Renal Lectures - 4 for UA 2024 PDF

Renal Physiology By Dr Onaadepo Other functions of the kidneys (NON-URINARY FUNCTIONS)  OTHER FUNCTION OF THE KIDNEYS Regulation of arterial blood pressure Blood pressure = C O X PR Blood pressure is maintained at a constant levels by the kidneys by ensuring that the product of CO and...

Renal Physiology By Dr Onaadepo Other functions of the kidneys (NON-URINARY FUNCTIONS)  OTHER FUNCTION OF THE KIDNEYS Regulation of arterial blood pressure Blood pressure = C O X PR Blood pressure is maintained at a constant levels by the kidneys by ensuring that the product of CO and PR is constant This it does by ensuring that the blood volume that influences CO and vascular resistance is maintained constant  OTHER FUNCTION OF THE KIDNEYS Regulation of arterial blood pessure The kidneys reabsorbs most of the filtered water and by so doing it helps in maintaining blood volume and thus help in maintaining blood pressure A stable blood volume is important in keeping cardiac output constant If the blood volume is high, the antidiuretic hormone secretion is less and so much water is lost in urine resulting in lower ECF , lower venous return, lower CO and eventually lowering the blood pressure If the blood volume is low, the reverse occurs  OTHER FUNCTION OF THE KIDNEYS Regulation of arterial blood pressure Also the juxtaglomerular cells of the kidneys produce Renin The stimuli that causes the JGA to releases renin are reduced stretching of the wall of the renal afferent as occurs in hypotension or hemorrhage Renin is eventually converted to a Angiotensin II a potent vasoconstrictor  OTHER FUNCTION OF THE KIDNEYS Regulation of arterial blood pressure It also stimulates the release of aldosterone which causes sodium and water retention, this leads to an increase in cardiac output Ang II causes vaso -constriction and increased peripheral resistance and this leads to an increase in blood pressure Conversion of Angiotensin I to Angiotensin II  OTHER FUNCTION OF THE KIDNEYS Regulation of Red blood cell production In condition of hypoxia, certain cells in the kidneys are stimulated to produce erythropoietin Erythropoietin stimulates the bone marrow to increase RBC production This increased RBC production increases the oxygen carrying capacity of the blood and the increased production continues until there is no more hypoxia  OTHER FUNCTION OF THE KIDNEYS Regulation of vitamin D activity Active form of vit D is 1,25 dihydroxyl- cholicalciferol The hydroxylation occurs in the liver first and the second in the kidneys. The first hydroxylation does not make the molecule active Hence it is the rate of hydroxylation that determines the quantity of active Vit D Hence the kidneys regulate the activity of Vit D  OTHER FUNCTION OF THE KIDNEYS Other Endocrine functions Kidneys also produce kinins and prostaglandins which are general vasodilators and play protective role when renal blood flow is compromised Glucose Synthesis. The kidneys synthesize glucose from amino acids and other precursors during prolonged fasting, a process referred to as gluconeogenesis. The kidneys’ capacity to add glucose to the blood during prolonged periods of fasting rivals that of the liver.  OTHER FUNCTION OF THE KIDNEYS With chronic kidney disease or acute failure of the kidneys, and complete renal failure, enough potassium, acids, fluid, and other substances accumulate in the body to cause death within a few days, unless clinical interventions such as hemodialysis are initiated to restore, at least partially, the body fluid and electrolyte balances.  MICTURITION  The kidneys filter the plasma to produce urine and it is transported to the urinary bladder via the ureters where it is stored till its expulsion  Micturition or urination is the process of expelling/emptying urine from the bladder..  The process of micturition is regulated by the nervous system and the muscles of the bladder and urethra.  MICTURITION Physiologic anatomy of the bladder. Bladder muscle (Detrusor) Internal sphincter External sphincter  MICTURITION Detrusor is smooth muscle found in the wall of the bladder. The detrusor muscle remains relaxed to allow the bladder to store urine, and contracts during urination to release urine. Related are the urethral sphincter muscles which envelop the urethra to control the flow of urine when they contract The internal sphincter is formed by smooth muscle fibres of the detrusor The external sphincter is made up of voluntary striated muscle fibres Nerve supply of the bladder  MICTURITION Afferent fibres from the bladder run with the sympathetic nerve to dorsal nerve root L1 and L2 Also in the parasympathetic nerve to dorsal nerve roots S2, 3 and 4 These sensory fibres convey information about the degrees of distension of the bladder  MICTURITION The sympathetic and parasympathetic also supply motor innervation to the detrusor muscle of the bladder and the internal sphincter Motor innervation contracts the smooth muscle The pudendal nerve also from S2,3 and 4 is a somatic motor nerve to the external urethral sphincter  MICTURITION Two processes are involved in micturition 1. Progressive filling of the bladder until the pressure rises to critical level 2. A neuronal reflex called micturition reflex which empties the bladder  MICTURITION Progressive filling of the bladder The urine that is formed by the kidneys passes through the ureters into the urinary bladder When there is no urine in the bladder, the pressure is almost zero As urine accumulates in the bladder, bladder pressure rises When volume of urine in the bladder is about 100ml, intravesical pressure is between 5 and 10 cm of water  MICTURITION As the volume of urine increases up to about 300 to 400ml, there is only a small and gradual rise in intravesical presure As the bladder volume increases beyond 400ml, there is a sharp rise in intravesical pressure As the bladder is distended with increasing volume of urine, intermittent waves of pressure rise occur These are micturition waves seen in the cystometrogram and they are caused by micturition reflex  MICTURITION Cystometrogram is a graph of the intravesical pressure against the volume inside the bladder Cystometry tests measure how well the bladder functions. They help diagnose problems related to urine control. These can be incontinence, difficulty emptying the bladder, overactive bladder, obstructions or frequent infections.  MICTURITION Neuronal reflex (micturition reflex) As the bladder becomes distended with urine The stretch receptors on its walls are stimulated This gives rise to a wave of contraction of the detrusor muscle This leads to the urge to micturate Afferent impulses travel through the spinal cord to the higher centres in the brain  MICTURITION If the person is not ready to void yet, inhibitory impulses are sent from the cerebral cortex so that there is increased sympathetic discharge and reduced parasympathetic discharge This leads to relaxation of the detrusor muscle and contraction of the internal urethral sphincter and the urge to void dies off  MICTURITION More urine continues to accumulate in the bladder and the micturition reflex is repeated When the volume of urine in the bladder is above 400m,the intravesical pressure starts to rise steeply This gives rise to frequent and intense desires to void At this point, it is not easy to suppress the urge for too long  MICTURITION Cortical and suprapontine centres in the brain normally inhibit the micturition reflex Thus until a socially acceptable opportunity to void presents itself, efferent impulses from the brain, in a learned reflex, inhibit the urge to void  MICTURITION When the individual is ready to void, there are facilitatory impulses from the higher centres leading to increased parasympathetic discharge and reduced sympathetic discharge The voiding phase begins with a voluntary relaxation of the external urinary sphincter followed by the internal sphincter When a small amount of urine reaches the proximal part of the urethra(i.e the part connecting it to the bladder ) afferent impulses alert the cortex that voiding is imminent  MICTURITION The micturition reflex is now allowed to progress uninhibited As a result, the bladder contracts expelling urine The diaphragm descends and respiration is arrested in the inspiratory phase The abdominal muscle contract and the external sphincter relaxes  MICTURITION The increased pressure due to contraction of the detrusor muscles, the increased intra-abdominal pressure due to diaphragmatic descent and the relaxation of the internal urethral sphincters leads to emptying of the bladder  MICTURITION Some Abnormalities of micturition a) Atonic bladder b) Automatic bladder c) Enuresis  Abnormalities of micturition Atonic bladder This is due to loss of afferent fibres from the bladder to the spinal cord so that the individual is no longer aware of the extent of distension of the bladder As a result of this, instead of emptying periodically, the bladder fills to capacity and overflows a few drops at a time through the urethral  Abnormalities of micturition Automatic bladder This is seen when the spinal cord is damaged above L1 Inhibitory cortical influences on the micturition reflex are absent Micturition occurs whether the place and time is convenient or not  Abnormalities of micturition Enuresis This is bedwetting It is normal in infants It takes some time for bladder control to be achieved However some grown ups still bedwet This can be due to variety of causes ranging from psychological factors to actual abnormalities of the urinary system Diseases of the Kidneys Diseases of the Kidneys are hard deposits made of minerals and salts that form inside the kidneys  Diuresis Passage of large volume of urine Can be Fluid diuresis Osmotic diuresis  Diuresis Fluid diuresis This is due to ingestion of large quantity of fluid, it can be water, soft drink, tea or beer The excess fluid is absorbed into the blood and this leads to increase in blood volume and a reduction of the plasma tonicity The increased blood volume leads to increase in cardiac output and thus increase GFR  Diuresis Reduced tonicity causes a reduction of ADH and walls of the terminal tubules are impermeable to water This leads to a loss of a lot of water leading to production of hypotonic urine, hence diuresis Beer causes diuresis not only because of its large content but because of its alcohol content Alcohol suppresses ADH release, the combined effect makes beer to produce a greater diuresis than equal volume of water will produce  Diuresis Solute diuresis Sometimes called osmotic diuresis It is due to the presence of unabsorbed osmotically active molecules in the tubular lumen Excess sodium, glucose or urea in the tubular lumen are osmotically active Since the excess cannot be reabsorbed, they draw water to themselves  Diuresis So that the excess solute and retained water is excreted leading to passage of large volume of urine This is the basis of polyuria in diabetes mellitus Mannitol is also an osmotic diuretic, it is not reabsorbed from the tubules once filtered, that is basis of the use of mannitol infusion in clinical medicine to reduce edema Certain drugs cause diuresis, they are known as diuretics  Renal function tests Various test that are used to evaluate how well the kidneys are performing their functions There are different ways of evaluating  Renal function tests Are categorized into the following types Analysis of urine Analysis of blood Renal clearance tests-(test of GFR with inulin) Radiological tests Renal biopsy  Renal function tests Analysis of urine( Urinalysis) Urine can be analyzed under the following parameters 1. Volume of urine 1-2L/day 2. Colour- pale yellow due to urobilinogen 3. Osmolality and specific gravity 50- 1200mOsm/l and 1.003 to 1.030 4. Urinary Ph 4.5 to 8.0  Renal function tests 5. Abnormal urine constituents- proteins, bilirubin amino acids blood glucose etc 6. Microscopic examination. Casts cells , epithelial cells, calcium oxalates 7. Bacteriological examination- pus cells, pathogenic bacteria  Renal function tests ANALYSIS OF BLOOD Blood urea normal 20-40mg/100ml Plasma creatinine normal 0.6 – 1.5 mg/100ml, increases in renal diseases Serum electrolytes  Renal function tests Radiological investigations Plain radiograph of the abdomen Intravenous pyelography Ultrasonic scanning Computed tomography scanning Magnetic resonance imaging