11. Urinary System Flashcards
Give urinary system components
Two kidneys
Two ureters
One bladder
One urethra
Name urinary system functions
- Filter/excretion of unwanted substances
- Water/electrolyte balance
- Body fluid pH regulation
- Hormone production (EPO, calcitriol)
- Regulation of red blood cell production
- Regulation of blood glucose levels
- Regulation of blood pressure, volume, osmolarity
What are electrolytes?
Electrolytes are charged atoms in solution (they conduct electricity)
What is the optimum blood pH balance?
Blood pH must remain between 7.35-7.45 (mildly alkaline)
What is calcitriol?
Active form of vitamin D
What is erythropoietin?
Protein hormone that stimulates erythropoiesis in the red bone marrow
What is the normal blood glucose level?
4-7 mmol/L
How does the amount of urine excreted affect blood volume, pressure, concentration?
More water excreted = lower BP
Less water excreted (more conserved in blood) = increased BP
Kidney shape and location
Reddish, bean-shaped
Retroperitoneal (behind peritoneum)
Partially protected by 11th and 12th pairs of ribs between vertebral levels T11-L3
Right kidney is lower due to liver on same side
Kidney: external layers
- Renal capsule (deep layer)
- Adipose capsule (middle layer)
- Renal fascia (outer layer)
Kidney: internal regions
- Renal cortex: outer, light red area
- Renal medulla: darker area composed of several cone-shaped structures (renal pyramids)
Minor calyces
These surround the renal papillae of each pyramid and collects urine from that pyramid
Major calyces
Formed where several minor calyces converge
Kidney blood supply
Renal artery
20-25% of cardiac output (despite kidney representing 0.5% of body weight!)
1.2L/min
Renal vein
drain deoxygenated blood to Inferior Vena Cava
Nephron: definition
Functional unit of the kidney
More than 1 million per kidney
Single epithelial layer throughout
Nephron: regions
Renal corpuscle
Renal tubule
Nephron: anatomical labels to know
Glomerulus
Bowman’s capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
Afferent arteriole
Efferent arteriole
Peritubular capillaries
Ureters: function and length
Two ureters transport urine from the renal pelvis to the bladder
Each ureter is around 25-30cm long and retroperitoneal
Ureters: layers
- Inner mucous membrane
- Muscularis
- Adventitia
Bladder: definition
Hollow, muscular organ held in place by folds of peritoneum
Acts as a reservoir for urine
Becomes spherical as it accumulates urine
Collapses when empty
Trigone
Small, triangular area on posterior floor of bladder
Bordered by two ureteral openings and the urethral opening
Bladder: layers
- Inner mucosa layer
- Muscularis (detrusor muscle)
- Adventitia
Urethra
Tube leading from the bladder to the exterior of the body
Between the internal urethral sphincter (involuntary) and the external urethral sphincter (voluntary)
Female urethra = 4cm
Male urethra = 20cm
Urethra: male
Around 20cm long
Divided into three sections:
- Prostatic
- Membranous
- Spongy
Passes through the prostate where it receives semen during ejaculation
Urine formation: processes
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
Blood constituents that CAN pass into the glomerular filtrate
Water
Mineral salts (electrolytes)
Amino acids
Glucose
Ketoacids
Hormones
Creatinine
Urea
Uric acid
Toxins
Blood constituents that CAN’T pass into the glomerular filtrate
Erythrocytes
Leukocytes
Platelets
Plasma proteins
Renal capsule
Deep layer of outer region of kidney
Smooth, transparent sheet of connective tissue
Maintains kidney shape
Adipose capsule
Middle layer of outer region of kidney
Mass of fatty tissue
Provides protection and support
Renal fascia
Outer layer of outer region of kidney
Thin layer of connective tissue
Anchors kidneys to surrounding structures and keeps them in place
Renal cortex
Superficial, light red area of the kidney
The renal corpuscle and both convoluted tubules (proximal and distal) lie in the renal cortex
This means that filtration of blood (in the renal corpuscle) occurs in the renal cortex
Renal medulla
Darker area of the inner region of the kidney
Composed of several cone-shaped structures (renal pyramids)
Contains Loop of Henle (part of renal tubules)
How does urine get from the kidneys to the bladder?
Peristaltic contractions of the ureters’ muscular walls propel urine towards bladder
Aided by gravity and pressure of urine
1-5 waves per min
Where do the ureters enter the bladder?
Through the posterior wall
What prevents the backflow of urine?
A physiological valve
Ureter: Inner mucous membrane
Transitional epithelium which is able to stretch
Also contains goblet cells which secrete mucous
Provides protection from urine
Ureter: Muscularis
Smooth muscle fibres
Produces peristaltic contractions
Ureter: Adventitia
Outer coat of connective tissue
Contains blood and lymph vessels, nerves
Bladder: Inner mucosa layer
Transitional epithelium supported by connective tissue
The mucosa folds to permit expansion of the bladder
Bladder: Muscularis (detrusor muscle)
Middle layer of smooth muscle
At urethral opening, smooth muscle fibres accumulate and form the internal urethral sphincter (involuntary)
Bladder: Adventitia
Outer layer of connective tissue
What enables filtration to take place at the golmerular capillaries?
- The diameter of the efferent arteriole is less than that of the afferent arteriole
- Glomerular capillaries are ~50x leakier than normal capillaries
- Glomerular capillaries have a large surface area
How is net pressure achieved in golmerular filtration?
- Blood pressure forces substances through the membrane
- Proteins present in blood plasma within the glomerular capillaries oppose filtration (colloid osmotic pressure)
- Back pressure of the fluid that’s already filtered opposes filtration (capsular hydrostatic pressure)
What is the glomerular filtration rate (GFR)?
The amount of filtrate formed in the renal corpuscles of both kidneys each minute
Normal GFR should be over 90ml/min
GFR males = 125ml/min
GFR females = 105ml/min
How is GFR calculated?
Through a blood test
What can the GFR test result determine?
The severity of kidney disease
What can affect the GFR?
Anything affecting the 3 filtration processes e.g. severe blood loss
What is colloid osmotic pressure?
Osmotic pressure exerted by plasma proteins e.g. albumin
What can affect colloid osmotic pressure?
Damage to the glomerular capillaries premitting plasma protein loss into urine (albuminuria)
What happens when albumin leaks from blood into the filtrate (urine)?
Blood volume decreases and interstitial fluid volume increases causing oedema (note: there are other causes of oedema)
Albuminuria
Albumin in urine
Where does most tubular reabsorption happen?
In the renal tubules and collecting ducts but mostly in the PCT
What substances are reabsorbed during tubular reabsorption?
Water (65% in PCT)
Amino acids
Glucose
Electrolytes
Which mode of transport is used when substances are reabsorbed during tubular reabsorption?
Active and passive
Substances pass into peritubular capillaries and return to general circulation
What substances are secreted into the urine during tubular secretion?
Waste products - creatinine, ammonium ions, urea
Certain drugs e.g. penicillin
Excess ions e.g. H+ for pH regulation
Which hormones are involved in kidney reabsorption?
Angiotensin II Aldosterone Antidiuretic hormone Atrial natriuretic peptide Parathyroid hormone