Urinary System Flashcards
3 functions of kidney and urinary tract
1 - maintain water and electrolyte homeostasis, body fluid osmolarity and acid-base balance
2 - excrete toxic metabolic waste products
3 - act as an endocrine gland, producing renin and erythropoietin
What is the kidney capsule continuous with?
What is it made from?
Connective tissue lining the renal sinus
Dense collagen fibres
What are medullary rays?
Collections of collecting ducts and the straight segments of convoluted tubules.
Found in the cortex.
4 properties of the nephron
1 - basic functional unit of the kidney
2 - composed of renal corpuscle and renal tubules
3 - each human kidney contains 600,000-1million nephrons
4 - total length of a nephron approx 45-65mm
Principle role of the renal corpuscle
Production and collection of glomerular filtrate
What is the renal corpuscle formed from?
Tuft of capillaries called the glomerulus and the cup of simple squamous epithelium (Bowman’s capsule) at the blind end of the nephron which
What is the glomerulus supplied and drained by?
Supplied - afferent arteriole
Drained - efferent arteriole
What are podocytes?
Specialised epithelial cells which lie on top of the glomerular capillaries
What separates the blood from the glomerular filtrate?
Two cell layers:
- capillary endothelium
- specialised epithelium
What is between the two cell layers separating the blood from glomerular filtrate?
Thicker than usual basal lamina made of a feltwork of GAGs
What is the mesangium?
A connective tissue core made from scattered mesangial cells.
Functions:
- support
- removal of debris
What are the 3 components of the glomerular filter?
1 - fenestrated endothelium of the capillary wall
2 - thick basement membrane
3 - filtration slits between pedicels
Principal role of proximal convoluted tubule
Reabsorption of water, proteins, amino acids, carbohydrates and glucose
What is quantitiy of products are reabsorbed in the proximal convoluted tubule?
70% of sodium by active transport
70% of water by diffusion
almost ALL glucose and amino acids by cotransport
Principle role of the loop of henle
Creation of hypertonic environment in the medulla
What is the Vasa Recta?
Thin loops of blood vessels that dip down into the medulla from above then return to the cortex.
(stop salts being carried away in the interstitial environment and maintains high osmotic gradient)
What structures are found in the outer medulla?
Collecting ducts
Blood vessels of vasa recta
Thin limb of loop of henle
Proximal and Distal straight tubules
Principle role of the distal convoluted tubule
Acid-base and water balance
Absorption of water, Na and bicarbonate
Excretion of K and H ions
What does aldosterone hormone do?
Controls the reapsorption of sodium in the DCT
Where is it secreted and what controls the secretion of aldosterone?
Secreted by the adrenal cortex
Controlled by the renin-angiotensin system
What does aldosterone hormone secretion result in?
Greater reabsorption of sodium and water retention, therefore increases blood pressure.
What is the principal role of the collecting duct?
To control reabsorption of water under the control of ADH
How does ADH affect the permeability of collecting ducts?
ADH from the posterior pituitary increases permeability to water.
In presence of ADH, permeability is high during the passage through the medulla.
Due to the high salt content in the surrounding tissue, the water passes out through the lumen and CONCENTRATED urine results.
What is the juxtaglomerular apparatus?
Specialised region formed when the distal convoluted tubule passes adjacent to the vascular pole of the SAME renal corpuscle that forms part of its own nephron.
What are the 3 components of the juxtaglomerular apparatus?
1 - macula densa
2 - juxtaglomerular cells
3 - extraglomerular mesangial cells (lacis cells)
Describe the macula densa and its function.
On the side of the distal convoluted tubule nearest the afferent arteriole, where the cells are taller, more crowded and their nuclei are intensely stained.
Believed to sense sodium content of fluid in DCT.
Describe the juxtoglomerular cells and their function.
Modified smooth muscle cells in wall of afferent arteriole.
Contain/excrete renin, initiating the renin-angiotensin system.
Describe the extraglomerular mesangial cells and their function.
Modified mesangial cells extending outside the renal corpuscle. Contact macula densa and are continuous with mesangial cells inside renal corpuscle.
Alters glomerular filtration.
What happens to urine after its produced?
Produced in the renal papilla and is collected into the minor calyx.
Flows into the major calyx, ureter and then to the bladder.
During voiding it flows into the urethra and exits the body.
What is transitional epithelium?
Special epithelium lining most conducting parts of urinary tract.
Properties of transitional epithelium.
Stratified
Found in 3-6 cell layers
Cells at luminal surface are domed = umbrella cells
Facing lumen, have special, thickened and inflexible membrane
What 2 facts describe the special structure of transitional epithelium?
The variability of thickness of cells represent different states of distension.
The special surface structures provide a highly impermeable barrier.
Describe the lining of the ureter.
Transitional epithelium backed by a basal lamina of connective tissue then covered by an inner longitudinal and outer circular layer of smooth muscle surrounded by adventitia.
Near the bladder: 3 layers of smooth muscle as another outer longitudinal layer is present.
What do the 3 layers of smooth muscle in the ureter form?
Detrusor Muscle
Internal urethral sphincter
What lines the female urethra?
Initially lined by transitional epithelium, which becomes stratified squamous as it nears the surface of the body just posterior to clitoris.
What does the middle of the female urethra contain?
Includes a sphincter of striated skeletal muscle - the voluntary sphincter.
