PHYSIOLOGY OF THE RENAL SYSTEM MADE EASY M. pptx

FOR students

1. PHYSIOLOGY OF RENAL SYSTEM DR. GRACE NGARUIYA

2. Glomerular Filtration Process of filtration of plasma across the glomerular basement membrane from the glomerulus into the Bowman's capsule" Nicola Thomas (2019) Renal Nursing , Care and management of People with Kidney Disease. During filtration blood enters the glomerulus from the series of branches of the renal artery ending in to the afferent arteriole .  

3. Composition of the glomerular filtrate Glomerular capillaries are impermeable to proteins The filtered fluids is essentially protein free and devoid of cellular elements including red blood cells. Other constituents of glomerular filtrate include salt and organic molecules.

4. Low molecular weight substances like calcium and fatty acids are not filtered because they are partially bound to plasma proteins .

5. PRESSURES DETERMINING FILTRATION Colloidal osmotic pressure in the glomeruli Hydrostatic pressure in the Bowman capsule. These pressures determine the GFR by either favoring or opposing the filtration.

6. Hydrostatic Pressure in Bowman Capsule Hydrostatic pressure is the pressure produced by a fluid against a surface. It is the pressure exerted by the filtrate in Bowman capsule (PBS). It is also called capsular pressure. It is about 15 mm Hg. It also opposes glomerular filtration. It is increased by constriction of the ureters. Increases in HPBC cause decreases in net ultrafiltration pressure and GFR .

7. Glomerular Hydrostatic Capillary Pressure Glomerular hydrostatic capillary pressure is the pressure exerted by the blood in glomerular capillaries. It is about 60 mm Hg . It is the highest capillary pressure in the body. This pressure favors glomerular filtration. constant along the length of the capillary. It is increased by dilation of the afferent arteriole or constriction of the efferent arteriole Increases in this pressure cause increases in net ultrafiltration pressure and GFR.

8. is the pressure exerted by plasma proteins in the glomeruli. The plasma proteins are not filtered through the glomerular capillaries and remain in the glomerular capillaries. These proteins develop the colloidal osmotic pressure, which is about 25 mm Hg. It opposes glomerular filtration. normally increases along the length of the glomerular capillary because filtration of water increases the protein concentration of glomerular capillary blood. It is increased by increases in protein concentration. Increase in pressure cause decrease in net ultrafiltration pressure and GFR. Colloidal Osmotic Pressure

9. Renal blood flow Blood flows from the abdominal aorta to the renal artery.   about 1200ml/min or 25% of cardiac output.   The kidneys receive extremely high blood flow compared to other organs which supplies them with nutrients and removes waste products. supplies enough plasma for the high rates of glomerular filtration that are necessary for regulation of body fluids volumes and solute concentration.

10. The kidneys normally consume oxygen at twice the rate of the brain, coming second to the heart. increasing O2 delivery to the kidney relative to demand via increased blood flow results in augmented tubular electrolyte load following elevated glomerular filtration, which, in turn, increases metabolic demand High Oxygen demand is associated primarily with tubular oxygen consumption necessary for solutes reabsorption especially active sodium reabsorption by the renal tubules

11. Reduced uptake of solutes in the proximal tubule increases load to the thick ascending limb. There, the increased load is reabsorbed, but at greater oxygen cost, which may lead tissue hypoxia if persistent

12. Filtration Barrier: specialized blood filtration interface that allows filtration of small to midsized solutes but is relatively impermeable to macro molecules

13. DETEREMINANTS OF RENAL BLOOD FLOW Pressure gradient across the renal vasculature( difference between renal artery and renal vein hydrostatic pressure) divided by the total renal vasculature resistance RBF= RENAL ARTERY PRESSURE- RENAL VEIN PRESSUR E TOTAL RENAL VASCULAR RESISTANCE Renal artery pressure is about equal to systemic arterial pressure, and renal vein pressure averages about 3-4 mmHg under most conditions.

14. Most of the renal vascular resistance resides in three major segments interlobular arteries afferent arterioles efferent arterioles . Increase in resistance of any of the vascular segments of the kidney tends to reduce renal blood flow.

15. The glomerular barrier consists of Endothelium of the capillary: Perforated by thousand of small pores called fenestrae About 70nm in diameter, they don’t restrict the movement of large molecules and proteins rather prevent filtration of red blood cells. surrounding the luminal surface of endothelial cells are glycocalyx ( surface layer that covers cell membranes of epithelial cells),

16. Basement membrane consists of meshwork of collagen and heparan proteoglycan ( macromolecular composed of polysaccharide chains at the core of proteins) fibrillate with large spaces that easy filters water and solutes proteoglycans help restrict movement of negatively charged molecules across basement membrane. Basement membrane consists of 3 layers An inner thin layer( lamina rara internal) A thick layer ( Lamina densa An outer layer ( lamina rara externa)

17. These layers help to limit the filtration of intermediate and large sized solutes like albumin. consisting of negatively charged glycosaminoglycan.( negatively charged carbohydrates compounds formed by long chains of repeated units linked together) Their function is to hinder diffusion of negatively charged molecules by repelling them due to like charges.

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19. Epithelium : Epithelial cells that line the outer surface of glomerulus. Have long foot-like processes ( podocytes) than encircle the outer surface of the capillaries. They have filtration slits , these slits are bridged by a thin diaphragm, called slit diaphragm, which has very small pores The pores prevent large molecules such as proteins, from crossing. Filterability of solutes is related to their size of the molecules

20. JUXTAGLOMERULAR APPARATUS The juxtaglomerular apparatus (JGA) is a specialized structure located in the kidney that plays a crucial role in regulating blood pressure and kidney function. It is composed of three main components: the macula densa, the granular cells (also known as juxtaglomerular cells), extraglomerular mesangial cells. The function of the juxtaglomerular apparatus is to monitor and regulate the filtration rate and blood flow within the kidney. helps to maintain a balance between sodium, water, and blood pressure in the body.

21. The macula densa cells located between the afferent arteriole and efferent arteriole of the same nephron They sense changes in sodium chloride concentration in the filtrate. When sodium chloride levels are low, the macula densa cells signal the granular cells to release the enzyme renin. Process called tubular glomerular feedback mechanism. The macula densa cells are not innervated ( does not have nerve supply)

22. The granular cells/ juxtaglomerular cells located in the walls of the afferent arterioles made of myoepithelial smooth muscles called Juxtaglomerular cells secrete renin in response to signals from the macula densa cells or changes in blood pressure. act as baroreceptors ( sensitive to changes in pressure ) and innervated by sympathetic nerve fibres. Renin is an enzyme that initiates the renin-angiotensin-aldosterone system (RAAS), which plays a key role in regulating blood pressure and fluid balance.

23. The extraglomerular mesangial cells Are granular cells also called lacis cells situated in the triangular region by the afferent arteriole, efferent arteriole and macula densa cells plays important role in glomerular filtration by their contractile properties they are phagocytic- consumes foreign microorganism and dead tissue cells provide structural support to the juxtaglomerular apparatus involved in the regulation of blood flow within the glomerulus

24. The renin-angiotensin-aldosterone system (RAAS) Is a hormonal system that plays a crucial role in regulating blood pressure and fluid balance in the body. It is primarily involved in maintaining the balance of sodium and water in the blood. 1. Renin: Renin is an enzyme released by the kidneys in response to low blood pressure or low blood volume. It acts on a protein called angiotensinogen, which is produced by the liver, to convert it into angiotensin I.

25. 2. Angiotensin I: Angiotensin I is an inactive peptide that is converted into angiotensin II by an enzyme called angiotensin-converting enzyme (ACE). This conversion primarily occurs in the lungs 3. Angiotensin II: Angiotensin II is a potent vasoconstrictor, meaning it causes the blood vessels to narrow. This leads to an increase in blood pressure. Angiotensin II also stimulates the release of aldosterone . 4. Aldosterone: Aldosterone is a hormone produced by the adrenal glands. It acts on the kidneys to increase the reabsorption of sodium and water, while promoting the excretion of potassium. This results in an increase in blood volume and blood pressure

26. ReplyForward Tubular selective Reabsorption Occurs in the proximal convoluted tubule where 85% of the glomerular filtrate is reabsorbed back into the bloodstream leaving urea and excess mineral ions behind.      

27. KEY ADAPTATIONS OF THE PROXIMAL CONVOLUTED TUBULE CELLS{epithelial cells} The cells have plenty of microvilli that provide a large surface area to maximise reabsorption of glucose. Lots of mitochondria within the cells to provide energy needed for active transport.

28. T he concentration of sodium ions in the proximal convoluted tubule is decreased as sodium ions are actively transported out of the proximal convoluted tubules back into the blood capillaries. Due to the concentration gradient,sodium ions diffuse down the gradient from the lumen of the proximal convoluted tubule into the cells lining the proximal convoluted tubule. This is an example of co-transport as the proteins which transport the sodium ions in, carry glucose with it. co-transport is carrier protein that allows the transport of 2 different species from one side of the membrane to the other at the same time.

29. The glucose can then diffuse from the proximal convoluted tubules epithelial cells into the bloodstream. This explains how all the glucose is reabsorbed back to the bloodstream.

30. In the proximal convoluted tubule, large volume of solutes are transported into the blood scream. As we move along the tubule the concentrations are decreasing while the solute concentration in the interstitium are increasing. The difference in concentration gradient results in water moving into the interstitium via osmosis .

31. Sodium is reabsorped by co-transport while secreting other substances into the tubular lumen especially hydrogen ions Hydrogen ions in the tubula lumen are important for removal of bicarbonate ions from the tubule, this is by combining hydrogen ions with bicarbonate to form hydrogen bicarbonate which then dissociates into water and carbondioxed.

32. acid base balance kidneys generate 4,320 mEq of bicarbonate per day and as much as 80% of the filtered bicarbonate is reabsorbed in the proximal tubule . filtered bicarbonate combines with hydrogen ions to form carbonic acid, which will dissociate into water and carbon dioxide. H + + HCO 3– H 2 CO 3 ↔ H 2 CO 3 ↔ CO 2 + H 2 O

33. THE LOOP OF HENLE Made of two limbs;the ascending and descending loop of henle Descending limb- the walls are much thinner hence they are permeable to water hence the water will move out by osmosis to be reabsorbed back to the blood. the main function of this nephron segment is to allow simple diffusion of substance through its wall

34. Here, sodium ions are actively transported out Ascending limb-its walls are impermeable to water because it has much thicker walls that do not allow water to pass through. The ascending limb has thick epithelial cells which are capable for active reabsorption of sodium, chloride and potassium.

35. the thin segment has lower reabsorptive capacity solute reabsorption in the thick ascending limb is by sodium-potassium ATPase pump which maintains a low intracellular sodium concentration low intracellular sodium concentration provides a favorable gradient for movement of sodium from the tubular fluid into the cell

36. HOW THE LOOP OF HENLE MAINTAINS A SODIUM ION GRADIENT It has mitochondria in the walls of the cells which provide energy to actively transport sodium ions out of the ascending limb. The accumulation of sodium ions outside the nephron in the medulla lowers the water potential. Hence water is able to move out by osmosis into the interstitial space and be reabsorbed back to the blood capillaries. At the very base of the ascending limb,some sodium ions are transported by diffusion because now there is a very dilute solution since all the water has been moved out.

37. At the thick ascending loop movement of sodium across the cell membrane is mediated by a 1-sodium ,2-chloride,1- potassium co-transport This co-transport uses the potential energy released by downfall diffusion of sodium into the cell to drive the absorption of potassium into the cell against a concentration gradient The thick ascending loop is virtually impermiable to water,therefore the tubular fluid becomes dilute as it flows to the distal convoluted tubule

38. THE DISTAL CONVOLUTED TUBULES The walls have numerous microvilli and mitochondria and carries out active transport. Reabsorption of ions takes place here. Divided into early and late section. In the early segment the reabsorption of ions to include sodium chloride and calcium. It is impermeable to water. The walls are permeable to water only in presence of the anti-diuretic hormone. Movement of these ions is dependent on the sodium potassium ATPase transporter. This excretes sodium ions into the extracellular fluid and reabsorbs potassium into the cell . sodium reabsorption and potassium secretion is depended on the activity of sodium potassium ATPase.

39. COUNTER CURRENT MECHANISM OF THE KIDNEY This refers to a system in which the kidney concentrates urine. It is a system in which the inflow runs parallel, counter to and in close proximity to the outflow. Osmolarity- refers to concentration of a solute in a solution.it is the number of osmoles of a solute per litre {Osm/L} Diffusion- process by which water movers from a region of high concentration to a region of low concentration to bring back equilibrium.

40. CONDITIONS TO BE FULFILLED: 2 tubes in parallel Movement of solute in opposite direction Should be in close proximity and selectively permeable

41. COUNTER CURRENT MECHANISM CONT….. This mechanism depends upon maintenance of a gradient of increasing osmolarity along the medullary pyramids Countercurrent multiplication system a system that allows for the formation of a hypertonic filtrate with an osmolarity gradient growing from the cortex to the depth of the kidney medulla. It occurs in the loop of henle

42. The descending limb of the loop is permeable to water but not to solutes while the ascending limb is impermeable to water but allows for reabsorption of solutes particularly sodium. filtrates flows down the descending limb, water is passively reabsorbed,leading to an increase in solute concentration.

43. As the filtrate ascend the assessing limb, sodium and other solutes are actively transported out,further increasing the concentration of solutes in the interstitial fluid of the medulla. This countercurrent flow of filtrate in opposite direction helps establish and maintain the concentration gradient.

44. Countercurrent exchange system represents the endless recirculation of solutes in and out of vasa recta{ the network of capillaries surrounding the loop of henle} The vasa recta acts as the countercurrent exchanger allowing for the exchange of water and solute between the descending and ascending limbs of the loop of henle.

45. This exchange helps to maintain the concentration gradient in the medulla without disrupting concentration of solutes in the interstitial fluid.

46. countercurrent exchanger cont… . The countercurrent mechanism is crucial for the kidney to concentrate urine and regulate water balance. It allows for the reabsorption of water in the presence of a concentrated interstitial fluid, hence preventing excessive water loss.

47. Additionally, it aids in the reabsorption of solutes such as sodium to maintain electrolyte balance in the body. Overall, the countercurrent mechanism is a complex and efficient process that enables the kidney to concentrate urine and maintain water and electrolyte balance in the body.

48. RENAL PELVIS- It is an expanded funnel shaped area through which urine flows. it is located within the medial, concave surface of the kidney , filling the renal sinus. The apex of the renal pelvis extends outwards from the kidney, and becomes continuous with the superior end of the ureter.

49. collecting ducts reabsorb less than 10% of the filtered water and sodium. they are the final site for processing urine they determine the final urine output of water and solutes cuboidal in shape with smooth surfaces and have fewer mitochondria ( less surface area)

50. Functions of the collecting ducts 1. Water Reabsorption from the filtrate. This process is regulated by the hormone antidiuretic hormone /ADH), which is secreted by the posterior pituitary gland in the hypothalamus. when high levels of antidiuretic hormone is present, it binds to receptors in the collecting ducts, leading to the insertion of water channels called aquaporins into the cell membranes. This allows water to be reabsorbed from the filtrate back into the bloodstream, resulting in concentrated urine. In the absence of antidiuretic hormone the aquaporins are removed from the cell membranes, leading to decreased water reabsorption and the production of dilute urine.

51. 2. Electrolyte Reabsorption: play a role in the reabsorption and excretion of electrolytes, such as sodium, potassium, and hydrogen ions. The specific transport mechanisms involved in electrolyte handling vary along the length of the collecting ducts and are regulated by the hormone aldosterone, which influences sodium and potassium reabsorption 3, acid base balance collecting ducts are capable of secreting hydrogen ions against a concentration gradient which leads to acid base balance.

52. PARATHYROID HORMONE It is secreted by the four thyroid glands located in the neck,and behind the thyroid gland. It acts to increase the concentration of calcium in blood. It is important in bone remodelling which is an ongoing process in which bone tissue is alternately resorbed and rebuilt Parathyroid hormone stimulates the release of calcium from large calcium stores in the bone into the bloodstream These process increases bone destruction. Parathyroid hormone reduces loss of calcium in urine increasing its reabsorption in the distal convoluted tubules. It also stimulates production of active vitamin D in the kidneys.

53. PARATHYROID HORMONE CONTI….. It increases the absorption of calcium in the intestine via its effect on vitamin D metabolism. Parathyroid hormone increases blood calcium concentrations when calcium ion levels falls below normal. First, PTH enhances reabsorption of calcium by the kidneys; it the stimulates osteoblast activity. Finally, PTH stimulates synthesis and secretion of calcitriol by the kidneys, which enhances Ca2+ absorption by the digestive system.

54. ERYTHROPOIETIN HORMONE This hormone is primarily produced by the kidney. It can also be produced by the liver but in small amounts. It stimulates the the bone marrow to produce red blood cells. Low Oxygen Levels- Erythropoietin production is primarily regulated by the oxygen levels in the body. When the oxygen levels in the blood are low, such as in the case of anaemia or decreased oxygen supply to tissue, the kidneys detect this hypoxia. Erythropoietin Production- in response to hypoxia, specialized cells in the kidney called interstitial fibroblasts, located in the peritubular capillaries release Erythropoietin into the bloodstream. Erythropoietin production can also be influenced by other factors such as hormones like angiotensin 2.

55. Erythropoietin Hormones Continuation….. Erythropoietin Receptors- Erythropoietin travels through the bloodstreams and binds to specific receptors from the surface of the cells and the bone marrow. This receptors are present in the surface of early red blood cell precursors Stimulation of red blood cell production-Binding of erythropoietin to its receptors triggers a series of intracellular signaling pathways within the erythroid progenitor cells (self-renewing stem cells that give rise to Erythrocytes).This signaling cascade promotes the survival, proliferation and differentiation of these cells into mature red blood cells.

56. Increased Red Blood Cell Production - As a result of Erythropoietin stimulation. the bone marrow increases production of its blood cells. This newly formed red blood cells are then released into bloodstream where they can carry oxygen to tissues and organs. red blood cells dont have a nucleus, this is an adaptive measure that increases oxygen carrying capacity and also that they can change shape and move easily throughout the body.

57. ALDOSTERONE HORMONE It is produced by the adrenal gland. ALDOSTERONE diffuses out of the mitochondria into cytoplasm and across the cell membrane to enter the circulation. ALDOSTERONE circulation rate per day is 100- 150 ug . Aldosterone is carried primarily by albumen. EFFECTS OF ALDOSTERONE Important in the regulation of salt balance and blood volume in the kidney. Aldosterone acts on the distal convoluted tubule and collecting tubule by increasing reabsorption of sodium excretion of both potassium and hydrogen ions.

58. ALDOSTERONE HORMONE Cont…. Effects of Aldosterone in sodium retention are important for the regulation of blood pressure. Aldosterone production circulation are controlled through the renin - and angiotensin Aldosterone system. it is stimulated by increased extracellular production, decline in sodium concentration, Adrenocorticotropic hormone, decreased blood pressure, decreased macula densa blood flow. These stimulus influences juxtaglomerular cells for renin secretion via beta 1 adrenoreceptors

59. TUBULAR SECRETION Tubular secretion is the process by which materials are transferred from peritubular capillaries to the renal tubular lumen. Active transport and passive transport are the primary cause of secretion. only few substances are secreted usually they are waste products.

60. MECHANISM OF SECRETION Here the mechanisms are similar to those of reabsorption, but the process takes place in the opposite direction. Usually happens in the following processes PASSIVE DIFFUSION -the movement of molecules within the nephron from the peritubular capillaries to the interstitial fluid.

61. 2.active transport - movement of molecules through ATPase pumps that transport the substances through the renal epithelial cells into the nephron lumen. Secretion filters and cleans substances from the blood instead of retaining them. the following substances are secreted into the tubular fluid for excretion. potassium,hydrogen,ammonium,creatinine some hormones some medications .

62. The role of the kidney in regulation of fluids and electrolytes Appreciate roles of ADH, Aldosterone, Atrial natriuretic peptide (ANP), Renin and Angiotensin II hormones. The hypothalamus has osmoreceptors that detect changes in blood osmotic pressure then neve impulses from the osmoreceptors stimulate the posterior pituitary to release ADH

63. As a result the DCT and collecting duct (CD) cells increase water reabsorption. This ultimately initiates a negative feedback that causes reduced blood osmotic pressure and ADH output to keep water and sodium in normal limits

64. Ideally, the pH of urine should be around 4.5 to 8.0 Any changes in pH can have a significant meaning as far as health is concerned the following condition can lead to acidic urine diabetic ketoacidosis-due to decrease in bicarbonate dehydration-this happens because some electrolytes are lost together with water. diarrhoea The kidneys maintain acid-base balance in the body by producing bicarbonate ions[HCO3-].On average the kidneys produce 50-100mEq[ milliequivalents ]of bicarbonate per kilogram of body weight per day .

65. SPECIFIC URINE GRAVITY; it compares the density of urine than that of water. normal ranges 1.000-1.030 high specific gravity can be suggestive of the following conditions dehydration as a result of diarrhea and/or vomiting congestive cardiac failure shock

66. low specific gravity suggests the following diabetes insipidus kidney failure drinking too much fluid i.e polydipsia use of diuretics like hydrochlorothiazide

67. urine pH high than normal can indicate the following conditions kidney failure gastric suctioning - gastric lavage respiratory alkalosis urinary tract infections

68. Adult urine output is between 1000 to 2000mls in 24 hours . T he hypothalamus has osmoreceptor cells that detect any osmotic pressure changes in blood . I ncrease in osmotic pressure triggers secretion of the hormone ADH which will increase water reabsorption at distal convoluted tubules and collecting ducts . T he opposite happens when blood osmotic pressure is reduced.

69. Urine output for age groups urinary output per kilogram of body weight decreases as the child ages because the kidney become more efficient. infants - 1ml/kg/ hr children 0.5ml-1ML/kg/ hr adolescents 1-1.5ML/kg/ hr

70. ADH/Vasopressin determines whether the kidney excretes dilute or concentrated urine. Antidiuretic Hormone regulates urine concentration. When bodily fluid osmolarity increases above normal, the posterior pituitary gland secretes more ADH, which increases permeability of the distal tubules and collecting ducts to water. This permits large amounts of water to be reabsorbed and decreases urine volume but does not alter the rate of Renal Excretion of solutes.

71. When there is too much water in the body, A ntidiuretic hormone is secreted and reduces permeability of distal tubules and collecting ducts. Which causes more dilute urine to be excreted.

72. EXCRETION

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74. 1. Reabsorption and Secretion: The renal tubules selectively reabsorb filtered bicarbonate ions and actively secrete hydrogen ions into the urine. This process helps to maintain the bicarbonate buffer system, which is essential for pH regulation. 2. Ammonia Production: The kidneys produce ammonia (NH3) from the metabolism of glutamine. Ammonia combines with hydrogen ions in the renal tubules to form ammonium (NH4+), which can be excreted in the urine, thereby helping to eliminate excess hydrogen ions.

75. 3. Acidification and Alkalinization of Urine: The kidneys can adjust the pH of urine by altering the secretion of hydrogen ions and bicarbonate ions. Acidic urine (low pH) helps to eliminate excess acid from the body, while alkaline urines base. (high pH) aids in excreting excess base. NB: renal regulation of pH is just one component of the body's overall acid-base balance. Other mechanisms, such as respiratory regulation (via the lungs) and buffering systems in the blood, also contribute to maintaining pH homeostasis.

76. RENAL NERVES The kidneys are primarily innervated by the renal nerves, which are part of the autonomic nervous system. The autonomic nervous system is responsible for regulating various involuntary functions of the body. The renal nerves play a role in regulating renal blood flow, glomerular filtration rate, and sodium and water balance.

77. There are two main nerves that supply the kidney 1.sympathetic nerves : arise from the sympathetic chain ganglia and travel to the kidneys r egulate blood pressure and maintain fluid balance. 2.parasympathetic nerves : parasympathetic innervation of the kidneys is minimal

78. functions of nerves in the kidney 1. Renal blood flow regulation: Nerves in the kidney play a role in regulating renal blood flow by controlling the constriction or dilation of blood vessels. Sympathetic nerves release norepinephrine, which can cause vasoconstriction of the renal arteries, reducing blood flow to the kidneys . This mechanism helps regulate blood pressure and maintain adequate blood flow to other vital organs during times of stress or low blood volume.

79. 2 . Renin release : Specialized nerve cells called juxtaglomerular cells in the kidney release the enzyme renin in response to signals from sympathetic nerves. Renin plays a crucial role in the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and fluid balance. 3 . Regulation of tubular function : Nerves influence the reabsorption and secretion of substances in the renal tubules. example, sympathetic nerves can stimulate the reabsorption of sodium and water in the proximal tubules, leading to increased fluid retentio n

80. 4. Sensory function : act as sensory receptors, detecting changes in blood pressure, blood flow, and electrolyte levels. These sensory signals are transmitted to the central nervous system, providing feedback for the regulation of kidney function. 5. Pain perception: transmit pain signals in response to kidney inflammation, infection, or other pathological conditions. This pain perception helps alert individuals to potential kidney problems and prompts them to seek medical attention.

81. PHYSIOLOGY OF THE BLADDER AND URETERS FILLING · The walls of the ureters contain smooth muscle arranged in spiral, longitudinal and circular bundles, but distinct layers of muscle are not seen. · Regular peristatic contractions occurring one to five times per minute move the urine from the renal pelvis to the bladder, where it enters in spurts synchronous with each peristaltic wave. · The ureters pass obliquely through the bladder wall and, although there are no ureteral sphincters as such, the oblique passage tends to keep the ureters closed except during peristaltic waves, preventing reflux of urine from the bladder.

82. · Expected bladder capacity =750ML EMPTYING · Contraction of the circular muscle, which is called the detrusor muscle, is mainly responsible for emptying the bladder during micturition. · Muscle bundles pass on either side of the urethra, and these fibers are sometimes called the internal urethral sphincter (smooth muscle) although they do not encircle the urethra. · Further along the urethra is a sphincter of skeletal muscle, the sphincter of the membranous urethra, external urethral sphincter.

83. BLADDER INNERVATION parasympathetic nerve enhances contractions, sympathetic nerve modulate/inhibit contractions,and the somatic nerve enhances voluntary control of the external sphincter

84. · TYPES OF NERVES NERVE FIBRE ACTION COMMENTS SYMPATHETIC HYPOGASTRIC NERVES (L1,L2,L3) INFERIOR MESNTERIC GANGLION Motor to internal urethral sphincter, inhibitory to detrusor No significant role in micturition, prevent reflux of semen into the bladder during ejaculation PARASYMPATHETIC PELVIC NERVES (S2,S3,S4) Motor to detrusor inhibitory to internal urethral sphincter Stretch receptors present on the wall of the urinary bladder Sensory fibers in the pelvic nerve Intermediolateral column of spinal cord Parasympathetic nerves Muscarinic receptors emptying of urinary bladder ·

85. SOMATIC PUDENDAL NERVES (S2,S3,S4) Voluntary control of External urethral sphincter This maintains the tonic contractions of the skeletal muscle fibers of the external sphincter, so that this sphincter is contracted always. During micturition this nerve is inhibited, causing relaxation of the external sphincter and voiding of urine

86. The Cystometrogram When there is no urine in the bladder, the intravesicular pressure is about 0. But by the time 30 to 50 milliliters – can collect with only a small additional rise in pressure; this constant level of pressure is caused by intrinsic tone of the bladder wall. Beyond 300 to 400 milliliters, collection of more urine in the bladder causes the pressure to rise rapidly . Superimposed on the tonic pressure changes during filling of the bladder are periodic acute increases in pressure that last from a few seconds to more than a minute.

87. · The pressure peaks may rise only a few centimeters of water or may rise to more than 100 centimeters of water. · These pressure peaks are called micturition waves in the Cystometrogram and are caused by the micturition reflex. Micturition Reflex · Once a micturition reflex has occurred but has not succeeded in emptying the bladder, · The nervous elements of this reflex usually remain in an inhibited state for a few minutes to 1 hour or more before another micturition reflex occurs.

88. Continuation · As the bladder becomes more and more filled, micturition reflexes occur more and more often and more and more powerful. · When the bladder is only partially filled these micturition contractions usually relax spontaneously after a fraction of a minute, the detrusor muscles stop contracting , and pressure falls back to the baseline. · As the bladder continues to fill, the micturition reflexes become more frequent and cause greater contractions of the detrusor muscle. · Once a micturition reflex begins, it is “self-regenerative.”

89. · Initial contraction of the bladder activates the stretch receptors to cause a greater increase in sensory impulse to the bladder and posterior urethra, which causes a further increase in reflex contraction of the bladder. · Cycle is repeated again and again until the bladder has reached a strong degree of contraction. · Then, after a few seconds to more than a minute, the self-regenerative reflex begins to fatigue and the regenerative cycle of the micturition reflex stops, permitting the bladder to relax. · The micturition reflex is a single complete cycle of · (1) progressive and rapid increase of pressure,

90. · (2) a period of sustained pressure, and · (3) return of the pressure to the basal tone of the bladder · Once a micturition reflex has occurred but has not succeeded in emptying the bladder, · the nervous elements of this reflex usually remain in an inhibited state for a few minutes to 1 hour or more before another micturition reflex occurs. · As the bladder becomes more and more filled, micturition reflexes occur more and more often and more and more powerfully.

91. · Once the micturition reflex becomes powerful enough, it causes another reflex, which passes through the pudendal nerves to the external sphincter to inhibit it. · If this inhibition is more potent in the brain than the voluntary constrictor signals to the external sphincter, urination will occur. · If not, urination will not occur until the bladder fills still further and the micturition reflex becomes more powerful.

92. Role of the brain · The micturition reflex is a completely autonomic spinal cord reflex, but it can be inhibited or facilitated by centers in the brain. · These centers include · (1) strong facilitative and inhibitory centers in the brain stem, located mainly in the pons, and · (2) Several centers located in the Cerebral cortex that are mainly inhibitory but can become excitatory. · The micturition reflex is the basic cause micturition, but the higher centers normally exert final control of micturition

93. · 1. The higher centers keep the micturition reflex partially inhibited, except when micturition is desired. · 2. The higher centers can prevent micturition, even if the micturition reflex occurs, by continual tonic contraction of the external bladder sphincter until a convenient time presents itself. · 3. When it is time to urinate, the cortical centers can facilitate the micturition centers to help initiate a micturition reflex. · And at the same time inhibit the external urinary sphincter so that urination occurs.

94. Voluntary urination · First, a person voluntarily contracts his or her abdominal muscles, which increases the pressure in the bladder · And allows extra urine to enter the bladder neck and posterior urethra under pressure, thus stretching their walls. · This stimulates the stretch receptors, which excites the micturition reflex and simultaneously inhibits the external urethral sphincter. · Ordinarily, all the urine will be emptied, with rarely more than 5 to 10 milliliters left in the bladder.

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