metab II: exam 4

roles of water in the body

• chemical reactions

• body temp + regulation

• lubrication & protection

• solvent + transport medium

• maintenance of blood volume

• acid-base balance

what are the two major resevoirs for water

• intracellular (67%)

• extracellular (33%)

what % of BW does water account for

• 60%

• men have more water than women

how much water is needed daily

• ~ 2,500 ml

  • 300 ml produced via cellular respiration/day

  • 110 g H2O/100 g fat

  • 42 g H20/100 g protein

  • 60 g H2O/100 g carb

how is water produced in ETC & ox-phos

• in the mitochondrial matrix

  • at the end of etc in complex IV

  • electron combines with O2 to form H2O

  • electrons can escape from complex I or III forming superoxide

  • MnSOD or SOD2 produces H2O2 → converted to water by catalase

• In intermembrane space

  • electrons can escape from complex III forming superoxide

  • Cu/ZnSOD or SOD1 produces H2O2 → converted to water by catalase or other peroxidases

what is osmolarity

• measures concentration of particles (electrolytes, proteins, glucose) in a solution

• regulates water transport in and out of blood vessels

• regulates blood volume by 2 mechanisms

  • direct effects: water transport due to osmosis

    • induces a short transient change in blood volume

  • indirect effects: controlling the release of hormones

    • long term effects on blood volume + blood pressure

regulators of water balance

• hypothalamus

  • sense of osmolarity

  • controls thirst

  • controls hormone (ADH)

• kidneys

  • regulates water excretion + absorption

  • responds to hormones

• hormones

  • ADH or vasopressin

  • renin angiotensin system (RAS)

thirst center in the hypothalamus

• monitors blood concentration (osmolarity) + volume via osmoreceptors

  • when blood concentration increases → triggers thirst

  • stimulates secretion of ADH from pituitary gland

  • ADH acts on kidney to increase water reabsorption

  • increases water in circulation → reduces osmolarity

  • heart can also stimulate secretion of ADH → heart senses blood pressure (regulated by volume) via baroreceptors

water reabsorption in the kidney

• ADH

  • stimulates expression of water channels (aquaporins or AQPs) on the cell membrane of collecting ducts

  • AQPs are not normally found on surface of cell - they are stored in internal vesicles which are delivered to cell surface by ADH

• diabetes insipidus

  • caused by lack of ADH

  • water is not reabsorbed and urine is diluted

  • excessive urination & dehydration

renin-angiotensin aldosterone system

• controls blood pressure by regulating sodium retention + potassium excretion

• organs involved: liver, kidney, adrenal glands, vascular system, brain

• enzymes/hormones involved:

  • renin (enzyme): secreted by kidney → produces ang I

  • angiotensin converting enzyme (ACE) → produces ang II

  • aldosterone: produced by adrenal gland functions in kidney → increases blood pressure by reabsorption of Na + excretion of K

    • acts on cortical collecting ducts of kidney

aldosterone: Na/K regulation

• increases Na reabsorption in kidney

• Na is reabsorbed while K+ is excreted

• at basolateral membrane: Na/K ATPase transports Na into circulation by taking K inside cells

• K is then elimated at apical membrane to maintain Na & K gradients

• water follows Na

  • transport of Na induces water reabsorption

  • water is transported via osmosis

antihypertensive drugs

direct effects of osmolarity

• osmosis: passage of water from a less concentrated solution to a more concentrated solution

• osmotic pressure: the result of movement of water across a semipermeable membrane

  • the pressure required to stop the movement of solvent to a more concentrated solution (osmosis) & depends on number of solute particles

  • if osmotic pressure > BP → water flows into vessels

  • osmotic pressure is caused by proteins that can’t cross capillaries

diffusion

• passage of molecules from a compartment with high concentration to a compartment with low concentration (volume doesn’t change)

  • not involved in water distribution

factors regulating water distribution

• filtration force

  • moves water from plasma to ISF

  • caused by pumping of heart

  • is different in arteries & veins

• reabsorption forces

  • moves water from ISF to plasma due to plasma’s high osmotic pressure

water movement is regulated by blood pressure

• veins

  • less layers of VSMCs in the media

  • prominent adventitia (external layer)

  • valves

• arteries

  • prominent media layer

  • vascular smooth muscle cells (VSMC)

  • elastic laminas