Urinary System- Kidney Overall function – Osmoregulation (water, salt) – Nitrogenous waste in tetrapods – Ammonia in amphibians – Urea in mammals – Uric.

Urinary System- Kidney

Overall function– Osmoregulation (water, salt)– Nitrogenous waste in tetrapods– Ammonia in amphibians– Urea in mammals– Uric acid in birds and reptiles– Note: uric acid in birds is 3000x more

concentrated than blood!

Kidney - Nephron

The functional unit of the kidneyFilters blood to make urineGlomerulus is a network of permeable

blood capillaries– Afferent glomerular arteriole– Efferent glomerular arteriole

Kidney - Nephron

Bowman’s capsule is a cup-shaped capsule around the glomerulus to catch filtrate

Renal corpuscle – Glomerulus plus the Bowman’s capsule since they function as a unit

Kidney - Nephron

Renal TubulesIncrease in complexity with higher

vertebratesFunction to secrete substances directly from

blood to tubuleFunction for reabsorption from tubules back

to bloodstream based on need

Kidney - Nephron

ADH = Antidiuretic hormone promotes water reabsorption from renal tubules

Aldosterone – hormone that promotes sodium reabsorption from renal tubules and water passively follows

Renal tubules are countercurrent for maximum efficiency

Key Points

Define countercurrent.Look at the following picture and explain

how countercurrent is advantageous.

Kidney - Nephron

Peritubular capillaries pick up substances being reabsorbed from renal tubules

Common collecting tubule collects urine from all renal tubules

Kidney

Longitudinal kidney duct – Carries urine to cloaca in all but placental

mammals– Various names for this duct depending on group

Kidney Types based on Embryology

Pronephros Forms from intermediate mesoderm

(mesomere) very far craniallyRenal tubules are temporary pronephric

tubulesPronephric duct carries urine to cloacaPronephric duct persists in anamniotes but

changes its name to Mesonephric duct

Pronephros is the functional embyronic kidney in anamniotes

Kidney Types

MesonephrosMiddle region of intermediate mesodermLongitudinal duct is Mesonephric duct (we

called it archinephric duct in lab)Functional embryonic kidney in amniotesAdult kidney of anamniotes

Kidney Types

Mesonephros– Mesonephric tubules invade testes and form the

Vasa efferentia which carry sperm from testicle to mesonephric duct

– Mesonephric duct carries sperm & urine in anamniotes

– Mesonephric duct in amniotes will only carry sperm & is called the Spermatic Duct or Vas Deferens

Mammalian Vasa Efferentia & Persistent Mesonephric Duct

Kidney Types

MetanephrosCaudal-most intermediate mesodermBecomes the adult amniote kidney

Kidney Types

Metanephros – adult amniote kidneyCortex –outer regionMedulla – inner region

– Pyramids– Papillae

Pelvis – slit-like funnel collecting urine from medulla

Kidney Types

Metanephros – adult amniote kidneyUreter = Metanephric ductCarries urine caudally

Urinary bladder

Cyclostomes & Elasmobranchs have noneMost fish have a widening of the

mesonephric ducts that form the urinary bladder

Dipnoans have a bladder that is an outpocketing of the cloaca

Urinary Bladder

Tetrapods have a urinary bladder that is an outpocketing of the cloaca

The urinary bladder then empties into the cloaca in all except placental mammals

Urinary Bladder

The urinary bladder is formed from the embryonic membrane called the allantois (cloacal derivative) in placental mammals

The remnant of the allantois is called the urachus which becomes an umbilical ligament

Urinary Bladder

In mammals, the urinary bladder is drained by the URETHRA

Urinary Bladder

Functions:– Water reservoir except placental mammals– Under ADH control– Holding tank in placental mammals– Pheromones– Marking territory

Key Points

What are two roots that both mean kidney?Can you live without one kidney? Can you

live without two? Why or why not?