Anatomy

Question 1

Urinary system: summarise the gross anatomy of the urinary system

Answer 1

function: to filter the blood, separating that which needs to be retained, from that which must be eliminated

1. Kidneys are responsible for the actual process of blood filtration
2. The remaining liquid, urine, is composed of all that should be eliminated from the blood
3. Urine leaves the kidneys, and is sent to the bladder, through tubes called ureters
4. The urine is stored in the bladder until it is time to urinate
5. The bladder will drain through the urethra.
   
   • This transport and storage system: stores the waste, protects the tissues from damage (wide range of pH and osmolarity of the urine), prevents infection by foreign organisms, provides reproductive functions (male)

Question 2

Recall the location and basic structure of the kidney

Answer 2

The Kidneys

• Retroperitoneal in upper abdomen lateral to vertebral column
• Overlapped postero-superiorly by the diaphragm and pleural cavity
• Full inspiration lungs bass between lower parts of diaphragm and ribs
• Kidneys extend from vertebra T12 to vertebra L3
• Right kidney is usually slightly lower than the left
• Superior pole of the R kidney lies at the level of the 11^th intercostal space and that of the L at the 11^th rib
• L nearer to the midline than R
• Hilum lies at about the level of L1 (R & L)

Basic structure:

• Bean-shaped
• Surrounded by (from inwards to outwards) :

1. dense fibrous capsule
2. Outside the capsule is a fascial pouch (renal fascia) containing the peri-renal adipose tissue (perinephric fat) : protective function
   
   • transversalis fascia splits around the kidney to give renal fascia
   • in some cases: fat is also posterior (close to transersalis fascia)
   • renal fascia is continuous to both sides
3. Transversalis abdominus muscle
4. Internal oblique muscle
5. External oblique muscle
6. Superficial fascia
7. Dermis
8. Epidermis (afta pou eipe o polonos gay sto anatomy)

Renal fat and fascia:

• lateral margins of kidney: the anterior and posterior layers of the renal fascia fuse with transversalis fascia
• above each adrenal gland, the anterior and posterior layers of the renal fascia fuse with the fascia of the diaphragm
• medially, the anterior fascia continues over the vessels in the hilum. connects to conective tissue of abdominal aorta and inferior vena cava (sometimes moves to other side to fuse with its companion fascia)
• posteriorly, it fuses with the fascia covering the psoas major muscle
• inferiorly, the anterior and posterior layers enclose the ureters
• final layer of paranephric fat (pararenal fat) acummulates posterior and posterolatery to the kidney

Question 3

Recall the kidney’s anterior relations to other structures

Answer 3

Anterior Relations

• Right kidney
  
  • small part of superior pole covered by right suprarenal gland
  • moving inferiorly, a big part of upper part of the anterior surface is against the liver, separated by petironeum
  • medially, hilus of right kidney lies behind descending part of duodenum (Part 2)
  • inferiorly associated with right colic flecure (hepatic flexure: underneath the liver, the large intestine turns to become transverse colon)
• Left: stomach:
  
  • superior pole - left suprarenal gland
  • superior pole: intraperitoneal stomach and spleen
  • moving inferiorly, retroperitoneal pancreas covers kidney
  • inferior lateral part covered by left colic flexure (splenic flexure: where transverse colon turns, flexure: attachments to posterior wall) and the beggining of descending colon and medially, by jejenum

Question 4

Recall the kidney’s posterior relations to other structures

Answer 4

Posterior relations:

• both kidneys related to similar structures
• superiorly
  
  • of both is the diaphragm
  • superior pole of right kidney is anterior to rib 12
  • superior pole of left kidney is anterior to ribs 11 and 12
• lateral edge: transversus abdominis
• midline: quadratus lumborum muscle
• medial edge: psoas major muscle (takes attachment from lumbar vertebrae)

Posterior to the kidneys:

• the pleural sacs (costodiaphragmatic recesses)
• subcostal vessels
• segmental nerves

1. last intercostal vessels
2. subcostal nerves
3. ilial-hypogastric and ilial-inguinal nerves

Question 5

Recall the macroscopic structure of the kidney and be able to identify these structures in histological sections

Answer 5

Kidney Structure

• Smooth anterior and posterior surface
• Covered by fibrous capsule
• Medial margin of kidney: hilum –> deep vertical slit through which renal vessels, lymphatics and nerves enter and leave
• Hilum is continuous with the renal sinus
• Perinephric fat continues into the hilum and sinus and surrounds all structures
• Human kidney is multilobar – like a lot of simple kidneys stuck together
• Each lobe drains through its own papilla and calyx

Kidney consist of renal cortex and inner renal medulla

• Cortex:
  
  • continous band of pale tissue surrounding medulla
  • granular-looking because of random organisation
  • extensions (renal columns) project into discontunuous aggregations of triangular shaped tissue (renal pyramids=medulla)
• Medulla:
  
  • Medulla striated because of radial arrangement of tubules and micro-vessels
  • bases of pyramids towards renal cortex while apex projects inward (towards renal sinus)
  • apical projection (renal papilla) is surrounded by minor caly
  • minor calices receive urine and represent the proximal parts of the tube (forming ureter)
  • renal sinus small callices unite to form major calyx
• Pelvis:
  
  • major calices unite to form renal pelvis (funnel shaped superior end of ureters)

Question 6

Renal vessels: explain the anatomy of blood vessels in the kidney and their functional significance (including filtration, reabsorption and countercurrent mechanism)

Answer 6

25% of resting cardiac output every minute is in the kidneys

• two major vessels: aortic and inferior vena cava
• left of the midline: aorta
• right of the midline: inferior vena cava
• implications for length of renal arteries and renal veins

Blood Supply via Renal arteries:

• Abundant blood supply via renal arteries - 2 lateral short direct branches from abdominal aortas
• Arise inferior to the origin of superioe mesenteric artery (between LI and LII)
• Left renal artery: arises a little higher than the right
• Right renal artery is longer and passes posterior to the inferior vena cava
• As each renal artery approaches the renal hilum, it divides into anterior and posterior branches –> supply the renal parenchyma
• Accesssory renal arteries: originate from the lateral aspect of abdominal aorta, enter the hilum (aka extrahilar arteries)

Renal Veins:

• left and right renal veins = anterior to renal arteries
• longer left renal vein: crosses the midline anterior to the abdominal aorta and posterior to the superior mesenteric artery –> can be compressed by an aneurism in either of these 2 vessels –> causing blood to be occluded from left kidney to IVC
• lymphatic drainage is to the lateral aortic (lumbar) nodes around the origin of the renal artery
• Renal veins drain into the IVC

Other vessels:

• Gonadal arteries are paired and arise below renal arteries (L2)
• Superior mesenteric (bifurcates at L1)
• Inferior mesenteric artery supplies the hindgut (bifurecation under superior mesenteric at L3)
• Lumbar arterires: L1-L4
• Gonadal veins
  
  • the gonado veins drain assymetrically
  • right gonado vein drains directly from IVC
  • left side drains from left renal vein

Arrangement of blood supply of hylum:

• inside the kidney: arteries & veins become very closely related
• large number of branches (rediograph with contrast)
• during development kidney develops as a number of functional discrete lobueles which coalesce into one structure (developmental lobules)
• accessory ureters are a possibility (not abnormality just failure of developmental process)
• structure: outter cortex and medulla drains into minor calis then –> major calis –> pelvis –> ureter
• Blood from gut drains to the portal system

Question 7

Ureters: recall the functional anatomy of the ureters and mechanisms preventing reflux of urine

Answer 7

The Ureters

• Muscular tubes that transport urine from kidneys to bladder
• Continuous superiorly with renal pelvis
• Renal pelvis narroes as it passes inferiorly through the hilum of kidney and becomes continuous with ureter at ureteropelvic junction
• They run vertically down posterior abdominal wall in the vertical plane of the tips of the transverse processes of the lumbar vertebrae (medial aspect of psoas major muscle)
• Cross the pelvic brim anterior to the sacro-iliac joint & bifurcation of the common iliac arteries
• Cross either the end of the common iliac artery or the beggining of the external iliac artery
• Descend anteromedially to enter bladder at the level of the ischial spine
• Ureters run obliquely into bladder to prevent backflow

At 3 points along their course the ureters are constricted:

1. pelviureteric junction (junction renal pervis and utreter)
2. where ureter crosses common iliac vessels atpelvic brim
3. where ureter traverses bladder wall

=kidney stones can become lodged at these constrictions

• Urine transported by peristalsis of their smooth muscle walls
• Move urine down by peristalsis
• Open obliquely through bladder wall
• Made of transitional endothelial : tight junctions –> when there is no urine the layers manage to move over each other so it looks multilayers but it isn’t
• If you strench the layers separate out to its is not strantified

Question 8

Discuss ureteric vasculature

Answer 8

Ureters receive arterial branches from adjacent vessels as they pass toward the bladder:

1. Renal arteries supply the upper end
2. Middle part: branches from abdominal. testicular or ovarian arteries, and the common iliac arteries
3. Pelvic cavity: the ureters are supplied by one or more arteries from branches of the internal iliac arteries

Question 9

Bladder: recall the structural and functional anatomy, and histological features of the bladder; recall the mechanisms involved in reflex contraction in response to distension

Answer 9

Bladder

• Pelvic organ / mainly abdominal
• Completely full: superior surface raises in abdominal cavity can be accessed from anterior wall catheter –> pushes the peritoneum upwards
• Lies anterior to the uterus in females, posterior to the pubic bone and anterior to the rectum
• Partially retroperitoneal, with its peritoneal-covered “dome” projecting into the abdomen when the bladder is distended with urine
• Triangular pyramid with apex pointing anteriorly and base posteriorly
• Lined by urothelium (transitional epithelium same with ureters - structurally suited for the large volume fluctuations of the bladder )
• 3-layered epithelium with very slow cell turnover (transitional epithelium - lamina propria - submucosa)
• Large luminal cells have highly specialised low-permeability luminal membrane –> Prevents dissipation of urine-plasma gradients
• Muscular layer of smooth muscle (aka detrusor muscle)–> able to change its length to accommodate the movement of urine into and out of the bladder.

Structure:

• Triangle formed by the entrance of ureters into the bladder and the exit of the urethra
• That triangle forms smooth area (triagnone of bladder)
• Tightly adherent to the layers below bladder (cancers usualy arise here)
• Ligament around the urethra (pubic vesicle ligament) –> holds it in place
• Urethra passes through perineal membrane (fixed structure: important because withtin it lies the external sphincter)
• Male: bladder is separated by the prostate gland (prosttatic ligament around it)–> urethra runs through the prostate

Question 10

Urinary sphincters: compare the sphincter urethrae and sphincter vesicae muscles and their nerve supplies

Answer 10

Urinary Sphincters

1)Sphincter vesicae (internal sphincter – smooth muscle)

• At neck of bladder
• Reflex opening
• In response to bladder wall tension
• Relaxed by parasympathetic NS
• Contracts by sympathetic NS

2) Sphincter urethrae (external sphincter – striated muscle)

• In perineum
• Tone maintained by somatic nerves in pudendal nerve (S2, 3, 4)
• Opened by voluntary inhibition of nerves
• In males:
  
  1. internal sphincter
  2. urogential diaphragm (where the porstate ends)
  3. urogenital sphincter

Innervation:

1) Internal sphincter opens by parasympathetic control and forces urine out

1. Bladder fills
2. stretch receptors in the wall sense the stretch
3. send signals by parasympathetic sensory fibre
4. parasympathetic nerves from S2,3,4 cause contraction of the bladder – wall- bladder contracts – releases the internal sphincter- forces urine out

2) External sphincter

1. Efferent axons from cerebral cortex send positive feedback down to external sphincter to keep it close at all times
2. This is kept close by parasympathetic nerves -> sometimes symphateic innervation – closes it during ejaculation to prevent backflow of semen
3. Stretch receptors in bladder wall run to spinal cord and at this level they can inhibit the voluntary action of the nerve by sending efferent negative input
4. The external sphincter opens

Question 11

Distinguish between male and female urethra

Answer 11

Urethra

• The urethra tracks posterior and inferior to the pubic symphysis
• Proximal urethra is lined by transitional epithelium, whereas the terminal portion is a nonkeratinized, stratified squamous epithelium
• Females: straight and short passes through the urogenital diaphragm
• Males:
  
  • Passes through the prostate (sometimes constrictions), pass through urogenital diaphragm –> through the penis (almost right angle) + another right angle