Embed Size (px)
Citation preview
Bio 12
Durley
1 | P a g e
Bio 12
Durley
Mr. Man – label the ones you already know!
2 | P a g e
Bio 12
Durley
Da NOTES - Digestive System 1. General a. Animals obtain energy by breaking food molecules into smaller pieces. b. The basic molecules are the monomers: amino acids, 3 fatty acids with 1 glycerol
and glucose. c. Digestion is the chemical breakdown of large food molecules into smaller
molecules that can be used by cells. The processing of food has four basic steps: i. Ingestion ii. Digestion iii. Absorption iv. Elimination d. Digestion occurs in two different ways i. Mechanical digestion - breaking food into smaller pieces. ii. Chemical digestion - breaking food into smaller molecules. 2. Food enters the digestive tract through the mouth. a. Chewing breaks food into smaller particles so that chemical digestion can occur
faster (this increase surface area). b. Teeth are important to animal digestion for capturing, tearing, and chewing food. i. Carnivores possess pointed teeth for capture, cutting and shearing. ii. Herbivores have large, flat teeth suited for grinding plant materials. iii. Omnivores (we are omnivores) have both types, front like carnivores, back
like herbivores. c. Food is moistened and lubricated (remember a function of water) in the mouth. i. Tongue (is a muscle) mixes food with saliva. ii. Saliva is secreted by salivary glands (6 of them). iii. Contains the enzyme salivary amylase to begin the breakdown of starch. iv. There is continuous secretion to keep the mouth moist and to lubricate
food. v. Secretion of saliva is stimulated by the presence of food (nerves send the
message via sight or smell). 3. Food passes to the stomach through the esophagus. a. Mucous (a watery mixture) lubricates and helps hold the chewed food together in
a clump called a bolus. b. The tongue is muscular and is used to move food. It pushes food to the back of the
mouth where it is swallowed. As the tongue moves the bolus to the back of the mouth, the swallowing reflex takes over to move the bolus down the esophagus.
c. The respiratory and digestive passages meet in the pharynx. They separate posterior to the pharynx to form the esophagus (leading to the stomach) and the trachea (leading to the lungs). When swallowing, the epiglottis automatically
3 | P a g e
Bio 12
Durley
moves up to block the passage to the trachea so that food does not end up in the lungs.
d. The bolus is moved to the stomach by peristalsis (rhythmic muscle contractions). e. A muscle called the cardiac sphincter (like a valve that can open and close)
controls the movement of food from the esophagus to the stomach. f. This muscle prevents food in the stomach from reentering the esophagus.
Sometimes acid splashes up into the esophagus causing what we call heartburn (or a puke burp!).
4. Preliminary digestion occurs in the stomach a. The lining of the stomach is highly folded and expands as it fills with food. b. The stomach has an extra layer of muscle to churn food. The mixture of partly
digested food and gastric juice is called acid chyme. c. Cells of the stomach lining secrete hydrochloric acid (HCl) which keeps the
stomach contents at a pH of about 2.5. The low pH also kills most bacteria. The cells of the lining are protected by a thick coating of mucous that is constantly replaced as the acid destroys it.
d. Cells also secrete pepsinogen, a protein digesting enzyme. Inactive pepsinogen is cleaved to form pepsin - the active form of the enzyme. This is important to protect the cells that produce pepsin from being digested themselves. Pepsin is most active in a pH of 2.5 (optimal pH).
e. The stomach produces about 2 L of acid and gastric secretions per day. Seeing, smelling, tasting, or thinking about food can result in the secretion of gastric juice.
f. Pepsin cuts proteins into shorter pieces (polypeptides) and they are not further digested until they reach the small intestine.
g. There is no digestion of carbohydrates or fats in stomach. h. If too much stomach acid is produced, it can dissolve a hole through the
protective mucous coating and a gastric ulcer results. Ulcers can also be caused by certain bacteria which can survive in the acidic environment of the stomach. The growth of the bacteria on sections of the stomach lining prevents it from secreting mucous, making it susceptible to the digestive action of pepsin. Duodenal (intestinal) ulcers are more common, resulting when excessive acidic chyme is passed to the duodenum.
i. Very little absorption occurs in the stomach, with some exceptions such as water, aspirin and alcohol. All other absorption occurs in the intestine.
5. Other digestion and absorption of molecules take place in the small intestine. a. The duodenum is the first part of the small intestine. The passage of food from the
stomach to the small intestine is regulated by a muscle called the pyloric sphincter, which allows chyme to enter the duodenum in small spurts.
b. The capacity of the small intestine is limited and digestion takes time so only small amounts of chyme are permitted to enter at a time.
4 | P a g e
Bio 12
Durley
c. The small intestine is where most chemical digestion occurs. i. The length is approximately three meters. The first part, the duodenum, is
about the first 25 centimeters. The other two sections are the jejunum and ileum.
ii. At this point, proteins and carbohydrates are only partially digested and lipid digestion has not begun.
iii. In the duodenum, chyme, pancreatic enzymes, and bile from the liver and gallbladder are mixed.
iv. The presence of food in the duodenum also triggers the release of various hormones
(1) The intestine must be protected from the acid contained in gastric juice. When chyme enters the small intestine, the cells of the duodenum release the hormone secretin. This hormone stimulates the pancreas to produce sodium bicarbonate, which neutralizes the acidic chyme and shuts off pepsin. It also stimulates the liver to secrete bile.
(2) Another hormone (CCK=cholecystokinin), stimulates the gallbladder to release bile and the pancreas to produce pancreatic enzymes.
(3) Another hormone (GIP, gastrin inhibitory protein) inhibits gastric glands in the stomach and inhibits the mixing and churning movement of stomach muscles. This slows the rate of stomach emptying when the duodenum contains food.
v. Digestion continues and absorption occurs in all three sections of the small intestine.
(1) Digestive enzymes secreted by the cells of the small intestine digest lactose, sucrose and other sugars. Some adults lose the ability to produce lactase, resulting in the condition called lactose intolerance.
(2) Absorption of food in the intestine. (a) The walls of the small intestine are covered with small
projections called villi. These increase the surface area of the small intestine to increase absorption.
(b) The villi themselves are covered with many tiny projections called microvilli, which increase the surface area still further.
(c) The molecules resulting from the digestion of proteins and carbohydrates are absorbed by cells of the intestinal lining.
(d) The villi contain capillaries, tiny blood vessels which allow efficient transfer of these molecules into the blood.
(e) The products of fat digestion are absorbed through the villi into the lymphatic system. They enter the blood stream near
5 | P a g e
Bio 12
Durley
the neck where the lymphatic system joins the circulatory system.
6. The pancreas secretes enzymes, bicarbonate and hormones. a. The pancreas is located below the stomach. b. Secretions of the pancreas reach the duodenum via the pancreatic duct. The fluid
contains i. The protein digesting enzyme trypsin. ii. The starch digesting enzyme pancreatic amylase. iii. The fat digesting enzyme lipase. iv. Bicarbonate to neutralize HCl from the stomach. c. The pancreas also produces hormones that regulate levels of sugar in the blood.
These hormones, insulin and glucagon, are produced by clusters of cells called islets of Langerhans. See the Liver below.
7. The liver produces bile and regulates blood composition. a. Role in Digestion i. Old red blood cells are destroyed by the liver and the hemoglobin from
these cells is used to make bile. The remains of the red blood cells are eliminated with feces and give it its characteristic brown color.
ii. Bile is stored and concentrated in gall bladder. The presence of fatty food in the duodenum triggers the gallbladder to release bile.
iii. Bile travels through the common bile duct to the doudenum. iv. Bile salts are soluble in both lipids and water. This enables them to break
apart fat droplets in chyme to create smaller droplets. This increases the surface area for lipase to work on and increases the speed of their digestion.
v. Cholesterol can bind bile together causing crystals to form. If these crystals become large enough they can block the common bile duct.
vi. If the common bile becomes blocked, bile salts can accumulation in the skin and produce a yellow color in a condition called jaundice.
b. Regulation of blood composition. i. Another role of the liver is to remove toxins from the blood. ii. The liver absorbs or chemically modifies toxic substances to prevent them
remaining in circulation. iii. Ammonia produced by the digestion of proteins is converted to a less toxic
compound (urea) by the liver. Urea is removed from the blood by the kidneys and eliminated in urine.
iv. Alcohol and drugs are metabolized by liver cells into less harmful compounds. Other toxins, pesticides, and carcinogens are also detoxified.
v. These less harmful compounds are returned to the blood and are removed by the kidneys.
6 | P a g e
Bio 12
Durley
vi. If the liver is chronically exposed to toxins, the cells become damaged and die. The result is cirrhosis of the liver.
c. Regulation of blood glucose levels. i. It is important to maintain a constant concentration of blood glucose so that
cells have a steady supply. This is especially important for brain cells which store little glucose, and cannot use fat or amino acids as an energy source.
ii. Vertebrates eat sporadically when food is available and, often, a period of fasting occurs between meals. Also, most food is digested rapidly, and the resulting molecules (including glucose) enter the blood stream. Without some control, the level of glucose (and other compounds) in the blood would be quite variable.
iii. The liver removes glucose from blood, converting it into glycogen. Glycogen is stored in both the liver and in skeletal muscle.
iv. The conversion of glucose to glycogen is stimulated by the pancreatic hormone, insulin. If blood glucose is high (such as after eating) the release of insulin from the pancreas causes the liver to store glucose. If blood glucose level is low (such as between meals), the opposing pancreatic hormone glucagon causes the liver to secrete glucose into the blood.
v. The liver stores enough glycogen for about 10 hours of fasting. If food is still unavailable after that, amino acids (from muscles) and fats (from fat stored in fat cells) are used as a source of energy.
8. The large intestine concentrates solids by reabsorbing water. a. The large intestine or colon comprises last meter of the digestive tract. b. It has no digestive function, but functions to absorb water. If water is not
absorbed, as can happen during certain bacterial infections, diarrhea can result, causing dehydration and salt loss.
c. The daily total volume of food and water we take in from eating is about 2 L (including about 800 g of solids). The body adds about 7 L of its own fluids making a total of 9 L.
i. 1.5 L saliva and salivary enzymes ii. 2 L of gastric secretions iii. 1.5 L of pancreatic secretions iv. 0.5 L of bile from the liver v. 1.5 L of intestinal secretions d. Nearly all fluids and solids are absorbed so that only 50 g of solids and 100 mL of
liquid leave as feces. The large intestine (along with some absorbed by the small intestine) recovers about 90% of the water that enters the digestive system. Remember that this is very important for a terrestrial vertebrate.
e. Undigested material is compacted and stored until the colon is full. When the colon is full, a signal to empty it is sent by sensors in the walls of the colon.
7 | P a g e
Bio 12
Durley
f. Bacteria (mostly E. coli) live and reproduce in the colon. Anaerobic digestion (fermentation) of material by these bacteria produces gas in the colon. They also produce vitamins for the host, including vitamin K some B vitamins. Bacteria are lost when feces is eliminated, making exposure to feces dangerous.
g. Fiber (cellulose) tends to fill up the colon and cause it to be emptied. Low fiber diets result in slower passage of food through colon and have been linked to colon cancer.
h. The rectum is the last section of the large intestine. Feces pass into the rectum by peristaltic contractions and material exits through the anus, a sphincter muscle.
i. Feces is composed of approximately 75% water and 25% solids. One third of the solids is intestinal bacteria, 2/3 is undigested materials.
8 | P a g e
Bio 12
Durley
9 | P a g e
Bio 12
Durley
Digestion – Pathway- Structure and Function
Part Structure Function1)
2)
3)
4)
5)
10 | P a g e
Bio 12
Durley
Enzymes
Level 1
Sketch out the digestive pathway, include the 3 accessory organs – list enzymes that are active in each location and provide ph.
11 | P a g e
Bio 12
Durley
Enzymes
Level 2
Organize enzymes by the macromolecule they digest. Show the enzymes in order of the digestive process for each macromolecule.
12 | P a g e
Bio 12
Durley
Blood Sugar Regulation
The pancreas is both a ______________________ and __________________________ gland.
In blood sugar regulation the pancreas release 2 _______________________________; _____________________ and _____________________________. These hormones target the _____________________________ where ___________________ can be stored as _________________________ when blood sugar is too _______________________________.
Normal blood sugar levels are ______________________________.
13 | P a g e
Bio 12
Durley
REVIEW TIME = GOOD TIMES!
Part 1. Vocab
1. enzyme
2. hormone
3. saliva
4. salivary amylase5. peristalsis
6. sphincter
7. pancreas
8. liver
9. chemical digestion
10. physical digestion
11. epiglottis
12. bile
13. emulsification14. absorption
15. pancreatic juice16. E Coli
17. insulin
18. glucagon
19. pepsin
20. gastric juice21. sodium bicarbonate22. appendix
14 | P a g e
Bio 12
Durley
23. villi
24. pancreatic amylase25. trypsin
26. nucleases
27. maltase
28. peptidases
29. emulsify
30. gallbladder
Part 2. ONE WORDS - Easy Peasy – Fill in the blank Spots.
1. There are 3 types of biochemicals in the food that we eat that have to be digested. These are: _________________ ______________________ and ______________________________.
2. The stomach is directly connected to the _______________________ above) and the _____________________ (below).
3. The major food tyope that is digested in the stomach is ________________________, which is hydrolysed by the enzyme ________________________.
4. Among its chemical aspects, every digestive enzyme has a preferred ____________.
5. Before fats are digested they are emulsified by _____________________.
6. Pancreatic juices enter the small intestine by way of th ___________________ duct and contain ________________________ for the digestion of all three types of biochemicals.
7. The finger like projections lining the walll of the small intestine are called ___________________.
8. A bacterium ____________________, lives I the colon, its metabolic activities release ______________ and ___________________.
9. Name 6 functions of the liver:
____________________________ ____________________________
____________________________ ____________________________
____________________________ ____________________________
15 | P a g e
Bio 12
Durley
16 | P a g e
Bio 12
Durley
Part 3 - Summary of Digestive Enzymes
Enzyme Source Substrate Product pH
3 stories of Digestion – Now Organize the enzyme by the biochemical they digest. Trace the chemical breakdown of the 3 biochemicals listed below. Give enzyme, substrate, product and pH.
1. Carbs
2. Proteins
3. Lipids
17 | P a g e
Bio 12
Durley
Part 4 - Digestive System Concept Questions
1. How do mechanical and chemical digestion work together to break down food?
2. How does chewing aid digestion?
3. What is the purpose of saliva?
4. Your friend notices that when they chew soda crackers they start to taste sweet. How would you explain this to your friend?
5. Your friend bets you that you cannot swallow food while standing on your head. Do you take the bet?
6. One of your friends laughs at pretty much anything and often chokes on food at lunch. How would you explain the connection?
7. What would be the result if the stomach did not have sphincter muscles?
8. What’s the deal with pepsinogen and pepsin?
9. Your friend’s father has been diagnosed with a peptic ulcer. Explain to them what this means and give some advice about how to treat it.
10. Why is surface area important in the small intestine and what features increase it?
11. How is the structure of villi adapted to their function?
12. How do food molecules get from the stomach to your blood?
13. How is the small intestine protected from the acid chyme? From pepsin?
14. Complete the following table
Nutrient Digestion Begins Digestion Completed
Carbohydrates
18 | P a g e
Bio 12
Durley
Proteins
Fats
Mr Man – now you should know them ALL!
19 | P a g e
Bio 12
Durley
A Villus – label it up!
20 | P a g e
