Anatomy of the Urinary System Exercise 40 Anatomy of the Urinary System

OBJECTIVES Function of urinary system Location & function of urinary system organs Blood flow through kidney Nephron A&P Glomerular filtration, tubular reabsorption, tubular secretion, micturtion

URINARY SYSTEM Excretion of nitrogenous wastes from the body Maintains electrolyte, acid-base, & fluid homeostasis in the body Filters & processes the blood: Removing toxins, metabolic wastes, and excess ions via urine Retaining needed water, ions, etc. & returning them to blood Fig 26-1

Fig 26-3

KIDNEYS Renal capsule: layer (collagen fibers) covering outer surface Renal cortex: superficial region Renal medulla: deep region, with triangular structures Fig 26-4

KIDNEYS Renal pyramid: each triangle Papilla of the pyramids: tip of each pyramid Renal columns: separate each pyramid Urine’s produced in pyramid/cortex/ column areas Fig 26-4

KIDNEYS Calyces: Minor calyx: cup-shaped drain (collects urine) at each papilla Major calyx: 4-5 minors merge into one major Fig 26-4

KIDNEYS Renal pelvis: 2-3 major calyces merge into this region Fig 26-4

KIDNEYS Fig 26-4

KIDNEYS: Blood Vessels Renal artery: brings oxygenated blood to kidney Segmental arteries: enters renal pelvis area, 5 branches Fig 26-5

KIDNEYS: Blood Vessels Lobar artery Lobar arteries: next branches, near papillae Interlobar arteries: next branches, in renal columns Fig 26-5

KIDNEYS: Blood Vessels Lobar artery Arcuate arteries: next (arching) branches, on top of pyramids Interlobular arteries: next branches, go into the cortex Fig 26-5

KIDNEYS: Blood Vessels Afferent arterioles: next branches, leads into capillary networks of nephrons (glomeruli) Fig 26-5

KIDNEYS: Blood Vessels Glomerulus: capillary bed inside each nephron Efferent arteriole: leads out of the glomerulus, back into the cortex, will flow into capillaries around tubules  Fig 26-5

KIDNEYS: Blood Vessels Peritubular capillaries: capillaries around the renal tubules of the nephrons, will drain into venules and go out of kidney (through veins) to renal vein Fig 26-7

Blood flow to/from nephron: KIDNEYS: Blood Flow Lobar arteries Blood flow to/from nephron: Fig 26-5

KIDNEYS: NEPHRONS Nephron: a functional unit of the kidney, urine is produced here—in the cortex of each renal lobe Each kidney has ~1.25 million!! Fig 26-7

KIDNEYS: NEPHRONS Glomerular (Bowman’s) capsule: round, cup-shaped structure enclosing the glomerulus Fig 26-8

Convuluted portions are in the cortex KIDNEYS: NEPHRONS Proximal convuluted tubule: 1st segment of renal tubule—absorb organic nutrients, ions, water, plasma proteins from tubular fluid, release to interstitial fluid around the tubule *reabsorption* Convuluted portions are in the cortex Fig 26-6

Loops extend into the medulla KIDNEYS: NEPHRONS Descending limb of Loop of Henle: 2nd segment of renal tubule—more reabsorption of water Ascending limb of Loop of Henle: 3rd segment—more reabsorption-Na+, Cl- Loops extend into the medulla Fig 26-6

Convuluted portions are in the cortex KIDNEYS: NEPHRONS Distal convuluted tubule: 4th segment of renal tubule—secretion of ions, acids, drugs, toxins; some reabsorption (water, Na+, Ca++) Convuluted portions are in the cortex Fig 26-6

KIDNEYS: NEPHRONS Distal convuluted tubule actually wraps around the glomerulus Fig 26-7

KIDNEYS: NEPHRONS Collecting tubule: Final segment of renal tubule—some secretion of ions (Na+, K+, H+, HCO3-), & some reabsorption of water Fig 26-6

KIDNEYS: NEPHRONS Juxtaglomerular apparatus: endocrine region of each nephron, important in filtrate formation—secretes the hormone erythropoietin & the enzyme renin Fig. 18-20

KIDNEYS: Juxtaglomerular apparatus Made up of: MACULA DENSA CELLS: Epithelial cells of distal convoluted tubule NEAR glomerulus (are taller than the rest along DCT, & nuclei are clustered together) JUXTAGLOMERULAR CELLS: smooth muscle fibers in the afferent arteriole walls

KIDNEYS: Juxtaglomerular apparatus Fig 26-8

Glomerular Filtration Passive transport (filtration) Blood (filtrate) passes from glomerulus (capillaries) to glomerular capsule Then enters proximal convoluted tubule Fig. 26-9

Tubular Reabsorption Mostly in proximal convoluted tubule Components of filtrate move through tubule cells & return to blood (peritubular capillaries) Passive (osmosis) or active (highly selective/specific) transport, depending on body’s needs and blood’s composition at that time Water, glucose, amino acids, ions, some waste products (urea) Fig. 26-9

Tubular Secretion Reverse of Absorption Mostly in distal conv tubule & collecting ducts Components of blood move from peritubular capillaries or tubular cells INTO the tubule’s filtrate—to be excreted in urine Active transport H+, K+, creatinine, drug metabolites Fig. 26-9

Urine Flow From collecting duct of renal tubule goes to minor calyx, to major calyx, to renal pelvis, to URETER: (1 for each kidney) drains urine from kidney to urinary bladder Fig 26-8

BLADDER Trigone: triangular region near uteral openings and entrance to the urethra Fig 26-19

Internal urethral sphincter: smooth muscle surrounding the opening from bladder to urethra—involuntary control Fig 26-19

External urethral sphincter: skeletal muscle surrounding the opening from urethra to outside—voluntary control (has resting muscle tone, must be voluntarily relaxed) Fig 26-19

Micturition Process of urination There is a micturition reflex Urine moves through ureters to bladder by peristaltic contraction Bladder fills with urine, stimulates stretch receptors in bladder wall Afferent fibersspinal cord, brainbecome aware of fluid pressure in your bladder Efferent fibers stimulate detrusor muscle (walls of bladder), which elevates fluid pressure If internal (involuntary) and external (voluntary) urethral sphincters BOTH relax urination If pressure builds too high, it can force the internal sphincter to open, which leads to reflexive relaxation of external sphincter

Bladder Location MALE FEMALE Fig. 26-19