Anatomy and physiology of the digestive system

These revision notes will help you remember the structure (anatomy) and function (physiology) of the digestive system
DIGESTION
•    Is the process, which breaks down food into substances that can be absorbed and used by the body for energy, growth, repair and heat

ANATOMY
•    Alimentary Canal (mouth – anus) which consists of:  Teeth, tongue, salivary glands, oesophagus, stomach, small and large intestine, rectum and anus

ACCESORY ORGANS
•    Liver, gall-bladder, pancreas

DIGESTIVE PROCESSES- Physiology

•    Ingestion
•    Movement of food
•    Digestion
•    Absorption
•    Elimination

DIGESTION IS CARRIED OUT

•    Mechanically e.g. chewing
•    Chemically through enzymes and acids

DIGESTION IN THE MOUTH

•    Mechanically by chewing
•    Chemically – enzyme in saliva
o    Amylase – initiates break down of starch
OESOPHAGUS

•    Secretes mucous
•    Transports food to stomach by peristalsis

STOMACH

•    Muscular sac with 2 curvatures – greater and lesser
•    3 parts: Cardiac, Body, Pyloric
•    With cardiac and pyloric sphincters

DIGESTION IN THE STOMACH

•    Mucous secreted to protect stomach lining
•    Mechanical – breaks down food and mixes it with digestive juices until it becomes thin liquid called chyme
•    Chemical - enzyme Pepsin to break down proteins
- hydrochloric acid – activates pepsin

SMALL INTESTINE

•    Duodenum       25cm
•    Jejunum          2.5m
•    Ileum         3.6m

DIGESTION IN THE SMALL INTESTINE

•    Duodenum - Pancreatic juices from Pancreas: Trypsin, Lipase and Amylase       + Bile from gall bladder enters Duodenum
•    Jejunum and Ileum – Secrete intestinal juices (2-3 litres a day): Lactase, Maltase, Sucrase
Have mucous membranes arranged in folds, which are covered with VILLI – finger like projections that absorb fatty acids, monosaccharides and amino acids
90% of absorption takes place in the small intestine.
•    Ileum – Studded with lymphatic nodes – PEYERS PATCHES

LARGE INTESTINE- also known as the Colon

•    Completion of Absorption (water)
•    Manufacture of certain vitamins
•    Formation and expulsion of faeces
 

ACCESSORY ORGANS:
Pancreas
•    Secretes pancreatic juices into the duodenum
•    Islets of Langerhans – secretes hormones – insulin/glucagon

Liver (weighs 3lb)
•    Made up of right and left lobes
•    Function:
o    Formation of bile – 1 litre/day (made of disintegrated red blood
  cells). Responsible for breaking down fats
o    Detoxifying organ – parcels up toxins for elimination
o    Stores vitamins and glycogen
o    Manufactures enzymes, cholesterol, vitamin A and clotting  
  factors
o    Activates vitamin D

Gall Bladder
•    Stores and concentrates bil

Salivary Glands

There are 3 pairs of salivary glands:
•    Sublingual – found underneath and either side of the tongue
•    Submandibular – under the angle of the jaw
•    Parotid – found just near the masseter muscle on each side of the face
Saliva helps to lubricate food, making it easier to swallow and also stimulates the taste buds. It plays an important role in keeping the tissues of the mouth moist and clean.
There is an enzyme called amylase present in saliva which is important for beginning the chemical breakdown of starches

Body Fat

Body fat is made from carbohydrates and proteins and fats eaten in excess of the body‘s needs and stored in the fat deposits mainly under the skin but also around organs such as the kidneys and liver.
When required the stored fat can be converted into energy.
In order to release these stores the energy output has to be greater than the calorie intake.

 
Inside the Small Intestine

Here we find the wonderful finger- like projections called villi. Nutrients are absorbed into the villi where they then pass into the blood stream. Blood vessels have corresponding lymph vessels.  

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