Collin College. BIOL Anatomy & Physiology WEEK 12. Urinary System INTRODUCTION. Main functions of the kidneys are

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1 Collin College BIOL Anatomy & Physiology WEEK 12 Urinary System 1 INTRODUCTION Main functions of the kidneys are regulate blood volume, water content regulate blood composition e..g. Na, Cl, K, ph remove waste products and toxins Kidneys are the guardians of the internal environment They receive 25 % of cardiac output. Thus blood is filtered every 4 minutes! 190 liters of fluid (plasma) is filtered daily to produce 1 liter of urine 2 1

2 Urinary System Organization The kidneys Produce urine The urinary tract eliminates the urine Ureters (paired tubes direct urine to bladder) The urinary bladder (muscular storage sac) Urethra (single tube elimates urine to outside) 3 Urinary System Organization Urination or micturition process of eliminating urine Contraction of muscular urinary bladder forces urine through urethra, and out of body Kidneys Ureters Organs of the Urinary System Produce urine Transport urine toward the urinary bladder Urinary bladder Temporarily stores urine prior to urination Urethra Conducts urine to exterior; in males, it also transports semen Anterior view 4 2

3 Kidneys Urinary System Organization Located on either side of vertebral column Left kidney is slightly superior to right kidney Superior surface is capped by adrenal gland Position is maintained by Overlying peritoneum Contact with adjacent visceral organs Supporting connective tissues 5 Adrenal gland Diaphragm 11th and 12th ribs Left kidney T 12 vertebra L 3 vertebra Ureter Inferior vena cava Iliac crest Right kidney Renal artery and vein Aorta Urinary bladder Urethra 2018 Pearson Education, Inc. a A posterior view of the trunk 6 3

4 Kidney Organization Kidneys are protected and stabilized by 3 layers 1. Fibrous capsule A layer of collagen fibers Covers outer surface of entire organ 2. Perinephric fat A thick layer of adipose tissue Surrounds fibrous capsule 3. Renal fascia A dense, fibrous outer layer Anchors kidney to surrounding structures 7 External Parietal Renal Renal Urinary System Organization oblique peritoneum Stomach vein artery Aorta Ureter Pancreas Spleen Left kidney Vertebra Connective Tissue Layers Fibrous capsule Perinephric fat Renal fascia 2018 Pearson Education, Inc. b Quadratus lumborum Psoas major Inferior vena cava A superior view of a transverse section at the level indicated in part a 8 4

5 Kidney Organization Typical adult kidney About 10 cm long, 5.5 cm wide, and 3 cm thick Weighs about 150 g Hilum Prominent medial indentation Point of entry for renal artery and renal nerves Point of exit for renal vein and ureter Hilum 9 Kidney Anatomy Pyramid Outer capsule Under capsule is an outer cortex area inner medulla Medulla contains pyramids. They contain the functional units of the kidneys = nephrons 10 5

6 Kidney Anatomy The medulla consists of 6-18 triangular shaped renal pyramid Renal columns are bands of cortical tissue that separates adjacent pyramids Tip of each pyramid (renal papilla) projects into renal sinus Ducts within each renal papilla Discharge urine into a minor calyx, a cup-shaped drain Major calyx Formed by four or five minor calyces Renal pelvis Large, funnel-shaped chamber Formed by two or three major calyces Fills most of renal sinus and connects to ureter, which drains kidney 11 Kidney Anatomy 12 6

7 A Renal artery feeds each kidney. It then shows repeated branches Segmental artery Interlobar artery Arcuate artery Renal Blood Supply Since the nephrons are the filters of the blood, blood needs to be carried to the nephrons. Interlobular artery (cortical radiate artery) Afferent arterioles supply blood to individual nephrons Blood leaves nephron via peritubular capillaries that feed into renal venules, and then follow a similar but opposing pattern ending with renal vein 13 Renal Blood Supply 14 7

8 Renal vein Renal artery Segmental artery Interlobar vein Interlobar artery Arcuate vein Arcuate artery Cortical radiate vein Cortical radiate artery Venule Afferent arteriole Peritubular capillaries NEPHRON Efferent arteriole Glomerulus c 2018 Pearson Education, Inc. A flowchart of renal circulation 15 Renal Blood Supply Bowman s capsule of each nephron is the filtering part and located in the cortex area. Blood enters the Bowman s capsule via the afferent arteriole. 16 8

9 Kidney Nerve Supply Renal nerves Innervate kidneys and ureters Enter each kidney at hilum Follow branches of renal arteries to individual nephrons Sympathetic innervation Adjusts rate of urine formation By changing blood flow at nephron Influences urine composition By stimulating release of renin 17 Nephron Anatomy The microscopic unit of filtration are the nephrons Nephrons Microscopic functional units of kidneys Each consists of renal corpuscle and renal tubule Each renal tubule empties into collecting system Renal corpuscle Spherical structure consisting of Glomerular (Bowman s) capsule Glomerulus (capillary network) 18 9

10 Nephron Anatomy Bowman s Capsule always located in cortex Proximal Convoluted Tubule always located in cortex Loop of Henle (dips into medulla) Descending limb Ascending limb Distal Convoluted Tubule located in cortex again Collecting Tubules and duct dips back into medulla 19 Nephron Anatomy COLLECTING SYSTEM Collecting Duct Intercalated cell Principal cell Papillary Duct Columnar cells Collecting ducts Receive fluid from many nephrons Each collecting duct Begins in cortex Descends into medulla Carries fluid to papillary duct, which drains into a minor calyx Minor calyx 20 10

11 Nephron Anatomy/Function Production of filtrate Reabsorption of organic nutrients Reabsorption of water and ions Secretion of waste products into tubular fluid This function of the nephron is correlated with the lining of the tubules; they are lined with simple epithelials. 21 a NEPHRON Proximal Convoluted Tubule Cuboidal cells with abundant microvilli Distal Convoluted Tubule Cuboidal cells with few microvilli Mitochondria Renal Corpuscle Renal tubule Squamous cells Efferent arteriole Afferent arteriole Glomerulus Glomerular capsule Capsular space Descending limb of loop begins Ascending limb of loop ends Nephron Loop Descending thin limb (DTL) Squamous cells Thick ascending limb (TAL) Low cuboidal cells 2018 Pearson Education, Inc. Ascending thin limb (ATL) Squamous cells 22 11

12 Nephron Anatomy/Function 23 Nephron Anatomy/Function There are 2 kinds of nephrons cortical nephrons : the loop of Henle barely reaches into the medulla juxta medullary nephrons : the loop of Henle dips deep into the medulla 15 % of nephrons are juxta medullary nephrons ; these are very important in water reabsorption 24 12

13 Nephron Blood Supply Afferent arteriole enters Bowman s capsule Glomerulus capillary network within Bowman s capsule Efferent arteriole leaves Bowman s capsule Peritubular capillaries surround the Proximal and Distal tubules 25 Nephron Blood Supply 26 13

14 Nephron Blood Supply Vasa Recta peritubular capillaries that surround and follow the loop of Henle in juxta medullary nephrons Thus we have 2 capillary beds associated with the nephrons First one helps to produce the filtrate inside the lumen of the nephron (glomerulus) Second one functions in re-absorption and secretion aspect of urine filtration (peritubular capillaries) 27 Diagram of nephron with associated electron microscope pictures. Note that all along the nephron, the cell layer of the tubules is only one cell layer thick ( indicates importance of diffusion, secretion, absorption)

15 Vacular Resistance in Kidneys Controls of Resistance are located at entrance and exit of glomerulus; this allows for a steady pressure within the glomerulus ( which is important for homeostasis of filtering process)(also see later discussion) 29 RENAL PHYSIOLOGY Main function of the kidneys is to regulate blood volume and composition Three basic nephron mechanisms are involved : Filtration Depends on Blood pressure Water and solutes are forced through glomerular capillaries and into Bowmans capsule Reabsorption The removal of water and solutes from the renal tubule filtrate Secretion Transport of solutes from the peritubular fluid into the tubular fluid 30 15

16 Nephron Anatomy/Function 31 RENAL PHYSIOLOGY Filtration occurs in the Bowmans Capsule at the Glomerulus While Filtration is very non-specific, the re-absorption and secretion processes are provided by membrane transport proteins such as Ion channels and Facilitated transporters Active transporters Cotransporters & Countertransport Diffusion and osmosis thus become very important in kidney function

17 RENAL PHYSIOLOGY Most regions of the nephron perform a combination of functions General functions can be identified Filtration in the renal corpuscle Nutrient re-absorption along the PCT Active secretion at PCT and DCT Loops of Henle regulate final volume and solute concentration 33 RENAL PHYSIOLOGY Goal of urine production is to maintain homeostasis By regulating volume and composition of blood Involves excretion of metabolic wastes Three main metabolic wastes are Urea (most abundant organic waste) Creatinine (from breakdown of creatine phosphate) Uric acid (from recycling of nitrogenous bases) Organic wastes Dissolved in bloodstream Eliminated only when dissolved in urine Removal is accompanied by water loss 34 17

18 RENAL PHYSIOLOGY Glomerular Filtration Filtration process that occurs in Bowman s Capsule, driven by hydrostatic pressure of blood system ( aka BP) Blood is filtered and the filtrate ends up in the tubule system of the nephron What creates the filter system? Combination of the membrane systems of the capillaries and Bowman s capsule cells 35 Microscopic Anatomy of Bowman s Capsule Special cells, called Podocytes, cover the capillaries 36 18

19 Microscopic Anatomy of Bowman s Capsule Scanning electron microscope picture of the fingerlike filtration slits of the podocytes! Compare this with the diagram on left side and previous slide! This system provides a filtering mechanism roughly similar to a coffee filter, but much more refined! It houses 3 filtering mechanisms! 37 Microscopic Anatomy of Bowman s Capsule Filtration System in Bowman s capsule Capillary endothelial cells have many pores let everything through except blood cells and large proteins Basement membrane or Basal Lamina Is negatively charged and repels most smaller proteins Foot process of the Podocytes Form additional filtration slits that only let small molecules through 38 19

20 Filtration System in Bowman s capsule What are the forces involved the filter system? Similar forces that are involved in capillary fluid exchange in the tissues! Hydrostatic pressure from the blood ( = blood pressure = pushing things out ) Hydrostatic pressure in capsule from the filtrate ( pushes things back into capillaries) Osmotic (oncotic) pressure from the blood ( pulls water back into capillaries) 39 Filtration System in Bowman s capsule Filtration occurs as fluids move across the glomerulus The positive filtration pressure is the glomerular hydrostatic pressure due to blood pressure in the glomerular capillaries (P H ) Capsular hydrostatic pressure opposes (P fluid ) Blood colloid osmotic pressure opposes (p) Net Filtration Pressure (NFP) = (P H ) - (P fluid ) - (p) 40 20

21 Filtration System in Bowman s capsule Net filtration pressure is thus a modest 10 mm Hg Net filtration pressure is determined by these 3 forces 41 Bowman s capsule Net Filtration pressure (NFP) Pressure force that drives fluid out of the blood (out of the glomerulus) and into Bowman s capsule Due to the characteristics of the filter, the filtrate that passes into the tubule system of the nephron equals blood minus formed elements and minus proteins Since proteins do not leave the blood stream, but water does, the efferent arteriole will have a higher concentration of proteins and blood cells ( will be more viscous) 42 21

22 Bowman s capsule Glomerular Filtration Rate (GFR) Total amount of filtrate formed per minute by the kidneys. Depends on : NFP what happens when NFP = 0? what happens to NFP when BP increases? what happens when afferent blood osmolarity increases? ( use next slide ) Total filtration area ( what happens with a unilateral nephrectomy? ) Filtration membrane permeability ( what happens when some Glomeruli get clogged up? ) 43 Bowman s capsule Blood proteins changes affect this force Blood pressure changes affect this force 44 22

23 Regulation of GFR Regulation of the GFR is an important homeostatic process. If GFR is too high, we would produce a high rate of filtrate and re-absorption of essential elements would not be efficient. If GFR is too low, we would not be able to secrete important waste products fast enough Regulation of the GFR occurs via 3 mechanisms Renal Auto-regulation Neural regulation Renin-Angiotensin Feedback 45 Regulation of GFR 1. Renal Auto-regulation a. Juxta Glomerular Apparatus (JGA) feedback Distal Convoluted tubule makes contact with afferent and efferent arteriole This region is called the JGA Contains 2 groups of cells that are important in kidney function Juxta glomerular cells : are part of the afferent arteriole wall and have mechano-receptors and endocrine cells Macula Densa cells : are part of the DCT and have chemoreceptors/endocrine cells

24 Regulation of GFR 47 Regulation of GFR 1. Renal Auto-regulation a. Juxta Glomerular Apparatus (JGA) feedback When GFR is too high, the flow through the nephron will be increased Re-absorption of salts will be less and the filtartae arriving at the macula densa cells will be saltier That induced the macula densa cells to secrete a vasoconstricting agent onto the afferent arteriole This result is increase resistance, less flow into the glomerulus and hence, reduced GFR

25 49 Regulation of GFR 1. Renal Auto-regulation b. Myogenic Effect When blood vessels and smooth muscles are stretched they tend to contract Increased blood pressure will cause vasoconstriction in the afferent arteriole and counteract a possible increase in NFP

26 Regulation of GFR Renal Autoregulation allows for tight control of GFR over a wide range of MAP s. 51 Regulation of GFR 2. Neural Regulation Mostly a sympathetic effect Produces powerful vasoconstriction of afferent arteriole Decreases GFR and slows production of filtrate Important for example during blood-loss ; prevents body from excreting more urine ( fluid) Changes the regional pattern of blood flow Alters GFR Also Stimulates release of renin by JGA 52 26

27 Regulation of GFR 53 Regulation of GFR 3. Renin-Angiotensin Feedback The following will result in a Renin release by the Juxtaglomerular cells in JGA apparatus Drop in Blood pressure (reduced stretch in afferent arteriole) Reduced release of the vasoconstrictor from the Macula Densa cells ( thus, reduced Na + flow in the DCT) Direct stimulation of JG cells by sympathetic stimuli All these stimuli release Renin, resulting in Angiotensin II production Efferent arterioles have more Ang II receptors than Afferent arterioles ; thus this will increase the Pressure in the glomerulus (why? ) Ang. II also results in release of Aldosterone and ADH ( what do they do? ) 54 27

28 Regulation of GFR 55 Regulation of GFR 56 28