Digestive 2 Flashcards
What are the main functions of the digestive system?
Digestion, secretion, absorption, and motility
What are the two main parts of the digestive system?
Gastrointestinal (GI) tract and accessory organs
List the layers of the alimentary canal wall.
Mucosa, submucosa, muscularis externa, and serosa/adventitia
What does the mucosa layer consist of?
Epithelium, lamina propria, and muscularis mucosae
What is the enteric nervous system (ENS)?
A network of neurons in the GI tract that controls gut function independently
What controls salivary secretion?
Parasympathetic and sympathetic nervous systems
What are the components of saliva and their functions?
Water (moistening), mucins (lubrication), α-amylase (starch digestion), lysozyme (antibacterial)
How is chewing controlled?
Both voluntary via somatic nerves and reflex via mechanoreceptors in the mouth
What are the functions of the stomach?
Storage, digestion, sterilisation, controlled delivery to small intestine, intrinsic factor production
What are the three phases of swallowing?
Oral (voluntary), pharyngeal (reflex), oesophageal (peristalsis)
What triggers receptive relaxation in the stomach?
Relaxation of the lower oesophageal sphincter and entry of bolus
What cells are found in gastric glands and what do they secrete?
Parietal (HCl, intrinsic factor), Chief (pepsinogen), Mucous neck cells (mucus)
What enzyme is involved in HCl secretion in the stomach?
Carbonic anhydrase
What is the role of intrinsic factor?
Binds vitamin B12 for absorption in the ileum; deficiency causes pernicious anaemia
What are the three phases of gastric acid secretion?
Cephalic, gastric, and intestinal
What stimulates gastric acid secretion?
Vagal reflexes, gastrin, histamine (neurocrine, endocrine, paracrine mechanisms)
What inhibits gastric acid secretion?
Enterogastric reflex, secretin, GIP, high acid or fat in duodenum
What is the role of gastric mucus?
Protects stomach lining from acid and pepsin
How does peristalsis differ between the stomach body and antrum?
Body: weak contractions; Antrum: strong contractions for mixing and propulsion
What is the function of Brunner’s glands?
Secrete bicarbonate to neutralise acid in the duodenum
What is the function of secretin?
Stimulates HCO3- secretion from the pancreas and liver in response to duodenal acid
What are the three parts of the small intestine and their main functions?
Duodenum (neutralisation, digestion, iron), Jejunum (nutrient absorption), Ileum (NaCl/H2O absorption)
How is the absorptive surface area of the small intestine increased?
By circular folds, villi, and microvilli
What do villus and crypt cells absorb and secrete?
Villus: absorb nutrients; Crypt: secrete Cl- and water
What enzymes digest disaccharides at the brush border?
Lactase, sucrase, maltase
What is the difference between starch and cellulose?
Starch: α-1,4 bonds (digestible), Cellulose: β-1,4 bonds (indigestible without bacteria)
How are glucose and galactose absorbed in the intestine?
Via SGLT1 (Na+-dependent transporter)
How is fructose absorbed?
Via GLUT-5 and GLUT-2 transporters
What enzymes digest proteins?
Proteases/peptidases
How are amino acids absorbed?
Na+-dependent transporters like SAAT1
How are di/tripeptides absorbed?
Via H+-dependent PepT1 transporter
What generates gastric peristaltic waves?
Pacemaker cells in longitudinal muscle layer producing slow waves (BER)
What are the two types of small intestine movement?
Segmentation and peristalsis
What initiates segmentation?
BER from pacemaker cells in longitudinal muscle
What is the migrating motility complex (MMC)?
Peristaltic activity moving undigested material to large intestine
What hormone initiates MMC?
Motilin
What is the gastroileal reflex?
Gastric emptying → increased ileal motility → opening of ileocaecal valve
What are haustra?
Pouches formed by contractions of teniae coli in the colon
What is the role of the large intestine?
Water absorption, forming faeces, housing microbiota, fermentation
What is the defaecation reflex?
Rectal distension → reflex contraction → relaxation of internal sphincter, external under voluntary control
