Urinary System Flashcards
What are the functions of the urinary system
- Maintain water and electrolyte homeostasis, body fluid osmolality, and acid-base balance
- Excrete toxic metabolic waste products
- Act as an endocrine gland
What hormones are produced by the kidneys
- Renin
2. Erythropoietin
Describe the gross structure of the kidney going from the ureter
Ureter -> renal pelvis -> major calyces -> minor calyces
What is the medulla of the kidney composed of
8-18 medullary pyramids, with apices pointing toward the hilum (papillae) ending on the minor calyces
What is the kidney surrounded by
A capsule composed of:
- Outer fibrous layer
- Inner more cellular layer (myofibroblasts)
What are the renal columns
Sections of cortical material either side of the medulla
What are the medullar rays
Collections of collecting ducts and the straight segments of the proximal and distal convoluted tubules
Where are the medullary rays found
In the cortex
What is the nephron
The basic functional unit of the kidney and it is composed of the renal corpuscle and renal tubules
How many nephrons are there in a human kidney
600,000 to 1 million
What is the total length of a single nephron, and the total length of the nephron tubing
Nephron = 45-65mm
Nephron tubing = 60km
What are the 4 different components to the nephron
- Renal corpuscle
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
What occurs in the renal corpuscle
Production and collection of glomerular filtrate
What occurs in the proximal convoluted tubule
Reabsorption of water, proteins, amino acids, carbohydrates, and glucose
What occurs in the loop of Henle
Creation of hypertonic environment in the medulla
What occurs in the distal convoluted tubule
Acid-base and water balance (absorption of water, Na and bicarbonate; excretion of K and H ions
How is the renal corpuscle formed
A tuft of capillaries called the glomerulus and the cup of simple squamous epithelium at the blind end of the nephron which the capillaries invaginate into (Bowman’s capsule)
How many, and what, cells separate the blood from the glomerular filtrate
Two cell layers:
- Capillary endothelium
- Specialised epithelium (podocytes)
What exists between the two layers that separate the blood from the glomerular filtrate
A thicker than usual (0.3um) basal lamina, made up of a feltwork of GAGs
What produces the mesangium (connective tissue core)
Scattered mesangial cells
How much glomerular filtrate is produced a minute
Around 125ml (only 1ml will be urine)
Where is the glomerular filtrate produced
In the urinary space
Describe the 3 components of the glomerular filter
- Fenestrated endothelium of the capillary wall
- Thick basement membrane (shared by endothelium and podocyte)
- Filtration slits between pedicels
What happens in the proximal tubule
- 70% of sodium and water is reabsorbed
2. Almost all glucose and amino acids reabsorbed
Where does the proximal convoluted tubule originate
From the urinary pole of the Bowman capsule
Describe the pathway of the proximal convoluted tubule
After the convoluted course, it enters the medullary ray to continue as the proximal straight tubule
What is the need for the several loops of Henle
To prevent the loss of the high osmotic gradient in the interstitial environment
What is the vasa recta
Thin-walled blood vessels that dop down into the medulla from above and then climb back up to the cortex
What happens to the blood as it gets deeper into the medulla
It gets saltier and saltier, and then turns back up to the cortex
What connects the distal convoluted tubule to the cortical collecting duct
Either or:
- An arched connecting tubule
- A shorter tubule simply called the connecting tubule
Why do the distal convoluted tubules have a clearly defined lumen histologically
They have only sparse microvilli; thus, there is more space in the lumen
What is the role of the hormone aldosterone in the distal convoluted tubule
It controls the reabsorption of Na+
What controls aldosterone secretion
The renin-angiotensin system
What is the net effect of Na+ retention
Greater Na+ and water retention will result in an increase in blood pressure
What is the function of the collecting ducts
They control the reabsorption of water under the control of vasopressin
In the presence of vasopressin, what is the effect on urine
Permeability is high during passage through the medulla; water will pass out of the lumen and a concentrated urine is produced
What do individual collecting ducts form
They merge at the apex of the pyramid to form papillary ducts that open into the minor calyx
What is the area cribrosa
The area on the papilla that contains the opening of the collecting ducts
What is the juxtaglomerular apparatus
Specialised region formed at the site where the DCT passes adjacent to the vascular pole of the same renal corpuscle that forms part of its very own nephron
What are the 3 components of the juxtaglomerular apparatus
- The macula densa
- The juxtaglomerular cells
- The extraglomerular mesangial cells (lacis cells)
What is the function of the macula densa
Sensing sodium content of fluid in the DCT
What are juxtaglomerular cells, and what is their function
Modified smooth muscle cells in the wall of the afferent arteriole; they secrete renin
What are lacis cells
Modified mesangial cells extending outside the renal corpuscle
Describe the lining of almost all of the parts of the conducting system
Transitional epithelium; stratified and found in 3-6 cell layers
Name the cells at the luminal surface of the conducting system
Umbrella cells, because they are domed
Describe the special structure fo the transitional epithelium
- Variability in the thickness of cells represents different states of distension
- Special surface structures are to provide a highly impermeable barrier
What exists below the transitional epithelium
- Lamina propria
- 2-3 layers of smooth muscle
- Adventitia
Describe the smooth muscle layers in the ureter
Inner longitudinal layer, and outer circular layer:
- Outer longitudinal layer exists close to the bladder
What do the smooth muscle layers of the bladder form
The detrusor muscle; responsible for micturition
Describe the lining of the female urethra
Initially lined by transitional epithelium. which becomes stratified squamous as it nears the surface of the body (just posterior to the clitoris)
