Digestive System: Structure and Function Flashcards
1
Q
Describe the alimentary tract.
A
- Tube extending from mouth to the anus
- Muscular tube structure lined internally by epithelium
2
Q
What is the function of the alimentary tract?
A
*Ingestion
*Processing
*Digestion
*Absorption
*Excretion
3
Q
Describe the epithelium of mucosa membrane.
A
- Type of epithelium differs with tissue function
- Moistened by glandular secretions
4
Q
Describe the lamina propria.
A
- Loose connective tissue
- Small blood vessels, lymphatics, nerve fibres
- Immune cells e.g. macrophages and lymphocytes
5
Q
Describe the muscularis mucosa
A
- Thin muscle layer
6
Q
What is the submucosa?
A
- 2nd layer of loose connective tissue
- Between mucosa and main muscle layers
- Blood vessels, lymphatics, nerves
- Neural tissue - submucosal plexus
7
Q
What Is the function of the submucosal plexus?
A
- Regulates contraction and glandular secretions
8
Q
What is the muscularis externa and how is it divided?
A
- Smooth muscle divided into two differentially orientated layers: inner circular layer and outer longitudinal layer
9
Q
How is the muscularis externa arranged?
A
- In layers which orientate in different directions; contractions propel materials along tract
10
Q
Where is the second nerve plexus located?
A
Between muscle layers - myenteric plexus
11
Q
What is outside of muscularis externa?
A
- Adventitia and/or serosa
12
Q
What is the alimentary canal suspended in and covered in and what does this allow?
A
- Alimentary canal suspended in peritoneal cavity, covered in SEROSA
- delimits adventitia from peritoneal cavity, allowing movement
13
Q
What is the retroperitoneal organs covered in and what does this allow?
A
- Retroperitoneal organs are covered in ADVENTITIA but NO SEROSA
- holds organ structures together
14
Q
What is the oral cavity?
A
- Cavity lined by stratified squamous epithelium
- Ingestion and fragmentation of food
- Salivary glands
15
Q
Where are the small salivary glands located?
A
- in submucosa of oral cavity and tongue
16
Q
What are the three main groups of the large salivary glands?
A
Sublingual: beneath tongue, many ducts
Submandibular: floor of mouth, inner surface of mandible, ducts behind teeth
Parotid : Largest, empties at the 2nd Molar
16
Q
What are the three ways of administering drugs (oral activity)?
A
- Oral
- Sublingual
- Buccal
17
Q
Describe oral drug administration.
A
- Given by mouth and swallowed
- Easiest and safest method but slow absorption
18
Q
Describe sublingual drug administration.
A
- Placed under the tongue – dissolves in saliva
- Rapid absorption, higher circulating levels
- Not for bad-tasting or irritating medications
19
Q
Describe buccal drug administration.
A
- Placed in mouth next to cheek (tablet form)
- Rapid absorption, higher circulating levels
- Disadvantage -Possibility of swallowing the pill
20
Q
Describe the structure and function of the oesophagus.
A
- ~25cm long, through diaphragm to stomach
- Contracts rhythmically toward stomach
- Lower oesophageal sphincter: Prevents reflux,
emesis and regurgitation
21
Q
Describe the structure of the mucosa of the oesaphagus.
A
- Above diaphragm: stratified squamous epithelium
- Below diaphragm (~2cm) oesophagogastric
junction: columnar epithelium - Defined lamina propria and muscularis mucosae
22
Q
Describe the structure of the muscalaris externa of the oesphagus.
A
- Striated muscle in upper one third
- Mixture of striated and smooth muscle in middle
- Smooth muscle lower one third
23
Q
What is the lower digestive tract composed of?
A
- Stomach
- Small intestine (Duodenum, Jejunum, ileum)
- Large intestine (Caecum, appendix, colon, rectum)
- Many epithelial cell types - both absorptive & secretory
24
How is the efficiency of absorption improved?
By increasing surface area od contact between epithelia and lumen
– Intrusions/folding of epithelium (villi or plicae)
– Inversions (tubular structures), the lumen of which communicate with
main lumen
– Formation complex glands
25
What are the functions of the stomach?
* Reservoir and Digestion
* Mixes food with gastric juices to form a semifluid mass called chyme
* Initiates protein breakdown and absorption of vitamin B12: release of
intrinsic factor
* Low absorption of nutrients or drugs
* Highly lipid-soluble substances e.g. alcohol and some drugs absorbed
26
State the 4 anatomical regions of the stomach.
– CARDIA (closest to heart)
– FUNDUS (upper area)
– BODY (middle portion)
– PYLORUS (narrow bottom)
27
Describe the structure of the gastric mucosa.
* Columnar epithelium
* Mucosa folded (Folds = RUGAE): Disappear when stomach distended
* Shallow depressions on surface (GASTRIC PITS)
* Entire mucosa has simple tubular gastric glands – open into gastric pits
28
What do the cardiac glands produce?
* Mucus producing glands - providing alkaline layer
29
What are the 4 cell types for corpus-fundic glands?
- Chief cells - pepsinogen, gastric lipase, chymosin
- Parietal cells - gastric (hydrochloric) acid secreting and release intrinsic factor
- Mucous neck cells
- Endocrine - stimulate secretion of other cell types
30
What is the pyloric gland made up of?
Endocrine cells more frequent, no chief cells
31
What is achlorhydria?
- Lack of gastric acid stomach
32
What is dyspepsia?
- Difficulty digesting food
33
What is gastritis?
Stomach inflammation
34
What is gastroenteritis?
Inflammation of stomach and small intestine
35
What is haematemesis?
Vomiting of blood
36
What is hiatal hernia?
Potrusion of the stomach through opening in diaphragm
37
What are the three subdivisions of the small intestine?
- Duodenum
- Jejunum
- Ileum
38
What is the plicae?
- folds of mucosa and submucosa (increase area x3)
– Permanent structures (not distension dependent)
– Absent from start of duodenum and distal ileum
39
What is the intestinal villi?
– entire intestinal mucosa
– Increase surface area by x10
– Main cell type – Enterocyte- absorptive function
40
What are microvilli?
- Enterocytes, increase area by x20
41
Describe the function of structure of tubular glands?
- From base of villi through lamina propria to muscularis mucosae
– Secretion of “intestinal juice”
– Paneth cells at base of crypt – secretion, control of infection
42
What is the function of goblet cells?
Secretion
43
Describe absorption from small intestine.
* Rich blood supply and large absorption area
* Almost all digestion of protein, fat and carbohydrate
* Most drug absorption occurs in the upper portion of the small intestine
* Secretin released upon appearance of chyme in small intestine, stimulates release
of bicarbonate (pancreas) to neutralise chyme
44
Describe absorption in duodenum.
– Carbohydrates are broken down into simple sugars, proteins are broken down
– Fat emulsified by bile salts, broken down into free fatty acids and monoglyceride
by pancreatic lipase. Form micelles, which are absorbed;
– Most minerals (excl. Na+, K+ and Cl-) absorbed
45
Describe absorption from jejunum.
– mono-saccharides, amino acids absorbed
– water-soluble vitamins (into bloodstream) fat-soluble vitamins (into lymph)
46
Describe absorption in the ileum.
– Bile salts are reabsorbed
– Vitamin B12 absorption
47
Describe the structure of the large intestine.
* Surface relatively smooth – no plicae or villi
* Crypts of Lieberkuhn – present and longer than Small Intestine
* Goblet (mucous) cells more numerous than Small Intestine
48
What are the main sections of the large intestine?
– CAECUM (including appendix)
* Appendix - large levels of lymphoid tissue
– COLON: Ascending, Transverse, Descending, Sigmoid
– RECTUM (including anal canal)
49
What is the large intestine primarily involved in?
* Absorption of fluids and electrolytes (Na+ , Cl- )
* Secretion of electrolytes (K+ and HCO 3-) and mucus
* Bacteria synthesize vitamin K and some B vitamins
* Peristalsis slow and irregular
* Formation, storage and periodic elimination of faeces
50
What is defecation?
* Faeces enters rectum
* Rectum distends, stimulating mass peristalsis
* Levator ani muscle relaxes
* Internal and external sphincter muscles relax
* Anus is pulled up and over faecal mass
* Faecal mass is expelled
51
Describe the absorption of water in GI tract.
* Absorption of water is a passive process
driven by the transport of solutes
(particularly Na+) from the lumen of the
intestines to the bloodstream
* Water ingested and secreted is normally in
balance with water absorbed
52
State the 6 medications for digestive system and their function.
* Antacid- Neutralises stomach acid
* Antidiarrheal - Controls loose stools
* Antispasmodic - Calms GI spasms
* Antiemetic - Prevents regurgitation
* Cathartic - Causes vomiting, or relieves constipation
* Laxative - Relieves constipation
53
What is the pancreas and state its functions?
* Pink/Grey organ with no distinct capsule,
* Retroperitoneal
* Exocrine and Endocrine Functionality
54
Describe the endrocrine functions of the pancreas.
- islets produce and secrete insulin, glucagon, somatostatin
55
Describe the exocrine functions of the pancreas.
- Glandular secretion
- Digestive enzymes; Trypsin/Chymotrypsin/Carboxypeptidase
Pancreatic amylase and pancreatic lipases
56
What are the 4 main cell types of the endocrine pancreas and describe them?
* β -cells which secrete insulin (70%)
– Stimulates glycogen, protein and fatty acid synthesis
– Facilitates glucose uptake, lowers blood glucose
* α-cells which secrete glucagon (20%)
– Generally opposite to insulin, raises blood glucose
* δ-cells which secrete somatostatin (5%)
– Locally acting hormone, inhibits other endocrine cells
* PP/F cells which secrete pancreatic polypeptide (2%)
– Stimulates gastric chief cells, inhibits bile secretion
– Inhibits pancreatic exocrine function
57
What is the ductal system?
Acini duct - interlobular duct - intercalated duct - pancreatic duct
58
How is glucagon secreted and what is its function?
* Secreted by α-cells of endocrine pancreas
* Prevents hypoglycaemia by elevating blood glucose levels
* promotes glycogenolysis & gluconeogenesis
59
What is glucagon stimulated and inhibited by?
* Stimulated by cholinergic system, β-sympathetic fibres
* Inhibited by glucose, insulin, somatostatin, α-sympathetic system
60
How is insulin synthesised ad what does it do?
* Synthesized in the β-cells of the islets of Langerhans
* Direct effects upon carbohydrate, fat and protein metabolism
61
How is insulin degraded and what is cellular activity controlled by?
- By insulinase primarily in liver
- By insulin receptors
62
What does low glucose level lead to?
Decreased brain activity (glucose only fuel source)
63
What does high glucose level lead do?
Osmotic water loss, damaged blood vessels, organ dysfunction etc.
64
Where is somatostatin secreted?
- by the δ-cells
65
What does the secretion of somatostatin lead to?
* Increased blood glucose
* Increased blood amino acids
* Increased blood fatty acids
* Increased concentrations of upper GI hormones (Gastrin, Secretin, CCK, VIP)
released in response to food intake
66
What are the actions of somatostatin?
* Acts locally within endocrine pancreas to depress insulin and glucagon
secretion
* Paracrine with glucagon to regulate insulin secretion
* Decreases GI tract secretions and absorption
* Decreased gastric, duodenal and gallbladder motility
