Chapter 12 Excretory Products and their Elimination
Introduction : The component structural and functional units of the bodies of all organism are cells which have been looked as "miniature chemical factories" because of continuous metabolism taking place in these. It yields certain waste products which are, not only useless, but harmful to the cells and the body. Cells, therefore, throw out these wates, by diffusion, into their surrounding medium. Finally, these wastes are eliminated by the body into its external environment. This is, thus an important vital activity of all organism. It is called excretion.
Besides removing the metabolic wastes and impurities from the blood, the kidney also perform the important function of osmoregulation by regulating the amount of water in body fluids. The normally functioning kidneys produce a large volume of dilute urine when more water is taken, and a small volume of concentrated urine when water intake by the body is poor.
and Paramecium carbon dioxide and ammonia are mostly excreted out by diffusion through general body surface. It is considered that the contractile vacuoles also play some role in the removal of excretory products.
Most of the sponges are marine and have no problem of surplus water in their cells. A few sponges lie in hypotonic fresh water and have contractile vacuoles in most of their cells.
A
SPONGIOME TUBULES
SPONGIOME VESICLES
NETWORK OF SPONGIOME TUBULES
CONTRACTILE VACUOLE
COLLECTING TUBULE
AMPULLA
SPONGIOME
TUBULES AND VESICLES
C
Excretory canals are present on each lateral side or the collecting tubules of which one is dorsal and the other ventral. In the last proglottid, they join to form a pulsatile caudal vesicle, which is open to a exterior by excretory pore.
Excretory materials diffuse from the surrounding tissues into the flame cells. Vibrations of the cilia cause these materials to remove in the excretory ducts. The walls of the ducts reabsorb useful substances and remaining excretory materials (e.g., ammonia) are expelled out through the excretory pores.
GRANULES
GLOBULES OF EXRETION
BASAL
TERMINAL DUCT
NUCLEUS
EXCRETORY PORE
ANTERIOR
CANAL SMALLER
CELL LUMEN
DUCTULE EXCRETORY
DUCT
GRANULES
CILIA (FLAME)
EXCRETORY PORE
POSTERIOR LATERAL LONGITUDINAL EXCRETORY CANALS
NUCLEI
NETWORK OF TRANSVERSE CANALS
Fig. – Flame cell of Platyhelminthes
Fig. – Renette cell of Ascaris
ANTERIOR
CANAL DISTAL
LIMB PROXIMAL
LIMB
CILIATED
the body through a small aperture called nephridiopore. However, in earthworm three types of nephridia are found. The septal nephridia situated on the septa (behind 15th segment) and pharyngeal nephridia (
NEPHROSTOME
FUNNEL
CANALS
TERMINAL DUCT
in three pairs of bundles in the 4th, 5th, and 6th segments) open into the alimentary canal and pour their excretory materials there. It is an
Fig. – Septal nephredium of Earthworm
adaptation for conservation of water. The integumentary nephridia (found scattered in the body wall in each segement except the first two segments) open directly on the body surface. Excretory materials help the earthworm in
keeping the skin moist for cutaneous respiration.
renal pores.
URETER
RENAL PORES
BLADDER
END SAC LABYRINTH
LATERAL DUCT
TRANSVERSE CONNECTIVE
RENAL SAC
GREEN GLAND
Fig. – Antennary gland of Prawn
tubules as their principal excretory organs. They are fine, spiral or convoluted, thread-like tubules which are attached to the alimentary canal. The distal closed end of each Malpighian tubule float freely in the haemolymph (blood). These tubules extract metabolic wastes like potassium and sodium urate, water and carbon dioxide from the blood. In the Malpighian tubules bicarbonates of potassium and sodium, water and uric acid are formed. A large amount of water and bicarbonates of potassium and sodium are reabsorbed by the cells of Malpighian tubules and then
transferred to the blood (haemolymph). Uric acid is carried to the alimentary canal of the insect and is finally passed out through anus.
ammonia, are eliminated by diffusion through dermal branchae (primitive gills) and tube feet.
ANUS
Fig. – Malpighian tubule of insecta
EFFERENT RENAL VEIN
EFFERENT RENAL VEIN
ENTERIOR RENAL CHAMBER
POSTERIOR RENAL CHAMBER
INTESTINE
BLADDE
EXCRETORY PORE
ENTERIOR RENAL SINUS
APERTURE INTO POSTERIOR RENAL CHAMBER
AURICLE
Fig. – Coxal gland or Scorpion
RENO-PERICARDIAL PERICARDIUM
|
AORTIC AMPULLA
Fig. – Organ of Bojanus (Pila – mollusca)
Excretory organs of different organisms
S.No. |
Phylum |
Excretory/osmoregulatory Organ/Organelle and principal N2-waste |
Function |
Example |
I. Invertebrates |
||||
(1) |
Protozoa |
Contractile vacuole Ammonia |
Ammonotelic Osmoregulatory |
Amoeba Paramecium |
(2) |
Porifera |
General surface of body |
Ammonotelic |
Sycon, Leucon |
(3) |
Coelenterata |
Ammonia, General surface of body |
Ammonotelic |
Hydra |
(4) |
Platyhelminthis |
flame cells (=Solenocytes) form the protonephridial system |
Ammonotelic |
Taenia, fasciola |
(5) |
Nematoda |
H-shaped excretory organ, Renette cells |
Ammonotelic |
Ascaris |
(6) |
Annelida |
Nephridial system, (Metameric), various types |
Ammonotelic |
Pheretima |
(7) |
Arthropoda |
|||
a. |
Class-Insecta |
Malpighian tubule |
Uricotelic |
Periplaneta |
|
|
(Uric acid) |
|
|
b. |
Class crustacea |
Antennary (=green) gland Uric acid |
Uricotelic |
Palaemon |
c. |
Class Arachnida |
Coxal glands Malpighian tubule Hepato pancreas Nephrocytes |
Uricotelic |
Spider |
(8) |
Mollusca |
Terrestrial forms Excrete uric acid |
Ammonotelic Uricotelic |
Pila
Pulmonate Mollusc Limax |
(9) |
Echinodermata |
Dermal branchiae (primitive gills) tube feet, body surface (Ammonia) |
Ammonotelic |
Cucumaria Asterias |
Mammalian (human) urinary system consists of a pair of kidneys, a pair of ureter, a urinary bladder and a urethra.
cavity just below the diaphragm, one on either side opposite the
RENAL ARTERY
RENAL VEIN
RIGHT KIDNEY
INFERIOR VENA
CAVA DORSAL AORTA
SUPRARENAL GLAND LEFT KIDNEY
PELVIS
LEFT
last thoracic and first three lumber vertebrae. The lower two pairs of ribs protect them.
The kidneys are covered by peritoneum on the front (ventral) side only. thus, they are retroperitoneal. The right kidney is attached more anterior than the left in rabbit. This asymmetry is just the reverse of that found in man.
In man left kidney occurs at a slightly higher level than the
RIGHT URETER
TRIGONIUM VESICAE
URETER
URINARY BLADDER
OPENING OF URETER
URETHRA
right one, because right side has prominent right liver lobe. In
Fig. – Human urinary system
rabbit the condition is little differ due to quadropedilism i.e. left kidney is in normal position while the right kidney shift ached to provide place for stomach below it.
In mammals, the kidney is bean-shaped i.e. concavo convex. The center of concave inner surface is called as hilum or hilus which gives out a ureter. From this hilus surface the renal artery enters into the kidney, the renal vein comes out and the renal nerves enter into the kidney.
Renal pyramids or medullary pyramids : The medulla is subdivided into 10 to 12 conical masses – the renal pyramid, each having broad base towards the cortex and a narrow end called renal papilla towards the pelvis.
Renal columns of bertini : Between the pyramids, the cortex extends into the medulla or renal columns of bertini.
Calyx : Each renal papilla projects into the cavity of a minor calyx, minor calyx join to form major calyx. The major calyx open into a wide funnel like structure, the pelvis. The latter
MINOR CALYX
MAJOR CALYX
CORTEX
RENAL PAPILLAE
PELVIS
HILUS
URETER
leads into the ureter. In rabbit, the pelvis is unbranched hence, it is without calyx.
In frog ventral surface of each kidney has many ciliated
MEDULLARY RENAL COLUMNS PYRAMIDS OF BERTINI
funnels called nephrostomes. They drain wastes from body cavity
Fig. – H.L.S. of human kidney
(coelom) and connect to renal veins in frog or to uriniferous tubules in tadpoles.
Histology of kidney : Histologically a kidney is made of innumerable thin, long, much convoluted tubular
units called uriniferous tubule or nephron.
Nephron is the structural and functional unit of kidney. One human kidney may contain about one million (10 lac nephron) nephron (In rabbit each kidney bear about 2 lac nephron). In frog each kidney bears about 2 thousand nephron.
Each capsule contains a network of blood capillaries the glomerulus which receives blood through afferent arteriole and the blood comes out through the efferent arteriole .The diameter of the efferent arteriole
DISTAL CONVOLUTED TUBULE
PROXIMAL CONVOLUTED TUBULE
MALPIGHIAN CORPUSCLE
BRANCH OF RENAL ARTERY
BRANCH OF RENAL VAIN
THICK SEGMENT OF ASCENDING LIMB OF HENLE'S LOOP
VASA RECTA
THIN SEGMENT OF ASCENDING LIMB OF HENLE'S LOOP
DESCENDING LIMB OF HENLE'S LOOP
RENAL CAPSULE
PERITUBULAR CAPILLARY NET WORK
RENAL CORTEX
CORTICAL NEPHRON
JUXTAGLOMERULAR NEPHRON
PYRAMID OF RENAL MEDULLA
COLLECTING TUBULE
BRANCH OF COLLECTING TUBULE
DUCT OF BELLINI
(=PAPILLARY DUCT)
is comparatively lesser. (Bowman's capsule and glomerulus receives about 20 – 25% of
VASA RECTA
PELVIS
RENAL
PAPILLA
the cardiac out put (blood) at rest.
The composite structure of Bowman's
Fig. – Position, structure and blood supply of cortical and juxtamedullary nephrons is a mammalian kidney
capsule and glomerulus is known as Malpighian body or Malpighian corpuscles after the Italian microscopist Marcello Malpighi.
The Bowman's capsule opens into a proximal convoluted tubule (P.C.T.) the anterior part of the P.C.T. is more coiled where as its posterior part is almost straight. The P.C.T. opens into a Henle's loop. The Henle's loop is a U- shaped structure which has a distinct descending limb and an ascending limb. The ascending limb opens in to the distal convoluted tube. The D.C.T. is a coiled structure. Many D.C.T. unit to form a collecting duct. The collecting ducts of one pyramid unit to form a duct of Bellini. The duct of Bellini lead into the pelvis part.
Arrangement of nephron : The malpighian body and a part of P.C.T. and D.C.T. are situated in the cortex.
Most of the part of P.C.T. and D.C.T., Henle's loop and collecting ducts are found in the medulla.
Vasa recta : The efferent arteriole of juxta-glomerular nephron forms a peritubular capillary system around the Henle's loop which is called vasa recta. Each of the vasa recta makes U turn at the inner most part of the medulla and return to the venous circulation near the junction of medulla and cortex. The efferent arteriole and peritubular capillaries technically constitute a renal portal system. In all amniotes as reptiles, birds and mammals have a renal portal system.
Types of nephron : Nephrons are of two types cortical and juxtamedullary, with regard to their location in the kidney. The cortical nephrons form about 80% to 90% of total nephron. They lie in the renal cortex and have very short loops of Henle that extend only little into the medulla.
The juxta medullary nephron have their Bowman's capsule close to (Juxta) the junction of the cortex and the medulla and have very long loops of Henle, extending deep into the medulla. This type of nephron is present in only birds and mammals. The cortical nephrons control the plasma volume when water supply is normal. The juxtamedullary nephrons regulate the plasma volume when water is in short supply (In advarse condition).
Differences between cortical and Juxtamedullary nephrons
Cortical Nephrons |
Juxtamedullary Nephron |
1. Form 80% of total nephrons. |
1. Form only 20% of total nephrons. |
2. Are small in size. |
2. Are large in size. |
3. Lie mainly in the renal cortex. |
3. Have Bowman's capsules in the cortex near its junction with the medulla. |
4. Henle's loops are very short and extend only a little into the medulla |
4. Henle's loop are very long and extend deep into the medulla. |
5. Control plasma volume when water supply is normal. |
5. Control plasma volume when water supply is short. |
Glomerulus : Glomerulus is a network of up to 50 parallel branching and anastomosing capillaries covered by endothelium, basement membrane and epithelium made of podocytes which has slit pores that restrict passage of colloids. However, small molecules and water can easily pass through them in to the P.C.T.
Bowman's capsule : The podocytes forming the inner wall of the Bowman's capsule have gaps (about 25 nm wide) the slit pores.
The outer wall of the Bowman's capsule consists of unspecialized squamous epithelium (flattened).
NUCLEUS OF A ENDOTHELIAL CELLPODOCYTE
OF GLOMERULAR PODOCYTE
FINGER LIKE PROCESSES OF
PODOCYTE NUCLEUS
Proximal convoluted tube : P.C.T. is made up of simple
Fig. – A glomerular capillary entwined
by processes of three podocytes
columnar epithelium. It has microvilli so it is also known as brush border epithelium.
Loop of Henle : The epithelium of descending limb of loop of Henle is very thin and composed of squamous epithelium and ascending limb is lined by cuboidal epithelium. The ascending limb is impermeable to water and permeable to NaCl.
Distal convoluted tube : It is made up of cuboidal epithelium which is glandular in nature.
Collecting ducts : The collecting ducts are lined
by cuboidal and columnar epithelium in different regions. At intervals, the cuboidal cells are ciliated.
Juxta-glomerular apparatus : This specialized cellular apparatus is located where the distal convoluted tube passes close to the Bowman's capsule and afferent arteriole. Cells of the D.C.T. epithelium in contact with afferent arteriole are denser than other epithelial cells known as maculla densa. Maculla densa has special Lacis cell or Polkisson's cell. These cells secrete renin hormone that modulate blood pressure and thus renal blood flow and G.F.R. are regulated.
EFFERENT ARTERIOLE
SMOOTH MUSCLE CELLS
DISTAL TUBULE
MACULA DENSA
GLOMERULAR EPITHELIUM
JUXTAGLOMERULAR CELLS
AFFERENT ARTERIOLE
INTERNAL ELASTIC LAMINA
BASEMENT MEMBRANE
vertebrate : Kidney tubules (nephrons) arise in the embryo in a linear series from a special part of mesoderm called mesomeare or nephrotome.
Number, complexity and arrangement of Nephrons are differ in different groups of vertebrates. A nephron is
Fig. Juxta glomerular apparatus
BOWMAN'S
CAPSULE MALPIGHIAN CORPUSCLE
differentiated into three parts – peritoneal funnel, tubule and
malpighian body. Peritonial funnel (nephrostome) are normally present in embryos and larvae and considered as vestigeal organ of hypothetical primitive kidneys.
Archeonephros kidney : Archeonephros is the name given to the hypothetical primitive kidney of ancestral vertebrate. It is also called as holonephros or complete kidney. (It extended entire length of coelom) It tubules are segmentally arragned and nephrostome is present. Glomerulus is external (without capsule). It duct is called as archeonephric duct. Ex. Larva of myxine.
Modern vertebrates exhibits three different kinds of adult kidney Pronephros, Mesonephros and Metanephros.
JUXTAGLOMERULAR
APPARATUS
GLOMERULUS
NECK
PROXIMAL CONVOLUTED TUBULE
DISTAL CONVOLUTED
TUBULE
LOOP OF HENLE; THICK ASCENDING LIMB
LOOP OF HENLE; THIN DESCENDING LIMB
in chick embryo which are segmentary arranged. Nephrostome present, glomerulus is external and unite to form glomus in
DUCT OF BELLINI
COLLECTING DUCT
some cases. Duct is pronephric duct or mullerian duct.
Fig. – Juxtamedullary nephron and epithelial cells in the wall of its various parts
Pronephros is functional in all embryos and larval stages. It is mostly transitory and soon replaced by the next stage or mesonephros.
Example – Adult myxine and petromyzones (cyclostomes) and some fishes but non urinary and lymphoid in function.
|
lined by transition epithelium which has great power of streaching. The neck of bladder is guarded by two sphincters, inner is involuntary controlled by spinal reflex and outer is voluntary controlled by cerebral cortex. A person feels the sensation of micturation when the quantity of urine in the bladder is about 300 c.c.
Urethra : The urinary bladder leads into the urethra. In a female, it is quite short, only about 3 to 5 cm long, and carries only urine. It opens by urethral orifice, or urinary aperture in the vulva infront of the veginal or genital aperture. In a male urethra is much longer, about 20 cm and carries urine as well as spermatic fluid. It
INNER LINING OF BLADDER
TRIGONE
URETHRAL ORIFICE
OPENINGS OF URETERS
URETER
WALL OF BLADDER
INTERNAL SPHINCTER
EXTERNAL SPHINCTER
URETHRA
passes through the prostate gland and the penis. It opens out at the tip of the penis by urinogenital aperture.
Fig. – Parts of ureters, trigone of the bladder, sphincters and urethra
Differences between male and female urethra
Male urethra |
Female urethra |
1. It is about 20 cm long. |
1. It is just 3 – 5 cm long. |
2. It has 3 regions : prostatic urethra (3–4 cm), membranous (1 cm) and penial (15 cm) |
2. It is not differentiated into regions. |
3. It opens out at the tip of the penis by urinogenital aperture. |
3. It opens into the vulva by urinary aperture. |
<