digestive system Flashcards
functions of digestive system (6)
- ingestion
- mechanical digestion and propulsion
- chemical digestion
- secretion
- absorption
- defecation
digestive organs part of digestive tract
mouth, pharynx, oesophagus, stomach, small intestine, large intestine
mouth
ingestion, start of mechanical digestion with teeth and tongue, moistening, mixing with salivary glands
pharynx
muscular propulsion of materials into the esophagus
esophagus
transport materials to stomach
stomach
chemical digestion with acids and enzymes, mechanical digestion by muscular contraction
large intestine
dehydration and compaction of indigestible material in preparation for elimination
accessory organs
teeth, tongue, salivary glands, liver, gall bladder, pancreas
mesenteries
-two sheets of serous membrane
- tissue between sheets
-nerve, blood and lymphatic supply
-stabilises and attaches digestive organs to the peritoneal cavity and stops the organs from entangling
Histological organisation
4 layers
-mucosa
-submucosa
-muscular layer
-serosa
layers of mucosa layer
-mucosal/digestive epithelium
-lamina proper
-muscularis mucosae
digestive epithelium (2 types)
- stratified squamous
-oral cavity, pharynx and oesophagus
-mechanical stresses - simple columnar
-stomach, intestines
-absorption
BOTH: PROTECTION AGAINST
-digestive acids and enzymes
-mechanical stresses, such as abrasion
-bacteria are ingested with food and reside in the digestive tract
what is lamina proper?
areolar tissue containing
-blood and lymphatic vessels
-sensory nerve endings
-lymphoid tissue
4 types of specialized epithelial cells
-stem cells (cell renewal)
-enteroendocrine cells (secrete hormones)
-goblet cells (secrete mucous)
-panteth’s cells (secrete antimicrobial peptides)
submucosa
-dense, irregular connective tissue
-large blood vessels and lymphatic vessels
-may contain exocrine glands that secrete buffers and enzymes in the digestive tract
submucosal plexus
-nerve plexus
-innervates the mucosa and submucosa
-sensory neurons, parasympathetic neurons and parasympathetic neurons
muscular layer (muscularis externa)
-two big layers of smooth muscle cells
-arranged in an inner circular layer and an outer longitudinal layer
-involved in mechanical processing and movement of materials along the digestive tract
-movements are coordinated by enteric nervous system, (ENS) and primarily innervated by the parasympathetic division of the ANS.
serosa
-serous membrane covering the muscularis externa
-attaches to mesentery
-not in the oral cavity, rectum and oesophagus, which have adventitia instead
digestive movement
-contraction and relaxation of smooth muscle
-mixes substances and propels content forward
-pacesetter cells have s spontaneous depolarisation that triggers a wave of contracting spreading through the entire muscular sheet
peristalsis
-wave like contractions
-circular muscles push contents forward
-longitudinal muscles shorten tract
segmentation
-mixing and churning
-fragments bolus
-non directional
-mix with intestinal secretions
regulation of digestive tract
-receptors detect change
-processing/control centre = nerves and glands
-effectors = smooth muscle and exocrine glands
stomach
-3 layers of smooth muscle and rugae
-storage and mixing chamber
-mechanical digestion
-chemical digestion (HCl, pepsinogen and gastric lipase)
secretory cells from gastric glands
-mucous cells
-parietal cells
-chef cells
-g cells
regulation of gastric activity (3 phases)
- cephalic phase
-see, smell, think about food
-CNS sends signals to submucosal plexus (vagus nerve)
-increased gastric secretions and motility - gastric phase
- food arrives at stomach
-triggers stretch and chemo-receptors
-increased secretions and gastric motility - intestinal phase
-when chyme enters duodenum
-controls the rate of chyme exiting stomach to maintain efficiency of small intestine
- increased intestinal secretion of secretin, CCK and GIP which all reduce gastric secretions and emptying.
hormonal control of food intake
- ghrelin
-appetite stimulant
- tells body it is ready for a meal - leptin
-appetite suppressant
-secreted by adipose tissue when fat stores increase
-acts by inhibiting the appetite stimulant NPY
3.Insulin and CCK
-released during food absorption
-signals feelings of fullness to depress hunger
vomiting reflex steps (6)
- deep inspiration + closure of the glottis
- contraction of diaphragm and abs, compressing stomach
- gastric contents forced out through gastroesophageal sphincter
- esophagus pushes contents back down to stomach
- cycle repeats - retching
- pressure in esophagus increases.
small intestine
-main site of digestion and absorption of nutrients
3 parts
-duodenum = receives chyme and mixes with bile, neutralises acids
-jejunum = nutrient absorption and end of chemical digestion
-ileum = nutrient absorption
small intestinal movement
-contraction and relaxation of smooth muscle
-weak peristaltic contractions, slow propulsion of bolus
-absorption made more efficient by allowing contact with villi
pancreas function
-controlled by duodenal hormones
pancreatic secretions:
- water, salts, and buffers
-enzymes to digest carbs. proteins, trigycerides and DNA and RNA
4 lobes of the liver
-right lobe
-left lobe
-caudate lobe
-quadrate lobe
liver function (3)
1.metabolic regualtion
-metabolism of carbs, lipids and proteins
-waste removal
-processes drugs
- hematological regulation
-remove bacteria, old blood cells, hormones, antibodies, and toxins
-make plasma and protein s
-activation of vitamin D into vitamin D3 - bile production
-secrete bile into duodenum
-excrete bilirubin
liver lobule structure
-hepatocytes arranged around sinusoids in central vein
-hepatic artery
-hepatic portal circulation
-bile duct
portal triad = interlobular vein, artery, and bile duct
bile
-contains water, ions, bile salts, bilirubin and cholesterol
-digestion of lipids thru emulsification
-increases the surface area of lipids for enzymatic attack and promotes absorption of lipids by epithelium
gall stones
-solifdified cholestrol and bile salts
-TOO CONCENTRATED BILE
-crystalised bile that forms stones in the gall bladder
epidemiology - 5Fs that make you more prone to gallstones
Female
Fair
Forty / Familial
Fertile
Fat
classes of digestive enzymes
-carbohydrases - break carbs into monosaccharides
-proteases / peptidases - break peptide bonds between amino acids
-nucleases - break nucleotides into sugar, phosphate, base
-lipases - break fatty acids from triglycerides
-brush border enzymes - includes some of the above
classes of digestive enzymes
-carbohydrases - break carbs into monosaccharides
-proteases / peptidases - break peptide bonds between amino acids
-nucleases - break nucleotides into sugar, phosphate, base
-lipases - break fatty acids from triglycerides
-brush border enzymes - includes some of the above
absorption of proteins and carbs
moves into the capillaries in villi
- monosacharides
-2nd degree active transport, cotransport with sidum
-faciliated diffusion - amino acids
-1st or 2nd degree active trsport, cotransport with sodium - di and tripeptides
- 2nd degree active transport, cotransport
lipid absorption
- small chain fatty acid
-simple diffusion
-moves into capillaries in villi or into lacteals - long chain fatty acids and monoglycerides combine to form micelles
-lipids diffuse through epithelial cell membrane
-resynthesised into triglycerides in epithelial cells
large intestine
-expands from ileocaecal sphincter to anus
-tonic contraction of 3 longitudinal muscles (TENIAE COLI)
-forms expandable pouches (HAUSTRA)
-epithelial cells absorb water and ions
-goblet cells secrete mucous
3 main divisions of large intestine
-caecum
-colon
-rectum
mechanical digestion in large intestine
-peristalsis slower than small intestine
-haustral churning (segmentation) - allow contact with all material
- mass movement - strong peristaltic wave that drives contents into the rectum immediately when new food enters the stomach
mechanical digestion in large intestine
