8.2 Overview of Digestive System Functions Flashcards
What is the function of the digestive system?
Transfer nutrients, water, and electrolytes from food into the internal environment
What is the process by which food is broken down so that it can be absorbed?
Digestion
What percentage of the food we ingest is digested?
95%
Is the gastrointestinal tract part of the internal environment?
No; it is continuous with the external environment (like the inside of a straw)
What comprises the digestive system?
Digestive tract+ accessory digestive organs
What is the digestive function of the mouth?
- Mastication
- Some carb. digestion
What is the digestive function of the pharynx & oesophagus?
Swallowing and transporting food to the stomach
What is the digestive function of the stomach?
Mixing, churning, digestion
What is the digestive function of the small intestine?
Digestion and most absorption (with help from liver and pancreas secretion)
What is the digestive function of the large intestine?
Completes absorption of water and electrolytes
What are the four accessory glands of the digestive system?
- Salivary glands
- Pancreas
- Liver
- Gall bladder
What is the digestive function of the salivary glands?
- Secretes amylase
- Mucous for lubrication
- Lysosyme
- Dilutes, cools, and buffers
What is the digestive function of the pancreas?
- Pancreatic juice (enzymes and aqueous, bicarbonate-rich solution)
- Enzymes can almost digest everything
What is the digestive function of the liver?
- Secretes bile
What is the digestive function of the gallbladder?
- Stores bile
What are the three layers of the digestive mucosa?
- Simple columnar epithelium (endo/excorine glands, secretion of mucous)
- Lamina propria (gut associated lymphoid tissue)
- Muscular mucosa (thin layer of smooth muscle separating mucosa from submucosa)
What is the function of the gut-associated lymphoid tissue? Where is it?
- Defending against pathogens
- Found in lamina propria of GI mucosa
What is contained within the submucosa?
- Larger blood vessels
- Larger lymph vessels
- Nerve network (submucosal plexus)
What are the two layers of the muscularis externa?
- Inner circular
- Outer longitudinal
What do the contractions of the two layers of the muscularis externa do?
Circular: changes diameter
Longitudinal: changes length
Where is the myenteric plexus located?
Between the circular and longitudinal layers of muscularis externa
What is the serosa continuous with? What does it secrete?
- Continuous with mesentery
- Secretes serous fluid for lubrication of organs
What are the four basic digestive processes?
- Motility
- Secretion
- Digestion
- Absorption
What are the two main kinds of digestion?
- Mechanical
- Chemical
Where are substances absorbed into from the digestive system?
Blood and lymph
What type of muscle is important in digestive motility? How does this make sense in terms of involuntary control?
- Smooth
- Makes sense: smooth muscle cannot voluntarily be controlled
Describe the tone of digestive smooth muscle
Constantly low; prevents permanent distension
What are the two types of phasic digestive mobility?
- Propulsive (peristalsis)
- Mixing (segmentation)
What is the main chemical process underlying digestion?
Hydrolysis
Which substances can be actively/passively absorbed?
Active: protein & carbs
Passive Fat (into lymph)
What are the four factors that regulate digestion?
- Autonomous smooth muscle function
- Intrinsic nerve plexuses
- Extrinsic nerves
- Gut hormones
What are the autonomic pacemakers of the GI tract? How are they connected to smooth muscle?
Cells of Cajal; connected by gap junctions to smooth muscle cells
Name one neurotransmitter that causes contraction/relaxation of enteric smooth muscle
Relax: NO
Contract: Ach
Do the inrinsic nerve plexuses coordinate long-range, local activity, or both?
Local (e.g. food stuck)
Describe the types of nerves in the enteric system
- Sensory (Intrinsic Primary Afferent)
- Interneurons
- Motor (excitatory and inhibitory)
What section of the nervous system makes up the extrinsic nerves of the enteric nervous system?
Autonomic
In what ways do extrinsic nerves influence the enteric nervous system?
- Acting on intrinsic nerves
- Changing hormone secretion
- Acting on effector cells
True or false: extrinsic nerves cannot coordinate activity between different regions of the digestive tract
False. They can, and do.
