Renal Physiology Lectures (PIO 402, Series 3, 2024) PDF

PIO 402 Professor Y. Raji Fellow, FAIMER Institute, Philadelphia, USA SERIES 3: 7. Autoregulation of renal blood flow 8. Kidney in Acid-base balance 9. Micturition. Tests of Kidney function 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 202...

PIO 402 Professor Y. Raji Fellow, FAIMER Institute, Philadelphia, USA SERIES 3: 7. Autoregulation of renal blood flow 8. Kidney in Acid-base balance 9. Micturition. Tests of Kidney function 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 1  Autoregulation of renal blood flow and Glomerular filtration rate (GFR). 16/December/2024 2 PIO 402-SERIES 3-YR-UI DEC. 2024 Autoregulation of renal blood flow GFR is also autoregulated Myogenic hypothesis attributes the increase in renal vascular resistance that accompanies an increase in systemic arterial pressure to contraction of the afferent arteriolar smooth muscle in response to stretch Juxtaglomerular hypothesis attributes autoregulation to changes in the rate of renin scretion. 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 3 Kidney in pH regulation pH= -log10[H+] pH= Pk + log10[Base/Acid] Normal body pH= 7.4+/- 0.04 Renal tubules secrete either H+ or OH- thus are able to change the pH of the filtrate from 7.4 to 4.5-8.5, the range of urine pH 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 4 System which lower PH 1. CO2 + H2O = H2CO3 adds acid to the body 2. Metabolism of proteins, H2SO4 and H3PO4 3. Diabetes mellitus, adds aceto-acetic acid to the body 4. Anaerobic respiration, exercise adds lactic acid to the body 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 5 Systems-remove acids or add alkali= increase pH 1. Hyperventilation 2. Vegetables are metabolized into alkaline substances 3. Persistent vomiting from upper GIT seen in chronic ulcer leads to alkalosis 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 6 Organs/Tissue in pH 1. Blood 2. Lungs 3. Kidneys KIDNEY regulates PH in three ways 1. Reabsorption of Bicarbonate 2. Excretion of non-volatile acid 3. Formation of NH3 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 7  Secretion of ammonia by the tubular epithelial cells and reaction of the ammonia with hydrogen ions in the tubules 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 8 Ammonia NH3 + H3PO4 = (NH4)2 SO4 2NH3 + H3PO4 = (NH4)2HPO4 NH3 + H3PO4 = NH4H2PO4 Urine also contains other inorganic salts such as CaCl2 and KCl 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 9 Principal ions in urine Cations Anions Na+ Cl- K+ SO42- Ca2+ H2PO4- Mg2+ HPO42- NH4+ HCO3-(alkaline urine only) 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 10 Principal ions in urine… The only relatively insoluble combinations of these ions are those between the alkaline earth elements (Ca and Mg) and the Phosphate radicals. In acid urine, the corresponding Phosphates, CaH4(PO4) and MgH4(PO4) are fairly soluble in water, BUT in alkaline urine the alkaline Phosphates are formed. 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 11 Principal ions in urine…. These are: Ca2H2(PO4)2 and Mg2H2(PO4)2, which are only slightly soluble in water. When urine is allowed to stand, the urea is converted to ammonia by bacterial action and the urine becomes alkaline. When this occurs the earthy Phosphates may be precipitated making the urine CLOUDY 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 12  Chemical reaction in the tubules involving hydrogen ions, sodium ions and the phosphate buffer system 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 13 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 14  Micturition Objectives: At the end of this lecture, you should be able to: 1. Describe the innervation of the bladder 2. Describe the process of bladder filling and emptying 3. Describe cystometrogram/micturition reflex 4. Describe the pathophysiology of bladder abnormalities 5. Highlight the various tests of kidney function 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 15 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 16 The general organizational plan of the urinary system  A B Innervation of the bladder. Dashed lines indicate sensory nerves. Parasympathetic innervation is shown at the left, sympathetic at the upper right, and somatic at the lower right of A and lower right of B [Culled from Ganong (A) and Green (B)] 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 17 Micturition The act of passing out urine is called Micturition. Involves the coordination of both the voluntary and the involuntary divisions of the nervous system. Bladder is reciprocally innervated. Urine flows to the bladder through the ureters. It is propelled by peristaltic contractions of the smooth muscle of the ureters. Bladder wall is highly folded and flattens out as the bladder fills with urine. 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 18 Micturition The bladder wall has stretch receptors, Stimulated by increases in pressure within the bladder. Bladder progressively fills with urine until the tension in its walls rises above a threshold value. This leads to a nervous reflex called Micturition reflex that either causes micturition or if it fails in this causes a conscious desire to micturate. 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 19  Bladder cystometrogram 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 20  Bladder cystometrogram A plot of intravesical pressure (cmH2O) against the volume of urine in the bladder is called Bladder Cystometrogram. Flatness of segment 1b is the manifestation of the law of Laplace. Laplace’s law: pressure in a spherical viscus is equal to twice the wall tension divided by the radius. Pressure = 2 Wall Tension/Radius Internal pressure is more or less constant. Tension increases as the bladder fills, but so does the radius. Therefore the pressure increase is slight until the organ is relatively full. 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 21  Control of the bladder MUSCLE I N N E RVAT I O N Type During Filling During Micturition Detrusor (Smooth Parasympathetic Inhibited Stimulated muscle) (causes contraction) Internal Urethral Sympathetic Stimulated Inhibited sphincter (smooth (causes muscle) contraction) External Urethral Somatic motor Stimulated Inhibited sphincter (causes (skeletal muscle) contraction) 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 22  Micturition….. Note: Voluntary control of micturition is poorly developed in infants. Micturition is thus a local spinal reflex, Place and time of urination are determined solely by the volume of urine in the bladder, acting via this reflex. Voluntary control of micturition is learned during childhood by way of skeletal muscles 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 23  Control of micturition Micturition reflex is self-regenerative It is a spinal cord reflex, which can be inhibited or facilitated by centers in the brain. --Strong facilitatory and inhibitory centers in the brain stem, the pons. --Several centers located in the cerebral cortex that are mainly inhibitory but can at times become excitatory. 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 24  Abnormalities of Micturition There are three major types of bladder dysfunction due to neural lesions: (1) the type due to interruption of the afferent nerves from the bladder; (2) the type due to interruption of both afferent (sensory) and efferent (motor) nerves; (3) the type due to interruption of facilitatory and inhibitory pathways descending from the brain. In all three types the bladder contracts, but the contractions are generally not sufficient to empty the viscus completely, and residual urine is left in the bladder. 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 25  Abnormalities of micturition 1. Atonic bladder 3. The uninhibited neurogenic Destruction of the sensory bladder. nerve fibers from the bladder to the cord prevents Partial damage in the spinal transmission of stretch signals cord or brain stem interrupts and therefore also prevents most of the inhibitory signals. micturition reflex contractions. Leads to overflow Gravid uterus presses down dribbling/incontinence on the bladder. Bladder is located anteriorly to the 2. The automatic bladder. uterus. Thus frequent micturition occurs during Damage of spinal cord above pregnancy. Progesterone the sacral region but with sacral segments still intact, causes muscle relaxation; micturition occurs but can no there is thus some degree of longer be controlled by the hydroureter. brain. Facilitatory impulses are lost. 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 26 Tests of Kidney Function 1.Do you pass urine? 2. Examination of urine 3. Chemical tests 4. Clearance 5. IVP-Intravenous pyelography 6. Kidney biopsy 7. Autopsy 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 27  Micturition Objectives: At the end of this lecture, you should be able to: 1. Describe the innervation of the bladder 2. Describe the process of bladder filling and emptying 3. Describe cystometrogram/micturition reflex 4. Describe the pathophysiology of bladder abnormalities 5. Highlight the various tests of kidney function 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 28  Study Questions Short notes: 1. Autoregulation of renal blood flow 2. Bladder Cystometrogram 3. Renal buffering mechanisms Essays: 1. What is pH? Discuss the role of the kidney in acid- base homeostasis 2. What is micturition? Discuss the physiology and pathophysiology of micturition in human 16/December/2024 PIO 402-SERIES 3-YR-UI DEC. 2024 29