Module 3: Digestive System Flashcards
1
Q
What is the gastrointestinal tract?
A
Series of hollow organs
2
Q
What organs comprise the gastrointestinal tract?
A
Mouth/oral cavity, esophagus, stomach, small intestine, large intestine, rectum, anus
3
Q
What are accessory organs of the digestive system?
A
Organs that produce secretions, detoxify, and store substances to aid digestion
4
Q
What accessory organs comprise the digestive system?
A
Salivary glands, liver, gallbladder, pancreas
5
Q
Main role of digestive system?
A
Converts food into its simplest components, which are then absorbed into the bloodstream or excreted as waste
6
Q
Five functions of digestive system?
A
- Ingestion
- Mechanical digestion
- Chemical digestion
- Absorption
- Elimination of waste
7
Q
Two functional divisions of digestive system organs?
A
Upper gastrointestinal tract and lower gastrointestinal tract
8
Q
Role of upper gastrointestinal tract?
A
Food breakdown
9
Q
Role of lower gastrointestinal tract?
A
Absorption, waste compaction and removal
10
Q
What organs comprise the upper gastrointestinal tract?
A
Mouth/oral cavity, esophagus, stomach, small intestine (duodenum)
11
Q
What organs comprise the lower gastrointestinal tract?
A
Small intestine (jejunum and ileum), large intestine, rectum, anus
12
Q
Role of mouth/oral cavity
A
- Mechanical digestion (mastication)
- Mixing of food with saliva; salivary enzymes commence chemical digestion
13
Q
What is mechanical digestion?
A
Crushing/shearing of ingested food
14
Q
What is mastication?
A
Chewing, by means of movement of the jaw/tongue and grinding by teeth
15
Q
What is chemical digestion?
A
Enzymatic breakdown of food into substances that may be absorbed
16
Q
What is the esophagus?
A
Collapsed tubular fibromuscular organ connecting the pharynx to the stomach; runs posteriorly to trachea
17
Q
Role of esophagus?
A
Transfers food (bolus) into stomach
18
Q
What is bolus?
A
Rounded mass of masticated food mixed with saliva
19
Q
Role of stomach?
A
- Chemical digestion: bolus is mixed with gastric juices (hydrochloric acid and digestive enzymes) and converted into chyme
- Mechanical churning also facilitates digestion
20
Q
What is chyme?
A
Semi-fluid, pulpy, acidic mass of partially digested food mixed with gastric juices, expelled by stomach
21
Q
Three components of small intestine?
A
Duodenum, jejunum, and ileum
(DJI)
22
Q
Length of jejunum + ileum?
A
3-6m of small intestine
23
Q
Length of large intestine?
A
Approximately 1.5m
24
Q
Role of large intestine?
A
- Chemical digestion of components not digested by small intestine
- Reabsorption of water
- Compacts waste (faeces) for elimination
25
Three main components of large intestine?
Cecum, colon, and rectum
26
Four components of colon?
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
27
What is the cecum (structure)?
Expanded pouch that begins the large intestine that has an attached appendix
28
Role of rectum?
Store faeces prior to defecation
29
Role of salivary glands?
Secrete salivary amylase
30
Role of pancreas?
Secrete pancreatic enzymes and buffers, to break down proteins, fats, and carbohydrates
31
Roles of liver? (3)
Secretes bile, inactivates toxins, and stores iron/glucose/fat-soluble vitamins
32
Role of bile?
Emulsifies fats into fatty acids; lipid absorption and digestion
33
Role of gallbladder?
Stores bile
34
What are the four general major layers of the GIT?
Mucosa
Submucosa
Muscularis externa
Serosa/adventitia
35
What is the mucosa?
Innermost layer of GIT
36
Is the mucosa epithelium comprised of a single type? Why/why not
No; epithelial composition depends of function
37
Epithelium of mouth/esophagus mucosa?
Stratified squamous; protection
38
Epithelium of stomach/small intestine/large intestine mucosa (cecum and colon)?
- Simple columnar; absorption
- In small intestine, contains microvilli to increase SA for nutrient absorption
39
Epithelium of rectum/anus mucosa?
Stratified squamous; protection
40
Characteristic of epithelium of mucosa of GIT?
Contains specialised goblet cells that secrete mucus, keeping the epithelium moist, defending against pathogens/injury
41
What is the mucosa comprised of? (3)
1. Epithelial mucous membrane
2. Loose connective tissue (lamina propria)
3. Muscularis (muscularis mucosa)
42
Why is the CT of the mucosa loose?
So nutrients may travel through easily
43
Characteristics of lamina propria?
- Richly vascularised
- Contain numerous immunologically competent cells (e.g. fibroblasts, macrophages, gut-associated lymphoid tissue (GALT))
- Has sensory nerve endings
44
What is the muscularis mucosa?
Thin layer of smooth muscle cells
45
Role of muscularis mucosa?
Still under debate, but believed to alter the shape of lumen and move mucosal folds/villi
46
What is the submucosa?
Second-innermost layer of GIT
47
What is the submucosa comprised of?
Dense irregular CT, which is still relatively loose
48
Role of submucosa?
Provides physical support to mucosa, supplies blood/lymph vessels and nerves to GIT, and connects mucosa to underlying muscularis
49
What vessels does the submucosa contain?
Large blood vessels and lymphatic vessel
50
What are the submucosal glands?
Exocrine glands that secrete enzymes and buffers into lumen via ducts
51
What is the submucosal plexus (Meissner's plexus)?
Local circuitry of sensory neurons and autonomic nerve fibres that innervate glands
52
Roles of submucosal plexus?
Controls glandular secretions, alters electrolyte and water transport, regulates blood flow
53
What is the muscularis externa?
Third-innermost layer of GIT
54
What is the muscularis externa comprised of?
Multiple muscle layers (organised in circular and longitudinal layers) + myenteric plexus (Auerbach plexus)
55
Is the composition of the muscle layers in the muscularis externa consistent? Why/why not?
No; depends on location within GIT
56
What type of muscle is the muscularis externa of esophagus?
- 2 layers of muscle
- Skeletal muscle and smooth muscle
57
What type of muscle is the muscularis externa of stomach?
- 3 layers (inner oblique, middle circular, outer longitudinal)
- Smooth muscle
58
What type of muscle is the muscularis externa of small intestine/large intestine/rectum?
- 2 layers (inner circular, outer longitudinal)
- Smooth muscle
59
Role of muscularis externa?
Contraction of muscle layers facilitate mechanical processing and movement of materials along GIT
60
What is the myenteric plexus (Auerbach plexus)? Location?
Network of sensory neurons and autonomic nerve fibres, located between circular and longitudinal muscle layers
61
Role of myenteric plexus (Auerbach plexus)?
Coordinates digestive muscle activity and thus motility
62
What is muscle tone?
Amount of tension (or resistance to movement) in muscles
63
How does the myenteric plexus carry out its function differently according to the type of neural stimulation?
- Parasympathetic stimulation = increased muscle tone
- Sympathetic stimulation = decreased muscle tone
64
What is the serosa/adventitia?
Outermost layer of GIT; either serosa or adventitia depending on region
65
Where is the serosa found?
Intraperitoneal (within peritoneal cavity) regions of GIT (i.e. most of stomach, parts of small/large intestine, and rectum)
66
Where is the adventitia found?
Retroperitoneal (behind peritoneal cavity) regions of GIT (i.e. oral cavity, pharynx, esophagus, parts of stomach, most of small/large intestine, and anus)
67
What is the serosa (composition and function)?
- Loose CT, covered with mesothelium to lubricate outer surface of GIT and thus lower friction
- Lubricates structures
68
What is the adventitia (composition and function)?
- Dense network of collagen fibres
- Binds/attaches structures
69
Role of mucosa?
Protects, secretes mucus, and mediates chemical digestion and absorption
70
What is the oral cavity lined by?
Oral mucosa, which is stratified squamous epithelium
71
Structures of oral cavity? (7)
Hard palate, soft palate, tongue, teeth, gingiva (gums), uvula, tonsils
72
Role of hard palate?
Bony support to oral cavity structure
73
What and where is soft palate?
Muscular structure, posterior to hard palate
74
What muscle is the tongue?
Skeletal muscle
75
Role of uvula?
Prevents food from entering pharynx prematurely, prior to effective mastication
76
What are the tonsils comprised of?
Lymphoid tissue
77
Functions of oral cavity?
- Mastication, formation of bolus
- Salivary amylase digests carbohydrates
- Lingual lipase digests lipids (triglycerides)
78
3 major pairs of salivary glands?
Sublingual
Submandibular
Parotid
79
Location of sublingual salivary glands?
Lie on either side of tongue
80
Location of submandibular salivary glands?
Lie of inner surface of mandible (jaw)
81
Location of parotid salivary glands?
Lie just in front of ears
82
Role of sublingual salivary glands?
Produce mucous secretion that acts as buffer/lubricant, as well as approximately 5% of saliva entering oral cavity
83
Role of submandibular salivary glands?
Produce mixed serous/mucous secretion containing buffers, mucin, and salivary amylase, as well as approximately 75% of saliva entering oral cavity; secretions released under tongue
84
Role of parotid salivary glands?
Produce serous secretion containing abundant salivary amylase, as well as approximately 20% of saliva entering oral cavity
85
What are mumps?
Viral infection of parotid glands
86
How much saliva is produced daily?
1-1.5L
87
Composition of saliva?
99.4% water, and 0.6% electrolytes/buffers/antibodies/enzymes/salivary mucin
88
Functions of saliva? (4)
Lubrication, chemical digestion, protection, dissolving food (taste)
89
Length/width of esophagus?
25cm long, 2cm in diameter
90
Two sphincters of esophagus?
Upper esophageal sphincter and lower esophageal sphincter
91
Role of upper esophageal sphincter (UES)?
Prevents air entering GIT, and prevents reflux of food into airways
92
Role of lower esophageal sphincter (LES)?
Prevents reflux of stomach contents
93
Function of esophagus?
Conveys food/liquids from oral cavity into stomach, w/o absorption
94
Three phases of swallowing (deglutition)?
1. Buccal phase
2. Pharyngeal phase
3. Esophageal phase
95
What is the buccal phase?
- Voluntary
- Contraction of tongue to push bolus up against soft palate into oropharynx
96
What is the pharyngeal phase?
- Mainly voluntary
- Tongue blocks oral cavity, epiglottis blocks larynx/trachea, UES relaxes and opens, food enters esophagus
97
What is the esophageal phase?
- Mainly involuntary
- UES contracts and closes, bolus forced through esophagus by peristalsis, LES relaxes and opens, food enters stomach and once it has, LES closes
98
What is the stomach and its role?
Expandable muscular organ that churns food into chyme
99
Four main regions of stomach?
Fundus
Cardia
Body
Pylorus
100
Where is the fundus?
Superior to gastroesophageal junction
101
Where is the cardia?
Within approximately 3cm of gastroesophageal junction
102
Role of cardia?
Entry point for foods/liquid into stomach, with an esophageal sphincter preventing reflux of stomach contents, and abundant mucus glands to protect from acid
103
Where is body of stomach?
Largest region; lies between fundus and pylorus
104
Role of body of stomach?
Facilitates/houses churning of ingested food
105
Where is the pylorus?
J-shaped curve leading to small intestine
106
Two subdivisions of pylorus?
Pyloric antrum
Pyloric canal
107
Role of pyloric sphincter?
Regulates process of chyme moving into small intestine
108
What are rugae?
Prominent folds/ridges of the mucosa and submucosa layers of the stomach wall, that form when stomach is empty
109
Role of rugae?
Facilitate expandable nature of stomach; increase SA of organ, as when stomach fills with food, rugae flatten out
110
Characteristic feature of mucosal layer of stomach?
Forms a series of gastric pits, each housing a number of gastric glands
111
What are gastric glands?
Mostly exocrine glands that open into the stomach through gastric pits in the mucosa
112
Role of gastric glands?
Secrete most of the acid and enzymes necessary for chemical digestion in stomach (1.5L/day) by means of specialised cells
113
Four types of cells of gastric glands?
Goblet cells
Parietal cells
G cells
Chief cells
114
Role of goblet cells?
Secrete mucus, which protects mucosal wall from acid
115
Role of parietal cells?
Secretes intrinsic factor which is needed for Vitamin B12 absorption by the small intestine, and HCl with kills microbes and denatures proteins
116
Role of G cells (enteroendocrine cells)?
Produce hormones, such as gastrin which increases stomach motility, stimulates HCl/enzyme production, and relaxes pyloric sphincter
117
Role of chief cells?
- Secrete pepsinogen (inactive), which is converted to pepsin (active) by HCl, which degrades proteins
- Secrete gastric lipase, which breaks down lipids
118
Length of small intestine?
3-5m
119
Length of duodenum?
First 20-25cm of small intestine
120
Length of jejunum?
1-2m
121
Length of ileum?
Longest segment of small intestine; 2-3m
122
Role of duodenum?
Receives chyme from the stomach, and digestive secretions from the
pancreas and liver; considered “mixing bowl” of small intestine
123
Structure of beginning of jejunum?
Marked by sharp bend at beginning
124
Role of jejunum?
Where majority of chemical digestion and nutrient absorption occurs
125
Role of ileum?
Absorption of Vitamin B12, fats (esp fatty acids and glycerol) and bile salts occurs
126
3 types of structures in the small intestine that increase SA for absorption?
- Microvilli
- Plicae circulares
- Villi
127
What are plicae circulares?
Deep ridges in mucosa and submucosa, that begin near proximal part of duodenum and extend to middle of ileum
128
Function of plicae circulares?
- Facilitate absorption
- Shape causes chyme to move in spiral motion, slowing movement of chyme and thus increasing time available for absorption
129
How much villi does the small intestine have?
Approximately 20-40 villi per mm2 of small intestine
130
What does a capillary bed of a villus have?
1x arteriole
1x venule
1x lacteal
131
How much microvilli does the small intestine have?
Approximately 200 million microvilli per mm2 of small intestine
132
By what factor do structural adaptations (plicae circulares, villi, microvilli) increase the SA of the small intestinal wall?
600x
133
Length of duodenum?
First 25cm of small intestine
134
Role of duodenum?
Receives chyme from stomach, and digestive secretions from pancreas and liver; must neutralise acid. Also stimulates release of specific digestive hormones
135
Characteristic features of duodenum? (3)
- Few circular folds
- Small villi
- Submucosa contains many duodenal glands to secrete mucus
136
Length of jejunum?
Middle 1-2m of small intestine
137
Role of jejunum?
Where majority of nutrient absorption occurs
138
Characteristic features of jejunum? (2)
- Many circular folds
- Abundant and very long villi
139
Length of ileum?
Final 2-3m of small intestine
140
Role of ileum?
Absorbs any final nutrients - especially Vitamin B12 and bile acids
141
Characteristic features of ileum? (3)
- Fewer circular folds than jejunum
- Stumpy villi
- Submucosa contains lymphoid nodules
142
Why does the ileum's submucosa contain lymphoid nodules?
To protect small intestine from bacteria colonising the large intestine
143
Do the duodenum, jejunum, and ileum have distinct or indistinct boundaries?
Indistinct
144
What are the four major hormones that regulate digestion?
Gastrin
Secretin
Gastric inhibitory peptide (GIP)
Cholecystokinin (CCK)
145
Source of gastrin?
Enteroendocrine G cells in stomach (gastric glands) and duodenum
146
When is gastrin released?
When food arrives in the stomach, and when large quantities of partially digested proteins are present in duodenum
147
Functions of gastrin in the stomach?
Stimulates acid production by parietal cells, and muscle contractions thus increasing gastric motility
148
Functions of gastrin in the duodenum?
Stimulates gallbladder to empty bile into duodenum, and pancreas to release pancreatic enzymes into duodenum
149
Source of secretin?
Enteroendocrine S cells in duodenum
150
When is secretin released?
When acidic (pH 2-4) chyme arrives in duodenum
151
Functions of secretin?
- Stimulates pancreas to secrete bicarbonate/buffers, liver to produce bile
- Inhibits acid secretion from parietal cells in stomach, and gastric emptying
152
Source of gastric inhibitory peptide (GIP)?
Enteroendocrine K cells in duodenum
153
When is gastric inhibitory peptide (GIP) released?
When fats and carbohydrates (especially glucose) enter duodenum
154
Functions of gastric inhibitory peptide (GIP)?
- Stimulates pancreas to release insulin, lipid synthesis so fat accumulation, and glucose uptake by skeletal muscle
- Inhibits lipid breakdown
- Regulates appetite
155
Source of cholecystokinin (CCK)?
Enteroendocrine I cells in duodenum
156
When is cholecystokinin (CCK) released?
When fats and undigested proteins enter duodenum
157
Functions of cholecystokinin (CCK)?
- Promotes digestion of fat and protein
- Stimulates pancreas to secrete pancreatic enzymes into duodenum, gallbladder to empty bile into duodenum
- Inhibits gastric activity
- Suppresses hunger
158
What is peristalsis?
Moving material (bolus/chyme) along GIT (propulsion) via involuntary contraction and relaxation of longitudinal and circular muscles
159
What is segmentation?
Mechanical mixing of chyme with digestive juices/mucosa via contractions of the circular muscles in GIT
160
4 steps of peristalsis?
1. Bolus arrives
2. Circular muscles contract behind bolus
3. Longitudinal muscles contract ahead of bolus
4. Waves of circular muscle contractions behind bolus force it forwards
161
Where does segmentation occur?
Mainly in small intestine, but also in large intestine
162
Is segmentation stationary?
Yes; does not push material forwards through GIT, and occurs in localised regions
163
When does segmentation cease?
When most of chyme has been absorbed
164
Is peristalsis rhythmic or irregular?
Rhythmic; consistent contractions
165
Is peristalsis unidirectional or multidirectional?
Unidirectional
166
Is segmentation rhythmic or irregular?
Irregular; random contractions with no pattern
167
Is segmentation unidirectional or multidirectional?
Multidirectional
168
Length/width of large intestine?
1.5m in length, 3 inches in diameter
169
Role of cecum?
Material from small intestine is stored and faecal compaction begins; ileocecal valve controls flow of chyme from small intestine
170
What is uniquely different about the outer longitudinal muscle layer of the large intestine wall's muscularis externa?
Incomplete; present in 3 separate longitudinal ribbons running down one side (teniae coli)
171
What are haustra?
Series of pouches that are formed due to teniae coli contracting lengthwise and bunching up colon
172
Frequency/length of haustral contractions?
Every 25 minutes; last 1 minute
173
Role of haustral contractions?
Stimulated by presence of chyme, so push intestinal contents from one pouch to the next, facilitating mixing and water reabsorption
174
How does the large intestine perform chemical digestion?
By means of bacteria; no digestive enzymes secreted by large intestine
175
What are faeces comprised of?
Undigested food (cellulose), dead epithelial cells, mucus, bacteria
176
Number of bowel movements?
Varies greatly; ranges from 2-3/day to 3-4/week
177
What percent of nutrient absorption occurs in large intestine?
Less than 10%
178
How does constipation occur?
Defecation is delayed, and additional water is absorbed
179
How does diarrhoea occur?
Faeces move too quickly through large intestine and not enough water is absorbed
180
How much faeces is eliminated daily?
200mL/day
181
Humans are colonised by how many microorganisms?
Estimated 100 trillion microorganisms
182
How much of a person's body weight do microorganisms account for?
1-2kg
183
What type of microorganisms colonise the human body?
Bacteria, fungi, viruses; most are symbiotic
184
Where does the human microbiome reside?
Reside all over the body, but bulk live in GIT
185
Where does the gut microbiota derive nutrients?
From host's diet
186
Correlation between gut microbiome and age?
Gut microbiome - whilst existent from birth - diversifies with age
187
Correlation between gut microbiome diversity and health?
Higher microbiome diversity = indicator of good health
188
Functions of gut microbiome? (5)
- Facilitates chemical digestion and absorption
- Synthesis specific vitamins (Vitamins K and B), enzymes, amino acids
- Ferments dietary fibre and thus produces short chain fatty acids (SCFAs)
- Affects drug metabolism
- Aids immune system
189
How does gut microbiome aid immune system?
Activates intestinal immune cells to secrete immunoglobulins (IgA)
190
Relationship between gut microbiome and disease?
- Still emerging field of research
- Disturbance in balance of gut microorganisms = decreased microbiome diversity = increased susceptibility to disease
- Not identified if gut microbiome alterations are the cause or effect
191
What 4 conditions have changes in gut microbiota been associated with?
- Inflammatory bowel disease (IBD)
- Diabetes
- Obesity
- Eczema/allergies
192
Size of the liver?
1.5kg - second largest organ and largest gland in body
193
Location of liver?
Sits just under rib cage on right side of abdomen
194
Unique characteristic of liver?
Capable of regeneration; may regenerate itself back to full size from as little as 51% of original liver mass
195
Structure of liver?
Two primary lobes (left and right); vascularised and attached to abdominal wall
196
What is the falciform ligament?
Divides liver into left and right lobes
197
What is the coronary ligament?
Attaches superior surface of liver to diaphragm
198
What is the round ligament?
Thickening in posterior end of falciform ligament, which connects liver to umbilicus
199
What is the caudate lobe?
Lies between the left lobe of the liver and the inferior vena cava
200
What is the quadrate lobe?
Sandwiched between left lobe of liver and the gallbladder
201
Role of hepatic artery?
Brings oxygenated blood from heart to liver
202
Role of hepatic portal vein?
Brings nutrient-rich blood from spleen and GIT to the liver
203
Role of inferior vena cava?
Takes de-oxygenated blood away from liver back to heart
204
Role of bile duct?
Carries bile away from liver to gallbladder and duodenum
205
How many liver lobules is the liver divided into?
Approximately 100,000 liver lobules
206
Structure of a liver lobule?
- Hexagonal in shape
- Packed with liver cells (hepatocytes)
- Separated by interlobular septa (connective tissue)
- Portal triad at each corner
207
What 3 components are the portal triads of liver lobules comprised of?
- Interlobular vein
- Interlobular artery
- Interlobular bile duct
208
Where does blood from interlobular veins and arteries go to?
Liver sinusoids (large, fenestrated capillaries)
209
What is at the centre of each liver lobule? Why?
Central vein, to take blood from sinusoids to inferior vena cava
210
What percent of liver's mass are hepatocytes?
80%
211
Functions of hepatocytes?
Secretory, metabolic, and endocrine functions
212
Structure of hepatocytes?
- Arranged in a series of irregular plates within liver lobules
- Tightly packed around fenestrated vessels (sinusoids), facilitating easy access to blood and therefore being able to process nutrients, toxins, and wasts in blood
213
What are liver sinusoids?
Open, fenestrated capillaries which lack a basement membrane and contain Kupffer cells (phagocytes)
214
Describe blood flow in the liver (5 steps).
1. O2-rich blood (1/3) arrives from heart via hepatic artery
2. Nutrient-rich blood (2/3) arrives from spleen and GIT via hepatic portal vein
3. Blood combines in liver sinusoids
4. Sinusoids all drain into central vein
5. All central veins merge to form hepatic veins, which empty into vena cava
215
Functions of liver?
Almost 200 known functions, including:
- Metabolism of carbohydrates, lipids, proteins
- Production of bile
- Detoxification of blood (alcohol, drugs)
- Absorption/breakdown of circulating hormones
- Storage of iron, vitamins, and glucose
- Removal of old/damaged blood cells
216
Structure of gallbladder?
Small, pear-shaped organ that has a capacity of 50mL
217
Functions of gallbladder? (2)
- Stores and concentrates bile by up to 20x
- Releases bile into duodenum when triggered by CCK
Note: does NOT make bile
218
Can a person live without a gallbladder? If so, are there any side effects/consequences?
Yes, can have gallbladder removed by via cholecystectomy; then, bile enters duodenum directly from liver. However, may be harder to digest large amounts of fatty, greasy food
219
What is bile? (structure/composition/origins)
Yellow-green fluid, comprising minerals, cholesterol, phospholipids, bile salts, and bile pigments, synthesised by hepatocytes in liver
220
Is the production of bile a consistent process?
Relatively; hepatocytes constantly produce bile, but the process is increased when secretin is released due to fatty chyme entering the duodenum
221
Role of bile salts?
Emulsify fats for absorption
222
Role of bile pigments (e.g. bilirubin)?
Yellow in colour; intestinal bacteria breaks down bilirubin to make urobilinogen
223
What is urobilinogen?
Brown pigment in faeces
224
Function of bile?
Emulsifies lipids in small intestine
225
Why is the function of bile important?
Lipids are hydrophobic, so cannot be digested in small intestine unless broken apart into smaller fragments. Bile salts and phospholipids tear large lipid globules into many tiny fragments through emulsification, thus increasing surface area available for lipases
226
Location of gallbladder?
Sits under liver's right lobe
227
Structure of pancreas?
Slender, fish-shaped organ, 15cm long
228
General functions of pancreas?
Mixture of exocrine and endocrine functions
229
Exocrine functions of pancreas?
Cells of pancreatic acini = secrete enzymes
- Makes digestive enzymes, which are released into duodenum and break down proteins, fats, and starches.
- Produces pancreatic enzymes (by acinar cells)
230
What do exocrine glands do?
Secrete their substances through ducts onto body's surfaces
231
What do endocrine glands do?
Secrete their substances directly into your bloodstream
232
Endocrine functions of pancreas? (cells in pancreatic islets)
Cells in pancreatic islets = secrete hormones
- Makes hormones via endocrine cells in pancreatic islets
- i.e. alpha cells = glucagon, beta cells = insulin, delta cells = growth hormone-inhibiting hormone
233
Role of glucagon?
Glycogen breakdown to form glucagon
234
Role of insulin?
Glucose uptake by cells from bloodstream
235
Role of growth hormone-inhibiting hormone?
Suppresses alpha and beta cells, and decreases food absorption/enzyme secretion in GIT
236
Role of pancreatic duct?
Delivers pancreatic juice into duodenum
237
3 components of pancreatic juice?
Water, sodium bicarbonate, digestive enzymes
238
Role of sodium bicarbonate in pancreatic juice?
Neutralises stomach acid
239
Role of alpha-amylase in pancreatic juice?
Breaks down certain starches (almost identical to salivary amylase)
240
Role of lipase in pancreatic juice?
Breaks down complex lipids into fatty acids
241
Role of nucleases in pancreatic juice?
Break down nucleic acids (RNA and DNA)
242
Role of proteolytic enzymes in pancreatic juice?
Break down proteins into amino acids
243
In what form are proteolytic enzymes existent in pancreatic juice?
Inactive forms; activated by enzymes in duodenum
(e.g. trypsinogen -> trypsin, chymotrypsinogen -> chymotrypsin, procarboxypeptidase -> carboxypeptidase)
244
Where is pancreatic juice secreted?
Exocrine glands in pancreas
245
Where is gastric juice secreted?
Secreted by gastric glands in the stomach
246
Components of gastric juice?
Contains HCl, pepsin, intrinsic factor, mucus, and water
247
Is pancreatic juice alkaline or acidic?
Alkaline (has sodium bicarbonate)
248
Is gastric juice alkaline or acidic?
Acidic (has HCl)
249
Main role of pancreatic juice?
Digest carbohydrates and fat
250
Main role of gastric juice?
Digest proteins
251
What is metabolism?
Sum of all chemical reactions that occur in the human body
252
What is nutrition?
Process of providing/obtaining nutrients (often via food) for health, growth, and survival
253
How are nutrients stored in the human body?
Simplest form: glucose, lipids, amino acids
254
What are catabolic reactions?
Breakdown processes; involve release of energy (ATP) and heat
255
What are anabolic reactions?
Synthesis processes; involve expenditure of energy (ATP) and heat
256
What is metabolic rate? How is it measured?
Amount of energy used by body per day; measured as calories/day
257
Formula for metabolic rate (MR)?
MR = BMR + energy used in physical activity + thermal effect of food
258
What is basal metabolic rate (BMR)?
Metabolic rate when in a quiet, resting, fasting state
259
Average adult metabolic rate?
2000 calories/day
260
Average adult basal metabolic rate?
1200-1800 calories/day
261
What is the thermic effect of food?
Energy required to digest, absorb, process, and transport ingested food (nutrients); peaks 2-3 hours subsequent to eating
262
How does amount of muscle vs fat affect metabolic rate?
Muscle requires more energy to function than fat
263
How does physical activity affect metabolic rate?
Physical activity increases amount of muscle, which thus increases metabolic rate
264
How does gender affect metabolic rate?
On average, males have a higher metabolic rate
265
How does body size affect metabolic rate?
Bigger people have bigger organs and thus a higher metabolic rate
266
How does thyroid activity affect metabolic rate?
Thyroid hormones cause an increased metabolic rate
267
How does environmental temperature affect metabolic rate?
Too hot/cold (extreme weather conditions) causes body to work harder, thus increasing metabolic rate
268
How does infection/illness affect metabolic rate?
Energy is required to fight infection, thus increasing metabolic rate
269
How do genes affect metabolic rate?
Metabolic rate is naturally faster/slower in some people according to their genetic predisposition
270
How does age affect metabolic rate?
Metabolic rate decreases with age, due to there being less muscle and hormonal changes
271
How does dieting affect metabolic rate?
Reduced calorie intake reduces metabolic rate
272
What controls appetite?
Hypothalamus
273
2 types for short-term regulators of appetite?
Ghrelin and peptide YY (PYY)
274
1 type of long-term regulators of appetite?
Leptin
275
Where is ghrelin secreted?
By empty stomach; conveys hunger to hypothalamus
276
Where is ghrelin secreted?
By ileum/colon when food enters stomach; conveys fullness to hypothalamus
277
Where is leptin secreted?
By adipocytes; conveys abundant fat stored to hypothalamus, decreasing appetite
278
What causes obesity?
Unresponsiveness to leptin
279
What is stockpiling of energy reserves?
When nutrient absorption by the GIT exceeds the body’s immediate needs
- Excess fatty acids -> stored as triglycerides in the liver or fat
- Excess glucose -> stored as glycogen in the liver and skeletal muscle
- Excess amino acids -> stored as carbohydrates or fats or degraded
280
What is mobilisation of energy reserves?
When nutrient absorption by GIT is insufficient for body's immediate needs
- Triglycerides -> fatty acids
- Glycogen -> glucose
- Contractile proteins (actin/myosin) within myofibrils -> release amino acids
281
Is stockpiling anabolic or catabolic?
Anabolic
282
Is mobilisation anabolic or catabolic?
Catabolic
283
6 key nutrients that we consume to sustain ourselves?
Water, carbohydrates, lipids, proteins, minerals, vitamins
284
Why are minerals a unique essential nutrient?
Nutrient that we cannot synthesise, and must be obtained from diet
285
What is a recommended daily allowance (RDA)?
Estimated safe daily intake of nutrients to meet standard metabolic needs
286
What are the 3 macronutrients?
- Glucose (carbohydrates)
- Fatty acids (lipids)
- Amino acids (proteins)
287
Where are carbohydrates predominantly found in?
Muscle, liver, blood
288
Food sources of carbohydrates?
Plants, pasta, bread, potatoes
289
Functions of carbohydrates?
Body's primary source of energy; carbohydrates -> glucose -> ATP (excess glucose -> glycogen)
290
RDA of carbohydrates?
175g/day
291
Chemical structure of carbohydrates?
Saccharide ring of 6 carbon atoms
292
What are polysaccharides?
Complex carbohydrates containing hundreds of carbon rings (e.g. glycogen, starch)
293
What are disaccharides?
Contain 2 carbon rings (e.g. sucrose, lactose)
294
What are monosaccharides?
Simplest sugars containing 1 carbon ring (e.g. glucose, fructose); only sugars absorbed in GIT
295
What are lipids?
Insoluble organic compounds
296
Role of lipids?
Long-term energy source (superior to carbohydrates as a stored energy source); also protection and insulation
297
Most abundant form of lipid?
Triglycerides
298
Food sources of lipids?
Fat and oil
299
Where do saturated fatty acids originate from?
Animal origin
300
Where do unsaturated fatty acids originate from?
Plant origin
301
Why is it difficult to transport lipids via blood?
Lipids are hydrophobic, and thus do not dissolve in plasma; so, tend to stick to vessel walls
302
How are lipids effectively transported despite being hydrophobic?
Lipoproteins surround lipids, and recognise target cells
303
4 types of lipoproteins?
- Chylomicrons
- Very Low Density Lipoproteins (VLDLs)
- Low Density Lipoproteins (LDLs)
- High Density Lipoproteins (HDLs)
304
Role of chylomicrons?
Transport cholesterol through lymphatic vessels to the liver
305
Role of Very Low Density Lipoproteins (VLDLs)?
Travel through bloodstream to adipose tissue
306
Role of Low Density Lipoproteins (LDLs)?
Known to stick to vessel walls forming plaque.
307
Role of High Density Lipoproteins (HDLs)
Collect LDLs through the blood stream and takes them back to the liver
308
Describe how carbohydrates are metabolised, absorbed and stored.
Complex carbohydrates are ingested.
Complex sugars are broken down into disaccharides and trisaccharides by salivary amylase.
Pancreatic enzymes in the small intestine break down the tri and disaccharides into simple sugars.
Absorbed glucose travels to the liver.
309
Describe how lipids are metabolised, absorbed and stored.
Lipids ingested.
Triglycerides begin being broken down into diglycerides and monoglycerides by lingual lipase.
Mixing of chyme creates large lipid globules.
Lipid digestion is completed in the duodenum through bile salts and pancreatic lipase.
310
Describe how proteins are metabolised, absorbed and stored.
Protein is ingested.
HCL denatures the proteins and pepsin breaks the peptide bonds.
Pancreatic enzymes and trypsin aid in chemical digestion and amino acid absorption.
Absorbed AAs travel to the liver.
AAs released into blood and used to synthesise plasma proteins.
311
Food sources of protein?
Meat, dairy, eggs, nuts, etc.
312
Main functions of proteins?
Make up tissues, constantly broken down into amino acids to produce ATP, synthesise new proteins, and convert into glucose/lipid (catabolic reactions)
313
Role of parietal cells?
Secrete HCl
