D3.3 Homeostasis Flashcards
1
Q
What is homeostasis?
A
Homeostasis = ability to maintain a constant internal environment at preset values despite fluctuations from external environment.
2
Q
How does homeostasis work?
A
It works by monitoring levels of variables & making corrections by negative feedback mechanisms.
3
Q
What does internal environment consists of?
A
Internal environment consists of blood circulating in body & fluid that circulates among cells (tissue fluid that forms from blood plasma), delivering nutrients & removing waste products while bathing cells. Mammals are excellent examples of animals that maintain remarkably constant internal conditions.
4
Q
Which factors must stay “the same” inside body to maintain a steady stage?
A
- glucose level of blood = blood glucose conc
- water content of blood = blood osmotic conc
- Conc of essential ions
- pH of blood
- heart rate
- pressure of blood in arteries
- conc of respiratory gases in blood (pCO2, pO2)
5
Q
What are all homeostatic functions controlled by?
A
All homeostatic functions of an organism are under control of a feedback loop, which uses info about outcome of a process to make adjustments.
6
Q
What a cell’s environment? And examples in plants & animal cells?
A
Immediate surroundings outside plasma membrane. E.g. plant cell, this is cell wall, & fluid held in it
E.g. animal cell, there may be an extracellular matrix of collagen, elastin & other materials, & there is always tissue fluid filling other gaps between cells. Blood is unusual in that volume of tissue fluid, in this case plasma, is very large & separates cells completely; blood is a liquid tissue.
7
Q
What is a positive feedback?
A
Positive feedback amplifies their initiating stimuli - they move systemawayfrom its starting state. It increases gap between original & new level.
Only few examples exist in human body (e.g. During menstrual cycle release of FSH stimulates follicle growth which in turn stimulates FSH release)
8
Q
What is a negative feedback?
A
Negative feedback counteracts changes of various properties from their target value (set points) – decreases gap – so original level is restored. They form basis of homeostatic control systems used to keep internal conditions within narrow limits. They require energy but keep body at stable conditions which allows extreme environments to be inhabited.
9
Q
What is homeostasis controlled by?
A
Homeostasis is controlled by negative feedback. This is type of control in which conditions are brought back to a set value as soon as it is detected that they have deviated from it.
10
Q
What is an examples of role of hormones in homeostasis?
A
Regulation of blood glucose as an example of role of hormones in homeostasis.
11
Q
What is role of glucose and what is its level in the blood?
A
Transport of glucose to all cells is a key function of the blood circulation. In human blood a set value of around 90mg/100ml (5 mmol L-1) blood is normal.
12
Q
What situations cause the blood sugar level to drop above or below that value?
A
For example, during an extended period without food, or after prolonged & heavy physical activity, blood glucose may fall to as low as 70 mg. After a meal rich in carbohydrate has been digested, blood glucose may rise to 150 mg.
13
Q
What are the two reasons for maintenance of a constant level of this monosaccharide in the blood plasma?
A
- Respiration is a continuous process in all living cells. To maintain their metabolism, cells need a regular supply of glucose, which can be quickly absorbed across cell membrane. Glucose is main respiratory substrate for many tissues. Most cells (including muscle cells) hold reserves in form of glycogen which is quickly converted to glucose during prolonged physical activity. However, glycogen reserves may be used up quickly. In brain, glucose is only substrate cells can use &, here, there is no glycogen store held in reserve. If our blood glucose falls below 60 mg per 100 cm3, we have a condition called hypoglycaemia. If this is not quickly reversed, we may faint. If body & brain continue to be deprived of adequate glucose levels, convulsions & coma follow.
- An abnormally high conc of blood glucose, known as hyperglycaemia, is also a problem. Since high conc of any soluble metabolite lowers water potential of the blood plasma, water is drawn from cells & tissue fluid by osmosis, back into blood. As volume of blood increases, water is excreted by kidney to maintain correct conc of blood. As a result, body tends to become dehydrated & circulatory system is deprived of fluid. Ultimately, blood pressure cannot be maintained. For these reasons, it is critically important blood glucose is held within set limits.
14
Q
why does hyperglycaemia increases the blood pressure?
A
Water moves in by osmosis bc of high con of glucose. Thus increasing volume, leading to an increased blood pressure.
15
Q
What two hormones adjust blood sugar levels?
A
Blood sugar levels are adjusted by two hormones: Insulin & Glucagon, which are produced in pancreatic cells (Langerhans islets), which are hormone-secreting glands (endocrine glands). Hormones are transported in body by blood to reach their target cells. Langerhans islets contain two types of cell, α cells (releases glucagon) & β cells (releases insulin).
16
Q
Which two hormones are responsible for the homeostatic control of blood sugar levels?
A
Insulin & Glucagon
17
Q
Where is insulin produced?
A
Islets of Langerhans, β cells
18
Q
Where is glucagon produced?
A
Islets of Langerhans, α cells
19
Q
What is an exocrine gland?
A
An exocrine gland is a gland which releases its products into a duct (e.g. digestive enzymes)
20
Q
What is an endocrine gland?
A
An endocrine gland is a gland which secretes products (e.g. hormones) into bloodstream.
21
Q
What happens when blood glucose levels are high?
A
- Stimulation of β cells , which secrete hormone insulin into blood stream ( capillary network).
- Insulin causes skeletal muscle fibre & liver cells to absorb insulin.
- Insulin causes conversion of glucose to glycogen in cells (glycogenesis), & to fatty acids & fats (adipose tissue). Excess insulin is removed via kidneys from blood.
22
Q
What happens when blood glucose levels are low?
A
- Stimulation of α cells of pancreas to secrete hormone glucagon.
- Glucagon activates enzymes to convert glycogen & amino acids to glucose (gluconeogenesis).
- It also reduces rate of respiration. Excess glucagon is removed from blood via kidneys.
23
Q
What are the consequences of the interactions between insulin and cell membrane receptor?
A
Insulin causes migration of membrane proteins & absorption into the cell
24
Q
What are the consequences of the interactions between glucagon and cell membrane receptor?
A
Glucagon causes breakdown of polymer storage products in liver.
25
What does hypoglycaemia cause? And what are the symptoms?
Can lead to seizures, coma, or death if severe. Symptoms include:
- Sweating
- Shakiness
- Extreme hunger
- Nausea
- Dizziness
- Confusion
- Fast heart rate
- Behaviour changes
26
What does hyperglycaemia cause? And what are the symptoms?
Can lead to heart disease, stroke, kidney damage and eye damage.
Symptoms include:
- Increased thirst
- Increased urination
- Fatigue
- Light-headedness
- Dry mouth
- Headache
- Blurry vision
- Shortness of breath
27
Why is it important to control blood glucose?
Blood glucose homeostasis is maintained by balancing amount of glucose removed from blood with the amount that is added.
28
What are the receptors involved in maintenance of blood glucose levels?
RECEPTOR: Chemoreceptor proteins in carotid artery in neck sense changes in blood glucose conc.
29
What are the control centre involved in maintenance of blood glucose levels?
CONTROL CENTER: hypothalamus in brain senses & responds to changes in blood glucose levels by triggering release of hormones from pancreas
30
What are the effectors involved in maintenance of blood glucose levels?
- Pancreas: endocrine cells in the pancreas secrete the hormones insulin and glucagon
- Liver: responds to hormones by storing or releasing glucose
31
What is the negative feedback for insulin? ( Receptor, control centre, stimulus, effector, response)
32
What is the negative feedback for glucagon? ( Receptor, control centre, stimulus, effector, response)
33
What happens once insulin is released?
34
What is diabetes?
Diabetes is condition in which a person has consistently elevated blood glucose levels even during prolonged fasting. It is a chronic disease. This leads to presence of glucose in urine. Continuously elevated glucose causes damage to tissues, particularly their proteins. It also impairs water reabsorption during urine production in kidney, resulting in greater loss of water in urine & therefore dehydration.
35
What are the two types of diabetes?
- Type I diabetes (early onset)
- Type II diabetes (late onset)
36
What is the cause of type I diabetes?
Type I diabetes is a disease resulting from insufficient or no insulin production usually due to autoimmune destruction of beta cells of pancreatic islets (when body's immune system mistakenly attacks healthy tissue).
Onset of Type I diabetes is sudden, often in childhood.
37
What happens during high blood glucose if they have type I diabetes?
38
What are the symptoms of Type I diabetes?
- Excessive thirst: Body tries to compensate for fluid loss due to frequent urination, leading to increased thirst.
- Blurred vision: High blood glucose can affect lens of eye, causing it to swell & change shape. This can lead to temporary blurred vision.
- Vaginal yeast infections: Yeast thrives on glucose, & excess sugar in bloodstream provides a plentiful food source
- Excessive hunger
- Unexplained weight loss: Even though food is consumed, body cannot effectively use glucose for energy. This can lead to weight loss, despite increased appetite.
- Slow healing of cuts & sores: Poor blood circulation & impaired immune function due to high blood sugar can hinder wound healing
- Fatigue: Cells are deprived of glucose, their primary energy source. This can lead to weakness & fatigue.
- Frequent urination: Kidneys attempt to filter out excess glucose from blood, leading to increased urine production.
39
What is the treatment of Type I diabetes?
- Type I diabetics must monitor blood glucose levels regularly to guard against sudden falls in blood glucose.
- Primary treatment for Type I diabetes is insulin therapy, which involves taking insulin injections or wearing an insulin pump to manage blood sugar levels.
- Scientists are working to differentiate stem cells into insulin-producing beta cells, which could then be transplanted into patients with Type I diabetes. This would potentially restore body's ability to produce insulin on its own.
40
What is the cause of type II diabetes?
Type II diabetes is a disease resulting from a deficiency of insulin receptors on target cells.
Onset of Type II diabetes is gradual, often in overweight adults
41
What happens during high blood glucose if they have type II diabetes?
42
What are the symptoms of Type II diabetes?
- Increased thirst: Body tries to compensate for fluid loss due to frequent urination, leading to increased thirst.
- Unexplained weight loss
- Increased hunger: Even though food is consumed, body cannot effectively use glucose for energy. This can lead to weight loss, despite increased appetite.
- Fatigue: Cells are deprived of glucose, their primary energy source. This can lead to weakness & fatigue.
- Blurred vision: High blood glucose can affect lens of eye, causing it to swell and change shape. This can lead to temporary blurred vision.
- Frequent urination: Kidneys attempt to filter out excess glucose from blood, leading to increased urine production.
- Slow heading: Poor blood circulation & impaired immune function due to high blood sugar can hinder wound healing
- Numbness in hands or feet: High blood sugar levels can damage nerves & impair their ability to send signals. High blood sugar can also damage small blood vessels that supply nerves with oxygen & nutrients.
43
What is the treatment type II diabetes?
Type II diabetes is treated by:
- Reduction in weight & modification of dietary habits.
- Sometimes antidiabetic drugs are also used to stimulate pancreas to produce more insulin.
44
What are risk factors that contribute to development of diabetes?
- Family history: Having a family history of diabetes increases risk of developing condition. If a close family member, such as a parent or sibling, has diabetes, risk is higher.
- Body weight: Being overweight or obese is a significant risk factor for developing type 2 diabetes. Excess body weight increases insulin resistance & impairs glucose metabolism. Adopting and maintaining a healthy weight through a balanced diet & regular physical activity is one of the most effective ways to prevent type 2 diabetes. Losing even a small amount of weight (around 5–7% of body weight) can significantly reduce risk.
- Lifestyle: Lack of physical activity or a sedentary lifestyle is linked to an increased risk of type 2 diabetes. Regular exercise helps maintain a healthy weight, improves insulin sensitivity & reduces risk of developing diabetes.
- Diet: Consuming a diet high in processed foods, sugary beverages & unhealthy fats increases risk of developing type 2 diabetes. A diet low in fruits, vegetables & whole grains contributes to weight gain & insulin resistance.
- Age: Risk of developing diabetes increases with age. Type 2 diabetes is more common in adults over age of 45, although it is increasingly being diagnosed in younger individuals as well.
45
What food should a type II diabetes eat?
- Foods need to have a low glycaemic index – which is percentage of area under blood glucose response curve as a percentage of area produced by ingesting same quantity of glucose.
- Glycaemic index therefore ranges from 0 to 100.
46
Distinguish between type I and type II diabetes with respect to their cause, effects and treatment.
47
Explain what happens in a person when they develop type I diabetes.
- insulin is necessary to control/regulate blood glucose conc OR insulin is necessary for cells to take up glucose (for energy);
- insufficient insulin is made by pancreas OR autoimmune response/antibodies destroy (β) cells of pancreas that make insulin;
- reduced uptake of glucose from blood / glucose accumulates in blood / elevated blood glucose levels;
“sugar” is NOT accepted in place of glucose. However, this should only be penalized once; i.e., utiltize ECF.
48
State how type I diabetes should be treated to avoid harmful health consequences of the condition.
- inject insulin / monitoring blood glucose / devices that release insulin;
- decrease consumption of sugars/CHO / diet modification;
- increase exercise;
- keep weight in healthy range;
49
What is an endotherms?
Endotherms generate heat internally to maintain a steady body temp. Endotherms can increase their internal heat production when they are cold, & decrease it when they are hot. They can also shiver to warm up, & sweat or pant to cool down. Examples of endotherms include birds & mammals.
50
What is an ectotherms?
Ectotherms rely on external heat sources to regulate their body temperature. Their body temperature changes with the temperature of their environment. Examples of ectotherms include lizards and most fish.
51
What is thermoregulation?
Thermoregulation is maintenance of a core body temp at a sett point (which might differ at different times of the day, year, organism, etc.) despite fluctuations in external temp by balancing heat generation with heat loss.
52
What is set body temperature for birds and mammals?
Birds and mammals are thermoregulators with a setpoint of 36-42°C depending on species.
53
What is body temp monitored by?
Body temperature is monitored by thermoreceptors, which are the free nerve endings of specialised sensory neurones.
54
What are the two types of thermoreceptors?
- central thermoreceptors
- peripheral thermoreceptors
55
What is the difference between the two thermoreceptors?
These include peripheral thermoreceptors in skin & by central thermoreceptors in core of body & hypothalamus.
56
What is the hypothalamuses role in thermoregulation?
Hypothalamus is also regulatory part, taking in info from thermoreceptors & initiating responses.
57
How is heat generated?
Heat is generated by metabolism in cells. Heat is then distributed by blood circulation. Some organs are more metabolically active (like heart & kidneys, lungs & brain, from which over 70% of body heat emerges)
58
How can heat generation be adjusted?
Metabolic rate can be decreased or lowered to adjust amount of heat generated. Once thermoreceptors have received a stimulus, hormones release by glands are coming into effect to increase metabolic rate.
59
What are the names of hormones involved in controlling body temperature?
Thyrotropin releasing hormone (TRH), which activates pituitary gland to release thyroid stimulating hormone (TSH), which in turn stimulates thyroxin (T4) production by thyroid gland.
60
What is the effect of Thyroxin on metabolic rate?
Thyroxin in blood circulation stimulates oxygen consumption & increases metabolic reactions that generate heat as a waste product.
- Increases cardiac output and heart rate
- Increases ventilation rate
- Increases basal metabolic rate (i.e. body temperature)
- Potentiates brain development
- Thickens endometrium in females
- increase metabolism of proteins and carbohydrates
61
What are the target cells for thyroxin?
Target cells for tyroxin are muscles, brain & liver which respond accordingly.
62
What is the role of adipose tissue in thermoregulation?
Adipose tissue also acts as an insulator & reduces heat loss. Brown adipose tissue can generate heat at a rapid rate – small mammals & new born babies have larger quantities of this type of adipose tissue, as they are particularly prone to heat loss.
63
How does muscle stimulation by thyroxin increase the body temperature?
Shivering is an involuntary thermoregulation reflex that occurs when body temperature drops. Shivering is caused by skeletal muscles rapidly contracting & relaxing. Heat generated from muscle contractions plays a crucial role in maintaining body temperature. Muscles produce heat when contracting because process of muscle contraction relies on the break down of ATP molecules. Breaking of ATP is an exothermic reaction, meaning it releases heat energy.
64
Why do small mammals and babies have more brown adipose tissue than adults or larger animals?
This is because they have a larger SA:V which means heat is more easily lost. Therefore, they have more brown adipose tissue, to insulate heat more.
65
What mechanisms has the body developed in order to respond to an increased core temperature?
Sweating, dilation of blood vessels (vasodilation),
Behavioral adaptations (taking off clothes), hydration (drinking)
66
How does sweating allow for a decrease in temperature?
Water molecules are held together by hydrogen bonds –
When bonds are breaking in process of evaporation, energy is required. Energy taken to break these bonds is removed from body --> temp reduced.
67
How does vasodilation (the widening of blood vessels) allow for lowering body temperature?
Blood vessels become wider and move closer to skin’s surface resulting in heat to be transported away easier (conduction & convection)
68
How does vasoconstriction (the narrowing of blood vessels) allow for increasing body temperature?
Blood vessels become more narrow and deeply buried inside muscle tissue – this will remove blood flow from surface of the skin, & therefore reduce heat loss through skin.
69
What are the receptors for thermoregulation?
RECEPTOR: Thermoreceptor proteins in nerve endings of sensory neurons that sense changes in temp
70
What are the control centre for thermoregulation?
CONTROL CENTER: hypothalamus in brain senses & responds to changes in body temp
71
What are the effectors for thermoregulation?
- Pituitary: releases a hormone that stimulates thyroid gland to release thyroxin
- Thyroid: increase or decrease release of hormone thyroxin to change basal metabolic rate
- Adipose tissue: brown fat cells generate heat through uncoupled cellular respiration
- Blood vessels: constrict or dilate to carry more or less blood towards diff regions of body
- Muscles: respond to signals to contract, causing shivering, hair erection & changes to ventilation rate
- Sweat glands: activate sweating to reduce body temp via evaporative cooling
72
What is our body's negative feedback to heat?
73
What is our body's negative feedback when it's too cold?
74
What is our body's response to heat?
When the body is getting too hot, homeostasis mechanisms will work to cool it down:
- Vasodilation
- Sweating
75
what is our body's response to the cold?
When the body is getting too cold, homeostasis mechanisms will work to warm it up:
- Vasoconstriction
- Shivering
- Uncoupled respiration
- Piloerection
76
How is blood and heat related?
Blood transports heat energy from core organs to skin where heat radiates away. By changing flow of blood to skin, more or less heat can be radiated from body.
77
What is the reason for vasodilation?
When body is hot, vessels near surface of skin will vasodilate. Vasodilation occurs when muscles within artery wall relax, causing diameter of artery to widen & an increase in blood flowing through vessel. Vasodilation will increase heat loss from body by increasing blood flow to skin. Heat will move from blood & radiate away from body.
78
What is the reason for vasoconstriction?
When body is cool, vessels near surface of the skin will vasoconstrict. Vasoconstriction occurs when muscles within artery wall contract, causing the diameter of artery to narrow & a decrease in blood flowing through vessel. Vasoconstriction will decrease heat loss from body by decreasing blood flow to the skin. Less heat will move from the blood & radiate away from the body.
79
What is the purpose of shivering?
Shivering is an involuntary thermoregulation reflex that occurs when body temp drops. Shivering is caused by skeletal muscles rapidly contracting & relaxing. Heat generation from muscle contractions plays a crucial role in maintaining body temp. Muscles produce heat when contracting bc process of muscle contraction relies on breakdown of ATP molecules. Breaking of ATP is an exothermic reaction, meaning it releases heat energy.
80
What is the purpose of sweating?
Sweating is a vital part of thermoregulation. When body temperature rises hypothalamus signals sweat glands to secrete sweat.
81
Why does sweating cool you down?
When sweat evaporates from skin, it cools body through a mechanism called evaporative cooling. Water molecules have a polar structure, with the oxygen atom having a partial negative charge & hydrogen atoms having a partial positive charge. This allows them to form hydrogen bonds with neighbouring water molecules, where positive hydrogen of one molecule is attracted to negative oxygen of another. As water evaporates, it absorbs heat energy from skin. Energy is used to break hydrogen bonds between water molecules, allowing them to transition into vapor. Heat being absorbed by water during evaporation is removed from body, resulting in a cooling effect.
82
What is the purpose of brown adipose cells in thermoregulation?
Located in neck, chest cavity, & shoulder regions, brown adipose (fat) tissue is dense in mitochondria. Thyroxine increases heat production in brown adipose cells by activating uncoupled cellular respiration.
Uncoupled cellular respiration is a metabolic process where all of energy produced by oxidation carbon compounds in cellular respiration is transformed into heat & no ATP is produced.
83
What is purpose of piloerection in thermoregulation?
Piloerection is contraction of muscles at base of hair follicles that causes hair to stand up. In most mammals, erect hairs act as a thermal insulator; thick coat traps warm air radiating from body. Humans have evolved to have less hair than other mammals, but the erector muscles can still make the hairs stand up, forming “goosebumps.”
84
What is the role of thermoreceptors?
Thermoreceptors are ion channel proteins in membrane of specific sensory neurons that help body detect changes in temp. They are located in skin & within core of body. When there's a change in temp, channels open & flow of ions leads to:
- Cell membrane depolarization which results in…
- Action potentials that are electrical impulses propagated along nerve fibres & conveyed to brain
85
What is the role of hypothalamus in thermoregulation?
Brain is central information integration organ in humans, processing information from several sensory inputs. Hypothalamus is region of brain that receives information from thermoreceptors & compares it to an internal set point. Hypothalamus then sends nerve impulses to effectors to return body's temp to normal.
86
What is the role of the pituitary in thermoregulation?
Hypothalamus communicates with pituitary, which responds by increasing or decreasing secretion of a hormone called thyroid-stimulating hormone (TSH) depending on whether body needs to increase or decrease heat production. When hypothalamus senses that body is cold, it causes pituitary to increase secretion of TSH.
TSH is a signalling molecule that trigger a response in target cells in thyroid gland.
87
Where is thyroid located?
Thyroid is an endocrine gland located in front of neck. It's made up of two lobes that sit on either side of trachea, connected by a narrow strip of tissue.
88
what happens when thyroid is stimulated b thyroid stimulating hormone?
When stimulated by thyroid stimulating hormone (TSH) from the pituitary, the thyroid will secrete a hormone called thyroxine. Thyroxine travels to target cells throughout the body, triggering the cells to increase their metabolic rate.
89
What is thyroxine role in thermoregulation?
When thyroxine binds to its intranuclear receptor in target cells, it activates genes for increasing metabolic rate, especially in liver & muscle cells. Increasing metabolic rate results in production of heat energy. Heat produced from increased metabolism will result in a rise in body temp. A significant portion of energy from glucose is not captured as usable energy during cellular respiration & instead escapes as heat energy into environment; this heat is crucial for maintaining an organism's body temp.
90
What do organisms have to do to convert ammonia?
Organisms have to expend energy to convert ammonia to less toxic forms of urea or uric acid, depending on their habitat. Amino group must be removed -> proteins are excreted only one that's not used for fuel.
91
How do birds release ammonia?
Birds release ammonia by converting it into non-water-soluble uric acid. This process requires a large amount of energy but has advantage of not needing water to dissolve. Birds therefore don`t need to carry water for excretion, which means less energy to be expended on flight.
92
What is excretion?
Excretion = removal of toxic waste products of metabolism from body. Nitrogen containing compounds are produced when excess amino acids are broken down. They become toxic if they accumulate in body, so must be excreted.
93
What is the main nitrogenous waste product in mammals?
In mammals main nitrogeneous waste product is urea, which subsequently is excreted by kidneys.
94
what is mean be the term "osmoregulation"?
Osmoregulation = regulation of osmotic conc in body (osmol/L). It maintains composition of blood & takes places in kidneys.
95
What is the pathway for removal of nitrogenous waste?
Each kidney is served by a renal artery & drained by a renal vein. Urine from kidney is carried to bladder by ureter, & from the bladder to exterior by urethra.
96
Draw and annotate a diagram of the human kidney.
97
What are nephrons?
Nephrons = basic functional units that make up kidney. They do the filtering! There are millions of these tiny structures inside kidney, & all eventually drain into ureter
98
What is : Bowman capsule, Vasa recta, Loop of Henle, Collecting duct, Distal convoluted tubule, Capillaries, Proximal convoluted tubule?
Bowman capsule (cup-shaped structure with a highly porous inner wall)
Vasa recta
(capillaries that are similar in shape to loops of Henle, with a descending limb going down into medulla & an ascending limb back up to cortex)
Loop of Henle
(a tube shaped like a hairpin – composed of ascending & descending limb)
Collecting duct
(a wider tube which carries filtrate back through cortex + medulla to renal pelvis.
Distal convoluted tubule
(highly twisted section with fewer, shorter microvilli + mitochondria)
Capillaries (low pressure capillary bed which runs around convoluted tubules)
Proximal convoluted tubule
(highly twisted tubule)
99
Annotate nephron.
100
What are the main steps of excretion?
1. Ultrafiltration: components of blood able to diffuse across vessel wall (not large proteins) are filtered out of blood vessels into kidney tubules. Small molecules & ions (salts, water, glucose, amino acids, waste products such as urea & carbonic acid) are unselectively filtered out of blood into renal capsule (Bowman)
2. Reabsorption: Useful substances such as water, glucose & amino acids are reabsorbed & selectively taken back into blood. This happens in proximal convoluted tubule. Harmful &/or excess substances are excreted from body (urea, drugs)
3. Osmoregulation: Water reabsorption along Loop of Henle collecting duct.
101
What substances are filtered out of blood in renal/bowman capsule?
Small molecules & ions (salts, water, glucose, amino acids, waste products such as urea & carbonic acid, sodium, chloride ions) are unselectively filtered out of blood into renal capsule (Bowman).
102
what substances remain in blood after filtration (Bowman')?
Large plasma proteins, platelets & blood cells.
103
What does high pressure in capillaries in glomerulus of kidney cause?
Blood in capillaries in glomerulus of kidney is at high pressure (like in many of tissues of body) – pressure forces some of plasma out through capillary wall into nephron tubule to form glomerular filtrate.
104
What are 3 important structural features of Bowman capsule?
1. Fenestration
2. Basement membrane
3. Podocytes
105
How does fenestrations assist in the ultrafiltration process?
Fenestrations are little pores in endothelium of capillaries (100nm), which allow large molecules & fluid to leave blood vessel but hold back blood cells.
106
How does basement membrane assist in the ultrafiltration process?
Basement membrane surrounds & supports capillary wall. It's made of a gel of negatively charged glycoproteins, which form a mesh. It filters out large plasma proteins but allows filtrate to pass.
107
How does podocytes assist in the ultrafiltration process?
Podocytes are cells of inner wall of Bowman's capsule with feet-like extensions which wrap around the arterioles. Small gaps allow most of filtrate to pass through.
108
How does re-absorption occur in the proximal convoluted tubule?
Re-absorption of glucose & salts (Na+) back into blood take place at least partly by active transport. Fluid in proximal convoluted tubule contains glucose, amino acids, vitamins, hormones, urea, salt ions & water. Water & some ions (Cl-) are following a conc gradient
109
What does the glomerular filtrate contain?
Glomerular filtrate, containing nearly 1.5kg of salt & 5.5kg of glucose flows in proximal convoluted tubule. Urine does not contain anywhere near as much salt & glucose – it's reabsorbed back in blood at this point.
110
What transport mechanism are used to attain Na^+ ion in the proximal convoluted tubule?
Na+ ions: active transport via protein pumps from filtrate to tubule cells, & from there back into capillaries.
111
What transport mechanism are used to attain Cl^- ion in the proximal convoluted tubule?
Cl- ions: active transport & facilitated diffusion
112
What transport mechanism are used to attain glucose in the proximal convoluted tubule?
Glucose: co-transported with Na+ out of filtrate by facilitated transport following a conc gradient which provides energy for glucose to move.
113
What transport mechanism are used to attain water in the proximal convoluted tubule?
Water: moves by osmosis due to conc gradient established by solutes
114
What is the function and use of the microvilli the proximal convoluted tubule?
To increase SA, thus increasing diffusion
115
What is the function and use of the mitochondria the proximal convoluted tubule?
Mitochondria produces ATP for active transport
116
How is water conserved in the Henle loop?
Henle loop concentrates salt in medulla & hence causing vigorous osmotic flow of water from collecting duct, therefore concentrating urine.
117
What is the overall purpose of the Henle loop?
Overall effect of loop of Henle is to create a gradient of solute conc in medulla. Energy to create this gradient is expended by wall cells in ascending limb.
118
What is the osmoregulation in descending limb of the Henle loop?
Walls of descending limb are permeable to water, & water is therefore leaving via osmosis due to high conc of salt in medulla.
119
What is the osmoregulation in ascending limb of the Henle loop?
Ascending Loop is impermeable to water & but salt is removed via active transport creating a high solute concentration in medulla.
120
What happens as filtrates flow down the Henle loop?
As filtrate flows down water permeable descending limb, increased solute concentration of fluid in medulla causes water to be drawn out by osmosis.
121
What happens as filtrates flow up the Henle loop?
It's ascending limb which causes fluid between cells of medulla to become more concentrated due to active (in upper thick walled part) & passive (lower, thin-walled part) transport of Na+ & Cl- ions out of limb.
122
What is systme called in the Henle loop?
This system is called a countercurrent system, bc solute conc raises due to flows of fluid in opposite directions. At each level in loop conc in descending limb is slightly higher than that in ascending limb.
123
What occurs in the distal convoluted tube?
Here fine adjustment of pH occurs. Water is permeable to distal tube’s membrane & passes from ultrafiltrate into blood. Conc of useful ions is regulated by actively secreting K+ from plasma into filtrate. Also, conc of Na+ ions is regulated by varying amount of NaCl reabsorption from the filtrate.
124
What does the hypertonic conditions of the medulla cause?
As collecting duct passes through medulla, hypertonic conditions of medulla will draw water out by osmosis.
125
Which hormone controls the release of water from the collecting ducts?
Anti-diuretic hormone (ADH)
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what is the effect of this hormone?
Anti-diuretic hormone (ADH) controls how many aquaporins, small water conducting protein channels, are recruited to cell membrane of collecting duct.
127
What happens when a person is dehydrated?
If a person is dehydrated, anti-diuretic hormone ADH is released from posterior pituitary gland after detection of water content by osmoreceptors in hypothalamus. ADH increases permeability of collecting duct to water, by increasing production of aquaporins.
128
What does up-regulating lead to?
Up-regulating production of aquaporins (water channels) will lead to less water in filtrate, urine becomes concentrated, & individual urinates less (i.e. anti-diuresis).
129
What happens when an individual is suitably hydrated?
When an individual is suitably hydrated, ADH levels decrease, & less water is reabsorbed (resulting in more dilute urine).
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Which factors can change the composition of urine?
It depends on diet (including salt intake & amount of protein consumed), H2O intake, degree of physical activity, environmental conditions, water loss by other routes (particularly in sweat) & depending on our state of health.
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What is the difference between blood and urine composition?
Composition of urine that is excreted from body is variable.
Composition of blood is held more or less constant.
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What effect the supply of blood to an organ?
Supply of blood to an organ is decreased or increased using circular muscles in cardiovascular system. Constriction of blood vessels (vasoconstriction) restricts blood flow. Vasodilation increases blood flow. Blood flow to kidneys must remain fairly constant to maintain osmoregulation & excretion of waste.
133
What is the tidal volume of blood in skeletal muscle, digestive system, kidneys and brain during vigorous physical exercise?
Skeletal muscle: Greatly increased supply - to provide maximum amounts of glucose & O2
Digestive system: reduced supply - digestion can be paused during relatively brief periods of vigorous exercise
Kidney: reduced supply - causing a reduction in glomerular filtration rate
Brain: increased supply - to supply more O2 & glucose as brain is particularly active
134
What is the tidal volume of blood in skeletal muscle, digestive system, kidneys and brain during wakeful rest?
Skeletal muscle: moderate supply - even sitting or standing requires some contraction of muscles
Digestive system: variable supply - increased when there is food in gut & reduced flow during fasting
Kidney: maximal supply - about 20% of cardiac output
Brain: moderate supply - brain tissue relies on continuous supply of O2 & glucose
135
What is the tidal volume of blood in skeletal muscle, digestive system, kidneys and brain during sleep?
Skeletal muscle: reduced supply - minimal muscle contraction when lying prone
Digestive system: variable supply - increased when there is food in gut & reduced flow during fasting
Kidney: reduced supply - avoiding need for urination during night
Brain: increased supply - possibly to increase rate of removal of toxins from brain tissue.
