Urinary System Li Jinxin, associate professor No.1020603 Department of Histology and Embryology

Objectives 1.Structure and function of each component of a nephron. 2.Ultrastructure of the filtration barrier of the renal glomerulus. 3.Components, structure and function of the juxtaglomerular complex.

Urinary System Components Functions: kidney,ureters,bladder,urethra Functions: remove waste products of metabolism regulate the homeostasis secrete some bioactive factors

1. Kidney 1.1 General structure capsule: DCT parenchyma: cortex: medullary ray cortical labyrinth renal columns medulla: renal pyramid interstitium: CT, BV, N

According to function, renal parenchyma is made up of numerous nephron and collecting duct. A nephron consists of two components: the renal corpuscle and the renal tubule. Each renal tubule and collecting duct is made up of numerous epithelial-line tubules termed uriniferous tubules.

cortical labyrinth cortex medullary ray medulla

renal lobe: one renal pyramid and its bounding cortical tissue renal lobule: renal tissue including one medullary ray and cortical tissue surround it.

1.2 Nephron The nephron is the structural and functional unit of the kidney, composed of two parts:renal corpuscle and renal tubule. There are about one to two million nephrons in each kidney. Depending on the location of the renal corpuscle ,nephrons may be classified as cortical or juxtamedullary nephron.

renal corpuscle: renal glomerulus renal capsule renal tubule: proximal tubule: --convoluted portion --straight portion thin segment distal tubule:

1.2.1 renal corpuscle spherical, 200µm in diameter. two poles: vascular pole and urinary pole two parts: glomerulus renal capsule (Bowman’s capsule)

renal corpuscle Afferent arteriole Efferent arteriole Vascular pole Bowman’s capsule Capillary network Podocyte Parietal layer Urinary pole

1.2.1.1 glomerulus afferent arterioles→capillary network →efferent arterioles capillary network: endothelial cell: pore, 50-100 nm no diaphragm

intraglomerular mesangium mesangial cell: LM:small, irregular, with processes EM: RER, Golgi, lysosome phagocytic vesicles Functions: i.   produce ground substance ii.  phagocytosis

1.2.1.2 renal capsule two layers capsule –formed by beginning part of renal tubule which is enlarged and invaginated. parietal layer simple squamous epi. visceral layer podocytes renel capsular cavity

Primary process Secondary process Slit pore Slit membrane podocyte

1.2.1.3 basal lamina basal lamina: 330nm type IV collagen, proteoglycan

filtration barrier or membrane the structure for filtration is located between the podocytes and the endothelial cells of the glomerulus. including: fenestrated endothelial cell basal lamina slit membrane

1.2.2 renal tubule proximal tubule convoluted portion straight portion 50-60µm in D, 14 mm long proximal tubule convoluted portion straight portion thin segment distal tubule

1.2.2.1 proximal tubule LM structure pyramidal or cuboidal eosinophilic round nuclear brush border longitudinal striation no clear boundary

plasma membrane infolding lateral extension EM structure: Microvilli plasma membrane infolding lateral extension

Function: reabsorption : 85% Na+ ions and water. All of glucose, aminoacid, polypeptide, proteins and vitamin. secrete H+, NH3, hippuric acid and creatinine.

1.2.2.2 thin segment 10-15 µm simple squamous epithelial. facilitate the passage of water and ions

LM structure: cuboidal slight-stained round nuclear no brush border 1.2.2.3 distal tubule LM structure: cuboidal slight-stained round nuclear no brush border

EM structure: less microvilli well-developed longitudinal striation plasma membrane infolding Function: i.   reabsorption of 8% water, Na+ ions ii.  excretion of K+, H+,NH3

Arched collecting tubules Straight collecting tubules Papillary ducts Epi. From simple cuboidal to simple columnar slight –stained have clear boundary Function:reabsorb water

1.4 Juxtaglomerular complex It is located at the vascular pole of the renal corpuscle. It consists of three structures: juxtaglomerular cell, macula densa and extraglomerular mesangial cell.

structure: larger, cuboidal in shaped, contain secretory granules. 1.4.1 juxtaglomerular cell Juxtaglomerular cells are derived from smooth muscle cells in the wall of the afferent arteriole. structure: larger, cuboidal in shaped, contain secretory granules. function: i. secrete renin ii. secrete erythropoietin

1.4.2 macula densa a group of cells derived from epithelium of distal tubule. cell becomes taller, narrow, with round nuclear apical part arranged. cells have processes connecting with other cells. function: chemoreceptors feel the Na+ ions concentration.

1.4.3 extraglomerular mesangial cell (polar cushion cell) similar to intraglomerular mesangial cell transfer the information

1.5 Blood supply to the kidney (self-study) Very large blood flow (1.2L/min) To form cap.two times Glomerular cap. have a high blood pressure Form vasa recta loop near medullary loop More larger blood flow in renal cortex

2. Urinary bladder (self-study) 2.1 Mucosa epithelium：transitional epithelium lamina propria 2.2 Muscularis 2.3 Adventitia

questions 1.state the conception and components of nephron? 2.describe the components and structure of renal corpuscle. 3.state the conception and components of filtration barrier? 4.Name the components of the juxtaglomerular complex ,and describe their structure and function.