week 10 - gastrointestinal system Flashcards
what is metabolism
sum of all chemical reactions in which energy is made available and consumed in the body
what does the body need energy for
Contraction of muscles for all movement
Accumulation of ions and other molecules against concentration gradients (nerve impulse transmission)
Biosynthesis and hence for the building of tissues
Waste disposal and hence for getting rid of the end products of bodily function
Generation of heat and hence maintenance of body temp
what is gibbs free energy and when is it positive and negative
it is usable energy or energy that is available to do work
deltaG = negative when the reaction gives out energy and is positive when the product contains more energy than the substrate
describe the structure of ATP
adenosine tri-phosphate is composed of adenine, ribose and three phosphate groups
ADP is only two phosphate groups
how is acetyl coenzyme A produced
glycolysis of glucose
beta-oxidation of fatty acids
transamination and oxidative deamination of amino acids
all of these reactions produce acetyl coA
vitamins and minerals play essential roles in these reactions
what kind of process is the TCA cycle
amphibolic meaning it has anabolic and catabolic components
steps of the TCA cycle
acetyl coA enters and condenses with oxaloacetate to produce citrate
decarboxylation phase - citrate is metabolised into succinyl coA (CO2 released)
reductive phase - succinyl coA to oxaloacetate
1 GTP produced
1 acetyl coA lead to 3 NADH and 1 FADH2 being produced
steps of the electron transport chain
NADH and FADH2 donate two electrons and one proton
electrons are passed along RADOX centres which have an increasing affinity for electrons - electrons moving along produces ATP
ATP used to pump protons against conc gradient from matrix through the inner mitochondrial membrane to the intermembrane space
protons return to matrix through ATP synthase as IMM is impermeable
as protons are driven through, ATP synthase rotates and ATP is produced
electrons at end of complex 4 are donated to molecular O2 with a proton to produce water
how are electrons passed between complexes in the ETC
As electrons reach end of RADOX centres in complex 1, they are passed via coenzyme Q to the next complex and so on… but from complex 3 to 4, cytochrome C passes electrons between complex
why is complex 2 different (in ETC)
it is not pump proteins
FADH2 joins at this complex
describe glycolysis
glucose is broken down to 2 pyruvate molecules in two phases
phase 1 - endergonic (2 ATP in) - glucose to glyceraldehyde-3-phosphate
phase 2 - exergonic - G-3-P is metabolised to pyruvate producing 4 ATP giving a net gain of 2 ATP
occurs in the cytosol
how is pyruvate converted into acetyl coA
Pyruvate undergoes further metabolism in the mitochondria where, on entry, the 3C pyruvate loses a carbon atom with the production of CO2 to form acetyl CoA by the action of pyruvate dehydrogenase - A molecule of NADH is also formed in this process and that can be fed into the electron transport chain
Acetyl CoA is then able to enter the TCA cycle
how is excess glucose stored in the body
in the form of glycogen mainly within the liver and also in muscle
what are lipids
highly efficient energy storage molecules and are important to the body’s ability to adapt to periods of fasting
examples - fats, oils, waxes, certain vitamins (such as A, D, E and K), hormones and most of the cell membrane that is not made up of protein
what are triglycerides and how can they be broken down
Fats are stored as triglycerides - triglycerides are three fatty acids attached to a glycerol backbone, these triglycerides can be broken down into their component parts of fatty acids and glycerol by an enzyme called lipase
how are fatty acids transported in the blood
Fatty acids are released and transported in the blood as a complex with albumin and are taken up by other cells for oxidation
they are hydrophobic so are transported within albumin which protects them from water
All enzymes required for fatty acid catabolism are within matrix of mitochondria but fatty acids need to be modified by the addition of acetyl coA molecule in order to enter the mitochondria
beta-oxidation occurs once they enter they matrix
describe fatty acid transportation into the mitochondrial matrix
addition of coA allows fatty acids to enter the mitochondria - forms fatty acyl coA
carnitine replaces coA to form fatty acyl carnitine - allowing it across the outer mitochondrial membrane
carnitine shuttle allows fatty acids to cross impermeable IMM into matrix
coA replaces carnitine to from fatty acyl coA and fatty acids can be degraded
describe fatty acid degradation
once in the matrix, beta-oxidation can occur
this process cleaves carbon backbone between alpha and beta carbons making the fatty acid smaller and smaller
each cleavage produces acetyl coA, 1 NADH and 1 FADH2 which can be fed into ETC
describe protein metabolism
transamination - removes amine group from AA and transfers it to an alpha ketoacid - when it accepts the amine group it transfers the keto group to the original AA
deamination - amine group removed from AA releasing the carbon backbone of the AA which can be regenerated into glucose, fatty acids or various TCA cycle intermediates - produces a side product of ammonium (toxic so kidneys exclude it)
describe glucogenic and ketogenic amino acids
glucogenic - breakdown products ultimately form glucose by conversion to pyruvate, or intermediates of TCA cycle
ketogenic - breakdown products form fatty acids via the intermediates of acetyl coA or acetoacetyl coA
sources of metabolic fuel in prolonged periods of starvation
fat - triglycerides in adipose tissue - sufficient to prolong life for 3 months
protein - provides approx. 14 days worth of energy but is spared for as long as possible to permit mobility
why is the BMI not always a good representation of an individual
does not take into account muscle mass or cardiovascular condition
factors influencing energy expenditure
menstruation, age, last three months of pregnancy and also lactation cause increase in expenditure
components of a balanced diet and their functions
carbohydrate - energy source
protein - repair and growth
fat - long term energy store, insulation
vitamins - A: vision C: antioxidant D: Ca absorption
minerals - Ca: bone mineralisation Fe: oxygen transport
fibre - effective bowel function
water - hydration
structure of triglycerides
glycerol and three fatty acids
where is cholesterol found
present in plasma membrane of cells but also serves as a precursor for the synthesis of a number of other molecules such as sex hormones, oestrogen and testosterone as well as bile salts and phospholipids
dietary sources for the components of a balanced diet
C - bread rice pasta potatoes p - meat fish dairy nuts fat - meat cheese cream fish v - A: sweet potato B: veg C: citrus D: oily fish m - Ca: milk Fe: red meat K: bananas f - plants
essential amino acids
9 AAs that cannot be produced by the body and must be obtained by the diet
types of carbohydrates and examples
monosaccharides - glucose, fructose, galactose
disaccharides - sucrose, maltose, lactose
polysaccharides - starch
bonds between monosaccharides in poly and disaccharides
glycosidic bonds
glands secreting saliva
parotid, submandibular and sublingual salivary glands
function of saliva in digestion
starts the digestion of carbohydrates by producing an enzyme called alpha-amylase
how alpha-amylase starts to digest carbohydrates
cleaves the 1-4 glycosidic bonds to produce maltose, a disaccharide, maltotriose, a trisaccharide and alpha limit dextrin
digestion in the mouth
alpha amylase starts carb digestion
Lingual lipase which breaks down triglycerides into fatty acids and glycerol is also present in saliva but most fat digestion takes place later in the small intestine
digestion in the stomach
start of protein digestion
secretion and activation going on in the stomach during digestion
chief cells secrete pepsinogen
parietal cells secrete HCl acid which denatures proteins and activates pepsin
pepsin then cleaves peptide bonds within the polypeptide chain to produce many smaller oligo peptides
what is a zymogen
some enzymes are synthesised as inactive precursors - these inactive precursors are called zymogens
exocrine function of the pancreas
pancreatic juice and alkali secretion
alkali secretions buffer any acid from the stomach and provide an optimal pH for. digestive enzymes in the duodenum
endocrine function of the pancreas
secretion of insulin and glucagon
function of the pancreatic secretions into the duodenum
Pancreatic secretions into the duodenum include a number of proteases such as trypsin and chymotrypsin and carboxypeptidase as well as other enzymes to digest elastin
function of liver in digestion
production and secretion of bile
role of bile in digestion
Stored in gallbladder and released into the duodenum after a meal
Important in the emulsification of fat particles so that fats are accessible for enzymes
Bile salts aid absorption of fats by forming complexes called micelles
properties of bile that allows it to help emulsify fats
Cholesterol derived potion of bile acid is hydrophobic and the amino acid conjugate is hydrophilic - bile acids are amphipathic
Due to these properties, bile salts have a detergent action of particles of dietary fat causing fat globules to break down or be emulsified into tiny droplets
why fats are emulsified
greatly increases the surface area of fat making it available for the digestion by lipases
what are enterocytes
cells of the intestinal lining
digestive enzymes provided by the duodenum
first is enterokinase which activates trypsin which then goes and activates all the other proteolytic zymogens produced from pancreas
Second group of enzymes are the brush border enzymes – digest disaccharides to monosaccharides
describe the different types of absorption
passive absorption - from a high to low concentration
facilitated transport - down concentration gradient - involves a membrane carrier
active transport - uses energy and a membrane carrier - low to high
what are micelles in digestion and how are they formed
mix of bile acids and lipids
Products of lipid digestion are solubilised in the intestinal lumen in mixed micelles with the aid of bile salts except glycerol which is water-soluble
describe how fatty acids are released into the bloodstream
Micelles diffuse to the apical brush border where the lipids are released from the micelle and diffuse down the concentration gradient into the cell
Inside the cells, if the fatty acid chains are short they will move directly into bloodstream
if larger, triglycerides are packaged into lipid structured called a chylomicron – secreted into lymphatics via lacteals – lymphatic circulation carries these chylomicrons to thoracic duct to enter the bloodstream
absorption of monosaccharides
glucose and galactose absorbed by mechanisms involving sodium dependent co-transport – they move from the intestinal lumen into the cell on the sodium glucose transporter called SGLT1
Sodium is rapidly shuttled out in exchange for potassium by sodium pumps on the basolateral membrane
Fructose is transported separately across both the apical and basolateral membranes by facilitated diffusion
all three monosaccharides are transported across the basolateral membrane into the bloodstream by the GLUT2 transporter
absorption of amino acids
Luminal plasma membrane of the absorptive cell has a number of sodium dependent amino acid transporters
Di- and tri- Peptides in the small intestine are absorbed by Co-transport with hydrogen ions, then further digested into amino acids once inside the cell
All the amino acids are then transported across the basolateral membrane into the blood by facilitated diffusion
final products of protein digestion
amino acids, dipeptides and some tripeptides
describe normal eating behaviour
normal eating is flexible
it varies in response to your hunger, your schedule, your proximity to food and your feelings
Usually having 3 meals a day
Overeating and undereating at times
common eating disorders
anorexia nervosa
bulimia nervosa
binge eating disorder
avoidant/restrictive food intake disorder (ARFID)
other feeding or eating disorders that do not fit into these categories
presentation of bulimia
recurrent episodes of overeating
binge eating accompanied by repeated inappropriate compensatory behaviours aimed at preventing weight gain
individual is preoccupied with body shape or weight which strongly influences self evaluation
not significantly underweight so does not meet AN criteria
management of bulimia nervosa in adults
if self-help programme does not work, try CBT - involve significant others in CBT if appropriate
management of bulimia nervosa in children and young people
family therapy or CBT if FT-BN does not work
what is cognitive behavioural therapy
evidence based treatment for a range of mental health diagnoses
talking therapy
changes the way the patient thinks and behaves which is turn changes they way they feel
presentation of binge eating disorder
Characterised by frequent recurrent episodes of binge eating (eg once a week or more over a period of several months) with compensatory behaviours Eating more quickly than usual Eating until uncomfortably full Eating a lot when not hungry Eating alone because of embarrassment Feeling very bad or guilty after eating
management of binge eating disorder
guided self help with therapy sessions
if unsuccessful or unacceptable offer group eating disorder focused CBT-ED
presentation of anorexia nervosa
A significantly low body weight for the individuals height, age and developmental stage (BMI less than 18.5, BMI under 5th percentile in children and adolescents)
Low body weight is accompanied by a persistent pattern of behaviours to prevent the restoration of normal weight
Low body weight is central to the person’s self-evaluation or is inaccurately perceived to be normal or excessive
management of anorexia nervosa in adults
consider CBT-ED
If CBT-ED, MANTRA or SSCM is unacceptable try one of the others or eating disorder focused focal psychodynamic therapy
Individual CBT-ED should consist of up to 40 sessions over 40 weeks
management of anorexia nervosa in children
Family therapy
Give patient the option to have single and family sessions
If FT-AN is unacceptable, contraindicated or ineffective consider CBT-ED or adolescent focused psychotherapy
presentation of ARFID
Characterised by abnormal eating or feeling behaviours that result in the intake of insufficient quantity or variety of food - extreme picky eating
Causes significant weight loss/failure to gain weight/nutritional deficiencies/ dependence on nutritional supplements or tube feeding/ negatively affects health/ significantly impairs functioning
The pattern of eating does not reflect concerns about body shape or weight
role of a psychiatrist in the MDT
works with the MDT in the following:
Assessment and diagnosis
Supporting psychologically informed formulation and treatment – finding the reason behind the ED
Physical monitoring
Risk assessment and management
Treating comorbidities
Developing services, improving quality, facilitating teaching and learning
complications of anorexia
impaired concentration, dry skin, brittle hair, hair loss, low bp, cardiomyopathy, anaemia, osteoporosis, amenorrhoea, infertility
2 groups of organs within the digestive system
gastrointestinal tract
accessory organs - salivary glands, gallbladder, liver, pancreas
function of gall bladder in the digestive system
helps store and concentrate bile
components of the GI tract
oral cavity pharynx oesophagus stomach small intestine large intestine
parts of the small intestine
duodenum
jejunum
ileum
as you move from the duodenum to the ileum you progress from more digestion to more absorption
large intestine components
Caecum, ascending, transverse and descending colon, sigmoid colon, rectum and anus
were is mucosa or mucous membrane found
lining the cavities of the body and surface of the internal organs
what is lamina propria
thin layer of loose connective tissue which lies beneath the epithelium - it contains inflammatory cells and provides support and nutrients to the overlying epithelium
what is muscularis mucosae
next layer deep to the lamina propria and is composed of smooth muscle and is continuous all the way through the entire length of the gastrointestinal tract
describe the submucosa
is deep to the muscularis mucosae - composed of dense irregular connective tissue and contains many blood vessels, nerves and also lymphatic vessels (which collects additional fluid around the body outside the vasculature)
describe the muscularis propria - also called the muscularis externa
comprised of inner circular muscle and outer longitudinal muscle - this muscle is smooth muscle and is responsible for peristalsis (movement of food and products of digestion)
describe the adventitia
outer layer of fibrous connective tissue surrounding an organ
describe the histology of the GI tract from deep to superior
Mucosa (mucous membrane) epithelium lamina propria muscularis mucosae submucosa muscularis propria (muscularis externa) adventita serosa
epithelium in the GI tract
Oesophagus epithelium is stratified, squamous
Change of epithelium at stomach which continues for the rest of the GI tract – simple columnar
function of brunners glands
secretes bicarbonate ions to neutralise acid from stomach
what are peyers patches
lymphoid follicles and form part of the immune function preventing the growth of dangerous bacteria
describe the pharynx and its three parts
conducts air
muscles direct food to oesophagus
made of the nasopharynx, oropharynx and laryngopharynx
9 sections of the abdomen
1 = Right hypochondrium 2 = Epigastric 3 = Left hypochondrium 4 = Right lumbar 5 = Umbilical 6 = Left lumbar 7 = Right iliac fossa 8 = Suprapubic 9 = Left iliac fossa
organs in Right hypochondrium
liver
organs in epigastric
Duodenum, liver, gall bladder, pancreas, stomach
organs in the left hypochondrium
spleen and stomach
organs in the right lumbar
ascending colon
kidney
organs in the umbilical
Stomach, Head of pancreas, Small intestine (duodenum), transverse colon, lower aspects of right and left kidneys
left lumbar organs
descending colon
left kidney
right iliac fossa organs
caecum, appendix, part of ascending colon
suprapubic organs
bladder, uterus, parts of small intestine
left iliac fossa organs
sigmoid colon, descending colon
where is the pyloric sphincter found and what is its function
in the pylorus of stomach
controls secretions to duodenum from stomach
what is anterior/superior to stomach
diaphragm and liver
posterior/inferior to stomach
Diaphragm, spleen, kidney (L.), adrenal gland, pancreas
three layers of muscle in stomach wall
longitudinal, circular, oblique
describe the histology of the stomach
Endocrine cells produce gastrin
This stimulates the parietal cells to produce hydrochloric acid
The hydrochloric acid then breaks down pepsinogen to become pepsin produced from the chief cells
Mucous and surface mucous cells protect the mucosa
what are villi
These are finger like projections and are well designed to increase surface area, and therefore aid in the digestion and absorption which typically happens in the small intestine, namely the duodenum, jejunum and ileum
role of duodenum in digestion
receives chyme
contains brunners glands
bile and pancreatic secretions enter
ends at duodenojejunal junction
functions of the pancreas
exocrine - Primarily produces many digestive enzymes but also Bicarbonate ions - These digestive enzymes help break down carbohydrates, proteins and fats
endocrine - islets of langerhans secrete insulin, glucagon and somatostatin
functions of the hormones secreted by endocrine portion of pancreas
Insulin – promotes glucose absorption from blood into liver, skeletal muscle and fat cells - enables the conversion to glycogen (storage of glucose in this form)
Glucagon – this does the opposite and results in the conversion of the stored glycogen into glucose for release into the bloodstream when levels are low
Somatostatin – this helps to reduce acid secretion and helps to slow down the digestive process - has a variety of other functions in the body
how many lobes does the liver have
four
functions of liver
It detoxifies and processes everything absorbed from the gastrointestinal tract (GIT), and regulates glucose in the blood
The liver synthesizes proteins including the clotting factors and platelet regulations
It inactivates hormones and drugs, as well as insulin and many waste products and is heavily involved in drug metabolism, and sometimes this can be of detriment when the product of metabolism is more toxic than the initial compound e.g. paracetamol
describe the blood supply for the liver
receives a dual supply of blood – the hepatic portal vein from the gut, spleen and related organs (approximately 75%)
The hepatic arteries account for 25% of blood flow, and this artery provides the oxygenated blood for the liver
functions of common hepatic duct and the cystic duct
duct that leaves gall bladder for bile secretions to pass out is called the cystic duct
Common hepatic duct comes from the left and right hepatic ducts which carry bile to the gall bladder
function of caecum
acts as a reservoir for chyme when it receives from the ileum
four parts of the colon
ascending, transverse, descending and sigmoid
where are the hepatic and splenic flexures
when colon meets the right lobe of the liver and turns 90 degrees = hepatic
when colon turns another 90 degrees to point inferiorly = splenic flexure
function of goblet cells
produce mucous as the role of the large intestine is to absorb fluid from the GI tract
3 main vessels that all arise from the abdominal aorta and the areas they supply
Coeliac trunk (foregut)
Superior mesenteric artery (midgut)
Inferior mesenteric artery (hind gut)
Foregut – supplies the oesophagus (lower portion), stomach, liver, spleen and first half of the duodenum
Midgut – supplies the last half of the duodenum, jejunum, ileum, caecum, appendix, ascending colon and first half to first 2/3 of the transverse colon
Hindgut – supplies last 1/3 of the transverse colon, descending colon, sigmoid colon and rectum
describe the venous drainage of GI tract
Portal venous drainage is for the unpaired abdominal organs i.e. the gut and spleen
Femoral veins drain the lower limb
Internal iliac veins drain the pelvis
Renal veins drain the kidneys
Hepatic vein is the main vein draining the liver
