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Urinary System
Francis Ian L. Salaver, RMT
Urinary System
Composed of the following organs: Paired Kidneys Ureters Urinary Bladder and; Urethra
Function of the Kidneys
Regulation of water and electrolytes
Acid base balance Acidic blood= release hydrogen into urine Basic blood = release bicarbonate in the urine
Excretion of metabolic waste products through urine formation (including drug metabolites)
Function of the Kidneys
Secretion of renin to increase blood pressure **
Secretion of erythropoietin Increases red cell production in the bone marrow
Activation of Vitamin D Gluconeogenesis
Kidney
Has a concave medial border called HILUM where nerves enter and ureter exits; where blood and lymph vessels enter and exits.
Has a convex lateral side. Each side is covered by capsule
Kidney
At the hilum, the ureter expands as the RENAL PELVIS and divides into 2-3 MAJOR CALYCES.
Smaller branches called MINOR CALYCES arise from the major calyces
Kidney
Outer cortex and Inner Medulla Inner medulla contains 8-12 conical structures called
RENAL PYRAMIDS which are separated by the structure from the cortex called RENAL COLUMNS
Kidney
Each pyramid and renal column along its side comprises one RENAL LOBE
Striations extending from the medulla into the cortex are called MEDULLARY RAYS
Tip of the pyramid that projects into the minor calyces are called RENAL PAPILLA
Kidney
Functional unit: NEPHRONS
1 million in number Major divisions
Glomerulus Proximal Convoluted Tubule Loop of Henle
Descending limb Ascending limb
Distal Convoluted Tubule Connecting Tubule
Nephron
Glomerulus/Renal Corpuscle = Dilated part; tuft of capillary loops and site of filtration
Proximal tubule – long convoluted tube; located on the cortex
Loop of Henle – Medulla
Distal tubule- ascending part from loop of Henle into the cortex
Connecting tubule – links nephrons to the collecting duct
Cortical versus Juxtamedullary Nephrons
Longer loop of Henle???
Most abundant?
Found mostly on the cortex?medulla?
Blood circulation of the Kidney
Renal artery
Segmental artery
Interlobar artery
Arcuate artery
Interlobular artery
Afferent arterioles
Peritubular capillaries surround the proximal and distal tubules
Vasa recta surrounds the loop of Henle
Nephron Function
Filtration Tubular Reabsorption Tubular Secretion
Renal corpuscle and filtration
Contains tuft of capillaries surrounded by a doulbe-walled epithelial capsule called the Bowmans capsule. Has a vascular pole and tubular pole
Internal visceral layer closely envelops the capillaries
Outer parietal layer forms the capsule
Between the two layers is the capsular/urinary space
Renal corpuscle and filtration
Outer layer of capsule is lined by simple squamous. At tubular pole, the lining epithelium changes to simple cuboidal.
Visceral layer forms the podocytes. From the body of the podocytes, several processes extend and curve around the capillary forming the pedicels with filtration slits in between them
Slit diaphragm
Spans two adjacent pedicels and bridges slit pores
Modified tight junctions
Process of filtration
Proximal Convoluted Tubule
Starts from the tubular pole of the renal corpuscle
Lined by simple cuboidal epithelium
Fills up the cortex
Tubular reabsorption and secretion
Almost half of water, glucose, amino acids, vitamins and salts are reabsorbed back into the blood in the PCT
Proximal Convoluted Tubule
Cells are well-stained; with numerous mitochondria, and long microvilli
Loop of Henle
U-shaped structure with thin descending and ascending limb
Lined by simple squamous epithelium
Situated in the hyperosmolar medulla
Countercurrent mechanism
Distal convoluted tubule
Lined by simple cuboidal epithelim
Less absorption and secretion than in PCT
Cells are smaller and no microvilli (more nuclei can be seen)
Macula Densa
Straight part of the DCT (macula densa) comes in contact with the arterioles at the vascular pole of the renal corpuscle (juxtaglomerular cells)
= JUXTAGLOMERULAR apparatus = RENIN
Collecting Ducts
Each nephron has connecting tubules which carry filtrate into collecting ducts
Simple cuboidal epithelium
At the medulla, collecting ducts fuse to form ducts of Bellini which run to the tips of the
At the apex of the pyramid, the papillary duct is formed.
Collecting Ducts
Principal cells = pale staining cells, few organelles, sparse microvilli and unusually distinct cell boundaries
Final site of water reabsorption
Responds to the ADH released from the posterior pituitary gland
Expresses aquaporin channels
Collecting Ducts
Intercalated cells – darkly stained cells interspersed within principal cells
Secrete Hydrogen or Bicarbonate ions
Ureter and Urinary Bladder
Transports urine from renal pelvis to the urinary bladder where urine is temporary stored.
Lined by Transitional epithelium or urothelium
• Single layer of basal cells
• Intermediate region of several or more columnar cells
• Superficial layer of bulbous cells called umbrella cells
Tight Junction in umbrella cells
Urethra
Tube that carries the urine from the urinary bladder to the exterior
In males, has three portion
1. Prostatic urethra
2. Membranous urethra
3. Spongy urethra