Comparative Anatomy of Vertebrates (Excretory System)

Comparative Anatomy of Vertebrates (Excretory System)

ASSIGNMENT
ON
ZOOLOGY



Subject:
Comparative Anatomy of Vertebrates
(Excretory System)



Submitted To:
Mr. Shameem Pavel
Associate Professor,
IER, DU.



Submitted By:
Ismat Jahan Tonny (07043)
Nazmun Nahar Nazu (07155)
13th Batch, IER, DU.

(With the help of saurav)

Date of Submission:
11 June, 2008






v CONTENTS

¨ THE UROGENITAL SYSTEM -01

¨ THE EXCRETORY SYSTEM -01
ØExcretory Organs- 02
ØBasic Structure of Vertebrate Kidney -03
ØTypes of Kidneys - 05
ØThe Excretory or Urinary System of Human -08
ØAt a Glance-10











THE UROGENITAL SYSTEM


Evolutionary survival of animals depends on doing many successful activities like escaping from predators, procuring for foods, adjusting to the environment and so on. All of these activities are included in a system called Genital system or Reproductive system.

On the other hand, the activities such as the elimination of waste products, primary ammonia and the regulation of water and electrolyte balance are included in the Urinary or Excretory system.

Although urinary and reproductive systems are quite different in function, we treat both systems together as the Urogenital System because of their sharing many of the same ducts.

So, in a nutshell, we can say the genital system (Reproductive System) and the urinary system (Excretory System) both are called together, The Urogenital System.


UROGENITAL SYSTEM =URINARY SUSTEM + GENITAL SYSTEM
(Excretory system) (Reproductive system)





THE EXCRETORY SYSTEM

All though the excretory system is a part of urigeniatl system, the excretory system has its own specialized structures and functions. Control of the salt and water content and elimination of metabolic waste products are functions of the excretory system. The end products of the metabolism include carbon dioxide, ammonia, urea, uric acid, creatine, pigments and inorganic salts. The elimination of carbon dioxide is accomplished by respiratory system. With certain exception, the other wastes are eliminated by excretory or urinary organs. Usually these substances are in soluble in water, in which case the final product, as eliminated by the body, is known as urine.


The Excretory System

Except for a few structure near the distal opening of some of the ducts, the entire excretory system is divided from the embryonic mesomere.




v Excretory Organs:

Ø Organs which eliminate nitrogenous waste from blood are called excretory system. In vertebrates urinary apparatus is used as excretory organ.
Ø In vertebrates, skin, gills, lungs etc. eliminate CO2 from blood, but nitrogenous waste ate eliminated by kidney.
Ø Kidney is absent in Protochordata. For excretion different typed of organs are used in Protochordates. Such some type of example are given bellow:
Balanoglossus have glomerulus.
Ascidia have pyloric glands, renal vesicle, partial vesicle, neural glands.
Amphioxuses have solenocytes for excretion.

Ø The main excretory system of vertebrates is kidney. It is different in structure in various types in animals. It consists of three types of nephridia. A pair of kidneys is present in every vertebrate, lying dorsal to coelom in trunk region, one or either side of dorsal aorta. They are all built in accordance with a basic pattern.









v Basic Structure of Vertebrate Kidney:

Nephron: Every vertebrate kidney has a basic structure. As for example, each kidney is composed of a large number of units called viniferous tubbtes or neprons. Their number, complexity and arrangement differ in different groups of vertebrates.


Origin of Uriniferous Tubules (Nephrons): Kidney tubules arise in the embryo in a linear series from a special part of mesoderm called mesomere or nephrotome. It is the ribbon like intermediate mesoderm running between segmental mesoderm (epimere) and lateral plate (hypomere) or either side along the entire trunk from heart to cloaca.



Parts of Nephrons: A uriniferous tubule is differentiated into three parts: (a) Peritoneal funnel, (b) Tubule and (c) Malpighian body.

(a) Peritoneal Funnel: Near the free end of a uriniferous tubule is a funnel like ciliated structure called peritoneal funnel.

It opens into coelom (splanchnocoel) by a wide aperture, the coelomostome or nephrostome. Nephrostome are usually confined to embryos and leave and considered vestiges of a hypothetical primitive kidney.




(b) Malpighian Bodies: Bowman’s capsule and enclosed glomerulus together form . a renal corpuscles or Malpighian bodies.

Bowman’s capsule: A tubule begins as a blind, cup like, hollow, doubled-walled Bowman’s capsule.

Glomerulus: It encloses a tuft of blood capillaries called glomerulus.
Ø It is supplied blood by a branch of renal artery, called afferent glomerular arteriole.
Ø An efferent glomerular arteriole emerges out of glomerulus to join the capillary network surrounding the tubule.
Ø Encapsulated glomerulus are termed internal glomeruli which are common.
Ø Those without a capsule and suspended freely coelomic cavity are called external glomeruli ^embryos and larvae^.
Ø Capsule without glomeruli are termed aglomerular such as found in embryos, larvae and some other fishes.


( c ) Nephric Tubules: At one end, the kidney tubule originates at a Bowman’s capsule and its walls are continuous with the outer wall of the capsule. The tubule may be elongated and coiled. At the other end it opens into a kidney duct called longitudinal duct.

Functions of Nephron:
Ø Peritonial funnel helps draining wastes from coelomic fluid.
Ø Malpighian bodies filter water, salts and other substances from blood.
Ø During passage through Nephric tubules more substances are secreted into filtrate, while some are reabsorbed.

































v Types of Kidneys:

Suring the evolution of the vertebrates, a series of kidney types replaced each other as the functional excretory organs.


Archniphrose: It seems probable that the excretory organ of the primitive, ancestral vertebrate was of a type that has been named archinephros.
.
Structure of Archinephros: Kidney is thought to have considered of a series of archinepheric tubules, one tubule on each side of each body segment. Each of these tubules opened into coelom by a ciliated, funnel –shaped opening called a nephrostome. Glomeruli were suspended segmentally in the coelomic cavity adjacent to the nephrostomes. Fluids eliminated by the glomeruli were collected by the nephrostomes and passed down the archinephric tubules.

The tubules emptied into a pair of archinephros ducts, one on each side of the dorsal wall of the body cavity. These ducts extended for the whole length of the body cavity.

Distribution of archinephros: No adults, living vertebrate possesses an archinephros, but it is present in the larval form of the hagfish ^Myxine^ and the larvae of some of the caecilians ^Apoda^.

Pronephros: The most primitive type of kidney functional in an adult vertebrate is the pronephros.

Structure of Pronephros: The pronephros is believed to represent the most anterior part of the ancestral archinephros.

Tubules and Malpighian Bodies: In the embryos of all vertebrates, the first kidney tubules arise from the anterior end of the mesomere. In a few primitive forms of glomeruli which are delivered from segmental branches of the dorsal aorta, project into the coelom near the nephrostomes. Such structures are known as external glomeruli. Usually, however, the glomeruli is internal that is, it is almost completely surrounded by the bowman’s capsule which projects from the tubule near its proximal end. The nepheostomes persist and still retains its opening to the coelom.Whether the glomruli are external or internal seems to have no particular significance.

Because of the segmental nature of the pronephros and the relatively small number off tubes and related structure, the diffuse pronephric kidney does not form a distinct organ identifiable to naked eye. For example, there are thirteen tubules and in the lamprey, seven in the 3mm, human embryo and four in the shark embryo.

Ducts of Pronephrose: The pronephric tubules fuse to form the pronephric ^originally archinephric^ ducts which grows backward and opens posteriorly into the cloaca. While the pronephros may be important to those organisms in which it is functional, its chief evolutionary significance seems to be the part it plays in forming the pronepheric duct, which persist after the pronephros itself has disapeard.

Distribution of Pronephrose: The pronephroic tubules continue to function in the adult hagfish and in occational teleosts. The pronephros is also a functional structure in many immature fishes and in the larvae of some of the amphibians and appears transitorily in the embryos of all the higher vertebrates.

Mesonephros and Opisthonephros: The mesonephros is the kidney tissue that develops posterior to the pronephros. Posterrior to the mesonrphros, the meta nephros (that portion of the kidney tissue that gives rise to the adult amniote kidney) develops. The adult kidney of the anamniotes involves not only the mesonephric tissue but some of the metanephric tissue as well. Thus, while the kidney of the anamniotes is frequently called a mesonephros, it is not completely homologous with the mesonephros of the amniote embryo, and for this reason is preferably referred to as the opisthonephros.

Structure of Mesonephros and opisthonephrose: These kidney structures form discrete organs that are readily apparent as kidneys. They resemble each other closely in structure and function.

Tubules and Malpighian Bodies: While the first few mesonephric tubules tend to be segmentally distributed, proliferation of many such tubules in each of the body segments eventually obliterates all evidence of metamerism. Thus, for the first time in evolution, the primary excretory organ becomes a discrete, bulky structure, lying against the dorsal body wall and tending to bulge into the coelom.

The embryonic tubules are first formed as solid structures, but they soon develop lumina and begin to elongate. One end off the tubule enlarges and is invaginated by the ball of capillaries forming the glomerulus and thus becomes the double-walled Bowman’s capsule described above. This capsule, with its included glomerulus, forms the renal or Malpighian bodies. All glomeruli in the opisthonephros are surrounded by Bowman’s capsules and hence are internal. In a few forms, peritoneal funnels (nephrostomes) may connect the tubules with the coelom, but this seems to be the exception. Most species that have been studied have lost the peritoneal funnels and the coelom is no longer continuous with the outside world through the excretory system.

At first, as the mesonephric tubule develops and enlongates it becomes ‘S’ shaped, and then the proximal and distal loops of the S fold further to form typical proximal and distal convolutions so characteristic of the mesonephric tubule.

Mesonephric duct: The distal ends of the tubules establish connections with the old pronephric duct, which is now known as the mesonephric duct ( also called Wolffian duct). The distal ends of several tubules may unite before they join the mesonephric duct, and sometimes the tube formed from the components of several tubules may establish an opening directly into the cloaca rather then into the mesonephric duct. The mesonephric duct may also transport sperm to the outside.

Distribution of Mesonephros and Opisthonephros: Mesonephric part functions in the embruos of reptiles, birds and mammals. The opisthonephros is the functional kidney of the adult lamprey, the cartilaginous fishes, the bony fishes and the amphibians.

Metanephros: The metanephric kidney develops from the most posterior portion of the mesomere and is the most compact of any of the vertebrate renal structures.


The Structure of the Malpighian Bodies in the Metanephric Kidney
RA- Renal Artery, BC- Bowman’s Capsule, G- Glomerulus, EA- Efferent Arteriole,
AA-Afferent Arteriole, UT- Uniferus Tubule, RV- Renal Vein, HL- Loop of Henle

Structure of metanephros: Thw body of the matenephros has a twofold origin. Part of it develops form the posterior end of the opisthonephros, while another part forms as a new and unique metanephric structure.

Malpighian Bodies and Nephric Tubules: The metanephric kidney is basically made up of the same structure as the mesonephros- the Malpighian bodies and they are associated tubules. No nephrostomes (peritoneal funnels) are ever present in the metanephros. The metanephric tubules are somewhat more complex in the mammals and (to a lasser extent) in the birds then are the mesonephric tubules. In these animals, each tubule develops a long loop called the loop of Henle with ascending and descending portions between the proximal and distal convoluted segments. These loops functions primarily in the re-absorption of water.

Collecting Tubules and Metanephric Duct: In the amniote embryo, a diverticulum develops near the posterior end of the mesonephric or Wolffian duct and grows outward and forward to make contact with the developing metanephros. This diverticulum branches and rebranches within the metanephros to form a large number of very fine collecting tubules. This collecting tubules establish connections with the S- shaped renal tubules, and henceforth the waste products pass through them to the new duct formed from the diverticulum. This duct is called a ureter. When this new pathway develops and the embryonic mesonephros degenerates, the Wolffian duct no longer transports urine from the kidney but remains as a reproductive duct transporting sperm from the testis.

Distribution of the Metanephros: The metanephros becomes functional in most reptile, bird and mammal embryos and is the functional kidney of all adult amniotes.


v The Excretory or Urinary System of Human

The human urinary system consists of the organs- Kidneys, Ureter, Uurinary bladder and Urinary duct (Urethra).

Kidney: The human kidneys are bean-shaped, reddish brown organs each about the size of a fist. They are located on either side of the vertebral column where they are partially protected by the lower rib-case.

Ureter: A ureter is a duct that carries urine from the kidneys to the urinary bladder. Each kidney is connected to a ureter.

Urinary Bladder: Urinary Bladder, where urine is stored until it is voived from the body.

Urethra: Urethra is a single urinary duct by which excretory substances like urine is voided from the body. In males, the urethra passes through the penis and in females, it opens ventral to the opening of the vagina.



The Urinary System of Human The structure of Kidney

Urine: Urine is a excretory substance made by kidneys is carried from the body by the other organs in the urinary systems.

There is no connection between the Genital (Reproductive) and the Urinary systems in females but there is a connection in males. In males, the urethra also carries sperm during ejaculation.

























At a Glance

Distribution of the types of vertebrate kidney

Class
Pronephros
Mesonephros
Or
Opisthonephros

Metanephros
Agnatha (Hagfish)
Adult
Adult

Agnatha (Lamprey)
Embryo
Adult

Chondrichthyes
Embryo
Adult

Osteichthyes
Embryo
Adult

Amphibia
Embryo
Adult

Reptilia
Embryo
Embryo
Embryo and
Adult
Aves
Embryo
Embryo
Embryo and
Adult
Mammalia
Embryo
Embryo
Embryo and
Adult


So, we can say that the Urinary System is the main Excretory System of vertebrates. But it also unavoidable that not only the Urinary System but also other organs like liver, skin, gills, sweat glands etc. are also included in the Excretory System in various species from the different perspective.


References

Comparative Anatomy of Vertebrates. –Goin.
Modern Textbook of Zoology, Vertebrates. - Kotpal R. L. (8th Revised Edition)
Chordate Zoology. –Jordan E.L. & P. S. Verma (8th Edition)

Course Lecture - Shameem Pavel Sir (Course Teacher)
Internet