Flashcards in Slide Set: 9: Digestive System Deck (118)
What is mass balance in the digestive system
To maintain homeostasis, the volume of fluid entering the GI tract by intake or secretion must equal the volume leaving the lumen.
4 processes of the digestive system
- Digestion: Chemical and mechanical breakdown
- Absorption: Movement of material from GI lumen to ECF
- Motility: movement by muscle contraction
- Secretion: hormones and enzymes
Primary function of the digestive system
–Transfer nutrients, water, and electrolytes from ingested food into body’s internal environment
–Ingested food is essential an energy source and for supplies for the building blocks of tissues
The stomach continues digestion that began in the mouth by mixing food with acid and enzymes to create chyme.
What happens to the products that are digested and absorbed?
- move into the blood or lymph for distribution
- waste remaining leaves the body through anus
a narrow tube that travels through the thorax to the abdomen.
a baglike organ that can hold as much as 2 liters of food and fluid when fully (if uncomfortably) expanded.
The stomach is divided into three sections:
opening between the stomach and the small intestine is guarded by the pyloric valve.
what is the function of pyloric valve
thickened band of smooth muscle relaxes to allow only small amounts of chyme into the small intestine at any one time.
small intestine is divided into three sections:
What happens in the large intestine?
water and electrolytes are absorbed out of the chyme to form feces
distension of the rectal wall triggers a defecation reflex.
Feces leave the GI tract through the anus, with its external anal sphincter of skeletal muscle, which is under voluntary control.
The GI tract wall consists of four layers:
(3) muscularis externa
1. mucous membrane
2. lamina propria
3. muscular mucosa
The entire wall is crumpled into folds called ____ in the stomach, and ____ in the small intestine.
The intestinal mucosa also projects into the lumen in small fingerlike extensions known as _____
Where is submucosa found and what is its function?
The layer of the gut wall adjacent to the mucosa, the submucosa, is composed of connective tissue with larger blood and lymph vessels
muscularis externa consists primarily of two layers of smooth muscle: (functions)
- inner circular layer --> contraction decreases diameter of lumen
- outer longitudinal layer --> shortens the tube
Motility in the gastrointestinal tract serves two purposes:
- moving food from the mouth to the anus
- mechanically mixing food
- mixing maximizes exposure of the particles to digestive enzymes by increasing particle surface area.
What happens during peristalsis? how does it propagate?
- wave movements
- circular muscles contract just behind bolus
- contraction pushes the bolus forward
- circular muscles are relaxed
- receiving segment then contracts
how do segmental contractions occur, which muscles are involved and what is the purpose
- segments of intestine alternately contract and relax.
- In the contracting segments, circular muscles contract while longitudinal muscles relax.
- Alternating segmental contractions churn the intestinal contents, mixing them and keeping them in contact with the absorptive epithelium.
migrating motor complex (MMC)
is a series of contractions that begin in the empty stomach and end in the large intestine.
What are Slow waves
are spontaneous depolarizations in GI smooth muscle
What are tonic contractions
that are sustained for minutes or hours occur in some smooth muscle sphincters and in the anterior portion of the stomach.
What are phasic contractions
with contraction-relaxation cycles lasting only a few seconds, occur in the posterior region of the stomach and in the small intestine.
________ deep in the gastric glands secrete hydrochloric acid into the lumen of the stomach.