Section 6: Renal System Flashcards
External anatomy of kidneys
Renal capsule (innermost layer) Adipose capsule Renal fascia (outermost layer)
All made of CT - provides padding, protection and packaging
Kidneys: Renal capsule
Physical barrier; protection against trauma
Maintains shape of kidneys
Kidneys: Adipose capsule
Padding; physical protection
Maintains position of kidneys
Kidneys: Renal fascia
Anchors kidneys to surrounding structures
Parenchyma of kidney
Functional portion
Contains ~1 million nephrons (functional units)
Focusing on juxtamedullary nephrons
Kidneys: Renal corpuscle - components
Glomerulus (blood) - endothelium
- input: afferent arterioles
- output: efferent arterioles
Glomerular (Bowman’s) capsule - epithelium
- visceral: podocytes (modified epithelium)
- parietal: from outer wall of capsule (simple squamous)
Kidneys: Filtration membrane - parts
Fenestration (pore) of glomerular endothelial cell
Basal lamina of glomerulus
Slit membrane between pedicles
Differential filtering
Kidneys: Filtration membrane - fenestration
Prevents filtration of blood cells, but allows all components of blood plasma to pass
Kidneys: Filtration membrane - basal lamina
Prevents filtration of larger proteins
Kidneys: Filtration membrane - slit membrane
Prevents filtration of medium-sized proteins
Filtration unit and substrate
Filtration unit = nephrons
Substrate = blood supply
Kidney mass
~150g
Kidneys: Renal columns
Extension of cortex into medulla
Lots of blood vessels and tissue embedded here
Kidneys: Interlobar
Between 2 lobes
Kidneys: Nephrons - arrangement
Not randomly arranged
Very tightly packed in organised ways and all collect into a bunch (bouquet)
Kidneys: Calyces
Cup-like structures that collect urine from papillary
Start with smaller cups which merge to form bigger cups
Kidneys: Interlobar artery
Red blood vessel found between 2 lobes
Kidneys: Nephrons - classes
Some located higher up near cortical area
Others located lower down near medulla
Kidneys: Juxtamedullary nephrons
Nephrons close to cortical-medullary junction
Responsible for helping us make concentrated urine
Kidneys: Arcuate artery
Where renal artery arches as it comes up to the cortex at cortical-medullary junction
Gives rise to interlobular arteries
Kidneys: Interlobular arteries
Feed the lobules
Kidneys: Glomerulus / glomerular capillaries - form an important part of…
The filtration barrier
Afferent arteriole is ____ of the filtration apparatus
Upstream
Efferent arteriole - pathways
Can stay in cortex and feed cells that make up tubular parts of nephron
Or can delve deep into medulla and feed cells of tubular parts of nephron located here
Ascending vs descending vasa recta
Ascending: venous blood; relatively O2-poor blood
Descending: arterial blood; relatively O2-rich blood
Peritubular capillaries of medulla
Where gas exchange happens
O2 is absorbed by cells of nephron and CO2 is transported back into blood in peritubular capillaries
Kidneys: Where does blood transition from arterial to venous
In the peritubular capillaries
Peritubular capillaries: Venous blood - pathway
Travels into interlobular veins –> arcuate vein –> interlobar vein –> converge and exit kidney by renal vein –> IVC –> heart
Where does filtration begin
Renal corpuscles
Corpuscles
Capsulated structures
Interaction between what enables filtration to take place
Podocytes and underlying glomerular capillaries
Tgt they form the filtration barrier
Kidneys: Capsular / urinary space
Space between visceral and parietal epithelium
Where filtrate accumulates and eventually flows out the renal corpuscle into the tubular portion
Kidneys: What is the basal lamina made up of
BM secreted by podocyte
BM secreted by endothelial cells
Kidneys: Glomerular capillaries - texture
Not a smooth surface because has pores
Kidneys: Differential filtering - what happens to the proteins that get trapped
Either bounce back into blood circulation or are phagocytosed and recycled
Kidneys: Proximal convoluted tubule - cells
Have microvilli on apical membrane
Involved in transport
Kidneys: Distal convoluted tubule of many nephrons…
Combine and feed into a single collecting duct
Kidneys: Distal convoluted tubule - function
Monitors how things are going and provide feedback to influence the beginning of the process
Main functions of kidney
Regulation of water and electrolyte balance
Regulation of arterial pressure
Filters blood
Kidney - homeostasis
Blood pressure
Water and electrolyte balance
pH
Waste product removal
Kidney is part of ______ system
Circulation
Kidney: When things go wrong - symptoms
Swelling High blood pressure Shortness of breath Fatigue Nausea
Dialysis
Prevents build up of waste products
e.g. build up of high K+ –> heart rhythms go bizarre –> sudden death
Osmosis
The movement of water through a selectively permeable membrane
From an area of lower solute conc (high water conc) to higher solute conc (low water conc)
Osmotic pressure
The pressure required to prevent net water movement, i.e. pressure generated by the water moving inside a cell
Osmolarity
A measure of the osmotic pressure exerted by a solution across a semi-permeable membrane compared to pure water
Dependent on no of particles in solution (but independent of nature of particles)
Basically a measure of the conc of all the components in the solution
Osmolarity =
Molarity x dissociation factor
150mL NaCl + 1L water dissociates to give…
150 mM/L Na+ + 150 mM/L Cl-
= 300 mOsm/L
300mM urea + 1L water gives..
300 mOsm/L
Osmolarity usually refers to…
A container / beaker, not necessarily a cell
Hyperosmotic
A solution with a higher Osm than another
Isosmotic
2 solutions with the same Osm
Hyposmotic
A solution with lower Osm than another
Tonicity
Takes into account the conc of a solute and the ability of the particle to cross a semi-permeable membrane
i.e. ability of a solution to change shape of a cell
‘effective osmolarity’
NaCl - permeability
Low permeability
Urea - permeability
Higher permeability
Hypertonic
A solution with a higher POsm than another
Water will leave cell –> shrinkage
Isotonic
2 solutions with same POsm
Not net water movement
Hypotonic
A solution with a lower POsm than another
Water will move into cell –> swelling (and burst)
Disturbances in water balance: Dehydration
Loss of H2O from ECF
ECF osmotic pressure rises
Cells lose H2O to ECF –> cells shrink
Disturbances in water balance: Hydration
H2O enters ECF
ECF osmotic pressure falls
H2O moves into cell –> cells swell
Why maintaining osmolarity is important
Sets MP
Generates electrical activity in nerve and muscle
Provides energy for uptake of nutrients and expulsion of waste
Generation of intracellular signalling cascades
Fluid distribution in body - average 70kg male
60% fluid = 42L 2/3 intracellular = 28L 1/3 extracellular = 14L - 20% plasma = 2.8L - 80% interstitial = 11.2L
Major sources of water intake
Metabolism 8%
Foods 28%
Beverages 64%
Major sources of water output
Feces 4%
Lungs 12%
Skin 24%
Urine 60%
Electrolyte composition: High extracellular conc
Na+, Cl-, Ca2+ ions have high extracellular conc
Electrolyte composition: High intracellular conc
K+ ions have high intracellular conc
Electrolyte composition - similarities?
Amount in blood plasma and interstitial fluid are usually very similar
About ___L of fluid enters the renal tubules each day
180L
In the average adult, the entire extracellular fluid V is filtered about __ times a day
12
How much fluid that enters the renal tubules is reabsorbed
~178.6L reabsorbed
~1.4L urine produced each day
Excretion = ?
Filtration + secretion - reabsorption
Renal handling of water and solutes: Water
Filtration = total Reabsorption = most of total Excretion = small amount of total
Renal handling of water and solutes: Sodium
Filtration = total Reabsorption = most of total Excretion = small amount of total
Renal handling of water and solutes: Glucose
Filtration = total Reabsorption = total Excretion = 0
Renal handling of water and solutes: Creatinine
Filtration = total Reabsorption = 0 Excretion = total
What is reabsorption
The idea that you’re taking fluid out of your nephron and back into blood
Nephrons - pathway
Glomerulus Proximal tubule Loop of Henle: descending limb Loop of Henle: ascending limb Distal convoluted tubule Collecting duct
Glomerular filtration rate %
~25% of total renal plasma flow
180 L/day
Very constant, especially over a mean pressure of 80-140
Glomerulus has a similar solute conc to…
Plasma
Glomerulus lacks..
Proteins and other high molecular weight compounds
Free from blood cells
Glomerulus - coming in and going out
Have an arteriole coming in, a capillary bed, and an arteriole going out
The only place in body to have an arteriole before and after a capillary bed
Glomerulus: Capillaries - holes
Capillaries in capillary bed have big holes in them - easy for fluid to be filtered out
Glomerulus: Podocytes sit on top of _____
Capillaries
Blood flow to kidneys - regulation
Tightly regulated, thus glomerular filtration rate is relatively constant
Urine output is directly proportional to….
Renal/blood pressure