Anatomy and Pattern recognition of the urinary system Flashcards
Overview of the urinary system
The main components of the urinary
system
• 2 kidneys – secret urine
• 2 ureters – transport urine to the
bladder
• Urinary bladder – collects and holds
urine
• Urethra – transports urine externally
• Adrenal glands – produces hormones
• The urinary system is closely linked with
the genitals – the genitourinary system
• Urology is the study of the male / female
urinary and male reproductive systems
Functions of the urinary system
It is the body’s main excretory system
• The kidneys are the main functional
component – specifically the nephrons
• Other structures are primarily for transport
and storage
• Functions of the kidneys include
• Homeostasis of water and electrolytes
• Excretion of metabolic waste, chemicals and
drugs
• Hormone and enzyme production
• Production, storage and excretion of urine
• Kidneys filter approximately 200litres of
fluid from blood per day
• Most water and solutes returns to blood
• Excesses, toxins and waste is removed in
the urine
Functions of the kidneys – detailed
• Excretion – fluid and waste are passed through the
urinary system and pass out of the body
• Regulation of blood composition and concentration
(osmolarity), electrolytes/ions
• Regulate the concentration of major ions such as calcium, potassium, calcium, vitamin D etc.
• Regulation of blood volume and interstitial fluid
• Excrete/preserve water
• Regulation of red blood cell synthesis – secretion
of erythropoietin
• Regulation of blood pressure
• Regulation of blood volume
• Production of enzyme renin, with the effect of
increasing blood pressure (renin-angiotensin
pathway)
• Regulation of blood pH
• Acid-base balance; H+ and HCO3
- ions
• Regulation of calcium homeostasis
• Release of hormone calcitriol – activated
form of Vitamin D
• Red blood cell production
• Release of hormone erythropoietin –
stimulates production of red blood cells
• Regulation of blood glucose
• Production of glutamine –
gluconeogenesis to produce glucose
• Excretion of metabolic waste products and toxins
• Urine
• e.g ammonia, urea, bilirubin, creatinine,
uric acid, drugs
The kidneys
The are paired structures on the posterior abdominal wall, lateral to the transverse process of the spine
Ovoid in shape – 10-12cm long, 5-7.5cms wide and 2.5cm thick.
They are retroperitoneal structures – fixed in place
Anatomical location – T12-L3
They are partially protected by the ribs (11 and 12th ribs)
The level of the kidney changes with respiration
The lie obliquely with the upper pole being more medial and posterior than the lower pole which is more anterior and lateral
Right kidney
Right kidney
• Situated in the right
hypochondrium and
right lumbar
regions
• Superior
• Right adrenal gland
• Anterior
• Right lobe of liver
• Duodenum
• Hepatic flexure
• Posterior
• Right hemidiaphragm
• Posterior
abdominal wall
Left kidney
• Approximately 2.5cm higher
than the right kidney
• Situated in the left hypochondrium
and left lumbar regions
• Superior
• Left adrenal
gland
• Anterior
• Spleen
• Stomach
• Pancreas
• Jejunum
• Splenic flexure
• Posterior
• Left
hemidiaphragm
• Posterior
abdominal wall
The kidneys – supporting tissues
Attachment and protection from trauma and infection
• Outer renal fascia –
• Fibrous connective tissue surrounding kidneys and
adrenal glands
• Anterior – Gerota fascia
• Posterior – Zuckerkandl fascia, fuses with
posterior abdominal wall
• Middle Perirenal / perinephric fat
• Approximately 2.5cm thick
• Deep peripheral fibrous capsule of kidney
• Smooth transparent membrane; collagen and elastin
• Maintains shape
Perirenal space / sin
• Deep to renal fascia
• Continuous across both
sides, passes anterior to
spine
• Contains both:
• Kidneys
• Adrenal glands
• Renal vessels and hila
• Perirenal fat
Gross anatomy of the kidney
• Bean-shaped
• Convex laterally
• Concave medially
• 10-12cm long, 5-7cm wide, 3cm thick
• Left normally slightly longer and
thinner
• 150 grams
• Hilum medially (small depression on
the concave, medial aspect)
The kidneys – internal structure
• Peripheral fibrous capsule
• Functional portion (parenchyma) of organs made up of:
• Cortex
• Reddish-brown granular tissue
• Surrounds and extends into medulla
• Extend internally between pyramids- renal columns
• Medulla
• Darker in colour
• Contains cone-shaped renal pyramids –
approximately 8-18
• Striped appearance – tubules and capillaries
• Central apex – renal papilla
• The tips of the pelvis drain into the minor calyces then the major calyces and then the single renal pelvis to the ureter
• Calyces (singular – calyx)
• Collect urine from papillae
• (8-18) minor to major (2/3) calyces
• Transitional epithelium lined –
impermeable
• Smooth muscle walls – peristalsis
of urine
• Renal pelvis
• Direct continuation from calyces
(similar structure)
• Funnel-shaped
• Continuous with ureter
Renal hilum
• Renal artery enters, renal vein exits
• Lymphatic vessels and nerves
• Ureter exits
• Renal sinus
• Cavity inside medulla
• Contains calyces, renal pelvis, and
blood vessels
Microscopic anatomy of the
kidney
• Made up of:
• Nephrons – the functional unit of the
kidney; 1-2million per kidney
• Collecting ducts
• Fewer in number (1000s); drain several
nephrons
• Drain urine from nephron through renal
pyramids to calyces
• Give striated appearance to pyramids
• Supported by connective tissue and
neurovascular structures to supply tissues
• Lined with:
• Principal cells – receptors for antidiuretic and aldosterone hormones; maintain water and Na+
• Intercalated cells – role in homeostasis of
blood pH. Microvilli on surface.
Nephrons – key fac
• Homeostasis of blood composition
• Urine production
• Three processes:
1.Glomerular filtration (takes it all
out to a separate vessel)
2.Tubular reabsorption (takes what
it needs back; most of it)
3.Tubular secretion (gets rid of
what’s left
• Fluid taken out of blood at first stage is
known as filtrate
• Urine only at the end of the three
processes (passed into collecting ducts)
What is the nephron?
• Ensure homeostasis of blood and urine
production
• Three main processes:
• Filtration of blood
• Return necessary substances to blood
• Remove unwanted substances from body
• Two parts:
• Renal corpuscle (in cortex) – filters blood
• Glomerulus
• Glomerular (Bowman’s) capsule
• Renal tubule (partly in medulla in mid part) –
carries fluid from plasma
• Surrounded by capillary networks to
reabsorb most of fluid and solutes
• Two types dependent on location and
minor differences in structure and
blood supply:
• Cortical 85%
• Located in renal cortex except small part
extending into medulla
• Surrounded by peritubular capillaries
• Juxtamedullary
• Located closer to cortex/medulla junction
• Loop extends deep into medulla
• Role in producing concentrated urine
• Surrounded by Vasa recta capillary network
Renal corpuscle - glomerulus
• Literally means ball of wool
• Very convoluted bunch of tiny arterial
capillaries
• From afferent arteriole, leaves via
efferent arteriole
• Fenestrated – lots of pores to allow
free passage of fluid and solutes
• High pressure throughout – helps
filtration process
What is the Glomerular (Bowman’s) capsule
• Cup which surrounds most of the
glomerulus; ‘catches the filtrate’
• Two epithelial layers:
• External parietal layer – simple
squamous epithelium
• Inner visceral layer – highly modified
cells called podocytes
• octopus-like ‘foot cells’
• cling to glomerulus
• Filtration slits between ‘foot cells’
• Capsular space between layers
drains into proximal convoluted
tubule
• One associated with each nephron
within ascending limb of nephron loop,
close to afferent arteriole
• Helps regulate:
• Rate of formation of filtrate
• Systemic blood pressure
• Three types of cells:
• Macula densa: chemoreceptors to
monitor NaCl levels entering the DCL
• Granular (or JG) cells:
• smooth muscle – mechanoreceptors to sense
blood pressure
• Secrete renin hormone
• Extraglomerular mesangial cells – pass
signals between other cells
What are renal tubules?
• About 3cm long, divided into 3 parts:
• Proximal convoluted tubule
• large mitochondria within epithelial cells
• covered in microvilli to increase surface area
to allow increased capacity
• Nephron loop (loop of Henle)
• Descending and ascending limbs
• Different types of epithelial cells result in
thin and thick segments
• Distal convoluted tubule
• Similar to PCT
• Fewer microvilli
Blood supply
• Essential to understand function and
physiology of the kidneys
• Quarter of entire blood volume passes through
kidneys every minute – approx. 1.2 litres per minute
• Each supplied by own renal artery
• Branch of abdominal aorta, inferior to superior mesenteric artery
• Left about L1
• Right about L2, longer, passes posterior to IVC
• Divide before hilum into anterior/posterior branches to parenchyma
• Additional accessory arteries common
• Considered vulnerable as no effective
anastamoses
• Branches of renal arteries into several
segmental arteries
• Divide into interlobular arteries towards
renal columns
• Arch along border of renal pyramids and
cortex as arcuate arteries
• Numerous branches radiate towards
periphery of cortex; cortical radiate
arteries
• Numerous afferent arterioles, one per
nephron…..
• Multiple small renal veins drain
into single left and right renal
veins
• Anterior to renal arteries
• Left longer and passes anterior
to abdominal aorta
• Drain into inferior vena cava at
similar level
• Lymphatic drainage into lumbar
lymph nodes near renal artery
origin
What are ureters?
• Carry urine from kidneys to urinary bladder
• Continuous with renal pelvis
• 25-30cm long, 3mm in diameter
• Retroperitoneal, anterior to Psoas muscles, over brim of pelvis
• Passes obliquely into posterior aspect of bladder –
vesico-ureteric junction (VUJ)
• Pressure in bladder compresses distal ureter to prevent reflux
• Peristalsis to help gravity propel urine – 1-5waves per minute
• Comprised of 3 layers:
• Peripheral protective fibrous
tissue (adventitia), continuous
with renal capsule
• Middle muscular layer to propel
urine:
• Internal longitudinal
• External circular
• External longitudinal (distal 1/3 only)
• Inner protective mucosa
• Transitional epithelium
• Protects from urine
The urinary bladder
• Temporary storage/reservoir for urine
• Smooth muscular sac, collapsed when
empty
• Retroperitoneal on pelvic floor,
posterior to symphysis pubis
• Relational anatomy dependent on sex
• Lies in pelvic cavity but changes
position and size when distended,
moves into abdominal cavity
• Three layers (similar to distal ureter):
• External fibrous tissue (peritoneum
superiorly)
• Middle thick smooth muscular layer;
detrusor
• Internal mucosal layer
• Three orifices on base for bilateral
ureters and urethra
• Smooth triangular region on base
called trigone; sensitive
• Allows micturition to be infrequent
and controlled
• Pyramidal shape when empty
• Walls fold into rugae (like
stomach)
• As fills, walls thins and rugae
lost
• Allows distension without increase in pressure
• Normally holds 300-500mls
• Can hold up to 800mls
What is the urethra?
• Tube extending from neck of bladder to
external urethral orifice
• Approximately 4cm in females
• Approximately 20cm in males (prostatic,
membranous, spongy sections)
• Differences in structure due to different roles
• Thickening of detrusor muscle at junction;
internal urethral sphincter
• Involuntary – autonomic nervous system
• External urethral sphincter – skeletal
muscle as passes urogenital diaphragm
• Voluntary, assisted by levator ani muscle
Urine formation
Involves three processes
• Glomerular filtration:
• Blood pressure in the glomerular capillaries forces fluid and small molecules
out of the blood. Filtration is non-selective; based on size of molecules, those
small enough to fit through the filtration membrane are removed
• Tubular reabsorption:
• cells in the renal tubules contain transport proteins that return water and
some filtered molecules back into the blood in the peritubular capillaries
• Tubular secretion:
• certain tubule cells transport additional solutes from the blood into the filtrate
which may have not been filtered by the filtration membrane
Urea and uric acid excretion
• Urea is a by-product of amino acid metabolism; uric acid
is a by-product of nucleic acid metabolism.
• Urea is passively reabsorbed by diffusion but about 20%
of urea is excreted in the urine.
• Most uric acid is reabsorbed by active transport and a
small amount is secreted into the renal tubule.
Composition of urine
• 95% water
• Usually contains metabolic waste products: urea, uric
acid, and creatinine.
• Likely to contain trace amounts of amino acids and
varying amounts of electrolytes.
• Urine volume: 0.6 – 2.5 L/day; 50-60 mL of urine
output/hour is normal
• Volume varies with fluid intake and environmental
factors.
• <30ml/hour can indicate a problem
Micturition
• Emptying of the urinary bladder, ‘voiding’
• To allow this, three processes occur:
• Contraction of the detrusor muscle (smooth, involuntary)
• Opening of the internal urethral sphincter (smooth,
involuntary)
• Opening of the external urethral sphincter (skeletal, voluntary)
• Only final stage is voluntary, but needs to be trained
Micturition process
- Urine leaves the bladder by the micturition reflex.
- Detrusor muscle contracts forcing urine out of the urinary bladder, the external urethral sphincter relaxes.
- Stretching of the urinary bladder triggers the micturition reflex centre in the sacral portion of the spinal cord
- Parasympathetic impulses cause the detrusor muscle to contract in waves, urge to urinate is sensed.
- Voluntary contraction of the external urethral sphincter and inhibition of the micturition reflex from the brainstem and the cerebral cortex prevent urination.
- During urination, the external urethral sphincter is relaxed, and impulses from the pons and the hypothalamus facilitate the micturition reflex.
- When the detrusor muscle contractions become strong enough, the internal urethral sphincter relaxes and
forced open. - The external urethral sphincter composed of skeletal muscle is under conscious control, this opens, and
urine is expelled - Bladder can hold up to 600ml of urine but urge to urinate begins at ~150ml
What are the The adrenal glands (suprarenal)?
• Part of endocrine, not urinary system
• Paired glands on superficial aspect of kidneys, within renal fascia and fat
• Pyramid-shaped, 4cm long, 3cm thick
• Produce hormones for stress response (and electrolyte balance) – directed by
hypothalamus
• Arterial supply from branches from renal arteries and abdominal aorta
• Venous drainage by suprarenal veins; left into left renal vein, right into IVC
• Two parts with different structure and functions (effectively separate glands):
• Adrenal cortex – essential for life
• Adrenal medulla
What is the adrenal cortex?
• Bulk of gland, external to medulla
• Produce over two dozen steroid hormones - corticosteroids
• Three layers:
• Zona glomerulosa:
• Mineralocorticosteroids (including aldosterone)
• Balance of minerals and water in blood (particularly Na+ and K+)
• Zona fasciculata:
• Glucocorticoids (e.g. cortisol)
• Body metabolism
• Zona reticularis:
• Gonadocorticoids
• Androgens, sex hormones (converted to testosterone/oestrogen)
What is the adrenal medulla?
• Knot of nervous tissue
• Part of sympathetic nervous system
• Cells produce ‘fight-or-flight’ hormones catecholamines
• epinephrine
• norepinephrine
• Short acting effects:
• Increase heart rate and blood pressure
• Divert blood to essential organs by dilating their arteries and constricting less
important ones (e.g. skin)
• Increase metabolic rate
• Dilate pupils
