Module 5 Flashcards
organs of the digestive tract
- mouth
- pharynx
- oesophagus
- stomach
- small intestine
- large intestine
accessory organs of the digestive tract
- teeth
- tongue
- salivary glands
- gall bladder
- liver
- pancreas
what are the 6 major processes of digestion
- Ingestion
- Propulsion
- Mechanical Digestion
- Chemical Digestion
- Absorption
- Deecation
Define Ingestion
- taking food into the digestive tract
- involves the oral cavity - lips and tongue
Define Propulsion
moving food through the digestive tract
- swallowing
- peristalsis (alternate waves of muscle contraction and relaxation)
Define Mechanical Digestion
physically breaking the food up into smaller fragments so it can be chemically digested
mouth: chewing and mixing food with saliva
stomach: churning and mixing with gastric juice
small intestine: (segmentation) mixes food with digestive juices and aids in nutrient absorption
define chemical digestion
- enzymes break down complex food molecules into chemical building blocks
- begins in the mouth and ends in the small intestine
define absorption
passage of digested end products from the digestive tract lumen into the blood or lymph
define defecation
elimination of indigestible substances, in the form of faeces, from the body via the anus
Composition of Digestive Tract - The Mucosa
- innermost layer
- rich in secretory cells
- contains capillaries for absorption of end product of digestion
- contains smooth muscle layer: produces folds in the mucosa of small intestine to increase surface area for absorption
- contains lymphoid follicles to provide protection from microbes
functions of the mucosa
- secrete
- absorb
- protect
Composition of the digestive tract - the submucosa
- external to mucosa
- contains elastic tissue allowing for stretch and recoil
rich supply of: blood vessels for nutrient absorption,
lymphatic vessels for transportation,
lymphoid tissue for immune function and nerves
Composition of the digestive tract - the muscularis externa
- surrounds submucosa
- contains 2 smooth muscle layers (inner = circular, outer = longitudinal)
- the circular muscle can form sphincters which act as valves to control passage of food
functions of the muscularis externa
responsible for propulsion (peristalsis) and segmentation (mechanical digestion)
Composition of the digestive tract - The Serosa
- outermost layer
functions: - protection
- anchors the digestive tract within peritoneal cavity
what lines the oral cavity
stratified, squamous epithelium
list the digestive functions of the mouth/oral cavity
- ingestion
- chewing
- mixing food with saliva
- taste sensation
- initiating chemical digestion of carbohydrates by enzymes of saliva
- propulsion (swallowing food)
list the salivary glands
- the parotid
- the sublingual
- the submandibular
what does saliva consist of
- water
- mucus
- enzymes
- antimicrobial proteins
list the functions of saliva
- mucus moistens and lubricates food (bolus formation)
- dissolves food chemicals and facilitates taste
- contains enzymes that begin chemical digestion of carbs
what is the digestive functions of the pharynx and oesophagus
propulsion of food to the stomach
Stomach - Gross Anatomy
extra layer of?, shape, oblique muscle
- extra muscle layer in muscularis externa
- circular + longitudinal = mix and churn to propel food
- oblique muscle = pummels the food and rems it into small intestine
Stomach - Microscopic Anatomy
what lining, what do gastric pits produce
- lining of simple columnar epithelium = mucosa contains gastric pits
- gastric pits contain cells to produce: hydrochloric acid, pepsin, mucus, hormones
Stomach - Mucosal barrier (what is it composed of)
- bicarbonate rich fluid under insoluble mucus on the stomach wall
- mucosal epithelial cells joined by tight junctions
- damaged mucosal epithelial cells shed and quickly replaces
List the functions of the stomach
- storage of food
- mechanical breakdown - mixing food with gastric juice
- initiates chemical digestion of proteins
- absorption
- propulsion
Small intestine - Gross Anatomy
how long, 3 subdivisions
2-4 metres long with muscle tone or 6-7 m without tone
subdivisions:
1. Duodenum - curls around the pancreas
- Jejunum
- ileum ends at the large intestine
Small intestine - function of duodenum
receives bile and pancreatic juice for chemical digestion
Small intestine - function of jejunum
major site of mechanical and chemical digestion and absorption
Small Intestine - Microscopic Anatomy
type of surface area, and structural modifications
length provides large surface area of nutrient absorption
structural modifications:
- circular folds
- villi
- microvilli
Small intestine - structural modifications - circular folds
structure + function
- deep + permanent folds of the mucosa and submucosa
- slows the movement of chyme; increasing time for nutrient absorption
Small intestine - structural modification - villi
structure + function
1 mm high finger like projections of the mucosa
absorptive epithelial cells bound by tight junctions = nutrient and electrolyte absorption
small intestine - structural modification - microvilli
structure and function
small, densely packed villi on the surface of individual absorptive epithelial cells = brush border
plasma membrane bears enzymes = completes carbs, protein and nucleic acid digestion
function of brush border enzymes
completes carbohydrate, protein and nucleic acid digestion
what are the major types of cells found in mucosal epithelium of Villi & Crypts
- epithelial cells = watery mucus = nutrient absorption
- cells to produce hormones = stimulates secretion of bile
- lymphoid tissue = defence
- stem cells that give rise to the epithelial cells as they renew 3-5 days
list the functions of the small intestine
- propulsion (peristalsis)
- mechanical digestion (segmentation)
- chemical digestion of all 4 food classes
- nutrient absorption
Small Intestine - digestive processes - segmentation
breaks up the chyme into smaller portions
small intestine - digestive processes - chemical digestion
- chyme delivered slowly
- alkaline intestinal mucus and pancreatic juice help neutralise
- lipids and nucleic acids + partially digested carbs + proteins are chemically digested
- brush border enzymes complete carbs, proteins and nucleic acid digestion
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small intestine - digestive processes - peristalsis
moves indigestible foodstuff to large intestine
small intestine - digestive processes - absorption
90% of absorption occurs in small intestine
- end product absorbed across the single epithelial cell layer of the mucosa and into the capillaries
- water soluble absorbed into blood travel in the hepatic portal vein to liver
- lipid soluble absorbed into lymphatic circulation enters the blood at thoracic duct
hepatic artery
supplies oxygenated blood from the abdominal aorta (20% input)
hepatic portal vein
supplies nutrient rich blood from the small intestine
define lobules
structural and functional unit of the liver
- made of liver cells called hepatocytes that radiate from from a central vein
what is in the portal triad
- arteriole branch of hepatic artery
- venule branch of the hepatic portal vein
- bile duct
function of leaky capillaries
allows heaptocytes to filter and process nutrient rich blood
list the 3 functions of the liver
- Haematologic functions (synthesis of plasma)
- Metabolic Functions
- Digestive Functions
Liver - metabolic functions
- processing of nutrients
- correcting nutrient deficiencies
Liver - production of bile (how, what does it contain and why)
- produced by hepatocytes in the gall bladder
- contains bile salts and phospholipids
- emulsifies fats = surface area, fat and cholesterol absorption, resorbed in the ilium to be recycled
Gall bladder - list functions
- stores and concentrates unused bile
- bile secreted into the duodenum directly from the liver or from fat in gall bladder
The Pancreas (what does it contain)
- endocrine tissue which secrete hormones into blood to regulate blood glucose levels
- contain cells that produce pancreatic juice (containing enzymes, and neutralises chyme)
what does pancreatic juice contain
- water
- electrolytes
- enzymes (proteases, amylases, lipases, nucleases)
what do proteases digest
proteins
what do amylases digest
carbohydrates
what do lipases digest
lipids
what do nucleases digest
nucleic acids
what are the subdivisions of the large intestine
- appendix
- cecum
- colon
- rectum
function of mucosa
- ease the passage of faeces
- protect the intestinal wall from bacterial acids and gases
List the functions of the large intestine (4)
- Absorption
- Temporary storage and compaction of waste materials
- Propulsion
- Defection
Defecation Reflex
- stretching of the rectal walls due to movement
- spinal reflex is initiated
- if possible voluntary motor neurons are inhibited
origin of the large intestine enteric flora
stomach, small intestine, or enter via anus
function of large intestine enteric flora
- metabolise mucus
- ferment cellulose, releasing acids and gases
- synthesise vitamins B and K
define chemical digestion
a catabolic process where complex food molecules are broken down into chemical building blocks which are small enough to be absorbed from the gastrointestinal tract into the blood
example of carbohydrates - polysaccharides
glycogen, starch, cellulose
example of carbohydrates - oligosaccharides
sucrose, lactose, maltose
example of carbohydrates - monosaccharides
glucose, fructose, galactose
what locations does carbohydrate digestion occur
mouth and small intestine
what are digested proteins broken down into (and by what)
amino acids by proteases and brush border enzymes
what are digested carbohydrates broken down into (and by what)
monosaccharides by amylase and brush border enzymes
what are digested proteins composed of
- dietary proteins
- digestive enzymes
- proteins from sloughed mucosal cells
when are proteases active
low pH
chemical digestion of lipids
- fats forms globules in water
- inaccessible to water soluble enzymes
- emulsified into bile salts
what do nucleic acids include
DNA and RNA
how are nucleic acids chemically digested
in the small intestine by pancreatic nucleases (broken into nucleotides)
and by brush order enzymes
( break nucleotides down to their component bases )
how are carbohydrates digested in the mouth
salivary amylase
where does the 10% of absorption occur
- Stomach (lipid soluble substances)
- Large Intestine (water, electrolytes and vitamins)
where does absorption occur
epithelial cells
absorption of water soluble nutrients
3 steps
- small proteins or carbs are digested into amino acids or monosaccharides by pancreatic or brush border enzymes
- monomers are then absorbed into epithelial cells and move to opposite side
- monomers enter the capillary e.g. liver
define metabolism
the sum total of the chemical reactions occurring in an organism
define anabolism
reactions that build larger molecules from smaller ones
define catabolism
reactions that break down complex structures into simpler ones
define metabolic rate
the energy the body uses to drive metabolism
define basal metabolic rate
the energy the body uses to perform only essential activities
what are the factors that influence basal metabolic rate
- body surface area
- age and gender
- body temp
- stress
- hormones
differentiate between ATP and Energy
ATP is the molecule that holds the energy within its bonds
energy is temporarily stored within cells as ATP
define cellular respiration
biochemical processes that lead to the production of ATP
breaking the chemical bonds in glucose molecules releases energy for ATP
Glucose Catabolism involves three biochemical processes
- glycosis
- TCA cycle
- electron transport chain
define glycosis
occurs in the cytoplasm of all cells (anaerobic) where one molecule of glucose is broken in half into 2 molecules
define tricarboxylic acid cycle
occurs in the mitochondria where Pyruvate is converted to acetyl CoA (by releasing co2, H ions and energy)
define electron transport chain
occurs in the mitochondria (aerobic) H ions proceed through chemical reactions that produce water and energy
what are the 2 nutritional states
- anabolic or absorptive state (nutrients in abundance, during and within 4 hours of eating)
- catabolic or post absorptive state (no food is digested and body reserves broken down)
Anabolic or Absorptive State - what cells
glucose = produce ATP
amino acids = protein synthesis or produce ATP
trigylcerides = produce ATP if needed
catabolic or post absorptive state
fasting state more than 4 hours after eating where stored nutrients are broken down and sources of blood glucose for use by neural tissue
glycogenesis
breakdown of glycogen in the liver and skeletal muscles
gluconeogenesis
production of new glucose in the liver
summary of absorptive state
all cells = ATP
- excess glycogen and stored in liver and skeletal muscles
- excess fat stored in adipose tissue e
summary of post absorptive state
blood glucose levels are maintained by
- glycogenesis
- gluconeogensis
Fate of Amino Acids - Summary
Absorptive State
- all cells = protein synthesis = ATP
- excess = fat
Post Absorptive State
- amino acids used to produce glucose and produce ATP
- used for protein synthesis
Fate of Triglycerides Summary
Absorptive State
- produce ATP
- stored as fat
Post Absorptive state
- glycerol = glucose and produce ATP
- fatty acids = acetyl coA and produce ATP
Summary of Ketones
occurs when carb levels are low fatty acids are converted to ketones in liver
- all non neural tissue uses ketones to produce ATP
- occurs during fasting
- decreases pH (increases rate and depth of breathing)
