Biology

• Mitosis is the process of asexual cell division that produces two identical daughter cells.
• what are the 2 major groups of organs which comprise the human digestive system? alimentary canal:consists of organs through which food actually passes oesophagus, stomach, small & large intestineaccessory organs:aid in digestions but do not actually transfer foodsalivary glands, pancreas, liver, gall bladder
• description and function of oesophagus (alimentary canal) hollow tube connecting the oral cavity to the stomach separated from the trachea by the epiglottisfood is mixed with saliva (begins chemical digestion) and then is moved in a bolus via the action of peristalsis
• description and function of the stomach (alimentary canal) food is mixed by churning (from muscular stomach wall)protein digestion begins as the stomach produces proteasestomach is lined with gastric pits that release digestive juices (including protease enzyme and HCl) which creates an acidic environment (pH 2)
• description and function of the small intestine long, highly folded tubewhere usable food substances (nutrients) are absorbedconsists of three sections:duodenumjejunumileumhas microvili (ruffled lining of epithelium layer)
• description and function of large intestine (alimentary canal) final section of the alimentary canalwhere water and dissolved minerals/ions are absorbedconsists of the ascending/transverse/descending/sigmoidal colon, as well as the rectum.
• function of salivary glands (accessory organs) release saliva to moisten food and contains enzymes (amylase, protease and lipase) to initiate starch, protein and fat breakdownsalivary glands include:the parotid glandsubmandibular glandsublingual gland
• function of the pancreas (accessory organ) produces a broad spectrum of enzymes that are released into the small intestine via the duodenumalso secretes certain hormones (insulin and glucagon) which regulate blood glucose concentrations
• function of the liver takes the raw materials absorbed by the small intestine and uses them to make key chemicalsits role includes:detoxificationstoragemetabolismbile production haemoglobin breakdown
• function of gall bladder stores the bile produced by the liver bile salts are used to emulsify fatsbile stored in the gall bladder is released into the small intestine via the common bile duct
• function of the rectum/anus stores and expels faeces
• food can be digested by a combination of which two methods? mechanical digestion (teeth)chemical digestion (enzymes)
• explain mechanical digestion "chewing (mouth) food is initially broken down in the mouth by grinding action of teeth (chewing or mastication) tounge pushes food towards the back of the throat, where is travels down the oesophagus (via peristalsis) as a bolusepiglottis prevents bolus from entering the tracheauvula prevents the bolus from entering the nasal cavity stomach stomach contais muscles which physically squeeze and mix the food with strong digestive juices (""churning"")food is digested in the stomach for several hours and is turned into a creamy paste called ""chyme""eventually the ...
• explain how food moves through the alimentary canal PERISTALSIS peristalsis is the principal mechanism of movement in the oesophagus although it occurs in both the stomach and the gutcontinuous segments of longitudinal smooth muscle rythmically contract and relaxfood is moved unidirectionally along the alimentary canal in a caudal direction (mouth to anus) SEGMENTATION involves the contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestinessegmentation contractions move chyme in both directions, allowing for a greater mixing of food with digestive juices.wh...
• explain how the stomach allows chemical digestion STOMACH ACIDS + pancreas alkalis stomach contains gastric glands which release digestive juices to create a low pH environment (pH2) acidic environment functions to denature proteins and other macromolecules (aiding overall digestion)stomach epithelium contains a mucous membrane which prevents the acids from damaging the gastric lining pancreas releases alkaline compounds (e.g. bicarbonate ions), which neutralise the acids as they enter the intestine.
• explain how bile allows chemical digestion liver produces a fluid called bile - it 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) - emulsification of fats increases the total surface area available for enzyme activity (lipase)
• what is an enzyme? a biological catalyst that speeds up the rate of a chemical reaction (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
• what do proteases/endopeptidases digest/break down? proteins --> peptides --> amino acids
• what does amylase digest/break down? starch --> maltose (digests sugars/carbohydrates)
• what do nucleases digest/break down? digest DNA /RNA nucleic acid --> nucleosides
• what does the combined action of the enzyme lipase and bile salts digest? lipase: digests fats bile salts: emulsifies fats dietary fat/triglycerides --> monoglycerides/fatty acids
• where does carbohydrate digestion occur? begins in the mouth with a release of amylase from the salivary glandsamylase = starch digestionamylase is also secreted by the pancreas in order to continue carbohydrate digestion in the small intestineenzymes for disaccharide hydrolysis are often immobilised on the epithelial lining of the small intestine, near channel proteins. human bodies do not have an enzyme capable of digesting cellulose (cellulase) and hence it passes through the body undigested.
• where does protein digestion occur? begins in the stomachwith the relase of proteases that function optimally in acidic pH (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 as it passes into the duodenumpancreas produces a digestive fluid containing enzymes and bicarbonate which is alkaline
• where does lipid digestion occur? lipid breakdown occurs in the intestines beginning with emulsification of fat globules by bile released by the gall bladder - the smaller fat droplets are then digested by lipases released from the pancreas.
• what do nucleases do and where are they released? pancreas releases nucleases nucleases digest nucleic acids (DNA / RNA) into smaller nucleosides
• give a summary of the locations of enzymatic digestion :) Oesophagus salivary amylase (starch -> maltose) Stomach Proteases (protein -> polypeptides)stomach acids, HCl (chemical digestion + kills microbes) Liver/Gall bladder Bile salts (emulsification of lipids) Pancreas amylase (starch -> maltose)lipase (triglycerides -> fatty acids)endopeptidase (peptides -> amino acids)nuclease (nucleic acids -> nucleosides)bicarbonate ions (neutralise stomach acid) Small intestine membrane-bound enzymes (e.g. maltase)
• what is the function of the human intestines? function to absorb the products of digestion and have specialised structures to fulfill this function. small intestine: absorbs usable food molecules nutrientsmonosaccharidesamino acidsfatty acidsvitaminslarge intestine: abosrbs water and dissolved mineral ions from the indigestible food residues (not taken up by small intestine
• desrcibe the structure of the small intestine composed of 4 main tissue layers: (inside to outside) Mucosa highly folded/ruffled inner layerabsorbs material through its surface epithelium from the intestinal lumen (inside the small intestine)Submucosacomposed of connective tissues separating the muscle layer from innermost mucosaMuscle Layerouter layer of longitudinal muscle (for peristalsis) inner layer of circular muscle (for segmentation)Serosa protective outer coveringcomposed of a layer of cells reinforced by fibrous connective tissues
• what is villi? inner epithelial lining of intestine is highly folded / ruffled into finger-like projections called villi. many villi protrude into the intestinal lumen, greatly increasing the available surface area for material absorption summary: villi increase SA of epithelium over which absorption is carried outvilli absorb monomers formed by digestion as well as mineral ions and vitamins
• what are the 6 features of villi (MR SLIM)? Microvilli ruffling of epthelial membrane further increases the surface areaRich blood supply dense capillary network rapidly transports absorbed productsmaintains the concentration gradient by transporting food molecules away in the bloodstream, concentration remains high in intestine and low in blood stream, hence diffusion happens more readily.Single layer epithelium minimises diffusion distance between lumen and bloodLacteals absorbs lipids from the intestine into the lymphatic systemIntestinal glandsexocrine pits release digestive juicesMembran...
• desribe the structure of villus epithelium (small intestine) and explain how it optimises its capacity to absorb digested materials. occluding associations between the plasma membrane of two adjacent cells creates an impermeable barrierkeeps digestive fluids separated from tissues and maintain a concentration gradient by ensuring one-way movementmicrovilli borderssignificantly increase surface area of plasma membrane = more absorptionmicrovilli membrane embedded with immobilised digestive enzymes and channel proteinsassist in material uptakemitochondria epithelial cells of intestinal villi con...