is infertile when oestrogen secretion stops
- Levels of gonadotrophins (FSH, LH) rise to a peak after menopause
- At menopause, oestrogen no longer secreted
- FSH and LH no longer inhibited by negative feedback
- SYMPTOMS: due to loss of oestrogen
- Intense sweating / uncomfortable warmth / psychological problems
- Increase risk of osteoporosis (loss of bone tissue) and heart diseases
- TREATMENT: Hormone replacement therapy (HRT)
- Postmenstrual woman take in small doses of oestrogen and progesterone
- As tablets (orally) or apply implants beneath skin (skin patches)
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References and Further Reading
AQA (2006) GCE Biology/Biology (Human) 2006 specification, [PDF]
