Lecture 3: Anatomy, Embryology and Imaging of the Kidneys Flashcards
What is the functional unit of the kidney?
Nephron
How are kidneys positioned in the body?
Right kidney is LOWER than the left kidney because of liver
Which kidney is higher than the other?
Left kidney is higher than the right
What is BUN?
Blood Urea Nitrogen
Normal values = 8-20 mmol/L
What is the difference between acute and chronic kidney disease?
Acute = reversible
Chronic = irreversible
Symptoms are similar
Symptoms of kidney failure are subtle up until patients lose more than 90% of kidney function
How do you tell the difference between chronic and acute injury of kidneys?
Look at kidney size
Small size = chronic irreversible disease
Bigger = better
What are the general gross features of the kidney?
Retroperitoneal
Surrounded by fascia and adipose tissue
Superior border = T12
Inferior border = L3
Is there a safe place to do an anterior needle biopsy?
No because there are too many structures in the way
You want to biopsy posteriorly
What is the kidney’s anatomical relationship to the diaphragm?
Kidney is close to diaphragm and moves when you breath
What are the pertinent points regarding the anterior and posterior relationships of the kidneys?
- Most of the posterior and lateral aspects of the kidney are protected by muscle and adipose
- Difficult to access kidneys from anterior approach
- Percutaneous approach from back
- Kidneys are susceptible to blunt and penetrating injuries
What are the pyramids of the kidney?
Sections of the medulla
Triangular structure ends in minor calices
What are the renal columns of Bertin?
They are the areas in between the
Medullary pyramids
What are the minor and major calices?
Urine first starts collecting into minor calices
Drains into 3 major major calices
What is the renal pelvis?
The area where the three main renal major calices drain into
Pelvis will then drain into the ureter
What are the renal sinuses?
Space between minor/major calices
Contains fat and vessels
What is the base of the renal pyramid?
The thicker portion of the pyramid of the medulla
After the urine goes through the collecting tubule, where does it go?
Goes into the ducts of Bellini
Goes into the ducts of Bellini
The ducts that collecting ducts drain into
Will then turn into the summit of the papilla
What is the papilla?
The location where the medullary pyramids empty urine into the minor calyx of the kidney
Marked histologically by medullary collecting ducts converging to form a duct of Bellini
Transitional epithelium begins to be seen here
Latin for nipple (area of the converging point of the pyramids)
What is the route of urine transport?
Pyramid (collecting ducts) Ducts of Bellini (at papilla) Minor calices Major calices Renal Pelvis Ureter
What is hydronephrosis?
The build up of fluid in the kidney due to obstruction
What supplies the kidney?
Renal artery
What are the characteristics of renal artery?
Gives off first the inferior suprarenal artery Then Gives off five SEGMENTAL arteries (segmental because each supplies a particular segment): i. superior segmental artery ii. anterior superior segmental artery iii. anterior inferior segmental artery iv. Inferior segmental artery v. Posterior segmental artery
What happens if segmental artery is occluded?
That segment of the kidney will become infarcted
Approximately 20% of tissue could be lost
Can occur by
i. embolus
ii. coil embolization of segmental artery
What is the order of renal arteries?
- Main renal artery
- Segmental renal arteries
i. superior
ii. anterior superior
iii. anterior inferior
iv. inferior
v. posterior - InterLOBar arteries
- Arcuate arteries
- InterLOBULar arteries
- INTRAlobular arteries/arterioles
What are voiding related problems?
Inability to excrete urine
What are the characteristics of ureters?
Tubing that connects renal pelvis to urinary bladder
Runs downward and medial toward the FRONT of the psoas muscle
Abdominal part lies behind the peritoneum on medial part of psoas major
Opens into the fundus of the bladder
Can run anterior to common iliac artery
What are the characteristics of the ureter tubes?
Thick walled narrow cylindrical tube Composed of 3 coats i. fibrous ii. muscular iii. mucous coat
How do ureters run into the bladder?
They run OBLIQUELY
Significance = if bladder contracts or overflows, the ureter opening into the bladder is very easily compressed and closed
If this lasts too long, it can obstruct the ureter
What is a viscus?
Singular for viscera
Any large interior organ in any of the three great body cavities
Usually abdomen
What are factors that can obstruct the ureters from within?
- kidney stones
5mm needs an intervention - tumors
- blood clot
What are possibilities of extrinsic obstruction of the ureters?
- iliac artery aneurysm
- malignancies in adjacent structures such as lymph nodes/cervical cancer
- retroperitoneal fibrosis
- damage during surgery
- bladder disease
- congenital anomalies along course of ureters
What are the key characteristics of the bladder?
A musculomembranous sac that acts as reservoir for urine
What is the trigone?
The tips at which the ureters enter and the opening through which urine leaves (these 3 points = trigone)
What is the muscle responsible for squeezing the urine?
The detrusor muscle
What is the detrusor muscle?
The muscle that is responsible contracting bladder
What are the layers of the bladder?
- mucosa
i. transitional epithelium
ii. Lamina propria - submucosa
- detrusor muscle
- adventitia
What are the key characteristics of the male urethra?
Extends from internal urethral orifice in urinary bladder to external urethral orifice at end of penis Up to 20 cm long Divided into three portions i. prostatic ii. membranous iii. cavernous
What are the three portions of the male urethra?
- prostatic
- membranous
- cavernous
What are the key characteristics of the female urethra?
- narrow membranous canal
- 4cm long
- situated BEHIND the symphysis pubis
- imbedded in anterior wall of the vagina
Easier to get UTI than males because it is about 16 cm shorter
Where do the kidneys arise from?
The intermediate mesoderm
Differentiates to nephrogenic cord
What is the relationship between the embryological formation of the urinary and reproductive systems?
They are viewed together because they both arise from common embryological origin
Both come from intermediate (lateral) mesoderm
What are the three excretory organs that develop from the nephrogenic cord?
- Pronephroi
- Mesonephroi
- Metanephroi (permanent kidney)
What are the characteristics of the pronephros?
Develops during 3rd week but regresses but 5th week
What are the characteristics of the mesonephros?
Present at 3rd/4th week until the 12th week where it appears caudal to pronephros
Can make urine at 5th week
Consists of excretory tubules that contact a blood vessel medially and enter the mesonephric (Wolffian) duct laterally
In women, the mesonephros completely regress
What does the mesonephros form in males?
- testes
- epididymal ducts
- vas deferens
What are the key characteristics of the metanephros?
Develops at fifth week
Arises from mesenchymal nephrogenic blastema by ureteric bud
Ureteric bud induces nephron formation
After week 36, no nephrons being formed…architecture is complete
What happens to premature babies?
Not enough nephrons are formed, since week 36 is when nephron formation is complete
What happens after termination of nephrogenesis?
Growth
Differentiation
Remodeling of kidney tissue
What induces the formation of nephrons?
The ureteric bud
What is the metanephric blastema?
The mesenchyme
Secretes growth factors that induce
Growth of ureteric bud from caudal
Portion of mesonephric duct
What are the characteristics of the ureteric bud (metanephrogenic diverticulum)?
Proliferates and responds by secreting growth factors that stimulates differentiation of metanephric blastema into glomeruli and kidney tubules
Undergoes mesenchymal to epithelial transition
What are the derivatives of the ureteric bud?
- ureters
- minor calyces
- major calyces
- collecting tubules
- Ducts of Bellini
Each of these are the result of ureteric bud differentiation or arborization
What is the relationship between the mesenchyme and the ureteric bud?
Mesenchyme and ureteric bud reciporocally induce each other to form 1 million nephrons in kidney
What happens if there is a premature division of the ureteric bud?
Duplication of urinary tract
Can even have two separate kidneys if premature division occurred early enough
What are the derivatives of the metanephric blastema (mesenchyme)?
- podocytes covering glomerular capillaries
- epithelial cells lining Bowman’s capsule
- Proximal convoluted tubules
- Descending thick limb of LoH
- Thin limbs of LoH
- Ascending thick limbs of LoH
- DCT
Basically all the portions of the glomerulus and nephrons
Where do nephrons/glomeruli come from?
The metanephric mesenchyme or the metanephric blastema
Where do the collecting ducts/major/minor calices/renal pelvis come from?
Ureteric bud which stems off the mesonephric duct
What is aplasia?
Aplasia implies that one or both kidneys have failed to develop
If aplasia is bilateral, no urine production in fetus = severe oligohydramnios
Leads to Potter sequence
What is the function of the kidney as an embryo?
Amniotic fluid is swallowed and reabsorbed by GI tract
Kidney excretes amniotic fluid to replenish the external amniotic fluid volume
Thus excretion = 1/3 of embryo’s amniotic fluid volume
If kidney’s don’t work or have undergone agenesis, then you get oligohydramnios (not enough amniotic fluid)
What is oligohydramnios characterized by?
Less amniotic fluid than normal in amniotic cavity
Caused by baby’s inability to excrete amniotic fluid
What is Potter’s sequence?
The result of oligohydramnios as a consequence Of in utero kidney dysfunction Fetus has following features: i. sloped forehead ii. parrot beak nose iii. low slung ears iv. shortened fingers v. internal organ abnormalities
How does the kidney migrate to its ultimate position?
Metanephric kidneys start at tail of embryo
Vascular buds from kidney grow toward and invade the common iliac arteries
Growth of embryo in length causes kidney to ascend to final position
Don’t drag blood supply with ascent
Sends out new, more cranial branches
Induces regression of more caudal blood vessels
What are ectopic kidneys?
Kidneys in an incorrect position
All ectopic kidneys are malrotated
What are malformations related to the ascent of the kidney?
- pelvic kidney
- horshoe kidney
- supernumerary arteries
What are the characteristics of pelvic kidney?
Kidney stays in the pelvis rather than ascending
What are the characteristics of horseshoe kidney?
Two developing kidneys fuse ventrally into a single horseshoe shape trapped in the abdomen by inferior mesenteric artery
What are the characteristics of supernumerary arteries?
More than one renal artery per kidney
Often asymptomatic but can sometimes compress the ureter
Causes hydronephrosis
Can complicate kidney transplant donation (not good to donate)
