NOTES NOTES ANATOMY & PHYSIOLOGY RENAL ANATOMY & PHYSIOLOGY osms.it/renal-anat-phys RENAL SYSTEM ▪ Two kidneys ▫ Filter the blood from harmful substances ▫ Regulate blood pH, volume, pressure, osmolality ▫ Produce hormones ▪ Located between T12, L3 vertebrae; partially protected by ribs 11, 12; behind peritoneal membrane (retroperitoneal) ▪ Right kidney slightly lower due to larger portion of the liver on right side ▪ Filter 150 liters of blood everyday; receive ¼ of cardiac output from renal arteries (from aorta) ▫ Renal arteries divide → segmental arteries → interlobar arteries (between renal columns) → arcuate arteries (cover bases of renal pyramids) → cortical radiate arteries (supply the cortex) → afferent arterioles (supply nephrons) ▪ Renal capsule (inner) ▫ Dense connective tissue ▫ Gives kidney shape Figure 57.1 Kidney placement in relation to ribs and vertebrae. MORPHOLOGY Renal hilum ▪ Indentation in the middle of each kidney ▪ Entry/exit point for ureter, arteries, veins, lymphatics, nerves Surrounding tissue (three layers) ▪ Renal fascia (outer) ▫ Dense connective tissue ▫ Anchors kidney ▪ Adipose capsule (middle) ▫ Fatty tissue ▫ Protects kidney from trauma 510 OSMOSIS.ORG Figure 57.2 Arterial bloodﬂow in the kidney.
Chapter 57 Renal Physiology: Anatomy & Physiology Renal cortex (outer portion) ▪ Outer cortical zone ▪ Inner juxtamedullary zone ▪ Renal columns project into the kidney, separating medulla Renal medulla (inner portion) ▪ 10-18 renal pyramids with pointy ends (renal papilla/nipples) towards center of kidney ▪ Renal lobes: renal pyramids including cortex above them ▪ Renal papilla → minor calyces → major calyces → renal pelvis → ureter Figure 57.3 Transverse cross-section showing retroperitoneal position of kidneys, surrounding tissue layers. Figure 57.4 Cross-section through kidney showing renal medulla, renal cortex, and urine ﬂow through kidney. Nephron ▪ Functional unit of kidney (about one million in each kidney) ▪ Composed of renal corpuscle, renal tubule ▪ Blood ﬁltration starts in renal corpuscle ▫ Includes glomerulus, a tuft of capillaries supplied by afferent arteriole, and Bowman’s capsule ▫ Blood ﬂows into glomerulus → water, solutes (e.g. sodium) pass through capillary endothelium → through basement membrane → through epithelium → into Bowman’s space (becoming ﬁltrate) ▫ Epithelium comprises podocytes wrapped around basement membrane; gaps called ﬁltration slits allow small solutes through but block large proteins, red blood cells ▫ Blood leaving glomerulus enters efferent arteriole → divides into peritubular capillaries → these reunite into cortical radiate veins → arcuate veins → interlobar veins → renal veins → inferior vena cava OSMOSIS.ORG 511
Figure 57.5 Nephron anatomy. ▪ Filtrate from Bowman’s capsule enters renal tubule ▫ Made up of proximal convoluted tubule, descending/ascending limbs of nephron loop (loop of Henle), distal convoluted tubule, collection ducts (which send urine to minor calyces) ▫ Filtrate is further ﬁltered by passing water, solutes between ﬁltrate, blood in peritubular capillaries ▪ Blood pressure, glomerular ﬁltration rate regulated by juxtaglomerular complex ▫ Located between distal convoluted tubule and afferent arteriole ▫ Contains three types of cells: macula densa, extraglomerular mesangial, juxtaglomerular (granular) cells Figure 57.6 Blood ﬂow through nephron and venial bloodﬂow in kidney. 512 OSMOSIS.ORG
Chapter 57 Renal Physiology: Anatomy & Physiology ▫ Macula densa cells in distal convoluted tubule sense ↓ sodium/blood pressure → juxtaglomerular cells secrete renin → ↑ sodium reabsorption, constricting blood vessels → ↑ blood pressure via the renin–angiotensin–aldosterone system (RAAS) ▪ Urine from renal tubules enters minor calyces → major calyces → renal pelvis → ureter Bladder ▪ Bladder receives urine from ureter ▫ Urine enters at ureterovesical junctions ▫ Muscular walls fold into rugae as bladder empties ▪ Bladder wall contains multiple layers ▫ Transitional epithelium: allows bladder to distend while maintaining a barrier ▫ Detrusor muscle: helps with bladder contraction ▫ Fibrous adventitia: holds bladder loosely in place ▪ Located in front of rectum in biologicallymale individuals; in front of vagina, uterus, and rectum in biologically-female individuals ▪ Holds 750mL of urine ▫ Biologically-female individuals: slightly less due to crowding from uterus ▪ Contains smooth triangular region (trigone region) on bladder ﬂoor ▫ Bounded by two ureterovesical junctions and internal urethral oriﬁce ▫ Highly sensitive to expansion → signals brain as bladder ﬁlls Figure 57.7 Cross-section through renal capsule showing juxtaglomerular complex. Figure 57.8 Bladder anatomy. Figure 57.9 Sagittal cross-section showing placement of bladder in relation to other organs. OSMOSIS.ORG 513
Figure 57.10 Coronal cross-section through bladder showing urethra anatomy. Urethra ▪ Drains urine from bladder ▪ Structured differently in biologically male and female people ▫ Starts at internal urethral oriﬁce ▫ Male: passes through prostate (prostatic urethra), deep peritoneum (intermediate urethra), penis (spongy urethra); also used during ejaculation (semen enters via seminal vesicles) ▫ Female: passes through perineal ﬂoor of pelvis, exits between labia minora (above vaginal opening but below clitoris) ▫ Detrusor muscle thickens at internal urethral oriﬁce forming internal sphincter (involuntary control; controlled by autonomic nervous system; keeps urethra closed when bladder isn’t full) ▫ External sphincter is located at level of urogenital diaphragm in ﬂoor of pelvis (voluntary control; can be used to stop urination with kegel exercises) Urination ▪ Involves close coordination between nervous system and bladder muscles ▪ Bladder volume of > 300–400mL, sends signals to micturition center in spinal cord (located at S2 and S3) → micturition reﬂex causes contraction of bladder and relaxation of both sphincters ▫ Pontine storage center in pons of brain can be activated to stop micturition reﬂex ▫ Pontine micturition center can be activated to allow micturition reﬂex Figure 57.11 Signal pathways of micturition reﬂex. 514 OSMOSIS.ORG