Homeostasis Flashcards
(192 cards)
1
Q
What fluids bathe the cells of a multicellular organism?
A
Body fluids such as blood lymph and intercellular (or tissue) fluid
2
Q
What do these fluids make up?
A
The internal environment of the organism
3
Q
What must be kept fairly constant for the health growth and efficient functioning of the body cells?
A
This internal environment
4
Q
What is homeostasis?
A
Maintaining a steady internal environment
5
Q
How does an organism regulate its internal environment?
A
By constantly adjusting any changes in the physical and chemical conditions of its body fluids
6
Q
What conditions are included in the regulation of the internal environment?
A
Temperature pH (hydrogen ion concentration) osmotic pressure and concentrations of dissolved substances in the body fluids such as carbon dioxide oxygen urea food substances (glucose amino acids etc.) and ions (sodium potassium chloride etc.)
7
Q
What are often used to detect and adjust changes in the internal environment of an organism?
A
Control mechanisms
8
Q
What do sensory detectors do?
A
recognize a change in a given condition and stimulate the relevant body parts involved in control [cite: 6 7]
9
Q
What do the body parts involved in homeostasis do?
A
receive the signals interpret them and send out instructions to the appropriate effector organs or glands to react and restore the normal state [cite: 7 8]
10
Q
What are the main organs and substances involved in homeostasis?
A
kidneys liver skin and hormones (substances secreted by endocrine glands)
11
Q
What has overall control over the homeostatic processes in the body?
A
the brain [cite: 9 10]
12
Q
What are the functions of the kidneys?
A
remove nitrogenous wastes and control the amounts of water salts and acids ie the excretory and osmoregulatory functions
13
Q
Where do the regulatory mechanisms which maintain the water salt and pH balance of the blood occur?
A
at the distal tubules and collecting ducts
14
Q
When is a large amount of dilute urine excreted?
A
When we drink a lot of water or on cold days when we sweat less [cite: 14 15]
15
Q
When is a small amount of concentrated urine excreted?
A
On hot days when we lose water from the body through sweating [cite: 15 16]
16
Q
Why do the kidneys regulate the amount of water excreted in urine?
A
to keep the osmotic pressure of blood constant [cite: 16 17]
17
Q
When does the solute concentration of blood rise?
A
when we eat too much salt drink very little water or sweat profusely
18
Q
What detects the increased solute concentration of blood?
A
osmoreceptors in the hypothalamus in the brain
19
Q
What do osmoreceptors do in response to increased solute concentration?
A
send nerve impulses to stimulate the release of anti-diuretic hormone (ADH) from the posterior pituitary gland
20
Q
Where is ADH carried by the blood?
A
to the kidneys [cite: 20 21]
21
Q
What does ADH cause?
A
an increased reabsorption of water by the tubules into the bloodstream by increasing the permeability of the distal tubules and the collecting ducts to water [cite: 20 21]
22
Q
What happens to the urine as water is reabsorbed?
A
it becomes concentrated and its volume decreases
23
Q
What happens to the blood as water is reabsorbed?
A
it becomes diluted and its osmotic pressure decreases
24
Q
How long does the process of water reabsorption continue?
A
until the osmotic pressure of blood reaches its normal level [cite: 23 24]
25
What happens when the osmoreceptors detect a normal osmotic pressure?
they stop stimulating the pituitary gland and the secretion of ADH decreases or ceases [cite: 24 25]
26
What happens to water reabsorption and urine production when ADH secretion decreases or ceases?
Less water is reabsorbed by the kidneys and the urine produced is dilute [cite: 25 26]
27
What else is kept constant by the regulation of water excretion?
the blood volume [cite: 26 27]
28
What sensation indicates the need for water intake to regulate blood osmotic pressure?
Thirst
29
What kind of mechanism is keeping the osmotic pressure constant?
a homeostatic process known as a negative feedback mechanism [cite: 27 28]
30
Define feedback mechanism
the regulation of a process by the results or products of the process [cite: 28 29]
31
Describe how negative feedback works in the regulation of blood osmotic pressure
A rise in blood osmotic pressure causes the operating homeostatic process to increase the concentration of ADH in blood This increased level of ADH would lower the osmotic pressure and thus inhibit the release of ADH from the pituitary gland ie the result of the operating homeostatic process has a negative (or opposite) effect on itself [cite: 29 30 31 32]
32
What happens to sodium ions in the blood when their concentration is higher than normal or lower than normal?
The excess is excreted or more sodium ions are reabsorbed [cite: 33 34]
33
What regulates the reabsorption or excretion of sodium ions?
aldosterone a hormone from the adrenal cortex [cite: 34 35]
34
What does aldosterone do?
stimulates the active uptake of sodium ions from the filtrate into the blood at the distal tubules and collecting ducts [cite: 35 36]
35
What happens to the distal tubules and collecting ducts in the absence of aldosterone?
they are impermeable to ions [cite: 36 37]
36
What accompanies the active uptake of sodium ions?
an equivalent reabsorption of water via osmosis [cite: 37 38]
37
What is the normal pH of blood?
7.4
38
How is the pH of blood adjusted when it is slightly alkaline?
by excreting its hydrogencarbonate ions and retaining its hydrogen ions ie the tubular secretion of hydrogencarbonate ions into the tubules [cite: 38 39]
39
What is the result of excreting hydrogencarbonate ions and retaining hydrogen ions?
the production of an alkaline urine [cite: 39 40]
40
What happens to the pH of blood if it is slightly acidic?
The reverse situation occurs [cite: 39 40]
41
What is the pH range of urine?
4.5 to 8.5 depending on the amount of hydrogen ions excreted [cite: 40 41]
42
How many urinary tubules are in each adult human kidney?
more than a million [cite: 41 42]
43
How often do the kidneys filter the body's blood completely?
every 45 minutes [cite: 42 43]
44
What do the kidneys excrete and regulate?
urea water salt and acid content [cite: 42 43]
45
How many kidneys can cope amply with these functions in a healthy adult?
one [cite: 43 44]
46
What can damage the kidneys?
diseases poisons and physical injury [cite: 44 45]
47
What is glomerular nephritis?
a kidney condition that occurs commonly in children and adolescents usually after a bacterial (streptococcal) infection like sore throat [cite: 46 47]
48
What happens to the glomeruli in glomerular nephritis?
they become inflamed increasing the porosity of the membranes [cite: 47 48]
49
What leaks into the glomerular filtrate as a result of the inflamed glomeruli?
proteins and red blood cells [cite: 48 49]
50
What collects in the inflamed glomeruli?
Large numbers of white blood cells and dead tissue cells sometimes totally blocking the blood flow and even filling the Bowmans capsules [cite: 49 50]
51
What happens to tubular function in glomerular nephritis?
it becomes impaired as the tubules do not receive sufficient nourishment from the reduced blood supply [cite: 50 51]
52
What is the usual outcome of glomerular nephritis?
the inflammation subsides and the kidneys become healthy again and function normally [cite: 51 52]
53
What is the outcome in a few cases of glomerular nephritis?
many of the glomeruli become permanently blocked the associated tubules degenerate and the kidneys may become completely damaged resulting in kidney failure [cite: 52 54]
54
What are kidney stones?
stony masses of minerals and organic matter that form in kidneys [cite: 55 56]
55
How are kidney stones produced?
when mineral salts in urine come out of solution as solid crystals [cite: 56 57]
56
When does this crystallization of mineral salts in urine occur?
when the intake of water is low the salt intake is high or the urine is abnormally acidic or alkaline [cite: 57 58]
57
What is the size range of kidney stones?
from tiny sand-like grains to large masses which can completely fill the renal pelvis [cite: 58 59]
58
What problems do large kidney stones cause?
They may block the flow of urine cause infections and the pressure build-up causes severe pain and damages the kidney tubules [cite: 59 60]
59
How can kidney stones be treated?
They may be dissolved by medicine or removed surgically if large [cite: 60 61]
60
What is diuresis?
a condition in which large quantities of dilute urine are produced [cite: 61 62]
61
When does diuresis happen?
if a person drinks a large quantity of water [cite: 62 63]
62
How long does water diuresis last?
two to three hours [cite: 63 64]
63
What happens in diabetes insipidus?
the production of ADH stops or is greatly reduced [cite: 64 65]
64
What is the result of diabetes insipidus?
diuresis causing a daily urine production of 5 to 20 liters [cite: 65 66]
65
How is the water loss in diabetes insipidus counteracted?
by drinking plenty of water [cite: 66 67]
66
When else does diuresis occur?
in diabetes mellitus where the excretion of glucose in urine is accompanied by excretion of water (due to osmosis) [cite: 67 68]
67
What are diuretics?
drugs that increase urine output either by increasing glomerular filtration or by decreasing tubular reabsorption of water [cite: 68 69]
68
Give examples of diuretics
caffeine theobromine urea and various salts [cite: 69 70]
69
What is another name for oedema?
dropsy [cite: 69 70]
70
What is oedema?
the accumulation of large amounts of intercellular fluid in tissues causing the affected parts to increase in volume [cite: 70 71]
71
What are well-marked outward signs of oedema?
a puffy face and swollen ankles [cite: 71 72]
72
When does kidney failure occur?
at the advanced stages of certain kidney diseases like chronic nephritis [cite: 72 73]
73
How can a patient with kidney failure be kept alive?
by a kidney transplant or using a dialysis machine (artificial kidney) [cite: 72 73]
74
Describe a dialysis machine
It consists of a long coiled cellophane tube immersed in a water bath The water in the bath contains all the useful ions and small molecules like glucose in the same concentration as in normal plasma and is maintained at body temperature [cite: 73 74]
75
How does a dialysis machine work?
The blood from an artery in the arm is allowed to flow through the tube The cellophane is semi-permeable and allows body wastes to diffuse out and excess amounts of ions and glucose to diffuse into the bath from the blood The cleansed blood is returned to the body via a vein in the arm This procedure takes about six hours [cite: 73 74]
76
How often does a person with complete kidney failure need dialysis?
twice a week [cite: 74 75]
77
Where is dialysis usually done?
in a hospital but it is possible to have a small dialysis machine at home [cite: 74 75]
78
How does the quality of life of a person with kidney failure compare with dialysis and a controlled diet?
They can live a fairly normal life [cite: 74 75]
79
What are the limitations of dialysis?
facilities are limited and expensive in many countries [cite: 75 76]
80
What is another treatment option for kidney failure?
a kidney transplant [cite: 76 77]
81
When are kidney transplants most likely to be successful?
if the patient (recipient) and kidney donor are closely related because a patients body tends to reject any tissues which are not its own [cite: 77 78]
82
When is the tendency for rejection less severe?
if the donor are twins Drugs are also used to suppress the bodys rejection reactions [cite: 78 79]
83
How does a kidney transplant compare to dialysis?
it is a better remedy [cite: 79 80]
84
What are the limitations of kidney transplants?
the procedure is extremely expensive and a suitable donor whose tissues are similar to the patients has to be found [cite: 79 80]
85
Where do transplant kidneys come from?
Many people donate their kidneys and other organs for transplant purposes These organs are removed from the bodies as soon as potential donors die and transplanted into the bodies of the recipients A healthy living person too can donate a kidney without adverse effects [cite: 81 83]
86
What can cause oedema?
reduced plasma osmotic pressure as in certain kidney diseases and other disease conditions [cite: 85 86]
87
What are the effects of kidney diseases?
impaired kidney function [cite: 86 87]
88
List the signs and symptoms of kidney diseases
High blood urea level presence of proteins and blood cells in urine impaired ability to produce sufficient urine diuresis oedema acidosis and high blood pressure [cite: 87 97]
89
When does high blood urea level occur?
when kidney function is reduced by at least 50 per cent [cite: 87 88]
90
What causes the presence of proteins and blood cells in urine?
increased porosity of membranes in the glomeruli and Bowmans capsule [cite: 88 89]
91
When does impaired ability to produce sufficient urine occur?
when the glomerular filtration rate is reduced and when the tubules are blocked or damaged [cite: 89 90]
92
What causes diuresis in kidney disease?
a high blood urea level since urea acts as a diuretic and in some kidney disorders the collecting ducts show a reduced response to the action of ACTH (adrenocorticotropic hormone) [cite: 90 92]
93
What causes oedema in kidney disease?
When proteins are excreted in urine their level in the blood drops causing the plasma osmotic pressure to fall Water then moves out into the intercellular spaces [cite: 92 94]
94
What causes acidosis in kidney disease?
a decreased ability by the tubules to secrete hydrogen ions causing the pH of blood to drop (become acidic) [cite: 94 95]
95
What causes high blood pressure in kidney disease?
Damaged or blocked glomeruli reduce blood flow through the kidneys stimulating them to produce renin an enzyme that causes the activation and release of angiotensin a hormone that constricts the arterioles in the whole body [cite: 95 97]
96
Are kidney diseases and disorders dangerous?
Yes potentially [cite: 98 99]
97
What are the three basic remedy procedures for most kidney diseases?
rest and warmth dietary control and removal of any chronic source of infection [cite: 99 100]
98
Describe the rest and warmth remedy procedure
The patient should be kept in bed and protected from cold draughts to allow the body to recover rapidly until the effects of the kidney disease disappear [cite: 100 102]
99
Describe the dietary control remedy procedure
Since the kidneys and liver break down excess amino acids to urea the protein content of the diet should be minimal (just sufficient for the bodys needs) The carbohydrate and fat content should be enough to supply energy without causing a breakdown of the bodys proteins and it is important to maintain a normal plasma water content and salt levels If oedema is present fluid intake should be restricted and salt should not be added to the food [cite: 102 107]
100
Describe the removal of sources of infection remedy procedure
Bacterial (streptococcal) infection should be treated with appropriate antibiotics and any chronic source of infection such as infected tonsils should be removed as soon as the effects of the kidney disease improve [cite: 107 109]
101
Describe the liver
a large reddish-brown organ with two lobes lying just below the diaphragm to the right side partly overlapping the stomach The bile duct leading from the liver to the small intestine has the gall bladder attached to it The liver is a soft organ with a rich and extensive blood supply [cite: 109 113]
102
Is the liver metabolically complex?
Yes with many functions including homeostasis [cite: 113 114]
103
What does the liver do with blood from the small intestine?
It screens the food-laden blood and adjusts its composition to suit the bodys immediate needs before releasing it into the circulatory system [cite: 114 115]
104
What is the normal blood glucose level?
90 mg/100 cm^3 blood [cite: 115 116]
105
What happens if the blood glucose level falls below 40 mg/100 cm^3 blood?
brain cells become affected leading to coma [cite: 117 118]
106
What happens if the blood glucose level rises above 160 mg/100 cm^3 blood?
the kidneys excrete the excess glucose [cite: 117 118]
107
How does the liver control blood glucose level?
The liver converts any excess glucose in the blood that reaches it after a meal to glycogen (stimulated by insulin from the pancreas) which is stored in the liver When blood glucose level falls below normal the liver converts glycogen into glucose and releases the required amount of glucose into the blood (stimulated by glucagon from the pancreas) If the glycogen level in the liver is depleted the hypothalamus stimulates the production of various hormones that cause the liver to convert amino acids and glycerol into glucose [cite: 118 123]
108
What does the liver do with amino acids?
It releases the required amount into the general circulation and breaks down excess amino acids into nitrogen-containing amino parts (converted to urea for excretion by the kidneys) and carbon compounds (keto acids) which it converts into glucose glycogen or fats (deamination) [cite: 123 126]
109
What does the liver convert one non-essential amino acid into?
another according to the bodys needs [cite: 127 128]
110
What can the liver not synthesize?
essential amino acids so they must be present in the diet [cite: 127 128]
111
What does the liver manufacture from dietary amino acids?
plasma proteins including albumins globulins and those essential for clotting like fibrinogen [cite: 129 130]
112
What does the liver do with lipids?
It breaks them down to produce glucose and other substances if needed and modifies what remains for transport to fat storage areas It also converts excess glucose (after its glycogen-storing capacity is exceeded) to fats for storage [cite: 130 133]
113
What does the liver produce
store
114
What does bile contain?
bile salts (for fat digestion) bilirubin (a yellowish pigment excretory product from haemoglobin breakdown) inorganic salts and cholesterol [cite: 134 136]
115
What does the liver store?
fat-soluble vitamins (A D E and K) water-soluble vitamins (B and C) iron and other minerals (zinc copper and potassium) [cite: 136 137]
116
How much blood can the liver store?
up to 1500 cm^3 [cite: 137 138]
117
How does the liver regulate blood volume and pressure?
By constricting its blood vessels to release more blood into general circulation or dilating its vessels to store more blood [cite: 138 140]
118
What does the liver do in the foetus and in adults?
Produces red blood cells in the foetus and breaks down worn out red blood cells in adults (with the spleen) [cite: 140 141]
119
What does the liver do to hormones?
inactivates them thus ending their period of activity [cite: 141 144]
120
Give examples of hormones inactivated by the liver
testosterone (rapidly destroyed) and insulin (more slowly destroyed) [cite: 141 144]
121
How does the liver exert a homeostatic effect on hormones?
by inactivating them [cite: 141 144]
122
What does the liver do to toxic substances?
converts them into harmless or inactive forms (detoxication) [cite: 144 147]
123
Give examples of substances detoxified by the liver
poisonous substances from the large intestine drugs and medicines food preservatives and additives and pollutants in air and water [cite: 144 147]
124
What by-product does the liver produce and what does it do?
heat which is distributed by the blood circulation to keep the body warm [cite: 147 149]
125
What are some important diseases of the liver and bile ducts?
gall stones viral hepatitis cirrhosis and amoebic liver abscess [cite: 149 150]
126
What is jaundice?
a condition caused by an increase in the blood bilirubin level giving a yellow coloration to the skin and whites of the eyes [cite: 150 152]
127
What are the three main causes of jaundice?
excessive breakdown of red blood cells obstruction of the bile duct and diseases of the liver [cite: 152 160]
128
Describe jaundice due to excessive breakdown of red blood cells
Large amounts of bilirubin are formed due to conditions like malaria in newborn babies inherited defects of red blood cells (e.g. sickle-cell anaemia) and certain poisons The stools are dark due to the excretion of large amounts of bilirubin via the bile and the urine contains a large amount of urobilinogen (a reduced product of bilirubin) [cite: 153 156]
129
Describe jaundice due to obstruction of the bile duct
Blocking of bile ducts usually by gall stones prevents bile from emptying into the intestines As a result the blood level of bilirubin becomes raised The stools are pale and contain undigested fats and the urine is dark yellow or brown [cite: 156 159]
130
Describe jaundice due to diseases of the liver
Damage to liver cells reduces their ability to extract bilirubin from the blood to form bile raising the blood bilirubin level Inadequate bile production results in pale stools containing undigested fatty substances [cite: 159 162]
131
What are gall stones?
stony masses that form in the gall bladder or bile ducts mostly composed of cholesterol [cite: 162 164]
132
What causes gall stones?
chemical changes in the composition of bile that leads to precipitation and stone formation ie abnormal bile production by the liver [cite: 162 164]
133
What problems do gall stones cause?
They obstruct the flow of bile increase infections of the gall bladder bile ducts and liver and are often accompanied by inflammation of the gall bladder [cite: 164 167]
134
How can gall stones be treated?
They may be dissolved by oral feeding of a bile acid or removed surgically if they cannot be dissolved [cite: 167 169]
135
What are the two types of viral hepatitis?
infective hepatitis (virus type A) and serum hepatitis (virus type B) [cite: 169 170]
136
What do both types of viral hepatitis cause?
inflammation and destruction of the liver cells but the liver usually recovers and functions normally when the infection subsides [cite: 170 172]
137
What is cirrhosis?
a serious liver disease in which the damaged liver cells become replaced by useless fibrous tissue making the liver feel very firm and irregular [cite: 172 173]
138
What are the causes of cirrhosis?
excessive drinking of alcohol over a prolonged period and hepatitis but in most instances the cause is not known [cite: 173 174]
139
What is amoebic liver abscess?
an infection caused by the parasitic amoeba Entamoeba histolytica which causes amoebic dysentery [cite: 174 175]
140
How does the parasite get into the liver and what does it do?
It gets into the liver from the large intestine via the hepatic-portal vein and produces an enzyme that destroys liver tissues and causes an abscess to form [cite: 175 177]
141
What are the effects of liver diseases?
They are due to the failure of liver cells to function properly [cite: 177 178]
142
List the common symptoms and signs of liver diseases
weakness and tiredness jaundice slight fever tendency to bleed and bruise easily oedema (especially accumulation of fluid in the abdomen) enlarged and tender liver (hepatitis and amoebic liver abscess) biliary colic (gall stones) high blood pressure in the hepatic-portal vein (cirrhosis leading to intestinal bleeding and death) and mental changes such as apathy [cite: 178 180]
143
What happens to blood enzyme levels in liver diseases?
They are high because these enzymes leak out of the damaged liver cells and get into the bloodstream [cite: 178 180]
144
How is liver function assessed?
by estimating the blood levels of liver enzymes bilirubin and cholesterol [cite: 180 181]
145
What is the livers capacity for repair?
It has a high capacity to divide and produce new cells ie to regenerate [cite: 181 182]
146
What is the aim of treatment for most liver diseases?
to give the liver a rest and allow it to heal itself [cite: 182 184]
147
What do basic treatment procedures for liver diseases include?
rest (preferably in bed until jaundice subsides and a long convalescence period) a nutritious but controlled low fat diet no taking of alcoholic drinks (for life in cirrhosis) and removing the cause of the liver disorder [cite: 184 186]
148
Give examples of removing the cause of a liver disorder
draining pus and giving anti-amoebic drugs for amoebic liver abscess and removing the obstruction in bile duct obstruction [cite: 186 187]
149
What treatment offers hope for patients with progressive liver cirrhosis and liver cancer?
Liver transplant [cite: 187 188]
150
What are the problems encountered in liver transplants?
the same as in kidney transplants [cite: 187 188]
151
Where do livers for transplant come from?
A living person can donate a lobe of his/her liver which can soon regenerate to its normal size [cite: 188 190]
152
What is the skin?
the outer covering of vertebrates forming a continuous layer over the entire body and the largest organ [cite: 190 191]
153
What does the skin usually bear in mammals?
a dense growth of hairs [cite: 191 192]
154
How is hair growth on human skin described?
sparse over most parts of their bodies [cite: 191 192]
155
What are the two main layers of mammalian skin?
the epidermis and the dermis [cite: 193 194]
156
How does the thickness of the epidermis vary?
it is thickest at the soles of the feet and palms of the hand [cite: 194 195]
157
How does the dermis compare in thickness to the epidermis?
it is much thicker [cite: 194 195]
158
What does Figure 19-6 show?
a generalized section of human skin showing all the structures that can be found in the skin [cite: 197 198]
159
Are all the structures shown in Figure 19-6 present in all regions of the skin?
No some are absent in certain regions eg hair is absent in the palms of the hand and soles of the feet [cite: 198 200]
160
What are the three layers of the epidermis?
the innermost Malpighian layer the middle granular layer and the outermost (surface) cornified layer [cite: 200 201]
161
Describe the Malpighian layer
It consists of actively dividing cuboidal cells containing melanin a pigment that gives the skin its color The Malpighian layer has many infoldings and some penetrate deep into the dermis to form hair follicles and sebaceous glands The cells of this layer get their nutrients and oxygen by diffusion from the blood in the capillaries found in the dermis [cite: 201 202]
162
Describe the granular layer
It consists of living cells constantly being pushed up from the Malpighian layer As they move up they become greatly flattened accumulate keratin (a fibrous protein) and eventually die [cite: 202 204]
163
Describe the cornified layer
It consists of scale-like dead cells impregnated with keratin The keratin makes this layer tough flexible and waterproof The cells in the cornified layer are constantly being rubbed off and replaced by cells from the layers below Thus the air around us is full of dead cells from this layer [cite: 204 207]
164
What does the dermis contain?
connective tissues blood capillaries hair follicles sweat glands sebaceous glands sensory nerve endings and fat cells [cite: 208 209]
165
What do blood capillaries do in the skin?
bring food and oxygen to the dermal and epidermal cells remove wastes and supply hair follicles and sweat glands Capillary loops close to the body surface help to regulate body temperature [cite: 208 209]
166
What is a hair follicle?
a deep pit formed by the infolding of the Malpighian layer [cite: 209 210]
167
What happens at the base of each hair follicle?
Malpighian cells keep dividing to produce a long cylindrical hair whose cells become impregnated with keratin and die [cite: 210 211]
168
What do nerve endings in the hair follicle respond to?
touch [cite: 211 212]
169
What is attached to each hair follicle?
a hair erector muscle [cite: 211 212]
170
What does contraction of the hair erector muscle do?
pulls the hair to a more upright position ie makes the hair stand up [cite: 212 213]
171
What does contraction of the hair erector muscles cause in furry mammals?
the fur to stand up and trap more air within it [cite: 213 214]
172
What causes goose pimples in humans?
contraction of the hair erector muscles when we feel cold [cite: 213 214]
173
What do sebaceous glands secrete?
sebum an oily substance [cite: 214 215]
174
What is the function of sebum?
to keep the hair and epidermis waterproof and supple and to keep out dust and micro-organisms [cite: 215 216]
175
Describe sweat glands
coiled tubes deep in the dermis that continue as sweat ducts opening at the surface of the skin as sweat pores [cite: 216 217]
176
What do the cells of the coiled tubes of sweat glands do?
absorb water from the capillaries surrounding them and secrete it into the tubes [cite: 217 218]
177
What does sweat contain?
small quantities of wastes such as mineral salts and urea [cite: 218 219]
178
What happens when sweat evaporates?
it cools the body [cite: 219 220]
179
Is the skin a sense organ?
Yes [cite: 220 221]
180
What does the skin contain?
sensory cells or receptors that can receive stimuli from the external surroundings and send them to the appropriate parts of the body [cite: 221 222]
181
What types of receptors are in the skin?
touch receptors (Meissners corpuscle) pressure receptors (Pacinian corpuscles) pain receptors (free nerve endings) and thermoreceptors (for detecting heat and cold) [cite: 222 223]
182
What is below the dermis?
a layer of connective tissue containing a variable number of fat cells [cite: 223 224]
183
What is the subcutaneous fatty tissue?
the layer of connective tissue below the dermis containing fat cells [cite: 223 224]
184
What are the functions of the subcutaneous fatty tissue?
a long term food store and an insulating layer that prevents heat loss [cite: 224 225]
185
What are the important functions of the skin?
protection sensitivity and temperature control [cite: 225 226]
186
What other functions does the skin perform?
excretes wastes and produces vitamin D when exposed to ultraviolet rays [cite: 226 227]
187
What are the protective functions of the skin?
The layer of dead epidermal cells forms a tough continuous barrier against micro-organisms The waterproof nature of the epidermis reduces water loss and prevents water from entering the body cells by osmosis Melanin in the Malpighian layer absorbs harmful ultraviolet rays [cite: 227 230]
188
What is the function of the skins sensitivity?
to make us aware of changes in our surroundings [cite: 231 233]
189
What does awareness of changes in our surroundings allow us to do?
take the necessary actions for our well-being and survival [cite: 231 233]
190
Do warm-blooded animals like humans have to maintain a constant body temperature?
Yes [cite: 233 234]
191
What temperature does body temperature refer to?
the temperature deep inside our body not the skin temperature [cite: 234 235]
192
How is body temperature usually measured?
by placing a thermometer in the mouth under the tongue for two minutes [cite: 235 236]
