EXCRETORY-URINARY SYSTEMS IN ANIMALS

Excretory systems

systems critical for removing waste to maintain homeostasis

Basic functions of an excretory system

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

Structures that filter wastes

gills lungs kidneys and skin

Nitrogenous wastes

toxic waste products animals must remove to survive

Forms of nitrogenous waste

ammonia ammonium ions urea and uric acid

Ammonia and ammonium ions

most toxic nitrogenous wastes disrupting pH and redox reactions

Aquatic animals waste type

primarily excrete ammonia and ammonium ions

Marine invertebrate excretion

ammonia excreted across skin and gills

Freshwater and marine fish excretion

ammonia excreted via gills and kidneys

Ammonia excretion timing

excreted immediately because extremely toxic

Advantage of ammonia excretion

no energy required to remove it

Disadvantage of ammonia excretion

requires large amounts of water for safe excretion

Urea

nitrogen waste produced by mammals amphibians some fishes reptiles and some invertebrates

Urea origin

produced from protein and amino acid metabolism

Urea advantage toxicity

less toxic so accumulation is tolerated

Urea advantage water loss

does not require large water volumes to excrete

Urea disadvantage

requires moderate metabolic energy to produce and break down

Uric acid

waste from nucleic acid and some protein breakdown

Uric acid producers

birds insects and most reptiles

Uric acid toxicity

less toxic than ammonia but energetically costly to produce

Uric acid solubility

not soluble in water thus not excreted in liquid form

Uric acid excretion form

semisolid waste with little to no water loss

Filtration

process where an organ filters water and solutes from body fluids

Filtration selectivity

large proteins are not removed

Filtrate

material produced by filtration

Reabsorption

process where filtrate materials are reclaimed into blood

Reabsorption characteristics

typical of mammalian kidneys

Reabsorption purpose

recaptures essential nutrients and most water removed in filtrate

Secretion

excreting solutes in greater quantities than present in filtrate

Secretion mechanism

active transport of solutes from blood or interstitial fluid into excretory tubules

Secretion example

observed in marine fish

Excretion

removal of harmful materials from body

Urine definition

filtrate remaining after reabsorption that is excreted outside the body

Protonephridia

branching tubes in flatworms for filtering body cavity fluids

Flame cells

ciliated cells forcing fluid through protonephridia

Protonephridia removal method

filtration with solute reabsorption and waste exit

Metanephridia

filtration structures in each earthworm segment

Metanephridia function

collect nitrogen wastes and reabsorb solutes

Malpighian tubules

excretory structures in insects

Malpighian tubule function

transport waste and water into tubule lumen and excrete with feces

Malpighian tubule removal method

secretion

Kidneys

mammalian filtration and secretion organs

Kidney shape

bean-shaped and located in lumbar region

Kidney function type

filtration with some secretion

Renal pelvis

kidney region where urine collects before ureter

Ureters

tubes delivering urine to urinary bladder

Urinary bladder

muscular sac temporarily storing urine

Urethra

muscular tube draining urine to outside of body

Renal cortex

light-colored superficial kidney region with granular appearance

Renal medulla

dark red/brown region containing renal pyramids

Renal pyramids

cone-shaped structures with collecting tubules and capillaries

Renal pyramid base

faces cortex

Renal pyramid apex (papilla)

points internally

Renal columns

tissue separating pyramids

Kidney lobes

each pyramid and surrounding tissue form a lobe

Renal pelvis anatomy

funnel-shaped tube continuous with ureter

Major calyces

branching extensions of renal pelvis

Minor calyces

subdivisions of major calyces enclosing papillae

Calyx function

collect urine draining from papillae

Urine pathway

papillae → minor calyces → major calyces → renal pelvis → ureter → bladder

Smooth muscle in urinary passages

lines calyces pelvis and ureter to push urine by peristalsis

Nephrons

structural and functional units of kidney over one million per kidney

Nephron components

glomerulus and renal tubule

Glomerulus

tuft of capillaries forming filtrate

Glomerular capsule (Bowman’s capsule)

cup-shaped renal tubule end of simple squamous epithelium

Podocytes

cells forming slits in capsule for blood filtration

Renal corpuscle

glomerulus plus glomerular capsule

Proximal convoluted tubule (PCT)

coiled tubule leaving glomerular capsule

Loop of Henle

hairpin loop between PCT and DCT

Distal convoluted tubule (DCT)

twisted tubule after Loop of Henle

Collecting duct

receives filtrate (now urine) from many nephrons

Urine flow from collecting ducts

papillary ducts → minor calyces → major calyces → renal pelvis → ureter → bladder

Glomerular capillaries

fenestrated capillaries producing filtrate

Filtration pores

allow passage of solute-rich material into capsule

Glomerular blood supply

afferent arteriole in efferent arteriole out

Glomerular pressure

extremely high to force solutes into capsule

Filtrate reabsorption site

peritubular capillaries

Afferent arteriole diameter

larger than efferent arteriole creating filtration pressure

Peritubular capillaries

low-pressure vessels absorbing solutes and water

Peritubular capillary origin

arise from efferent arterioles

Peritubular capillary function

reabsorb filtrate into blood

Filtrate definition recap

blood plasma minus proteins

Urine composition

metabolic wastes and unneeded materials

Three urine formation processes

glomerular filtration tubular reabsorption tubular secretion

Glomerular filtration

passive process using hydrostatic pressure

Filtration membrane efficiency

high permeability and large surface area

Molecules filtered

water glucose nitrogen wastes

Molecules retained

large molecules kept in blood

Tubular reabsorption

reclaiming filtered materials via countercurrent multiplication

Reabsorption start

begins in proximal tubule

Reabsorption barriers

luminal membrane basolateral membrane and peritubular capillary endothelium

Reabsorbed nutrients

glucose and amino acids

Water and ion absorption regulation

controlled by hormones

Passive reabsorption

occurs by diffusion osmosis or facilitated diffusion

Active reabsorption

requires ATP

Sodium reabsorption

active process with sodium-potassium pumps

Aldosterone

hormone causing renal tubules to reabsorb sodium increasing blood volume

Aldosterone source

adrenal gland

Water nutrient ion reabsorption summary

mostly passive transport

Non-reabsorbed materials

large molecules or substances lacking carriers