Lecture 13 - Digestion and Intestinal Absorption] Flashcards
What are the 3 primary macronutrients that get broken down to produce energy
Carbohydrates
Fats
Protein
What are the sections of the gastrointestinal tract
Mouth
* Pharynx
* Oesophagus
* Stomach
* Small Intestine
* Large Intestine
What are accessory organs Salivary Glands
Salivary Glands
* Liver
* Gallbladder
* Exocrine Pancreas
What are the layers to a gastrointestinal wall
Lumen
Mucosa
Submucosa
Muscular externa
Serosa
Enteric Nervous System
What makes up the mucosa
Mucous membrane
Lamina Propria
muscuoaris Mucosae
What are parts of the muscular externa
Circular muscle
Longitudinal muscle
What are the parts of the enteric nervous system
Submucosal plexus
Myenteric plexus
What is laminate propia
Loose connective tissue in the GIW
What does the muscularis mucosa do
Layer of smooth muscle
What do epithelium do in the mucosa in the GIW
Contain both endocrine and exocrine cells
what are in the submucosa
Blood and lymphatic vessels– Penetrate the layers above
and below
Submucosal Plexus– A network of neurons for control of
muscular activity
what are the functions of the composites of the muscular externa
Circular muscle– Contraction produces narrowing of lumen
Myenteric plexus– Innervated from autonomic nervous system,
also connected to submucosal plexus
Longitudinal muscle – Contraction shortens the tract
What does the serosa do
Connective tissue surrounding outer surface of the tract
Sheets of connective tissue connect serosa to the abdominal wall
and hold GI tract in place
What is the Cephalic phase
Brain’s anticipation of food:
sight, smell or thought
Saliva production increases - parasympathetic
nervous system activity
Stimulation of gastric juice secretion & insulin
secretion
What does the mouth do
Mechanical breakdown of food
Mixing of food with saliva
Initiate chemical digestion of carbohydrates (salivary
amylase)
Antibacterial action
What does saliva do
Bicarbonate – neutralise acid
Mucus – lubricates & protects from abrasion
Salivary amylase – breakdown CHO
Lysozyme – destroys certain bacteria (prevent tooth
decay)
What does Salivary amylase do
Begins CHO digestion
Starts starch hydrolysis
Limited: <5% of starch digestion…
…unless chewing is prolonged
What does the pharynx do
Conducts food into the oesophagus
What does the oesophagus do
Conducts food into the stomach
What do the epiglottis do
closes to prevent aspiration into trachea
What do the sphincters at the bottom of the pharynx do
Sphincters at bottom of Pharynx and opening to
stomach prevent movement of air and stomach
contents entering oesophagus
What is peristalsis
Food moves towards stomach due to
progressive muscular contraction
This “wave” compresses the lumen
and forces food along
If a particularly large bolus does not
reach the stomach then reflexes
initiate repeated waves of activity
Known as ”secondary peristalsis”
What are the parts of the small intestine
Duodenum
Jejunum
Ileum
What does the stomach do
Mechanical breakdown of food (and mixing -> chyme)
Secretion of acid (HCl) – kill bacteria
Pepsin (secreted as pepsinogen) – begin protein digestion
Gastric lipase
Storage
What does the small intestine do
Chemical digestion all nutrients (pancreatic & brush border
enzymes)
Absorption of digestive end-products, water, ions and vitamins
Secretion of hormones
Secretion of bicarbonate-rich fluid
What does the colon do
Absorption of ions and water
Transformation of chyme into faeces
Storage of faeces
What does the rectum do
Stores faeces
What do mucous cells do
Secrete mucous - Alkaline solution released along with mucus to protect the stomach lining
What do parietal cells do
Secretes HCl and intrinsic factor - necessary for vitamin B12 absorption
What do Chief cells do
Secrete pepsinogen - Inactive - activated by acidic environment
What do Enteroendocrine cells do
Secrete Gastrin
What do Entero-chromaffin-like cells (ECLs) do
Release histamine
What do D cels do
Secrete somatostatin - important for H+ secretion
What is potentiation
Action of 3
substances combined
is greater than the
sum of the individual
effects
Negative feedback
What are the parts of the stomach
Antrum
Sphincters
main body
What does the pancreas do
Secretion of pancreatic juice (bicarbonate)
Proteases
Pancreatic lipase
What does the gall bladder do
Storage and concentration of bile
TABLE OF ENZYMES AND JUICES
What does the liver do
Secretes bile (bile salts and bicarbonate)
Processes absorbed nutrients
What are the bile components important for digestion
Bile salts
Phospholipids
HCO3-
What are the bile substances removed from the blood
Cholesterol
Bile Pigments
Trace metals
What are the incretin hormones
GIP (glucose dependant insulinotropic polypeptide)
GLP-1 (glucagon-like peptide-1)
What does GLP-1 do
Stimulated by nutrients in the small intestine
Secreted by L-cells in the ileum
Promotes insulin release
Inhibits glucagon release
Delays gastric emptying
Suppresses appetite and energy intake
What does GIP do
Stimulated by nutrients in small intestine
Secreted by K-cells in duodenum and jejunum
Stimulates insulin secretion
HORMONES OF THE GI TRACT
How are fats emulsified
Bile salts - lipid insoluble in water
Lipase can only act of the surface of droplets
Emulsification increases surface area
What is micelle formation used for
Increasing fat absorption
Constant turnover
equilibrium of micelles and fattu acids
How is fat turned into chylomicrons
- Emulsified
- Hydrolysed by
lipase - Temporarily stored
as micelles - Transported into
epithelial cells - Re-esterified to TAG
- Packaged as
chylomicrons
protein absorption **
What are the 2 main processes in small intestine
Peristalsis
Segmentation
More segmentation than peristalsis
Rythmic contraction and relaxation of longitudinal muscles
Greater mixing of material
Net flow through small intestine
What is the Gastroileal reflex
Segmentation increased in the ileum with gastric emptying
Once the majority of the meal has been
absorbed, segmentation is replaced with
peristalsis
What is the MMC -
migrating myoelectric complex (MMC)
Movesundigested material to the large intestine
Prevents bacteria from remaining in the small
intestine too long
What is the role of the large intestine
Primarily storage of
material prior to defacation
Some digestion of
undigested material (via
bacteria)
Fluid absorption
concentrates fecal matter
What does the ileocecal sphincter do
Opens to allow chyme through when ileum contracts
Closes when large intestine distends to prevent
