Flashcards
Gastrointestinal
Flashcards do conjunto (190)
- 1Where does the foregut begin and end?The foregut starts from the mouth and ends at the common bile duct
- 2Where does the midgut begin and end?The midgut starts from the common bile duct and ends 2/3 of the way across the transverse colon
- 3Where does the hindgut begin and end?The hindgut begins from 2/3 of the way across the transverse colon and ends at the anal canal
- 4Describe the foregut?Blood supply: Celiac artery
Components:
- Pharynx
- Oesophagus
-Stomach
- Proximal half of the duodenum and the derivative (liver, biliary apparatus and the pancreas) - 5Describe the midgut?Blood supply: superior mesenteric artery
Components:
- Distal half of the duodenum
- Jejunum
- Ileum
- Caecum
- Appendix
- Ascending colon
- Proximal 2/3 of the transverse colon - 6Describe the hindgut?Blood supply: Inferior mesenteric artery
Components:
- Distal 1/3 of the transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Anal canal - 7What happens during the 4th week to the embryo?During the fourth week development, the embryo begins to fold and change shape from a flat trilaminar disc into a cylinder - this process is known as embryonic folding
- 8How does embryonic folding occur?Folding occurs in two planes due to the differing rates of growth of the embryonic structures however they are simultaneous
Horizontal plane folding: Two lateral body folds
Medial plane folding: cranial and caudal folds - 9Which of the layers of the trilaminar disc is mainly responsible from the development of the GI tract?Endoderm
- 10How is the primitive gut tube formed?As embryonic folding continues, the endoderm moves towards the mid line and fuses - incorporating the dorsal part of the yolk sac to form the primitive gut tube
- 11What does the endoderm give rise to?1. Epithelial lining of the digestive tract
2. Hepatocytes of the liver
3. Endocrine and exocrine cells of the pancreas - 12What does the visceral mesoderm give rise to?1. Muscle, connective tissue and peritoneal components of the wall of the gut
2. Connective tissue for the glands - 13What closes the foregut?The foregut is temporarily closed by the oropharyngeal membrane which at the end on the 4th week ruptures to form the mouth
- 14When is the midgut connected to the yolk sac?Midgut lies between foregut and hindgut
Remains connected to yolk sac until 5th week
As folding continues the connection narrows into a stalk called the vitelline duct - 15What closes the hindgut?The hindgut lies at the caudal end of the embtyo and is temporarily closes by the cloacal membrane
Which during the 7th week ruptures for from the anus - 16—Vitelline duct
- 17—Cloacal membrane
- 18Describe the development of the pharyngeal arches?- Part of the foregut
- Extends from the oropharyngeal membrane to respiratory diverticulum
- Develop in 4th and 5th week
- Formed of masses of mesenchymal tissue (mesoderm) invaded by cranial neural crest - 19What are the cranial arches?1,2,3,4 and 6
Each arch has its own nerve supply, arterial supply, and venous supply - 20What covers the pharyngeal arches?Each pharyngeal arch is covered externally by endoderm forming pharyngeal crests
Each pharyngeal arch is covered interally by ectoderm forming the pharyngeal pouches - 21Describe the first pharyngeal arch?Innervation: Mandibular nerve V3
Muscles: Mastication, tensor tympani, digastric and myolohyoid
Bone: Maxilla, mandible, incus and malleus - 22Describe the second pharyngeal arch?Innervation: Facial nere
Muscles: Facial expression, stapedius, stylohyoid
Bone: Stapes, styloid and lesser horn of hyoid cartilage - 23Describe the third pharyngeal arch?Innervation: Glossopharyngeal nerve
Muscle: Stylopharyngeus of the pharynx
Bone: body and greater horn of the hyoid cartilage - 24Describe the fourth pharyngeal arch?Innervation: Superior laryngeal anerve of the Vagus
Muscles: Cricothyroid
Bone: Thyroid cartilage and epiglottic cartilage - 25Describe the sixth pharyngeal arch?Innervation: Recurrent laryngeal nerve of the vagus
Muscles: All muscles of the larynx except the cricothyroid
Bone: Cricoid cartilage, arytenoid cartilages, corniculate and cuneifrom cartilage - 26Describe the formation of the oesophagus?4th week the end of the pharynx and the beginning of the oesophagus, at ventral wall of the foregut respiratory diverticulum (lung buds) appear
Trancheoesophageal septum develops and separates the respiratory diverticulum from the dorsal part of the foregut (divided into ventral respiratory primordium and dorsal oesophagus)
Initially the oesophagus is short but it lengthens rapidly with the desecnd of the heart and lungs - 27What are mesenteries?Parts of the gut tube are suspended from the dorsal and ventral body walls by mesenteries
Mesenteries are double layers of peritoneum that surround an organ and connect it to the body wall, such an organ is called intraperitoneal - 28Define: retroperitoneal organ?When an organ is sitting directly on the posterior abdominal wall, and covered by peritoneum on its anterior surface only
- 29Define: ligament?Double layers of peritoneum which pass from one organ to another or from one organ to the body wall
- 30What do mesenteries and ligaments provide?Provide pathways for blood vessels, lymphatics, and nerves to go to and come from the abdominal viscera
- 31When is the dorsal mesentery formed by and what does it suspend?5th week
Lower foregut, midgut, hindgut are suspended from posterior abdominal wall by dorsal mesentery extending from lower oeseophagus to cloacal region - 32Where is ventral mesentery present?Only in foregut - terminal oeseophagus, stomach and upper duodenum
- 33What is ventral mesentery derived from?Septum transversum
- 34What do the free lower margins of the ventral mesentery contain?Hepatic artery, portal vein and bile duct
The liver develops in the ventral mesentery and divides it into lesser omentum and falciform ligament - 35What is the first sign of the stomach formation?Appears as a fusiform dilation in the foregut in the 4th week
- 36Which mesenteries are attached to the developing stomach?Dorsal and ventral mesenteries
- 37Which nerves flank the left and right side of the developing stomach?The left and right vagus nerves
After stomach rotates 90 degrees left vagus is on anterior and right vagus is on the posterior thus becoming the anterior and posterior vagal trunks - 38What forms the greater and lesser curvatures of the stomach?The dorsal wall grows faster than the ventral wall
- 39What happens to the developing stomach during the 7th week of development?The stomach rotates 90 degrees clockwise about a longitudinal axis - this rotation produces a space behind the stomach called the lesser sac
Greater curvature now faces left and lesser curvature faces the right - 40What happens to the stomach during the 8th week of development?The stomach and the duodenum rotate about a ventrodorsal axis pulling the end of the stomach upwards, the pull the duodenum into a C shape
- 41What to the rotations of the stomach result in?Thinning of the dorsal mesentery which now hangs from the greater curvature of the stomach
It is now called the greater omentum - 42What forms the lesser omentum?The ventral mesentery which is attached to the developing liver after the 8th week
- 43What are the spaces in the peritoneal cavity posterior and anterior to the stomach called?Posterior = the lesser sac
Anterior = the greater sac - 44How to the greater and lesser sacs communicate?Small opening near the hilum of the liver called the epiploic foramen
- 45What happens to the anterior and posterior folds of the greater omentum during the fetal period?They fuse to form one thick sheet formed from 4 layers of peritoneum
- 46What initiates swallowing?When pressure receptors in the walls of the pharnyx are stimulates by food or drink forced into the rear of the mouth by the tongue
- 47What makes to the pharnyx?3 continuous segments shared by the GI and respiratory tracts
Nasopharynx - Maxillary nerve
Ororpharynx - Glossopharyngeal nerve
Laryngopharynx - Vagus nerve - 48Describe stage one of swallowing?Stage one - VOLUNTARY
- Food is compressed against the roof of the mouth and pushed towards the oropharynx
- The buccinator and suprahyoid muscles manipulate food during chewing, they also elevate hypoid bond and flatten floor of mouth - 49Describe stage 2 of swallowing?Stage two - Involuntary
Nasopharynx closed off by the soft palate via action of the muscles of the palate which tense and elevate it
Pharynx is shortened and widened by elevation of hyoid bone
Impulses from swallowing centre inhibit respiration, raise the larynx and close the glottis
As tongue forces food further back into pharnx, food tilts epiglottis to cover glottis preventing aspiration - 50Describe stage 3 of swallowing?Stage 3 - INVOLUNTARY
- Sequential contraction of the constrictor muscles (circular) followed by the depression of the hyoid bone and pharynx
- Depression of the infrahyoid muscle of the neck - they fix the hyoid bone enabling the opening of the mouth - 51Describe the pharyngeal constrictor muscles?3 overlapping muscles that form the posterior and lateral sides of the pharynx
Innervated by the vagus nerve
They contract sequentially from above down to drive the bolus of into the oesophagus - 52Describe swallowing in the oesophagus?Skeletal muscle in the upper 1/3 of the oesophagus
Smooth muscle in the lower 2/3 of the oesophagus
Luminal pressure in the pharynx at opening of oesophagus = atmospheric pressure
Pressure at opposite end next to stomach greater than atmospheric forcing air up from below, however sphincter muscles prevent this - 53What are the oesophageal sphincters?Upper oesophageal sphincter = A ring of skeletal muscle that surrounds the oesophagus just below the pharynx
Lower oesophageal sphincter = A ring of smooth muscle that surrounds the oesophagus in the last portion - 54What happens once food is in the oesophagus?Food moves towards the stomach by a progressive wave of muscle contractions that proceed along the oesophagus compressing the lumen and forcing the food ahead - PERISTALTIC WAVES
One oesophageal peristaltic wave takes 9 seconds to reach the stomach
The lower oesophageal sphincter opens and remains relaxed throughout the process of swallowing allowing the arriving food to enter the stomach - 55What must happen before food can enter the oesophagus?Upper oesophageal sphincter relaxes - immediately after the food has passed through the sphincter closes, the glottis opens and breathing resumes
- 56Describe the gag reflex?The reflex elevation of the pharynx
Often followed by vomiting causes by irritation of the oropharynx - back of tongue
Reflex arc between the glossopharyngeal IX and vagus X nerves - 57What are the functions of saliva?Lubricant for mastication
Maintaining oral pH (needs to be maintained around 7.4 and this is achieved by the bicarbonate/carbonate buffer system)
Release digestive enzyme - salivary alpha amylase is released from the parotid gland for starch digestion - 58What is the daily secretion of saliva in adults?800 to 1500mls per day for adults
- 59What is the serous secretion?Alpha amylase for starch digestion
- 60What is the mucous secretion?Mucins for lubrication of mucosal surfaces
- 61What does the parotid gland secrete?Serous
- 62What does the submandibular gland secrete?Mucous and serous secretions
(M for Mixed) - 63What does the sublingual gland secrete?Mucous and serous but mainly mucous
- 64What factors effect the composition and amount of saliva produced?Flow rate
Circadian rhythm
Type and size of gland
Duration and type of stimulus that causes saliva to be produced
Diet
Drugs
Age
Gender
Time of day - 65What are the defences of the oral cavity?The mucosa- physical barrier
Salivary glands - salvia washes away food particles which bacteria or viruses may use as metabolic support
Palatine tonsils - act as surveillance system
Salivary glands surrounded by lymphatics - 66Describe the structure of salivary glands?Two morphologically and distinct epithelial tissues
1. Acinar cells (functional unit of a salivary gland)
2. Ducts (collect to form the large cut entering the mouth, equipt with channels and channels in the apical and basolateral memmbranes - 67What are the two types of acini?Serous and mucous
- 68Describe serous acini?Dark staining nucleus
Nucleus in basal third
Small central duct
Secrete water and alpha amylase
Found mainly in the parotid gland
- 69Describe mucous acinus?Pale staining 'foamy'
Nucleus at base
Large central duct
Secrete mucous (water and glycoproteins)
Found in submandibular and sublingual glands
- 70How are interlobular ducts divided?Intercalated and striated
Intercalated: Short narrow duct segments with cuboidal cells that connect acini to larger striated ducts
Striated: Straited like thick lawn, major site for reabsorption of NaCl, appear striated at basal end, basal end highly folded into microvilli for active transport of HCO3 - 71What makes up the salivary flow?Three major pairs make up 80% of flow
Parotid, submandibular, sublingual
Minor salivary glands contribute to 20% of flow and they are found in the submucosa of lips, cheeks, hard and soft palate and the tongue - 72Describe the parotid duct?Also called stensons duct
Crosses masseter muscle and pierces through the buccinator muscle where it enters the oral cavity near the second upper mole
Can be palpated a fingers breadth below the zygomatic arch - 73What is the innervation of the parotid gland?Sympathetic sensory innervation = auriculo-temporal nerve (branch of V3 mandibular)
Parasympathetic innervation is supplied by glossopharyngeal which stimulates secretion - 74What structures pass through the parotid gland ?External carotid cavity
Retromandibular vein
Facial nerve VII - 75Describe the location of the submandibular glands?Two lobes separated by mylohyoid muscle - larger superficial lobe and a smaller deep lobe in the floor of the mouth
- 76Describe the submandibular duct?Begins in the superficial lobe, wraps around the free posterior border of the mylohyoid, then runs along the floor of the mouth and empties into the oral cavity at the sublingual papillae
SP is more posterior than the sublingual gland - 77Describe the histology of the submandibular gland?Mixed gland with serous and mucous acini
Some serous acini are arranged in crescent shaped groups of glandular cells at the bases of mucous acini = serous demilunes
- 78What innervates the submandibular and sublingual glands?Parasympathetic innervation = chorda tympani branch of the facial nerve
Sympathetic innervation = lingual nerve branch of the facial nerve - 79Describe the sublingual glands?Located more anteriorly than the submandibular glands
Located in the floor of the mouth between the mylohyoid muscles and the oral mucosa of the floor of the mouth
Saliva is transmitted to submandibular duct
Much smaller but variable in size - 80Describe the minor salivary glands?Concentrated in the buccal, labial, palatal and lingual regions
ALL minor salivary glands are mucous except serous glands of von Ebner
The lack a branching network of draining ducts so each unit has its own simple duct - 81Describe Xerostomia?Dry mouth
May be a consequence of cystic fibrosis or Sjorgren's sydrome (no saliva prodcued)
Most common causes are medication and irradiation for head and neck cancers - 82Describe obstruction? (of salivary glands)Saliva contains calcium and phosphate ions that can form from salivary calculi (stones)
Most common in submandibular glands (80% incidence) that block the duct at the bend around mylohyoid or SL papillae - 83Describe inflammation of salivary glands?Can be caused by infection secondary to obstruction
Infections caused by mumps which can cause swelling of the glands - 84Describe degeneration of the salivary glands?Complication of radiotherapy to head and neck for cancer treatment
Also by Sjorgren's syndrome - mainly in post menopausal females also affects lacrimal glands (tears) - 85Effects of salivary gland dysfunction?Low lubrication = oral function becomes difficult
Low natural oral hygiene - poor pH control
Accumilation or plaque = dental caries increase and thrush - 86What are the functions of the stomach?- Store and mix food
- Dissolve and continue digestion
- Regulate emptying duodenum
- Kill microbes
- Secrete protease
- Secrete intrinsic factor
- Activate protease
- Lubrication
- Mucosal protection - 87What are the key cell types in the stomach? (6)Mucous cells: produce mucous
Parietal cells: produce gastric acid and intrinsic factor
Chief cells: produce pepsinogen
Enterochromaffin-like cells: release histamine
G cells: release gastrin
D cells: relesae somatostatin - 88Describe the stomach epithelium?Epithelial layer of the stomach invaginates into the mucosa forming many tubular glands
Glands in the thin upper portion of the body of stomach sercrete: mucous, HCl (parietal cells) , and pepsinogen (chief cells)
Lower portion of the stomach (antrum) has much thicken layer has much thicken smooth muscle and responsible for mixing contents and secretes little acid but G cells secrete gastrin - 89Describe gastric acid production but not the process?Occurs from parietal cells
Hydrochloric acid: very strong with pH of 2
Approx 2 litres per day
Energy depended
Neurohormonal regulatuon - 90How is gastric acid produced?1. CO2 and H2O from respiration are converted into H2CO3 (bicarbonate) via carbonic anhydrase
2. H2CO3 rapidly breaks down into H+ and CO3-
3. H+ can react with OH- to regenerate H2O
4. H+ from breakdown of H2O are pumping into stomach via H+/K+ ATPase pumps
5. K+ can diffuse back out via K+ channels
6. HCO3- from breakdown of H2CO3 secreted into capillary in exchange for Cl- ions
7. Cl- ions enter stomach by diffusing through Cl- channels in plasma membrane
8. H+ and Cl- combine in the stomach to form HCl - 91What does the removal of end produced in the production of gastric acid cause?Removal of end products of this reaction enhance the forward rate of reaction and in this way the production and secretion of H+ are coupled
- 92What are the phases of turning on gastric acid secretion?Cephalic phase: during a meal
Gastric phase: once food has reached the stomach - 93How do the products from G cells and enterochromaffin like cells increase acid production?G cells = Gastrin
Enterochromaffin like cells = Histamine
Gastrin and histamine act on parietal cells increased the fusion of intracellular vesicles containing H+/K+ ATPase protein within the parietal cells to the plasma membrane
Increasing the no. of pump proteins - increasing the amount of H+ - increasing acid production - 94Describe the cephalic phase of the secretion of gastric acid?Parasympathetic nervous system
Initiated by sight, smell and taste of food and chewing
Ach is released and acts indirectly on parietal cells triggering the release of gastrin from G cells and histamine from ECL cells
Both gastrin and histamine increase the number of H+/K+ ATPase pumps on the plasma membrane of the parietal cell
Net effect = increased acid production - 95Describe the gastric phase of gastric acid secretion?Initiated by gastric distension of the volume of ingested material and the presence of peptides and amino acids
Gastrin released acts directly
Gastrin triggers histamine release which acts directly
Net effect - increased acid production - 96Why is histamine important?Because it mediates the effects of gastrin and acetyl choline and thus can be a good therapeutic target e.g. for acid overproduction
- 97What does protein in the stomach cause?Direct stimulus for gastrin release
Proteins of foods in the lumen act as a buffer reducing H+ and increase pH causing decreased secretion of somatostatin, more parietal cell activity and more acid production - 98Describe the gastric phase of turning off stomach acid production?Low luminal pH (high H+) directly inhibites gastrin secretion thereby indirectly inhibiting histamine release
Low pH also stimulates somatostatin which inhibits parietal cells activity - 99Describe the intestinal phase of turning off stomach acid production?In the duodenum
Initated by duodenal distension, low pH, hypertonic solutions, presence of amio acids and fatty acids
These all trigger the release of locally produced chemical messengers such as secretin and cholecystokinin
They also trigger short and long neural pathways reducing ACh release - 100What controls the regulation of gastric acid?Brain
Stomach
Duodenum - 101What are the key messengers?1 parasympathetic neurotransmitter: ACh(+)
1 hormone: Gastrin (+)
2 paracrine [produced in stomach]:
Histamine (+) and somatostatin(-)
2 Key enterogastrones:
Secretin (-) and CCK (-) - 102What is an ulcer?An ulcer is a breach in a mucosal surface
- 103What is the most common cause of a peptic ulcer?Helicobacter pylori infection
Livers in gastric mucus
Secrets urease splitting urea into CO2 and ammonia
Ammonia + H+ = ammonium
Secreted proteases, phospholipase and vacuolating cytotoxin A and then begin attacking gastric epithlium further reducing the mucous production
Inflammatory response and less mucosal defense - 104What is the treatment for an ulcer caused by helicobacter pylori infection?Eradicate organism by using triple therapy:
Proton pump inhibitor increased gastric pH making conditions inhospitable
Antibiotics - 105What drugs can cause a peptic ulcer?NSAIDs e.g. asprin
Mucous secretion is stimulated by prostaglandins
Cyclo-oxygenase 1 is needed for prostaglandin synthesis this reduced mucosal defence
Treatment is to use prostaglandin analogues that mimic effect and reduce acid secretion - 106What are some other things that can cause peptic ulcers?Chemical irritants: alcohol, bile salts
Secreted into duodenum but can reflux into stomach and wash away protective mucous lining
Gastrinoma: rare tumours of the parietal cells = excessive gastrin release = increase in gastric acid = increased attack on gastric mucosa = ulcer - 107What are some synthetic ways to reduce gastric acid secretion?- Proton pump inhibitors: inhibits pumps pumping H+ into the stomach lumen they only block pumps NOT activators e.g. omeprazole
- H2 receptor agonists: block receptors for histamine thereby reducing acid secretion e.g.ranitidine - 108What are the protective mechanisms of the gastric mucosa?Alkaline mucous on the luminal surface
Tight junctions between epithelial cells
Replacement of damaged cells - stem cells at the base of pits to produce new cells
Feedback loops - 109Describe the production of proteases?Chief cells produce pepsinogen
Pepsin is secreted as inactive zymogen and it is stored this way to prevent it digesting chief cells and the rest of the body
Pepsinogen is mediated by input from the enteric nervous system via neurotransmitter ACh
Secretion parallels HCl secretion
When pepsinogen is released into stomach lumen, low pH activates an autocatalytic process in which pepsinogen - pepsin
Positive feedback loop as pepsin helps cleave pepsinogen - 110What pH is most efficient for pepsin?pH 2>
HCO3- released in the duodenum irreversibly inactivates pepsin - 111Describe the role of pepsin in protein digestion?NOT ESSENTIAL - protein digestion can occur if stomach is removed however then then no vitamin B12 absorption can occur in the small intestine since parietal cells produce intrinsic factor
Accelerates protein digestion
Normally accounts for 20% of total protein digestion
Breaks down collagen in meat thereby helping shred meat resulting in small pieces with a greater surface area for digestion - 112Describe gastric motility?Empty stomach has volume of around 50ml
When eating it can accomodate roughly 1.5L with little increase in luminal pressure
It does this by the smooth muscles in the in the body and fundus - 113Describe receptive relaxation?Mediated by parasympathetic nervous system acting on the enteric nerve plexuses with coordination provided by afferent input from the stomach via the vagus nerve and the swallowing centre in the brain
Nitric oxide and serotonin released by enteric nerves mediate relaxation
Acetyl choline activates parietal and chief cells and initiates receptive relaxation - 114Describe peristalsis?In the oesophagus, the stomach produces peristaltic waves in response to the arriving food
Each wave begins in the body of the stomach producing a ripple as it proceeds towards antrum
Initial contract in body is too weak to produce much mixing of luminal contents
There are more powerful contractions in the antrum which enables better mixing
Pyloric sphincter (ring of smooth muscle) closes as peristaltic waves reach it
This contact means every time a wave reaches it little chyme can enter duodenum and is forced back into the body for more mixing and digestion - 115What controls the frequency of peristaltic waves?Pacemaker cells called the interstitial cells of cajal in the muscular propria and is constant
Pacemaker cells undergo slow depolarisation-repolarisation cycles
The depolarisation waves are transmitted through gap junctions to adjacent smooth muscle cells
These do not cause significant contraction - 116How does the strength of peristaltic contraction vary?Action potentials are generated when the threshold is reached
The interstitial cells of cajal are active all the time but the action potential threshold for muscle contraction can be altered by the enteric nervous system - 117What can increase the strength of peristaltic contractions?Gastrin
Gastric distension (mediated by mechanoreceptors) - 118What can decrease the strength of peristaltic contractions?Duoedenal distension
Increase in duodenal fat
Increase in osmolarity
Decrease in duodenal pH
Increase in sympathetic nervous system stimulation
Decrease in parasympathetic nervous system stimulation - 119What happens when duodenum is overfilled and why?The capacity of the stomach is greater than the duodenum so the over filling by a hypertonic solution results in dumping syndrome
Vomitting, bloating, dizziness, fatigue, weakness, sweating and electrolyte imbalances - 120What regulates gastric emptying?Parietal and chief cells
- 121What is gastroparesis?Delayed gastric emptying
- 122What can cause gastroparesis?- Idiopathic
- Autonomic neuropathies
- Abdominal surgery
- Parkinsons disease
- MS
- Scleroderma
- Amyloidosis
- Female gender - 123What are the symptoms of gastroperesis?- Nausea
- Early satiety
- Vomiting undigested food
- GORD
- Pain /bloating
- Anorexia - 124What drugs can cause gastroparesis?H2 receptor anatagonists
Proton pump inhibitors
Opiod analgesics
Benadyrl
Beta adrenergic receptor agonits
Calcium channel blockers
Levodopa - 125What is the most abundant substance in chyme?Water
- 126Where is water reabsorbed?8000ml is ingested and secreted water enters small intestine but only 1500ml passes onto large intestine
Jejunum reabsorbs the most water
98% fluid is reabsorbed with 2% excreted in stool - 127How much water is absorbed in the stomach and why?Small amounts of water are absorbed in the stomach but the stomach has a much smaller surface area available for diffusion and lacks the solute absorbing mechanisms that created osmotic gradient necessary for absorbing water
- 128How is water reabsorbed in the small intestine?The epithelial membranes of the small intestine are very permeable to water and the net water diffusion occurs across epithelium whenever are water concentration difference is established by the active absorption of solutes
Na+ accounts for the most actively transported solutes because it constitues the most abundant solute in chyme - is actively transported from lumen in cell membranes of ileum and jejunum
Luminal membrane transport is variably coupled - 129How is water reabsorbed in the colon?The contents are iso-osmoticin the colon so Na+ is actively pumped and the water follows
- 130Describe potassium reabsorption in the colon?In general, K+ absorption is by passive diffusion, the net movement determine by the potential difference between the lumen and the intestinal capillaries
n.b diarrhoea can result in severe hypokalaemia - 131Describe chloride reabsorption in the colon?Cl- is actively reabsorbed in exchange for bicarbonate resulting in the intestinal contents becoming more alkaline
- 132What are the two functional states the the body undergoes in providing energy for cellular activities?Absorptive: During which ingested nutrients enter the blood from the GI tract, during this state some of the ingested nutrients provide requirements for the body and remainder added to bodies energy stores
Post absorptive: During which the GI tract is empty of nutrients and the body's own store must supply energy - 133What re the three main important fatty acids?Palmitic
Stearic
Oleic - 134What are triglycerides?A glycerol molecule with 3 fatty acids attached
- 135Describe fat digestion?Triglyceride digestion occurs to a limited extent in the mouth and stomach but it predominantly occurs in the small intestine
The major digestive enzyme is lipase (synthesised in the pancreas) - 136Describe the action of lipase?Lipase is synthesised in the pancreas
It catalyses the splitting of bonds linking fatty acids to the 1st and 3rd carbon atoms of glycerol, producing two free fatty acids and a monoglyceride as products
Triglyceride —> Monoglyceride + 2 Fatty acids - 137What happens to lipids in the stomach?The lipids in ingested food are insoluable in water, so aggregate into large lipid droplets in the upper portion of the stomach
These lipid droplets are then converted into very small droplets via the process of emulsification - 138Describe emulsification?1. Mechanical disruption of the large droplets of lipids into smaller ones provided by the motility of the GI tract, in the lower portion of the stomach and in the intestine which grinds and mixes
2. Emulsifying agent provided by the phospholipids in food and bile salts secreted in biele - 139Why are phospholipids amphipathic?Phospholipids are amphipathic molecules - both hydrophobic and hydrophilic
Contain polar or ionised groups on one and and non polar groups on the other
They consist of 2 non fatty acid chains attached to glycerol with a charged phosphate on one end - 140What are emulsifying agents?Amphipathic molecules such as bile salts or phospholipids
- 141How do emulsifying agents help to break down fats?The non polar portion of the phospholipids and bile salts assoiciate with the non polar interior of the lipid droplet
Leaving the polar portions exposed at the water surface
Here they repel other lipid droplets that are similarly coated with these emulsifying agents thereby preventing their reaggregation into larger fat droplets - 142What are the negatives of emulsifying agents?The coating of the lipid droplets with these emulsifying agents impairs the accessibility of the droplet for lipase
- 143How does lipase work in the presence of an emulsifying agentThe pancreas secretes a protein called colipase which binds to the lipid droplet surface as well as binding to lipase
Thereby holding it onto the surface of the lipid droplet - 144Describe micelles?Under further action of bile salts, micelles 4-7 nm are formed
Consisting of bile salts, fat soluble vitamins A, D, E K, cholesterol, fatty acids, monoglycerides and phospholipids clustered with their non polar ends facing inwards - 145Are there any fatty acids in solution?Despite the fact that fatty acids and monoglycerides have an extrememly low soluablility in water, some do still exist in solution and are able to diffuse across the luminal plasma membranes of epithelial cells in small intestine
- 146What happens to the fatty acids in the small intestine?The fatty acids are re-synthesied into triglycerides in the smooth ER where they enzymes for triglyceride synthesis are
This process decreased the cytosolic concentration of free fatty acids and monoglycerides
Maintains a diffusion gradient for these molecules into the cell from the intestinal lumen - 147What happens to fat after it leaves the smooth ERThe resynthesises fat aggregates into small droplets coated by proteins that perform an emulsifying function that is similar to that of bile salts
The fat droplets then pinch off the ER in vesicles where the are processed through GA into chylomicrons - 148Describe chylomicronsContain triglycerides, phospholipids, chloesterol and fat soluable vitamins
Chylomicrons enter the lymphatic vessels (lacteals) in intestinal villi which have large pores enabling them to pass
The lymph from the small intestines eventually empties into the systemic veins - 149Why are chylomicrons absorbed by lymph vessels and not capillariesThe basement membrane on the capillaries provide a barrier to diffusion
- 150What happens to chylomicrons once absorbed?Once they have entered circulation the processing of triglycerides in chylomicrons in blood plasma is similar to that for the VLDLs produced by the liver
Fatty acids are released mainly within the adipose tissue capillaries by the action of endothelial lipoprotein lipase
Fatty acids diffuse into adipocytes and combine with alpha glyerol phosphate synthesised in the adipocytes from glucose metabolites to from triglycerides - 151Why is glucose essential for triglyceride synthesis?Adipocytes do not have the enzyme required for phosphorylation of glycerol to alpha glycerol so it can only be produced by reduced dihydroxyacetone phosphate from glycolysis and NOT from glycerol or any other fat metabolites
- 152What are the three main sources for fatty acids for triglyceride synthesis?1. Glucose that enters adipose tissue and is broken down to from building blocks for the synthesis of fatty acids
2. Glucose that is used in the liver to form VLDL triglycerides which are transported in the blood and taken up by adipocytes
3. Ingested triglycerides transported in blood in chylomicrons - 153What vitamins are absorbed in the ileum?Fat soluble vitamins such as A, D, E and K
- 154What vitamins are absorbed in the jejunum?Water soluble vitamins such as C and B with one exception
- 155What is the exceptional vitamin absorbed in the jejunum?Vitamin B-12
A very large and charged vitamin, must first bind to the protein intrinsic factor and then binds to specific sites on the epithelial cells in the lower portion of the ileum where vitamin B-12 is absorbed via endocytosis - 156What is vitamin B12 essential for?Needed for erythrocyte formation and a deficient B12 can lead to pernicious anaemia and is usually caused due to a deficiency in intrinsic factor
- 157Where does the digestion and absorption of a protein occur?Mainly in the duodenum
A healthy adult only requires 40 to 50g of protein a day to supply essential amino acids and replace the nitrogen in amino acids that are convered to urea - 158What is an essential amino acid?The are 8 essential amino acids and we cannot manufacture them
Only 20 amino acids found in proteins are used - 159Which form of optical isomer of amino acids are used by us?the L form
- 160Describe the digestion of amino acids?1. Begins in the stomach where the enzyme pepsin cleaves some of the peptide linkages forming peptide fragments
2. Pepsins hydrolyse the bonds between an aromatic amino acids
3. In the small intestine these smaller peptides are further fragmented by enzymes produced in the pancreas which can be divided into endopeptidases and exopeptidases - 161What are the different types of pepsinogens?Pepsinogen I - found only in the HCl secreting region (mainly body) of the stomach
Pepsinogen II - found only in the pyloric region - 162What are the pH's of: Optimum pH for pepsins? pH in duodenal cap? pH in rest of duodenum?Optimum pH for pepsins = 1.6 - 3.2
pH in duodenal cap = 2 - 4
pH in rest of duodenum = 6.5 - 163What are the endopeptidases?Trypsin, chymotrypsin and elastase
- 164What are the exopeptidases?Carboxyl dipeptidases and the amino peptidases of the brush border
- 165Where does the final digestion of peptides occur?Some di and tripeptides are absorbed and broken down by intracellular peptidases, this happens in:
1. Intestinal lumen
2. The brush border
3. Within the cell - 166Where does the digestion and absorption of carbohydrates occur?Duodenum
- 167Describe lactose?Lactose forms beta linkages since OH groups lie above the plane of the molecule thus it requires its own enzyme to be broken down, cant use the same one as sucrose since it has alpha linkages
- 168Define the following: Monosaccharide Oligosaccharide PolysaccharideMonosaccharide = single sugars e.g. glucose, fructose and galactose
Oligosaccharide = several sugar molecules e.g. lactose and sucrose
Polysaccharide = many sugar molecules e.g. starch and glycogen - 169What optical isomer of sugars are used in metabolism?D form
- 170Describe glycogen?The principal dietary polysaccharide from animal sources, polymer of glucose molecules which are joined by alpha 1-4 and some alpha 1-6 linkages
- 171Describe starch?Majority alpha 1- 4 linkages with some chain branching by alpha 1-6 but less than glycogen
- 172Describe cellulose?1-4 only
- 173Describe the digestion of starch?1. Starch is first degraded by ptyalin - the alpha amylase of saliva in the mouth, only a small fraction of starch digestion here
2. Once in the small intestine, pancreatic alpha amylase catalyses the alpha 1- 4 linkages
3. Not all alpha 1 - 6 linkages, 1-4 next to branch points or the terminal alpha 1 -4 linkages - 174What are the end products of the first part of digestion?Disaccharide maltose
Trisaccharide maltriose
Large polymers of glucose with alpha 1-4 linkages
Branched polymers of glucose with 8 units called alpha-limit dextrins - 175Describe the final stages of digestion?Oligosaccharidases located at the outer portion of the membrane of the microvilli break down previous digestion products into:
Maltase
Lactase
Sucrase
Alpha limit dextrinase - 176Describe the absorption of carbohydrates?Hexoses and pentoses are rapidly absorbed across the intestinal mucosa, these then enter the capillaries which drain into the hepatic portal vein
Glucose and Na+ share the same transporter (SGLT) thus high Na+ concentration facilitates glucose absorption
Galactose transported by SGLT
Fructose uses different carrier independent of luminal Na+, via GLUT - 177Where are most carbohydrates digested and absorbed?first 20% of the small intestine i.e. the duodenum
- 178What happens to the the carbohydrates once absorbed?After entering hepatic portal vein thus liver, they are converted into glucose
Skeletal muscle makes up the majority of the body so is the major consumer of glucose even at rest
Skeletal muscle catabolises glucose as well as converts some into glycogen for future use
The liver stores some glucose as glycogen as well as converting into alpha glycerol phosphate and fatty acids which are then used in triglyceride synthesis - 179What happens to the fat synthesised in the liver?1. Packed into lipoproteins
2,. Secreted by hepatocytes
3. VLDL since more lipid and protein
4. Due to large size to not readily penetrate capillary walls so tri hydrolysed to mono by lipoprotein lipase
5. Lipoprotein lipase located on blood facing surface of capilarly endothelial cells especially those in adipose - 180How are amino acids, triglycerides and glucose converted storage molecule?Adipose tissue for fats
Muscle for glycogen - 181How to calculate BMI?Weight kg / Height ^2 m
- 182How long can glycogen stores last?12 hours
- 183How long can lipid stores last?3 months
- 184When is tissue protein used as a source of energy supply?During prolonged starvation
- 185What fuels are used by the brain and muscles?Brain: glucose and ketone bodies
muscles: glucose, ketone bodies (in starvation), triaglycerol and alcohol - 186What fuels are used by the liver?Amino acids, fatty acids, glucose and alcohol
NOTE ketone bodies are not used by the liver although they are produced there - 187What fuels are used by the kidneys?Cortex - glucose and ketone bodies
Medulla - glucose only - 188What fuels are used by the small intestine?Ketone bodies (mainly in starvation)
Glutamine (amino acid) - 189What fuels are used by the large intestine?Short chain fatty acids
Glutamine - 190What is the basal metabolic rate?Minimum amount of energy required to keep the body alive
Informações
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- PHASE 1 MED (Gastrointestinal and the Liver ) FlashCards sobre Gastrointestinal , criado por Erin Dunn em 11-03-2019.
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- Erin Dunn
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