Renal 4 Flashcards
(197 cards)
1
Q
To most accurately calculate GFR we need to look at the clearance of a substance that is freely ______ and neither _________ or ________.
A
Filtered, reabsorbed, secreted.
2
Q
What is the most accurate way of measuring GFR? What is this? Is this method practical?
A
- Inulin.
- Inulin is a polysaccharide found in a variety of plants was found in isolated nephrons to be completely filtered and not reabsorbed.
- MOST ACCURATE BUT NOT MOST PRACTICAL.
3
Q
What is the most practical/commonly used method of measuring GFR?
A
- Creatinine clearance.
- Used as an indicator of renal function and to measure GFR.
- Freely filtered.
- GFR slightly overestimated (slightly secreted).
4
Q
If plasma creatine is 1.8mg/100 ml and urine creatine is 1.5mg/ml and urine volume is 1100ml in 24 hours, what is the creatine clearance and GFR?
A
Plasma creatine: 1.8 / 100 = 0.018.
Excretion rate: 1.5 (1100) = 1650/24 hrs.
1650 / 1440 mins = 1.15mg/min.
GFR: 1.15 / 0.018 = 63.9.
5
Q
How can we determine how a nephron handles a substance?
A
By comparing filtered load (assuming freely filtered) with excretion rate. Or by comparing GFR to clearance.
6
Q
How is filtered load calculated?
A
Filtered load of x = [x] in plasma (GFR).
7
Q
What is the receptor called that binds plasma proteins?
A
megalin
8
Q
The majority of substances transported in the nephron use _____ ______.
A
membrane proteins
9
Q
What is the transport rate at saturation known as?
A
the transport maximum
10
Q
When plasma glucose exceeds the transport maximum and there is solute in the urine, what condition is this?
A
diabetes
11
Q
What is renal threshold?
A
- the plasma concentration of a solute when it first begins to appear in the urine
- occurs at transport maximum
- glucose in the urine known as glucosuria or glycosuria
12
Q
The peritubular capillaries favour what?
A
reabsorption
13
Q
What drives secretion? Is this an active or passive process? Why is secretion important?
A
- Membrane proteins
- An active process requiring the movement of substances against their concentration gradients
- Homeostatic regulation of K+ and H+ (distal) and organic compound removal (medications, food additives in proximal region) by secretion is important
14
Q
What is an example of secretion of organic solutes?
A
tertiary active transport, this is indirect transport
15
Q
Explain secretion in the proximal tubule by OAT transports as an example of tertiary active transport.
A
- Direct active transport - Na+/K+-ATPase keeps intracellular (Na+) low
- Secondary indirect transport - use Na+ concentration gradient to move dicarboxylates in the cells
- Tertiary indirect active transport - basolateral OAT transporters concentrate organic anions inside the cell using the dicarboxylate concentration gradient
16
Q
What does probenecid do when given with penicillin?
A
competes with penicillin so that the effects of penicillin last longer
17
Q
T or F - although excretion tells us what the body is eliminating, it cannot on its own tell us details of renal function.
A
true
18
Q
T or F - GFR is not an indicator of overall kidney function.
A
F - it is
19
Q
What is the clearance of a solute?
A
- the rate at which a solute disappears from the body by excretion or metabolism
20
Q
How is clearance calculated?
A
excretion rate of x / [x] in plasma
21
Q
To most accurately calculate GFR we need to look at the clearance of a substance that is freely ______ and neither _________ or ________.
A
filtered, reabsorbed, secreted
22
Q
What is the most accurate way of measuring GFR? What is this? Is this method practical?
A
- Inulin
- Inulin is a polysaccharide found in a variety of plants was found in isolated nephrons to be completely filtered and not reabsorbed
- MOST ACCURATE BUT NOT MOST PRACTICAL
23
Q
What is the most practical/commonly used method of measuring GFR?
A
- Creatinine clearance
- used as an indicator of renal function and to measure GFR
- freely filtered
- GFR slightly overestimated (slightly secreted)
24
Q
If plasma creatine is 1.8mg/100 ml and urine creatine is 1.5mg/ml and urine volume is 1100ml in 24 hours, what is the creatine clearance and GFR?
A
plasma creatine: 1.8 / 100 = 0.018
excretion rate: 1.5 (1100) = 1650/24 hrs
1650 / 1440 mins = 1.15mg/min
GFR: 1.15 / 0.018 = 63.9
25
How can we determine how a nephron handles a substance?
by comparing filtered load (assuming freely filtered) with excretion rate. Or by comparing GFR to clearance
26
How is filtered load calculated?
filtered load of x = [x] in plasma (GFR)
27
- How do we know if net reabsorption occurred?
- How do we know if net secretion has occurred?
- filtered>excreted, GFR>excreted (reabsorption)
- filtered
28
- A non-invasive method using collected urine and a blood sample to:
1. Calculate GFR: if you can find a substance that is filtered, not reabsorbed and not secreted. Filtered load=excreted load
2. Understand the net renal handling of any filtered solute
29
Urea clearance is an example of what?
- net reabsorption (filtration greater than excretion, clearance less than GFR)
30
Penicillin clearance is an example of what?
- net secretion (excretion greater than filtration, clearance greater than GFR)
31
What is the micturition reflex? How is it initiated?
- ureter cells undergo rhythmic contractions (pacemaker cells), sensation to urinate
- filling of the bladder activates stretch receptors initiating the reflex
32
- The inside of the bladder has _____ muscle, which is known as ______ muscle. The outside of the bladder has _____ muscle. _______
- __________ activity is needed for this reflex.
- internal and external sphincters _______ while detrusor muscle _______
- smooth, detrusor, skeletal
- paracellular
- relax, contract
33
- How many ml are present in the bladder for the urge to urinate?
- How much is left after micturition?
- 200ml
- 10ml
34
What is incontinence?
- the inability to urinate voluntarily
- present in infants, mother after childbirth, spinal cord damage and aging
35
- Homeostatic mechanisms for fluid/electrolyte balance focus on maintaining four parameters:
fluid volume, osmolarity, concentrations of individual ions, pH
36
H2O and Na+ determine _____ ______ and
__________.
ECF volume, osmolarity (Na+ is the main determinant)
37
In a hypotonic solution what happens to the cell?
more solute is present in the cell (hypertonic cell), fluid moves in and this causes the cell to swell and burst
38
In a hypertonic solution what happens to the cell?
more solute is present in the solution than the cell (hypotonic cell), causing the fluid to move out of the cell and the cell shrinks.
39
Cardiovascular and respiratory systems are under neural control and are quite ______, renal responses occur more ______ because kidneys are primarily under endocrine and neuroendocrine control.
rapid, slowly
40
- Water balance makes up what percent of our total body weight?
- How much is in the ICF and ECF?
- 50-60%
- 2/3 in ICF, 1/3 in the ECF
*water intake in the body must match excretion (otherwise this will change pressure and volume)
41
T or F - The kidneys can remove excess fluid or conserve what is in the body but can also replace what is lost to environment.
F - kidneys cannot replace what is also lost in the environment
42
If GFR is reduced, does this conserve or release water?
if GFR is reduced, so is blood pressure and water is conserved
43
- When removal of excess water required, the kidneys produce a ______ volume of ______ urine.
- if the kidneys need to conserve water, a ______ volume of ______ urine is produced.
- large, dilute
- low, concentrated
44
What is diuresis?
- removal of excess urine
- high volume of low concentrated urine excreted
45
How is urine concentration determined? Where does this occur?
the kidneys control urine concentration by varying the amounts of water and Na+ reabsorbed in the distal nephron (distal nephron is a distal tubule and collecting duct)
46
What happens to osmolarity as you move down the medulla?
osmolarity increases (progressively more concentrated)
47
What is the distal nephron?
The distal nephron consists of the distal tubule and collecting duct.
48
What happens to osmolarity as you move down the medulla?
Osmolarity increases (progressively more concentrated).
49
What is the role of vasopressin (AVP)/antidiuretic hormone?
- Increases the volume of concentrated urine, leading to significant water reabsorption.
- Maximal vasopressin makes the collecting duct freely permeable to water, concentrating urine.
- Absence of vasopressin makes the collecting duct impermeable to water, resulting in dilute urine.
50
AVP secretion occurs when osmolarity is _______, blood volume is ______ and blood pressure is ______.
Increased, decreased, decreased.
51
True or False: With increased binding of vasopressin, AQP2 water pores bind to the BL membrane and water is reabsorbed through the apical membrane.
False - AQP2 pores are on the apical membrane and water leaves through the BL to be absorbed into the blood.
52
What stimuli control vasopressin secretion?
- Osmolarity (main driver)
- Blood volume
- Blood pressure
- Activated osmoreceptors
53
Increased osmolarity results in...
- Increased vasopressin release (insertion of channels in apical membrane)
- Increased water reabsorption to conserve water.
54
How does our circadian rhythm and vasopressin work at night?
Increases vasopressin at night to enhance water reabsorption and decrease urination during the night.
55
Where is vasopressin produced and secreted?
- Produced by magnocellular neurosecretory cells (MNCs).
- Stored in the posterior pituitary.
- Stretch inactivated channels linked to cytoskeleton close in response to stretch based on osmolarity.
- Increased osmolarity means increased vasopressin release.
56
What creates the hyperosmotic interstitium and why isn't it reduced as water is reabsorbed?
Countercurrent exchange systems and urea contribute to the hyperosmotic interstitium.
57
What are countercurrent exchange systems?
- Evolved in mammals and birds to reduce heat loss.
- Allows warm blood to enter the limb and transfer heat directly to blood flowing back into the body.
- This is how the kidney transfers water and solutes between the loop of Henle and the peritubular capillaries.
58
What is urea and how does it contribute to the hyperosmotic interstitium?
- Urea acts as a solute and is a nitrogenous by-product of metabolism.
- A large amount of urea is reabsorbed in the distal portion of the nephron, creating a recycling loop.
59
What are the 2 components of the renal countercurrent exchange system?
- Countercurrent multiplier (Loop of Henle)
- Countercurrent exchanger (vasa recta/peritubular capillaries)
- These flow in opposite directions.
60
Filtrate entering the descending limb becomes progressively more ______ as it loses water. Blood in the vasa recta ______ water leaving the loop of Henle. The ascending limb pumps out Na, K, Cl and filtrate becomes ______.
- Concentrated
- Removes
- Hypoosmotic.
61
What happens in the descending limb of the Loop of Henle? What about the ascending limb?
- Descending limb: Water flows and is removed, but solutes are not transported.
- Ascending limb: Actively transports solutes into the interstitium by active transport (dilute filtration).
62
How does active transport occur in the Loop of Henle?
- NKCC transporter on apical membrane uses energy from [Na+] gradient to move solutes into the cell.
- Na+ is transported against concentration gradient on the BL membrane.
63
What is the target of diuretic drugs for treatment of hypertension and edema?
NKCC transporter.
64
The opposite direction loop of the vasa recta picks ____ solute up and ______ water as it travels by the ascending limb creating ________ blood.
Some, loses, hyperosmotic.
65
The main job of the multiplier is to create the ______ interstitium, the main job of the exchanger is to prevent the _______ of the interstitium.
- Hypertonic (bring solutes in)
- Washout (dilution).
66
What is the [Na+] in the plasma?
135-145 milliosmoles/L.
67
Although we talk about ingesting and excreting NaCl, only Na+ absorption is ________, Cl- tends to follow through the ________ _______ set up by Na+ movement or co-transported with Na+.
Regulated, electrochemical gradient.
68
What is aldosterone? Where is it created? What is its target?
- Steroid hormone responsible for altering Na+ reabsorption and K+ secretion (alters transcription by binding to mineralocorticoid receptor).
- Created by zona glomerulosa cells.
- Targets the last third of the distal tubule and the portion of the collecting duct located in the cortex of the kidney.
69
How does aldosterone function when it works as a rapid response?
- In seconds and minutes.
- Increased ion movement (Na+ pump, ROMK, ENaCs).
- Aldosterone binds and moves solutes through leak channels, spending more time open than closed.
- Slight increase in ATPase and ROMK and ENaCs.
70
How does aldosterone function when it works as a slow response?
- Hours.
- Creation of new transporters.
- Increases ROMK, ENaCs.
- Increase Na+ reabsorption and K+ secretion.
71
How does aldosterone act on principal cells?
- Aldosterone binds to cytoplasmic mineral corticoid receptor in P cells.
- Increases opening of Na+ and K+ channels, enhancing Na+ reabsorption and K+ secretion.
- Increased Na+ entry speeds BL Na-K pump, increasing Na+ reabsorption and speeding up K+ secretion.
- Hormone ligands translocate into the cell nucleus, increasing the transcription of apical and BL Na+ and K+ channels.
72
How is aldosterone secreted?
- K+ prevents hyperkalemia (high K+ stimulates secretion and low K+ decreases secretion).
- Decreased blood pressure leads to the production of angiotensin.
- Aldosterone is released (increased osmolarity during dehydration inhibits release; large Na+ drops can stimulate secretion).
- Decrease in blood pressure leads to production of ANGII, secreting aldosterone and Na+ reabsorption.
73
What is the renin-angiotensin-system (RAS)?
- Multistep pathway for maintaining blood pressure.
- Granular cells secrete renin, which cleaves plasma protein angiotensinogen; angiotensin I is converted to angiotensin II, the main product of the pathway to raise blood pressure when it's low.
74
What are the 3 stimuli that result in renin secretion in the renin-angiotensin pathway?
- Low blood pressure causing arteriole granular cells to secrete renin (direct).
- Sympathetic neurons activated by low blood pressure, granular cells secrete renin (indirect).
- Paracrine feedback (prostaglandins) from macula densa cells signal granular cells to secrete renin (indirect).
75
What is renin?
- Secreted by granular (juxtaglomerular) cells to convert inactive plasma protein angiotensinogen into angiotensin I.
76
What is the renin-angiotensin pathway?
- Renin converts angiotensinogen to ANG I.
- ANG I is converted to ANG II by angiotensin-converting enzyme (ACE) in blood vessel endothelium.
- ANG II stimulates aldosterone production in the adrenal cortex, leading to Na+ reabsorption, increased thirst if blood pressure is low, and increased water reabsorption and vasopressin secretion.
77
What are the effects of ANGII?
- Increases vasopressin secretion (receptors in hypothalamus).
- Stimulates thirst.
- Causes vasoconstriction.
- Increases sympathetic output to the heart and blood vessels.
- Increases proximal tubule Na+ reabsorption (Na/H+ exchanger, increasing H2O reabsorption).
- These all restore blood pressure.
78
How can hypertension be treated by pharmaceuticals?
- ACE inhibitors prevent the conversion of ANG I to ANG II, leading to relaxation of vasculature and lowering blood pressure.
- AT receptor antagonists.
- Renin inhibitors.
79
What is atrial natriuretic peptide (ANP)?
- ANP does the opposite of ANG II, promoting water and Na+ excretion due to increased blood volume and filling.
- Kicks in when blood pressure and Na+ are too high.
- Decreases sympathetic input and causes vasodilation.
80
How does ANP work in the kidney?
- Relaxes afferent arterioles (increases GFR).
- Reduces renin release (reducing aldosterone and ANG II).
- Reduces Na+ reabsorption.
81
How does ANP work in the kidney?
- relaxes afferent arterioles (increases GFR)
- reduced renin release (reducing aldosterone and ANGII)
- reduces Na+ reabsorption
82
How does ANP work in the hypothalamus, adrenal cortex and medulla?
- hypothalamus: reduces AVP release, inhibits thirst
- adrenal cortex: inhibits aldosterone release
- medulla: acts on the CVCC to decrease blood pressure
83
What is the narrow range that K+ needs to be maintained in?
3.5-5 mM
84
What do alterations in K+ affect in the cell?
resting membrane potential
85
Explain hyperkalemia
reduced efflux of potassium, more retained in the cell, positively charged and resting membrane potential is depolarized, and reached threshold (AP)
86
Explain normal K+ conditions
normal resting membrane pot. At -70, subthreshold stimulus, cell not excited
87
Explain hypokalemia
increase potassium leakage, more than normal leaks, less in the cell, hyperpolarized, a stimulus that normally reaches threshold doesn't reach threshold
88
Why can hypokalemia and hyperkalemia be dangerous?
- hypokalemia - causes muscle weakness, hard to fire APs
- hyperkalemia - (more dangerous) hyperexcitability, cells unable to repolarize, can lead to arrhythmias
89
What stimulates thirst?
- increased osmolarity, decreased blood volume, decreased blood pressure, dry mouth
90
What is the result after thirst?
- decreases osmolarity, increases blood volume and pressure, relieves dry mouth
91
Where in the brain do behavioural mechanisms occur?
in the hypothalamus
92
What helps to prevent dehydration?
avoidance behaviours
93
What are the main behavioural drivers for salt intake?
Increased aldosterone and angiotensin II
94
CV system responds to changes in...
blood volume and pressure
95
The renal system responds to changes in...
blood volume and osmolarity
96
Behavioural mechanisms respond to changes in...
both the CV and renal system
97
When does increased volume and increased osmolarity occur?
- may occur with eating salty foods and drinking liquids at the same time
- salt>water
- a. need to therefore excrete the solute and liquid to match what was taken in
98
When does increased volume, no change in osmolarity occur?
- if salt and water ingested is equivalent to isotonic solution
- salt and fluid amounts are equal
99
When does increased volume and decreased osmolarity occur?
- simply drinking pure water without ingesting solute -the kidneys cannot excrete pure water
- solute lost
- behavioural mechanism to bring in more solute
100
When does no volume change and increased osmolarity occur?
- eating salt without drinking water, increases ECF osmolarity shifting water from cells to ECF
- triggers intense thirst and kidneys make concentrated urine
101
When does no volume change and decreased osmolarity occur?
- water and solutes would be lost in sweat but only water is replaced
- can lead to hyponatremia/hypokalemia
- sports drinks can help replace lost solutes
102
When does decreased volume and increased osmolarity occur?
- dehydration could be due to heavy exercise or diarrhea
- need for increased water intake
- can result in adequate perfusion and cell dysfunction
103
When does decreased volume and no change in osmolarity occur?
- hemorrhage, need blood transfusion or ingestion of isotonic solution
104
When does decreased volume, decreased osmolarity occur?
may result from incomplete compensation for dehydration, but is uncommon
105
Decreased blood pressure can result in...
- renin secretion
- decreased GFR
- increased sympathetic and decreased parasympathetic
- thirst
- vasopressin secretion
106
Increased blood pressure can result in...
- increased GFR
- ANP secretion
- decreased sympathetic and increased parasympathetic
- thirst inhibition
- vasopressin inhibition
107
Increased osmolarity can result in...
- decreased aldosterone, thirst, vasopressin secretion
108
Decreased osmolarity can result in...
- increased aldosterone, vasopressin inhibition
109
Severe dehydration results in a ____ of ECF volume, ______ in blood pressure and an ______ in osmolarity
- decrease, decrease, increase
- decreased ECF signals increase aldosterone release but at the same time an increased osmolarity inhibits aldosterone release
- osmolarity reigns and aldosterone is not secreted
110
What 3 mechanisms can restore severe dehydration?
1. Conserving fluid to prevent additional loss
2. Trigger cardiovascular reflexes to increase blood pressure
3. Stimulate thirst so normal fluid volume and osmolarity can be restored
111
- _____ blood pressure directly _____ GFR
- decreased, decreased
112
- Paracrine feedback at ___ ___ cells causes granular cells to release ____
- macula densa, renin (less stretch secretes renin)
113
- ______ blood pressure, volume, ____ osmolarity, and _____ ANGII all stimulate vasopressin and the thirst centers of the hypothalamus. ANG II reinforces CV response
- decreased, increased, increased
114
When is a solution considered alkaline?
pH above 7 is alkaline
115
When is a solution considered acidic?
pH below 7 is acidic
116
What are some symptoms of acidosis?
CNS depression, confusion, coma
117
What are some characteristics of alkalosis?
- hyperexcitability in sensory neurons and muscles
- sustained respiratory muscle contraction
118
What are the 3 homeostatic mechanisms pH depends on?
- buffers (first line of defense)
- ventilation (75% of disturbances)
- renal regulation of H+ and HCO3- (slowest mechanism)
- buffers and renal regulation used in pH range of 7.38-7.42
119
What is a common intracellular buffer?
- intracellular: Hb, HPO4
120
What is a common extracellular buffer?
- extracellular: HCO3-
121
Increasing CO2 shifts equation to right creating ____ H+ and ____ HCO3, this causes a ____ in pH
1, 1, decrease
122
What is hypoventilation?
- hypoventilation: shift to the right, increase in CO2, pH drop, acidosis
123
What is hyperventilation?
- hyperventilation: shift to the left, increase in pH, alkalosis
124
How does the kidney handle disturbances directly and indirectly?
- directly: by altering the rates of excretion or reabsorption of H+
- indirectly: by changing the rate at which HCO3- buffer is reabsorbed or excreted.
- Alkalosis absorb H+, acidosis remove H+
125
- the proximal tubule ____ H+ and _____ HCO3-
- secretes, reabsorbs
126
- How does this pathway work?
- HCO3 is converted to CO2 to cross the membrane then reconverts to HCO3
- Na+ moves down its concentration gradient moves H+ out
- glutamine can be used as a secondary mechanism
127
- the distal nephron controls acid ______
excretion
128
- acidosis
- Type ___ intercalated cells function to increase H+ _____ and HCO3- ______
usually accompanied by increase K+ ______ (hyperkalemia)
129
- alkalosis
- Type ___ intercalated cells function to increase H+ _____ and HCO3- ______
usually accompanied by increase K _____ (hypokalemia)
130
What is respiratory acidosis?
- occurs when alveolar hypoventilation results in CO2 retention (increase) and elevated plasma CO2 (increase pH)
131
What are some common causes of respiratory acidosis?
- medicine/opioids
- asthma
- pulmonary fibrosis/edema, skeletal muscle disorders (reduced ability to ventilate)
132
What is respiratory acidosis? What are some common causes?
- occurs when alveolar hypoventilation results in CO2 retention (increase) and elevated plasma CO2 (increase pH)
- common causes: medicine/opioids, asthma, pulmonary fibrosis/edema, skeletal muscle disorders
133
Is respiratory alkalosis or respiratory acidosis more common?
respiratory acidosis
134
What is respiratory alkalosis? What are some common causes?
- occurs as a result of hyperventilation in the absence of increased metabolic CO2 production, CO2 levels drop (increase in pH)
- common causes: artificial respiration, anxiety induced hyperventilation
135
What is metabolic acidosis? What are some common causes?
- occurs when dietary and/or metabolic input of H+ exceeds H+ excretion
- common causes: lactic acid, ketoacidosis (breakdown of fats), excessive HCO3- (diarrhea)
- fixed by increased ventilation and slow renal compensation
136
What is metabolic alkalosis? What are some common causes?
- two common causes: excessive vomiting of acidic stomach contents or excessive ingestion of bicarbonate-containing antacids
- usually rapidly resolved by a decrease in ventilation, but effectiveness is limited because it can cause hypoxia
137
When is HCO3- excreted and H+ reabsorbed? When is HCO3- reabsorbed and H+ excreted?
- HCO3- is excreted and H+ is reabsorbed in respiratory alkalosis and metabolic alkalosis
- HCO3- is reabsorbed and H+ is excreted in respiratory acidosis and metabolic acidosis
138
What is the primary function of the digestive system?
move nutrients, water and electrolytes from the external environment into the body's internal environment
139
What is the GI tract? What is digestion?
- GI tract: a long tube with muscular walls lined by transporting and secretory epithelial
- Digestion: mechanical and chemical breakdown of food primarily occurs in the gut, mostly in the small intestine
140
What are the accessory glandular organs?
salivary glands, liver, gallbladder, pancreas
141
What are the functions of the salivary glands (sublingual, submandibular, parotid)?
- Moisten and lubricate food
- Amylase partially digests polysaccharide (starch)
- Dissolve some food molecules (taste)
- Lysozyme kills bacteria (antibodies)
142
What does the esophagus do?
Passageway from mouth to stomach (serves motility function, moves food via peristaltic waves)
143
The top part of the stomach wall is 1/3 _____ muscle, the bottom part of the stomach is 2/3 ____ muscle.
skeletal, smooth
144
What are the 3 segments of the small intestine?
- duodenum, jejunum, ileum
- duodenum has bile and pancreatic secretions
- jejunum and ileum have non-hormonal excretions
- most digestion occurs here
145
What happens in the large intestine?
- water and electrolyte absorption
- ileocecal separates ileum and cecum
146
What are the 4 tissue layers in the GI?
- mucosa (lumen)
- submucosa (connective tissue)
- muscularis externa (motility function)
- serosa (external connective tissue)
*ENS is able to function as its own nervous system
147
What is the innermost lumen layer called? What are the mucosa and folds in the stomach and their function?
- epithelial
- lamina propria: contains small muscles for absorption (lipid absorption/immune function)
- muscularis mucosae: thin muscle layer, no mobility role, influences the amount of SA for secretion or absorption
- muscularis externa: 2/3 layers of smooth muscle, stirs food and exposes to digestive enzymes
- Serosa: holds the intestine in place
- Rugae: large folds seen by the eye and allow the stomach to expand to increase the SA
148
What are the mucosa and folds in the small intestine and their function?
- Villi: increase SA for absorption
- Crypts: invaginations increasing SA, secretion function
- Plicae: large folds to increase the SA (rugae equivalent)
149
What are the 4 digestive functions and processes?
digestion, secretion, absorption, motility
150
What is digestion?
starts in the mouth, protein digestion in stomach, chemical digestion in the small intestine
151
What is secretion?
secretory cells secreting substances into the lumen, into the blood stream, to the interstitial fluid (or movement of substance into the lumen like in renal)
152
What is absorption?
movement from lumen to ECF
153
What is motility?
movement through the GI tract
154
What are challenges of the digestive system?
- avoiding autodigestion: break food small enough to not digest the cells of the GI tract
- maintaining mass balance: total body water through secretions, most is reabsorbed and small amount is excreted
- defense: absorb water and nutrients while preventing bacteria, viruses and other pathogens (lymphoid) tissue
155
Where are 80% of lymphocytes found?
small intestine
156
What are the different types of fluid secretions?
water, digestive enzymes, mucus
157
How is water a fluid secretion?
- Ions are transported from ECF into the lumen
- Creates osmotic gradient for water movement
158
How are digestive enzymes a fluid secretion?
- exocrine and epithelial cells in stomach and small intestine with enzymatic activity
- some are bound to apical membrane as brush border enzymes
- inactive zymogens are released that are activated by a second enzyme
159
How is mucus a fluid secretion?
- glycoproteins (mucins) serve protection and lubrication
- fluids facilitate digestion
- mucus cells in stomach and salivary glands
- goblet cells in intestine
160
What are the 2 purposes of motility?
1. Moves food from mouth to anus
2. Mechanically mixing food breaks it into uniformly small pieces
161
GI motility determined by properties of ______ muscle and modified by chemical/mechanical input from _____, ______ and ______ signals.
smooth, nerves, hormones, paracrine signals
162
Sphincters are ____ active and remain mostly contracted, but the small and large intestine are ______ active and switch between being contracted and relaxed.
tonically, phasically
163
What is a common characteristic of phasic contractions? What is an example?
- slow waves by pacemaker cells are always occurring at different frequencies in different regions in the GI tract, additional input brings to threshold
- Always occurring in the stomach but food in the stomach will cause slow wave to reach threshold and contraction occurs due to AP's
164
Where do slow wave potentials originate?
- network of cells known as the interstitial cells of Cajal (ICC)
- pacemaker for slow wave activity
- slow waves begin spontaneously in ICC and spread to adjacent smooth muscle through gap junctions
165
What are the three patterns of contraction in the GI?
- migrating motor complex (motilin)
- peristaltic contractions
- segmental contractions
166
How do migrating motor complexes (motilin) work?
- occurs between meals
- sweeps food remnants and bacteria out of the upper GI tract and into the large intestine
- begins in the stomach going from section to section ending in the ileum
167
How do peristaltic contractions work?
- during a meal
- Progressive wave of contraction of circular muscle behind a mass (bolus) of food
- forward movement
168
How do segmental contractions work?
- during a meal
- Small segments alternatively contact and relax, circular and longitudinal smooth muscle
- mixing and churning
169
Which of the 4 functions of the GI tract are regulated?
motility and secretion
170
How are the submucosal and myenteric plexuses regulated?
171
How are the submucosal and myenteric plexuses regulated?
- neural by ENS
- short and long reflexes
172
What are GI peptides?
- hormones (act in low concentrations and target tissue is far away)
- neuropeptides
- cytokines (meet hormone criteria but also targets local tissues)
173
What are similarities between the ENS and CNS?
- intrinsic neurons (entirely in GI)
- Neurotransmitters and neuromodulators (serotonin, ACh, VIP, NO)
- glial support cells (similar to astrocytes)
- diffusion barrier (like BBB, protects 2 plexuses)
- integrating center (function autonomously)
174
What is the role of the myenteric plexus?
- motility
175
What is the role of the submucosal plexus?
- secretion from GI secretory cells
176
How do short reflexes occur?
- originate entirely within the ENS
177
What is a cephalic reflex?
- feedforward control, emotional. driven by CNS input (smell and sight), drives secretion and prepares for food to hopefully enter
178
What are long reflexes?
- long reflexes have input from the CNS (symp and parasym)
179
Parasympathetic _____ motility and sympathetic ______ motility
stimulates, inhibits
180
What do the GI peptides cholecystokinin and ghrelin drive?
- cholecystokinin - drives satiety
- ghrelin: drives hunger
181
Which 2 hormones are a part of the gastrin family?
gastrin and cholecystokinin
182
Which hormones are a part of the secretin family?
- secretin
- vasoactive intestinal peptide
- gastric inhibitory peptide
- glucagon-like peptide-1 (GLP-1)
183
What are the 3 integrated functions of the digestive system?
- cephalic/oral phase: digestive processes before entering the stomach
- gastric phase: digestive processes in the stomach
- intestinal phase: digestive processes in the intestines
184
What drives the cephalic phase of the digestive system?
- long reflexes beginning in the brain initiating secretion
- increased parasympathetic output from medulla to salivary glands and ENS (vagal reflex)
185
Where does chemical and mechanical digestion occur?
In the mouth by mastication (chewing food)
186
What are the four functions of saliva?
- soften and moisten food
- digestion of carbs (amylase)
- dissolve foods (taste)
- defense (lysozymes)
187
What are the electrolytes found in saliva?
Na+, Cl-, K+, HCO3-, PO4-
188
What are the enzymes in saliva?
amylase, lysozyme, mucus, immunoglobulin A
189
What are secretory cells found in clusters known as?
acini
190
What cells are present in parotid glands and what do they secrete?
- serous cells, watery solution with amylase
191
What cells are present in the submandibular and what do they secrete?
- serous and mucus cells, watery solution and mucus
192
What cells are present in sublingual cells and what do they secrete?
- mucous cells, mucus
193
What is deglutition?
- reflex that pushes a bolus of food or liquid into the esophagus
194
What triggers the deglutition reflex?
- tongue pushes bolus against soft palate and back of mouth triggering swallowing reflex
195
What is the role of the medulla in swallowing?
- swallowing centre
- somatic output to pharynx and upper esophagus
- autonomic output to the lower esophagus
196
What is GERD?
- Gastroesophageal reflux disease (heartburn)
197
What are some causes of GERD?
- churning of the stomach causes back flow into the lower esophageal sphincter (not a true sphincter)
- negative intrapleural pressure from inspiration causes esophagus wall to expand
