Digestive system and Liver Flashcards
1
Q
What is digestion?
A
The breakdown of food to a useful form that can be absorbed and used by cells – liberating useful components (amino acids, fatty acids, glucose and nucleotides)
2
Q
What is food used for?
A
- Energy creation in cellular respiration – catabolism (break down of molecules) to produce ATP
- Repair and building – production of building blocks – known as anabolism
3
Q
How is food broken down?
A
- Mechanical – physical breakdown – mastication and churning
- Chemical - acids, surfactants and enzymes
4
Q
What are the two divisions of the digestive system?
A
- Alimentary canal (tube like structure including small and large intestine, rectum mouth to anus)
- Accessory organs – outside GI tract (biliary tract and liver (gallbladder bile ducts), pancreas (digestive enzymes), salivary glands)
5
Q
What is the process of digestive system?
A
- Ingestion (eating)
- Propulsion (moving)
- Digestion (mechanical, chemical)
- Absorption (into bloodstream)
- Defecation (avoiding waste materials)
6
Q
What are the components of saliva?
A
- 99% water (change in sympathetic and parasympathetic (more watery)
- Amylase (starch breakdown into simple sugers like glucose)
- Lingual lipase (breakdown fatty materials and control growth of bacteria)
- Antibodies \lysozyme (immune system)
- Defensins (perforin (break membrane)
- ‘friendly bacteria’
7
Q
What are the layers of the GI tract wall?
A
- Outer = serosa
- Muscularis – muscular
- Submucosa
- Mucosa – secrets enzymes and mucus into the lumen and absorptive
8
Q
What is the serosa layer of the the GI tract wall?
A
(adventitia)
- bounding defining membrane epithelium
- more fibrous when attached to body walls it becomes adventitia here
- can stretch to accommodate food
- Outer layer
9
Q
What is the muscularis layer of the GI tract wall?
A
Two muscular (nervous supply)
1. Longitudinal muscle - layers giving tone and help gut change length
2. Circular muscle – churing process called segmentation – processes peristalsis (muscular wave moving food down)
- Onward movement
- Regulated by sphincters
10
Q
What is the submucosa layer of the GI tract wall?
A
- Rich blood supply and associated with nerve supply
- Contains mucus glands dumping mucus through glandular tubes into gut
- Rich lymphatic supply for secretory glands (mucus production and digestive juices)
- Rich nervous supply
- Lymph vessels and lymphoid tussis
11
Q
What is the mucosa layer of the GI tract wall?
A
- Protective and for absorption
- muscularis mucosae(longitudinal muscle) – tone to push lumen layer into spiralised folds
- Mucosal lining - simple columnar epithelium around lumen – goblet cells (mucus secretion) – enzyme secretion and hormone secretion
- Lamina propria - areolar connective tissue layer rich capillary supply for absorption – contains lymphoid tissue (/folicus) act as early warning system to immune system containing macrophages and dendritic cells
12
Q
What are the three layers of the mucosa?
A
- Muscularis mucosae
- Mucosal lining
- Lamina propria
13
Q
What is chyme?
A
- In lumen
- Food that is digesting as well as enzymes and mucus
- Food in the process of digestion
14
Q
What are Mesenteries and lymph nodes?
A
- Continuous with saros
- Provides rich blood, nervous system and lymphatic drainage supply
- Keeps GI tract suspended
15
Q
What is peristalsis?
A
- Using circular muscles – contracting pushing bolus of good in peristatic wave down the oesophagus and to the stomach
- Controlled by nervous system – enteric nervous system – local reflex arcs between receptors and motor activators of muscles
- Contracting and relaxation of muscle
- Autonomic NS has overall control of amount of digestion however enteric local reflex’s in control of peristalsis
16
Q
What are the Two Intrinsic nerve plexuses – in wall of gut?
A
- Myenteric (Auerbach’s) plexus – main muscular - motor (symp and parasympathetic)
- Submucosal (Meissner’s) Plexus – secretomotor (para onlu) – controls glands for digestice juices
17
Q
What is the enteric nervous system?
A
- Secondary brain – in gut
- Diffuse net of nerve cells as not same compact setup as central nervous system
- Semi automatic of gut mobility
18
Q
What is the oesophagus?
A
- Up to 30cm
- Conveys food from oropharynx to stomach
- Mucosa subject to considerable friction
- Thick protective squamous epithelium – sloughs off to prevent friction – 10-40% of faeses is made of body cells
19
Q
How does structure effecting the function of oseophagus?
A
Passage of food facilitated by:
- Flattening of mucosal folds
- Mucous glands
- Loose and elastic submucosa
20
Q
What is the muscularis externa?
A
- Muscle layer of oesophagus
- Upper third – skeletal muscle (initiation of swallowing voluntary)
- Lower 2 thirds smooth muscle only – peristalsis
21
Q
Whats does the stomach do?
A
- Stores food up to 2 hours – mechanical and chemical breakdown
- Extra layer in muscularis – oblique (helps mechanical breakdown)
- Highly secretory mucosa (HCl (hydrochloric acid to sterilise and breakdown food – helps acyivate pepsin), pepsin (protein breakdown) and mucus(protects us from HCl and pepsin enzyme without you can get gastric ulcers))
22
Q
Whats the structure of the stomach?
A
- Oesphagus – into stomach
- Cardia – nearest to heart – rich in mucus glands – produce alkaline mucus to neutralise to stomach before chance of leaking back into oesophagus – found right next to oesophagus – can cause acid reflux if ineffective
- Fundus and body – producing pepsin and HCl
- Pyloric end (antrum, canal and spincter valve at pylorus) – mucus glands
- Duodenum – end and into intestine
23
Q
Whats the stomach lining?
A
- Simple columnar epithelium
- Each epithelial cell is held together with tight junctions – proteins keeping compact structure – prevent pepsin and HCl leaking into tissues of stomach
- Gastric pits
- Sheets – alkaline containing mucus - bicarbonate secreted to make mucus alkaline
- Layer turn over every 2/3 days
24
Q
Give examples of mucus glands in the stomach
A
- **Surface mucous cells **– produce alkaline mucus – bicarbonate
- Mucous neck cells – simple columnar – secreted acidic mucus
- Parietal cells secrete HCl and intrinsic factor (vitamin B12 absorption in intestine)
- Chief cells secrete pepsinogen (precursor to pepsin not functioning to prevent breakdown) and lipases (fatty lipid break down)
-
G-Cells secrete gastrin (stimulates parietal cells)
- Three areas – duodenum – jejunum – ileum
- Glands secrete intestinal juice
- Completes chemical digestion
- Absorption of nutrients (very long structures help)
25
What do surface mucous cells do?
produce alkaline mucus – bicarbonate
26
What do mucous neck cells do?
simple columnar – secreted acidic mucus
27
What do parietal cells do in stomach?
secrete HCl and intrinsic factor (vitamin B12 absorption in intestine)
28
What do chief cells do in the stomach?
secrete pepsinogen (precursor to pepsin not functioning to prevent breakdown) and lipases (fatty lipid break down)
29
What do G-Cells do in the stomach?
secrete gastrin (stimulates parietal cells)
30
What do the small intestine do?
- Three areas – duodenum – jejunum – ileum
- Glands secrete intestinal juice
- Completes chemical digestion
- Absorption of nutrients (very long structures help)
31
Three areas of small intestine
– duodenum – jejunum – ileum
32
What do the foldings of the small intestine lining do?
- Mucosal folds, villi and microvilli increase surface area for digestion and absorption
33
What cells are found in small intestine cells?
1. Absorptive cells
2. Goblet cells – mucus secretion
3. Peneth cells – defensins and lysozyme (help bacterial load)
4. Secretory cells – intestinal juice (emulsify and bulk up cyme in gut, absorption of nutrients from cyme is easier)
5. Entero-endocrine cells – secretin(inhibits gastric emptying to pace digestion) and cholecyokinin (CCK, control pancreatic, bile secretion and stimulates vagal tone in homeostasis (from rest and digest to fight and flight)
6. Intestinal crypt (crypt of lieberkuhn)
34
What does the duodenum do in small intestine?
- Brunners glands
- Secrete alkaline mucus – neutralize chyme, protect mucosa
- Cholecystokinin (CCK) production
- Chemical digestion of fatty lipids – bile to neutralise
35
What does the jejunum do in the small intestine?
- Main absorption region – glucose, vitamins, amino acids and fats
- Few brunner glands
- pH from neutral to alkaline
- mucosal folds – large and numerous
- rapid absorption
- longest villi found here
36
What does the ileum do in the small intestine?
- Distal part of small intestine
- Peyer patches – in lamina propria - Immune system warning – surveying the gut to prevent pathogens
- Huge domes of lymphoid tissue
- Absorption of vitamin B12 using intrinsic factor produced in stomach
- Bile salts recovered 95%
37
How is intestinal secretion controlled?
- 1-2l intestinal juice (water, mucus, secretin, CCK) – secreted daily
- Stimulus for production – presence of chyme in intestine
- Secretin stimulates liver cells to release bile and pancreatic secretion
- CCK stimulates gallbladder contraction and pancreatic secretion
38
Explain the mechanical mechanism of segmentation
- Physically mixing condense of gut
- Segmentation – all content of cyme fits absorption areas
- Differential contractions under enteric nervous system into series of pockets which then differentiate due to different circular muscles again to mix contence of gut
39
What does the colon do?
- Absorption of water and elimination of faeces and absorption of salt
40
State components of colon
1. 3 bands Teniae coli
2. Epiploic appendage
3. Haustra
4. Thick muscukar wall
41
What is 3 bands Teniae coli?
bands of longitudinal smooth muscle – shorten length of tube causing pocket like sacks so cyme moved between then as water and salt is removed
42
What is an epiploic appendage?
fat filled pouches – may have sensory role but know one knowns
43
What is haustra?
pocket like sacs
44
What does the thick muscular wall do in colon?
water is removed helps consistency of faeces gets more hard throughout
45
What is the appendix?
- If removed theres higher chance of bowel infections
- Heavy level of lymphatic protective tissue - Safe haven for bacteria – to protect from immune response
46
Whats the structure of the colon?
- Thick mucosa – simple columnar epithelium – except anal canal
- Many crypts – absorptive cells, goblet cells (mucus production)
- No circular folds
- No villi Cyme cells produce hormone polypeptide y y - inhibiting motility promotes water and salt absoption
47
Whats the bacterial flora in colon?
- 10 million types
- Synthesize vitamins B and K
- Metabolize molecules eg. Heparin, mucin
- Ferment indigestible carbohydrates – produce 500ml flatus daily (farting)
48
What is the rectum and anal canal stucture?
- Rectum valve (3/4) – support weight of faecal matter – also sensory difference between faeces and gas
- Anal canal – stratified squamous epithelium – level of protection
- Anal column (between which are sinus) – produce mucus when compressed
- Anal sinus – releases mucus when compressed
- External anal sphincter - voluntary – skeletal muscle – trying not to go to loo to contract – under central control
- Internal anal sphincter – involuntary – smooth muscle
- Hemorrhoidal material – gorges when not defecating to close anus
49
What is the defecation reflex?
- Relaxation of internal anal sphincter due to relax arc
- stretch receptors in wall of rectum
- stretch sends signal to spine
- local reflex loop to relax muscle and internal anal sphincter
