6.1 Digestive System

Question 1

what are the 2 major groups of organs which comprise the human digestive system?

Answer 1

• alimentary canal -> organs which food pass through
• accessory organs - aid digestion but don’t actually transfer food

Question 2

what does the oesophagus do and what is it? (2)

Answer 2

• hollow tube connect oral cavity to stomach
• food mixed with saliva and moves in a bolus via peristalsis action

Question 3

what is the stomach and how does it function? (2)

Answer 3

• temporary tank where food is mixed by churning and protein
• lined by gastric pits that release digestive juices (acidic environment pH-2)

Question 4

what is the small intestine and how does it function? (2)

Answer 4

• long, highly folded tube where usable food substances are absorbed
• consists of 3 parts (duodenum, jejunum and ileum)

Question 5

what is the large intestine and how does it function? (2)

Answer 5

• final section of alimentary canal, where water and dissolved minerals are absorbed
• consists of ascending/transverse/descending/sigmoidal colon as well as rectum

Question 6

what is the salivary gland and its function? (2)

Answer 6

• release saliva to moisten food and contains enzymes (starch breakdown)
• includes parotid gland, submandibular gland and sublingual gland

Question 7

what is the pancreas and its function? (2)

Answer 7

• produce a broad spectrum of enzymes that are released into the small intestine via duodenum
• secretes certain hormones (insulin/glucagon) regulates sugar conentrations

Question 8

what is the liver and its function? (2)

Answer 8

• takes raw material absorbed by the small intestine and uses them to make key chemicals
• includes detoxification, storage, metabolism, bile production and haemoglobin breakdown

Question 9

what is mechanical digestion? (3)

Answer 9

• food is initially broken down in mouth by grinding of teeth
• tongue pushes the food towards the back of the throat where it travels down oesophagus as a bolus
• epiglottis prevents the bolus from entering the trachea while the uvula prevents the bolus from entering the nasal cavity

Question 10

what is churning digestion? (3)

Answer 10

• stomach lining contains muscles which physically squeeze and mix the food with strong digestive juices
• food is digested within the stomach for several hours and turned into a creamy paste called chyme
• eventually chyme enters the small intestine where absorption will occur

Question 11

what is peristalisis? (3)

Answer 11

• peristalisis is the principal mechanism of movement in oesophagus although it also occurs in both stomach and gut
• continuous segments of longitudinal smooth muscles rhythmically contract and relax
• food is moved unidirectionally along the a causal direction

Question 12

what is segmentation? (3)

Answer 12

• segmentation involves the contraction and relaxation of non-adjacent segments of circular smooth muscle in intestines
• segmentation contractions move chyme in both directions, allowing for a greater mixing of food with digestive juices
• segmentation helps to physically digest food particles, its bidirectional propulsion of chyme can slow overall movement

Question 13

how do stomach acids work? (4)

Answer 13

• stomach contains gastric glands which release digestive acids to create a low pH environment
• the acidic environment function to denature proteins and other macromolecules aiding in overall digestion
• stomach epithelium contains a mucous membrane which prevents acids from damaging gastric lining
• pancreas alkaline compounds which neutralise the acids as they enter the intestine

Question 14

how does bile work? (3)

Answer 14

• liver produces (stored in gall bladder)
• bile contains bile salts which interact with fat globules and divide them into smaller droplets
• emulsification of fats increase SA for enzyme activity

Question 15

how are carbohydrates digested? (4)

Answer 15

• digested by amylase from salivary glands
• also secreted by pancreas
• enzyme for disaccharide hydrolysis are immobilised on epithelial lining of small interesting near channel proteins
• humans don’t possess an enzyme for digesting cellulose and it passes through the body

Question 16

how are proteins digested? (3)

Answer 16

• protein digested in stomach by protease (acidic pH)
• smaller polypeptide chains enter small intestines where they are broken down by endopeptidases released by pancreas
• endopeptidases work optimally in neutral environment in acid

Question 17

how are lipids broken down? (2)

Answer 17

• lipid breakdown occurs in intestines beginning emulsification of fat globules by bile from gall bladder
• smaller fat droplets are digested by lipases release from pancreas

Question 18

how are nucleic acids broken down?

Answer 18

• pancreas also release nucleases which digest nucleic acids (DNA/RNA) into smaller nucleosides

Question 19

what is the structure of the small intestine? (4)

Answer 19

• Serosa - protective outer covering composed of a layer of cells reinforces 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 form the innermost mucosa
• mucosa - highly folded inner layer which absorbed material through its surface epithelium from intestinal lumen

Question 20

what are the features of villi? (6)

Answer 20

• microvilli - ruffling of epithelial membrane increase SA
• rich blood supply - dense capillary network absorbed products
• single layer epithelium - minimises diffuses distance between lumen and blood
• lacteals - absorbs lipids from the intestine lymphatic system
• intestinal glands - exocrine pits release digestive juices
• membrane proteins - facilitated transport of digested material into epithelial cells

Question 21

what are structures of intestinal villi? (4)

Answer 21

• tight junction - occluding associations between the plasma membrane of two adjacent cells, creating an impermeable barrier
• microvilli - increase SA
• mitochondria - epithelial cells of intestinal villi will possess large numbers of mitochondria to provide ATP for active transport
• pinocytotic vesicles - pinocytosis is non-specific uptake of fluids and dissolves solutes

Question 22

what are the 4 different membrane transport mechanisms?

Answer 22

• secondary active transport
• facilitated diffusion
• osmosis
• simple diffusion

Question 23

what is secondary active transport?(2)

Answer 23

• transport protein coupkees the acrtive translocation of 1 molecule to the passive movement of another
• glucose and amino acids are co-transported across the epithelial membrane by the active translocation of sodium ions

Question 24

what is facilitated diffusion? (3)

Answer 24

• channel proteins help hydrophilic food molecules pass through the hydrophobic portions of the plasma membrane
• channel proteins are often situated near specific membrane-bound enzyme (creates localised conc grad)
• certain monosaccharides, vitamins and some minerals are transported by facilitated diffusion

Question 25

what is osmosis? (2)

Answer 25

- water molecules will diffuse across the membrane in response to the movement of ions and hydrophilic monomers - absorption of water and dissolved ions occur in both small and large intestine

Question 26

what is simple diffusion? (2)

Answer 26

- hydrophobic materials freely pass through the hydrophobic portion of plasma membrane - once absorbed, lipids will often pass into lacteals than being transported via blood

Question 27

how does endocytosis? (4)

Answer 27

- involves invagination of plasma membrane to create internal vesicle containing extracellular material - requires breaking and reforming of phospholipid bilayer (energy-dependent) - in intestine, vesicles form around fluid containing dissolves materials - pinosytosis allows material to be ingested in mass (less time than shuttling via membrane proteins

Question 28

how is starch digested?

Answer 28

- initiated by salivary amylase in the mouth - continued by pancreatic amylase in the intestines

Question 29

how does amylase work?

Answer 29

- amylase digests amylose into maltose subunits and digests amylopectin into branched chains called dextrin - maltose and dextrin digested by enzymes in the epithelial lining of small intestine - the hydrolysis of maltose/dextrin results in formation of glucose monomers

Question 30

what is the role of pancreas? (2)

Answer 30

- it produces the enzyme amylase which is released from exocrine glands into the intestinal tract - produces the hormones insulin and glucagon which are released from endocrine glands into the blood

Question 31

what does insulin and glucagon do? (3)

Answer 31

- insulin and glucagon regulate concentration of glucose in bloodstream - insulin lowers blood glucose levels by increasing glycogen synthesis and storage in the liver and adipose tissue - glucagon increases blood glucose levels by limiting the synthesis and storage of glycogen by the liver and adipose tissue