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Urophysiology 1


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# a breif detail about the anatomical and physiological of kidney.
# micturation reflex (the role of sympathetic, parasympathetic, and somatic nerves).
# the process of urine formation "filtration, reabsorption, secretion, and excretion".

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Urophysiology 1

  1. 1. The Urinary System: Functional Anatomy and Urine Formation by the Kidneys
  2. 2. Function of the kidney: 1. Excretion of metabolic waste products and foreign chemicals. 2. Regulation of water and electrolyte balances 3. Regulation of body fluid osmolality and electrolyte concentrations. 4. Regulation of arterial pressure. 5. Regulation of acid-base balance. 6. Regulation of erythrocyte production. 7. Secretion, metabolism, and excretion of hormones Gluconeogenesis.
  3. 3. PHYSIOLOGICAL ANATOMY OF THE KIDNEYS: • The two kidneys lie on the posterior wall of the abdomen, outside the peritoneal cavity, 150 grams. • The Renal hilum through which pass the renal artery and vein, lymphatics, nerve supply, and ureter. • The kidney is surrounded by a tough, fibrous capsule that protects its delicate inner structures. • The two major regions that can be visualized are the: • (1) outer cortex and the (2) inner medulla regions. • renal pyramids: 8 to 10 cone-shaped masses of tissue. • The papilla, which projects into the space of the renal pelvis. • The renal pelvis a funnel-shaped continuation of the upper end of the ureter.
  4. 4. • The outer border of the pelvis is divided into open- ended pouches called major calyces that extend downward and divide into minor calyces, which collect urine from the tubules of each papilla. • The walls of the calyces, pelvis, and ureter contain contractile elements that propel the urine toward the bladder, where urine is stored until it is emptied by micturition.
  6. 6. • Afferent arterioles, which lead to the glomerular Capillaries. • Efferent arteriole, which leads to the peritubular capillaries Blood flow to the two kidneys is normally about 22% of the cardiac output, or 1100 ml/min.
  7. 7. • The renal circulation is unique in having two capillary beds that help regulate the hydrostatic pressure in both sets of capillaries: 1- The glomerular Capillaries (High hydrostatic pressure = about 60 mm Hg, causes rapid fluid filtration). 2- The peritubular capillaries (lower hydrostatic pressure = about 13 mm Hg) permits rapid fluid reabsorption).
  8. 8. THE NEPHRON IS THE FUNCTIONAL UNIT OF THE KIDNEY: • Each human kidney contains about 800,000 to 1,000,000 nephrons, each of which is capable of forming urine. • The kidney cannot regenerate new nephrons. • After age 40 years, the nephrons usually decreases about 10% every 10 years. • Each nephron contains: (1) a tuft of glomerular capillaries called the glomerulus, through which large amounts of fluid are filtered from the blood. (2) a long tubule in which the filtered fluid is converted into urine on its way to the pelvis of the kidney. • Kidney is made up of closely arranged tubular structures called uriniferous tubules (urine formation – Nephron, and trasnportation – Collecting Ducts ).
  9. 9. Regional Differences in Nephron Structure: 1- Cortical nephron: • Have short loops of henle that penetrate only a short distance into the medulla. • The entire tubular system is surrounded by an extensive network of peritubular capillaries. 2- Juxtamedullary Nephrons: • Have long loops of Henle that dip deeply into the medulla, in some cases upto renal papillae. • specialized peritubular capillaries called vasa recta that extend downward into the medulla, lying side by side with the loops of Henle. • Site for formation of concentrated urine
  11. 11. MICTURITION: • Micturition: is the process by which the urinary bladder empties when it becomes filled. • This process involves two main steps: 1. First, the bladder fills progressively until the tension in its walls rises above a threshold level 40mmhg. 2. Second, this tension elicits a nervous reflex called the micturition reflex that empties the bladder or, if this fails, at least causes a conscious desire to urinate. • Although the micturition reflex is an autonomic spinal cord reflex, it can also be inhibited or facilitated by centers in the: A. Cerebral cortex or B. Brain stem.
  12. 12. PHYSIOLOGICAL ANATOMY OF THE BLADDER: • The urinary bladder: is a smooth muscle chamber composed of two main parts: (1) the body, and (2) the neck. • The lower part of the bladder neck is also called the posterior urethra. • The smooth muscle of the bladder is called the detrusor muscle. • Contraction of the detrusor muscle is a major step in emptying the bladder. • Trigone: is a small smooth triangular lying immediately above the bladder neck. • The rest of mucosal bladder have a rugea. • The urinarry bladder have also internal sphincter and external sphincter.
  13. 13. 1- Sympathetic (Hypogastric) nerve (Nerve of Filling): • Relaxation of detrusor muscle and constriction of the internal sphincter. Filling urinary bladder. 2- Parasympathetic (pelvic) nerve (Nerve of Empyting): • Contraction of detrusor muscle and relaxation of the internal sphincter. Emptying of urinary bladder. • Pelvic nerve has also the sensory fibers, which carry impulses from stretch receptors present on the wall of the urinary bladder and urethra to the central nervous system. 3- Somatic (Pudendal) nerve: • Innervates external sphincter. • maintains the tonic contraction of the skeletal muscle fibers of the external sphincter. • During micturition, this nerve is inhibited. • It causes relaxation of external sphincter leading to voiding of urine.
  14. 14. MICTURITION REFLEX: • is the reflex by which micturition occurs. • This reflex is elicited by the stimulation of stretch receptors situated on the wall of urinary bladder and urethra. • When about 300 to 400 mL of urine is collected in the bladder, intravesical pressure increases. • Generation of sensory impulses.
  15. 15. Higher Centers for Micturition: • Spinal centers for micturition are present in sacral and lumbar segments. • These spinal centers are regulated by higher centers. 1- Inhibitory centers for micturition: • Centers in midbrain and cerebral cortex inhibit the micturition by suppressing spinal micturition centers. 2- Facilitatory centers for micturition: • Centers in pons facilitate micturition via spinal centers. • Some centers in cerebral cortex also facilitate micturition.
  16. 16. TRANSPORT OF URINE FROM THE KIDNEY THROUGH THE URETERS AND INTO THE BLADDER: 1. Urine flowing from the collecting ducts. 2. Pass in the renal calyces. 3. Renal calyces stretch and initiates peristaltic contraction. 4. Urine spreads in the renal pelvis. 5. Pass downward along the ureters. 6. Finally urine stored in the bladder. Wall of the ureters contains smooth muscle which innervated by: 1- Parasympathetic stimulation – increase peristaltic contraction. 2- Sympathetic stimulation – decrease peristaltic contraction. •Vesicoureteral reflex: is a reflex In which urine in the bladder is backflow to the ureters leading to increase pressure in the renal and kidney structure which causes a damage •Ureterorenal reflex: is a reflex In which blockage of ureters by stones leads to constrict the renal arterioles preventing excessive flow fluid in the pelvis and ureters
  18. 18. Urinary excretion rate = Filtration rate − Reabsorption rate + Secretion rate Substance A = Creatinine, uric acid, urea. Substance B = Na, Cl. Substance C = Amino acid, Glucose. Substance D = Foreign substance and Drugs
  19. 19. FILTRATION, REABSORPTION, AND SECRETION OF DIFFERENT SUBSTANCES: • In general, tubular reabsorption is quantitatively more important than tubular secretion in the formation of urine. end products of metabolism such as urea, creatinine, uric acid, and urates, are poorly reabsorbed and are therefore excreted in large amounts in the urine. Certain foreign substances and drugs are also poorly reabsorbed but, in addition, are secreted from the blood into the tubules, so their excretion rates are high. Electrolytes, such as sodium ions, chloride ions, and bicarbonate ions, are highly reabsorbed, so only small amounts appear in the urine. Certain nutritional substances, such as amino acids and glucose, are completely reabsorbed from the tubules and do not appear in the urine even though large amounts are filtered by the glomerular capillaries.
  20. 20. Why Are Large Amounts of Solutes Filtered and Then Reabsorbed by the Kidneys • a high GFR is that it allows the kidneys to rapidly remove waste products from the body that depend mainly on glomerular filtration for their excretion.