Chapter 6. Human Physiology

Question 1

Which pancreatic cells secrete insulin?

Answer 1

β

Question 2

Which pancreatic cells secrete glucagen?

Answer 2

α

Question 3

What is the role of insulin? And how does it function?

Answer 3

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

Question 4

What is the role of glucagen? And how does it function?

Answer 4

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

Question 5

Describe type 1 diabete

Answer 5

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

Question 6

Describe type 2 diabete

Answer 6

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

Question 7

Distinguish type 1 and 2 diabete

Answer 7

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

Question 8

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

Answer 8

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

Question 9

Describe the effects of melatonin

Answer 9

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

Question 10

Jet lag symptoms

Answer 10

Daytime fatigue
Excessive sleepiness + disturbed sleep
Unable to concentrate
Mood changes
Stomach problems: diarrhea

Question 11

Causes of jet lag

Answer 11

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

Question 12

Ways to alleviate jet lag

Answer 12

Taking melatonin: yet long term side effects are not being studied; some studies show not effective
Drink water
Walk around the cabin
Light treatment

Question 13

Leptin

Answer 13

Inhibits appetite to achieve energy homeostasis
Secreted by adipose cells
Acts on receptors on hypothalamus
Was used to treat obesity –> failure

Question 14

Why leptin treatments were not successful in controlling obesity?

Answer 14

• 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

Question 15

Mouth/teeth

Answer 15

Mechanical digestion: chewing

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

Question 16

Esophagus

Answer 16

Move food from the mouth to the stomach by peristalsis

Question 17

Stomach

Answer 17

Mechanical digestion: churning
Mixing with secreted HCI –> kills pathogens
Initial stages of protein digestion

Question 18

Duodenum (small intestine)

Answer 18

Final stages of digestions of carbohydrates, proteins and nucleic acids
Initial stage of lipid digestion
Stomach acid is neutralized by bile

Question 19

Functions of bile

Answer 19

Emulsifying lipid molecules –> increasing surface area
Neutralizing acidic macromolecules from the stomach

Secreted by liver, stored in the gall bladder

Question 20

Digestion

Answer 20

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

Question 21

Pancrease

Answer 21

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

Question 22

Large intestine

Answer 22

Reabsorption of water
Further digestion, especially of carbohydrates by symbiotic bacteria
Formation and storage of faeces in rectum

Question 23

Peristalsis

Answer 23

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.

Question 24

Function of amylase and example

Answer 24

Breaking down of amylose into maltose
Ex) salivary amylase

Amylose is unbranched.
Amylopectin is branched

Question 25

Function of endopeptidase and example

Answer 25

Typsin breaking down polypeptides into AAs

Question 26

Function of lipase and example

Answer 26

Breaking down triglycerides into glycerol and fatty acids

Ex) pancreatic lipase

Question 27

Phospholipase

Answer 27

Breaks down phospholipids into fatty acids, phosphate, and glycerol

Question 28

Why do the epithelium cells of the small intestine has immobolized enzymes attached to it?

Answer 28

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

Question 29

Villi and absorption

Answer 29

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.

Question 30

Transport of digested food to liver

Answer 30

Sugar monomers --> glycogen
Harmful substances (e.g. alcohol) are detoxified in liver

Question 31

Digestion of starch in the small intestine

Answer 31

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

Question 32

Absorption of triglyceride

Answer 32

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

Question 33

Absorption of glucose

Answer 33

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

Question 34

Use of dialysis tubing

Answer 34

Dialysis tubing is made from cellulose
Used to model the human small intestine
Semi-permeable and porous
Models passive diffusion and osmosis

Question 35

Order of tissue layers of small intestine from inside out

Answer 35

lumen –> epithelium –> mucosa –> circular M –> longitudinal muscle