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What are the functions of the excretory system?

-regulation of blood pressure
-blood osmolarity
-acid-base balance
-removal of nitrogenous wastes


What are the structures in the excretory system?

-renal vein
-urinary bladder


Kidney Structure

-cortex: kidney's outermost layer
-medulla: sits within the cortex
-renal hilium: deep slit in the center of the kidney's medial surface, the renal pelvis (widest part of ureter) spans this entire split; renal artery, renal vein, and ureter enter and exit here


Portal Structure

-kidney has one of these
-consists of two capillary beds in series through which blood must travel before returning to the heart


List the structures in the excretory pathway, from where filtrate enters the nephron to the excretion of urine (10)

1. bowman's space
2. proximal convoluted tubule
3. descending limb of the loop of henle
4. ascending limb of the loop of henle
5. distal convoluted tubule
6. collecting duct
7. renal pelvis
8. ureter
9. bladder
10. urethra


List the vessels in the renal vascular pathway, starting from the renal artery and ending at the renal vein (6)

1. renal artery
2. afferent arteriole
3. glomerulus
4. efferent arteriole
5. vasa recta
6. renal vein


What are the 3 different functions of the kidneys?




-movement of solutes from blood to filtrate at Bowman's capsule
-20% of blood that passes through the glomerulus is filtered into bowman's space
-fluid moves into bowman' space via starling forces (accounts for pressure differentials in both oncotic and hydrostatic pressures)


Hydrostatic pressure in the ____ is higher than that in ____ ____ which causes fluid to move into the nephron

-bowman's space


Osmolarity of _____ is higher than that of _____ ____, resulting in pressure opposing the the movement of fluid into the nephron

-Bowman's Space


What is the composition of filtrate?

similar to that of blood but does not contain cells or proteins due to the filter's ability to select based on size


How often is the entire volume of a person's blood filtered?

every 40 minutes



-movement of solutes from blood to filtrate anywhere besides Bowman's capsule
-can secrete salts, acids, bases, and urea directly into the tubule by active or passive transport
-mechanism for getting rid of wastes that are too large to pass through glomerular pores


Where is urea made?

liver -- converts ammonia to urea which travels to the kidney and is secreted into the nephron for excretion



-movement of solutes from filtrate to blood
-substances that are often reabsorbed include glucose, amino acids, and vitamins
-ADH and aldosterone can alter reabsorption of water


What are the major waste products secreted in the urine?

*dump the HUNK*


Proximal Convoluted Tubule

-substances reabsorbed here: amino acids, glucose, water-soluble vitamins, majority of salts along with water
-70% of filtered sodium reabsorbed here
-filtrate remains isotonic to interstitium
-solutes that enter the interstitium (connective tissue surrounding the nephron) are picked up by the vasa recta to be returned to bloodstream
-substances secreted here: waste products like H+ ions, potassium ions, urea, ammonia


Descending Limb of the Loop of Henle

-filtrate enters here from the proximal convoluted tubule
-dives deep into the medulla
-permeable only to water so has an increasing osmolarity as it goes deeper into the medulla which favors the outflow of water for reabsorption into the vasa recta


Ascending Limb of the Loop of Henle

-filtrates enter here from the descending loop of henle and then pass into the distal convoluted tubule
-permeable only to salts and is impermeable to water
-at the deeper parts of the medulla, salt concentrations are high but decrease as the limb rises -- salt is removed from filtrate as it goes up loop of henle


Countercurrent Multiplier System

-created through the combined efforts of the vasa recta and nephron
-flow of filtrate through the loop of henle is in the opposite direction from the flow of blood through the vasa recta
-flow in opposite directions means the filtrate is constantly exposed to hypertonic blood which allows for reabsorption of water


Diluting Segment

-part of the loop of henle that occurs at the transition from the inner to outer medulla
-thicker part of the loop of henle because the cells lining the tube are larger and contain large amounts of mitochondria which allows for the reabsorption of Na+ and Cl- by active transport
-only portion of the nephron that can produce urine that is more dilute than blood -- filtrate is hypotonic compared to the interstitium


At the beginning of the loop of henle, the filtrate is ____ to the interstitium



Dital Convoluted Tubule

-responds to aldosterone which promotes sodium reabsorption along with the water that follows
-leads to concentration of urine
-site of waste product secretion


Collecting Duct

-responsive to both aldosterone and ADH (vasopressin)
-as permeability increases here, so does water reabsorption, resulting in further concentration of the urine
-water is reabsorbed into the interstitium then the vasa recta then it can re-enter the bloodstream
-anything not reabsorbed here will be secreted in the urine
-from here, the filtrate enters the renal pelvis


Bladder Structure

-detrusor muscle: muscular lining of bladder, contracts when parasympathetic NS acts on it
-internal urethral sphincter: consists of smooth muscle, contracted in its normal state
-external urethral sphincter: consists of skeletal muscle (voluntary control)


How does someone know when their bladder is full?

1. stretch receptors convey to the NS that the bladder is full
2. parasympathetic neurons fire, causing the detrusor muscle to contract, which causes the internal sphincter to relax -- known as the micturition reflex
3. person relaxes the external sphincter
4. urination occurs which is facilitated by the contraction of abdominal muscles


How does the excretory system partake in blood pressure control?

secretion of hormones ADH and aldosterone allow for maintenance of BP



-steroid hormone
-secreted by adrenal cortex in response to decreased BP
-alters the ability of the distal convoluted tubule and collecting duct to reabsorb sodium, which also means water reabsorption because it follows sodium
-increases both blood volume and pressure
-increases potassium and hydrogen ion excretion


Explain the pathway that promotes aldosterone release from the adrenal cortex (4)

1. decreased BP stimulated release of renin from juxtaglomerular cells in the kidney
2. renin cleaves angiotensinogen (liver protein) to form angiotensin I (peptide)
3. angiotensin I is metabolized by angiotensin-converting enzyme in the lungs to form angiotensin II
4. angiotensin II promotes release of aldosterone from the adrenal cortex


Antidiuretic Hormone (ADH, Vasopressin)

-peptide hormone
-synthesized by the hypothalamus and stored in the posterior pituitary
-released in response to high blood osmolarity
-directly alters permeability of the collecting duct by making the cell junctions of the duct leaking and thus allowing more water reabsorption
-increased concentration in the interstitium (hypertonic to the filtrate) cause reabsorption of water from tubule
-inhibited by alcohol and caffeine