Week 7 Flashcards
Key functions of kidney
Removal of waste products
Regulation of fluid and electrolyte levels
Regulation of pH
Maintaining blood pressure
Maintaining blood osmolarity
Production of hormones and renin
Gluconeogenesis
Kidney structure
Around 10-12cm long, 5-7cm wide and 3cm thick
Dent on medial side known as hilum
Renal cortex: outer region of kidney and contains nephrons
Renal medulla: inner region containing renal pyramids separated by renal columns
How many nephrons in each kidney?
1-1.25 million
Basic Nephron Structure
Blood flows into the renal corpuscle from the afferent arteriole, plasma is filtered, the filtrate flows into the proximal tubule, loop of henle, distal tubule and collecting duct
Cortical nephrons
80-85% of all nephrons
Renal corpuscle located in cortex, with renal papilla going through the pyramid
Juxtamedullary nephrons
Renal corpuscle located nearer medulla
Flow: Bowman’s capsule, descending limb,ascending limb (thin then thick), distal convoluted.
Glomerulus
Fenestrated capillaries
Receive blood from afferent arteriole
Bowman’s capsule
Inner visceral layer consists of specialised cells called podocytes
Pedicels extend from podocytes and form filtration slits around the capillaries
Outer parietal layer constructed from squamous epithelial cells
Renal tubule
Surrounded by peritubular capillaries
Proximal tubule
Greatest reabsorption due to simple cuboidal epithelium and microvilli
100% of glucose and amino acids reabsorbed
Nephrons loop - cell types
Descending - simple squamous
Thin ascending - Simple squamous
Thick ascending - cuboidal or low columnar
Reabsorption 20% of water in descending limb, 25% sodium and chloride thick ascending
Distal tubule
Main role is regulating fluid composition
The ureters
3 layers:
Inner mucosa: transitional epithelium
Muscularis: Circular and longitudinal muscle
Adventitia: loose connective tissue
Glomerular filtration
Afferent arterioles feed blood into the renal corpuscle. It then goes through the filtration membrane
What is the filtration membrane made up of?
Fenestrated capillaries
Podocytes
Factors that drive net filtration
Glomerular blood hydrostatic pressure
Capsular hydrostatic pressure
Blood colloid osmotic pressure
Glomerular blood hydrostatic pressure
Forces fluid out of the glomerular capillaries
Capsular hydrostatic pressure
Hydrostatic pressure within the glomerular capsule
Resists fluid exiting the glomerular capillaries
Blood colloid osmotic pressure
Osmotic pressure of blood solutes
Opposes fluid loss into the capsular space
Glomerular filtration rate
The amount of filtrate produced in both kidneys
It is maintained around 105-125ml/min
Renal autoregulation
Myogenic mechanism: uses changes to the vascular tone of either the afferent or efferent arteriole to maintain the desired blood flow
Tubuloglomerular feedback mechanism uses alterations to the vasodilator, nitric oxide
Tubuloglomerular feedback mechanism
Macula densa cells detect an increase in tubular fluid ion and water flow in the kidney tubules
They act to inhibit the release of nitric oxide from the juxtaglomerular apparatus. Results in vasoconstriction of the afferent arteriole
Neural regulation
Sympathetic division of ANS acts on Alpha 1 receptors in the smooth muscle of afferent and efferent arterioles
Norepinephrine induces vasoconstriction, which reduces GFR
Hormonal regulation of GFR
Atrial natriuretic peptide- increases the glomerular capillary surface area by relaxing glomerular mesangial cells (increasing GFR)
Angiotensin II - powerful vasoconstrictor (decrease GFR)
Glomerular diseases
Can cause oedema due to loss of albumin through filtration slits- reducing blood volume
Tubular reabsorption
99% will be reabsorbed through the renal tubules and into peritubular capillaries and vasa recta.
Once reabsorbed into peritubular capillaries, blood flows into interlobular veins and then through the renal vein
Paracellular reabsorption
Paracellular reabsorption is a process that occurs primarily in the kidneys, particularly in the renal tubules, where substances move between adjacent cells (rather than through them) to reabsorb water, ions, and other solutes back into the bloodstream. Occurs through tight junctions and occurs in the PCT and loop of henle
Transcellular reabsoprtion
Involves substances passing through the cell membrane via specific transport proteins. This process can be active (requiring energy) or passive (driven by concentration gradients).
Reabsorption in PT
65% water
100% of glucose and amino acids
65% of NA and K
50% cl
85% HCO3
50% urea
Nephrons loop reabsorption
15% water
20-30% Na and K
35% of Cl
15% HCO3
Distal tubule (early)
10% water
5% Na
5% cl
Late distal tubule
Principle cells: Na and K
Intercalated cells: secretes H, Secretes or reabsorbs HCO3
Where does most secretion take place and what part fine-tunes blood solute concentration
Proximal tubule
Distal tubule and collecting duct
