Homeostasis: Fluid and Gas Level Regulation

Vocabulary terms and definitions covering homeostatic regulation of body fluids, the urinary system, gas concentrations, and the respiratory control mechanisms described in Chapter 6.

Homeostasis

The process involving nerves and hormones to maintain the body’s internal environment within tolerance limits through the control of metabolism and physiological and behavioural activities.

Intracellular fluid

Also known as cytosol, this is the fluid found inside the cells and accounts for approximately two-thirds of total body water.

Extracellular fluid

Fluid found outside the cells, including blood plasma, interstitial fluid, and transcellular fluid, accounting for approximately one-third of total body water.

Intravascular fluid

Also known as blood plasma, it is the fluid part of the blood located within the blood vessels.

Interstitial fluid

Also known as intercellular fluid or tissue fluid, it is the fluid located between the cells.

Transcellular fluid

Fluid found in specific body regions such as the brain and spinal cord (cerebrospinal fluid), eyes, joints, and surrounding the heart.

Osmotic pressure

The tendency of a solution to take in water; a higher difference in osmotic concentrations between two solutions results in greater osmotic pressure.

Metabolic water

A small amount of water obtained as a by-product of chemical processes occurring within the cells, such as cellular respiration.

Excretion

The removal of the waste products of metabolism from the body to prevent them from reaching harmful or toxic concentrations.

Nephron

The functional unit of the kidney, with roughly 1.2 million per kidney, responsible for excretion and water regulation through filtration, reabsorption, and secretion.

Ureter

The tube that leaves each kidney and drains urine into the muscular urinary bladder.

Urethra

The tube that carries urine from the bladder to the outside of the body.

Osmoreceptors

Specialized receptors located in the hypothalamus that detect changes in the osmotic pressure of the blood.

Antidiuretic hormone (ADH)

Also known as vasopressin, it is produced by the hypothalamus and released by the posterior pituitary to increase the permeability of the distal convoluted tubules and collecting ducts to water.

Aldosterone

A hormone secreted by the adrenal cortex that increases sodium ion reabsorption into the blood and potassium ion secretion into the urine via a sodium-potassium pump.

Thirst centre

A region in the hypothalamus that, when stimulated by osmoreceptors, creates the conscious feeling of thirst to prompt fluid intake.

Dehydration

A condition occurring when water loss exceeds water intake, causing cells to shrink as water moves into the plasma and interstitial fluid.

Water intoxication

Also known as water poisoning, it occurs when body fluids become so diluted that cells take in extra water by osmosis and swell.

Cellular respiration equation

The process described by $6O_2 + C_6H_{12}O_6 \rightarrow 6CO_2 + 6H_2O + \text{energy}$, requiring oxygen and producing carbon dioxide as waste.

Phrenic nerve

The spinal nerve that carries impulses from the spinal cord to the diaphragm to initiate contraction for breathing.

Intercostal nerves

Spinal nerves that carry impulses to the intercostal muscles to initiate contraction for breathing.

Respiratory centre

Located in the medulla oblongata, this area regulates the rate and depth of breathing and contains regions for both inspiration and expiration.

Carbonic acid formation

The chemical reaction where carbon dioxide dissolves in water: $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$.

Aortic and Carotid bodies

Peripheral chemoreceptors located in the walls of the aorta and carotid arteries sensitive to changes in the concentration of $O_2$, $CO_2$, and $H^+$ in blood plasma.

Central chemoreceptors

Receptors located in the medulla oblongata sensitive to changes in the concentration of $CO_2$ in the blood and $H^+$ in the cerebrospinal fluid.

Hyperventilation

Rapid, deep breathing that provides more oxygen and removes more carbon dioxide than necessary, potentially leading to a loss of the urge to breathe.