Homeostasis Flashcards
1
Q
What are the organs of the excretory system?
A
kidneys, ureters, bladder, urethra
2
Q
Describe kidney anatomy.
A
- functional unit is nephron; each kidney has about 1 mill nephrons
- all nephrons empty to renal pelvis, which narrows to form ureter (urine travels thru ureter to bladder thru urethra out)
- each kidney has a cortex (outermost layer) and medulla (inside)
- each kidney also has a renal hilum, a deep slit in the center of medial surface, thru which renal artery, renal vein, and ureter enter and exit from
- renal pelvis spans width of hilum
- has portal system
3
Q
Describe the kidney portal system.
A
- Renal artery enters cortex as afferent arterioles
- highly convoluted capillaries derived from these arterioles are called glomeruli
- after blood passes thru a glomerulus, the efferent arterioles then form a secondary capillary bed
- these surround loop of Henle and are called vasa recta
4
Q
Describe nephron structure.
A
- around glomerulus is a cuplike structure - Bowman’s capsule
- Bowman’s capsule leads to a long tubule with different areas: (in order) proximal convoluted tubule, descending and ascending limbs of Loop of Henle, distal convoluted tube, and collecting duct
5
Q
Describe the anatomy of the bladder.
A
- muscular lining known as detrusor muscle; contracts with parasympathetic activity
- urine must pass thru internal (smooth muscle, autonomic, normally contracted) and external (skeletal muscle, somatic control) urethral sphincter
6
Q
How does urinating work?
A
- when bladder is full, stretch receptors convey to nervous system that bladder requires emptying
- this causes parasympathetic neurons to fire, and detrusor muscle contracts, causing internal sphincter to relax - known as micturition reflex
- if individual relaxes external sphincter, will urinate
- if not, the process will keep repeating itself
- urination itself is done by contraction of abdominal musculature, which increases pressure within abdominal cavity, resulting in bladder compression and increased flow rate
7
Q
What are the 3 main functions of the kidney?
A
- kidney filters blood to form urine
1. filtration, 2. secretion, 3. reabsorption
8
Q
Where does filtration take place in the kidney, and how?
A
- blood passes thru glomerulus
- 20% of blood is filtered as filtrate into Bowman’s space
- movement into Bowman’s is Starling forces - hydrostatic P in glomerulus > in Bowman’s, causing fluid to move into nephron (even tho oncotic pressure opposes this movement, hydrostatic is much bigger)
- proteins and cells don’t enter filtrate
- entire volume of blood is filtered every 40 min
9
Q
What would happen to filtration if there was a kidney stone in the ureter?
A
- urine would buildup behind the stone
- fluid would build up and cause distention of renal pelvis and nephrons
- the hydrostatic P in Bowman’s would increase to the point that filtration could no longer occur
10
Q
What is kidney secretion?
A
- nephrons can secrete salts, acids, bases, urea directly into tubule by either active or passive transport
- occurs relative to body’s needs
- can eliminate substances in excess in blood (metabolites of meds, H+, K+)
- can also excrete wastes that are too big to pass thru glomerulus pores
11
Q
What occurs during reabsorption in the kidney?
A
- some compounds that are filtered/secreted may be taken back
- ex: glucose, amino acids, vitamins
- ADH and aldosterone can alter quantity of water reabsorbed to maintain blood pressure
12
Q
What is the movement of solutes in each of the three functions of the kidney?
A
- Filtration - movement of solutes from blood to filtrate at Bowman’s capsule
- Secretion - movement of solutes from blood to filtrate anywhere besides Bowman’s
- Reabsorption - movement of solutes from filtrate to blood
13
Q
What does the proximal convoluted tubule (PCT) of the nephron do?
A
- filtrate enters and majority of AAs, glucose, vitamins, salts, water are reabsorbed
- but filtrate remains isotonic to interstitium (connective tissue around nephron)
14
Q
What are the major waste products excreted in the urine?
A
- H+
- Urea
- NH3
- K+
15
Q
Why does interstitium solute concentration matter?
A
- kidney can alter osmolarity of interstitium depending on water levels in body
- if normal physiology, osmolarity in medulla is isotonic with blood, leading to water excretion in urine
- if need to conserve water, kidney will make interstitium much more concentrated so water moves out of tubule, into interstitium, and eventually back to blood thru vasa recta
16
Q
What is the countercurrent multiplier system?
A
- the vasa recta and nephron
- flow of filtrate in vasa recta + in loop of Henle are in opposite directions
- allows filtrate to constantly be exposed to hypertonic blood for max reabsorption of water
17
Q
How do the descending and ascending limbs of the loop of Henle differ?
A
- ascending is only permeable to salts and is impermeable to water
- so descending maximizes water reabsorption by taking advantage of increasing medullary osmolarity
- but ascending maximizes salt reabsorption by taking advantage of decreasing medullary osmolarity
18
Q
What is the diluting segment?
A
- loop of Henle becomes thicker from inner to outer medulla because cells lining tube are larger
- cells contain lots of mitochondria, allowing the active transport of Na and Cl
- filtrate becomes hypotonic compared to interstitium
- only portion of nephron that can produce urine more dilute than blood - important during periods of overhydration to eliminate excess water
