Ch. 10: Homeostasis Flashcards
(133 cards)
1
Q
what are the 4 main functions of the excretory system? what is the one major organ of the excretory system?
A
- regulation of blood pressure
- blood osmolarity
- acid-base balance
- removal of nitrogenous wastes
the kidneys!
2
Q
what are the 4 components of the excretory system?
A
- kidneys
- ureters
- bladder
- urethra
3
Q
structure: kidneys
A
two bean-shaped structures located behind the digestive organs at the level of the bottom rib
4
Q
what is the functional unit of the kidney?
A
the nephron!
each kidney has approximately 1 million
5
Q
defn + func: renal pelvis
A
narrows to form the ureter
all nephrons eventually empty into here
6
Q
where does urine travel? (4 steps)
A
- leaves the kidneys
- goes through the ureter
- to the bladder (for storage)
- through the urethra to exit
7
Q
kidney structure (5 + diagram)
A
subdivided into a 1. cortex (outermost layer) and a 2. medulla (sits within the cortex)
also has a 3. renal hilum (a deep slit in the center of its medial surface)
- the renal pelvis (the wides part of the ureter) spans almost the whole width of the renal hilum
- the renal artery, vein, and ureter enter and exit through the renal hilum
8
Q
defn: portal system
A
consists of 2 capillary beds in series through which blood must travel before returning to the heart
9
Q
explain the kidney’s portal system (6 + diagram)
A
- the renal artery branches out
- passes through the medulla
- and enters the cortex as afferent arterioles
- the highly convoluted capillary tufts derived from these afferent arterioles are known as glomeruli
- after blood passes through a glomerulus, the efferent arterioles then form a second capillary bed
- these capillaries surround the loop of Henle and are known as the vasa recta
10
Q
components of the nephron (6)
A
- around the glomerulus is a cup-like structure known as 2. Bowman’s capsule which leads to a long tubule with distinct areas in order:
- proximal convoluted tubule
- descending and ascending limbs of the Loop of Henle
- distal convoluted tubule
- collecting duct
11
Q
what is the kidney’s ability to excrete waste intricately linked to?
A
the specific placement of the structures of the nephron and their physiology
12
Q
defn + what causes it to work: detrusor muscle
A
the muscular lining of the bladder
parasympathetic activity causes it to contract
13
Q
char (3): internal urethral sphincter
A
- smooth muscle
- contracted in its normal state
- under involuntary control
14
Q
char (2): external urethral sphincter
A
- skeletal muscle
- under voluntary control
15
Q
what happens when the bladder is full (3)? what is this called?
A
- when the bladder is full, stretch receptors convey to the nervous system that the bladder requires emptying
- this causes the parasympathetic neurons to fire and the detrusor muscle contracts
- this contraction causes the internal sphincter to relax
called: micturition reflex
16
Q
what happens after the micturition reflex? (3)
A
- the next step is up to the individual (the person can choose to relax the external sphincter to urinate or can maintain the tone of the external sphincter to prevent urination)
- this can cause a few moments of discomfort, but the reflex usually dissipates in a few minutes
- if the bladder is NOT emptied, then the process will begin anew shortly thereafter
17
Q
how is urination itself facilitated?
A
by the contraction of the abdominal musculature, which increases pressure within the abdominal cavity, resulting in compression of the bladder and increase urine flow rate
18
Q
what does the kidney do to blood?
A
filters the blood to form urine
19
Q
what is the composition and quantity of urine determined by?
A
the present state of the body
if blood volume is low and blood osmolarity is high, then it is most beneficial to the body to maximally retain water resulting in low-volume, highly-concentrated urine
a patient receiving lots of IV fluids is likely to produce a larger volume of less concentrated urine
20
Q
what is the primary job of the kidneys? what is true about the kidney for this to occur?
A
to regulate blood volume and osmolarity
the kidney function must be divided into 3 different processes: filtration, secretion, and reabsorption
21
Q
defn: filtrate
A
approximately 20% of the blood that passes through the glomerulus is filtered as fluid into Bowman’s space
this is that collected fluid
22
Q
defn + func: Starling forces
A
governs the movement of fluid into Bowman’s space
accounts for the pressure differentials in both hydrostatic and oncotic pressures between the blood and Bowman’s space
23
Q
what causes fluid to move into the nephron?
A
the hydrostatic pressure in the glomerulus is significantly higher than that in Bowman’s space
24
Q
what causes pressure opposing the movement of fluid into the nephron?
A
the osmolarity of blood is higher than that of Bowman’s space
25
why is the net flow of blood into the nephron?
the hydrostatic pressure is much larger than the oncotic pressure
26
diagram: Starling forces
27
what would happen if the ureter was obstructed by a kidney stone? (3)
1. would result in a buildup of urine behind the stone
2. enough fluid will build up and cause distention of the renal pelvis and the nephrons
3. the hydrostatic pressure in Bowman's space would increase to the point that filtration could no longer occur because there would be excessive pressure opposing movement of fluid into the nephron
28
composition (3): filtrate
1. similar in composition to blood
2. does not contain cells or proteins due to the filter's ability to select based on size (molecules or cells larger than glomerular pores will remain the blood
3. isotonic to blood so that neither the capsule nor the capillaries swell
29
how often is the entire volume of a person's blood filtered?
about every 40 minutes
30
analogy: glomerulus
like a sieve or colander
small molecules dissolved in the blood will pass through the tiny pores, large molecules like proteins and blood cells will not
31
defn: secretion
the nephrons are able to secrete salts, acids, bases, and urea directly into the tubule by either active or passive transport
it is also a mechanism for excreting wastes that are simply too large to pass through glomerular pores
32
what determines the quantity and identity of the substances secreted into the nephron? + example
the needs of the body at that time
example: a diet heavy in meat means large protein intake, which contains a lot of nitrogen. Ammonia (NH3) is a byproduct of the metabolism of nitrogen-containing compounds and can disturb the pH of blood and cells
the liver converts the ammonia to urea (neutral) which travels to the kidney and is secreted into the nephron for excretion in the urine
33
what are examples of 3 things that the kidneys are capable of eliminating when present in excess in the blood?
1. potassium cations
2. hydrogen ions
3. metabolites of medications
34
func: reabsorption
some compounds that are filtered or secreted may be taken back up for use
35
what are 3 examples of substances that are almost always reabsorbed?
1. glucose
2. amino acids
3. vitamins
36
what 2 substances can alter the quantity of water reabsorbed within the kidney in order to maintain blood pressure?
1. ADH (vasopressin)
2. aldosteron
37
summary: functions of filtration, secretion, and reabsorption
FILTRATION: movement of solutes from blood to filtrate at Bowman's capsule
SECRETION: movement of solutes from blood to filtrate anywhere besides Bowman's capsule
REABSORPTION: movement of solutes from filtrate to blood
38
what are the 2 main goals of the kidney?
1. keep what the body needs and lose what it doesn't (reabsorb certain minerals for reuse and selectively eliminate waste)
2. concentrate the urine to conserve water
39
mnemonic: horizontal vs. vertical segments of the nephron
HORIZONTAL (Bowman's capsule, the proximal convoluted tubule, the distal tubule) focused on IDENTITY of the particles in the urine (keep what the body needs and lose what it doesn't)
VERTICAL (loop of Henle, collecting duct) focused on the VOLUME and CONCENTRATION of the URINE (concentrate the urine to conserve water)
40
diagram: nephron
41
what happens in the proximal convoluted tubule (PCT)? (4)
1. the filtrate enters here first
2. amino acids, glucose, water-soluble vitamins, and most salts are reabsorbed along with water
3. almost 70% of filtered sodium is reabsorbed here, but the filtrate remains isotonic to the interstitium, as other solutes and a large volume of water are also reabsorbed
4. also the site of secretion for a number of waste products (hydrogen ions, potassium ions, ammonia, urea)
42
defn: interstitium
the connective tissue surrounding the nephron
43
what happens to solutes that enter the interstitium?
they are picked up by the vasa recta to be returned to the bloodstream for reuse within the body
44
mnemonic: major waste products excreted in the urine
Dump the HUNK
H+
Urea
NH3
K+
45
what happens to filtrate after the proximal convoluted tubule? (2)
1. it enters the descending limp of the loop of Henle, which dives deep into the medulla before 2. turning around to become the ascending limb of the loop of Henle
46
how is the flow of water affected by characteristics of the descending limb and the medulla?
descending limb: permeable only to water
medulla: has an ever-increasing osmolarity as the descending limb travels deeper into it
as the descending limb traverses deeper into the medulla, the increasing interstitial concentration favors the outflow of water from the descending limb, which is reabsorbed into the vasa recta
47
what effect is had by the fact that the kidney is capable of altering the osmolarity of the interstitium?
this creates a gradient (coupled with selective permeability of the nephron) that allows maximal reabsorption and conservation of water
48
osmolarity in the cortex at normal physiological state
approximately the same as blood, stays at that level
49
osmolarity in the interstitium deeper in the medulla
can range from isotonic with blood (when trying to excrete water) to 4 times as concentrated (when trying to conserve water)
50
what happens if the concentration is the same in the tubule and the interstitium?
what happens if the interstitium is more concentrated?
SAME: there is no driving force (gradient) and water is lost in the urine
INTERSTITIUM CONCENTRATED: water will move out of the tubule, into the interstititum, and eventually back into the blood
51
defn + components + reason for why: countercurrent multiplier system
defn: the flow of filtrate through the loop of Henle is in the opposite direction from the flow of blood through the vasa recta
reason: if the two flowed in the same direction, they would quickly reach equilibrium and the kidney would be unable to reabsorb as much water
by making the two flow opposite, the filtrate is constantly being exposed to hypertonic blood, which allows maximal reabsorption of water
components: vasa recta + nephron
52
what happens as the descending limb transitions to become the ascending limb?
there is a change in permeability
the ASCENDING limb is only permeable to SALTS (maximizes salt reabsorption by taking advantage of DECREASING medullary osmolarity), impermeable to water
the DESCENDING limb maximizes WATER reabsorption by taking advantage of increasing medullary osmolarity
53
what happens at the transition from the inner to outer medulla? why does this happen?
the loop of Henle becomes thicker in the diluting segment
this happens because the cells lining the tube are larger
54
why are the cells lining the tube larger in the diluting segment of the loop of Hnele?
they contain large amounts of mitochondria, allowing for reabsorption of sodium and chloride by active transport
55
what happens as a result of some much salt being reabsorbed while water is stuck in the nephron?
the filtrate becomes hypotonic compared to the interstitium
56
why is the diluting segment noteworthy?
it is the only portion of the nephron that can produce urine that is more dilute than blood
which is important during periods of overhydration and provides a mechanism for eliminating excess water
57
what happens from the beginning of the loop of Henle to the end? (2)
1. there is a slight degree of dilution (the filtrate at the beginning is isotonic to the interstitium)
2. the volume of the filtrate has been much reduced, showing a net reabsorption of a large volume of water
58
where does the filtrate enter after the proximal convoluted tubule?
the distal convoluted tubule (DCT)
59
what happens with the distal convoluted tubule? (3)
1. it responds to aldosterone, which promotes sodium reabsorption
2. because sodium ions are osmotically active particles, water will follow, concentration the urine and decreasing its volume
3. the DCT is also a site of waste product secretion
60
func + how does it function: diuretics
can help the body get rid of excess fluid
typically inhibit the reabsorption of sodium in one or more nephron regions, thus increasing sodium excretion
sodium will pull water with it, thus getting rid of excess fluid
61
what does the final concentration of the urine depend largely on?
the permeability of the collecting duct
62
what is the collecting duct responsive to? (2)
1. aldosterone
2. ADH
63
what happens with the collecting duct? (2)
1. as permeability of the collecting duct increases, so too does water reabsorption, resulting in further concentration of the urine
2. the reabsorbed water enters the interstitium and makes its way to the vasa recta, where it reenters the bloodstream again to become part of the plasma
64
how much water does the collecting duct reabsorb?
the amount is variable
WELL HYDRATED BODY: collecting duct fairly impermeable to salt and water
BODY IN CONSERVATION MODE: ADH and aldosterone act to increase water reabsorption (greater water retention and concentrated urine output)
65
what happens to anything that is not reabsorbed from the tubule by the end of the collecting duct?
it will be excreted
66
why is the collecting duct the point of no return?
after it, there are no further opportunities for reabsorption
67
what happens to the filtrate as it leaves the tubule? (2)
1. it collects in the renal pelvis
2. it flows through the ureter to the bladder where it is stored until voiding
68
at the end of the tubule, what is the fluid/filtrate mostly made of? (3)
1. urea
2. uric acid
3. excess ions (sodium, potassium, magnesium, and calcium)
69
what are the 3 systemic impacts that is made by the selective elimination of water and solutes by the kidneys?
control of:
1. blood pressure
2. blood osmolarity
3. acid-base balance
70
what are the 2 hormones important for blood pressure maintenance?
1. aldosterone
2. ADH (vasopressin)
71
defn + func: aldosterone
a steroid hormone that is secreted by the adrenal cortex in response to decreased blood pressure
func: increases blood pressure by increasing the reabsorption of sodium
72
what does decreased blood pressure stimulate?
the release of renin from juxtaglomerular cells in the kidney
73
what does renin do?
it cleaves angiotensinogen, a liver protein, to form angiotensin I
74
what happens to angiotensin I?
it is metabolized by angiotensin-converting enzyme in the lungs to form angiotensin II
75
func: angiotensin II
promotes the release of aldosterone from the adrenal cortex
76
how do we exploit aldosterone's functionality in medicine? (2)
1. by using drugs that block angiotensin-converting enzyme or the angiotensin II receptor
2. blocking this receptor limits aldosterone release, which limits salt and water reabsorption, and therefore results in lowered blood pressure
77
notation: most ACE inhibitors
end with -pril
78
notation: angiotensin II receptor blockers
end with -sartan
79
how does aldosterone work? (4)
by altering the ability of the distal convoluted tubule and collecting duct to reabsorb sodium
if we reabsorb more sodium, water will flow with it
the reabsorption of isotonic fluid has the net effect of increasing blood volume and thus blood pressure
also increases potassium and hydrogen ion excretion
80
defn + func (2) + aka (2): ADH
defn: a peptide hormone synthesized by the hypothalamus and released by the posterior pituitary in response to high blood osmolarity
func: directly alters the permeability of the collecting duct, allowing more water to be reabsorbed by making the cell junctions of the duct leaky
2. increased concentration in the interstititum (hypertonic to the filtrate) will then cause water reabsorption from the tubule
aka: antidiuretic hormone, vasopressin
81
what 2 things inhibit ADH release and what is the net effect?
1. alcohol
2. caffeine
net effect: frequent dilute urination
82
how does the cardiovascular system regulate blood pressure in relation to the kidneys?
by vasoconstricting or vasodilating to keep it maintained
CONSTRICTION of afferent arteriole --> lower pressure of blood reaching glomeruli (adjacent to the juxtaglomerular cells) --> secondarily leads to renin release, helps to raise blood pressure
83
why must blood osmolarity be tightly controlled?
to ensure correct oncotic pressures within the vasculature
84
defn: osmotic vs. oncotic pressure
OSMOTIC = the "sucking" pressure that draws water into the vasculature caused by all dissolved particles
ONCOTIC = the osmotic pressure that is attributable to dissolved proteins specifically
85
value: blood osmolarity
~ 290 milliosmoles per liter (mOsm)
86
what happens when blood osmolarity is low? high?
LOW: excess water will be excreted, while solutes will be reabsorbed in higher concentrations
HIGH: water reabsorption increases, solute excretion increases
87
what is the major regulator of blood pH?
bicarbonate buffer system
88
summary: how the respiratory system contributes to acid-base balance by increasing or decreasing the respiratory rate?
if blood pH too low: increasing respiratory rate blows off more CO2, favors conversion of H+ and HCO3- to water and CO2, increasing the pH
if blood pH too high: decreasing the respiratory rate causes opposite effects
89
how does the excretory system contribute to the maintenance of acid-base balance?
the kidneys are able to selectively increase or decrease the secretion of hydrogen ions and bicarbonate
low blood pH: kidneys excrete more hydrogen ions and increase bicarbonate reabsorption, increasing pH
high blood pH: kidneys excrete more bicarbonate, increase hydrogen ion reabsorption
90
how does the excretory system effects on acid-base balance compare to the respiratory system's effects?
excretory system is slower, but highly effective
91
what is the largest organ in our bodies by weight and size?
the skin!
92
aka: skin
integument
93
main func: skin
nonspecific immune defense, protecting us from exposure to the elements and invasion by pathogens
94
layers of the skin from in to out (3) + diagram
1. hypodermis (subcutaneous layer)
2. dermis
3. epidermis
95
what is skin derived from?
the ectoderm
96
defn: strata
the layers that the epidermis is subdivided into
97
what are the names of the layers (strata) of the epidermis from inside to outside? (5) + diagram
1. stratum basale
2. stratum spinosum
3. stratum granulosum
4. stratum lucidum
5. stratum corneum
98
defn + func (2): stratum basale
the most inner layer of the epidermis
func: 1. contains stem cells
2. responsible for proliferation of keratinocytes (the predominant cells of the skin) that produce keratin
99
defn + func (2): stratum spinosum
the second inner layer of the epidermis
func: 1. the cells from the stratum basale become connected here
2. the site of Langerhans cells
100
defn + func: stratum granulosum
the middle layer of the epidermis
func: keratinocytes die and lose their nuclei
101
defn + char (2): stratum lucidum
the second to outer layer of the epidermis
char: 1. only present in thick, hairless skin (like the sole of the foot or palms)
2. nearly transparent
102
defn + func: stratum corneum
the outermost layer of the epidermis
func: contains several dozen layers of flattened keratinocytes, forming a barrier that prevents invasion by pathogens and helps to prevent loss of salt and fluids
103
what are the main cells of the epidermis?
keratinocytes
104
func: keratin
resistant to damage and provides protection against injury, water, and pathogens
105
what do calluses form from?
excessive keratin deposition in areas of repeated strain due to friction
106
what are fingernails and hair formed from?
keratin
107
mnemonic: layers of the epidermis (superficial to dep)
Come: stratum Corneum
Let's: stratum Lucidum
Get: stratum Granulosom
Sun: stratum Spinosum
Burned: stratum Basale
108
defn + func: melanocytes
a cell type derived from neural crest cells and found in the stratum basale
func: produce melanin
109
defn: melanin
a pigment that serves to protect the skin from DNA damage caused by ultraviolet radiation
110
what happens to melanin once produced?
it is transferred to the keratinocytes
111
what is skin color caused by?
humans actually have comparable numbers of melanocytes
skin color is caused by varying levels of ACTIVITY of the melanocytes (more active = darker skin tones)
upon UV radiation, melanocytes INCREASE activity, resulting in darker skin
112
defn: albinism
a genetic metabolic disorder characterized by the inability to synthesize melanin
typically inherited in an autosomal recessive fashion
113
defn: vitiligo
an autoimmune disorder in which melanocytes are killed by the individual's immune system
114
defn + func: Langerhans cells
special macrophages that reside within the stratum spinosum
func: capable of presenting antigens to T-cells in order to activate the immune system
115
what are the 2 layers of the dermis (from outer to inner)?
papillary layer
reticular layer
116
char: papillary latyer
consists of loose connective tissue
117
char: reticular layer
denser than the papillary layer
118
what 3 things originate in the dermis?
1. sweat glands
2. blood vessels
3. hair follicles
119
where are most sensory receptors located?
the dermis
120
defn + char + func: Merkel cells (discs)
sensory receptors present at the epidermal-dermal junction
connected to sensory neurons
responsible for deep pressure and texture sensation within the skin
121
what are 4 other sensory organs in the skin and what do they respond to?
1. free never endings = pain
2. Meissner's corpuscles = light touch
3. Ruffini endings = stretch
4. Pacinian corpuscles = deep pressure and vibration
122
defn + char: hypodermis
a layer of connective tissue that connects the skin to the rest of the body
char: contains fat and fibrous tissue
123
what is thermoregulation achieved by? (4)
1. sweating
2. piloerection
3. vasodilation
4. vasoconstriction
124
what is sweating controlled by
the autonomic nervous system
125
what happens when body temperature rises above the set point determined by the hypothalamus? (3)
thermoregulation processes must occur in order to rid the body of heat
1. postganglionic sympathetic neurons that utilize ACh innervate sweat glands and promote the secretion of water with certain ions onto the skin
2. heat is then absorbed from the body as the water molecules undergo a phase change to evaporate
3. at the same time, arteriolar vasodilation occurs to maximize heat loss, bringing a large quantity of blood to the skin, which accelerates the evaporation of sweat by maximizing the heat energy available for the liquid-gas phase change
126
is sweating the main mechanism of cooling?
no, technically it is the evaporation of water from the skin which absorbs body heat
127
why are the neurons that innervate sweat glands unusual?
they are cholinergic whereas all other postganglionic sympathetic neurons are noradrenergic
this means that they release ACh and not norepinephrine
128
defn + func: piloerection
in the cold, arrector pili muscles contract, causing the hairs of the skin to stand up on end
func: helps to trap a layer of heated air near the skin
129
what 2 other things happen in the cold along with piloerection?
1. arterioles that feed the capillaries of the skin constrict, limiting the amount of blood reaching the skin
2. skeletal muscle may begin to contract rapidly, causing shivering
130
what does shivering require?
a sizeable amount of ATP
131
func + location: white fat
func: helps to insulate the body
location: just below the skin
132
char (3): brown fat
1. more common in infants
2. has a much less efficient ETC than white fat
3. more heat energy is released as fuel is burned
133
how and why does the skin help maintain the body's osmolarity? in what situation is this especially important/
because the skin is relatively impermeable to water
this prevents the entrance of water through the skin and the loss of water from tissues which is especially important with burns or large losses of skin because dehydration of tissues is a threat to survival
