Kidney Structure and Function Flashcards
1
Q
What is the Gross Anatomy of the Kidneys?
A
- Found in Retroperitoneal space
- Between 11th thoracic and 3rd lumbar vertebra
- Either side of vertebral column
- Right situated slightly lower than left
- ~12cm long (x6x4cm), ~150g male, ~135g female
2
Q
What are some functions of the kidney?
A
Homeostasis
- Plasma sodium: Renin is released from the kidneys as the first step in the RAA axis for sodium conservation (more on which next lecture).
- Blood pressure: Low arterial pressure stimulates the RAA axis to increase plasma volume.
- Blood pH: Excretion of H+ ions is controlled by the kidney, specifically in the distal convoluted tubule.
Hormone production
- Bones: Vitamin D is activated by 1α hydroxylation in the kidney.
- Blood oxygen levels: The hormone erythropoetin (EPO) is produced by the kidney and is necessary for red blood cell synthesis.
Elimination of toxins
- Waste Disposal: Toxins, nitrogenous compounds and excess electrolytes are filtered from plasma into the urine.
3
Q
What is the Renal Blood Supply?
A
- The kidneys utilise 25% of cardiac output. 90% of which supplies the renal cortex and is required to maintain highly active tubular cells
- Most of this is distributed to the capillaries of the glomeruli, which acts as a high pressure filter.
- Each kidney receives its blood supply from a single renal artery derived from the abdominal aorta.
- Renal artery feeds into the afferent arterioles exands into the glomerulus. The capillaries of the glomerulus rejoin to form the efferent arteriole then renal venules then renal veins then inferior vena cava.
4
Q
Describe the Microstructure of the Kidney?
A
- Medulla is formed of pyramids.
- Within these pyramids are nephrons which are the functional unit of the kidney. They received blood supply to filter it and return components to circulation.
- Waste-collecting duct of nephron drains into the calyces and then into the renal pelvis and then into the ureter and then bladder.
5
Q
How is Urine excreted?
A
- Filtered toxins and water leave each kidney through the ureter.
- Each ureter drains into the urinary bladder.
- Urine is then excreted through the urethra.
6
Q
What are the main functional units of nephron?
A
- Glomerulus
- Proximal Tubule
- Loop of Henle
- Distal Tubule
- Collecting Duct
Exists as long or short variations
7
Q
What is the Glomerulus?
A
- Formed from specialised capillary network enclosed within Bowman’s capsule
- It is used to form an ‘ultra-filtrate’ of plasma. This depends on the blood flow through normal glomeruli and on the difference between hydrostatic pressure gradient and the plasma effective colloid osmotic (oncotic) pressure gradient across membranes
- Blood is filtered to maintain important constituents like blood cells in the blood but remove excess fluid, waste products and regulate H+, Na+, K+
8
Q
Describe the Glomerular Filtration Barrier
A
- Capillary endothelium - barrier to wbc and rbc
- Glomerular basement membrane - largely impermeable to macromolecules (based on size (<68kDa filtered) and charge (-ve less easily than +ve)
- Podocytes
9
Q
How does filtration take place?
A
- Filtration is a passive process, taking place due to the difference between the bp of the capillaries and hydrostatic pressure of the lumen.
- GFR is affected by blood supply to nephron, the intergrity of the glomerular basement membrane, endo and epithelial cells and the number of nephrons – all can be altered in disease and affect the GFR
10
Q
What makes up the composition of the Glomerular Filtrate?
A
An ‘ultra-filtrate’ of the blood enters the lumen of the glomerulus.
- Composition similar to plasma except blood cells and molecules of protein around >50kDa are absent.
- Molecules around the size of albumin (68kDa) and larger are prevented from entering the lumen.
- Proteins prevented according to charge as well as size (more negatively charged proteins retained in blood).
11
Q
What is the function of the Proximal Convoluted Tubule?
A
Bulk reabsorption of electrolytes from the glomerular filtrate back into circulation
- Active reabsorption: Na+ (~75%)
- Passive reabsorption: Glucose, Amino acids, HCO3-, K+, HPO4 (99% of absorption of these compounds)
- Secretion: H+ (90%), Organic anions, Organic cations
12
Q
What is the function of the Loop of Henle?
A
- Consists of a descending and ascending limb. Extends from the cortex down into the medulla and back up.
- Responsible for creating a hyperosmolar medulla - necessary for the production of a concentrated urine.
- Counter-current Multiplication System
13
Q
What is the purpose of the Counter Current Multiplication System?
A
- Allows formation of a dilute urine after H2O load
OR
- Allows formation of a concentrated urine after H2O restriction via the action of ADH (anti-diuretic hormone) on the collecting duct
14
Q
Describe the Counter-current Multiplication system?
A
- Descending limb is highly permeable to water. The increased osmolality of the medulla causes water to be absorbed, concentrating the tubular fluid.
- Ascending limb is impermeable to water, but reabsorbs solute from the tubular fluid (~25% of sodium/chloride). Fluid in the ascending limb becomes more dilute.
- Owing to NaCl reabsorption by the thick ascending limb, fluid reaching the collecting duct is hyposmotic.
- Vasa recta capillary plays an important role in the process by quickly removing any water that is reabsorbed from the descending limb to maintain a high medullary osmolality.
- The result is a hypertonic medullary fluid compared to filtrate going into the distal convoluted tubule.
- Dilute fluid enters the DCT and CD where water can be reabsorbed by passive diffusion (ADH) down the concentration by the medullary hyperosmolality that has been created.
15
Q
What is the function of the Distal Convuluted Tubule?
A
Function: To carry out the ‘fine-tuning’ of electrolyte reabsorption or secretion.
- Specifically Na+, K+, H+
- Depends on concentration of electrolytes in plasma
- Under hormonal control (e.g. aldosterone)
