L1 Flashcards
What is homeostasis?
maintain a steady state environment temp - 37 C PO2 - 95 mmHg PCO2 - 40 mmHg Water - 600 g kg pH - 7.4
what is an important barrier mechanism? where can you find it?
mucus - skin and surfaces near external environment
how much of humans is water?
60%
where is most water in our bodies found?
intracellular - 40% of body weight, 28L
what percent makes up water found in interstitial fluid and lymph?
15% of body weight, 10.5L
what percent makes up water found in plasma?
5% body weight, 3.5 L
how much of the water found in our bodies is extracellular?
20% body weight, 14L = interstitial fluid + lymph + plasma
what are transcellular fluids and what are examples?
CSF and joints - about 1L
-rightly regulated encapsulated spaces - water cannot freely pass
regulated by special epithelium…
what are the constituents of plasma?
Na - 142 K - 4.4 Cl - 102 protein - 1 (resp. for osmotic pressure) osmolality - 290 mOsm
what are the constituents of interstitial fluid?
na - 145 K - 4.5 Cl - 4.5 protein - 0 mM osmolality - 290 mOsm
what are the constituents of cellular fluid?
na - 15 K - 120 cl - 20 protein - 4 osmolality - 290 mOsm
why is osmolality the same across the 3 compartments?
water can flow freely from each compartment
which two compartments are very similar? what do they have high and low levels of?
plasma + interstitial
high NaCl
low K+
what is high and low in cellular fluid?
high K+
low NaCl
what ions are found inside the cell and outside (mostly)?
- TONS of Na inside (10X more inside)
- TONS of K+ outside (25 X more outside)
what is pumped in and out of the cell with the Na+K+ pumps?
Na+ pumped out – 3
K+ pumped in – 2
what is the difference of homeostasis between single cell and multicellular organisms?
- single cell organisms biochem and physiology is controlled by the environment they live in
- multicell organisms generate their own environment in which cells live - organism maintains its own environment
What does the milieu interieur say?
environment must be maintained within limits for optimum functioning
- gas tensions, glucose concentration, osmotic pressure, ion concen., pH, temp
by controlling its mileu the organism is no longer at the mercy of the environment
what are the requirements for a feedback system?
sensor
integrator/comparator
effector
(controlled variable + set point)
what is negative feedback?
reverse the change
what is positive feedback?
make the change even worse - associated with a discrete end point
what happens during anticipation of exercise?
- symp outflow increases to maintain BP = vasoconstriction
- hypothalamus senses heat increase and inhibits symp flow = vasodilation
*BP trumphs everything - without BP can’t supply O2 to tissue…
what are set points?
vary form person to person - or over time within the individual
- deviations can either be 1. protective or 2. pathological
carcadian rhythm - since daily routine is so variable set points vary between active and passive times (day and night)
what is feed forward control?
“excitement” or anticipation of change - gets the body ready!
explain why homeostatic mechanisms can sometimes be redundant?
more than 1 control mech. – the more important, there are more things to back it up – if one fails, there are more to back it up.
what is equilibrium?
no net energy transfer - there is balance
equal potential energy between compartments
forward rnx = reverse rnx
what is steady state?
consistency over time - provide new stuff for decay
there is a rate of input and output - constant energy demands, constant metabolic expenditure
does not change over time
-most human mechanisms require a lot of energy to keep systems in steady state
ex. - cortisol
