Chapter 6. Human Physiology Flashcards
Which pancreatic cells secrete insulin?
β
Which pancreatic cells secrete glucagen?
α
What is the role of insulin? And how does it function?
Lowers blood glucose level.
Secreted by β pancreatic cells –> circulates around the body in blood –> enabling glucose to enter cells –> blood glucose level drops –> insulin secretion drops
What is the role of glucagen? And how does it function?
Increases blood glucose level.
Secreted by α pancreatic cells –> circulates around the body in blood –> breaks down glycogen from stores (e.g. liver) into glucose in blood stream –> blood glucose level rises –> glucogen secretion drops
Describe type 1 diabete
Immune system mistakenly destroys the insulin-secreting pancreatic cells (usually in young people) –> no/less insulin is produced –> glucose level build up in blood –> life-threatening complications
Treatments:
Daily injections of insulin
Monitoring blood glucose level using simple glucose testing kit
Diet: avoid large ingestions of carbohydrates + keeping some sugary food at hand
Describe type 2 diabete
Beta cells still functioning but patient’s body becomes resistant to insulin and/or less insulin is produced than needed (usually in overweight people) –> reduced sensitivity to insulin –> blood glucose level increases
Treatments:
Injections of insulin is usually unnecessary
Controlled diet
Monitoring of blood glucose level
Distinguish type 1 and 2 diabete
- Patient: young people v.s. overweight people
- Cause: beta cells destroyed/functioning
- Treatment: one needs insulin injections v.s. one does not
What happens when a mammal lives in a particularly cold environment for several weeks?
- Hypothalamus increases the secretion of thyrotropin releasing hormone
- Thyrotropin releasing hormone causes the thyroid gland to enlarge and secrete more thyroxin
- Thyroxin increases the body’s metabolic rate, and so the rate at which heat is being produced
Describe the effects of melatonin
Secreted by pineal gland in the brain
Controls the circadian rhythym
Increases in mid/late evening –> remains high during night –> falls in morning
Melatonin level is determined by light. During winter (early nights + late mornings): body producing melatonin earlier in night, and remains high in late morning –> seasonal affective disorder, winter depression
Melatonin secretion falls with age –> elderly people need less sleep
Jet lag symptoms
Daytime fatigue Excessive sleepiness + disturbed sleep Unable to concentrate Mood changes Stomach problems: diarrhea
Causes of jet lag
Crossing over 2 or more timezones –> circadian rhythm being disturbed and out of sync with the time in your new locale
Pressure changes in cabin and latitude changes
Dehydration
Ways to alleviate jet lag
Taking melatonin: yet long term side effects are not being studied; some studies show not effective
Drink water
Walk around the cabin
Light treatment
Leptin
Inhibits appetite to achieve energy homeostasis
Secreted by adipose cells
Acts on receptors on hypothalamus
Was used to treat obesity –> failure
Why leptin treatments were not successful in controlling obesity?
- People suffering from obesity usually have leptin resistance (receptors being less insentitive to leptin, despite high leptin level and high energy stores in adipose tissues)
- Leptin is a short-lasting protein: patients might be reluctant to take a number of injections per day
- Affects the reproductive system: not applicable to children and young adults
- Only a very small portion of obesity is caused by mutations in genes for leptin systhesis
- Hunger is not the only reason to eat –> pleasure/stress
Mouth/teeth
Mechanical digestion: chewing
Mixing food with saliva (which contains amylase and lubricants to start starch digestion)
Esophagus
Move food from the mouth to the stomach by peristalsis
Stomach
Mechanical digestion: churning
Mixing with secreted HCI –> kills pathogens
Initial stages of protein digestion
Duodenum (small intestine)
Final stages of digestions of carbohydrates, proteins and nucleic acids
Initial stage of lipid digestion
Stomach acid is neutralized by bile
Functions of bile
Emulsifying lipid molecules –> increasing surface area
Neutralizing acidic macromolecules from the stomach
Secreted by liver, stored in the gall bladder
Digestion
Breaking down of macromolecules from food into monomers for absorption and assimilation.
Pancrease
Secretion of pancreatic juice into the lumen of small intestine.
Pancreatic juice contains: endopeptidases (protease), lipases, amylases, phospholipase for hydrolysis reactions
Pancreatic juice is 7-8 pH –> optimum pH for enzyme activities
Enzymes synthesized by ribosomes in pancreatic gland cells –> released into small ducts by exocytosis –> small ducts unit to form pancreactic duct which leads into the lumen of the small intestine
Large intestine
Reabsorption of water
Further digestion, especially of carbohydrates by symbiotic bacteria
Formation and storage of faeces in rectum
Peristalsis
The circular (inside) and longitudinal muscle layers in the wall exert continuous moderate force, leading to waves of vigorous contractions along the alimentary canal.
Circulary M behind the bolus contract, restricting the gut to prevent the bolus from being pushed back –> longitudinal M at where the bolus is located also contracts, moving the bolus along the gut.
M contractions controlled unconsciously by the enteric nervous system.
Uni-directional: vomiting use different muscles
Slow to allow maximum digestion and absorption: mixing with enzymes, diffusion etc.
Function of amylase and example
Breaking down of amylose into maltose
Ex) salivary amylase
Amylose is unbranched.
Amylopectin is branched
Function of endopeptidase and example
Typsin breaking down polypeptides into AAs
Function of lipase and example
Breaking down triglycerides into glycerol and fatty acids
Ex) pancreatic lipase
Phospholipase
Breaks down phospholipids into fatty acids, phosphate, and glycerol
Why do the epithelium cells of the small intestine has immobolized enzymes attached to it?
The products of hydrolysis reactions by pancreatic enzymes are not monomers (e.g. amylase is broken down into maltose, a dissacharide)
Therefore, these macromolecules need to be broken down further by enyzmes secreted by gland cells in the intestine wall in intestinal juice.
Ex) nucleases, maltase, lactase, sucrase, exopeptidase (breaks down polylpeptides into dipeptides) –> dipeptidase
Villi and absorption
Lacteal: lipid
Thin epithelium: one-cell thick
Intense network of capillaries: shortened diffusion pathway
Microvilli: increases SA
Channel proteins and pumps for facilitated diffusion and active transport
A lot of mitochondria –> ATP for active transport
Continuous blood flow in capillaries –> sustained concentration gradient
Absorbed monomers from digestion, mineral ions, and vitamins.
Transport of digested food to liver
Sugar monomers --> glycogen Harmful substances (e.g. alcohol) are detoxified in liver
Digestion of starch in the small intestine
Hydrolysis of starch is catalyzed by pancreatic amylase and maltase, glucosidase and dextrinase found in intestinal epithelium cells.
Amylase breaks 1-4 bonds in amylose and amylopectin. 1-6 bonds cannot be broken down by amylase –> enzyme-substrate specifity.
1-6 bonds in amylopectin are broken by dextrinase (charbohydrate fragments with undigested 1-6 bonds are called dextrins)
Products then enter the villus capillaries –> liver –> glycogen for storage
Absorption of triglyceride
Products of digestion of triglycerides: fatty acids and monoglycerides can be trasported by simple diffusion (hydrophobic)
Fatty acid can also be transported facilitated diffusion by fatty acid transporters
Once inside epithelium cells, they recombine to form triglyceride to prevent being diffused back into the lumen –> combien with glycerol to form droplets –> droplets being coated in phospholipids and protein, forming lipoprotein particles –> released by exocytosis into interstitial spaces –> lacteal
In short: simple/facilitated diffusion (fatty acid transporter) –> diffusion –> combining + coating –> exocytosis
Absorption of glucose
Glucose are polar (hydrophilic) –> cannot diffuse through by simple diffusion
Sodium-potassium pumps on the in-ward facing membrane of epithelium cells generate low Na concentration by pumping 3 Na ions out to interstitial space and 2 K in per time.
Na-glucose co-transporter transfer a Na and a glucose molecule together by facilitated diffusion, depending on the concentration gradient of Na generated by the Na/K pump.
Glucose then move into the fluid in the intersitial space by facilitated diffusion through glucose channels.
In short: active transport generates concentration gradient –> faciliated diffusion –> diffusion –> facilitated diffusion
Use of dialysis tubing
Dialysis tubing is made from cellulose
Used to model the human small intestine
Semi-permeable and porous
Models passive diffusion and osmosis
Order of tissue layers of small intestine from inside out
lumen –> epithelium –> mucosa –> circular M –> longitudinal muscle
