Detailed notes on the following lectures:
Lecture 17: Kidney Histology - Overview and General Organisation, Cortex, medulla, urinary epithelium and bladder - (Prof Ivor Mason)
Lecture 18: Kidney Function I - (Sarah Thomas)
Lecture 19: Kidney Function II - (Sarah Thomas)
Lecture 20: Kidney Fu...
Urinary System: Two kidneys // Two ureters // One bladder // One urethra
Urine is produced in the kidneys and is conducted by the ureters to the bladder
where it is stored until voided via the urethra.
Blood supply: renal arteries arise from the abdominal aorta, one or more renal
veins drain each kidney to the inferior vena cava.
Functions of the kidney:
- Homeostasis: water, electrolytes, acid/base
- Excretion: soluble toxic metabolic waste products, particularly nitrogenous
urea and creatinine.
- Hormonal: Synthesizes renin of the renin-angiotensin-aldosterone system
controlling blood pressure.
o Synthesis erythropoietin which stimulates erythrocyte production
in bone marrow, so regulates O2 carrying capacity of blood.
- Metabolic: Vitamin D converted to an active form in kidney.
Mechanism of function:
- Filtration: of most small molecules from blood plasma to form ultrafiltrate
in glomerulus
- Selective reabsorption: of most water and some molecules from
ultrafiltrate, leaving behind excess and waste to be excreted (in tubules)
- Secretion: of renin, erythropoietin, and H+ ions for acid/base balance (in
tubules)
Total blood balance column is circulated through kidneys -300 times per day.
120ml/min of glomerular filtrate but 119ml/min reabsorbed producing 1ml/min of
urine.
Kidney Structure:
- Consists of (outer) cortex and (inner) medulla
- Medullary pyramids (cone-shaped masses of
medullary substance) project into subdivisions of
the renal pelvis (calyces)
- Renal Pelvis narrows as it leaves the kidney to
give entry to the ureter
- The hilum is the site of entry and exit of the renal
blood vessels and ureter
- The whole kidney is surrounded by a fibrous
capsule, which also surrounds the attached
adrenal gland. Also surrounded by a thick later of fat-protection against
impact trauma.
Kidney organization:
Medullary pyramid and its associated cortex forms a lobe
- Human kidney 10-18 lobes
- Functional unit of a kidney is the nephron
- Kidney zonation reflects the way that the 106 nephrons arrange into lobes
(per kidney)
, - Arcuate and interlobular vessels
The nephron and collecting system:
A nephron is the functional unit of the kidney;
consists of renal corpuscle and renal tubule.
Renal corpuscle – plasma filtration, consists of 2
structures:
Bowman’s capsule (BC): distended blind end of
the renal tubule
Glomerulus (G): packed capillaries that
invaginate Bowman’s capsule deriving from the
afferent arteriole.
Renal tubule: reabsorbtion. Extends from
Bowman’s capsule to the collecting duct.
Convoluted in shape, four histological-physiological zones.
- Proximal convoluted tubule (PCT)
- Loop of Henle
- Distal convoluted tubule (DCT)
- Collecting tubule (CT)
Kidney Cortex: Renal corpuscles and proximal convoluted tubules.
- Wide afferent arteriole enters BC at the vascular pole, branches out to
form a network of capillaries.
- Efferent arteriole is smaller in diameter, so to
maintain a pressure gradient that drives filtration
of plasma in Bowman’s space.
Glomerular filter: Plasma filtrate from the glomerular
capillaries pass through 3 layers before entering the
renal tubule.
Capillary endothelium – fenestrated. (F)
- Have negatively charged protein deposits to repel
the proteins from entering into bowmans space.
Glomerular basement membrane – thick (300nm) formed by 2 basement
membrane of podocytes and endothelia.
- Podocytes – interdigitating pedicels (interwined).
o Divide secondary and primary pedicels
o Nephrin and podocin are important
filtration slit proteins
- Secondary pedicels attach directly to the
glomerular basement membrane
- Gaps between pedicels are filtration slits (FS)
(above 25 nm)
Proximal Convoluted Tubule (PCT): Longest part of the renal tubule. Appx
75% of filtrate is reabsorbed.
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