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Flashcards in GI tract Deck (34):
1

Describe the peritoneum

Double layered serous membrane covering abdominal and pelvic cavities
Parietal peritoneum lines the body wall
Visceral peritoneum lines the organs
Peritoneal cavity lies in between parietal and visceral and contains serous fluid

2

Intraperitoneal organs

Organs fully covered by the peritoneum eg. stomach

3

Retroperitoneal organs

Organs pushed up against posterior abdominal wall and partially covered by peritoneum eg. pancreas

4

Mesentery

A double layer of visceral peritoneum, attaches an organ to the body wall

5

Omentum

A double layer of visceral peritoneum that attaches one organ to another eg. lesser and greater omentum

6

Name the 4 basic layers of the GI tract

Mucosa - epithelium, lamina propia and muscularis mucosa
Submucosa - dense irregular connective tissue
Muscalaris externa - smooth muscle cells, peristalsis
Serosa/adventia - serous membrane

7

Arterial supply to tract

Celiac trunk
Superior mesenteric artery
Inferior mesenteric artery

8

Venous drainage

Blood from stomach, pancreas, S and L intestines drain to liver via hepatic portal vein

9

Hormonal control

Enteroendocrine glands secrete gastrin, secretin and CCK

10

Functional processes of digestive system

Motility
Digestion
Secretion
Absorption
Protection

11

Motility

Mechanical digestion:
- chewing
- churning
- segmentation
Propulsion:
- swallowing
- peristalsis
- mass movements
- elimination

12

Mechanical digestion

Breaks down food into bolus so easier to move through tract and increases SA
Chewing - teeth, tongue, salivary glands
Churning - includes stomach and L intestine
Segmentation - cycles of contraction that fragment the bolus and mix it with digestive juices, in S intestine

13

Propulsion

The movement of digestive materials along the tract
Swallowing - 3 stages, oral, pharyngeal and oesophageal
Peristalsis - waves of muscular contraction that move bolus along
Mass movements - occur in L intestine, powerful contractions that push bolus into rectum, produce urge to defecate
Elimination - defecation reflex, internal anal spincter relaxes, external anal spincter contarcts, conscious effort requires to relax external sphincter

14

chemical digestion

Breakdown of food into smaller fragments that can be easily absorbed
Carbs = simple sugars
Proteins = amino acids
Lipids = fatty acids
Secretion
Absorption
Protection

15

Secretion

Exocrine glands (salivary, pancreas) release enzymes, water, salts, buffers and mucus
Cells of stomach, S intestine and liver release enzymes, water, bile, salts and buffers
Endocrine glands eg. pancreas release hormones

16

Absorption

Passage of substances across digestive epithelium into blood or lymph
Occurs in stomach and S intestine

17

Protection

GI tract protects itself against:
- acids
- mechanical trauma
bacteria

18

Mouth

Mechanical digestion = chewing
Chemical digestion = salivary amylase causes carb digestion, lingual lipase causes lipid digestion

19

Salivary glands

1-1.5 L saliva a day
- salivary amylase
- serous fluid
- mucin (lubrication)
lysozyme
immunoglobulin A

20

Oesophagus

Extends from pharynx to stomach
25cm long
Lined by stratified squamous epithelium
Innervated by ANS

21

Stomach

Located in epigastrium
- storage
- mechanical and chemical digestion
- protection
- absorption
- production of intrinsic factor
Extra layer of muscle:
> inner - obliqe
> middle - circular
> outer - longitudinal

22

Cells of the stomach

Mucous cells and mucous neck cells - secrete mucous
Parietal cells - hydrochloric acid and intrinsic factor
Chief cells - pepsinogen
Enterendocrine - gastric

23

Gastric juice

1.5/2 L/day
Secretion activated by low pH, gastrin, histamine and Ach
HCl = kills microbes, breaks down connective tissue
Pepsin = protein digestion
Gastrin = stimulates secretion of pepsinogen and HCl, contractions of gastric wall
Intrinsic factor aids absorption of Vit. B12

24

Regulation of gastric activity

1. cephalic phase - site, smell and taste of food
2. gastric phase - food in stomach = gastrin secretion, stimulates gastric juice production
3. intestinal phase - partially digested food arriving in duodenum slows down production of gastric juices

25

Pancreas

Retroperitoneal
Sits in curve of duodenum, posterior to stomach
Head, body and tail
Pancreatic duct opens into duodenum at sphincter of Oddi
Exocrine - acini cells secrete enzymes eg. propeptidases, lipase, amylase, duc cells swcrete water and sodium bicarbonate
Endocrine - islets of Langerhans (alpha cells = glucagon, beta cells = insulin)

26

Liver

Lies in right hyochondrium and epigastrium
4 lobes = right left, caudate and quadrate
Bile production
Important for metabolism

27

Gall baldder

Stores and concentrates bile
Inner mucosa folded to rugae for expansion
Holds 40-70ml

28

Small intestine

6 metres long
3 parts:
- duodenum
- jejunum
- ileum
Has villi and microvilli to increase SA
Mechanical and chemical digestion, absorption

29

What does CCK act on in small intestine?

Pancreatic acini to release enzymes
Gall balder to release bile
Sphincter of Oddi to relax
Stomach to decrease gastric motility and secretion

30

What does secretin act on in small intestine?

Pancreatic duct cells to release water and sodium bicarbonate
Liver to secrete bile
Stomach to decrease gastric motility and secretion

31

Protein Digestion & Absorption

Trypsinogen converted to trypsin by enterokinase
Trypsin activates other pro-peptidases
Activated peptidases breakdown proteins into amino acids - absorbed by FD and co-transport

32

Carbohydrate Digestion and Absorption

Maltase converts maltose - glucose + glucose
Lactase converts lactose - glucose + galactose
Sucrase converts sucrose - glucose + fructose

33

Large intestine

Special features:
- goblet cells
- haustra
- epiploic appendages
- taenia coli
Absorption of water and electrolytes
Storage of undigested materials eg. fibre

34

Bacterial flora

Bacteria populate large intestine
Ferment undigested carbs
Synthesise Vitamins B and K