Human Anatomy/Physiology Chapter 25

Adipose tissue. Obese persons have less water than thin persons.

• 1. Intracellular
• 2. Extracellular

The intracellular compartment includes the water located in all the cells of the body. Most water, about 63%, is located in the intracellular compartment. 

The extracellular compartment includes the fluid located outside all the cells and represents about 37% of the total body water. The extracellular compartment includes the water located between cells, called Interstitial fluid; water within blood vessels (plasma); and water within lymphatic vessels (lymph). 

• 1. Interstitial fluid: water located between cells.
• 2. Plasma fluid: 90% water.
• 3. Lymph fluid
• 4. Transcellular fluid
•     a. cerebrospinal fluid (CSF)
•     b. aqueous and vitreous humors in the eyes
•     c. synoival fluids of joints
•     d. serous fluids in body cavities
•     e. glandular secretions

• 1. Interstitial fluid
• 2. Plasma

• 1. Sodium - Na+
• 2. Chloride - Cl-
• 3. Bicarbonate HCO3- ions.

* The plasma portion contains more protein than other extracellular fluids do.

• 1. Potassium - K+
• 2. Phosphate - PO4,3-
• 3. Magneisum - MG2+

Water of metabolism is when water comes from the breakdown of foods. 

Thirst is the primary regulator of water intake. The thirst center is in the hypothalamus of the brain. As the body loses water, the thirst center in the hypothalamus is stimulated, thus causing you to drink. 

• 1. kidneys - about 60%
• 2. skin - about 28%
• 3. lungs - its own percentage plus skin makes the 28%
• 4. digestive tract - 12%

The kidneys are the primary regulator of water output. Water regulation occurs mainly through the action of antidiuretic hormone (ADH) on the collecting duct. 

When body water content is low, the posterior pituitary gland releases ADH. It stimulates the collecting duct to reabsorb water, thereby decreasing water in the urine and increasing blood volume. When body water content is high, the secretion of ADH decreases. As a result, less water is reabsorbed from the collecting duct, and the excess water is eliminated in the urine. 

A dehydrated person usually has poor skin turgor. "Skin turgor" is assessed by pinching the skin and then observing how quickly the skin flattens, or returns to its normal position. If a person is well hydrated, the pinched skin quickly flattens out. The skin of a dehydrated person, however, flattens out more slowly, giving the skin the appearance of a tent, hence the term tenting for the appearance of the skin of a dehydrated person. 

Tenting is due to the depletion of fluid in the interstitial space. If untreated blood volume and blood pressure continue to decline, the person develops a low volume (hypovolemic) shock.

Fluid retention is called edema. The body can retain excess water and deposit it in various compartments, especially the interstitial space. 

• 1. Hypoxemia and Cyanosis caused by Pulmonary Edema (excessive body water in the lungs).
• 2. Neurological Dysfunction caused by Cerebral Edema (excessive water within the brain).

Fluid shifts because of a change in the "pushing and pulling" forces of the capillaries. The forces include: the capillary filtration force, the plasma oncotic pressure, the effect of lymphatic drainage, and the effects of plasma protein that is trapped in the tissue space. Alteration of any of these factors affects water movement.

• 1. First spacing: this refers to the normal distribution of water as described earlier. 
• 2. Second spacing refers to the accumulation of water in the interstitial spaces (interstitial edema). Generally, with adequate treatment this water can be reabsorbed and excreted.
• 3. Third spacing refers to the accumulation of water in spaces from which it is not easily absorbed. For instance, the water that accumulates in the abdominal cavity as ascites is not easily reabsorbed. 

Sodium. 

Aldosterone. Aldosterone stimulates the distal tubule of the nephron unit to reabsorb sodium. Usually, when "sodium moves, water moves"; this means that aldosterone causes the reabsorption of both sodium and water. 

Hypernatremia. The kinds of patients who develop this are elderly persons following surgery or fever, patients who have been on prolonged diuretic therapy because of the loss of excessive water as urine, or uncontrolled diabetic patients with hyperglycemia. 

Hyponatremia refers to a decrease in the concentration of plasma sodium. Normal plasma sodium levels are essential for normal brain function. Often a patient becomes hyponatremic because of excess water in the blood. 

Potassium is the chief intracellular cation and aldosterone regulates its concentration just like it regulates sodium (extracellular). 

The kidney is the primary organ responsible for the excretion of excess potassium. 

Hyperkalemia refers to excess potassium in the blood. The primary cause of hyperkalemia is kidney disease, since the kidneys play a major role in the elimination of potassium. 

Hypokalemia refers to a lower-than-normal amount of potassium in the blood. Hypokalemia usually presents as muscle fatigue, leg cramps, abdominal distention, and cardiac rhythm disturbances. The most common cause of hypokalemia is the prolonged use of potassium-losing diuretics (kaliuretics). 

Ninety-nine percent of the body's calcium is in the bones and teeth. Parathyroid hormone is the primary regulator of plasma levels of calcium.

Magnesium is important in the function of the heart, muscles, and nerves. Kidney disease is the major cause of hypermagnesemia. 

Chloride is the chief extracellular anion. Chloride usually follows sodium. That is, when sodium is actively pumped from the tubules into the peritubular capillaries, chhloride follows the sodium passively. 

Bicarbonate is an important anion in acid-base balance. icarbonate is an alkaline (basic) substance that helps remoe excess acid from the body. It is also the form in which carbon dioxide (CO2) is transported in the blood. Bicarbonate excretion is controlled by the kidneys. Bicarbonate can be either reabsorbed or excreted, depending on the body's needs.

• 1.) Buffers
• 2.) Respirations
• 3.) Kidney function

• 1.) Acidosis - when high in acid and H+
• 2.) Alkalosis - opposite of acidosis; less H+

A decrease in pH number below 7.35 (acidosis) is an imbalance causes by an increase in H+ ions within the body.

The two types of acidosis are respiratory acidosis and metabolic acidosis.

Renal compensation.