Hydration, Water Balance, and the Urinary Sys

osmoregulation

regulation of the water-salt balance to maintain a normal balance within internal fluids

excretion

elimination of metabolic wastes by an organism at exchange boundaries such as the plasma membrane of single-celled organisms and excretory tubules of multicellular animals

ammonia

nitrogenous end product that takes a limited amount of energy to produce but requires much water to excrete because it is toxic

urea

main nitrogenous waste of terrestrial amphibians and most mammals

uric acid

main nitrogenous waste of insects, reptiles, and birds

urine

liquid waste product made by the nephrons of the vertebrate kidney through the processes of glomerular filtration, tubular reabsorption, and tubular secretion

kidneys

paired organs of the vertebrate urinary system that regulate the chemical composition of the blood and produce a waste product called urine

ureters

tubular structure conducting urine from the kidney to the urinary bladder

urinary bladder

organ where urine is stored

urethra

tubular structure that receives urine from the bladder and carries it to the outside of the body

nephrons

microscopic kidney unit that regulates blood composition by glomerular filtration, tubular reabsorption, and tubular secretion

glomerular capsule

cuplike structure that is the initial portion of a nephron

proximal convoluted tubule

portion of a nephron, following the glomerular capsule, where tubular reabsorption of filtrate occurs

loop of the nephron

portion of a nephron between the proximal and distal convoluted tubules; functions in water reabsorption; also called the loop of Henle

distal convoluted tubule

final portion of a nephron that joins with a collecting duct; associated with tubular secretion

collecting duct

duct within the kidney that receives fluid from several nephrons; the reabsorption of water occurs here

glomerulus

capillary network within the glomerular capsule of a nephron

glomerular filtration

movement of small molecules from the glomerulus into the glomerular capsule due to the action of blood pressure

tubular reabsorption

movement of primarily nutrient molecules and water from the contents of the nephron into blood at the proximal convoluted tubule

tubular secretion

movement of certain molecules from blood into the distal convoluted tubule of a nephron, so that they are added to urine

erythropoietin (EPO)

hormone produced by the kidneys that speeds red blood cell formation

aquaporins

channel protein through which water can diffuse across a membrane

antidiuretic hormone (ADH)

hormone secreted by the posterior pituitary that increases the permeability of the collecting ducts in a kidney

renin

enzyme released by the kidneys that leads to the secretion of aldosterone and a rise in blood pressure

angiotensin II

hormone produced from angiotensinogen (a plasma protein) by the kidneys and lungs; raises blood pressure

aldosterone

hormone secreted by the adrenal cortex that regulates the sodium and potassium ion balance of the blood

atrial natriuretic hormone (ANH)

hormone secreted by the heart that increases sodium excretion