Gross structure of the Kidney
Each kidney has upper and lower poles and medial and lateral borders.
Two poles and Two borders of Kidney
Upper pole is broad, close contact with suprarenal gland.
Lower poles is pointed.
Near center of medial border is notch called Hilum or Hilus where enter and leaves artery, vein, nerves and ureters of the kidney.
Hilus is enterance to cavity in kidney called renal sinus.
Capsules or covering of kidney
There is three layers-
1. Renal capsule fibrous capsule
Innermost layer. A fibrous capsule surrounding the kidney.
Prevent spread of infection in kidney.
2. Adipose capsule
Middle layer lying outside fibrous capsule, provide protection against friction and jolts.
3. Renal fascia
Outermost layer. Provide flexibility to permit kidney to shift slightly as diaphragm moves during breathing.
Internal anatomy of kidney
1. Renal cortex
2. Renal medulla
3. Renal pelvis
1. Renal cortex
Outer cortical region
Inner juxta medullary
Outmost reddish brown portion of kidney (layer of tissue).
Extends from outermost renal capsule to base of renal pyramids.
Extension of cortex between renal medulla from renal columns ( collecting tubules that drain and empty urine lumen of minor calyx
2. Renal medulla
Inner reddish between region.
It consist 8-18 cone shaped structure called renal pyramids.
Presence of straight tubules and blood vessels.
Apex ends in renal papillae, which point towards renal sinus and opens into minor calyx.
Renal pyramid consist of tubules and collection ducts of nephrons.
Tubules of pyramids are involved with reabsorption of filtered materials.
Urine passes from collecting tubules in pyramids to minor calyces -- major calcyes-- renal pelvis-- urine drain into ureters.
3. Renal Pelvis
Funnel shaped structure in renal sinus of kidney is large cavity called renal pelvis.
Renal pelvis branches into small cavities called major calcyes (2-3 major) and minor calcyes (8-18 minor).
Urine formed by nephrons drain into large papilla duct (renal papilla).
Papillary ducts drain into minor calyces.
Each minor calyces receives urine from papillary duct of one papilla and deliver urine into major calyx.
From major calyces, urine drains into the renal pelvis and
Out through the ureter to the urinary bladder.
Renal pelvis structure act as receptor for the urine formed by the kidney.
Renal Sinus
Hilum of kidney expands into a cavity within the kidney called renal sinus.
Contains part of renal pelvis, calyces, branches of renal blood vessel and nerve.
Adipose tissue helps to stabilize portion of these structure in renal sinus.
Renal lobe
Renal lobe consist of renal pyramid.
Each minor calyx receives urine from lobe of kidney.
Renal Parenchyma
Together cortex and renal pyramids constitute Parenchyma (functional tissue) of kidney.
Parenchyma of each kidney consist of about one million microscopic structure called nephrons. (Functional units of kidney).
Microscopic structure of kidney
Kidney is composed of about 1 million uriniferous tubules.
Each tubules consist of two parts -
1. Secretory part called nephron (functional unit of kidney). PCT, Loop of Henle, DCT.
2. Collecting tubules
Nephron
Nephron s microscopic structural and functional unit of kidney.
Nephron accomplishes initial filteration of blood, selective reabsorption back into blood of filtered substances that are useful to the body and the secretion of unwanted substances.
Nephron composed of -
1. Renal corpuscle
2. Renal tubule
1. Renal corpuscle or Malpighian corpuscle
Part of nephron where fluid is filtered, it is made up of glomerulus and glomerular capsule or Bowman's capsule.
2. Renal tubule
Part into which filtered fluid passes.
Renal tubule composed of -
1. Proximal convoluted tubule
2. Loop if Henle
3. Distal convoluted tubules
Continuing from glomerular capsule, remainder of the nephron is about 3cm long.
1. Glomerular (Bowman's capsule)
Glomerular capsule is portion of nephron that encloses the glomerulus.
Glomerular capsule is always located in cortex of kidney.
Space between visceral and parietal layer is called Bowman's space.
Blood flows through glomerular capillaries, water and most kind of solutes filter from blood plasma into capsular space.
Larger plasma protein and formed element in blood normally don't pass through.
Alteration of blood take place in renal corpuscle cross three layer-
1. Endothelium of glomerulus
2. Basement membrane of glomerulus (middle layer)
3. Visceral layer of glomerular capsule and podocytes (3rd layer).
2. Renal tubules
Part of nephron that leads away from glomerulus.
Renal tubules has 3 main section-
1. PCT
2. Medullary loop
3. DCT
4. Collecting duct
1. Proximal convoluted tubules (PCT)
PCT is portion attached to glomerular capsule. (Highly coiled)
It lie in cortex of kidney.
14mm long and 60 micrometer in diameter.
Brush border of microvilli on apical surface increase the surface area for reabsorption and secretion.
PCT is site for reabsorption of many substances filtered from blood such as -
Water, glucose, electrolytes, some amino acids and polypeptides.
About 65% water and upto 100% of some solute that pass through endothelial capsular membrane return to blood stream from PCT.
2. Loop of Henle
U shaped
After passing through PCT - glomerular filtrate enter straightened portion of excretory tubules called loop of Henle.
Loop of Henle is continuation of PCT.
It connect proximal convoluted tubules and distal convoluted tubules.
Major function bis active reabsorption of sodium and chloride and
Passive diffusion of water resulting in urinary concentration.
3. DCT
Irregularly shaped
DCT is highly coiled portion of kidney nephron between loop of Henle and collecting tubule.
Reabsorption of HCO3-
Selective secretion of H+ and potassium ion and NH3 to maintain the PH and Na+/k+ balance in blood.
4. Collecting duct
This is a long duct extends from cortex of kidney to the inner parts of medulla.
Large amount of water could be reabsorbed from this region to produce concentrated urine.
Collecting tube unit forming larger duct
Papillary duct
Minor calyx
Major calyx
Renal pelvis
Urine drain into ureters
After collecting duct glomerular filtrate is called urine.
Nephron
Nephron consist of
1. Renal corpuscle; glomerulus capsule
2. Renal tubules; PCT, LOh, DCT, collecting duct
Renal capsule consist a tuft of capillaries called glomerulus.
At one end tube is closed fold and expanded into doubled walled cup shaper structure called Bowman's capsule, which encloses cluster of microscopic blood vessel called glomerulus.
Afferent arteriole that brings blood to glomerulus.
Efferent arteriole that carries blood away from glomerulus.
Afferent arteriole is branch of renal vein, which carries blood containing nitrogenous waste.
Wall of afferent arteriole lumen size is larger than size of efferent arteriole that causes generate pressure in glomerulus, and filtration occurs.
Types of Nephron
1. Cortical nephrons
Loop of Henle too short
Extend very little into medulla
Vasa recta absent (hair pin like loop)
80-85% have renal corpuscle in superficial renal cortex.
2. Juxta medullary nephron
Loop of Henle runs deep into medulla.
Vasa recta present
15-20% are located near renal medulla.
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