What are the functions of the urinary system?
- water and electrolyte homeostasis
- excretion of toxic metabolite waste products and excess water
- production of hormones: renin and erythropoietin
- regulation of blood pressure
- activation of vitamin D
What is the functional unit of the kidney and what does it include?
the nephron
- renal corpuscle and renal tubules
- not including collecting ducts and tubules
What does the cortex of the kidney contain?
- renal corpuscles
- proximal convoluted tubules
- nephron loops of Henle
- distal convoluted tubules
- collecting ducts
- peritubular capillary plexuses
What does the medulla of the kidney contain?
- nephron loops of Henle
- collecting ducts, vasa recta
- interstitial cells
Describe the renal corpuscle
- glomerulus surrounded by Bowman’s capsule
- vascular pole urinary pole, urinary space
- only present in cortex of kidney
What are the cells within the renal corpuscle?
- podocytes: visceral layer of glomerular capsule
- squamous cells: parietal layer of glomerular capsule
- endothelial cells: form fenestrated glomerular capillaries
- mesangial cells: between the fenestrated capillaries
Describe the path of potential urine through the kidney
- fenestrated capillaries allow small molecules to pass into urinary space
- filtrate enters proximal convoluted tubule
- enters descending loop of Henle, the ascending loop
- goes to distal convoluted tubule
- some molecules are reabsorbed and returned to blood of perilobular plexus or vasa recta
- others empty into ureter and become urine
Describe the path of blood through the kidney
renal a. > segmental a. > interlobular a. > arcuate a. > interlobular a. > afferent arteriole > glomerulus > efferent arteriole > peritubular capillaries or vasa recta
interlobular vein > arcuate vein > interlobular vein > renal vein
Describe the layers of the blood-urine barrier
- endothelium of glomerular capillary (numerous pores, fenestrations)
- glomerular basement membrane (fused basal lamina of capillaries and podocytes)
- podocytes (inter-digitating trabeculae and pedicles form slit pores between processes)
Describe Mesangial cells
- between glomerular capillaries
- phagocytic cells
- contractile
- receptors for Angiotensin II and ANP
- provide some structural support to capillaries
Describe proximal tubules
- begin at urinary pole of renal corpuscle
- convoluted in cortex
- lined by single layer of cuboidal cells with apical microvili
- cells absorb Na+, water, glucose, and amino acids
- basal striations
Describe nephron loops
- thin descending and ascending segments, and thick ascending segment
- squamous lines the thin segments, cuboidal lines the thick segments
- parallel course of vasa recta for ion and water exchange
Describe distal convoluted tubules
- begin at vascular pole of renal corpuscle
- do not have microvilli
- absorptive cells (Na+, PO4, Ca2+)
- basal striations
- cells are main target of aldosterone
- contain Macula Densa
Describe the Juxtaglomerular apparatus
- macula densa cells: chemoreceptors sense Na+ concentrations in filtrate
- juxtaglomerular cells: specialized smooth muscle cells detect variations in blood pressure and secrete renin
Describe the collecting ducts
- lined by low columnar to cuboidal
- principal (light) cells: reabsorb Na and water under ADH control
- intercalated (dark) cells: act in acid-base balance
- terminal portion are papillary ducts which empty at area cribrosa of renal crest
Describe the Ureter
- lined by transitional epithelium
- mucosa, thick muscularis, adventitia (surrounded by adipose)
- autonomic and somatic innervation
Desribe the Urinary Bladder
- lined by transitional epithelium (urothelium)
- mucosa, muscularis, serosa (mesothelium)
- muscularis has smooth and skeletal muscle sphincters
- bulging epithelial cells: umbrella cells
Describe the Urethra
- lined by transitional epithelium
male: - pelvic and penile segments
- last part lined by stratified squamous
- deferent ducts and accessory sex glands empty into urethra
- may have mucous glands
- tunica muscularis is mostly skeletal, smoth close to bladder
What are the stages of renal development?
- pronephros
- mesonephros
- metanephros
Where does the renal system develop from?
intermediate mesoderm
