The renal system Flashcards
Where are the kidneys located?
In the retro-peritoneal cavity extending from T12-L3
Which kidney is slightly higher?
The left
What is the functional unit of the kidney?
The nephron
What is the structure of the kidney?
8-10 conical renal medullas separated and encased by the renal cortex. All encapsulated by the renal capsule, a protective layer of adipose tissue
What are the renal calyces?
Cup like projections of the renal pelvis that collect urine, sat at the base of the renal medullas.
Grouped into minor and major
What is the renal pelvis?
A large cavity containing major and minor calyces, blood vessels, nerves and adipose tissue
Which parts of the nephron sit in the renal cortex?
The glomerulus, bowmans capsule and convoluted tubes
Which parts of the nephron are in the renal medulla?
The loops of Henle
What proportion of cardiac output do the kidneys receive?
20-25% (≈1200ml/min in adults)
What blood vessels supply the kidneys?
Renal artery
Segmental artery
Interloblar arteries
Arcuate arteries
Interlobular arteries
Afferent arterioles
What is the vein structure of the kidneys?
Interlobular veins
Arcuate veins
Interlobar veins
Segmental veins
Renal vein
What layers line the glomerulus side of the bowmans capsule?
Negatively charged basement membrane
Visceral layer of epithelial podocytes and pedicels
What forms the slit diaphragm of the nephrons?
Podocytes linked with nephrin
What forms the renal corpuscle?
The glomerulus and the bowmans capsule
What is filtered in the renal corpuscle?
Blood plasma
What constitutes the renal tubules?
Proximal convoluted tubules
Loop of Henle
Distal convoluted tubules
What constitutes the loop of Henle?
Descending and ascending limb
What’s the difference between cortical and juxtamedullary nephrons?
Cortical nephrons have a loop of Henle lying mainly within the cortex
Juxtamedullary nephrons have a loop Henle extending deep into the medulla
What percentage of nephrons are cortical?
80-85%
What blood vessels supply cortical nephrons?
Peritubular capillaries
What blood vessels supply juxtamedullary nephrons?
The vasa recta
What are the functions of the kidney?
A WET BED
Acid base balance
Water balance
Electrolyte balance
Toxin removal
Blood pressure control
Erythropoietin production
D (Vitamin D synthesis)
How do the kidneys regulate acid base balance?
Excreting hydrogen ions (H+) in the urine
Conserving bicarbonate ions (HC03-) in the blood
How do the kidneys regulate water balance?
Separately regulating loss of water and solutes in urine
How do the kidneys maintain electrolyte balance?
Regulating reabsorption of blood ionic compounds.
How do the kidneys excrete waste and foreign substances?
Excreting them in urine
How do the kidneys regulate blood pressure?
Excreting renin
How do the kidneys contribute to erythropoesis?
Excreting erythropoietin
Where is vitamin D metabolised?
Kidneys and the liver
What 3 processes lead to the final production of glomerular filtrate?
Glomerular filtration
Tubular reabsorption
Tubular secretion
What three pressures contribute to glomerular filtration?
Glomerular blood hydrostatic pressure
Capsular hydrostatic pressure
Blood colloid osmotic pressure
What is usual glomerulus net filtration pressure?
10mmHg
What is glomerular blood hydrostatic pressure?
The blood pressure in the glomerular capillaries ≈ 55mmHg
What is capsular hydrostatic pressure?
Pressure exerted by the fluid already in the bowmans capsule and renal tubes back against filtration ≈ 15mmHg
What is blood colloid osmotic pressure?
The pressure difference created due to plasma proteins being present in blood ≈30mmHg
What is a healthy glomerular filtration rate?
125ml/min
Why are substances like amino acids and glucose not usually present in urine?
They are usually completely reabsorbed, unless present in the blood in excessive amounts
Which substances are not reabsorbed in the nephrons?
Substances that are not normal blood constituents i.e. waste
What is tubular reabsorption?
Transfer of substances from the renal tubules to the peritubular capillaries
What is tubular secretion?
Transfer of substances from the peritubular capillaries back to the renal tubes
Why may certain materials not be cleared from the blood via glomerular filtration?
Because of the short time blood remains in the glomerulus
Is tubular reabsorption a passive or active process?
Passive
Is tubular secretion a passive or active process?
Both passive and active
What are diuretics?
Substances that cause the kidneys to produce more urine
What is diuresis?
Increased or excessive production of urine
What is anti diuretic hormone?
A hormone that decreases the production of urine
How does anti diuretic hormone work?
It increases the permeability of the distal convoluted tubules and collecting tubules, increasing water reabsorption
Where is ADH secreted?
The posterior lobe of the pituitary gland
What cells release renin?
The juxtaglomerular cells located in the kidney
Where is angiotensin converting enzyme produced?
The lungs
What does angiotensin converting enzyme do?
Converts angiotensin 1 to angiotensin 2
What does angiotensin 2 do?
It is a generalised vasoconstrictor which increases blood pressure and stimulates the adrenal glands to release aldosterone
What does aldosterone do?
Increases sodium and water reabsorption and potassium excretion
When is atrial natriuretic peptide released?
In response to stretching of the atrial wall
What is the action of atrial natriuretic peptide?
Dilates the afferent arteriole of the glomerulus leading to increased blood flow and filtration.
It also suppresses reabsorption of Na+ in the collecting duct and other segments of the nephron
Where is calcitonin released?
The thyroid gland
When is calcitonin released?
When the calcium levels in the blood rise above a set point
What does calcitonin do?
Reduces blood calcium levels in the blood
How does calcitonin work?
It inhibits osteoclast activity and decreases calcium re-absorption in the kidneys
When is parathyroid hormone released?
When blood calcium levels fall below a set point
How does parathyroid hormone work?
Stimulates release of calcium from bone tissue by enhancing osteoblast activity
Reduces secretion of calcium in the kidneys
Stimulates production of active vitamin D
Increases calcium absorption from food in the intestine through its effects on vitamin D metabolism
What is the usual length of ureters?
25-30cm
What is the usual diameter of ureters?
3mm
How is backflow of urine to the kidneys prevented?
When the bladder fills the pressure closes the ureters
What is the structure of the walls of the ureter?
An outer layer of fibrous tissue
A middle muscular layer consisting interlacing smooth muscle fibres
An inner layer of mucosa consisting of transitional epithelium
What propels urine through the ureters?
Peristalsis of the smooth muscle along the ureter
What is the average bladder capacity of the bladder?
700-800ml
What is the structure of the bladder wall?
An outer layer of loose connective tissue containing blood and lymphatic vessels and nerves
A middle later consisting of smooth muscle and elastic tissue
An inner layer of transitional epithelium
What controls the outflow of urine from the bladder?
Internal urethral sphincter
What is the structure of the urethra wall?
An inner layer of mucosa with smooth muscle fibres (involuntary control) and an outer layer of striated muscle (voluntary control)
What are the specialised epithelial cells that cover the glomerular capillaries called?
Podocytes
What are pedicels?
Foot like projections that come off of podocytes
What do the distal convoluted tubes drain in to?
Collecting ducts
What is the path of renal urine drainage?
Collecting duct
Papillary duct
Minor calyx
Major calyx
Renal pelvis
Ureter
Urinary bladder
What percentage of filtered calcium is reabsorbed?
Over 95%
Atrial natriuretic peptide affects the reabsorption of which electrolyte?
Na+
