Respiration. Outlines. Lectures 1-2.1. Describe the composition of food.2. Relate food to energy.3. Present an overview of digestion.4. Define the major processes required for digestion.5. Describe the anatomy of the digestive system at organ, tissue and

cellular level.6. Describe the role of the mouth in digestion.7. Describe the role of the oesophagus in digestion.8. Describe the role of the stomach in digestion.

6 Major components for life:- Carbs- Fats- Proteins- Water- Vitamins- Minerals

Most are NOT produced by body, thus ingested. Diet should/must contains above in complex forms.Digestion provides above in usable form.

Nutrient intake – total quantity of food and quantity of individual components important for healthy diet.*UK RDA Adult Males: 2550kcal; Females: 1940 kcal;1kcal – energy to heat 1L of water by 1C.

So:Carbs= 3.45 kcal/gramFats= 9 kcal/gramProteins= 4 kcal/gramBasal use: resting man- 1kcal/min to stay alive = 1220 kcal/day

BMI = Body Mass Index = Measure of Obesity:Classification BMI kg/m2 Risk of co-morbidity*Underweight <18.5 Low

Healthy range 18.5-24.9 AverageOverweight (pre-obese) 25.0-29.9 Slight increaseObese Class I 30.0-34.9 Significant increaseObese Class II 35.0-39.9 High riskObese Class III >40 Very high risk

Overweight causes: cardiovascular disease, hypertension, diabetes.Obesity in UK increases despite less calories: due lack of exercises.

- GI tracks is very efficient at water retention = very little water is excreted that enters GI.

- Huge volumes secretes as a result of digestion, and then reclaimed.Water Intakemls/24h

Water Lossmls/24h

Through Drinking 1600 Urine 1500Through Food 500 Skin 500Made by metabolism

500 Lungs 500

Faeces 100Total 2600 2600

- Mouth to anus constitute digestive system.- Oesophagus(stemple) to anus – alimentary canal – from embryonic

origin.

4 Major processes in digestion:- Breakdown of large molecules: mechanical or chemical- Secretion of substances-not always into lumen.- Absorption- Movement of gut.

Note: not all 4 processes occurs at all parts of digestive system.

4 Layered tissue organisation from stomach to anal canal.- Mucosa( 3 components );- Submucosa- Muscularis externa- Serosa.

Each layer zone is made of numerous tissue. Structure in different GI tract areas depends on the composition of the zone mentioned above.

Composition layer 1 – THE MUCOSA:

3 Components:

a) Mucous membraneo Columnar organised epithelial layer.o Function – protects the gut from abrasiono Secretes substances into gut e.g. enzymes or mucus.o Secrete hormones (enteroendocrine cells) into lamina properia to

capillaries. Never into gut lumen.o Absorbs material into capillaries or thin lymph vessel-lacteals.

b) Lamina propriao Connective tissueo Contains blood capillaries – nourishes epithelial, carries away

absorbed molecules.o Lymph vesselso Contains - kill bacteria.

c) Muscularis mucosaeo Thin layer of smooth muscle.o Controls folding of the mucosa e.g. in small intestine.

COMPOSITION OF Sub-Mucosa, Muscularis externa and Serosa:

Layer 2 Sub-Mucosa-loose connective tissue contains:• Blood vessels• Lymph vessels• At deep boundary- neurons-organised to form intrinsic or Sub-Mucosal

Plexus.

Layer 3 Muscularis externa• Thick inner layer of circular smooth layer• Thick outer layer of longitudinal smooth layer• Produce waves of contraction- peristalsis or segmentation.• Myenteric plexus - Between thin and thick muscle.• MP-network of neurons. Connected to sub-muccosal plexus. Together form

the Enteric Nervous System.

Layer 4 Serosa• Connective tissue and membrane that protects GI tract when it moves.

Organisation of the epithelia of the GI-Small Intestine as an example

1. Columnar epithelium lines gut. Reasonable strong and small resistance to diffusion.

2. Substances move through epithelium into capillaries or lymph vessels.3. Epithelium has specialised cells for secretion. Release substances into

Lumen.4. Some secretory cells found throughout GI e.g. goblet cells secrete

mucus. 5. Other secretory cells regionalised. e.g. acid producing cells in

stomach. Water secreting cells in SI.

Organisation of the epithelia for GI Hormone Production1. Hormones control the activity of the gut- motility, secretion and

absorption.2. Hormones produced by single dispersed cells not glands-

enteroendocrine cells.3. Hormones secreted into mucosa and not lumen.4. All are simple polypeptides.5. All promote growth of tissue where they are produced.6. All have additional specialised functions:

Hormone Structure Site of production Stimuli Action

Gastrin 17-34 amino acids

G cells-stomach Stomach distension,Amino acids, pH>3

HCl production

Enteroendocrine cell

Somatostatin 14-28 amino acids

D- cells-stomach Low pH Inhibits HCl production

Motilin 22 amino acid

Small Intestine Content of stomach and SI.

Contraction of smooth muscle in stomach and SI.

Secretin 27 amino acids

Small Intestine pH<4.5Acid Duodenum!

Increase bicarbonate secretion from pancreas.

CCKcholecystokinin (mover of bile from bladder)

Small as 8 amino acids!

Small intestine Fat and protein content of chyme

Release of digestive juices and bile

Function of the mouth in digestion:(1). Reduce size of food- teeth break up food, Tongue grinds food- between dorsal surface and hard palate.(2). Prepare food for swallowing- moistens.(3). Start chemical breakdown of carbohydrates.

Histology - reflects function- Mouth and pharynx lined by stratified squamous epithelial-

withstands abrasion and high temp.- Tongue and Hard Palate lined with tougher epithelium- keratinised

stratified squamous epithelium.

Secretion in the Mouth-Saliva:

1. Adults produce about 1.5 litres saliva per day!2. Content >97% water - highly hypotonic. pH approx. 73. Three major glands produce saliva:• Parotid-serous type mainly watery saliva containing enzymes,

electrolytes (Na+, K+, Cl-, PO4- HCO3-) and mucin• Submandibular gland - serous and mucosal cells-thicker saliva

• Sublingual gland - serous and mucosal cells-thicker saliva4. Delivered through ducts into the mouth.5. Saliva has 4 main functions:ProtectionTasteLubricationDigestion

Function of Saliva:Protection(1) Controls temperature- cools hot drinks.(2) Neutralises acids(3) IgA antibodies that attack bacteria and viruses.(4) Lysozyme- breaks down bacterial cell walls.(5) Cyanide based compounds- kill bacteria.(6) Definsins- kills bacteria and attract bacteria fighting cells (lymphocytes

and neutorphils) to the mouth.Taste(1) Taste detected through aqueous phase. Molecules need to be dissolved.

Saliva being mainly water, dissolves small molecules.Lubrication(1) Mucus coats food, less abrasive and easier to swallow.

Digestion of carbohydrates in the mouth:

1. Starch and glycogen most abundant carbohydrates in diet.2. Digestion beings in the mouth. Saliva contain Salivary Amylase. 3. Salivary amylase works at pH 7.0.4. Breaks carbohydrates into three produced:

= Glucose

Starch or glycogen

LimitDextrin

Maltotriose

Maltose

5. Amylase functions until acid denatured in stomach.6. Ligual lipase- breaks down lipids but only at pH <4, so acts only in

stomach.

Anatomy of the Oesophagus (stemple):1) Oesophagus conveys bolus to stomach.2) Oesophagus- NO absorptive or digestive function.3) Lining- No need to be thin (above). Stratified squamous epithelium -

tough. 4) Secretes mucus- promoting bolus movement.5) Upper region made of striated (skeletal muscle).6) Middle region of striated and smooth muscle.7) Lower region made of smooth muscle.8) Moves bolus by peristalsis.

Anatomy of the Stomach- Part 1

• Stores food- expands and contracts• Digests food- chemically and mechanically. Produces partially digested

food- chyme.• Absorbs only alcohol and aspirin! Ulcers made worse by these two

compounds!• Secretes enzymes and other molecules for digestion and protection• Makes Intrinsic Factor - needed to absorb Vitamin B12.

Stomach made of 4 parts• Cardiac• Fundus• Body• Pyloric- two parts- antrum at anterior, pylorus at the terminal.1. Contracted stomach (empty) -capacity 50mls.2. Small volume due to inner surface folding called rugae.3. Full stomach hold 4 litres - rugae (esp. in fundus and body) stretched out

and disappear.

Anatomy of the Stomach- Part 2 1. Stomach has additional layer of muscle in the muscularis externa zone-

the oblique muscle layer.2. Muscle layer thickness varies- thick where contractions needed.3. Fundus and Body only expand therefore muscle strength not critical-

therefore thin layers of muscle.4. Pyloric region responsible for churning food and emptying food. Strong

contractions needed- thick muscle layers.

INCOMPLETE NOTES

Retropulsion – forces chyme backward.Gastrin is a key regulator in digestion juices – stimulates release of hcl, histamine and pepsinogen. But is inhibited by Somatostatin.

Lecture 3-4 outlines:1. Describe structure of the small intestine.2. Describe the secretions of the pancreas and liver.3. Describe the digestion and absorption of proteins, carbohydrates

and fats.

4. Describe the absorption of water and Na ions by the small intestine.

5. Describe the function of the large intestine.