3.3 Gastric enteroendocrine

Question 1

what does secretion of gastrin do

Answer 1

• Inc HCl secretion care0 8 3 activators

- Stimulates gastric emptying (minor effect)

• Stimulates parietal cell maturation
• Stimulates chief cells to secrete pepsinogen
• INC intestine muscle contraction
• Relaxes ileocecal valy and stimulates mass movements

Question 2

what does secretion of histamine do

Answer 2

• secreted from enterochromaffin cells
• inc parietal cells HCl release (one of the 3 thigns needed to activates secretion of HCl)

Question 3

what does secretion of serotonin do

Answer 3

• from enterochromaffin like cells
• inc contraction of stomach muscle

(makes 90% of total body serotonin, SSRI)

Question 4

what does release of Somatostatin do

Answer 4

• inhibits secretion from stomach and pancreas
• inhibts small intestine absorption
• inhibits gall bladder and liver release of bile

Question 5

Question 6

describe the regulation of gastric secretion

Answer 6

• neural & hormonal mechansims that alter secretions
• Stimulatory and Inhibitory events occur in phases
  • Cephalic (reflex) phase: few min prior to food entry (short)
  • Gastric phase: food entering stomach t0 3-4 hours later
  • intestinal phase: brief sitmulatory effect as partially digested food enters duodenum, followed by inhibitory effects

Question 7

describe the Cephalic Phase of gastric digestion

Answer 7

• starts with sight, smell, taste or thgouht of food
• > CNS sends impulse via CNX
• Stim mucous cells -> muscus, Chief cells -> pepsinogen, Parietal cells -> HCl, and G cells to make Gastrin

Question 8

describe the Hastric phase of gastric secretion

Answer 8

• can be triggered by
  
  • psrtially digested proteins, caffeine, inc in pH
    
    • acts on G cells to secrete gastrin which encourages all the stomach actions
  • Chemo and stretch receptors
    
    • trigger mucous, chief, parietal and G cells

Question 9

describe the intestinal phase of gastric secretion

Answer 9

• decreased pH (more acidic) or prescence of lipids and carbs caues release of secretin, GIP and CCK -> goes in blood stream and inhibits chief and parietal cells, and peristalsis
• duodenal stretch & chemoreceptors act via enterogastic reflax and inhibt myenteric plexus

Question 10

describe the gross anatomy of the small intestine

Answer 10

* major organ of digestion and absorption

• diameter: 2.5-4cm
• Duodenum: 25cm, jejunum (upper left) 2.5m, ileum (lower right) 3.5 m

Question 11

what surface modifcation are made to the SI to increase SA

Answer 11

• need inc SA for nutrient abs
• circular fold (plicae circulares) ~1 cm deep (ones you can see)
• villi 1mm high (on folds make it look fuzzy)
• microvilli ~100-2000nm high
• total SA of SI = 200m²

Question 12

describe the structure of the intestinal mucosa

Answer 12

• Absorptive cells (simple columnar epithelium)

goblet cells and enteroendocrine cells in epithelium

• lacteal running thi middle
• Paneth cells: found deep in crypts that release antimicrobial agents
• villus epithelium replaced every 2-4 days

Question 13

what are the modifcations in the diff regions of the SI

Answer 13

• Duodenum: in submucosa -> secretes bicar
  
  • Duodenal glands
  • Serosa
  • muscularis externa
• Ileum
  
  • aggregated lymphoid modules (big colelction of lymphocytes
• Jejunum

* call have plicucircularis

Question 14

describe the secretions of your SI

Answer 14

• secreted in response to distension or iritation of mucosa by hypertonic or acidic chyme
• slightly alkaline pH (7.4-7.8) & isotonic with blood plasma
• largely water, enzyme-poor, but contains mucus
• facilitates transport and absorption of nutrients

Question 15

describe the process of digestion in the small intestine

Answer 15

• Chyme from stomach contains
• > patially digested carbohydrates & proteins
• > undigested fats (lipase so far has been minmal
• spends 3-6 h in SI: most water is absorbed, all nutriends are absorbed

Question 16

what are the requirements for digestion and absorptoin in the small intestine

Answer 16

1. Slow delivery of acidic, hypertonic chyme
2. Delivert of bile, enzymes & bicarbonate ions from liver and pancreas
3. mixing

Question 17

how are things released into SI

Answer 17

1. Propfulsion: peristaltic waves move from fundus -> pylorus (starts @ cardiac region)
2. Grinding: Most vigorous peristalsis and mixing occur close to pylorus
3. Retropulsion: pyloric end of stomach act as pump to deliver 3mL of chyme to duodenum, when it closes material that doesnt go throuhg splashes back (helps with mixing)

Question 18

describe the ileocecla sphincter/valve

Answer 18

• closed when chyme exerts backward pressure (prevents regurgitation into ileum
• relaxes to admit chyme into LI when
• > gastroileal reflex enhances force of segmentation in ileum
• > gastrin increase motility of ileum

Question 19

describe the liver

Answer 19

• largest gland in body (3 lbs)
• 4 lobes based on surface features (8 based on vascular & biliary suply)
• right, left, caudate and quadrate lobe
• has a falciform ligament (actually a mesentary)

Question 20

what does the calciform ligament do

Answer 20

Suspends liver from diaphragm & anterior abdominal wall (a mesentery)

Separates right & leftl obes
Round ligament (ligamentum teres): Remnant of fetal umbilical vein

Question 21

How does blood get to the liver

Answer 21

blood enters liver at Porta hepatis via

1. Hepatic arteries
2. Hepatic portal veins
   - blood exits liver through hepatic veins (into IVC)

*have two capillary networks in row: artery -> cap -> vein -> vap

Question 22

locations of hepatic veins and arteries

Answer 22

Question 23

Describe the microscopic anatomy of Liver

shape of lovules

Answer 23

• liver lobules: hexagonal structure
• filter & process nutrient rich blood
• copmosed of plates of hepatocytes radiating from longitudinal central vein

Question 24

liver microscopic anatomy

describe the innervation

Answer 24

• middle central vein
• Portal triad: at each corner of lobule (bile duct, branch of hepatic portal bein and branch of hepatic artery)
• liver sinusoids (leaky capillaries between hepatic plates)
• kupffer cells (stellate macrophages)

Question 25

describe Kupffer cells

Answer 25

aka stellate macrophages - in liver sinusoids - self-sustaining population of macrophages within liver - remove debris (bacteria, worn out blood cells) - act as gate keeper for mmune response (in addition to lymphoid tissues)

Question 26

what are the functions of hepatocytes

Answer 26

Process blood borne nutrients Synthesize & secrete hormones Storage Performdetoxification Immune surveillance Produce bile

Question 27

describe hepatocyte function for processing blood borne nutrients

Answer 27

- metabolism: carbohydrates, proetins and fats - metabolism & detoxification of enobiotics (CYP450) - use aa to make plasma proteinsL albumins, lipoproteins (VLDL, LDL, HDL), alpha/beta globulins for transport, clotting proteins (fibrinogen & prothombin), anti-clotting proteins - makes immune proteins - amkes apoproteins (lipoprotein metabolism) - convers unconjugates bilirubin (indirect) to conjugated bilirubin (direct)

Question 28

role of hepatocytes to synthesize and secrete hormones

Answer 28

Insulin-like growth factor 1 (Growth hormone mediator) Angiotensinogen (Blood pressure & fluid balance) Thrombopoietin (platelet production) Hepcidin (iron homeostasis)

Question 29

role of hepatocytes for storage

Answer 29

store: Fat soluble vitamins (A, D, K, E) & Vit B12 - iron & copper - store glycogen (glycogenesis); makes glucose from non carb sources (gluconeogenesis ^ release when needed (glycogenolysis) - fat

Question 30

role of hepatocytes in detoxificaiton

Answer 30

- turn ammonia (NH3) -\> urea \*ammonia is toxic to CNS (crosses BBB) sources of ammonia: colon, kidneys, erythrocyte breakdown, muscle breakdown

Question 31

role of hepatocytes in immune surveillance

Answer 31

Kupffer cells (aka stellate macrophages) destroy bacteria, worn out erythrocytes & other foreign substances in blood

Question 32

role of hepatocytes in bile production + what is in bile

Answer 32

\* Hepatocytes produce ~900mL of bile/day (~500 mg bile acids) \*Yellow-green alkaline solution containing 1. water 65%-97% 2. Bile salts (bile acid (hydrophobic) conjugated w/ taurine r glycine (hydrophilic) - \> Primary acids synthesized by liver from cholesterol (cholic & chenodeoxycholic acids) - \> Secondary bile acids synthesized from primary bile acids by colonic bacterial enzymes (deoxycholic & lithocholic acids) 3. Bilirubin (conjugated/direct)-\> metabolism by small intestines bacteria produces sterobilin 4. phospholipids 5. electrolytes (Na, Ca, HCO3) 6. Xenobiotics 7. IgA

Question 33

describe the biliary tree

Answer 33

- right and left hepatic druct feed into the common hepatic duct - the common hepatic duct and cystic duct from the gall bladder feed into bile duct -\> pacreas

Question 34

what is the gall bladder

Answer 34

Thin-walled muscular sac on a n inferior/anterior surface of liver Stores & concentrates bile by absorbing its water & ions \*doesnt make bile just holds onto it

Question 35

describe hte functional relationship involved in the storage and ejection of bile

Answer 35

1. Liver continuously secretes bile 2. Bile is stores & concentrated in the gallbladder 3. Duodenum releases CCK whcih triggers dilation of hepatopancreatic sphincter & contraction of gall bladder \*ejects bile into duodenum thru duodenal ampulla 4. Bile salt emulsificating lipid droplet in digestive tract lumen

Question 36

describe enterohepatic circulation

Answer 36

1. Bile salts (cholic & chenodeoxycholic acids) are secreted into duodenum 2. As bile salts travel through small intestine they allow **lipid digestion & absorption** to occur (bc of emulsification) 3. 95% of bile salts are reabsorbed by ileum 4. Reabsorbed bile salts travel via hepatic portal bein back to liver \*only 5% of bile salts are newly synthesized each time \*blood goes to liver so bile salts recycled

Question 37