Renal System Flashcards
Describe the kidneys
The inner surface of the lower back.
Account for ~ one percent of total bodyweight
They receive about 25% of total cardiac output
Their function is filtering the blood
What are the functional units of the kidney
Nephron - also known as the renal tubules or kidney tubules.
Each nephron is an intricate epithelial tube
How many nephron are there per kidney?
Approximately 1.25 million nephron
How thick is the nephron wall?
It is one cell thick (simple cuboidal epithelium)
These cells are specialised for absorption and secretion of material
Describe the flow of fluid through a cortical nephron
What are found on the inner surface?
Microvilli - this increases surface area for ion and water transport
What are adjacent cells joined by?
Tight junctions - this restricts diffusion between the lumen (inside of nephron) and the extra cellular space
What is happening at stage one and stage two?
- Glomerulus - a network of capillaries with relatively high blood pressure forcing fluid out of the vessels.
- Bowman capsule - fluid from the blood is filtered into the cavity of the capsule
What is happening at stage 3,4 and 5?
- Filtration of blood.
- Proximal convoluted tubule - site of re absorption of glucose, vitamin C, and some salts (75% Na) and some water
- Loop of Henle - site of water reabsorption to adjust osmotic pressure of the blood and concentrate the urine in the collecting duct
What is happening in stages Six and seven?
- Distal convoluted tubule - site of further absorption of material and also secretion of material. Thereby affecting the acidity of the urine and the blood.
- Collecting duct - final site of water absorption affecting the overall concentration of the urine. Collecting duct serves several nephron and empties into the renal calyx and from there to the renal pelvis and then the ureter.
What does the filtration membrane in the glomerulus act like?
A sieve
Large particles such as blood cells and proteins can’t leave.
Water and small molecules can flow through the slits.
What is the journey through a Nephron?
How does filtration occur?
- Filtration from blood plasma into nephron.
- Tubular reabsorption from fluid into blood.
- Tubular secretion from blood into fluid.
Urine contains excreted substances
Blood contains reabsorbed substances
What is the glomerular filtration rate?
125ml/min
180l/day
99% of the filtered water water is reabsorbed
What does filtrate consist of?
Water and non-protein solutes (Na, K, Cl, glucose and urea)
What is filtration driven by?
- The sievelike properties of the capillary walls and the walls of the Bowman capsule.
- The pressure gradient from capillaries to Bowman capsule.
What is the overall filtration pressure and how is it worked out?
- Capillary blood pressure (60mmHg) - OUT
- Bowman’s capsule pressure (20mmHg) - IN
- Capillary osmotic pressure (plasma proteins) (30mmHg) - IN
Overall filtration pressure = 10mmHg OUT
Where does reabsorption begin?
Proximal convoluted tubule
~65-75% of filtered Na is reabsorbed here.
ACTIVE process involving membrane pumps and ATP
What is the transport maximum?
Maximum amount of material which can be transported
How does diabetes mellitus work?
Lack of insulin > glucose not absorbed into the cells > plasma glucose increases > filtered glucose increases > glucose infiltrate exceeds the transport Max for glucose > glucose appears in the urine
What is hyperglycaemia?
Increased urine volume and glycosuria (glucose in urine)
