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Movement of water across the membranes of cells, role of water in the body, chemical reactions within the body to maintain homeostasis

Role of water in the body

all water is used as a medium to carry solutes, like electrolytes and metabolites, throughout the body

Males contain how much water by weight?


Women contain how much water by weight?


How is water distributed throughout the body?

2/3 - intracellular compartments - inside cells
1/3 - extracellular compartments - outside cells

Examples of Extracellular compartments (ECF)

1. interstitial spaces
2. plasma
3. lymph
4. fluid in the eyes
5. synovial fluid in joint capsules
6. cerebrospinal fluid
7. serous fluids in cavities
8. lumens
9. glandular secretions - medium that carries hormones

Intracellular Fluids (ICF) contain what types of substances?

1. K⁺
2. Mg²⁺
3. PO₄³⁻
4. SO₂⁴⁻
5. Proteins

Extracellular Fluids (ECF) contain what types of substances?

1. Na⁺
2. Cl⁻
3. Ca²⁺
4. CO₂³⁻

Ions move by

1. diffusion
2. active transport
3. through protein channels or protein transporters

How does water shift with solute?

1. movement of solutes will shift water by osmosis
2. solvent drag - fluid will shift solutes

Daily water input

1500/3000mL/ day

Where do we get all that water from?

10% from metabolic reactions like aerobic respiration
90% from oral consumption

Thirst Reflex

- maintained by the Hypothalamus within Thirst Center that alerts the body for the need of water

Regulation of Thirst Reflex

1. Osmoreceptors - cells that monitor the osmolarity of bodily fluids
2. Baroreceptors - cells that monitor BP (↓BP will trigger thirst reflex to add more volume to blood)

How is thirst reflex suppressed?

stretching the stomach and moistening of oral mucosa will suppress thirst reflex immediately.

Increased H₂O Toxicity?

1. ↑ BP
2. bodily fluids dilute
3. ↓ in solute concentration


1. insufficient amounts of water either by lack of consumption, elevated temperatures, or high activity
2. ↓BP
3. body will compensate by removing H₂O out of ICF and into ECF

Water Output

1. 61% in urine
2. 4% in poop
3. 35% by respiratory tract (exhalation) and skin (sweat)


1. sweat glands secrete sweat
2. excretory mechanism
3. shedds - NH₄, Urea, K⁺, and Na⁺ - forming acid mantle

Insensible Perspiration

1. tiny amounts of sweat shedding at all times
2. not noticeable
3. important for heat regulation
4. lowers body temperature
5. each day .5L of water is shed this way

Sensible Perspiration

1. ↑ temp will ↑ sweat by 100-150mL
2. Diaphoresis
3. associated withe exercise and hot environments
4. an increase in activity can increase visible sweat by 8-10L/day


visible sweat

Causes of body to ↑ Temp?

1. sexual arousal
2. emotional states
3. physical condition

Osmolarity of ECF

285 mOsm/ kg of tissue

Effect of ↑ Osmolarity

1. thirst reflex will trigger
2. ↑ ADH - acts on kidneys to retain water

Effect of ↓ Osmolarity

1. inhibits thirst reflex
2. ↓ ADH - water will be excreted in urine

Affects of BP on Osmolarity

1. ↑ BP will ↑ Glomerular Pressure to ↑ filtration, and pass out more water in urine which will lead to ↓ BP
2. ↓ BP which ↓ Glomerular which will ↓ filtration which will ↓ urine flow. A result is to trigger thirst reflex to ↑ BP.


1. ions or molecules with electrical charges
ie) Na⁺, K⁺, Ca²⁺, Cl⁻, PO₄³⁻
2. electrolytes concentrations will change during weight changes and growing stages

How are electrolytes secreted?

by the kidneys, skin, and lungs

Where are electrolytes stored?

1. skeleton
2. mainly Ca²⁺ and PO₄³⁻
3. downfall is that bone can also store Pb, As, and Hg


1. Cation in ECF
2. involved in sodium-potassium pump
3. vital for glucose absorption
4. essential for muscular contraction
5. Neurotransmitter
6. maintains pH balance with Cl⁻

Body's daily sodium requirement

1. <.5g/ day

how much do we actually consume?

1. 15-20g/ day
2. excess is removed via kidneys and sweat
3. regulated by ANH and Aldosterone

How does salt affect osmolarity?

↑ in salt requires an ↑ in water to balance osmolarity


1. Na⁺ deficiency

Causes of Hyponatremia

- poor diet
- severe burns
- vomiting
- diarrhea
- insufficient Aldosterone secretion
- excessive urination
- Hyperglycemia- ↑ blood sugar

Hyponatremia leads to

- lethargy
- disorientation
- nervous agitation
- seizures
- coma


elevated Na⁺ levels

Causes of Hyernatremia

- dietary
- hypersecretion of Aldosterone
- significant water loss

Hypernatremia leads to

- thirst
- dry mucous membranes
- ↑ body temperature
- hypertension
- bounding pulse
- tendencies toward edema
- convulsions
- death at extremely high Na⁺ levels


1. pH balancer in the body
2. Cl⁻ compounds activate digestive enzymes made of gastric juices
3. can be exhaled, excreted by the kidneys and skin

Chlorine Deficiency

1. causes - impaired digestion, vomiting, diarrhea
2. Leads to Blood Alkalosis

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