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Certificate Biology - New Mastering Basic Concepts20 Oxford University Press 2005

1199 HHoommeeoossttaassiiss iinn mmaammmmaallss

19.1 What is homeostasis? (Book 3, p.54)

�

• (1)� Homeostasis (��) is the maintenance of a constant internal environment

inside our body.

•� Homeostasis ensures the best conditions in our body for body cells to function efficiently.

•� Examples of homeostasis in mammals:

(2)� Osmoregulation (��)

and (3)� excretion () by

the kidneys

Regulation of body

temperature by the

(4)� skin

Regulation of blood glucose

level by the (5)� liver

and the (6)� pancreas

• E Homeostasis is maintained by (7) negative feedback

mechanism .

19.2 How are the amounts of water and minerals regulated bythe kidney? (Book 3, p.55)

•� The regulation of the amounts of water and minerals is important to avoid unnecessary

changes in the (8)� water potential inside cells which greatly affect

normal metabolism.

•� The amount of water and minerals in our body are regulated by the (9)� kidneys of

the urinary system (�� ).


Certificate Biology - New Mastering Basic Concepts Oxford University Press 2005 21

The mammalian urinary system (Book 3, p.55)

A

B

CD

E

FG

inferior vena cava

dorsal aorta

♦ The mammalian urinary system

Structure Function

A(1) Renal

artery (��)•� Carries blood from the aorta to the kidney

B(2) Renal

vein (��)

•� Returns blood from the kidney to the inferior

vena cava

C (3) Kidney (�) •� Purifies blood and produces urine

D (4) Ureter (��) •� Carries urine to the urinary bladder

E(5) Urinary

bladder (�)•� For temporary storage of urine

F(6) Sphincter

muscles (��)

•� Relax when the bladder is full so that urine is

� passed to the outside, i.e. urination

G (7) Urethra (� ) •� Passes urine from the urinary bladder to the outside

Go To …Practical 19.1 Examination of the mammalian urinary system

(Student’s Book 3 p.55; Activity Book 3 p.31)



E Kidney (Book 3, p.56)

• A kidney consists of:

1 outer, lighter coloured (1) cortex (��)

2 inner, darker coloured (2) medulla (��)

• Inside the medulla, a number of cone-like structures stick out

into the (3) pelvis (��).

♦ Longitudinal section of a kidney

E Nephron (Book 3, p.56)

• A (4) nephron (��) is the functional unit of the kidney. A kidney is composed of

one to two million nephrons.

• The structure of a nephron:

(11) proximal

convoluted

tubule

(��)

(13) renal

vein

(15) collecting

duct

(��)

(5) glomerulus(��)

(7) efferent

arteriole(��)

(10) loop of

Henle( ��)

(8) afferent

arteriole(��)

(9) renal

artery

(12) distal

convoluted

tubule

(��)

(6) Bowman’s

capsule(��)

(14) capillary

Key: blood flow in arteries

blood flow in veins

flow of glomerular filtrate

Go To …Practical 19.2 Examination of the mammalian kidney (Student’s Book 3 p.56; Activity Book 3 p.32)



E Functioning of a nephron (Book 3, p.58)

1 Ultrafiltration (Book 3, p.58)

• (1) Ultrafiltration (��) is the process in which plasma is filtered under high

pressure into the Bowman’s capsule. (2) Glomerular filtrate (��)

will be formed.

• The glomerulus of a nephron is adapted to ultrafiltration:

♦ Diagram showing ultrafiltration in a glomerulus and a Bowman’s capsule�

• The contents of glomerular filtrate are similar to those of blood plasma but no

(6) proteins are present in the glomerular filtrate.

The efferent arteriole is (3) narrower than the afferent arteriole. The

high (4) hydrostatic pressure developed at the glomerulus

forces small molecules from the plasma out into the Bowman’s capsule.

The capillary walls of the glomerulus are (5) differentially permeable

and allow only small molecules to pass through.



2 Reabsorption (Book 3, p.59)

•� (1) Reabsorption (��) is the process in which useful substances are absorbed

back into the blood when the filtrate flows through the kidney tubules.

• The kidney tubules are coiled in order to increase their (2) surface area

and the time taken for the filtrate to flow through them.

• Reabsorption of glucose and amino acids only takes place along the (3) proximal

convoluted tubule , while salts, water and urea are reabsorbed throughout

the renal tubules and the collecting ducts.

• Different substances are reabsorbed by different processes:

glucose

amino acids

salts

urea

water

Key: (4) diffusion

and active transport

(5) osmosis

(6) diffusion

bloodflow

proximalconvoluted tubule

bloodcapillary

♦ Reabsorption of different substances along the proximal convoluted tubule

•� The remaining glomerular filtrate after reabsorption is called (7) urine .

It contains urea, water, salts and other metabolic waste.

• Urine passes through the collecting ducts to the pelvis, then through the (8) ureters �

to the urinary bladder for temporary storage.



E Functions of the kidneys in homeostasis (Book 3, p.61)

1 Osmoregulation (Book 3, p.61)

The osmoregulatory function of the kidneys in terms of water and salt regulation when the body is

facing different conditions:

When taking in a large amount of water

Concentration of blood (1) Dilute / Concentrated

Proportion of water reabsorbedinto capillaries

(2) Greater / Smaller

Volume of urine produced (3) Larger / Smaller

Concentration of urine (4) Dilute / Concentrated

When losing a large amount of water e.g. by sweating

Concentration of blood (5) Dilute / Concentrated

Proportion of water reabsorbedinto capillaries

(6) Greater / Smaller


Concentration of urine (8) Dilute / Concentrated



When taking in excess salts

Concentration of salt inglomerular filtrate

(1) Higher / Lower

Volume of water flows fromblood into tubules

(2) Larger / Smaller


Salt concentration in urine (4) Higher / Lower

2 Excretion (Book 3, p.62)

• (5) Metabolic waste is constantly produced and a high concentration of

the waste in the body is toxic. That is why excretion is necessary.

• The kidneys produce (6) urine to get rid of the metabolic waste, such as urea,

from the blood.

Go To …STS connection 19.1 Kidney failure and the related community supports


STS connection 19.2 Issues associated with kidney transplants

(Student’s Book 3 p.63)

Section concept diagram (Student’s Book 3 p.65)

Quick check (Student’s Book 3 p.65)

19.3 How is body temperature regulated by the skin? (Book 3, p.66)

Importance of regulating body temperature (Book 3, p.66)

• A constant body temperature enables mammals to stay (7) active at all times.

• A constant body temperature keeps the (8) enzyme activity and the

(9) metabolic rate relatively constant.



Go To …Practical 19.3 Examination of the mammalian skin


Structure and functions of skin (Book 3, p.67)

The skin consists of two layers: (1) epidermis (��) and (2) dermis (��).

A

B

C

D

E GHI

J

F

♦ Diagram showing a longitudinal section through the mammalian skin

Epidermis (Book 3, p.67)

Structure Function

A

Outermost layer • Reduces water loss by (3) evaporation

• Protects the body from (4) mechanical

injury

• Prevents the entry of (5) pathogens

BMiddle layer • When pushed towards the surface, cells die and form the

outermost layer

C

Innermost layer • Produces new cells by cell division

• Contains (6) melanin (��) which protects the

body against harmful ultraviolet light

• Produces (7) vitamin D



Dermis (Book 3, p.68)

Structure Function

D Sensory receptors • Detect (1) stimuli

E(2) Sweat

gland (��)

• Secretes (3) sweat

• Evaporation of sweat helps cool down the body

F

Blood vessels and

capillaries

• Supply (4) oxygen and nutrients to the

skin cells and remove (5) waste

• Help regulate (6) body temperature

G

(7) Sebaceous

gland

(��)

• Secretes (8) sebum (��) which

a keeps the hairs and skin (9) supple (��)

and waterproof

b reduces the growth of harmful

(10) micro-organisms

H

(11) Hair

follicle

(��)

• Produces new hair from the base

• Controls the erection of hair to help regulate

body temperature

erector muscles contractto pull hairs upright

erector muscles relax andhairs lie down

I

(12) Erector

muscle

(�)

♦ Action of erector muscles on hairs

J(13) Subcutaneous

fat

• Stores (14) fat

• Forms a heat insulating layer



Regulation of body temperature by skin (Book 3, p.70)

Structure in the skin Response under hot conditions

greater amount of heat loss

1 Erector muscles (1) Relax / Contract

2 Hairs (2) Lie flat / Pulled upright

3 Sweat glands Secrete (3) more / less sweat

4 Arterioles supplyingblood to the bloodcapillaries in the skin

(4) Dilate (vasodilation ��) /

Constrict (vasoconstriction ��)

5 Subcutaneous fat (5) Thinner / Thicker

Structure in the skin Response under cold conditions

very littleheat loss

1 Erector muscles (6) Relax / Contract

2 Hairs (7) Lie flat / Pulled upright

3 Sweat glands Secrete (8) more / less sweat

4 Arterioles supplyingblood to the bloodcapillaries in the skin

(9) Dilate (vasodilation) /

Constrict (vasoconstriction)

5 Subcutaneous fat (10) Thinner / Thicker



Go To …STS connection 19.3 Heat exhaustion, heatstroke and hypothermia




�

E 19.4 How is blood glucose level regulated? (Book 3, p.73)

Roles of liver and pancreas in regulating blood glucose level (Book 3, p.73)

The pancreas releases different amounts of (1) insulin and (2) glucagon which

lead to a number of actions by the liver to bring the blood glucose level back to normal.

Consequences of failing to regulate blood glucose level (Book 3, p.74)

• If the blood glucose level is too high, cells lose water by osmosis and their metabolic

activities will be affected. Glucose may be lost in urine, causing (3) diabetes

mellitus (��). This disease is usually caused by insufficient (4) insulin

production in the body.

• After the intake of glucose, the blood glucose level of a healthy person returns to normal

within a short period of time. However, that of a diabetic (��) will remain high for a

long time.

♦ The graph showing the changes in blood glucoselevels of a healthy person and of a diabetic

♦ The graph showing the change inglucose level in the urine of a diabetic

• If the blood glucose level is too low, the (5) brain cannot function properly.



Go To …STS connection 19.4 Discussion on the control of diabetes (Student’s Book 3 p.75)



Review (Student’s Book 3 p.76)

Summary concept diagram (Student’s Book 3 p.77)

�

Practice question

The glucose tolerance test measures the body’s ability to metabolize glucose. It is used by doctors to

diagnose diabetes. After an overnight fast (no eating), a blood sample is drawn from the patient for

measuring the blood glucose level. The patient then drinks a solution containing 75 g of glucose and

blood is drawn again at intervals for up to 3 hours. The table below shows the test results of two

persons, A and B.

Blood glucose level (mg / 100 cm3)Time (hour)

Person A Person B

0 84 150

0.5 140 220

1 150 245

2 100 255

3 80 260

E a Plot the test results of the two persons in the form of a graph. (4 marks)

GlusoePerson B

bloo

dgl

ucos

ele

vel(

mg

per

100

cm3

bloo

d)

50

100

150

200

250

300

time (hr)

0 1 2 3

Person B

Person A

Glucose tolerance test results

(4m)



E b One of the two persons can metabolize glucose normally and the other person has diabetes.

Which one is the diabetic? (1 mark)

Person B (1m).

E c After one hour, what happens to the blood glucose level of the person with normal glucose

metabolism? Describe how the blood glucose level is regulated in his body after drinking

the glucose solution. (5 marks)

After one hour, the blood glucose level drops slowly and eventually returns to the normal

level (1m). After drinking the glucose solution, the blood glucose level increases (1m).

This stimulates the pancreas to secrete more insulin (1m). Insulin decreases the blood

glucose level by converting more glucose to glycogen (1m) and increasing the glucose

uptake by cells for oxidation (1m).

E d Apart from performing the glucose tolerance test, suggest another screening test for

possible diabetes. (2 marks)

Test for glucose in urine (1m) using Clinistix paper (1m).

Total: 12 marks� END �

class: name: ()date: 19 homeostasisinmammalswebsites.lstlcw.edu.hk/.../worksheet/ws_ch19e_ts.pdf ·...

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