body balance

Question 1

body fluid distirbution

Answer 1

-lean adults contain between 55-60% fluids
-comprised of
-intracellular fluid 2/3rd of total fluid
-extracellular fluid 1/3rd of total fluid
-80% interstitial fluid
-20% plasma
[Na+ and Cl- main extracellular solutes]

Question 2

what is the bodies primary source of water

Answer 2

ingested fluids [1600ml/day] and food [700ml/day]

Question 3

what is metabolic water

Answer 3

water ‘made’ by electron acceptance and H+ binding by 02 during oxidative phosphorylation [during dehydration synthesis -formation of covalent bonds]

Question 4

water loss

Answer 4

-urine production by kidneys
[1500ml/day]
-evaporation from skin [600ml/day]
-exhalation of water vapour from lungs [300ml/day]
-water content of faeces
[100ml/day]

Question 5

osmolality

Answer 5

measure of the concentration of a solution by expressing the total number of solutes per 1Kg of tissue - mOsm/Kg

Question 6

osmolarity

Answer 6

Measure of the concentration of a solution by expressing the total number of solutes per 1L of solvent - mOsm/L

Question 7

2% loss of body mass due to water loss triggers thirst

Answer 7

-detected by osmoreceptors in the thirst centre of hypothalamus
-also neurons triggered by a dry mouth/low saliva flow

Question 8

diuretics

Answer 8

-xanthines
-caffeine, theophylline [tea], and theobromine [chocolate]
-inhibits Na+ reabsorption and promoting water loss
-alcohol [ethanol]
-inhibits ADH secretion
-reduces water resorption and increases water loss

Question 9

RAAS

Answer 9

-renin-angiotensin-aldosterone system
-the loss of water reduces blood volume and pressure [detected by baroreceptors]
-kidneys respond to this by releasing the enzyme renin

Question 10

fluid and solute relationship

Answer 10

Na+ and Cl- regulation plays a key role in body fluid volume
need to maintain a constant Na+ and Cl- concentration [increased consumption results in higher fluid volume and increased blood pressure] the more we excrete the more water we lose due to osmosis

Question 11

3 major hormones dictate Na+ concentration

Answer 11

Angiotensin 2
Aldosterone [increase Na+ reabsorption]
Atrial natriuretic peptide [reduces Na+ reabsorption]

Question 12

ADH regulation of water loss

Answer 12

-primary regulator
-secreted from posterior pituitary
-acts to promote insertion of water channels in the collecting ducts [aquaporins]
-also reduces water lost in sweat and is a vasoconstrictor

Question 13

osmolality in the kidney

Answer 13

-varies on location
-lowest in renal cortex [300 mOsm/kg or iso-osmotic]
-greater towards inner medullary region [up to 1200 mOsm/kg or hyper-osmotic]

Question 14

dilute urine formation

Answer 14

osmolality changes in nephron loop
-increases in descending limb
-decreases a solutes are removed in ascending limb
we are usually slightly over-hydrated, ADH secretion will be low, lack of ADH means little water reabsorbed in late DCT and collecting duct

Question 15

concentrated urine formation

Answer 15

-juxtamedullary nephrons utilised when dehydrated [very long nephron loop passes deep into hyper-osmotic renal medulla]
-tubular fluid osmolality increases to around 1200 mOsm/kg [due to more water leaving the tubules]

Question 16

water intoxication

Answer 16

-when fluid intake is high and constant kidneys cannot match removal to intake. [also occurs if blood loss or excessive sweating followed by consumption of large quantities of plain water]
-cells swell to dangerous levels, hazardous in CNS, neurons contained in cranium, swelling increases intracranial pressure
-result in confusion, headache, drowsiness, cerebral oedema and death

Question 17

function of minerals

Answer 17

-can be a part of enzymes that catalyse biochemical reactions
-plays an important role in immunity
-essential for muscle contraction and cell activation

Question 18

2 groups of minerals based on daily requirement

Answer 18

-macrominerals
->100 mg per day
-microminerals
-<20 mg per day

Question 19

calcium

Answer 19

-most abundant mineral
-present in blood as either free calcium, bound to plasma proteins
-daily requirement 100mg/day
-makes up inorganic component of bone [form extracellular matrix of bone together with collagen], very hard but brittle structure [extremely tough when combined with collagen]

Question 20

functions of calcium -signalling

Answer 20

release of neurotransmitter across neuron synapses
-ca2+ enter axon terminal and trigger exocytosis of synaptic vesicles containing neurotransmitter [Ca+ flow into synaptic end bulb due to concentration gradient]

Question 21

functions of calcium -muscle contraction

Answer 21

Ca2+ released from terminal cisterns in skeletal muscle bind to troponin
-causes tropomyosin to move from binding site on actin filament
-myosin heads can now bind to actin
-muscle can contract

Question 22

functions of calcium - blood clotting

Answer 22

helps catalyse conversion of prothrombin to thrombin, thrombin converts fibrinogen to insoluble fibrin [forms the network of the clot]

Question 23

phosphate

Answer 23

-most of phosphate in body [85%] in combined with calcium and used in bones and teeth
-15% left is in form of phosphate ions
-ions are dihydrogen phosphate [H2PO4-], hydrogen phosphate [HPO4^2-], phosphate [PO4^3-]

Question 24

function of phosphate

Answer 24

-all three phosphate ions act as buffers [mainly in cells but also in extracellular fluid]
-most [phosphate ions are bound to other substrates]
-lipids to form phospholipids
-proteins
-CHO
-nucleic acid
-ATP

Question 25

regulation of calcium and phosphate

Answer 25

-bones provide a ‘bank’ where both are deposited and withdrawn
-hormones responsible for regulation
-parathyroid hormones [PTH]
-calcitriol [active Vit D]
-calcitonin

Question 26

parathyroid hormone

Answer 26

-released from parathyroid glands in response to low blood calcium ion conc.
-stimulates osteoclasts to increase reabsorption of bone
-calcium and phosphate ions from bone matrix released into circulation
-calcium in increased
-however reduces phosphate reabsorption in PT and kidneys

Question 27

calcitonin

Answer 27

-secreted by parafollicular cells of thyroid
-acts to decreased blood calcium ion conc. [reduces activity of osteoclasts, reduces gut absorbance of calcium]
-does not appear to be a major influence [surgical removal has little/no effect on blood calcium conc.

Question 28

sulphur

Answer 28

-exists in its oxidised from called sulphate [SO4^2-]
-found in AA methionine and cysteine [helps provide 3D shape necessary for protein function] and B vitamins thiamine [B1] and biotin [B7]

Question 29

magnesium

Answer 29

-50-60% of bodies magnesium is found in bone matrix as magnesium salts
-remaining 40-50% found in tissues -especially muscle fibres
-has major metabolic roles in production of DNA, RNA and proteins
-acts as a cofactor in enzymes [non-protein component required for enzymes catalytic function]

Question 30

magnesium functions

Answer 30

-facilitates nerve conduction via NMDA receptors [prevents weak signal activation/overactivation]
-muscle contraction and normal heart rhythm [competes with Ca++ facilitating muscle relaxation and subsequent contraction
-modulates insulin secretion and intracellular signalling [reduces risk of type 2 diabetes]

Question 31

iron

Answer 31

-65% found in haemoglobin
-15% found in myoglobin and as an element of enzymes
-remaining 20% stored in form of haemosiderin in tissues
-free iron dangerous in human body [catalyses in formation of free radicals]
-not regulated by excretion
-to much absorption via digestive system can result in haemochromatosis [disorder that can damage organs and increase risk of cancer]

Question 32

acid effects on protein

Answer 32

-protein shape is determined by electrostatic interactions between regions on their side chains [hydrogen bonds, salt bridges (electrostatic attractions)]
-large increase/decrease in H+ conc. causes disruption to these bonding mechanisms
-results in denaturation
-alters protein shape and function

Question 33

protein buffer systems

Answer 33

-haemoglobin in RBC and albumin in plasma [most abundant]
-AA all contain
-a carboxyl group
[-COOH]
-amino group [-NH2]
-when pH rises carboxyl group release a H+ [increase conc. of H+ reduces pH]
-when pH falls amino group bind to excess H+ [reduces conc. of H+, increased pH]

Question 34

dihydrogen buffer system

Answer 34

-functions as a weak acid
-buffers hydroxide ions [OH-] by donating a H+
[OH- strong acid]

Question 35

monohydrogen phosphate buffer system

Answer 35

-acts as a weak base
-binds H+ in solution to form dihydrogen phosphate

Question 36

renal secretion of H+

Answer 36

-both proximal tubule and late distal tubule/collecting duct can secrete H+ and reduce acidity
-mechanisms of secretion differ
-PT involves bicarb ions and carbonic acid
-late DT/collecting duct involves: ammonia conversion of ammonium ions and monohydrogen phosphate to dihydrogen phosphate