11th Class

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 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 more...

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 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 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}} 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 more...

Human have binocular vision. The eye can discriminate colour, appraise length, width and depth visually and form true inverted image. Structure of eye The eyes are two in number and lodged in orbits (bony socket) of skull. The eye is a hollow, spherical organ, about 2.5 cm in diameter and about 6 to 8 gram in weight. It has two parts - (1) Protective devices : Eye has four protective devices. (i) Eye brows : The outwardly directed hair of the eyebrows carry the sweat and rain drops trickling down the forehead to the sides to prevent their falling into the eyes. (ii) Eye lids (Palpebrae) : In man two eyelids are present, upper is movable. They are regularly closed at short intervals to clean the cornea. This is called blinking. In frog out of two upper eyelid is immovable and lower eyelid is movable. Nictitating membrane is present in more...

(1) Important tangoreceptor (i) Merckel's corpuscles : Found in epidermis (stratum malphighi) of skin. (ii) Merckel's disk : Found in epidermis (stratum malphighi) of skin. (iii) Meissner's corpuscles : Present in skin around the base of hair and feather. These are sensitive for touch and pressure both. (iv) Genital corpuscles : These are sensitive cells with nerve endings in skin around the genital organ. (v) Grandey's corpuscles : Found in birds at the base of the beak. These are kidney shaped in structure. (vi) Herbert corpuscles : Found in buccal cavity of birds. (vii) Capsulated corpuscles : These are sensitive cells encapsulated  and found in skin. (viii) Paccinian corpuscles : Found in deep layer of dermis and sensitive to touch, pain and pressure. (x) Golgi corpuscles and Mazzoni corpuscles : These are sensitive to touch and found in subcutaneous region. (2) Important Olfactoreceptor Jacobson's organ (Vomero-nasal organ) : It is more...

Also known as stato-acuostic organ. It is the receptor for balancing and hearing which is sensitive for gravity and sound waves. It is also sensitive in orientation of body. It is also known as mechano receptor because of it change mechanical energy of sound waves in to action potential. Structure of Ear Ear of mammal is divided in to 3 parts - (1) External ear : It is made up of pinna and auditory meatus. Pinna is found in only mammals. Its upper rounded part is helix and lower is ear lobe. It is made up of adipose connective tissue and elastic cartilage and has ear muscles which are vestigeal in case of human beings. Pinna collect the sound waves and drive towards auditory meatus. Auditory meatus is 25 mm. long canal lined by simple columnar epithelia and made up of fibro elastic cartilage. It possesses ceruminus gland which secrete more...

(1) Exteroreceptors : Receive stimulation directly from external environment. These may be of following type (i) Photoreceptor : Sensitive to light (Eye)                            (ii) Thigmoreceptor : Sensitive to touch. (iii) Tectoreceptor : Sensitive to touch. (iv) Tangoreceptor : Sensitive to touch pressure. (v) Phonoreceptor : Sensitive to sound (Ear). (vi) Olfactoreceptor : Sensitive for smell (Nose). (vii) Gustoreceptor : Sensitive to taste (Tongue). (viii) Thermoreceptor : Sensitive to temperature. (ix) Calo receptor : Sensitive to heat. (x) Frigido receptor : Sensitive to cold. (xi) Galvano receptor : Sensitive to electric current. (xii) Rheoreceptor : Sensitive to water or air current. (xiii) Geo receptor : Sensitive to gravity. (xiv) Telero receptor : Sensitive to distance. (Receptors of vision, hearing and smell receive stimuli from a distance hence called teleroreceptor). (2) Proprioceptors : Proprioceptors are located in skeletal muscles, joints, tendons etc. It is from these receptors that we know the position of more...