BIOH122 Human Biological Science 2 Session 17 Urinary System 2 Glomerular Filtration Bioscience Department Endeavour College of Natural Health endeavour.edu.au
Session Plan o Overview of Renal Physiology Glomerular filtration Tubular reabsorption Tubular secretion o Glomerular Filtration Filtration Membrane Net Filtration Pressure Glomerular Filtration Rate o Regulation of GFR Renal Autoregulation Neural Regulation Hormonal Regulation Endeavour College of Natural Health endeavour.edu.au 2
Overview of Renal Physiology Endeavour College of Natural Health endeavour.edu.au 3
Overview of Renal Physiology o Nephrons and collecting ducts perform 3 basic processes Glomerular filtration: Filtration of waste-laden blood in the glomerulus. Tubular reabsorption: The process of returning important substances from the filtrate back to the body. Tubular secretion: The movement of waste materials from the body to the filtrate. Endeavour College of Natural Health endeavour.edu.au 4
Overview of Renal Physiology o Rate of excretion of any substance= its rate of filtration + its rate of secretion - its rate of reabsorption Endeavour College of Natural Health endeavour.edu.au 5
Glomerular Filtration Endeavour College of Natural Health endeavour.edu.au 6
Glomerular Filtration o Glomerular filtration: The formation of a protein-free filtrate (ultra filtrate) of plasma across the glomerular membrane. o Glomerular filtrate: Fluid that enters capsular space Daily volume 150-180 liters more than 99% returned to blood plasma via tubular reabsorption In the average adult, the body s entire extracellular fluid volume is filtered about 12 times per day. Endeavour College of Natural Health endeavour.edu.au 7
Glomerular Filtration o Filtration membrane: A leaky barrier formed by the glomerular capillaries and the podocytes, which completely encircle the capillaries o Significance: Permits filtration of water and small solutes Prevents filtration of most plasma proteins, blood cells and platelets Endeavour College of Natural Health endeavour.edu.au 8
Glomerular Filtration o Three filtration barriers: Glomerular endothelial cells fenestrations Basal lamina between endothelium A filtration slit formed by a podocyte o Volume of fluid filtered is large because of large surface area, thin and porous membrane, and high glomerular capillary blood pressure Endeavour College of Natural Health endeavour.edu.au 9
Glomerular Filtration Endeavour College of Natural Health endeavour.edu.au 10
Net Filtration Pressure o Net Filtration Pressure (NFP): The total pressures that drive glomerular filtration o Pressures that determine NFP: Glomerular Blood Hydrostatic Pressure (GBHP): Promotes filtration. Capsular Hydrostatic Pressure (CHP): Opposes filtration. Blood Colloid Osmotic Pressure (BCOP): Opposes filtration. o NFP = GBHP - CHP - BCOP The NFP of only about 10 mm Hg causes a normal amount of blood plasma (minus plasma proteins) to filter from the glomerulus into the capsular space. Endeavour College of Natural Health endeavour.edu.au 11
Net Filtration Pressure Endeavour College of Natural Health endeavour.edu.au 12
Glomerular Filtration Rate o Glomerular Filtration Rate (GFR): The amount of filtrate formed in all the renal corpuscles of both kidneys each minute. average adult male rate is 125 ml / min o Homeostasis of body fluids: requires constant GFR Too high: Useful substances are lost due to the speed of fluid passage through the nephron Too low: Sufficient waste products may not be removed from the body o Directly related to NFP Endeavour College of Natural Health endeavour.edu.au 13
Glomerular Filtration Tortora, and Derrickson, 2012 Endeavour College of Natural Health endeavour.edu.au 14
Regulation of GFR Endeavour College of Natural Health endeavour.edu.au 15
Regulation of GFR o Three principal mechanisms: Renal autoregulation occurs when the kidneys themselves regulate GFR. Neural regulation occurs when the ANS regulates renal blood flow and GFR. Hormonal regulation involves angiotensin II and atrial natriuretic peptide (ANP). Endeavour College of Natural Health endeavour.edu.au 16
Renal Autoregulation of GFR o Renal autoregulation: Mechanisms that maintain a constant GFR despite changes in arterial BP Myogenic mechanism Increases in Systemic BP, stretch the afferent arteriole Smooth muscle contraction reduces the diameter of the arteriole returning the GFR to its previous level in seconds Endeavour College of Natural Health endeavour.edu.au 17
Renal Autoregulation of GFR Tubuloglomerular feedback Elevated systemic BP raises the GFR so that fluid flows too rapidly through the renal tubule and Na+, Cl- and water are not reabsorbed Macula densa detects that difference and releases a vasoconstrictor from the juxtaglomerular apparatus Afferent arterioles constrict and reduce GFR Endeavour College of Natural Health endeavour.edu.au 18
Renal Autoregulation of GFR Endeavour College of Natural Health endeavour.edu.au 19
Neural Regulation of GFR o Sympathetic input: Blood vessels of the kidney are supplied by sympathetic fibers that release norepinephrine cause vasoconstriction of afferent arterioles Tortora, and Derrickson, 2012 Endeavour College of Natural Health endeavour.edu.au 20
Neural Regulation of GFR o At rest, renal blood vessels are maximally dilated because sympathetic activity is minimal renal autoregulation prevails o With moderate sympathetic stimulation, both afferent and efferent arterioles constrict equally decreasing GFR equally o With extreme sympathetic stimulation (exercise or haemorrhage), vasoconstriction of afferent arterioles reduces GFR & reduced urine blood flow lowers urine output and permits blood flow to other tissues Endeavour College of Natural Health endeavour.edu.au 21
Hormonal Regulation of GFR o Atrial natriuretic peptide (ANP) increases GFR stretching of the atria that occurs with an increase in blood volume causes hormonal release relaxes glomerular mesangial cells increasing capillary surface area and increasing GFR o Angiotensin II reduces GFR potent vasoconstrictor that narrows both afferent and efferent arterioles reducing GFR Endeavour College of Natural Health endeavour.edu.au 22
Regulation of GFR: Summary Myogenic Tubuloglomerular Feedback Hormonal Neural Marieb, and Hoehn, 2011
Myogenic Regulation of GFR Marieb, and Hoehn, 2011 Endeavour College of Natural Health endeavour.edu.au 24
Tubuloglomerular Feedback regulation of GFR Endeavour College of Natural Health endeavour.edu.au 25
Hormonal regulation of GFR Renin Angiotensin Aldosterone System (RAAS) Endeavour College of Natural Health endeavour.edu.au 26
Neural Regulation of GFR Sympathetic Nervous System Endeavour College of Natural Health endeavour.edu.au 27
Readings and Resources o Tortora, GJ & Derrickson, B 2014. Principles of Anatomy and Physiology, 14th edn, Wiley. o Harris, P, Nagy, S & Vardaxis, N 2010, Mosby s Dictionary of Medicine, Nursing and Health Professions, 2nd edn, Mosby Elsevier. o Guyton, AC & Hall, JE 2011, Textbook of Medical Physiology, 12th edn, Saunders Elsevier. o Marieb, EN & Hoehn, K 2011, Human Anatomy and Physiology, 9th edn, Benjamin Cummings Pearson. o Moore, KL, Dalley, AF & Agur, AMR 2010, Clinically Orientated Anatomy, 6th edn, Lippincott, Williams & Wilkins. Endeavour College of Natural Health endeavour.edu.au 28
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