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Flashcards in Gastrointestinal System Deck (15)
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1

CONTRIBUTION OF THE GIS TO HOMEOSTASIS

- GIS helps deliver nutrients to circulatory system (humans get water & nutrients from external environment)
- Serves as excretory functions

2

DIGESTION

Breaking down food into molecules that can be absorbed (2 types)
- Mechanical→ apply physical force to food (chomping, mixing)
- Chemical→ Converts complex large molecules into simpler ones (through enzymes and chemicals)

3

DIGESTION STARTS AT ORAL CAVITY

- Mechanical→ teeth + tongue + saliva→ forms bolus
- Chemical→ Starch breakdown by salivary amylase (enzyme) into simpler molecules

4

OESOPHAGUS

- Food swallowed enters oesophagus→ bolus transported to stomach by peristalsis
- Peristalsis→ muscle contraction and relaxation (GI contents move along tract this way)

5

FROM OESOPHAGUS TO STOMACH

- Bolus goes inferiorly along oesophagus (throat→ neck→ thoracic cavity→ abdominal cavity)
- Sphincter (smooth muscle) and diaphragm contact and close of oesophagus at this point

6

THE STOMACH

- Mechanical→ churning action combines bolus with gastric acids (forms chyme)
- Chemical→ Gastric juice contains hydrochloric acid and pepsin (enzyme) → starts protein digestion
- Gastric juice contains intrinsic factor→ essential for B12 absorption

7

LEAVING THE STOMACH

- Approx 3ml chyme released into small intestine with each wave of peristalsis
- Only small amounts of chyme delivered to SI→ food needs to be completely mixed with digestive enzymes

8

UNIQUE STRUCTURAL FEATURES OF THE LINING OF THE SMALL INTESTINE

- Mucosa (made of villi; finger-like projections) and submucosa are in circular folds
- Mucosa cells’ plasma membrane in contact with chyme→ made of microvilli
- Microvilli→ primary surface of nutrient absorption in GI tract; membrane packed with enzymes (helps break down complex nutrients)

9

LIVER AND GALL BLADDER: BILE

- Bile essential for fat digestion
- Produced in liver; travels to duodenum via bile duct (enters duodenum via Sphincter of Oddi)
- Between meals sphincter closed and bile backs up; drains to gall bladder where it’s stored
- Arrival of chyme in duodenum→ sphincter opens and gall bladder contracts (forces bile out)

10

PANCREATIC JUICE SECRETION

- Pancreatic juice reached duodenum via same sphincter of Oddi
- Juice rich in enzymes; degrades all types of nutrient molecules

11

DIGESTION IN SMALL INTESTINE

- Involves bile, pancreatic juice and digestive enzymes attached to surface of mucosal cells of SI
- Net result→ soup of smaller and simpler molecules

12

ABSORPTION

- Smaller and simpler molecules produced by digestion, transported across mucosa cells and into submucosa
- Most nutrients absorbed into submucosal capillaries; blood in them drains to hepatic portal vein
- Exception; fats (these are transported from GIT via lymphatic vessels of tract)

13

ABSORPTION OF WATER

- In addition to what is ingested; 9L of water secreted into GIT
- 80% of osmosis (water reabsorption) occurs in SI
- Nearly all water entering LI is reabsorbed→ only 100-150mL lost in faeces

14

PROCESSING CHYME IN LARGE INTESTINE

- Every day approx 1L of chyme delivered to LI
- Absorption of nutrients in LI restricted to ions and water
- Resident bacteria of LI; important source of vit B and vit K
- Reabsorption of water renders liquid chyme to semisolid feces

15

DEFECATION

- Local reflex triggered by bloating of rectum by feces→ initiates colon contractions
- Relaxation of internal smooth muscle sphincter occurs
- External anal sphincter must be relaxed for feces to be expelled; under voluntary control