Phase 1 - Week 9 (GI tract, Digestion, Eating Disorders) Flashcards
(88 cards)
1
Q
List the classes of food
A
- Carbohydrates
- Proteins
- Fats
- Vitamins
- Minerals
2
Q
Describe the types of carbohydrates
A
- 3 carbons = triose
- 4C = tetrose
- 5C = pentose
- Sugars linked by glyosidic bonds to form complex glycans
- Saccharides - homoglycans, single suger/heteroglycans, complex composition
3
Q
How do carbohydrates provide energy?
A
Broken down into glucose, then undergo glycolysis:
Glucose -> glucose-6-phosphate (2ATP -> 2ADP)-> fructose-6-phosphate -> fructose-1,6-biphosphate -> glyceraldehyde-3-phosphate ->->->->-> 2 x pyruvate (NAD, Pi -> NADH and 4 ADP -> 4 ATP)
In the presence of oxygen, the products of glycolysis then go on to complete the citric acid cycle which is followed by the electron transport chain.
Overall, aerobic respiration fuelled by one molecule of glucose gives a net production of 38 ATP.
4
Q
Where are lipids found?
A
In plasma, adipose tissue and biological membranes
5
Q
How do fats provide energy?
A
Fats are released from triglyceride stores in adipose tissue (with glycerol) via action of lipase enzyme - short chains can enter cells directly, long chains go along carnitine shuttle.
Fats -> fatty acids and glycerol
Fatty acids -> acetyl coA by beta oxidation
Acetyl coA can be used in the Krebs cycle (follows normal aerobic respiration).
6
Q
How do proteins provide energy?
A
Broken down into amino acids then alpha ketoglutarate by transamination then oxidative deamination.
7
Q
Transamination
A
Converts one amino acid into a different amino acid
8
Q
Oxidative deamination
A
An amino group is lost from an amino acid, converting it into alpha ketoglutarate so that it can enter the Krebs cycle
9
Q
Why do cells require energy?
A
- Contraction of muscle cells
- Accumulation of ions + other molecules against concentration gradients (e.g. for nerve impulse transmission + control)
- Biosynthesis - building of tissue
- Waste disposal - getting rid of end products of bodily function
- Generation of heat and maintenance of body temperature
10
Q
Which enzymes are involved with glycolysis?
A
- Fructose-6-phosphate -> fructose-1,6-biphosphate mediated by phosphofructokinase
- Glyderaldehyde-3-phosphate -> 1,3-biphosphoglyceric acid mediated by phosphate dehydrogenase
11
Q
Describe the energy investment stage of glycolysis
A
Glucose -> fructose-1,6-biphosphate = energy investment stage, as 2 ATP are converted to 2 ADP
12
Q
Describe the energy payoff stage of glycolysis
A
Glyceraldehyde-3-phosphate -> 2 pyruvic acid = energy payoff stage as 4 ADP are converted to 4 ATP and NAD is converted to NADH
13
Q
Describe the process of acetyl coA formation
A
Pyruvic acid -> acetyl coenzyme A (CO2 lost, coA added)
also,
NAD+ -> NADH
14
Q
Describe the process of lipolysis
A
- Triglyceride -> glycerol and 3 fatty acids
- Glycerol -> glyceraldehyde-3-phosphate, then continues through glycolysis or undergoes glucogenesis to form glucose + 2 pyruvate
- Fatty acids undergo beta oxidation to form acetyl coA + NADH + FADH2
15
Q
Describe the Krebs cycle
A
Acetyl coA + oxaloacetate -> citrate -> isocitrate -> alpha-ketoglutarate (5C) -> succinyl coA (4C) -> succinate -> fumarate -> malate -> oxaloacetate
16
Q
What is the overall yield of the Krebs cycle?
A
- 2ATP from GTP
- 6 NADH
- 2 FADH2
- 2 CO2
17
Q
List the enzymes involved with the Krebs cycle
A
- Citrate -> isocitrate, enzyme is acontinase
- Isocitrate -> alpha-ketoglutarate, enzyme is isocitrate dehydrogenase
- Alpha ketoglutarate -> succinyl coA enzyme is alpha ketoglutarate dehydrogenase complex
18
Q
Describe the steps involved in the electron transport chain
A
- NADH gives 2 electrons to NADH dehydrogenase complex, NADH oxidised to NAD+
- 2 electrons pass to coenzyme Q, 2 hydrogen protons pumped from mitochondrial matrix into space between inner + outer mitochondrial membranes
- Coenzyme Q shuttles elevtron to cytochrome b-cl complex - pumps electrons across membrane
- Electrons return to mitochondrial matrix, combine w/ oxygen atom + 2 hydrogen atoms, 2 hydrogens pumped across membrane (oxygen = final electron acceptor)
- Oxidative phosphorylation - protons passing through matrix allows ATP synthase to synthesise ATP
19
Q
How is FADH2 used to produce ATP
A
Follows similar pathway to NADH - bypasses first complex straight to coenzyme Q
20
Q
Describe glycolysis in anaerobic respiration
A
Glucose converted to 2 pyruvate by same process as aerobic, pyruvate converted to lactate in reversible step (will be turned back to pyruvate when oxygen is present)
21
Q
Summarise the number of ATP produced in each stage of respiration
A
Glycolysis =
2 ATP from substrate level phosphorylation
4-6 ATP from oxidative phosphorylation of 2NADH + H+ in ETC
Acetyl coA formation =
6 ATP from oxidation of NADH + H+ in ETC
Krebs Cycle + ETC =
2 ATP from conversion of GTP -> ATP
18 ATP from oxidative phosphorylation of 6 NADH + H+ in ECT
4 ATP from oxidative phosphorylation of 2 FADH2 in ECT
22
Q
Give the total net yield of ATP from aerobic respiration
A
34-36 ATP (theoretical)
29-30 ATP (realistic)
23
Q
Describe the path followed by food during digestion
A
- Oral cavity
- Pharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine
24
Q
Describe digestion of food in the oral cavity
A
- Salivary glands - saliva moistens food and amylase in saliva breaks down starch
- Chewing = mechanical digestion
25
Describe the structural features of the pharynx involved with digestion
- Lined with mucosa to protect from friction caused by swallowing
- Has superior, middle and inferior pharyngeal constrictors to perform sphincteric and peristaltic actions during swallowing
26
Describe the structural features of the oesophagus involved with digestion
- Lined with lamina propria, muscularis mucosae and stratified squamous epithelium - protects from extreme temperatures, chemicals and abrasion from food particles
- Upper oesophageal sphincter - opens to allow food bolus to enter and closes to prevent regurgitation into the pharynx , under voluntary control
- Lower oesophageal sphincter - formed by portion of the diaphragm, constricts during respiration to prevent regurgitation into the oesophagus, under involuntary control
27
Describe the histology of the oesophagus
- Non-keratinised stratified squamous
- Lamina propria
- Muscularis mucosae
- Submucosa
- Muscularis propria (inner circular, outer longitudinal)
- Adventitia
28
Describe the histology of the stomach
- Same as oesophagus but has a 3rd muscular layer (oblique muscular layer)
- Chief cells - secrete pepsinogen
- Parietal cells - secrete hydrochloric acid + intrinsic factor
- G (gastric) cells - secrete gastrin
- Mucous neck cell - secrete mucus
29
List the functions of the stomach
1. As a mixing compartment, breaking up food (mechanical digestion) and mixing it into chyme (a semi-fluid pulp)
2. Storage of partially digested food - food is eaten much faster than body can digest/absorb it
3. Secretes gastric juice containing water, mucus, hydrochloric acid, intrinsic factor and pepsinogen which contributes to the chemical digestion process
30
Describe the regions of the stomach
From oesophagus -> duodenum
1. Cardiac region
2. Fundus
3. Body
4. Pyloric antrum
5. Pyloric canal
6. Pyloric sphincter
7. Pylorus
31
How does the stomach contribute to mechanical digestion?
Peristaltic movements created by the 3 layers of smooth muscle - longitudinal layer, circular layer and oblique layer
32
Parietal cells of the stomach
- Produce hydrochloric acid - denatured ingested proteins, activates digestive enzymes (e.g. pepsinogen) and kills microorganism
- Also produce intrinsic factor which aids the absorption of vitamin B12 from the small intestine
33
Chief cells of the stomach
- Major producers of digestive enzymes e.g pepsin
- Pepsin is secreted as inactive pepsinogen, converted into active pepsin by hydrochloric acid
- Also secretes gastric lipase which breaks down lipids
- Lingual lipase (in saliva) is activated by the acidic environment of the stomach
34
Mucous neck cells of the stomach
Produce mucus, which helps to protect the lining of the stomach from hydrochloric acid and digestive enzymes
35
List the accessory glands/organs of the digestive system
- Pancreas
- Liver
- Gallbladder
36
Describe the digestive function of the pancreas
- Produces pancreatic juice - rich in enzymes
- Helps to break down proteins to amino acids, starch to maltose, fats into fatty acids and glycerol and nucleases which digest DNA and RNA
37
Describe the exocrine and endocrine functions of the pancreas
```
Exocrine = production of pancreatic juice for digestion
Endocrine = islets of Langerhans which secrete hormones e.g. insulin
```
38
Describe the composition of pancreatic juice
- Water
- Salts
- Sodium bicarbonate
- Digestive enzymes - pancreatic amylase, pancreatic lipase, trypsin, elastase, carboxypeptidase, chymotrypsin, ribonuclease and deoxyribonuclease
39
What is the function of the sodium bicarbonate of pancreatic juice?
Makes pancreatic juice slightly alkaline, acts as a buffer against acidic chyme and denatures the action of pepsin. Also creates the optimal pH in the intestines for the activity of digestive enzymes
40
Trypsin
- Secreted as its inactive precursor typsinogen
- Enzyme enteropeptidase cleaves trypsinogen to activate it
- This prevents it from digesting the cells from which it is secreted or the cells of the duodenum
- Protease enzyme
- Active trypsin activates other enzymes - elastase, carboxypeptidase
41
Describe the digestive function of the liver
Produces bile, essential in the digestion of lipids, and metabolises carbohydrates, lipids, proteins, drugs and hormones. Also excretes urea and bilirubin, and stores vitamins, minerals and glycogen.
42
Describe the digestive function of the gallbladder
Stores and concentrates bile, releasing it into the duodenum during digestion where it emulsifies fats, stimulates intestinal peristalsis and acts as a channel for the excretion of toxic substances
43
Describe the function of the small intestine
Main digestion and absorption site for water, proteins, carbohydrates and lipids
44
Describe the gross anatomy of the small intestine
From pylorus -> cecum
1. Duodenum
2. Jejunum
3. Ileum
45
Duodenum
- First part of small intestine, continues from pylorus of the stomach
- Chyme triggers the release of hormones that stimulate the gall bladder and liver to secrete bile and the pancreas to secrete pancreatic juice
- These chemicals enter the duodenum on its medial side via the hepatopancreatic ampulla (ampulla of Vater)
46
Describe the junction of the small and large intestines
Ileum connects to medial side of the junction of the cecum at the ileocecal valve
47
Describe the layers of the small intestine wall
1. Mucosa - epithelium, lamina propria, muscularis mucosae
2. Submucosa - areolar connective tissue
3. Muscularis propria - circular and longitudinal layer
4. Serous - simple squamous epithelium
48
List the cells of the epithelium of the small intestines
1. Absorptive cells - simple columnar epithelial cells, for uptake of nutrients and production of digestive enzymes
2. Goblet cells - columnar epithelial cells, produce mucus to protect wall from digestive enzymes
3. Enteroendocrine cells - secrete hormones
4. Paneth cells - secrete lysozyme to protect from bacteria
5. Stem cells - give rise to cell types of intestinal mucosa
49
List the brush border enzymes
1. Aminopeptidases
2. Dextrinase
3. Dipeptidease
4. Enteropeptidase
5. Lactase
6. Maltase
7. Nucleosidase
8. Phosphatases
9. Sucrase
50
Describe the function of the large intestine
Absorbs water and salts, eliminates waste
51
List the parts of the large intestine
From ileum -> anus
1. Cecum
2. Vermiform appendix
3. Ascending colon
4. Transverse colon
5. Descending colon
6. Sigmoid colon
7. Rectum
8. Anal canal
52
Describe the histology of the large intestine
Same as small intestine:
1. Mucosa - epithelium, lamina propria, muscularis mucosae
2. Submucosa
3. Muscularis propria - circular and longitudinal muscle
4. Serosa - simple squamous epithelium
53
List the cells of the epithelium of the large intestine
1. Absorptive cells - simple columnar epithelial cells covered in microvilli for absorption of water and salts
2. Goblet cells - columnar epithelium cells, produce mucus to protect from digestive enzymes
3. Stem cells - columnar epithelial cells, produce new cells
54
Describe the digestion of carbohydrates
- Oral cavity - salivary amylase
- Small intestine - pancreatic amylase
- Large intestine - fermentation
55
Describe the absorption of carbohydrates
- Monosaccharides - brush border -> apical membrane (small intestine) of absorptive cells, facilitated diffusion/active transport. Once cells exit basolateral surface, enter blood capillary via facilitated diffusion
- Fructose - facilitate diffusion
- Glucose - active transport, symporter
56
Describe the digestion of proteins
- Stomach - pepsin from pepsinogen secreted by chief cells (activated by hyrochloric acid)
- Small intestine - pancreatic juice - trypsin, chemtrypsin, carboxypeptidase + elastase, brush border enzymes - aminopeptidase, dipeptidase
57
Describe the absorption of proteins
- Absorbed as di- and tri- peptides
- Cotransported from intestinal lumen to surrounding cells with hydrogen ions
- Hydrogen ions and peptides pumped into absorptive cells via hydrogen ion pump
58
Describe the digestion of lipids
- Stomach - lingual + gastric lipase (lingual = salivary glands, activated in stomach, lipase = breaks down triglycerides)
- Small intestine - pancreatic lipase, bile salts emulsify
59
Describe the absorption of lipids
- Monoglycerides and fatty acids - water insoluble
| - Through brush border of small intestines into cells as micelles
60
Define anorexia nervosa
An emotional/mental eating disorder characterised by a distortion of body image, a pathological desire for thinness and self-induced weight loss by a variety of methods.
61
What mortality rates are associated with anorexia nervosa?
10-15% - 2/3 from physical complications, 1/3 from suicide
62
List the diagnostic criteria for anorexia nervosa
1. Low body weight - 15% less than expected for height/weight, BMI < 17.5
2. Self-induced weight loss
3. Body image distortion - dread of fatness, self-imposed low weight threshold
4. Endocrine disorders
63
Describe how BMI is calculated
BMI = W (kg) / h (m squared)
64
List the BMI thresholds
```
<18.5 = underweight
18.5 - 24.9 = normal range
25 - 29.9 = overweight
30 - 34.9 = obesity I
35 - 39.9 = obesity II
>40 = obesity III
```
65
Describe the methods of self-induced weight loss characteristic of anorexia nervosa
- 'Compensatory behaviours'
- Avoidance of 'fattening' foods
- Vomiting
- Purging - use of laxatives etc.
- Excessive exercise
- Use appetite suppressants
66
List the endocrine disorders associated with anorexia nervosa
- Hypothalamic-pituitary-adrenal (HPA) axis
- Amenorrhoea (absence of menstruation)
- Decreased sexual interest/impotence
- High GH levels
- High cortisol levels
- Abnormal insulin secretion
- Delayed/arrested puberty (if onset is prepubescent)
67
List the risk factors associated with anorexia nervosa
- Genetic predisposition
- Adverse life events
- Personality type
- Other mental disorders e.g. OCD, anxiety etc.
68
List the physical/medical consequences associated with anorexia nervosa
- Dental cavities - crumbling/decay of teeth
- Hypotension, prolonged QT, arrhythmias, cardiomyopathy
- Prolonged GI transit (delayed gastric emptying, gastric atrophy, decreased intestinal motility), constipation
- Hypokalaemia, hyponatremia, hypoglycemia, hypothermia, altered thyroid function
- Amenorrhoea, delay in puberty, arrested growth, infertility, decreased birth weight of offspring
- Renal calculi (kidney stones)
- Dry scaly skin, hair loss due to brittle hair, lanugo (fine downy body hair)
- Peripheral neuropathy, loss of brain volume, ventricular enlargement, sulcal widening, cerebral atrophy - reversed with weight gain
- Anaemia, leukopenia (decreased WBC), thrombocytopenia (decreased platelets)
- Osteopenia - thinning of bones
69
List the physical signs associated with anorexia nervosa
- Loss of muscle mass
- Dry, scaly skin
- Brittle hair and nails
- Callused skin over IP joints (Russell's sign) due to repeated self-induced vomiting
- Anaemia
- Hypercarotenaemia (yellow skin and sclera)
- Lanugo body hair
- Eroded tooth enamel
- Peripheral cyanosis - blue/purple skin due to low O2 saturation
- Hypotension
- Bradycardia
- Atrophy of breasts
- Swelling of parotid + submandibular glands
- Swollen, tender abdomen - intestinal dilation (reduced motility and constipation)
70
Describe the management of anorexia nervosa
- Aim is to treat as outpatients
- Pharmacological - antidepressants e.g. Fluoxetine
- Psychological - family therapy, individual therapy (CBT)
- Education - nutritional education, self-help manuals
- Hospital admission only if serious medical problems - compulsory admission may be required
71
List the criteria for compulsory admission in anorexia nervosa
- Extremely rapid/excessive weight loss
- Severe electrolyte imbalance
- Temp. <36 degrees, fainting due to bradycardia, drop in BP
- Marked changes in mental status due to severe malnutrition
- Psychosis, significant risk of suicide
72
Describe the process of re-feeding syndrome
1. Starvation/malnutrition
2. Glycogenolysis, gluconeogenesis + protein catabolism
3. Protein, fat, mineral, electrolyte + vitamin depletion - salt + water intolerance
4. Re-feeding (switch to anabolism)
5. Fluid, salts, nutrients (CHO major energy source)
6. Insulin secretion
7. Increased protein and glycogen synthesis - increased glucose uptake, increased utilisation of thiamine, increased uptake of potassium, magnesium + phosphate ions
8. Hypokalaemia, hypomagnesaemia, hypophosphateamia, thiamine deficiency, salt + water retention - oedema
73
Define re-feeding syndrome
Syndrome consisting of metabolic disturbances that occur as a result of reinstitution of nutrition to patients who are starved, severely malnourished or metabolically stressed due to severe illness
74
How is re-feeding syndrome prevented
Caloric intake is increased slowly - by 200-300 kcal every 3-5 days
75
Define bulimia
An eating disorder characterised by recurrent episodes of binge eating with compensatory behaviours + overvalued ideas about 'ideal' body shape and weight. Often have a past history of anorexia nervosa.
76
List the risk factors of bulimia
- Family/personal history of obesity
| - Family history of substance misuse
77
Describe the criteria used to diagnose anorexia/bulimia
SCOFF Questions
1. Do you make yourself Sick because you feel uncomfortably full?
2. Do you worry you have lost Control over how much you eat?
3. Have you recently lost more than One stone in a 3-month period?
4. Do you believe yourself to be Fat when others say you are too thin?
5. Would you say that Food dominates your life?
78
List the thoughts/behaviours associated with bulimia
- Persistent preoccupation with eating/food
- Irresistible craving for food
- Binges - episodes of overeating
- Compensatory behaviours e.g. self-induced vomiting
- Self-imposed low weight threshold
79
List the physical signs of bulimia
- Arrhythmias
- Cardiac failure
- Electrolyte disturbances
- Oesophageal/gastric erosions
- Gastric duodenal ulcers
- Pancreatitis
- Constipation
- Dental erosion
- Leukopenia/lymphocytosis
- Russel's sign
80
Describe the treatment of bulimia
- Usually managed as outpatient
- Admission only for serious risk of suicide, physical problems, extreme refractory cases or pregnancy
- Pharmacological - antidepressants e.g. Fluoxitine
- Psychotherapy - CBT, interpersonal therapy, guided self-help, education + support often in group setting
81
List other eating disorders
1. Binge eating disorder
| 2. Atypical eating disorder
82
Describe the criteria for binge eating disorder
3/5 of
- Eating more quickly
- Eating until uncomfortably full
- Eating a lot when not hungry
- Eating alone because of embarrassment
- Feeling guilty after eating
83
What is metabolism?
The sum of all chemical reactions in which energy is made available and consumed in the body
84
What is ATP?
Adenosine triphosphate - energy 'currency' of all living systems, undergoes hydrolysis to give ADP and a phosphate, liberating a large amount of energy
85
List the processes which give rise to acetyl coenzyme A in respiration
Carbohydrates -> glucose -> acetyl coA through GLYCOLYSIS
Fats -> fatty acids -> acetyl coA by BETA OXIDATION
Proteins -> amino acids -> acetyl coA by TRANSAMINATION then OXIDATIVE DEAMINATION
86
How many amino acids must be obtained from the diet?
9
87
Describe the nervous control of digestion
Enteric nervous system:
Myenteric plexus - control is primarily ove GI motility
Submucous plexus - senses environment within lumen, regulates GI blood flow, controls epithelial cell function
88
What happens to carbohydrate and protein not digested in the small intestine?
It is fermented by the colonic microflora to short chain fatty acids and gases
