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  3. Peter Symonds College Winchester
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  5. IB Biology

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Summary Human Physiology
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very detailed Human Physiology notes, including: circulatory system, gas exchange (respiratory system), male and female reproductive systems, neurons and synapses, defence against infectious diseases, nervous system, and homeostasis.

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  • April 3, 2023
  • 19
  • 2020/2021
  • Summary

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HUMAN PHYSIOLOGY

CIRCULATORY SYSTEM


Arteries
➔ Thick, muscular walls to withstand high pressure from heart
➔ Muscle cells and elastic fibres in cell walls
➔ Smaller lumen compared to walls → keeps high pressure
➔ Carry blood at high pressure out of heart
➔ Largest artery is aorta
➔ Aorta → arteries → arterioles


Veins
➔ Thin, less muscular walls
➔ Carry blood at low pressure back to heart
➔ Skeletal muscles squeeze veins to maintain blood flow
➔ Have valves in their lumen to prevent backflow (except pulmonary vein)
➔ Wider lumen, thinner walls → allows blood to flow despite low pressure
➔ Largest vein is vena cava
➔ Venules → veins → vena cava


Capillaries
➔ Microscopic, very thin-walled (one cell)
➔ Permeable walls to allow exchange of materials between tissue cells + blood
➔ Inside tissues, they split to form capillary beds
➔ Arterioles → capillaries → venules

, Cardiac Cycle
➔ Initiated by sino-atrial (SA) node (a group of specialised muscle cells) which sends out
nerve impulses to heart muscle
◆ sinoatrial node acts as a pacemaker
◆ it sends out an electrical signal that stimulates contraction
➔ Atrio-ventricular (AV) node receives messages from SA node
➔ Myogenic muscle contraction: trigger for muscle contraction occurs within muscle itself
➔ Diastole: relaxation // Systole: contraction
◆ atria relax (atrial diastole) + fill with blood from veins
◆ atria contract (atrial systole) + push blood into relaxed ventricles (ventricular
diastole)
◆ nervous signals are sent to AV node
◆ AV node sends nervous signals down the ventricles
◆ ventricles contract (ventricular systole) + push blood into arteries
◆ atria relax again + start to fill with blood


➔ Parasympathetic nervous system: slows down heart rate, relaxes body
➔ Sympathetic nervous system: speeds it up, “survival mode”


Double circulation system
❖ Pulmonary loop: RV → pulmonary artery → lungs → pulmonary veins → LA
❖ Systemic loop: LV → aorta → body → venae cavae → RA




DIGESTIVE SYSTEM
- Absorption: process of taking small food
chemicals from intestines + moving them into the
blood
- Assimilation: process of food chemicals being
used to form more complex molecules in
cells of the body
- Absorption must happen first in the body

, - Alimentary canal: mouth → oesophagus → stomach → small intestine → large intestine →
rectum → anus
- liver → gallbladder → small intestine
- pancreas → small intestine


➔ Ingestion: taking in food through mouth
◆ Chewing helps increase surface area to speed up digestion
◆ Bolus: ball of food
◆ Salivary amylase breaks down starch into glucose
➔ Peristalsis: wave-like contractions of oesophagus to push food down + mix with enzymes
◆ Contraction of circular + longitudinal muscles
➔ Food enters stomach
◆ Acid (pH 2 to 4) kills bacteria
◆ Pepsin enzyme digests protein
◆ Mucus protects stomach wall + adds fluid
◆ Food becomes chyme
➔ Small intestine - majority of digestion happens here
◆ Muscles also contract to move food along
◆ Duodenum, jejunum, ileum
◆ Pancreas produces alkaline substance to neutralise acidic chyme and allow
enzymes to work + adds enzymes
● Endopeptidase (trypsin) for protein digestion
● Pancreatic amylase for carbohydrate digestion
● Lipase for lipid digestion
◆ Bile from liver enters through gallbladder, required for emulsification/digestion of
fats
◆ Villi increase surface area of epithelium to make absorption of food molecules
efficient - network of capillaries + central lacteal (lymph vessel)
● Products of starch + protein digestion absorbed by capillaries
● Products of lipid digestion absorbed by lacteal
➔ Large intestine
◆ Water, vitamins + minerals absorbed mostly here
◆ Undigested waste compacted together to form faeces
◆ Contains a lot of bacteria which make folic acid + vitamin K

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