Histology Urinary system

Transcription

1 Histology Urinary system

2 By the end of the topic the learner should be able to: Describe the histological structure of the kidney. Illustrate the ultrastructure of the blood renal barrier. Illustrate the histological structure of the urinary passages.

3 Parts Paired kidneys Paired ureters Bladder Urethra Urinary system (Wheater's Functional Histology, A Text and Color Atlas, 6 th Ed.)

4 Kidney - Functions 1. Controlling the water content of the body 2. Regulating the salt content of the blood 3. Regulating the extracellular fluid volume 4. Eliminating waste products, toxins and drugs; most importantly Urea 5. Controlling the acid-base balance of blood 6. Has a hormonal and metabolic function Secretion of Renin by juxtaglomerular cells to increase blood volume and pressure Secretion of Erythropoietin that stimulates the production of erythrocytes in the bone marrow and thus regulates the oxygen-carrying capacity of the blood Conversion of Vitamin D, which regulates calcium balance, to an active form in the kidney

5 Stroma Capsule Trabeculae Reticular stroma Parenchyma Uriniferous tubules Kidney structure

6 Divided into cortex and medulla Kidney General structure The cortex forms an outer shell and also forms columns that lie between the individual units of the medulla The medulla is composed of medullary pyramids the base of each cone is continuous with the inner limit of the cortex and the apex of the pyramid protruds into the calyceal system that is known as the papilla

7 Kidney lobes and lobules Lobe :medullary pyramid and the associated cortical tissue at its base and sides Lobule: a central medullary ray and the surrounding cortical tissue. The medullary ray contains the collecting ducts for a group of nephrons that drain into it Therefore, the lobule consists of a collecting duct and all the nephrons that it drains constituting the renal secretory unit

8 Uriniferous tubule Functional unit of the kidney Highly convoluted Consists of nephron and collecting tubule 1.3 million nephrons in each kidney Several nephrons are drained by a single collecting tubule Uriniferous tubules are densely packed

9 Nephron Consists of: Renal corpuscle PCT DCT Loop of Henle

10 Two types: A. Cortical nephrons Most numerous Present in superficial part of cortex Short loop of Henle B. Juxastamedullary nephrons. Near the junction of cortex & medulla Long loop of Henle Nephron

11 Renal Corpuscle Oval to round structure Found in renal cortex. Composed of glomerulus & Bowman's capsule

12 Renal Corpuscle Bowman s capsule Originally was a hollow epithelial sphere (blind end of nephron) Has two poles: Urinary pole which is continuous with the PCT. Vascular pole at which it became invaginated by vascular tuft of capillaries converting it into double walled cup enclosing a capsular space.

13 Renal Corpuscle Bowman s capsule It has two layers: Outer (parietal) layer Called capsular epithelium Lined by simple squamous epithelium Inner (visceral) layer Called glomerular epithelium Lined by modified epithelium (podocytes)

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15 Renal Corpuscle podocytes Modified flat cells Have numerous long primary cytoplasmic (major) processes resemble feet Each primary process bears many secondary processes, known as pedicels which: Completely envelop the glomerular capillaries Terminate around BM of glomerular capillaries The spaces between the minor processes are called filtration slits which are closed by diaphragm

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18 Renal Corpuscle podocytes Function Play an important role in filtration Concerned with the renewal of glomerular capillaries BM

19 Renal Corpuscle Glomerulus Tuft of about 50 tortuous capillary loops Arising from afferent arteriole, enter the corpuscle then recollect into efferent arteriole which leave the corpuscle Capillaries lined by fenestrated endothelial cells Resting on thick continuous BM

20 When a filter gets dirty it must be cleaned- mesangial cells are the janitors Mesangial cells - located within stalk of capillary tuft (intraglomerular mesangium) as well as the vascular pole (extraglomerular mesangium) Participate in maintenance of basement membrane through phagocytosis, also structural support

21 Renal Corpuscle Function Forms the glomerular filtrate by dialysis of the plasma (plasma minus its proteins) through the filtration barrier

22 Blood renal barrier (filtration barrier) It is the barrier that separates the blood (in the glomerular capillaries) from the capsular space of Bowman s capsule It consists of: 1-The pores in the capillary endothelium; prevent the passage of RBCs but anything less than RBCs diameter can pass

23 Blood renal barrier 2- The continuous BM of glomerular capillaries basal lamina fused with basal lamina of the podocytes By EM the BM has 3 layers: a) Lamina rara externa (adjacent to epithelium). b) Lamina rara interna (adjacent to endothelium). Both of them are electron lucent area c) The intermediate zone appears more electron dense.

24 Blood renal barrier 3- The filtration slits and their closing diaphragm Function of the filteration barrier: Polyanionic charge barrier Filters blood plasma Allows water, ions & small molecules to enter the capsular space Prevents large plasma protein molecules from entering the capsular space.

25 Renal tubules PCT Loop of Henle DCT

26 PCT The longest segment (15 mm long) Highly convoluted Diameter (60um) & narrow lumen Lined with pyramidal cells with indistinct cell boundaries Number of cells in TS is 3-4 cells Cytoplasm: darkly acidophilic & granular Short (5mm long) Less convoluted DCT Diameter (30-50 um) & wide lumen Cubical cells with distinct or indistinct cell boundaries 4-8 cells Lightly acidophilic & less granular Basal striations: cells have acidophilic basal striations due to extensive plasma membrane infoldings having mitochondria Free acidophilic brush border (long microvilli) rich in alkaline phosphatase. Absorption of water(80%), amino acids, K & Na Reabsorption of all glucose Excretion of certain metabolites, dyes & drugs Few microvilli Reabsorption of water (10%) Secretion of ammonia Site of action of ADH Control acid base balance.

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28 Loop of Henle Present between the proximal and distal convoluted tubules A U-shaped structure with; A thick descending limb A thin descending limb A thin ascending limb A thick ascending limb (TAL) The thin parts are lined by simple squamous epithelia The nuclei of the cells lining the thin limbs bulge into the lumen of the tubule; hence, in paraffin section, these limbs resemble capillaries in cross section

29 Connecting tubules The connecting tubule joins the distal convoluted tubule to the collecting duct Connecting tubules of the subcapsular nephrons join directly to the cortical collecting duct Connecting tubules from the midcortical and juxtamedullary nephrons merge with other connecting tubules first to form an arched connecting tubule before uniting with the cortical collecting duct.

30 Collecting ducts Collecting duct are not part of the nephron Cortical collecting ducts They begin in the cortex Connecting tubules or arched connecting tubules of many nephrons merge to form cortical collecting ducts They proceed within the medullary rays toward the medulla Medullary collecting ducts Formed as the cortical collecting ducts reach the medulla Several medullary collecting ducts merge and form papillary duct at the apex of the pyramid and open at area cribrosa into a minor calyx

31 Collecting ducts The collecting ducts are distinguished from proximal and distal tubules by virtue of the cell boundaries that can be seen in the light microscope They are composed of simple epithelium Cortical collecting ducts have flattened cells, somewhat squamous to cuboidal in shape Medullary collecting ducts have cuboidal cells, with a transition to columnar cells as the ducts increase in size

32 Collecting ducts Two distinct types of cells are present in the collecting ducts: I. Principal (light) cells Cuboidal, then increase in tall distally to become columnar Central round nuclei Light cytoplasm Basal infoldings Short microvilli reabsorb Na +, secrete K +, respond to aldosterone and ADH. ADH causes increased permeability so urine becomes more concentrated.

33 II. Dark (intercalated) cells Rich in organells Well developed microvilli No basal infoldings Reabsorb K +, secrete H + Collecting ducts

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35 JUXTA-GLOMERULAR COMPLES It is involved in the regulation of systemic blood pressure It is located between glomerular afferent arteriole and distal convoluted tubule of corresponding nephron Composition 1- Macula densa: It is an area of closely packed, specialised cells lining the DCT close to the vascular pole They are columnar, crowded with prominent deeply stained nuclei It is sensitive to the concentration of sodium ions in the fluid within the DCT

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37 2- Juxta-glomerular (JG) cells (Renin producing cells): They are modified smooth muscle cells of the afferent arteriole, small numbers are present in the efferent arteriole. It have features of myoepithelial cells with rounded nuclei and granular cytoplasm Contain mature and immature membrane bound granules of the enzyme renin

38 3- Polar cushion (Polkissen cells- Extraglomerular mesangial cells or Lacis cells) Formed of a mass of small cells with pale nuclei. It is found in the triangular region between the afferent and efferent arterioles at sides and macula densa at the base. The apex of the triangle is formed by the glomerular mesangial cells at the vascular pole Three structures of the JG complex are in direct contact with each other

39 Function : Secretion of erythropoietin Secretion of renin

40 Ureter Small muscular tubule. It carries urine from the renal pelvis to the urinary bladder. Mucosa, muscularis, and adventitia. Mucosa consists of: Transitional epithelium loose connective tissue (lamina propria). Muscularis: Inner longitudinal and outer circular smooth muscle layers. Difficult to distinguish. As it approaches the urinary bladder, the ureter may also contain a third layer of smooth muscle. Adventitia : connective tissues, nerve fibers, and blood vessels.

41 Urinary bladder Three layers (mucosa, muscularis, and adventitia/serosa), The mucosa is composed of: transitional epithelium and lamina propria. The muscularis consists of three smooth muscle layers collectively called the detrusor muscle: These are the inner longitudinal, middle circular, and outer longitudinal smooth muscle layers. These three smooth muscle layers are arranged in two different orientations to help the urinary bladder contract to empty urine efficiently. The outer layer of the bladder is mainly covered by adventitia (connective tissue); its superior (free) surface is covered by serosa, which is a layer of connective tissue with a lining of mesothelium.

42 Urinary bladder

43 Male urethra The prostatic urethra: Extends through the prostate gland and is lined by urothelium (transitional epithelium ) The membranous urethra: Passes through an external sphincter of striated muscle of the deep perineal pouch Lined by stratified columnar and pseudostratified columnar epithelium The spongy urethra: Enclosed within the erectile tissue of the penis Lined by stratified columnar and pseudostratified columnar epithelium, with stratified squamous epithelium distally

44 Female urethra The urethra is short, measuring 3 to 5 cm in length from the bladder to the vestibule of the vagina. The lining epithelium is initially transitional epithelium, a continuation of the bladder epithelium, but changes to stratified squamous epithelium before its termination The lamina propria is a highly vascularized layer of connective tissue The urethra penetrates the urogenital diaphragm whose striated muscle forms the external urethral sphincter

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