Chapter 23: digestive system

A fat globule is broken down by the following process...

1). Bile salts in the duodenum emulsify large fat globules (physically break them into smaller fat droplets) The fat droplets are coated with bile salts to by more hydrophillic. 2). Digestion of fat by the pancreatc enzyme liase yields free fatty acids and monoglycerides. These then associate with bile sallts to form micelles which "ferry" them to the intestinal mucosa. Outside of micelle is hydophillic and inside is hydrophobic. 3). Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other fatty substances and proteins to form chylomicrons. 4). Chylomicrons are extrded from the epithelial cells by exocytosis. The chylomicrons enter lacteals and are carried away from the intestine in lymph. Eventually are dumped into bloodstream

Enteric Nervous System

Intrinsic nerve supply of alimentary canal. The enteric neurons controls motility: segmentation and peristaltci patterns are largely automatic

Trypsinogen is activated into

Trypsin

Neural & hormonal mechanisms which regulate gastric secretion.

Vagus nerve stimulation increases secretion. Sympathetic stimulations decreases secretion. Hormonal control is largely controlled by gastrin.

Hormonal control largely comes from....

gastrin

Segmentation & peristalsis mixes & moves contents toward the ____ ____.

ileocecal valve

Segmentation & peristalsis mixes & moves content toward the ________ ____. Motility coordinated via ______ _____ (long & short) & _____ _____

ileocecal valve. Neural reflexes; hormonal input

Gastrocolic reflex

initiated by presence of food in stomach

Liver in the digestive system

its only digestive function is bile production

Haustral contractions

local contractions; move material from one haustrum to the next.

Gastrin stimulates HCl release

low pH inhibits gastrin secretion (as between meals). Buffering action of ingested proteins cause a rise in pH, and gastrin is secreted

Lipids enter the _____ system

lymphatic

An increase in stomach contraction initiates _____ ______ which is a _____ (short or long) reflex also called the ____ reflex

mass peristalsis. short; gastrocolic.

Gastrin increases...

motility of ileum

Regulation of Bile Secretion

1). Chyme entering the duodenum causes duodenal enteroendocrine cells to release cholecystokinin (CCK) and secretin. 2). CCK and secretin enter the bloodstream. 3). CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of bicarbonate-rich pancreatic juice. ).BIle salts and, to a lesser extent, secretin transported via bloodstream stimulate livert o produce bile mroe rapidly. 5). CCK (via bloodstream) causes gall bladder....

Stomach functions

1). Stores ingested foods. 2). Mechanical digestion: churning and breaking down of food--> exposing carbohydrates to chemical digestion and proteins to HCl and pepsin. 3). Breaks chemical bonds via enzymes & acids. 4). Produces intrinsic factor = needed for vitamin B12 absorption in digestive tract. 5). Delivers chyme to small intestine.

The three phases of gastric secretion.

1. Cephalic (reflex) phase: in the fundus. 2. Gastric phase: lasts 3-4 hours; 2/3 gastric juice is released. 3. Intestinal phase

6 functions of the digestive system

1. Ingestion (putting something in your mouth). 2. Mechanical processing (chewing/ mastication). 3. Digestion (catabolism). 4. Secretion (accessory glands. 5. Absorption (through walls of GI tract into hepatic circulation). 6. Excretion (defacation; used everything from food and leftovers are extreted).

_____% f water is absorbed in the small intestine by ______

95; osmosis

What two juices are secreted from he pancreas?

Alkaline solution. Proteases.

Deglutition (swallowing)

Buccal phase: voluntary contraction of tongue Pharyngeal-esophogeal phase:

Deglutiotion (swallowing)

Buccal phase: voluntary contraction of tongue. Pharyngeal-esophageal phase: involuntary primarilly through the bagus nerve. the control center is in the medulla & lower pons.

Receive digestive juices from accessory organs; controlled by enterogasterones. Molecules called...

CCK & secretin

What acts on liver to release bile?

CCK (helps secretin do it's job) & Secretin. Bile.

What causes gallbladder to cause contractions and release of concentrated bile?

CCK. Causes relaxation of he bile ducts and contraction of gall bladder.

Enteric Nervous System is linked to the _____ via _____ visceral fibers. Longs ____ fibers synapse with enteric plexuses

CNS. afferent. ANS

Neural control

Cephalic (reflexive) phase, gastric phase (lasts 3-4 hours; 2/3 gastric juice released), intestinal phase

Trypsin activates

Chymotrypsiongen to chymotrypsin & Procarboxyeptidase to carboxypeptidase

Receptive relaxation reflex

Coordinated by swallowing center of brain stem. Relaxation of smooth muscle anticipating incoming food

Propusion

Deglutition (swallowing)

Chyme delivery

Delivered in 3 mL spurts to the duodenum (when the pyloric sphincter contracts) as a liquid

Gastric glands produce _____ ______. The types of cells in the glands are...

Gastric juice. Parietal cells, chief cells, ,and enteroendocrine cells.

parietal cells secrete

HCl and intrinsic factor. They have high surface area for secretion.

Pepsingen

Has a positive feedback loop. HCl activates Pepsinogen into Pepsin, but Pepsin continues the process activatin Pepsinogen.

What type of contractions in the large intestine?

Haustral contractions (local).

Motility of the large intestine begins with ______ contractions

Haustral.

Gastrin

Hormonal control of gastric secretion. Icnreases enzymes & HCl secreation. Most of the hormones secreted in the small intestine (particularly the duondenum) is a gastrin inhibitor.

Gastric phase

Mechanoreceptors and chemoreceptors. Stomach distention (stretch) which stimulates mechanoreceptors to send to the vagal nerve into the medulla. The medulla will then send info back. Food chemicals (peptides) stimulate the release of gastrin. A rise in pH releases gastrin stimulation because eating proteins buffer the HCl secreted into the stomach, so the H+ ions raise pH to more alkaline. Stomach responds by secreting the building blocks for HCl.

Accessory organs

Most digestive activities require cooperation of several organs.

Digestive processes in the Large intestine

Most of water is reabsorbed, but it is reabsorbed into the large intestne. Reabsorption of biles salts in the cecum (most is within the ileum). Absorption of vitamins produced by bacteria which process chyme. Absorption of organic wastes. Propulsion of feces to anus; defecation

HCl

Only secreted from cells within the stomach. Only place with enough protection so it doesn't. HCl activates Pepsinogen into Pepsin

Submucosal nerve plexus

Part of the enteric nervous system that regulates glands & smooth muscle in the mucosa.

Myenteric nerve plexus

Part of the enteric nervous system: controls GI tract motility

chief cells secrete

Pepsinogen & lipases

The stomach stretches...

To accommodate incoming food: The pressure is constant until 1.5 L food is ingested

Food enters the stomach with the help of _____ ____ called propulsion.This moves waves from the _____ toward the ____.

Peristaltic waves. fundus; pylorus

Ingestion (1st step in Digestive Process)

Physically putting something in your mouth, and the beginning of mechanical digestion with chewing.

Gastric accommodation

Plasticity (stress-relaxation response) of smooth muscle

duodenal atresia

Polyhydramnios, bilous vomiting, Double-Bubble Sign on X-Ray.

What releases bicarbonate rich pancreatic juice?

Secretin

Cholecystokinin and secretin are responsible for...

Secretion of bile and pancreatic juices. Cholecystokinin causes relaxation of hepatic sphincter a causes the contraction of the gall bladder so that stored bile can be released

Cephalic (reflex) phase

Seeing food causes hypothalamus to react. Causes the cerebral cortex to react. Smelling or tasting food sends nerve impulses through the vagus nerve to increase secretion.

Digestion

Series of catabolic steps whereby food molecules are broken down to their chemical building blocks to be absorbed within the GI tract.

Gastrocolic Reflex (short reflex)

Short reflex. Food hits the stomach, increases motility in the colon and increases frequency of mass movements.

Intestinal Phase

Stimulated as a result of partially digested food in the duodenum. Stage in which the duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes. Pyloric sphincter remains closed until signals are sent to allow more chyme to go through.

Gastric Emptying is based on the communication betwenn the _____ & ____.

Stomach; duodenum

Functions of the stomach

Stores ingested foods (up to 1.5 liters of food w/out distention). Plays a role in mechanical digestion (churning). Breaks chemical bonds via enzymes & acids (Hcl, which helps denature proteins and chews away plant cell walls). Produces intrinsic facter, which is needed for vitamin B12 absorption in digestive tract (small intenstine). Delivers chyme (liquid food) to small intestine.

Grinding

The most vigorous peristalsis and mixing action occur close to the pylorus. Distention & gastrin increase force of contraction

Retropulsion

The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum....

Stomach converts food into liquid chyme after....

The sphincter relaxes, allowing the bolus to enter the stomach.

ileocecal valve

a sphincter located on the terminal end of the ileum that prohibits backflow of chime into the small intestine

G cells secrete

a variety of hormones including gastrin

Absorption in the small intestine:

all food molecules; 80% electrolytes; most water; fat-soluble vitamins A,D,E, &K; water-soluble C & B; intrinsic factor.......

Gallbladder's chief function is ____ _____. What does it absorb to concentrate the substance it holds?

bile stotrage. ions & water.

Gallbaldder in the digestive system

chief function is bile storage (when there is no fatty chyme).

Ileocecal valve flaps close when... which prevents. ____ into the ileium

chyme exerts backward pressure. Regurgitation.

scaphoid abdomen

condition of the anterior abdomincal wall is sunken & presents a concave rather than a convex contour

Mass peristalsis

contractile waves that force contents toward the rectum.

Hypochloremia

decreased Cl-

Hypokalemia

decreased K+

hyponatremic

decreased Na+

Gastroileal reflex

enhances force of segmentation in ileum

Membrane-bound ______ helps activate proteases

enteropeptidase

bile

fat emulsifier

Mastication

partly voluntary and partly reflexive (stretch reflexes; pressure receptors in cheeks, gums, tongue). Salivary glands secrete salivary amylase, lingual lipase, & mucin

Absorption

passage of digested end products from lumen of GI tract

Liver: only digestive function is

production of bile

ileocecal sphincter

relaxes, admits chyme into large intestine when the gastroileal reflex kicks in and gastrin is secreted.

Chemical digestion

sailivary glands

Pancreas in the digestive system

secretes a very bicarbonate-rich juice and peptide-rich juice. Watery, alkaline solution (pH8) neutralizes chyme. Has electrolytes (primarily (HCO3-). Secrete amylase, lipases, nucleases (breaks down DNA and RNA) secreted in active form, but they require ions or bile for optimal activity. Proteases secreted in inactive form.

Basic electrical rhythm (BER)

set by enteric pacemaker cells. the rate at which peristaltic waves move food (3 per minute).

Defacation reflex is a ____ reflex.

spinal.

Mastication is partially _____ and partly ____

voluntary and reflexive. stretch reflexes; pressure reeceptors in cheeks, gumms, tongue