The Nephron Flashcards
What is the nephron?
Nephron are the functional units of the kidney, approximately one million per kidney and are responsible for urine formation
What are the two types of nephrons?
Cortical nephrons make up 85% - filtration is occurring higher up, situated towards fibrous capsule, relatively short nephron loops
Juxtamedullary nephrons make up 15%- located close to the medulla, extend deep into medulla via long nephron loops, very important for formation of concentrated urine
What is the function of the nephron?
Selectively filter blood (blood enters glomerulus and is filtered through glomerular capsule to reach nephron)
Can reabsorb water, glucose and salts, return these to blood to be kept. Carry waste away for storage and expulsion
Comprised of a glomerular capsule (surrounds glomerulus), renal tubules (reabsorption) and a collecting duct. Associated with a glomerulus and peritubular capillaries
What are glomerular capillaries?
Glomerular capillaries are specialised for filtration
They are thin walled single layers of fenestrated (leaky) endothelial cells. Fed and drained by arterioles (afferent = fed, efferent = drained). Blood pressure tightly regulated
Fenestrations allow small substances to pass through
What are peritubular capillaries?
Peritubular capillaries are specialised for absorption and wrap around renal tubules (nephrons). Receives filtered blood from glomerulus via efferent arterioles. Some non-filtered solutes that need to be excreted can pass from here into nephron
What is vasa recta?
Vasa recta - extensions that follow nephron loops deep into the medulla, long capillaries only found with juxtamedullary nephrons , arrangement of vasa recta means we can concentrate sodium chloride in medulla and remove water hence inner part of medulla is very concentrated in comparison to the cortex
What encloses the glomerulus?
Glomerulus are enclosed by the glomerular capsule, this is where capillary and nephron meet and is the site of filtration barrier
What is the glomerular capsule?
Glomerular capsule (Bowman’s capsule) is the first part of the nephron. Consists of two layers: outer parietal layer of simple squamous cells (prevents leakage) and inner visceral layer of podocytes (wraps around glomerular capsule)
Between the two layers is the capsular space which receives filtrate
What are podocytes?
Podocytes surround the glomerular capillaries, they’re very branched, specialised epithelium
Branches form intertwining foot processes called pedicels (processes extend away from podocytes cell body which form smaller pedicels that intertwine with each other). Filtration slits form between pedicels (allows some things to get through) Filtered blood goes through these slits and passes into capsular space
What is the filtration barrier?
Filtration barrier/blood-urine barrier allows free passage of water and small molecules however restricts passage of most proteins and restricts RBC’s
Lie between blood and capsular space
What are the three layers of the filtration barrier?
Consists of three layers
1. Fenestrated endothelium of glomerular capillary
2. Basement membrane fuses endothelium and filtration slits together and acts as a barrier for diffusion of substances (contains collagen fibres, peptidoglycan etc.)
3. Filtration slits between the pedicels of podocytes
What is proximal convoluted tubule (PCT)?
In the proximal convoluted tubule bulk reabsorption occurs, of the water and solutes you filter about 2/3 are reabsorbed here
Surrounded by peritubular capillaries
What is the structure of the proximal convoluted tubules?
Cuboidal epithelial cells with a dense microvilli on luminal membrane for reabsorption (increased SA), highly folded basolateral membrane for reabsorption (increased SA), many mitochondria for active transport of solutes (Na+/K+ pump) and a leaky epithelium (at apical surface there are tight junctions which are relatively leaky, allowing water and solutes to pass through)
What is the nephron loop/loop of Henle?
Thick descending limb is the first part of loop, made up of cubodial cells. Thin descending limb is the second part, cells go from cubodial to simple squamous and are permeable to water. Thin ascending limb is the third part, cells are simple squamous. Thick ascending limb is the last part, cells are cubodial
Water can move out of thin descending limb, in thick ascending limb solutes (sodium and potassium) are actively transported from nephron into capillary
What is the distal convoluted tube?
In the DCT fine tuning occurs, lined by cuboidal epithelium but thinner than PCT as lots of solutes have already been reabsorbed hence less microvilli needed, cells are influenced by hormones - reabsorption influenced by aldosterone
