Jimmy, a five year old boy, was admitted into the hospital by his pediatrician. He is small for his age at 3ft. tall and weighs 37lbs. He has no known health issues. Jimmy walked into the hospital looking fatigued, his skin was pale, and when we pinched the skin it stayed pinched. His eyes were sunken. Jimmy had caught a stomach virus; he had been vomiting and had diarrhea so severe that he lost 5lbs in just four days. Jimmy was severely dehydrated.
Dehydration is a condition that occurs when a person loses more fluid than they take in. It is a loss of water content and electrolytes (sodium, potassium, calcium and bicarbonate) that are needed for normal body functioning. There are three types of dehydration; mild, moderate and severe. Severe dehydration is a loss of 10%-15% of body fluids. At this point, dehydration becomes a medical emergency. Jimmy was severely dehydrated and immediate steps were taken to rehydrate him. He was given intravenous fluids to restore his water and electrolytes that he had lost.
What was happening in Jimmy’s body is that the osmolarity of his blood is higher than that of his tissues. This naturally causes water to be drawn from the cells and into the blood, since water follows a higher solute. (Where salt goes water follows.) The movement of water into the blood causes increases in blood volume, which increases blood pressure. Giving the blood enough pressure to pass though the glomerulus, the glomerulus is a capillary tuft surrounded by a Bowman’s capsule in the nephron of the kidneys. This is where your blood is filtered.
If dehydration continues the tissues in the body start to die and the cells begin to shrivel. To maintain the homeostasis of the body’s water content or osmoregulation the body secretes a hormone called antidiurect hormone, ADH. ADH is secreted by part of the brain called the hypothalamus, located in an organ called the pituitary gland. When the cells in the hypothalamus detects an increase in blood osmolarity, the pituitary gland secrets ADH. The hormone enters the bloodstream and reaches the kidneys. To the nephrons in a section called the distal convoluted tubules and the collecting ducts that become permeable to water from ADH. That increases water reabsoption which reduces the blood osmolarity. This is an example of negative feedback.
Osmoregulation is also regulated by specialize tissue called the juxtaglomerular apparatus (JGA). It is located by the afferent arterioles that supplies blood to glomerulus. When the blood pressure drops in the afferent arteriole the JGA secrets an enzyme called renin into the bloodstream. Within the blood renin activates a plasma protein called angiotensin. In the capillaries of the lungs angiotensin is converted into angiotensin II. Angiotensin II causes the adrenal gland to secrete a hormone aldosterone, which causes the sodium to be reabsorbed from the nephrons of the kidneys back into the bloodstream. ADH and aldostone work togther to maintain homeosasis. ADH alone would maintain sodium concentrations by the absorption of water, but aldostone helps maintain balance by the absorption of sodium. Another hormone called atrial naturietic peptide (ANP) released by the wall of the heart response to an increase of blood pressure and blood volume. ANP opposes the renin-angiotensin system. ANP inhibits renin release and the secretion of ADH that lowers blood pressure and volume. ANP, ADH and aldostone all regulate the kidneys to maintain proper osmolariy, salt concentration, blood pressure and blood volume. Before Jimmy left the hospital I inform him on importance of drinking lots of fluids.