Week 7 Flashcards
(216 cards)
1
Q
What is digestion?
A
The breakdown of ingested food into chemical building blocks via catabolism.
2
Q
What are the three main processes of the digestive system?
A
Digestion (breakdown of food)
Absorption (nutrients into blood)
Metabolism (production of ATP)
3
Q
Why is the digestive system essential to life?
A
It converts food into raw materials that build and fuel body cells.
4
Q
What are the four main functions of the digestive system?
A
Takes in food
Breaks food into nutrient molecules
Absorbs nutrients into bloodstream
Rids body of indigestible remains
5
Q
What are the two main groups of the digestive system?
A
Alimentary canal (GI tract)
Accessory digestive organs
6
Q
What is the alimentary canal and what does it do?
A
A muscular tube from mouth to anus that digests food and absorbs nutrients into blood.
7
Q
Why is the inside of the GI tract considered outside the body?
A
It’s open to the external environment at both the mouth and anus.
8
Q
What are accessory digestive organs?
A
Organs that aid in the digestive process.
9
Q
What are the six essential digestive activities?
A
Ingestion
Propulsion
Mechanical digestion
Chemical digestion
Absorption
Defecation
10
Q
What is ingestion and how does it begin the digestive process?
A
Ingestion is the process of taking food into the mouth. It begins with chewing (mastication) and swallowing (deglutition), and is broken down by enzymes like salivary amylase and lingual lipase (chemical digestion). This leads to the food entering the digestive tract.
11
Q
What is propulsion and how does it occur?
A
Propulsion is the movement of food through the digestive tract, facilitated by peristalsis, which are muscular contractions that move food forward.
12
Q
What is peristalsis and how does it help digestion?
A
Peristalsis is a wave-like muscular contraction that moves food along the gastrointestinal (GI) tract, mixing contents and aiding in the transportation of food between digestive organs. It helps move contents from the small intestine to the large intestine.
13
Q
How does mechanical digestion occur?
A
Mechanical digestion breaks down food physically through chewing in the mouth and churning in the stomach, increasing surface area for enzymes to act on.
14
Q
What happens in the mouth during mechanical digestion?
A
In the mouth, chewing breaks food into smaller pieces, increasing surface area for digestion by enzymes.
15
Q
How does the stomach contribute to mechanical digestion?
A
In the stomach, muscular contractions mix food with gastric juices, turning it into a semi-liquid mixture called chyme.
16
Q
How does mechanical digestion occur in the small intestine?
A
Peristalsis and segmentation contractions in the small intestine mix and move chyme, aiding nutrient absorption.
17
Q
What is chemical digestion and how does it work?
A
Chemical digestion breaks down food into simpler molecules through enzymes, beginning in the mouth and continuing in the stomach and small intestine.
18
Q
How does chemical digestion occur in the mouth?
A
In the mouth, amylase breaks down carbohydrates into simpler sugars.
19
Q
How does chemical digestion occur in the stomach?
A
In the stomach, hydrochloric acid and pepsin break down proteins into amino acids.
20
Q
What happens during chemical digestion in the small intestine?
A
Enzymes from the pancreas and bile from the liver break down carbohydrates, proteins, and fats into simple sugars, amino acids, and fatty acids, respectively, for absorption.
21
Q
What is absorption and where does it mostly occur?
A
Absorption is the process of taking up nutrients, water, and electrolytes into the bloodstream. It mostly occurs in the small intestine.
22
Q
How does the small intestine facilitate absorption?
A
The small intestine has villi and microvilli, which increase surface area for nutrient absorption through diffusion, facilitated diffusion, and active transport.
23
Q
How is water and electrolytes absorbed?
A
Water and electrolytes are absorbed primarily in the small intestine, with some absorption occurring in the large intestine to maintain fluid and electrolyte balance.
24
Q
What happens to nutrients after absorption?
A
Absorbed nutrients are transported via the bloodstream to cells for energy, growth, and repair.
25
What is defecation and why is it important?
Defecation is the process of expelling waste material from the body. It is important for eliminating undigested food, bacteria, and waste products, maintaining digestive health.
26
What happens during the process of defecation?
When faeces accumulate in the rectum, nerve signals trigger the relaxation of the internal anal sphincter, allowing faeces to move into the anal canal. The external anal sphincter then relaxes to expel faeces.
27
How do hormones affect the gastrointestinal tract?
Hormones stimulate smooth muscle in the gastrointestinal tract to mix contents and move them along the tract. They can also be absorbed into the blood to influence various digestive processes.
28
Where are hormones secreted in the digestive system?
Hormones are secreted by endocrine cells located in the epithelium of the stomach and small intestine.
29
How are hormones released and transported in the digestive system?
When stimulated, endocrine cells release hormones into the interstitial fluid, which then enter the bloodstream to reach target cells.
30
What are some examples of hormones secreted in the digestive system and their roles?
Examples of hormones include gastric secretion and cholecystokinin (CCK). Their roles are wide and varied, influencing processes like gastric acid secretion, enzyme release, and the regulation of digestion.
31
What is segmentation in digestion?
Segmentation is a mechanical digestion process where alternating contractions of smooth muscle mix intestinal contents and slowly move them toward the ileocecal valve, aiding digestion and absorption.
32
What are the key concepts that regulate digestive activity?
The regulation involves neurons, mechanical and chemical stimuli, and hormones to ensure effective food breakdown and absorption.
33
What is the enteric nervous system and how does it function?
The enteric nervous system, also called the gut brain, controls digestive activity using local reflexes (short reflexes) and reflexes involving the central nervous system (long reflexes).
34
What are short reflexes in digestion?
(Intrinsic) Short reflexes are mediated by the enteric nervous system, responding to stimuli within the gastrointestinal tract.
35
What are long reflexes in digestion?
(Extrinsic) Long reflexes are initiated by stimuli from inside or outside the gastrointestinal tract, involving the central nervous system and autonomic nervous system to regulate digestive activity.
36
How do sympathetic and parasympathetic nervous systems affect digestion?
Sympathetic activity inhibits digestive function, decreasing secretions and motility. Parasympathetic activity stimulates digestion, increasing secretions and muscle movements.
37
What are the two intrinsic nerve plexuses in the gastrointestinal system?
The two intrinsic nerve plexuses are the myenteric plexus (which controls smooth muscle contractions) and the submucosal plexus (which controls secretion).
38
How do mechanoreceptors and chemoreceptors regulate digestion?
Mechanoreceptors and chemoreceptors in the gastrointestinal tract walls detect stretch, osmolarity, and pH changes. They initiate reflexes that regulate gland secretion, hormone release, and smooth muscle activity.
39
How are hormones involved in digestive regulation?
Hormones are secreted by endocrine cells in the stomach and small intestine. They enter the bloodstream and regulate digestive processes, such as gastric secretion and enzyme activity, by targeting specific cells.
40
Three regulatory mechanisms that control the digestive system.
Hormones
Neurons
Chemical and Mechanical stimuli
41
How do the lips and cheeks assist in digestion?
The lips and cheeks help keep food between the teeth during chewing.
42
What are the functions of the tongue in digestion and speech?
The tongue repositions food between the teeth, mixes it with saliva to form a bolus, initiates swallowing, and helps form consonants in speech.
43
What is a bolus and how is it formed?
A bolus is a compact mass of food formed by the tongue mixing food with saliva during chewing.
44
What role do the teeth play in digestion?
The teeth chew (masticate) food by grinding it into smaller pieces through opening and closing of the mouth.
45
What is the function of the palate in digestion?
The hard palate provides a surface for food during chewing, while the soft palate closes off the nasopharynx during swallowing.
46
What is the oral cavity and what type of epithelium lines it?
The oral cavity is the mouth, lined with thick squamous epithelium that resists friction from eating.
47
Why are the gums, hard palate, and back of the tongue slightly keratinised?
These areas are slightly keratinised to provide extra protection against friction during eating.
48
What are the main roles of saliva in digestion?
Saliva helps form the bolus, moistens the mouth, begins chemical digestion of starch, and protects against microbes with lysosomes and antibodies.
49
Which major salivary glands secrete saliva into the mouth?
The parotid, submandibular, and sublingual glands.
50
What is deglutition and how long does it take for food to reach the stomach?
Deglutition is swallowing. It takes about 8 seconds for solids and 1–2 seconds for liquids to reach the stomach.
51
What occurs during the buccal phase of swallowing?
The tongue pushes the bolus into the oropharynx, then laryngopharynx. Skeletal muscles contract to propel food, and multilayered epithelial cells protect the pharynx.
52
What is the role of the pharyngeal phase in swallowing?
The bolus is directed to the oesophagus as the epiglottis blocks the larynx, and breathing temporarily stops. This phase is involuntary.
53
Describe the oesophageal phase of swallowing.
The bolus is moved by peristalsis through the oesophagus, and the lower oesophageal sphincter opens to allow entry into the stomach. This is also involuntary.
54
What is the function of the stomach in digestion?
The stomach stores food, begins protein digestion, and converts food into a creamy paste called chyme.
55
What are rugae and when do they form?
Rugae are large folds in the stomach that form when it is empty and contracted.
56
What does the pyloric sphincter do?
It separates the stomach from the duodenum and controls the passage of chyme into the small intestine.
57
What do mucus cells in the stomach do?
They secrete alkaline mucus to protect the stomach lining from gastric acid.
58
What is the role of parietal cells?
Parietal cells secrete hydrochloric acid, making the stomach contents highly acidic.
59
What do chief cells and enteroendocrine cells do?
Chief cells secrete lipases to digest fats; enteroendocrine cells release chemical messengers that aid digestion.
60
What are the three phases of gastric secretion and where do they act?
Cephalic (before food enters the stomach), gastric (when food is in the stomach), and intestinal (as food enters the small intestine).
61
What triggers the cephalic phase of gastric secretion?
The sight, smell, taste, or thought of food, which stimulates the vagus nerve to prepare the stomach for digestion.
62
What occurs in the gastric phase of secretion?
Food in the stomach triggers neural and hormonal responses to increase secretion. Stress or low pH can inhibit this.
63
What are the effects of the intestinal phase on gastric secretion?
Gastrin stimulates secretion, while the enterogastric reflex inhibits it to prevent too much chyme entering the small intestine.
64
What is retropulsion and where does it occur?
Retropulsion is the back-and-forth movement of chyme at the pyloric valve to break it up before it enters the duodenum.
65
How long does it take for the stomach to empty after a meal?
About four hours.
66
What is the function of mucus neck cells in the stomach?
The exact function of mucus neck cells is unknown, but they are located in the neck region of gastric glands and secrete a thinner, acidic mucus.
67
What are the four main cell types of the gastric glands and their functions?
Mucous cells: Secrete alkaline mucus to protect the stomach lining.
Mucous neck cells: Function unclear; secrete acidic mucus.
Parietal cells: Secrete hydrochloric acid.
Chief cells: Secrete lipase for fat digestion.
Enteroendocrine cells: Release hormones/chemical messengers to aid digestion.
68
What are the three phases of gastric secretion?
The cephalic phase, gastric phase, and intestinal phase.
69
What initiates the cephalic phase of gastric secretion?
Sensory input (sight, smell, taste, or thought of food) stimulates the hypothalamus, which activates the vagus nerve to prepare the stomach for digestion.
70
What initiates the gastric phase of secretion?
Food entering the stomach triggers stretch receptors and activates local reflexes; food chemicals like peptides and caffeine also stimulate secretion via gastrin.
71
What inhibits the gastric phase of secretion?
Emotional stress or very acidic stomach contents (low pH) inhibit gastric secretion.
72
What triggers the intestinal phase of gastric secretion?
Entry of partially digested food into the small intestine initially stimulates gastric glands via gastrin release.
73
What inhibits the intestinal phase of secretion?
The enterogastric reflex inhibits gastric secretion to control the rate of chyme entering the small intestine.
74
What is the digestive function of the liver?
The liver produces bile, which is essential for digestion.
75
What is the function of the gallbladder?
The gallbladder stores bile produced by the liver and releases it when needed.
76
What are the main bile-related ducts and associated structures?
Right and left hepatic ducts, common hepatic duct, cystic duct, bile duct and sphincter, hepatopancreatic ampulla and sphincter, and major duodenal papilla.
77
What is the digestive role of the pancreas?
The pancreas produces pancreatic juice, which contains enzymes that digest all major food categories.
78
What enzymes are found in pancreatic juice?
Amylases (carbohydrates), lipases (lipids), nucleases (nucleic acids), and proteases (proteins).
79
What is the composition and function of pancreatic juice?
Pancreatic juice is made of water, enzymes, and electrolytes. It neutralises stomach acid and aids digestion.
80
How much pancreatic juice is produced daily and where does it go?
About 1.5 litres daily; it is exported to the duodenum.
81
What is the function of the bicarbonate secreted by the pancreas?
Bicarbonate neutralises the hydrochloric acid from the stomach.
82
What are the four basic layers of the small intestine wall?
Mucosa, submucosa, muscularis externa, and serosa.
83
What are the three components of the mucosa layer?
Epithelium (secretes mucus, enzymes, hormones), lamina propria (absorptive capillaries), and muscularis mucosa (smooth muscle for movement).
84
What does the submucosa contain?
Blood vessels, lymphatics, lymphoid follicles, and nerve fibres.
85
What is the function of the muscularis externa in the small intestine?
It is responsible for segmentation and peristalsis.
86
What is the role of the serosa layer?
It is the outermost protective layer.
87
What is the function of the small intestine and how long is it?
It is the major digestive organ responsible for digestion and absorption; about 4 metres long.
88
What are the three regions of the small intestine?
Duodenum, jejunum, and ileum.
89
What separates the small intestine from the stomach and large intestine?
The pyloric sphincter (stomach) and the ileocaecal valve (large intestine).
90
What structural features increase absorption in the small intestine?
Circular folds, villi, and microvilli.
91
What are circular folds and their function?
Permanent folds of mucosa and submucosa that spiral chyme through the lumen.
92
What are villi and where are they most prominent?
Fingerlike mucosal projections; largest in the duodenum for absorption.
93
What are microvilli and what do they contain?
Projections on epithelial cells (enterocytes); they contain brush border enzymes to complete digestion.
94
What remains to be digested when chyme enters the small intestine?
Carbohydrates and proteins are partially digested; fat digestion has just begun.
95
How long does chyme stay in the small intestine, and where does most absorption occur?
About 3–6 hours; most absorption occurs before reaching the ileum.
96
What is absorbed by the small intestine?
All nutrients, ~80% of electrolytes, and most water (95%).
97
What is segmentation and its function?
The main motility pattern post-meal; mixes chyme with digestive juices and brings it into contact with mucosa.
98
What is the migrating motor complex?
A peristaltic pattern that moves contents toward the large intestine between meals.
99
What is the gastroileal reflex?
A long reflex triggered by stomach activity; it increases ileum segmentation and relaxes the ileocaecal sphincter.
100
What hormone aids the gastroileal reflex and what does it do?
Gastrin; it increases ileum motility and relaxes the ileocaecal sphincter.
101
How is regurgitation from the large intestine into the ileum prevented?
Backward pressure closes the ileocaecal valve once chyme passes through.
102
What are the major digestive functions of the large intestine?
Absorb remaining water, store residues, and eliminate them as faeces.
103
What does the large intestine absorb besides water?
Metabolites from bacterial fermentation of undigested carbohydrates.
104
What are the main regions of the large intestine?
Caecum (with appendix), colon, rectum, and anal canal.
105
Does food breakdown occur in the large intestine?
No; its role is to move and eliminate faeces, not to digest food.
106
What are haustral contractions?
Slow segmenting movements every 30 minutes that mix and move contents.
107
What are mass movements in the large intestine?
Long, powerful contractions that push contents toward the rectum, often after eating.
108
What triggers the defecation reflex?
Stretching of the rectal wall as faeces enter the rectum.
109
What is the Valsalva manoeuvre and how does it assist defecation?
It increases abdominal pressure to help expel faeces.
110
What are the three steps of defecation?
1. Stretch receptors in rectum send signals to spinal cord.
2. Parasympathetic signals contract the colon/rectum and relax internal sphincter.
3. Conscious control relaxes the external sphincter to allow defecation.
111
What happens if it's not a convenient time to defecate?
Reflex contractions stop, rectum relaxes, and the urge is delayed until the next mass movement.
112
Where does most digestion and absorption occur?
In the small intestine, which absorbs virtually all foodstuffs, 80% of electrolytes, and most water.
113
In what form can carbohydrates be absorbed?
Only as monosaccharides (glucose, galactose, and fructose).
114
Where does starch digestion occur?
In the mouth (salivary amylase), small intestine (pancreatic amylase), and brush border enzymes (e.g., lactase, maltase).
115
What enzymes are involved in final carbohydrate digestion?
Brush border enzymes like lactase and maltase.
116
What is the end product of protein digestion?
Amino acids.
117
Where does protein digestion begin and with what enzyme?
In the stomach with pepsin, activated from pepsinogen by HCl.
118
What enzymes continue and complete protein digestion?
Pancreatic proteases and brush border enzymes in the small intestine.
119
Why is pepsin only active in the stomach?
It is inactivated by the high pH of the duodenum.
120
What pretreatment is required for lipid digestion?
Emulsification by bile salts from the liver.
121
What enzymes digest lipids, and into what?
Lipases; they break lipids into fatty acids and monoglycerides.
122
What are micelles and their role?
Tiny droplets that carry lipids to the epithelial surface for absorption via diffusion.
123
What happens after lipids are absorbed?
They are reassembled into triglycerides, packaged as chylomicrons, and transported via the lymphatic system.
124
Where does nucleic acid digestion occur?
In the small intestine.
125
What enzymes digest nucleic acids and what are the products?
Pancreatic nucleases and brush border enzymes; they produce bases, pentose sugar, and phosphate ions.
126
Why is saliva important in dentistry?
Saliva plays a key role in digestion and protects the oral cavity, making it one of the most important secretions for dentists.
127
What are the main functions of saliva?
Lubrication, digestion, buffering, and immune defence.
128
How does saliva help with digestion?
It contains salivary amylase, which starts breaking down carbohydrates in the mouth.
129
What does saliva do to protect the mouth?
It moistens and cleans the mouth, contains buffers to maintain pH ~7, and has antibodies and lysosomes to defend against microbes.
130
What are the two main types of saliva secretions?
Serous (watery) and mucous (thick/viscous).
131
What is the role of serous saliva?
It is thin, enzyme-rich (especially amylase), and helps with digestion and lubrication.
132
What is the role of mucous saliva?
It is thick, rich in mucins, and protects, lubricates, and helps form the food bolus for swallowing.
133
What are the three major pairs of salivary glands?
Parotid, submandibular, and sublingual glands.
134
Where are the parotid glands located?
In front of and below the ears.
135
What type of saliva do the parotid glands produce?
Serous (watery) saliva rich in enzymes.
136
Where are the submandibular glands located?
Beneath the jawbone (mandible).
137
What type of saliva do the submandibular glands produce?
Both serous and mucous saliva.
138
Where are the sublingual glands found?
Under the tongue.
139
What type of saliva do the sublingual glands produce?
Mainly mucous saliva.
140
What is the main enzyme in saliva that begins digestion?
Salivary amylase.
141
What are some other components of saliva besides enzymes?
Water, mucus, electrolytes, and antibacterial compounds.
142
What are the key roles of saliva?
Lubrication, digestion, tasting, and protecting the mouth.
143
Where are the parotid glands located?
In front of and just below each ear.
144
What type of secretion do parotid glands produce?
Serous (watery, enzyme-rich).
145
What percentage of saliva do parotid glands produce?
About 25%.
146
Where are the submandibular glands located?
Under the jawbone (mandible).
147
What type of secretion do submandibular glands produce?
Mixed (mostly serous, some mucous).
148
What percentage of saliva do submandibular glands produce?
About 70%.
149
Where are the sublingual glands located?
Beneath the tongue.
150
What type of secretion do sublingual glands produce?
Mostly mucous.
151
What percentage of saliva do sublingual glands produce?
About 5%.
152
What happens to the large nutrient molecules we eat?
They are broken down into smaller molecules like amino acids, glucose, and fatty acids.
153
Why are smaller molecules important for cells?
They provide energy for cell activities and can be stored for later use.
154
What is metabolism?
The sum of all chemical reactions in the body that involve storing or using energy (ATP).
155
When does the absorptive state occur?
After eating, when food is being digested and nutrients are absorbed.
156
What is the main goal of the absorptive state?
To use and store the nutrients just absorbed.
157
What happens to glucose during the absorptive state?
It’s used for energy or stored as glycogen or fat.
158
What happens to amino acids during the absorptive state?
They are used to build proteins or converted to fat if in excess.
159
What happens to lipids during the absorptive state?
They are stored in fat tissue or used for energy.
160
When does the postabsorptive state occur?
When the nutrients from a meal have been used or stored — usually between meals or during fasting.
161
What is the body’s goal in the postabsorptive state?
To maintain blood glucose levels for energy, especially for the brain.
162
What happens to glycogen during the postabsorptive state?
It’s broken down into glucose for energy.
163
What happens to fats during the postabsorptive state?
They are broken down into fatty acids and glycerol for energy.
164
What happens to proteins during the postabsorptive state?
In long fasting, proteins can be broken down into amino acids for energy.
165
What is metabolism?
Metabolism is all the chemical reactions in the body that break down and rebuild molecules to store or use energy.
166
What are the two nutritional states of metabolism?
The absorptive (fed) state and the postabsorptive (fasting) state.
167
What does the body use during the postabsorptive state?
It draws on stores of amino acids, carbohydrates, and fats.
168
Which organs control nutrient conversion?
Liver, adipose tissue, and skeletal muscle.
169
How are amino acids used for energy?
They must first be converted to keto acids.
170
What happens during the absorptive state?
Anabolism (building up) is greater than catabolism (breaking down), and nutrients are stored.
171
How long does the absorptive state last?
During a meal and for about four hours after eating.
172
What happens to excess nutrients in the absorptive state?
They are converted to fat for storage.
173
What happens to monosaccharides after absorption?
Fructose and galactose are converted to glucose in the liver; glucose is released or stored.
174
What happens to fats after digestion?
They enter lymph as chylomicrons and are used or stored, mainly in adipose tissue.
175
What happens to amino acids in the absorptive state?
They are used for protein synthesis, energy, or converted to fat/glycogen for storage.
176
What is the main energy fuel during the absorptive state?
Glucose.
177
What hormone controls the absorptive state?
Insulin.
178
How does insulin affect glucose uptake?
It increases GLUT-4 transporters on cell membranes, increasing glucose entry into cells.
179
Which organs take up glucose regardless of insulin?
The brain and liver.
180
What does insulin do besides glucose uptake?
It promotes amino acid uptake and protein synthesis.
181
What is the postabsorptive state?
The fasting state, when body stores are broken down for energy.
182
When does the postabsorptive state occur?
Late morning, late afternoon, or overnight—when the GI tract is empty.
183
What is the goal of the postabsorptive state?
To maintain normal blood glucose levels for the brain.
184
How does the liver provide glucose early in fasting?
By breaking down glycogen (glycogenolysis).
185
Can skeletal muscle glycogen supply glucose directly?
No, it lacks the enzyme to release glucose into the blood.
186
What happens to muscle glycogen during fasting?
It’s converted to pyruvic or lactic acid, then the liver turns it into glucose.
187
How do fats help during the postabsorptive state?
Lipolysis splits triglycerides into glycerol and fatty acids, used for energy.
188
What is gluconeogenesis?
Making glucose from non-carbohydrate sources like glycerol and amino acids.
189
What happens in prolonged fasting?
Tissue proteins are broken down for energy.
190
What is glucose sparing?
Other tissues use fats or ketones so the brain can use the available glucose.
191
What hormone controls the postabsorptive state?
Glucagon.
192
What triggers glucagon release?
Falling blood glucose levels.
193
What are glucagon’s main effects?
It promotes glycogen breakdown (glycogenolysis) and gluconeogenesis in the liver.
194
What is the major energy fuel in carbohydrates?
Glucose.
195
Where are fructose and galactose converted to glucose?
In the liver.
196
What happens to glucose after it's made in the liver?
It's released into the blood and used by all tissues.
197
Which hormone controls blood glucose levels?
Insulin.
198
What happens to excess glucose in the body?
It's stored as glycogen in the liver and muscles, or as fat in adipose tissue.
199
What are dietary amino acids used for?
Protein synthesis, energy (via keto acids), or fat storage in the liver.
200
Where are dietary amino acids mainly found?
Meat, poultry, eggs, dairy, and fish.
201
How does dietary fat enter the body after digestion?
Through the lymph in the form of chylomicrons.
202
Where are excess fats stored?
In adipose tissues.
203
What is the role of the enteric nervous system (ENS) in digestion?
The ENS is the gut’s own nervous system; it regulates digestive tract motility, secretions, and blood flow independently of the CNS.
204
How does the pharynx contribute to digestion?
The pharynx is a passageway for food and air that propels food from the mouth to the oesophagus using muscular contractions.
205
What prevents food from entering the trachea during swallowing?
The epiglottis folds over the larynx to block food from entering the respiratory tract.
206
What are rugae in the stomach?
Rugae are folds in the stomach mucosa that allow it to expand after meals.
207
What is the function of parietal cells in the stomach?
They secrete hydrochloric acid (HCl) and intrinsic factor for vitamin B₁₂ absorption.
208
What is bile, and where is it produced and stored?
Bile is a fat-emulsifying substance produced by the liver and stored in the gallbladder.
209
What role does the duodenum play in digestion?
It receives chyme from the stomach and digestive enzymes from the pancreas and bile from the liver to continue digestion.
210
What structural features of the small intestine increase surface area for absorption?
Circular folds, villi, and microvilli.
211
What is the major function of the large intestine?
Absorption of water and electrolytes, and formation and elimination of faeces.
212
How are carbohydrates processed during digestion?
Enzymes like amylase and brush border enzymes break polysaccharides down to monosaccharides (mainly glucose) for absorption.
213
How are proteins processed during digestion?
Pepsin in the stomach and proteases from the pancreas and brush border break proteins into amino acids for absorption.
214
How are dietary fats digested and absorbed?
Bile emulsifies fats; pancreatic lipases digest them into monoglycerides and fatty acids, which are absorbed into lacteals as chylomicrons.
215
What triggers the secretion of insulin in the absorptive state?
Rising levels of blood glucose and amino acids after a meal stimulate insulin release from pancreatic beta cells.
216
How does the body maintain blood glucose in the postabsorptive state?
By promoting glycogenolysis, gluconeogenesis, and lipolysis through glucagon and other hormones.
