Homeostasis Flashcards
(176 cards)
1
Q
What is homeostasis?
A
Homeostasis is the process of maintaining a constant internal environment. It ensures that conditions inside the body are kept within preset limits, despite fluctuations in the external environment.
2
Q
Why is homeostasis critically important for organisms?
A
Homeostasis is critically important for organisms as it ensures the maintenance of optimal conditions for enzyme action and cell function.
3
Q
How do sensory cells contribute to homeostasis?
A
Sensory cells can detect information about the conditions inside and outside the body. If conditions have changed, then the body can respond to keep conditions constant.
4
Q
What are four examples of physiological factors controlled by homeostasis in mammals?
A
Core body temperature, blood pH, concentration of glucose in the blood, and osmotic concentration of the blood.
5
Q
What is the significance of preset limits in homeostasis?
A
Homeostasis ensures that conditions inside the body are kept within preset limits, allowing for optimal functioning of the organism despite external environmental fluctuations.
6
Q
What type of feedback loop is primarily used in homeostatic control mechanisms, and why?
A
The majority of homeostatic control mechanisms in organisms use negative feedback loops because they work to return values to a set point by reversing the effects of any change within a system.
7
Q
How do negative feedback loops maintain homeostasis compared to positive feedback mechanisms?
A
Negative feedback loops are essential for maintaining conditions within set limits by counteracting changes, whereas positive feedback mechanisms amplify changes and do not maintain stability.
8
Q
What are the key components involved in negative feedback control loops?
A
Negative feedback control loops involve a receptor that detects changes in a physiological factor, a coordination system (such as the brain and nervous system) that transfers information, and an effector (muscles or glands) that brings about a response.
9
Q
What is the outcome of a negative feedback loop when there is an increase in a physiological factor?
A
If there is an increase in a physiological factor, the body responds to make the factor decrease, returning it to the set point.
10
Q
What happens in a negative feedback loop when there is a decrease in a physiological factor?
A
If there is a decrease in a physiological factor, the body responds to make the factor increase, restoring it to the set point.
11
Q
What is diabetes?
A
Diabetes is a condition in which the homeostatic control of blood glucose has failed or deteriorated. The insulin function of diabetic individuals is disrupted, allowing the glucose concentration in the blood to rise.
12
Q
What are the main symptoms of diabetes?
A
The main symptoms of diabetes include: excess glucose appearing in urine, increased urine production leading to thirst and dehydration, reduced cellular respiration resulting in fatigue, and potential organ damage if blood glucose levels become dangerously high after meals.
13
Q
What are the two main types of diabetes?
A
The two main types of diabetes are Type 1 diabetes and Type 2 diabetes.
14
Q
What characterizes Type 1 diabetes?
A
Type 1 diabetes is a condition where the pancreas fails to produce sufficient insulin to control blood glucose levels. It typically begins in childhood due to an autoimmune response that attacks the β cells of the islets of Langerhans in the pancreas, preventing insulin production.
15
Q
How is Type 1 diabetes typically treated?
A
Type 1 diabetes is normally treated with regular blood tests, insulin injections, and a modified diet that may involve a reduction in carbohydrate intake.
16
Q
What characterizes Type 2 diabetes?
A
Type 2 diabetes is more common than Type 1 and usually develops in older adults. In Type 2 diabetes, the pancreas still produces insulin, but the cell membrane receptors to which insulin binds have reduced in number or no longer respond, leading to insulin resistance.
17
Q
What is insulin resistance?
A
Insulin resistance is the inability of cells to respond to insulin, which occurs in Type 2 diabetes. The pancreas attempts to compensate by secreting more insulin, but eventually, insulin production can no longer compensate for the reduced cellular response.
18
Q
How is Type 2 diabetes managed?
A
Type 2 diabetes is managed through medication to lower blood glucose and a low carbohydrate diet.
19
Q
What effect does rapidly digested food have on blood sugar?
A
Any food that is rapidly digested into sugar will cause a sudden, dangerous spike in blood sugar.
20
Q
How does exercise affect blood glucose levels?
A
An exercise regime lowers blood glucose.
21
Q
What is a major risk factor for type 2 diabetes, and how does it contribute to the condition?
A
Obesity is a major risk factor for type 2 diabetes. The over-production of insulin in response to a high-carbohydrate diet triggers the development of insulin resistance.
22
Q
What is the cause of Type 1 diabetes?
A
Inability of pancreas to produce insulin.
23
Q
What is the cause of Type 2 diabetes?
A
Cells of the body become resistant to insulin or insufficient insulin produced by pancreas.
24
Q
How is Type 1 diabetes treated?
A
Monitoring blood glucose levels and injecting human insulin throughout the day (particularly after meals consumed).
25
How is Type 2 diabetes treated?
Maintain a low-carbohydrate diet and regular exercise to reduce need for insulin.
26
What is the importance of maintaining blood glucose concentration within narrow limits?
Glucose is essential for respiration, so it's important that blood glucose levels do not drop too low. Glucose is soluble, so blood glucose concentration affects the osmotic balance between the cells and the blood. The control of blood glucose concentration is a key part of homeostasis.
27
How is blood glucose concentration controlled?
Blood glucose concentration is controlled by two hormones which are secreted into the blood by specialised tissue in the pancreas. This tissue is made up of groups of cells known as the islets of Langerhans.
28
What are the two cell types in the islets of Langerhans and what do they secrete?
The islets of Langerhans contain two cell types: α cells that secrete the hormone glucagon, and β cells that secrete the hormone insulin. These α and β cells are involved with monitoring and responding to blood glucose levels.
29
What is the difference between the endocrine and exocrine tissue of the pancreas?
The islets of Langerhans form the endocrine tissue of the pancreas, while the exocrine tissue is involved with the production of digestive enzymes.
30
What triggers the secretion of insulin?
An increase in blood glucose concentration, which typically occurs after a meal that contains carbohydrate, is detected by the β cells in the pancreas, which then synthesise and secrete insulin.
31
How does insulin reach its target cells?
Insulin is transported in the blood to target cells all over the body. Insulin's main target cells are in the liver and muscles.
32
What are the effects of insulin?
The text doesn't provide a complete list of insulin's effects, but it mentions that insulin has effects on its target cells, particularly in the liver and muscles.
33
What happens to glucose channels in cell surface membranes when insulin is present?
Glucose channels in cell surface membranes open, and glucose moves out of the blood and into the body cells by facilitated diffusion.
34
How do liver and muscle cells respond to excess glucose in the presence of insulin?
Liver and muscle cells convert excess glucose into glycogen to be stored; this is glycogenesis.
35
What effect does insulin have on the rate of respiration?
Insulin causes an increase in the rate of respiration, using up glucose.
36
How does insulin affect fat storage?
Insulin leads to the conversion of glucose to fatty acids, resulting in fat storage.
37
What is the overall effect of insulin on blood glucose concentration?
Insulin lowers blood glucose concentration.
38
When is glucagon synthesized and secreted?
Glucagon is synthesised and secreted by α cells when blood glucose falls.
39
What situations can cause blood glucose to fall?
Blood glucose could fall after a period of fasting, or after exercise.
40
How does glucagon reach its target cells?
Glucagon is transported in the blood to target cells.
41
What is glycogenolysis and how does glucagon affect it?
Glycogenolysis is the hydrolysis of glycogen in liver and muscle cells, releasing glucose that enters the blood. Glucagon activates enzymes that enable this process.
42
How does glucagon affect the rate of respiration?
Glucagon causes a decrease in the rate of respiration.
43
What is gluconeogenesis and how does glucagon influence it?
Gluconeogenesis is the conversion of amino acids to glucose. Glucagon promotes this process.
44
What is the overall effect of glucagon on blood glucose concentration?
Glucagon increases blood glucose concentration.
45
What is the difference between glucagon and glycogen?
Glucagon is the hormone, while glycogen is the storage polysaccharide of animal cells.
46
What is thermoregulation?
Thermoregulation is the control of internal body temperature.
47
How does thermoregulation exemplify a negative feedback mechanism?
When body temperature deviates from pre-set limits, the responses of the body act to reverse the change and bring temperature back to normal.
48
What are the two types of receptors involved in thermoregulation?
External body temperature is monitored using peripheral thermoreceptors in the skin. Internal body temperature is monitored using receptors located inside the hypothalamus of the brain.
49
How do effectors respond to deviations from normal temperature levels?
Effectors respond by controlling heat loss at the skin to the external environment and modifying the generation of heat inside the cells by metabolism.
50
What role does the hypothalamus play in thermoregulation?
The hypothalamus regulates secretion of thyrotropin-releasing hormone, which stimulates the pituitary gland to release thyroid-stimulating hormone. This in turn stimulates the thyroid gland to release thyroxin, which increases metabolic rate.
51
How does thyroxin contribute to thermoregulation?
Altering the level of thyroxin alters heat generation by cell metabolism, aiding regulation of body temperature.
52
How does muscle tissue contribute to thermoregulation?
Shivering in the muscles raises the metabolic rate of muscle cells, releasing heat energy.
53
What are the two types of adipose tissue involved in thermoregulation?
White adipose tissue stores lipids in a layer beneath the skin and around the internal organs, providing insulation. Brown adipose tissue can generate heat energy before shivering begins in the muscles, known as non-shivering thermogenesis.
54
Why is a stable core temperature vital for enzyme activity?
Human enzymes have evolved to function optimally at a core body temperature of about 37°C. Lower temperatures either prevent reactions from proceeding or slow them down, while temperatures that are too high can cause enzymes to denature.
55
What are endotherms and how do they regulate body temperature?
Endotherms are animals that maintain a constant internal body temperature, such as mammals and birds. They regulate their body temperature using physiological mechanisms (e.g., shivering and altered metabolism) and behavioral mechanisms (e.g., seeking shade or sunbathing).
56
What happens to molecules at lower temperatures in relation to enzyme activity?
At lower temperatures, molecules have little kinetic energy, so collisions are infrequent and few enzyme-substrate complexes form.
57
How does high temperature affect enzymes?
Temperatures that are too high can cause enzymes to denature, meaning that they lose their tertiary structure and enzyme-substrate complexes can no longer form.
58
What are the two main categories of thermoregulation mechanisms in mammals and birds?
Physiological mechanisms and behavioral mechanisms.
59
Give an example of a behavioral mechanism for thermoregulation.
Seeking the shade of an underground burrow or sunbathing.
60
What is the function of white adipose tissue in thermoregulation?
White adipose tissue stores lipids in a layer beneath the skin and around the internal organs, providing insulation that aids temperature regulation.
61
What is non-shivering thermogenesis?
Non-shivering thermogenesis is the generation of heat energy by brown adipose tissue before shivering begins in the muscles.
62
How does the pituitary gland contribute to thermoregulation?
The pituitary gland releases thyroid-stimulating hormone in response to thyrotropin-releasing hormone from the hypothalamus.
63
What is the relationship between thyroxin and metabolic rate?
Thyroxin increases metabolic rate, which in turn affects heat generation and body temperature regulation.
64
How do peripheral thermoreceptors differ from those in the hypothalamus?
Peripheral thermoreceptors monitor external body temperature in the skin, while receptors in the hypothalamus monitor internal body temperature.
65
What is the optimal core body temperature for human enzyme function?
Human enzymes have evolved to function optimally at a core body temperature of about 37°C.
66
How do endothermic animals detect external temperatures?
Endothermic animals detect external temperatures via peripheral receptors, e.g. thermoreceptors found in the skin. There are receptors for both heat and cold.
67
What is the role of the hypothalamus in thermoregulation?
The thermoreceptors in the skin communicate with the hypothalamus to bring about a physiological response to changing external temperatures.
68
What structures in human skin are involved in thermoregulation?
Human skin contains a variety of structures that are involved in processes that can increase or reduce heat loss to the environment. These structures are involved with monitoring and responding to temperature change.
69
What is vasodilation and how does it help in thermoregulation?
Vasodilation occurs when muscles in arterioles relax, causing the arterioles near the skin to dilate and allowing more blood to flow through skin capillaries. The increased blood flow to the skin means that more heat is lost to the environment by radiation from the skin surface.
70
How does sweating contribute to thermoregulation?
Sweat is secreted by sweat glands. This cools the skin by evaporation which uses heat energy from the body to convert liquid water into water vapour.
71
What happens to body hair during heat regulation?
The hair erector muscles in the skin relax, causing hairs to lie flat.
72
What are arterioles and how do they function in thermoregulation?
Arterioles are small vessels that connect arteries to the skin capillaries. They have muscles in their walls that can relax or contract to allow more or less blood to flow through them, helping to regulate body temperature.
73
How does the body respond to an increase in temperature?
The body responds to an increase in temperature through vasodilation, sweating, and flattening of hairs.
74
What is the primary function of peripheral thermoreceptors in the skin?
Peripheral thermoreceptors in the skin detect external temperatures, with separate receptors for both heat and cold.
75
How does the evaporation of sweat help in cooling the body?
The evaporation of sweat uses heat energy from the body to convert liquid water into water vapour, thereby cooling the skin.
76
What happens to body hair when temperature increases?
The hair erector muscles in the skin relax, causing hairs to lie flat. This stops the hairs from forming an insulating layer of air and allows air to circulate over skin, meaning that heat energy lost by radiation can be moved away from the skin surface.
77
What are the three main responses of human skin to high temperatures?
The skin responds to high temperatures with vasodilation, sweating, and relaxation of hair erector muscles.
78
What is vasoconstriction and how does it help in thermoregulation?
During vasoconstriction, the muscles in the arteriole walls contract, causing the arterioles near the skin to constrict and allowing less blood to flow through capillaries. Instead, the blood is diverted through shunt vessels, which are deeper in the skin and therefore do not lose heat to the environment. The reduction in blood flow to the skin surface means that less heat energy is lost by radiation.
79
How do hairs respond to a decrease in temperature?
The hair erector muscles in the skin contract, causing hairs to stand on end. This forms an insulating layer over the skin's surface by trapping air between the hairs and stops heat from being lost by radiation.
80
Why is the hair erection response less effective in humans compared to their evolutionary ancestors?
Humans have very little hair on their skin, so this response is less effective than it would have been in their evolutionary ancestors.
81
What are shunt vessels and how do they contribute to thermoregulation?
Shunt vessels are blood vessels deeper in the skin. During vasoconstriction, blood is diverted through these vessels, which do not lose heat to the environment, thus helping to conserve body heat.
82
How does vasodilation contribute to heat loss?
During vasodilation, arterioles near the skin dilate, allowing more blood to flow through skin capillaries. This increased blood flow to the skin means that more heat is lost to the environment by radiation from the skin surface.
83
What is the purpose of sweating in thermoregulation?
Sweat is secreted by sweat glands. This cools the skin by evaporation, which uses heat energy from the body to convert liquid water into water vapor.
84
How does the relaxation of hair erector muscles contribute to cooling?
When hair erector muscles relax, it allows air to circulate over the skin, meaning that heat energy lost by radiation can be moved away from the skin surface.
85
What are the main mechanisms for reducing heat loss via the skin when temperature decreases?
The main mechanisms for reducing heat loss via the skin when temperature decreases are vasoconstriction and erection of hairs.
86
What is thermoregulation?
Thermoregulation is the process by which the human body maintains its core temperature within a narrow range (36.5–37.5 °C) despite fluctuations in the external environment.
87
How does thermoregulation exemplify negative feedback?
Thermoregulation is an example of negative feedback because it counteracts changes in body temperature, bringing it back towards the set point when it deviates above or below the normal range.
88
What are the roles of peripheral thermoreceptors in thermoregulation?
Peripheral thermoreceptors are specialized cells located in the skin that detect changes in external temperature. They send signals to the control center (hypothalamus) when they detect temperature changes.
89
How does the hypothalamus function in thermoregulation?
The hypothalamus acts as the control center for thermoregulation. It receives signals from thermoreceptors, compares the body temperature to the set point, and coordinates appropriate responses to maintain the core temperature.
90
What is vasodilation and how does it contribute to thermoregulation?
Vasodilation occurs when muscles in arterioles relax, allowing more blood to flow through skin capillaries. This increases heat loss to the environment by radiation from the skin surface, helping to cool the body.
91
What is vasoconstriction and how does it help in thermoregulation?
During vasoconstriction, muscles in arteriole walls contract, reducing blood flow through skin capillaries. Blood is diverted through deeper shunt vessels, reducing heat loss to the environment and helping to conserve body heat.
92
How does shivering contribute to thermoregulation?
Shivering involves rapid contraction and relaxation of muscles. The metabolic reactions required to power shivering generate sufficient heat to warm the blood and raise the core body temperature.
93
What is the role of sweating in thermoregulation?
Sweating cools the skin through evaporation, which uses heat energy from the body to convert liquid water into water vapor, thus helping to lower body temperature.
94
What is uncoupled respiration in brown adipose tissue?
Uncoupled respiration in brown adipose tissue is a process where all energy released from lipid metabolism is released as heat, without producing ATP. This non-shivering thermogenesis occurs mainly in newborn infants who cannot shiver.
95
How does thyroxine contribute to thermoregulation?
Thyroxine, released from the thyroid gland, acts to increase the basal metabolic rate (BMR), thereby increasing heat production in the body.
96
What are the two main roles of the kidney in mammals?
The kidney has two roles in the body of mammals: excretion and osmoregulation.
97
What is excretion?
Excretion is the process by which toxic waste products of metabolism are removed from the body.
98
What type of waste are the kidneys involved in excreting?
The kidneys are involved with the excretion of nitrogenous waste.
99
Where does nitrogenous waste come from?
Nitrogenous waste comes from the breakdown of excess dietary amino acids and nucleic acids.
100
What is the initial form of nitrogenous waste and why is it problematic?
The waste is first converted into ammonia. Ammonia is highly toxic; it cannot be stored in the body and must therefore be removed quickly from the body.
101
How do some organisms deal with toxic ammonia?
Some organisms convert highly toxic ammonia into less toxic urea; urea can remain in the body at low concentrations, but needs to be excreted before it builds up to a harmful level.
102
How is urea excreted from the body?
Organisms that excrete urea need to dilute it with water to form urine before it is excreted. Urine is produced in the kidneys.
103
What is osmoregulation?
Osmoregulation is the maintenance of a safe balance of water and solutes in cells, which is the osmotic concentration of the cells.
104
Why is osmoregulation important?
Failure to maintain this balance will mean that an organism's cells could either take on water and burst, or lose water and shrink due to the effects of osmosis.
105
What happens to cells with a lower water potential than their surrounding environment?
Cells with a lower water potential than their surrounding environment will gain water by osmosis and the resulting internal pressure increase could cause the cell to burst. Note that plant cells are protected from bursting by their strong cell walls.
106
What happens to cells with a higher water potential than their surrounding environment?
Cells with a higher water potential than their surrounding environment will lose water by osmosis and the resulting drop in internal pressure will cause the cell to shrink.
107
What are the units for osmotic concentration?
The units for osmotic concentration are osmoles per litre (osmol L⁻¹).
108
What is the main function of the kidneys?
Humans have two kidneys, which remove waste products from the blood and maintain the blood's balance of water and solutes.
109
How is blood supplied to and removed from the kidneys?
The renal artery supplies blood to the kidneys, while the renal vein carries blood away.
110
What is the path of urine from the kidneys to outside the body?
The filtrate produced by the kidneys forms urine which is transferred to the bladder via a tube called the ureter. Urine is then released outside of the body through the urethra.
111
What is the function of the renal artery?
The renal artery carries oxygenated blood (containing urea and salts) to kidneys.
112
What is the function of the renal vein?
The renal vein carries deoxygenated blood (that has had urea and excess salts removed) away from kidneys.
113
What are the three main regions of the kidney beneath the fibrous capsule?
Beneath the fibrous capsule, the kidney has three main regions: the cortex, the medulla, and the renal pelvis.
114
What is the function of the bladder?
The bladder stores urine (temporarily).
115
What surrounds the kidney?
The kidney itself is surrounded by an outer layer known as the fibrous capsule.
116
What are nephrons and where are they located?
Each kidney contains thousands of tiny tubes, or tubules, known as nephrons. Nephrons are the functional unit of the kidney and are responsible for the formation of urine.
117
What structures are found in the cortex of the kidney?
The cortex contains the glomerulus, Bowman's capsule, proximal convoluted tubule, and distal convoluted tubule.
118
What structures are found in the medulla of the kidney?
The medulla contains the loop of Henle and collecting duct.
119
What is the function of the renal pelvis?
All kidney nephrons drain into the renal pelvis, which connects to the ureter.
120
What is the glomerulus and how is it supplied with blood?
The glomerulus is a structure within the Bowman's capsule of each nephron. It is supplied with blood by an afferent arteriole which carries blood from the renal artery.
121
How does blood flow through the glomerulus?
The afferent arteriole splits into a ball of capillaries that forms the glomerulus itself. The capillaries of the glomerulus rejoin to form the efferent arteriole.
122
What happens to the blood after it leaves the glomerulus?
Blood flows from the glomerulus into a network of capillaries that run closely alongside the rest of the nephron and eventually into the renal vein.
123
What is ultrafiltration and where does it occur?
Ultrafiltration is carried out by the glomerulus and Bowman's capsule together.
124
Why is the blood pressure high in the glomerulus?
The blood in the glomerulus is at high pressure because the afferent arteriole is wider than the efferent arteriole, increasing the blood pressure as the blood flows through the glomerulus.
125
How does the outward pressure in the glomerulus compare to other capillaries?
While all capillaries exert outward pressure, forcing tissue fluid out towards the surrounding cells, the outward pressure in the glomerulus is much higher than in other capillaries.
126
What is ultrafiltration in the kidney?
Ultrafiltration is the process where high blood pressure in the glomerulus forces small molecules into the Bowman's capsule, forming glomerular filtrate.
127
What small molecules are forced out of the capillaries of the glomerulus during ultrafiltration?
Chloride ions, sodium ions, glucose, urea, and amino acids.
128
What is the resulting fluid in the Bowman's capsule called?
The resulting fluid in the Bowman's capsule is called the glomerular filtrate.
129
What molecules remain in the blood and do not pass into the filtrate?
Large molecules such as proteins remain in the blood and do not pass into the filtrate.
130
What are the three layers that separate the blood in the glomerular capillaries from the lumen of the Bowman's capsule?
- The endothelium of the capillary
- The basement membrane
- The epithelium of the Bowman's capsule
131
What are fenestrations and where are they found?
Fenestrations are gaps between the cells of the capillary endothelium. Fluid can pass through these gaps but not blood cells.
132
What is the composition of the basement membrane?
The basement membrane is made up of a network of collagen protein and glycoproteins. This mesh-like structure acts as a sieve, allowing small molecules through but preventing passage of large proteins from the blood plasma.
133
What are podocytes?
Podocytes are the epithelial cells of the Bowman's capsule that have many foot-like projections which wrap around the capillary. The gaps between the projections allow the passage of small molecules.
134
What substances make up the glomerular filtrate?
The main substances that form the glomerular filtrate are amino acids, water, glucose, urea and salts (Na+ and Cl- ions).
135
Why do red and white blood cells and platelets remain in the blood during ultrafiltration?
Red and white blood cells and platelets remain in the blood as they are too large to pass through the fenestrations between the capillary endothelial cells.
136
What is selective reabsorption?
Selective reabsorption is the process by which useful substances that pass into the glomerular filtrate are reabsorbed into the blood as the filtrate passes along the nephron. Not all substances are reabsorbed, hence the term "selective.
137
What substances are reabsorbed during selective reabsorption?
Reabsorbed substances include water, salts, glucose, and amino acids.
138
Where does most reabsorption occur in the nephron?
Most reabsorption occurs in the proximal convoluted tubule. However, the loop of Henle and collecting duct are also involved in the reabsorption of water and salts.
139
What are the adaptations of the proximal convoluted tubule for selective reabsorption?
The proximal convoluted tubule is adapted with:
- Microvilli: tiny finger-like projections that increase surface area for diffusion
- Co-transporter proteins
- Many mitochondria
- Tightly packed cells
140
How do microvilli aid in reabsorption?
Microvilli increase the surface area for reabsorption.
141
What is the function of co-transporter proteins in the luminal membrane?
Each type of co-transporter protein transports a specific solute (e.g., glucose or a particular amino acid) across the luminal membrane.
142
Why are there many mitochondria in the proximal convoluted tubule cells?
Mitochondria provide energy for sodium-potassium (Na⁺-K⁺) pump proteins in the basal membranes of the cells.
143
Why are the cells in the proximal convoluted tubule tightly packed?
Tightly packed cells ensure that no fluid can pass between the cells, meaning all substances reabsorbed must pass through the cells.
144
How are sodium ions transported in the proximal convoluted tubule?
Sodium ions (Na⁺) are transported from the proximal convoluted tubule into the surrounding tissues by active transport.
145
What happens to the substances that leave the proximal convoluted tubule?
All substances that leave the proximal convoluted tubule for the surrounding tissues eventually make their way into nearby capillaries down their concentration gradients.
146
What is the main role of the loop of Henle?
The role of the loop of Henle is to enable the production of urine that is more concentrated than the blood, and to therefore conserve water. It also allows for the production of urine less concentrated than blood when water intake is high.
147
What happens in the ascending limb of the loop of Henle?
Sodium and chloride ions are pumped out of the filtrate in the ascending limb of the loop of Henle into the surrounding medulla region, lowering its water potential. The ascending limb is impermeable to water, so water is unable to leave the loop here by osmosis.
148
How does the water potential change in the ascending limb?
The water potential of the ascending limb increases as it rises back into the cortex due to the removal of solutes and retention of water.
149
What occurs in the descending limb of the loop of Henle?
The descending limb is permeable to water, so water moves out of the descending limb by osmosis due to the low water potential of the medulla created by the ascending limb. The descending limb has few transport proteins in the membranes of its cells, so has low permeability to ions.
150
How does the water potential change in the descending limb?
The water potential of the filtrate decreases as the descending limb moves down into the medulla due to the loss of water and retention of ions.
151
How does the loop of Henle affect water reabsorption in the collecting duct?
The low water potential in the medulla created by the ascending limb also enables the reabsorption of water from the collecting duct by osmosis.
152
What happens to the water and ions that leave the loop of Henle?
The water and ions that leave the loop of Henle for the medulla make their way into nearby capillaries.
153
What is the vasa recta?
The vasa recta is the capillary that flows directly alongside the loop of Henle. It also supplies oxygen to and removes carbon dioxide from the respiring cells of the loop of Henle.
154
What is osmoregulation and how does it relate to homeostasis?
Osmoregulation is the process by which living organisms maintain a safe balance of water and solutes in their bodies. It is an example of homeostasis.
155
How do kidneys contribute to osmoregulation?
The kidneys play an important role in osmoregulation by altering the amount of water reabsorbed from the glomerular filtrate into the blood.
156
How is water reabsorption regulated in the kidneys?
The amount of water reabsorbed by the kidneys can be regulated by changing the permeability of the walls of the distal convoluted tubule and collecting duct to water.
157
What hormone regulates the permeability of the distal convoluted tubule and collecting duct?
The permeability of these parts of the nephron is regulated by a hormone called antidiuretic hormone, or ADH.
158
Where is ADH released from and what controls its release?
ADH is released from the posterior section of the pituitary gland in the brain, which is regulated by a region of the brain called the hypothalamus.
159
How does the hypothalamus monitor blood composition?
The hypothalamus monitors the composition of the blood as it flows past osmoreceptor cells in the brain, as well as receiving signals from receptors elsewhere in the body.
160
What causes low blood water content?
Blood water content might drop as a result of reduced water intake, sweating, or diarrhoea. Low blood water content can also be referred to as high blood solute concentration.
161
How is low blood water content detected and what is the initial response?
A reduction of blood water content is detected by the hypothalamus in the brain. The hypothalamus causes the pituitary gland to secrete ADH into the blood.
162
What are the target cells of ADH and how does it affect them?
The target cells of ADH are in the distal convoluted tubule and collecting duct in the kidneys. ADH increases the permeability of the walls of these structures to water.
163
How does ADH increase the permeability of the collecting duct walls?
ADH increases the number of channel proteins called aquaporins in the cell surface membranes of the cells lining the nephron lumen. Aquaporins are stored in vesicle membranes; ADH causes these vesicles to fuse with the cell surface membranes, incorporating the aquaporins.
164
How does the loop of Henle contribute to water reabsorption in the collecting duct?
The activity of the loop of Henle generates a concentration gradient across the medulla, meaning that as the collecting duct descends into the medulla the osmolarity of the tissues increases. This means that water is reabsorbed by osmosis all the way down the length of the collecting duct.
165
What is the result of low blood water content on urine production?
The blood water content increases and a small volume of concentrated urine is produced.
166
What causes high blood water content?
Blood water content might increase due to increased water intake or loss of salts during sweating. High blood water content can also be referred to as low blood solute concentration.
167
How does the body respond to high blood water content?
High blood water content is detected by the hypothalamus. The hypothalamus no longer stimulates the pituitary gland to release ADH and ADH levels in the blood drop.
168
How does the collecting duct respond to decreased ADH levels?
The distal convoluted tubule and collecting duct walls become less permeable to water. Fewer aquaporins are present. The cell surface membrane is pinched inwards to reform the vesicles in which aquaporins are stored.
169
What is the result of high blood water content on urine production?
Blood water content decreases and a large quantity of dilute urine is produced.
170
What is the role of the circulatory system?
The role of the circulatory system is to supply the cells of the body with oxygen and nutrients, and to remove the waste products of metabolism.
171
How do the requirements of cells in different parts of the body change?
The requirements of the cells in different parts of the body will differ depending on the activity levels of the body. For example, during exercise, muscles require more oxygen and glucose, and after a meal, the digestive system needs more oxygen and glucose.
172
How does the circulatory system adjust blood flow to different organs?
The circulatory system can divert blood flow to increase or decrease the blood supply to different organs. This is achieved by vasodilation or vasoconstriction in the arterioles that supply the capillary beds in different parts of the body.
173
How does blood flow to skeletal muscles change during sleep, wakefulness, and exercise?
During sleep, blood flow to skeletal muscles is relatively low. During wakefulness, blood flow increases as some muscle groups work to keep the body upright. During physical exercise, there is a large increase in blood flow due to rapid contraction of many muscle groups.
174
How does blood flow to the gut change after a meal and during exercise?
Soon after a meal, the blood flow to the gut increases. During exercise, blood flow to the gut decreases so that more blood can be diverted to the skeletal muscles.
175
How does blood flow to the brain change during different activity levels?
The blood flow to the brain remains relatively constant regardless of the activity levels of the body, as it carries out processes that need to occur all the time. Blood flow increases slightly during a stage of sleep known as REM.
176
How does blood flow to the kidneys change during different activity levels?
Blood flow to the kidneys does not change significantly based on activity level, but it will increase slightly during sleep and rest, and decrease slightly during prolonged exercise.
