EXCRETORY/URINARY SYSTEMS (overview)

Excretory system

system responsible for removing waste to maintain homeostasis

Basic functions of excretory system

removing soluble wastes maintaining ion nutrient and water balance removing nitrogenous wastes

Gills as excretory structures

structures that help filter wastes in some animals

Lungs as excretory structures

eliminate carbon dioxide from the body

Kidneys

major organs that filter blood and remove wastes

Body surface skin

site where some organisms remove wastes

Nitrogenous wastes

toxic byproducts of protein and nucleic acid metabolism

Three forms of nitrogenous waste

ammonia and ammonium ions urea uric acid

Waste form depends on

organism species and its environment

Ammonia and ammonium ions

most toxic nitrogenous wastes disrupting pH and redox reactions

Ammonia producers

aquatic animals especially marine invertebrates and fish

Ammonia excretion method

across skin and gills in invertebrates and via gills and kidneys in fish

Immediate excretion of ammonia

occurs because ammonia is extremely toxic

Advantage of ammonia excretion

requires no energy to produce or eliminate

Disadvantage of ammonia excretion

requires large amounts of water

Urea

less toxic waste produced by mammals amphibians some fish reptiles and invertebrates

Urea advantages

less toxic small buildup tolerated requires less water

Urea disadvantage

moderate energy required to form

Uric acid

nitrogen waste from nucleic acids and some proteins

Uric acid producers

birds insects and most reptiles

Uric acid toxicity and cost

less toxic but energetically expensive to produce

Uric acid solubility

not water soluble excreted as semisolid paste

Water conservation in uric acid excretion

no water loss during excretion

Filtration definition

removal of water and dissolved solutes through filtration organ

Filtration excludes

large proteins needed for life

Filtration product

filtrate

Reabsorption definition

recapturing valuable materials from filtrate back to blood

Hormonal regulation of reabsorption

common in mammalian kidney

Nutrient reabsorption

essential nutrients reclaimed even if fully filtered out

Secretion definition

excreting solutes in greater quantities than found in filtrate

Secretion mechanism

active transport of solutes from blood into excretory tubes

Secretion example

common in marine fish

Excretion definition

removal of harmful materials from the body

Urine

filtrate remaining after reabsorption and secreted outside body

Protonephridia

branching tubes in flatworms for filtration

Flame cells

ciliated cells that drive fluid through protonephridia

Protonephridia function

filter body fluids reabsorb solutes and expel excess water and wastes

Metanephridia

excretory structures in earthworms

Metanephridia function

collect nitrogenous wastes and reabsorb important solutes

Malpighian tubules

insect excretory structures

Malpighian tubule function

secrete wastes and water into tubule lumen to be excreted with feces

Kidneys (in mammals)

filtration and secretion structures producing urine

Kidney location

bean-shaped organs in lumbar region

Renal pelvis

region where urine collects before moving into ureters

Ureters

tubes that carry urine to bladder

Urinary bladder

muscular sac temporarily storing urine

Urethra

muscular tube draining urine outside body

Three kidney regions

renal cortex renal medulla renal pelvis

Renal cortex

light superficial granular region

Renal medulla

dark region with renal pyramids

Renal pyramids

cone-shaped structures containing collecting tubules and capillaries

Renal columns

tissues separating pyramids

Kidney lobes

each pyramid and its surrounding tissue

Renal pelvis function

funnels urine to ureter

Major calyces

branches of renal pelvis

Minor calyces

cup-shaped sacs collecting urine from papillae

Calyces function

collect drain and funnel urine via peristalsis

Nephrons

structural and functional units of kidneys over 1 million per kidney

Nephron functions

cleanse blood and produce urine

Glomerulus

tuft of capillaries inside glomerular capsule

Glomerular capsule (Bowman’s capsule)

cup-shaped structure with podocyte slits filtering blood

Renal corpuscle

glomerulus plus glomerular capsule

PCT (proximal convoluted tubule)

coiled tubule with microvilli for reabsorption

Loop of Henle

hairpin loop with descending and ascending limbs

DCT (distal convoluted tubule)

last convoluted tubule before collecting duct

Collecting duct

receives urine and sends it to papillary ducts

Filtrate

material filtered from blood into capsule

Urine (nephron definition)

filtrate that has reached collecting ducts

Glomerular capillaries

fenestrated capillaries producing filtrate under high pressure

Afferent arteriole

vessel feeding glomerulus

Efferent arteriole

vessel draining glomerulus

Afferent vs efferent arterioles

larger afferent diameter creates pressure for filtration

Peritubular capillaries

low-pressure vessels absorbing reabsorbed materials

Filtrate produced by glomerulus

solute-rich fluid minus large proteins

Urine contains

metabolic wastes and unneeded substances

Urine formation steps

glomerular filtration tubular reabsorption tubular secretion

Glomerular filtration

passive process using hydrostatic pressure to force fluid out of capillaries

Filtration efficiency

due to membrane permeability and large surface area

Molecules filtered

small molecules like water glucose nitrogen waste

Tubular reabsorption

reclamation of needed materials beginning in PCT

Reabsorption barriers

luminal membrane basolateral membrane and capillary endothelium

Organic nutrient reabsorption

nearly all nutrients like glucose and amino acids reabsorbed

Water and ion reabsorption

regulated by hormones

Active vs passive reabsorption

requires ATP or not depending on substance

Sodium reabsorption

active process via sodium-potassium pumps

Aldosterone

hormone increasing sodium reabsorption and water via osmosis

ADH (antidiuretic hormone)

opens aquaporins to increase water reabsorption

Substances not reabsorbed

large materials or those that lack carrier attachment including nitrogenous wastes

Tubular secretion

movement of substances from blood to filtrate or secretion by tubule cells

PCT secretion site

primary location of secretion

Collecting duct secretion

also participates in secretion

Secretion importance

disposing unfilterable drugs eliminating toxins and removing nitrogenous wastes

Ureters definition

tubes carrying urine from kidneys to bladder

Urinary bladder definition

muscular sac storing urine

Urethra definition

tube draining bladder to outside

Polyuria

excessive urine production from diabetes mellitus or insipidus

Renal calculi

kidney stones from mineral salt buildup causing severe pain

Renal failure

complete reduction in urine formation

Anuria

cessation of urine production

Hemodialysis

external filtering of blood using semipermeable membranes