this unit provided a brief histological overview of the kidneys and the tubular architecture of the urinary system. the basic function of the kidneys is to filter the blood and excrete waste through the urine, which leaves the kidney via the ureter, is pooled in the bladder, then goes from the bladder to the body's exterior by means of the urethra. inside the kidney itself there is an outer layer called the cortex and an inner layer called the medulla, which contains triangular shaped lobes called medullary pyramids. the pyramids collect urine at their tips, called area cribosa, into the calyces, which drain into the renal sinuses, renal pelvis, and out to the ureter. the kidney is filled with functional tubular units called the nephron, of which there are two types: juxtamedullary and cortical, depending on their location.
the site of filtration of blood occurs at the glomerulus, which is a ball of type 2 fenestrated capillaries inside a Bowman's capsule. the Bowman's capsule is similar to a pericardium or pleura in that it has a visceral and parietal layer and a space in between; in this case, the visceral layer is made up of the layer of podocytes that encase the ball of capillaries and provide an extra filtration layer, outside of which there is the bowman's space, and then the parietal bowman's capsule. the blood supply to the ball of capillaries comes from the afferent arteriole and leaves through the efferent arteriole; this end of the glomerulus is called the vascular pole. on the other side of the glomerulus is the urinary pole, which collects the filtrate from the blood into the proximal tubule, which is a convoluted tubule made of simple cuboidal epithelium with extensive apical microvilli. this tubule descends into the medullary region and becomes the loop of Henle, which is thin and squamous on the way down and thick and cuboidal on the way up. this turns into the distal convoluted tubule, which comes back to the glomerulus to form the juxtamedullary complex, which is a junction of the distal tubule and the efferent arteriole, with a group of cells called the macula densa in between. the distal tubule then dumps into a collecting duct, which empties into the papillary ducts that empty into the area cribrosa of the medullary pyramids, and out the body as covered above.
the blood flow in and out of the kidney is as follows: the visceral abdominal aorta supplies the blood to the renal artery, which branches into the interlobular arteries, which branch into the arcuate arteries, which branch into the interlobular arteries, which branch into the intralobular arteries, which turn into afferent arterioles and enter the glomerulus. the blood is filtered in the capillaries in the glomerulus, then flows out through the efferent arteriole, then enters peritubular capillaries, which are small capillaries that run alongside nephron tubules and are the link between the arteries and veins in the kidneys. from the peritubular capillaries, blood flows into veins and exits in the opposite order: intralobular, interlobular, etc etc.
some details about the epithelium of the plumbing of the urinary system: there is transitional epithelium basically from the ureter to the end of the urethra, which switches to non-keratinized stratified squamous. the muscularis externa of the ureter and urethra has opposite layers than other tubes of the body in that has an inner longitudinal and outer circular layer. the urinary bladder has a thick and choatic muscularis externa.
questions
1. what are four functions of the urinary system?
2. describe the anatomy of the kidney.
3. describe the blood flow in and out of the kidney.
4. what are the two types of nephrons?
5. describe the anatomy of a glomerulus.
6. what are the two poles in a glomerulus?
7. what is the glomelular membrane composed of?
8. describe the proximal tubule.
9. describe the loop of Henle.
10. describe the distal tubule.
11. what is a juxtaglomerular apparatus?
12. describe the collecting ducts.
13. describe juxtaglomerular cells.
14. what are peritubular capillaries?
15. describe the ureter.
16. describe the urinary bladder.
17. describe the epithelium of the urethra.
18. describe the muscularis externa of the urethra.
answers
1. chemically balance the blood, remove wastes, regulate blood pressure, and regulate red blood cell production.
2. kidneys have an outer layer called cortex and inner layer called medulla. in the medulla there are medullary pyramids from which urine is collected from the tips (area cribrosa) to the minor and major calyces, which converge into the renal sinuses, which converge into the renal pelvis, which leads out to the ureter.
3. renal artery to interlobar artery to arcuate artery to interlobular artery to intralobular artery to afferent arteriole to glomelular capsule to intralobular vein to interlobular vein to arcuate vein to interlobar vein to renal vein.
4. cortical nephrons and juxtamedullary nephrons.
5. 1-20 type II capillaries held together by a mesangium, encased in podocytes which make up the visceral Bowman's capsule, outside of which is the Bowman's space, and then the parietal Bowman's capsule.
6. vascular pole contains the afferent and efferent arterioles. urinary pole is on the other end of the glomerulus, where the proximal tubule starts.
7. type II capillary endothelium, endothelial basement membrane, podocyte basement membrane, podocyte, occasional mesangial cell.
8. long, convoluted, does most of the absorption, simple cuboidal with extensive apical microvilli.
9. has a thin, squamous descending section and a thick, ascending, cuboidal section.
10. simple suboidal, no microvilli. convolutes and feeds into a collecting duct.
11. the junction between a distal tubule and a vascular pole, with a macula densa in between
12. a large diameter tube that is the common collecting point for a number of nephrons, and merges into papillary ducts to the area cribrosa. simple cuboidal with rounded apical surfaces.
13. modified smooth muscle cells that secrete renin, which catalyzes formation of angiotensin-- regulates blood pressure.
14. the capillaries found of the back sides of nephric tubules and serve as points for absorption, the link between arterial and venous blood vasculature.
15. long muscular tube from renal pelvis to bladder with transitional epithelium and lamina propria (but no muscularis mucosa) muscularis externa has "reversed" layers -- inner longitudinal outer circular.
16. distensible sac with transitional epithelium and lamina propria but no muscularis mucosa. muscularis externa thick and chaotic.
17. PSC epithelium, near bladder is more transitional, near exterior is more non keratinzed stratified squamous. muscularis externa has inner longitudinal, outer circular.
No comments:
Post a Comment