Lecture Exam 4 Flashcards
Nutrient undergo what before absorption?
digestion
What two things aid digestion & absorption?
motility & secretion
Where does absorption occur?
GI lumen
Where does secretion occur?
endocrine & exocrine glands
Path of the GI tract
- mouth
- pharynx
- esophagus
- stomach
- small intestine
- colon
- rectum
- anus
What do hepatocytes in the liver secrete?
bile
What are the 2 main functions of the liver?
remove old RBC’s (catalyzes Hb & generates bilirubin)
eliminates wastes & toxins
What stores bile?
gallbladder
makes bile more concentrated & ejects it into the small intestine when needed
What transports bile from the liver or gallbladder to the duodenum for digestion?
common bile duct
The common bile duct joins with the pancreatic duct to form what?
ampulla of Vater
What regulates flow from the pancreas & gallbladder to the duodenum?
sphincter of oddi
Materials to make bile are taken up from blood in the what?
sinusoids
(similar to capillaries)
What drain into the bile ducts?
canaliculi
What do the bile ducts drain into?
common hepatic duct
What are the most common forms of carbohydrates?
disaccharides or polysaccharides
In order for carbohydrates to be absorbed, what form must they be in?
monosaccharide
(glucose, galactose, fructose)
What digests starch (carbohydrates)?
amylase
(salivary or pancreatic)
What are the 2 ways glucose & galactose (monosaccharides carbohydrates) are absorbed?
apical membrane: secondary active transport
basolateral membrane: facilitated diffusion
How is fructose (monosaccharide carbohydrate) absorbed?
apical & basolateral membrane: facilitated diffusion
In order for proteins (peptides) to be absorbed, what forms must they be in?
amino acids
dipeptides
tripeptides
What proteases break down proteins (peptides) for digestion?
endopeptidases
exopeptidases
zymogens
What is the FIRST site of protein digestion?
gastric pits in the stomach
What enzyme does the stomach lumen secrete?
pepsin
What does pepsin do?
breaks down peptides (proteins) into a form that the body can digest
What is pepsinogen?
the inactive form of pepsin
What cells in the stomach secrete pepsinogen?
chief cells
What cells in the stomach secrete acid in order to activate pepsinogen?
(acid activates pepsinogen into pepsin)
parietal cells
How are amino acids (form of proteins) absorbed?
apical membrane: facilitated diffusion or Na+ linked secondary active transport
basolateral membrane: facilitated diffusion
How are dipeptides & tripe-tides (form of proteins) absorbed?
apical membrane: active transport
basolateral membrane: broken down into amino acids & use facilitated diffusion
What is the most common form of lipids in a typical diet?
triglycerides
Typical diet contains how many g of lipids a day?
50 g of lipids a day
Typical diet contains how many g of proteins a day?
125 g of proteins a day
Typical diet contains how many g of carbohydrates a day?
500 g of carbs a day
What do lipases do?
break down triglycerides into monoglycerides
digest lipids
What are the 4 events that are ESSENTIAL for digestion & absorption of lipids?
- secretion of bile & lipases
- emulsification
- enzymatic hydrolysis
- micelle formation
What secretes lipases?
pancreas
What form should lipids be in for absorption?
micelle
What are the 3 functions of bile salts?
- emulsify lipid
- form micelle
- remove waste products
What molecules within the fat droplet can lipases act on?
only molecules near the edge of fat droplet
Describe absorption of monoglycerides & fatty acids
- micelle absorbed by simple diffusion
- enter smooth ER, reform triglyceride
- enter Golgi, packaged into chylomicrons
- exocytosis
- chylomicrons enter lymphatic system
How are vitamins A, D, E, & K (fat-soluble) absorbed?
vitamins dissolve in lipids & are absorbed with them
What do water-soluble vitamins need in order to be absorbed?
special transport proteins
Vitamin B12 must be bound to what in order to be absorbed?
an intrinsic factor
Where is sodium absorbed?
actively absorbed in jejunum, ileum, & colon
How is chloride absorbed?
passively follows sodium absorption
How is potassium absorbed?
passively absorbed
How are bicarbonate ions absorbed in the jejunum?
passively absorbed
In the ileum & colon, how are bicarbonate ions secreted?
secreted in exchange for chloride ions
Where is calcium absorbed?
actively absorbed in duodenum & jejunum
What does calcium require for absorption?
vitamin D
increases concentration of calcium-binding protein thus increases calcium absorption
Describe the process of calcium absorption
- calcium binds to calcium-binding protein
- transported into epithelial cells
- transported out across basolateral membrane by Ca2+ pump
What secretes transferrin & where is it secreted?
secreted by enterocytes into lumen of the small intestine
What does transferrin do?
binds iron for transport through blood or into cells
Describe process of iron absorption
- transferrin binds iron
- complex binds receptor
- taken into cells by receptor-mediated endocytosis
Iron is stored as what in enterocytes?
ferritin
Is water absorption active or passive?
passive
Where is water absorbed?
small intestine & colon
What does the hepatic artery do?
supplies O2 to the liver
What does the hepatic PORTAL vein do?
delivers nutrients from mesenteric veins to the liver
What does the hepatic vein do?
delivers nutrients from the liver to the heart
Where are GI hormones secreted?
from endocrine cells in the stomach & small intestine
Where is gastrin secreted & what does it do?
secreted in stomach
stimulates gastric secretions
Where is cholecystokinin (CCK) secreted & what does it do?
secreted in duodenum & jejunum
stimulates pancreatic enzyme secretion
stimulates bile secretion
stimulates gallbladder contraction
inhibits gastric secretion
Where is secretin secreted & what does it do?
secreted in duodenum & jejunum
stimulates pancreatic bicarbonate secretion
inhibits gastric secretion
Where is GIP secreted & what does it do?
secreted in duodenum & jejunum
stimulates insulin secretion by pancreas
inhibits gastric secretion
The hormone leptin is release from what?
adipose (fat) cells
When leptin (hormone) is released, what does it cause?
an increase in metabolism
a decrease in hunger
What hormone regulates food intake?
leptin
When orexigenic factors are released, what does it cause?
an increase in hunger
a decrease in metabolism
Satiety factors (fullness) causes the release of what?
alphaMSH
CART
Orexigenic factors (hunger) causes the release of what?
NPY
AgRP
ghrelin (produced in stomach when its empty)
What 2 enzymes are present in saliva?
salivary amylase (carb digestion)
lysozyme (anti-bacterial)
Characteristics of saliva
rich in bicarbonate ions
contains mucus
has enzymes present
What kind of saliva is produced under parasympathetic activation?
watery saliva
What kind of saliva is produced under sympathetic activation?
thick, protein-rich saliva
Where are gastric pits located?
in stomach lining
What is the first place of digestion for lipids & carbohydrates?
the mouth
Acid (HCl) & pepsinogen secretion in the stomach is regulated by what?
parasympathetic nervous system
What cephalic phase stimuli activate PNS & increase acid, pepsinogen, & gastrin secretion?
sight, smell or taste of food
chewing & swallowing
Where does cephalic phase stimuli originate?
in the head
requires CNS input
Where does gastric phase stimuli originate?
in stomach
Where does intestinal phase stimuli originate?
in small intestine
What gastric phase stimuli increase acid, pepsinogen, & gastrin secretion?
proteins & digestion products being in the stomach
dissension of stomach
What inhibits secretion in the gastric phase (stomach)?
exit of food
increased acidity in stomach
What portion of the pancreas produces pancreatic juice?
exocrine portion
What cells secrete pancreatic juice?
acinar & duct cells
What are the primary stimulants of pancreatic juice & bile secretion?
CCK & secretin
CCK stimulates what kind of cells?
acinar cells
to contract gallbladder & eject bile into duodenum
Secretin stimulates what kind of cells?
duct cells
to secrete more bile
What is the function of GI motility?
mix & propel GI tract contents
GI motility is due primarily to contractions of the what?
muscularis externa (outer muscle layers)
What does peristalsis do?
propels contents forwards
What does segmentation do?
mixes contents
Define segmentation
type of motility of the small intestine
alternating contractions between intestinal segments
Define bolus
chewed food + saliva
Process of swallowing reflex
- bolus arrives at inferior esophagus
- lower esophageal sphincter relaxes
- bolus enters stomach
What initiates the swallowing reflex?
tongue moving bolus to pharynx
What factors affect the gastric emptying rate?
volume of chyme in the stomach
strength of gastric peristalsis
Secretion of what increases the force of gastric motility?
gastrin
Secretion of what decreases the force of gastric motility?
CCK
secretin
GIP
What cephalic phase (head) stimuli increase gastric motility?
anger, aggression
What cephalic phase (head) stimuli inhibit gastric motility?
pain, fear, depression
What gastric phase (stomach) stimuli increase gastric motility?
distension of stomach
What intestinal phase (intestine) stimuli inhibits gastric motility?
distension of duodenum
Gastric means…
of the stomach
What increases motility in the small intestine?
distension
Define intestino-intestinal reflex
injury or severe stress that inhibits intestinal contractions
Define oleo-gastric reflex
distension of ileum inhibits gastric motility
Define gastro-ileal reflex
presence of chyme in stomach increases motility in ileum
In the colon, what mixes contents?
haustrations
In the colon, what propels bolus towards rectum?
mass movement
Define colono-colonic reflex
distension of colon in one area causes relaxation of other areas
Define gastro-colic reflex
food in stomach increases colonic motility
What enzyme turns dextrins into glucose?
dextrinase
What enzyme turns polysaccharides into glucose?
glucoamylase
What enzyme turns sucrose into fructose & glucose?
sucrase
What enzyme turns lactose into galactose & glucose?
lactase
What enzyme turns maltose into 2 glucose?
maltase
What are the functions of the urinary system?
regulate plasma ionic composition
regulate plasma volume
regulate plasma osmolarity
regulate plasma pH
remove waste products from plasma
secrete erythropoietin & renin
activate vitamin D3 & calcitrol
What is the functional unit of the kidney?
nephron
What 2 things make up the nephron?
renal corpuscle & renal tubules
What 2 things make up the renal corpuscle?
glomerulus
glomerular (Bowmans) capsule
What is the glomerulus?
the capillary network for filtration
What does the glomerular (Bowmans) capsule do?
receives the filtrate & inflow to renal tubules
What are the 4 renal tubules?
proximal tubule
loop of henle
distal convoluted tubule
collecting duct
What 2 things make up the proximal tubule?
proximal convoluted tubule
proximal straight tubule
What 3 things make up the loop of henle?
descending limb
thin ascending limb
thick ascending limb
What makes up the distal convoluted tubule?
connecting tubule
What makes up the cortical nephron?
short loop of henle
What makes up the juxtamedullary nephron?
long loop of henle
What is responsible for the medullary osmotic gradient?
juxtamedullary nephron
What 2 nephron produce urine?
cortical & juxtamedullary nephron
Define filtration
flow of protein free plasma from glomerular capillaries into the bowmans capsule
Define reabsorption
selective transport of solute & water from renal tubule to interstitial fluid
Define secretion
selective transport of solute & water from interstitial fluid into renal tubule
What are the 3 barriers that filtrate must cross to enter the capsule?
capillary endothelial layer
surrounding epithelial layer (podocytes)
basement membrane
Define filtration fraction
fraction of blood filtered by the kidneys
GFR/renal plasma flow (found as %)
What starling forces FAVOR filtration?
glomerular capillary hydrostatic pressure (60 mmHg)
bowmans capsular oncotic pressure (0 mm Hg)
What starling forces OPPOSE filtration?
bowmans capsular hydrostatic pressure (15 mm Hg)
glomerular oncotic pressure (29 mm Hg)
The kidneys account for how much of cardiac output at rest?
20%
What is typical renal blood flow amount?
625 ml/min
What is typical GFR amount?
125 ml/min or 180 L/day
What is typical filtration rate amount?
3 L/day
Define filtered load
amount of a substance filtered by the kidneys
How many liters of urine is excreted per day?
1.5 L
What percentage of filtered fluid is reabsorbed?
99%
A small increase in GFR causes a large increase in what?
large increase in volume of fluid filtered & excreted
How does increasing mean arterial pressure affect GFR?
increase in MAP increases GFR
What happens during myogenic (intrinsic) regulation of GFR?
- an increase in pressure activates mechanoreceptors
- smooth muscle contracts
- decrease in radius, increase in resistance
- GFR increase
How does tubuloglomerular feedback affect intrinsic regulation of GFR?
macula densa cella secrete paracrine factors when flow increases
this causes smooth muscle to contract, increasing resistance, & increasing GFR
How does extrinsic control directly effect GFR?
decreases in BP decreased filtration pressure thus decreases GFR
How does extrinsic control indirectly affect GFR?
decreases in BP decreases blood volume, decreases MAP, decreases GFR
Where does the majority of solute reabsorption occur?
proximal tubule (PCT)
Where is reabsorption regulated?
distal tubule (DCT) & collecting ducts
Where is reabsorption unregulated?
proximal tubule (PCT)
What are the 2 barriers for reabsorption & secretion?
epithelial cells of renal tubules
endothelial cells of capillaries
How are solutes reabsorbed?
through active & passive reabsorption
How is water reabsorbed?
through osmosis, it follows the solute
Define transport maximum
the rate of transport when carriers are SATURATED
Define renal threshold
solute concentration in the plasma when carriers are saturated & the solute first appears in the urine
Why is there no glucose in the urine of healthy patients?
because 100% of glucose will be reabsorbed
Where is glucose freely filtered?
glomerulus
Where is glucose actively reabsorbed?
proximal tubules (unregulated)
During secretion what direction does solute move?
peritubular capillaries into tubules
What are secreted substances?
potassium
hydrogen
choline
creatinine
penicillin
Where does water conservation happen?
nephron loop
Why is the proximal tubule the mass reabsorber & nonregulated?
it has leaky junctions & a large surface area
Why do the distal tubule & collecting ducts have regulated reabsorption & secretion?
they have tight junctions that limit paracellular transport
Define excretion rate
amount of a solute exerted in the urine over time
What does the amount of solute excreted depend on?
filtered load
secretion rate
reabsorption rate
If the amount of solute excreted per minute is less than the filtered load, the solute was…
reabsorbed
If the amount of solute excreted per minute is greater than the filtered load, the solute was…
secreted
Define clearance
the volume of plasma from which a substance has been completely removed
What is the clearance of inulin?
125 mL/min
What does the clearance of inulin tell us?
tells us about the clearance of a substance that is freely filtered
this is the GFR value
What is at the clearance of glucose?
0 ml/min
What is renal blood flow value?
1136 ml/min
If clearance is GREATER than GFR, the solute was what?
solute was secreted
If clearance is LESS than GFR, the solute was what?
solute was reabsorbed
Where is urine formed?
in the renal tubules
What give control over urination?
sphincters
What is the flow of urine?
kidney, ureters, bladder
Define balance
solutes & water enter & exit plasma at the same rate
quantity stays the same
Define positive balance
solute or water ENTERS plasma faster than it exits
quantity INCREASES
Define negative balance
solute or water EXITS plasma faster than it enters
quantity decreases
Regulation of renal excretion depends on what 2 things?
the late distal tubule & collecting ducts
What cells in the late distal tubule & collecting ducts regulate balance of water & electrolytes?
principal cells
What cells in the late distal tubule & collecting ducts regulate acid-base balance?
intercalated cells
What establishes the medullary osmotic gradient?
water reabsorption in the proximal tubule
Define normovolemia
normal blood volume
Define hypervolemia
high blood volume
Define hypovolemia
low blood volume
What is the osmolarity of body fluids?
300 mOsm
What organ alters osmolarity of extracellular fluid?
kidneys
Is water reabsorption an active or passive process?
passive
happens through osmosis
Where is 70% of filtered water reabsorbed?
proximal tubules
Where is 20% of filtered water reabsorbed?
distal tubules
What hormones regulate water reabsorption in the distal tubules?
ADH (vasopressin) and aldosterone
When being reabsorbed, water follows what?
the solute
this is why it is passive
What establishes the osmotic gradient for water reabsorption?
Na+ being actively transported across the basolateral membrane
What establishes the medullary osmotic gradient?
the countercurrent multiplier
The medullary osmotic gradient is dependent on what?
the loop of henle
What part of the loop of henle is permeable to water & has NO transport of Na+, Cl-, or K+?
the descending loop
What part of the loop of henle is impermeable to water & has active transport of Na+, Cl-, and K+?
the ascending loop
Where is 10% of filtered water reabsorbed?
collecting ducts
What hormone regulates water reabsorption in the collecting ducts?
ADH
Water reabsorption in the distal tubule & collecting duct is dependent on what?
the medullary osmotic gradient that is established by the countercurrent multiplier & epithelium permeability to water
What is water permeability dependent on?
water channels (aquaporins)
Where is aquaporin 3 always present?
in basolateral membrane
Aquaporin 2 is present where & under what conditions?
present in apical membrane only when ADH is present in blood
How does ADH affect water reabsorption?
it promotes water reabsorption & reduces urine volume
it stimulates insertion of aquaporin 2
Where is ADH secreted from?
posterior pituitary (after stimulation from hypothalamus)
How does increased extracellular fluid osmolarity affect ADH?
it increases ADH
How does decreased baroreceptor activity affect ADH?
it increases ADH
If blood pressure drops below 80 mmHg what happens to GFR, water filtered, & water excretion?
decrease in GFR
decrease in amount of water filtered
decrease in water excretion
If blood pressure increases to more than 180 mmHg what happens to GFR, water filtered, & water excretion?
increase in GFR
increase in amount of water filtered
decrease in water excretion
Define hypernatremia
high plasma sodium
Define hyponatremia
low plasma sodium
What is the primary solute in extracellular fluid?
sodium
Sodium is critical for what 2 things?
normal osmotic pressure
function of excitable cells
What does aldosterone do?
it increases sodium reabsorption
How does aldosterone increase sodium reabsorption?
it acts on principal cells of distal tubules & collecting ducts to increase the number of Na/K pumps on the basolaterla membrane and Na+, K+ channels on the apical membrane
What organ secretes angiotensinogen?
the liver
What turns angiotensinogen into angiotensin 1?
renin
What turns angiotensin 1 into angiotensin 2?
ACE
What stimulates aldosterone production?
angiotensin 2
What 3 factors increase renin release?
- decrease in BP in afferent arteriole
- increase in renal sympathetic nerve activity
- decreased Na+ and Cl-
What cells secrete ANP (atrial natriuretic peptide)?
atrial cells
ANP is secreted in response to what?
atrial wall stretch
patients with heart failure will show high levels of ANP
An increase in ANP causes what chain of events?
increase in afferent arteriole radius
decrease of efferent arteriole radius
increase in glomerular pressure
increase in GFR
increase in Na+ EXCRETION
increased urine volume
Where is K+ freely filtered?
glomerulus
Where is K+ reabsorbed?
proximal & tubules
Where is K+ secreted?
distal tubules & collecting ducts
Which hormone affects K+ secretion?
aldosterone
an increase in aldosterone release = an increase in K+ secretion
Define hypercalcemia
high plasma calcium
Define hypocalcemia
low plasma calcium
Why is calcium balance critical?
it triggered exocytosis, secretion, and muscle contraction
Where is the majority of calcium reabsorbed?
in the proximal tubules
Where is the rest of calcium reabsorbed?
loop of henle & distal tubules
Reabsorption of Ca2+ in the loop of henle & distal tubules is regulated by what 2 hormones?
parathyroid hormone (PTH)
calcitonin
How does parathyroid hormone (PTH) affect [Ca2+]?
it increases Ca2+ reabsorption thus increasing plasma [Ca2+]
How does calcitonin affect [Ca2+]?
it decreases plasma [Ca2+]
How does a decrease in blood pressure & blood volume affect ADH?
it increases its secretion
Where is aldosterone secreted?
adrenal gland
How does a decreased in blood pressure and blood volume affect ADH?
it increases its secretion
