Urinary System

  • Functions of urinary system

    • Storage and excretion of urine

    • Filtration of blood

    • release of hormones (erythropoietin)

    • regulation of erythrocyte production

    • Regulation of ions and acid/base levels

  • Clinical progression of kidney disease

    • Kidneys are unable to filter imbalances, resulting in accumulation of uremic toxins

    • Kidney is no longer able to excrete erythropoietin, and therefore bones aren’t able to produce RBCs

    • Anemia leads to heart failure

  • Embryology

    • Urogenital system derives from embryonic tissue called intermediate mesoderm, which runs down the posterior abdominal wall

    • Urogenital ridge is formed from condensed intermediate mesoderm

    • 3 sets of embryonic organs

      • Pronephros/pronephric duct

        • Used to start development of the kidneys; exist only to degenerate. Degeneration triggers formation of mesonephros

        • Pronephric duct remains

      • Mesonephros

        • Develop as sacs that functions in urine production

        • Pronephric duct becomes mesonephric duct

        • Remain until around week 10

      • Metanephros

        • Begin developing at week 5, are fully functional by week 10

        • Develop from ureteric buds and metanephric blastema

    • Ureteric buds will develop into structures that COLLECT urine

      • Ureter

      • Renal calyces

      • Renal pelvis

      • Collecting ducts

    • Metanephric blastema will develop into structures that PRODUCE urine

      • Glomerular capsule

      • Proximal convoluted tubule

      • Nephron looop

      • Distal convoluted tubule

    • Urorectal septum divides the cloaca into urogenital sinus and anorectal canal at week 7

      • Urogenital sinus will develop into urinary bladder and urethra

    • Weeks 6-9, kidneys migrate to more superior position in natal abdominal cavity

      • During ascent, kidneys receive bloodflow from temporary vessels

      • Week 9, kidneys are in final location and receive permanent renal arteries from abdominal aorta

    • Indifferent duct system

      • Developed by all embryos, genetics will determine which duct system is retained

      • Retention of mesonephric duct results in penis and associated structures

      • Retention of paramesonephric duct results in uterus and associated structures

  • Organs of urinary system

    • Paired kidneys

      • Filter waste from bloodstream

      • convert filtrate into urine

      • Location/description of kidney

        • Superior border is just below T12

        • Inferior border is around L3

        • Retroperitoneal (covered, not wrapped with peritoneum)

        • Suprarenal/adrenal gland sits on top each kidney

        • Kidney is reddish brown

        • R is slightly inferior to L

      • Surrounded by two layers of fat to absorb trauma

    • Ureters, urinary bladder, urethra

      • referred to as urinary tract, transport urine out of body

  • Structure of kidney

    • Renal capsule

      • Dense, irregular connective tissue

      • maintains shape of kidney and protects from damage/infection

      • Concave medial border referred to as HILUM

    • Divided into cortex (outer) and medulla (inner) and renal pelvis

      • Medullary pyramids act to increase surface area of medulla

      • Renal papilla connect medullary pyramids to renal pelvis

  • Urine is produced:

    • in nephrons

    • Flows to renal papilla → minor calyx → major calyx → renal pelvis → ureter → urinary bladder

  • Primary function of kidney is blood filtration

  • Renal veins bring deoxygenated blood back to IVC

  • Renal veins lie ANTERIOR to renal arteries

    • Asymmetrical due to location of IVC on R side of body

    • L Gonadal vein drains into L renal vein

    • L Renal vein is longer than R renal vein

  • Nutcracker syndrome

    • Entrapment of renal vein between sup mesenteric artery and abdominal aorta, blocking gonad drainage

  • 5 segmental arteries branch from renal artery

  • Order of blood supply to kidney WILL BE TESTED

    • Renal artery

    • Segmental arteries

    • Interlobar arteries (between pyramids)

    • Arcuate arteries (across tops of pyramids)

    • Cortical arteries (penetrate cortex and give afferent atrioles)

  • Blood supply to Glomerulus

    • Cortical arteries branch off arcuate arteries and penetrate cortex

    • AFFERENT arterioles are the smallest branches

      • Created capillary balls called glomeruli

    • Efferent arterioles exit glomerulus

  • Nephron: functional unit of kidney

    • Corpuscle

    • Proximal convoluted tubule

    • Nephron loop of henle

    • Distal convoluted tubule

    • Collecting ducts

  • Nephron MODIFIES blood filtrate to form urine from 3 processes

    • Filtration

      • Movement of substances from blood to capsular space

    • Reabsorption

      • Movement of substances from tubular fluid back to blood

    • Secretion

      • Movement of substances from blood to tubular fluid

  • Structure of renal corpuscle

    • Renal corpuscle is made of

      • Glomerulus

      • glomerular capsule

    • 2 poles

      • vascular

      • tubular

    • 2 layers

      • Visceral

        • adhered to glomerulus and made of podocytes

      • parietal

        • simple squamous epithelium

    • capsular space lies between 2 layers and collects filtrate

      • filtration occurs because of increased pressure in glomerulus

    • Afferent arteriole is larger than efferent

    • glomerulus is tangle of capillaries that extend from afferent arteriole

    • glomerular capsule surrounds glomerulus

  • Filtration membrane is made of

    • Fenestrated endothelium (glomerulus)

    • Visceral layer of glomerular capsule

      • made of podocytes with filtration slits

    • allows only smallest solutes to exit glomerulus

      • pressed out due to high pressure in glomerulus

      • not selective filtration

  • Proximal convoluted tubule

    • Simple cuboidal epithelium w/ microvilli

    • increase reabsorption capacity

    • Actively reabsorbs and secretes substances to modify filtrate

    • Lumen looks “fuzzy” bcuz of microvilli

  • Nephron loop

    • has 2 limbs

    • Loop down into medulla and back into cortex

    • primary function is reabsorption of water back to blood

  • 2 types of nephrons

    • Cortical nephrons

      • active during normal conditions

    • juxtamedullary nephrons

      • active during periods of high activity, produce concentrated urine

  • Distal convoluted tubule

    • Simple cuboidal epithelium with SPARSE microvilli

    • primary function is secretion and absorption

    • Lumen is clear and crisp

  • Blood flow around nephron

    • Peritubular capillaries

      • surround proximal and distal convoluted tubules

    • vasa recta

      • surrounds nephron loop

  • Collecting tubules

    • act under influence of anti diuretic hormone and aldosterone

      • Limits loss of water and Na ions from blood

    • Increase absorption of water back to blood

  • Urine exits kidney through ureter

    • fibromuscular tubes that carry urine from pelvic cavity to empty into urinary bladder

    • insert into posterolateral wall of bladder

    • 3 layers of ureter

      • mucosa (transitional epithelium)

      • muscularis (smooth muscle)

        • produce peristaltic contractions to produce unidirectional movement (like esophagus/intestines)

      • adventitia (collagen/elastic fibers)

    • Ureter enters bladder at acute angle to allow ureter wall to form 1 way valve

  • Bladder is posterior and “tipped over” pubic symphysis

    • allows bladder to stand up and expand

    • bladder is retroperitenial

    • 4 tunics of urinary bladder

      • mucosa

        • transitional epithelium

        • allows epithelium to stretch

        • mucosal folds called rugae allow for increased storage

      • submucosa

        • dense irregular CT

      • Muscularis

        • detrusor muscle

      • adventitia

        • outer loose ct, collagen and elastic fibers

    • Trigone is triangular area formed by entrance of ureters and formation of internal urethral sphincter

  • Urethra is made of smooth muscle from bladder

    • Internal urethral sphincter

      • made of smooth muscle

      • under autonomic control

    • external urethral sphincter

      • at distal end of urethra

      • made of skeletal muscle

      • voluntary control

  • Nervous control of bladder

    • Parasympathetic = pee

      • stimulate micturition

    • sympathetic = storage

      • inhibit micturition

    • Stretch receptors in bladder trigger micturition reflex center

      • impulses travel to detrusor muscle and internal sphincter

        • smooth muscle in internal sphincter relaxes

        • smooth muscle in detrusor contracts

      • person must consciously relax external sphincter