Lec 34 - Urinary passages

• The epithelium in the thin segments is squamous and is cuboidal in the thick segments of the ascending and descending limbs
• The proximal convoluted tubule is the initial and major site of reabsorption. Resorption of Na+, Cl-, water, glucose, amino acids, and proteins. It is made up of simple cuboidal epithelium with microvilli. The epithelial cells will have abundant mitochondria that are arranged longitudinally with basal infoldings. Contains few cilia for fluid transport.
• The proximal convoluted tubule can be differentiated by an irregular star-shaped lumen, very eosinophilic cytoplasm, and basal nuclei
• The basal infoldings of the proximal convoluted tubule epithelium contains mitochondria for active transport
• What portion of the nephron is this - proximal convoluted tubule

  
• The proximal straight tubule/thick descending reabsorbs glucose and Na+. It reabsorbs what glucose hasn't already been absorbed with glucose/Na+ co-transporters
• Proximal straight tubules/thick descending tubules will be found in longitudinal section because they are straight and make up medullary rays. They can be identified by a simple cuboidal epithelium with brush border
• What portion of the nephron is this - proximal straight tubule

  
• The thin descending limb is highly permeable to water and thin ascending limb is highly permeable to Na+ and Cl-. They can be identified by squamous epithelium that have nuclei that bulge into the lumen
• What portion of the nephron is this - thin ascending or descending limb

  
• The distal straight tubule/thick ascending reabsorbs ions including Cl-, Na+, K+, Ca2+, Mg2+ through secondary active transport. It can be identified by simple cuboidal epithelium with a pale staining cytoplasm
• What portion of the nephron is this - distal straight tubule/thick ascending

  
• Secretion and reabsorption occurs in the distal convoluted tubule. Secretion of ammonium, K+, H+ and reabsorption of Na+, Cl-, HCO3-, Ca2+ through co-transporters. It can be identified by simple cuboidal epithelium with microvilli and a apical nucleus. It has microvilli but because it doesn't have a huge reabsorption function its microvilli is not as developed.
• This portion of the nephron is - distal convoluted tubule

  
• The collecting duct is responsible for reabsorption of water, Na+, urea. It is identifiable by simple cuboidal to columnar epithelium, pale staining, and distinct cell boundaries. As the collecting duct moves closer to the renal papilla, the epithelium will become more columnar
• This portion of the nephron is the - collecting duct

  
• The renal cortex contains the distal and proximal convoluted tubules and medullary rays that contain straight tubules
• The medulla contains proximal straight tubules, distal straight tubules, thin limbs, and collecting ducts
• The juxtaglomerular apparatus is at the junction where the distal straight tubule turns into distal convoluted tubule and right at the vascular pole of the renal corpuscle
• Macula densa cells are in the distal tubule and have been modified so that they can sample to sodium concentration within the filtrate. They are taller and narrower cells than the tubule cells. The nuclei look crowded.
• Extraglomerular mesangial cells are found outside of the glomerulus and found between afferent and efferent arterioles in close proximity to macula densa
• Juxtaglomerular cells are modified smooth muscle cells that produce and secrete secretory vesicles that contain renin. They are found in the wall of afferent arteriole
• Label

  A) macula densa cells

  B) macula densa cells

  C) extraglomerular mesangial cells

  D) juxtaglomerular cells

  
• Increased sympathetic innervation to the kidneys is caused by decreased pressure and decreased Na+ delivery to the distal tubule. When BP is low, pressure at the afferent arteriole will be low and will decrease filtration at the glomerulus therefore less Na+ and less Na+ will be sensed by the macula densa cells in the distal tubule. The macula densa cells will then tell the juxtaglomerular cells to produce renin
• Renin binds to angiotensinogen (produced by the liver) which becomes angiotensin I this is then converted to angiotensin II by angiotensin converting enzyme (produced in the lungs)
• The release of angiotensin II causes the release of ADH from the posterior pituitary and aldosterone from the adrenal cortex. Angiotensin II is also a vasoconstrictor so will increase vascular resistance, increasing arterial pressure. ADH will increase blood volume and cardiac output all together increasing blood pressure
• The goal of the renin-angiotensin-aldosterone system (RAAS) is to increase blood pressure
• The papillary ducts can be distinguished by tall columnar epithelium with very strong cell boundaries

  
• Transitional epithelium can also be called uroepithelium because it is specific to the urinary tract. Its function is to accommodate for stretch. Uroepithelium is stratified epithelium with squamous or dome-shaped cells. When the urinary passage is empty, the cells are dome-shaped. When the urinary passage is full, the cells are squamous
• The ureter layers are

  • transitional epithelium
  • lamina propria
  • inner longitudinal smooth muscle layer
  • outer circular smooth muscle layer
• If the lumen is folded in the ureter, then the ureter is relaxed
• This is an image of the ureter

  A) transitional epithelium

  B) lamina propria

  C) inner longitudinal smooth muscle layer

  D) outer circular smooth muscle layer

  
• Depending on where you are looking in the urinary bladder, you will either have a serosa or adventitia
• In the urinary bladder there is not layers of smooth muscles, there are randomly oriented because the bladder contracts in all directions