Abstract
In all organisms, the excretory system maintains the internal aqueous and ionic environment for homeostasis. The organs of the renal system, constituted by paired kidneys, ureters, urinary bladder and urethra, help in the excretion of waste products and hydrogen ions, harmful drugs and toxins.
Nephrons, the kidney’s functional units, are concerned with the glomerular filtration, tubular reabsorption and tubular secretion to form urine. Glomerular filtration is a passive, non-selective process where fluids and electrolytes are filtered through the three layers of the glomerular membrane into Bowman’s space under the influence of physical forces. Kidneys maintain relatively constant renal blood flow and glomerular filtration rate (GFR) within a wide range of mean systemic arterial pressure by autoregulatory mechanisms. Tubular reabsorption is a highly selective process by which water and solutes are reabsorbed to the peritubular capillaries. The concentration of urine occurs by the countercurrent multiplier and countercurrent exchange systems existing in the hypertonic renal medullary interstitium. Urine formed in the kidneys is conveyed to the urinary bladder through ureters for temporary storage and removed from it periodically through the urethra by a process called micturition. The avian excretory system is structurally and functionally modified to avoid excess water loss and eliminate the major nitrogenous waste product, the uric acid.V. Beena (X)
Department of Veterinary Physiology, College of Veterinary and Animal Sciences, Thrissur, Kerala, India
e-mail: beenav@kvasu.ac.in
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023
P. K. Das et al. (eds.), Textbook of Veterinary Physiology, https://doi.org/10.1007/978-981-19-9410-4_9
Description of the graphic: The renal system is structurally organised (1) to eliminate end products of metabolism and other foreign waste materials. The process of urine formation (2) involves glomerular filtration, tubular reabsorption and tubular secretion. Glomerular filtration (3) is controlled by physical forces acting across the glomerular capillary wall and autoregulated by the kidney. Tubular reabsorption (4) is a highly selective process that occurs passively and actively. The tubular filtrate is concentrated by countercurrent exchange and countercurrent multiplier mechanisms (5). The urine formed is voided out by a process known as micturition (6). The avian renal system (7) is also structurally and functionally modified to eliminate the major nitrogenous end product, uric acid
Keywords
Urinary bladder and its functions
Peculiarities of avian excretion
Avian excretion ∙ Micturition ∙ Nephron ∙ Urine formation
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