Renal System
Kidney
The kidney is organized into main areas, the capsule which covers and protects this retroperitoneal organ, the cortex which is where we find the major structures of the kidney the nephron and its connecting tubules, moving inwards we see medulla pyramids which have the loop of hence and the collecting ducts.
Capsule
Cortex
Medulla
Cortex
Nephron
Nephrons are found within the cortex and can be in one of two locations, juxtamedullary nephrons are located near the medulla while cortical nephrons are located further into the cortex.
E
I
G
Part of the Nephron
1)Bowmans Capsule is a double walled epithelial capsule
a) Internal visceral layer (I)
- envelopes the capillaries of the glomerulus, cells are called podocytes.
- Podocytes have primary and secondary processes coming from cell body (pedicels) that embrace the capillaries of the glomerulus.
- The processes create filtration slits that determine what can and cannot be filtered through the capillaries in the urinary space.
b) External Parietal layer (E)
- Simple squamous epithelia
- At the urinary pole it turns into simple cuboidal low columnar
​
Between both layers of Bowmans Capsule is the urinary space that receives fluid and filtered through the capillaries.
​
The Renal corpuscle consists of Bowmans capsule and the Glomerulus (G).
​
The following tubule is the loop of henle which has an ascending and descending limb. For cortical nephrons the loop of henle does not reach deep into the medulla, however for the juxtamedullary nephrons the loop descends deep into the medulla and this is where most of the concentration occurs. the descending limb is lined with cudoial to squamous cell, while the ascending is squamous to cuboidal.
The nephron opens to the proximal convoluted tubule at the macula densa, the filtrate will flow through the PCT is lined with eosinophilic cuboidal cells with microvilli, it has a small lumen. The PCT basal plasma membrane has many ion channels as this area functions in reabsorption of ions, water, amino acids, etc.
The Distal convoluted tubule is the final one, it is found in the cortex. The DCT is also lined with cuboidal cells with a few short microvilli. The lumen is much larger in the DCT than the PCT so it should be easy to tell most apart. There are many basal infoldings of the
The DCT drains into the collecting duct which transports filtrate to the medullary papillae. This tube is line with Principle and Intercalated cells, principle cells reabsorb sodium and water while secreting potassium; intercalated cells (dark cells) secrete H ions or HCO3, while reabsorbing potassium. The collecting ducts permeability to water is regulated by ADH, an increase in osmolarity in the blood will trigger the hypothalamus to cause the release of ADH from the posterior pituitary, the ADH activates membrane bound receptors to cause the insertion of aquaporins into the membrane facilitating the reabsorption of water back into the bloodstream from the lumen of the collecting tubule.