Post on 09-Apr-2018
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Digestive System
Top to Bottom
Physiology Group
Dr Usama ALAlami
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Digestion
³Breakdown of huge food molecules into small ones´
Digestive Process
[1] Ingestion ³Taking food into the digestive tract´
[2] Propulsion ³Move food through alimentary canal´
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Propulsion
In olun ary
(Peristalsis)
Volunta y
(Swallowing)
opulsion
Peristalsis ³Adjacent sections of the alimentar y canal
alternately contract and relax´
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Coordin ted Muscul r Contr ctions
Produce Perist ltic Movements
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Mechanical Digestion
Chewing
Mixing of food with saliva using tongue
Churning of food in the stomach
Segmentation
Chemical Digestion
Begins in the mouth and ends in the small intestine.
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[4] Absorption´Digested end products (+minerals,
vitamins and water) absorbed to blood
and lymph supply´
[5] Defecation´Need I explain this ?´
Digestive Tr act (Alimentar Canal)
Mouth Rectum
Pharynx Anal canal
Oesophagus AnusStomach
Small intestine
Large intestine
ARSE
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Digestive Tr act
(Alimentar
Canal)
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1. Buccal cavity.
2. Tongue.
3. Oesophagus.
4. Diaphragm.
5. Stomach.
6. Pyloric sphincter.
7. Liver. 8. Gall bladder.
Ke To The Diagr am Of The Digestive
S stem
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Ke To The Diagr am Of The Digestive
S stem
9. Bile duct.
10. Pancreas.
11. Duodenum. 12. Ileum.
13. Caecum.
14. Appendix.
15. Colon. 16. Rectum.
17. Anus.
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Accessor Digestive Organs
Teeth
Tongue
Gallbladder
Salivary Glands (Saliva)
Liver (Bile)
Pancreas (Enzymes) Aid in food breakdown
Blood Suppl
Arteries branch off the abdominal aorta to:
a) Digestive Organs
b) Hepatic Portal Circulation
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Arterial Suppl
Hepatic Artery (supply liver)
Splenic (supply spleen)
Left gastric (supply stomach)Branch from celiac trunk
Superior/inferior mesenteric arteries
(supply small and large intestine)
Digestive system receives approximately 25% of cardiac
Output.
This increases after a meal.
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Histolog of
the Alimentar
Canal
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b) Lamina Propria
Well vascularized (nerves and lymph vessels)
Defence against intestinal bacteria bacteria
c) Muscularis Mucosa
Outer layer of smooth muscle
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[2] Submucosa
Thick layer of connective tissue.
Provide distensibility and elasticity
Contain large blood and lymph vessels.
Contains nerve networks = SUBMUCOUS PLEXUX
Therefore, controls local activity of each gut region.
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[3] Muscularis Externa
rtenin f t e tu e
C ntracti n
uter l n itu inal area
ecrease lu en ia eter
C ntracti n
Inner circular area
Muscul ris Ext r
Major smooth muscle layer.
MYENTERIC PLEXUS between the two layers = regulate
local gut activity.
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[4] Serosa
Outer covering of digestive tract.
Secretes serous fluid lubricate and prevent friction
between digestive organs and surrounding viscera.
Serosa is continuous with mesentery.
Mesenteric tearing H ERNIA
Hernia ³Protrusion of an organ through the muscular wall
of the cavity that contains them´
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Regulation Of Digestive Function
Digestive function is controlled by four factors:
* Autonomous smooth muscle function.
* Intrinsic nerve plexuses
* Extrinsic nerves
* Gastrointestinal hormones
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Autonomous Smooth Muscle Function
Smooth muscle cells of the digestive system possess
³Basic Electrical Rhythm´ (BER).
This does not directly induce contraction
When a large group of cells reach excitation contraction
Whether contraction is achieved depends on:
@ Mechanical effects
@ Nervous system
@ Hormonal effects
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Intrinsic Nerve Ple uses
Nerve Plexus³Interconnecting network of nerve cells´
(1) Submucous (Meissner¶s) plexus in submucosa
(2) Myenteric (Auerbach¶s) plexus between longitudinal and
circular smooth muscle cell layers.
They run the entire length from oesophagus to anus.
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Intrinsic plexuses influence:
a) Smooth muscle contractility
b) Exocrine cell secretion (digestive juices)
c) Endocrine cell secretions (digestive hormones)
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Extrinsic Nerves
Sympathetic and parasympathetic nerve branches.
Sympathetic ³fight or flight´ = slow digestive function.
Parasympathetic dominant in quiet relaxed situations.
Arrive by way of V AGUS nerve increase smooth muscle
contractility + secretion of digestive enzymes and
hormones.
Autonomous nervous system also coordinates between
different organs of the digestive tract.
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Extrinsic Nerves
Alter digestivemotility
Directlyonsm. muscleandgland Alter levelsof GI hormones
Alter digestivetract secretio
Modifyintrinsicplexuses
ExtrinsicNerves
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Gastrointestinal Hormones
Endocrine cells within mucosa release hormones into blood
They affect:
@ Exocrine gland secretions
@ Smooth muscle cells
@ Pancreatic endocrine cells influence food storage
and uptake.
Effect is direct on endocrine glands or indirect on nerve
plexuses or extrinsic autonomous nerves.
GI hormones released in response to changes in luminal
content (protein, fat or acid).
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Receptors Of The Digestive Tr act
[1] Chemoreceptors
[2] Mechanoreceptors (Pressurereceptors)
[3] Osmoreceptors
Activities of these receptors results in:
a) Short neural reflex (via intrinsic nerve plexuses)
b) Long neural reflexes (via autonomous nerves)
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Palate
Arched roof separating mouth from nasal passage
Allows chewing, breathing and sucking to take place
Simultaneously.
Failure of this fusion causes CLEFT PALATE .
Anterior = Hard palate = bone
Posterior= Soft palate = skeletal muscle
Uvula = Hangs from soft palate seals off nasal passage
during swallowing.
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Tongue
Composed of voluntary skeletal muscle
Houses taste buds, serous and mucous glands
Helps reposition food between teeth and mix it with saliva
(Bolus)
Non digestive functions:
* Speech
* Snogging
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Teeth
First step in digestive process is mastication (chewing).
Exposed portion of tooth = enamel = hardest substance in
body.
Occlusion ³Upper and lower teeth fit together when jaws are
closed´
Malocclusion due to:
1) Overcrowding of teeth too large to fit in the jaw space
2) One jaw displaced in relation to the other
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This results in inefficient chewing and pain in the
temporomandibular joint.
Purpose of mastication:
1} Grind food into smaller pieces to fascilitate swallowing
2} Mix food with saliva
3} Stimulate taste buds
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Also known as cavities
Tooth and Gum Diseases
[1] Dental Caries (Rottenness)
Due to dental decay
Decay due to dental plaque (film of sugar, bacteria and
mouth debris)
Bacteria metabolise sugar acid decay
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Effect of plaque on gums
[2] Calculus (Stone)
Disrupt seal between gingivae and teeth
Risk of gum infection
Gums bleed, sore and swollen (Gingivitis) (reversible)
If plaque not removed, this leads to ..
[3] Peridontal Disease (Peridontitis)
Treated by antibiotics
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Salivar Glands
Saliva secreted by
[1] Extrinsic salivary glands (Major)
[2] Intrinsic salivary glands (minor)
(in mucosa lining the cheeks)
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Extrinsic Salivar Glands
Sublingual
ParotidSubmandibular
Extrinsic Salivar Glands
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Extrinsic
Salivar Glands
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Lie outside oral cavity and discharge saliva through small
ducts into mouth.
Sublingual: Below tongue
Submandibular: Below mandible
Parotid: (par=near, otid=ear) anterior to ear.
Mumps ³Inflammation of the parotid gland caused by the
mumps virus (myxovirus) resulting in fever and
pain upon chewing´
Composed mainly of serous cells (watery secretion of
enzymes and ions) and mucous cells (viscous secretion
of mucus).
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Sublingual: Mostly mucous cells
Submandibular and buccal: Equal proportion of both
Parotid: Only serous cells
Composition Of Saliva
99.5% water, 0.5% protein and electrolytes
Saliva begins digestion of carbohydrates in mouth by
salivary amylase.
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Saliva facilitates swallowing by moistening food particles
via mucus (thick and slippery)
Saliva possesses antibacterial action through:
@ Lysozymes
@ Rinsing away material that may serve as food
source for bacteria.
Saliva is neither sugary or salty important for perception
of sweet and salty tastes.
Bicarbonate in saliva neutralizes acid in food.
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Facilitates speech via moistening of lips and tongue
X er ostomia ³Diminished saliva secretion´
Result in difficulty in chewing, swallowing, inarticulate speech
and dental caries.
Control Of Salivar Secretion
1-2 litres daily
Basal secretion due to direct autonomic nerve stimulation
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Enhanced secretion of saliva due to:
(1) Simple unconditional salivary reflex
(2) Acquired or conditional salivary reflex
Very little digestion action in mouth
Amylase action accomplished in body of stomach
No absorption of foodstuff
However, absorption of therapeutic agents occurs via oral
mucosa (e.g. nitroglycerine)
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Phar nx and Oesophagus
Motility associated with pharynx and oesophagus is
³swallowing or deglutition´.
Bolus from mouth through oesophagus into stomach.
Swallowing is initiated voluntarily.
But once initiated it can¶t be stopped
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Peristalsis In
The
Oesophagus
(Anterior View)
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Mechanism Of Swallowing
S O ING
Smmot muscl cell contr ct
ff er ent Impulses to Swallowing entr e in udulla
Pr essur e eceptor s
Bolus
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Swallowing
[1] Orophar ngeal Stage
Lasts about 1 second
Mouth to pharynx to oesophagus
Food must be prevented from re-entering:
a) Mouth: Position of tongue against hard palate.
b) Nasal Passages: Uvula elevated against back of throat.c) Trachea: Cartilaginous flap = epiglottis = seals trachea.
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[2] Oesophageal Stage
Muscular tube (approx 25 cm long)
Connects pharynx to stomach.
Penetrates diaphragm at oesophageal hiatus
Stomach protrusion through this Hiat al Hernia
Two locks or sphincters:
1) Pharyngooesophageal sphincter (top): Prevents large
volumes of air entering digestive tract eructation
(burping).
2) Gastrooesophageal sphincter (lower)
Food moves down oesophagus by active process
(peristalsis)
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Diseases Of The Gastrooesophageal
Sphincter
GES closed except during swallowing
When gastric contents (acidic) enter oesophagus despiteGES being closed H EARTBURN
This is followed by opening of sphincter to allow contents
back into stomach
If sphincter remains shut AC H ALASIA
Complications of achalasia = ASPIRATION PNEUMONIA
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Stomach
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StomachFundus
Bod
Antrum
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Diagr am Of
The Stomach
Showing TheThree Muscle
Layers
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Stomach
J-shaped saclike chamber lying between the oesophagus
and the small intestine.
Divided according to anatomical and histologicalparameters to:
[a] Fundus: Dome-shaped, this smooth muscle portion of
the stomach.
Lies above oesophageal opening
[b] Body: Midportion of the stomach
This layer of smooth muscle
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[c] Antrum: Pyloric antrum narrows to form pyloric anal and
ends in pylorus (gatekeeper).
Main function of stomach is storing ingested food until
it can be emptied into small intestine at a r ate
appropriate for optimal digestion and absorption.
Second function is secretion of HCl and protein-
digesting enzymes
Final product from the stomach is C H YME
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Microscopic Anatomy
Extra oblique layer of muscle to allow churning and mixing
of food.
Muscularis mucosa has mucus-secreting goblet cells.
Also contains gastric pits leading to gastric glands with
specialized cells (secrete gastric juice)
[1] Mucous Neck Cells
Secrete thin mucus
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[2] Chief Cells
Secrete inactive pe psinog en (ac t ive pe psin = pr ot ein- di g est ing enzy me).
[3] Parietal (Oxyntic) Cells
Secrete HCl and intrinsic factor
Pepsinogen activated by HCl
Intrinsic factor = absorption of vitamin B12 in small
intestine
Gastric mucosa atrophy or gastrectomy loss of chief
and parietal cells treated by regular vitamin B12
injections
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Surf ace View of
the Gastric
Mucosa ShowingEntr ance To
Gastric Pits
SEM (x35)
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[4] Enteroendocrine Cells
Secret hormones (Gastrin, Serotonin, Endorphine,«) intoblood
Occur in antrum region
Gastrin secreted by G cells into blood
Travels back to oxyntic mucosa stimulate chief and
Parietal cells stimulate gastric juices
Also stimulates growth of stomach and small intestine
mucosa.
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Control Of Gastric Secretions
[1] Cephalic Phase
Seeing/smelling food
Vagus stimulates HC
l and pepsinogen secretion viaintrinsic nerve plexuses
Vagus stimulates Gastrin secretion by G cells increased
secretion of HCl and pepsinogen
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[2] Gastric Phase
Stomach distension causes activation of stretch receptors
As with cephalic phase, HCl and pepsinogen secretion is
stimulated via vagal pathways
Caffeine and alcohol stimulate gastric juices even if
stomach is empty aggravate existing ulcer.
[3] Intestinal Phase
Protein fragments entering duodenum stimulate
intestinal gastrin travel by blood to stomach
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Control Of
Gastric
Secretions:The Cephalic
Phase
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Control Of
Gastric
Secretions:The Gastric
Phase
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Control Of
Gastric
Secretions:The Intestinal
Phase
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Gastric Mucosal Barrier (GMB)
[1] Luminal membrane impermeable to HCl
[2] Tight junctions between cells
Ulcer
Peptic ulcer in oesophagus, stomach or duodenum
Weakness in GMB.
Increased acidity leads to increased histamine leading to
increased acidity and a vicious cycle
Helicobacter Pylori 90% of peptic ulcers
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Treatment Of Peptic Ulcers:
@ Antihistamine (Cimetidine)
@ Cutting vagus nerve supply to stomach
@ Removal of stomach antrum
@ Diet void of caffeine and alcohol
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Gastric Ulcer
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A Donor Kebab, A Curr y and Get Pissed.
WHY?
No food could be absorbed through the stomach
Alcohol can be however.
Alcohol more rapidly absorbed through small intestine into
blood.
Fat-rich food (kebab/curry) delays gastric motility delay
arrival of alcohol into duodenum delay alcohol fromproducing its effects rapidly
Aspirin can also be absorbed through stomach exert
effect more quickly.
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Regulation Of Stomach Motility
[1] Gastric Filling
Plasticity ³Ability of stomach smooth muscle to be
stretched without greatly increasing its tension
As food is travelling down oesophagus R ece pt ive
R el axat i on.
As food enters stomach Ada pt ive R el axat i on.
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[2] Gastric Stor age
BER means slow weak contraction of smooth muscle infundus and body while stronger in antrum
Therefore, food is stored in fundus and body.
[3] Gastric Mixing
Peristaltic movement in antrum mixing chymepush forward to pyloric sphincter
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[4] Gastric Emptying
Expulsion of chyme into duodenum.
Amount of chyme emptied depends on strength of
peristalsis.
Rate depends on:
(a) Volume of chyme
(b) Fluidity of chyme
(c) Duodenal factors such as fat, acid and distension
Emotions may influence gastric motility via autonomous
nervous system (e.g. sad reduced emptying)
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Vomiting
Induced by:
a) Bacterial toxins
b) Unpleasant odours
c) Stressful situationd) Excessive alcohole) Drugs
Mediated by emetic centre in the medulla
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Pancreas
Tadpole-shaped gland behind and below the stomach
Contains both endocrine and exocrine tissue
Acini ³ Cluster of secretor y cells that form sacs´
Acini empty into main pancreatic duct
Endocrine portion = Islets of Langerhans (secrete insulin
and glucagon)
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Acini
Main Pancreatic
Duct
Bile Duct From
Liver
Duodenum
(Small Intestine)
Empty
Fuse
Empty
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Composition Of Pancreatic Juices
[1] Enzymatic secretions
[2] Aqueous secretions rich in sodium bicarbonate
[1] Enzymatic Secretions
a) Proteolytic enzymes
b) Pancreatic amylase
c) Pancreatic lipase
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a) Proteolytic Enzymes
-Trypsinogen-Chymotrypsinogen
-Procarboxypeptidase
Trypsinogenp Trypsin in small intestine by enterokinase
Cymotrypsinogen and procarboxypeptidase both activated
in the small intestine by the activated trypsin
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b) Pancreatic Amylase
Secreted in the active form
Digest carbohydrates
c) Pancreatic Lipase
Secreted in the active form
Only enzyme in digestive system that can digest fats to
monoglycerides and fatty acids
St eatorrhea = Pancreatic exocrine insufficiency60-70% indigested fat in faeces
Protein/carbohydrate digestion impaired to
a lesser extent
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[2] Pancreatic Aqueous Alkaline
SecretionsFact 1: Pancreatic enzymes work at neutral to alkaline
environment.
Fact 2: They start their function in the duodenum
Fact 3: Chyme emptied from stomach into duodenum is
highly acidic
OH SHIT WE HAVE A PROBLEM
Solution: Neutralize acidity of chyme in duodenum by
alkaline secretions from the pancreas
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Regulation Of Pancreatic Secretions
Pancreatic enzymes released
Acinar cells stimulated
Cholecystokinin secreted
Protein/Fat/Carb
Sodium bicarbonate released
Duct cells in pancreas stimulated
Secretin secreted
Acid
Chyme Enters Duodenum
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Summar y Of
Information
Relating ToIntestinal
Hormones
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Liver and Gallbladder
Liver and gallbladder form the biliary system secrete
bile into duodenum
Bi l e: Breaks down bid fat molecules into smaller ones that
are accessible to digestive enzymes
Liver: Detoxifies waste and drugs
Removal of bacteria due to resident kupffer cells.
Liver cells = He patocy t es and Kupff er cells.
Blood enters liver via hepatic artery
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All digestive organs drain venous blood into hepatic portal
vein of the liver for:
a) Processing
b) Storage
c) Detoxification
Blood from hepatic portal vein drains into hepatic vein and
subsequently into the inferior vena cava.
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Microscopic Structure
Liver made of four lobules
Each lobule is hexagonal
Each hexagonal part has
1) Hepatic artery branch
2) Hepatic portal vein branch
3) Bile duct
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a) Blood from hepatic artery branch and hepatic portal
vein branch flow into an expanded capillary =
S inusoid s
b) Kupffer cells line inside of sinusoids and hepatocytes
on outside.
c) The blood from sinusoids from all six sections of lobule
drains into central vein
d) Central vein from all four lobules drains into hepatic
vein
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e) Bile secreted by hepatocytes flows into canaliculi
between cells.
f) Bile canaliculi carry bile to bile duct in each lobule
g) Bile ducts from each of four lobules drains into commonbile duct
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Gallbladder: Why?
Bile produced by liver enters duodenum ONLY during
digestion of a meal.
Therefore, must be stored somewhere before it is released
Gallbladder is site for storage of bile
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Gallstones
Biliary calculi
Due to excess proportion of cholesterol compared to bile
salts and lecithin.
Obstruct flow of bileSymptoms: Pain radiating to right thoracic region
Treatment: - Drugs to dissolve crystals
- Pulverising them with ultrasound (Lithotripsy)
- Vaporising with laser - Surgical removal of gallbladder
75% due to cholesterol, 25% due to precipitation of bilirubin
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Bilirubin
Pigment resulting from breakdown of haem portion of haemoglobin.
Bilirubin converted to urobilinogen by small intestine
bacteria (this gives faeces its brown colour).
Diseases Of The Liver
[1] Jaundice
Prehepatic: excessive breakdown of RBC.
Hepatic: Liver is diseased and not able to deal with normal
levels of bilirubin.
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Posthepatic: Obstructive jaundice due to bile duct
obstruction bilirubin cannot be eliminated in faeces
Patients appear yellowish especially in the whites of their
eyes
[2] Hepatitis
Due to toxins such as alcohol, tranquillisers and mushroom
poisoning.
Viruses: Hepatitis A = Transmitted through sewage-
contaminated water
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Hepatitis B = Transmitted via blood transfusions and could
results in cancer.
Vaccines for hepatitis A and B have now been developed.
HepatitisC
= Treated by combination drug therapy of immunosuppressing steroid prednisone and
genetically engineered interferon.
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[3] Cirr hosis (Or ange Coloured)
Due to chronic alcoholism or chronic hepatitis
Connective fibrous tissue mass of the liver increases.
Blocks blood flow through hepatic portal system portal
hypertension
Hepatic portal vein drains into small veins
Excess blood small veins burst vomit blood
Snakelike network of veins surrounding the naval (Caput
medusae = medusae head)
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Small Intestine
Site of digestion and absorption
6.3 m long and 2.5 cm wide
Coiled between stomach and large intestine
Duodenum, J ej u num and i l eum
Food is mixed and moved along small intestine by
segment at i on
Segmentation influenced by:
1) Intestinal distension
2) Gastrin
3) Extrinsic nerve activity
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Structure/Function Relationship
Most absorption in duodenum and jejunum
Vitamin B12 and bile salt absorption in ileum
[1] Inner surface of small intestine lined by finger-like
projections = V i ll i (I ncrease su r f ace area)
[2] Villi have mucous and epithelial cells
[3] Epithelial cells have microvilli on their surface
(digestion of protein and carbohydrates finished and
absorption occurs)
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[4] Crypts of Lieberkuhn between villi regenerate
epithelial cells on villi
Radiation and anticancer agents inhibit this epithelial cell
regeneration reduced absorption weak, lethargic
patient.
Structure Of The
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Structure Of The
Ileum
Villi Form A
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Villi Form A
Dense Covering
Over TheSurf ace Of The
Ileum
Longit dinal Section Of A Vill s
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Blood
capillaries
Brush
border
Goblet
cells
Longitudinal Section Of A Villus
Light Microscope Image (x252)
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Digestion and Absorption
Digestion
Exocrine glands in small intestinal mucosa secrete 1.5
litres/day of water and mucus
In the lumen:
1) Fat digestion is complete
2) Proteins reduced to peptides and amino acids
3) Carbohydrates reduced to disaccharides.
How is protein and carbohydrate digestion complete ?
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Epithelial cells contain:
E nt er ok inase: Activates pancreatic trypsinogen
Di saccharidase: Reduced disaccharides to
monosaccharides
Aminope pt idase: Reduces peptides to amino acids
Thus, carbohydrate and protein digestion is completed inthe epithelial cells of brush border
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Lactose Intoler ance
Lactase deficiency
Lactose accumulates in small intestine lumen
Water, carbon dioxide and methane gas accumulate as aresult abdominal cramps and diarrhoea
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Absorption
Portal Vein
Vein
Capillar y Within Villi
Epithelial Cells
Microvilli
Lumen
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Di h
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Diarr hoea
Excessive defecation of highly fluid faecal material.
Eliminates harmful material from the body
Also eliminates water (dehydration), nutrient material and
HCO3 (metabolic acidosis)
Caused by:
@ Viral/bacterial infection leading to excessive
intestinal motility
@ Lactase deficiency
@ Toxins of V ibri o C hol erae (bacterium) secretion
of vast amounts of fluid by small intestinal mucosa
L I t ti
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Large Intestine
Cecum: Pouch shaped
Appendix: Lymphoid tissue housing lymphocytes
Colon: Ascending, transverse, descending (last section is
sigmoid colon)
Rectum: (Meaning straight)
Walls of large intestine = pocketlike sacs = haustra
Material reaching large intestine = indigestible food (e.g.
Cellulose), unabsorbed biliary compounds and fluid.
Large intestine absorbs more water and salt and stores
faeces
Absorptive &
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Absorptive &
Stor age
Functions Of The Colon
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Histological
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Histological
Detail Of The
Colon
Histological
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Histological
Detail Of The
Colon
D f ti
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Defecation
Haustral contractions = slow =allow bacteria to brow inlarge intestine
Ascending and transverse colon contract simultaneously to
drive faeces to descending colon.
Once faeces reaches the rectum, it stretches and
sphincters relax
External sphincter is skeletal voluntary muscle
Abdominal muscles contract and the individual breaths a
sigh of relief.
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Reading
Human Physiology from cells to systems.
Lauralee Sherwood. West Publishing Company
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THE END