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Flashcards in The digestive system Deck (33):
1

Processes of the GI tract

motility, secretion, digestion and absorption

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Mucosa tissue layer

Innermost layer - lines luminal surface and tightly folded.
Mucous membrane: serves as a protective surface, secretes and absorbs, contains exocrine gland cells, endocrine gland cells and epithelial cells.
Lamina propria: houses gut-associated lymphoid tissue (GALT) = defence against disease
Muscularis mucose: smooth layer of muscle

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Submucosa tissue layer

Thick layer of connective tissue giving distensibility and elasticity. Contains larger blood and lymph vessels and a nerve network

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Muscular externa tissue layer

Major smooth muscle coat of the digestive tube. Has a circular inner layer in which contraction decreases the diameter of the lumen, and a longitudinal outer layer in which contraction shortens the tube. Produces propulsive and mixing movements.

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Serosa tissue layer

Secretes serous fluid to lubricate and prevent friction between digestive organs and surrounding viscera. Is continuous with mesentery throughout the tract - attachment provides relative fixation, supports digestive organs in place

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Enteric nervous innervation

Intrinsic - myenteric plexus and sub mucous plexus. Interconnected motor, secretory and sensory neurons

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Extrinsic nervous innervation

Autonomic - parasympathetic increases activity and sympathetic decreases
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Salivary glands

3 pairs; secrete salt, water, mucus, amylase. pH rises as secretion increases as bicarbonate ions not absorbed as fast

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Tongue

Secretes lingual lipids, IgA, lysozyme

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Stomach

Secretes HCl, pepsin, music, HCO3- to stabilise food, protein digestion and protection

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Pancreas

Secretes many enzymes, HCO3- to digest fats, CHO3, protease and neutralise chyme

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Liver

Secretes bile salts, HCO3- and waste products to solubilise fats, adjust pH and remove toxic material

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Gall bladder

Stores and concentrated bile used in fat digestion

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Small intestine

Secretes enzymes, salt, water and mucous for digestion and to maintain fluidity of contents

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Carbohydrate

Salivary/pancreatic amylase hydrolyses 1:4 alpha link --> oligosaccharides --> monosaccharides. Absorbed by active co-transport with Na+ and facilitated diffusion into capillary

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Proteins

Pepsin in stomach hydrolyses various size aromatic AA-PPs. Small intestine endopeptidases, exopeptidase and dipeptidase. Absorbed by transcytosis or co-transport with Na+.

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Fats

Lingual lipase digests up to 30% triglyceride, duodenum = pancreatic lipase - triglyceride --> monoglyceride + 2FAs. Fats aid digestion by forming large liquid droplets, lipases are water double and emulsification. To speed up, micelles form due to bile salts much smaller than emulsion droplets.

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Sodium, Cl- and HCO3- absorption

Follow Na+ => absorbed with glucose

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Water absorption

Passive, follows solutes to maintain osmotic equilibrium

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Vitamin absorption

Fat soluble with fats, water soluble by diffusion/mediated transport. B12 bind to intrinsic factor and then specific sites on epithelial cells of ileum by endocytosis

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GI control systems respond to...

distention of walls by luminal contents, chyme osmolality, chyme acidity, conc of specific digestive products

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Types of GI control systems

Neural - autonomic
Enteric - stomach
Hormonal - endocrine
Paracrine - local
Local muscle response

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Long and short reflects and stimuli outside GI tract

Sub mucous plexus endocrine and exocrine secretions, myenteric plexus control of peristaltic activity, interconnections between the two, neural info to and from tract

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Hormonal control of the GI tracts

Cells in GI epithelium, receptors on surface in contact with luminal content, hormones released into interstitial fluid - endocrine action via blood and paracrine action via luminal content, each hormone subject to -ve feedback. Hormones together produce a bigger effect

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Phases of GI control

Cephalic - receptors in head, efferent pathway, primarily neural
Gastric - receptors in stomach (vol), efferent pathway, neural, long and short reflexes, hormonal
Intestinal - receptors in intestine (vol), efferent pathway, neural, long and short reflexes, hormonal

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Mouth

Mastication - somatic nerves to skeletal muscle, voluntary control, reflex in gyms and hard palate
Saliva secretion
Swallowing - complex reflex

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Oesophagus

Peristalsis. upper 1/3 skeletal, lower 1/3 smooth. Skeletal and autonomic nerves, secondary peristalsis = afferent/efferent pathway. Food bolus moves in one direction

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Stomach gastric motility

Filling involves receptive relaxation - extra volume of food with little rise in pressure, mediated by vagus nerve.
Storage in body, mixing in antrum
Emptying controlled by factors n duodenum and stomach (vol chyme). Either neural or autonomic nerves

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Stomach gastric secretory activity

2 regions of gastric mucosa secrete gastric juice - oxyntic mucosa and pyloric gland area. Gastric pits at base of gastric glands. 3 types of gastric exocrine cells: mucous, chief and parietal
Hal stomach secretion bu parietal
Pepsinogen stimulated by nerves
Control of Hal during a meal: cephalic (sight etc in HCl), gastric (distention etc in HCl), intestinal (dec HCl)
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Bile secretion

HCO3- by epithelial cells of bile duct stimulate by secretion
Bile salts by rate of secretion, storage of bile in gall bladder, CCK

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SI motility

Mixing, decreased frequency of segmentation from duodenum to ileum, slow forward movement of chyme, force affected by hormonal and neural influences, gastro-ileac reflex increases segmentation, migrating motility complex, short peristaltic waves, contents moved to LI in 2hrs

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LI motility

Ilocecal sphincter relaxed by gastroileal reflex - chyme moves in to LI, reflux prevented by closure of ilocecal spinchter, enteric NS, LI segmentation, mass movement 3-4 times a day

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Defection

Anus - internal anal sphincter (smooth) abd external sphincter (skeletal), neural control, voluntary modification
Rectal distention - defecation reflex: internal s relaxes, external contracts, inc peristalsis in sigmoid colon, inc rectal pressure, external s relocation