The Digestive System and Nutrition

Autotroph photosynthesis Nutrition Herbivores Carnivores Omnivores Heterotroph

Nutrition Balenced diet includes all 7 components Carbohydrate- Protein – Fats- 17kJ/g 38kJ/g Obesity New Food Pyramid emphasise importance of controlling weight and physical activity -dietary fats –limit saturated fats 20-35% 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 canal 2 main functions: Digesting and absorbing nutrients Protecting from invasion

Oesophagus -transfers food to stomach by peristalsis Cardiac sphincter -opens to allow food oesophagus stomach -heartburn –acid escapes stomach oesaphagus

Stomach Short 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 1-2 Kills bacteria Loosens fibrous foods Activates pepsinogen Denatures salivary amylase Activated to pepsin Converts proteins peptides Controls gastric motility and acid secretion

Small Intestine Around 6m in an adult Food takes 1-6 h to pass through 2 main tasks = digestion, absorption 3 parts Duodenum Jejenum Ileum

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 salts Neutralise 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

Liver Weighs about 1.5kg Holds about 13% of total blood Liver cell = hepatocyte Unique ability to regenerate – average life = 150 days Right lobe Left 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 thick Villi, microvilli – increase surface area for absorption Rich 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 Colon Reabsorbs water – so waste is converted to semi-solid = faeces – egested Diarrhoea, 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

The Immune System

The Immune System Defends body against pathogens Can distinguish between self and non-self General Defence System (innate) Non-specific = acts against all pathogens Rapid 1. First line of general defence Skin = barrier. Sweat (acidic pH) Clotting = also helps protect skin Lysozyme = enzyme in saliva, sweat, tears. Attacks bacterial cell walls Mucous (respiratory, digestive, urinary & reproductive tracts) = traps pathogens Cilia = little hairs that help clear mucous (and pathogens) from respiratory tract Alimentary 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 defence Phagocytic white blood cells (leukocytes) = destroy pathogens that enter Complement Inflammation Phagocytes – (Phago= eat; cyte=cell) attracted to a site of infection (chemotaxis) by chemicals released by injured cells Three 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

Macrophage Phagocytoses pathogen and displays antigens on surface B-cells Each recognise a different antigen. The correct one develops into… Plasma cells Clones of the correct B-cell, which produce antibodies 1st meeting a pathogen, this process takes days Memory 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-Cells Also 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 immunity Memory 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 immunity Production of a person’s own antibodies. Long lasting Passive immunity An individual is given antibodies by another Short-term resistance (weeks- 6months) Natural Active When pathogen enters body in the normal way, we make antibodies Natural Passive Baby in utero (placenta) Breast-fed babies Artificial Passive Gamma globulin injection Extremely fast, but short lived (e.g. snake venom) Edward Jenner Artificial Active Vaccination – usually contains a safe antigen from the pathogen. Person makes antibodies without becoming ill

Career in Science ? BSc – Biochemistry in UCC PhD – Cell biology/virology in Heidelberg, Germany (met my French husband) Post-doc – Cell biology in San Francisco, USA Industry – Elan Now – juggle 2 jobs: General Manager of the Alimentary Pharmabiotic Centre

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…?