Renal system: L33 - The Nephron Flashcards
Briefly describe the difference between the 2 types of nephron.
Cortical nephron - 85%, their renal corpuscle is in the cortex, their loop of Henle doesn’t not descend far into the medulla. Mainly in the cortex.
Juxtamedullary nephron - Renal corpuscle is close to the medulla, their loop of Henle descends deep into the medulla. These nephrons are important as they allow for production of concentrated urine.
What are the components of the nephron and associated parts?
Each nephron is comprised of: A Bowman’s capsule (catches filtrate), renal tubules (carry filtrate away), a collecting duct.
Each nephron is associated with: a glomerulus and peritubular capillaries (wrap around nephron).
What are the glomerular capillaries?
Specialised for filtration, are a thin walled single layer of fenestrated endothelial cells. Fed and drained by arterioles delivering blood at high pressure that is regulated.
What are peritubular capillaries?
Specialised for absorption. Adjacent to renal tubules. Arise from efferent arterioles draining glomeruli. Blood flowing through these has not much fluid but lots of proteins, so useful substances are reabsorbed from tubules into peritubular capillaries. Low pressure and porous.
What are the vasa recta?
Extensions of the peritubular capillaries, long straight vessels that are associated with the loop of Henle in Juxtamedullary nephrons. They form capillary networks surrounding the ascending limbs of the loop of Henle and collecting ducts.
Describe the renal corpuscle.
Glomerulus (ball of vessels) ‘cupped’ by Bowman’s capsule. This is the site of blood filtration. Glomerulus has afferent and efferent arterioles entering/leaving.
Describe the Bowman’s capsule.
2 layers: Outer parietal layer of simple squamous cells (keeps filtrate in). Inner visceral layer of podocytes. Between these 2 layers is the Bowman’s space. Mesangial cells are intraglomerular (between the capillaries themselves), regulate filtration flow (little contractile ability) and produce extracellular matrix.
Explain the podocytes structure.
Podocytes surround the glomerular capillaries, are very branched, very specialised epithelium. Branches form intertwining foot processes called pedicels. Filtration slits form pedicels. Filtered blood (filtrate) goes through these slits and pass into the Bowman’s space.
Explain the filtration barrier.
Lies between blood and Bowman's space. Allows free passage of water and small molecules. Restricts passage of most proteins and no RBCs into nephron. 3 layers: Fenestrated endothelium of glomerular capillary. Fused basement (network of collagen with gaps) Filtration slits between the pedicels of the podocytes.
Explain the change in epithelium throughout the renal tubules and collecting duct.
Proximal convoluted tubule (PCT) is where bulk reabsorption takes place, PCT has cuboidal epithelial cells with dense brush border and many mitochondria in cells (for Na+/K+ pump, coupling for absorption).
The thick descending part of loop of Henle has same cuboidal epithelium, thin descending and ascending loop of Henle has simple squamous epithelium. The thick ascending loop of Henle is similar to the distal convoluted tubule in that it is cuboidal epithelium but slightly thinner to that of PCT. Fewer microvilli in the DCT and fewer mitochondria. Many DCTs empty into one collecting duct which is lined with simple cuboidal epithelium. The collecting duct empties into papilla.
Explain the juxtaglomerular apparatus (JGA).
Specialised zone in every nephron, located where DCT lies against afferent arteriole. Both vessels have specialised cells.
The DCT contributes macula dense cells to the JGA:
-Control glomerular filtration rate (GFR), important this is constant no matter the systemic blood pressure.
-Macula densa cells are chemoreceptors which monitor NaCl concentration as an indicator for blood flow to glomerulus. High NaCl = high blood flow and vice versa.
-If blood flow too low, macula densa work to increase flow to increase GFR to correct level. Vice versa for high.
The afferent arterioles contributes ‘juxtaglomerular cells’ which work to control systemic blood pressure. JG cells are mechanoreceptors that sense stretch in blood vessel wall to determine pressure. If pressure is low, JG cells release ‘renin’ which in turn stimulates angiotensin II, causing vasoconstriction in systematic arterioles and increases blood pressure.
