Essentials of Human Histology: Urinary System PDF

Faculty Of Medicine Human Histology Urinary System By Prof. Dr. Ezzat EL Drieny 2024 -- 2025 URINARY SYSTEM **Urinary system** is concerned with: - - - - It is formed of: KIDNEY ------ \- The **[main excretory organ in the body.]** \- Each kidney **[is bean shaped with 11cm long...

Faculty Of Medicine Human Histology Urinary System By Prof. Dr. Ezzat EL Drieny 2024 -- 2025 URINARY SYSTEM **Urinary system** is concerned with: - - - - It is formed of: KIDNEY ------ \- The **[main excretory organ in the body.]** \- Each kidney **[is bean shaped with 11cm long, 5cm wide and 2cm thick]**. \- Each kidney is surrounded with **[tough CT capsule]** that can be **[easily stripped off.]** \- Outside the capsule there is a mass of peri-renal fat, which [supports kidney]. \- Each kidney has a [concave medial border ( **hilum**)] that leads to a **[concavity]** in the kidney substance called [**the renal sinus**.] \- **Within** the **[sinus]** lie renal vessels, lymphatics, sympathetic nerves, pelvis of ureter and adipose tissue. \- Renal pelvis is divided into **2-3 major calyces**, **each** of which is subdivided **into 2-3 minor calyces** (Figure 5-1). - Longitudinal section of kidney reveals differentiation of the substance into [outer dark **cortex** and inner pale **medulla**] (Figures 5-1&2). - - - - - **- Renal lobe**: **consists of [one medullary pyramid] and the [corresponding cortical tissues]**. \- **Renal lobule**: formed of **[one medullary]** **ray** and the **associated cortical tissues.** \- **[Connective tissue between renal lobes and lobules is scanty. ]** \- Human kidney is **[multilobular formed of 8-18 lobes.]** **Histological** **structure** ***1-Stroma**:* ***2-Parenchyma**:* \- [Compound tubular gland] \- Formed of **uriniferous tubules** \- **Highly vascular** **Uriniferous** tubules consist of: a- Nephrons produce urine. b- Collecting tubules concentrate urine. ##### ##### **NEPHRON** \- [Structural and functional unite] of the kidney. \- Each kidney is formed of [1-3 million nephrons. ] \- **Two or three nephrons** can be drained by **one collecting tubule** that join others to form [**duct of Bellini**.] \- Each nephron consists of (Figure 5-3): - **Present in the cortex**. - Formed of: - **Has two poles**; **vascular** and **urinary**. - Vascular pole: the site where **afferent arteriole** enters and efferent \- Urinary pole: the site where **the proximal convoluted tubule begins**. ***a) Glomerulus:*** - - **Glomerular capillaries:** lined by **fenestrated endothelium** that has - - the **middle is the lamina densa** formed of **collagen type IV**. - the outer layer (less electron dense), called **lamina rara externa.** - the inner layer ( less electron dense), called **lamina rara interna**. - **[Intra-glomerular mesangial cells]**: - - - - - - - - - ***b) Bowman\'s capsule:*** - The outer parietal layer: lined with **simple squamous epithelium**. - The inner visceral layer: lined with **modified cells called podocytes** which are **adherent to glomerular capillaries**. - The space between parietal and visceral layers is called **capsular space**: **Podocyte:** ***- L/M:*** - **Star shaped with multiple processes.** - [Basement membrane]: **well developed** and can be demonstrated as **PAS** +ve line (**formed of glycoprotein**). - Large cell that consists of **body**, **primary processes** (**major**) and secondary processes (**minor**). - Cell body consists of cytoplasm and central nucleus with extended chromatin. - Cytoplasm contains **mitochondria**, **Golgi** body, **rough endoplasmic** reticulum, **microtubules** and **microfilaments**. - Cell body gives rise to several primary processes that extend parallel to long axis of blood capillaries. - Each primary (major) process gives rise to numerous secondary (minor) processes **called [pedicles]** that end in **foot like structures [implanted on the basement membrane]** of [glomerular blood capillaries.] - **Pedicles (minor processes)** from **one podocyte embrace more than one capillary**, i.e. the pedicles of two podocytes alternate in **position on a single capillary**. - In between the foot process, there are filtration slits that are covered with diaphragm. - Primary and secondary processes contain [only] microtubules & microfilaments. - Podocytes are separated from glomerular capillaries by sub-podocytic space. **- *Function of Podocyte:*** - **Has an important role in the blood renal barrier**. - **Regeneration of basement membrane.** *- **Blood-renal barrier is formed of*** (Figure 5-4): ***- Function of blood-renal barrier:*** **Formation of the glomerular filtrate**. A. B. C. Filtration slits and the overlying diaphragms prevent the passage of **[2- Proximal convoluted tubule]** - Begins in the cortex at the urinary pole of renal corpuscle. - At first highly convoluted then straightens to become continuous with descending thick segment of loop of Henle in the medulla. - Each tubule is 60um in diameter and **14mm long** with small lumen. - Lined with a single layer of pyramidal cells that rest on basement membrane. - ***By L/M*** (Figure 5-6): cross section of proximal convoluted tubule shows: - - - - - - - - ***E/M*** shows that (Figure 5-7): - apical surface has numerous long microvilli. - basal part has basal infoldings (basal striation). - Numerous mitochondria in between basal infoldings (which is the cause of acidophilia). - Lateral **cell membrane interdigitations** (indistinct border by LM). N. **B**. These are the characters of **ion transporting cells**. **Function of proximal convoluted tubules:** 1. 2. 3. 4. 5. \- **The end result is isotonic solution.** **[3- Loop of Henle:]** \- U shaped tube present mainly in medulla. \- Consists of four parts: **1. Thick descending part:** - Starts in the cortex and extends to the medulla. - **Similar to proximal convoluted tubule in structure and function.** **2. Thin descending part:** - **Present in the medulla.** - **Lined with simple squamous epithelium** - - The descending limb **is highly permeable to water** and **im**permeable to **3. Thin ascending part:** - In the medulla. - lined with simple squamous epithelium. **4. Thick ascending part:** - Starts in the medulla and extends to the cortex. - **Similar to the distal convoluted tubule in structure and function.** - The thick ascending limb is permeable to sodium and **im**permeable to **[4- Distal convoluted tubules:]** - It is the continuation of thick ascending loop of Henle in the [corticomedullary zone] and then [joins collecting tubules in the cortex. ] - ***By L/M*** (Figure 5-6) cross section of distal convoluted tubule shows: - Lumen: wide. - It is formed of [ **5-8 simple cubical small cells**]. - Cells are **acidophilic but less than PCT.** - **nuclei** are rounded nearly **apical**. - Apical surface has **no brush border**. - Basal part has **acidophilic striation.** - Cell boundaries are **more distinct than PCT.** - **E/M** shows that: - Apical part has **few short microvilli**. - Basal part c**ontains mitochondria inbetween basal infoldings**. - **Function of distal tubules:** 1. 2. 3. ### Juxtaglomerular apparatus ### Composed of (Figure 5-9): 1- **Juxtaglomerular cells.** **2- Macula densa.** ### **3- Polar cushion or lacis cells or extraglomerular mesangial cells.** ### 1- Juxtaglomerular cells: - Modified **smooth muscle** cells of the tunica media of **a**fferent arteriole. - Large cubical with rounded nuclei - Cytoplasm **contains many secretory granules which are (PAS) +ve**. - By **EM**, it shows rER, Golgi and mitochondria. - **Internal elastic lamina is absent,** so juxtaglomerular cells are in contact in one side with blood and the endothelium and with cells of macula densa on the **other side due to [absence] of [basement membrane of macula densa.]** - **Function of Juxtaglomerular cells:** i. ii. **2- Macula densa:** - The **part of distal convoluted tubule** in the [concavity between afferent and] - Cells become **columnar** and their **nuclei are packed.** - By **E/M**, cells have **numerous microvilli** and **infranulear Golgi apparatus.** - Absence of basement membrane. - **Functions:** **3- [Extra-glomerular mesangial cells], ([Polar cushion or Lacis cells]):** - [Occupy the space] between [afferent and efferent arterioles and macula densa. ] - **With pale staining.** - **Function:** **Supportive, contractile and phagocytic** **COLLECTING TUBULES** - **Not** a part of the nephron. - Has **different embryonic origin**. - Starts at the **medullary rays** in the cortex by [union of two or three distal] [convoluted tubules.] - **The main collecting** tubule enters the medullary pyramid. - Union of several medullary collecting tubules form straight papillary duct (**duct of** **Bellini**) that **opens on the apex of renal papillae** into a **minor calyx**. - Two to four minor calyces join to form a major calyx that **opens in renal pelvis**. - ***By L/M:*** - - - - - - By **E/M :** - Cytoplasm has **few organelles**. - **Interdigitations between the cells** [are not marked.] - Few microvilli and basal infoldings. - **Function of collecting tubules:** **[Renal circulation]** **1-Arteries** - Each kidney receives a renal artery (branch of abdominal aorta) that enters the hilum of the kidney. - Each renal artery is **divided near the hilum into anterior and posterior branches**. - These branches give several **interlobar arteries** which pass in between **medullary pyramids**. - Interlobar arteries give **arcuate arteries** that run at the cortico-medullary junction at the bases of the pyramids. Arcuate arteries **are end arteries** and they never anastomose with each other. - **Interlobular arteries** arise from arcuate artery as straight branches that pass in-between medullary rays and give at their end branches to outer part of cortex and capsule. - **Afferent arteriole** arises from intelobular artery and enters [Malpigian corpuscle] to give the **glomerular capillaries** ([**the first arterial capillary plexus**)] that drain into **efferent arterioles**. - In cortical nephrons the efferent arterioles branch into **peritubular capillaries** (the [second arteriovenous capillary plexus]) **around the proximal and distal convoluted** tubules then drain into **interlobular veins**. - In **juxta medullary nephrons** the efferent arterioles form straight capillary loops (**arteriolae rectae**) that descend to the **medulla to branch around loop of Henle and collecting tubules.** - Each artery has a corresponding vein. - **[Venae rectae] drain the arteriolae rectae in the [medulla] and [pour] in the [interlobular veins] then [arcuate veins], [interlobar] veins and [finally renal vein.]** [ ] **N.B:** - - - - - Glomerular capillaries, filtrate the blood - Peritubular capillaries for nutrition of the renal tubules. **Excretory passages:** - Formed of minor calyces, major calyces, renal pelvis, ureter, urinary bladder and urethra. - Urine is collected from **ducts of Bellini** to minor calyces that join major calyces and drain in renal pelvis. ###### URETER Ureter, **starts from renal pelvis** and ends in urinary bladder. Has thin wall and its **lumen is stellate** or star shaped. **Histological structure** (Figure 5-11): **a-** **Epithelium:** **Transitional** **2- Muscle layer**: formed of smooth muscles arranged as follows: - In the **upper two** thirds of ureter inner longitudinal and outer circular - In the **lower third** there is an a**dditional outer longitudinal** layer. ###### ###### URINARY BLADDER \- The wall is thick and folded in **empty bladder with wide lumen**. \- The folds disappear on distention. **Histological structure** (Figure 5-12): 1. **Mucosa** consists of: a. - - - - - When the bladder contracts - b. **2.** **Muscular layer**: - - **3.** **Adventitia:** - **Dense fibro-elastic connective tissue.** - The upper surface of the bladder is covered by peritoneum. ###### ###### URETHRA **[Female urethra: ]** \- Length : from 4-5 cm. \- Extends from internal orifice at urinary bladder to external orifice above & anterior to vagina. **Histological structure:** **1-Mucosa:** ***a) Epithelium***: - - **b) Lamina propria**: fibroelastic along its length. **2-Muscle layer:** - In inner longitudinal and outer circular smooth muscle. \[like the upper ureter \] - As the urethra pierces the uro-genital diaphragm, skeletal muscle forms an external sphincter around the urethra that gives voluntary control of micturition. - - - - - - - -