Kidney and Urinary tract Flashcards
What are the two umbrella functions of the urinary system?
Formation of urine
Endocrine function
What are the three layers of the kidney?
Fibrous capsule
Dark brown granular outer cortex
Inner medulla
What is the concave border of the kidney known as?
The hilum
What enters and leaves the kidney at the hilum?
Nerves, blood vessels and ureter
What is the morphology of the ureter at the hilum?
It is expanded and forms the renal pelvis
How does urine flow from cortex to medulla to ureter?
Renal pyramids drain into minor calyx via papilla then into major calyx to renal pelvis to ureter
What is distinct of the cortex?
Glomeruli renal corpuscles
Where are medullary rays present and what are they?
Cortex, extension of medulla into the cortex forming core of kidney lobule consisting of straight tubes
How many renal pyramids are there?
10-18
Each renal pyramid constitutes a …
lobe of the kidney
How many papillary ducts at renal pyramid papilla?
15-20
What is another word for the papilla of renal pyramid?
Cribrosa
What is characteristic of medulla?
Many tubules, no glomeruli
Vasa recta
How does vasa recta appear on histology?
Parallel darker patches (seem to be concentrated nuclei)
Describe the increasing complexity of blood supply to the kidney?
Aorta Renal artery Interlobar arteries Arcuate arteries Small interlobular arteries Afferent glomerular arterioles - glomerulus
When do interlobar arteries give rise to arcuate arteries?
At the cortico-medullary junction
Which arteries enter the cortical labyrinth?
Small interlobular
What drains the kidney?
Efferent arterioles Interlobular veins Arcuate veins Interlobar veins Renal vein IVC
What is the functional unit of the kidney?
Uriniferous tubule (nephron and collecting duct)
What are the two different types of nephron, how are they classified?
Juxtamedullary nephron (close to the medulla) Cortical nephron (periphery of cortex)
What is described by the renal corpuscle ?
Glomerulus and Bowman’s capsule
What is the glomerulus?
Tuft of anastomosing fenestrated capillaries invaginated into the capsule.
What supplies and drains the Bowman’s capsule?
Supplied by the afferent arterioles and drained by the efferent arterioles (into medulla).
What is the vascular and urinary pole of the renal corpuscle?
Vascular: where afferent and efferent arterioles enter and leave
Urinary: where Bowman’s space is drained by the PCT
What is the role of the glomeruli’s connective tissue layer?
Regulates blood flow through the capillaries
What cells regulate glomerulus extraglomerularly?
Mesangial cells on vascular pole
What cells regulate glomerulus intraglomerularly?
Mesangial cells situated within the corpuscle, respond to vasoactive hormones and can secrete them like NO.
Pericytes, smooth muscle cells with phagocytotic properties.
What is the difference between intra/extraglomerular cell?
Intraglomerular - within corpuscle
Extraglomerular - outside corpuscle on the vascular pole
What are the two layers of the Bowman’s capsule?
Parietal layer (outside) - simple squamous epithelium
Visceral layer (envelops capillary) - highly specialised epithelia with podocytes.
Inbetween - Bowman’s space
What are the three filtration layers?
Fenestrated capillary
Basal lamina
Podocytes in visceral layer
How is the fenestrated capillary suited to filtration?
Endothelial cells with large pores between 70-90nm (very permeable), low amount of tight junctions.
What are the three layers of basal lamina, how do they separate?
Lamina rara interna
Lamina densa (type IV collagen): Collagen in basal lamina separates by size
Lamina rara externa (heparin sulfate): Heparin sulphate separates by charge
How do podocytes cover glomerulus, what are their primary and secondary processes?
Podocytes interdigitate to cover the basal lamina
Primary processes describe the numerous long tentacle like cytoplasmic extensions
Secondary processes are called pedicels which completely envelope most of the capillaries.
What holds podocytes to eachother (to slow passage of molecules) and to the capillary?
Held to laminin of BM by integrins
Nephrin molecules of adjacent pedicels interact to form negatively charged slit pores, this slows passage of molecules.
What epithelia does the PCT have?
Simple cuboidal (leaky)
True or false, at the urinary pole, the BC simple squamous epithelia meets the PCT simple cuboidal?
True
What is distinctive about the PCT?
Extensive brush border
What makes up the brush border of the PCT?
Microvilli and canaliculi (invaginations)
Why may the PCT have a striated appearance under a light microscope?
Folding of plasmalemma region rich in mitochondria
What are the two regions of the PCT?
Pars convuluta (tortuous region) Pars recta (straight portion, descending thick limb of henle)
Describe epithelia of thin descending limb
Simple squamous with few mitochondria but aquaporins
How is the pars recta histologically different to the pars convuluta of the PCT?
Shorter brush border
Describe the epithelia of the thick loop of henle
Simple cuboidal epithelium, no brush border, rich in mitochondria
Describe epithelia in thin ascending limb
Similar to thin descending limb i.e. simple squamous but low water permeability
What is the role of vasa recta?
Reabsorb water/solutes, slow blood flow helps to generate hypertonic interstitium by counter current exchange
How does LoH differ in cortical nephrons and juxtamedullary nephrons?
Cortical nephrons have shoort loops do don’t enter medulla but juxtamedullary have long loops that invaginate deeper into medulla
Are the descending endothelial cells on vasa recta continuous or fenestrated?
Continuous
Are the ascending endothelial cells on vasa recta continuous or fenestrated?
Fenestrated
Describe epithelia of DCT
Simple cuboidal, no brush border but with tall thin, central nuclei macula densa cells which contact vascular pole at renal corpuscle
Where do macular densa cells lie?
Contact vascular pole at renal corpuscle
What ion movement occurs at DCT?
Na+, Cl- reabsorbed
K+ screted
What is the juxtaglomerular apparatus
Cells from last part of LOH or beginning DCT (macula densa) contact afferent glomerulus arteriole
Describe the epithelia in the collecting duct
Simple cuboidal epithelium.
Describe the cortical and medullary components of collecting duct
Cortial: epithelium consists of
1) Principle cells: aldosteorne controlled Na+ reabsorption and K+ Loss
2) Intercalated cells: acid base regulation
Medullary: ADH controlled reabsorption of H20 and urea
What are ducts of Bellini?
Merging of several collecting ducts
What is the role of the JGA?
When fall in Na/Cl/K in DCT (indicative of low ECV)
Juxtaglomerular cells produce Renin (promote reabsorption of water and Na+, vasoconstriction)
Describe blood supply (microscopic) to kidney
Afferent arterioles give rise to glomerulus.
Efferent arterioles give rise to peritubular capillaries around renal tubules, arterioles close to medulla (vasa recta around loop of Henle)
Peritubular capillary to stellate vein
Vasa recta to arcuate veins
What is the juxtaglomerulus apparatus?
Macula densa cells, extraglomerular mesangial cells, juxtaglomerular cells
What are functions of juxtaglomerular cells?
Regulate renal blood flow, GFR and bp
What do macula densa cells do?
Sense low ionic content in distal tubule and respond by releasing prostaglandis, activate extraglomerular mesangiual cells
Relay info to juxtaglomerular cells of afferent arterioles
Secrete renin
Peripheal vasoconstriction
Describe epithelium of lower urinary tract
Transitional epithelium,
Superficial layer of large cells with uroplakins on apical surface
Describe function of ureter
Muscular tube produces muscular contractions to move urine from kidney to bladder
Structure of the ureter (layers)
Mucosa (3-5 layers transitional epithelium) lines lumen, muscular coat and fibrous tissue covering.
What is the function of transitional epithelium?
Accommodate changes in fluid
What is the function of uroplakins?
Protective glycoprotein plaques (keep urine in lumen) and osmotic barrier - impermeable to salt/water
What are the 3 layers of the detrusor muscle?
2 layers of longitudinal
sandwiching a circular muscle
What does the lamina propria of the urethra contain in both sexes?
Mucous glands of littre
Intraepithelial glands
What is the function of both urethral glands?
Lubricate the lining of the urethra, facilitating the passage of urine to the outside.
Damage to podocytes leads to
Proteinuria
What type collagen does the BM contain?
type IV
What do podocytes originate from?
Intermediate mesoderm
Where is Erythropoietin, the other hormone produced by the kidney, produced?
Fibroblast-like cells of the renal interstitium.
