DS: Overview and Gut Wall Flashcards
What is the main role of the digestive system?
Responsible for the sequential processing of food into smaller elements for absorption by intestinal mucosal cells. Responsible for meeting the energy needs of the body by converting macromolecules (in their polymeric form) to their corresponding subunits for energy and ATP production in the mitochondria
What are the main organs of the digestive system?
- Oral cavity
- Pharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine (colon)
What are the accessory organs of the digestive system?
- Teeth
- Tongue
- Salivary glands
- Liver
- Gall bladder
- Pancreas
What are the 3 main salivary glands?
- Parotid gland
- Sublingual Glands
- Submandibular gland
What is the role of the oral cavity in the digestive system?
Serves as an entrance to the alimentary canal and initiates the digestive process by salivation and propulsion of the food bolus to the pharynx for deglutition. Begins the digestion of carbs and lipids though lingual lipase and salivary amylase.
What is the role of the small intestine in the digestive system?
Largely responsible for the uptake of nutrients and minerals from food
What is the role of the large intestine in the digestive system?
Largely responsible for the uptake of water. Excessive water uptake can led to constipation.
What is the role of the teeth is the digestive system?
Responsible for mechanical digestion.
What is the role of the tongue in the digestive system?
Responsible for manipulating food and positioning it near the teeth for mechanical digestion, and propelling the bolus towards the pharynx for swallowing.
What is the role of the liver in the digestive system?
Responsible for bile production
What is the role of the gall bladder in the digestive system?
Stores bile, produced by the liver, until it is needed for the digestion of fatty foods in the duodenum of the small intestine
What is the role of the pancreas in the digestive system?
Production of hormones responsible for blood glucose production and the production of pancreatic juice to aid in digestion.
What is the role of the parotid salivary gland?
Major salivary gland. Secretes serous saliva through the parotid duct into the mouth to facilitate mastication and deglutition and initiate the digestion of carbs.
What is the role of the sublingual salivary gland?
Smallest, most diffused glands. Provide only 3-5% of the total salivary volume.
What is the energy requirement of the human body at rest?
30 kcal per kg of body weight
What are the main processes carried out by the digestive system to release energy from food?
Ingestion Propulsion Mechanical digestion Chemical digestion Secretion Absorption
What is ingestion?
The process of introducing food and liquid nutrients into the digestive system via the oral cavity
What is propulsion?
The process that moves food through the digestive system at a rate that permits optimal digestion and absorption
How is propulsion achieved?
Peristalsis and deglutition
What does deglutition mean?
Swallowing
What triggers peristalsis?
Induced by (mechanical) distension of the gut wall which is registered by pressure receptors.
What is peristalsis?
Peristalsis is the main mechanism for the movement of food along the digestive tract. Peristalsis is an involuntary process resulting in successive waves of contraction and relaxation of the smooth muscle layers in the gut wall.
Describe the process of peristalsis
- Contraction of circular muscles behind food mass.
- Contraction of longitudinal muscles ahead of food mass.
- Contraction of circular muscle layer forces food mass forward.
What is mechanical digestion?
Process of physically breaking down food to increase its surface area to help facilitate subsequent chemical digestion by enzymes
What are some examples of mechanical digestion in the digestive system?
- Sheering action of teeth
- Stomach churning and muscle contractions
- Small intestine segmentation to ensure food is mixed well with the digestive enzymes
How and where is carb and lipid digestion initiated?
Carb and lipid digestion initially takes place in the oral cavity. Lingual lipase and salivary amylase enzymatically breakdown the carbs and lipids. Von Ebner glands are responsible for the production of lingual lipase.
How is the stomach adapted for mechanical digestion?
3 layers of powerful smooth muscle cells. Additional oblique muscle layer that allows it to trigger powerful muscle contractions to churn and breakdown food in the stomach
What is chemical digestion?
Chemical digestion is the complex series of enzymatic reactions that is required to convert macromolecules into their subunits so that they can be absorbed by the gut epithelial cells in the small intestine
What is secretion?
The release of water, acids, enzymes, and buffer by the gut epithelium and accessory glands to aid chemical digestion
What are some of the secretions released by the gut epithelium to aid chemical digestion?
- Saliva: carb and lipid digestion in the oral cavity.
- Gastric juice: protein digestion in the stomach.
- Bile: emulsification of lipids.
- Alkaline mucous: protects tissue in acidic environment.
- Pancreatic juice: digestion in the small intestine.
What is the process of absorption?
The movement of breakdown products of digestion across the gut epithelium into the lymph vessels, and eventually the circulatory system for distribution around the body.
How is the gut wall of the small intestine adapted for absorption of nutrients?
The small intestine is very long, has villi and microvilli that increase surface area, uses muscular contractions to move and mix food, and receives and houses digestive enzymes and bile that help the breakdown of food.
What are the 4 major layers of the gut wall?
- Mucosa
- Submucosa
- Muscularis externae
- Serosa/ Adventitia
What does regional specialisation of the gut wall mean?
Gut wall differs through the digestive system, depending on the functions of the organs within the system
What are the 3 layers of the mucosa?
- Epithelium
- Lamina propria
- Muscularis mucosae
Describe the mucosal epithelium of the gut wall
Most organs of the digestive system possess simple stratified epithelial cells in their mucosa. The stomach consists of simple columnar epithelium, which protects against the acidic environment of the stomach.
What is the lamina propria?
The lamina propria is a highly vascularised region of the mucosa that is made up of loose (areole) connective tissue. The region is rich in capillaries, which provide nutrients and oxygen, and lymph vessels which help protect the gut for microbial infections due to MALT. Also contains sensory nerve endings and mucous secreting cells.
What is the function of the capillaries located in the mucosa layer of the small intestine?
Absorption of nutrients
Where in the small intestine would expect the mucosa to be most well developed?
Jejunum
What is the main function of the lymphoid MALT cells in the lamina propria?
Protection against pathogens and microbial infection
What is the muscularis mucosae?
Smooth muscle layer comprised of elastic fibres. The main function of this portion of the mucosa is to aid in propelling nutrients and food.
Describe the composition and motion of the muscularis mucosae
Inner circular layer of smooth muscle cells are concentric with the lumen of the digestive system; when this layer contracts, the diameter of the lumen decreases in size. Outer longitudinal layer is smooth muscle cells are parallel with the lumen of the digestive system; when this layer contracts, the gut wall gets shorter.
What is the submucosa?
A thick irregular layer of connective tissue that is rich in large blood vessels that extend into the mucosal layer. Contains lymph vessels, (exocrine) glands, and lymphoid tissue (MALT).
How is the submucosa innervated?
Intrinsic innervation of the submucosa of the gut wall by the enteric nervous system (ENS), also known as the submuocsal plexus.
What does innervation mean?
Innervation means ‘to supply vessels to’ and ‘to supply with energy’.
What is the composition of the muscularis externae?
The muscularis externa (ME) is comprised predominantly of visceral smooth muscle cells (SMCs).
These visceral SMCs are arranged into 2 layers as in the muscularis mucosae.
1. Inner concentric SMC layer
2. Outer parallel longitudinal SMC layer
What is the role of the muscularis externae?
Plays a major role in mechanical digestion and peristalsis movement of food along the digestive system, and is responsible for gut motility
What is gut motility?
Defined by the movement of the digestive system, and the transit of the contents within it.
How is the muscularis externae regulated?
Regulated by the ENS; large myenteric nerve plexus and the Auberbachs plexus.
Describe the Auberbachs plexus
The cells of the Auerbach’s (myenteric) plexus are located between the inner circular and outer longitudinal layers of the muscularis externa. These nerve cells are the portion of the enteric nervous system responsible for generating peristaltic movements.
What determines peristaltic contractions?
Peristaltic contractions of the SMCs is set by pacesetter cells located in the muscularis mucosae and the muscularis externe. The pacesetter cells are electrically coupled to adjacent SMCs by gap junctions. Depolarisation spreads rapidly and induces a wave of contraction in the entire muscle layer.
What is the resting membrane potential of pacemaker cells?
-60 to -50 mV
What is the serosa?
The serosa is a thin layer of connective tissue that contains blood and lymph vessels. Also composed of adipose tissue and covered in simple squamous epithelium; mesothelium.
How does serosa differ from adventitia?
Serous membranes line and enclose several body cavities, known as serous cavities, where they secrete a lubricating fluid which reduces friction from muscle movement. Serosa is entirely different from the adventitia, a connective tissue layer which binds together structures rather than reducing friction between them.
