Current Affairs 11th Class

(1) Axial endoskeleton : (Skull + Vertebral column + Sternum + Ribs) (2) Appendicular endoskeleton : (Girdle + Limb bones)       Axial skeleton (Human) It occupies the body's main longitudinal axis. It includes four structure : skull in the head, vertebral column in the neck, trunk and tail if present, sternum and ribs in the thorax. It form the upright axis of body and includes 80 (87 in children) bones are as follows in man -     (1) Skull (General structure) : It is anterior most axial skeleton. It is divisible into two main parts – (i) Chondrocranium                                         (ii) Splanchnocranium    (i) Chondrocranium : Chondrocranium is formed by (a) brain box or cranium proper and (b) two sense capsules - Orbit or optic capsule (eye) and  auditory or otic capsule (ear). (a) Cranium proper : It is a strong and firm bony box with a helmet-like covering over the brain, called vault of skull, and a relatively thicker and stronger floor of base upon which the brain rests. Its cavity is called cranial cavity. Size of cranial cavity averages 1475 cubic centimetres \[(c{{m}^{3}})\] in adult men. At about the middle of the floor of cranium, there is a large opening of cranial cavity called foramen magnum. The brain is connected to spinal cord at this foramen. Cranium proper of mammal has following distinct zone -
  • Occipital zone : Occipital zone has one supra-occipital bone on dorsal side, one basioccipital on ventral side and two exoccipital on both lateral side of foramen magnum. Foramen magnum is present in ventral side of skull, which fills on Ist atlas vertebra. Two occipital condyles forming dicondylic skull at the junction of supra and exo-occipital.
  • Parietal zone : In the dorsal side of cranium parietal zone has three bone, that is two parietal, one inter parietal and ventral side of cranium has 3 bone i.e. one basisphenoid with pituitary foramen and two alisphenoid bone.
  • Frontal : Frontal part of cranium has two frontal bone in dorsal side, each frontal bone has one process called supra orbital process of frontal. Two orbitosphenoid, one presphenoid bone in ventral side.
  • Ethmoidal : Ethmoidal part has one circular plate called cribriformplate. That plate is having two perforation for exit of I cranial nerve.
(b) Sense capsule : Chondrocranium contains two sense capsule.
  • Optic or orbital capsule
  • Otic or auditory capsule
Optic capsule : One pair of optic or orbital capsule are present in frontal zone of chondrocranium. It is made up of 7 pairs of bones which are - \[IPre\text{ }frontalIIPost\text{ }frontalIIIAnterior\text{ }orbital\] \[IVPosterior\text{ }orbitalV\text{ }\text{ }Infra\text{ }orbitalVI\text{ }\text{ }Supra\text{ }orbital\]                       \[VIILacrymal\] In frog optic capsules are absent but in place of optic capsule more...

(1) Characteristics of female's skeleton : In female's skeleton, (i) skull is lighter, (ii) shoulders are narrower (iii) sacrum is shorter but wider, (iv) pelvis in wider, has a broader front and larger bottom opening to facilitate child birth, and (v) coccyx is more movable than in male's skeleton. (2) Adaptations in skeleton for upright posture : Human skeleton shows many adaptive features for upright posture – (i) Foramen magnum is directed downward so that the head may rest vertically on the vertebral column. (ii) Four curves in the backbone keep the centre of gravity near the heels. This helps to maintain balance and makes walking erect on two legs much easier. (iii) Thorax is wider from side-to-side than from front-to-back. This helps to maintain equilibrium. (iv) Bowel-like pelvis supports the lower abdominal viscera. (v) Metacarpals form a wide palm and the pollex is opposable. This make the hand a grasping organ to work with it. (vi) Leg bones are stronger than the arm bones as the femur carry the entire weight of the body in locomotion.  (vii) Broad feet provide stability in the upright posture. (viii) The arches of the feet enable the body to move with a degree of springiness. (ix) Increased mobility of the neck to see all round. (x) Increased skeletal height provides greater range of vision. (3) Types of bones : Bones are divided into 4 categories regarding their size and shape – (i) Long bones, e.g., humerus of upper arm, radius and ulna of forearm, femur of thigh, and tibia and fibula of leg. (ii) Short bones, e.g., metacarpals of palm and metatarsals of foot, phalanges of fingers and toes. (iii) Flat bones, e.g., scapula of shoulder girdle, sternum, cranial bones. (iv) Irregular bones, e.g., vertebrae, carpals of wrist and tarsals of ankle. (4) Bone movement : Movements of bones occur only at the joints. The movements are brought about by contractions of skeletal muscles inserted onto the articulating bones by firm cords of white fibrous tissue called tendons. Cords of yellow elastic tissue, termed ligaments, stabilise the joints by holding the articulating bones together. (5) Disorder of skeleton and joints : Any violent movement, such as jump, fall or knock, may cause injury to the skeleton. The injury can be of 5 types - sprain, dislocation, fracture, arthritis and slipped disc. (i) Sprain : Sprain refers to injury to a joint capsule, typically involving a stretching or tearing of tendons or ligaments. Unfortunately, both these structures have much poorer regenerative power than bone, and once stretched often remain weak. Sprain is often considered a minor disorder, but it may become chronic. (ii) Arthritis or Aching Joints : Arthritis refers to inflammation of the joints. It is a common disease of the old age. Its common symptoms are pain and stiffness in the joints. It has many forms. Three more common forms are described here - osteoarthritis or degenerative arthritis, the rheumatoid arthritis and gout. (a) Osteoarthritis : Secretion of the lubricating synovial fluid more...

In the body of all the multicellular animals muscles are found. The movement of the body takes place by these muscles. If the muscles become weak, the functioning of the body become difficult. The muscles are capable of contraction and relaxation, hence these are elastic. A muscle can pull a part of the body by its contraction (shortening). It cannot push that part by relaxation (elongation). Hence, the muscles are typically arranged in antagonistic (opposing) pairs, one muscle moves a body part in one direction by its contraction and the other muscle moves that part in the opposite direction by its contraction. Of course, when one muscle contracts, its opposing muscle relaxes. The principle of antagonistic muscles is true of both vertebrate as well as invertebrate muscles. Animal movements depend upon interaction of muscles and skeleton. (1) Action of body muscles : As mentioned above, the body muscles are arranged in antagonistic (opposing) pairs. One muscle of a pair moves a body part in one direction and the other in the opposite direction. For example, the muscle named biceps brings the forearm toward the upper arm, and the muscle called the triceps moves the forearm away from the upper arm. When biceps contracts to cause movement, the triceps relaxes to allow that movement to occur and vice versa. Similar pairs of opposing flexor and extensor muscles occur at the wrist, ankle and knee. The type of movement that results from the contraction of a muscle depends entirely upon the way the muscle is attached to the levers of the skeleton. (2) Classification of body muscles : According to the type of motion they cause, the muscles are divided into the following types. The muscles that act together to produce a movement are called synergists and the muscle that act in opposition to each other are antagonists. The muscles that act most powerfully during any given movements are called prime movers. (i) Flexor and Extensor : Muscles that bend one part over another joint is called flexor. Extensor muscle is antagonist of flexor muscle. The contraction of an extensor extends a joint by pulling one of the articulating bone apart from another.     (ii) Pronator and Supinator : The contraction of a pronator rotates the forearm to turn the palm downward or backward. Supinator is antagonist of pronator. A supinator contracts to rotate the forearm and thus to make palm face upward or forward.   (iii) Abductor and Adductor : An abductor contracts to draw a bone away from the body midline. Muscle that brings the limb away from midline is called abductor. An adductor draws a bone towards the body midline. Muscles that brings the limb towards midline is called adductor. Abductor muscle is antagonist of adductor muscle. Abduction is elevation and adduction is depression.   more...

The fluid and dissolved waste substances excreted by the kidneys constitute urine. Quantity : An adult man normally passes about 1 to 1.8 litres of urine in 24 hours. The volume of urine depends upon (i) the fluid intake, (ii) level of physical activity, (iii) type of food taken and (iv) environmental temperature increase urine output. Less fluid intake and profuse sweating due to heavy physical work and high temperature reduce urine output. Certain substances, such as tea, coffee and alcohol, increase urine output. These are said to be diuretic. Physical properties : Urine is transparent yellowish fluid, but becomes turbid (cloudy) on standing, its colour depending on its concentration. Its colour is due to a pigment urochrome derived from the breakdown of haemoglobin from the worn-out RBCs. Colour of the urine is altered by certain materials taken such as beet, vitamin B complex and some drugs diseases. It is hypertonic to blood plasma. Its specific gravity ranges between 1.001 to 1.035, being slightly higher than that of water. Its pH is 6. It depends on the diet. High protein food and fruits increase acidity whereas vegetables increase alkalinity. Urine has a characteristic unpleasant odour. If allowed to stand, urea is degraded by bacteria to ammonia which imparts a strong smell to urine. Chemical composition : Urine consists of water and organic and inorganic substances. Water alone forms about 95% of it, other substances form only 5%. The organic substances are mainly nitrogenous organic compounds include urea, uric acid, creatinine and hippuric acid. Of these, urea is the principal component of human urine. The non nitrogenous organic compounds include vitamin C, oxalic acid, phenolic substances include ammonia, and mineral salts such as chlorides, sulphates and phosphates of sodium, potassium, calcium and magnesium. Sodium chloride is the principal mineral salt of the urine. Urine also contains some other substances, such as pigments and drugs, and some epithelial cells, leucocytes, mucin, enzymes, and hormones. Abnormal materials : Presence of proteins (albumins), bile salts, bile pigments, ketone bodies, blood, pus, microbes and more than a trace of glucose in the urine is pathological condition. Presence of glucose, protein, blood, ketone bodies and pus in the urine is called glucosurea, proteinuria, haematuria, ketonuria and pyuria respectively. Renal threshold : A negligible amount of glucose is present in the urine. The highest concentration of a substances in the blood upto which it is fully reabsorbed from the glomerular filtrate is called its threshold. If its concentration in the blood exceeds its renal threshold, some of the filtered out substance is not reasborbed and is excreted in the urine. For example, the renal threshold of glucose is 180 mg. per 100 ml. of blood. If its blood level exceeds 180 mg., some of the filtered out glucose is not reabsorbed and is passed in urine. Conduction of urine and Micturition : Urine is produced and drained continuously by the nephrons into the renal pelvis. From here, it is carried down the ureters by peristaltic waves into more...

Major nitrogenous excretory substance in frog, rabbit and human is urea, i.e. these are ureotelic animals. The excretory physiology in these animals may be considered under two phases, viz urea synthesis and formation and excretion of urine.     Synthesis of urea in liver : Urea is formed in liver by two processes. (1) Deamination                               (2) Ornithine cycle (1) Deamination : The amino acid is oxidised using oxygen. This result in removal of the amino group \[(N{{H}_{2}})\] and leaves pyruvic acid. the pyruvic acid can enter the Krebs cycle and be used as a source of energy in cell respiration. The amino group is converted to ammonia \[(N{{H}_{3}})\] during deamination. Deamination is also known as oxidative deamination.     \[\underset{\left( \text{Amino}\,\,\text{acid} \right)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}{\mathop{\begin{array}{*{35}{l}} C{{H}_{3}}  \\ |  \\ CH-N{{H}_{2}}+\frac{1}{2}{{O}_{2}}  \\   |  \\ COOH  \\\end{array}\xrightarrow{{}}}}\,\underset{\left( \text{Pyruvic}\,\text{acid} \right)}{\mathop{\begin{array}{*{35}{l}} C{{H}_{3}}  \\ |  \\ CO+N{{H}_{3}}  \\ |  \\ COOH  \\\end{array}}}\,\]   With the help of a number of enzymes and energy of A.T.P. two molecules of ammonia are combined with \[C{{O}_{2}}\] to form urea according to the ornithine cycle. (2) Ornithine cycle (Kreb-Henseleit cycle) : In liver one molecule of \[C{{O}_{2}}\] is activated by biotin and combines with two molecules of \[N{{H}_{3}}\]in the presence of carbamyle phosphate synthatase enzyme (C.P.S.) and 2 ATP to form carbamyle phosphate and one molecule of \[{{H}_{2}}O\] release. Carbamyle phosphate react with ornithine and form citrulline. Citrulin combines with another molecule of ammonia and form arginine. Arginine is broken into urea and ornithine in the presence of an enzyme arginase and water. \[2N{{H}_{3}}+C{{O}_{2}}\xrightarrow{\text{Arginase}}\underset{\text{(Urea)}}{\mathop{N{{H}_{2}}-CO-N{{H}_{2}}+{{H}_{2}}O}}\,\] Liver cells, thus, continuously remove ammonia and some \[C{{O}_{2}}\] from blood and release urea into the blood. Kidneys continuously remove urea from the blood to excrete it in urine.     Urine formation : Urine formation occurs in the kidneys. It involves three processes glomerular filtration, reabsorption and tubular secretion. (1) Ultra filtration (Starling’s hypothesis) (i) It is passive process which takes place from the glomerulus into the Bowman's capsule. The glomerular epithelium has various micropores (diameter\[=50100\,\,nm\,\,or\text{ }0.050.1\,\,\mu m\]) which increase the rate of filtration. (ii) The non colloidal part of the plasma as urea, water, glucose, salts, vitamin, minerals, nitrogenous waste are forced out from the glomerular capillaries into the Bowman's capsule by the high pressure of the blood in the glomerular capillaries. The pressure and resistence is high because the glomerular capillaries are narrower than the afferent renal arteries. Glomerular capillaries are about 50 times more permeable than capillaries elsewhere. Pressure highest in glomerular capillaries than in capillaries else where, produce more filtrate.     (iii) The effective filtration pressure that causes ultrafiltration is determined by three pressures.     (a) Glomerular blood hydrostatic pressure (G.B.H.P.) : Hydrostatic pressure is force that a fluid under pressure exerts against the walls of its container. \[G.B.H.P.=+70\,\,mm\text{ more...

The regulation of solute movement, and hence, water movement, which follows solutes by osmosis, is known as osmoregulation. Osmosis may be defined as a type of diffusion where the movement of water occurs selectively across a semipermeable membrane. It occurs whenever two solutions, separated by semipermeable membrane (the membrane that allows water molecules to pass but not the solutes) differ in total solute concentrations, or osmolarity. The total solute concentration is expressed as molarity or moles of solute per litre of solution. The unit of measurement for osmolarity is milliosmole per litre (mosm\[{{L}^{1}}\]). If two solutions have the same osmolarity, they are said to be isotonic. When two solutions differ in osmolarity, the solution with higher concentration of solute is called hypertonic, while the more dilute solution is called hypotonic. If a semipermeable membrane separates such solutions, the flow of water (osmosis) takes place from a hypotonic solution to a hypertonic one. Osmoconformers are the animals that do not actively control the osmotic condition of their body fluids. They rather change the osmolarity of body fluids according to the osmolarity of the ambient medium. All marine invertebrates and some freshwater invertebrates are strictly osmoconformer. Osmoconformers show an excellent ability to tolerate a wide range of cellular osmotic environments. Osmoregulators, on the other hand, are the animlas that maintain internal osmolarity, different from the surrounding medium in which they inhabit. Many aquatic invertebrates are strict or limited osmoregulators. Most vertebrates are strict osmoregulators, i.e. they maintain the composition of the body fluids within a narrow osmotic range. The notable exception, however, are the hagfish (Myxine sp., a marine cyclostome fish) and elasmobranch fish (sharks and rays). Osmoregulators must either eliminate excess water if they are in hypotonic medium or continuously take in water to compensate for water loss if they are in a hypertonic situation. Therefore, osmoregulators have to spent energy to move water in or out and maintain osmotic gradients by manipulating solute concentrations in their body fluids.

Hormonal controls of the kidney function by negative feedback circuits can be identified : (1) Control by antidiuretic hormone (ADH) : ADH, produced in the hypothalamus of the brain and released into the blood stream from the pituitary gland, enhances fluid retention by making the kidneys reabsorb more water. The release of ADH is triggered when osmoreceptors in the hypothalamus detect an increase in the osmolarity of the blood above a set point of 300 mosm \[{{L}^{1}}.\] In this situation, the osmoreceptor cells also promote thirst. Drinking reduces the osmolarity of the blood, which inhibits the secretion of ADH, thereby completing the feedback circuit. (2) Control by Juxtaglomerular apparatus (JGA) : (Low Blood pressure triggers the Reninangiotension pathway) JGA operates a multihormonal Renin-Angiotensin-Aldosterone System (RAAS). The JGA responds to a decrease in blood pressure or blood volume in the afferent arteriole of the glomerulus and releases an hormone, renin into the blood stream. In the blood, renin initiates chemical reactions that convert a plasma protein, called angiotensinogen, to a peptide, called angiotensin II, which works as a hormone. Angiotensin II increases blood pressure by causing arterioles to constrict. It also increases blood volume in two ways - firstly, by signaling the proximal convoluted tubules to reabsorb more \[NaCl\] and water, and secondly, by stimulating the adrenal gland to release aldosterone, a hormone that induces the distal convoluted tubule to reabsorb more Na+ and water. This leads to an increase in blood volume and pressure, completing the feedback circuit by supporting the release of renin.     (3) Parathormone : The hormone increases blood \[C{{a}^{++}}\] (Hypercalcium) and decreases \[P{{O}_{4}}\] accordingly, it increases absorption of \[C{{a}^{+}},\]increases excretion of \[P{{O}_{4}}.\] (4) Thyrocalcitonin : It increases excretion of \[C{{a}^{++}}\] in the kidney. (5) Prostaglandin : The renal pyramids produce fatty acids of prostaglandins (P.G.) which participates in blood pressure regulation. (6) Erythropoeitin : It is secreted by juxtaglomerular apparatus and plays an important role in erythropoeisis (blood production).   Differences between Rennin and Renin
S.No. Rennin Renin
1. It is secreted by peptic (zymogen) cells of gastric glands into the stomach. more...
By continuously eliminating metabolic wastes and other impurities, and even the surplus quantity of useful materials from blood plasma in the form of urine, kidneys play a vital role in homeostasis. Kidneys also operate certain other homeostatic regulatory mechanisms. Proper maintenance of the internal environment is knows as homeostasis. All regulatory functions of kidneys can be enumerated as follows - (1) Osmoregulation : Being the universal solvent, water is the actual vehicle in ECF to transport materials between various parts of body. Water volume in ECF tends to vary considerably due to several reason, such as drinking, perspiration, diarrhoea, vomiting, etc. As described in previous pages, the kidneys maintain the water balance in ECF by diluting or concentrating urine. (2) Regulation of osmotic pressure : Osmolality of cytoplasm is mainly due to proteins and potassium and phosphate ions, whereas that of the ECF is mainly due to sodium, chloride and bicarbonate ions. Inspite of marked difference in chemical composition, the two fluids - intracellular (cytoplasm) and extracellular (interstitium) - must be isotonic, because if ECF becomes hypotonic, cells will absorb water, swell retaining apropriate number, mainly of sodium and chloride ions, kidneys maintain the normal osmolality of ECF. (3) Regulation of pH : Concentration of hydrogen ions \[(Na{{H}_{2}}P{{O}_{4}})\] in ECF is to be regulated at a constant value usually expressed as pH (minus log of\[{{H}^{+}}\]). The normal pH of ECF is about 7.4. A low pH, i.e. a high \[{{H}^{+}}\] concentration causes acidosis, while a high pH, i.e. a low \[{{H}^{+}}\] concentration causes alkalosis. Both of these conditions severely affect cellular metabolism. Several special control systems, therefore, operate in the body to prevent acidosis and alkalosis. These system are called acid-base buffer system. Kidneys play a key role in maintenance and operation of these systems. Further, the kidneys regulate hydrogen ion concentration in ECF by excreting acidic or basic urine. (4) Regulation of electrolyte concentrations in ECF : The kidneys regulate, not only the total concentrations of water and electrolytes in ECF, but also the concentrations of individual electrolytes separately. This regulation is complex and is accomplished by tubular reabsorption and secretion under the control of hypothalamic and adrenal hormones. (5) Regulation of RBC-count in blood : In oxygen deficiency (hypoxia), kidneys secrete an enzyme into the blood. This enzyme reacts with plasma globulin to form erythropoietin. The latter substance stimulates bone marrow to produce more RBCs for enhancing \[{{O}_{2}}-\]intake in lungs. (6) Regulation of renal blood flow : See (R.A.A.S.).

Mammalian (human) urinary system consists of a pair of kidneys, a pair of ureter, a urinary bladder and a urethra. (1) Kidneys : The kidneys are dark-red, bean-shaped organs about 11 cm long, 5 cm wide and 3 cm thick, each weight about 150 gm in an adult male and about 135 gm in adult female. They are placed against the back wall of the abdominal cavity just below the diaphragm, one on either side opposite the last thoracic and first three lumber vertebrae. The 11th and 12th 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 one, because right side has prominent right liver lobe. In rabbit the condition is little differ due to quadropedilism i.e. left kidney is in normal position while the right kidney shift ahead to provide place for stomach below it. In mammals, the kidney is 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.   (i) Structure of kidney : The kidneys are metanephric in mammals. The kidney is divisible into two parts outer-cortex and inner-medulla. Three layers of tissue surround each kidney. (a) The innermost, renal capsule made up of fibrous connective tissue. (b) The intermediate layer, adipose capsule of fatty tissue. (c) The outermost, renal fascia of dense connective tissue.  Renal pyramids or medullary pyramids : The medulla is subdivided into 8 to 18 conical masses - the renal pyramid, each having broad base towards the cortex and a narrow end called renal papilla towards the pelvis.     Path of urinary drainage : Collecting duct\[\to \]Papillary duct in renal pyramid\[\to \]Minor calyx\[\to \]Major calyx\[\to \]Renal pelvis\[\to \]Ureter\[\to \]Urinary bladder 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 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 funnels called nephrostomes. They drain wastes from body cavity (coelom) and connect to renal veins in frog or to uriniferous tubules in tadpoles.   (ii) Histology of kidney : Histologically a kidney is made of innumerable thin, long, much convoluted tubular units more...

(1) Protozoans : In protozoans like Amoeba 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.   (2) Sponges : In sponges, the nitrogenous metabolic waste (ammonia) leaves the body in the outgoing water current by diffusion. 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.     (3) Coelenterates : Hydra also lacks special excretory organs. The nitrogenous waste products like ammonia are removed through the general surface of the body by diffusion. Some nitrogenous waste products are also thrown along with indigestible matter through the mouth.   (4) Platyhelminthes : Planaria, liverfluke and tapeworm possess a large number of excretory cells called the flame cells (solenocytes) or protonephridia and long excretory ducts (also called canals of vessels). The flame cells open into the ductules which in turn open into the excretory duct.       (5) Nematoda : The round worms such as Ascaris have H-shaped excretory system. It is made up of a single Renette cell. in entire length of body. It consists of two longitudinal excretory canals connected anteriorly by a network of transverse canals. A short terminal duct opens outside via excretory pore. Ascaris is excretes both ammonia and urea.     (6) Annelids (Earthworm) : In earthworm excretory system also known as nephridial system, which consist of 3 types of nephridia Pharyngeal, septal, and integumentary nephridia. All nephridia commonly called micronephridia. Earthworm excrete 40% urea, 20% ammonia, 40% amino acids. Earthworm mainly ureotelic. Chloragogen cells found in coelomic fluid also excretory in nature. Blood gland in earthworm found in 4, 5, 6 segment, serves for excretion, manufacture of blood corpuscles and Hb.     (7) Arthropods : The excretory system of the adult Prawn (crustacean) consists of a pair of antennary or green glands, a pair of lateral ducts and a single renal sac. Insects, centipedes, millipedes and arachnids like scorpion and spider posses Malpighian tubules as their principal excretory organs. 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. Spiders and scorpions possess Malpighian tubules and coxal glands both for excretion.     more...


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