chapter 15 digestionstream.mhcc.edu/videos/thatchev/bi100_ch15.pdf · small intestine a. the...
TRANSCRIPT
7/19/11
1
Chapter 15 Digestion
Introduction A. Digestion refers to the mechanical and
chemical breakdown of foods so that nutrients can be absorbed by cells.
B. The digestive system carries out the process of digestion.
C. The digestive system consists of the alimentary canal, leading from mouth to anus, and several accessory organs whose secretions aid the processes of digestion.
Fig15.01
ALIMENTARY CANAL
Anus
ACCESSORY ORGANS Salivary glands!Secrete saliva, which contains!enzymes that initiate breakdown!of carbohydrates
Mouth!Mechanical breakdown!of food; begins chemical!digestion of carbohydrates Pharynx!Connects mouth with!esophagus.
Esophagus!Peristalsis pushes!food to stomach
Stomach!Secretes acid and!enzymes. Mixes food!with secretions to!begin enzymatic!digestion of proteins Small intestine!Mixes food with bile!and pancreatic juice.!Final enzymatic breakdown!of food molecules;!main site of!nutrient absorption Large intestine!Absorbs water and!electrolytes to form feces Rectum!Regulates elimination!of feces
Pancreas!Produces and secretes!pancreatic juice, containing!digestive enzymes and!bicarbonate ions,!into small intestine
Gallbladder!Stores bile and!introduces it into!small intestine
Liver!Produces bile, which!emulsifies fat
7/19/11
2
B. Structure of the Wall 1.The wall of the alimentary canal
consists of the same four layers throughout its length, with only slight variations according to the functions of specific sections of the canal.
a. Mucosa (epithelium) b. Submucosa (connective tissue) c. Muscularis (smooth muscle) d. Serosa (epithelium)
Fig15.03
Intestinal gland Lymph nodule!
Villi Lacteal Epithelium
Mucosa
Serosa
Mesentery
Mucosa
Serosa
Nucleus
Artery Vein
Circular fold
Submucosa Microvilli Goblet cell
Simple columnar!epithelium
Circular muscle Longitudinal muscle
Nerve!plexuses
Mucous gland in submucosa Circular muscle Longitudinal muscle Muscular!
layer
C. Movements of the Tube 1. The motor functions of the
alimentary canal are of two types- mixing movements and propelling movements.
2. Mixing movements occur when smooth muscles contract rhythmically in small sections of the tube.
7/19/11
3
3. Propelling movements include a wavelike motion called peristalsis, which is caused by contraction behind a mass of food as relaxation allows the mass to enter the next segment of the tube.
Fig15.04
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(c)
(a)
Movement of contents (b)
Digesting material
Wave of!contraction
Mouth A. The mouth is the first portion of the
alimentary canal; it functions to receive food and begins mechanical digestion by chewing or mastication.
7/19/11
4
Fig15.06
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Frontal sinus
Nasal cavity
Hard palate
Hyoid bone
Esophagus
Laryngopharynx
Epiglottis Lingual tonsil Oropharynx Palatine tonsil Uvula Oral cavity Nasopharynx Soft palate Opening of auditory tube Pharyngeal tonsil Sphenoidal sinus
Lip
Larynx
Vestibule
Tongue Tooth
Trachea
E. Teeth 1. Two sets of teeth develop in sockets
within the alveolar processes of the maxillary and mandibular bones.
2. The 20 primary teeth are shed in the order they appeared and are replaced by 32 secondary teeth.
3. Through the actions of chewing, teeth break food into smaller pieces, beginning mechanical digestion.
Fig15.08
Incisors
Canine (cuspid)
Canine (cuspid)
Premolars!(bicuspids)!
Premolars!(bicuspids)!
Molars
Incisors
Molars
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
7/19/11
5
Salivary Glands A. The salivary glands secrete saliva, which
moistens and dissolves food particles, binds them together, allows tasting, helps to cleanse the mouth and teeth, and begins carbohydrate digestion.
Sublingual gland
Parotid!gland!
Mandible (cut)
Submandibular!duct!
Masseter!muscle
Submandibular!gland
Tongue
Fig15.10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pharynx and Esophagus A. The pharynx is a cavity lying behind the
mouth, and the esophagus is a muscular tube leading to the stomach.
7/19/11
6
D. Esophagus 1. The esophagus is a straight,
collapsible passageway leading to the stomach, through a diaphragm opening (esophageal hiatus).
2. Mucous glands are scattered throughout the submucosa of the esophagus and produce mucus to moisten and lubricate the inner lining of the tube.
3. The lower esophageal sphincter helps to prevent regurgitation of the stomach contents into the esophagus.
Stomach A. The stomach is a J-shaped muscular organ
that receives and mixes food with digestive juices, and propels food to the small intestine.
B. The stomach produces gastric juice consisting of enzymes, acid (HCl), and mucous. It also produces the hormone gastrin which helps regulate digestion (that is released into the blood, not the stomach)
Fig15.11
Lower esophageal!sphincter!
Fundus
Body
Greater!curvature!
Lesser!curvature!
Gastric folds (rugae) Pyloric!antrum!
Pyloric!canal!Pylorus
Pyloric opening
Duodenum Pyloric!sphincter!
Cardia
Esophagus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
7/19/11
7
F. Mixing and Emptying Actions 1. Following a meal, mixing actions of
the stomach turn the food into chyme and pass it toward the pyloric region using peristaltic waves.
2. The rate at which the stomach empties depends on the fluidity of the chyme and the type of food.
3. As chyme fills the duodenum, accessory organs—the pancreas, liver, and gallbladder—add their secretions.
Pancreas A. The pancreas has an exocrine function of
producing pancreatic juice with many enzymes that aid digestion.
7/19/11
8
Fig15.14
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Right hepatic duct Left hepatic duct Cystic duct Common hepatic duct Bile duct
Bile duct
Gallbladder
Head of pancreas
Duodenum
Major duodenal papilla
Intestinal lumen
Pancreatic duct
Pyloric sphincter
Minor duodenal!papilla
Major duodenal!papilla
Hepatopancreatic!sphincter
Pancreatic!duct
Tail of pancreas
Hepatopancreatic!ampulla Hepatopancreatic!
sphincter
Liver A. The reddish-brown liver, located in the
upper right quadrant of the abdominal cavity, is the body’s largest internal organ.
Fig15.16
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Right lobe Left lobe
Right lobe Cystic duct Left lobe
Hepatic duct
Bile duct
Caudate lobe (b) (a)
Inferior vena cava Coronary ligament
Gallbladder
Round!ligament Gallbladder
Inferior vena cava
Quadrate lobe
Hepatic artery Hepatic portal!vein
7/19/11
9
Liver Functions A. The liver carries on many diverse
functions for the body. B. The liver is responsible for many
metabolic activities, such as the metabolism of carbohydrates, lipids, and proteins.
C. The liver also stores glycogen, vitamins A, D, and B12, iron, and blood.
4. The liver filters the blood, removing damaged red blood cells and foreign substances, and removes toxins.
5. The liver's role in digestion is to secrete bile which helps digest fats.
Gallbladder A. The gallbladder is a pear-shaped
sac lying on the interior surface of B. A sphincter muscle controls the
release of bile from the common bile duct.
7/19/11
10
Small Intestine A. The lengthy small intestine receives
secretions from the pancreas and liver, completes digestion of the nutrients in chyme, absorbs the products of digestion, and transports the remaining residues to the large intestine.
B. Parts of the Small Intestine 1. The small intestine consists of the
duodenum, jejunum, and ileum. 2. The duodenum is the shortest and
most fixed portion of the small intestine; the rest is mobile and lies free in the peritoneal cavity.
3.The small intestine is suspended from the posterior abdominal wall by a double-layered fold of peritoneum called mesentery.
Fig15.21
Stomach
Jejunum
Duodenum
Ascending colon
Mesentery Appendix
Cecum
Ileum
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
7/19/11
11
C. Absorption in the Small Intestine 1. The small intestine is the major site
of absorption within the alimentary canal.
2. The small intestine carries on segmentation and peristaltic waves.
Large Intestine A. The large intestine absorbs water and
electrolytes and forms and stores feces.
Fig15.27
Anal canal
Anus
Sigmoid colon
Haustra
Descending colon
Tenia coli
Rectum
Appendix
Cecum
Orifice of appendix
Ileocecal sphincter
Ascending colon
Serous layer Mucous membrane
Transverse colon
Muscular layer
Ileum
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
7/19/11
12
B. Parts of the Large Intestine 1. The large intestine consists of the
cecum (pouch at the beginning of the large intestine with the appendix projecting downward from it.), colon (ascending, transverse, descending, and sigmoid regions), the rectum, and the anal canal.
2. The anal canal opens to the outside as the anus; it is guarded by an involuntary internal anal sphincter and a voluntary external anal sphincter muscle.
C. Functions of the Large Intestine 1. The large intestine does not digest
or absorb nutrients, but it does secrete mucus.
2. The large intestine absorbs electrolytes and water.
3. The large intestine contains important bacteria (intestinal flora) which synthesize vitamins and use cellulose.
D. Movements of the Large Intestine 1. The movements of the large
intestine are similar to those of the small intestine.
2. Peristaltic waves (mass movements) happen only two or three times during the day.
3. Defecation is stimulated by a defecation reflex that forces feces into the rectum where they can be expelled.
7/19/11
13
E. Feces 1. Feces are composed of undigested
material, water, electrolytes, mucus, and bacteria.
2. Both the color of feces and its odor is due to the action of bacteria.