ANHB1102 Lecture Notes - Lecture 13: Muscularis Mucosae, Simple Columnar Epithelium, Hepatic Portal System
25 May 2018
School
Course
Professor
Digestive System:
Phylogeny (Evolution) of Digestive System:
-Intracellular digestion
-Protozoa and sponges
-Limitations to intracellular digestion (cant ingest
particle bigger than self and multi cell
organisms need to be able to transfer nutrients
to other cells)
-Gastrovascular Cavity:
-Digestive compartment with single opening
-Functions in digestion and distribution of
nutrients
-Specialisation of cells lining the lumen o the
cavity for forming digestive secretions and
absorption (e.g secretion of enzymes, flagella,
absorb nutrients)
-Alimentary Canal:
-Tube between two openings (mouth and anus)
-Food moves in one direction
-Extracellular digestion
-Increasing regional specialisation
Stages of Digestion:
1. Ingestion: selective intake of food
2. Digestion: mechanical and chemical breakdown of food
3. Absorption: uptake of nutrient molecules into epithelial cells of
digestive tract and then to blood and lymph
4. Compaction: absorption of water and consolidation of the
indigestible residue
5. Defecation: elimination of waste
Major Regions of the Alimentary Canal:
-Regionalisation and specialisation
-Digestion occurs sequentially
-Regions of the alimentary canal vary
-Sphincters and valves control flow
-Accessory organs and glands
General Anatomy:
-Digestive tract
(alimentary canal) =
muscular tube
extending from mouth
to anus
-Gastrointestinal tract
(GI) = stomach and
intestines
-Accessory organs =
teeth, tongue, salivary
glands, liver,
gallbladder and
pancreas
Functions of Digestive System:
-Mechanical Digestion: physical break down of food
-Cutting and grinding: teeth
-Churning and mixing: Stomach and SI
-Chemical Digestion:
-Enzymes (produced by glands associated with digestive tract):
-Carbohydrates (polysaccharides) ——> monosaccharides
-Proteins (peptides) ——> amino acids
-Fats ——> monoglycerides and fatty acids
-Nucleic acids ——> nucleotides
-Some nutrients can be absorbed without being digested:
-Vitamins, free amino acids, minerals, cholesterol, water
Layers of the digestive tract wall:
Motility:
1. Peristalsis:
-Waves of contraction of circular muscle behind the food bolus and
relaxation of muscle in front of the bolus
-Moves food along the gut
2. Segmentation:
-Alternate constriction of rings of smooth muscle
-Divide and squeeze contents back and forth
-Mixes food
-Doesn't move along the gut much
-IE: Mostly simple
columnar
epithelium
-LP: thin CT
-MM: smooth
muscle
-Inner: contracts
diameter
-Outer: contracts to
make shorter
-Adventitia: binds
to other organs
-Mesothelium:
different
embryological
origin
Peritoneum:
-Peritoneum: 2 layered serous membrane
-Binds viscera to body wall or suspends viscera from the
body wall
-Outer layer = parietal peritoneum = lines abdominal cavity
-Inner later = visceral peritoneum = turns inward from the
body wall and wraps around the abdominal viscera forming
the series
-Peritoneal Cavity: space between parietal and visceral layers
-Lubricated by peritoneal fluid
-Retroperitoneal organs = lie behind peritoneum
-Intraperitoneal organs = surrounded by peritoneal cavity (not
in cavity)
Serous Membranes:
-Mesenteries = a fold of the peritoneum that attaches the
stomach, small intestine, pancreas, spleen and other organs
to the posterior wall of the abdomen
-Allow for movement of organs
-Provides a passage for blood vessels, nerves and lymphatic vessels
-Greater omentum, Lesser omentum & Mesocolon
Neural Control of the Digestive Tract:
-Enetric Nervous System: regulates digestive tract motility,
secretion and blood flow
-Myentric Plexus (between 2 layers of muscularis): controls
frequency and strength of contractions of muscularus
externa
-Submucosal Plexus (in submucosa): Controls glandular
secretion of mucosa and movement of muscularis mucosae
-Autonomic Nervous System:
-Parasympathetic: Vagus nerve (X) and Sacral spinal cord
-Inc secretion and Inc motility (REST AND DIGEST)
-Sympathetic: thoracid and upper lumbar spinal cord
-Dec secretion and Dec motility (FIGHT OR FLIGHT) -
inhibitory effect
-Sensory Receptors: chemoreceptors and mechanoreceptors
MP
SP
Document Summary
Limitations to intracellular digestion (cant ingest particle bigger than self and multi cell organisms need to be able to transfer nutrients to other cells) Functions in digestion and distribution of nutrients. Specialisation of cells lining the lumen o the cavity for forming digestive secretions and absorption (e. g secretion of enzymes, agella, absorb nutrients) Tube between two openings (mouth and anus) Digestive tract (alimentary canal) = muscular tube extending from mouth to anus. Gastrointestinal tract (gi) = stomach and intestines. Accessory organs = teeth, tongue, salivary glands, liver, gallbladder and pancreas. Mechanical digestion: physical break down of food. Enzymes (produced by glands associated with digestive tract): Some nutrients can be absorbed without being digested: Vitamins, free amino acids, minerals, cholesterol, water. Waves of contraction of circular muscle behind the food bolus and relaxation of muscle in front of the bolus. Moves food along the gut: segmentation: Alternate constriction of rings of smooth muscle. Divide and squeeze contents back and forth.
