T1 Phys - Topic 11 - Urinary - Apr 2020 PDF

Module #11 – The Urinary System structures kidneys (2) ureters (2) the bladder urethra p.230 p.231 Functions 1) 2) 3) 4) 5) 6) Regulation of the volume and composition of body fluids Regulation of electrolyte/ion balance Regulation of acid‐base (pH) balance Hormone production and secretion Waste exc...

Module #11 – The Urinary System structures kidneys (2) ureters (2) the bladder urethra p.230 p.231 Functions 1) 2) 3) 4) 5) 6) Regulation of the volume and composition of body fluids Regulation of electrolyte/ion balance Regulation of acid‐base (pH) balance Hormone production and secretion Waste excretion Regulation of blood glucose levels 1) Regulation of the Volume & Composition of Body Fluids the maintenance of normal body fluid levels is important for: maintaining normal cell volume normal function of the cardiovascular system the urinary system does this by: regulating the excretion of water and NaCl enzyme secretion (renin) which results in water retention retaining water __________________ blood pressure eliminating water __________________ blood pressure p.232 2) Regulation of Electrolyte/Ion Balance the urinary system regulates several important ions including (but not limited to): hydrogen (H+) sodium (Na+) potassium (K+) calcium (Ca2+) chloride (Cl‐) bicarbonate (HCO3‐) phosphate (PO43‐) if intake exceeds excretion, the amount of that electrolyte in the body increases if excretion exceeds intake, the amount of that electrolyte in the body decreases 3) Regulation of Acid‐Base (pH) Balance many functions of the body are very sensitive to pH therefore it must be maintained within strict homeostatic limits the kidneys play a key role in regulating the acid‐base balance the kidneys regulate it by excreting hydrogen ions (H+) and reabsorbing bicarbonate 4) Hormone production and secretion the kidneys secrete: erythropoietin (EPO) – stimulates red blood cell production calcitriol – the active form of vitamin D renin – an enzyme that activates the renin‐angiotensin‐aldosterone system (helps in the regulation of blood pressure and Na+ and K+ balance) 5) Waste excretion the kidneys excrete metabolic by‐products that are not needed by the body the formation and elimination of urine (which contains…) ammonia and urea (waste products from protein metabolism) bilirubin (waste product from the breakdown of hemoglobin) uric acid (waste product from the breakdown of nucleic acids) creatinine (waste product from skeletal muscle) medications, toxins 6) Regulation of blood glucose levels with hypoglycemia, kidneys can produce and release glucose into the blood stream p.233 The Kidneys retroperitoneal located between T12 and L3, partially protected by ribs 11 and 12 renal cortex: superficial layer renal medulla: inner portion nephron: the functional unit of the kidney 3 parts proximal convoluted tubule (PCT) loop of Henle (nephron loop) distal convoluted tubule (DCT) renal artery and vein the kidneys get 20‐25% of resting CO p.234 p.235 Urine Production and Flow (Blood Flow) blood enters the kidney (renal artery) and branches into smaller and smaller vessels afferent arteriole leads into the glomerulus glomerulus: a tangled ball‐like network of capillaries (pl. glomeruli) at the level of the glomerulus, water and solutes in blood plasma are filtered through the capillary walls, into the glomerular (Bowman’s) capsule space and into the renal tubule blood flows out of the glomerulus into the efferent arteriole the efferent arteriole leads to another capillary network – the peritubular capillaries the peritubular capillaries merge to ultimately form the renal vein which leaves the kidney p.236 p.237 Urine Production and Flow (the Glomerulus) at the level of the glomerulus, water and solutes in blood plasma are filtered through the capillary walls, into the glomerular (Bowman’s) capsule space and into the renal tubule the fluid that enters the capsular space is called the glomerular filtrate as filtered fluid moves along the renal tubule and collecting duct: most of the water and useful solutes are reabsorbed and returned to the blood in the peritubular capillaries wastes are drawn from the peritubular capillaries and are secreted into the fluid for removal from the body urine: fluid produced by the kidneys that contains wastes and excess materials p.238 p.239 p.240 p.241 Glomerular Filtration Rate (GFR) the amount of filtrate formed per minute GFR is an indicator of kidney function GFR is fairly constant under normal conditions increased GFR = increased urine production decreased GFR = decreased urine production Regulation of GFR in general, the body will regulate GFR by: adjusting blood flow into and out of the glomerulus altering the capillary surface area available for filtration specifically, there are 3 ways the body controls GFR: 1) renal auto‐regulation 2) neural regulation 3) hormonal regulation p.242 1) Renal Auto‐Regulation of GFR a) myogenic mechanism an increase in BP increases renal blood flow which increases GFR it also stretches of the walls of the afferent arterioles this stretching triggers the contraction of smooth muscle in the walls of the afferent arterioles vasoconstriction reduces blood flow and reduces GFR to previous level the opposite happens with a decrease in BP b) tubuloglomerular feedback an increase in BP increases renal blood flow which increases GFR this also increases the Na+, Cl‐, and water in tubular fluid the increased Na+, Cl‐, and water in tubular fluid triggers vasoconstriction of the afferent arteriole vasoconstriction reduces blood flow and decreases GFR to the previous level the opposite happens with a decrease in BP p.243 2) Neural Regulation of GFR kidney BVs get SyNS innervation SyNS activation causes vasoconstriction (both afferent and efferent) with increasing SyNS activation, vasoconstriction of the afferent arteriole is greater which decreases GFR this reduces GFR and helps redirect blood flow to other tissues 3) Hormonal Regulation of GFR angiotensin II strong vasoconstrictor (both afferent and efferent) reduces GFR atrial natriuretic peptide (ANP) released by the heart in response to atrial stretching (i.e. increased blood volume) increases GFR p.244 Hormonal Regulation of Re‐Absorption & Secretion re‐absorption and secretion occur once the filtrate (the fluid that comes out of the glomerulus) is formed normally, most water and solutes return to the body and many wastes (H+, ammonium, medications) are secreted into the tubule for elimination 5 hormones affect the re‐absorption and secretion of water and ions by the renal tubules: 1) 2) 3) 4) 5) angiotensin II aldosterone ANP ADH PTH 1) the renin‐angiotensin‐aldosterone system 2) 3) 4) 5) decreased BP  kidneys secrete renin (an enzyme) renin converts angiotensinogen (made by the liver) into angiotensin I angiotensin I is converted to angiotensin II at the lungs by angiotensin‐ converting enzyme (ACE) angiotensin II  GFR (afferent arteriole vasoconstriction)  re‐absorption of Na+ and Cl‐ ions and water stimulates the release of aldosterone aldosterone:  re‐absorption of Na+, Cl‐ , & water ANP: increases excretion of sodium and water ADH: increases water reabsorption parathyroid hormone: increases re‐absorption of calcium p.245 p.246 Ureters, Bladder and Urethra collecting ducts (which receive urine from several nephrons), collect and form larger and larger pathways to the level of the ureter (1 from each kidney) peristaltic contractions in the ureter move urine to the bladder the bladder is a hollow muscular organ that sits posterior to the pubic symphysis, anterior to the rectum, and in females sits inferior to the uterus internal urethral sphincter: controls the flow of urine from the bladder into the urethra urethra: the tube from the floor of the bladder to the exterior external urethral sphincter: part of the pelvic floor mm., controls the flow of urine out of the urethra p.247 Elimination/The Micturition Reflex micturition/urination/voiding: the discharge of urine pressure within the bladder stimulates stretch receptors which initiate a reflex via the PaNS – the bladder contracts, the internal sphincter relaxes the external sphincter also relaxes bladder filling gives a sensation of fullness before the micturition reflex occurs after early childhood, we have conscious control Incontinence urinary incontinence: the lack of voluntary control over micturition causes increased abdominal pressure (stress incontinence) nerve damage aging disease/injury some medications smoking Aging and the Urinary System kidneys decrease in size renal blood flow and GFR decrease glomeruli become less (or non‐) functional kidney diseases become more common Diuretics substances (including medications) that decrease the reabsorption of water medications, food/drink Dialysis artificial cleansing of the blood p.248 p.249