The Digestive System and Nutrition

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Autotroph photosynthesis

Nutrition

Herbivores

Carnivores

Omnivores

Heterotroph

Nutrition Balenced diet includes all 7 components

Carbohydrate-Protein – Fats-

17kJ/g17kJ/g38kJ/g

Obesity

New Food Pyramid 2005-emphasise importance of controlling weight and physical activity

-dietary fats –limit saturated fats20-35% of energy should come from fats, especially monounsaturated and polyunsaturated fats

Energy content of food measured in

Joules (J)

Amount of food required depends on..?

Approx 9600kJ girls

12,600kJ boys

-limit sugar intake-stress benefits of wholegrains

Mouth-mechanical digestion (mastication) = teeth, tongue-chemical digestion = saliva (amylase, lysozyme)

Trachea - windpipe

Uvula – prevents food entering the nose

Epiglottis – safety hatch. A flap of cartilage prevents food from entering the trachea

Alimentary canal2 main functions:•Digesting and absorbing nutrients•Protecting from invasion

Oesophagus-transfers food to stomach by peristalsis

http://library.thinkquest.org/11226/main/c03txt.htm

Cardiac sphincter

-opens to allow food oesophagus stomach

-heartburn –acid escapes stomach oesaphagus

http://35.9.122.184/images/41-AnimalNutrition/41-16-Duodenum-L.gif

StomachShort term storage reservoir (1L for up to 4h)

Digestion = chemical (HCl and enzymes) - proteins

= mechanical - liquefication of food

Slowly releases food into intestine

chyme

Cardiac sphincter

Pyloric sphincter

Acid (HCl) – parietal cells

Hormone (gastrin) – G cells

Mucous – goblet cells

Enzymes (pepsinogen) – chief cells

Stomach epithelial cells are some of the fastest growing cells in the body, typically replacing themselves about every 3 days

Stomach Epithelium

Ulcers (stomach, duodenum) – peptic ulcers. Most commonly caused by H. pylori

Prevents self-digestion

pH 1-2Kills bacteriaLoosens fibrous foodsActivates pepsinogenDenatures salivary amylase

Activated to pepsinConverts proteins peptides

Controls gastric motility and acid secretion

Small IntestineAround 6m in an adultFood takes 1-6 h to pass through2 main tasks = digestion, absorption

3 partsDuodenum JejenumIleum

Pancreas –pancreatic juice= NaHCO3, enzymes (insulin, glucagon) pH of duodenum = 7-8 Amylase, lipase, trypsinogen, chymotrypsinogen

Liver – bile made in liver, stored in gall bladder = Water, salts, bile saltsNeutralise HCl Digestion and absorption of fats and fat soluble vitamins (emulsification)Waste products eliminated by secretion into bile and elimination in feces

(e.g. bilirubin, biliverdin)

Duodenum = digestion = 25cm long

LiverWeighs about 1.5kgHolds about 13% of total bloodLiver cell = hepatocyteUnique ability to regenerate – average life = 150 days

http://www.britishlivertrust.org.uk/content/liver/about.asp

Right lobeLeft lobe

Blood rich in food from ileum

The liver performs over 500 jobs. Some of these are:•Makes bile (600mls/day)•Detoxifies body (alcohol, drugs etc)•Breaks down excess amino acids urea (deamination) kidney•Converts glucose glycogen for storage (source of quick energy)•Converts excess carbohydrates fat•Stores vitamins - A, D, E and K •Stores minerals – Fe, Cu, Zn•Makes plasma proteins e.g. fibrinogen – blood clotting•Makes cholesterol – needed to form many hormones•Produces heat to warm blood •Clears blood of particles, including bacteria•Fights infections –half the body’s macrophages -destroy bacteria •Produces hormones, including the sex hormones

Jejenum – digestion/ absorption. 2.5m long

Ileum – absorption. 4m long

Walls only one cell thickVilli, microvilli – increase surface area for absorptionRich blood supply – capillaries absorb water and soluble nutrients (glucose, amino acids, vitamins, minerals) and the blood carries the nutrients to the liver, which stores nutrients and releases them as required

Lacteal – contains lymph. Fatty acids and glycerol are absorbed by the epithelial cells where they reform into fats. They become coated in protein (chylomicrons) and pass into the lymph in the lacteals. It takes around 18h for lymph to rejoin the blood, the protein coat dissolves and fats are absorbed into cells

Small Intestine cont.

Large Intestine

1.5m long, 6cm diameter

Food stays 10h to a few days

ColonReabsorbs water – so waste is converted to semi-solid = faeces – egestedDiarrhoea, constipation (fibre helps stimulate peristalsis)

Caecum

Appendix

Function unknown – in herbivores they contain bacteria that help digest cellulose

Bacteria

1-2kg of bacteria in your gut = 4000 species

Good – symbiotic bacteria. These live in close harmony with the body without causing harm, and have additional health benefits. Probiotics are live micro-organisms that, when consumed in adequate amounts, confer a health benefit to the host. e.g. bifidobacteria, lactobacillus

Bad - bacteria that can cause illness e.g. H pylori (ulcers), Salmonella, E. coli, Listeria (food poisoning)

•Aid digestion

•Break down toxins

•Produce vitamins B12 and K

•Stimulate the immune system

•Help prevent growth of cancers

•Convert prodrugs to drugs

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The Immune System

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The Immune System

Defends body against pathogensCan distinguish between self and non-self

General Defence System (innate)Non-specific = acts against all pathogensRapid

1. First line of general defenceSkin = barrier. Sweat (acidic pH)Clotting = also helps protect skinLysozyme = enzyme in saliva, sweat, tears. Attacks bacterial cell wallsMucous (respiratory, digestive, urinary & reproductive tracts) = traps pathogens Cilia = little hairs that help clear mucous (and pathogens) from respiratory tractAlimentary canal = lysozyme in saliva, stomach HCl kills many pathogens, specialised immune areas in the GI tract, very high turnover of epithelial cells, antibodies

Specific Defence System (adaptive)

2. Second line of general defencePhagocytic white blood cells (leukocytes) = destroy pathogens that enterComplementInflammation

Phagocytes – (Phago= eat; cyte=cell) attracted to a site of infection (chemotaxis) by chemicals released by injured cellsThree types – neutrophils (short lived),

monocytes (short-lived..in blood) and macrophages (long-lived..in tissue)

Macrophages – very large white cells that can move around body, or remain in certain tissues. Long lived, act as scavengers

Immune organs

Complement• set of 30 proteins found in plasma that are activated by infection• complicated chain reaction that leads to the bursting of viruses and bacteria• made in the liver

Interferons• set of proteins produced by virally infected cells cells to limit the spread of viral infections, by inducing a state of resistance in healthy cells. • induced by viruses, bacteria and other signals from the immune system

Inflammation• infected cells (mast cells) release histamine, which is a vasodilator. This causes localised swelling, redness, heat, pain. Can also cause high temperature.• brings white cells to the area of infection• Anti-histamines

2. Second line of general defence cont.

Specific Defence System (Adaptive Immune System)

Antigens – foreign molecules that generate antibody production

Antibodies (immunoglogulins) – proteins produced by lymphocytes in response to antigens

Monocytes – develop into macrophages which phagocytose foreign particles (antigens) Lymphocytes -

B lymphocytes – mature in Bone marrow lymphatic tissue, especially spleen and lymph nodes

T lymphocytes – mature in the Thymus

Lymphocytes

Large nucleus

B lymphocytes make antibodies = immunoglobulins

1000s of different B cells, each recognises a different antigen on the surface of a macrophage. Each antigen stimulates production of a single specific antibody

B cells (along with T cells) come in contact with antigen. They are stimulated (by T cells) to produce many clones, plasma cells, which make antibodies.

B-lymphocytes

Antibodies•Can bind to pathogens and prevent them from infecting cells. Pathogens are then destroyed by phagocytes•Can inactivate pathogens by causing them to clump together

•Can trigger the complement system, resulting in pathogens being burst

Memory B cells – faster, more sensitive reaction = secondary response

MacrophagePhagocytoses pathogen and displays antigens on surface

B-cellsEach recognise a different antigen. The correct one develops into…

Plasma cellsClones of the correct B-cell, which produce antibodies

1st meeting a pathogen, this process takes 10-14 daysMemory B cell= subesquent meetings, takes about 5 days

How B-cells work…

Pathogen (e.g. bacteria, virus)

Macrophage

T-lymphocytes

Helper T-Cells•Recognise antigens on surface of leukocytes, especially macrophages•Enlagre and form a clone of T-helper cells•Secrete interferon and cytokines which stimulate B-cells and stimulate killer -cells•Can be infected by HIV

Killer T-CellsAlso called cytotoxic•Destroy abnormal body cells, e.g. virus infected or cancer cells•Stimulated by cytokines (THcells)•Release perforin, which forms pores in target cells. This allows water and ions in = lysis

Suppressor T-Cells•Control the immune system when the antigen /pathogen has been destroyed•Only recently discovered so little is known about them

Memory T-Cells•Can survive a long time and give lifelong immunity from infection•Can stimulate memory B-cells to produce antibodies•Can trigger production of killer T cells

Mature in Thymus, which is most active just before and after birth. The thymus starts to shrink during puberty.

Duration of immunityMemory B-cells circulate for a long time. If the same pathogen infects the body again, these B-cells can produce large amounts of specific antibody very quickly. This is why you usually don’t suffer from the same infection twice.Memory T-cells survive a long time and trigger an immune response

•Tumours – in most cases the body recognises tumours as being bad, because they express abnormal molecules on the cell surface. However sometimes the body doesn’t notice and cancers can develop

Immune disorders•Sometimes the body produces antibodies against its own tissues e.g. autoimmune diseases e.g. rhumatoid arthritis, Crohn’s disease, SCID (bubble boy disease)asthma

•Allergies occur when the body reacts to materials which should not be antigenic e.g. peanuts

Induced Immunity

Active immunityProduction of a person’s own

antibodies. Long lasting

Passive immunityAn individual is given antibodies by

another Short-term resistance (weeks- 6months)

Natural ActiveWhen pathogen

enters body in the normal way, we make antibodies

Natural PassiveBaby in utero

(placenta)Breast-fed babies

Artificial PassiveGamma globulin

injectionExtremely fast, but

short lived (e.g. snake venom)

Edward Jenner

Artificial ActiveVaccination –

usually contains a safe antigen from

the pathogen. Person makes antibodies

without becoming ill

Career in Science ?BSc – Biochemistry in UCCPhD – Cell biology/virology in Heidelberg, Germany (met my French husband)Post-doc – Cell biology in San Francisco, USAIndustry – Elan

Now – juggle 2 jobs:

General Manager of the Alimentary Pharmabiotic Centre

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Why Science?

•Interesting and challenging work – no two days the same•Interesting people – APC has 19 nationalities•International qualification•Travel•Satisfaction•Career, not just a job

• Pharmaceutical• Medical Devices• Biotechnology• Healthcare• Food & Drink

• Environmental• Health & Safety• Electronics• Academia• Business

What can you do…?

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