IB Biology Topic 6 Human Physiology
esophagus/ oesophagus
- A hollow tube connecting the oral cavity to the stomach (separated from the trachea by the epiglottis) - Food is mixed with saliva and then is moved in a bolus via the action of peristalsis
Secondary Active Transport
- A transport protein couples the active translocation of one molecule to the passive movement of another (co-transport) - Glucose and amino acids are co-transported across the epithelial membrane by the active translocation of sodium ions (Na+)
Enzymes in pancreatic juice include
- Amylaze(catalyses starch to maltose) - Lipase(catalyses triglycerides to fatty acids+glycerol/monoglycerides) - Protease(catalyses proteins/polypeptides to shorter peptides) - Phospholipase(catalyses phospholipids to fatty acids, glycerol and phosphate) - Nucleases(digests DNA and RNA into nucleotides) Maltase(digests maltose into glucose) - Lactase(digests lactose into glucose and galactose) - Sucrase(digests sucrose into glucose and fructose) - Dipeptidase (digests dipeptides into amino acids) - Exopeptidase (digests peptides by removing single amino acids and leaving a dipeptide) Note: Cellulose cannot be digested in humans
Facilitated Diffusion
- Channel proteins help hydrophilic food molecules pass through the hydrophobic portion of the plasma membrane - Certain monosaccharides (e.g. fructose), vitamins and some minerals are transported by facilitated diffusion
Digestive enzymes
- Enzymes are biological catalysts which speed up the rate of a chemical reaction (i.e. digestion) by lowering activation energy - Enzymes allow digestive processes to therefore occur at body temperatures and at sufficient speeds for survival requirements - Enzymes are specific for a substrate and so can allow digestion of certain molecules to occur independently in distinct locations
Mitochondria (Structure of Villus Epithelium)
- Epithelial cells of intestinal villi will possess large numbers of mitochondria to provide ATP for active transport mechanisms - ATP may be required for primary active transport (against gradient), secondary active transport (co-transport) or pinocytosis
Chewing (Mouth)
- Food is initially broken down in the mouth by the grinding action of teeth (chewing or mastication) - The tongue pushes the food towards the back of the throat, where it travels down the oesophagus as a bolus - The epiglottis prevents the bolus from entering the trachea, while the uvula (a fleshy hanging structure in an organ of the body) prevents the bolus from entering the nasal cavity
Simple diffusion
- Hydrophobic materials (e.g. lipids, fatty acids, monoglycerides) may freely pass through the hydrophobic portion of the plasma membrane - Once absorbed, lipids will often pass first into the lacteals rather than being transported via the blood
The process of digestion
- It breaks down insoluble molecules into smaller subunits which can be readily absorbed into body tissues - It breaks down inert molecules into usable subunits which can be assimilated by cells and reassembled into new products
The role of pancreas in the breakdown of starch:
- It produces the enzyme amylase which is released from exocrine glands (acinar cells) into the intestinal tract - It produces the hormones insulin and glucagon which are released from endocrine glands (islets of Langerhans) into the blood
Microvilli (Structure of Villus Epithelium)
- Microvilli borders significantly increase surface area of the plasma membrane (>100×), allowing for more absorption to occur - The membrane will be embedded with immobilised digestive enzymes and channel proteins to assist in material uptake
Tight Junctions (Structure of Villus Epithelium)
- Occluding associations between the plasma membrane of two adjacent cells, creating an impermeable barrier - They keep digestive fluids separated from tissues and maintain a concentration gradient by ensuring one-way movement
Pinocytotic Vesicles (Structure of Villus Epithelium)
- Pinocytosis ('cell-drinking') is the non-specific uptake of fluids and dissolved solutes (a quick way to translocate in bulk) - These materials will be ingested via the breaking and reforming of the membrane and hence contained within a vesicle
salivary glands function
- Release saliva to moisten food and contains enzymes (e.g. amylase) to initiate the starch breakdown - Salivary glands include the parotid gland, submandibular gland and sublingual gland
Segmentation
- Segmentation involves the contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestines - Segmentation contractions move chyme in both directions, allowing for a greater mixing of food with digestive juices - While segmentation helps to physically digest food particles, its bidirectional propulsion of chyme can slow overall movement
Structure of the small intestine
- Serosa: a protective outer covering composed of a layer of cells reinforced by fibrous connective tissue - Muscle layer: outer layer of longitudinal muscle (peristalsis) and inner layer of circular muscle (segmentation) - Submucosa: composed of connective tissue separating the muscle layer from the innermost mucosa - Mucosa: a highly folded inner layer which absorbs material through its surface epithelium from the intestinal lumen
large intestine function
- The final section of the alimentary canal, where reabsorption of water and dissolved minerals takes place - Consists of the ascending/transverse/descending/sigmoidal colon, as well as the rectum - further digestion of carbohydrates by symbiotic bacteria
gall bladder function
- The gall bladder stores the bile produced by the liver (bile salts are used to emulsify fats) - Bile stored in the gall bladder is released into the small intestine via the common bile duct
Bile
- The liver produces a fluid called bile which is stored and concentrated within the gall bladder prior to release into the intestine - Bile contains bile salts which interact with fat globules and divide them into smaller droplets (emulsification) - The emulsification of fats increases the total surface area available for enzyme activity (lipase)
Stomach acids
- The stomach contains gastric glands which release digestive acids to create a low pH environment (pH ~2) - The acidic environment functions to denature proteins and other macromolecules, aiding in their overall digestion - The stomach epithelium contains a mucous membrane which prevents the acids from damaging the gastric lining - The pancreas releases alkaline compounds (e.g. bicarbonate ions), which neutralise the acids as they enter the intestine
Churning (stomach)
- The stomach lining contains muscles which physically squeeze and mix the food with strong digestive juices ('churning') - Food is digested within the stomach for several hours and is turned into a creamy paste called chyme - Eventually the chyme enters the small intestine (duodenum) where absorption will occur
Endocytosis: Pinocytosis
- Triglycerides and cholesterol in lipoprotein molecules - allows materials to be ingested en masse and hence takes less time than shuttling via membrane proteins
Artery wall structure
- Tunica externa: a tough layer of connective tissue - Tunics media: A thick layer containing smooth muscle and elastic fibres made of protein elastin - Tunica intima: a smooth endothelium forming the lining of the arteries
Osmosis
- Water molecules will diffuse across the membrane in response to the movement of ions and hydrophilic monomers (solutes) - The absorption of water and dissolved ions occurs in both the small and large intestine
carbohydrate digestion
- begins in the mouth with the release of amylase from the salivary glands (amylase = starch digestion) - Amylase is also secreted by the pancreas in order to continue carbohydrate digestion within the small intestine - Enzymes for disaccharide hydrolysis are often immobilised on the epithelial lining of the small intestine, near channel proteins - Humans do not possess an enzyme capable of digesting cellulose (cellulase) and hence it passes through the body undigested
Protein digestion
- begins in the stomach with the release of proteases that function optimally in an acidic pH (e.g. pepsin = pH 2) - Smaller polypeptide chains enter the small intestine where they are broken down by endopeptidases released by the pancreas - These endopeptidases work optimally in neutral environments (pH ~ 7) as the pancreas neutralises the acids in the intestine
small intestine function
- chemical digestion of lipids, proteins, carbohydrates, nucleic acids - neutralising stomach acids - absorption of nutrients
Liver functions
- detoxification, storage, haemoglobin breakdown, bile production - secretion of surfactants in bile to break down lipid droplets - Takes the raw materials absorbed by the small intestine and uses them to make key chemicals
stomach function
- food storage, - mechanical digestion: muscles in the stomach lining physically squeeze and mix the food with digestive juices (=churning) - chemical digestion: initial stages of protein digestion (e.g. pepsin) production of chyme
Lipids breakdown
- occurs in the intestines, beginning with emulsification of fat globules by bile released from the gall bladder - The smaller fat droplets are then digested by lipases released from the pancreas
pancreas function
- produces digestive enzymes (lipase, amylase, proteases e.g. trypsin) which are releases into the small intestine - screte hormones (insulin, glucagon), which regulate blood sugar concentrations
enzymes from small intestine
- secreted in the intestinal juice - immobilised in the plasma membrane of epithelium cells living (continue to be active when mixed with semi-digested food)
William Harvey and the circulation of blood
- showed that blood flow is unidirectional with valves to prevent backflow - rate of flow is too high for blood to be consumed in the body, so it must return to the heart and be recycled. - predicted presence of very small vessels (blood capillaries) that cannot be seen with a naked eye and which link arteries and veins - predicted pulmonary and systemic circulations
mouth function
- voluntary control of eating and swallowing - mechanical (chewing) digestion: food is broken down by grinding action of teeth - chemical digestion: food is mixed with saliva that contains lubricants (usually organic substance) and enzymes
Blood coagulation pathway
-Clotting factors cause platelets to become sticky and adhere to the damages region to forma solid plug. -These factors initiate localised vasoconstriction to reduce blood flow -Zymogen prothrombin is converted to the enzyme thrombin -Thrombin catalyses the conversion of soluble plasma protein fibrinogen into insoluble fibrin -Fibrin strands forma mesh of fibres around platelet plug which traps blood cells to form a temp clot -When the damaged region is repaired, an enzyme plasmin is activated to dissolve the clot.
How does the body respond to the skin being cut?
-Clotting occurs -Blood flowing out the cut vessels become a semi-solid gel that stops bleeding -Triggers a blood clotting process
How is the contraction of the heart controlled?
-Contraction is myogenic(generated by muscle itself) -Sinoatrial node initiates each heartbeat bu activating the cells around it. -SA node sends out electrical impulse that stimulates contraction of the myocardium -Directly causes atria to contract and stimulates the AV node -AV node sends signal down to septum via the bundle of His which initiates nerve fibres(parkinje fibres) in verntricular wall, causing ventricular contraction.
William Harvey's contributions
-Described the circulation of blood to and from the heart. -Demonstrated the unidirectional flow through large vessels. -Falsified previous theories
General organisation of mammalian circulatory system
-Double circulation system -Seperate system that supplies the lungs with blood -Pulmonary circulation: to and from lungs -Systemic circulation:to and from all other organs including heart.
Mechanisms that help the flow of blood in veins
-Gravity -Pressure exerted by other tissue fx contraction of skeletal muscles. Walking, sitting or fidgeting improves venous blood flow.
How do muscle and elastic fibres help with maintaining blood pressure between pump cycles.
-Muscle fibres can contract to narrow the lumen that increases the pressure between pumps and helps maintain pressure throughout. -The pressure exerted on the arterial wall is returned to the blood when the artery returns to normal size(elastic recoil) -The elastic recoil helps to push the blood forward through the artery as well as maintain pressure.
Structure and function of capillaries
-Narrowest blood vessels. Branch and rejoin repeatedly to form a large network of capillaries. -The wall is one layer of epithelium cells, coated with a filter like protein. -Very permeable wall and a part of plasma flows out. Cell can receive substances from the plasma fx. O2 and glucose. -Transport blood through almost all tissues of the body.
The skin as a barrier
-The outermost layer is tough, it provides a physical barrier against the entry of pathogens and protection against physical and chemical damage. -The skins pH is slightly acidic which inhibits the growth of bacteria and fungi. -It is lowered by a chemical called sebum that also moisturises the skin.
Function of valves in veins
-They maintain circulation when blood pressure is very low. -If blood starts to flow back it gets caught in the flaps of the pocket vein which fills up and blocks the lumen. -When blood flows towards the heart, it pushes the flaps to the sides of the vein. The pocket valve opens and blood can flow freely.
How can the heart rate be increased or decreased?
-Two nerves in the nedulla can either dignal an increase or decrease in the heart beat, connected to the SA node. Increase: high blood pressure, low O2 conc., low pH, exercise, hormones Decrease:low blood pressure, neurotransmitters, high O2 conc, high pH
Differences between veins and arteries
-Veins don't have as thick of a wall and contain fewer muscle and elastic fibres. -They transport blood from capillary networks back to the atria but the blood is at much lower pressure. -They can dilate more and hold more blood.
What substances are absorbed by villi in the small instestine?
-glucose, fructose, galactose and other monosaccharides -any of the 20 amino acids -fatty acids, monoglycerides and glycerol -bases from digestion of nucleotides -mineral irons, calcium, potassium and sodium -vitamins
Method of absorption
1. nutrients absorbed into epithelium cells 2. pass out of these cells towards the lacteal and blood capillaries
Lacteals (features of villi)
Absorbs lipids from the intestine into the lymphatic system
accessory organs
Aid in digestion, but do not transfer food. e.g. salivary glands, liver, gallbladder, pancreas
Enzymes involved in the breakdown of starch
Amylase breaks down the 1-4 bond in amylose into maltose and maltotriose Maltase, glucosidase and dextrinase digest maltose, maltotriose and dextrins into glucose. Glucose moves into capillaries and brought to cells as nutrition.
The cardiac cycle
Atrial systole: Atrium contracts, ventricle relaxed, blood flows from atrium to ventricle, AV valve open. Aortic valve closed. Ventricular systole: Atrium relaxed, ventricle contracts, blood flow from ventricle to aorta/pulmonary artery, AV valve closed, aortic valve open. Diastole: Atrium and ventricle relaxed, blood flows into atrium and ventricles, AV valve open, aortic valve closed
Why are enzymes needed to digest starch and other macromolecules?
Because they are too large to pass through the plasma membrane and need to broken down. Without the enzymes the reaction would take such a long time.
Role of human digestive system
Breaking down large carbon compounds in food to yield ions and smaller compunds that can be absorbed
pulmonary artery
Carries deoxygentated blood from the heart to the lungs
Atherosclerosis
Condition in which fatty deposits called plaque build up on the inner walls of the arteries. Narrows the lumen and impedes the blood flow. Cause: high blood pressure, high conc. cholestrole
pulmonary veins
Deliver oxygen rich blood from the lungs to the left atrium
Rich blood supply (features of villi)
Dense capillary network rapidly transports absorbed products
septum
Divides the right and left chambers of the heart
Endocrine and exocrine functions of pancreas
Endocrine: Release of hormones, insulin and glucagon Exocrine: Synthesise and secrete digestive enzymes into the gut
Intestinal glands (features of villi)
Exocrine pits (crypts of Lieberkuhn) release digestive juices
Membrane proteins (features of villi)
Facilitates transport of digested materials into epithelial cells
Single layer epithelium (features of villi)
Minimises diffusion distance between lumen and blood
Human Digestive System
Mouth, esophagus, stomach, small intestine, large intestine, + gall bladder and liver
Structure function relationship in arteries.
Narrow lumen-to maintain high blood pressure Thick wall w/an outer layer of collagen-to prevent artery from rupturing Inner layer of muscle and elastic fibres-to help maintain pulse flow
How does the role of the exocrine pancreas in digestion of food?
Pancreatic juice contains enzymes that digest the 3 main macromolecules found in food.
dialysis tubing
Plastic-like cellulose tubing with tiny holes to allow small molecules to pass through (semi-permeable). Models absorption by passive diffusion and osmosis.
left ventricle
Pumps oxygenated blood into the aorta
Systolic and distolic blood pressure
Systolic-the peak pressure reached in artery Distolic-the minimum pressure in artery
How does adrenaline affect heart rate?
The SA node responds by increasing the heart rate
Aorta
The large artery that carries blood from the heart to be distributed by branch arteries through the body.
Nucleic acids digestion
The pancreas also releases nucleases which digest nucleic acids (DNA, RNA) into smaller nucleosides
right semilunar (pulmonary) valve
This valve prevents blood from flowing back into the right ventricle from the pulmonary artery.
Role of villi
Villi increases the surface area of epithelium over which absorption is carried out. It increases the rate of absorption.
Perastalsis
Waves of muscle contractions - contraction of circular muscle behind the food constricts the gut to prevent it from being pushed back - contraction of longitudinal muscle where the food is located moves it along the gut - contractions controlled unconsciously by enteric nervous system (not the brain) - one direction movement (away from the mouth) - vomiting: abdominal muscles involved
inferior vena cava
carries blood from lower regions of the body to right atrium
Peristalsis in the intestine
churning of semi-digested food to mix it with enzymes, hence slower progression through the intestine
right atrioventricular valve (tricuspid valve)
controls the opening between the right atrium and the right ventricle
digestion in small intestine
enzymes from pancreas + enzymes produced by the wall of small intestine: - DNA, RNA --(nucleases)--> nucleotides - maltose --(maltase)--> glucose - lactose --(lactase)--> glucose + galactose - sucrose --(sucrase)--> glucose + fructose - dipeptides --(dipeptidase)--> amino acids - polypeptide --(exopeptidase)--> dipeptide (remove single amino acids from carboxyl or amino terminal until a dipeptide is left)
chemical digestion
food is broken down by the action of chemical agents (such as enzymes, acids and bile)
Mechanical Digestion
food is physically broken down into smaller fragments via the acts of chewing (mouth), churning (stomach) and segmentation (small intestine)
Insulin lowers blood glucose levels by
increasing glycogen synthesis and storage in the liver and adipose tissues
Glucagon increases blood glucose levels by
limiting the synthesis and storage of glycogen by the liver and adipose tissues
active transport
mineral ions: Na+, Ca2+, Fe3+
left semilunar valve (aortic valve)
prevents blood from flowing back into the left ventricle from the aorta
arteries (Harvey)
pumped blood from the heart (to the lungs and body tissues)
right ventricle
pumps deox blood into the pulmonary artery
superior vena cava
receives blood from the head and arms and chest and empties into the right atrium of the heart
right atrium
receives deoxygenated blood from the body through the vena cava and pumps it into the right ventricle
left atrium
receives oxygenated blood from the lungs through pulmonary veins
Veins (Harvey)
returned blood to the heart (from the lungs and body tissues)
The function of microvilli (features of villi)
ruffing of epithelial membrane further increases surface area
Starch digestion in the small intestine
starch composed of two types of molecules: - amylose: unbranched chains of x-glucose linked by 1, 4 bonds. - amylopectin: chains of x-glucose linked by 1, 4 bonds with 1, 6 bonds that make it branched
alimentary canal
the whole passage along which food passes through the body from mouth to anus. It includes the esophagus, stomach, and intestines.
left atrioventricular valve (bicuspid)
valve between the left atrium and the left ventricle.
Arteries
vessels that convey blood from the heart to body to body tissues at high pressure
