Structure and Functions Flashcards
How many kidneys do we have
2
Where are the kidneys found
lie extraperitoneally on either side of the vertebral column
What are the kidneys surrounded by
Fat in the retroperitoneal space
What is the kidney made up of
- Outer correct that contains glomeruli, tubules and vessels,
- Inner medulla, containing the loop of Henle and medullary collecting tubules.
What is found in kidneys
Nephrons
What are nephrons
A functional filtering unit of the kidney comprising a glomerulus and the renal tubule
What happens at the glomerulus
The afferent arteriole divides into several golmerilar capillaries to form a loop of capillaries that make up the glomerular
What are the glomerulus enclosed in
An epithelial cell capsule called Bowmans capsule
What is Bowmans capsule connected with
It is continuous with the basement membrane of the glomerulus and also with the start of the tubule
What does the tubule consist of
- First proximal tubule
- Loop of Henle
- Distal tubule that drains into the collecting ducts
What happens to uri found int eh collecting ducts
It drains into the pelvis of the kidney
Then travels to the bladder via the ureters
What does teh structure of the glomerulus allow for
Permits the production of an ultra filtrate of plasma consisting of water containing only small solutes
Where does the ultra filtrate of plasma go in the glomerulus
Passes across the glomerular filtration barrier into the urinary space and then into the tubule
What is found next to the glomerulus
The juxtaglomerular apparatus (JGA)
What is the juxtaglomerular apparatus
Where the afferent arteriole arrives and the efferent arteriole leaves the glomerulus
What are the cells of the juxtaglomerular apparatus a rich source of
Renin
What is renin
A hormone
What does renin do and how
Contributes to the control of blood pressure, salt and water homeostasis via the renin-angiotensin-aldosterone system
Also maintains vascular tone
What happens to the ultra filtrate of plasma as it passes through the tubules
It is modified
ie some substances may be reabsorbed into the capillaries
and some may be actively transported out the capillaries secreted to the tubular lumen
Where does most of the absorption of the ultra filtrate of plasma occur
At the proximal tubule
What is reabsorbed at the proximal tubule
60% of filtered water, sodium, chloride and potassium
100% of glucose
95% of amino acids
When is 100% of glucose not reabsorbed at the proximal tubule
If the filtered load of glucose exceeds reabsorption capacity when the plasma glucose level is very high
What can incomplete reabsorption of glucose lead to and in whom
glycosuria in diabetes
Other than absorption and secretion what else does the kidney do
It can vary the volume and concentration of urine depending on water intake and body fluid status
What happens when the water intake is high
Water is excreted in excess of solute in a dilute urine that is hypo osmolar compared to plasma
What happens when water intake is low
Water is retained by the kidney and a concentrated urine that is hyperosmolar compared with plasma is excreted
Where does the formation of dilute vs concentrated urine occur
depends on the countercurrent multiplier mechanism in the loop of Henle
What is special about the loop of Henly
There is a different permeability of the ascending and descending limbs of the loop of henly
Where is teh medullary osmotic gradient highest in the loop of henly
Highest at the tip of the loop in the inner medullar and papilla
How is renal function described
As the glomerular filtration rate (GFR)
What is the glomerular filtration rate equal to
The sum of all the filtering nephrons
How do we assess the glomerular filtration rate
- Insulin clearance
- Plasma creatine concentrations
How does insulin clearance give an assessment of glomerular filtration rate
As insulin can only be cleated by filtration at the glomerulus it provides a very accurate estimate of the GFR
What is the problem with using insulin clearance to measure GFR
Insulin as to be infused intravenously so this method is more of a research tool
What is creatine produced by
Muscle turnover
What happens to creatine in teh kidneys
As it is small it is freely filtered at teh glomerulus and NOT reabsorbed or metabolised to any significant extent
Why can we use plasma creating concentration to assess GFR
As creating is not reabsorbed in the kidneys it can be used as a rough guide to GFR
What is the drawback of using plasma creatine concentration to assess GFR
Creatine is secreted by the renal tubules so may be higher concentration than expected
What does metabolism produce
Hydrogen ions (proteins)
What is the problem with hydrogen ions
They are acidic so lower pH so myst be buffered to maintain body pH
Name the most widespread buffer system in THE body
Bicarbonate (HCO3)
State the chemical formula of how bicarbonate buffers hydrogen ions
H+ +HCO3− => H2CO3 => CO2 +H2O
Can the bicarbonate buffering system go on forever
no as there is limited bicarbonate in teh body
What happens when the buffering system needs to be regenerated
Protons need to be excreted from the body
How is bicarbonate regenerated
By the kidneys Where it is remade and also reabsorbed from the urine
How do the kidneys achieve net secretion of protons
by generating and excreting ammonium (NH4+) in urine
Also by excreting protons bound to other buffer
Describe the ultra filtrate of plasma found at teh glomerulus
Consists of water and very small solutes only
Talk through the journey the ultra filtrate of plasma goes through from the glomerulus
- Passes into the Bowmans capsule
- Passes into proximal tubule
- Travels down the nephron where it is modified via active and passive ion transport
- Reaches collecting duct
Name the main determinants of extracellular volume
Sodium (Na+) and chloride (Cl-)
The amount of these 2 ions controls body extracellular volume
List the main functions of the kidney
- Control of acid base balance
- Regulation of body fluid volume and composition
- Excretion
- Endocrine activity
- Blood pressure control
What do ten kidneys need to excrete
Waste products of metabolism, urea, creatine, potassium and hydrogen ions (protons)
Also excretes many drugs and their metabolites
What do we need to consider if kidney function is reduced
The dose of water soluble drugs needs to be reviewed and reduced as they are excreted via kidneys
Which vitamin does the kidney have a role in synthesising
Synthesises the vitamin D metabolite
Name the vitamin D active metabolite
1,25 dihydroxyvitamin D3 or calcitriol
What is the significance of calcitriol
Acts on the gut to increase calcium and phosphate uptake
Also feeds back to suppress the parathyroid hormone
Reduces osteoclast activity
Where is the parathyroid hormone released from
Parathyroid glands
Which hormone does the kidney produce
erythropoietin
What is the significance of erythropoietin
Acts on the bone marrow to maintain red cell production and thus haemoglobin concentration
Name the system that controls blood pressure via the kidneys
renin–angiotensin– aldosterone system
How are the kidneys involved in controlling arterial blood pressure
Through the regulation of salt, water balance and vasoconstriction
What is renin synthesised by
The juxtaglomerular apparatus (JGA) in response to carious stimulus
What does renin do
It cleaved to angiotensin to form angiotensin I
Where is angiotensin synthesised
The liver
What happens to angiotensin 1
If is converted into angiotensin II By angiotensin converting enzyme (ACE)
Where are angiotensin converting enzymes (ACE) found
In the lungs and endothelial cells
What does angiotensin II do
Binds to at least 2 receptors:
1. AT1
2. AT2
What effect does the binding to AT1 by angiotensin II have
- Vasoconstriction
- Aldosterone and vasopressin release
- Water and salt retention in kidneys
- Sympathetic nervous system activation
What effect does the binding to AT2 by angiotensin II have
Anti proliferative and remodelling effects
