Gastro-intestinal system Flashcards
1
Q
What are the organs occupying the anterior part of the abdominal and pelvic cavities?
A
- diaphragm
- right liver lobe
- gall bladder
- part of omentum
- ascending colon
- caecum
- appendix
- stomach
- spleen
- transverse colon
- descending colon
- small intestine
2
Q
What are the organs occupying the posterior part of abdominal and pelvic cavities?
A
- inferior surface of diaphragm
- inferior vena cava
- aorta
- adrenal gland
- right and left kidney
- pancreas
- duodenum
- ascending colon
- caecum
- appendix
- rectum
- oesophagus
- spleen
- splenic artery
- ureter
- vertebral column
- descending colon
- sigmoid colon
3
Q
What are the functions of the GI tract?
A
-
ingestion: taking food into mouth
2.** secretion**: within the walls of the GI tract and accessory digestive organs - mastication: chewing food and mixing with saliva
- digestion: mechanical & chemical breakdown of food
- peristals: wave like contractions moving through GI
- absorption: passage of digested food from GI into CVS
4
Q
Mouth (oral cavity)
A
- entrance to GI system
- formed by cheeks, hard and soft palates and tongue
- lined with mucuous membrane which consists of stratified squamous epithelium containing mucus-secreting glands
- epithelium on gums hard palate and dorsum of tongue slightly keratinised.
5
Q
Lips and cheeks
A
- core of skeletal muscle covered externally by skin
- helps keep food between the teeth when we chew
- plays a role in speech
- much larger than people think
- extend from the inferior margin of the nose to the superior boundary of the chin
6
Q
The palate
A
- forming the roof of the mouth
- has two distinct parts: hard and soft palate
7
Q
Difference between hard and soft palate
A
- hard palate: forms rigid surface against which food is forced during chewing
- soft palate: rises reflexively to close off nasopharynx when we swallow
8
Q
Tongue
A
- voluntary muscle which occupies the floor of the mouth
- superior surface consists of epithelium with papillae
- contain the taste buds
- functions are chewing, swallowing, speech, taste
9
Q
Salivary glands
A
- 3 pairs
- saliva consists of secretions from salivary glands and mucus
- contains enzymes to help breakdown sugars
- about 1.5L of saliva produced daily
10
Q
Control of salivation
A
- the intrinsic salivary glands produce saliva and just enough to keep mouth moist
- when food enters the mouth the extrinsic glands are activated producing copious amounts of saliva (1000-1500mls per day)
- salivation controlled by thr parasympathetic ANS
11
Q
Digestion in the mouth
A
- when we eat we chew our food with teeth
- through chewing the tongue manipulates the food and the teeth grind and the food is mixed with saliva
- as a result the food is reduced to a soft mass called a bolus that is easily swallowed
12
Q
Chemical digestion in the mouth
A
- digestion of food begins in the mouth
- saliva contains the enzyme salivary amylase which begins the breakdown of sugars
- the sugar molecules can only be absorbed if broken down into smaller units
- digestion continues as food is swallowed
13
Q
3 stages of swallowing
A
1.** voluntary stage: mouth is closed and voluntary muscles of tongue and cheek push bolus into pharynx
2. pharyngeal stage**: bolus stimulates receptors in oropharynx sends message to swallowing centre in medulla which causes airway passage to close
3. oesophageal stage: bolus in pharynx stimulates wave of peristals which propels food into stomach
14
Q
Control of swallowing
A
- swallowing centre in lower pons and medulla oblongta
- afferent messages transmitted via X cranial nerve
- effectiveswallowing also requires intact voluntary control of tongue lips and cheeks
15
Q
The oesophagus
A
- means to carry food
- muscular tube 25cm long
- collapsed when not involved in food propulsion
- unlike mouth and pharynx oesophagus has all 4 basic layers of the alimentary canal
16
Q
The peritoneum
A
- largest serous membrane of the body
- closed sac containing serous fluid within the abdominal cavity
- richly supplied by blood and lymph vessels
- provides barrier to local spread of infection
17
Q
Anatomy of the gut wall
A
- serosa outer covering
- muscle layer
- sub mucosa
- mucosa lining
18
Q
serosa
A
- visceral peritoneum
- outermost layer
- wraps around gut like cling film
- attach gut to anchor pounts
- houses blood and nerve supply to gut between two layers of peritoneum
19
Q
muscle layer
A
- provides the gut with the ability to move food along the length
- three thock layers of smooth muscle: oblique, circular, and longitudinal
- squeeze and shorten allowing the stomach to chrun the bolus
20
Q
submucosa
A
- external to the mucosa
- moderately dense connective tissue
- extensive vascular network
21
Q
mucosa
A
- inner most layer
- moist epithelial membrane
- secretion, absorption, protetion 3 major functions
- 3 sub layers: lining epithelium, lamina propria, muscularis mucosa
22
Q
muscle fibres of the stomach muscle
A
- oesophagus
- oblique fibres
- circular fibres
- longitudinal fibres
23
Q
chemical digestion
A
- after a meal accumulates in the stomach in layers it gradually mixes with gastric juice
- about 2L gastric juice secreted everyday
24
Q
mechanical digestion
A
- when food enters the stomach gentle peristalic waves pass over the stomach
- mixing waves macerate food mix with gastric juice and reduce to a liquid called chyme
- stomach contents propelled towards the pylorus in waves
- contents are forced into duodenum
25
gastric juice secretion
- small quantity of gastric juice present in stomach even when it contains no food
- 3 overlapping phases of secretion of gastric juice: cephalic, gastric, intestinal
26
Gastric juice- cephalic juice
- the flow of juice commences before food reaches stomach
- initiated by reflex simulation of the vagus nerve by the sight smell or taste of food
- sympathetic stimulation e.g. during stress can inhibit the release of gastric juice in this phase
27
Gastric phase
- when stimulated by the presence of food the enteroendocrine cells in the pyloric atrium secrete gastrin into the blood stream
- circulating gastrin reaches the stomach and stimulates the gastric glands to produce more juice.
- gastrin secretion is suppressed when the Ph in the pyloric atrium falls to 1.5
28
Gastric juice- intestinal phase
- occurs when partially digested contets of the stomach reach the small intestine
- once they reach the duodendum there is a release of hormone complex enterogastrone
- CCK slows down secretion of gastric jucie and reduces gastric mobility
- secretin inhibits secretion of gastric juice
- stimulates secretion of pancreatic juice and bile
29
absorption in the stomach
- stomach wall is impermeable to the passage of the most substances into blood
- substances which are absorbed are water, ions, certain drugs, alcohol
30
small intestine
- extends from pyloric sphincter of stomach to the large intestine at the ileocaceal valve
- about 5cm long and lies in the abdominal cavity surrounded by large intestine
- comprised: duodenum, jejunum, ileum
31
functions of the small intestine
- onward movement of contents from stomach by peristalsis
- secretion of intestinal juice
- secretion of hormones: CCK and secretin
- complete chemical digestion of carbs, proteins and fats
- protectiom against infection by microbes
- absorb 90% of nutrients
32
villus in the small intestine
- tiny finger like projections into the intestinal lumen
- about 0.5-1mm long
- walls consist of enterocytes and inside villi
33
microvilli
- also called the brush border
- greatly increase surface area
- make several digestive enzymes ans store them in their plasma membrane
- called brush border enzymes
34
intestinal juice
- 1500ml per day
- alkaline ph 7.8-8
- mechanical stimulation of the intestinal glands by chyme the hormone secretin may also be involved
- the hormone secretin may also be involved
- prinicpal constitutes: water, mucus, mineral salts
35
digestive hormones
- the presence of acid chyme from the stomach stimulates the production of secretin, cholecystokinin
- they stimulate the secretion of pancreatic juice and bile
36
exocrine function of the pancreas
- pancreas is a dual purpose organ
- endocrine: produces hormones that regulates carbohydrates metabolism and enter directly into the blood stream
- exocrine: produces digestive enzymes
37
exocrine function- pancreatic juice
- 1-1.5L pancreatic juice daily
- clear alkaline fluid high in biocarbonate
- pH: 7.1-8.2
- neutralises stomach chyme
- optimise pH for pancreatic and intestinal enzyme activity
- contains enzymes aiding the digestion of all food categories
38
pancreatic juice
- biocarbonate: neutralises acid chyme
- amylase: continues polusaccharide digestion to disaccharides
- lipase: triglycerides to fatty acids & monoglycerides
- proteases: protein digestion
39
absorption
- digested food absorption via the villi
- absoption of nutrients takes places by diffusion and active transport
- monosaccharides and amino acids pass into the capillaries
- fatty acids and glycerol pass into the lacteals
40
absoroption in small bowel
specific areas of are associated with the absorption of particular nutrients
most absorption takes place in jejunum and ileum
41
neoplasm
- a new growth which is abnormal, disorganised growth in a tissue or oragn
- such a growth is called a neoplasm also known as a tumor
- neoplasia is the correct term for diseases commonly called cancer, tumour growth
42
anatomy
- terminal portion of GI tract and is divided into four regions: caecum, colon, rectum, anal canal
- 1.5m long, 6.5cm diameter
43
ileocaecal sphincter
- ileum opens into large intestine
- gaurded by mucous membrane
- allows material to pass from small intestine
- inferior to the sphincter is the caecum
44
functions of large intestine
completion of absorption
production of certain vitamins
formation of faeces
expulsion of faeces
45
Histology
- epithelium of large intestine contains mostly absorptive and goblet cells
- absorptive cells: water
- goblet cells: mucous
- contains both longitudinal and circular muscle
- contraction of these bands gather the colon into pouches which gives the organ its puckered appearance (**haustra**)
46
Defecation reflex
- distention of rectal wall
- receptors send sensory nerve impulses to spinal cord
- motor impulses from the cord travel along the parasympathetic nerves back to descending, sigmoid colon, rectum and anus
- contraction of rectal muscles occurs shortening and increasing pressure in rectum
- this pressure along with other movements and stimulation open the internal sphincter
- external sphincter is voluntary controlled
