Renal Histology Flashcards
What are the function of the renal system?
Maintain water and electrolyte homeostasis, body fluid osmolarity and acid-base balance
Excrete toxic metabolic waste products = urea, creatine
Endocrine gland = produces renin and erythropoeitin
What is the gross appearance of the kidney?
Bean shaped organ = 10-12cm long, 5-6cm wide, 3cm thick
Where is the kidney located?
In the upper retroperitoneal area = covered by a thin but strong capsule of dense collagen fibres
What is the function of the hilum of the kidney?
Site of entry of the renal artery, and exit of the renal vein and ureter
What are the structures present working from the ureter and in towards the kidney?
Renal pelvis, major calyces, minor calyces,
What are the two main features of the kidney?
Has inner cortex and outer medulla = medulla is further divided into layers
What is the medulla of the kidney divided into?
Medullary pyramids (8-18 per kidney) = apices point towards hilum (called papillae) ending on minor calyces
What makes up a lobe of the kidney?
Each medullary pyramid and its associated cortical tissue
What is the capsule of the kidney continuous with?
The connective tissue that lines the renal sinus
What is the basic functional unit of the kidney?
The nephron = composed of a renal corpuscle and tubules, total length is 45-65mm
What is the function of the renal corpuscle of the nephron?
Production and collection of glomerular filtrate
What is the function of the proximal convoluted tubule of the nephron?
Reabsorption of water, proteins, amino acids, carbohydrates and glucose
What is the function of the loop of Henle in the nephron?
Creation of hyperosmotic environment in the medulla
What is the function of the distal convoluted tubule of the nephron?
Acid-base and water balance = absorbs water, sodium, bicarbonate, and excretes of potassium and hydrogen
What forms the renal corpuscle?
Glomerulus and the Bowman’s capsule
What is the Bowman’s capsule?
Cup of simple squamous epithelium at the blind end of the nephron which capillaries invaginate into
What is the glomerulus?
Tuft of capillaries = supplied by an afferent arteriole and drained by an efferent arteriole
What separates the blood from the glomerular filtrate?
Capillary endothelium and the specialised epithelium which lies on top of the glomerular capillaries
What are some features of the capillary endothelium that helps separate blood from the glomerular filtrate?
Fenestrated with pores of 70-90mm diameter
What makes up the specialised epithelium that lies on top of the glomerular capillaries?
Made of podocytes that have interdigitating cell processes = form filtration slits, causes sawtooth appearance
What is between the capillary endothelium and the specialised epithelium in the renal corpuscle?
Thicker than usual (0.5 micrometers) basal lamina = made up of a feltwork of GAGs
What makes up the mesangium of the renal corpuscle?
Scattered mesangial cells = produce a connective tissue core
What is the glomerular filtrate?
100-125 ml/min ultrafiltrate of plasma (only 1 ml/min of urine)
Where does the renal tubule begin?
Opposite where arterioles enter the Bowman’s capsule
What are the two poles present in the renal corpuscle?
Vascular pole and urinary pole
What are the three components of the glomerular filter in the renal corpuscle?
Fenestrated endothelium of capillary wall
Thick basement membrane
Filtration slits between pedicels
What structures share the thick basement membrane present in the glomerular filter of the renal corpuscle?
Endothelium and podocytes
Where is most sodium and water reabsorbed?
The proximal convoluted tubule = water reabsorbed by diffusion, sodium reabsorbed by active transport
How are amino acids and glucose reabsorbed in the proximal convoluted tubule?
By co-transport
How does the appearance of the proximal convoluted tubule differ from the distal convoluted tubule?
Larger and has less well defined luminal margin due to brush border
What makes up the medulla?
Parallel tubules, loops of Henle and collecting ducts as well as a looping vascular network
What does the loop of Henle consist of?
Thick descending limb, thin descending limb and thick ascending limb
What is significant about the thin descending limb of the loop of Henle?
Makes hairpin turn and begins the journey back out of the medulla as the thin ascending limb
What lines the limbs of the loop of Henle?
Thick limbs = simple cuboidal epithelium
Thin limbs = simple squamous epithelium
Why can the medulla not have a regular blood supply?
This would carry away salts in the interstitial environment and destroy the osmotic gradient
What is the vasa recta?
Loops of thin walled vessels that dip down into medulla from above and climb back into the cortex
How are the microvilli arranged in the distal convoluted tubule?
Contains sparse apical microvilli
What controls the reabsorption of Na+ in the distal convoluted tubule?
Aldosterone = increases Na+ and water retention which increases blood pressure
Are the collecting ducts part of the nephron?
No
What controls water reabsorption in the collecting ducts?
ADH = increases permeability to water, causes concentrated urine
How are the collecting ducts organised?
Gathered into parallel bundles running perpendicular to the surface of the kidneys = called medullary rays (along with straight segments of tubules)
What do medullary rays cause grossly?
Cause stripes in the cortex that point towards the medulla
Where is urine produced at the renal papillae collected?
Into the minor calyx = flows into major calyx, ureter and then into bladder
Where does urine flow during voiding?
Flows into the urethra and out of the body
What lines most parts of the conducting parts of the renal system?
Urothelium = also called transitional epithelium, stratified and found in 3-6 cell layers
What cells are at the luminal surface of the conducting parts of the renal system?
Umbrella cells = domed, have thickened inflexible membrane facing the lumen
What causes the urothelium?
Due to the variability in thickness of cells due to different states of distension and special surface structures causing an impermeable barrier
What is below the epithelium of the conducting parts of the renal system?
Lamina propria of connective tissue and 2-3 layers of smooth muscle
What lines the lumen of the ureter?
Urothelium backed by a lamina propria of connective tissue
What covers the urothelium and connective tissue that lines the lumen of the ureter?
Inner longitudinal layer of muscle smooth muscle and an outer circular layer surrounded by adventitia
What happens to the lining of the lumen of the ureter as it nears the bladder?
It gains a third layer = extra longitudinal layer
What forms the detrusor muscle?
Smooth muscle layers = responsible for micturition and the internal urethral sphincter
What controls the micturition reflex?
Parasympathetic ganglia = innervated by neurons in the sacral spinal cord, found in muscle and adventitia of bladder
How long is the urethra in females?
3-5cm long = initially lined by urothelium which then transitions to stratified squamous epithelium near its termination
How long is the urethra in males?
20 cm in length = split in to prostatic, membranous and penile urethras
What are some features of the prostatic urethra?
3-4cm long, extends from bladder and through the prostate gland, lined by urothelium
What are some features of the membranous urethra?
1cm long, extends from prostate to bulb of the penis, urothelium changes to stratified columnar epithelium
What are some features of the penile urethra?
15cm long, lined by stratified columnar epithelium which becomes stratified squamous epithelium near the tip of the penis
