Homeostasis Flashcards
(154 cards)
1
Q
What is the immediate environment of a cell?
A
The tissue fluid that surrounds it
2
Q
Name one feature of tissue fluid that influences cell activities.
A
Temperature
3
Q
What effect does low temperature have on metabolic reactions?
A
Slows down metabolic reactions
4
Q
What happens to proteins at high temperatures?
A
They are denatured and cannot function
5
Q
How does decreased water potential affect cells?
A
Water may move out of cells by osmosis, slowing or stopping metabolic reactions
6
Q
What occurs if the water potential increases?
A
Water may enter the cell, causing it to swell and maybe burst
7
Q
What is the role of glucose in the blood concerning respiration?
A
It is the fuel for respiration
8
Q
What happens if there is a lack of glucose in the blood?
A
Respiration slows or stops, depriving the cell of an energy source
9
Q
What can happen if there is too much glucose in the blood?
A
Water may move out of the cell by osmosis, disturbing metabolism
10
Q
What is the pH range of cytoplasm?
A
The pH of cytoplasm is between 6.5 and 7.0.
11
Q
How does pH affect enzyme activity?
A
Enzyme activity is influenced by pH; if it fluctuates outside the range of 6.5 to 7.0, enzymes will function less efficiently and may be denatured at extreme pH values.
12
Q
What do homeostatic mechanisms control?
A
Homeostatic mechanisms work by controlling the composition of blood, which in turn controls the composition of tissue fluid.
13
Q
What physiological factors are involved in homeostatic control?
A
There are control mechanisms for different aspects of blood and tissue fluid, including water potential and blood glucose concentration.
14
Q
What is the focus of this chapter regarding homeostasis?
A
This chapter focuses on two aspects of homeostatic control: water potential (Section 14.2) and blood glucose concentration (Section 14.4).
15
Q
What type of feedback control loop do most control mechanisms use?
A
Most control mechanisms in living organisms use a negative feedback control loop.
16
Q
What is homeostasis?
A
The maintenance of a relatively constant internal environment for the cells within the body.
17
Q
What is a negative feedback control loop?
A
A process in which a factor rises above or falls below a set point, and effectors act to restore balance.
18
Q
What role do receptors play in homeostatic control?
A
Receptors sense change in a factor.
19
Q
What happens when a factor rises above the set point?
A
Effectors act to decrease the factor.
20
Q
What happens when a factor falls below the set point?
A
Effectors act to increase the factor.
21
Q
How do effectors receive information in a negative feedback loop?
A
Effectors receive information from receptors.
22
Q
What are the components involved in homeostasis?
A
The components involved in homeostasis are a receptor (or sensor), a central control, and an effector.
23
Q
What is a stimulus?
A
A stimulus is any change in a physiological factor, such as a change in blood temperature or the water content of the blood.
24
Q
What types of stimuli do receptors detect?
A
Receptors detect external stimuli and internal stimuli.
25
What is the role of the central control in homeostasis?
The central control receives sensory information and instructs an effector to carry out an action, known as the output.
26
What is negative feedback?
Negative feedback is the mechanism that keeps changes in a physiological factor at or near a set point.
27
How does negative feedback respond to changes in a factor?
An increase in the factor results in actions that decrease it, while a decrease in the factor results in actions that increase it.
28
What is the purpose of homeostatic mechanisms?
Homeostatic mechanisms minimize the difference between the actual value of a factor and the ideal value or set point.
29
How does human body temperature fluctuate?
Human body temperature often fluctuates between 36.4 °C and 37.6 °C, depending on factors such as age, sex, and time of day.
30
What are the two coordination systems in mammals?
The two coordination systems in mammals are the nervous system and the endocrine system.
31
How does the nervous system transmit information?
The nervous system transmits information in the form of electrical impulses along neurones.
32
What is the role of hormones in the endocrine system?
Hormones are chemical messengers that travel in the blood, facilitating long-distance cell signaling.
33
What happens when a person breathes air with high carbon dioxide content?
A high concentration of carbon dioxide in the blood results, which is sensed by carbon dioxide receptors.
34
What do carbon dioxide receptors cause in response to high carbon dioxide levels?
They cause the breathing rate to increase.
35
What is the effect of increased breathing rate on carbon dioxide levels?
The person breathes faster, taking in even more carbon dioxide.
36
What type of feedback is illustrated by the increasing breathing rate due to high carbon dioxide levels?
This is an example of positive feedback.
37
What role does positive feedback play in maintaining body conditions?
Positive feedback cannot play any role in keeping conditions in the body constant.
38
What is the process of removing unwanted metabolic products called?
The removal of unwanted products of metabolism is known as excretion.
39
What are the two primary excretory products in humans?
The two primary excretory products are carbon dioxide and urea.
40
How is carbon dioxide produced in the body?
Carbon dioxide is produced continuously by cells that are respiring aerobically.
41
How is carbon dioxide transported from the cells to the lungs?
The waste carbon dioxide is transported from the respiring cells to the lungs in the bloodstream.
42
What happens to carbon dioxide in the lungs?
Gas exchange occurs within the lungs, and carbon dioxide diffuses from the blood into the alveoli.
43
How is carbon dioxide excreted from the body?
Carbon dioxide is excreted in the air we breathe out.
44
Where is urea produced in the body?
Urea is produced in the liver.
45
What is urea produced from?
Urea is produced from excess amino acids.
46
How is urea transported to the kidneys?
Urea is transported from the liver to the kidneys in solution in blood plasma.
47
How do the kidneys handle urea?
The kidneys remove urea from the blood and excrete it dissolved in water.
48
What is the solution called that contains excreted urea?
The solution is called urine.
49
What happens to excess protein in the body?
Excess protein cannot be stored in the body and would be wasteful to eliminate completely.
50
What process does the liver use to utilize excess amino acids?
The liver removes the amine groups in a process known as deamination.
51
What is produced when the amine group is removed from an amino acid?
The removal of the amine group (-NH2) and an extra hydrogen atom produces ammonia (NH3).
52
What can the remaining keto acid do after deamination?
The remaining keto acid may enter the Krebs cycle, be respired, or be converted to glucose, glycogen, or fat for storage.
53
What is ammonia?
Ammonia is a very soluble and highly toxic compound.
54
How does ammonia affect aquatic animals?
In many aquatic animals, ammonia diffuses from the blood and dissolves in the water around the animal.
55
How does ammonia affect terrestrial animals?
In terrestrial animals such as humans, ammonia increases the pH in cytoplasm and interferes with metabolic processes such as respiration and cell signalling in the brain.
56
How is damage from ammonia prevented in humans?
Damage is prevented by immediately converting ammonia to urea, which is less soluble and less toxic.
57
What is the urea cycle?
The urea cycle involves several reactions that combine ammonia and carbon dioxide to form urea.
58
How much urea does an adult human produce per day?
An adult human produces around 25-30 g of urea per day.
59
What is the main nitrogenous excretory product of humans?
Urea is the main nitrogenous excretory product of humans.
60
What other nitrogenous excretory products do humans produce?
Humans also produce small quantities of creatinine and uric acid.
61
How is creatine produced and used in the body?
Creatine is made in the liver from certain amino acids and is used in the muscles as creatine phosphate, acting as an energy store.
62
What happens to some of the creatine in the body?
Some creatine is converted to creatinine and excreted.
63
How is uric acid produced?
Uric acid is made from the breakdown of purines from nucleotides, not from amino acids.
64
Where does urea diffuse from?
Urea diffuses from liver cells into the blood plasma.
65
What happens if urea concentration in the blood builds up?
All of the urea made each day must be excreted, or its concentration in the blood would build up and become dangerous.
66
How is urea filtered out of the blood?
As the blood passes through the kidneys, the urea is filtered out and excreted.
67
What carries blood to each kidney?
Each kidney receives blood from a renal artery.
68
How does blood return from the kidney?
Blood returns via a renal vein.
69
What tube carries urine from the kidney to the bladder?
A narrow tube, called the ureter, carries urine from the kidney to the bladder.
70
What carries urine from the bladder to the outside of the body?
A single tube, called the urethra, carries urine to the outside of the body.
71
What are the three main areas of the kidney?
The three main areas of the kidney are the cortex, medulla, and renal pelvis.
72
What covers the whole kidney?
The whole kidney is covered by a fairly tough fibrous capsule.
73
What is the structure that surrounds a network of capillaries in a nephron?
Bowman's capsule surrounds a network of capillaries called a glomerulus.
74
Where are the glomeruli and capsules of all the nephrons located?
The glomeruli and capsules of all the nephrons are located in the cortex of the kidney.
75
What is the first part of the nephron tubule called?
The first part of the nephron tubule is called the proximal convoluted tubule.
76
What is the U-shaped tubule in the medulla called?
The U-shaped tubule in the medulla is called the loop of Henle.
77
What are the two limbs of the loop of Henle?
The two limbs of the loop of Henle are the descending limb and the ascending limb.
78
What does the ascending limb of the loop of Henle lead to?
The ascending limb leads back into the cortex, forming the distal convoluted tubule.
79
What does the distal convoluted tubule join?
The distal convoluted tubule joins a collecting duct that leads down through the medulla and into the renal pelvis.
80
What is closely associated with the nephrons?
Blood vessels are closely associated with the nephrons.
81
How is each glomerulus supplied with blood?
Each glomerulus is supplied with blood from a branch of the renal artery through an afferent arteriole.
82
What do the capillaries of the glomerulus rejoin to form?
The capillaries of the glomerulus rejoin to form an efferent arteriole.
83
Where does blood flow after the efferent arteriole?
Blood flows through the efferent arteriole into a network of capillaries running closely alongside the rest of the nephron and the collecting duct.
84
What happens to blood from the capillaries running alongside the nephron?
Blood from these capillaries flows into venules that empty into a branch of the renal vein.
85
What is the first stage of urine production in the kidney?
The first stage is ultrafiltration, which involves filtering small molecules out of the blood and into the Bowman's capsule to form filtrate.
86
What happens to the filtrate after it leaves Bowman's capsule?
The filtrate flows along the nephron towards the collecting duct.
87
What is the second stage of urine production in the kidney?
The second stage is selective reabsorption, which involves taking back any useful molecules from the filtrate as it flows along the nephron.
88
What separates the blood in the glomerular capillaries from the lumen of Bowman's capsule?
The blood is separated by two cell layers and a basement membrane.
89
What is the first cell layer in the glomerular filtration barrier?
The first cell layer is the endothelium of the capillary.
90
What features do endothelial cells in the glomerular capillaries have?
Each endothelial cell is perforated by many thousands of tiny membrane-lined circular holes, about 60-80mm in diameter.
91
What constitutes the basement membrane in the glomerular filtration barrier?
The basement membrane is made up of a network of collagen and glycoproteins.
92
What is the second cell layer in the glomerular filtration barrier?
The second cell layer is formed from epithelial cells that make up the inner lining of Bowman's capsule.
93
What are podocytes?
Podocytes are epithelial cells with many tiny finger-like projections and gaps in between them.
94
What do the holes in the capillary endothelium and gaps between podocytes allow?
They allow substances dissolved in blood plasma to pass from the blood into the capsule.
95
What prevents large protein molecules from passing through into the capsule?
The basement membrane acts as a filter, stopping large protein molecules from getting through.
96
What is the approximate relative molecular mass limit for protein molecules to pass through the basement membrane?
Protein molecules with a relative molecular mass over about 69,000 cannot pass through.
97
Which blood components are too large to pass through the perforations in the endothelium?
Red blood cells, white blood cells, and platelets are too large to pass through and remain in the blood.
98
How is glomerular filtrate similar to blood plasma?
Glomerular filtrate is almost identical to blood plasma, except that it contains almost no plasma proteins.
99
What role does the basement membrane play in the glomerular capillaries?
The basement membrane acts as a filter, allowing smaller substances to pass but blocking large proteins.
100
Why can’t red and white blood cells, and platelets pass into the glomerular filtrate?
They are too large to pass through the perforations in the endothelium, so they stay in the blood.
101
What is the glomerular filtration rate?
It is the rate at which fluid filters from the blood in the glomerular capillaries into the Bowman’s capsule, typically around 125 cm³ per minute in humans.
102
What determines the speed at which fluid filters into the Bowman’s capsule?
It is determined by the differences in water potential between the plasma in the glomerular capillaries and the filtrate in the Bowman’s capsule.
103
What factors affect water potential?
Water potential is lowered by the presence of solutes and raised by high pressures.
104
Why is blood pressure relatively high in the capillaries of the glomerulus?
Because the afferent arteriole (entering the glomerulus) is wider than the efferent arteriole (leaving the glomerulus), causing a build-up of pressure in the glomerulus.
105
How does blood pressure in the glomerulus affect water potential?
The high blood pressure tends to raise the water potential of the blood plasma above that of the contents of the Bowman’s capsule.
106
Why is the concentration of solutes higher in the blood plasma of glomerular capillaries than in the filtrate in the Bowman’s capsule?
Plasma protein molecules are too large to pass through the basement membrane, so they remain in the blood, increasing the solute concentration.
107
What overall effect causes water to move from the blood to the capsule in the glomerulus?
The effect of pressure differences outweighs the solute concentration differences, resulting in a higher water potential in the glomerulus than in the filtrate, causing water to move into the capsule.
108
What happens to water movement as blood flows through the glomerulus?
Water continues to move down the water potential gradient from the blood into the capsule.
109
Which factor has a greater impact on water potential in the glomerulus: pressure or solute concentration?
Pressure differences have a greater effect, resulting in a higher water potential in the glomerulus than in the Bowman’s capsule.
110
What is osmoregulation?
Osmoregulation is the control of the water potential of body fluids, an essential part of homeostasis.
111
Which organs and glands are involved in osmoregulation?
The hypothalamus, posterior pituitary gland, and kidneys.
112
What cells monitor the water potential of the blood?
Osmoreceptors, which are specialized sensory neurons located in the hypothalamus.
113
What happens when osmoreceptors detect a decrease in blood water potential below the set point?
They send nerve impulses to the posterior pituitary gland, triggering the release of antidiuretic hormone (ADH).
114
What is ADH, and what is its structure?
ADH, or antidiuretic hormone, is a peptide hormone made of nine amino acids.
115
How does ADH reach the kidneys?
ADH enters the blood in capillaries and is carried throughout the body.
116
What is the primary effect of ADH?
ADH reduces water loss in urine by increasing water reabsorption in the kidneys.
117
Why is ADH named “antidiuretic” hormone?
Because it prevents the production of dilute urine by promoting water reabsorption.
118
What are the target cells for ADH?
The cells of the collecting duct in the kidneys are the target cells for ADH.
119
How does ADH affect the collecting duct cells?
ADH increases the permeability of the collecting duct cells to water by increasing the number of aquaporins in their luminal membranes.
120
What are aquaporins?
Aquaporins are water-permeable channels that allow water to move across cell membranes.
121
How does ADH stimulate the insertion of aquaporins into the cell membrane?
ADH binds to receptor proteins, which stimulates the production of cyclic AMP (cAMP), leading to a signaling cascade that causes aquaporin-containing vesicles to fuse with the luminal membrane.
122
What role does cyclic AMP (cAMP) play in ADH’s effect on the collecting duct?
cAMP acts as a second messenger that initiates a signaling cascade, resulting in the phosphorylation and activation of aquaporin molecules.
123
Why does water move out of the collecting duct cells into the surrounding tissue fluid?
Water moves out because the tissue fluid in the medulla has a very low water potential, while the fluid in the collecting duct has a high water potential, creating a gradient for water to follow.
124
What effect does ADH secretion have on urine concentration?
ADH causes water reabsorption, leading to a small volume of concentrated urine.
125
What happens to ADH secretion when blood water potential is high?
The osmoreceptors in the hypothalamus are no longer stimulated, and ADH secretion from the posterior pituitary gland stops.
126
What happens to aquaporins when ADH is no longer present?
Aquaporins are removed from the cell surface membrane of the collecting duct cells and moved back into the cytoplasm in vesicles.
127
How does urine change when there is no ADH present?
Without ADH, the collecting duct becomes impermeable to water, leading to the production of large volumes of dilute urine.
128
Why doesn’t the effect of ADH stop immediately when secretion stops?
ADH already present in the blood takes time to be broken down, with half-life around 15-20 minutes.
129
How quickly can aquaporins be removed from the cell membrane once ADH stops arriving?
It takes 10-15 minutes for aquaporins to be removed from the cell surface membrane once ADH stops arriving.
130
In what form is carbohydrate transported in the human bloodstream?
Carbohydrate is transported as glucose dissolved in the blood plasma.
131
What is the normal concentration range of glucose in the blood?
Between 80 mg and 120 mg per 100 cm³ of blood, or 4.4-6.7 mmol/dm³.
132
Why is it important to maintain a normal blood glucose concentration?
If glucose is too low, cells may not have enough for respiration, affecting normal activities. High glucose levels can also disrupt cellular behavior.
133
Why is blood glucose particularly important for brain cells?
Brain cells can only respire glucose, so they depend on a stable glucose supply to function properly.
134
Which organ is responsible for the homeostatic control of blood glucose concentration?
The pancreas, specifically the endocrine tissue within it.
135
What are the islets of Langerhans?
Groups of endocrine cells in the pancreas that control blood glucose levels.
136
What are the two types of cells found in the islets of Langerhans, and what do they secrete?
Alpha (α) cells, which secrete glucagon, and beta (β) cells, which secrete insulin.
137
What role do alpha and beta cells play in blood glucose regulation?
They act as receptors and the central control for blood glucose homeostasis.
138
What are the roles of the hormones glucagon and insulin?
Glucagon and insulin coordinate the actions of effectors to regulate blood glucose levels.
139
How do the alpha (α) and beta (β) cells in the pancreas respond to an increase in blood glucose concentration?
Alpha cells stop secreting glucagon, while beta cells start secreting insulin into the blood.
140
Why can’t insulin pass directly through cell membranes?
Insulin is a protein, which cannot cross cell surface membranes.
141
How does insulin affect target cells if it can’t enter them directly?
Insulin binds to specific receptors on the cell surface, triggering intracellular messengers to indirectly stimulate changes within the cell.
142
Which types of cells have insulin receptors?
Cells in the liver, muscle tissue, and adipose (fat storage) tissue.
143
What are two main effects of insulin on cells with insulin receptors?
Insulin increases the rate of glucose absorption by these cells and stimulates the conversion of glucose into glycogen.
144
What is the overall effect of insulin on blood glucose concentration?
Insulin decreases blood glucose concentration by promoting glucose absorption and utilization.
145
How does glucose enter cells?
Through facilitated diffusion via transporter proteins known as GLUT.
146
What type of GLUT protein is found in muscle cells?
GLUT4.
147
How does insulin affect GLUT4 proteins in muscle cells?
Insulin binding to muscle cell receptors causes vesicles with GLUT4 proteins to move to the cell surface membrane, allowing glucose entry into the cell.
148
Which GLUT proteins are found in brain and liver cells?
Brain cells have GLUT1 proteins, and liver cells have GLUT2 proteins.
149
Do GLUT1 and GLUT2 proteins respond to insulin in the same way as GLUT4?
No, GLUT1 and GLUT2 are always present in the cell surface membrane and are not influenced by insulin.
150
How does insulin help trap glucose inside cells?
Insulin activates glucokinase, which phosphorylates glucose, preventing it from leaving the cell.
151
What is glycogen, and why is it important?
Glycogen is a large, insoluble polysaccharide made of glucose units, serving as a short-term energy store in liver and muscle cells.
152
What is glycogenesis?
Glycogenesis is the process of adding glucose molecules to glycogen, which is stimulated by insulin.
153
Which enzymes does insulin activate for glycogenesis?
Insulin activates phosphofructokinase and glycogen synthase.
154
What happens to glycogen granules in liver and muscle cells when insulin is secreted?
The size of glycogen granules increases as more glucose is stored.
