Digestion & Intestinal Absorption Flashcards
Primary functions of digestive system
- Digestion
- Absorption
- Secretion
- Motility
- Contain endocrine and exocrine cells
- Detect nutrients and secrete hormones
- Where nutrients absorbed
Epithelium
- Loose connective tissue
- Provide support
Lavria Propria
- Layer of smooth muscle
- Helps with motility
Muscularis Mucosa
Point at which CHOs and amino acids enter circulation
Blood and lymphatic vessels
Network of neurons for control of muscular activity
Submucosal plexus
Contraction narrows lumen
Circular muscle
- Innervated autonomically
- Connected submuscal plexus
Myenteric externa
Contraction shortens tract
Longitudinal muscle
Mucosa
- Epithelium
- Lavria propria
- Muscularis mucosa
Submucosa
- Blood and lymphatic vessels
- Submucosal plexus
Muscularis Externa
- Circular muscle
- Myenteric externa
- Longitudinal muscle
- Connective tissue surrounding outer surface of tract
- Sheets of connective tissue connect it to abdominal wall and hold GI tract in place
Serosa
Gastrointestinal Wall
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
Digestion phases
1 - Cephalic phase 2 - Mouth 3 - Saliva 4 - Pharynx 5 - Oesophagus 6 - Epiglottis 7 - Sphincters 8 - Peristalsis 9 - Stomach 10 - Small intestine 11 - Colon 12 - Rectum
- Brain’s anticipation of food
- Saliva production increases - parasympathetic
- Stimulation of gastric juice secretion & insulin secretion
Cephalic phase
- Mechanical breakdown
- Mixing of food with saliva
- Salivary amylase - CHO
- Antibacterial action
Mouth
- Bicarbonate - neutralise acid
- Mucus - lubricates and protects from abrasion
- Salivary amylase - CHO
- Lysozyme - destroy bacteria
Saliva
Prevent aspiration into trachea
Epiglottis closes
Prevent air and stomach contents entering oesophagus
Sphincters at bottom of pharynx and opening to stomach
- Food moves towards stomach due to progressive muscular contraction
- Compresses lumen and forces food along
Peristalsis
- Mechanical breakdown of food into chyme
- Secretion of HCl - kill bacteria
- Peptin begins protein digestion
- Gastric lipase - digestion of fat
- Temporary storage site
Stomach
- Chemical digestion all nutrients - pancreatic and brush border enzymes
- Absorption of end-products, water, ions, vitamins
- Secretion of hormones
- Secretion of bicarbonate-rich fluid
Small intestine
- Absorption of ions and water
- Transformation of chyme into faeces
- Storage of faeces
Colon
Pancreas
- Secretion of pancreatic juice
- Proteases
- Pancreatic lipase
Gall Bladder
Storage and concentration of bile
Liver
- Secretion of bile
* Bile salts
* Phospholipids
* HCO3 - Processing of absorbed nutrients
Presence of CHO in GI tract is an important factor for insulin secretion
Incretin Effect
- Stimulated by nutrients in small intestine
- Secreted by K cells in duodenum & jejunum
- Stimulates insulin secretion
GIP
- Stimulated by nutrients in small intestine
- Secreted by L cells in ileum
- Promotes insulin release
- Inhibits glucagon release
- Delays gastric emptying
- Suppresses appetite & energy intake
GLP-1
Fat
- 100,000 kcal
- 12kg adipose tissue
- 300g muscle triglyceride
- 4.4g in blood
Carbohydrate
- > 3200 kcal
- 350-700g muscle glycogen
- 5g in blood as glucose and lactate
- Increases whole body utilisation
- Maximum rate = 105g/h
- Reduces gut discomfort
- Improves performance
Sucrose
Stomach
- Mucus cells
- Parletal cells
- Chief cells
- Enterochromaffin-like cells
- D cells
Alkaline solution released with mucus to protect stomach lining
Mucus cells
Intrinsic factor necessary for Vitamin B12 absorption
Parletal cells
- Secretes pepsinogen
- Pepsinogen activated by acidic environment
Chief cells
Release histamine to stimulate HCl secretion
Enterochromaffin-like cells
Secrete somatostatin
D cells
- Secreted in gastric pit as pepsinogen
- Activated by acidic environment
- Breakdown proteins into 2-4 amino acids
- Feedback loops prevent self-digestion
Activation of pepsin
- Stimulation by acetylcholine
- Gastrin released, stimulates release of histamine, stimulates HCl production
- When high HCl, somatostatin released. Inhibits histamine, ECL cell and G cell
- Enterogastric reflex
* Pylous detects food enters intestine
* Stimulates negative feedback loop
HCl Production
Fat digestion
1 - Emulsified 2 - Hydrolysed by lipase 3 - Temporarily stored as micelles 4 - Transported into epithelial cells 5 - Re-esterified to triglycerides 6 - Packaged as chylomicron 7 - Transferred into lymphatic system, then bloodstream
Protein digestion
1 - Protein digested by pancreatic proteases & peptidases
2 - Small peptides absorbed via H dependent transport / amino acid enter via Na dependent transport protein
3 - Peptides broken down into amino acids
4 - Amino acids transported into blood
- Rhythmic contraction of longitudinal muscles
- Greater mixing of material
- Net flow through small intestine
Segmentation in small intestine
- Segmentation increased in ileum with gastric emptying
- After majority absorbed, peristalsis increases
Gastroileal reflex
- Moves undigested material to large intestine
- Prevents bacteria remaining too long
Migrating Myoelectric Complex (MMC)
Small intestine motility
- Segmentation
- Gastroileal reflex
- MMC
- Primary storage of material prior to defecation
- Some digestion
- Fluid absorption concentrates faetal matter
Large intestine
Large intestine motility
- Ileocecal sphincter
- Segmentation
- Intense contraction across transverse colon
