PHYS20008 Lecture Notes - Lecture 29: Gastrointestinal Physiology, Muscularis Mucosae, Lamina Propria
12 Jun 2018
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Lecture 29
PHYS20008 - HUMAN PHYSIOLOGY
LECTURE 29
DIGESTION 1: STRUCTURE, FUNCTION & REGULATION
TODAY
•Functions of digestive system
•Anatomy: gross and histology
•Motility
•Smooth muscle
•Regulation
•Long reflexes
•Short reflexes
•GI peptides
•Fermentation of food is not a major function of the human digestive system.
GASTROINTESTINAL DIGESTION FUNCTIONS
•Roles include:
•Digestion
•Absorption (via gastrointestinal tract wall and IF)
•Motility
•Secretion
•Tract made up largely of smooth muscle.
•Protect body from pathogens from the external environment.
•Average SA is the side of a tennis court.
•Waste excretion.
•Very important as nowadays we eat lots of processed/
synthetic foods and we can’t absorb all of the so called
‘nutrients’ in them.
DIGESTIVE TRACT ANATOMY
•Salivary glands secrete things to break down food. Amylase and
lipase?
•Oesophagus; muscular tube leading to stomach.
•Stomach: digesting proteins, leads to intestines.
•Liver, gall bladder & pancreas release enzymes, buffers and peptides
to break shit down.
•Densest concentration of lymph within entire body inside
gastrointestinal tract.
•Same general structure from Oesophagus to anus.
•With four layers:
•Mucosa
•Epithelial cells
•Lamina propria
•Muscularis mucosae
•Helps to move vili inside gastrointestinal tract, which
help chyme move around a little bit. All help increase SA
of tract.
•Modifications ↑ SA
•Submucosa
•Larger lymph and blood vessels, as well as some nerve tissues
as well. Enteric nervous system; NS entirely housed within
gastrointestinal tract.
Lecture 29
PHYS20008 - HUMAN PHYSIOLOGY
•Muscularis externa
•Consists of 2 layers of thicker muscular
tissue. Inside (closet to lumen): circular
muscle, forming concentric rings, and
longitudinal muscle running along the
length of the tract itself.
•Serosa
•Another form of connective tissue to
hold things together and to release a
lubricant to help gastrointestinal tract
to move around to other viscera
without getting caught on anything.
FROM BIOL10004:
•Digestion is the breaking down of large
molecules into smaller ones.
•Large molecules, such as fats, proteins and
carbohydrates, must be broken down
into molecules small enough to be
transported across the gut wall, and
this needs to be done quickly and is
often aided by the physical breakdown
of food.
•The mammalian digestive (or
alimentary) system is a hollow
muscular tube, consisting of;
‣buccal cavity/mouth (+
salivary glands)
‣pharynx
‣oesophagus
‣stomach
‣small intestine (+ pancreas,
liver)
‣large intestine (including caecum)
‣anus
•Physical digestion (mastication,
grinding or chewing) occurs in the buccal cavity, the mouth.
•Saliva secreted into the buccal cavity at the time of feeding lubricates food for its passage through
the gut, and also contains enzymes involved in enzymatic breakdown, such as amylase involved in
initial chemical digestion of starch.
•Enzymatic digestion involves the breakdown of complex molecules by hydrolytic enzymes, usually
secreted into the gut lumen, and is similar in all animals.
•Digestive enzymes are the end products of enzymatic digestion.
•Amylase digests starch during enzymatic breakdown.
•Different enzymes come from different locations in the digestive tract, including salivary glands,
stomach, liver, pancreas and the small intestine. They appear to have a sequential order of action,
and their action is heavily pH dependent. pH varies throughout the digestive system, meaning that
some enzymes work well in specific areas and some don’t.
•In the stomach, enzyme secretion is under hormonal control.
•Food reaching the stomach stimulates secretion of the hormone gastrin from stomach mucosal
cells, which then circulates in the blood and stimulated the release of HCl and enzyme pepsin
from cells of the stomach lining.
•In the stomach there is mechanical breakdown, whereby the muscular walls churn the food, and
there is also chemical breakdown, whereby the enzyme pepsin breaks down protein.
Document Summary
Today: functions of digestive system, anatomy: gross and histology, motility, smooth muscle, regulation, long reflexes, short reflexes, gi peptides, fermentation of food is not a major function of the human digestive system. Digestive tract anatomy: salivary glands secrete things to break down food. All help increase sa of tract: modifications sa, submucosa, larger lymph and blood vessels, as well as some nerve tissues as well. Enteric nervous system; ns entirely housed within gastrointestinal tract. Phys20008 - human physiology: muscularis externa, consists of 2 layers of thicker muscular tissue. Large intestine: the caecum is a blind ended pouch at the start intestine involved in the digestion of cellulose. Not all animals have a caecum; humans don"t: the colon is involved in the removal of water, formation of faeces and the elimination through anus. System: somatic motor (from cns, skeletal muscles, autonomic (from cns, parasympathetic & sympathetic, enteric, entirely contained within walls of digestive tract, independent of cns.
