5.1.1 Communication and Homeostasis

Question 1

What is homeostasis?

Answer 1

-maintenance of a constant internal environment in response to changes in external/internal environment
-involves control systems that keep internal environment roughly constant for metabolic reactions

Question 2

Changes to internal environment

Answer 2

-internal body temp
-blood glucose levels
-water levels
-pH

Question 3

Changes to external environment

Answer 3

-external temp
-humidity
-light(plants)
-harmful stimuli i.e sudden sounds/pain

Question 4

Why is homeostasis important?

Answer 4

-essential for enzyme activity/cell function
-respond to changes in their external environment i.e by avoiding harmful environments
-respond to changes in their internal environment to make sure conditions are optimal for metabolic reactions

Question 5

Why are receptors and effectors needed?

Answer 5

-restore dynamic equilibrium in response to conditions
-receptors trigger and co-ordinate the correct responses
-info from sensory receptors is transmitted to the brain + impulses are sent along motor neurons to effectors(muscles/glands) that react to bring about change in response to stimulus

Question 6

Why do multicellular organisms need communication systems?

Answer 6

-organs, cells and tissues have different functions, are found in different parts of the body and may have different roles to one another
-need to communicate

Question 7

Short paracrine cell signalling

Answer 7

-occurs between cells that are close together i.e neurotransmitters between nerves or muscle cells

Question 8

Long distance endocrine signalling

Answer 8

-involves signalling over long distances
-signalling molecules are transported in the circulatory system

Question 9

What is a hormone?

Answer 9

-a chemical messenger, secreted by glands and found in the endocrine system

Question 10

similarities between the endocrine + nervous system

Answer 10

-both have coordination centres(brain, spinal cord)
-both send signals in the body
-both have receptors to detect stimuli
-both have effectors(muscles/glands) to carry out response

Question 11

Differences between nervous + endocrine system

Answer 11

-chemical messengers vs nerve impulses
-hormones are longer lasting vs nerves are shorter lasting
-nerves work faster than hormones
-hormones are widespread vs nerve impulses are specific

Question 12

What do cell surface receptors do?

Answer 12

-allow cells to recognise the chemicals involved in cell signalling

Question 13

What is negative feedback?

Answer 13

-control mechanism that elicits response to help restore changed value to norm
-receptors detect when a level is too high/low-}info communicated via nervous/hormonal system –} effectors respond to counteract the change

Question 14

What happens if the change from normal is too big?

Answer 14

-effectors may not be able to counteract it, i.e a huge drop in body temp caused by prolonged exposure to cold

Question 15

What is positive feedback?

Answer 15

-amplifies the change away from normal
-not involved in homeostasis because internal environment isn’t constant
-rapidly activates processes in the body i.e platelets forming blood clots

Question 16

Why is it important to maintain core body temp?

Answer 16

• temp affects enzyme activity and enzymes control the rate of metabolic reactions

Question 17

How does high body temp have an effect?

Answer 17

-rise in temperature makes the enzyme’s molecules vibrate more
-if temp goes above a certain level, vibration breaks some H bonds in the tertiary structure
-active site changes shape and enzyme + substrate no longer fit together
-enzyme denatures

Question 18

How does low body temp have an effect?

Answer 18

-enzyme activity / RoR
-enzyme-substrate complexes cannot form

Question 19

Why does body temp fluctuate throughout the day?

Answer 19

-it is dependent on the external environment
-respiration is an exothermic reaction, so the temp it works at changes

Question 20

How are temp changes in the body detected?

Answer 20

-the peripheral temp receptors are in the skin + detect changes in the skin surface temp
-temp receptors in the hypothalamus detect temp of blood in the body

Question 21

What is an ectotherm?

Answer 21

-an animal that uses their surroundings in order to maintain a relatively constant core temp
-change their behaviour i.e migration

Question 22

Sources for ectotherms to regulate temp

Answer 22

-radiation= absorbing thermal energy
-evaporation
-convection= thermal energy transferred with air/liquids
-conduction= transfer of thermal energy through solid surfaces

Question 23

What are endotherms?

Answer 23

-can control their body temperature internally via homeostasis i.e mammals and birds

Question 24

Difference in metabolic rate between ectotherms and endotherms

Answer 24

-ectotherms don’t have a constant body temp so their metabolic rate varies
–} more active at higher temps and vice versa
-endotherms can keep internal temp constant so they have a constantly high metabolic rate–} largely independent of external temp

Question 25

Mechanisms to reduce body temp: vasodilation

Answer 25

-atertioles near the surface of the skin dilate when temp rises -vessels that provide a direct connection between the arterioles + the venules constrict -this forces blood through the capillaries in the surface layers of the skin -more heat is lost from the skin in radiation +temp is lowered

Question 26

Mechanisms to reduce body temp: Sweating

Answer 26

-more sweat secreted from sweat glands as core temp increases -water in sweat evaporates from the surface of the skin(uses heat energy to turn water into vapour)—} cools the skin

Question 27

Mechanisms to reduce body temp: Hairs lie flat

Answer 27

-as temp increases, the erector pilli muscles in the skin relax, causing hairs to lie flat -avoids trapping an insulating layer of air--} skin is less insulated and heat can be lost more easily

Question 28

Mechanisms to increase body temp: vasoconstriction

Answer 28

-arterioles near me surface of the skin constrict--} less blood flows through the capillary networks close to the surface of the skin -very little radiation takes place--} the warm blood is kept well below the surface to reduce heat loss

Question 29

Mechanisms to increase body temp: Decreased sweating

Answer 29

-less sweat is secreted from sweat glands when it's cold--} reducing the amount of heat loss -less evaporation of water from the skin's surface

Question 30

Mechanisms to reduce body temp: Hairs stand up

Answer 30

-erector pilli muscles in the skin contract, making the hairs stand up -traps an insulating layer of air, so reduces cooling through the skin

Question 31

Mechanisms to reduce body temp: Shivering

Answer 31

-muscles contract in spasms--} rapid, involuntary contracting + relaxing of muscles -metabolic heat from the increased exothermic reactions (respiration) warm up the body

Question 32

Mechanisms to reduce body temp: Hormones

Answer 32

-body releases adrenaline + thyroxine -increases metabolism + so more heat is produced

Question 33

What is the endocrine system?

Answer 33

-made up of endocrine glands--} group of cells which are specialised to secrete hormones -glands can be stimulated to release hormones by a change in conc of a substance/electrical impulse

Question 34

Hormones

Answer 34

-chemical messengers i.e steroids, proteins, glycoproteins, polypeptides, amines etc -secreted directly into the blood and transported through the body in blood plasma -then diffuse out of the blood and bind to receptors of membranes on target cells--} stimulate hormone to produce response

Question 35

action of hormones in cell signalling (non-steroid/peptide hormones)

Answer 35

-first messenger(hormone) with a complimentary shape binds to the specific receptor on the cell surface membrane of the target cell from the endocrine gland -this activates an enzyme in the cell membrane which catalyses the production of a secondary messenger--} activates a cascade of reactions inside the cell(to do with protein synthesis/activation) i.e adrenaline

Question 36

action of hormones in cell signalling (steroid hormones)

Answer 36

-because they are non-polar + lipid soluble molecules, they can pass through the lipid component of the cell membrane and bind to complimentary receptors **inside the cell** to form a hormone-receptor complex--} acts as a transcription factor which facilitates/inhibits the transcription of a specific gene i.e oestrogen

Question 37

Hormonal vs neuronal communication

Answer 37

-communication via hormones vs nerve impulses -hormone transmission via bloodstream vs nerve transmission is by neurones -hormones work slow vs nerves work faster -widespread response in hormones vs localised response in nerves -slow vs rapid -long lasting vs short lived -permanent and irreversible vs temporary and reversible

Question 38

Structure of the adrenal glands

Answer 38

-two small endocrine glands located just above the kidney -produce effects that help prepare the body for the 'fight or flight' response -the cortex= outer region of glands, produce hormones that are vital to life released by the pituitary gland i.e cortisol and aldosterone -the medulla= inner region of the glands, controlled by the nervous system, produces hormones i.e adrenaline and noradrenaline -these parts are surrounded by a capsule

Question 39

Cortex: Cortisol

Answer 39

-helps regulate metabolism by stimulating the breakdown of proteins , fats + carbs to glucose which increases the amount of energy available so the brain and muscles can form a response -works with other hormones to suppress the immune system so the body does not attack itself in the fight or flight response

Question 40

Cortex: Aldosterone

Answer 40

-helps control blood pressure -regulates the balance of sodium ions + reabsorption of water in the kidneys

Question 41

Cortex: Androgens

Answer 41

-small amounts of male + female sex hormones are released--} small impact but important especially for women after menopause

Question 42

Medulla: Adrenaline and Noradrenaline

Answer 42

work together to: -increase heart rate -increase breathing rate -constrict some blood vessels in non-essential organs so blood is diverted to brain and muscles(high bp) -widening of air passages in the lungs -convert glycogen to glucose in the liver--}**glycogenolysis**= increases respiration because more glucose is supplied to muscles, produce more energy

Question 43

Main functions of the pancreas

Answer 43

-to secrete hormones into the bloodstream as an **endocrine gland** -to secrete enzymes/pancreatic juice and release them via a duct i.e digestive enzymes (amylase, lipase etc) into the digestive system as an **exocrine gland**

Question 44

3 important digestive enzymes and how they are secreted

Answer 44

-amylase: breaks down starch into simple sugars i.e maltose(disaccharide broken down further by maltase into alpha glucose) -protease: breaks down proteins into amino acids -lipase: breaks down lipids into fatty acids and glycerol **the digestive enzymes alongside pancreatic juice are delivered to the small intestines via a duct**

Question 45

Islets of Langerhans and their role

Answer 45

-small regions of endocrine tissue within the exocrine tissue -found in clusters around the blood capillaries and they secrete **insulin and glucagon** directly into the bloodstream -alpha cells secrete glucagon and beta cells secrete insulin--} help to control blood glucose concentration

Question 46

Histology of Islets of Langerhans

Answer 46

-lightly stained(differential staining normally used to distinguish alpha cells from beta cells) -large spherical clusters

Question 47

Histology of exocrine pancreatic tissue(acinus)

Answer 47

-darker stained -small, berry-like clusters

Question 48

Blood glucose concentration

Answer 48

-normal level= 90 mg per 100cm3 of blood -the body uses glucose to produce ATP during respiration -high levels after a meal but low levels later -low levels don't have enough glucose for respiration

Question 49

Increasing blood glucose concentration: diet

Answer 49

-after eating food containing carbohydrates --} hydrolysed in the digestive system to release glucose into the bloodstream i.e starch=(amylase) maltose= glucose(maltase)

Question 50

Increasing blood glucose concentration: glycogenolysis

Answer 50

-glycogen stored in liver + muscle cells is hydrolysed into glucose which is released into the bloodstream

Question 51

Increasing blood glucose concentration: gluconeogenesis

Answer 51

-production of glucose from a non-carbohydrate source -produces glucose from amino acids/ glycerol(from lipids) in the liver

Question 52

Decreasing blood glucose concentration: respiration

Answer 52

-glucose is needed as a substrate for respiration -higher levels needed to generate more energy for muscle cells to contract during exercise

Question 53

Decreasing blood glucose concentration: glycogenesis

Answer 53

-formation of glycogen from excess glucose which is stored in the liver when BGC is too high

Question 54

Role of insulin

Answer 54

-rise of BGC is detected by the B cells in the islets of Langerhans -Insulin secreted to lower BGC, which targets liver + most body cells: -increases the rate of absorption of glucose in liver + muscle cells -increases rate of respiration in cells(more glucose needed) -increases rate of glycogenesis(store as glycogen in liver + muscle cells) -increases rate of glucose to fat conversion -inhibits release of glucagon from a cells

Question 55

How does insulin enter cells?

Answer 55

-most body cells have insulin receptors on cell surface membrane(not RBCs) -insulin binds to glycoprotein receptor which changes tertiary structure of glucose transport protein channels -causes channels to open allowing more glucose to enter -can also activate enzymes(secondary messengers) in some cells to covert glucose to glycogen/fat

Question 56

Regulating insulin secretion

Answer 56

-broken down by enzymes in liver cells--} has to be constantly secreted to maintain effect -when BGC falls below a certain level, B cells reduce insulin secretion= negative feedback

Question 57

Role of glucagon

Answer 57

-produced by alpha cells of the Islets of Langerhans after drop in BGC is detected -target liver + fat cells(highest store of glycogen + lipids) -Raises BGC levels: -gluconeogenesis--} increasing conversion of amino acids + glycerol in the liver -glycogenolysis--} liver breaks down its glycogen store into glucose and releases it back into bloodstream -reducing the amount of glucose absorbed the liver cells

Question 58

How does glucagon enter cells?

Answer 58

-only liver and fat cells have specific glucagon receptors--} only cells that respond to glucagon

Question 59

Negative feedback in glucagon

Answer 59

-when BGC rises above a certain level, the a cells reduce glucagon secretion

Question 60

Why is maintaining blood glucose self-regualting?

Answer 60

-the level of glucose determines the quantity of insulin and glucagon secreted

Question 61

Membrane potential

Answer 61

-generated through an unequal distribution of ions either side of the plasma membrane -most cells have a resting -70 mv

Question 62

3 things that generate resting potential

Answer 62

-permeability -electrical gradient -concentration gradient

Question 63

Difference between depolarised and repolarised

Answer 63

-mv of membrane closer to 0= depolarising -mv of membrane further from 0= repolarising

Question 64

Control of insulin secretion by B cells

Answer 64

-B cells are at rest with -70 mv(potassium ion channels are open) -high BGC is detected--} more glucose enters the cell via glucose transporter(facilitated diffusion) -glucose is metabolised in mitochondria= production of ATP via respiration -Influx of ATP causes K+ channels to close(binds to ATP sensitive K+ channels) -K+ conc increases inside of the cell -potential difference of B cells gets more positive and depolarises(-30mv) -depolarisation causes voltage gated calcium channels to open--} Ca2+ ions diffuse into the cell -increase of calcium ions causes insulin vesicles to move to and fuse with the plasma membrane (cascade of reactions) -insulin secreted via exocytosis

Question 65

hyperglycaemia vs hypoglycaemia

Answer 65

-hyper= high BGC -hypo= low BGC

Question 66

What is diabetes?

Answer 66

-condition where blood glucose concentration cannot be controlled properly

Question 67

Type 1 diabetes

Answer 67

-autoimmune disease where the body attacks and destroys B cells in the islets/B cells don’t function properly --} insulin no longer produced -BGC conc stays high after eating and can result in death if untreated -normally develops in childhood -risk slightly increased with family history

Question 68

Treating type 1

Answer 68

-regular insulin injections throughout the day -insulin pump--} delivers insulin via a tube beneath the skin -regular testing of BGC(normally pricking finger to analyse blood to calculate conc of insulin needed)

Question 69

What happens if a person in injected with too much/little?

Answer 69

-too much= may experience hypo and can result in unconsciousness -too little= hyper= unconsciousness/ death if untreated

Question 70

Type 2 diabetes

Answer 70

-when B cells don't produce enough insulin or body cells don't respond properly to insulin -insulin receptors on membranes may not work properly--} cells don't take up enough glucose -often linked with obesity + overeating -risk increased from asian/ Afro Caribbean descent, high blood pressure, age, males, physical inactivity

Question 71

Treating type 2

Answer 71

-reducing carb intake and matching it to exercise level(diet and excercise) -medication to stimulate insulin production or slows down rate of glucose absorption from intestine

Question 72

What is synthetic biology?

Answer 72

-using other organisms to produce something man-made

Question 73

Potential treatments: transplants

Answer 73

-pancreas transplants--} 80% success rate -B cell injections--} less than 8% success -hard to source -over exhausting immunosuppressants

Question 73

Where did insulin used to get extracted from?

Answer 73

-from animal pancreases i.e pigs and cows -expensive -may cause allergic reactions

Question 74

Potential treatments: Stem cells

Answer 74

-totipotent cells could differentiated to B cells which would be implanted into patient :( embryos have to be destroyed :) no need to wait for donor, less likelihood of rejection

Question 75

Role of pancreatic acini

Answer 75

-produce and secrete digestive enzymes