Digestive System Flashcards
1
Q
What are the 3 primary functions of the digestive system
A
To digest food into absorbable nutrients, move (absorb) nutrients, water, and electrolytes from the GI lumen into blood and ISF using transport mechanisms, and repel foreign invaders via secretions
2
Q
What are the 3 kinds of ingested macromolecules
A
Carbohydrates, proteins, and lipids (fats)
3
Q
Describe digestion
A
Mechanical (chewing and churning) and chemical (enzymatic) breaks down food into absorbable units
4
Q
What 6 secretions happen in the digestive system and where (4 places)
A
Saliva, mucus, digestive enzymes, bile, H2O, and ions all for chemical digestion and lubrication, coming from salivary glands, the pancreas, liver, and epithelial cells of the stomach and small intestine
5
Q
What is absorption in the digestive system
A
Nutrients moved into the blood or lymph mainly in the small intestine using brush borer cells (enterocytes) on villi, but also some of ions and H2O in large intestine
6
Q
What is motility
A
The movement of material through the GI tract via smooth muscle contractions
7
Q
Where does carbohydrate digestion begin
A
The mouth via amylase from saliva (glucose polymers like starch and glycogen are broken down into disaccharides)
8
Q
Where does carbohydrate chemical digestion continue
A
In the small intestine, epithelial cells secrete disaccharidase that breaks down disaccharides into monosaccharides, and the pancreas secretes amylase as well
9
Q
What is the absorbable end unit of carbs
A
Monosaccharides
10
Q
What glucose transporters move glucose and galactose in the small intestine
A
Apical entry: SGLT (Na+-linked cotransporter)
Basolateral exit: GLUT2
11
Q
What glucose transporters move fructose in the small intestine
A
Apical entry: GLUT5
Basolateral exit: GLUT2
12
Q
How do glucose, galactose, and fructose enter the blood in the small intestine
A
Simply diffuse through fenestrated (leaky) capillaries
13
Q
Where does chemical digestion of proteins occur
A
The stomach (HCl denatures proteins and peptidases digest into di&tri peptides, and oligopeptides) and continues in small intestine (peptidases from epithelium and pancreas)
14
Q
What triggers the pancreas to release peptidases into the small intestine
A
CCK
15
Q
What do endopeptidases do
A
Break the peptide bond internally (in the middle)
16
Q
What do exopeptidase do
A
Break the peptide bond on the terminal end (can be aminopeptidase or carboxypeptidase)
17
Q
What are the absorbable units for proteins
A
Di-peptides, tri-peptides, oligopeptides, and free amino acids
18
Q
How are free amino acids absorbed
A
Secondary active cotransport with Na+
19
Q
How are di- and tri-peptides absorbed
A
Secondary active cotransport with H+
20
Q
How are oligopeptides absorbed
A
Transcytosis (moving in vesicles through the cell)
21
Q
What are the absorbable units of lipids
A
Free fatty acids and monoglycerides
22
Q
Where are lipids chemically digested
A
In the small intestine (CCK triggers release of bile that forms emulsions and pancreas secretes lipase that breaks triglycerides into monoglycerides and free fatty acids)
23
Q
Where is bile made and stored, and secreted
A
Made in the liver, stored in the gal bladder, secreted into the duodenum of the small intestine
24
Q
How does bile work
A
Bile salts break down the fat droplets into smaller ones (emulsions then micelles) which increases the surface area for enzymatic digestion by lipase
25
How are fats absorbed
Via simple diffusion through the enterocytes (brush border) of lumen of the small intestine, cholesterol is actively transported to speed up absorption (too slow because of size)
26
Once monoglycerides and free fatty acids enter the smooth ER, what happens
They are reassembled into triglycerides which will combine with cholesterol and proteins to form large droplets (chylomicrons)
27
How are chylomicrons absorbed
Leave enterocytes into interstitial fluid where they are exocytosed into lacteals (lymphatic system) and venous blood
28
What are the characteristics of the smooth muscle of the GI tract
Circular (diameter) and longitudinal (length) muscle connected via gap junctions
29
What causes phasic contractions in the GI tract
Spontaneous slow wave potentials created by the interstitial cells of Cajal (pacemaker cells)
30
What are the 3 characteristics of the enteric nervous system
Neurons in the GI was that control motility and secretion, can work independently (short reflexes) or with CNS (long reflexes) via ANS
31
Where can GI peptides act
in digestive system to increase or decrease motility and secretion or outside the GI tract to influence hunger/satiety, food intake, and insulin/glucagon secretion
32
What 4 GI peptides influence motility and secretion
Cholecystokinin (bile), motlin (migrating complex), gastrin (HCl and pepsin), and secretin (gastric secretion to neutralize acid)
33
What GI peptides influence hunger/satiety and food intake
Cholecystokinin (satiety) and gherlin (hunger)
34
What GI peptides influence insulin/glucagon secretions (via pancreas)
Incretins
35
What parts of the body does the cephalic phase deal with
Oral cavity, esophagus, and stomach
36
What parts of the body does the gastric phase deal with
Stomach and intestines
37
What parts of the body does the intestinal phase deal with
Small intestine, large intestine, and rectum
38
What triggers the cephalic phase
Long, feedforward reflexes from brain (sight, smell, or taste of food) trigger saliva secretion (ANS control) from salivary glands (chemical digestion) and mastication/chewing begins (mechanical digestion), and triggers swallowing reflex
39
What 5 things is saliva made of
Water, ions, mucus, enzymes (amylase), and antibodies to moisten, lubricate, and digest food
40
What is the swallowing reflex (4 steps)
Integrated by the medulla oblongata, the tongue pushes bolus (food) against the soft palate, it passes through the closed airway (epiglottis) while breathing is inhibited and the food moves into the esophagus and stomach via peristaltic contractions
41
What is aspiration
Fluid or food entering the lungs during ingestion
42
Describe your upper esophageal sphincter at rest vs. during the cephalic phase
At rest, it is tonically contracted, when you swallow it relaxes
43
What happens during the integration of the cephalic and gastric phase reflexes
Before food arrival, long reflex of cephalic phase and PS ANS travels through vagal nerve to increase secretion and motility, then food entry initiates short reflexes that activate gastric phase
44
What are the 2 stimuli for the gastric phase
Distention (stretch) of the stomach and presence of peptides and amino acids in the gastric lumen
45
What are the 3 functions of the gastric phase of digestion
Storage of food (upper stomach relaxes and expands), digestion (lower stomach), and protection (destroyed pathogens with swallowed with food)
46
Describe digestion during the gastric phase (4 things)
Chemical and mechanical digestion turn food into chyme (watery mixture), digests proteins, secretes HCl, enzymes, paracrine signals, and hormones, and regulates entry into the small intestine via peristaltic contractile waves
47
How is acid secreted in the stomach during the gastric phase
Parietal cells (gastric cells) secrete hydrochloric acid using a proton pump (primary active for H+), regulated by gastrin (stimulated by peptides and amino acids - short reflex)
48
What are 3 functions of hydrochloric acid
To denature proteins for enzyme access, to activate a peptidase (chief cells secrete pepsin), and to kill pathogens
49
What protection occurs during the gastric phase
Mucus and bicarbonate buffer are continuously secreted by gastric mucous cells to form a barrier of gastric mucosa
50
What are the 4 things chyme does once it enters the small intestine
Slows chyme delivery (via ENS and GI peptides like secretin, CCK, and incretins), decreases stomach acid and increases SI bicarbonate (secretin breaks down acids), increase digestive enzymes and bile (CCK to break down fats and proteins), and increase insulin (incretins to break down carbs)
51
What are the 2 kinds of incretins
GIP (gastric inhibitory peptide) and GLP-1 (glucagon-like peptide-1)
52
What happens during the intestinal phase in the small intestine
Chyme mixes with enzymes for chemical digestions (enterocytes secrete disaccharides and peptidases), exocrine pancreas secretes amylase and peptidases, and the gallbladder secretes bile
53
Where does most of the bicarbonate come from in the intestinal phase
The pancreas, some also comes from duodenum
54
What does the exocrine pancreas secrete
Acing cells secrete digestive enzymes and duct cells secrete sodium bicarbonate (NaHCO3)
55
What does the endocrine pancreas secrete
Alpha islet cells secrete glucagon and beta islet cells secrete insulin, both to regulate blood glucose levels
56
What 3 things happen in the large intestine during the intestinal phase
Water is concentrated for secretion and most water in chyme is absorbed, bacteria in the colon break down undigested carbs and proteins via fermentation, and some absorption of ions, minerals, vitamins, and water
57
What happens in the rectum during the intestinal phase
Defecation (waste material eliminated from digestive tract)
58
What triggers the defecation reflex and what does it do
Distention of rectum creates urge to defecate, then internal anal sphincter relaxes (ENS and PSNS control) and external anal sphincter contracts (skeletal muscle, somatic control)
59
What are the two key hypothalamic control centers in the digestive system
Appetite center (always on) and satiety center (inhibits feeding center)
60
What 3 input signals go to the appetite and satiety centers
Neural inputs (cerebral cortex and limbic system), peptide hormones (GI tract), and adipocytokines (adipose tissue)
61
What are adipocytokines
Chemical signals released by adipose tissue involved in energy homeostasis and regulation of glucose and lipid metabolism
62
What does neuropeptide Y (NPY) do
Released from the brain, it increases food intake and energy storage (fat)
63
What does gherlin do
Secreted by empty stomach, increases hunger
64
What does leptin do
Made by adipocytes, as fat stores increase, more leptin is secreted to decrease food intake (negative/inhibitory feedback for NYP)
65
What do CCK and incretin (GLP-1) do to the hypothalamic feeding center
Released from the duodenum in response to fats and carbs in chyme, they promote satiety and decrease food intake
66
What is metabolism
Chemical processes occurring in a living organism to maintain life (all anabolic and catabolic reactions)
67
What are wastes from nutrient conversion
Urea, CO2, H2O, etc.
68
How are absorbed nutrients stored
Glycogen (mostly liver and muscle) or triglycerides in adipose tissue
69
Which macromolecule provides the most energy
Fat
70
What 3 processes are involved in ATP production
Glycolysis (cytosol), citric acid/Kreb cycle (mitochondria), and electron transport system (mitochondria)
71
Where do carbohydrates enter the production of ATP
Glycolysis as glucose, then broken into 2 3-carbon chains)
72
Where do lipids enter the production of ATP
Glycerol enters glycolysis, fatty acids go through beta-oxidation to become acyl units (2 carbons) which then enter the Kreb cycle as acetyl CoA
73
Where do amino acids enter the production of ATP
At various points
74
What is glycogenesis
Production of glycogen
75
What is lipogenesis
Production of fat
76
What is lipolysis
Breakdown of fat into fatty acids
77
What is glycogenolysis
Breakdown of glycogen into glucose
78
What is gluconeogenesis
Making glucose from amino acids
79
Which state of digestion of anabolic and which state is catabolic (fed vs fasted)
Fed/absorptive is anabolic and fasted/post-absorptive if catabolic
80
What happens to amino acids during the fed state
Amino acids are made into proteins and excess is converted into fat
81
What happens to proteins in the fasted state
Proteins broken into amino acids (only during extended fasting), amino acids are deaminated for glycolysis, or made into glucose (gluconeogenesis)
82
What is created when amino acids are deaminated for glycolysis
Ammonia (NH3) is made, goes to urea
83
What happens to carbs during the fed state
Carbs are used for ATP (glycolysis) or stored as glycogen (glycogenesis) in the liver, excess converted into fat
84
What happens to lipids during the fed state
Lipids are converted into fat in adipocytes (lipogenesis)
85
What happens to liver glycogen during the fasted state
Liver glycogen broken down to glucose (glycogenolysis) to use in glycolysis
86
What happens to lipids during the fasted state
Triglycerides are broken down to glycerol and fatty acids by lipases which are used to produce ATP
87
What is the dominant hormone in the fed state and why
Insulin because of high blood glucose and amino acid levels, resulting in secretion of insulin from beta-cells of the pancreas
88
What is the dominant hormone in the fasted state and why
Glucagon because low blood glucose levels result in secretion of glucagon from alpha-cells of the pancreas
89
Describe the 3 characteristics of insulin
Anabolic hormone that promotes glucose uptake, glucose metabolism (glycolysis), and energy storage as glycogen and fat (glycogenesis and lipogenesis) to decrease plasma glucose and increase fat storage
90
What kinds of glucose uptake are insulin-sensitive and why
Adipose tissue and resting skeletal muscle because GLUT4 (carrier protein) is either in the membrane of hepatocytes (liver) or not to aid in facilitated diffusion
91
What factors influence insulin secretion
Feedforward effects of GI hormones, PSNS activity (increased during and after a meal), and SNS activity (inhibits beta-cells of pancreas)
92
What is the endocrine response to hypoglycemia
Glucagon promotes the breakdown of glycogen (glycogenolysis) and makes it into glucose (gluconeogenesis) to increase plasma glucose
93
What does homeothermic mean
Homeostatically regulate internal temperature within narrow range
94
What does hyperthermia cause
Denatures enzymes
95
What does hypothermia cause
Chemical reactions are too slow
96
What is the average oral temperature
98.6 degrees F (~96-99.99) with daily fluctuations of about 1.8 degrees
97
What is heat loss equal to
Internal heat production from metabolism and movement + external heat input
98
What are the four mechanisms of heat exchange
Conduction, convection, evaporation, and radiation
99
What is conduction
Gain or loss of heat through contact
100
What is convection
Gain or loss of heat by bulk flow of air or water
101
What is radiation
Gain or loss of heat via gradient energy (warm surfaces emit and absorb electromagnetic waves)
102
What is evaporation
Loss of heat from skin and respiratory tract
103
What are the 2 unregulated sources of heat production
Metabolism (~75% of nutrient energy), and "waste heat" generated by voluntary muscle contractions
104
What are the 2 kinds of regulated heat production
Shivering thermogenesis (involuntary tremors in skeletal muscles caused by hypothalamic thermoregulatory center) and non-shivering thermogenesis
105
What receptors feed into the hypothalamic thermoregulatory center
Central thermoreceptors sense changes in core body temp and peripheral thermoreceptors sense changes in environmental temperature
106
What are 3 characteristics of non-shivering thermogenesis
Important for thermoregulation in newborns, only in brown adipose tissue, and involves mitochondrial coupling
107
What is brown adipose tissue/brown fat
Higher density of mitochondria and less lipids
108
What is mitochondrial uncoupling
Energy from electron transport system released as heat instead of making ATP
109
What are the bodies 3 thermoregulatory reflexes
Vascular (vasoconstriction or vasodilation), sweat secretion, and/or shivering
110
How does the body respond to decreased temperature
Hypothalamic thermoregulatory neurons activate sympathetic neurons causing cutaneous vasoconstriction and possibly non-shivering thermogenesis, while somatic motor neurons activate shivering thermogenesis
111
How does the body respond to increased temperature
Hypothalamic thermoregulatory neurons activate sweat glands which secrete sweat, and cutaneous vasodilation
112
What kinds of neurons are used for in the SNS for thermoregulaiton
Sympathetic cholinergic neurons release ACh onto muscarinic receptors
113
What is the therm-neutral zone
Range of environmental temps in which thermoregulation requires only vascular adjustments (don't need to sweat or shiver)
114
When does the body's set point for temperature change
During fever due to pyrogens (from macrophages in WBCs) that act on the hypothalamus or postmenopausal hot flashes (changes in hormone levels act on hypothalamus)
115
What are 3 benefits to having a fever
Slow down bacterial and viral growth, increases WBCs, and reduces severity of illness and shortens illness duration
