Lecture 8: Intestinal Transport and Liver Physiology Flashcards
Secretory fluids from accessory organs, stomach, and intestine itself take up a
Substantial fraction of ECF volume
Enterosystemic cycle
Daily exchange of several times total volume of body water
Net movement of fluid into and out of intestinal lumen every 24 hours
Enterosystemic cycle
Where are the major reabsorptive sites?
Distal SI + LI
What kind of eater has the largest volumes of secretions
Herbivores
Apical membrane has what channels
Cl channels
When Cl goes into the lumen, what follows, and what follows after?
Na follows Cl, water follows NaCl
What transporters does basolateral membrane have?
Na+/K+ ATPase
Na+/K+/2Cl co-transporter
Cl channels are normally
Closed
What will Cl channels open in response to?
Hormones and neurotransmitters binding basolateral membrane
What does cholera cause
Secretory diarrhea
What routes for fluid and electrolyte absorption
Transcellular and paracellular
What determines the route taken
Permeability of tight junctions between enterocytes
What locations are tight junctions “tight”
Stomach and colon
What locations are tight junctions “leaky”
Duodenum and jejunum
When tight junctions are leaky, is it easier or harder for fluid and ions to move paracellular?
Easier
Fluid absorbed is always
isosmotic
What is the major site for Na+ absorption
Jejunum
What transporter is used for Na absorption in jejunum?
Na-dependent co-transporters
Ileum net absorption or secretion of NaCl?
Absorption
What transporter is in the enterocyte apical membrane of ileum?
Cl-/HCO3-
What transporter is in the enterocyte basolateral membrane?
Cl- transporter
Apical membrane of colon has what channels?
Na and K channels
Synthesis of Na+ channels in colon is induced by
Aldosterone
Synthesis of Na+ channels in colon is induced by aldosterone, which leads to absorption of what and secretion of what
Increased absorption of Na
Increased secretion of K+
Fecal concentrations of K+ in
Herbivores
Why are fecal concentrations of K+ in herbivores
K+ high in forages
Loss of large volumes of ECF-type fluid from GIT leads to (ECF volume, intravascular volume, arterial blood pressure)
All decrease
Large loss of volumes of ECF-type fluid from GIT leads to what receptors being stimulated?
Baroreceptors to restore BP
High K+ losses in ECF =
Hypokalemia
Circulatory collapse is an issue associated with
Severe diarrhea
High HCO3 losses relative to Cl losses can lead to
Hypochloremic metabolic acidosis with normal anion gap
Loss of bicarb from GIT signals what to the kidneys
To reabsorb NaCl (because Na usually lost from GIT with bicarb lost)
What is activated when bicarb is lost from GIT and Na needs to be reabsorbed
RAAS activated -> Stimulates Na/H exchanger
Decreased surface area (cause of diarrhea) can be due to
Infections
Inflammation of SI
Osmotic diarrhea can be due to
Non-absorbable solutes
Secretory diarrhea can be due to
Excessive secretions of fluid by crypt cells which permanently activates adenylyl cyclase and cAMP levels high
Excessive secretions of fluid by crypt cells activate? Leading to?
Adenylyl cyclase;
High cAMP levels
Liver receives portal blood from
Stomach, SI, LI, pancreas, spleen
Functions of liver
- Process absorbed substances
- Synthesis and excretion of bile acids
- Bilirubin production and excretion
- Metabolism of nutrients
- Detoxification and excretion of waste products
Bile equation/formation
Cholesterol > Bile acids > Conjugate with glycine or taurine > Bile salts
Mononuclear phagocyte system removes ______ _____
Senescent RBC
Mononuclear phagocyte system degrades ________
Hemoglobin
Mononuclear phagocyte system degrades hemoglobin > _______
Biliverdin
Mononuclear phagocyte system degrades hemoglobin > Biliverdin > _______
Bilirubin
Bilirubin binds
Albumin in blood
Bilirubin binds albumin in blood > _____
Liver
Bilirubin binds albumin in blood > Liver > conjugated to
Glucuronic acid
Conjugated bilirubin excreted in ____ AND secreted in ____
Urine; bile
Conjugated bilirubin excreted in urine and secreted in bile –> ______ and ____
Terminal ileum and colon
Conjugated bilirubin excreted in urine and secreted in bile –> terminal ileum and colon –> deconjugated to ______ AND ____ + _____
urobilinogen AND urobilin + stercobilin
Which bilirubin deconjugation is excreted in feces
urobilin and stercobilin
Some of this bilirubin conjugation goes back to the liver
urobilinogen
Increased destruction of RBC and build up of unconjugated bilirubin
Jaundice
Jaundice can be due to what 2 things
Obstruction of bile duct
Liver disease
Use glycerol + glucogenic AA to synthesize glucose AFTER stored glycogen exhausted
Gluconeogenesis
Occurs after meal –> Synthesizing glycogen [highly branched chains of glucose]
Glycogenesis
Glycogen
Highly branched chains of glucose
Breakdown of glycogen to release glucose –> Stimulated by glucagon and epinephrine
Glycogenolysis
Liver synthesizes what kind of amino acids
Non-essential
Liver modifies amino acids using
Glucogenic AA to make glucose
What plasma proteins does liver synthesize
Albumin, clotting factors
Liver converts ammonia to
urea
What does liver do in lipid metabolism for fatty acids
Fatty acid oxidation (energy)
Liver synthesizes what as far as lipid metabolism goes
Lipoproteins, cholesterol, phospholipids, bile acids, HDLs, LDLs
What stimulates glycogenolysis?
Glucagon and epinephrine
First pass metabolism
Liver receives ALL substances absorbed from the GIT
In liver, bacteria are phagocytized by
Hepatic Kupffer cells
Liver modifies toxin to be; for
Water soluble for excretion in urine or bile
Phase I reactions include
Oxidation/reduction/hydrolysis/cyclization reactions
Phase II reactions include
Conjugation reactions (solubilize compound; transferases)
