BIOL 2020U Lecture Notes - Osteoporosis, Saltatory Conduction, Ovulation

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Published on 29 Jan 2013
The Decline of Physiological Effectiveness
Rate of cell division and number of cells reduce
o All cells are capable to divide during embryological development
o Cells lose ability to divide after birth or have a lower growth rate
o Born with a fixed number of neurones → cannot divide/be replaced
Decline in functional effectiveness of cells and organ systems
o 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
o Regular (and adequate) sleep, (well balanced) meals, exercise
o Refrain from smoking and alcohol
o Keep body mass close to desirable mass for your height
Effect of Age on
o Number of cells decreases during ageing → lowers BMR
o BMR decreases by ≈ 5% every 10 years above the age of 55
o 10-20 years - rapid decrease associated with adolescent growth spurt
o 20-35 - no change as body same size / same level of activity
o 30-70 - slow decrease associated with loss of muscles / gain of fat / reduced
o Cardiac output decreases even though heart rate does not decline
o Due to cardiac muscle fibres weaken (mainly left ventricle)
o Decreases stroke volume of ventricles/volume of blood pumped per beat/cycle
o 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
o LOSS OF MYELIN: no saltatory conduction / impulses cannot jump from node to
node / impulses must pass through greater amount of membrane
o 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)
o SLOWER SYNAPTIC TRANSMISSION: presynaptic neurones produce less
Female reproductive capacity → MENOPAUSE (45-55 year old women)
o 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
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