Whole Body Growth Lecture Flashcards
Cumulative growth over time is shaped like
sigmoidal curve
Cumulative weight is expressed as
total weight at any given time
Shape of cumulative growth is really
stair stepped due to sporadic growth spurts
Self accelerating phase is characterized by
exponential growth
rapid growth with little complexity
In the Self-accelerating phase velocity of growth continues to increase because
there are more and more cells available to divide
rate at which each cell divides soon begins to slow because it becomes
difficult to supply each cell with nutrients and efficiently remove harmful waste
How does the embryo respond to the slowing of the rate at which each cell divides
develops increasingly complex transport mechanisms to supply nutrients and remove waste
when acceleration force is in balance with the counteracting effects of increased complexity and limited nutrients, growth becomes
linear
Point of Inflection
point of maximum growth velocity after which the animal will continue growing but at a decreasing rate
Maximum growth velocity=
period of greatest ADG
Point of inflection occurs during
puberty
Self-decelerating phase
animal approaches mature weight at a decreasing rate of growth
Reduced growth rate is controlled by
many signals including the secretion of somatostatin by the hypothalamus
Asymptote
Point at which food intake matches maintenance requirement
Mature body weight
Mature body weight fluctuates throughout life depending on
available food
reproductive cycle
season
Failure of vital systems is usually after the
reproductive phase of life
Growth may be compared as a function of
chronological age
physiological age
why is the death of an animal important
ensures space for the next generation
Growth over time may be described using different types of curves:
Cumulative
absolute
relative
Chronological age
age in absolute time units
not the same for every animal
Factors that influence growth that can alter the shape of the growth curve
Nutrition
disease
stress
activity level
Physiological age is used to
overcome drawbacks of using chronological age as a point of comparision
Physiological age refers to specific physical or chemical stages of maturity including
height
weight
composition
puberty
sexual maturity
the age at which animals are successfully able to reproduce
Cumulative growth curve
plot of total animal weight over time
sigmoidal curve
Cumulative curves are useful to compare growth but are
not easy to interpret to determine the period of maximum growth (point of inflection)
Absolute growth rate curve
plots gain per unit of time against time
ADG per unit of time
Calculating overall absolute growth rate
ADG=(Y2-Y1)/(t2-t1)
Is absolute growth rate curve a true growth rate of the animal
no- rate changes as an animal grows
ADG is only accurate if the time interval is short
Are we measuring growth relative to where the animal is on its Growth curve using ADG
No
Relative growth rate curve
growth in relation to total weight
whole body or individual tissue growth
Relative growth is greatest
During initial stages of development because animal is small
decreases as the animal continues to grow
Relative growth rate curve equation
RGR=(LnY2-LnY1)/(t2-t1)
whole body growth curves represent a
sum of growth of many different tissues that develop at dramatically different rates
First person to fully appreciate whole body growth curve
John Hammond (1889-1964)
Hammond studies animals under
typical conditions and under malnutrition
Hammond’s observations
body components that are physiologically more important develop first
Extremities complete their development first
Allometric growth
study of how body parts change in size as an animal develops
Julian Huxley studies
allometric growth in fiddler crabs fighting claw compared to the rest of the body
b>1
tissue is growing at a faster rate than the whole and has a high growth impetus and are considered late developing tissues
b<1
tissue is growing at a slower rate than the whole body and has a low growth impetus and are considered early developing tissues
b=1
tissue is growing at a similar rate than the whole and has an average growth impetus
also called isometric growth
Allometric growth based on proportions does not fully describe
growth changes
When nutrition is limiting the tissues have
a different priority for nutrients, based on the sequence in which they developed and on their functional priority
Is allometric growth useful
yes- some tissues do grow in proportion to the whole
early developing muscles
distal aspects of thoracic and hind limbs
proximal thoracic and hind limb
late developing muscle
abdominal muscle
neck to thoracic limb- increased weight bearing duties and potential increases from secondary sex characteristics
Muscles developing at similar rate to the rest of the body
muscles surrounding the spinal column
we can measure changes in tissue or chemical composition on an
absolute basis
percent basis
absolute basis
cumulative weight gain over time
percent basis
proportion of the total body weight over time
Maximum growth for each tissues occurs
Bone>Muscle>Fat
chemicals in bone, muscle and fat
water
protein
lipid
ash
Fat becomes a ______ proportion of the body with age
larger
muscle and bone make up a ______ proportion with age
smaller
water and protein make up a _____ proportion with age
smaller
Water is how much of muscle
68-85%
Water content is greatest
early in life and decreases with age
Absolute and percentage protein content
increases with age
Water content of fat cells is ___ early on and _____ with age
high
decreases
Protein content in bone is ___ early and ____ later in life
greatest
decreases
Absolute mineral content
increases with age
Fat content tends to ____ in bone
increase
Connective tissue ____ with age
increases
collagen and elastin increase significantly with muscle development but as a percentage it _____ with age
decreases
as muscle atrophies with age, percentage of connective tissue
increases
