Lecture 2: Anatomy of the urinary system Flashcards
What are the functions of the kidney and urinary tract?
- Excretion of waste products and drugs: filter plasma
- Regulation: Controls body fluid volume and ionic compounds. Major role in homeostasis. Involved in the acid-base balance
- Endocrine: site of synthesis of renin (BP and sodium balance), site of EPO production (erythrocyte production), site of prostaglandins (regulation of renal function)
- Metabolism: where vit D is metabolised into its active form. Site of catabolism for low-molecular-weight proteins (insulin/PTH/calcitonin)
Where is the anatomical location of the kidneys?
Retroperitoneal on the posterior abdominal wall, either side of the vertebral column
-located between T12 and L3 vertebrae
-partially protected by ribs 11 and 12
(look at size difference b/w to two kidneys in one person)
What is the size of the kidneys?
11cm long
6cm wide
140g
Which kidney is higher up?
Left
As the liver sits on top of the right kidney, pushing it down slightly
What is the hilum of the kidney?
Part of the kidney that makes it bean shaped, where all the tubes enter the kidney.
-located at L1
What structure comes out of the kidneys?
Ureter, which travels down the lumbar spinal processes into the pelvis
When do the ureters move inwards towards the bladder?
At the level of the ischial spine
How is the kidney held in place?
-pararenal fat (in line with kidney)
-renal fascia
-perirenal fat (near to kidney)
-renal capsule
Then withing the capsule is the kidney
(however the kidneys aren’t in a fixed position)
What is the blood supply to the kidney?
-abdominal aorta (left/right renal artery comes directly off the aorta to supply the left/right kidneys)
In front of this is the inferior vena cava (IVC)
-the IVC has branches coming directly off called the right/left renal vein
What is the structure of the inner kidney?
- cortex
- medulla (renal pyramids found here)
What is encompassed in the renal lobe?
The renal pyramid as well as the cortex above it. There are many renal lobes
What is found between the renal lobes?
Renal columns
Where are the nephrons found?
Within the renal lobes, collecting ducts run into the minor calyces, which in turn feed into the major calyces, which then feeds into the renal pelvis, and then the ureter
How does the osmolality change in the medulla?
Gets more salty the further in you go
What are the two different types of nephron?
- cortical, short LoH (85% of nephrons in body)
- juxtamedullary, long LoH (15% of nephrons in body): good at concentrating urine ad have lots of space for water reabsorption
What feeds the blood supply into the nephron?
Afferent arteriole, which then forms a network of capillaries known as the glomerulus which is encased by Bowman’s capsule
How does the blood leave the glomerulus?
Efferent arteriole (leaving through an arteriole and NOT A VEIN!)
What cells sit on top of the capillaries in Bowman’s capsule?
Podocytes (large cells)
- protrusions (foot processes), which wrap around the capillaries forming slits: one part of the filtration system
- stop really large solutes passing through
Whats the first part of the nephron after the glomerulus?
Proximal convoluted tubule
- reabsorb a high proportion of solutes
- all AA’s and glucose absorbed here
What are the different part of the LoH?
LoH is found after the proximal convoluted tubule
- descending limb (thin)
- ascending limb (thick and thin)
What is found after the LoH in the nephron?
Distal convoluted tubule
-nestles near the glomerulus forming the juxtaglomerular apparatus
What feeds into the collecting duct?
Distal convoluted tubule. Many nephrons feed into one collecting duct
Where do the blood vessels for the nephrons come off?
Arcuate artery- arc across the lobe
Interlobular artery comes off the arcuate artery, and off this artery the afferent arterioles branch off
What comes off the efferent arteriole?
Web of capillaries that flow around the nephrons.
Known as the peritubular capillaries
What is different about the capillaries on the juxtamedullary nephron in contrast to the cortical nephron?
The juxtamedullary have vesa recta, which is almost like an extension of the peritubular capillaries. This is where we can absorb more water back into the body
Why is the juxtaglomerular apparatus important?
Helps glomerulus sense what is happening to the composition of fluid in the distal tubule.
What special cells line the distal convoluted tubule in the juxtaglomerulus apparatus?
Macula Densa cells: sense how salty the fluid is, to determine how much flow should be coming through the glomerulus
What cells do the macula densa cells communicate with?
Granular cells, which can produce renin/cause constriction of afferent/efferent arterioles: altering the flow of blood through the glomerulus
What are the supporting cells in the juxtaglomerular apparatus?
Extraglomerular mesangial cells
- pass the messages
- secrete substances
- provide skeleton to hold the capillary network
What is an important landmark to look for coming off the aorta?
Superior mesenteric artery
-comes off aorta and lies over the top of the left renal vein
Where does the adrenal gland drain into?
Right- adrenal vein directly into the IVC
Left- adrenal vein into the left renal vein
Which renal vein is longer?
Left
Which renal artery is longer/greater distance?
Right, as it has to go behind the IVC to reach the kidney
How does the artery continue through the kidney?
- renal artery
- renal artery then splits into the segmental artery (which then splits into 5), which then go on to split into the interlobar arteries
- interlobar arteries split into the arcuate artery
- the arcuate artery splits into the interlobular arteries
- the interlobular artery splits into the afferent arteriole
- afferent arteriole > glomerulus > efferent arteriole
Where does the blood go after it leaves the efferent arterioles?
- peritubular capillaries
- vasa recta
What is the venule system within the kidney towards the renal vein?
- interlobular vein
- arcuate vein
- interlobar vein
- renal vein
What are the ureters made from?
Lining of smooth muscle fibres that propel urine (peristaltic waves) to the bladder
How long are the ureters?
25-30 cm long
1.5 mm diameter
Where are the ureters found?
- retroperitoneal
- lateral to the tips of the transverse processes of the lumbar vertebrae
What are the different segments on the ureter?
Ureter comes out of the kidney at the pelviureteric junction (PUJ)
- abdominal segment (proximal)
- pelvis segment (middle)
- intramural segment (distal)
Where is the most common area for ureteric injury?
Pelvic brim
Where does the ureter cross the sacrum?
S1 joint
Where do the ureters enter the bladder?
Posteriorly
How do the ureters enter the bladder and what is the point called where they enter?
At an oblique angle
- Vesicoureteral junction is where the ureters enter the bladder
- the urine then pushes the opening closed, stopping reflux of the urine back up the ureters due to the oblique angle
What forms the trigone?
-2 ureteric openings in the bladder
-tip of the bladder
Forms a triangle down to the internal urethral meatus (sphincter of the bladder)
What muscle is our bladder made from?
Detrusor muscle. This has folds called rugae. As people age, sometimes the muscle can thin.
What is the function of rugae?
To allow the bladder to contract and expand
What is the bladder lined with?
Transitional epithelium: urothelium
Where does the bladder rest when it is empty?
Rests on symphysis pubis (behind)
Women-in front of vagina/uterus/rectum
Men- in front of rectum
How much can the bladder hold?
750ml of fluid
Where do you find the urothelium?
- lumen of ureter
- bladder
- pelvis of kidney
Why are women more prone to UTI’s?
Because the external urethral meatus is very close to the vaginal opening
What are the urethral divisions in women?
- uteric openings
- trigone
- internal urethral sphincter
- urogenital diaphragm including external urethral sphincter (voluntary control here)
What are the urethral divisions in men?
- internal urethral sphincter (meatus)
- prostatic urethra (urethra through prostate gland)
- external urethral sphincter (urogenital diaphragm)= voluntary control of urination, here it is called the membranous urethra
- bulbous urethra (as it passes through bulbous muscle)
- penile/spongy urethra (as passes through penis)
- navicular fossa (opens out slightly)
- external urethral meatus
