physiology chapter 18

function of pancreas

-secretes the hormones insulin and glucagon into blood -produces "pancreatic juices" - which is rich in bicarbonate and other digestive enzymes (amylase, trypsin, lipase) -these join the common bile duct from the liver before entering the duodenum

how products from pancreas enter the GI tract

-secretion of HCO3 from the ductule cells is obtained from the plasma using a Na/HCO3 cotransport carrier -secretion of HCO3 from the ductule cells into the lumen is accompanied by movement of Cl in opposite direction

function of liver

-secretory organ, produce and secrete bile -also processes and stores nutrients -Serves as a filter and functions in the removal of old red blood cells which leads to hemoglobin processing and the generation of bilirubin.

function of small intestine

-sections rhythimcally contract to mix chyme up and down via segmentation (rhythm set by pacemaker cells) -material is digested and abosrbed due to the high absorptive surface area -enzymes break down food to smallest form possible

motility of small and large intestine

-smooth muscle contract by segmentation slowly, 1 contraction every 30 min

function of the stomach

-store food -initiate the digestion of proteins -kill bacteria -move food into SI as chyme

parietal cells secrete ___ liters of HCL per day

2 liters

If the salivary glands were unable to secret amylase, what effect would this have on starch digestion?

Digestion will solely occur in the small intestine by pancreatic amylase

pepsin

Enzyme that breaks down proteins into smaller polypeptide fragments

pressure receptors stimulated by food or drink on the pharynx send ____ impulses to medulla oblongata. ____ fibers tell muscles of the pharynx and esophagus to swallow

afferent; efferent

how are most carbohydrates consumed

as disaccharides or polysaccharides: sucrose, lactose, maltose, starch, glycogen

trypsin

breaks down proteins

structure of large intestine

cecum: first part, absorbs salts and fluids that still remain, internal wall composed of thick mucus membrane colon: long, coiled, tubelike organ, removes water from material, moves stool to rectum rectum: final section, any residual molecules (Na, K, Cl) are absorbed and indegistable food is decomposed by anaerobic bacteria, stool is is thickened anus: end of GI tract, when rectum is full, body feels the urge to have bowel movement, internal anal sphincter relaxes and pushes stool out

Bile is ejected from the gallbladder through the cystic duct into the ____ emptying into the ____.

common bile duct; duodenum

structure of small intestine

duodenum: first and shortest part, connected to stomach, plays vital role in chemical digestion jejunum: second part, also responsible for absorption, lined with villi ileum: last part, connected to cecum, absorbs whatever nutrients not taken up (B12 and bile salts), also has villi

The process in which fat droplets are broken up by bile is termed __________.

emulsification

lipase

enzyme that breaks down fat

amylase

enzyme that breaks down starch/carbs

secretion of HCL by the parietal cells is stimulated by

gastrin = hormone ACh = neurotransmitter histamine = paracrine

What is the name of the vessel that delivers blood to the liver from the intestine?

hepatic portal vein

rate of digestion ____ after emulsification

increases

lower esophageal sphincter

involuntary muscle control that prevents acid and stomach contents from travelling back into esophagus

bilirubin

is a bile pigment absorbed into blood and when modified by bacterial enzymes it is converted to Urobilinogen. This is secreted into renal system to give urine its yellow color. Derivatives also give feces its brown color.

upper esophageal sphincter

muscles under voluntary control that keeps food and secretions from going down windpipe

what other systems work with digestive

nervous, respiratory, and renal

emulsifying agents

phospholipids and bile salts

function of digestive system

process ingested foods into molecule forms and transfer, with water and salts, to circulatory system (digest and absorb)

fat droplets coated in emulsification agent repel each other and dont

re-aggregate

migrating myoelectrical complex (MMC) ____ segmentation and moves undigested food into large intestine

segmentation

the emulsification of fat aids digestion because the ____ and more ____ emulsification droplets presents a greater _______ than the unemulsified fat droplet

smaller; numerous; surface area

functions of gallbladder

stores and concentrates bile

functions of hydrochloric acid (HCL) in stomach

the high concentration of HCL from the parietal cells make gastic juices very acidic, with a pH of less than 2. the strong acidity serves 3 functions: 1. proteins are denatures - easier to digest 2. weak pepsin enzymes partially digest each other - which frees the fully active pepsin 3. pepsin is more active under acidic conditions - the fully active pepsin is able to partially breakdown protein

hepatic portal system

the veins that carry blood from the digestive organs to the liver for processing before they enter the general systemic circulation

n adults, most fat digestion takes place in the small intestine.

true

motility of large intestine

-eating a meal stimulates contractions in colon -there are no villi in LI -outer surface of colon buldges outward to form pouches, called haustra -haustral contractions move chyme slowly -material stays here for 18-24 hours -movement of fecal material initiates the defecation reflex - similar to when you have to urinate

role of hepatic portal circulation in digestion

-important because it captures substances from the digestive system and sends them to the liver to be metabolized -rids the body of toxins

structure of liver

-largest internal organ -can hold one pint of body's blood -2 main lobes -small ducts that form the common hepatic duct which transports bile made by liver

motility of small intestine

-mainly segmentation -overall motility is slow so proper absorption can take place -after majority of food has left small intestine, bursts of powerful contractions occur about every 90 min to clear residual food into LI (housekeeper)

structure of stomach

-muscular organ -muscular lining enables it to perform peristalsis and churn the food -has ridges called rugae which grip and move food during digestion

structure of esophagus

-muscular tube connecting throat to stomach -soft palate (uvula) prevents food from entering nasal cavity -epiglottis covers glottis to prevent aspiration

function of esophagus

-once food is in esophagus, upper sphincter closes -peristalsis moves food down esophagus to stomach -once food is through the esophagus, lower sphincter closes

function of large intestine

-primarily stores feces -small amount of fluid absorption -houses gut microflora - converts indigestible food into short fatty acids for absorption

how bile from liver enters GI tract

-bile enters from liver, exits to the duodenum via common bile duct -bile is continuously produced by the liver and drains through the common bile duct to the duodenum. when the small intestine is empty of food, the sphincter closes the common bile duct, and bile is forced up the cystic duct and then to gallbladder for storage

digestion/absorption of dietary lipids

1. bile salts and phospholipids emulsify fat droplets in stomach 2. then in SI, lipase breaks emulsified fat droplets into triglycerides 3. through hydrolosis, lipase removes 2 of the 3 fatty acids from the triglyceride resulting in free fatty acids and monoglycerides 4. dissolving of fatty acids and monoglycerides into micelles 5. the mixed micelles then move to the border of the intestinal epithelium where absorption occurs 6. the fatty acids and monoglycerides can then leave the micelles and pass through the membrane of the microvilli to enter the intestinal epithelial cells 7. these products are then used to resynthesize triglycerides and phospholipids within the epithelial cell 8. triglycerides, phopsholipids and cholesterol are then combined with protein inside the epithelial cells to form small particles called chylomicrons 9. the chylomicrons are secreted by exocytosis into the lymphatic capillaries of the intestinal villi 10. absorbed lipids (chylomicrons) then pass through the lymphatic system eventually entering the venous blood via the thoracic duct

digestion/absorption of carbohydrates

1. digestion of starch (carbs) begins in the mouth with the action of salivary amylase 2. the digestion of starch occurs mainly in the duodenum (SI) as a result of pancreatic amylase 3. the amylase produces disaccharides and polysaccharides which are further broken down to its simplest form: monosaccharides 4. monosaccharides are absorbed by the intestinal cell for use in the body

digestion/absorption of proteins

1. protein digestion begins in stomach with the action of pepsin (secreted from pancreas) 2. proteins are broken down into peptide fragments and moves to SI 3. most protein digestion occurs in SI by trypsin and chymotrypsin, secreted by the pancreas 4. the fragments are further digested to free amino acids by carboxypeptidase secreted from pancreas 5. the free amino acids then enter the epithelial cells via secondary active transport coupled to Na 6. the free amino acids move across the basolateral membrane by facilitated diffusion to the interstitial fluid and then to the capillary blood 7. the absorbed amino acids enter the blood delivered to the liver by the hepatic portal vein