Vertebrate kidneys consist of glomeruli, tubules surrounded by peritubular capillaries, & longitudinal ducts. Variations in
 kidney structure among vertebrates are primarily in the number & arrangement of the glomeruli & tubules.

• Glomeruli are masses of capillaries that (along with Bowman's capsule) 'filter' the blood - the first step in eliminating waste products from the blood.
• Kidney tubules collect the glomerular filtrate & conduct it to a longitudinal duct. Tubules consist of several segments & begin as a Bowman’s (or glomerular) capsule. A glomerulus plus its surrounding Bowman's capsule is called a renal corpuscle.
• Longitudinal ducts = begin developing at anterior end of kidney & grow caudally until opening into the cloaca

1 = Bowman's capsule, 2 = glomerulus, 3 = afferent arteriole, 4 = efferent arteriole,
5 = proximal convoluted tubule, 6 = distal convoluted tubule, 7 = collecting duct,
8 = loop of Henle, 9 = peritubular capillaries

Archinephros - earliest vertebrate kidneys probably extended the entire length of the body cavity & had external glomeruli that drained the coelomic fluid

Pronephros - 1st embryonic tubules in all vertebrates; called pronephric tubules because they are the 1st to develop & are anteriorly located

• Number - never very many (e.g., 3 in frogs, 7 in human embryos, & 12 in chicken embryos)
• The duct that drains the pronephros is called the pronephric duct.
• The pronephros is temporary & function only until glomeruli & tubules further back become functional.

Mesonephros:

• formed by corpuscles & tubules that develop caudal to pronephric region; form connections with existing pronephric duct (which is now called the mesonephric duct)
• the embryonic kidney in reptiles, birds, & mammals
• the functional adult kidney in fish & amphibians (& sometimes called the opisthonephros)

Jawed fishes & amphibians - among males, some anterior tubules of mesonephros conduct sperm from testis to mesonephric duct. That part of the mesonephros is called the SEXUAL KIDNEY while the rest is the URINIFEROUS KIDNEY.

Amniote embryos - mesonephros functions for a short time after hatching or birth &, during that time, a new kidney called the
  metanephros is developing

Metanephros:

• the adult amniote kidney
• the number of corpuscles is large; up to about 4.5 million is some species
• drained by a duct called the metanephric duct or ureter

Mammalian kidneys are divided into the CORTEX(#5), MEDULLA (#6), & PELVIS(#4):

• Cortex - contains renal corpuscles & lots of capillaries
• Medulla - contains collecting ducts and loops of Henle; divided into pyramids (#7) & columns (#2)
• Pelvis - hollow; receives the urine (which exits the kidney via the ureter - #3)

Blood supply:

• kidney is supplied by 2 or more renal arteries in reptiles & birds, & by a single renal artery in mammals (below).
• Pathway of blood in mammalian kidney: renal artery > segmental arteries > interlobar arteries > arcuate arteries > interlobular arterioles.

Urinary bladders are found in all vertebrates except agnathans, snakes, crocodilians, some lizards, & birds (except ostriches).

• Fish - bladders are terminal enlargements of the mesonephric ducts called TUBAL BLADDERS
• Amphibians through Mammals - bladders arise as evaginations of ventral wall of the cloaca

Value of tetrapod urinary bladder:

• void urine when desired rather than continuously as it is formed
• uses of urine:
• reproduction (e.g., providing males with information concerning the reproductive status of a female)
• behavioral (e.g., marking territories)
• moisten soil (some freshwater turtles use urine to soften the ground and make it easier to dig holes for egg-laying)

• arise as paired ridges just medial to mesonephroi
• due to fusion or failure of 1 ridge to differentiate, some vertebrates (agnathans, some female lizards & crocodilians, & most female birds) have a single testis or ovary
• hormones cause differentiation of early gonads into either testes or ovaries

• In some teleosts, ovaries are hollow sacs, either because the ovary develops around coelom or the ovary becomes hollow at ovulation (eggs are discharged into cavity which is continuous with the oviduct)
• In other teleosts plus agnathans, the ovaries are compact & eggs are discharged into coelom
• Amphibians - ovaries are hollow & eggs are discharged into the coelom

• Reptiles, birds, & monotremes - ovaries solid but develop irregular, fluid-filled lacunae (cavities); eggs discharged into coelom

• Mammals - ovaries compact; no large chambers or lacunae

Testes:

• usually smaller than ovaries because sperm, although numerous, are much smaller than eggs (especially eggs with yolk)
• In mammals, testes are larger than ovaries

• testes descend permanently into scrotal sacs in many mammals
• some mammals - testes lowered into scrotal sacs & retracted at will
• inguinal canal - passage between abdominal cavity & scrotum
• scrotal sacs - do not develop in some mammals; testes remain in abdomen

• Some fishes (e.g., gar & sturgeon) & amphibians - mesonephric duct transmits sperm & urine
• Some amphibians - mesonephric duct transports only sperm; new accessory urinary duct drains the kidney
• Sharks - mesonephric duct is used primarily for sperm transport; accessory urinary duct develops
• Teleosts - mesonephric duct drains kidney; separate sperm duct develops
• Amniotes - embryonic mesonephric ducts transport sperm in adults

Source: http://gwis2.circ.gwu.edu/~atkins/newwebpages/Reproductive/breed.html

Intromittent organs:

• useful when fertilization is internal; introduce sperm into female reproductive tract
• found in some fish, some birds, reptiles, & mammals
• cartilaginous fish - appendages of pelvic fins called claspers direct sperm into female reproductive tract

• snakes & lizards - have pair of HEMIPENES (pocketlike diverticula of wall of cloaca)

• turtles, crocodilians, a few birds, & mammals - exhibit an unpaired erectile penis
• penis - usually a thickening of floor of cloaca consisting of spongy erectile tissue (corpus spongiosum) with grooves to direct sperm & ending in a glans penis (sensory endings that reflexly stimulate ejaculation)
• mammals (except monotremes) - penis extends beyond body. The embryonic corpus spongiosum becomes a tube with urethra inside & 2 additional erectile masses develop (corpus cavernosa).

• typically consists of a pair of gonoducts (or oviducts) that extend from ostia to the cloaca
• different segments of ducts perform special functions
• when internal, fertilization occurs near beginning of ducts

Source: http://gwis2.circ.gwu.edu/~atkins/newwebpages/Reproductive/breed.html

• anatomy in various vertebrate groups:
• cartilaginous fish - 2 ostia fuse to form single ostium (or osteum); shell gland secretes albumen & a shell; uterus holds eggs until laying
• teleosts - ducts are continuous with cavity of the ovary
• lungfish & amphibians - oviducts long & convoluted; lining secretes jelly-like material around each egg
• crocodilians, some lizards, & nearly all birds (diagram below) - 1 coiled oviduct lined with glands that add albumen, shells, &, sometimes, pigment

• monotremes - tract is reptilian; caudal end secretes a shell before egg passes into the cloaca
• placental mammals - embryonic ducts give rise to oviducts, uteri, & vaginas. Adult tract is paired anteriorly & unpaired posteriorly (typically terminating as an unpaired vagina).
• oviducts (fallopian tubes) are relatively short, small in diameter, convoluted, & lined with cilia; begin at ostium bordered with fimbria
• uterus:
• Marsupials - no fusion of embryonic ducts so there are 2 tracts (DUPLEX UTERUS)

• Other placental mammals - varying degrees of fusion:
• bipartite uterus - 2 uterine horns, a uterine body (with 2 lumens), & a single vagina
• bicornuate uterus - 2 uterine horns, a uterine body (with a single lumen), & a single vagina
• simplex uterus - no uterine horns & oviducts open directly into body of uterus

Vagina - fused terminal portion of oviducts that opens either into urogenital sinus or to the exterior; receives male intromittent organ

Related links:

Vertebrate Urinary Systems

Vertebrate Reproductive Systems

BIO 342 Nervous System

Back to BIO 342 Syllabus