Histology of the Urinary System (Sheet 21) 2024 PDF

21 Baree abu ghanam Jeyad Alkhzouz Ghada abu el ghanam  Urinary system The urinary system consists of the paired kidneys and ureters, the bladder, and the urethra. This system’s primary role is to ensure optimal properties of the blood, filter it of wastes and excre...

21 Baree abu ghanam Jeyad Alkhzouz Ghada abu el ghanam  Urinary system The urinary system consists of the paired kidneys and ureters, the bladder, and the urethra. This system’s primary role is to ensure optimal properties of the blood, filter it of wastes and excrete them via urine. Urine passes through the ureters (mature urine) and is stored in the urinary bladder until it is excreted from the body through the urethra. Kidneys Anatomy of the kidney: READ ONLY - Reddish, bean-shaped located just above the waist between the peritoneum and the posterior wall of the abdomen. - Retroperitoneal: Is it within the abdominal cavity? No, it's not. It rests on the posterior abdominal wall. - Located between the levels of T12-L3. - Partially protected by ribs 11&12. - The right kidney is lower than the left because it is being pushed by the right lobe of the liver.  External anatomy of the kidney: THE FIRST THREE ARE READ ONLY - 10-12 cm long, 5-7 cm wide, 3 cm thick in adult and 135-150 g. - Each kidney has a concave medial border facing the vertebral column hilum, and a convex lateral surface, both covered by a thin fibrous capsule. - Near the center is the renal hilum. You can see dark staining cortex and light staining medulla that is organized into units Attached to each minor calyx is a renal pyramid. Note: hilum is where nerves enter, the ureter exits, and blood and lymph vessels enter and exit  Are the kidneys covered? Yes. Now, the kidneys are located directly on the posterior abdominal wall. So, they are protected, but we have extra protection for the kidneys, From the innermost all the way to the outer: 1. The renal capsule (deep layer) is a smooth, transparent sheet of dense irregular connective tissue that is continuous with the outer coat of the ureter. 2. The adipose capsule (middle layer) is a mass of fatty tissue surrounding the renal capsule. It protects and cushions the kidney from trauma. 3. The renal fascia (superficial layer) thin layer of dense irregular connective tissue which is an extension of the surrounding fascia that anchors the kidney to the surrounding structures and to the abdominal wall. Internal anatomy of the kidney: → Each kidney has 2 distinct regions: The renal cortex (lighter region): a superficial, light red region. Smooth- textured area extending from the renal capsule to the base of the renal pyramids and into the spaces between them, and it consists of corpuscles and tubules. The renal medulla (darker): deep, darker reddish-brown inner region, consisting mostly of aligned linear tubules and ducts and several cone-shaped renal pyramids (from 8-15). Pay attention that the cortex extends between the pyramids, and it is the center of the lobe. Renal pyramids: all with their bases meeting the cortex (at the corticomedullary junction) and separated from each other by extensions of the cortex called renal columns: portions of the renal cortex that extend between renal pyramids. - The tip of each pyramid (apex) pointed toward hilum, called the renal papilla: projects into a minor calyx that collects urine formed by tubules in one renal lobe. - Renal lobe = renal pyramid + renal cortex + some of the renal column - Parenchyma = renal cortex + renal pyramids Within the hilum the upper end of the ureter expands as the renal pelvis and divides into two or three major calyces. Smaller branches, the minor calyces, arise from each major calyx. The area surrounding the renal pelvis and calyces contains adipose tissue.  If we section a kidney, and we look at the end of the microscope what shall we find? We will find the building blocks, the functional units of the kidneys within the parenchyma that we call nephrons (from 1-4 million in each kidney), each consisting of a corpuscle and a long, simple epithelial renal tubule with three main parts along its length, those are the ones that will eventually produce the urine, this urine will pass through a duct system. Filtrate formed by the nephrons drains into large papillary ducts. They pass through the minor calyces then the major calyces, (Once the filtrate enters the calyces it becomes urine because no further reabsorption can occur, 8-18 as several minor calyces that will empty into around 2-3 major calyces.). And in the major calyces, they pass through the pelvis, from the pelvis, where does the urine go? the ureters. After the ureters, where do they go? To the bladder. ❖Nephrons (the functional unit of the kidneys) A. The part that we just saw, that's the one that will receive the glomerulus (capillary network), or glomerular capillaries. This is called the renal corpuscles (always located in the cortex).  - What is the renal corpuscle? The renal corpuscle is the initial part of a nephron where blood filtration occurs. It consists of two main components: i. Glomerulus: A network of capillaries where blood filtration occurs. ii. The Bowman's capsule (or glomerular capsule): A double-layered epithelial structure that surrounds the glomerulus and collects the filtrate. What are the capillaries made up of? The endothelium and the basal membrane. The glomerulus is further covered by a capsule, this capsule is made up of two layers. Outer parietal and inner visceral, what does the inner visceral cover? A layer immediately covering the endothelium of the capillaries. *The visceral layer consists of modified simple squamous epithelial cells called podocytes (wrap around the single layer of endothelial cells of the glomerular capillaries form inner wall of the capsule). *The parietal layer of the consists of simple squamous epithelium and forms the outer wall of the capsule. The basal membrane and then the visceral and the last layer, which is called the parietal leg, Between the two capsular layers is the capsular (or urinary) space, continuous with the renal tubule, it receives the fluid filtered through the capillary wall and visceral layer.  B. At the end of the renal corpuscle, a small tube called the renal tubule begins. This tubule carries the filtered fluid (filtrate) that has been collected from the glomerulus through the filtration process. The filtrate exits the renal corpuscle into the renal tubule, where it undergoes further processing through reabsorption and secretion. The Renal tubule consists of: 1. Proximal convoluted tubule (PCT): a long-convoluted part, located entirely in the cortex, with a shorter straight part that enters the medulla. The cells are simple cuboidal epithelium with a prominent brush border of microvilli (increase the surface area) then end up with something called loop of henle. 2. Loop of Henle (or nephron loop), Part of it is thin, part of it is thick, in the medulla. The descending limb of the nephron loop and the first part of the ascending limb of the nephron loop (the thin ascending limb) are composed of simple squamous epithelium. The thick ascending limb of the nephron loop is composed of simple cuboidal to low columnar epithelium 4. Distal convoluted tubule (DCT): is the continuation of the ascending limb of the loop of Henle. It consists of a thick straight part ascending from the loop of Henle back into the cortex, and a convoluted part that is located completely in the cortex. C. Then DCT will empty into what we call the collecting duct, converge into several hundred large papillary ducts, which drain into the minor calyces, which then empties into the major calyces, this will then empty into the pelvis, and then it will pass through the ureters into the bladder. (Connecting tubule, a short minor part linking the nephron to collecting ducts) - What is the capsular space? The capsular space is the space between the two layers of the Bowman’s capsule, the parietal layer (outer) and the visceral layer (inner). Fluid filtered from the glomerular capillaries enters this space as glomerular filtrate.  This space is continuous with the renal tubule, where the filtrate flows for further processing. However, not everything in the blood is filtered into this space. The filtration process is governed by several structural components including: - The size of the pores in the capillary endothelium, the basement membrane, and the filtration slits formed by the foot processes (pedicels) of the podocytes in the visceral layer of the Bowman’s capsule. These barriers allow only small molecules, such as water, ions, glucose, and small proteins, to pass into the capsular space while preventing larger structures, such as blood cells and large plasma proteins, from being filtered. But this is not the final urine. This filtrate still needs processing and reabsorption. A lot of things will return to the blood. Whatever is left is the waste, a small amount of H2O, the excess sodium, and the other ions that we don't need. The filtrate is collected in this space, and then it will continue its journey with the tubule. So, it will enter the proximal convoluted tubule. Their lining is cuboidal cells with microvilli. The proximal convoluted tubule (PCT) has cuboidal cells with microvilli that increase surface area for reabsorption. Most reabsorption of water, ions, and nutrients occurs here. The filtrate at this stage is not yet mature urine. The filtrate will pass, and then it will go down where? In the loop of Henle. Now, notice, there is a part of the proximal convoluted tube not convoluted (twisted) rather it’s straight, this is just right before the loop of Henley. Now, notice the loop of Henle. - The thin part of the loop of henley penetrates the medulla, while the thick part of the loop is located in the cortex. The filtrate continues its path through the loop of henley and passes to the distal convoluted tube. A part of the blood pressure is also processed and controlled by special cells called macula densa, which are cells located in the distal convoluted tubule specifically at the point where the DCT comes into close contact with the afferent arteriole and efferent arteriole of the same nephron (check the picture). Finally, the distal convoluted tubule (DCT) delivers partially processed filtrate to the connecting tubules, which lead to the collecting ducts. The collecting ducts extend into the renal medulla, where the filtrate undergoes further concentration and modification as it transitions into mature urine.  ❖Blood circulation: You'll be surprised. Around a quarter (20-25%) of each cardiac output will go to the kidneys, we filter the blood every four cardiac outputs. In adults, renal blood flow, the blood flow through both kidneys, is about 1200 mL per minute. - Blood supply to the kidneys is provided by the renal arteries, which are direct branches from the abdominal aorta. - When renal arteries enter the kidneys, they will soon divide into the hilum region, or the hilum area, into what we call segmental arteries. - The arteries will advance inside the kidney structure and then they will divide into interlobar arteries (between lobes), then the arcuate arteries. - These will give rise to smaller ones, called cortical radiate arteries, they will give us the tiny blood vessel that enters the nephrons. The cortical will give what we call the afferents arterioles. - The afferent arteriole branches into the glomerular capillaries, collectively known as the glomerulus, where the filtration of blood occurs. This filtration process takes place in the renal cortex. The glomerular capillaries are highly permeable and among the leakiest capillaries in the body, facilitating the movement of plasma into the Bowman's capsule to form filtrate.  - After filtration, blood exits the glomerulus via the efferent arteriole. - The efferent arteriole then forms another complex network of capillaries, such as the peritubular capillaries (around the renal tubules) and the vasa recta (associated with the nephron loop in the medulla). These secondary capillary networks are involved in reabsorption (and secretion) processes, allowing substances to be reabsorbed into (or secreted) from the blood. - Finally, the blood is collected into veins that converge into the renal vein, which exits the kidney at the renal hilum and returns venous blood to the inferior vena cava. The structure in the kidney is designed for reabsorption, it has nothing to do with lymphatics. Understanding this information will make memorization much easier. Draw the path on a piece of paper and track it using images as well. It is very important to know where the afferent arterioles come from. You need to know which one comes right before the afferent. The rest, just understand. ‫هذا الي حكته الدكتورة عنهم اذا بتحبوا تشوفوا‬ ‫تفاصيل زياده ارجعوا للكتاب عند قسم ال‬ ‫ فش اشي زياده غير‬blood circulation ‫انه محطوط مكان كل وريد وشريان‬ We use a section taken by a light microscope right here. We see rounded structures. The corpuscle of the nephron. tubule ‫الي عشكل مسارات هو ال‬ This is the cortex corpuscle, what's inside? The glomerulus. The capillaries are covered by the visceral layer of the Bowman's capsule, while the parietal layer contains nuclei along its structure. The basement membrane of the capillaries is located on the outside, supporting the filtration barrier Parietal layer → Capsular space → Visceral layer > Basal lamina of podocytes → Basal lamina of endothelial cells → The lumen of the endothelial cells We also see large nuclei and the smaller ones.  This is the brush border of the proximal nucleus small, rounded cell with darker staining and the lumen is not as clean because it has a lot of microvilli (because lots of reabsorption takes place here). Distal tubule smaller and more cell Arteriole present in the picture So key differences between proximal convoluted tubule and distal convoluted tubule can be summarized in the following text (main differences): Brush Border: - PCT: Dense brush border (microvilli) visible under the microscope, crucial for reabsorption. - DCT: Sparse microvilli, so no prominent brush border. Lumen Size: - PCT: Smaller, irregular lumen due to microvilli (not clear lumen) - DCT: Larger, clearer lumen. Cytoplasmic Staining: - PCT: Eosinophilic (pink under H&E staining) due to mitochondria (darker staining). - DCT: Paler cytoplasm with less granular staining.  ‫‪This table was generated with the help of ChatGPT‬‬ ‫تمت كتابة هذا الشيت صدقة جارية عن روح والدة زميلنا عمرو رائد من دفعة تيجان‬ ‫دعواتكم لها بالرحمة والمغفرة‬ ‫‪Thank you‬‬