Chapter 44 ~ Regulating the Internal Environment

Homeostasis : regulation of internal environment

Thermoregulation internal temperature

Osmoregulation solute and water balance

Excretion nitrogen containing waste

Regulation of body temperature

Thermoregulation

4 physical processes :

Conduction ~transfer of heat between molecules of body and environment

Convection ~transfer of heat as water/air move across body surface

Radiation ~transfer of heat produced by organisms

Evaporation ~loss of heat from liquid to gas

Sources of body heat :

Ectothermic: determined by environment

Endothermic: high metabolic rate generates high body heat

Regulation during environmental extremes

Torpor ~ low activity; decrease in metabolic rate

1- Hibernation long term or winter torpor (winter cold and food scarcity); bears, squirrels

2- Estivation short term or summer torpor (high temperatures and water scarcity); fish, amphibians, reptiles

Both often triggered by length of daylight

Water balance and waste disposal

Osmoregulation: management of the body’s water content and solute composition

Nitrogenous wastes: breakdown products of proteins and nucleic acids; ammonia-very toxic

Deamination~

Ammonia: most aquatic animals, many fish

Urea: mammals, most amphibians, sharks, bony fish (in liver; combo of NH 3 and CO 2 )

Uric acid: birds, insects, many reptiles, land snails

Osmoregulators

Osmoconformer: no active adjustment of internal osmolarity (marine animals); isoosmotic to environment

Osmoregulator: adjust internal osmolarity (freshwater, marine, terrestrial)

Freshwater fishes (hyperosmotic)- gains water, loses; excretes large amounts of urine salt vs. marine fishes (hypoosmotic)- loses water, gains salt; drinks large amount of saltwater

Excretory Systems

Production of urine by 2 steps: • Filtration (nonselective) • Reabsorption (secretion of solutes)

Protonephridia ~ flatworms (“flame-bulb” systems)

Metanephridia ~ annelids (ciliated funnel system)

Malpighian tubules ~ insects (tubes in digestive tract)

Kidneys ~ vertebrates

Kidney Functional Units

Renal artery/vein: kidney blood flow

Ureter: urine excretory duct

Urinary bladder: urine storage

Urethra: urine elimination tube

Renal cortex (outer region)

Renal medulla (inner region)

Nephron: functional unit of kidney

Cortical nephrons (cortex; 80%)

Juxtamedullary nephrons (medulla; 20%)

Nephron Structure

Afferent arteriole: supplies blood to nephron from renal artery

Glomerulus: ball of capillaries

Efferent arteriole: blood from glomerulus

Bowman’s capsule: surrounds glomerulus

Proximal tubule: secretion & reabsorption

Peritubular capillaries: from efferent arteriole; surround proximal & distal tubules

Loop of Henle: water & salt balance

Distal tubule: secretion & reabsorption

Collecting duct: carries filtrate to renal pelvis

Basic Nephron Function

Nephron Function, I

Proximal tubule: secretion and reabsorption

Nephron Function, II

Loop of Henle: reabsorption of water and salt

Distal tubule: secretion and reabsorption

Nephron Function, III

Collecting duct: reabsorbs water, salt, some urea

Kidney regulation: hormones

Antidiuretic hormone (ADH) ~ secretion increases permeability of distal tubules and collecting ducts to water (H2O back to body); inhibited by alcohol and coffee

Juxtaglomerular apparatus (JGA) ~ reduced salt intake--->enzyme renin initiates conversion of angiotension (plasma protein) to angiotension II (peptide); increase blood pressure and blood volume by constricting capillaries

Angiotension II also stimulates adrenal glands to secrete aldosterone; acts on distal tubules to reabsorb more sodium, thereby increasing blood pressure (renin-angiotension-aldosterone system; RAAS)

Atrial natriuretic factor (ANF) ~ walls of atria; inhibits release of renin, salt reabsorption, and aldosterone release

Hormonal Control