Lecture 13 - Anatomy (Development of the Urinary System) Week 10 PDF

KIDNEY ONTOGENY & PHYLOGENY Thomas Wilson Adapted from material by Nick Milne Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure,...

KIDNEY ONTOGENY & PHYLOGENY Thomas Wilson Adapted from material by Nick Milne Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s & Abrahams Clinical Atlas of Anatomy, Human Anatomy Colour Atlas & Textbook [email protected] Goal: How salt homeostasis organs develop in response to environmental challenges, and why that is important Outline: Outcomes: 3 stages of renal phylogeny & Recognise the development of the human kidney development as a ontogeny reflection of vertebrate development. Evolutionary pressures Describe the structure and function of each type of kidney Resulting progression (pro/meso/metanephric). Describe the mechanism and path of the ascent of the kidney, Embryonic kidney function relating that to its final position and anatomical relations. Ascent of the metanephric kidney Describe the process of cloacal septation and how it relates to the bladder’s trigone. Anatomical relations Renal ontogeny Mesoderm differentiates by the end of week 4 urogenital ridge ~ Axial, Paraxial, Intermediate (IMM), Lateral plate Urogenital paired glands develop in the abdomen & pelvis 1. Kidneys 2.Gonads 3. Accessory reproductive glands Note: Adult adrenal gland from lateral plate µ similar to somites IMM becomes segmented column: cranial  caudal Nephrotomes ← primitive component to a kidney Column develops into 3 different kidneys at different stages 1. Pronephros: Develops in cervical region 2. Mesonephros: Thoracic / lumbar £¥q 3. Metanephros: Pelvic → what will become the adult kidney ↳ derives from the sacral spine & ascends cranial/ y ≤ Appearance of each type of kidney recapitulates vertebrate evolution… Emphasises how ‘copycat systems’ reduce developmental errors  Pronephros phylogeny: The ‘first’ kidney Found in primitive freshwater fish 2. Adaptation: Create a glomerulus E.g. Lampreys Bundles of blood vessels bulge into coelomic space created in the urogenital ridge 1. Challenge/stress Allows selective osmotic control of plasma Body [salt] > [salt] in the water Water is ‘less concentrated’ in body 3. Result: Gets rid of water Molecules move down their [gradient] Excess water filtered into coelomic cavity Which links to pronephric duct  drains into cloaca Water movement & direction =  Inside body: High S / Low W Paraxialmesodermic Intermediate mesoderm condensations ↓ Somite Sss , -7 External Internal s g environment environment ÷ [Salt] coelomic cavity Fresh water: Low S / High W glomerulus  Human pronephros ontogeny Derived from cervical nephrotomes Does not function in humans Day ~24 (present for 2 days ) Why is it there? µ helps to reduce developmental error Degenerates by day ~26 Shows a mechanism of divergence (repurposing of parts) Signalling required ontogenetically (basis of all copycat systems) ↳ need the signalling for the next kidney to develop because it goes from cranial to caudal end  Mesonephros phylogeny: The ‘middle’ kidney Some fish returned to the sea: 3. Preadaptation to life on land 1. Reverse osmotic challenge Air has ‘less water & salt’ than body fluid does… Body [salt] < [salt] in the sea = Tendency to dry out Salt pressured to enter and water pressured to leave the body → isritdraining.in/-othecoeIomiccavityitself-oisbetteral- reclaiming through more selective processes Tubular network connects directly with mesonephric duct (AKA Wolfian duct) 2. How do you adapt a suitable filter? t& YA  Drains into cloaca (bladder) Need to:…..Filtration &……Reabsorption Mesonephros: smaller glomerulus & larger tubular network ↳ excretion is more Found in bony fish & some amphibians Compared to pronephros geared towards reabsorption Water movement & direction =  Ocean: High S / Low W 1- glomerulus tubular network External Internal mesonephricdvc.tl environment environment [Salt] Inside body: Low S / High W Human mesonephros ontogeny Appears towards the end of week 4 (~D28) Derived from thoracic & lumbar nephrotomes Cranial to caudal succession ↳ starts to regress in the same order Produces some ‘urine’ that drains through mesonephric duct into the cloaca Between weeks 6-12 Patency of cloaca and mesonephric duct Resemble primitive adult nephrons ↳ not quite as complex & transient Thoracic segments regress in week 5 Lumbar segments survive until weeks 10-12 Metanephros: Ontogeny meets phylogeny The higher vertebrate definitive kidney Metanephric ducts (AKA ureteric buds ) ↳ derived from sacral region Grow from dorsal side of pelvic mesonephric duct Appear in week 5 What regresses in week 5? ↳ thoracic segments of the meson ephros Metanephric duct induces sacral IMM to form metanephric blastema bilateral & join together ← is can later on Glomeruli & nephron tubules ↳ includes Metanephric ducts repeatedly bifurcate within blastema Collecting ducts  calyces  renal pelvis  ureters lumbar µ segments of mesonephros start off being due to Metanephric urine produced from week 12 dying taken over by tanephric components me Not for waste purposes: Placenta present for that Increases and circulates amniotic fluid volume  Mum’s kidneys do the heavy lifting  Fetal kidneys filter blood to make amniotic ‘urine’ ☆ Amniotic fluid swallowed & also fills lungs is ↳ helps maintain potency of all the endodermat tubes (gut needs fluid to create a tube) AF AF AF AF Healthy amount of amniotic fluid implies functioning kidneys Ascent of the metanephric kidneys Begins in week 6 → regression of me some phros (cranial caudal) Coexists with mesonephros → & the meta nephric kidney ascends cranial ly Note gonad and kidney relation  ↳ starts more ventrally than kidney & is descending when the kidney is signalled to ascend How do the renal structures/connections change? Urinary component: Metanephric ducts extend (ureters) with the kidney cranially Arterial component: ‘Acquires’ new paired branches as kidneys ascend to upper abdomen ↳ a quires vessel new & drops lower vessel as it ascends ↑ - Venous component: Climbs as well ' Subcardinal venous system appears ‘ladder-like’ What happens if this fails? ☆ always start as bilateral structures Pelvic kidney: When a kidney fails to ascend Horseshoe kidney: ← kidneys join together ↑ ! L & R metanephric kidneys become attached in the pelvis & cannot ascend I above the inferior mesenteric artery Example of this in the lab and Len Freedman Room Multiple renal arteries, major calyces, ureters renal pelvis has ↳ can be extended ↳ normal to have uptos forming ↳ can bifurcate & then rejoin again normal 2 minorcalyces divided unequally Y' shaped ' ureter - relates # amount of forming major calyx a fluid passing through to forma renal pelvis during development arteries accessory 2 ureters inferior { mesenteric A. ← extended normal ureter configuration major calyces Is Position and some relations of the adult kidney → across the very front of the muscles Sits on the margins of the Psoas muscles & quadratus lumborum Surrounded in perirenal fat, renal fascia, and pararenal fat ↳ surrounds kidney itself within renal fascia ↳ outside renal fascia PM Upper poles sit on diaphragm and ribs 11 & 12 → """ " E. left kidney QL Move about when you breathe *µ*,☒↑☒☒ Hilum: at L1/2 Vein most anterior (explains it crossing anterior to aorta) Artery behind vein - middle 12 normal Ureter behind artery - posterior 13 L4 More relations when we look in the lab L5 Contralateral differences: One sits higher (why?) → because of the liver on the right One vein is longer (why?) → to cross infront of aorta Remember, these are patterns not rules Left renal vein is longer… Why did it develop that way?? VENTRAL ooo9 supraCardinals [email protected] cardinals [email protected] components from supra cardinal , ☆ kidney is sitting just under adrenal gland there when the , GGG cross section into left renal vein & passes infront of aorta because subcardina/ system is already anastomosis that cross between the lefts, right /from the is more ventral than the others at that time original cardinal veins in the trunk that have obliterated/, ⑨ ⑧⑧ subcardinals Subcardinal system in snot-green they so are repurposed & hijacked from the left side & brought over to the right DORSAL ↑crown - rump measurement ☆ Kidney already has ladder system to move up through Left renal vein is longer… Why did it develop that way?? Developmental anatomy: Subcardinal veins have a L & R L&R vasculature joined via subcardinal anastomoses Appear ‘ladder-like’… Left cardinal veins mostly obliterate leaves IVC on the right side Right renal vein doesn’t have to go far Left paired glands have to cross to the right side Via subcardinal anastomosis Reason why left adrenal & gonadal veins join left renal vein Mechanism for variation in left iliac veins joining left renal The bladder Éct Lining is mostly derived from hindgut (Cloaca): to ✓ comes off of pleure dorsal side Trigone: Internal area for ureter input & urethral output \É"÷÷"" " ☆ t.me/-anephricducts come into the bladder From I.M. mesoderm ( ) of urogenital sinus - from mesonephric ducts… mesonephric ducts front of meta nephric ☆ pass in "" Septum forms & divides cloaca in 6th week note: when kidneys ascend dorso-cranially via metanephric ducts Anal canal, vagina, urethra present at 12th week (relate to kidney development) """ """ " " " " "" [ " " " " "" " """" " nephric epnrg Gaetanephric meson duct duct ✗ Allantois  Bladder + Urachus… Or not? ↳ primordial bladder ↳ the remnant of where the atlantic component went out to the umbilicus & is now a fibrous ligament at the apex of the bladder µ un closed allantois important implications in UTIS → stagnant urine in cyst deviation into the umbilicus ↑ (deepened umbilicus) Why it’s important to recognise hind gut origin of the bladder