Digestive System Flashcards
Learning outcomes
- Describe the functions of the digestive system.
- Describe the anatomy of the digestive system and identify the gross and microscopic anatomical features.
- Describe the general arrangement of the layers of the gut
- Describe the major processes of digestion.
- Describe the structure of each part of the digestive tract and relate it to function.
Digestive system
- General characteristics of digestive systems
- Specialisations of the human digestive system
- Organs
- Accessory glands
- Enzymes
- Motility
- Regulation
- Circulation
Gastrovascular cavity
- Digestive compartment with a single opening (mouth)
- Functions in both digestion &
distribution of nutrients
> Extracellular digestion of large
food masses
> Specialisation of cells lining the lumen of the cavity for forming digestive secretions & absorption - Enables an organism to ingest food much larger than any of its cells
could take in directly
Phylogeny of the digestive system
Intracellular digestion:
* Protozoa & sponges
* Digestion is entirely intracellular (occurs within the cell)
* Food particle is enclosed within a food vacuole by phagocytosis
* Digestive enzymes added to vacuole (= compartmentalisation)
Limitations to intracellular digestion:
* Only particles small enough to be phagocytised can be ingested
* Every cell must be capable of secreting the necessary enzymes and
* Absorbing the products of digestion into its cytoplasm
Major regions of the alimentary canal
- Regionalisation and specialisation
- Digestion occurs sequentially
- Regions of the alimentary canal vary
- Sphincters & valves control flow
- Accessory organs and glands
Layers of the digestive tract wall
Digestive Function
Stages of digestion
Restion: mlective intakerical reakdown of
food
* Absorption: uptake of nutrient molecules into
epithelial cells of digestive tract and then to blood
and lymph
* Compaction: absorption of water and consolidation
of the indigestible residue
* Defecation: elimination of waste
Alimentary canal
Evolution of complete mouth to anus alimentary systems
: Vales et senties centrol mathg the di estive oves in one direction
* Extracellular digestion: digestion of large food particles
* Increasing regional specialisation: sequencing of processes
Major regions of the alimentary canal
Digestive processes
Mechanical digestion: Physical breakdown of food
* Cutting and grinding: teeth
* Churning and mixing: stomach & SI
Chemical digestion: Enzymes (produced by glands associated with the digestive tract)
* Amylase: Carbohydrates (polysaccharides) → monosaccharides
* Pepsin, proteases & peptidases: Proteins (polypeptides) → amino acids
* Lipase: Fats → monoglycerides and fatty acids
Some nutrients can be absorbed without being digested
* E.g. vitamins, free amino acids, minerals, cholesterol, water
Motility
Arterial circulation
Serous Membranes
Peritoneum
Neural control of the digestive tract
Hepatic portal circulation
ANS control of the digestive system
Herbivore or carnivore?
Salivary Glands
Learning outcomes
- For each organ & gland of the digestive tract:
- Macroanatomy
o Microanatomy
o Relate structure to function
o Digestive processes
The Oral (Buccal) Cavity
glands
Tongue
Lips & Cheeks
- Lined with stratified squamous epithelium.
Hold & retain food and drink - Essential for suckling by infant mammals
Saliva and the Salivary Glands
Salivation
* Controlled by the brainstem
* Stimuli = presence of food and odour, sight, or thought of food
* ANS response:
* Parasympathetics stimulate salivary glands to produce much thin, enzyme-rich saliva
> Sympathetics stimulate salivary glands to produce less saliva but thicker mucus-rich saliva
Saliva
* Moistens and lubricates food
* Contains water &
- Salivary amylase: enzyme that begins carbohydrate digestion in the mouth
- Lingual lipase: enzyme that begins fat digestion in the mouth and is further activated by
stomach acid & continues to digest fat after food is swallowed
- Mucus: binds & lubricates food & aids in swallowing
- Lysozyme: enzyme that kills bacteria
- Antibodies that inhibits bacterial growth
- Electrolytes
-ase = denoting an enzyme
Summary: Digestion in the oral cavity
- Mechanical digestion of food
- Salivary amylase begins digestion of carbohydrates (starch)
(polysaccharides > oligosaccharides + maltose) - Lingual lipase begins digestion of fats
poly-= many
oligo-= few
saccharon = sugar
-ose = pertaining to sugar
lipose = fat, grease
Pharynx
Swallowing (deglutition)
Swaroin oscurs inting peater in medulla oblongata
> Buccal phase: under voluntary control
* Pharyngoesophageal phase: involuntary
Swallowing (deglutition) photo
swallowing photo
Esophagus
Esophagus (oesophagus)
Esophagus
MUCOSA
* Nonkeratinised stratified squamous epithelia
> For protection from abrasion from food bolus
Stomach
Esophagus
Gastro-esophageal junction
Stomach
Gastric mucosa
Pepsin
Gastric Motility
Summary: Digestion in the stomach
- Mechanical digestion of food (churning)
- Pepsin partially digests proteins into shorter peptide chains
- Gastric lipase & lingual lipase begin fat digestion
- However, most digestion and absorption occurs after the food (chyme) leaves the stomach
Gastroduodenal junction
Small Intestine
Accessory glands associated with the small intestine: Liver photo
Accessory glands associated with the small intestine: Liver
LIVER
: Sle aids in fat digestion & absorpkion by
emulsifying fats
GALLBLADDER
* Stores & concentrates bile
Accessory glands associated with the small intestine: Pancreas
- Secretes pancreatic enzymes into the SI
*Pancreatic amylase: digests carbohydrates
*Pancreatic lipase: digests fat - Secretes zymogens (digestive enzymes secreted as inactive proteins & converted to active enzymes)
*= proteases & peptidases - digest proteins & small peptides
- Secretes bicarbonate into the SI
- Neutralizes stomach acids
- Secretes insulin & glucagon into the blood
- Maintains blood sugar levels
Accessory glands associated with the small intestine: Pancreas photo
Small intestine
PLICAE CIRCULARES
* Circular folds of the mucosa & submucosa
: Focur from the do dina ido the middle
of the ileum
* Cause chyme to flow in spiral path contact with mucosa
* Slows passage of chime
* Promotes more thorough mixing &
nutrient absorption
* increase surface area by a factor of 2 to 3
VILLI
* Fingerlike projections
* Are folds of the epithelia
* increase surface area by a factor of 10
Small intestine
Intestinal villi
Villus
Carbohydrate digestion & absorption in SI
Carbohydrate (starch) → Oligosaccharides → maltose (disaccharide) → glucose
Salivary amylase (mouth) hydrolyzes starch into oligosaccharides
Salivary amylase stops working in stomach at pH less than 4.5
Carbohydrate digestion & absorption in SI photo
Protein digestion & absorption in SI
Pepsin (stomach) digests 10 - 15% of dietary protein into shorter peptides and
some free amino acids.
Pepsin is inactivated when it enters the duodenum
Protein digestion & absorption in SI photo
Other nutrients digested & absorbed in the Sl
- Nucleic acids
- Nucleases - pancreas
#DNA & RNA → nucleotides - Brush border enzymes
nucleotides → phosphate ions, ribose or deoxyribose sugar, and nitrogenous bases - Vitamins
Absorbed unchanged
By absorbed poorly unless bound to Intrinsic Factor from the stomach - Minerals
Absorbed along the entire length of the Si
・ Water - Most water is absorbed in the small intestine by osmosis
÷ (Some water absorbed in the large intestine)
unit outline requirement being satisfied: What is the most important substance absorbed by the small intestine?
Fat digestion & absorption in SI
Lipases-fat-digesting enzymes
Lingual lipase is active in stomach
Lingual lipase & gastric lipase digest 10 - 15% of lipids before reaching duodenum
The Large Intestine photo
Fat digestion & absorption in SI photo
Large intestine
Large intestine
Large intestine
Large intestine
Anal canal
Anorectal junction
Neural Control of
Defecation
