Digestive system Flashcards
Abdominal Quadrants
Abdominal can be divided into 9 anatomical quadrants. The locations are divided into 3 main lines;
1) Right & left hypochondrium, epigastric region
2) Right & left flank, umbilical region
3) Right & left groin, pubic region
Amino acids
The basic building blocks used to make proteins
Bile
An agent that emulsifies fats. Produced by hepatocytes. Carried from hepatic ducts-gall bladder via cystic duct & stored. Stimulation=ejection
Contain bile salts, phospholipids, cholesterol, bilirubin, electrolytes, water
Bolus
Mixed digested food & digestive juices
Cholecystokinin (CCK)
A peptide hormone that is secreted by enteroendocrine cells in the duodenum. Stimulates pancreas to secrete pancreatic enzymes and increases hepatic production of bile & stimulates contraction of the gall bladder (bile=fat digestion), mediates satiety
Chyme
Partially digested food
Defecation
Mass peristaltic movements push faecal matter into the rectum from the sigmoid colon.
Denature
to destroy or alter properties of a molecule
Dietary carbohydrates - function and categories
Function = energy source (connective tissues, cell-to-cell recognition).
Inc: Monosaccharides, Disaccharides, Polysaccharides
Dietary carbohydrates: Monosaccharides
Monosaccharides = One sugar unit; Glucose (key source of energy)
Fructose (fruits)
Galactose (dairy)
(All absorbed in the small intestines)
Dietary carbohydrates:
Disaccharides
Disaccharides =
Two sugar units;
Maltose - digested into glucose + glucose
Sucrose - digested into glucose + fructose
Lactose - digested into glucose + galactose
Dietary carbohydrates: Polysaccharides
Polysaccharides =
Many sugar units:
Starch - digested into glucose (potatoes, wheat, rice, etc.)
Glycogen - digested into glucose
Cellulose - indigestible (it’s indigestible fibre – in the cell walls of green plants)
Dietary lipids - functions and categories
Functions = energy, insulation, cell membranes, hormones production, protection of organs. Include Triglycerides, phospholipids, cholesterol
Dietary lipids;
Triglycerides
Predominant dietary lipid.
Composed of glycerol & 3 fatty acid chains (tri = three, glyceryl = glycerol)
Fatty acids are saturated or unsaturated
Dietary lipids;
phospholipids
Composed of two fatty acid tails & phosphate head.
Digested to free fatty acids & absorbed.
Dietary lipids;
cholesterol
A steroid particularly in animal foods
Vital for cell membrane integrity, vit D synthesis & sex hormone synthesis
Dietary lipids;
Saturated fatty acids
A molecule containing the greatest number of hydrogen atoms, without any double bonds
Dietary lipids;
Unsaturated fatty acids
Have one or more double bonds between atoms (C=C)
Dietary lipids;
Cis fatty acids
A cis configuration is when the H atoms are on the same side of the double bond (cis = same). In nature nearly all fats have a cis structure
Dietary lipids;
Trans fatty acids
A trans configuration is when the H atoms are on separate sides of the double bond. Trans fats are associated with heart disease (made in labs)
Digestive accessory organs
Organs that support the functions of the digestive system; Salivary glands, pancreas, liver, gall bladder and biliary tract
Digestive components (anatomical)
Mouth, pharynx, oesophagus, stomach, small intestine, large intestine (inc. rectum and anal canal)
Digestion processes
Ingestion
Oral intake of substances (into mouth)
Digestion processes
Secretion
Digestive juices; water, acid, emulsifiers, buffers and enzymes (saliva, gastric juices, pancreatic juices)
Digestion processes
Mixing & propulsion
Contraction / relaxation in walls help mix and propel food through the GI tract
Digestion processes
Digestion
Mechanical and chemical processes break down ingested food and liquids into absorbable substances
Digestion processes
Absorption
Substances passing through walls in the alimentary canal into blood and lymph
Digestion processes
Elimination
Excretion of waste and indigestible materials
Enteric nervous system
The brain of the gut, extends from oesophagus to anus. Contains 100 million neurons. Regulated by ANS (2 parts): Parasympathetic & sympathetic nervous system. Arranged in two plexuses (networks); myenteric & submucosal plexuses (M = motility, S = secretions)
Enteric nervous system Parasympathetic
(rest/digest)
Increases muscular activity (peristalsis – myenteric plexus)
Increases glandular secretion (submucosal plexus)
Enteric nervous system Sympathetic
(fight or flight) i.e. stress
Decreases muscular activity (peristalsis – myenteric plexus)
Decreases glandular secretion (submucosal plexus)
Enteric nervous system Myenteric plexus
Controls strength & frequency of muscle contraction; gut motility.
Network of sympathetic & parasympathetic nerve fibres between the circular & longitudinal muscles of the muscularis.
Enteric nervous system Submucosal plexus
Controls digestive secretions & detects sensory information. Network of sympathetic & parasympathetic nerve fibres within the submucosa
Enteric nervous system Neurons (motor)
Outgoing / action signal in the myenteric plexus control peristalsis & in the submucosal plexus control secretions
Enteric nervous system Neurons (sensory)
Incoming signal receive information about the mucosal environment; chemoreceptors and stretch
Enteric nervous system Neurons (interneurons)
Connect the two plexuses; myenteric and submucosal
Enteric nervous system; Neural feedback
- Food distends the stomach stimulating stretch receptors in its walls.
- Chemoreceptors monitor pH changes.
- Activate submucosal and myenteric plexus causing waves of peristalsis and gastric juice flow.
Enterohepatic circulation
The circulation of biliary acids – the movement of bile from the liver to the small intestine and back to the liver. 90-95% of bile are absorbed and transported back to the liver from the ileum
Enzymes
Biological catalysts which speed up chemical reactions up to thousands of times. Specific to what substrate they react with (lock & key). Not changed or consumed in chemical reaction (can perform the same reaction many times). Usually names are based on the substrate they react with and end in e.g. Lactase (some involved in protein digestion end in in)
Gallbladder
Pear shape sac in the liver, ejects bile which helps emulsify fats (emulsify = disperse)
GALT (gut associated lymphoid tissue).
Part of the first line of defence against indigested pathogens. Composed 25% of the intestine mucosal mass.
GALT contains 70% of body’s immune cells (70% of immune system in gut).
Gastrointestinal tract (GIT) and layers
The organs that good and liquids travel through when they are swallows, digested, absorbed and excreted. Runs from the mouth to the anus. Aka digestive tract or alimentary canal.
The entire GIT contains the same basic four layer arrangement of tissues: 1) Mucosa, 2) Submucosa, 3) Muscularis, 4) Serosa (peritoneum)
GIT layers
1st layer - Mucosa;
The innermost layer of the GIT, divided into three layers; Epithelium, Lamina Propria and Muscularis Mucosa
2nd layer - Submucosa layer
(sub = below):
A connective tissue layer that lies between the mucosa & muscularis. Contains blood & lymph vessels which receive absorbed food molecules. Contains network of neurons called submucosal plexus (brain of the gut)
3rd layer - Muscularis Externa; The mouth, pharynx, upper oesophagus & anal sphincter = skeletal muscle - allows voluntary swallowing & defecation
Rest of the GIT = smooth muscle – contains 2 layers; 1) inner circular muscle, 2) outer longitudinal. Between the layers are neurons (myenteric plexus). Involuntary smooth muscle contraction aids mixing & propelling food (Myo = muscle, Enteric = intestines)
Layer 4 - serosa (peritoneum);
Largest serous membrane in the body. Provides physical barrier to local spread of infection. Contains 2 layers; 1) parietal – covers the wall of the abdomen and pelvis cavity, 2) visceral – covers the organs. The peritoneal cavity is the space between the 2 layers & contains serous fluid.
GIT layers; Mucosa layers
Three layers;
Epithelium
Lamina Propria
Muscularis Mucosa
Later 1; Epithelium tissue for protection (mouth, pharynx, oesophagus & anus) & columnar (=cells with height> width) epithelium (stomach & intestine) with:
Microvilli ;(small intestines) – raised surface area for absorption
(Villi = mucosal projections)
Goblet cells; Secretion of mucus to lubricate food and protect against digestive juice erosion
Enteroendocrine cell; Specialised cells that secrete hormones (e.g. CKK) into blood. (entero = intestine, endocrine = hormones)
Layer 2; Consists of connective tissue containing many blood and lymphatic vessels that allow the absorption of nutrients. Contains MALT (mucosa associated lymphoid tissue
Layer 3; Muscularis Mucosa
A very thin layer of smooth muscle – creates the villi (small folds) = increase surface area for absorption & digestion
Greater Omentum
(Omentum = apron)
Largest fold of peritoneum. Drapes over transverse colon & small intestine. Stores fat (adipose tissue) & lymph nodes (antibodies/ GIT infections)
Large intestine: structure and functions
The terminal portion of the GIT, where the final stages of digestion, absorption, some vitamin synthesis (through bacterial activity) & stool formation occurs.
Four regions; 1) caecum, 2) colon, 3) Rectum, 4) Anal canal
Large intestine; 1ST part Caecum
A twisted tube about 8cm in length. Part of immune system; contains macrophages, lymphocytes, bacteria. Appendix is attached
Large intestine; 2nd part Colon - structures
Ascending, transverse, descending, sigmoid regions
Large intestine; 3rd part
Rectum
Rectal muscles work with abdominal muscles and diaphragm to contract and open the internal sphincter for defecation
Large intestine; 4th part Anal canal
Final segment of GIT. Role - defecation. Has Mucous membrane folds and Contains an internal & external anal sphincter that relax to allow faeces to leave your body.
Large intestine; Microbes
Hosts a rich community of microbes. Final stages of nutrient extraction occur in colon through microbial fermentation. Mostly symbiotic but pathogenic species may flourish according to local pH, water content, digestive processes upstream and anti-biotic use
Large intestine; Microbes; Faeces
Bacterial fermentation of carbohydrates = hydrogen, CO2, Methane = flatulence – smell
Fermentation of amino acids = hydrogen sulphide = Fecal odour
Bilirubin = decomposed into simpler molecules = pigment - faecal colour
Production of vitamin B12, K and fatty acids
Faeces are 30-50% bacteria
Lesser Omentum
Peritoneum fold - suspends the stomach & duodenum from the liver. 1st part of small intestine. Pathway for blood vessels entering liver. Contains hepatic portal vein, common hepatic artery, common bile duct & lymph nodes
Liver
Heaviest gland, second largest organ. Highly energy dependant (ATP) and nutrient dependant.
Functions:
Cleansing blood of microbes
Detoxification – metabolising drugs, toxins, alcohol
Bile production and secretion
Haemolysis (Kupffer cells)
Synthesis of plasma proteins – blood clotting & coagulation factors
Hormone homeostasis – deactivating all hormones
Metabolism of glucose (glycogen), fats (hepatocytes store triglycerides) & amino acids
Heat production – thermogenesis
Synthesis – Vit A (from beta carotene), CoQ10 & activation of Vit D
Storage – Vit (A,D,E,K,B12), iron, copper, glycogen
Liver – Kupffer cells
Phagocytic cells which remove foreign bodies from the blood (type of WBC) that specialise in engulfing microbes
Liver; detoxification
There are two major classifications of chemical compounds:
1) Hydrophilic; Excreted in urine or bile
2) Lipophilic; Must be chemically altered into hydrophilic compounds to facilitate elimination, 2 phases; bio-activation & conjugation
Liver; detoxification (Bio-activation)
Phase 1;
* Involves CYP450 family of enzymes. These enzymes are particularly important in metabolising toxins and medications.
* The enzymes are mostly found in liver cells but are also found in the small intestine, lungs, placenta and kidneys
* Converts water-insoluble toxins into water soluble substances to be excreted by the kidneys
* Converts toxins to more reactive substances which can be metabolised in Phase 2
Liver; detoxification (Conjugation)
Phase 2;
* Molecules are attached to the toxins to neutralise them making them stable (non-reactive) and water-soluble to be excreted.
* Various enzymes are involved to induce many chemical reactions
Liver; Hepatic first pass
All blood (nutrient and toxin rich) from the GIT is transported to the liver (via the portal vein) to be filtered / metabolised before entering the systemic circulation.
Liver; Hepatocytes
Liver cells; convert toxins into non-toxic metabolites which can then be excreted from the body
MALT (mucosa associated lymphoid tissue)
A collection of immune cells (e.g. lymphocytes, macrophages, etc.). Found in many places in the body, esp. prevalent in the tonsils, oesophagus, small intestine, appendix & large intestine. In the GIT is called GALT
Oesophagus
Long muscular tube attached to the larynx, posterior to trachea, passes through diaphragm. Food travels down to stomach via peristalsis. Middle contains skeletal muscle and lower contains smooth
Oesophagus; epiglottis
Flap cartilage that prevents food entering trachea
Oesophagus; lower oesophageal sphincter
Seal on stomach to prevent reflux/stomach contents back into oesophagus
Oral cavity: structures and function
Functions = mastication (chewing), speech, taste, swallowing. Contains:
Hard palate; bony partition between oral and nasal cavities. Allows simultaneous chewing and breathing
Soft palate; an arch of muscle
Uvula; swings up & blocks nasopharynx preventing food from entering nasal cavity
Tongue; voluntary skeletal muscle structure attached to hyoid bone & mandible. Superior surface covered in papillae – taste buds
Oral cavity - swallowing
Swallowing – bolus (mixed digested food and digestive juices) is pushed by the tongue into the pharynx closing the nasopharynx (pharynx reflex action)
Pancreas
An accessory digestive organ of the digestive system. Connected to duodenum via pancreatic duct. Has both exocrine & endocrine functions
Pancreatic duct
The pancreatic duct (carries pancreatic enzymes) meets the common bile duct to form the ‘Ampulla of water’, before entering the duodenum. The sphincter of odd allows pancreatic juices into the duodenum
Pancreas; endocrine function
Hormones secreted (into the blood). Insulin, glucagon and somatostatin (growth hormone inhibiting hormone)
Pancreas; exocrine function
Pancreatic juice is a clear liquid that is excreted into the small intestines (1.2-1.5L day). includes:
Sodium bicarbonate and water, Protease enzymes, Pancreatic lipase and Pancreatic amylase
Pancreas; exocrine function; pancreatic and Protease enzymes
Pancreatic enzymes imperative for digestion. Secreted by the pancreas into the lumen of the duodenum. Proteases are secreted in their inactive form
Pancreatic amylase - Breaks down starches into sugars
Pancreatic lipase - Breaks down lipid / fat digestion
Trypsin - Protein digestion
Chymotrypsin - Protein digestion
Ribonuclease - Digest RNA
Deoxyribonuclease - Digest DNA
Peristalsis
Gut motility. Waves of muscle contraction that move food along the GIT - peristalsis
Polysaccharides
Long chain sugars (mainly starch)
Proteins - structure and functions
Long molecules of amino acids that make up 15% of the total body mass. Each protein has a unique 3D shape (body temp regulation allows them to keep shape), and requires lock and key model for particular receptors. Functions = Immunity (immunoglobulins, antibodies), structures (muscles, collagen), enzymes, hormones, neurotransmitters, energy.
Must be denatured before protease enzymes are able to effectively cleave amino acids apart
Saliva functions
Produced by the various glands via a reflex controlled by the ANS
Functions;
Digestion (chemical breakdown polysaccharides)
Lubricating & dissolving food
Cleansing oral cavity / teeth
Defence (non-specific (IgA & lysozymes)
Taste
Buffer (for acidic foods)
Waste removal (urea/uric acid) from body
Saliva composition
Water – 95%0
Mineral salts - (Na, K, Ca, Cl, bicarbonate, P
Enzymes – Salivery amylase (parotid), lysozymes (found in many body secretions, break down bacteria walls)
Mucus
Immunoglobulins - (IgA)
Blood clotting factors
pH 6.35 – 6.85 (mildly acidic)
Small intestine: structure, cells, functions
A long structure (6.5m) where 90% of absorption occurs. Has 3 regions; Duodenum, jejunum, Ileum. Has villi & contains variety of cells; goblet, endocrine, absorptive.
Functions = movement / peristalsis of food, digestion (duodenum), absorption of nutrients & water, hunger / satiety, immunity (peyers patches & bacterial microflora)
Small intestine; Duodenum
Emulsification & most digestion occurs ehere (30cm)
Small intestine; Jejunum
Most absorption occurs here (3.5m)
Small intestine; Ileum
Vitamin B12 is absorbed here (3.5cm). Intrinsic factor (IF) is needed for absorption
Small intestine; Villi
Finger like projections that increase surface area, with blood & lymph capillaries; absorbed nutrients enter the blood; fatty acids enter the lymph
Small intestine; microvilli(brush border)
Projections of absorptive cell membranes that increase surface area
Small intestine; brush border enzymes
Attached to the lining of the intestine. Imperative for absorption.
1) Maltase, sucrase & lactase -Break down sugars into glucose, fructose, galactose
2) Dipeptidase & Aminopeptidase - Break down proteins into amino acids
3) Nucleosidases & phosphatases - 3) Digest RNA & DNA)
Sphincter
Ring of muscle that normally maintains constriction of a body passage
Stomach
J shaped organ with 4 main regions; cardia, fundus, body, pyloric and two sphincters; cardiac & pyloric. Secretes 2-3L of acidic gastric juice & mucus a day.
Functions:
Mixing chamber – churns up food
Holding reservoir – storage
Defence – non specific defence from gastric acidity
Absorption (limited) – water, alcohol, drugs
Digestion – mechanical but also chemical digestion ofmproteins & lipids
Irion – made more soluble with stomach acid
Satiation – tells you to stop eating
Hormones (below)
Stomach; Hormones:
- Ghrelin – stimulates hunger
- Gastrin – responds to stomach distention. Stimulates gastric juice secretion & gastric motility
Stomach; Exocrine cells
Three types of exocrine cells inc. parietal, chief & goblet cells
Parietal cells: Secrete:
* Intrinsic factor (IF); required for Vit B12 absorption
* Hydrochloric acid (HCl); 1) activates pepsin (enzyme) Denatures proteins, 2) anti-microbial agent, 3) Converts ingested iron into soluble form, 4) assists in activating bile & pancreatic juice flow.
*Vit B6 & zinc used to make HCI
Chief cells: Secrete:
* Pepsinogen and Gastric lipase - Protein & lipid digestion, HCl converts pepsinogen to active enzyme pepsin (digests protein)
Goblet cells: Secrete:
Mucus - Protects against acid
Stomach; Neural feedback (enteric nervous system)
Food distends stomach, stimulating stretch receptors. Chemoreceptors monitor PH changes, activate my enteric and submucosal plexus’ = peristalsis & gastric juices
Teeth
Adults have 32. Children (temporary) -20. Function = mastication. Have a crown, neck & root. Dentin makes up bulk of internal tooth, covered externally by enamel (hardest tissue in body)
Vitamin B12
I take of food containing B12z Absorbed in the terminal ileum (needs intrinsic factor for absorption)
Later made in colon - not absorbed?
Liver metabolism
Carbohydrate; Excess glucose converted to glycogen for storage
Glycogen to glucose as required
Fat; Fat from storage as required Synthesises cholesterol and triglycerides
Protein; Converts essential amino acids into non-essential amino acids
Removes nitrogen groups from amino acids to form urea to be excreted
Breaks down nucleotides to form uric acid to be excreted.
