Do Now 4/9/15 1.Based on what you already know, what is the pathway food takes through your body. Be as specific as possible. 2.Describe the function of the stomach 3.What was your most recent meal?

Upcoming Dates Tuesday, 4/7: Blood Quiz Corrections due Thursday, 4/9: Blood, Immune/Lymphatic BIG Quiz Friday, 4/17: Digestive Quiz Thursday, 4/23: Digestive Project due Monday, 4/27: Urinary Quiz; Urinary Project due Friday, 5/1: Urinary & Reproductive Test Thursday, 5/7: Semester 2 Final Exam

Quick Review 1. Tissues are composed of cells, and tissues functioning together make up A) organs. B) membranes. C) organ systems. D) organelles. E) organisms. 2. To increase the effectiveness of exchange surfaces lining the lungs, evolutionary pressures have A) increased the exchange surface area with folds and branches. B) increased the thickness of the membranes in these linings. C) increased the number of cell layers in these linings. D) decreased the metabolic rate of the cells in these linings. E) increased the volume of the cells in these linings.

By the end of this class period, we will be able to … List and describe the steps of digestion, and locate these steps in the GI tract. Name and locate the four parts of the stomach. Describe the production and function of gastric juices in digestion in the stomach.

Stages of Human Nutrition There are six main processes of digestion in the following reading. Find and define each in your notebook on p. 1015

Chemical vs Mechanical Digestion Compare the two types of digestion. Come up with one similarity and one difference.

Thought Question: What usually happens first in a given organ, mechanical or chemical digestion? Why?

The Alimentary Canal How many organs can you identify?

Stomach Four Major Regions: 1.Cardia 2.Fundus 3.Body 4.Pyloric region

Stomach Size Empty volume: 50 mL When full: 2L

Rugae Folds on the wall of the stomach that can unfold to increase volume.

From the stomach to the small intestines… Between these two organs is the pyloric sphincter This circular, smooth muscle must relax in order to allow food to enter the small intestines.

Which part of the stomach is most superior? Pyloric region Body Cardia Fundus

Which part of the stomach is most inferior? Pyloric region Body Cardia Fundus

If you get heart burn, where is the last place gastric juices flow through?

What do the walls look like?

The Stomach Lining It contains microscopic openings called gastric pits.

Gastric Pits

The gastric pits secrete mucous into the stomach

Gastric Glands

Secrete hydrochloric acid, pepsinogen, and gastrin. pH of the stomach: 1.5 – 2.5

What is the difference between Gastric glands and pits?

What does most of the “digesting” in your stomach? A protein-digesting enzyme called pepsin

Pepsin Stomach cells do not make pepsin directly, they actually make pepsinogen the inactive form of the enzyme. The pepsinogen is stored until needed and even released from the cell in this inactive form! It is only when the pepsinogen encounters HCl in the lumen of the stomach that it is activated and becomes pepsin

What is the advantage of making and storing this enzyme in its inactive form, pepsinogen?

To activate pepsinogen, HCl cleaves off an unnecessary part of the pepsinogen, and exposes its active site. Now activated, this pepsin can digest proteins in food, BUT ALSO it can cut the necessary bonds in other pepsinogen molecules! Thus it can activate more pepsin enzymes, which can all in turn activate others. This is an example of ____________________

Stomach Secretions SecretionFunction Mucus (gastric pit) HCl (gastric gland) Pepsinogen (gastric gland)

Gastrin Gastrin is a hormone that stimulates the secretion of HCl (gastric acid) What is the relationship between gastrin, pepsin, and HCl?

What does food look like when it leaves the stomach? The food mixed with gastric juices is called chyme. Proteins have been broken down into smaller molecules but carbohydrates are largely still intact.

Quick Check Pepsin (A) Digests starch (B) Converts other pepsin molecules into pepsinogen molecules (C) Breaks bonds between amino acids in various molecules (D) Uses several types of macromolecules as substrates (E) Both A and B

Because of the low pH of the stomach and the general harsh environment, cells of the stomach erode quickly and must be replaced every three days. What process is responsible for this regeneration?

Check your Understanding 1. Where in the human body is protein digestion initiated? What enzyme catalyzes this digestion?

2. Which process is illustrated in the diagrams? A)IngestionD) absorption B)circulation E) digestion C)peristalsis

3. Pepsinogen can be activated by A)Pepsin B)HCl C)Chyme D)Either A or B E)A, B or C

4.How would you describe the pH of the stomach? (Acidic or Basic? Low or High?). Identify the compound responsible for the pH in the stomach

5. When stimulated by the presence of food, secretions by stomach cells A) release the enzyme pepsin B) initiate the mechanical digestion of lipids in the stomach. C) initiate the chemical digestion of lipids in the stomach. D) initiate the digestion of protein in the stomach. E) delay digestion until the food arrives in the small intestine.

6. Stomach cells are moderately well adapted to the acidity and protein-digesting activities in the stomach by having A) a sufficient colony of H. pylori. B) a high level of secretion of HCl by parietal cells C) a high level of secretion of pepsinogen by chief cells D) a thick, mucous secretion and active mitosis of epithelial cells. E) secretions enter the stomach from the pancreas.

7. The production of pepsin is an example of a positive feedback mechanism. Justify this statement.

What you eat. All day. Every day.

Exit Ticket 1.Which of the four regions of the stomach is closest to the small intestines? 2.What do the gastric pits secrete into the stomach? Why is this necessary? 3.What do gastric glands secrete into the stomach? 4.Which enzyme breaks down proteins? 5.Explain how the enzyme from #4 is stored and then released.