Cairan tubuh farmasi

Keseimbangan Cairan Tubuh & Elektrolit

Departemen Fisiologi

Fak. Kedokteran USU

Total Cairan Tubuh Infant mempunyai kandungan lemak, tulang

lebih rendah & sedangkan kandungan air sebesar 73% atau lebih

Total cairan tubuh berkurang seiring pertambahan usia

Pria sekitar 60% berat badan; Wanita sekitar 50% berat badan

Hal ini disebabkan karena pada wanita: Kandungan lemak lebih tinggi Otot rangka lebih sedikit

Pada usia tua, kandungan air sekitar 45%

Fluid Compartments Water occupies two main fluid compartments Intracellular fluid (ICF) – about two thirds by

volume, contained in cells Extracellular fluid (ECF) – consists of two major

subdivisions Plasma – the fluid portion of the blood Interstitial fluid (IF) – fluid in spaces between cells

Other ECF – lymph, cerebrospinal fluid, eye humors, synovial fluid, serous fluid, and gastrointestinal secretions

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Electrolyte Composition of Body Fluids

Figure 26.2

Beberapa mekanisme sehingga suatu zat dapat melewati membran

1. Difusi

2. Difusi yang dipermudah

3. Osmosis

4. Endositosis dan eksositosis, dan

5. Epithelial transport

Difusi Yang Dipermudah

Transport Aktif Transport Aktif Primer Pompa

Natrium-Kalium Transport Aktif Primer Pompa

Kalsium Transport Aktif Sekunder:

Kotransport Natrium pada Glukosa dan Asam Amino

Transport Aktif

Saat membran sel menggerakkan molekul zat untuk mendaki melawan gradien konsentrasi (atau mendaki melawan arus listrik atau melawan gradien tekanan,) maka proses ini disebut transport aktif.

Memerlukan energi Transport aktif primer: dalam bentuk ATP Transport aktif sekunder: gradien

konsentrasi ion natrium

Osmosis

Keadaan pergerakan netto air yang disebabkan karena adanya pebedaan konsentrasi disebut osmosis

Endositosis dan Eksositosis

Endositosis merupakan suatu mekanisme dimana membran meliputi (membungkus) bahan – bahan yang penting atau cairan ekstraseluler dan isinya.

Dua bentuk dasar dari endositosis adalah pinositosis dan fagositosis.

Cerebrospinal Fluid

Kapasitas Cerebral cavitiy sekitar 1600-1700 mililiter 150 ml merupakan cerebrospinal fluid, sisanya otak dan medulla spinalis

Cerebrospinal fluid tersebut terdapat pada ventricle otak, cisterna dan subarachnoid space antara otak & medulla spinalis

Fungsi utama CSF sebagai bantalan otak, keduanya memiliki gravitasi yg hampir sama

Blood–Cerebrospinal Fluid andBlood-Brain Barriers

Terdapat antara darah & CSF & cairan otak Barriers antara choroid plexus dan membran

kapiler jaringan semua area parenkhim otak kecuali sebagian hipothalamus, kelenjar pineal, area postrema yang mana pada daerah ini bahan-bahan (substans) jaringan lebih mudah berdifusi ke jaringan

Pembentukan

CSF dibentuk dengan kecepatan 500ml per hari. 2/3 dari CSF berasal dari plexus choroideus

pada ventrikel 4, terutama pada 2 ventrikel bagian lateral

Sebagian CSF merupakan hasil sekresi ependymal seluruh permukaan ventrikel dan membran arachnoid, dan sebagian berasal dari otak sendiri melalui bagian perivascular sekeliling pembuluh darah yang melewati otak

Aliran CSF Melalui choroid plexuses dan kemudian melalui

sistem cerebrospinal. Cairan yang disekresikan di lateral ventricles mula-mula menuju third ventricle; kemudian setelah bertambah mengalir kebawah menuju aqueduct of Sylvi sampai fourth ventricle, tempat cairan bertambah.

Akhirnya cairan keluar melalui 3 lubang kecil ; 2 foramen Luschka sebelah lateral dan sebuah midline foramen Magendie, memasuki cisterna magna, (ruangan cairan yang berada di belakang medulla dan antar acerebellum). Cisterna magna merupakan lanjutan ruangan subarachnoid yang berada di sekeliling otak dan medulla spinalis

Hampir seluruh CSF kemudian mengalir dari cisterna magna melalui ruang subarachnoid sekeliling cerebrum. CSF mengalir melalui arachnoidal villi menuju sinus venous sagittal dan sinuses venous yang lain. Dan CSF dikosongkan menuju aliran vena melalui pori-pori vili ini

Teori Pembentukan CSF

Sekresi CSF oleh plexus choroideus merupakan active transport sodium ions melalui epithelial cells yang berada di bagian luar plexus.

Ion sodium menarik ion chlorida. Kedua ion in meningkatkan konsentrasi sodium chloride di CSF yang mana kemudian segera menyebabkan osmosis air

Glukosa memasuki CSF dan ion potassium dan bicarbonate keluar CSF menuju kapiler

Susunan CSF

Karakteristik CSF sebagai berikut: Tekanan osmotik, kira-kira sama dengan plasma, konsentrasi ion , juga kira-kira sama dengan plasma; ion chlorida sekitar 15 per cent Lebih besar dari plasma; ion potassium, kira-kira 40 per cent lebih sedikit; dan glucosa, sekitar 30 per cent lebih sedikit


Water Intake and Output

Figure 26.4


Acid-Base Balance

Normal pH of body fluids

Arterial blood is 7.4

Venous blood and interstitial fluid is 7.35

Intracellular fluid is 7.0

Alkalosis or alkalemia – arterial blood pH rises above 7.45

Acidosis or acidemia – arterial pH drops below 7.35 (physiological acidosis)


Regulation of Water Intake: Thirst Mechanism

Figure 26.5


Figure 26.6

Mechanisms and Consequences of ADH Release


Regulation of Sodium Balance: Aldosterone

Figure 26.8


Figure 26.10

Mechanisms and Consequences of ANP Release


Disorders of Water Balance: Dehydration

Water loss exceeds water intake and the body is in negative fluid balance

Causes include: hemorrhage, severe burns, prolonged vomiting or diarrhea, profuse sweating, water deprivation, and diuretic abuse

Signs and symptoms: cottonmouth, thirst, dry flushed skin, and oliguria

Prolonged dehydration may lead to weight loss, fever, and mental confusion

Other consequences include hypovolemic shock and loss of electrolytes


Figure 26.7a

Disorders of Water Balance: Dehydration

Excessive loss of H2O from ECF

1 2 3ECF osmotic pressure rises

Cells lose H2O to ECF by osmosis; cells shrink

(a) Mechanism of dehydration


Renal insufficiency or an extraordinary amount of water ingested quickly can lead to cellular overhydration, or water intoxication

ECF is diluted – sodium content is normal but excess water is present

The resulting hyponatremia promotes net osmosis into tissue cells, causing swelling

These events must be quickly reversed to prevent severe metabolic disturbances, particularly in neurons

Disorders of Water Balance: Hypotonic Hydration


Figure 26.7b

Disorders of Water Balance: Hypotonic Hydration

Excessive H2O enters the ECF

1 2 ECF osmotic pressure falls

3 H2O moves into cells by osmosis; cells swell

(b) Mechanism of hypotonic hydration


Disorders of Water Balance: Edema

Atypical accumulation of fluid in the interstitial space, leading to tissue swelling

Caused by anything that increases flow of fluids out of the bloodstream or hinders their return

Factors that accelerate fluid loss include:

Increased blood pressure, capillary permeability

Incompetent venous valves, localized blood vessel blockage

Congestive heart failure, hypertension, high blood volume


Edema

Hindered fluid return usually reflects an imbalance in colloid osmotic pressures

Hypoproteinemia – low levels of plasma proteins

Forces fluids out of capillary beds at the arterial ends

Fluids fail to return at the venous ends

Results from protein malnutrition, liver disease, or glomerulonephritis, sindroma nefrotik


Edema

Blocked (or surgically removed) lymph vessels:

Cause leaked proteins to accumulate in interstitial fluid

Exert increasing colloid osmotic pressure, which draws fluid from the blood

Interstitial fluid accumulation results in low blood pressure and severely impaired circulation

Occur s with net loss of sodium or net water excess

Kidney disease with salt wasting, adrenal insufficiency, GI losses, increased sweating, diuretics, SIADHS&S: personality change, postural hypotension, postural dizziness, abd cramping, diarrhea, tachycardia, convulsions and coma

Caused by excess water loss or overall sodium excess

Excess salt intake, hypertonic solutions, excess aldosterone,diabetes insipidus, increased water loss, water deprivation S&S: thirst, dry, flushed skin, dry, stick tongue and mucous

membranes

Hypernatremia (Na > 145, sp gravity < 1.010)

Hyponatremia

(Na < 135,

sp gravi ty > 1.030


Regulation of Potassium Balance

Hyperkalemia and hypokalemia can:

Disrupt electrical conduction in the heart

Lead to sudden death

Hydrogen ions shift in and out of cells

Leads to corresponding shifts in potassium in the opposite direction

Interferes with activity of excitable cells


Regulation of Calcium

Ionic calcium in ECF is important for:

Blood clotting

Cell membrane permeability

Secretory behavior

Hypocalcemia:

Increases excitability

Causes muscle tetany


Regulation of Calcium

Hypercalcemia:

Inhibits neurons and muscle cells

May cause heart arrhythmias

Calcium balance is controlled by parathyroid hormone (PTH) and calcitonin


Regulation of Calcium and Phosphate

PTH promotes increase in calcium levels by targeting:

Bones – PTH activates osteoclasts to break down bone matrix

Small intestine – PTH enhances intestinal absorption of calcium

Kidneys – PTH enhances calcium reabsorption and decreases phosphate reabsorption

Calcium reabsorption and phosphate excretion go hand in hand


Influence of Calcitonin

Released in response to rising blood calcium levels

Calcitonin is a PTH antagonist, but its contribution to calcium and phosphate homeostasis is minor to negligible

InterActive Physiology®: Fluid, Electrolyte, and Acid/Base Balance: Electrolyte HomeostasisPLAYPLAY


Acid-Base Balance

Normal pH of body fluids

Arterial blood is 7.4

Venous blood and interstitial fluid is 7.35

Intracellular fluid is 7.0

Alkalosis or alkalemia – arterial blood pH rises above 7.45

Acidosis or acidemia – arterial pH drops below 7.35 (physiological acidosis)


Hydrogen Ion Regulation

Concentration of hydrogen ions is regulated sequentially by:

Chemical buffer systems – act within seconds

The respiratory center in the brain stem – acts within 1-3 minutes

Renal mechanisms – require hours to days to effect pH changes


Respiratory Acidosis and Alkalosis

Result from failure of the respiratory system to balance pH

PCO2 is the single most important indicator of respiratory inadequacy

PCO2 levels

Normal PCO2 fluctuates between 35 and 45 mm Hg

Values above 45 mm Hg signal respiratory acidosis

Values below 35 mm Hg indicate respiratory alkalosis


Respiratory Acidosis and Alkalosis

Respiratory acidosis is the most common cause of acid-base imbalance

Occurs when a person breathes shallowly, or gas exchange is hampered by diseases such as pneumonia, cystic fibrosis, or emphysema, impaired activity of diaphragm muscle and impaired respiratory control in the brain stem

Respiratory alkalosis is a common result of hyperventilation and is caused by low level of oxygen in the plasma, meningitis, head injury and anxiety


Metabolic Acidosis

All pH imbalances except those caused by abnormal blood carbon dioxide levels

Metabolic acid-base imbalance – bicarbonate ion levels above or below normal (22-26 mEq/L)

Metabolic acidosis is the second most common cause of acid-base imbalance

Typical causes are ingestion of too much alcohol and excessive loss of bicarbonate ions,such as diarrhea, and excessive vomitting

Other causes include accumulation of lactic acid, shock, ketosis in diabetic crisis, starvation, and kidney failure,high extracellular K+


Metabolic Alkalosis

Rising blood pH and bicarbonate levels indicate metabolic alkalosis

Typical causes are:

Vomiting of the acid contents of the stomach

Hypokalemia

Intake of excess base (e.g., from antacids)

Constipation, in which excessive bicarbonate is reabsorbed


Respiratory and Renal Compensations

Acid-base imbalance due to inadequacy of a physiological buffer system is compensated for by the other system

The respiratory system will attempt to correct metabolic acid-base imbalances

The kidneys will work to correct imbalances caused by respiratory disease


Respiratory Compensation

In metabolic acidosis:

The rate and depth of breathing are elevated

Blood pH is below 7.35 and bicarbonate level is low

As carbon dioxide is eliminated by the respiratory system, PCO2 falls below normal

In respiratory acidosis, the respiratory rate is often depressed and is the immediate cause of the acidosis


Respiratory Compensation

In metabolic alkalosis:

Compensation exhibits slow, shallow breathing, allowing carbon dioxide to accumulate in the blood

Correction is revealed by:

High pH (over 7.45) and elevated bicarbonate ion levels

Rising PCO2


Renal Compensation

To correct respiratory acid-base imbalance, renal mechanisms are stepped up

Acidosis has high PCO2 and high bicarbonate levels

The high PCO2 is the cause of acidosis

The high bicarbonate levels indicate the kidneys are retaining bicarbonate to offset the acidosis


Renal Compensation

Alkalosis has Low PCO2 and high pH

The kidneys eliminate bicarbonate from the body by failing to reclaim it or by actively secreting it

InterActive Physiology®: Fluid, Electrolyte, and Acid/Base Balance: Acid/Base HomeostasisPLAYPLAY

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Cairan tubuh farmasi