Renal System Anatomy & Physiology Notes PDF

RENAL SYSTEM ​ Renal system functions ○​ Excretion: removal of organic waste products from body ○​ Elimination: discharge waste products into environment ○​ Homeostatic regulation: regulate fluid balance, electrolytes level & pH ​ Function of kidneys (Can be asked for SAQ) ○​ Re...

RENAL SYSTEM ​ Renal system functions ○​ Excretion: removal of organic waste products from body ○​ Elimination: discharge waste products into environment ○​ Homeostatic regulation: regulate fluid balance, electrolytes level & pH ​ Function of kidneys (Can be asked for SAQ) ○​ Regulation of blood volume & BP ○​ Regulation of plasma conc. of electrolytes/ ions ○​ Helps in stabilisation of blood pH ○​ Conservation of valuable nutrients eg glucose & amino acids ○​ Elimination of organic waste products such as urea & uric acid ○​ Production of vit. D for strong bones ​ Gross anatomy of kidneys ○​ Location and description ​ Location: lie on either side of vertebral column; located on trans-pyloric plane —> lvl L1 of vertebra ​ Right kidney slightly lower than left kidney ○​ Large size of right lobe of liver ​ Description: bean-shaped, reddish-brown organs in retroperitoneal region ○​ Anatomy of kidney ​ Renal capsule ​ Fibrous capsule covering kidney ​ Hilus/ hilum: entrance (medial) of kidney which transmits ​ Consists of renal pelvis (upper expanded end of ureter) ○​ Renal artery ○​ Renal vein ○​ Lymph vessels ○​ Sympathetic nerve fibres ○​ Sectional anatomy ​ Cortex: outer layer ​ Medulla: inner layer composed of about a dozen renal pyramids separated by renal columns ​ Renal pyramids (8-16): apex projects medically into minor calyx ​ Minor calyces: few of minor calyces subsequently form 2-3 calyces ​ Major calyces: unite to form pelvis continuing downwards as ureter ○​ Blood supply of kidney ​ Arterial supply: ​ Renal artery carries (20% of cardiac output) (posteriorly) ​ Venous drainage: ​ Renal veins drains into IVC (anteriorly) ​ Flow of blood flow in kidneys: ​ Renal artery enters renal sinus —> forms segmental arteries —> interlobar arteries —> arcuate arteries —> interlobular arteries  gives off afferent arterioles (entering glomerulus) of nephrons —> returns to venous system (peritubular capillary) ​ Microscopic structure of kidney: Nephron ○​ Structural organisation of kidney ​ Nephron = functional unit of kidney ​ Renal corpuscle: ​ Glomerulus & bowman’s capsule ​ Blood arrives at glomerulus via afferent arteriole & leaves via efferent arteriole ​ Filtration membrane: ​ Located inside glomerulus ​ Lumen of afferent arteriole (bringing blood into glomerulus) wider than efferent arteriole (brings blood away) —> creates high blood pressure in glomerulus —> forces blood plasma out of glomerular blood capillaries into bowman’s capsule. ​ Consists of 2 layers: 1) endothelial cells of fenestrated capillaries & 2) podocytes ​ Prevents passage of large molecules ​ Allows water, metabolic waste, ions, nutrients & other solutes to enter capsular space ​ Renal tubule: ​ Long tube which many processes take place & urine formed. Urine emptied into collecting duct system ​ 50mm long passageway ​ Consists of: ○​ Proximal convoluted tubule (PCT) ○​ Loop of Henle ​ Descending & ascending limbs ○​ Distal convoluted tubule (DCT) ​ Located near afferent & efferent arterioles of glomerulus ​ PCT, DCT → renal cortex ​ Loop of Henle extends into medulla ○​ Components of a nephron (Can be asked for SAQ) ​ Renal corpuscle → consists of bowman’s capsule and glomerulus ​ Production of filtrate ​ Proximal convoluted tubule ​ Reabsorption of water, ions & all organic nutrients ​ Loop of Henle ​ Further reabsorption of water (descending limb) & both Na+ & Cl- (ascending limbs) ​ Distal convoluted tubule ​ Secretion of ions, acids, drugs, toxins  ​ Variable reabsorption of water, Na+ & Ca2+ (under hormonal control) ​ Collecting duct ​ Variable reabsorption of water & reabsorption/ secretion of Na+, K+, H+ & HCO3- (bicarbonate ions). ​ Papillary duct ​ Delivery of urine to minor calyx ○​ Function of nephron (Can be asked for SAQ) ​ Renal corpuscle → produce filtrate ​ Proximal Convoluted Tubule → reabsorb water, ions & other nutrients ​ Loop of Henle → reabsorb water (descending limb), reabsorb Na+ & Cl- ions (ascending limb) ​ Distal convoluted tubule → active secretion of ions (H+, K+), drugs, toxins. ​ Na+ absorption w water in exchange of H+, K+ → under control of hormone aldosterone ​ Collecting system: consists of collecting duct → papillary duct → minor calyx ​ Makes final adjustments to composition of urine ​ Begins as collecting duct → receives tubular fluid from many nephrons ​ Several collecting ducts merge → papillary duct ​ Delivers urine to minor calyx ​ Reabsorbs water only in presence of ADH. ○​ Function of renal tubules ​ Changes composition of filtrate to eventually form urine through renal absorption & secretion ○​ Juxtaglomerular Apparatus (JGA) ​ Formed by macula densa → cells of DCT, DCT closest to glomerulus ​ Juxtaglomerular cells → smooth muscle fibres in wall of afferent arteriole ​ Secretes renin, erythropoietin ​ Ureters ○​ Histology ​ 30 cm long muscular tubes, upper end expanded forming funnel → renal pelvis ​ Contains transitional epithelium ​ Smooth muscle in 2 layers ○​ Course of ureter ​ Emerges from hilus of kidney ​ Enters pelvis by crossing bifurcation (division of sth into 2 divisions/ parts) @ common iliac artery ​ Ends @ posterior wall of bladder  ○​ Ureteric constrictions ​ Lumen of ureter narrow @ 3 places → junction of renal pelvis & ureter, where ureter crosses pelvic brim & junction of ureter & bladder ​ Clinical importance → renal stones could be impacted @ these places ​ Urinary bladder ○​ Hollow muscular organ → stores urine temporarily ○​ Situated behind pubic bones & its dimensions vary ​ Empty bladder → pyramidal in shape ​ In adults, lies entirely within pelvis ​ Bladder fills → becomes rounded ​ Superior wall rises into hypogastric region ○​ ENDS OF URINARY BLADDER ​ Apex ​ Points anteriorly ​ Connected to umbilicus by medial umbilical ligament ​ Base ​ Lies posteriorly ​ Neck ​ Faces inferiorly ​ Site of entrance to urethra ○​ INTERNAL ANATOMY OF URINARY BLADDER ​ Rugae = mucosal linings thrown into folds ​ Contains transitional epithelium ​ Trigone = triangular area formed by 2 ureteric openings & entrance to urethra ​ Surface smooth ​ Acts as funnel channeling urine into urethra during urination ​ Detrussor muscle = muscular coat of bladder ​ Consists of 3 layers of smooth muscles ​ Function → compresses, empties bladder during micturition ​ Internal urethral sphincter = smooth muscle surrounding urethral entrance @ neck of bladder ​ Function → provides involuntary control over discharge of urine from bladder ○​ BLOOD SUPPLY OF BLADDER ​ Arterial supply → superior & inferior vesicle arteries ​ Venous drainage → vesicle veins drains into internal iliac veins ​ Urethra ○​ Small tube leading from neck of bladder to exterior ○​ Urinary meatus → opening of urethra on external surface ○​ Urethra in male ​ Conveys semen to exterior  ○​ MALE URETHRA ​ Is 20 cm long, extends from neck of bladder to tip of penis ​ Divided into 3 parts → prostatic, membranous & penile urethra ​ Prostatic urethra ​ Runs through prostate hence prostatic ​ Widest & most dilatable portion of entire urethra ​ Membranous urethra ​ Surrounded by band of circular skeletal muscles → external urethral sphincter AKA ​ Shortest & least dilatable part of urethra ​ Penile urethra ​ Surrounded by erectile tissue of penis ○​ FEMALE URETHRA ​ Is 3.8cm long, extends from neck of bladder to vestibule (channel opening into another) of perineum ​ Micturition reflex & urination ​ Urine expelled from bladder by micturition; coordinated by micturition reflex ​ Stretch receptors in bladder wall stimulated when bladder fills 200ml w urine ​ Stimulation of stretch receptors in bladder ​ Sends signals to parasympathetic motor neurons in spinal cord ​ Adequate simulation causes contraction of bladder ​ Brain causes conscious awareness of bladder fullness & micturition occurs ​ Key points to take note in micturition reflex & urination ​ Urination only occurs when both internal & external sphincters relaxed ​ External sphincter relax voluntarily, internal sphincter relaxes too → urination occurs ​ Urge to urinate can be suppressed temporarily → external sphincter under voluntary control ​ Each increase in bladder volume, sensation of fullness & urgency increases as well ​ Bladder vol. >500ml, both sphincters open & urination occurs despite voluntary opposition ​ End of micturition,