Digestive System Flashcards
What are the parts which are part of the GI tract (alimentary canal)?
Oral cavity
Pharynx (part of throat)
Oesophagus
Stomach
Small intestine
Large intestine
What are accessory organs
Structures which help with mechanical or chemical digestion
What are the accessory organs
Teeth
Tongue
Salivary glands
Liver
Gallbladder
Pancreas
What are the four layers of the GI tract (oesophagus to anal canal)
Serosa/Adventitia
Muscularis externae
Submucosa
Mucosa
(Outside to inside)
What is the function of the serosa/adventitia
Thin layer of connective tissue containing blood vessels, fat etc. Helps GI tract slide against organs
The serous membrane (or serosa) is a smooth tissue membrane of mesothelium lining the contents and inner walls of body cavities, which secrete serous fluid to allow lubricated sliding movements between opposing surfaces.
What is the function of the muscularis externae
The muscularis externa is responsible for segmental contractions and peristaltic movement in the GI tract. These muscles cause food to move and churn together with digestive enzymes down the GI tract. The muscularis externa consists of an inner circular layer and a longitudinal outer muscular layer.
2 types of muscles help with contraction to move food along the tract
What is the function of the submucosa
Passageway for blood vessels and ___ to go into GI tract
The submucosa has subdivisions of connective tissue, lymph nodules, and nerve fibers. Its major functions are nutrition and protection.
What is the function of the mucosa
Several layers of tissue - epithelium which is close to lumen
The mucosa is the innermost layer, and functions in absorption and secretion. It is composed of epithelium cells and a thin connective tissue. The mucosa contains specialized goblet cells that secrete sticky mucus throughout the GI tract.
What are the main functions of the digestive system
Ingestion
Secretion
Motility
Digestion
Absorption
Protection
Elimination
What does ingestion involve
Intake of food into the mouth
What does secretion involve
Cells of GI tract and accessory glands. Acid, buffers, enzymes, hormones, mucus
What does motility involve
Mixing and propulsion resulting from contractions and relaxation of muscle fibres
What does digestion involve
Breakdown of food into absorbale components (chemical or mechanical digestion
What does absorption involve
Mainly in small intestine. Molecules pass into blood or lymph
What does protection involve
Mucus and acidic fluid protect against pathogens
What does elimination involve
Removal of wastes as faeces, undigested material, bacteria, old cells lining GI tract are
Organic compounds such as carbohydrates, proteins, lipids, nucleic acids
What is mechanical digestion
Involves the physical breakdown of food into smaller particles
I.e. breakdown of carbs, proteins, lipids (triglycerides)
What are the accessory organs of the oral cavity
Teeth, tongue and salivary glands
What is chemical digestion
It is assisted via enzymatic activity to form absorbable compounds such as monosaccharides, amino acids, fatty acids etc.
What are the 3 major pairs of salivary glands
Parotid (in front of ear)
Submandibular (under mandible)
Sublingual (under tongue)
What is the function of the oral cavity (4)
Ingestion (location for food to enter body which will eventually turn into bolus (ball of food))
Digestion (teeth used for mechanical digestion via mastication). Chemical digestion is done via action of two enzymes in saliva; salivary amylase and lingual lipase
Secretion (saliva secreted by salivary glands lubricates the food)
Protection (oral cavity prodvides an ideal habit for microbes, thus the saliva has anti microbial properties)
What is salivary amylase
Digests starch to maltose
What is lingual lipase
Digests triglycerides
What is the anatomy of the pharynx
Funnel shaped tube of skeletal muscle between oral cavity and oesophagus
What is the function of the pharynx
Shared by two organ systems (digestive and respiratory systems)
During swallowing, structures close to ensure bolus moves to the oesophagus
I.e. ensures food isn’t in the wrong tube
What is the anatomy of the oesophagus
It is a muscular tube around 25cm long, and the upper tube is made of skeletal muscle, middle tube is a mix of skeletal and smooth muscle, and lower is smooth muscle
This allows upper to be voluntary, and lower to be automatic
What is the function of the oesophagus
Motility: Propulsion of bolus to stomach via peristalsis
What is peristalsis
Continuous waves of contraction and relaxation of muscles
Explain the anatomy of the stomach
J shaped chamber
4 main regions, with the most distal portion being the pylorus
It has 3 layers of muscles (compared to 2 everywhere else)
Has 2 sphincters (muscular valves) to prevent backflow (gastro-oesophageal sphincter, pyloric sphincter)
Explain the function of the stomach
and how it functions
Mechanical digestion and motility
Peristaltic contractions = ~3 /min to push bolus towards pylorus, grinding bolus into chyme
Pylorus allows 1/10 of chyme it holds to pass through pyloric valve per contraction
Contractions also close the pyloric valve, and remaining contents are propelled back (retropulsion)
What is chyme
the pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food.
What are the 3 steps to digestion in the stomach
1) Propulsion: peristaltic waves move from the fundus towards the pylorus
2) Grinding: the most vigorous persitalsis and mixing action occur close to the pylorus. The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum
3) Retropulsion: The peristaltic wave closes the pyloric valve, forcing most of the contents of the pylorus backward into the stomach
What are the unique anatomical features of the stomach
Mucosa extends towards the submucosa to columns of specialised secretory cells called gastric glands
There are also 3 muscle layers in the muscularis externa compared to the 2 which is normal in the digestive tract
What are the 3 muscle layers in the muscularis externa of a stomach
Oblique layer
Circular layer
Longitudinal layer
What do gastric glands do
Secrete components of gastric juice
They have important roles in chemical digestion, protection and absorption
What are the components of gastric juices
Gastrin
Pepsinogen
HCl
Bicarbonate-rich mucous
Gastric lipase
Intrinsic factor
What does gastrin do
Hormone that stimulates secretion of HCl and pepsinogen
What does pesinogen do
Activated to pepsin in the presence of HCl
Pepsin chemically digests proteins into peptides in the stomach
What does Hcl do
Denatures proteins, converts pepsinogen to pepsin
Kills microbes
What does bicarbonate rich mucous do
Protects stomach wall from protein digestion and corrosion from Hcl
What does gastric lipase do
Digests triglycerides into fatty acids and monoglycerides
What does intrinsic factor do
It is needed for transporation and absorption of vitamin B12 in small intestine
What is the anatomy of small intestine
3-6m in length
3 regions: Duodenum (closest to stomach), jejunum (in between duodenum and ileum), ileum (closest to the large intestine)
What are the specialised features of the small intestine which allow for increased surface area for absorption
Villi - finger like projections of mucosa layer into the lumen
Microvilli - hair like projections of enterocytes (absorptive cells)
Ultimately all allow for a greater surface area for absorption in the guts
What is the function of the small intestine
Chemical digestion
Motility
Absorption in jejunum and ileum
Chemical digestion largely occurs in the duodenum. All forms of organic compounds such as carbs, proteins lipids etc are digested in the small intestine
Most digestive enzymes secreted from pancreas
Explain chemical digestion as a function of the small intestine
Largely occurs in the duodenum
All forms of organic compounds are digested in the small intestine such as carbs, proteins, lipids and nucleic acids
Most digestive enzymes are secreted from the pancreas by pancreatic juices
Explain motility as a function of the small intestine
Peristalsis (regular contractions of smooth muscle) moves chyme through intestinal tract at around 16 contractions per minute
Segmentation is the most common motion in the jejunum - localised contractions and relaxations move chyme back and forth a few minutes, which promotes mixing, absorption of nutrients and water
Explain absorption as a function of the small intestine (jejunum, ileum)
jejunum:
Electrolytes (Na+, Cl-, HCO3-) - 80%
Water - 90%
Vitamins
Products of carbohydrate and protein digestion (95%)
ileum:
Water insoluble products of lipid digestion, fat soluble vitamins, cholestrol from micelles with bile salts. Components in micelle is transferred to enterocytes (absorptive cells).
WHat is the function of the liver in digestion
It secretes bile:
bile salts and bilirubin
What are bile salts
Bile salts emulsify fats, and facilitates absorption of fat and cholestrol
What is bilirubin
A pigment that is a waste product from the breakdown of red blood cells in the liver. Gut microbes further breaks down bilirubin to other compounds and eliminated in faeces
What is the function of the gallbladder in the digestive system
Stores and concentrates bile by absorbing water and ions
What is the function of the pancreas in the digestive system
Endocrine cells release insulin and glucagon
Exocrine cells secrete pancreatic juice
What does pancreatic juice contain and what does it do
Contains water, bicarbonate ions, pancreatic proteases, pancreatic amylase, lipases, nucleases
What do bicarbonate ions do
Neutralises HCL from stomach
What do pancreatic proteases do
This enzyme breaks down proteins in your diet. It also helps protect you from germs that may live in your intestines, like certain bacteria and yeast.
What does pancreatic amylase do
This enzyme helps break down starches into sugar, which your body can use for energy.
What do lipases do
Lipase is an enzyme the body uses to break down fats in food so they can be absorbed in the intestines.
What do nucleases do
Nuclease enzymes helps in digesting DNA and RNA present in our dietary substances.
What are the substrates and products of pancreatic amylase?
Substrates : starch
products: maltose, maltotriose
Comes from pancreatic juices
What are the substrates and products of pancreatic lipase?
Substrates: Triglycerides emulsified by bile salts
Products: Fatty acids, monoglycerides
Comes from pancreatic juices
What are the substrates and products of maltase?
Substrates: Maltose
Products: glucose
comes from brush border enzymes
What are brush border enzymes
The brush border contains several key enzymes that digest the products of luminal digestion to produce monosaccharides.
Explain the anatomy of the large intestine
~1.5m in length
4 major regions: caecum, colon, rectum, anal canal
Internal anal sphincter (involuntary)
External anal sphincter (voluntary)
What are the functions of the large intestine
Digestion
Absorption
Motility
Elimination
Explain digestion as a function of the large intestine
Some digestion by resident bacteria. Insoluble carbohydrates broken down via fermentation –> SCFAs
Explain absorption as a function of the large intestine
Absorbs remaining water and electrolytes (Na+, Cl-)
Absorbs vitamins synthesised by resident bacteria (vitamin B complexes, vitamin K) - this helps solidify faeces
Explain motility as a function of the large intestine
Haustral contractions in asecending and transverse colon. This occurs every 30 mins and each contraction lasts around 1 minute. It is similar to segmentation in the small intestine but less frequent and slower. Aids with mixing and water absorption
Peristalsis occurs 3-4 times/day. This allows for mass movement of content towards rectum
Explain elimination as a function of the large intestine
Formation of solid or semi solid material (faeces)
Faecal material stored in rectum until enouhg accumuates to initiate defacation reflex
Expelling of faeces via anus
Why is slow delivery of chyme from stomach to small intestine important
Slow delivery of chyme prevents rapid movement of water from blood to intestinal lumen.
It is also allows for greater absorption of nutrients?!
LO: Describe anatomy and functions of structures within digestive system
GI tract: oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine
Accessory organs: teeth, salivary glands, liver, gallbladder, pancreas
Other structures: sphincters
LO: Describe layers of gastrointestinal tract and specialised modifications in the stomach and small intestine
Mucosa, submucosa, muscularis externa, serosa/adventitia
Gastric glands, villi, microvili
LO: Describe function of digestive enzymes
Salivary and pancreatic amylase ; lingual, gastric and pancreatic lipase; pepsin, maltase
LO: Discuss importance of slow delivery of chyme from stomach to small intestine
LO: Analyse the role of different digestive secretions in the processes of protection, chemical digestion and absorption and predict potential impacts of inadequate or excess secretion
Gastric juice: gastrin, pepsinogen, HCl, bicarbonate ions
Bile, pancreatic juice
LO: Understand how nutrients and water are absorbed
Products of carbs, protein and lipid digestion
LO: Describe waste products from our digestive system; how these are made and how they are eliminated
Bilirubin
Faeces
What is maltase and its function
What is maltose and its function
