ch 21 digestive system exam 5

Gastric phase Explain how digestive enzymes are activated and the role of pH.

Different enzymes are more effective at different pH levels. If the pH levels are too high or too low for a particular enzyme, it might get denatured and will no longer perform its function. Pepsin for example is a digestive enzyme. It is secreted as an inactive enzyme (pepsionogen) by cells in gastric glands. Once in the stomach lumen pepsinogen is now in an acidic environment and becomes activated.

Explain the process of vomiting as a protective reflex

Vomiting is the forceful expulsion of stomach and intestinal contents through the mouth. It removes toxic materials from the GI tract before they can be absorbed. Efferent signals from the vomiting center in the medulla initiate a wave of reverse peristalsis that begins in the small intestine and moves upward until content is expelled through the mouth.

TC2: Which of the following digestive hormones stimulates gallbladder contraction and pancreatic enzyme secretion? a)motilin b)gastrin c)cholecystokinin (CCK) d)gastric inhibitory peptide (GIP) e)secretin

C

TC1: Food is pushed through the digestive tract by a)swallowing more food that pushes along food ingested earlier. b)beating cilia on the epithelial cells lining the lumen. c)peristaltic contractions of smooth muscle in digestive tract walls. d)contraction of skeletal muscles surrounding the digestive tract. e)the effects of gravity.

C

Explain how hormones control digestive processes.

GI hormones are secreted by endocrine cells of GI tract into the blood and throughout body. This is in response to stimuli. These hormones control digestive processes.

Motilin: MMC

Motilin is secreted by endocrine "M" cells in the duodenum and jejunum during fasting, and the only known function of this hormone is to increase gastrointestinal motility. It is associated with fasting.

State where each process of the digestive system occurs (digestion,secretion,absorption and motility

Motility occurs all throughout the GI tract. Secretion - all throughout GI tract Absorption - stomach and intestines digestion - everywhere but large intestine

List the functions of these accessory digestive organs: pancreas

Produces and secretes digestive enzymes and bicarbonate to regulate pH. Enzymes produced by the pancreas are secreted into the small intestine to further break down food after it has left the stomach.

Explain how water is balanced in the GI tract including the process of sodium, chloride, potassium and water reabsorption.

THIS IS FOR SECRETION OF WATER INTO INTESTINAL LUMEN. Negative ions in the lumen (Cl-) attract Na+ which is in the ECF. This makes lumen have more ions and therefore water will flow from ECF to inside lumen to compensate that. THIS IS FOR WATER REABSORPTION INTO ECF Absorption of nutrients and ions from intestinal lumen to ecf creates an osmotic gradient that makes water flow to ecf and be absorbed. This happens by Na+ being absorbed by intestinal cells. The Na+ K+ ATPase in those cells then pumps Na+ into ECF. Water and K+ then follow this gradient and exit intestinal lumen and go to ECF.

List the functions of these accessory digestive organs: teeth salivary glands

Acessory digestive organ - An organ that helps with digestion but is not part of the digestive tract. Teeth - help with mechanical digestion, breaking down of food. Salivary glands - Before our body can absorb glucose from starch, we secrete saliva which contains an enzyme called amylase. This enzyme is responsible for hydrolysis (chemical breakdown) of starch that we ingest. Starch is then converted to Maltose.

TC2: Of the 8-10 L of fluid entering the GI tract daily, a)most comes from dietary/liquid intake. b)only 100-200 mL are excreted in the stool. c)most is absorbed in the large intestine. d)most is absorbed by active transport. e)None of the above.

B

Describe the processes involved in the phases of the digestive process and map how these phases are integrated

Cephalic phase - Starts even before food enters oral cavity. Thoughts, appetites and smells stimulate the CNS to get digestive system ready for food. . REQUIRES INPUT FROM CNS. Gastric Phase - is a period in which swallowed food and semi-digested protein activate gastric activity. Long and short reflexes. Stimuli originate in the stomach. Intestinal Phase - Begins when chyme (gastric juices and partly digested food) passes into small intestine so, stimuli for intestinal phase is when chyme reaches the small intestine. Long and short reflexes during this phase. Most digestion and absorption occur here.

Gastrin family: Gastrin, CCK -> hormones. What are their functions?

Gastrin - Presence of proteins and amino acids in gastric lumen stimulates release. It then stimulates gastric acid secretion and mucosal growth. CCK - Presence of fatty acids and amino acids stimulates the release. It then stimulates secretion of pancreatic enzymes and gallbladder contraction.

List the functions of these accessory digestive organs: liver

Produces bile which facilitates the digestion of fats.

Secretin family: Secretin

Secretin helps regulate the pH of the duodenum by (1) inhibiting the secretion of gastric acid from the cells of the stomach and (2) stimulating the production of bicarbonate

Describe the enteric nervous system, and explain why it is unique to the digestive system.

The ENS has the ability to carry out reflexes independent of CNS control. The nerves on the GI tract act as a little brain allowing local reflexes to happen. These reflexes are called short reflexes. They need no input from outside sources.

Explain how the digestive system handles the challenges of autodigestion, mass balance, and defense. (throughout the chapter)

The food we eat must be digested into smaller particles. Powerful enzymes must be secreted in the digestive system to accomplish this. But these enzymes must not digest the cells of GI tract themselves... Protective mechanisms for this are: pancreatic enzymes are secreted as inactive or else they would digest the pancreas itself. This is identical to what happens in stomach. The cells lining the stomach release pepsinogen which is only converted to its active form (pepsin) when it reaches the actual stomach and combines with stomach acid to become activated. This prevents the cell from digesting themselves.

Explain the role of the hepatic portal system

The portal vein or hepatic portal vein is a blood vessel that carries blood from the gastrointestinal tract to the liver. It functions to supply the liver with metabolites and ensures that ingested substances are processed in the liver before reaching the systemic circulation, limiting the damage ingested toxins may cause.

Movement: Compare the different types of smooth muscle contraction (phasic and tonic) and two types of movement (peristalsis, segmental)

Tonic contractions - keeps bolus from moving backwards, can be sustained minutes to hours. Occur in smooth muscle sphincters and stomach. Phasic contractions - Occur in the stomach and small intestine. Brief periods of both relaxation and contraction. Moves bolus forward. Peristaltic - forward movement (a squeeze in one spot of GI tract that moves bolus forward) Segmental - Mixing of stuff contraction (several squeezings in a spot of GI tract which causes little or no movement forward but causes mixing). THESE CONTRACTIONS FALL UNDER THE CATEGORY OF MOTILITY.

Recall the regulation of digestive function by the autonomic nervous system

When there is sympathetic activation, blood is directed and flows to other areas other than the digestive system. This inhibits or at least slows down digestion. The parasympathetic branch is responsible for stimulating digestion by increasing blood flow to the GI tract. Salivary glands are stimulated and peristaltic contractions increase. Some of the stuff that the ANS controls are: saliva secretion, peristaltic contractions to move food along, gastric acid production, sphincter opening and closing, hormone release from digestive system glands.

List the functions of these accessory digestive organs: Gallbladder

stores bile

Recognize the similarities in the four layers of the GI tract wall and how the variations in each organ suit the function.

1. Mucosa - the inner lining of the GI tract. Simple epithelial cells. Absorptive and secretory layer of GI tract. Comes in direct contact with digested food. 2. Submucosa - Connective tissue with blood and lymph vessels that run through it and support the mucosa. 3. Muscularis Externa - Outer wall of GI tract.. Smooth muscle. Responsible for contractions and peristaltic movement in the GI tract. 4. Serosa - connective tissue. Outer covering of the entire GI tract. Cells in it secrete serous fluid. In the stomach, the mucosa contains invaginations called gastric glands that increase surface area. In the small intestine, surface area is increased by fingerlike villi and invaginations called crypts. These are on the mucosa. Thus we see that the layers (in this case mucosa) can differ depending on the organ to suit its function.

Cephalic phase: List the steps of the deglutition (swallowing) reflex: contrast voluntary and involuntary

1. Tongue pushes bolus against soft palate and back of mouth, triggering swallowing reflex. 2. Upper esophageal sphincter relaxes while epiglottis closes to keep swallowed material out of the airways. 3. Food moves downward into the esophagus, propelled by peristaltic waves and aided by gravity. THE ONLY VOLUNTARY STAGE OF THE DEGULTITION REFLEX IS THE ORAL STAGE IN WHICH MASTICATION OF FOOD MAKES IT INTO A BOLUS FIT TO BE SWALLOWED.

Explain the process and function of bicarbonate secretion Describe how digestive enzymes are activated.

1.When chyme comes in from stomach into first part of small intestine (duodenum), it is very acidic. To neutralize that acidity, bicarbonate is secreted by cells of small intestine or pancreas that have high concentrations of carbonic anhydrase. 2. Cl- enters cell by active transport and then leaves to the lumen of pancreas or intestine through a chloride channel. 3. Cl- then reenters the cell and bicarbonate leaves to the lumen making lumen less acidic. 4. Leaky junctions also allow movement of water and ions to the lumen.

Secretion: volumes/composition

7L of fluid is secreted into Lumen and that combines with about 2L from food and drink that we ingest per day. The composition is saliva, water, ions, enzymes, bile and etc. This whole 9L will then be removed from lumen by absorption. Only 0.1L will be excreted from body.

Digestion is: A. The chemical and mechanical breakdown of food B. the process by which nutrients cross from the GI tract into the blood C. The conversion of glucose to glycogen D. Dependent on CNS for all activity E. All of the above

A

TC3: Which function(s) is/are NOT continuously regulated by the GI tract? a)absorption b)motility c)Secretion D)Chemical digestion e)All of the above

A

TC3: Which of the following is NOT directly associated with fat digestion? a)chyme b)Cholecystokinin (CCK) c)chylomicron d)colipase e)All of the above are associated with fat digestion.

A

***Absorption: explain why absorption is not regulated and does not adhere to rules of homeostasis

Because what is secreted must also be absorbed (law of mass balance) ?? So technically, what is regulated is secretion and absorption just follows that.

Track the trek of food through the alimentary canal: name the organs through which it passes and the activity of each.

Digestion begins with: 1. Mouth - chewing(mechanical digestion), salivary glands are activated (chemical digestion) 2. Pharynx - ensures passage of food into esophagus 3. Esophagus - Movement of food via peristalsis. (wavelike movements that push the contents of the canal forward.) 4. Stomach - 3 functions here. Storage, digestion, and defense. 5. Small intestine - digestion and absorption 6. large intestine: absorption of water, elimination 7. anus and sphincters: elimination

Digestion: mechanical vs chemical

Mechanical digestion involves chewing and breaking down food with teeth, while chemical digestion involves the breaking down of food by enzymes and acids in the digestive system. Mechanical digestion mainly occurs directly after ingestion of food, while chemical digestion occurs primarily in the stomach and intestines. The main form of mechanical digestion is called mastication, in which the teeth manually break down food so that it can be swallowed. The food is then broken down by hydrolysis, a chemical process involving water and enzymes.After hydrolysis, food is then further digested in the stomach after being mixed with stomach acid by stomach contractions called peristalsis, which is a form of mechanical digestion. Once the food is properly broken down, nutrients can be provided to the body from the intestines, while any undigested food is removed from the body as waste.

*** Describe the 4 coordinated processes of the digestive system: State where each process occurs and how each is regulated:

Motility - Moves food from mouth to the anus and mechanically mixes food to break it into uniform small particles. Motility is determined by the properties of GI smooth muscle and is modified by chemical input from nerves, hormones and paracrine signals. Occurs throughout whole digestive system. Secretion - Movement of material from cells lining lumen into Lumen or ECF. Everyday, about 7L of fluid is secreted into lumen (saliva from saliva glands, bile, ions, enzymes, etc). This combines with about 2L from food and drink to make about 9L. 9L MUST then equal the volume of fluid leaving the lumen. About 8.9L will be absorbed and only 0.1L will be excreted in feces. occurs throughout whole digestive system. Absorption - Movement of material from GI lumen to ECF and therefore blood vessels too. This is how food (nutrients) enter the body. This is basically regulated by the amount of secretion. (law of mass balance). Occurs mostly in small intestine. ABSORPTION IS NOT REGULATED. Digestion - Chemical and mechanical breakdown of food into absorbable units. Occurs everywhere besides large intestine. MOTILITY AND SECRETION AID AND DETERMINE DIGESTION AND ABSORPTION. MOTILITY AND SECRETION ARE REGULATED BY HORMONES AND NEURAL REFLEXES

State the location (organ), mechanism of digestion and absorption for the major classes of nutrients: carbohydrates, proteins, fats, vitamins

carbohydrates - Carbohydrates like starch start to be digested in the mouth by saliva (amylase breaks it down into smaller units). In the small intestine digestion is then continued to break it down even further and then be absorbed. Proteins - Protein digestion begins in the stomach with Pepsin, meaning that it breaks down peptide bonds in an amino acid. Digestion then continues in the small intestine with other enzymes. This keeps happening until we are left with just dipeptides, tripeptides or free amino acids which are then absorbed through the small intestine into bloodstream. Fats - Only starts to be digested in small intestine. Bile will be released from pancreas and has the ability to break down fats. Enzymes in the small intestine can then finish digesting these smaller fat molecules. These then go to lymphatic system. From there, they will enter the venous blood before it flows into right side of heart. Thus we see that carbs and proteins enter directly the blood stream while fats go through lymphatic system. Vitamins - Can have same path as fats or be absorbed directly into bloodstream