Dr.gehan Eloleimy.lectures 1 2 3 Digestive System 1

8/8/2019 Dr.gehan Eloleimy.lectures 1 2 3 Digestive System 1

http://slidepdf.com/reader/full/drgehan-eloleimylectures-1-2-3-digestive-system-1 1/117

1

Digestive System

Top to Bottom

Physiology Group

Dr Usama ALAlami



2

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´



3

Propulsion

In olun ary

(Peristalsis)

Volunta y

(Swallowing)

opulsion

Peristalsis ³Adjacent sections of the alimentar y canal

alternately contract and relax´



4

Coordin ted Muscul r Contr ctions

Produce Perist ltic Movements



6

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.



7

[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



8

Digestive Tr act

(Alimentar

Canal)



9

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



10

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.



11

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



12

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.



14

Histolog of

the Alimentar

Canal



16

b) Lamina Propria

Well vascularized (nerves and lymph vessels)

Defence against intestinal bacteria bacteria

c) Muscularis Mucosa

Outer layer of smooth muscle



17

[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.



18

[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.



19

[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´



20

Regulation Of Digestive Function

Digestive function is controlled by four factors:

* Autonomous smooth muscle function.

* Intrinsic nerve plexuses

* Extrinsic nerves

* Gastrointestinal hormones



21

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



22

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.



23

Intrinsic plexuses influence:

a) Smooth muscle contractility

b) Exocrine cell secretion (digestive juices)

c) Endocrine cell secretions (digestive hormones)



24

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.



25

Extrinsic Nerves

Alter digestivemotility

Directlyonsm. muscleandgland Alter levelsof GI hormones

Alter digestivetract secretio

Modifyintrinsicplexuses

ExtrinsicNerves



26

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).



27

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)



30

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.



31

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



32

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



33

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



34

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



35

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



36

Salivar Glands

Saliva secreted by

[1] Extrinsic salivary glands (Major)

[2] Intrinsic salivary glands (minor)

(in mucosa lining the cheeks)



37

Extrinsic Salivar Glands

Sublingual

ParotidSubmandibular

Extrinsic Salivar Glands



38

Extrinsic

Salivar Glands



39

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).



40

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.



41

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.



42

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



43

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)



44

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



45

Peristalsis In

The

Oesophagus

(Anterior View)



46

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



47

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.



48

[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)



49

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



50

Stomach



51

StomachFundus

Bod

Antrum



52

Diagr am Of

The Stomach

Showing TheThree Muscle

Layers



53

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



54

[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



55

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



56

[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



57

Surf ace View of

the Gastric

Mucosa ShowingEntr ance To

Gastric Pits

SEM (x35)



58

[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.



59



60

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



61

[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



62

Control Of

Gastric

Secretions:The Cephalic

Phase



63

Control Of

Gastric

Secretions:The Gastric

Phase



64

Control Of

Gastric

Secretions:The Intestinal

Phase



66

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



67

Treatment Of Peptic Ulcers:

@ Antihistamine (Cimetidine)

@ Cutting vagus nerve supply to stomach

@ Removal of stomach antrum

@ Diet void of caffeine and alcohol



68

Gastric Ulcer



69

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.



70

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.



71

[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



72

[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)



73

Vomiting

Induced by:

a) Bacterial toxins

b) Unpleasant odours

c) Stressful situationd) Excessive alcohole) Drugs

Mediated by emetic centre in the medulla



74

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)



75

Acini

Main Pancreatic

Duct

Bile Duct From

Liver

Duodenum

(Small Intestine)

Empty

Fuse

Empty



76

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



77

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



78



79

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



80

[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



81

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



82

Summar y Of

Information

Relating ToIntestinal

Hormones



83

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



84

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.



85

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



86

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



87

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



88

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



90

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



91

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.



92

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



93

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.



94

[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)



95

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



97

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)



98

[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



99

Structure Of The

Ileum

Villi Form A



100

Villi Form A

Dense Covering

Over TheSurf ace Of The

Ileum

Longit dinal Section Of A Vill s



101

Blood

capillaries

Brush

border

Goblet

cells

Longitudinal Section Of A Villus

Light Microscope Image (x252)



102

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 ?



103

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



104

Lactose Intoler ance

Lactase deficiency

Lactose accumulates in small intestine lumen

Water, carbon dioxide and methane gas accumulate as aresult abdominal cramps and diarrhoea



105

Absorption

Portal Vein

Vein

Capillar y Within Villi

Epithelial Cells

Microvilli

Lumen



Di h



107

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



108

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 &



109

Absorptive &

Stor age

Functions Of The Colon



Histological



111

Histological

Detail Of The

Colon

Histological



112

Histological

Detail Of The

Colon

D f ti



113

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.



116

Reading

Human Physiology from cells to systems.

Lauralee Sherwood. West Publishing Company



THE END

Dr.gehan Eloleimy.lectures 1 2 3 Digestive System 1

Documents

Transcript of Dr.gehan Eloleimy.lectures 1 2 3 Digestive System 1