Physiology: Kidney Structure & Function Flashcards
List some functions of the kidney (10 possible answers below)
- Water balance (~1.5L of urine excreted /day)
- Salt balance (~10g of salt excreted /day)
- Maintenance of plasma volume and osmolarity (due to H2O and salt balance + fluid compartment shift)
- Acid-base balance (excrete H+ and reabsorb HCO3-)
- Excrete metabolic waste products (e.g., urea, bilirubin, uric acid)
- Excrete exogenous foreign compounds (e.g., drugs, food additives, pesticides)
- Control arterial blood pressure (through granular cell secretion of renin)
- Stimulate rbc production (through secretion of erythropoietin)
- Convert vitamin D to active calcitrol (promoted Ca2+ absorption in the GI tract)
Why do the kidneys play such a vital role in the body’s homeostasis?
Balance of water and electrolytes in the body depends on balance between body input and outputs
The kidneys control excretion of water and electrolytes
What does the urinary system consist of?
The kidneys (produce urine) The structures that store and carry the urine from the kidneys to the outside of the body e.g., ureter, bladder, urethra
The kidney receives ~X% of cardiac output
20-25%
What is a nephron?
How many are found in each kidney?
The functional unit of the kidney i.e., the smallest unit which is able to produce urine
~1 million nephrons are found in each kidney
What are the 3 processes a nephron goes through to produce urine?
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
Describe the unique blood supply to a nephron
- The renal artery gives off afferent arterioles
- These supply the glomerulus (a tangle of capillaries within the Bowman’s capsule)
- The efferent arteriole carries blood exiting the glomerulus
- Peritubular capillaries follow the loop of Henle down into the medulla
- Deoxygenated blood drains to the renal venules, then back to the renal vein
What are the 5 parts of the tubular component of the nephron?
- Bowman’s capsule (where the initial tubular fluid is formed and drains)
- Proximal tubule
- Loop of Henle (descends into medulla then ascends back into cortex)
- Distal tubule
- Collecting duct (receives tubular fluid from many different nephrons and passes it down the collecting duct to the renal pelvis)
Name the two types of nephron and state what proportion of the nephrons they make up
Cortical nephrons (~80%) Juxtamedullary nephrons (~20%)
What are the 3 main differences between the cortical and juxtamedullary nephrons?
Juxtamedullary nephrons have…
- A longer Loop of Henle which descends further down into the renal medulla
- A single vasa recta that follows the Loop of Henle rather than peritubular capillaries
- Produce more concentrated urine
Describe the structure of the glomerulus
- A tangle of capillaries held within the Bowman’s capsule
- Supplied by an afferent arteriole and drained by an efferent arteriole
- Capillary wall made up of fenestrated endothelium cells
- Basement membrane separates endothelium from the podocytes making up the inner layer of the Bowman’s capsule
What is the function of the glomerulus?
As blood is delivered through the glomerulus, a portion is filtered and enters the lumen of the Bowman’s capsule to form the initial tubular fluid -> i.e., it is the site where filtration begins
What is the juxtaglomerular apparatus?
The region of the distal convoluted tubule that passes between the afferent and efferent arterioles of the nephron
(juxta-glomerular = next to the glomerulus)
Name two specialised cell types found in the juxtaglomerular apparatus
Macula densa cells
Granular (aka juxtaglomerular) cells
Where are the macula densa cells found in the juxtaglomerular apparatus and what do they do?
- Located in the wall of the distal convoluted tubule
- They detect the amount of NaCl (salt) in the tubular fluid passing through them, then send signals to the smooth muscle cells lining the afferent arteriole to cause vaso- constriction or dilation in order to reduce or increase blood flow to the glomerulus
