Renal Flashcards
What are the two fundamental functions of the kidneys?
Osmoregulation and Excretion
What is excreted from the kidneys?
Removal of the products of nitrogen metabolism e.g. ammonia which is toxic. Either via:
-Direct excretion (Ammonotelism) by fish as NH3 is soluble in water
- Via uric acid (uriotelism) by birds and snakes
- Via urea (ureotelism) by mammals and some fish
What is osmoregulation?
The regulation of salt and water balance through maintaining osmotic levels.
Water elimination - filtration via kidneys glomerular filtrate
Water conservation - occurs in Loop of Henle, where urine becomes concentrated.
How much of the cardiac output goes to the kidneys?
Receive 25% of the total cardiac output and filter the whole system every 30 mins.
20% of plasma is converted to filtrate and all but 1% is reabsorbed.
Important vessels of the kidneys
Renal arteries and veins are branches of the descending aorta.
These turn into afferent arterioles which travel through the glomerulus to efferent arterioles and out to interlobular veins.
Internal iliac artery is anastomosed end-to-end with the renal artery.
Gross anatomy of kidneys
Right kidney more cranial than your left
Adrenal glands cranial and medial to kidney
Upper urinary tract: kidneys and ureters
Lower urinary tract: bladder and urethra
Layers of the kidneys
Renal fascia - collagenous connective tissues separating perineal fat from pararenal fat
Perirenal fat - fat surrounding each kidney
Renal capsule - outer tough connective tissue surrounding each kidney
3 regions within the kidney
Outer/renal cortex - granular due to nephrons
Middle/medulla - ~8 renal pyramids with renal columns. In-between these are blood vessels. Tip of pyramid is renal papillae, where the openings of collecting ducts enter and urine goes into ureters. This combines with cortical part and produces the lobes of the kidney
Inner/renal pelvis into the hilium - branches into 2/3 extensions (major calyces and minor calyces)
Species differences in kidney structure
Ox - lobular
Pig - artery on top of vein (all others the other way)
Horse - right kidney pyramid shape
Cat - veiny
What is a nephron?
The functional unit of the kidney. Made up of :
Renal corpuscle (glomerulus, capillaries and Bowmans capsule)
Tubule (proximal convoluted, Loop of Henle, distal convoluted, and collecting ducts)
How does the filter/renal corpuscle work?
Renal corpuscle contains the glomerulus (tuft of capillaries) which is surrounded by the Bowmanns capsule.
This is first step of filtration, with three layers to the filtration barrier:
-glomerulus endothelial cells - fenstrated to restrict blood cells
-basal laminar - main filtration barrier, non-cellular composed of collagen and a glycoprotein matrix
-Podocytes (epithelial cells of Bowmanns capsule) - restrict medium sized proteins and phagocytose macromolecules
These filter out soluble ions and small molecules to ensure filtrate is protein free.
What is the anatomy of the nephron?
Renal corpuscle
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Late distal convoluted tubule and collecting ducts
What happens in the proximal convoluted tubule ?
High capacity for reabsorption (lined with cuboidal epithelial) with brush border and mitochondria. Antiporters (Na+K+ATPase pumps) on basolateral create electrochemical gradient. SGLTs on apical then follow this transporting Na+ with Glucose or Amino acids and Cl- further. Water follows paracellular.
Absorbed here:
65% water
Na+
K+
Cl-
100% Glucose
85-90% CaCl3-
What occurs at the Loop of Henle?
Two loops, descending and ascending.
The descending is made up of squamous epithelium, which is highly permeable to water (lots of aqua porin channels) and less so to Na+2.
The ascending tubule is made up of cuboidal epithelial cells and is split into thick and thin, which are both impermeable to water. The thin has Na2+ movement paracellularly, and the thick has Na+K+ATPase pumps which create an electrogradient moving Na+, Cl- and K+ into the intersitium.
This movement pulls more water out of the descending tubule.
COUNTER CURRENT MULTIPLIER
What happens at the distal convoluted tubule?
Made up of macula densa cells that are impermeable to water.
Na+K+ATPase pumps create an electrochemical gradient.
Secondary transport is done by Na+Cl- co-transporters and Ca2+ uniporter
What happens at the late distal convoluted tubule and collecting ducts?
Basolateral membrane have Na+K+ATPase pumps, so within the cell Na+ is taken from the lumen via epithelial channels and move K+ out in to the lumen.
If ADH is present, water is absorbled as it binds to V2 receptors leading to an increase in aquaporins being placed in.
What is plasma osmolality?
Osmolality is the concentration of particles within the plasma. So:
If plasma osmolality is low/too much water in blood = net movement into cells
If plasma osmolality is high/too little water in bloody = net movement out of cells
What is the determinant of extracellular and plasma volume? Regulated by what?
Na+, regulated by distal tubule and collecting ducts with aldosterone and the RAAS.
What regulates osmolality?
ADH and osmoreceptors working independently of each other.
How is ADH/Vasopressin released?
In response to too little water.
It is secreted by the posterior pituitary gland in response to increase plasma osmolality (decrease in water in the blood).
This is regulated by osmoreceptors in the supraoptic and paraventricular nuclei of the hypothalamus. This causes the insertion of water permeable channels into the late distal convoluted tubule and collecting duct, making it permeable to water.
-Also when decrease in blood pressure or blood volume sense by baroreceptors in aortic arch and carotid sinus.
What is the RAAS?
Renin-Angiotensin-Aldosterone System
This is also in response to too little water.
When Na+ levels are low in distal convoluted tubule, macula densa cells (main cells lining the distal tubule) signal to granular cells in the juxtaglomerular apparatus of the distal tubule to secrete renin into the blod.
Renin converts angiotensinogen into angiotensin I
Angiotensin I is converted to Angiotensin II by ACE. Angiotensin converting enzyme is released by capillary endothelium of lungs.
Angiotensin II works on zona glomerulosa cells of the adrenal cortex leading to Aldosterone being secreted into the blood.
Aldosterone stimulates the synthesis and insertion of epithelial Na+ channels and Na+ pump in the distal tubule and collecting ducts which promotes the Na+ reabsorption from tubular fluid.
When is the Atrial Natriuretic Peptide is released?
When there is too much water.
There is an increase in total body Na+ which increases plasma volume. This is sensed by atrial myocytes that stimulate the release of ANP. ANP inhibits renin, aldosterone and ADH release. This leads to vasodilation and decreasing vascular resistance.
What are the two methods of resorption in kidneys?
Paracellular - between cells e.g. concentration gradients
Transcellular - through cells
e.g. Active transport of solutes via tubular cells
- Primary AT - uses ATP breakdown e.g. Na+K+ATPase
- Secondary AT - uses energy stored in ionic concentration differences between the two sides e.g. SGLT1
What does hypertonic mean?
Higher concentration of solute in blood than in cell. This leads to cells shrinking, as the water moves out of the cells.
What does hypotonic mean?
Lower concentration of solute in blood than in the cell. This leads to cells bursting, as the water moves into the cells.
What is hypernatremia/hypertonic dehydration?
Too much sodium in the body leads to dehydration, as water loss is greater than water intake or excessive sodium intake. This could be caused by sweating.
An infusion of pure water in this case will lead to hypotonic lysis of RBCs.
What is hyponatremia/hypotonic dehydration?
This is excessive water loss accompanied with excessive sodium loss.
Extra water moves into cells leading to cell damage.
Why is an infusion of K+ beneficial for a vomiting animal?
The animal will be dehydrated, and needs to conserve water to stop hypernatremia.
This is infused as helps enhance Na+ uptake, when couples to Cl- uptake.
Aldosterone inserts Na+ pumps, with Na+K= pumps
Administration of
Hypertonic fluids results in movement of water into the intravascular compartment
Hypotonic fluids results in rehydration of intracellular fluid compartment
Isotonic fluids rehydrate the extracellular fluid
