Chapter 6. Human Physiology Flashcards Preview

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Flashcards in Chapter 6. Human Physiology Deck (35):

Which pancreatic cells secrete insulin?



Which pancreatic cells secrete glucagen?



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

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

Injections of insulin is usually unnecessary
Controlled diet
Monitoring of blood glucose level


Distinguish type 1 and 2 diabete

1. Patient: young people v.s. overweight people
2. Cause: beta cells destroyed/functioning
3. Treatment: one needs insulin injections v.s. one does not


What happens when a mammal lives in a particularly cold environment for several weeks?

1. Hypothalamus increases the secretion of thyrotropin releasing hormone
2. Thyrotropin releasing hormone causes the thyroid gland to enlarge and secrete more thyroxin
3. 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


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



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



Mechanical digestion: chewing
Mixing food with saliva (which contains amylase and lubricants to start starch digestion)



Move food from the mouth to the stomach by peristalsis



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



Breaking down of macromolecules from food into monomers for absorption and assimilation.



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



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



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