BIOL 10: Excretory System Flashcards
What are the functions of the excretory system?
Regulation of blood pressure, blood osmolarity, acid-base balance, and removal of nitrogenous waste
List the structures of the secretory pathway (formation of urine).
Urine is filtrate starting at the glomerulus.
Glomerulus -> Bowman’s capsule -> proximal convoluted tubule -> descending limb of loop of Henle -> ascending limb loop of Henle -> distal convoluted tubule -> collecting duct
What is the renal corpuscle?
It is composed of the glomerulus and the Bowman’s capsule.
List the vessels in the renal vascular pathway.
Aorta -> renal artery -> afferent arterioles -> glomerulus -> efferent arterioles -> vasa recta -> renal veins -> inferior vena cava
What is a portal system? Examples?
It consists of 2 capillary beds in series through which blood must travel before returning to the heart; e.g. renal portal system (afferent arterioles, glomerulus, efferent arterioles, vasa recta), hepatic portal system (connects the liver to the digestive tract), and hypophyseal portal system (connects the hypothalamus to the anterior pituitary).
Detrusor muscle
Muscular lining of the bladder controlled by the parasympathetic nervous system
Explain what happens physiologically when released urine out of the body.
Urine that is stored in the bladder must pass through the 2 urethral sphincters to exit the body.
First, stretch receptors in the bladder will convey to the NS that the bladder needs emptying - signalling the parasympathetic NS to contract the detrusor muscle.
Then, the internal urethral sphincter must relax from its default contracted state - it is controlled by the parasympathetic NS and will involuntarily relax through the micturition reflex once the detrusor muscle contracts.
Finally, through voluntary control (under somatic NS control), the external urethral sphincter is relaxed from its default contracted state to let out urine.
*If the individual does not wish to urinate yet, the reflex will eventual pass but will return again if bladder still needs to be emptied.
What is the micturition reflex?
It is the reflex associated with the need to urinate/empty the bladder - controlled by the parasympathetic NS, the detrusor muscle contracts and internal urethral sphincter relaxes.
Describe the processes by which the components of the kidney are able to exchange material between the filtrate and the blood (7).
1) The glomerulus acts as a filter, allowing smaller materials (glucose, amino acids, salts, ions, vitamins) from the blood to pass through and form the filtrate. Materials that stay in the blood and do not become part of filtrate are proteins and blood cells.
2) The Bowman’s capsule captures the filtrate and directs it towards the subsequent components of the nephron.
3) In the proximal convoluted tubule, glucose, amino acids, water-soluble vitamins, and majority of salts are reabsorbed into the blood with water. It also secretes waste products, such as urea.
4) The descending limb of the Loop of Henle is permeable only to water and allows water to move out of the filtrate into the blood. Since the direction of blood flow runs opposite the direction through the Loop of Henle, the osmolarity of blood increases as we go deeper into the Loop of Henle, allowing for water to be continuously reabsorbed into the blood stream as we go down the descending limb.
5) The ascending limb of the Loop of Henle is permeable only to salts and allows salts to be reabsorbed into the blood stream (decreasing medullary osmolarity in this direction as opposed to increasing in the previous section of the Loop of Henle). This portion of the nephron creates urine that is more diluted than (hypotonic to) blood in the interstitium.
6) The distal convoluted tubule responds to aldosterone, promoting salt reabsorption. Water follows salt as it is reabsorbed, creating more concentrated urine in lower volumes. The DCT also secretes waste, like the PCT.
7) The collecting duct is responsive to both aldosterone and ADH. Aldosterone controls permeability to salts while ADH controls permeability to water, depending on what the body’s needs.
What are Starling forces?
They govern the movement of fluid into the Bowman’s capsule, accounting for the differentials between oncotic and hydrostatic pressures between the blood and Bowman’s space.
Differentiate between hydrostatic and oncotic pressures.
- hydrostatic: force that pushes fluid out of the capillaries (i.e. in physics, pressure of fluid onto the container walls)
- oncotic: force that pushes fluid into the capillaries (specifically, the osmotic pressure attributable to dissolved proteins)
What is the interstitium? What happens here?
It is the connective tissue surrounding the nephron; solutes that enter the interstitium are picked up by the vasa recta and directed into the blood.
Explain the ‘Countercurrent Multiplier System’.
The flow of filtrate through the loop of Henle runs opposite the blood flow through the vasa recta, allowing for the filtrate to be constantly exposed to hypertonic blood to allow reabsorption of water.
Where is the diluting segment within the nephron? Why is it called such?
The diluting segment of the nephron is the ascending limb of the Loop of Henle. It is called such as it produces more dilute urine/filtrate than blood through active transport of salts out of the filtrate. The ascending limb of the LoH is permeable only to salts and is thicker than the descending limb due to the presence of mitochondria to produce the necessary ATP to pump salts out of the nephron into the interstitium.
Differentiate between aldosterone and vasopressin.
- Aldosterone is secreted in response to low blood pressure. It is a (cortico)steroid hormone produced and secreted by the adrenal cortex. It alters the permeability to salts in the DCT and collecting duct, and increases H+ and K+ secretion. *To bring up BP, water follows reabsorbed salts through higher permeability resulting from aldosterone secretion.
- ADH is secreted in response to high blood osmolarity. It is a peptide hormone produced in the hypothalamus and secreted in the posterior pituitary. It alters the permeability of the collecting duct (“leaky duct”) to increase water reabsorption to lower blood osmolarity.
