A&P 202 (Chap. 27)

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Chapter 27
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1

Intracellular fluid compartment

  • All fluids inside cells of body
  • About 40% of total body weight
2

Extracellular fluid compartment

  • All fluids outside cells
  • About 20% of total body weight
  • Subcompartments
  • Interstitial fluid and plasma; lymph, CSF, synovial fluid
3

Effect of Blood Osmolarity and Blood pressure on thirst

  1. Baroreceptors in heart
  2. Juxtaglomerular apparatuses in kidney
  3. Osmoreceptors in hypothalamus (increased osmolality)
  4. Increased thirst
  1. The baroreceptors in the carotid sinuses and aortic arch detect reduced blood pressure, which signals the hypothalamic thirst center.
  2. Simultaneously, the juxtaglomerular apparatuses detect low blood pressure, which activates the renin-angiotensin system to produce angiotensin II. Angiotensin II stimulates the hypothalamic thirst center.
  3. Osmoreceptors in the hypothalamus shrink when blood osmolality goes up, triggering action potentials that stimulate thirst.
  4. The combination of these inputs activates thirst and promotes water consumption
4

Increase Hormonal Regulation of Blood Osmolality

  1. Blood osmolality increases: Homeostasis Disturbed
  2. Control Center: Osmoreceptors in the hypothalamus control center detect the increase in blood osmolality and signal the posterior pituitary to secrete ADH, which causes thirst. ADH also increases the permeability of the distal convoluted tubule and collecting ducts to water
  3. Effectors Activated: Water reabsorption at the distal convoluted tubule and collecting duct increases; water consumption increases.
  4. Blood osmolality decreases: Homeostasis Restored
5

Decreased Hormonal Regulation of Blood Osmolality

  1. Blood osmolality decreases: Homeostasis Disturbed
  2. Control Center: Osmoreceptors in the hypothalamus detect the decrease in blood osmolality and signal the posterior pituitary to reduce ADH secretion, which decreases thirst.
  3. Effectors Activated: Water reabsorption at the distal convoluted tubule and collecting duct decreases; water consumption decreases.
  4. Blood osmolality increases: Homeostasis Restored
6

Increased Regulation of Blood Volume

  1. High blood volume induces elevated blood pressure: Homeostasis Disturbed
  2. Blood vessels: Sympathetic division baroreceptors detect increased blood
    volume, which causes vasodilation of renal arteries. Heart: Atrial cardiac muscle cells secrete ANH when blood volume increases. Kidneys Juxtaglomerular apparatuses inhibit renin release when blood volume increases, which decreases aldosterone secretion. Pituitary: Baroreceptors inhibit posterior pituitary ADH secretion when blood volume increases.
  3. Increased renal blood flow increases the rate of filtrate formation, and more water is excreted in the urine. Decreased aldosterone and increased ANH decrease Na+ reabsorption into the distal convoluted tubule and
    collecting duct. More Na+ in urine, which decreases blood volume. Decreased ADH decreases water reabsorption by the distal convoluted tubules and collecting ducts. Less water returns to the blood, and more water is excreted in the urine.
  4. Reduced blood volume due to loss of water and Na+ in the urine Homeostasis Restored: lowers blood pressure
7

Decreased Regulation of Blood Volume

  1. Low blood volume induces lowered blood pressure: Homeostasis Disturbed
  2. Blood vessels: Sympathetic division baroreceptors detect decreased blood volume, which causes vasoconstriction of renal arteries. Heart: Atrial cardiac muscle cells do not secrete ANH when blood volume decreases. Kidney: Juxtaglomerular apparatuses stimulate renin release when blood volume decreases, which increases aldosterone secretion. Pituitary: Baroreceptors stimulate posterior pituitary ADH secretion when blood volume decreases. Increased ADH also increases the sensation of thirst.
  3. Decreased renal blood flow decreases filtrate formation, and less water is excreted in urine. Increased aldosterone and decreased ANH increase
    Na+ reabsorption in the distal convoluted tubule and the collecting duct. Less Na+ and water are excreted in the urine. Increased ADH increases the permeability of the distal convoluted tubule and the collecting duct to water. Less water is excreted in urine.
  4. Increased blood volume due to decreased Na+ and water loss in the urine raises blood pressure: Homeostasis Restored
8

Primary intracellular ions (interstitial fluid ions, and plasma ions)

  • Intracellular cation = K+
  • Interstitial fluid cation = Na+
  • Plasma cation = Na+
  • Intracellular anion = Phosphate
  • Interstitial fluid = Cl-
  • Plasma anion = Cl-
9

Regulation of Body Fluid Concentration and Volume

  • Content regulated
  • total volume of water in body remains constant
  • Kidneys
  • primary regulators of water excretion
  • Regulation processes
  • Osmosis
  • Osmolality
  • Baroreceptors
  • Learned behavior
  • Sources of water
  • Ingestion
  • Cellular metabolism
  • Routes of water loss
  • Urine
  • Evaporation
  • Perspiration
  • Respiratory passages
  • Feces
10

Extracellular Fluid Osmolality

  • Osmolality
  • Measure of water vs. solute concentration; the higher the solute concentration, the higher the osmolality
  • Adding or removing water from a solution changes osmolality
  • Increased osmolality: triggers thirst and ADH secretion
  • Decreased osmolality: inhibits thirst and ADH secretion
11

Regulation of ECF Volume

  • ECF can increase or decrease even if osmolality of extracellular fluid is maintained
  • Carotid sinus and aortic arch baroreceptors monitor blood pressure, juxtaglomerular apparatuses monitor pressure changes, receptors in walls of atria and large vessels respond to small changes in BP
  • These receptors activate these mechanisms
  • Neural: increase in BP recognized by baroreceptors. Decreased sympathetic stimulation of afferent arteriole leads to increased pressure in glomerulus leading to increased filtration and increased urine output.
  • Renin-angiotensin-aldosterone
  • Atrial natriuretic hormone (ANH)
  • Antidiuretic hormone (ADH)
12

Regulation of ICF

  1. Large organic molecules, such as proteins, which cannot cross the plasma membrane, are synthesized inside cells and influence the concentration of solutes inside the cells
  2. The transport of ions, such as Na+, K+, and Ca2+, across the plasma membrane influences the concentration of ions inside and outside the cell.
  3. An electrical charge difference across the plasma membrane influences the distribution of ions inside and outside the cell.
  4. The distribution of water inside and outside the cell is determined by osmosis.
13

Regulation of ECF Osmolality

  • Electrolytes
  • Molecules or ions with an electrical charge
  • ngestion adds electrolytes to body
  • Kidneys, liver, skin, lungs remove from body
  • Concentration changes only when growing, gaining or losing weight
  • Na+ Ions
  • Dominant ECF cations
  • Responsible for 90-95% of osmotic pressure
  • Regulation of Na+ ions
  • Kidneys major route of excretion
  • Small quantities lost in sweat {sweat = (in decreasing amounts) water, Na+, urea, Cl-K+, NH3}.
  • Insensible perspiration: is water evaporating from skin. Sensible
  • perspiration: is secreted by the sweat glands. Contains solutes
  • Terms
  • Hypernatremia: elevated plasma Na+
  • Hyponatremia: decreased Na+
14

HYPONATREMIA

  • Causes
  • Inadequatedietary intake of sodium
  • Extrarenal losses
  • Dilution
  • Hyperglycemia
  • Symptoms
  • Lethargy, confusion, apprehension, seizures, and coma
  • When accompanied by reduced blood volume: reduced blood pressure, tachycardia, and decreased urine output
  • When accompanied by increased blood volume: weight gain, edema, and distension of veins
15

HYPERNATREMIA

  • Causes
  • High dietary sodium (rarely causes symptoms)
  • Administration of hypertonic saline solutions
  • Over secretion of aldosterone
  • Water loss
  • Symptoms
  • Thirst, fever, dry mucous membranes, and restlessness
  • Most serious symptoms are convulsions and pulmonary edema
  • When occurring with increased water volume: weight gain, edema, elevated blood pressure, and bounding pulse
16

Regulation of Specific Electrolytes

  • Chloride ions
  • Predominant anions in ECF
  • Magnesium ions
  • Capacity of kidney to reabsorb is limited
  • Excess lost in urine
  • Decreased extracellular magnesium results in greater degree of reabsorption
  • Potassium ions
  • Maintained in narrow range
  • Affect resting membrane potentials
  • Aldosterone increases amount secreted
  • Terms
  • Hyperkalemia: abnormally high levels of potassium in extracellular fluid
  • Hypokalemia: abnormally low levels of potassium in extracellular fluid.
17

Regulation of Calcium Ions

  • Regulated within narrow range
  • Elevated extracellular levels prevent membrane depolarization
  • Decreased levels lead to spontaneous action potential generation
  • Terms
  • Hypocalcemia
  • Hypercalcemia
  • PTH: increases Ca2+ extracellular levels and decreases extracellular phosphate levels
  • Vitamin D: stimulates Ca2+ uptake in intestines
  • Calcitonin: decreases extracellular Ca2+ levels
18

Regulation of Phosphate Ions

  • Under normal conditions, reabsorption of phosphate occurs at maximum rate in the nephron
  • An increase in plasma phosphate increases amount of phosphate in nephron beyond that which can be reabsorbed; excess is lost in urine
  • Hypophosphatemia: reduced absorption from intestine due to vitamin D deficiency or alcohol abuse.
  • Hyperphosphatemia: renal failure, chemotherapy, hyperparathyroidism (secondary to elevated plasma calcium levels)
19

Regulation of Acid-Base Balance

  • Acids
  • Release H+ into solution
  • Bases
  • Remove H+ from solution
  • Acids and bases
  • Grouped as strong or weak
  • Buffers: Resist changes in pH
  • When H+ added, buffer removes it
  • When H+ removed, buffer replaces it
  • Types of buffer systems
  • Carbonic acid/bicarbonate
  • Protein
  • Phosphate
20

Regulation of Acid/Base Balance

  • Buffers: if pH rises, buffers bind H+; if pH falls, buffers release H+
  • Protein buffer: Intracellular and plasma proteins absorb H+. Provide ¾ of buffering in body. E.g., hemoglobin.
  • Bicarbonate buffering system: Important in plasma
  • Phosphate buffer system: important as an intracellular buffer
  • Respiratory center: if pH rises, respiratory rate decreases; if pH falls, respiratory rate increases
  • Respiratory center: if pH rises, respiratory rate decreases; if pH falls, respiratory rate increases
21

Respiratory Regulation of
Acid-Base Balance

  • Achieved through carbonic acid/bicarbonate buffer system
  • As carbon dioxide levels increase, pH decreases
  • As carbon dioxide levels decrease, pH increases
  • Carbon dioxide levels and pH affect respiratory centers
  • Hypoventilation: increases blood carbon dioxide levels
  • Hyperventilation: decreases blood carbon dioxide levels
22

Renal Regulation of
Acid-Base Balance

  • Secretion of H+ into filtrate and reabsorption of HCO3- into ECF cause extracellular pH to increase
  • HCO3- in filtrate reabsorbed
  • Rate of H+ secretion increases as body fluid pH decreases or as aldosterone levels increase
  • Secretion of H+ inhibited when urine pH falls below 4.5
23

Acidosis and Alkalosis

  • Acidosis: pH body fluids below 7.35
  • Respiratory: Caused by inadequate ventilation- reduced elimination of CO2, asthma, damage to respiratory center in brain, emphysema.
  • Metabolic: Results from all conditions other than respiratory that decrease pH- diarrhea, vomiting, ingesting overdose of aspirin, untreated diabetes mellitus, anaerobic respiration
  • Alkalosis: pH body fluids above 7.45
  • Respiratory: Caused by hyperventilation, high altitude (reduced partial pressure of O2
  • Metabolic: Results from all conditions other than respiratory that increase pH- severe vomiting, too much aldosterone, ingestion of substances like bicarbonate of soda.
  • Compensatory mechanisms