COMPANA Lec LE3 (Urinary)

Urinary system

• Production of urine

• Fundamentally similar from fish to mammals 

• Maintain chemical and physical constancy of blood

Genital system

• generation of gametes

• Secretion of hormones by the gonads to promote fertilization

• Excretory and reproductive systems are anatomically associated (share structures)

• Two systems that are physiologically and functionally dissimilar 

Combined urogenital system 

• Both from mesomeric mesoderm

• Both originate retroperitoneally

• Share ducts to greater or lesser extent 

Ontogenetic similarities 

Kidney

Excretory and osmerogulatory systems sometimes combined

• Nitrogen excretion is usually by diffusion of NH3

• Kidneys are responsible for osmoregulation and not excretion 

Kidney for aquatic vertebrates 

• Kidneys are responsible for both excretion and osmoregulation

Kidney for terrestrial vertebrates

Ammonia 

Most aquatic animals, including bony fishes 

Urea 

Mammals, most amphibians, sharks, some bony fishes 

Uric acid

Many reptiles (including birds), insects, land smells

• Environment is hypoosmotic

• Excessive water uptake

• Must excrete excess water and conserve salt

Primary osmotic problem for freshwater

• waste excreted as ammonia

• Use excess water as solvent 

• Actively transport solutes (for retention)

Solution for freshwater 

• environment is hyperosmotic 

• Excessive water loss

• Excessive uptake of sales (in food and drinking water)

• Must retain water and eliminate salts

Primary osmotic problem for salt water 

• Isosmotic

• Lose glomerulus (water loss)

• Become hyperosmotic relative to environment

• Retain urea to achieve

• increases water uptake

• Retain glomerulus to excrete water

• Salt excretion glands:

• Rectal glans

• Salt glands on gills

Solution for salt water

• Environment is dry

• Water and salts are limited

• Must retain both water and salts

• A secondary return to water

• Reintroduces above aquatic concerns

Primary osmotic problem of terrestrial

• N excreteed in all three forms:

1. Balance costs vs benefits

2. Variable among taxa

3. Variable in life histories

• Reduce glomerulus

• Solute recovery

• Loop of henie requirement

• Salt glands (elimination)

Solution for terrestrial 

1. Freshwater fishes and amphibians - water constantly enters bodies from the environment, and salt is lost through urine; short proximal and distal tubules to return solutes; nitrogen released as ammonia or urea

2. Marine Body fishes - body fluids constantly leak away to the sea; pass very little urine, and drink freely to introduce more water; special cells in gills excrete salt; little or no distal tubules

Osmoregulation by fishes

• Have insufficient water to excrete urea, so excrete uric acid; short nephric tubules, salt glands used to excrete excess salt 

Osmoregulation of birds and reptiles 

• Highly effective at retaining water; only 1/100 of filtered water is passed as urine - concentration dependently on loops of Henle, essential for establishing an interstitial salt gradient needed for the production of concentrated urine

Osmoregulation in mammals

to excrete waste early on

Kidney is created early because

Mesodermal

Origin of kidney

Intermediate mesoderm 

forms the kidney 

Posterior region of the intermediate mesoderm

expands to form a nephric ridge

Ciliated kidney tubules

develop from mesomere of each segment

Archinephric

duct develops early

exterior 

Duct connects nephron to 

Nephrostomes (embryonic forerunner of the nephric tubule)

open into coelom

Pronephros 

Depends on position and head kidney

• Glomerulus produces ultrafiltrate into coelom and not into the Bowman’s capsule

• Ciliated kidney tubule removes and modifies ultrafiltrate

• Coelom later evaginates to form Bowman’s capsule

Early vertebrate embryo

Ultrafiltrate

is no longer released into general coelom but bowman’s capsule remains connected to coelom

the result is a typical vertebrate nephron

when the connection between the tubule and the coelom is closed,

Vertebrate nephron

Produces an ultrafiltrate of the blood into a space. Renal corpuscle + renal tubule + associated capillaries

Ultrafiltrate 

is modified as it passes through a duct to the outside 

Renal corpuscle

glomerulus + surrounding capsule

Holonephros (Arhinephros)

Original vertebrate kidney

A long dorsal band of nephrons

extends the length of the coelom

archinephric duct 

drained by

One pair of nephron

per segment

• Cranial pronephros

• Middle mesonephros

• Caudal metanophros

regions of the holonephros

opisthonepthros 

Mesonephros + posterior nephric ridge 

Primitive opisthonephros

with 1 pair of nephron/ segment

Typical opisthonephros

with many nephrons/segment

• in advanced opisthonephros, metamerism is gone and testis is formed 

• In metanephros, the archinephric duct becomes the sperm duct, ureter is formed. For females another duct is formed called Uralian to form the female reproductive system 

• In Primitive opisthonephros, head kidney is formed

• Kidney is opisthonephros or mesonephric 

• Multiple nephrons per segment

• A new duct develops to drain the caudal regions

• Testis begins to utilize the archinephric duct 

Kidney for fishes 

• Holonephros in larval stages only

• Opisthonephros in adults

• Gonads don’t have a duct

Kidney for agnathans

• kidneys are metanephric

• Small and compact with lobulated surface

• Degree of symmetry varies especially in snakes and limbless lizards

• snakes and crocodilians, urinary bladder is absent

• turtles have accessory urinary bladder function as respiratory organ

• Turtles and lizards have well-developed bilobed bladder

Kidney for reptiles

• Kidney is opisthonephric or mesonephric 

• Primitive archinephric kidney found in larval caecilians 

• Urodeles have opisthonephric kidneys similar o elasmobranchs

• Anuran kidneys are dorsoventrally flattened 

Kidney for amphibians

• Kidneys situated in the pelvic region 

• Complex, lobed structures with short ureter 

• Do not have loops

• Urinary bladder is absent

• Urinary waste in the form of uric acid 

Kidney for birds

1. Pronephros

2. Mesonephros

3. Metanephros

Development of the mammalian kidney

• Pronephros forms first

• forms the archinephric duct

• Degenerates after the mesonephros forms

Characteristics of Pronephros

• forms from the middle of the mesomere

• functional kidney of amniote embryonic life

Characteristics of Mesonephros

• develops from caudal nephrogenic tissue

• ureter develops to drain the metanephros

• Metanephros is not segmental 

• Mesonephros deteriorates

• Adult metanephros is small, compact, retroperitoneal, dorsal to posterior coelom  

Characteristics of metanephros

• less important but present in some fishes

• expansions of the archinephric duct

• independent of the cloaca

• open independently via urinary pores

Urinary and cloaca for fishes

• develops from the allantois as a pocket in the floor of the cloaca

• Originally without direct connection with urinary ducts

• Archinephric ducts open into the cloaca and not the bladder

• Tetrapod bladder is homologous to the allantois 

Urinary and cloaca for amphibians

• resembles that of amphibians when present

• ureters empty into bladder directly

• absent in some lizards, snakes, crocodiles and birds (except ostrich)

• Absence of bladder results to uric acid being stores in the cloaca

Urinary and cloaca for reptiles and birds

• bladder loses connection with the gut

• A new duct, called the urethra, develops. Common feature with the reproductive system 

Urinary and cloaca for mammals 

Gonads and ducts 

almost all vertebrates reproduce sexually and are gonochoric (sexes are separate) 

External fertilization

is ancestral and typical of fishes

internal fertilization

require complicated ducts

Parthenogenetic reptiles

about 50 species of lizard and 1 species of snake

hermaphrodites 

some fishes are consecutive 

Secondary sexual characteristics 

• morphology, behavior, color patterns, size, muscular development, antlers, mammary glands, etc

• Less evident in mammals, most fishes, amphibians, reptiles 

secondary sexual characteristics 

is pronounced in many birds and some fishes 

• development begins later than most organ systems

• Early embryos are indifferent

• Sexual structure are present but sex is unrecognizable

• Gonads develop from genital ride of the mesomere, medial to the nephric ridge

ontogeny of the gonad

1. Yolk sac mesoderm

2. Peritoneal mesoderm

3. Mesomeric mesoderm 

Sources of cells

Yolk sac mesoderm 

origin of primordial germ cells that undergo meiosis to become gametes 

Peritoneal mesoderm

Origin of germinal epithelium that will later become the outer covering of the gonad, Sertoli cells in testis and follicle cells in ovary

Mesomeric mesoderm

Origin of gonad medulla/interstitial gonadal cells

• in most taxa the testes shares or take over the archinephric duct in males

• Ureter develops to drain the metanephric kidney

• The archinephric duct becomes the vas deferens 

• In females, the ovary develops a new duct called oviduct and the female archinephric duct is lost

• Males have ureter and vas deferens while females have only ureters 

Phylogeny of the male genital duct

• Oviduct and archinephric duct are both present in the indifferent embryo 

• Oviduct degenerates in male 

• Archinephric duct is retained as the urinary duct in female anamniotes

• No direct connection between ovary and oviduct

• Proximal end of oviduct is the ostium tubae, a ciliated funnel

• Eggs are shed into coelom and then enters the ostium 

Phylogeny of the female genital duct

• No reproductive ducts

• Gametes shed into coelom and exit via the abdominal pores (as in invertebrates)

• Archinephric duct used solely by kidney

• Fertilization is external

Reproductive ducts for agnathans

• Origins from archinephric tubules

• Mullerian duct (new structure in jawed vertebrates)

• Testes are primitive ampullary type

• Bony fishes have gonoducts derived from the gonads (some have coelomic transport similar to jawless fish)

• There may be specialized regions for shell secretion, gestation or copulation. Claspers used for internal fertilization

• Oviduct opens into the cloaca

Reproductive ducts for fishes

• Similar to primitive bony fishes and tetrapods

• Some oviparous and all viviparous forms have developed internal fertilization

• Caecilians - most terrestrial of the amphibians

• Oviducts of viviparous species produce uterine milk for the young

• No placenta within the oviduct

Reproductive ducts for amphibians

1. Mesonephric tubules - taken over by the testes for sperm transport

2. Urine is carried across the ureter

3. Oviducts are similar to amphibians and most fishes

4. Hemipenis and penis - adaptation towards terrestrial mode of life

5. Specialized regions for albumen secretion, shell deposition, sperm storage, sperm reception and brooding

Reproductive ducts for reptiles

• Similar to reptilian reproductive organs (except in females - only left gonad develop into ovary)

• Penis occurs only in primitive birds

Reproductive ducts for birds

Albumen, shell membrane and the shell

added around the egg 

Chalazae

spiral band of material added at each end of the egg

Sperm nests

pockets at posterior end of oviduct for storing sperm

• Universal: copulation → internal fertilization → gestation

• Kidney abandons archinephric duct to the testis 

Reproductive ducts for mammals

Oviduct 

• With specialized regions for gestation and penis reception

• Paired proximally and unpaired distally

Fallopian tube and ostia 

• For egg transport

• Always paired

• similar to reptilian reproductive tubular (except penis is tubular)

• Have distinct cloaca

• Ureters lies between the Wolffian or Mullerian ducts

• Produce shell similar to reptilian eggs and secrete uterine milk

Reproductive duct in Monotremes of mammals

• Ureters lies lateral to the reproductive duct

Reproductive duct in Eutherians of mammals

• Prostate gland

• Vesicular glands

• Bulbourethral glands

Male reproductive accessory glands

Prostate glands

• adds prostatic secretions to the ejaculate to provide an optimum environment for sperm survival and motility

• present in some form in all domestic species

• Consists of a body and a disseminate part

Vesicular glands

secrete alkaline fluid rich in fructose

Bulbourethral glands 

found near the bulb of the penis